Abstract 265: TGF Beta Signaling and Fibrosis in cMyBP-C-dependent Cardiac Disease

Abstract

Background: Mutations in cardiac myosin binding protein C ( MYBPC3 ) account for more than one third of identified hypertrophic cardiomyopathy (HCM). Data from both human patients and mouse models suggest that cardiac fibrosis preceeds hypertrophy and cardiac dysfunction, implying that fibrosis related signaling may be one of the initial signs of developing cardiac disease. We wished to determine if cardiomyocyte-autonomous TGFβ signaling is sufficient to initiate pathogenic fibrosis in the heart in the context of a cMyBP-C-induced disease. Methods and Results: Neonatal rat ventricular cardiomyocytes (NRVMs) expressing either wild-type or Mybpc3 mutations were mediated by adenovirus for 48 hours. Both cells and culture medium (conditional medium) were harvested. The fibrotic effects of the conditional medium on neonatal rat ventricular fibroblasts (NRVFs) were determined using “fibrotic” gene promoters driving luciferase (luc) expression ( αSMA-luc , postn-luc and col1a1-luc ). TGFβ levels in the conditional medium were determined using ELISA assays. Expression of cMybpc3 mutations activated TGFβ promoter activity ( Tgfb1-luc , Tgfb2-luc and Tgfb3-luc ) in a TGFβ receptor(s) (TβRs) dependent manner. Upregulation of TGFβ was also confirmed in transgenic mice expressing a fragment of cMyBP-C (cMyBP-C 40kDa ) whose expression results in significant fibrosis and cardiac disease. To establish causality, we genetically ablated TGFβ receptors ( Tgfbr1 and Tgfbr2 ) in the cardiomyocytes of the cMybpc3 40kDa mice. TGFβ receptors ablation blocked the induction of TGFβ expression, alleviating cardiac fibrosis and decreasing cardiac hypertrophy. Cardiac function was significantly improved and survival of the cMyBP-C 40kDa mice was increased. Conclusions: Cardiomyocytes are a critical source of TGFβ in cMyBP-C 40kDa hearts during the initial stages of pathogenesis. Thus, TβRs ablation at the early stage completely prevent the progression of the pathological process in vivo .