Abstract 1432: Cardiomyocyte Myostatin Contributes to Skeletal Muscle Wasting in Heart Failure

Introduction: Skeletal muscle wasting during heart failure constitutes a major therapeutic challenge. The TGFβ superfamily member myostatin is a negative regulator of skeletal muscle growth. For example, elimination of myostatin (MSTN) in adult mice through an inducible Cre/lox recombination strategy has been shown to increase skeletal muscle mass by about 25%. Previous studies identified skeletal muscle and to a lesser extent cardiac and fat tissue as the source of MSTN production in the body. MSTN is produced as a precursor protein, which has been suggested to constitute the main reservoir of the protein in skeletal muscle. In mouse serum, however, MSTN is abundantly present in its mature form, which consists of the C-terminal fragment of the precursor protein. Results: We detected high levels of the mature MSTN protein (MM) in the mouse myocardium by western blotting. Interestingly, MM was significantly upregulated in the myocardium of mice subjected to long-term myocardial pressure overload (TAC, 12 weeks; protein levels: sham 100±22% vs. TAC 218±18%, p<0.01). In contrast, MM was barely detectable in mouse skeletal muscle. Immunhistochemical staining confirmed enhanced cardiomyocyte MSTN production after TAC. To determine the impact of cardiomyocyte MSTN on skeletal muscle growth during heart failure, we crossed cardiomyocyte specific Nkx2.5-Cre mice with mice in which the MSTN exon3 was flanked by loxp sites to eliminate expression of mature MSTN selectively in cardiomyocytes (CKO mice). While CKO mice did not have significant changes in skeletal muscle mass after a sham operation (e.g. quadriceps, normalized to tibia length: sham control 111±3.8 g/cm vs. sham CKO 106±4.3 g/cm), a 16% increase in skeletal muscle mass was observed in CKO mice after longterm TAC (quadriceps: TAC control 100±3.3 g/cm vs. TAC CKO 116±5.3 g/cm, p<0.05). In line with these results, mice with cardiomyocyte specific overexpression of MSTN (MSTN-Tg) showed a reduction in skeletal muscle mass (quadriceps: control 91±2.5 g/cm vs. MSTN-Tg 82±1.5 g/cm, p<0.05). Conclusion: Myocardial MSTN contributes to the development of skeletal muscle wasting in heart failure, most likely through an endocrine mechanism involving its secretion into the circulatory system.