Cardiac hypertrophy is clinically defined as a relative increase in heart size associated with a thickening of the ventricular wall. It is a common feature of individuals suffering from different cardio-vascular or metabolic conditions and leads to heart failure. The structural, functional and molecular mechanisms which induce hypertrophy independent of hemodynamic alterations are poorly characterized. In this study, questions about whether cardiac-specific neuro-endocrine activation or metabolic imbalance are sufficient to induce hypertrophic structural and functional remodeling are addressed using genetically manipulated mouse models of primary cardiac hypertrophy. (For complete abstract open document)

Background: Maternal obesity pre-programme offspring to develop obesity and associated cardiovascular disease later in life. In health, perivascular adipose tissue (PVAT) reduces vascular contractility, an effect lost in obesity and during pregnancy. However, neither the effect of obesity during pregnancy on PVAT function in the mothers nor the possible epigenetic effect in the offspring is known. This study sought to identify detrimental vascular changes in post-partum dams and their offspring resulting from maternal obesity. Methods: Six-eight week old female Sprague-Dawley rats were fed a 10% fat (control) or 45% fat diet (HFD) for 12 weeks before mating, throughout pregnancy and during lactation. Offspring received the control diet until sacrifice at 12 (12wo) or 24 (24wo) weeks of age. PVAT-denuded (with or without exogenous PVAT) and PVAT-intact mesenteric arteries from mothers and pups were mounted on a wire myograph and vascular contractility to thromboxane A2 agonist (U46619) and norepinephrine was assessed in the presence of pharmacological tools. Western blotting, immunoprecipitation and an AMPK activity assay were used to detect any changes in the PVAT environment. Results: Offspring of obese mothers were overweight, mildly hypertensive and insulin resistant. Contractions in PVAT-denuded arteries from HFD dams and their offspring were reduced by a mechanism involving increased protein O-GlcNAcylation. PVAT exerted an anti-contractile effect in vessels from control offspring and their mothers through the release of relaxant factors, which included nitric oxide (NO). The anti-contractile effect of PVAT was lost in HFD offspring due to reduced NO bioavailability and increased O-GlcNAcylation, which lead to decreased AMPK activity within PVAT. However, simultaneous AMPK activation within PVAT partially restored the anti-contractile capability in HFD offspring. Reduced NO bioavailability also lead to PVAT dysfunction in HFD mothers. Conclusions: Elevated insulin levels in the HFD offspring may lead to enhanced glucose uptake and increased protein O-GlcNAcylation, which contributes to the PVAT dysfunction in HFD offspring. The PVAT dysfunction, which is associated with reduced NO bioavailability in HFD mothers and their offspring may be the result of reduced AMPK phosphorylation of nitric oxide synthase within PVAT.

Plasma membrane calcium ATPase 4 (PMCA4) is a calcium extrusion pump which may also modulate Ca2+-triggered signal transduction pathways. Previous studies postulate that PMCA4 modulates signalling via an interaction with neuronal nitric oxide synthase (nNOS) in localised plasmalemmal microdomains. The effect of PMCA4 on vascular contractility is unclear. This project has utilised PMCA4 ablated mice (PMCA4 KO (-/-)) and a novel specific PMCA4 inhibitor (termed AP2) to study the role of PMCA4 in mouse resistance artery contractility.Immunohistochemistry, Western blotting and polymerase chain reaction (PCR) confirmed the absence of PMCA4 in the brain, vasculature and ear snips obtained from PMCA4 KO (-/-) mice whereas it was present in those from wild type (WT (+/+)) mice. Pressure myography was employed to assesss contractile function of isolated, pressurised (to 60 mmHg) mesenteric resistance arteries from 3 months old male PMCA4 KO (-/-) and WT (+/+) mice, in response to high K+ physiological salt solution (KPSS) (40mM & 100mM) and noradrenaline (NA) (Log[NA] -9.0 to -5.0M). Passive lumen diameter and left and right wall thicknesses of arteries from PMAC4 KO (-/-) and WT (+/+) mice were taken at transmural pressures of 5-140 mmHg. Effects of acute PMCA4 inhibition with AP2 (10µM and 1µM), nitric oxide synthase (NOS) inhibition with LNNA (100µM) and specific nNOS inhibition with Vinyl-L-Nio (10µM) were also investigated. Effects of PMCA4 ablation and AP2 (10µM) on global intracellular Ca2+ changes ([Ca2+]i) in pressurised mesenteric arteries were assessed after loading arteries with the Ca2+-sensitive indicator indo-1. PMCA4 ablation had no effect on the magnitude of arterial constrictions or on the changes of [Ca2+]i in response to KPSS (40mM & 100mM) or to noradrenaline. The passive intra-lumen diameter, wall thickness, wall to lumen diameter and cross sectional area of mesenteric arteries across the intravascular pressure range studied were also not modulated by PMCA4 ablation. A leftwards shift in the stress to strain relationship and significant increase in beta elastic modulus (β) were revealed in arteries from PMCA4 KO (-/-) mice compared to those from WT (+/+) mice, suggesting that PMCA4 ablation reduces mesenteric arterial distensibility. Acute PMCA4 inhibition with AP2, significantly reduced arterial constrictions and the increase in [Ca2+]i in response to noradrenaline in arteries from WT (+/+) mice, but had no effect on arterial constrictions elicited by arteries from PMCA4 KO (-/-) mice. Inhibitory effects of AP2 were not present in arteries after NOS inhibition by LNNA and also after nNOS inhibition with Vinly-L-Nio. Hence, PMCA4 inhibition with AP2 reduces vascular constriction by a nNOS-dependent mechanism.In conclusion, the main findings of the study were that ablation and acute inhibition of PMCA4 with AP2 have different effects on mouse mesenteric resistance arterial contractility. This study provides more insight into PMCA4 as a significant modulator of signalling within the vasculature via effects on nNOS.

White adipocytes surround almost all blood vessels in the human body. It was thought previously that these cells merely provide mechanical support for the adjacent small vessels and are little more than fat storage units. Recent studies have identified these cells as metabolic and vasoactive engines that produce and secrete molecules that can affect the function of their adjacent small vessels. The adipocytes and a number of other cell types (including inflammatory cells) surrounding the vessels are collectively termed the PeriVascular Adipose Tissue (PVAT). Work from our group has shown previously that, in health, PVAT conveys a vasorelaxant effect on adjacent small arteries and that this effect is not observed in obesity thus the vessels must exist at an elevated level of basal tone. It is plausible that increased basal vessel constriction can explain the elevated blood pressure amongst the obese population and a better understanding of the obesity-induced PVAT damage may lead to clues to a new approach in the treatment of the condition which burdens its sufferers with a greater cardivascular risk profile. In this thesis we have studied individuals with morbid obesity at baseline and six months following surgery and observed that PVAT function following dramatic weight loss restores the PVAT vasorelaxant effect close to that observed in lean patients. Moreover, we have concluded that inflammation plays a significant role in this process and indeed using protocols with antioxidant enzymes we were able to restore the damaged PVAT function at baseline. We have have shown also that in health, PVAT vasorelaxant function is independent of the endothelium, and that obesity-induced PVAT damage and its reversal following weight loss and ex-vivo anti-oxidant treatment are both independent of the endothelium and at least in part due to nitric oxide bioavailability. Finally, we have observed that in sleep apnoea, which often coexists with morbid obesity and hypertension, there is a greater degree of PVAT inflammation.

Cardiomyopathies represent a heterogeneous group of diseases of the heart muscle that often lead to progressive heart failure with high morbidity and mortality. In a significant and increasing percentage of the patient population, cardiomyopathies have been associated with hereditary mutations in genes encoding critical cellular components that make up the cytoarchitecture of cardiac muscle cells, or cardiomyocytes. While specific mutations have been linked to different classes of cardiomyopathies, it is however not well understood how these mutations cause cytostructural abnormalities that ultimately lead to dysfunction of cardiomyocytes. To gain insights into the pathogenesis of inherited cardiomyopathies, we focus in this thesis on a particular set of mutations in the cardiac cytoskeleton and desmosomes that are associated with dilated and arrhythmogenic cardiomyopathies, and probe their pathogenic mechanisms using cardiomyocytes derived from human induced pluripotent stem cells and bioengineered culture platforms. In part one, we describe the mechanical and molecular basis for the assembly of sarcomeres, the fundamental contractile units within cardiomyocytes, and reveal how mutations in titin (TTN) abolish this process by disrupting cell-matrix interaction and impairing diastolic force generation, a hallmark of dilated cardiomyopathy. In the second part of this thesis, we reveal that plakophilin-2 (PKP2) mutations that are associated with arrhythmogenic cardiomyopathy lead to impaired systolic function by destabilizing cell-cell junctions and in turn disrupting sarcomere stability and organization. Together, our studies establish a deeper understanding of how cell-matrix and cell-cell interactions contribute to the organization and function of cardiomyocytes and how disruption of these interactions by pathogenic mutations lead to cardiac dysfunction. / 2022-05-18T00:00:00Z

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