Abstract 391: Endogenous Drp1 Modulates Cardiac Respiration Through mPTP and Independent of Fission

Abstract

Background: The cardiac mitochondria exhibit a stable morphology with a rather low level of dynamic changes. However, fission and fusion proteins, such as dynamin-related protein 1 (DRP1) are abundant in the heart. Whether these proteins bear other functions in the heart than mitochondrial dynamics regulation are largely unknown. We hypothesize that endogenous DRP1 in the heart regulates mitochondrial respiration independent of fission. Methods: Mitochondrial respiration was determined by measuring the OCR with Seahorse assay or Clark type electrode in adult rat cardiomyocytes or mitochondria isolated from adult mouse heart. Confocal imaging was used to quantify mitochondrial morphology in adult cardiomyocytes and H9C2 myoblasts. To evaluate the role of mitochondrial permeability transition pore (mPTP), we monitored superoxide flashes (SOF) and laser-induced mPTP openings, and used cyclophilin D knockout mice (CypD KO). Mitochondrial ROS and Ca2+ were also monitored. Results: Inhibiting the DRP1 GTPase activity by Mdivi-1 or overexpression of the dominant-negative mutant (DRP1-K38A) induced mild mitochondrial morphological changes in adult cardiomyocytes, and inhibited mitochondrial respiration. Modulation of fission/fusion by overexpressing DRP1 or treating cells with S3, a compound facilitates fusion, exhibited significant morphological changes, but failed to influence respiration. Therefore, endogenous DRP1 activity may regulate respiration in the heart and this effect is dissociated with morphological changes. Further, inhibiting DRP1 activity attenuated the frequency of SOF, indicating decreased transient mPTP openings, delayed laser-induced permanent mPTP opening, and increased mitochondrial Ca2+. Inhibiting DRP1 activity decreased mitochondrial ROS levels. The role of DRP1 inhibition on respiration absents in CypD KO myocytes, suggesting the involvement of mPTP in the modulation of respiration by endogenous DRP1. Conclusion: These results suggest that endogenous DRP1 positively regulates respiration in the heart. This effect is likely independent of its role in mitochondrial fission. DRP1 regulation of respiration may involve transient opening of mPTP and contribute to mitochondrial Ca2+ and ROS signaling.