Academic literature on the topic 'Heart Hypertrophy Molecular aspects'

Copper Deficiency (CuD) leads to hypertrophic cardiomyopathy in various experimental models. The morphological, electrophysiological, and molecular aspects of this hypertrophy have been under investigation for a long time. However the transition from compensated hypertrophy to decompensated heart failure has not been investigated in the study of CuD. We set out to investigate the contractile and hemodynamic parameters of the CuD mouse heart and to determine whether heart failure follows hypertrophy in the CuD heart. Dams of FVB mice were fed CuD or copper-adequate (CuA) diet starting from the third day post delivery and the weanling pups were fed the same diet for a total period of 5 weeks (pre- and postweanling). At week 4, the functional parameters of the heart were analyzed using a surgical technique for catheterizing the left ventricle. A significant decrease in left ventricle systolic pressure was observed with no significant change in heart rate, and more importantly contractility as measured by the maximal rate of left ventricular pressure rise (+dP/dt) and decline (−dP/dt) were significantly depressed in the CuD mice. However, left ventricle end diastolic pressure was elevated, and relaxation was impaired in the CuD animals; the duration of relaxation was prolonged. In addition to significant changes in the basal level of cardiac function, CuD hearts had a blunted response to the stimulation of the β-adrenergic agonist isoproterenol. Furthermore, morphological analysis revealed increased collagen accumulation in the CuD hearts along with lipid deposition. This study shows that CuD leads to systolic and diastolic dysfunction in association with histopathological changes, which are indices commonly used to diagnose congestive heart failure.

The development and progression of cardiac hypertrophy often leads to heart failure and death, and important modulators of hypertrophy include the histone deacetylase proteins (HDACs). Estrogen inhibits cardiac hypertrophy and progression in animal models and humans. We therefore investigated the influence of 17-β-estradiol on the production, localization, and functions of prohypertrophic (class I) and antihypertrophic (class II) HDACs in cultured neonatal rat cardiomyocytes. 17-β-Estradiol or estrogen receptor β agonists dipropylnitrile and β-LGND2 comparably suppressed angiotensin II–induced HDAC2 (class I) production, HDAC-activating phosphorylation, and the resulting prohypertrophic mRNA expression. In contrast, estrogenic compounds derepressed the opposite effects of angiotensin II on the same parameters for HDAC4 and 5 (class II), resulting in retention of these deacetylases in the nucleus to inhibit hypertrophic gene expression. Key aspects were confirmed in vivo from the hearts of wild-type but not estrogen receptor β (ERβ) gene–deleted mice administered angiotensin II and estrogenic compounds. Our results identify a novel dual regulation of cardiomyocyte HDACs, shown here for the antihypertrophic sex steroid acting at ERβ. This mechanism potentially supports using ERβ agonists as HDAC modulators to treat cardiac disease.

Cardiac hypertrophy was viewed as a compensatory response to hemodynamic stress. However, cumulative evidence obtained from studies using more advanced technologies in human patients and animal models suggests that cardiac hypertrophy is a maladaptive process of the heart in response to intrinsic and extrinsic stimuli. Although hypertrophy can normalize wall tension, it is a risk factor for QT-prolongation and cardiac sudden death. Studies using molecular biology techniques such as transgenic and knockout mice have revealed many important molecules that are involved in the development of heart hypertrophy and have demonstrated signaling pathways leading to the pathogenesis. With the same approach, the consequence of heart hypertrophy has been examined. The significance of hypertrophy in the development of overt heart failure has been demonstrated and several critical molecular pathways involved in the process were revealed. A comprehensive understanding of the threats of heart hypertrophy to patients has helped to develop novel treatment strategies. The recognition of hypertrophy as a major risk factor for QT-prolongation and cardiac sudden death is an important advance in cardiac medicine. Cellular and molecular mechanisms of this risk aspect are currently under extensively exploring. These studies would lead to more comprehensive approaches to prevention of potential life threatening arrhythmia and cardiac sudden death. The adaptation of new approaches such as functional genomics and proteomics will further advance our knowledge of heart hypertrophy.

The contraction of the heart is dependent on a process named the excitation-contraction coupling (E-C coupling). In hypertrophy and failing heart models, the expression, phosphorylation and function of key calcium handling proteins involved in E-C coupling are altered. It’s important to figure out the relationship changes between calcium channel activity and calcium release from sarcoplasmic reticulum (SR). This review will therefore focus on novel components of E-C coupling dysfunction in hypertrophy and failing heart, such as L-type Ca2+ channel (LCC), ryanodine receptor type-2 channel (RyR2) and SR Ca ATPase (SERCA), and how these molecular modifications altered excitation-contraction coupling. A lot of literature was well read and sorted. Recent findings in E-C coupling during hypertrophy and heart failure were focused on. Most importantly, the electrophysiological and signal pathway data was carefully analyzed. This review summarizes key principles and highlights novel aspects of E-C coupling changes during hypertrophy and heart failure models. Although LCC activity changed little, the loss of notch in action potential, reduced Ca2+ transient amplitude and desynchronized Ca2+ sparks resulted in a decreased contraction strength in hypertrophy and heart failure models. What’s more, L-type Ca2+ current becomes ineffective in triggering RyR2 Ca2+ release from SR and the SR uptake is reduced in some models. It has great meanings in understanding the E-C coupling changes during different heart diseases. Theses novel changes suggest potential therapeutic approaches for certain types of hypertrophy and heart failure.

The concepts underlying hypertrophic cardiomyopathy (HCM) pathogenesis have evolved greatly over the last 60 years since the pioneering work of the British pathologist Donald Teare, presenting the autopsy findings of “asymmetric hypertrophy of the heart in young adults”. Advances in human genome analysis and cardiac imaging techniques have enriched our understanding of the complex architecture of the malady and shaped the way we perceive the illness continuum. Presently, HCM is acknowledged as “a disease of the sarcomere”, where the relationship between genotype and phenotype is not straightforward but subject to various genetic and nongenetic influences. The focus of this review is to discuss key aspects related to molecular mechanisms and imaging aspects that have prompted genotype–phenotype correlations, which will hopefully empower patient-tailored health interventions.

The aim of this opinion paper is to point out the knowledge gap between evidence on the molecular level and clinical diagnostic possibilities in left ventricular hypertrophy (LVH) regarding the prediction of ventricular arrhythmias and monitoring the effect of therapy. LVH is defined as an increase in left ventricular size and is associated with increased occurrence of ventricular arrhythmia. Hypertrophic rebuilding of myocardium comprises interrelated processes on molecular, subcellular, cellular, tissue, and organ levels affecting electrogenesis, creating a substrate for triggering and maintaining arrhythmias. The knowledge of these processes serves as a basis for developing targeted therapy to prevent and treat arrhythmias. In the clinical practice, the method for recording electrical phenomena of the heart is electrocardiography. The recognized clinical electrocardiogram (ECG) predictors of ventricular arrhythmias are related to alterations in electrical impulse propagation, such as QRS complex duration, QT interval, early repolarization, late potentials, and fragmented QRS, and they are not specific for LVH. However, the simulation studies have shown that the QRS complex patterns documented in patients with LVH are also conditioned remarkably by the alterations in impulse propagation. These QRS complex patterns in LVH could be potentially recognized for predicting ventricular arrhythmia and for monitoring the effect of therapy.

Left ventricle hypertrophy is a common outcome of pressure overload stimulus closely associated with hypertension. This process is triggered by adverse molecular signalling, gene expression, and proteome alteration. Proteomic research has revealed that several molecular targets are associated with pathologic cardiac hypertrophy, including angiotensin II, endothelin-1 and isoproterenol. Several metabolic, contractile, and stress-related proteins are shown to be altered in cardiac hypertrophy derived by hypertension. On the other hand, exercise is a nonpharmacologic agent used for hypertension treatment, where cardiac hypertrophy induced by exercise training is characterized by improvement in cardiac function and resistance against ischemic insult. Despite the scarcity of proteomic research performed with exercise, healthy and pathologic heart proteomes are shown to be modulated in a completely different way. Hence, the altered proteome induced by exercise is mostly associated with cardioprotective aspects such as contractile and metabolic improvement and physiologic cardiac hypertrophy. The present review, therefore, describes relevant studies involving the molecular characteristics and alterations from hypertensive-induced and exercise-induced hypertrophy, as well as the main proteomic research performed in this field. Furthermore, proteomic research into the effect of hypertension on other target-demerged organs is examined.

The cardiac fibroblast is a remarkably versatile cell type that coordinates inflammatory, fibrotic and hypertrophic responses in the heart through a complex array of intracellular and intercellular signaling mechanisms. One important signaling node that has been identified involves p38 MAPK; a family of kinases activated in response to stress and inflammatory stimuli that modulates multiple aspects of cardiac fibroblast function, including inflammatory responses, myofibroblast differentiation, extracellular matrix turnover and the paracrine induction of cardiomyocyte hypertrophy. This review explores the emerging importance of the p38 MAPK pathway in cardiac fibroblasts, describes the molecular mechanisms by which it regulates the expression of key genes, and highlights its potential as a therapeutic target for reducing adverse myocardial remodeling.

Gene expression is needed for the maintenance of heart function under normal conditions and in response to stress. Each cell type of the heart has a specific program controlling transcription. Different types of stress induce modifications of these programs and, if prolonged, can lead to altered cardiac phenotype and, eventually, to heart failure. The transcriptional status of a gene is regulated by the epigenome, a complex network of DNA and histone modifications. Until a few years ago, our understanding of the role of the epigenome in heart disease was limited to that played by histone deacetylation. But over the last decade, the consequences for the maintenance of homeostasis in the heart and for the development of cardiac hypertrophy of a number of other modifications, including DNA methylation and hydroxymethylation, histone methylation and acetylation, and changes in chromatin architecture, have become better understood. Indeed, it is now clear that many levels of regulation contribute to defining the epigenetic landscape required for correct cardiomyocyte function, and that their perturbation is responsible for cardiac hypertrophy and fibrosis. Here, we review these aspects and draw a picture of what epigenetic modification may imply at the therapeutic level for heart failure.

Vasodilator-stimulated phosphoprotein (VASP) is a major substrate for cyclic nucleotide-dependent kinases that has been implicated in cardiac pathology, yet many aspects of VASP's molecular regulation in cardiomyocytes are incompletely understood. In these studies, we explored the role of VASP, both in signaling pathways in isolated murine myocytes, as well as in a model of cardiac hypertrophy in VASPnull mice. We found that the β-adrenergic agonist isoproterenol promotes the rapid and reversible phosphorylation of VASP at Ser157 and Ser239. Forskolin and the cAMP analog 8-(4-chlorophenylthio)-cAMP promote a similar pattern of VASP phosphorylation at both sites. The effects of isoproterenol are blocked by atenolol and by compound H-89, an inhibitor of the cAMP-dependent protein kinase. By contrast, phosphorylation of VASP only at Ser239 is seen following activation of particulate guanylate cyclase by atrial natriuretic peptide, or following activation of soluble guanylate cyclase by sodium nitroprusside, or following treatment of myocytes with cGMP analog. We found that basal and isoproterenol-induced VASP phosphorylation is entirely unchanged in cardiomyocytes isolated from either endothelial or neuronal nitric oxide synthase knockout mice. In cardiomyocytes isolated from diabetic mice, only basal VASP phosphorylation is increased, whereas, in cells isolated from mice subjected to ascending aortic constriction (AAC), we found a significant increase in basal VASP expression, along with an increase in VASP phosphorylation, compared with cardiac myocytes isolated from sham-operated mice. Moreover, there is further increase in VASP phosphorylation in cells isolated from hypertrophic hearts following isoproterenol treatment. Finally, we found that VASPnull mice subjected to transverse aortic constriction develop cardiac hypertrophy with a pattern similar to VASP+/+ mice. Our findings establish differential receptor-modulated regulation of VASP phosphorylation in cardiomyocytes by cyclic nucleotides. Furthermore, these studies demonstrate for the first time that VASP expression is upregulated in hypertrophied heart.

Thesis (MScMedSc)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Left ventricular hypertrophy (LVH) occurs when the cardiomyocytes in the left ventricle become enlarged by increasing in mass in response to haemodynamic pressure overload. This can either be attributed to a normal physiological response to exercise or can be the result of a maladaptive process or disease state, such as chronic hypertension. Hypertrophic cardiomyopathy (HCM) is the most common form of Mendelian-inherited cardiac disease. A defining characteristic thereof is primary LVH that occurs when there are no other hypertrophy-predisposing conditions present. Therefore, HCM provides a unique opportunity to study the molecular determinants of LVH in the context of a Mendelian disorder, instead of in more complex disorders such as hypertension. Over 1000 HCM-causing mutations in 19 genes have been identified thus far, most of them encoding sarcomeric proteins residing in the sarcomeric C-zone. However, for many HCM patients no disease-causing genes have been identified. Moreover, studies have shown phenotypic variation in presentation of disease in, as well as between, families in which the same HCM-causing mutation segregates. This has led many investigators to conclude that genetic modifiers of hypertrophy exist. The aim of the study was to identify novel plausible HCM-causing or modifier genes by searching for interactors of a known HCM-causing protein, namely titin. The hypothesis was that genes encoding proteins, which interact with proteins that are encoded by known HCM-causative genes, may also be considered HCM-causing or may modify the HCM phenotype. To this end, the aim was to identify novel interactors of the 11-domain super-repeat region of titin, which resides within the sarcomeric C-zone, using yeast two-hybrid analysis. Five putative interactors of the 11-domain super-repeat region of titin were identified in this study. These interactions were subsequently verified by colocalisation in H9C2 rat cardiomyocytes, providing further evidence for possible interactions between titin and these proteins. The putative interactor proteins of titin determined from the Y2H library screen were: filamin C (FLNC), phosphatidylethanolamine-binding protein 4 (PEBP4), heart-type fatty acid binding protein 3 (H-FABP3), myomesin 2 (MYOM2) and myomesin 1 (MYOM1). The FLNC gene could be a candidate for cardiac diseases, especially cardiomyopathies that are associated with hypertrophy or developmental defects. The putative interaction of titin and PEBP4 is speculated to be indicative of the formation of the interstitial fibrosis and myocyte disarray seen in HCM. Heart-type fatty acid-binding protein 3 has prognostic value to predict recurrent cardiac events. Its suggested interaction with titin is speculated to play a role in inhibiting its functional abilities. Myomesin 2 is jointly responsible, with MYOM1, for the formation of a head structure on one end of the titin string that connects the Z and M bands of the sarcomere. This is speculated to be linked to a developmental error with the result being a defect in sarcomeric structure formation, which could result in pathologies such as HCM. Therefore, these identified proteins could likely play a functional role in HCM due to their interactions with titin. This research could thus help with new insights into the further understanding of HCM patho-aetiology.
AFRIKAANSE OPSOMMING: Linker ventrikulêre hipertrofie (LVH) ontstaan wanneer die kardiomyosiete in die linkerventrikel vergroot as gevolg van 'n verhoging in massa in reaksie op hemodinamiese drukoorlading. Dit kan toegeskryf word aan 'n normale fisiologiese respons op oefening of kan die gevolg wees van 'n wanaangepaste of siektetoestand, soos chroniese hipertensie. Hipertrofiese kardiomiopatie (HKM) is die mees algemene vorm van Mendeliese oorerflike hartsiekte. 'n Bepalende eienskap daarvan is primêre LVH, wat plaasvind wanneer daar geen ander hipertrofie-predisponerende voorwaardes teenwoordig is nie. Gevolglik bied HKM 'n unieke geleentheid om die molekulêre derterminante van LVH te bestudeer, in die konteks van 'n Mendeliese oorerflike siekte, in plaas van om dit in die meer komplekse siektes soos hoë bloeddruk te bestudeer. Meer as 1000 HKM-veroorsakende mutasies is tot dusver in 19 gene geïdentifiseer. Die meeste van hulle kodeer vir sarkomeriese proteïene wat in die C-sone voorkom. Egter, vir baie HKM-pasiënte is geen siekte-veroorsakende gene al geïdentifiseer nie. Daarbenewens het studies getoon dat variasie in fenotipiese aanbieding van die siekte in, sowel as tussen, families voorkom wat dieselfde HKM-veroorsakende mutasie het. Dit het daartoe gelei dat baie navorsers tot die gevolgtrekking gekom het dat genetiese wysigers van hipertrofie wel bestaan. Die doel van die studie was om nuwe moontlike HKM-veroorsakende of wysiger-gene te identifiseer deur te soek vir interaktors van 'n bekende HKM-veroorsakende proteïen, naamlik titin. Die hipotese was dat gene wat vir proteïene kodeer, wat in wisselwerking is met proteïene wat geïnkripteer word deur bekende HKM-veroorsakende gene, ook oorweeg kan word om HKM te veroorsaak. Dit kan ook die HKM fenotipe verander. Dus was die doel om nuwe interaktors van die 11-domein super-herhaalstreek van titin, soos gevind binne die sarkomeriese C-sone, te identifiseer deur middel van gis-twee-hibried-analise. Vyf vermeende interaktors van die 11-domein super-herhaalstreek van titin is in hierdie studie geïdentifiseer. Hierdie interaksies is later geverifieer met behulp van ko-lokalisering in H9C2-rotkardiomyosiete, wat verdere bewyse vir moontlike interaksies tussen titin en hierdie proteïene verskaf. Die vermeende interaktor-proteïene van titin wat bepaal is vanaf die gis-twee-hibried-biblioteeksifting was as volg: filamin C (FLNC), phosphatidylethanolamine-bindingsproteïen 4 (PEBP4), hart-tipe-vetsuur bindingsproteïen 3 (H-FABP3), myomesin 2 (MYOM2) en myomesin 1 (MYOM1). Die FLNC-geen kan 'n kandidaat vir kardiale siektes, veral kardiomiopatieë, wees wat geassosieer word met hipertrofie of ontwikkelingsafwykings. Die vermeende interaksie van titin en PEBP4 dui daarop om 'n aanduiding te wees vir die vorming van die interstisiële fibrose en miokardiale wanorde, soos gesien in HKM. Hart-tipe-vetsuur bindingsproteïen 3 het prognostiese waarde om herhalende kardiale gebeure te voorspel. Verder dui sy voorgestelde interaksie met titin moontlik daarop dat dit 'n rol kan speel in die inhibering van sy funksionele vermoëns. Myomesin 2 tesame met MYOM1 is verantwoordelik vir die vorming van 'n kopstruktuur aan die een kant van die titinstring wat dan die Z- en M-bande van die sarkomeer verbind. Daar word vermoed dat dit gekoppel is aan 'n ontwikkelingsfout, met die gevolg dat daar 'n defek is in sarkomeriese struktuurvorming, wat weer kan lei tot patologieë soos HKM.
Mrs Wendy Ackerman
Prof Paul van Helden
National Research Foundation (NRF)
Stellenbosch University

The a of TNFa in title is the Greek alpha.
Thesis (MSc)--University of Stellenbosch, 2002.
ENGLISH ABSTRACT: Background: Cardiac hypertrophy is an adaptive process occurring in response to mechanical overload or tissue injury. The stimuli for cardiac hypertrophy are diverse and vary from increased afterload on the heart to cardiac remodeling in response to cytokines. Amongst others, obesity is characterized by excessive body weight resulting in metabolic disorders. This excess body weight necessitates an increased blood and oxygen delivery to the peripheral tissues, which is achieved by an elevated cardiac output. Total blood volume is also increased in the obese due to the increased tissue volume and vascularity. With time, the obesity induced increase in cardiac preload results in left ventricular hypertrophy and dilatation. Obesity is also associated with complications such as hypertension, insulin resistance and impaired glucose metabolism. In addition, adipose tissue has been implicated to contribute to elevated circulating TNFa levels in obesity and may contribute to the pathophysiology of the heart in obese individuals. The heart is a major cytokine-producing organ that generates amongst others tumor necrosis factor a (TNFa). TNFa is a proinflammatory cytokine, which acts to increase its own production, has cytotoxic and cytostatic effects on certain tumor cells and influences growth and differentiation in virtually all cell types including cardiomyocytes. Elevated levels of TNFa are detected peripherally in almost all forms of cardiac injury and in hypertrophic cardiomyopathy. These elevations are proposed to be deleterious to the heart, although an adaptive role for low levels of TNFa has been proposed. Aim: The aim of the study was to determine whether there is a correlation between obesity and serum, myocardial, and adipose tissue TNFa levels and cardiac hypertrophy. We also wished to determine whether the hearts from the obese animals functioned normally under normoxic conditions and whether they responded differently to ischaemia/reperfusion when compared with their concurrent controls. Materials and Methods: Male Sprague-Dawley rats (n=100) were fed a high caloric diet (HCD) containing 33% rat chow, 33% condensed milk, 7% sucrose and 27% water, or standard laboratory rat chow for 6-12 weeks. Food consumption, body weight gain, heart weight and tibia length were measured. Serum glucose, insulin and lipid levels were also determined. Hearts were excised and perfused on the isolated Working Heart perfusion apparatus and cardiac function was monitored and documented. Hearts were then subjected to 15 minutes of total global ischaemia at 370C, and reperfused for 30 minutes. Cardiac function was again documented. A separate series of hearts were freeze-clamped at different time points during the experimental protocol and stored in liquid nitrogen for the determination of myocardial TNFa and cGMP levels. Serum TNFa levels were determined after 12 weeks on the high caloric or normal/control diet. After 12 weeks on the diet myocardial TNFa levels of the HCD fed animals and their concurrent controls were determined before and during ischaemia. Adipose tissue and myocardial tissue TNFa levels were also determined after 6, 9 and 12 weeks on the respective diets. Myocardial cGMP levels were measured in the HCD fed rats and the control rats after 6, 9, and 12 weeks. These data were used as an indirect index to determine whether the myocardial NOcGMP pathway was activated in the normoxic hearts on the respective diets. Results: The body weight of the HCO fed animals was significantly higher compared with their respective controls after 12 weeks on the diet (459.9 ± 173.8 g and 271.5 ± 102.6 g respectively (p<0.05». The HCO fed animals also had heart weight to body weight ratios that were significantly greater compared with the controls (4.2 ± 0.1 mglg and 3.7 ± 0.1 mglg respectively (p<0.05». The plasma glucose levels of the HCO fed animals were higher than their respective controls (9.2 ± 0.3 mmoiII and 7.8 ± 0.3 mmoiII respectively (p<0.05)), but their insulin levels were similar (12.87 ± 1.02 IlIUlml and 12.42 ± 5.06 IlIU/ml). Plasma lipid profiles (plasma cholesterol, high density lipoprotein (HOL) cholesterol and plasma triacylglyceride (TAG)) were abnormal in the HCO fed animals compared with the control rats. Plasma TAG levels in the HCO fed animals were significantly higher compared with the control rats (0.664 ± 0.062 mmoiII and 0.503 ± 0.043 (p<0.05», while plasma cholesterol levels (1.794 ± 0.058 mmoIII and 2.082 ± 0.062 mmoiII (p<0.05» and HOL cholesterol levels were significantly lower (1.207 ± 0.031 mmoiII and 1.451 ± 0.050 mmoiII (p<0.05». Cardiac mechanical function was similar for both groups before ischaemia, but the percentage aortic output recovery was lower for the hearts from the HCO fed animals when compared with their controls (47.86 ± 7.87% and 66.67 ± 3.76 % respectively (p<0.05». Serum TNFa levels of the HCO fed animals were higher compared with the control animals (51.04 ± 5.14 AU and 31.46 ± 3.72 AU respectively (p<0.05», but myocardial TNFa levels remained lower in these animals (312.0 ± 44.7 pglgram ww and 571.4 ± 132.9 pg/gram ww respectively (p<0.05)). During ischaemia these myocardial TNFa levels increased above those of the controls (442.9 ± 12.4 pg/gram ww and 410.0 ± 12.5 pg/gram ww respectively (p<0.05)). The adipose tissue TNFa levels were significantly increased after 12 weeks on the high caloric diet compared with the control animals (4.4 ± 0.4 pg/gram ww and 2.5 ± 0.3 pg/gram ww respectively (p<0.05)). There was no significant difference in the myocardial cGMP levels of the HCD rats compared with the conrol rats after 6, 9 and 12 weeks. Conclusion: 1) The high caloric diet induced obesity, which lead to cardiac hypertrophy in this study. 2) There was a strong correlation between elevated adipose tissue and serum TNFa levels, and cardiac hypertrophy. 3) Elevated serum TNFa levels did not lead to activation of the myocardial NO-cGMP pathway in the normoxic hearts in this model. 4) The hypertrophied hearts from the HCD fed animals had poorer post-ischaemie myocardial functions than their concurrent controls.
AFRIKAANSE OPSOMMING: Agtergrond: Miokardiale hipertrofie is In aanpassing wat gebeur as In gevolg van meganiese oorbelading of weefsel beskadiging. Verskillende stimuli kan tot miokardiale hipertrofie aanleiding gee soos byvoorbeeld In verhoging in nalading, of miokardiale hermodellering in respons op sitokiene. Verhoging van voorbelading in vetsug mag ook tot hipertrofie aanleiding gee. Vetsug word gekenmerk deur In oormatige liggaamsmassa wat tot metaboliese versteurings lei. Die oormatige liggaamsmassa vereis In verhoging in bloed- en suurstofverskaffing aan die perifere weefsel wat deur In verhoging in die kardiale uitset vermag kan word. Die bloed volume van In vetsugtige individu word ook verhoog as gevolg van In verhoging in weefselvolume en vaskulariteit en met verloop van tyd induseer die verhoogde kardiale voorbelading linker ventrikulêre hipertrofie en dilatasie. Vetsug word ook met verskeie ander siekte toestande soos hipertensie, insulien weerstandigheid en versteurde glukose metabolisme, geassosieer. Vetweefsel dra ook by tot verhoging van tumor nekrose faktor alfa (TNFa) vlakke in die bloed, wat op sy beurt tot miokardiale hipertrofie mag bydra. TNFa is In proinflammatoriese sitokien wat sy eie produksie kan stimuleer. Dit het ook sitotoksiese en sitostatiese effekte op sekere tumor selle en kan groei en differensiasie in bykans alle seltipes, insluitende kardiomiosiete, stimuleer. Die hart kan ook TNFa produseer en verhoogde TNFa vlakke word feitlik in alle vorms van miokardiale besering en hipertrofiese kardiomiopatie waargeneem. Daar word voorgestel dat verhoogde TNFa vlakke vir die hart nadelig is, ten spyte van die vermoeding dat die sitokien In potensiële aanpassings rol by laer vlakke het. Doelstelling: Die doel van hierdie studie was om vas te stelof daar 'n verband tussen vetsug en serum, miokardiale en vetweefsel TNFa vlakke en miokardiale hipertrofie, bestaan. Ons het ook gepoog om te bepaal of harte van vetsugtige diere normaal funksioneer en of die response van sulke harte op isgemie-herperfusie van die van ooreenstemmende kontroles verskil. Materiaal en tegnieke: Manlike Sprague-Dawley rotte (n=100) is vir 6-12 weke op 'n hoë kalorie dieët (HKD) geplaas. Die HKD het uit 33% rotkos, 33% gekondenseerde melk, 7% sukrose en 27% water bestaan. Kontrole diere het standaard laboratorium rotkos ontvang. Voedselinname, liggaamsmassa toename, serum insulien, glukose en lipied vlakke is ook bepaal. Harte is geïsoleer en geperfuseer volgens die Werk Hart perfusie metode en hart funksie is gemonitor en gedokumenteer. Harte is vervolgens aan 15 minute globale isgemie by 3rC blootgestel en daarna weer vir 30 minute geherperfuseer waartydens hartfunksie weer gedokumenteer is. 'n Aparte groep harte is op spesifieke tydsintervalle gedurende die eksperimentele protokol gevriesklamp en in vloeibare stikstof gestoor vir die bepaling van miokardiale TNFa en sGMP vlakke. Serum TNFa vlakke is bepaal na 12 weke op die dieët. Na die diere 12 weke op die HKD was, is hierdie diere en hulooreenstemmende kontroles se miokardiale TNFa vlakke voor en na isgemie bepaal. Vetweefsel en miokardiale TNFa vlakke is ook onderskeidelik na 6, 9 en 12 weke bepaal. Miokardiale sGMP vlakke is in die HKD diere en in die kontrole diere na 6, 9 en 12 weke bepaal. sGMP vlakke is gebruik as 'n indirekte indeks van aktivering van die miokardiale NO-sGMP boodskapper pad. Resultate: Na 12 weke op die dieët was die liggaamsmassa van die HKD diere beduidend hoër in vergeleke met hulooreenstemmende kontroles (459.9 ± 173.8 g en 271.5 ± 102.6 g (p<0.05)). Die HKD diere se hart massa tot liggaam massa verhouding was ook beduidend hoër in vergelyking met die van kontroles (4.2 ± 0.1 mglg en 3.7 ± 0.1 mglg (p<0.05)). Alhoewel insulien vlakke dieselfde was (12.42 ± 5.06 j.lIU/ml en 12.87 ± 1.02 j.lIU/ml), was serum glukose vlakke van die HKD diere hoër as die van die ooreenstemmende kontroles (9.2 ± 0.3 mmoiii en 7.8 ± 0.3 mmoiii (p<0.05)). Plasma lipied profiele (HOL cholesterol, plasma cholesterol en trigliseriede) was abnormaal in die HKD diere. Plasma TAG vlakke in die HKD diere was beduidend hoër as die van die kontroles (0.664 ± 0.062 mmoiii en 0.503 ± 0.043 (p<0.05)), terwyl plasma cholesterol vlakke (1.794 ± 0.058 mmoiii en 2.082 ± 0.062 mmoiii (p<0.05)) en HOL cholesterol vlakke beduidend laer was (1.207 ± 0.031 mmoiii en 1.451 ± 0.050 mmoiii (p<0.05)). Miokardiale meganiese funksie was dieselfde vir beide groepe voor isgemie, maar die persentasie aorta omset herstel tydens herperfusie was laer in die HKD diere in vergelyking met die van kontrole diere (47.86 ±. 7.87% en 66.67 ± 3.76% (p<0.05)). Serum TNFa vlakke van die HKD diere was beduidend hoër as die van kontrole diere (51.04 ± 5.14 AU en 31.46 ± 3.72 AU (p<0.05)), maar miokardiale TNFa vlakke was laer (312.0 ± 44.7 pglgram nat gewig en 571.4 ± 132.9 pglgram nat gewig (p<0.05)). Die vetweefsel TNFa vlakke was ook beduidend verhoog na 12 weke op "n hoë kalorie dieët wanneer dit vergelyk word met die van kontrole diere (4.4 ± 0.4 pglgram nat gewig en 2.5 ± 0.3 pglgram nat gewig respektiewelik (p<0.05)). Daar was geenbeduidende verskille in die miocardiale vlakke van sGMP in die HKD diere in vergelyking met die kontroles na 6, 9 en 12 weke. Gevolgtrekkings: 1) "n Hoë kalorie dieët het in dié studie vetsug geïnduseer en tot miokardiale hipertrofie gelei. 2) Daar was "n positiewe korrelasie tussen verhoogde vetweefsel en serum TNFa vlakke, en miokardiale hipertrofie. 3) Verhoogde serum TNFa vlakke het nie tot die aktivering van die miokardiale NO-sGMP pad in hierdie model gelei nie. 4) Die hipertrofiese harte het tydens herperfusie ná isgemie swakker as hulooreenstemmende kontroles gefunksioneer.

Rho guanosine triphosphatases (GTPases) act as molecular switches, cycling between two conformational states: an active, GTP-bound state and an inactive, GDP-bound state to control many complex cellular events in eukaryotic cells. Many Rho GTPases, including RhoA, Cdc42 and Rac1, have been extensively characterized and are involved in actin reorganization, activation of MAPK cascades, cell cycle progression, cellular proliferation, invasion, differentiation and apoptosis. TC10 was identified and classified as a Rho GTPase over ten years ago, however the precise role of this protein, which is highly expressed in cardiac and skeletal muscle, has only recently been explored in vitro and remains unexplored in vivo. Based on the unique expression pattern of TC10, we set out to investigate the role of TC10 by generating transgenic mice over-expressing activated TC10Q75L under the control of the cardiac-specific alpha-myosin heavy chain promoter. Transgenic mice expressing high levels of TC10Q75L showed pronounced atrial enlargement, evidence of left ventricular hypertrophy and diminished cardiomyocyte membrane integrity. In vitro, transgenic primary cardiomyocytes showed marked reorganization of the actin cytoskeleton, leading to the formation of actin-containing filopodial extensions, loss of stress fibers and actin aggregation. Together, these data suggest that TC10 functions to regulate cellular signalling to the actin cytoskeleton and processes associated with cell growth, leading to cardiac hypertrophy in TC10Q75L transgenic mice.

Physiology
Ph.D.
Pathological hypertrophy leads to cardiac dysfunction and heart failure. It is not clearly defined how this process occurs in the cardiomyocyte, or how the pathology can be effectively treated. There are numerous processes that lead to pathological hypertrophy. We developed two models to study pathological hypertrophy and the role that Ca2+ plays. In one model, we administered clinical doses of the leukemia therapeutic drug imatinib to neonatal ventricular cardiomyocytes. This drug has recently been found to be cardiotoxic, and we set out to understand if Ca2+ is involved. In the second model, we developed mice with overexpression of the Ca2+ entrance channel, the L-type calcium channel (LTCC), which leads to pathological hypertrophy over time. We instituted a chronic exercise regimen on these mice to learn if physiological hypertrophy can ameliorate detrimental aspects of pathological hypertrophy. After cardiomyocytes were treated with imatinib, they expressed enhanced Ca2+ activity. Levels of atrial natriuretic peptide (ANP) were up, signifying pathological hypertrophy. We determined that Ca2+ was activating Calcineurin, leading to translocation of nuclear factor of activated T-cells (NFAT) into the nucleus, resulting in hypertrophy. This activity was blocked by Ca2+ and Calcineurin inhibitors. We concluded that imatinib causes Ca2+ induced pathological hypertrophy. When mice with LTCC overexpression were exercised, they exhibited enhanced cardiac function. They also had thicker septal walls and increased chamber diameter, hallmarks of physiological hypertrophy. Heart weight to body weight ratio was significantly higher after exercise. When isolated hearts were administered ischemia/reperfusion injury, the exercised hearts showed a significant improvement in recovery compared to sedentary LTCC overexpressed hearts. Calcium activity was enhanced at the cardiomyocyte level in both mouse lines of exercised mice. In conclusion, hearts with a pathological hypertrophic phenotype can enhance function and achieve cardioprotection through chronic exercise.
Temple University--Theses

The regulation of cardiac-specific genes such as GATA-4 and its co-factor FOG-2 is paramount for normal heart development and function. Indeed, those mechanisms that regulate GATA-4 and FOG-2 function, such as nuclear transport and the post-translational modification of SUMOylation, are of critical importance for cardiogenesis. Therefore the aims of this study were to: i) elucidate the nuclear transport mechanisms of GATA-4; ii) determine the function of SUMOylation on the biological activity of both GATA-4 and FOG-2; and iii) examine how these mechanisms impact on the role of GATA-4 and FOG-2 in cardiac hypertrophy. Firstly, we characterised a non-classical nuclear localisation signal that mediates active import of GATA-4 in both HeLa cells and cardiac myocytes. Fine mapping studies revealed four crucial residues within this region that interacted with importin ?? to mediate GATA-4 import via the non-classical import pathway. In addition, a cardiac myocyte-specific CRM1-dependent nuclear export signal, which consists of three essential leucine residues, was identified. We also investigated the residues of GATA-4 that are responsible for its DNAbinding activity and therefore transcriptional control of cardiac-specific genes. Secondly, we demonstrated that SUMOylation of both GATA-4 and FOG-2 is exclusively carried out by SUMO-2/3. Moreover, SUMOylation is involved in the nuclear localisation of both GATA-4 and FOG-2 in cardiac myocytes as well as the transcriptional regulation of cardiac-specific genes, such as cardiac troponin I. Finally, and perhaps most biologically significant, we showed that nuclear transport as well as SUMOylation of GATA-4 is imperative for the ability of GATA-4 to induce cardiac hypertrophy. Moreover, it was determined that FOG-2 SUMOylation is involved in the ability of FOG-2 to protect against cardiac hypertrophy. In conclusion, the current study provides detailed information on the nuclear transport pathways of GATA-4 as well as the SUMOylation of both GATA-4 and FOG-2 and the role these two mechanisms play in gene transcription and cardiac hypertrophy.

Thesis (MScMed)--Stellenbosch University, 2008.
ENGLISH ABSTRACT: In hypertrophic cardiomyopathy (HCM), an autosomal dominant disorder, hypertrophy is variable within and between families carrying the same causal mutation, suggesting a role for modifier genes. Associations between left ventricular hypertrophy and left ventricular pressure overload suggested that sequence variants in genes involved in the Renin-Angiotensin Aldosterone System (RAAS) may act as hypertrophy modifiers in HCM, but some of these studies may have been confounded by, amongst other things, lack of adjustment for hypertrophy covariates. To investigate this hypothesis, twenty one polymorphic loci spread across six genes (ACE1, AGT, AGTR1, CYP11B2, CMA and ACE2) of the RAAS were genotyped in 353 subjects from 22 South African HCM-families, in which founder mutations segregate. Genotypes were compared to 17 echocardiographically-derived hypertrophic indices of left ventricular wall thickness at 16 segments covering three longitudinal levels. Family-based association was performed by quantitative transmission disequilibrium testing (QTDT), and mixed effects models to analyse the X-linked gene ACE2, with concurrent adjustment for hypertrophy covariates (age, sex, systolic blood pressure (BP), diastolic BP, body surface area, heart rate and mutation status). Strong evidence of linkage in the absence of association was detected between polymorphisms at ACE1 and posterior and anterior wall thickness (PW and AW, respectively) at the papillary muscle level (pap) and apex level (apx). In single-locus analysis, statistically significant associations were generated between the CYP11B2 rs3097 polymorphism and PW at the mitral valve level (mit) and both PWpap and inferior wall thickness (IW)pap. Statistically significant associations were generated at three AGTR1 polymorphisms, namely, between rs2640539 and AWmit, rs 3772627 and anterior interventricular septum thickness at pap and rs5182 and both IWpap and AWapx. Furthermore, mixed effects model detected statistically significant association between the ACE2 rs879922 polymorphism and both posterior interventricular septum thickness and lateral wall thickness at mit in females only. These data indicate a role for RAAS gene variants, independent of hypertrophy covariates, in modifying the phenotypic expression of hypertrophy in HCM-affected individuals.
AFRIKAANSE OPSOMMING: Hipertrofiese kardiomiopatie (HCM), ‘n autosomale dominante afwyking, toon hoogs variërende hipertrofie binne en tussen families wat dieselfde siekte-veroorsakende mutasie het, hierdie dui op die moontlike betrokkenheid van geassosieerde modifiserende gene. Assosiasies tussen linker ventrikulêre hipertrofie en linker ventrikulêre druk-oorlading stel voor dat volgorde variasies in gene betrokke in die Renin-Angiotensin Aldosteroon Sisteem (RAAS) mag optree as hipertrofie modifiseerders in HCM. Sommige van hierdie soort studies is egter beperk omdat hulle nie gekompenseer het vir kovariante van hipertrofie nie. Om hierdie hipotese te ondersoek, is die genotipe bepaal by een-en-twintig polimorfiese lokusse, verspreid regoor ses RAAS gene (ACE1, AGT, AGTR1, CYP11B2, CMA and ACE2), in 353 kandidate vanuit 22 Suid-Afrikaanse HCM-families in wie stigter mutasies segregeer. Genotipes was vergelyk met 17 eggokardiografies afgeleide hipertrofiese indekse van linker ventrikulêre wanddikte by 16 segmente wat oor drie longitudinale vlakke strek. Familie-gebaseerde assosiasies was bestudeer deur kwantitatiewe transmissie disequilibrium toetsing (QTDT) en gemengde effek modelle om die X-gekoppelde geen ACE2 te analiseer, met gelyktydige kompensasie vir hipertrofie kovariate (ouderdom, geslag, sistoliese bloed druk (BP), diastoliese BP, liggaamsoppervlak area, hartritme en mutasie-status). Sterk indikasies van koppeling in die afwesigheid van assosiasie is waargeneem tussen ACE1 lokusse en posterior wanddikte (PW) asook anterior wanddikte (AW) by die papillêre spier vlak (pap) en die apeks vlak (apx). In enkel-lokus analises is statisties-betekenisvolle assosiasies gevind tussen die CYP11B2 rs3097 polimorfisme en PW by die mitraalklep vlak (mit) en beide die PWpap en inferior wanddikte (IW)pap. Statisties-betekenisvolle assosiasies was verder gevind by drie AGTR1 polimorfismes, naamlik, tussen rs2640539 polimorfisme en AWmit, rs3772627 en die anterior interventrikulêre septumdikte (aIVS) by die pap en rs5182 by beide die IWpap en AWapx. Gemengde-effek modelle het verder assosiasies aangetoon tussen die ACE2 rs879922 polimorfisme en die posterior interventrikulêre septumdikte en die laterale wanddikte by die mit, slegs in vrouens. Hierdie data dui op ‘n kovariaat-onafhanklike rol vir RAAS genetiese variante in die modifisering van die fenotipiese uitdrukking van hipertrofie in HCM-geaffekteerde individue.

Thesis (MSc)--Stellenbosch University, 2000.
ENGLISH ABSTRACT: Progressive familial heart block type I (PFHBI) is a cardiac ventricular conduction disorder of unknown cause associated with risk of sudden death, which has been described in several South African families. Clinically, PFHBI is characterised by right bundle branch block on ECG, which may progress to complete heart block, necessitating pacemaker implantation. The disease shows an autosomal dominant pattern of inheritance with evidence of genetic anticipation. Using genetic linkage analysis, the PFHBI-causative gene was mapped to a 10 eentimorgan (cM) gene-rich area of chromosome (C) 19q13.3, which has, subsequently, been reduced to 7cM by fine mapping with polymorphic dinucleotide (CA)n short tandem repeat (STR) markers. Several attractive candidate genes, including muscle glycogen synthase (GSY 1) and histidine-rich calcium binding protein (HRC), lie within this region. The aim of the present study was two-fold: 1) to identify and characterise tetranucleotide (AAAT)n STRs within the PFHBI critical region that could be developed as polymorphic markers for use in genetic fine mapping and 2) to screen selected regions of GSY 1and HRC, positional candidate genes, for the presence ofPFHBI-causing mutation(s). Cosmids harbouring CI9q13.3 insert DNA were screened for the presence of (AAAT)n STRs by dot blot and Southern blot hybridisation using a radiolabelled (AAAT)lO oligonucleotide probe. To characterise the harboured (AAAT)n STRs, the positively hybridising fragments identified by Southern blot were sub-cloned, sequenced and primers designed from the unique repeat-flanking sequences. These primers were used to genotype the (AAAT)n repeat locus to assess its polymorphic nature in a panel of unrelated individuals. Alternatively, vectorette PCR, a rapid method of identifying repeat sequences and obtaining the flanking sequences in large inserts, was employed to develop polymorphic markers from the positively hybridising clones. Selected exons of GSY1 and HRC were screened for the presence of potentially disease-causing mutations by PCR-SSCP analysis and direct sequencing, respectively, in PFHBI-affected and unaffected family members. Of the available cosmid clones that gave strong signals on dot blot and Southern blot hybridisation, three, 29395, 24493 and 20381, were located within the critical PFHBI area and were used for marker development. An interrupted (AAAT)n repeat motif (n less than 5) was identified in cosmid 29395, however, the repeat locus was not polymorphic in the tested population. No (AAAT)n motif, single or repeated was observed in the partial sequence of the sub-cloned fragment of cosmid 24493. Using vectorette peR, no repeated (AAAT)n motif was identified on sequencing the generated products in either cosmid 24493 or 2038l. However, diffuse single AAAT motifs were detected in both cosmids. Exons 4, 5, 11, 12 and 16 of GSY 1, containing domains that are conserved across species, and the conserved eterminus- encoding exons 2-6 of HRC were selected for screening for potential PFHBI-causing mutation(s). However, no sequence variations were detected. The interrupted (AAAT)n repeat identified in cosmid 29395 was not polymorphic, which confirmed reports that complex repeats, especially those containing AAAT motifs of less than 6 repeats, are not polymorphic. One possible explanation for the absence of a repeated AAAT motif in cosmids 24493 and 20381, which both gave positive hybridisation signals, is that the low annealing temperature of the AfT -rich repeat-anchored primers used in vectorette peR may have resulted in transient annealing to the diffuse single AAAT motifs detected on sequencing. The screened regions of candidate genes GSYI and HRC were excluded from carrying the disease-causing mutation(s). The availability of new sequence data generated by the Human Genome Project will influence future strategies to identify the PFHBI gene. Electronic searches will allow identification of STR sequences for development of polymorphic markers and gene annotation will allow selection of new candidate genes for mutation screening.
AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Heterotaxy refers to the abnormal arrangement of internal organs in relation to each other. Model organism studies have shown that functions of more than eighty genes are required for normal asymmetric left-right organ development. CRELD1 has been shown to be necessary for proper heart development and mutations in CRELD1 are known to increase risk of cardiac atrioventricular septal defects (AVSD). AVSD is the most common form of heart defect associated with heterotaxy, and we have previously shown that some individuals with heterotaxy-related AVSD have mutations in CRELD1. Therefore, we propose to examine the CRELD1 gene in a large sample of patients with heterotaxy syndrome. Our goal was to determine if mutations in CRELD1 are associated with other manifestations of heterotaxy or if they only coincide with AVSD. To achieve this aim, a sample size of 126 patients with heterotaxy collected by Dr. Belmont, Baylor college of Medicine, Texas, with approximately 66% of the heterotaxy population with different types of heart defects, were used for this study. Ten exons, promoter regions, and regulatory elements in the introns of CRELD1 gene were sequenced and analyzed. In this study three different heterozygous missense mutations in CRELD1 were identified in three unrelated individuals. These three individuals were diagnosed with different forms of heart defects in addition to AVSD. All three mutations were identified in highly conserved regions of CRELD1 possibly altering the CRELD1 properties. This demonstrates that mutations in CRELD1 may increase the susceptibility of AVSD in heterotaxy population. This information can help us to find factors effecting disease susceptibility in heterotaxy patients since the heart defects are a complex trait with incomplete penetrance.

Evidence has shown that hypoxic hearts have greater heart/fetus mass ratio. However, it is still unclear if either hyperplasia or hypertrophy causes the relatively increased heart mass. Furthermore, the genes that might be involved in the process have not yet been identified. In the present study, the cardiac transcriptome was analyzed to identify differentially expressed genes related to hypoxia. Eggs were incubated for 15 and 19 days in two different environments, normoxic and hypoxic. Normalized microarray results were analyzed to isolate differentially expressed probes using the Affymetrix chip. Total RNA was also isolated from another set of fetuses incubated in the same conditions and used to perform a qPCR in order to confirm the microarray results. In the four groups (15N, 15H, 19N, 19H), some probes were differentially expressed. From the eggs incubated for 15 days, the microarray revealed five probes that were differentially expressed according to the criteria (p<0.01 and absolute fold change FC>2) in the two programs (PLIER & RMA) used to normalize the data. From the eggs incubated up to 19 days, eight probes were differentially expressed in both programs. No further tests were performed on the 19 days fetuses since there was no significant difference in that group after incubation for the heart/fetus mass ratio. Apolipoprotein-A1, p22, similar to ENS-1 and b2 adrenergic receptor were further tested in qPCR (15 days sample). The differently expressed genes are linked to cell division and should be further studied to identify their function, especially the similar to ENS-1.

Thesis (MSc)--University of Stellenbosch, 2004.
ENGLISH ABSTRACT: Progressive familial heart block type II (PFHBII) is an inherited cardiac conduction disorder of unknown aetiology, which has been described in a South African family. The disorder was mapped to a 2.9 centimorgan (cM) locus on chromosome 1q32.2-32.3. Clinically, PFHBII manifests cardiac conduction aberrations, that progress to a disease of the heart muscle, dilated cardiomyopathy (DCM). DCM is also reported as an end phase in hypertrophic cardiomyopathy (HCM), another heart muscle disorder. These cardiomyopathies are genetically heterogeneous with some of the genes reported as causes of both disorders. Therefore, genes identified as causes of HCM and DCM were considered plausible candidates for PFHBII mutation analysis. Additionally, this study provided an opportunity to assess potential modifiers of HCM. HCM exhibits marked phenotypic variability, observed within and between families harbouring the same causative mutation. Genes within the PFHBII locus were selected for PCR-SSCP analysis based on homology to genes previously reported as causing conduction system disorders associated with arrhythmias, DCM and/or HCM. Results were confirmed by direct sequencing and association between the detected variants and HCM parameters was assessed using a quantitative transmission disequilibrium test (QTDT). Eleven plausible candidate genes were selected within the PFHBII locus and two of the genes, PFKFB2 and ATF3, that encode for 6-phosphofructo-2,6-bisphosphatase (PFK-2/FBPase-2) and activating transcription factor 3 (ATF3), respectively, were analysed for PFHBII-causing and HCM main locus and/or HCM modifying mutations. Mutation analysis of PFKFB2 and ATF3 in the PFHBII family revealed no PFHBII causal mutation. PFKFB2 and ATF3 were later localised outside the PFHBII locus, and, therefore, were excluded as PFHBII plausible candidates. Further analysis of the two genes for HCM main locus and/or HCM modifying mutations in the HCM panel identified several sequence variants. QTDT analysis of these variants showed no significant association. Completion of the Human Genome Project (HGP) and annotation of new genes within the PFHBII locus allowed the identification of more PFHBII plausible candidate genes. Identification of causal mutations in plausible PFHBII candidate genes will allow molecular diagnosis of PFHBII pathophysiology. Furthermore, identification of both HCM-modifying and HCM-causing genes will give insight into the phenotypic variability noted among South African HCM-affected individuals and into the molecular cause of the disease among individuals with HCM-like clinical features.
AFRIKAANSE OPSOMMING: Progressiewe familiële hartblok tipe II (PFHBII) is ʼn oorgeërfde hart geleidingsiekte van onbekende etiologie wat in ʼn Suid-Afrikaanse familie beskryf is. Die siekte is ʼn 2.9 sentimorgan (cM) lokus op chromosoom 1q32.2-32.3 gekarteer. Klinies presenteer PFHBII met geleidingsfwykings wat uitloop op gedilateerde kardiomiopatie (DCM). DCM word ook gerapporteer as ʼn endfase in hipertrofiese kardiomiopatie (HCM), ʼn ander hartspiersiekte. Die kardiomiopatieë is geneties heterogeen, met ʼn aantal gene wat as oorsaak van altwee siektetoestande gerapporteer word. Daarom is alle gene wat geïdentifiseer is as oorsake van DCM en HCM, as moontlike kandidaatgene vir PFHBII mutasieanaliese beskou. Bykomend het hierdie studie die geleentheid gebied om potensiële modifiseerders van HCM te assesseer. HCM toon beduidende fenotipiese variasie binne en tussen families wat dieselfde siekteveroorsakende mutasie het. Gene binne die PFHBII-lokus is geselekteer vir PCR-SSCP-analiese gebaseer op homologie met gene wat voorheen gerapporteer is om betrokke te wees by geleidingsiesisteemsiektes, geassosieerde arritmieë, DCM en/of HCM. Resultate is bevestig deur volgordebepaling. Assosiasie tusssen ontdekte variante en die siekteparameter is bepaal met ʼn kwantitatiewe transmissie disekwilibrium toets (QTDT). Elf moontlike kandidaatgene in die PFHBII-lokus is geselekteer en twee van die gene, PFKFB2 en ATF3, wat kodeer vir 6-fosfofrukto-2,6-bifosfatase (PFK-2/FBPase-2) en aktiveringstranskripsiefaktor 3 (ATF3) respektiewelik, is vir PFHBII-oorsakende en HCMhooflokus en/of HCM-modifiseerende mutasies ondersoek. Mutasie-analiese van PFKFB2 en ATF3 in die PFHBII-familie het nie ʼn siekteveroorsakende mutasie onthul/uitgelig nie. PFKFB2 en ATF3 is later buite die PFHBII-lokus geplaas en dus ook as moontlike PFHBII-kandidate uitgesluit. Verdere ondersoek van díe twee gene vir HCM-hooflokus en/of HCM-modifiserende mutasies in die HCM-paneel het ʼn aantal volgorde variante geïdentifiseer. QTDT-analiese van die variante het geen beduidende assosiasies aangetoon nie. Voltooiing van die Menslike Genoom Projek (HGP) en annotasie van nuwe gene in die PFHBIIlokus het tot die identifikasie van verdere moontlike PFHBII-kandidaatgene gelei. Identifikase van siekte-veroorsaakende mutasies in die moontlike PFHBII-kandidaatgene sal die molekulêre diagnose van PFHBII toelaat en insig in die patofisiologie van die siekte gee. Verder, identifikasie van beide HCM-veroorsakende of HCM-modifiserende gene kan insig gee in die fenotipiese varieerbaarheid wat onder Suid-Afrikaanse HCM-geaffekteerde individue waargeneem word en ook in die molekulêre oorsake van die siekte in individue met HCMsoortige kliniese kenmerke.