Mechanical stretch via transforming growth factor-β1 activates microRNA-208a to regulate hypertrophy in cultured rat cardiac myocytes

Background/PurposeMicroRNA-208a (miR208a) and mechanical stress play a key role in cardiac hypertrophy. The relationship between miR208a and mechanical stress in cultured cardiomyocytes has not been investigated. The molecular mechanisms underlying miR208a-induced hypertrophy of cardiomyocytes by mechanical stress is poorly understood. This study investigated whether miR208a is a critical regulator in cardiomyocyte hypertrophy under mechanical stretch.MethodsNeonatal rat cardiomyocytes grown on a flexible membrane base were stretched at 60 cycles/minute. MiR real-time quantitative assays were used to quantify miRs. A quantitative sandwich enzyme immunoassay technique was used to measure transforming growth factor-β1 (TGF-β1). A 3H-proline incorporation assay was used to measure protein synthesis.ResultsMechanical stretch significantly enhanced miR208a expression. Stretch significantly induced cardiomyocyte hypertrophic protein expression such as β-myosin heavy chain (MHCβ), thyroid hormone receptor-associated protein 100, myostatin, connexin 40, GATA4, and brain natriuretic peptide. MHCα was not induced by stretch. Overexpression of miR208a significantly increased MHCβ protein expression while pretreatment with antagomir208a significantly attenuated MHCβ protein expression induced by stretch and overexpression of miR208a. Mechanical stretch significantly increased the secretion of TGF-β1 from cultured cardiomyocytes. Exogenous addition of TGF-β1 recombinant protein significantly increased miR208a expression and pretreatment with TGF-β1 antibody attenuated miR208a expression induced by stretch. Mechanical stretch and overexpression of miR208a increased protein synthesis while antagomir208a attenuated protein synthesis induced by stretch and overexpression of miR208a.ConclusionCyclic stretch enhances miR208a expression in cultured rat cardiomyocytes. MiR208a plays a role in stretch-induced cardiac hypertrophy. The stretch-induced miR208a is mediated by TGF-β1.