Abstract 117: Regulation of Cardiac Mitochondrial Function by Chaperone Mediated Autophagy

Abstract

Macroautophagy is required for normal cardiac function. Chaperone mediated autophagy (CMA) is distinct in that substrates are transported to lysosomes in complex with Hsc70, rather than within autophagosomes; restricted to cytoplasmic proteins; and selectively marked with a CMA-targeting motif. The role of CMA in the heart has not been assessed. We determined that CMA is induced in the heart by pressure overload with kinetics that differ markedly from those of macroautophagy in response to the same stimulus. In CMA, cargo is imported into the lysosome by LAMP2A, which is necessary, specific, and rate-limiting for this process. Accordingly, we created knockout mice lacking LAMP2A in cardiomyocytes to inactivate CMA specifically in those cells. Unexpectedly, these mice exhibited resistance to stress-induced cardiac dysfunction in both pressure overload and myocardial infarction models. Functional assessment of cardiac mitochondria from L2AKO mice and MEFs exhibited increased rates of O 2 consumption and ATP generation. Mitochondrial proteomics showed increased levels of ATP5L, a component of mitochondrial Complex V (ATP synthase). Overexpression of ATP5L phenocopied LAMP2A KO with respect to augmentation of mitochondrial function. Conversely, knockdown of ATP5L reversed increases in mitochondrial function resulting from L2AKO. We showed that ATP5L, which possesses a KFERQ motif, is a bona fide CMA substrate as it interacts with Hsc70 in a KFERQ-dependent manner; and localizes to lyososmes in a LAMP2A-dependent manner when CMA is induced. ATP5L is thought to mediate oligomerization of Complex V to enhance ATP production. In fact, we observed increases in complex V oligomerization in L2A KO mouse hearts in both basal and TAC-induced states. In summary, cardiomyocyte-specific inhibition of CMA, which renders mice resistant to stress-induced cardiac dysfunction, augments cardiac mitochondrial function through accumulation of ATP5L. Conversely, activation of CMA by cardiac stress may function as a new pathway to heart failure.