Abstract 12606: Autophagy is Required for Mitochondrial Biogenesis in the Heart

Abstract

Autophagy is an essential process that maintains cellular homeostasis via lysosomal degradation pathways. Autophagy has been found to be involved in various pathophysiological conditions in the heart, including myocardial hypertrophy and ischemic heart disease. However, the precise mechanism by which autophagy maintains cardiac function in the non-stressed heart is incompletely understood. We generated cardiac-specific ATG3 deficient mice (cATG3 KO mice) by crossing αMHC-Cre mice with floxed ATG3 mice. Relative to their wild type (WT) littermates, cATG3 KO mice revealed reduced ATG3 expression and inhibited autophagy specifically in the heart. At 4 months of age, cATG3 KO mice showed impaired cardiac contractile function, characterized by a 25% reduction in fractional shortening by echocardiography (p <0.01), Moreover, cATG3 KO mice revealed increased lipid accumulation, reduced fatty acid oxidation and impaired mitochondrial respirations in the heart, without evidence of fibrosis or inflammation. Mitochondrial dysfunction in cATG3 KO mice was accompanied with mitochondrial content loss and reduced expression of mitochondrial biogenesis related genes (PGC1α, NRF1, NRF2 and TFAM). Interestingly, autophagy inhibition, induced mitochondrial biogenesis defects and mitochondrial dysfunction in neonatal cATG3 KO mice (1 week old), prior to the onset of cardiac contractile dysfunction and heart failure, suggesting that cardiac mitochondrial dysfunction may be an early event in the progression of heart failure in the autophagy deficient mice. Finally, in response to exercise training mitochondrial biogenesis (PGC1 alpha induction and increased respiration rates) was completely inhibited in ATG3 deficient mice. In conclusion, autophagy is essential for generating signals that promote mitochondrial biogenesis, and is indispensable for normal heart function under basal conditions.