Articles de revues : « Sarcomeric protein mutation »

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Becker, K. David, Kim R. Gottshall, Reed Hickey, Jean-Claude Perriard et Kenneth R. Chien. « Point Mutations in Human β Cardiac Myosin Heavy Chain Have Differential Effects on Sarcomeric Structure and Assembly : An ATP Binding Site Change Disrupts Both Thick and Thin Filaments, Whereas Hypertrophic Cardiomyopathy Mutations Display Normal Assembly ». Journal of Cell Biology 137, n^o 1 (7 avril 1997) : 131–40. http://dx.doi.org/10.1083/jcb.137.1.131.

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Hypertrophic cardiomyopathy is a human heart disease characterized by increased ventricular mass, focal areas of fibrosis, myocyte, and myofibrillar disorganization. This genetically dominant disease can be caused by mutations in any one of several contractile proteins, including β cardiac myosin heavy chain (βMHC). To determine whether point mutations in human βMHC have direct effects on interfering with filament assembly and sarcomeric structure, full-length wild-type and mutant human βMHC cDNAs were cloned and expressed in primary cultures of neonatal rat ventricular cardiomyocytes (NRC) under conditions that promote myofibrillogenesis. A lysine to arginine change at amino acid 184 in the consensus ATP binding sequence of human βMHC resulted in abnormal subcellular localization and disrupted both thick and thin filament structure in transfected NRC. Diffuse βMHC K184R protein appeared to colocalize with actin throughout the myocyte, suggesting a tight interaction of these two proteins. Human βMHC with S472V mutation assembled normally into thick filaments and did not affect sarcomeric structure. Two mutant myosins previously described as causing human hypertrophic cardiomyopathy, R249Q and R403Q, were competent to assemble into thick filaments producing myofibrils with well defined I bands, A bands, and H zones. Coexpression and detection of wild-type βMHC and either R249Q or R403Q proteins in the same myocyte showed these proteins are equally able to assemble into the sarcomere and provided no discernible differences in subcellular localization. Thus, human βMHC R249Q and R403Q mutant proteins were readily incorporated into NRC sarcomeres and did not disrupt myofilament formation. This study indicates that the phenotype of myofibrillar disarray seen in HCM patients which harbor either of these two mutations may not be directly due to the failure of the mutant myosin heavy chain protein to assemble and form normal sarcomeres, but may rather be a secondary effect possibly resulting from the chronic stress of decreased βMHC function.

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Riaz, Muhammad, Jinkyu Park, Lorenzo R. Sewanan, Yongming Ren, Jonas Schwan, Subhash K. Das, Pawel T. Pomianowski et al. « Muscle LIM Protein Force-Sensing Mediates Sarcomeric Biomechanical Signaling in Human Familial Hypertrophic Cardiomyopathy ». Circulation 145, n^o 16 (19 avril 2022) : 1238–53. http://dx.doi.org/10.1161/circulationaha.121.056265.

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Background: Familial hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease and is typically caused by mutations in genes encoding sarcomeric proteins that regulate cardiac contractility. HCM manifestations include left ventricular hypertrophy and heart failure, arrythmias, and sudden cardiac death. How dysregulated sarcomeric force production is sensed and leads to pathological remodeling remains poorly understood in HCM, thereby inhibiting the efficient development of new therapeutics. Methods: Our discovery was based on insights from a severe phenotype of an individual with HCM and a second genetic alteration in a sarcomeric mechanosensing protein. We derived cardiomyocytes from patient-specific induced pluripotent stem cells and developed robust engineered heart tissues by seeding induced pluripotent stem cell–derived cardiomyocytes into a laser-cut scaffold possessing native cardiac fiber alignment to study human cardiac mechanobiology at both the cellular and tissue levels. Coupled with computational modeling for muscle contraction and rescue of disease phenotype by gene editing and pharmacological interventions, we have identified a new mechanotransduction pathway in HCM, shown to be essential in modulating the phenotypic expression of HCM in 5 families bearing distinct sarcomeric mutations. Results: Enhanced actomyosin crossbridge formation caused by sarcomeric mutations in cardiac myosin heavy chain ( MYH7 ) led to increased force generation, which, when coupled with slower twitch relaxation, destabilized the MLP (muscle LIM protein) stretch-sensing complex at the Z-disc. Subsequent reduction in the sarcomeric muscle LIM protein level caused disinhibition of calcineurin–nuclear factor of activated T-cells signaling, which promoted cardiac hypertrophy. We demonstrate that the common muscle LIM protein–W4R variant is an important modifier, exacerbating the phenotypic expression of HCM, but alone may not be a disease-causing mutation. By mitigating enhanced actomyosin crossbridge formation through either genetic or pharmacological means, we alleviated stress at the Z-disc, preventing the development of hypertrophy associated with sarcomeric mutations. Conclusions: Our studies have uncovered a novel biomechanical mechanism through which dysregulated sarcomeric force production is sensed and leads to pathological signaling, remodeling, and hypertrophic responses. Together, these establish the foundation for developing innovative mechanism-based treatments for HCM that stabilize the Z-disc MLP-mechanosensory complex.

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Piroddi, Nicoletta, E. Rosalie Witjas-Paalberends, Claudia Ferrara, Cecilia Ferrantini, Giulia Vitale, Beatrice Scellini, Paul J. M. Wijnker et al. « The homozygous K280N troponin T mutation alters cross-bridge kinetics and energetics in human HCM ». Journal of General Physiology 151, n^o 1 (21 décembre 2018) : 18–29. http://dx.doi.org/10.1085/jgp.201812160.

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Hypertrophic cardiomyopathy (HCM) is a genetic form of left ventricular hypertrophy, primarily caused by mutations in sarcomere proteins. The cardiac remodeling that occurs as the disease develops can mask the pathogenic impact of the mutation. Here, to discriminate between mutation-induced and disease-related changes in myofilament function, we investigate the pathogenic mechanisms underlying HCM in a patient carrying a homozygous mutation (K280N) in the cardiac troponin T gene (TNNT2), which results in 100% mutant cardiac troponin T. We examine sarcomere mechanics and energetics in K280N-isolated myofibrils and demembranated muscle strips, before and after replacement of the endogenous troponin. We also compare these data to those of control preparations from donor hearts, aortic stenosis patients (LVHao), and HCM patients negative for sarcomeric protein mutations (HCMsmn). The rate constant of tension generation following maximal Ca2+ activation (kACT) and the rate constant of isometric relaxation (slow kREL) are markedly faster in K280N myofibrils than in all control groups. Simultaneous measurements of maximal isometric ATPase activity and Ca2+-activated tension in demembranated muscle strips also demonstrate that the energy cost of tension generation is higher in the K280N than in all controls. Replacement of mutant protein by exchange with wild-type troponin in the K280N preparations reduces kACT, slow kREL, and tension cost close to control values. In donor myofibrils and HCMsmn demembranated strips, replacement of endogenous troponin with troponin containing the K280N mutant increases kACT, slow kREL, and tension cost. The K280N TNNT2 mutation directly alters the apparent cross-bridge kinetics and impairs sarcomere energetics. This result supports the hypothesis that inefficient ATP utilization by myofilaments plays a central role in the pathogenesis of the disease.

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Chun, M., et S. Falkenthal. « Ifm(2)2 is a myosin heavy chain allele that disrupts myofibrillar assembly only in the indirect flight muscle of Drosophila melanogaster. » Journal of Cell Biology 107, n^o 6 (1 décembre 1988) : 2613–21. http://dx.doi.org/10.1083/jcb.107.6.2613.

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Using a combination of molecular and genetic techniques we demonstrate that Ifm(2)2 is an allele of the single-copy sarcomeric myosin heavy chain gene. Flies homozygous for this allele accumulate wild-type levels of mRNA and protein in tubular muscle of adults, but fail to accumulate detectable amounts of myosin heavy chain mRNA or protein in the indirect flight muscle. We propose that the mutation interferes with either transcription of the gene or splicing of the primary transcript in the indirect flight muscle and not in other muscle tissues. Biochemical and electron microscopic analysis of flies homozygous for this mutation has revealed that thick filament assembly is abolished in the indirect flight muscle resulting in the instability of wild-type thick filament proteins. In contrast, thin filament and Z disc assembly are marginally affected. We discuss a working hypothesis for sarcomere assembly and define and experimental approach to test the predictions of this proposed pathway for sarcomere assembly.

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Clay, Sarah A., Timothy L. Domeier, Laurin M. Hanft, Kerry S. McDonald et Maike Krenz. « Elevated Ca2+ transients and increased myofibrillar power generation cause cardiac hypercontractility in a model of Noonan syndrome with multiple lentigines ». American Journal of Physiology-Heart and Circulatory Physiology 308, n^o 9 (1 mai 2015) : H1086—H1095. http://dx.doi.org/10.1152/ajpheart.00501.2014.

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Noonan syndrome with multiple lentigines (NSML) is primarily caused by mutations in the nonreceptor protein tyrosine phosphatase SHP2 and associated with congenital heart disease in the form of pulmonary valve stenosis and hypertrophic cardiomyopathy (HCM). Our goal was to elucidate the cellular mechanisms underlying the development of HCM caused by the Q510E mutation in SHP2. NSML patients carrying this mutation suffer from a particularly severe form of HCM. Drawing parallels to other, more common forms of HCM, we hypothesized that altered Ca2+ homeostasis and/or sarcomeric mechanical properties play key roles in the pathomechanism. We used transgenic mice with cardiomyocyte-specific expression of Q510E-SHP2 starting before birth. Mice develop neonatal onset HCM with increased ejection fraction and fractional shortening at 4–6 wk of age. To assess Ca2+ handling, isolated cardiomyocytes were loaded with fluo-4. Q510E-SHP2 expression increased Ca2+ transient amplitudes during excitation-contraction coupling and increased sarcoplasmic reticulum Ca2+ content concurrent with increased expression of sarco(endo)plasmic reticulum Ca2+-ATPase. In skinned cardiomyocyte preparations from Q510E-SHP2 mice, force-velocity relationships and power-load curves were shifted upward. The peak power-generating capacity was increased approximately twofold. Transmission electron microscopy revealed that the relative intracellular area occupied by sarcomeres was increased in Q510E-SHP2 cardiomyocytes. Triton X-100-based myofiber purification showed that Q510E-SHP2 increased the amount of sarcomeric proteins assembled into myofibers. In summary, Q510E-SHP2 expression leads to enhanced contractile performance early in disease progression by augmenting intracellular Ca2+ cycling and increasing the number of power-generating sarcomeres. This gives important new insights into the cellular pathomechanisms of Q510E-SHP2-associated HCM.

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Marcu, Andreea Sorina, Radu Vătăşescu, Sebastian Onciul, Viorica Rădoi et Ruxandra Jurcuţ. « Intrafamilial Phenotypical Variability Linked to PRKAG2 Mutation—Family Case Report and Review of the Literature ». Life 12, n^o 12 (18 décembre 2022) : 2136. http://dx.doi.org/10.3390/life12122136.

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PRKAG2 syndrome (PS) is a rare, early-onset autosomal dominant phenocopy of sarcomeric hypertrophic cardiomyopathy (HCM), that mainly presents with ventricular pre-excitation, cardiac hypertrophy and progressive conduction system degeneration. Its natural course, treatment and prognosis are significantly different from sarcomeric HCM. The clinical phenotypes of PRKAG2 syndrome often overlap with HCM due to sarcomere protein mutations, causing this condition to be frequently misdiagnosed. The syndrome is caused by mutations in the gene encoding for the γ2 regulatory subunit (PRKAG2) of 5′ Adenosine Monophosphate-Activated Protein Kinase (AMPK), an enzyme that modulates glucose uptake and glycolysis. PRKAG2 mutations (OMIM#602743) are responsible for structural changes of AMPK, leading to an impaired myocyte glucidic uptake, and finally causing storage cardiomyopathy. We describe the clinical and investigative findings in a family with several affected members (NM_016203.4:c.905G>A or p.(Arg302Gln), heterozygous), highlighting the various phenotypes even in the same family, and the utility of genetic testing in diagnosing PS. The particularity of this family case is represented by the fact that the index patient was diagnosed at age 16 with cardiac hypertrophy and ventricular pre-excitation while his mother, by age 42, only had Wolff–Parkinson–White syndrome, without left ventricle hypertrophy. Both the grandmother and the great-grandmother underwent pacemaker implantation at a young age because of conduction abnormalities. Making the distinction between PS and sarcomeric HCM is actionable, given the early-onset of the disease, the numerous life-threatening consequences and the high rate of conduction disorders. In patients who exhibit cardiac hypertrophy coexisting with ventricular pre-excitation, genetic screening for PRKAG2 mutations should be considered.

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Ojala, Marisa, Chandra Prajapati, Risto-Pekka Pölönen, Kristiina Rajala, Mari Pekkanen-Mattila, Jyrki Rasku, Kim Larsson et Katriina Aalto-Setälä. « Mutation-Specific Phenotypes in hiPSC-Derived Cardiomyocytes Carrying Either Myosin-Binding Protein C Orα-Tropomyosin Mutation for Hypertrophic Cardiomyopathy ». Stem Cells International 2016 (2016) : 1–16. http://dx.doi.org/10.1155/2016/1684792.

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Hypertrophic cardiomyopathy (HCM) is a genetic cardiac disease, which affects the structure of heart muscle tissue. The clinical symptoms include arrhythmias, progressive heart failure, and even sudden cardiac death but the mutation carrier can also be totally asymptomatic. To date, over 1400 mutations have been linked to HCM, mostly in genes encoding for sarcomeric proteins. However, the pathophysiological mechanisms of the disease are still largely unknown. Two founder mutations for HCM in Finland are located in myosin-binding protein C (MYBPC3-Gln1061X) andα-tropomyosin (TPM1-Asp175Asn) genes. We studied the properties of HCM cardiomyocytes (CMs) derived from patient-specific human induced pluripotent stem cells (hiPSCs) carrying eitherMYBPC3-Gln1061XorTPM1-Asp175Asnmutation. Both types of HCM-CMs displayed pathological phenotype of HCM but, more importantly, we found differences between CMs carrying eitherMYBPC3-Gln1061XorTPM1-Asp175Asngene mutation in their cellular size, Ca2+handling, and electrophysiological properties, as well as their gene expression profiles. These findings suggest that even though the clinical phenotypes of the patients carrying eitherMYBPC3-Gln1061XorTPM1-Asp175Asngene mutation are similar, the genetic background as well as the functional properties on the cellular level might be different, indicating that the pathophysiological mechanisms behind the two mutations would be divergent as well.

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Masum, Md Mohiuddin, Md Abdullah Al Sayeef, Rayhan Shahrear, Devjani Banik, Gonopati Biswas et Zinnat Ara Yesmin. « Hypertrophic Cardiomyopathy : The Molecular Genetics ». Faridpur Medical College Journal 14, n^o 1 (26 mars 2020) : 44–49. http://dx.doi.org/10.3329/fmcj.v14i1.46168.

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Hypertrophic Cardiomyopathy (HCM) is the common monogenic form familial pathological cardiac hypertrophy. HCM is an important cause of sudden cardiac death in the young adult and a major cause of morbidity in the elderly. We discuss here the molecular genetics and recent advances in the molecular genetics of HCM. HCM became the first cardiac disease for which a molecular genetic mechanism was identified. More than 100 mutations in nine genes, that encoding sarcomeric proteins have been identified in patients with HCM, which had led to the belief that HCM is a disease of contractile sarcomeric proteins of the cardiac muscle. Approximately two-thirds of all HCM cases are caused by the mutation of the myosin heavy chain (MyHC), cardiac troponin T (cTnT) and myosin binding protein-C (MyBP-C). Genotype-phenotype correlation studies suggest that mutations in the MyHC gene are associated with more extensive hypertrophy and a higher risk of SCD as compared to mutations in genes coding for other sarcomeric proteins, such as MyBP-C and cTnT. However, there is a noteworthy variability and factors, such as modifier genes and probably the environmental factors affect the phenotypic expression of HCM. The results of different functional studies suggest that in spite of the variety of the mutations, the initial defects in HCM is abnormal cardiac myocyte function. In this era of genetics and upcoming future of precision medicine, good knowledge of its molecular basis of any disease is crucial for patient management, and HCM is not different. Faridpur Med. Coll. J. Jan 2019;14(1): 44-49

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Ahmad, Syed Abrar, Chandrakant Chavan, Rajesh Badani et Varsha Wankhade. « Sarcomeric gene mutations in phenotypic positive hypertrophic cardiomyopathic patients in Indian population ». Cellular and Molecular Biology 67, n^o 6 (27 février 2022) : 1–10. http://dx.doi.org/10.14715/cmb/2021.67.6.1.

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HCM is a monogenic cardiac disorder with a high risk of sudden cardiac death, heterogeneous phenotypic expression and genetic profile. HCM is expressed as autosomal dominant in fashion with the prevalence of 1:500 in the general population. The main objective of the current study was to unravel the mutation status in sarcomeric genes in urbanizing Pune population. HCM patients were recruited from Bharti hospital and Poona hospital and research centre, Pune after being screened by 2-D echocardiography. DNA was extracted from whole blood samples and PCR amplification was performed for selected exons from pre-selected genes, amplimers of >300 b.p were restriction digested and the SSCP technique was optimized for maximum result output. HCM patients shows the maximum prevalence of mitral regurgitation (23.3%) while the minimum prevalence was left auricular diameter (10%). Maximum variation spectrum was present in MYBPC3 genes as most of them were “benign” type as per Polyphen-2 tool status. Mutations in the MYH7 gene produce a prominent impact on splicing by the creation of a new SRP40 binding site (Exon Splicing Enhancer) as predicted by Human Splicing Finder 3.1. I736T mutation in the MYH7 gene results in replacement of β-strand by α-helix upstream from mutation site which may have a profound impact on protein tertiary structure as predicted by Polyphen-2 tool (probably damaging-1.00). Also, two ‘novel’ mutations and one ‘novel’ variation were reported in the present study. Thus, the MYBPC3 gene shows maximum mutation load among other sarcomeric genes. Double gene mutations do not represent much severe pathophysiology as compared to single gene mutated and genotypic negative HCM patients.

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Ниязова, С. С., Н. Н. Чакова, С. М. Комиссарова et М. А. Сасинович. « Mutation spectrum in sarcomeric protein genes and their phenotypic features in Belarusian patients with hypertrophic cardiomyopathy ». Nauchno-prakticheskii zhurnal «Medicinskaia genetika», n^o 6() (28 juin 2019) : 21–33. http://dx.doi.org/10.25557/2073-7998.2019.06.21-33.

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Введение. Гипертрофическая кардиомиопатия (ГКМП) относится к наследственной патологии, основной причиной которой являются мутации в генах, кодирующих белковые компоненты миофибрильного аппарата кардиомиоцитов, при этом спектр этих генетических изменений имеет популяционные особенности. Целью данного исследования являлось определение спектра мутаций в генах, кодирующих саркомерные белки, у пациентов с ГКМП из Беларуси, а также изучение взаимосвязей между генотипом и фенотипическими проявлениями заболевания. Материалы и методы. В исследование были включены 340 неродственных пациентов с ГКМП, проживающих в Беларуси. Обнаружение мутаций в кодирующих последовательностях генов ACTC1, MYBPC3, MYH7, MYL2, MYL3, TNNI3, TNNT2, TNNС1 и TPM1 у 89 пациентов проводили методом высокопроизводительного секвенирования (NGS). Направленный поиск выявленных методом NGS генетических дефектов осуществлялся методом автоматического секвенирования по Сэнгеру, а также с использованием ПЦР-ПДРФ анализа. Результаты. У 51,7% пациентов методом NGS обнаружены мутации в генах: MYBPC3 (20,2%), MYH7 (16,9%), TPM1 (3,4%), ACTC1 (2,3%), MYL2 (1,1%) и TNNC1 (1,1%). У 6,7% индивидуумов встречались две (5,6%) или три (1,1%) замены. Обнаружены новые мутации p.Ala49Asn, p.Val1407Phe в гене MYH7; р.Tyr501Ser, р.Trp1007fs, р.Tyr1043*, р.Pro1066Arg, p.Arg1138fs, р.Pro1181Gln, р.Cys1202Arg в гене MYBPC3. Установлены часто встречающиеся мутации: р.Gln1233*, р.Ser871Alafs, комбинация р.Glu1265Val+р.Cys1266Arg, р.Gln401* и р.Trp1214Arg в гене MYBPC3, p.Arg403Trp, p.Arg663Cys, p.Arg663His, p.Ala729Pro, p.Glu924Lys и p.Glu1356Lys в гене MYH7. По данным ЭхоКГ-исследования носители мутаций в генах белков саркомера, особенно обладатели миссенс-мутаций в гене MYBPC3, имели более выраженную гипертрофию миокарда и раннюю манифестацию заболевания по сравнению с пациентами без мутаций в этих генах. Для носителей наиболее распространенной среди белорусских пациентов мутации р.Gln1233* характерны позднее начало заболевания, умеренная гипертрофия миокарда левого желудочка, частое развитие фибрилляции предсердий. Выводы. Распределение встречаемости мутаций в генах, кодирующих саркомерные белки, у пациентов с ГКМП из Беларуси не отличалось от других европейских популяций. 84,9% обнаруженных мутаций локализовано в генах MYBPC3 и MYH7. Background. Hypertrophic cardiomyopathy (HCM) is a hereditary pathology, the main cause of which is mutations in the genes encoding the protein components of the myofibril apparatus of cardiomyocytes, and the spectrum of these genetic changes has population features. The aim of the study was to determine the spectrum of mutations in the genes encoding sarcomeric proteins in patients with HCM from Belarus, as well as to study the association between the genotype and the phenotypic manifestations of the disease. Materials and methods. The study included 340 unrelated patients with HCM from Belarus. Mutation detection in the coding sequences of ACTC1, MYBPC3, MYH7, MYL2, MYL3, TNNI3, TNNT2, TNNС1 и TPM1 genes was performed by next generation sequencing (NGS) in 89 patients. The directed search for genetic defects detected by the NGS method was carried out by the automatic sequencing method using Sanger and PCR-RFLP analysis. Results. The NGS method allowed to detect mutations in the genes of 51,7% of patients: MYBPC3 (20,2%), MYH7 (16,9%), TPM1 (3,4%), ACTC1 (2,3%), MYL2 (1,1 %) and TNNC1 (1,1%). In 6,7% of individuals two (5,6%) or three (1,1%) substitutions were observed. New mutations were found: p.Ala49Asn, p.Val1407Phe in the MYH7 gene; p.Tyr501Ser, p.Trp1007fs, p.Tyr1043*, p.Pro1066Arg, p.Arg1138fs, p.Pro1181Gln, р.Cys1202Arg in the MYBPC3 gene. The most frequently occurring mutations were identified: p.Gln1233*, p.Ser871Alafs, the combination of the р.Glu1265Val + p.Cys1266Arg, R.Gln401*, and Trp1214Arg in the MYBPC3 gene, p.Glu924Lys and p.Glu1356Lys in the MYH7 gene. According to the ECG study, carriers of mutations in sarcomere protein genes, especially with missense mutations in the MYBPC3 gene, had more severe myocardial hypertrophy and early disease manifestation then patients without mutations in those genes. The p.Gln1233* mutation was the most common among Belarusian patients and characterized by late onset of the disease, mild left ventricular myocardial hypertrophy and the more frequent development of atrial fibrillation. Conclusions. In general, the distribution of mutations in the genes encoding sarcomeric proteins in patients with HCM from Belarus didn’t differ from other European populations. 84,9% of the detected mutations were localized in MYBPC3 and MYH7 genes.

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Smelter, Dan F., Willem J. de Lange, Wenxuan Cai, Ying Ge et J. Carter Ralphe. « The HCM-linked W792R mutation in cardiac myosin-binding protein C reduces C6 FnIII domain stability ». American Journal of Physiology-Heart and Circulatory Physiology 314, n^o 6 (1 juin 2018) : H1179—H1191. http://dx.doi.org/10.1152/ajpheart.00686.2017.

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Cardiac myosin-binding protein C (cMyBP-C) is a functional sarcomeric protein that regulates contractility in response to contractile demand, and many mutations in cMyBP-C lead to hypertrophic cardiomyopathy (HCM). To gain insight into the effects of disease-causing cMyBP-C missense mutations on contractile function, we expressed the pathogenic W792R mutation (substitution of a highly conserved tryptophan residue by an arginine residue at position 792) in mouse cardiomyocytes lacking endogenous cMyBP-C and studied the functional effects using three-dimensional engineered cardiac tissue constructs (mECTs). Based on complete conservation of tryptophan at this location in fibronectin type II (FnIII) domains, we hypothesized that the W792R mutation affects folding of the C6 FnIII domain, destabilizing the mutant protein. Adenoviral transduction of wild-type (WT) and W792R cDNA achieved equivalent mRNA transcript abundance, but not equivalent protein levels, with W792R compared with WT controls. mECTs expressing W792R demonstrated abnormal contractile kinetics compared with WT mECTs that were nearly identical to cMyBP-C-deficient mECTs. We studied whether common pathways of protein degradation were responsible for the rapid degradation of W792R cMyBP-C. Inhibition of both ubiquitin-proteasome and lysosomal degradation pathways failed to increase full-length mutant protein abundance to WT equivalence, suggesting rapid cytosolic degradation. Bacterial expression of WT and W792R protein fragments demonstrated decreased mutant stability with altered thermal denaturation and increased susceptibility to trypsin digestion. These data suggest that the W792R mutation destabilizes the C6 FnIII domain of cMyBP-C, resulting in decreased full-length protein expression. This study highlights the vulnerability of FnIII-like domains to mutations that alter domain stability and further indicates that missense mutations in cMyBP-C can cause disease through a mechanism of haploinsufficiency. NEW & NOTEWORTHY This study is one of the first to describe a disease mechanism for a missense mutation in cardiac myosin-binding protein C linked to hypertrophic cardiomyopathy. The mutation decreases stability of the fibronectin type III domain and results in substantially reduced mutant protein expression dissonant to transcript abundance.

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Richard, Pascale, Richard Isnard, Lucie Carrier, Olivier Dubourg, Yves Donatien, Bénédicte Mathieu, Gisèle Bonne et al. « Double heterozygosity for mutations in the β-myosin heavy chain and in the cardiac myosin binding protein C genes in a family with hypertrophic cardiomyopathy ». Journal of Medical Genetics 36, n^o 7 (1 juillet 1999) : 542–45. http://dx.doi.org/10.1136/jmg.36.7.542.

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Familial hypertrophic cardiomyopathy is a genetically heterogeneous autosomal dominant disease, caused by mutations in several sarcomeric protein genes. So far, seven genes have been shown to be associated with the disease with the β-myosin heavy chain (MYH7) and the cardiac myosin binding protein C (MYBPC3) genes being the most frequently involved.We performed electrocardiography (ECG) and echocardiography in 15 subjects with hypertrophic cardiomyopathy from a French Caribbean family. Genetic analyses were performed on genomic DNA by haplotype analysis with microsatellite markers at each locus involved and mutation screening by single strand conformation polymorphism analysis. Based on ECG and echocardiography, eight subjects were affected and presented a classical phenotype of hypertrophic cardiomyopathy. Two new mutations cosegregating with the disease were found, one located in the MYH7 gene exon 15 (Glu483Lys) and the other in the MYBPC3 gene exon 30 (Glu1096 termination codon). Four affected subjects carried the MYH7 gene mutation, two the MYBPC3 gene mutation, and two were doubly heterozygous for the two mutations. The doubly heterozygous patients exhibited marked left ventricular hypertrophy, which was significantly greater than in the other affected subjects.We report for the first time the simultaneous presence of two pathological mutations in two different genes in the context of familial hypertrophic cardiomyopathy. This double heterozygosity is not lethal but is associated with a more severe phenotype.

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Rosen, Samantha M., Mugdha Joshi, Talia Hitt, Alan H. Beggs et Pankaj B. Agrawal. « Knockin mouse model of the human CFL2 p.A35T mutation results in a unique splicing defect and severe myopathy phenotype ». Human Molecular Genetics 29, n^o 12 (11 mars 2020) : 1996–2003. http://dx.doi.org/10.1093/hmg/ddaa035.

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Abstract Cofilin-2 is an actin-binding protein that is predominantly expressed in skeletal and cardiac muscles and belongs to the AC group of proteins, which includes cofilin-1 and destrin. In humans, cofilin-2 (CFL2) mutations have been associated with congenital myopathies that include nemaline and myofibrillar myopathy. To understand the pathogenicity of the human CFL2 mutation, p.A35T, that first linked cofilin-2 with the human disease, we created a knock-in mouse model. The Cfl2A35T/A35T (KI) mice were indistinguishable from their wild-type littermates at birth, but they rapidly worsened and died by postnatal day 9. The phenotypic, histopathologic and molecular findings mimicked the constitutive Cfl2-knockout (KO) mice described previously, including sarcomeric disruption and actin accumulations in skeletal muscles and negligible amounts of cofilin-2 protein. In addition, KI mice demonstrated a marked reduction in Cfl2 mRNA levels in various tissues including skeletal muscles. Further investigation revealed evidence of alternative splicing with the presence of two alternate transcripts of smaller size. These alternate transcripts were expressed at very low levels in the wild-type mice and were significantly upregulated in the mutant mice, indicating that pre-translational splicing defects may be a critical component of the disease mechanism associated with the mutation. Evidence of reduced expression of the full-length CFL2 transcript was also observed in the muscle biopsy sample of the patient with p.A35T mutation.

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Kaneda, Tomoya, Chie Naruse, Atsuhiro Kawashima, Noboru Fujino, Toru Oshima, Masanobu Namura, Shinichi Nunoda et al. « A novel β-myosin heavy chain gene mutation, p.Met531Arg, identified in isolated left ventricular non-compaction in humans, results in left ventricular hypertrophy that progresses to dilation in a mouse model ». Clinical Science 114, n^o 6 (12 février 2008) : 431–40. http://dx.doi.org/10.1042/cs20070179.

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Mutations in the βMHC (β-myosin heavy chain), a sarcomeric protein are responsible for hypertrophic and dilated cardiomyopathy. However, the mechanisms whereby distinct mutations in the βMHC gene cause two kinds of cardiomyopathy are still unclear. In the present study we report a novel βMHC mutation found in a patient with isolated LVNC [LV (left ventricular) non-compaction] and the phenotype of a mouse mutant model carrying the same mutation. To find the mutation responsible, we searched for genomic mutations in 99 unrelated probands with dilated cardiomyopathy and five probands with isolated LVNC, and identified a p.Met531Arg mutation in βMHC in a 13-year-old girl with isolated LVNC. Next, we generated six lines of transgenic mice carrying a p.Met532Arg mutant αMHC gene, which was identical with the p.Met531Arg mutation in the human βMHC. Among these, two lines with strong expression of the mutant αMHC gene were chosen for further studies. Although they did not exhibit the features characteristic of LVNC, approx. 50% and 70% of transgenic mice in each line displayed LVH (LV hypertrophy) by 2–3 months of age. Furthermore, LVD (LV dilation) developed in approx. 25% of transgenic mice by 18 months of age, demonstrating biphasic changes in LV wall thickness. The present study supports the idea that common mechanisms may be involved in LVH and LVD. The novel mouse model generated can provide important information for the understanding of the pathological processes and aetiology of cardiac dilation in humans.

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Broughton, K. M., J. Li, E. Sarmah, C. M. Warren, Y. H. Lin, M. P. Henze, V. Sanchez-Freire, R. J. Solaro et B. Russell. « A myosin activator improves actin assembly and sarcomere function of human-induced pluripotent stem cell-derived cardiomyocytes with a troponin T point mutation ». American Journal of Physiology-Heart and Circulatory Physiology 311, n^o 1 (1 juillet 2016) : H107—H117. http://dx.doi.org/10.1152/ajpheart.00162.2016.

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We have investigated cardiac myocytes derived from human-induced pluripotent stem cells (iPSC-CMs) from two normal control and two family members expressing a mutant cardiac troponin T (cTnT-R173W) linked to dilated cardiomyopathy (DCM). cTnT is a regulatory protein of the sarcomeric thin filament. The loss of this basic charge, which is strategically located to control tension, has consequences leading to progressive DCM. iPSC-CMs serve as a valuable platform for understanding clinically relevant mutations in sarcomeric proteins; however, there are important questions to be addressed with regard to myocyte adaptation that we model here by plating iPSC-CMs on softer substrates (100 kPa) to create a more physiologic environment during recovery and maturation of iPSC-CMs after thawing from cryopreservation. During the first week of culture of the iPSC-CMs, we have determined structural and functional characteristics as well as actin assembly dynamics. Shortening, actin content, and actin assembly dynamics were depressed in CMs from the severely affected mutant at 1 wk of culture, but by 2 wk differences were less apparent. Sarcomeric troponin and myosin isoform composition were fetal/neonatal. Furthermore, the troponin complex, reconstituted with wild-type cTnT or recombinant cTnT-R173W, depressed the entry of cross-bridges into the force-generating state, which can be reversed by the myosin activator omecamtiv mecarbil. Therapeutic doses of this drug increased both contractility and the content of F-actin in the mutant iPSC-CMs. Collectively, our data suggest the use of a myosin activation reagent to restore function within patient-specific iPSC-CMs may aid in understanding and treating this familial DCM.

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Ono, Shoichiro, Kazumi Nomura, Sadae Hitosugi, Domena K. Tu, Jocelyn A. Lee, David L. Baillie et Kanako Ono. « The two actin-interacting protein 1 genes have overlapping and essential function for embryonic development in Caenorhabditis elegans ». Molecular Biology of the Cell 22, n^o 13 (juillet 2011) : 2258–69. http://dx.doi.org/10.1091/mbc.e10-12-0934.

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Disassembly of actin filaments by actin-depolymerizing factor (ADF)/cofilin and actin-interacting protein 1 (AIP1) is a conserved mechanism to promote reorganization of the actin cytoskeleton. We previously reported that unc-78, an AIP1 gene in the nematode Caenorhabditis elegans, is required for organized assembly of sarcomeric actin filaments in the body wall muscle. unc-78 functions in larval and adult muscle, and an unc-78–null mutant is homozygous viable and shows only weak phenotypes in embryos. Here we report that a second AIP1 gene, aipl-1 (AIP1-like gene-1), has overlapping function with unc-78, and that depletion of the two AIP1 isoforms causes embryonic lethality. A single aipl-1–null mutation did not cause a detectable phenotype. However, depletion of both unc-78 and aipl-1 arrested development at late embryonic stages due to severe disorganization of sarcomeric actin filaments in body wall muscle. In vitro, both AIPL-1 and UNC-78 preferentially cooperated with UNC-60B, a muscle-specific ADF/cofilin isoform, in actin filament disassembly but not with UNC-60A, a nonmuscle ADF/cofilin. AIPL-1 is expressed in embryonic muscle, and forced expression of AIPL-1 in adult muscle compensated for the function of UNC-78. Thus our results suggest that enhancement of actin filament disassembly by ADF/cofilin and AIP1 proteins is critical for embryogenesis.

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Schwäbe, Frederic V., Emanuel K. Peter, Manuel H. Taft et Dietmar J. Manstein. « Assessment of the Contribution of a Thermodynamic and Mechanical Destabilization of Myosin-Binding Protein C Domain C2 to the Pathomechanism of Hypertrophic Cardiomyopathy-Causing Double Mutation MYBPC3Δ25bp/D389V ». International Journal of Molecular Sciences 22, n^o 21 (4 novembre 2021) : 11949. http://dx.doi.org/10.3390/ijms222111949.

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Mutations in the gene encoding cardiac myosin-binding protein-C (MyBPC), a thick filament assembly protein that stabilizes sarcomeric structure and regulates cardiac function, are a common cause for the development of hypertrophic cardiomyopathy. About 10% of carriers of the Δ25bp variant of MYBPC3, which is common in individuals from South Asia, are also carriers of the D389V variant on the same allele. Compared with noncarriers and those with MYBPC3Δ25bp alone, indicators for the development of hypertrophic cardiomyopathy occur with increased frequency in MYBPC3Δ25bp/D389V carriers. Residue D389 lies in the IgI-like C2 domain that is part of the N-terminal region of MyBPC. To probe the effects of mutation D389V on structure, thermostability, and protein–protein interactions, we produced and characterized wild-type and mutant constructs corresponding to the isolated 10 kDa C2 domain and a 52 kDa N-terminal fragment that includes subdomains C0 to C2. Our results show marked reductions in the melting temperatures of D389V mutant constructs. Interactions of construct C0–C2 D389V with the cardiac isoforms of myosin-2 and actin remain unchanged. Molecular dynamics simulations reveal changes in the stiffness and conformer dynamics of domain C2 caused by mutation D389V. Our results suggest a pathomechanism for the development of HCM based on the toxic buildup of misfolded protein in young MYBPC3Δ25bp/D389V carriers that is supplanted and enhanced by C-zone haploinsufficiency at older ages.

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Vaikhanskaya, T. G., L. N. Sivitskaya, T. V. Kurushko, T. V. Rusak, O. D. Levdansky, N. G. Danilenko et O. G. Davydenko. « Non-compaction cardiomyopathy. Part I : clinical and genetic heterogeneity and predictors of unfavorable prognosis ». Russian Journal of Cardiology 25, n^o 11 (5 décembre 2020) : 3872. http://dx.doi.org/10.15829/29/1560-4071-2020-3872.

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Non-compaction cardiomyopathy (NCM) is a rare heart disease characterized by a two-layered ventricular wall, comprising a thinner compact epicardial layer and an inner non-compacted layer. However, only structural and morphological data without a thorough clinical assessment does not determine the NCM (regardless of the diagnostic criterion used).Aim. To study the NCM-related genes, phenotypic and genetic correlations, predictors of life-threatening ventricular tachyarrhythmias (VTA) and adverse clinical outcomes.Material and methods. Of 93 individuals with identified morphological criteria of NCM (median follow-up, 5 years), the study included 60 unrelated patients (38,5±13,8 years of age; men, 33 (55%); left ventricular ejection fraction (LVEF), 42,1±12,9%) with clinical verification of NCM (>1 obligate phenotypic trait). Adverse cardiovascular events were taken as the composite end point: life-threatening VTA, death, heart transplantation.Results. Pathogenic (or probably pathogenic) mutations were detected in 33 (55%) patients with NCM. The most common variants (57,9%) were identified in the sarcomere protein genes (TTN, MYBPC3, MYH7); digenic mutations were found in 21,6% of patients. Digenic mutations were associated with low LVEF and the highest risk of systolic dysfunction (OR, 38; 95% CI, 4,74-305; p=0,0001). Multivariate regression provided a predictive model (R=0,90; R2=0,81; F (5,41) =34,8; p<0,0001) and independent predictors of adverse clinical outcomes of NCM (genetic cause of the disease (pathogenic mutation), LV systolic dysfunction, myocardial fibrosis in 2 or more ventricular segments, and QRS prolongation. Regression and ROC-analysis identified electrical predictors of life-threatening VTA (fragmented QRS, QT prolongation, spatial QRS-T angle increase) and morphofunctional markers (myocardial fibrosis, systolic dysfunction).Conclusion. The study revealed a significant clinical and genetic heterogeneity of NCM with predominant mutations in the sarcomeric protein genes and determined the criteria for identification and prognosis of NCM.

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Viricel, Amélia, et Patricia E. Rosel. « Looking into a whale’s heart : investigating a genetic basis for cardiomyopathy in a non-model species ». Genome 60, n^o 8 (août 2017) : 695–705. http://dx.doi.org/10.1139/gen-2016-0203.

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Understanding the pathogenesis of complex diseases can benefit from multi-species comparative studies. Yet these studies rarely include natural populations of non-model species. Here, we focused on the cause of a heart muscle disease, cardiomyopathy (CM), affecting multiple mammalian species including humans, cats, dogs, and certain species of whales. Mutations in genes coding for sarcomeric proteins have been identified as a leading cause for CM in humans, and some were also revealed to be responsible for CM in cats. We investigated whether similar mutations could be detected in the deep-diving pygmy sperm whale (Kogia breviceps), which is one of two cetacean species known to display CM. We sequenced portions of two candidate genes (MYH7: 3153 bp and MYBPC3: 3019 bp) in 55 whales including affected and unaffected individuals. Mutation screening revealed six nonsynonymous substitutions that were predicted to have an effect on protein function. However, the etiology of CM is likely complex and probably multi-factorial as three of these mutations were observed in unaffected individuals from our control group. This incomplete penetrance could be partly age-related and could also be due to the influence of environmental factors on the development of CM, as seen in humans.

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Lu, Serena Huei-An, Kang-Zheng Lee, Paul Wei-Che Hsu, Liang-Yu Su, Yu-Chen Yeh, Chien-Yuan Pan et Su-Yi Tsai. « Alternative Splicing Mediated by RNA-Binding Protein RBM24 Facilitates Cardiac Myofibrillogenesis in a Differentiation Stage-Specific Manner ». Circulation Research 130, n^o 1 (7 janvier 2022) : 112–29. http://dx.doi.org/10.1161/circresaha.121.320080.

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Background: Mutations in genes encoding sarcomeric proteins lead to failures in sarcomere assembly, the building blocks of contracting muscles, resulting in cardiomyopathies that are a leading cause of morbidity and mortality worldwide. Splicing variants of sarcomeric proteins are crucial at different stages of myofibrillogenesis, accounting for sarcomeric structural integrity. RBM24 (RNA-binding motif protein 24) is known as a tissue-specific splicing regulator that plays an essential role in cardiogenesis. However, it had been unclear if the developmental stage-specific alternative splicing facilitated by RBM24 contributes to sarcomere assembly and cardiogenesis. Our aim is to study the molecular mechanism by which RBM24 regulates cardiogenesis and sarcomere assembly in a temporal-dependent manner. Methods: We ablated RBM24 from human embryonic stem cells (hESCs) using CRISPR/Cas9 techniques. Results: Although RBM24 −/− hESCs still differentiated into sarcomere-hosting cardiomyocytes, they exhibited disrupted sarcomeric structures with punctate Z-lines due to impaired myosin replacement during early myofibrillogenesis. Transcriptomics revealed >4000 genes regulated by RBM24 . Among them, core myofibrillogenesis proteins (eg, ACTN2 [α-actinin 2], TTN [titin], and MYH10 [non-muscle myosin IIB]) were misspliced. Consequently, MYH6 (muscle myosin II) cannot replace nonmuscle myosin MYH10, leading to myofibrillogenesis arrest at the early premyofibril stage and causing disrupted sarcomeres. Intriguingly, we found that the ABD (actin-binding domain; encoded by exon 6) of the Z-line anchor protein ACTN2 is predominantly excluded from early cardiac differentiation, whereas it is consistently included in human adult heart. CRISPR/Cas9-mediated deletion of exon 6 from ACTN2 in hESCs, as well as forced expression of full-length ACTN2 in RBM24 −/− hESCs, further corroborated that inclusion of exon 6 is critical for sarcomere assembly. Overall, we have demonstrated that RBM24-facilitated inclusion of exon 6 in ACTN2 at distinct stages of cardiac differentiation is evolutionarily conserved and crucial to sarcomere assembly and integrity. Conclusions: RBM24 acts as a master regulator to modulate the temporal dynamics of core myofibrillogenesis genes and thereby orchestrates sarcomere organization.

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Lange, Stephan, Sue Perera, Phildrich Teh et Ju Chen. « Obscurin and KCTD6 regulate cullin-dependent small ankyrin-1 (sAnk1.5) protein turnover ». Molecular Biology of the Cell 23, n^o 13 (juillet 2012) : 2490–504. http://dx.doi.org/10.1091/mbc.e12-01-0052.

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Protein turnover through cullin-3 is tightly regulated by posttranslational modifications, the COP9 signalosome, and BTB/POZ-domain proteins that link cullin-3 to specific substrates for ubiquitylation. In this paper, we report how potassium channel tetramerization domain containing 6 (KCTD6) represents a novel substrate adaptor for cullin-3, effectively regulating protein levels of the muscle small ankyrin-1 isoform 5 (sAnk1.5).Binding of sAnk1.5 to KCTD6, and its subsequent turnover is regulated through posttranslational modification by nedd8, ubiquitin, and acetylation of C-terminal lysine residues. The presence of the sAnk1.5 binding partner obscurin, and mutation of lysine residues increased sAnk1.5 protein levels, as did knockdown of KCTD6 in cardiomyocytes. Obscurin knockout muscle displayed reduced sAnk1.5 levels and mislocalization of the sAnk1.5/KCTD6 complex. Scaffolding functions of obscurin may therefore prevent activation of the cullin-mediated protein degradation machinery and ubiquitylation of sAnk1.5 through sequestration of sAnk1.5/KCTD6 at the sarcomeric M-band, away from the Z-disk–associated cullin-3. The interaction of KCTD6 with ankyrin-1 may have implications beyond muscle for hereditary spherocytosis, as KCTD6 is also present in erythrocytes, and erythrocyte ankyrin isoforms contain its mapped minimal binding site.

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van der Velden, Jolanda, et Ger J. M. Stienen. « Cardiac Disorders and Pathophysiology of Sarcomeric Proteins ». Physiological Reviews 99, n^o 1 (1 janvier 2019) : 381–426. http://dx.doi.org/10.1152/physrev.00040.2017.

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The sarcomeric proteins represent the structural building blocks of heart muscle, which are essential for contraction and relaxation. During recent years, it has become evident that posttranslational modifications of sarcomeric proteins, in particular phosphorylation, tune cardiac pump function at rest and during exercise. This delicate, orchestrated interaction is also influenced by mutations, predominantly in sarcomeric proteins, which cause hypertrophic or dilated cardiomyopathy. In this review, we follow a bottom-up approach starting from a description of the basic components of cardiac muscle at the molecular level up to the various forms of cardiac disorders at the organ level. An overview is given of sarcomere changes in acquired and inherited forms of cardiac disease and the underlying disease mechanisms with particular reference to human tissue. A distinction will be made between the primary defect and maladaptive/adaptive secondary changes. Techniques used to unravel functional consequences of disease-induced protein changes are described, and an overview of current and future treatments targeted at sarcomeric proteins is given. The current evidence presented suggests that sarcomeres not only form the basis of cardiac muscle function but also represent a therapeutic target to combat cardiac disease.

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VANDIJK, S., D. DOOIJES, D. DEKKERS, J. LAMERS, F. TENCATE, G. STIENEN et J. VANDERVELDEN. « Alterations in sarcomeric protein expression, phosphorylation and contractile function in hypertrophic cardiomyopathy patients carrying a founder mutation in myosin binding protein C ». European Journal of Heart Failure Supplements 7 (juin 2008) : 30–31. http://dx.doi.org/10.1016/s1567-4215(08)60086-7.

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Adalsteinsdottir, Berglind, Michael Burke, Barry J. Maron, Ragnar Danielsen, Begoña Lopez, Javier Diez, Petr Jarolim et al. « Hypertrophic cardiomyopathy in myosin-binding protein C (MYBPC3) Icelandic founder mutation carriers ». Open Heart 7, n^o 1 (avril 2020) : e001220. http://dx.doi.org/10.1136/openhrt-2019-001220.

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ObjectiveThe myosin-binding protein C (MYBPC3) c.927-2A>G founder mutation accounts for >90% of sarcomeric hypertrophic cardiomyopathy (HCM) in Iceland. This cross-sectional observational study explored the penetrance and phenotypic burden among carriers of this single, prevalent founder mutation.MethodsWe studied 60 probands with HCM caused by MYBPC3 c.927-2A>G and 225 first-degree relatives. All participants underwent comprehensive clinical evaluation and relatives were genotyped.ResultsGenetic and clinical evaluation of relatives identified 49 genotype-positive (G+) relatives with left ventricular hypertrophy (G+/LVH+), 59 G+without LVH (G+/LVH−) and 117 genotype-negative relatives (unaffected). Compared with HCM probands, G+/LVH+ relatives were older at HCM diagnosis, had less LVH, a less prevalent diastolic dysfunction, fewer ECG abnormalities, lower serum N-terminal pro-B-type natriuretic peptide (NT-proBNP) and high-sensitivity cardiac troponin I levels, and fewer symptoms. The penetrance of HCM was influenced by age and sex; specifically, LVH was present in 39% of G+males but only 9% of G+females under age 40 years (p=0.015), versus 86% and 83%, respectively, after age 60 (p=0.89). G+/LVH− subjects had normal wall thicknesses, diastolic function and NT-proBNP levels, but subtle changes in LV geometry and more ECG abnormalities than their unaffected relatives.ConclusionsPhenotypic expression of the Icelandic MYBPC3 founder mutation varies by age, sex and proband status. Men are more likely to have LVH at a younger age, and disease manifestations were more prominent in probands than in relatives identified via family screening. G+/LVH− individuals had subtle clinical differences from unaffected relatives well into adulthood, indicating subclinical phenotypic expression of the pathogenic mutation.

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Eden, Matthias, et Norbert Frey. « Cardiac Filaminopathies : Illuminating the Divergent Role of Filamin C Mutations in Human Cardiomyopathy ». Journal of Clinical Medicine 10, n^o 4 (4 février 2021) : 577. http://dx.doi.org/10.3390/jcm10040577.

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Over the past decades, there has been tremendous progress in understanding genetic alterations that can result in different phenotypes of human cardiomyopathies. More than a thousand mutations in various genes have been identified, indicating that distinct genetic alterations, or combinations of genetic alterations, can cause either hypertrophic (HCM), dilated (DCM), restrictive (RCM), or arrhythmogenic cardiomyopathies (ARVC). Translation of these results from “bench to bedside” can potentially group affected patients according to their molecular etiology and identify subclinical individuals at high risk for developing cardiomyopathy or patients with overt phenotypes at high risk for cardiac deterioration or sudden cardiac death. These advances provide not only mechanistic insights into the earliest manifestations of cardiomyopathy, but such efforts also hold the promise that mutation-specific pathophysiology might result in novel “personalized” therapeutic possibilities. Recently, the FLNC gene encoding the sarcomeric protein filamin C has gained special interest since FLNC mutations were found in several distinct and possibly overlapping cardiomyopathy phenotypes. Specifically, mutations in FLNC were initially only linked to myofibrillar myopathy (MFM), but are now increasingly found in various forms of human cardiomyopathy. FLNC thereby represents another example for the complex genetic and phenotypic continuum of these diseases.

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Candasamy, Alexandra J., Robert S. Haworth, Friederike Cuello, Michael Ibrahim, Sriram Aravamudhan, Marcus Krüger, Mark R. Holt et al. « Phosphoregulation of the Titin-cap Protein Telethonin in Cardiac Myocytes ». Journal of Biological Chemistry 289, n^o 3 (26 novembre 2013) : 1282–93. http://dx.doi.org/10.1074/jbc.m113.479030.

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Telethonin (also known as titin-cap or t-cap) is a muscle-specific protein whose mutation is associated with cardiac and skeletal myopathies through unknown mechanisms. Our previous work identified cardiac telethonin as an interaction partner for the protein kinase D catalytic domain. In this study, kinase assays used in conjunction with MS and site-directed mutagenesis confirmed telethonin as a substrate for protein kinase D and Ca2+/calmodulin-dependent kinase II in vitro and identified Ser-157 and Ser-161 as the phosphorylation sites. Phosphate affinity electrophoresis and MS revealed endogenous telethonin to exist in a constitutively bis-phosphorylated form in isolated adult rat ventricular myocytes and in mouse and rat ventricular myocardium. Following heterologous expression in myocytes by adenoviral gene transfer, wild-type telethonin became bis-phosphorylated, whereas S157A/S161A telethonin remained non-phosphorylated. Nevertheless, both proteins localized predominantly to the sarcomeric Z-disc, where they partially replaced endogenous telethonin. Such partial replacement with S157A/S161A telethonin disrupted transverse tubule organization and prolonged the time to peak of the intracellular Ca2+ transient and increased its variance. These data reveal, for the first time, that cardiac telethonin is constitutively bis-phosphorylated and suggest that such phosphorylation is critical for normal telethonin function, which may include maintenance of transverse tubule organization and intracellular Ca2+ transients.

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Da'as, Sahar I., Khalid Fakhro, Angelos Thanassoulas, Navaneethakrishnan Krishnamoorthy, Alaaeldin Saleh, Brian L. Calver, Bared Safieh-Garabedian et al. « Hypertrophic cardiomyopathy-linked variants of cardiac myosin-binding protein C3 display altered molecular properties and actin interaction ». Biochemical Journal 475, n^o 24 (14 décembre 2018) : 3933–48. http://dx.doi.org/10.1042/bcj20180685.

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The most common inherited cardiac disorder, hypertrophic cardiomyopathy (HCM), is characterized by thickening of heart muscle, for which genetic mutations in cardiac myosin-binding protein C3 (c-MYBPC3) gene, is the leading cause. Notably, patients with HCM display a heterogeneous clinical presentation, onset and prognosis. Thus, delineating the molecular mechanisms that explain how disparate c-MYBPC3 variants lead to HCM is essential for correlating the impact of specific genotypes on clinical severity. Herein, five c-MYBPC3 missense variants clinically associated with HCM were investigated; namely V1 (R177H), V2 (A216T), V3 (E258K), V4 (E441K) and double mutation V5 (V3 + V4), all located within the C1 and C2 domains of MyBP-C, a region known to interact with sarcomeric protein, actin. Injection of the variant complementary RNAs in zebrafish embryos was observed to recapitulate phenotypic aspects of HCM in patients. Interestingly, V3- and V5-cRNA injection produced the most severe zebrafish cardiac phenotype, exhibiting increased diastolic/systolic myocardial thickness and significantly reduced heart rate compared with control zebrafish. Molecular analysis of recombinant C0–C2 protein fragments revealed that c-MYBPC3 variants alter the C0–C2 domain secondary structure, thermodynamic stability and importantly, result in a reduced binding affinity to cardiac actin. V5 (double mutant), displayed the greatest protein instability with concomitant loss of actin-binding function. Our study provides specific mechanistic insight into how c-MYBPC3 pathogenic variants alter both functional and structural characteristics of C0–C2 domains leading to impaired actin interaction and reduced contractility, which may provide a basis for elucidating the disease mechanism in HCM patients with c-MYBPC3 mutations.

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Antoniutti, Guido, Fiama Giuliana Caimi-Martinez, Jorge Álvarez-Rubio, Paula Morlanes-Gracia, Jaume Pons-Llinares, Blanca Rodríguez-Picón, Elena Fortuny-Frau, Laura Torres-Juan, Damian Heine-Suner et Tomas Ripoll-Vera. « Genotype-Phenotype Correlation in Hypertrophic Cardiomyopathy : New Variant p.Arg652Lys in MYH7 ». Genes 13, n^o 2 (9 février 2022) : 320. http://dx.doi.org/10.3390/genes13020320.

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Hypertrophic cardiomyopathy (HCM) is a genetic disease characterised by increased left ventricle (LV) wall thickness caused by mutations in sarcomeric genes. Finding a causal mutation can help to better assess the proband’s risk, as it allows the presence of the mutation to be evaluated in relatives and the follow-up to be focused on carriers. We performed an observational study of patients with HCM due to the novel p.Arg652Lys variant in the MYH7 gene. Eight families and 59 patients are described in the follow-up for a median of 63 months, among whom 39 (66%) carry the variant. Twenty-five (64%) of carriers developed HCM. A median maximum LV wall thickness of 16.5 mm was described. The LV hypertrophy was asymmetric septal in 75% of cases, with LV outflow tract obstruction in 28%. The incidence of a composite of serious adverse cardiovascular events (sudden death, aborted sudden death, appropriate implantable cardiac defibrillator discharge, an embolic event, or admission for heart failure) was observed in five (20%) patients. Given the finding of the p.Arg652Lys variant in patients with HCM, but not in controls, with evident segregation in patients with HCM from eight families and the location in an active site of the protein, we can define this variant as likely pathogenic and associated with the development of HCM.

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Zhou, Qifeng, Scott Kesteven, Jianxin Wu, Parwez Aidery, Meinrad Gawaz, Michael Gramlich, Michael P. Feneley et Richard P. Harvey. « Pressure Overload by Transverse Aortic Constriction Induces Maladaptive Hypertrophy in a Titin-Truncated Mouse Model ». BioMed Research International 2015 (2015) : 1–6. http://dx.doi.org/10.1155/2015/163564.

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Mutations in the giant sarcomeric protein titin (TTN) are a major cause for inherited forms of dilated cardiomyopathy (DCM). We have previously developed a mouse model that imitates a TTN truncation mutation we found in a large pedigree with DCM. While heterozygousTtnknock-in mice do not display signs of heart failure under sedentary conditions, they recapitulate the human phenotype when exposed to the pharmacological stressor angiotensin II or isoproterenol. In this study we investigated the effects of pressure overload by transverse aortic constriction (TAC) in heterozygous (Het)Ttnknock-in mice. Two weeks after TAC, Het mice developed marked impairment of left ventricular ejection fraction(p<0.05), while wild-type (WT) TAC mice did not. Het mice also trended toward increased ventricular end diastolic pressure and volume compared to WT littermates. We found an increase in histologically diffuse cardiac fibrosis in Het compared to WT in TAC mice. This study shows that a pattern of DCM can be induced by TAC-mediated pressure overload in a TTN-truncated mouse model. This model enlarges our arsenal of cardiac disease models, adding a valuable tool to understand cardiac pathophysiological remodeling processes and to develop therapeutic approaches to combat heart failure.

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Warmke, J., M. Yamakawa, J. Molloy, S. Falkenthal et D. Maughan. « Myosin light chain-2 mutation affects flight, wing beat frequency, and indirect flight muscle contraction kinetics in Drosophila. » Journal of Cell Biology 119, n^o 6 (15 décembre 1992) : 1523–39. http://dx.doi.org/10.1083/jcb.119.6.1523.

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We have used a combination of classical genetic, molecular genetic, histological, biochemical, and biophysical techniques to identify and characterize a null mutation of the myosin light chain-2 (MLC-2) locus of Drosophila melanogaster. Mlc2E38 is a null mutation of the MLC-2 gene resulting from a nonsense mutation at the tenth codon position. Mlc2E38 confers dominant flightless behavior that is associated with reduced wing beat frequency. Mlc2E38 heterozygotes exhibit a 50% reduction of MLC-2 mRNA concentration in adult thoracic musculature, which results in a commensurate reduction of MLC-2 protein in the indirect flight muscles. Indirect flight muscle myofibrils from Mlc2E38 heterozygotes are aberrant, exhibiting myofilaments in disarray at the periphery. Calcium-activated Triton X-100-treated single fiber segments exhibit slower contraction kinetics than wild type. Introduction of a transformed copy of the wild type MLC-2 gene rescues the dominant flightless behavior of Mlc2E38 heterozygotes. Wing beat frequency and single fiber contraction kinetics of a representative rescued line are not significantly different from those of wild type. Together, these results indicate that wild type MLC-2 stoichiometry is required for normal indirect flight muscle assembly and function. Furthermore, these results suggest that the reduced wing beat frequency and possibly the flightless behavior conferred by Mlc2E38 is due in part to slower contraction kinetics of sarcomeric regions devoid or partly deficient in MLC-2.

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Cimiotti, Diana, Heidi Budde, Roua Hassoun et Kornelia Jaquet. « Genetic Restrictive Cardiomyopathy : Causes and Consequences—An Integrative Approach ». International Journal of Molecular Sciences 22, n^o 2 (8 janvier 2021) : 558. http://dx.doi.org/10.3390/ijms22020558.

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The sarcomere as the smallest contractile unit is prone to alterations in its functional, structural and associated proteins. Sarcomeric dysfunction leads to heart failure or cardiomyopathies like hypertrophic (HCM) or restrictive cardiomyopathy (RCM) etc. Genetic based RCM, a very rare but severe disease with a high mortality rate, might be induced by mutations in genes of non-sarcomeric, sarcomeric and sarcomere associated proteins. In this review, we discuss the functional effects in correlation to the phenotype and present an integrated model for the development of genetic RCM.

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Cimiotti, Diana, Heidi Budde, Roua Hassoun et Kornelia Jaquet. « Genetic Restrictive Cardiomyopathy : Causes and Consequences—An Integrative Approach ». International Journal of Molecular Sciences 22, n^o 2 (8 janvier 2021) : 558. http://dx.doi.org/10.3390/ijms22020558.

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The sarcomere as the smallest contractile unit is prone to alterations in its functional, structural and associated proteins. Sarcomeric dysfunction leads to heart failure or cardiomyopathies like hypertrophic (HCM) or restrictive cardiomyopathy (RCM) etc. Genetic based RCM, a very rare but severe disease with a high mortality rate, might be induced by mutations in genes of non-sarcomeric, sarcomeric and sarcomere associated proteins. In this review, we discuss the functional effects in correlation to the phenotype and present an integrated model for the development of genetic RCM.

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Braun, T., E. Bober, M. A. Rudnicki, R. Jaenisch et H. H. Arnold. « MyoD expression marks the onset of skeletal myogenesis in Myf-5 mutant mice ». Development 120, n^o 11 (1 novembre 1994) : 3083–92. http://dx.doi.org/10.1242/dev.120.11.3083.

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The expression pattern of myogenic regulatory factors and myotome-specific contractile proteins was studied during embryonic development of Myf-5 mutant mice by in situ hybridization and immunohistochemistry. In contrast to somites in wild-type embryos, no expression of myogenin and Myf-6 (MRF4), or any other myotomal markers was detected in mutant animals at E9.0 and E10.0 indicating that Myf-5 plays a crucial role during this developmental period. Significantly, the onset of MyoD expression in rostral somites of E10.5 embryos was unaffected by the Myf-5 mutation suggesting that the activation of the MyoD gene occurs independently of Myf-5 at the correct developmental time. Immediately after the activation of MyoD myogenin transcripts and protein accumulated within the myotome. The first contractile proteins of the sarcomeric apparatus appeared slightly later. By E11.5 the expression of muscle markers were indistinguishable between wild-type and Myf-5 mutant mice. The migration of muscle precursor cells that leave the somites to form limb musculature was monitored in Myf-5-mutant mice by Pax-3 expression. Pax-3-positive cells were equally found in somites and limbs of E10.0 wild-type and mutant mice indicating that myogenic factor expression at the level of somites is not a prerequisite for determination and subsequent migration of limb precursor cells.

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Cho, J. H., Y. S. Oh, K. W. Park, J. Yu, K. Y. Choi, J. Y. Shin, D. H. Kim et al. « Calsequestrin, a calcium sequestering protein localized at the sarcoplasmic reticulum, is not essential for body-wall muscle function in Caenorhabditis elegans ». Journal of Cell Science 113, n^o 22 (15 novembre 2000) : 3947–58. http://dx.doi.org/10.1242/jcs.113.22.3947.

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Calsequestrin is the major calcium-binding protein of cardiac and skeletal muscles whose function is to sequester Ca(2+)in the lumen of the sarcoplasmic reticulum (SR). Here we describe the identification and functional characterization of a C. elegans calsequestrin gene (csq-1). CSQ-1 shows moderate similarity (50% similarity, 30% identity) to rabbit skeletal calsequestrin. Unlike mammals, which have two different genes encoding cardiac and fast-twitch skeletal muscle isoforms, csq-1 is the only calsequestrin gene in the C. elegans genome. We show that csq-1 is highly expressed in the body-wall muscles, beginning in mid-embryogenesis and maintained through the adult stage. In body-wall muscle cells, CSQ-1 is localized to sarcoplasmic membranes surrounding sarcomeric structures, in the regions where ryanodine receptors (UNC-68) are located. Mutation in UNC-68 affects CSQ-1 localization, suggesting that the two possibly interact in vivo. Genetic analyses of chromosomal deficiency mutants deleting csq-1 show that CSQ-1 is not essential for initiation of embryonic muscle formation and contraction. Furthermore, double-stranded RNA injection resulted in animals completely lacking CSQ-1 in body-wall muscles with no observable defects in locomotion. These findings suggest that although CSQ-1 is one of the major calcium-binding proteins in the body-wall muscles of C. elegans, it is not essential for body-wall muscle formation and contraction.

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Tucholski, Trisha, Wenxuan Cai, Zachery R. Gregorich, Elizabeth F. Bayne, Stanford D. Mitchell, Sean J. McIlwain, Willem J. de Lange et al. « Distinct hypertrophic cardiomyopathy genotypes result in convergent sarcomeric proteoform profiles revealed by top-down proteomics ». Proceedings of the National Academy of Sciences 117, n^o 40 (23 septembre 2020) : 24691–700. http://dx.doi.org/10.1073/pnas.2006764117.

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Hypertrophic cardiomyopathy (HCM) is the most common heritable heart disease. Although the genetic cause of HCM has been linked to mutations in genes encoding sarcomeric proteins, the ability to predict clinical outcomes based on specific mutations in HCM patients is limited. Moreover, how mutations in different sarcomeric proteins can result in highly similar clinical phenotypes remains unknown. Posttranslational modifications (PTMs) and alternative splicing regulate the function of sarcomeric proteins; hence, it is critical to study HCM at the level of proteoforms to gain insights into the mechanisms underlying HCM. Herein, we employed high-resolution mass spectrometry–based top-down proteomics to comprehensively characterize sarcomeric proteoforms in septal myectomy tissues from HCM patients exhibiting severe outflow track obstruction (n = 16) compared to nonfailing donor hearts (n = 16). We observed a complex landscape of sarcomeric proteoforms arising from combinatorial PTMs, alternative splicing, and genetic variation in HCM. A coordinated decrease of phosphorylation in important myofilament and Z-disk proteins with a linear correlation suggests PTM cross-talk in the sarcomere and dysregulation of protein kinase A pathways in HCM. Strikingly, we discovered that the sarcomeric proteoform alterations in the myocardium of HCM patients undergoing septal myectomy were remarkably consistent, regardless of the underlying HCM-causing mutations. This study suggests that the manifestation of severe HCM coalesces at the proteoform level despite distinct genotype, which underscores the importance of molecular characterization of HCM phenotype and presents an opportunity to identify broad-spectrum treatments to mitigate the most severe manifestations of this genetically heterogenous disease.

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Crocini, Claudia, et Michael Gotthardt. « Cardiac sarcomere mechanics in health and disease ». Biophysical Reviews 13, n^o 5 (octobre 2021) : 637–52. http://dx.doi.org/10.1007/s12551-021-00840-7.

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AbstractThe sarcomere is the fundamental structural and functional unit of striated muscle and is directly responsible for most of its mechanical properties. The sarcomere generates active or contractile forces and determines the passive or elastic properties of striated muscle. In the heart, mutations in sarcomeric proteins are responsible for the majority of genetically inherited cardiomyopathies. Here, we review the major determinants of cardiac sarcomere mechanics including the key structural components that contribute to active and passive tension. We dissect the molecular and structural basis of active force generation, including sarcomere composition, structure, activation, and relaxation. We then explore the giant sarcomere-resident protein titin, the major contributor to cardiac passive tension. We discuss sarcomere dynamics exemplified by the regulation of titin-based stiffness and the titin life cycle. Finally, we provide an overview of therapeutic strategies that target the sarcomere to improve cardiac contraction and filling.

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Clippinger, Sarah R., Paige E. Cloonan, Lina Greenberg, Melanie Ernst, W. Tom Stump et Michael J. Greenberg. « Disrupted mechanobiology links the molecular and cellular phenotypes in familial dilated cardiomyopathy ». Proceedings of the National Academy of Sciences 116, n^o 36 (19 août 2019) : 17831–40. http://dx.doi.org/10.1073/pnas.1910962116.

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Familial dilated cardiomyopathy (DCM) is a leading cause of sudden cardiac death and a major indicator for heart transplant. The disease is frequently caused by mutations of sarcomeric proteins; however, it is not well understood how these molecular mutations lead to alterations in cellular organization and contractility. To address this critical gap in our knowledge, we studied the molecular and cellular consequences of a DCM mutation in troponin-T, ΔK210. We determined the molecular mechanism of ΔK210 and used computational modeling to predict that the mutation should reduce the force per sarcomere. In mutant cardiomyocytes, we found that ΔK210 not only reduces contractility but also causes cellular hypertrophy and impairs cardiomyocytes’ ability to adapt to changes in substrate stiffness (e.g., heart tissue fibrosis that occurs with aging and disease). These results help link the molecular and cellular phenotypes and implicate alterations in mechanosensing as an important factor in the development of DCM.

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Malkovskiy, Andrey V., Nadezda Ignatyeva, Yuanyuan Dai, Gerd Hasenfuss, Jayakumar Rajadas et Antje Ebert. « Integrated Ca2+ flux and AFM force analysis in human iPSC-derived cardiomyocytes ». Biological Chemistry 402, n^o 1 (18 novembre 2020) : 113–21. http://dx.doi.org/10.1515/hsz-2020-0212.

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AbstractWe developed a new approach for combined analysis of calcium (Ca2+) handling and beating forces in contractile cardiomyocytes. We employed human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from dilated cardiomyopathy (DCM) patients carrying an inherited mutation in the sarcomeric protein troponin T (TnT), and isogenic TnT-KO iPSC-CMs generated via CRISPR/Cas9 gene editing. In these cells, Ca2+ handling as well as beating forces and –rates using single-cell atomic force microscopy (AFM) were assessed. We report impaired Ca2+ handling and reduced contractile force in DCM iPSC-CMs compared to healthy WT controls. TnT-KO iPSC-CMs display no contractile force or Ca2+ transients but generate Ca2+ sparks. We apply our analysis strategy to Ca2+ traces and AFM deflection recordings to reveal maximum rising rate, decay time, and duration of contraction with a multi-step background correction. Our method provides adaptive computing of signal peaks for different Ca2+ flux or force levels in iPSC-CMs, as well as analysis of Ca2+ sparks. Moreover, we report long-term measurements of contractile force dynamics on human iPSC-CMs. This approach enables deeper and more accurate profiling of disease-specific differences in cardiomyocyte contraction profiles using patient-derived iPSC-CMs.

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Nishikawa, Kiisa, Stan L. Lindstedt, Anthony Hessel et Dhruv Mishra. « N2A Titin : Signaling Hub and Mechanical Switch in Skeletal Muscle ». International Journal of Molecular Sciences 21, n^o 11 (1 juin 2020) : 3974. http://dx.doi.org/10.3390/ijms21113974.

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Since its belated discovery, our understanding of the giant protein titin has grown exponentially from its humble beginning as a sarcomeric scaffold to recent recognition of its critical mechanical and signaling functions in active muscle. One uniquely useful model to unravel titin’s functions, muscular dystrophy with myositis (mdm), arose spontaneously in mice as a transposon-like LINE repeat insertion that results in a small deletion in the N2A region of titin. This small deletion profoundly affects hypertrophic signaling and muscle mechanics, thereby providing insights into the function of this specific region and the consequences of its dysfunction. The impact of this mutation is profound, affecting diverse aspects of the phenotype including muscle mechanics, developmental hypertrophy, and thermoregulation. In this review, we explore accumulating evidence that points to the N2A region of titin as a dynamic “switch” that is critical for both mechanical and signaling functions in skeletal muscle. Calcium-dependent binding of N2A titin to actin filaments triggers a cascade of changes in titin that affect mechanical properties such as elastic energy storage and return, as well as hypertrophic signaling. The mdm phenotype also points to the existence of as yet unidentified signaling pathways for muscle hypertrophy and thermoregulation, likely involving titin’s PEVK region as well as the N2A signalosome.

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Wernicke, Dirk, Corinna Thiel, Corina M. Duja-Isac, Kirill V. Essin, Matthias Spindler, Derek J. R. Nunez, Ralph Plehm et al. « α-Tropomyosin mutations Asp175Asn and Glu180Gly affect cardiac function in transgenic rats in different ways ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 287, n^o 3 (septembre 2004) : R685—R695. http://dx.doi.org/10.1152/ajpregu.00620.2003.

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To study the mechanisms by which missense mutations in α-tropomyosin cause familial hypertrophic cardiomyopathy, we generated transgenic rats overexpressing α-tropomyosin with one of two disease-causing mutations, Asp175Asn or Glu180Gly, and analyzed phenotypic changes at molecular, morphological, and physiological levels. The transgenic proteins were stably integrated into the sarcomere, as shown by immunohistochemistry using a human-specific anti-α-tropomyosin antibody, ARG1. In transgenic rats with either α-tropomyosin mutation, molecular markers of cardiac hypertrophy were induced. Ca2+ sensitivity of cardiac skinned-fiber preparations from animals with mutation Asp175Asn, but not Glu180Gly, was decreased. Furthermore, elevated frequency and amplitude of spontaneous Ca2+ waves were detected only in cardiomyocytes from animals with mutation Asp175Asn, suggesting an increase in intracellular Ca2+ concentration compensating for the reduced Ca2+ sensitivity of isometric force generation. Accordingly, in Langendorff-perfused heart preparations, myocardial contraction and relaxation were accelerated in animals with mutation Asp175Asn. The results allow us to propose a hypothesis of the pathogenetic changes caused by α-tropomyosin mutation Asp175Asn in familial hypertrophic cardiomyopathy on the basis of changes in Ca2+ handling as a sensitive mechanism to compensate for alterations in sarcomeric structure.

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Pasternak, C., S. Wong et E. L. Elson. « Mechanical function of dystrophin in muscle cells. » Journal of Cell Biology 128, n^o 3 (1 février 1995) : 355–61. http://dx.doi.org/10.1083/jcb.128.3.355.

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We have directly measured the contribution of dystrophin to the cortical stiffness of living muscle cells and have demonstrated that lack of dystrophin causes a substantial reduction in stiffness. The inferred molecular structure of dystrophin, its preferential localization underlying the cell surface, and the apparent fragility of muscle cells which lack this protein suggest that dystrophin stabilizes the sarcolemma and protects the myofiber from disruption during contraction. Lacking dystrophin, the muscle cells of persons with Duchenne muscular dystrophy (DMD) are abnormally vulnerable. These facts suggest that muscle cells with dystrophin should be stiffer than similar cells which lack this protein. We have tested this hypothesis by measuring the local stiffness of the membrane skeleton of myotubes cultured from mdx mice and normal controls. Like humans with DMD mdx mice lack dystrophin due to an x-linked mutation and provide a good model for the human disease. Deformability was measured as the resistance to indentation of a small area of the cell surface (to a depth of 1 micron) by a glass probe 1 micron in radius. The stiffness of the membrane skeleton was evaluated as the increment of force (mdyne) per micron of indentation. Normal myotubes with an average stiffness value of 1.23 +/- 0.04 (SE) mdyne/micron were about fourfold stiffer than myotubes cultured from mdx mice (0.34 +/- 0.014 mdyne/micron). We verified by immunofluorescence that both normal and mdx myotubes, which were at a similar developmental stage, expressed sarcomeric myosin, and that dystrophin was detected, diffusely distributed, only in normal, not in mdx myotubes. These results confirm that dystrophin and its associated proteins can reinforce the myotube membrane skeleton by increasing its stiffness and that dystrophin function and, therefore, the efficiency of therapeutic restoration of dystrophin can be assayed through its mechanical effects on muscle cells.

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Dorsch, Schuldt, Remedios, Schinkel, Jong, Michels, Kuster, Brundel et Velden. « Protein Quality Control Activation and Microtubule Remodeling in Hypertrophic Cardiomyopathy ». Cells 8, n^o 7 (18 juillet 2019) : 741. http://dx.doi.org/10.3390/cells8070741.

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Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disorder. It is mainly caused by mutations in genes encoding sarcomere proteins. Mutant forms of these highly abundant proteins likely stress the protein quality control (PQC) system of cardiomyocytes. The PQC system, together with a functional microtubule network, maintains proteostasis. We compared left ventricular (LV) tissue of nine donors (controls) with 38 sarcomere mutation-positive (HCMSMP) and 14 sarcomere mutation-negative (HCMSMN) patients to define HCM and mutation-specific changes in PQC. Mutations in HCMSMP result in poison polypeptides or reduced protein levels (haploinsufficiency, HI). The main findings were 1) several key PQC players were more abundant in HCM compared to controls, 2) after correction for sex and age, stabilizing heat shock protein (HSP)B1, and refolding, HSPD1 and HSPA2 were increased in HCMSMP compared to controls, 3) α-tubulin and acetylated α-tubulin levels were higher in HCM compared to controls, especially in HCMHI, 4) myosin-binding protein-C (cMyBP-C) levels were inversely correlated with α-tubulin, and 5) α-tubulin levels correlated with acetylated α-tubulin and HSPs. Overall, carrying a mutation affects PQC and α-tubulin acetylation. The haploinsufficiency of cMyBP-C may trigger HSPs and α-tubulin acetylation. Our study indicates that proliferation of the microtubular network may represent a novel pathomechanism in cMyBP-C haploinsufficiency-mediated HCM.

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FULLER, Stephen J., Elizabeth L. DAVIES, Judith GILLESPIE-BROWN, Hong SUN et Nicholas K. TONKS. « Mitogen-activated protein kinase phosphatase 1 inhibits the stimulation of gene expression by hypertrophic agonists in cardiac myocytes ». Biochemical Journal 323, n^o 2 (15 avril 1997) : 313–19. http://dx.doi.org/10.1042/bj3230313.

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The effect of constitutive expression of mitogen-activated protein kinase (MAPK) phosphatase 1 (MKP-1) on gene expression in response to hypertrophic agonists was examined in cultured neonatal rat ventricular myocytes. Luciferase (LUX) reporter genes linked to promoters for atrial natriuretic factor, ventricular myosin light chain 2, β-myosin heavy chain, skeletal muscle α-actin (SkM α-actin) and serum response element-regulated c-fos (c-fos-SRE) were transfected into cardiomyocytes. Phenylephrine (PE; 10 μM), phorbol 12-myristate 13-acetate (1 μM) and endothelin 1 (10 nM) stimulated the expression of these various reporter genes by 2.5–20-fold. MKP-1 inhibited these effects by 60–85%. In contrast, MKP-1 had no effect on the expression of a constitutively active Rous sarcoma virus–LUX reporter gene. A catalytically inactive mutant MKP-1CS (cysteine → serine mutation) and the broad-specificity protein tyrosine phosphatase 1B (PTP-1B) had no significant effect on any reporter gene tested. MKP-1 had much less effect on the morphological features accompanying agonist-induced cardiac hypertrophy. PE (10 μM) increased myocyte area by 59% but this effect was only decreased by one-third by MKP-1 and was also partly decreased (by 25%) by expression of PTP-1B. PE also altered cell shape but this was unaffected by MKP-1. There was also no clear effect of MKP-1 on the organization of the contractile apparatus into sarcomeric structures in the presence of 10 μM PE. We conclude that the transcriptional responses accompanying cardiac myocyte hypertrophy are dependent on an MKP-1-sensitive step, presumably the activation of one or members of the MAPK family, but that cell size, shape and myofibrillar organization are much less sensitive to inhibition by MKP-1.

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Hertig, C. M., M. Eppenberger-Eberhardt, S. Koch et H. M. Eppenberger. « N-cadherin in adult rat cardiomyocytes in culture. I. Functional role of N-cadherin and impairment of cell-cell contact by a truncated N-cadherin mutant ». Journal of Cell Science 109, n^o 1 (1 janvier 1996) : 1–10. http://dx.doi.org/10.1242/jcs.109.1.1.

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N-cadherin is a transmembrane Ca(2+)-dependent glycoprotein that is part of adherens junctions. It functions with the cell adhesion N-terminal extracellular domain as a site of homophilic cell-cell contacts. The intracellular C-terminal domain provides via a catenin complex the interaction with the cytoskeleton. Ectopic expression of chicken N-cadherin in adult rat cardiomyocytes (ARC) in culture was obtained after microinjection into non-dividing cardiomyocytes; it was demonstrated that the exogenous protein colocalized with the endogenous N-cadherin at the plasma membrane of the cell and formed contact sites. A dominant negative chicken N-cadherin mutant was constructed by a large deletion of the extracellular domain. This mutant was expressed and inhibited the function of the endogenous rat N-cadherin probably by competing for the catenin complex binding domain, which is essential for the formation of a stable cell-cell contact of ARC. The injected cells lost contact with neighbouring cells and retracted; the connexons of the gap junctions were pulled out as well. This could be avoided by another N-cadherin mutation, which, in addition to the N-terminal truncation, contained a deletion of the catenin binding domain. In the case of the truncated N-cadherin at the N terminus, the sarcomeric structure of the myofibrils of ARC was also affected. Myofibrils were the most vulnerable cytoskeletal structures affected by the overexpressed dominant negative N-cadherin mutation. Similar behaviour was shown when cardiomyocytes separated following Ca2+ depletion and when new cell-cell contacts were formed after Ca2+ replenishment. N-cadherin is thought to be the essential component for establishing new cell-cell contacts which eventually led to a new formation of intercalated disc-like structures in the cardiac cell culture.

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Berger, Joachim, Silke Berger, Yu Shan G. Mok, Mei Li, Hakan Tarakci et Peter D. Currie. « Genetic dissection of novel myopathy models reveals a role of CapZα and Leiomodin 3 during myofibril elongation ». PLOS Genetics 18, n^o 2 (11 février 2022) : e1010066. http://dx.doi.org/10.1371/journal.pgen.1010066.

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Myofibrils within skeletal muscle are composed of sarcomeres that generate force by contraction when their myosin-rich thick filaments slide past actin-based thin filaments. Although mutations in components of the sarcomere are a major cause of human disease, the highly complex process of sarcomere assembly is not fully understood. Current models of thin filament assembly highlight a central role for filament capping proteins, which can be divided into three protein families, each ascribed with separate roles in thin filament assembly. CapZ proteins have been shown to bind the Z-disc protein α-actinin to form an anchoring complex for thin filaments and actin polymerisation. Subsequent thin filaments extension dynamics are thought to be facilitated by Leiomodins (Lmods) and thin filament assembly is concluded by Tropomodulins (Tmods) that specifically cap the pointed end of thin filaments. To study thin filament assembly in vivo, single and compound loss-of-function zebrafish mutants within distinct classes of capping proteins were analysed. The generated lmod3- and capza1b-deficient zebrafish exhibited aspects of the pathology caused by variations in their human orthologs. Although loss of the analysed main capping proteins of the skeletal muscle, capza1b, capza1a, lmod3 and tmod4, resulted in sarcomere defects, residual organised sarcomeres were formed within the assessed mutants, indicating that these proteins are not essential for the initial myofibril assembly. Furthermore, detected similarity and location of myofibril defects, apparent at the peripheral ends of myofibres of both Lmod3- and CapZα-deficient mutants, suggest a function in longitudinal myofibril growth for both proteins, which is molecularly distinct to the function of Tmod4.

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Chang, Audrey N., et James D. Potter. « Sarcomeric Protein Mutations in Dilated Cardiomyopathy ». Heart Failure Reviews 10, n^o 3 (septembre 2005) : 225–35. http://dx.doi.org/10.1007/s10741-005-5252-6.

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McCarthy, John J., Jessica L. Andrews, Erin L. McDearmon, Kenneth S. Campbell, Brigham K. Barber, Brooke H. Miller, John R. Walker, John B. Hogenesch, Joseph S. Takahashi et Karyn A. Esser. « Identification of the circadian transcriptome in adult mouse skeletal muscle ». Physiological Genomics 31, n^o 1 (septembre 2007) : 86–95. http://dx.doi.org/10.1152/physiolgenomics.00066.2007.

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Circadian rhythms are approximate 24-h behavioral and physiological cycles that function to prepare an organism for daily environmental changes. The basic clock mechanism is a network of transcriptional-translational feedback loops that drive rhythmic expression of genes over a 24-h period. The objectives of this study were to identify transcripts with a circadian pattern of expression in adult skeletal muscle and to determine the effect of the Clock mutation on gene expression. Expression profiling on muscle samples collected every 4 h for 48 h was performed. Using COSOPT, we identified a total of 215 transcripts as having a circadian pattern of expression. Real-time PCR results verified the circadian expression of the core clock genes, Bmal1, Per2, and Cry2. Annotation revealed cycling genes were involved in a range of biological processes including transcription, lipid metabolism, protein degradation, ion transport, and vesicular trafficking. The tissue specificity of the skeletal muscle circadian transcriptome was highlighted by the presence of known muscle-specific genes such as Myod1, Ucp3, Atrogin1 ( Fbxo32), and Myh1 (myosin heavy chain IIX). Expression profiling was also performed on muscle from the Clock mutant mouse and sarcomeric genes such as actin and titin, and many mitochondrial genes were significantly downregulated in the muscle of Clock mutant mice. Defining the circadian transcriptome in adult skeletal muscle and identifying the significant alterations in gene expression that occur in muscle of the Clock mutant mouse provide the basis for understanding the role of circadian rhythms in the daily maintenance of skeletal muscle.

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Kontrogianni-Konstantopoulos, Aikaterini, Maegen A. Ackermann, Amber L. Bowman, Solomon V. Yap et Robert J. Bloch. « Muscle Giants : Molecular Scaffolds in Sarcomerogenesis ». Physiological Reviews 89, n^o 4 (octobre 2009) : 1217–67. http://dx.doi.org/10.1152/physrev.00017.2009.

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Myofibrillogenesis in striated muscles is a highly complex process that depends on the coordinated assembly and integration of a large number of contractile, cytoskeletal, and signaling proteins into regular arrays, the sarcomeres. It is also associated with the stereotypical assembly of the sarcoplasmic reticulum and the transverse tubules around each sarcomere. Three giant, muscle-specific proteins, titin (3–4 MDa), nebulin (600–800 kDa), and obscurin (∼720–900 kDa), have been proposed to play important roles in the assembly and stabilization of sarcomeres. There is a large amount of data showing that each of these molecules interacts with several to many different protein ligands, regulating their activity and localizing them to particular sites within or surrounding sarcomeres. Consistent with this, mutations in each of these proteins have been linked to skeletal and cardiac myopathies or to muscular dystrophies. The evidence that any of them plays a role as a “molecular template,” “molecular blueprint,” or “molecular ruler” is less definitive, however. Here we review the structure and function of titin, nebulin, and obscurin, with the literature supporting a role for them as scaffolding molecules and the contradictory evidence regarding their roles as molecular guides in sarcomerogenesis.

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Tsukamoto, Osamu. « Direct Sarcomere Modulators Are Promising New Treatments for Cardiomyopathies ». International Journal of Molecular Sciences 21, n^o 1 (28 décembre 2019) : 226. http://dx.doi.org/10.3390/ijms21010226.

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Mutations in sarcomere genes can cause both hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM). However, the complex genotype-phenotype relationships in pathophysiology of cardiomyopathies by gene or mutation location are not fully understood. In addition, it is still unclear how mutations within same molecule result in different clinical phenotypes such as HCM and DCM. To clarify how the initial functional insult caused by a subtle change in one protein component of the sarcomere with a given mutation is critical for the development of proper effective treatments for cardiomyopathies. Fortunately, recent technological advances and the development of direct sarcomere modulators have provided a more detailed understanding of the molecular mechanisms that govern the effects of specific mutations. The direct inhibition of sarcomere contractility may be able to suppress the development and progression of HCM with hypercontractile mutations and improve clinical parameters in patients with HCM. On the other hand, direct activation of sarcomere contractility appears to exert unexpected beneficial effects such as reverse remodeling and lower heart rate without increasing adverse cardiovascular events in patients with systolic heart failure due to DCM. Direct sarcomere modulators that can positively influence the natural history of cardiomyopathies represent promising treatment options.

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Kazmierczak, Katarzyna, Priya Muthu, Wenrui Huang, Michelle Jones, Yingcai Wang et Danuta Szczesna-Cordary. « Myosin regulatory light chain mutation found in hypertrophic cardiomyopathy patients increases isometric force production in transgenic mice ». Biochemical Journal 442, n^o 1 (27 janvier 2012) : 95–103. http://dx.doi.org/10.1042/bj20111145.

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FHC (familial hypertrophic cardiomyopathy) is a heritable form of cardiac hypertrophy caused by mutations in genes encoding sarcomeric proteins. The present study focuses on the A13T mutation in the human ventricular myosin RLC (regulatory light chain) that is associated with a rare FHC variant defined by mid-ventricular obstruction and septal hypertrophy. We generated heart-specific Tg (transgenic) mice with ~10% of human A13T-RLC mutant replacing the endogenous mouse cardiac RLC. Histopathological examinations of longitudinal heart sections from Tg-A13T mice showed enlarged interventricular septa and profound fibrotic lesions compared with Tg-WT (wild-type), expressing the human ventricular RLC, or non-Tg mice. Functional studies revealed an abnormal A13T mutation-induced increase in isometric force production, no change in the force–pCa relationship and a decreased Vmax of the acto-myosin ATPase. In addition, a fluorescence-based assay showed a 3-fold lower binding affinity of the recombinant A13T mutant for the RLC-depleted porcine myosin compared with WT-RLC. These results suggest that the A13T mutation triggers a hypertrophic response through changes in cardiac sarcomere organization and myosin cross-bridge function leading to abnormal remodelling of the heart. The significant functional changes observed, despite a low level of A13T mutant incorporation into myofilaments, suggest a ‘poison-peptide’ mechanism of disease.

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Articles de revues sur le sujet « Sarcomeric protein mutation »

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