Both hypertrophic (HCM) and dilated cardiomyopathy (DCM), though differing in their aetiologies, share features of impaired resting energetics. The aim of this thesis was to determine if cardiac high energy phosphate metabolism, measured as the phosphocreatine (PCr)/ATP ratio using 31Phosphorus magnetic resonance spectroscopy (31P MRS), is further impaired during exercise in these pathologies. This would provide a possible explanation for the high incidence of exercise related death in HCM and DCM as well as the blunted inotropic response to exercise in DCM. Furthermore, this thesis investigates the role of stress perfusion and stress tissue oxygenation in HCM (as these are hypothesized to exacerbate the primary defect in energetics) and exercise training in DCM (which is hypothesized to improve function though the mechanisms are uncertain). This work developed a novel protocol for measuring 31P MRS in a clinically acceptable time frame. The traditional acquisition is at least 20 minutes (as much as 40 minutes in subjects with lower pulse rates). This is a particularly long time to allow for exercise in the magnet particularly in the symptomatic DCM cohort. Hence this work meticulously developed a shorter 8 minute protocol. Its validity, reproducibility and application to exercise were confirmed. The post processing of the MRS data was further improved for calculating blood contamination and tested with both simulated and patient data, including normal, hypertrophied and thinned myocardium. Applying this new method, this thesis is the first to report a further decrease in exercise energetics in HCM. The relationship between perfusion, tissue de-oxygenation and energetic compromise during exercise was then explored in HCM. Athletes, with physiological hypertrophy, were used as an additional control group in these experiments. These results demonstrated a strikingly blunted oxygenation response of the HCM heart to stress even in the pre-hypertrophy HCM mutation carriers. However, as a group, the data did not show a correlation between the blunted oxygenation response and the percentage change in PCr/ATP during exercise. None-the-less, these results can potentially be useful for distinguishing between hypertrophy in the athletes and pathological hypertrophy in HCM and for distinguishing HCM mutation carriers’ pre hypertrophy and the normal heart. In the DCM cohort, this thesis explored the impact of exercise training on cardiac metabolism and function. The results showed no change in cardiac energetics and left ventricular ejection fraction during 8 minutes of exercise. In addition, an eight week home exercise programme did not alter resting or exercise cardiac PCr/ATP, but improved cardiac function during rest and exercise, and increased exercise tolerance and quality of life scores. In conclusion, this thesis reports further insights into cardiac exercise energetics in HCM and DCM and its relationship to perfusion and oxygenation in HCM and to exercise training in DCM. Therapies that decrease the energy cost of cardiac work during exercise may prove beneficial targets to explore further in these conditions.

Heart failure is a leading cause of death in the United States, impacting approximately 6.7 million people. Several comorbidities are associated with heart failure, contributing to adverse clinical outcomes. Among these comorbidities, diabetes is highlighted as a prominent risk factor for heart failure, with approximately 20-40% of heart failure patients having type 2 diabetes. As the prevalence of heart failure continues to rise, there is a need for novel therapeutic methods to address this concern. PPARGC1 and ESRR Induced Regulator in Muscle 1 (PERM1) is a striated muscle-specific regulator of mitochondrial bioenergetics, predominantly expressed in skeletal and cardiac muscle. Our group has previously demonstrated that PERM1 is downregulated in both human and mouse failing hearts, and that Perm1-knockout mice exhibit reduced cardiac contractility and energy reserve. However, the role of PERM1 in cardiac dysfunction in diabetes remains unknown. We hypothesized that loss of PERM1 increases vulnerability to metabolic insults and exacerbates diet-induced insulin resistance and cardiac dysfunction. To test this, C57BL/6N male wild-type (WT) and Perm1-knockout (Perm1-KO) mice were fed either a normal diet or a high-fat diet (HFD; 60% calories from fat) for up to 43 weeks. We found that PERM1 expression was upregulated in the hearts of WT mice after 8 weeks of HFD feeding, coinciding with an increased level of carnitine palmitoyltransferase 2 (CPT2), a key enzyme involved in mitochondrial fatty acid uptake. Importantly, both WT and Perm1-KO mice exhibited similar increases in total body weight, fat mass, and fasting blood glucose levels throughout 43 weeks of HFD feeding, suggesting that loss of PERM1 did not accelerate the development of either obesity or diabetes. Echocardiographic assessments showed that WT mice maintained systolic and diastolic function, despite moderate cardiac remodeling, manifested as a subtle but significant increase of left ventricle posterior (LVPW) wall thickness. Unexpectedly, 8 weeks HFD feeding partially restored systolic function in Perm1-KO mice with no change in LVPW thickening. These findings show that while HFD feeding induced obesity and insulin resistance, its effect on cardiac function was relatively moderate and neither was exacerbated by the loss of PERM1. Unexpectedly, this study suggests that HFD feeding in Perm1-KO mice could partially compensate for cardiac dysfunction. / Master of Science / Heart failure is a major health issue in the U.S, affecting 6.7 million people. About 20-40% of heart failure patients also have type-2 diabetes, making their condition worse. Due to its high prevalence, there is a need for new treatments to address this problem. One potential therapeutic strategy is a protein called PPARGC1 and ESRR Induced Regulator in Muscle 1 (PERM1), which plays a role in energy production in the heart and skeletal muscle. Our group has previously shown that levels of PERM1 drop in the failing heart, leading to weaker heart function. However, the role that PERM1 plays in heart failure with diabetes is unknown. We hypothesized that loss of PERM1 increases metabolic stress, insulin resistance, and cardiac dysfunction. To study how PERM1 affects the heart, we used mice with and without the PERM1 gene and fed them either a normal diet or a high-fat diet (HFD) to mimic conditions like obesity and diabetes. After 8 weeks of a HFD, we found that, while both groups of mice developed obesity and insulin resistance, the absence of PERM1 did not make these issues worse. Interestingly, we also found that HFD increased levels of PERM1 in the heart and increased levels of the protein carnitine palmitoyltransferase 2 (CPT2), which promotes fatty acid uptake in cells. In addition, HFD feeding appeared to partially improve systolic heart function in the mice lacking PERM1. Overall, this study suggests that losing PERM1 does not worsen heart problems in response to a high-fat diet, and in some cases, the diet might even help compensate for heart failure. These findings could lead to new insights into how the heart adapts to stress and metabolic changes.

No description available.

Cardiac myosin binding protein-C (cMyBP-C) is a structural and regulatory component of cardiac thick filaments. It is observed in electron micrographs as seven to nine transverse stripes in the central portion of each half of the A band. Its C-terminus binds tightly to the myosin rod and contributes to thick filament structure, while the N-terminus can bind both myosin S2 and actin, influencing their structure and function. Mutations in the MYBPC3 gene (encoding cMyBP-C) are commonly associated with hypertrophic cardiomyopathy (HCM). In cardiac cells there exists a population of myosin heads in the super-relaxed (SRX) state, which are bound to the thick filament core with a highly inhibited ATPase activity. This report examines the role cMyBP-C plays in regulating the population of the SRX state of cardiac myosin by using an assay that measures single ATP turnover of myosin. We report a significant decrease in the proportion of myosin heads in the SRX state in homozygous cMyBP-C knockout mice, however heterozygous cMyBP-C knockout mice do not significantly differ from the wild type. A smaller, non-significant decrease is observed when thoracic aortic constriction is used to induce cardiac hypertrophy in mutation negative mice. These results support the proposal that cMyBP-C stabilises the thick filament and that the loss of cMyBP-C results in an untethering of myosin heads. This results in an increased myosin ATP turnover, further consolidating the relationship between thick filament structure and the myosin ATPase. Crown Copyright (C) 2016 Published by Elsevier Ltd. All rights reserved.