Abstract P446: Cyclophilin D Inhibition Rescues Cardiac Function And Electron Transport Chain Assembly And Activity In Hypoxia Exposed Neonatal Mice

Introduction: Mitochondria play a critical role in cardiac myocyte physiology and differentiation. Hypoxia decreases cardiac function. Changes in embryonic heart metabolism at the level of the electron transport chain (ETC) are regulated by a chaperone protein known as cyclophilin D (CypD). Inhibition of CypD with chemicals such as cyclosporin A (CsA) and N-methyl-4-isoleucine cyclosporin (NIM811) leads to more complex mitochondrial structure and effective oxidative phosphorylation. Hypothesis: Inhibition of CypD with CsA or NIM811 will rescue the detrimental effects of hypoxia on cardiac function and on ETC assembly and activity. Methods: Mice were exposed to continuous hypoxia (12% oxygen) immediately before birth (gestational age E19.5) to postnatal day 7 (P7). Hypoxic mice received no treatment (No Tx) or intraperitoneal injections 10mg/kg of vehicle (VEH), CsA, or NIM811 from P1 to P6. Litters of mice born into room air served as controls. On P7, mice were anesthetized and underwent echocardiography and/or hearts were harvested for mitochondrial isolation. Enzymatic activity of ETC complexes was quantified using spectrophotometry and normalized to total protein. To measure physical assembly of complex I & V of the ETC, high resolution clear native polyacrylamide gel electrophoresis (HCRN PAGE) followed by in-gel assays were utilized using appropriate protein loading controls. Results: Cardiac ejection fraction was decreased in hypoxic No Tx (P<0.0001) and VEH (P<0.0001), but was rescued by CsA or NIM811 when compared to room air controls (P>0.05). Heart weight to body weight ratio was increased in No Tx and VEH groups (P< 0.0001) and rescued in the CsA and NIM811 groups when compared to room air controls (P>0.05). Complex I enzymatic activity was rescued with treatment with CsA and NIM811. HCRN PAGE followed by in-gel ETC complex assay demonstrated assembly of complexes I and V into dimers and tetramer in the room air, CsA, and NIM811 groups that was not seen in the No Tx and VEH groups. Conclusion: Pharmacologic inhibition of CypD reversed the effects of hypoxia on cardiac function and ETC activity and assembly in the neonatal heart. Our studies may help develop therapies to treat neonatal cardiomyopathies and the effects of hypoxia on the neonatal heart.