Chronic expression of Ski induces apoptosis and represses autophagy in cardiac myofibroblasts

Inappropriate cardiac interstitial remodeling is mediated by activated phenoconverted myofibroblasts. The synthesis of matrix proteins by these cells is triggered by both chemical and mechanical stimuli. Ski is a repressor of TGFβ1/Smad signaling and has been described as possessing anti-fibrotic properties within the myocardium. We hypothesized that overexpression of Ski in myofibroblasts will induce an apoptotic response, which may either be supported or opposed by autophagic flux. We used primary myofibroblasts (activated fibroblasts) which were sourced from whole heart preparations that were only passaged once. We found that overexpression of Ski results in distinct morphological and biochemical changes within primary cardiac myofibroblasts associated with apoptosis. Ski treatment was associated with the expression of pro-apoptotic factors such as Bax, caspase-7, and -9. Our results indicate that Ski triggers a pro-death mechanism in primary rat cardiac myofibroblasts that is mediated through the intrinsic apoptotic pathway. Myofibroblast survival is prolonged by an autophagic response, as the dataset indicate that apoptosis is hastened when autophagy is inhibited. We suggest that the apoptotic death response of myofibroblasts is working in parallel with the previously observed anti-fibrotic properties of Ski within this cell type. As myofibroblasts are the sole mediators of matrix expansion in heart failure, we suggest that Ski, or a putative Ski-mimetic, may induce graded apoptosis in myofibroblasts within the failing heart and may be a novel therapeutic approach towards controlling cardiac fibrosis. Future studies are needed to examine the potential effects of Ski overexpression on other cell types in the heart.