Myocardial Fibrosis and Cardiomyopathy Risk: A Genetic Link in the MESA

Circulation: Heart Failure, Ahead of Print.
BACKGROUND:Common genetic variants are associated with risk for hypertrophic cardiomyopathy and dilated cardiomyopathy and with left ventricular (LV) traits. Whether these variants are associated with myocardial fibrosis, an important pathophysiological mediator of cardiomyopathy, is unknown.METHODS:Multi-Ethnic Study of Atherosclerosis participants with T1-mapping cardiac magnetic resonance imaging in-whom extracellular volume was assessed, and genotyping information was available were included (N=1255). Log extracellular volume (%) was regressed on 50 candidate single nucleotide polymorphisms (previously identified to be associated with hypertrophic cardiomyopathy, dilated cardiomyopathy, and LV traits) adjusting for age, sex, diabetes, blood pressure, and principal components of ancestry. Ancestry-specific results were pooled by fixed-effect meta-analyses. Gene knockdown experiments were performed in human cardiac fibroblasts.RESULTS:TheSMARCB1rs2186370 intronic variant (minor allele frequency: 0.18 in White and 0.50 in Black participants), previously identified as a risk variant for dilated cardiomyopathy and hypertrophic cardiomyopathy, was significantly associated with increased extracellular volume (P=0.0002) after adjusting for confounding clinical variables. TheSMARCB1rs2070458 locus previously associated with increased LV wall thickness and mass was similarly significantly associated with increased extracellular volume (P=0.0002). The direction of effect was similar in all 4 ancestry groups, but the effect was strongest in Black participants. The variants are strong expression quantitative loci in human LV tissue and associated with genotype-dependent decreased expression ofSMARCB1(P=7.3×10-22).SMARCB1knockdown in human cardiac fibroblasts resulted in increased TGF (transforming growth factor)-β1–mediated α-smooth muscle actin and collagen expression.CONCLUSIONS:Common genetic variation inSMARCB1previously associated with risk for cardiomyopathies and increased LV wall thickness is associated with increased cardiac magnetic resonance imaging–based myocardial fibrosis and increased TGF-β1 mediated myocardial fibrosis in vitro. Whether these findings suggest a pathophysiologic link between myocardial fibrosis and cardiomyopathy risk remains to be proven.



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