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Distinct Hypertrophic Cardiomyopathy Genotypes Result in Convergent Proteoform Profiles Revealed by Top Down Proteomics

ABSTRACT: Hypertrophic cardiomyopathy (HCM) is a common genetic heart disease and a leading cause of sudden cardiac death in young adults. HCM has been linked to mutations in genes encoding sarcomeric proteins, but how different mutations can result in a similar clinical phenotype is unknown. Analysis of surgical heart tissue samples from HCM patients with severe outflow track obstruction using high-resolution mass spectrometry-based top-down proteomics revealed a common pattern of altered sarcomeric proteoforms across HCM tissues compared to non-failing donor heart tissues. Our data suggest that common pathways are associated with clinical phenotypes in patients diagnosed with obstructive HCM, opening the door for the development of interventions that target the HCM phenotype rather than the individual sarcomeric gene mutation.

INSTRUMENT(S): solariX, impact

ORGANISM(S): Homo Sapiens (ncbitaxon:9606)

SUBMITTER: Ying Ge

PROVIDER: MSV000085823 | MassIVE | Fri Jul 24 09:59:00 BST 2020

REPOSITORIES: MassIVE

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Project description: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.

Project description:Background – Hypertrophic cardiomyopathy (HCM) is a common genetic cardiac disorder that is characterized by the presence of left ventricular hypertrophy with histological evidence of myocyte disarray and fibrosis. Pathologic DNA variants in sarcomeric genes are seen in 50–60% of families, but the mechanistic origins of hypertrophy and disarray remain poorly understood. More molecular insights could contribute to a better understanding of these origins and improve therapeutic strategies for HCM. Methods – To identify gene expression patterns relevant to HCM pathology, we quantified intercellular heterogeneity in cardiomyocyte gene expression by performing single-cell RNA sequencing (scRNA-seq) on myectomy tissue from HCM patients. Results – Septal myectomy samples provide a unique opportunity to access diseased human heart tissue for scRNA-seq. We analysed gene expression of individual cardiomyocytes for three HCM patients, who each showed a similar presence of cardiomyocyte subpopulations. This similarity indicated these subpopulations emerge from biological processes, and not from experimental variability. Moreover, our data revealed functional links between genes important to HCM. A subpopulation characterized by elevated titin (TTN) expression showed increased expression of genes involved in muscle contraction and development. A subpopulation of Natriuretic Peptide A (NPPA)-enriched cells showed elevated expression of Natriuretic Peptide B (NPPB). Further analysis of gene co-expression revealed five groups of genes with tightly correlated expression (regulons), one consisting of mostly sarcomeric genes and another containing some well-known stress markers. These correlations were confirmed in 97 additional HCM myectomy samples and allowed us to de novo identify transcription factors related to sarcomeric gene expression and stress. Finally, using forward scatter, we charted functional implications of regulon expression and showed a link between the stress-marker regulon and cell size. Histology samples independently confirmed that regulon member skeletal alpha actin (ACTA1) correlates with cell size. Conclusion – We have shown that single-cell sequencing on myectomy samples from HCM patients identified new functional links between genes, transcription factors, and a functional link between genes and cell size. This highlights the relevance of cardiomyocyte heterogeneity, and additionally provides a wealth of novel insights into molecular events at the base of HCM, which potentially contribute to understanding disease progression.

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Distinct Hypertrophic Cardiomyopathy Genotypes Result in Convergent Proteoform Profiles Revealed by Top Down Proteomics

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