Abstract P3030: Fundc1 Mediated Mitochondrial Protein Import As A Novel Mechanism Exacerbating Dilated Cardiomyopathy

Background: Dilated cardiomyopathy (DCM) is a common cause of heart failure and an indication for heart transplantation worldwide. FUN14 Domain Containing 1 (FUNDC1), a canonical mitophagy receptor and mitochondria-associated ER membranes (MAMs) protein, plays an essential role in ischemic heart disease. However, the role of FUNDC1 in DCM remains unidentified. The current study attempted to clarify whether and how FUNDC1 regulates DCM development. Methods: Cardiomyocyte-specific F UNDC 1 gene knockout (CM-FUNDC1 KO) mice were generated to study the impact and potential mechanisms of FUNDC1 in the heart. Mitochondria were isolated from heart tissues, primary mouse neonatal/adult cardiomyocytes, or H9C2 cell lines to probe the role of FUNDC1 in mitochondrial protein import (MPI). Results: All CM-FUNDC1 KO mice developed severe DCM spontaneously and died before 15 months old. The expression of MPI-associated proteins was significantly upregulated in the hearts of CM-FUNDC1 KO mice. Experiments with purified mitochondria demonstrated that MPI efficiency was enhanced by CM-FUNDC1 KO, whereas reduced by FUNDC1 overexpression in an autophagy-independent fashion. We further identified that FUNDC1 selectively downregulated the TIM23 complex without altering other MPI translocases (e.g., TOM20, TIM22 complexes). Downregulation of subunits of TIM23 complex partly reversed the FUNDC1 KO-induced MPI enhancement. Importantly, we demonstrated that FUNDC1 selectively inhibited the import of nuclear gene-encoded respiratory subunits on complex I, IV but not on complex II, III, V or mitochondrial gene-encoded subunits. Finally, FUNDC1 deleted cells exhibited enlarged cell size, retarded cell growth, impaired oxygen consumption rate, and increased mitochondrial superoxide level. All of these phenomena were partly reversed by silence TIM23 complex or reproduced by TIM23 complex overexpression. Conclusions: We demonstrate for the first time that: 1) MPI system plays an important role in the progress of DCM; 2) FUNDC1 is a novel negative regulator of MPI via TIM23 pathway; and 3) FUNDC1 is a promising therapeutic target for DCM.