Dissertations / Theses on the topic 'Heart – Hypertrophy'

Heart failure (HF) is a pathological state indicating insufficient blood supply to the peripheral tissues from the heart. The pathophysiology of HF is multifactorial like cardiac remodeling including cardiac hypertrophy, perivascular fibrosis and apoptosis to compensate for the heart?s inability to pump enough blood. Cardiac hypertrophy is initially adaptive to hemodynamic overload; however, it chronically contributes to heart failure and sudden cardiac death. The extracellular regulatory factors and intracellular signaling pathways involved in the cardiac remodeling are not yet fully clear. PI3-kinase is an important intracellular kinase in organ size control. Cardiac overexpression of Class I PI3-kinase caused heart enlargement in transgenic mice. Autophagy as a dynamic process involving the degradation of damaged mitochondria prevents ROS overproduction which leads to the cardiac remodeling. Therefore, our aim was to study the relationship between PI3-kinases and Ang II-induced cardiac remodeling via an autophagy-dependent mechanism. Ang II significantly increased autophagy with two distinctive phases: an increasing phase at low doses and a decreasing phase at high doses in cardiomyocytes. The Ang II-induced autophagic depression was attenuated by a Class I PI3-kinase inhibitor and potentiated by Class III PI3-kinase inhibitor. Besides, Ang II-induced cardiac hypertrophy and mitochondria ROS generation were attenuated via blockade of Class I PI3-kinase or mTOR. To further validate our in vitro data, we studied the role of Class I PI3-kinase in Ang II-induced cardiac remodeling in vivo. We successfully transferred Lv-DNp85 (Class I PI3-kinase blockade) and Lv-GFP (control) into adult rat hearts and found that cardiac transfer of Lv-DNp85 did not alter Ang II-induced pressor effect, but attenuated Ang II-induced cardiac hypertrophy, perivascular fibrosis and cardiac dysfunction. Ang II-induced cardiac remodeling was associated with impaired autophagy and mitochondrial ROS overproduction, which were significantly attenuated by Lv-DNp85-induced blockade of Class I PI3-kinase. Taken together, these data suggest that Class I PI3-kinase is involved in Ang II-induced impairment of autophagy via Akt/mTOR pathway, leading to mitochondrial ROS overproduction and cardiac remodeling. These results are not only highly significant from a pathophysiological perspective, but also have important pharmacological implications in the control of cardiac hypertrophy to prevent decompensation and failure in cardiac function.
National Institute of Neurological Disorders and Stroke
National Institutes of Health (NIH, NS55008)

p38-mitogen activated protein kinases (p38-MAPKs) are stress activated serine/threonine kinases that are activated during several different cardiac pathologies. Classically, studies have focused solely on p38α signaling in the heart. However, there is also high cardiac expression of the p38γ isoform but little is known about its cardiac function. The aim of this study was to elucidate the signaling pathway of p38γ, with a particular focus on its role in the progression of pathological cardiac hypertrophy. Comparisons of cardiac function and structure of wild type (WT) and p38γ knock out (KO) mice, in response to abdominal aortic banding, found that KO mice developed less ventricular hypertrophy than their corresponding WT controls, and have preserved cardiac function. Basal p38γ myocardial staining was primarily localised at the membranes and throughout the cytoplasm. Following aortic constriction, nuclear staining of p38γ increased, but no accumulation of p38α was observed. This suggests that the two isoforms play distinct roles in the heart. To elucidate its signaling pathway, we generated an analogue sensitive p38γ, which is mutated at a gatekeeper residue, to specifically track and identify its endogenous substrates in the myocardium. The mutation allows only the mutant kinase, but not WT kinases, to utilise analogues of ATP that are expanded at the N6 position and contain a detectable tag on the γ-phosphate. Transfer of this tag to substrates allows subsequent isolation and identification. Furthermore, unlike other p38-MAPKs, p38γ contains a C-terminal PDZ domain interacting motif. We have utilised this motif in co pull-down assays to identify interacting proteins of p38γ in the heart. Using these techniques we have identified, amongst other substrates, LDB3 and calpastatin as novel substrates of p38γ and we have determined the residues that are targeted for phosphorylation. Lastly we have shown that phosphorylation of calpastatin reduces its efficiency as a calpain inhibitor in vitro, hence proposing a mechanism by which p38γ may mediate its pro-hypertrophic role.

Left ventricular hypertrophy (LVH) in response to pressure overload is associated with increased cardiovascular morbidity and mortality, making its prevention an important therapeutic goal. The role of a calcineurin-dependent molecular pathway in the induction of pressure-overload LVH is controversial. The present study tested the hypothesis that, in the setting of LV pressure overload, activation of the systemic renin-angiotensin system was necessary for activation of this calcineurin pathway. Mild LV pressure overload was induced in male Wistar rats by abdominal aortic constriction (AAC) or transverse aortic arch constriction (TAC), producing well-matched pressure gradients of 37 ?? 8 and 35 ?? 15 mmHg, respectively. Tight transverse aortic arch constriction (TTAC) in additional animals produced a pressure gradient of 75 ?? 15 mmHg. Only AAC increased plasma renin concentration and activated the calcineurin pathway, indicated by increased nuclear NFAT3 content. Plasma renin concentration and nuclear NFAT3 content were unchanged in TAC and TTAC animals. AAC animals developed more LVH 21 days post-banding than TAC and TTAC animals: the slope of the relationship between LV/body weight ratio and systolic blood pressure was much steeper in AAC animals than the combined TAC and TTAC animals (20x10-6 versus 5x10-6, p<0.001). Treatment with the calcineurin inhibitor FK506 did not significantly alter the slope of this relationship in the combined TAC and TTAC animals (8x10-6), but FK506 abolished this relationship in AAC animals (-5x10-6, R =0.0003). These data indicate that activation of the calcineurin pathway occurs only in high-renin hypertension, providing an additional stimulus to LVH induction. Calcineurin plays no role in the induction of LVH in low-renin hypertension, which is much more common clinically.

Biomedical Sciences
Ph.D.
Increases in cardiac afterload caused by disease conditions results in remodeling of heart structure by hypertrophy and alterations in the molecular regulation of contractile performance. These adaptations can be regulated by various Ca2+-dependent signaling processes. STIM1 is an important regulator of Ca2+ signaling in different cell types by sensing endoplasmic reticular Ca2+ levels and coupling to plasma membrane Orai channels. The role of STIM1 in heart is not well understood, given the robust Ca2+ regulatory machinery present within cardiac myocytes. Previous reports indicate that STIM1 may play a role in regulation of cardiac hypertrophy. The goal of this work is to understand how STIM1 can affect contractile Ca2+ regulation in normal and diseased myocytes. We induced cardiac hypertrophy by slow progressive pressure overload in adult cats. Isolated adult feline ventricular myocytes (AFMs) exhibited increased STIM1 expression and activity, which correlated with altered Ca2+ handling. Use of BTP2 to block Orai channels resulted in a reduction of action potential (AP) duration and diastolic spark rate of hypertrophied myocytes, without affecting myocytes from sham-operated animals. Overexpressed STIM1 in cultured AFMs caused persistent Ca2+ influx that resulted in increased diastolic spark rates and prolonged APs, similar to myocytes from banded animals. STIM1 mediated Ca2+ influx could load the sarcoplasmic reticulum and activated CaMKII, which increased spark rates and lead to spontaneous APs. Importantly, STIM1 operated by associating with Orai channels because these effects could be blocked with either BTP2 or with a dominant negative Orai construct. Prolonged Ca2+ entry through this pathway eventually causes cell death. In conclusion, the work presented in this thesis establishes a role for STIM1-Orai in contractile Ca2+ regulation.
Temple University--Theses

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.

This thesis aims to investigate differential changes in Ca2+ and Na+ regulation during the development from cardiac hypertrophy to heart failure (HF) between sexes. Clinical evidences show females are more resistant to the development of cardiac hypertrophy and have better survival in HF than males. Oestrogen is postulated to provide cardioprotection although this is still under debate. This work used guinea pigs (GPs), a species with electrophysiology akin to human, that were subjected to aortic constriction (AC) to study the progression from pressure-overload cardiac hypertrophy to HF between sexes. Selected female animals underwent ovariectomy (OVx), mimicking postmenopausal status, to examine the effects of long-term deprivation of ovarian hormones. The effect of oestradiol supplementation was also investigated. Ventricular myocytes isolated from hearts at cardiac hypertrophy had prolonged action potential duration (APD), increased Ca2+ transient amplitudes and SR Ca2+ content, reduced Na+/K+ ATPase (NKA) function and increased late sodium current (INa,L). Fractional shortening (FS) remained unchanged in these hearts. Compromised FS with detrimental Ca2+ handling, more reduced NKA function and enhanced INa,L were noted at HF. Males showed earlier declined NKA function, more compromised FS and more detrimental Ca2+ handling than females at HF. Ventricular myocytes from OVx animals showed increased L-type Ca2+ channel current with gating shifts and larger window current, larger Ca2+ transient amplitudes, greater SR Ca2+ content, and increased Ca2+ sparks and waves. OVx myocytes showed more early and delayed afterdepolarisations (EADs and DADs) with DAD-induced extrasystoles following β-adrenergic stimulation. AC with OVx GPs showed more reduced FS, more dysregulated Ca2+ handling, more reduced NKA function and larger INa,L than AC females. In conclusion, females were more resistant to pressure-overload. Long-term deprivation of ovarian hormones abolishes the slower onset of HF in females, and provides pro-arrhythmic substrates to females. Oestradiol supplementation offered protective effects on OVx GPs.

Introduction: Cardiac hypertrophy is an adaptive response to increased myocardial workload that becomes maladaptive when hypertrophied hearts are exposed to an acute metabolic stress, such as ischemia/reperfusion. Acceleration of glycolysis occurs as part of the hypertrophic response and may be maladaptive because it enhances glycolytic metabolite accumulation and proton production. Activation of AMP-activated protein kinase (AMPK), a kinase involved in the regulation of energy metabolism, is proposed as a mechanism for the acceleration of glycolysis in hypertrophied hearts. However, this concept has not yet been proven conclusively. Additionally, several studies suggest that AMPK is involved in hypertrophic remodeling of the heart by influencing cardiac myocyte growth, a suggestion that remains controversial. Hypothesis: AMPK mediates hypertrophic remodeling in response to pressure overload. Specifically, AMPK activation is a cellular signal responsible for accelerated rates of glycolysis in hypertrophied hearts. Additionally, AMPK influences myocardial structural remodeling and gene expression by limiting hypertrophic growth. Experimental Approach: To test this hypothesis, H9c2 cells, derived from embryonic rat hearts, were treated with (1 µM) arginine vasopressin (AVP) to induce hypertrophy. Substrate utilization was measured and the effects of AMPK inhibition by either Compound C or by adenovirus-mediated transfer of dominant negative AMPK were determined. Subsequently, adenovirus-mediated transfer of constitutively active form of AMPK (CA-AMPK) was expressed in H9c2 to specifically increase AMPK activity and, thereby, further characterize the role of AMPK in hypertrophic remodeling. Results: AVP induced a metabolic profile in hypertrophied H9c2 cells similar to that in intact hypertrophied hearts. Glycolysis was accelerated and palmitate oxidation was reduced with no significant alteration in glucose oxidation. These changes were associated with AMPK activation, and inhibition of AMPK ameliorated but did not normalize the hypertrophy-associated increase in glycolysis. CA-AMPK stimulated both glycolysis and fatty acid oxidation, and also increased protein synthesis and content. Howver, CA-AMPK did not induce a pathological hypertrophic phenotype as assessed by atrial natriuretic peptide expression. Conclusion: Acceleration of glycolysis in AVP-treated hypertrophied heart muscle cells is partially dependent on AMPK. AMPK is a positive regulator of cell growth in these cells, but does not induce pathological hypertrophy when acting alone.

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.

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

Alors que l’entrée SOC (store-operated Ca2+ entry) portée par les canaux calciques TRPCs (transient receptor potential canonical) et Orai1 est essentielle dans les cellules non-excitables, son rôle physiologique dans les cardiomyocytes adultes reste à élucider. Néanmoins, il est largement admis qu’une entrée SOC exacerbée dépendante des canaux TRPCs et de la protéine régulatrice STIM1 participe à la pathogenèse de l’hypertrophie et de l’insuffisance cardiaque (IC) par induction de voies pro-hypertrophiques telles que la CaMKII (Ca2+/calmoduline-dépendante kinase II ) et la calcineurine (CaN)/NFAT (Nuclear factor of activated T-cells). Au contraire, une inhibition fonctionnelle ou une extinction génique des canaux TRPCs et de la protéine STIM1 serait cardioprotectrice contre le stress hypertrophique. Cependant, le rôle physiopathologique des canaux calciques Orai1 dans le cœur reste, à ce jour, méconnu et débattu puisque son extinction in vitro présente un effet bénéfique contre l’hypertrophie des cardiomyocytes alors que son extinction in vivo présente des effets délétères avec le développement d’une cardiomyopathie dilatée. De plus amples investigations quant au rôle d’Orai1 dans la physiopathologie cardiaque apparaissent donc primordiales. De ce fait, les objectifs de ma thèse sont d’explorer le rôle de la signalisation calcique dépendante d’Orai1 dans le cœur dans des conditions physiologiques et pathologiques grâce à un modèle de souris transgéniques exprimant un mutant non fonctionnel d’Orai1, spécifiquement dans le cœur (dn-Orai1R91W/tTa) et un inhibiteur pharmacologique sélectif, le JPIII. Tout d’abord, nous montrons que les souris dn-Orai1R91W/tTa présentent une fonction cardiaque normale et une homéostasie calcique impliquée dans le couplage excitation-contraction conservée suggérant qu’Orai1 n’a pas de rôle majeur dans le coeur adulte en condition physiologique. Cependant, nous avons démontré une augmentation de l’expression et de l’activité d’Orai1 dans un modèle murin d’hypertrophie cardiaque induite par surcharge de pression, qui serait délétère pour la fonction ventriculaire. Au contraire, l’inhibition fonctionnelle d’Orai1 par manipulation génétique ou par l’outil pharmacologique (JPIII) semble protéger le coeur des dysfonctions ventriculaires au cours de l’hypertrophie. Cet effet bénéfique passerait par une restauration de l’homéostasie calcique et notamment par un maintien de l’expression de la pompe ATPase SERCA2a. Nous avons également mis en évidence que la voie de l’aldostérone/récepteurs aux minéralocorticoïdes modulait l’expression des canaux TRPC1, -C4, -C5 et notamment Orai1 via la protéine SGK1 (Serum and Glucocorticoid-regulated Kinase 1) dans les cardiomyocytes ventriculaires de rat nouveaux-nés. L’activation de cette voie de signalisation pourrait être à l’origine de la surexpression des canaux TRPCs/Orai1 retrouvée au cours de l’hypertrophie cardiaque. Ces travaux décrivent donc Orai1 comme une cible thérapeutique potentielle dans le traitement de l’hypertrophie cardiaque et de l’IC
While the SOCE (store-operated Ca2+ entry), carried by TRPCs (transient receptor potential canonical) and Orai1 channels, is essential in non-excitable cells, its physiological role in adult cardiomyocytes remains elusive. Nevertheless, it is well established that exacerbated TRPCs/STIM1-dependent Ca2+ entry participates in the pathogenesis of hypertrophy and heart failure (HF) via the induction of pro-hypertrophic signaling pathways, such as CaMKII (Ca2+/calmodulin-kinase II) and calcineurin (CaN)/ NFAT (nuclear factor of activated T-cells). By contrast, functional inhibition or gene silencing of TRPCs and STIM1 is cardioprotective against hypertrophic insults. As for Orai1 Ca2+ channels, their pathophysiological roles in the heart remain unknown and under debate, since in vitro Orai1 silencing has a beneficial effect against cardiomyocyte hypertrophy, whereas in vivo silencing has deleterious effects with the development of dilated cardiomyopathy. Further investigations are necessary to determine the pathophysiological role of Orai1 in the heart. My thesis objectives are to explore the role of Orai1-dependent Ca2+ signaling in the heart under physiological and pathological conditions using a transgenic mouse model expressing a non functional mutant of Orai1, specifically in the heart (dn-Orai1R91W/tTa) and a selective pharmacological inhibitor, JPIII. First, we showed that dn-Orai1R91W/tTa mice have normal cardiac function and conserved Ca2+ homeostasis involved in the excitation-contraction coupling suggesting that Orai1 is not instrumental in regulating cardiac function under physiological conditions. However, we demonstrated an increased Orai1 expression and activity in a mouse model of cardiac hypertrophy induced by pressure overload, which is a maladaptive alteration involved in pathological ventricular dysfunction. By contrast, functional inhibition of Orai1 by genetic manipulation or by the pharmacological tool (JPIII) protects the heart from ventricular dysfunction after pressure overload-induced cardiac hypertrophy. This beneficial effect is related to a restoration of Ca2+ homeostasis and more specifically, is due to preserved ATPase SERCA2a pump expression. We also showed that the aldosterone/mineralocorticoid receptor signaling pathway modulates the expression of TRPC1, -C4, -C5 channels and also the Orai1 channels expression via the SGK1 (Serum and Glucocorticoid-regulated Kinase 1) protein, in neonatal rat ventricular cardiomyocytes. The activation of this signaling pathway could be the cause of the TRPCs/Orai1 channels overexpression found during cardiac hypertrophy. In conclusion, our studies highlighted that Orai1 Ca2+ channels could constitute potential therapeutic target in the treatment of cardiac hypertrophy and HF

Thesis (MScMedSc (Biomedical Sciences. Molecular Biology and Human Genetics))--University of Stellenbosch, 2009.
Hypertrophic cardiomyopathy (HCM), an inherited primary cardiac disorder mostly caused by defective sarcomeric proteins, is considered a model for studying left ventricular hypertrophy (LVH) in the absence of increased external loading conditions. The disease manifests extreme variability in the degree and pattern of LVH, even in HCM patients with the same causal mutation. The clinical phenotype of HCM can therefore be viewed as a product of the effect of sarcomere dysfunction and of additional genetic modifiers. Components of the renin-angiotensin-aldosterone system (RAAS) are plausible candidate modifiers because of their effect on blood pressure and their direct hypertrophic effect on cardiomyocytes. The present study investigated genes encoding components of the RAAS for association with cardiac hypertrophy traits, in 353 individuals comprised of genetically and echocardiographically affected and unaffected family members, belonging to 22 HCM families with HCM founder mutations by employing a multi-SNP approach with TaqMan allelic discrimination technology. Gene-gene interaction analysis was also performed to investigate the effect of epistasis on hypertrophy. Candidate genes for analysis included the angiotensin II type 2 receptor (AT2 receptor), renin, renin-binding protein (RnBP), the (pro)renin receptor, the mineralocorticoid receptor as well as genes encoding subunits of the epithelial sodium channels (ENaC) and Na+/K+-ATPase that showed evidence for cardiac expression. The present study demonstrates for the first time that variations in the renin and RnBP genes play a role in modulating hypertrophy in HCM, independent of blood pressure and confirms the involvement of the AT2 receptor in hypertrophy in HCM. Additionally we report an association between Na+/K+-ATPase α1- and β1-subunits as well as the ENaC α- and β-subunits and hypertrophy. Significant evidence for epistasis was found between renin and downstream RAAS effectors, suggesting a complex interplay between these RAAS variants and the hypertrophic phenotype in HCM. The identification of such modifiers for HCM may offer novel targets for hypertrophy research and ultimately antihypertrophic therapy.

Background: Heart attack or myocardial infarction (MI) is a major cause of death worldwide. MI is generally attributed to the detrimental effects of myocardial ischemia/reperfusion (I/R) injury. I/R injury induces cell death and reduces heart function. To compensate, the heart remodels with an associated increase in cell death, fibrosis, and hypertrophy, which can further compromise heart function. Ubiquitin (UB) is an evolutionarily conserved protein. Our lab has shown that pre-I/R injury treatment with exogenous UB preserves heart function and reduces fibrosis 3-days post-I/R in mice. A major objective of this study is to analyze the long-term cardioprotective potential of UB post-I/R injury. Here the UB treatment was continued until 28 days post-I/R to include the entire remodeling period. To enhance the clinical applicability, UB treatment was started at the time of reperfusion. Methods: C57BL/6 mice (aged ~3 months) underwent myocardial I/R surgery. Mice were anesthetized and the left anterior descending coronary artery (LAD) was ligated for 45 minutes. The ligature was then removed for reperfusion. Mice were treated with UB (1µg/g body weight; intraperitoneal (IP) injection) or saline at the time of reperfusion; followed by 3-days of saline or UB IP treatment twice per day. The mice were then implanted with micro-osmotic pumps containing UB (1 μg·g−1·h−1) or saline to continue treatment 28-days post I/R. Mice were sacrificed at 28-days post I/R injury. Sham animals underwent the same surgery without LAD ligation. Heart functional parameters (percent ejection fraction and fractional shortening) were analyzed by echocardiography in a time-dependent manner (3, 7, 14 and 28 days post-I/R). Extracted hearts were embedded in paraffin. Heart sections (5µm) were stained with Mason’s Trichrome to measure fibrosis, TUNEL to measure apoptosis, and fluorescein-conjugated wheat germ agglutinin to measure hypertrophy. Index of fibrosis was quantified as a percentage of total left ventricular area, apoptosis was quantified as a percentage of the total number of nuclei, and hypertrophy was quantified by measuring the myocyte cross-sectional area. Major findings: 1) I/R+saline exhibited a significant decrease in the functional parameters of the heart at 3, 7, 14 and 28 days post-I/R vs sham (n=4-12). No significant decrease in heart function observed between I/R+UB vs sham, and heart function was significantly lower in I/R+saline compared to UB+I/R (n=7-12); 2) I/R surgery significantly increased fibrosis in the myocardium of I/R+saline vs sham. No significant difference was observed between UB+I/R and sham, and fibrosis was significantly lower in UB+I/R vs I/R+saline (n=4-6); 3) Apoptosis was significantly higher in I/R+saline vs sham (p4) Myocyte hypertrophy was significantly higher in I/R+saline vs sham (pConclusion: Long-term UB treatment has the potential to preserve heart function with effects on myocardial fibrosis, myocyte apoptosis, and hypertrophy following myocardial I/R injury.

Heart failure is responsible for one in twenty deaths in the UK, and as the average age of the general population increases that number is predicted to rise over the coming years. Hypertrophic growth is believed to be an adaptive response to a chronic increase in workload under circumstances such as hypertension, yet it is also known to contribute to the pathological progression into heart failure. Abnormal calcium handling is known to play a critical role in determining disease progression, not only through its function as the driving force behind myocardial contraction and relaxation but also through directing the signals which regulate hypertrophic growth. Both isoforms 1 and 4 of the diastolic calcium extrusion pump plasma membrane calcium ATPase (PMCA) are present in the heart, yet unlike in other cell types their contribution to overall calcium clearance is only small; however their role in the disease process is yet to be defined. A novel mouse line was generated in which both PMCA1 and 4 were deleted from the myocardium (PMCA1:4dcko mice). Through comparison with PMCA1 knockout mice (PMCA1cko) this thesis set out to identify the specific function of each pump under normal conditions and during the development of pathological hypertrophy induced by pressure overload through transverse aortic constriction (TAC).Under basal conditions each isoform functioned independently, PMCA1 to extrude calcium during diastole and PMCA4 to regulate calcium levels during systole; however the loss of neither isoform impacted significantly on cardiac function. In response to TAC, PMCA1cko mice progressed rapidly into decompensation and displayed signs of systolic failure after just 2 weeks, whilst cardiac function was preserved in TAC controls. Calcium handling analysis revealed that prior to the onset of failure PMCA1cko mice displayed a distinct lack of adaptive changes to calcium cycling which were present in controls. In stark contrast, the additional loss of PMCA4 led to an attenuated hypertrophic response to TAC in PMCA1:4dcko mice which remarkably preserved cardiac function despite the absence of PMCA1. This adds to accumulating evidence which suggests that the inhibition of PMCA4 may be protective during the development of pathological hypertrophy, whilst highlighting the possibility for a novel role for PMCA1 in coordinating essential adaptations required to enhance calcium cycling in response to the increased demands imposed on the left ventricle during pressure overload.

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

Cardiac hypertrophy leading to heart failure remains a leading cause of morbidity and mortality in the 21st century despite major therapeutic advances. Improved understanding of novel molecular and cellular processes contributing to cardiac hypertrophy therefore continues to be important. Cyclin-dependent Kinase 9 (CDK9), part of a family of proteins controlling cell cycle and growth, has emerged as one such potential candidate over the last 5 years. CDK9 is the catalytic subunit of the CDK9/CyclinT complex and acts by phosphorylating the carboxy-terminal domain of RNA polymerase II. Hypertrophic signals, such as Endothelin-1 (ET-1) and phenylephrine, have been shown to cause CDK9 activation leading to a hypertrophic response in cultured mouse cardiomyocytes associated with reactivation of the foetal gene program. CDK9 also forms a complex with GATA4 to play a role in differentiation of mouse ES cells into cardiomyocytes. These findings suggest a specific role for CDK9 in controlling growth and differentiation of cardiomyocytes and merits further study in models where cardiomyocyte differentiation and proliferation are key contributors. In contrast to mammals, zebrafish retain a high cardiomyocyte proliferative capacity throughout their life span and can readily repair following injury. I have examined the role of CDK9 on global and cardiac development in the zebrafish embryo. I have also assessed the impact of CDK9 manipulation on response to ventricle injury using a laser-induced injury model developed and validated as part of my thesis. My findings confirm that normal growth of the embryonic ventricle is associated with a rapid increase in cardiomyocyte number, that was of 50% in the period 96-120 hpf, accompanied by increasing chamber trabeculation. This is also characterized by an increase in the gene expression of most of cardiac development relevant transcription factors, i.e. GATA4, 5 and 6, and MEF2c. The significant reduced cardiovascular function (14% of Ejection Fraction compared to 20% in controls) at 2 h post laser injury in the zebrafish embryonic heart promptly recovers at 24 hour post-laser, accompanied by acceleration of cardiomyocyte proliferation, that increased of 49% in injured ventricles compared to 20% in controls in the period 2-24 h post-laser. Pharmacological and genetic inhibition of CDK9 activity also significantly reduced cardiac growth, cardiomyocyte number, ventricle function and impairs functional recovery following laser injury. Conversely, genetic inhibition of LARP7, a CDK9 repressor, resulted in increased cardiomyocyte number and was associated with full functional and cellular recovery following laser-injury. In conclusion, I have provided evidence, in the zebrafish embryonic heart, that CDK9 plays an important role in cardiac growth and development and impacts significantly on cardiomyocyte proliferation. I have also shown that CDK9 manipulation significantly affects cellular and functional recovery following laser-induced injury. Further studies are required to further define the role of CDK9 and LARP7 in the heart and develop therapeutic strategies using this pathway that could contribute to cellular repair mechanisms in the adult mammalian heart.

The development and function of the heart is governed by a conserved set of transcription factors (TFs) that regulate gene expression in a cell-type, time point and stimulus driven manner. Of these core cardiac TFs, the most ubiquitously expressed is the zinc finger protein GATA4. In cardiomyocytes, GATA4 is central to proliferation, differentiation, hypertrophy and induction of pro-survival pathways. In cardiac endothelial cells, it is required for valve and septal development, although the exact mechanisms remain unclear. To regulate such a wide array of functions in a spatially and temporally controlled manner, GATA4 interacts with specific protein partners, the majority of whom have been identified in cardiomyocytes. However, a complete understanding of the protein interactome of GATA4, particularly in cardiac endothelial cells, has not yet been achieved. Using a mass spectrometry-based approach, we have identified a series of novel GATA4 interacting partners in cardiac endothelial cells. 3xFlag GATA4 was stably overexpressed via retroviral transduction in the TC13 cardiac endothelial precursor cell line, immunoprecipitated from nuclear protein extracts and sent for HPLC-ESI-MS/MS. Several novel GATA4 interacting partners were identified including the chaperone protein Heat Shock Protein 70 (HSP70), the inducible orphan nuclear receptor Nerve Growth Factor 1β (NGFIβ, NUR77) and the Drosophila-Binding/Human Splicing protein family members Non-POU Domain Containing Octamer Binding Protein (NONO) and Paraspeckle 1 (PSPC1). Chapter 1 discusses the interaction between GATA4 and HSP70 and its role in cardiomyocyte survival upon exposure to chemotherapeutic agent Doxorubicin (DOX). HSP70 binds directly to GATA4, preventing DOX-mediated cleavage and degradation by Caspase-1, cardiomyocyte cell death and heart failure. Chapter 2 focuses on the cooperative interaction between GATA4 and NUR77 in cardiac microvascular endothelial cells and its central role in myocardial angiogenesis in response to pressure overload. The GATA4-NUR77 complex transactivates the promoter of Angiopoietin-Like 7 (ANGPTL7), a secreted pro-angiogenic chemotactic factor, triggering endothelial cell proliferation and tube formation in cultured cardiac endothelial cells and increasing myocardial capillary density in vivo. Chapter 3 discusses the interaction between GATA4 and the DBHS proteins NONO and PSPC1 in the regulation of cardiac development. These proteins play opposing roles when bound to GATA4 as PSPC1 enhances GATA4 activation of critical cardiac promoter targets and NONO acts as a rheostat to repress GATA4 activity. In vivo, loss of NONO results in left ventricular non-compaction consistent with humans with loss-of-function mutations. However, simultaneous Gata4 haploinsufficiency partially rescues this phenotype. Together, this data identifies multiple novel cell type and time point specific GATA4 protein partners and sheds light on GATA4 regulatory mechanisms in cardiac development and disease.

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.

Cardiac hypertrophy and heart failure (HF) remains one of the major health problems in the UK and worldwide. However, advances in their management are limited because the underlying pathological mechanisms are not completely understood. Therefore, it is important to understand novel signalling pathways leading to HF. Myocardial hypertrophy is a crucial pathophysiological process that can lead to the development of HF. Signalling initiated by members of G-protein-coupled receptors (GPCRs) proteins plays an important role in mediating cardiac hypertrophy. One member of this family, the G-protein coupled receptor 99 (GPR99), may have a crucial role in the heart because it acts as a receptor for alpha-ketoglutarate, a metabolite that is elevated in heart failure patients. GPR99 is expressed in the heart, but its precise function during cardiac pathophysiological processes is unknown. The aim of this PhD study is to investigate the role of GPR99 during cardiac hypertrophy. In this study I used in vivo and in vitro approaches to investigate whether GPR99 is directly involved in mediating cardiac hypertrophy. Mice with genetic deletion of GPR99 (GPR99-/-) exhibited a significant increase in hypertrophy following two weeks of transverse aortic constriction (TAC) as indicated by heart weight/tibia length ratio (HW/TL). In addition, GPR99-/- mice displayed increased cardiomyocytes cross-sectional area (CSA) after TAC compared to wild-type (WT) littermates. Hypertrophic markers such as brain natriuretic peptide (BNP) and β-myosin heavy chain (β-MHC) were also elevated in GPR99-/- mice following TAC compared to WT mice. Although interstitial fibrosis was indistinguishable in both genotypes after TAC, a precursor of fibrosis, collagen, type III, alpha1 (COL3A1) was elevated in GPR99-/- mice compared to WT mice after TAC. The baseline cardiac function as indicated by ejection fraction (EF) and fractional shortening (FS) were reduced in GPR99-/- mice compared to WT littermates following TAC. Furthermore, left ventricular end-diastolic diameter (LVEDD), left ventricular end-systolic diameter (LVESD), interventricular septum wall thickness (IVS) and posterior wall thickness at diastole (PW) indicated profound wall thickening and enlargement of the left ventricular (LV) chamber in GPR99-/- mice compared to WT littermates after TAC. In an attempt to examine the mechanism through which GPR99 signals during hypertrophy, I performed molecular analyses based on the data from yeast two hybrid screening showing that GPR99 interacted with COP9 signalosome element 5 (CSN5). Using immunoprecipitation assay, I found that GPR99 formed a ternary complex with CSN5 and non-receptor tyrosine kinase 2 (TYK2). TYK2 is known as a regulator of pro-hypertrophic molecules including signal transducer and activation of transcription 1 (STAT1) and STAT3. I found that the activation of these molecules was increased in GPR99-/- mice following TAC and correspondingly, adenovirus-mediated overexpression of GPR99 in neonatal rat cardiomyocytes (NRCM) blunted TYK2 phosphorylation. In conclusion, my study has identified GPR99 as a novel regulator of pathological hypertrophy via the regulation of the STAT pathway. Identification of molecules that can specifically activate or inhibit this receptor may be very useful in the development of a new therapeutic approach for cardiac hypertrophy in the future.

Abstract Cardiac hypertrophy is an adaptive response of the heart to a variety of mechanical, hemodynamic, neurohumoral, and pathologic stimuli. Prolonged pathophysiological load leads to development of left ventricular hypertrophy and ultimately to heart failure. The natriuretic peptides including the B-type natriuretic peptide (BNP) provide the physiological feedback mechanism to suppress the load signal. The aim of the present study was to evaluate the cis elements within the BNP promoter that mediate the cardiac load responses in vivo, and to study the involvement of paracrine factors, such as endothelin-1 (ET-1) and angiotensin II (Ang II) in activating these transcription factors. In this study, cardiac overload was produced by bilateral nephrectomy, and infusions of arginine8-vasopressin (AVP) or Ang II. In isolated perfused rat heart, the direct wall stretch was achieved by inflating the left ventricular balloon. To identify the cis elements within the BNP promoter that mediate hemodynamic overload response, the approach of DNA injection into the myocardium was used. Mutation or deletion of proximal BNP GATA sites abrogated the response to nephrectomy. AVP-induced acute pressure overload increased left ventricular BNP mRNA and peptide levels. In gel mobility shift assays, pressure overload produced rapid activation of transcription factor GATA4 DNA binding, which was completely inhibited by the ET-1 receptor antagonist bosentan. Both ET-1 and Ang II receptor antagonism inhibited the wall stretch-induced increases in left ventricular GATA4 and AP-1 binding activities in isolated perfused heart preparation. BNP promoter activity and BNP mRNA and peptide levels were regulated distinctly in chronic hemodynamic overload produced by Ang II. In conclusion, GATA4 appears to be necessary and sufficient to confer transcriptional activation of BNP gene during hemodynamic stress in vivo. ET-1 is a signaling molecule mediating the cardiac response to acute pressure overload in vivo. In isolated rat heart, Ang II and ET-1 are required for the stimulation of GATA4 and AP-1 binding activity in response to direct left ventricular wall stretch. Finally, posttranscriptional mechanisms play an important role in the regulation of BNP gene expression in pressure overload produced by Ang II in vivo.

[Truncated abstract] The enlargement of the heart, also known as myocardial hypertrophy, is thought to be a compensatory process that maintains the mechanical function of the heart in response to stress factors such as pressure or volume overload. Although this process is initially compensatory, it frequently results in heart failure and death. Cardiac hypertrophy is a complex process involving changes in the individual cardiac muscle cells, cardiac myocytes. As well as the morphological changes that result from hypertrophy, there are molecular changes within each cell that regulate the hypertrophic process. These molecular changes involve many different pathways within the cardiac myocytes and remain poorly understood . . . Both STAT3α and β overexpression resulted in the upregulation of the VEGF, MnSOD and SOCS-3 genes. This indicates that in the heart, STAT3β is able to activate the gene expression of these genes in a similar manner to STAT3α. However, STAT3α or β activation alone is not enough to induce cardiac hypertrophy. In conclusion, the results presented in this thesis determined a novel role for ERK in the induction of cell death in the heart and revealed many changes in cardiac gene expression following ERK activation. These genes may be the mediators of ERK responses and their identification provides valuable information and direction for further research in this area. One consequence of ERK activation was the negative regulation of the STAT3 pathway. Further investigation revealed for the first time that the STAT3 proteins themselves may not be involved in the induction of cardiac hypertrophy and that STAT3β, initially thought to be a transcriptional repressor, can induce the expression of genes that are known to be activated by STAT3α in the heart. Therefore, these results help to better understand the roles of these two signalling pathways in the heart.

Heart failure induced by cardiac hypertrophy is a cause of high mortality in the world and has been the fastest growing cardiovascular disease over the past decade. Cardiac hypertrophy is characterised as a reactive increase in cardiac mass growth with a complex of ventricular remodelling. It occurs initially as a compensatory response to an increased workload but eventually leads to cardiac dysfunction. An in-depth understanding of cardiac hypertrophy and the capacity to regulate it has profound clinical implications. The MAPK pathways provide an important connection between external stimuli and intracellular signals for cardiac hypertrophic response. At least four MAPK subfamilies have been identified: extracellular-regulated protein kinases 1 and 2 (ERK1/2), ERK5, c-Jun NH2-terminal protein kinases (JNKs) and p38 MAPKs. Mitogen-activated protein kinase kinase 4 (MKK4), a vital activator of JNK and p38 is implicated as an important mediator of hypertrophy. ERK5, an atypical MAPK, is also involved in both hypertrophic growth and cardiomyocyte survival. However, conflicting data have been yielded from previously-published studies, since the results are based entirely on experiments conducted in cultured cardiomyocytes or transgenic and conventional knockout mouse models. To elucidate their biological roles and underlying signalling mechanisms in hypertrophy, mice with a cardiomyocyte-specific deletion of MKK4 or ERK5 (MKK4cko and ERK5cko mice) were generated in the present study. In response to pathological hypertrophic stresses including pressure overload or isoprenaline stimulation, MKK4cko mice developed exacerbated pathological hypertrophy with increased cardiomyocyte apoptosis, impaired cardiac function and remarkably upregulated NFAT (nuclear factor of T-cell) transcriptional activity. However, MKK4cko mice exhibited a similar extent of swimming exercise-induced physiological hypertrophy compared with the controls. In response to pathological hypertrophic stimuli, ERK5cko mice were resistant to hypertrophic growth, foetal gene induction and ventricular fibrosis, which is associated with repressed activation of MEF2 (myocyte enhancer factor 2). ERK5 deficiency also caused a profound increase in cardiomyocyte apoptosis which accounted for the impaired cardiac function. In conclusion, the present study provides biological evidence that clarifies in vivo functions of MKK4 and ERK5 in hypertrophy. MKK4 acts a protective role against pathological hypertrophy through inhibiting NFAT signalling, but it is not necessary for the regulation of physiological hypertrophy. ERK5 is essential for pathological hypertrophic remodelling and cardiomyocyte survival and its function in hypertrophic remodelling is mediated through regulation of MEF2 activity. Taken together, these data presented in my thesis advances knowledge about biological functions of MAPK pathways in the heart.

L’insuffisance cardiaque (IC) est une cause majeure de mortalité dans les pays industrialisés. Ce syndrome est le résultat de nombreuses maladies cardiaques qui induisent dans un premier temps un remodelage adaptatif du myocarde : l’hypertrophie du ventricule gauche (HVG). Dans le cœur, le calcium libéré à partir du réticulum sarcoplasmique (RS) est à l’origine de la contractilité. Ce mécanisme est contrôlé par un macro-complexe moléculaire, composé du récepteur de la ryanodine (RyR2), et de protéines stabilisatrices associées dont la junctine (JCN), la calséquestrine (CSQ2), et la triadine (Trd). Ces dernières années, des dysfonctionnements de ce complexe, par des relâchements aberrants de Ca2+ du RS (vu comme des fuites de Ca2+ hors du RS) ont été remarqué au cours de l’IC, conduisant à une HVG associée à une dysfonction contractile et à la survenue d’arythmies cardiaques létales. De très nombreuses études se sont intéressées aux protéines principales du RS, telles que RyR2 et CSQ2, mais peu de données sont disponibles sur le rôle de Trd, protéine considérée comme mineure en physiopathologie cardiaque. Afin d’étudier son rôle dans le cœur, notre travail s’est articulé autour de trois modèles de pathologie cardiaque : 1-une surcharge de pression par une sténose de l’aorte transverse (TAC), 2-une diffusion de catécholamines (isoprotérénol, Iso) par mini-pompe osmotique et 3-une IC chronique par un infarctus du myocarde (IM), chez des souris dont le gène de la triadine a été invalidé (KO Trd). En réponse à une TAC ou à l’ISO, les animaux développent une HVG plus importante que les souris WT. Suite à une TAC, cette HVG est supérieure et excentrique et s’accompagne d’une dysfonction cardiaque comparativement aux animaux sauvages. Suite à un IM, les souris KO Trd présentent une mortalité accrue post-chirurgie. L’accroissement de cette mortalité accrue résiderait dans l’augmentation significative d’arythmies ventriculaires sévères (tachycardies ventriculaires, TV) chez ces souris suite à une stimulation catécholaminergique, pouvant être la conséquence d’une augmentation des fuites de Ca2+ hors du RS. Nous avons également observé qu’en réponse à la TAC la réexpression du gène TRDN avec un adénovirus AAV9 dans notre modèle KO Trd permet le maintien de la fonction cardiaque et de prévenir le développement de l’HVG. Au final, ces travaux montrent que l’absence de la triadine accélère la transition vers l’IC en modulant à la fois l’HVG et la dysfonction contractile associée mais également la survenue d’arythmies ventriculaires létales
Heart failure (HF) is a serious public health issue with a growing prevalence in industrialized countries. This syndrome results from several cardiac diseases which begin with an adaptative myocardial remodeling: left ventricular hypertrophy (LVH). In heart, contractility depends on calcium release from sarcoplasmic reticulum (SR). This release is controlled by a macro-molecular complex, composed by ryanodine receptor (RyR2) and its associated regulatory protein junctin (JCN), calsequestrin (CSQ2) and triadin (Trd). During the past years, alterations of this complex by disturbed calcium release outside SR (as « sparks ») was often observed during the development of HF, being associated with LVH, dysfunction and fatal ventricular arrhythmias. Most studies were focused on RyR2 and CSQ2 function but few data are available regarding the role of Trd, considered until now having minor role in cardiac physiopathology. To elucidate its role, we realized 3 cardiac pathological experimental models on mice with triadin gene invalidation (KO Trd): 1- a pressure overload with transversal aorta constriction (TAC) 2-a chronic infusion of catecholamines (Isoproterenol, Iso) with osmotic minipumps and 3- a chronic HF with myocardial infarction (MI). In response to TAC or Iso, KO mice developed a greater LVH compared to wild-type mice. Also, with TAC, KO mice show an eccentric LVH associated with a severe cardiac dysfunction, as compared to wild-type mice. After MI, we observed a greater mortality post-surgery in KO Trd mice. This prevalence may be due to increasing of severe ventricular arrhythmias (ventricular tachycardia, VT) after catecholaminergic stimulation. This observation could be a consequence of increasing number of « sparks », and thus an increased calcium release during diastole. More interestingly, delivery of TRDN gene using AAV9 in KO mice, prevent adverse remodeling and the associated cardiac dysfunction following 28 days TAC surgery. To conclude, this work shows that the lack of triadin accelerate the transition towards heart failure, acting on LVH , contractile dysfunction, and the occurrence of lethal ventricular arrhythmias

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.

Both hypertrophied and failing hearts are characterised by pathological left ventricular (LV) remodelling, impaired myocardial energy status and alteration in substrate metabolism. Cardiac magnetic resonance imaging (CMR) and magnetic resonance spectroscopy (MRS) are powerful tools in the characterisation of these disease conditions. More recent techniques have allowed assessment of myocardial steatosis using ¹H-MRS and tissue oxygenation using blood oxygen level dependent (BOLD) CMR. In hypertrophy and heart failure, studies on steatosis and the relationship with other parameters such as myocardial function and fibrosis, especially in humans are limited. I therefore investigated the presence of steatosis in severe aortic stenosis (AS) and dilated cardiomyopathy (DCM), and further assessed its relation to contractile function. This study found that myocardial triglyceride (TG) content is increased in both symptomatic and asymptomatic AS patients (lipid/water ratio 0.89±0.42% in symptomatic AS; 0.75±0.36% in asymptomatic AS vs. controls 0.45±0.17%, both p<0.05) and DCM patients (lipid/ratio 0.64±0.44% vs. controls 0.40±0.13%, p=0.03). Circumferential strain was lower in both AS (-16.4±2.5% in symptomatic AS; -18.9±2.9% in asymptomatic AS vs. controls 20.7±2.0%, both p<0.05) and DCM patients (-12.3±3.4% vs. controls -20.9±1.7%, p<0.001). In AS, myocardial contractility is related to the degree of steatosis, and were both reversible following aortic valve replacement (AVR), lipid/water ratio 0.92±0.41% vs. pre AVR 0.45±0.17%, p=0.04 and circumferential strain -17.2±2.0% vs. pre AVR -19.5±3.2%, p=0.04. A novel finding of this study was significant correlation of MRS-measured TG content with histological staining of TG of the myocardium, taken from endomyocardial biopsy during AVR. In DCM, myocardial TG was independently associated with LV dilatation and correlated significantly with hepatic TG, which suggests that both cardiac and hepatic steatosis might be a common feature in the failing heart. Additionally, although the hypertrophied heart is characterised by impaired perfusion, it is unknown if this is severe enough to translate into tissue deoxygenation and ischaemia. I assessed this by using adenosine vasodilator stress test and BOLD-CMR in patients with severe AS. It was found that AS patients had reduced perfusion (myocardial perfusion reserve index-MPRI 1.0±0.3 vs. controls 1.7±0.3, p<0.001), and blunted tissue oxygenation (blood-oxygen level dependent-BOLD signal intensity-SI change 4.8±9.6% vs. controls 18.2±11.6%, p=0.001) during stress. Importantly, there was a substantial improvement in perfusion and oxygenation towards normal after AVR, MPRI 1.5±0.4, p=0.005 vs. pre AVR and BOLD SI change 16.4±7.0%, p=0.014 vs. pre AVR. Overall, the work in this thesis supports the powerful role of CMR in assessing LV function and elucidating metabolic mechanisms in the hypertrophied and failing heart.

A seminal study by Morganroth et al (1975) demonstrated a differential pattern of cardiac adaptation with prolonged exercise training; of eccentric pattern of left ventricular hypertrophy (LVH) in endurance trained athletes (ET) and concentric LVH in resistance trained athletes (RT). Specific inconsistencies related to the nature of any adaptation to RT; the value of new imaging technologies; the relative importance of scaling of cardiac data for differences in body size; the impact of training on the right ventricle (RV) and the fit of differential pattern of adaptation in athletes with Black ethnicity have driven the rationale for the studies included in this thesis. Study one employed meta-analysis techniques to critically evaluate the evidence base supporting or refuting that MH exists in elite male Caucasian ET & RT. Modern echocardiographic techniques were used to test whether a dichotomous LV and RV structural as well as global and regional functional adaptation was apparent in elite Caucasian ET & RT in studies 2 & 3. The final study (exploratory) was to characterize the athletic heart phenotype in a homogenous population of elite RT of West African origin (WRT) to provide new insight in relation to cardiac adaptation and ECG characteristics in non-Caucasian athlete groups. Allometric scaling approach was deployed to index LV and RV data for individual body variance in body size. The novel findings of this thesis; larger LV data in ET (LVMg: ET 232 (200 to 260), RT 220 (205 to 234), CT 166 (145 to 186)) but no concentric hypertrophy in RT within the meta-analysis, predominance of normal geometry in male athletes (65% of ET and 95% of RT) and the lack of concentric pattern of hypertrophy in RT in a cross-sectional study; no RV adaptation in RT athletes (RVD1mm: ET 45 ± 5 (39 to 57), RT 40 ± 5 (32 to 51) CT 39 ± 4 (31 to 45)); no LV or RV adaptation in WRT athletes; the importance of appropriate scaling of cardiac parameters; provide a useful re-evaluation of concepts and models in the athletic heart literature. The findings have important implications for cardiovascular screening of athletes.

[Truncated abstract] The innate ability of the heart to compensate for an increase in workload as a result of disease or injury, through an increase in size and mass is known as cardiac hypertrophy. The hypertrophy of the heart compensates for an increase in workload with an increase in cardiac output. However, excessive hypertrophy can result in cardiac dysfunction and substantially increases the risk of cardiac failure and mortality. The molecular mechanisms that regulate the development of cardiac hypertrophy and cardiac failure are not entirely understood. Traditionally, the G-protein Coupled Receptor (GPCR) and the downstream Mitogen-Activated Protein Kinase (MAPK) family of proteins have been implicated. However, elevated circulating and ventricular levels of several classes of cytokines also suggested that signaling by the downstream effectors of cytokine receptors, such as the Signal Transducers and Activators of Transcription (STATs), may be important. The aim of this thesis was, therefore, to characterize the involvement of MAPK and STAT pathways in regulating cardiac hypertrophy and cardiac failure. A function for MAPK and STAT signaling in regulating cardiac hypertrophy stimulated by the inflammatory cytokine IL-1Β was initially defined in primary cultures of neonatal rat cardiac myocytes. In this study, it was demonstrated that the chemical inhibition of ERK or p38MAPK was sufficient to inhibit IL-1Β-stimulated ANF expression. In contrast, simultaneous inhibition of both ERK and p38MAPK was required to ablate the hypertrophic morphology of cardiac myocytes treated with IL-1Β. These results demonstrated differential signaling from the MAPK isoforms in regulating the gene expression and morphological components of cardiac hypertrophy. In addition, it was revealed that IL-1Β treatment resulted in a delayed response (>60 min) in STAT3α tyrosine phosphorylation, which was subsequently shown to require the initial rapid activation of either ERK or p38MAPK. IL-1Β-stimulated STAT3 phosphorylation was also dependent on the de novo synthesis of secondary signaling molecules. The ablation of the STAT3 tyrosine phosphorylation by the inhibition of ERK or p38MAPK activity, correlated with the attenuation of IL-1Β-stimulated ANF expression, suggesting that signaling through STAT3α may be involved in regulating gene expression associated with IL-1Β cardiac hypertrophy