Abstract 17015: Mitophagy Facilitates Cytosolic Proteostasis to Preserve Cardiac Function

Abstract

Introduction: Protein quality control (PQC) is critical for maintaining sarcomere structure and function in cardiac myocytes. Mutations in PQC pathway proteins, such as CRYAB (arginine to glycine at position 120, R120G) and BAG3 (proline to lysine at position 209, P209L), induce protein aggregates with cardiomyopathy in humans. Novel observations in yeast and mammalian cells demonstrate mitochondrial uptake of cytosolic protein aggregates. The functional relevance of this pathway in myocardial proteostasis is unknown. Hypothesis: We hypothesize that mitophagy removes cytosolic protein aggregates in cardiac myocytes. Methods: Mice with inducible cardiac myocyte specific ablation of TRAF2 (TRAF2icKO), which impairs mitophagy, were assayed for protein aggregates with biochemical fractionation and super-resolution imaging in comparison to floxed controls. Transgenic mice expressing R120G CRYAB (R120G TG) were subjected to both TRAF2 gain-of-function (with AAV9-cardiac Troponin T promoter-driven TRAF2 transduction) and TRAF2 loss-of-function (with tamoxifen-inducible ablation of one Traf2 allele) in cardiac myocytes to determine the effect of mitophagy modulation on cardiac structure, function, and protein aggregate pathology. Results: Poly-ubiquitinated protein-rich aggregates accumulate in the cytosol and within mitochondria with desmin mislocalization in TRAF2icKO myocardium. CRYAB R120G and BAG3 P209L mutant proteins are taken up by isolated mitochondria. CRYAB R120G protein aggregates co-localize with damaged mitochondria and lysosomes by Coupa imaging, and accumulate in the mitochondrial fraction in R120G TG myocardium with upregulation of TRAF2 and induction of mitophagy. Adult-onset haplo-insufficiency of Traf2 accelerated mortality (P=0.003), impaired left ventricular (LV) fractional shortening (P<0.001) and worsened mitochondrial morphology in R120G TG mice. AAV9-cTnT-TRAF2 transduction delayed mortality (P=0.027), rescued LV fractional shortening (P=0.039), reduced mitochondrial protein aggregates and improved desmin localization in R120G TG mice. Conclusions: Mitophagy facilitates removal of cytosolic protein aggregates and can be stimulated to ameliorate proteotoxic cardiomyopathy.