Abstract 2956: Growth Differentiation Factor-5 (GDF-5) Prevents Cardiomyocyte Apoptosis and Limits Adverse Cardiac Remodeling Following Myocardial Infarction
Background: GDF5, a member of the BMP family, is expressed in various tissues including heart. We showed in wild-type (WT) mice that cardiac GDF5 levels are elevated after myocardial infarction (MI) induced by LAD ligation. We also showed that GDF5-knock out (KO) mice exhibited increased infarct expansion, infarct thinning and LV dilatation, as well as decreased arteriolar density and impaired cardiac function post-MI as compared to WT littermates. However, the source of increased GDF5 expression post-MI and its mechanisms of action were not known.
Methods & Results: In WT mice, GDF5 levels are elevated in peri-infarct cardiomyocytes. At 4d post-MI, GDF5-KO mice exhibited greater cardiomyocyte apoptosis and lesser expression of anti-apoptotic genes Bcl2 and Bcl-xL compared to WT. Unexpectedly, GDF5-KO hearts displayed increased Smad 1/5/8 phos-phorylation, but decreased p38-MAPK phosphorylation compared to WT. The latter was associated with increased collagen (Col1a1, Col3a1) mRNA levels and fibrosis. In cultured cardiac fibroblasts from WT mice, recombinant GDF5 (rGDF5) induced p38-MAPK phosphorylation. In cultured neonatal cardiomyocytes, rGDF5-induced survival despite serum withdrawal was associated with increased Bcl2 and Bcl-xL expression. The mRNA levels of the pro-apoptotic gene Bax remained unchanged in buffer or rGDF5-tretaed cardiomyocytes. To further delineate the signaling pathway mediating the anti-apoptotic effect of rGDF5 in neonatal cardiomyocytes, RNAi against Smad4 and p38-MAPK were employed. RNAi to Smad4, but not p38-MAPK, blocked rGDF5-induced expression of Bcl-xL and suppression of apoptosis. These effects of rGDF5 in vitro are consistent with our in vivo findings of increased apoptosis and decreased Bcl2 and Bcl-xL expression in GDF5-KO hearts post-MI.
Conclusion: Increased GDF5 expression in peri-infarct cardiomyocytes appears to prevent progressive cardiomyocyte loss by Smad-dependent Bcl2 and Bcl-xL expression. GDF5 may also affect fibrosis via p38-MAPK-dependent increases in collagen gene expression by cardiac fibroblasts. Together, these data suggest that endogenous GDF5 levels play critical salutary paracrine and autocrine roles in cardiac repair and posit a therapeutic role for GDF5 post-MI.