Abstract 437: PRMT5-induced Arginine Methylation Mediates Energy Stress-induced Autophagy in the Heart

Autophagy is a self-degradative process that is important for protecting cells and organisms against stress and plays a protective role in the heart. However, the underlying mechanism by which autophagy protects the heart against stress is poorly understood. ATG proteins are required for autophagy and modulated by post-translational modifications (PTMs) such as phosphorylation, ubiquitination, and acetylation. The level of arginine methylation, another form of PTM, is altered in the heart in response to stress. Our hypothesis is that arginine methylation plays an important role in the regulation of autophagy in the heart during stress. To this end, we examined the level of arginine methylation in response to energy stress in vivo . We observed a time-dependent increase in arginine methylation in the mouse heart under starvation conditions for 24 to 48 hours. Arginine methylation was increased (2.32-fold, p<0.01) after 48 hours of fasting compared to in those without fasting. Expression of protein arginine methyltransferase 5 (PRMT5) was increased at both the mRNA and protein level (1.6- and 1.72-fold, p<0.05) in the mouse heart after 48 hours of starvation. In order to investigate the role of endogenous PRMT5, we knocked down PRMT5 with adenovirus harboring sh-RNA. LC3-II, a marker of autophagy activity, was increased during glucose deprivation in sh-scramble-treated cardiomyocytes (CMs) (2.14-fold, p<0.01), but not in sh-PRMT5-treated CMs. Arginine methylation was reduced in response to glucose deprivation in CMs when PRMT5 was downregulated. Mice were also injected intraperitoneally with a PRMT5-specific inhibitor (EPZ015666, 2 mg/kg) and hearts were harvested after 48 hours of starvation. Both arginine methylation levels and autophagy activity in the heart were decreased in the presence of EPZ015666 compared to in non-treated mice. Increased arginine methylation was also observed in the mouse heart in response to 1 hour of myocardial ischemia (1.87-fold, p<0.01), which was accompanied by upregulation of PRMT5 (1.54-fold, p<0.05). Taken together, these data suggest that arginine methylation mediated through PRMT5 may play a key role in mediating autophagy during energy stress conditions such as starvation and ischemia.