Expression of Ski induces apoptosis and represses autophagy in cardiac myofibroblasts (868.8)

Abstract

Following myocardial infarction (MI), relatively quiestent cardiac fibroblasts undergo phenoconversion to active, hyper‐synthetic myofibroblasts. During the late stages of wound healing, myofibroblasts are removed from the infracted region through apoptosis thus decreasing scar cellularity. Apoptosis and autophagy regulate cell fate. The role of apoptosis within the remodeling heart has been well described however the role that autophagy plays following an MI is relatively unknown. Ski is a negative regulator of TGF‐β signaling and has been implicated to play a role in the post‐MI heart. Herein we investigated the regulatory role that Ski has on apoptosis and autophagy using first passage primary rat cardiac myofibroblasts. Using an adenoviral approach for gene delivery, both MTT and Live/Dead viability/cytoxicity assays demonstrated a reduction in the number of viable cells and an increase in the number of dying cells due to the over‐expression of Ski. Additionally, over‐expression of Ski led to distinct morphological changes characteristic of apoptosis. These findings were confirmed via Western blot analysis, and caspase GLO analysis showing induction of executioner caspases‐3 and ‐7, as well as the mitochondrial regulator Bax. Furthermore, evidence of caspase‐9 cleavage, but not caspase‐8, indicated that this was primarily an intrinsic apoptotic response. Markers for autophagosome formation including LC3‐B and ATG‐7 were found to be significantly reduced following Ski over‐expression. In summary, we found that over‐expression of Ski in primary cardiac myofibroblasts leads to an induction of the intrinsic apoptotic pathway and reduction in autophagy leading to cell death.Grant Funding Source: Canadian Institutes of Health Research