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Altered Cardiac Energetics and Mitochondrial Dysfunction in Hypertrophic Cardiomyopathy

ABSTRACT: Hypertrophic cardiomyopathy (HCM) is a complex disease partly explained by the effects of individual gene variants on sarcomeric protein biomechanics. At the cellular level, HCM mutations most commonly enhance force production, leading to higher energy demands. Despite significant advances in elucidating sarcomeric structure-function relationships, there is still much to be learned about the mechanisms that link altered cardiac energetics to HCM phenotypes. In this work, we test the hypothesis that changes in cardiac energetics represent a common pathophysiologic pathway in HCM. We performed a comprehensive multi-omics profile of the molecular (transcripts, metabolites, and complex lipids), ultrastructural, and functional components of HCM energetics using myocardial samples from 27 HCM patients and 13 normal controls (donor hearts). Integrated omics analysis revealed alterations in a wide array of biochemical pathways with major dysregulation in fatty acid metabolism, reduction of acylcarnitines, and accumulation of free fatty acids. HCM hearts showed evidence of global energetic decompensation manifested by a decrease in high energy phosphate metabolites (ATP, ADP, and phosphocreatine) and a reduction in mitochondrial genes involved in the creatine kinase and ATP synthesis. Accompanying these metabolic derangements, quantitative electron microscopy showed an increased fraction of severely damaged mitochondria with reduced cristae density, coinciding with reduced citrate synthase (CS) activity and mitochondrial oxidative respiration. These mitochondrial abnormalities were associated with elevated reactive oxygen species (ROS) and reduced antioxidant defenses. However, despite significant mitochondrial injury, HCM hearts failed to upregulate mitophagic clearance. Overall, our findings suggest that perturbed metabolic signaling and mitochondrial dysfunction are common pathogenic mechanisms in patients with HCM. These results highlight potential new drug targets for attenuation of the clinical disease through improving metabolic function and reducing mitochondrial injury.

ORGANISM(S): Homo sapiens

PROVIDER: GSE180313 | GEO | 2022/07/17

REPOSITORIES: GEO

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Project description:Rationale Hypertrophic cardiomyopathy (HCM) is the most common cardiac genetic disorder caused by sarcomeric gene variants and is associated with left ventricular hypertrophy and diastolic dysfunction. The role of the microtubule network has recently gained interest with findings that microtubule detyrosination (dTyr-MTs) is markedly elevated in heart failure. Acute reduction of dTyr-MTs by inhibition of the detyrosinase (VASH/SVBP complex) or activation of the tyrosinase (tubulin tyrosine ligase, TTL) markedly improved contractility and reduced stiffness in human failing cardiomyocytes, presenting a new perspective for HCM treatment. Objective In this study, we tested the impact of chronic tubulin tyrosination in a HCM mouse model (Mybpc3-knock-in; KI), in human HCM cardiomyocytes, and in SVBP-deficient human engineered heart tissues (EHTs). Methods and Results AAV9-mediated TTL transfer was applied in neonatal wild-type (WT) rodents, in 3-week-old KI mice, and in HCM human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes. We show: i) TTL for 6 weeks dose-dependently reduced dTyr-MTs and improved contractility without affecting cytosolic calcium transients in WT cardiomyocytes. ii) TTL for 12 weeks reduced the abundance of dTyr-MTs in the myocardium, improved diastolic filling, compliance, cardiac output, and stroke volume in KI mice. iii) TTL for 10 days normalized cell area in HCM hiPSC-cardiomyocytes. iv) TTL overexpression activates transcription of several tubulin isoforms, and omics GO analysis revealed enrichment of components of the cytoskeleton, sarcomere Z-disc, mitochondria, and intercalated disc in KI mice. v) SVBP-deficient EHTs exhibited reduced dTyr-MT levels, higher force, and faster relaxation than TTL-deficient and WT EHTs. RNA-seq and mass spectrometry analysis revealed distinct enrichment of cardiomyocyte components and pathways in SVBP-KO vs. TTL-KO EHTs. Conclusion This study provides the first proof-of-concept that chronic activation of tubulin tyrosination in HCM mice and in human EHTs improves heart function and holds promise for targeting the non-sarcomeric cytoskeleton in heart disease.

Project description:Muscle ring finger-1 (MuRF1) is a muscle-specific protein implicated in the regulation of cardiac myocyte size and contractility. MuRF2, a closely related family member, redundantly interacts with protein substrates, and hetero-dimerizes with MuRF1. Mice lacking either MuRF1 or MuRF2 are phenotypically normal whereas mice lacking both proteins develop a spontaneous cardiac and skeletal muscle hypertrophy indicating cooperative control of muscle mass by MuRF1 and MuRF2. In order to identify the role that MuRF1 plays in regulating cardiac hypertrophy in vivo, we created transgenic mice expressing increased amounts of cardiac MuRF1. Adult MuRF1 transgenic (Tg+) hearts exhibited a non-progressive thinning of the left ventricular wall and a concomitant decrease in cardiac function. Experimental induction of cardiac hypertrophy by trans-aortic constriction (TAC) induced rapid failure of MuRF1 Tg+ hearts. Microarray analysis identified that the levels of genes associated with metabolism (and in particular mitochondrial processes) were significantly altered in MuRF1 Tg+ hearts, both at baseline and during the development of cardiac hypertrophy. Surprisingly, ATP levels in MuRF1 Tg+ mice did not differ from wild type mice despite the depressed contractility following TAC. To explain this discrepancy between the ongoing heart failure and maintained ATP levels in MuRF1 Tg+ hearts, we compared the level and activity of creatine kinase (CK) between wild type and MuRF1 Tg+ hearts. Although mCK and CK-M/B protein levels were unaffected in MuRF1 Tg+ hearts, total CK activity was significantly inhibited. We conclude that MuRF1’s inhibition of CK activity leads to increased susceptibility to heart failure following TAC, demonstrating for the first time that MuRF1 regulates cardiac energetics in vivo. Keywords: Genetic modification, physiological manipulation. Three-condition experiment, MuRF1 Tg+ vs. WT mice. Biological replicates: 4 WT baseline, 3 MuRF1 Tg+ baseline, cardiac overpressure hypertrophy induced by trans-aortic banding at 1 week (3 WT, 3 MurF Tg) and 4 weeks (3 WT, 3 MurF Tg), hearts harvested. One replicate per array.

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Altered Cardiac Energetics and Mitochondrial Dysfunction in Hypertrophic Cardiomyopathy

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