191 - Cyclophilin D Inhibition Rescues Cardiac Function in Neonatal Hypoxia

Poster Number: 191
Publication Number: 191.219

Jonathan Burris, University of Rochester, Rochester, NY, United States; Gisela Beutner, University of Rochester School of Medicine and Dentistry, Rochester, NY, United States; MIN YEE, university of Rochester, Pittsford, NY, United States; Michael A. O'Reilly, The University of Rochester, Rochester, NY, United States; George A. Porter, University of Rochester, Rochester, NY, United States

Background: Congenital heart disease (CHD) affects 40,000 newborns yearly and is the leading cause of birth defect related mortality. The heart develops in utero under hypoxic conditions. At birth ambient oxygen levels rise, activating changes in cardiac bioenergetics to allow survival ex-utero. This transition to normoxia does not occur in infants with CHD.  Mitochondria are critical in terminal cardiac myocyte differentiation after birth, and inhibition of the mitochondrial chaperone protein cyclophilin D (CypD) enhances this process by regulating the function of the electron transport chain (ETC) to meet metabolic demands of the beating heart. In CHD and cardiomyopathies, oxidative phosphorylation and cardiac function are impaired due to mitochondrial abnormalities and/or hypoxia. This work seeks to understand the bioenergetic pathways in the normoxic and hypoxic neonatal heart and how intervention on CypD may recover the effects of hypoxia.

Objective: Inhibition of CypD with cyclosporin A (CsA) or N-methyl-4-isoleucine cyclosporin (NIM811) will rescue the effects of hypoxia on cardiac function and on ETC activity.

Design/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 (NoTx) or intraperitoneal injections 10mg/kg of vehicle (VEH), CsA, or NIM811 from P1 to P6. Room air neonates served as controls. On P7, mice underwent echocardiography and hearts were harvested for mitochondrial isolation. Enzymatic activity of ETC complexes, mitochondrial oxygen consumption, and tissue histology were analyzed.

Results: Overall survival decreased in the hypoxic mice. Neonatal hypoxia caused decreased body weight, cardiomegaly, and markedly decreased cardiac function in the NoTx and VEH groups when compared to room air controls (P < 0.0001). The enzymatic function of ETC complexes I and III (P < 0.01) and complex I-mediated respiration (P < 0.0001) was decreased in the untreated hypoxic groups. Histology revealed decreased cellular organization and increased nuclear size of hypoxic myocytes. Treatment of hypoxic neonates with CsA and NIM811 normalized cardiomegaly, cardiac function, ETC activity of complexes I and III and the mitochondrial respiratory capacity for complex I. Histology showed a return to mature cellular structure and decreased nuclear size. Conclusion(s): Pharmacologic inhibition of CypD reversed the effects of hypoxia on ETC activity and overall cardiac function in the neonatal heart. Our study may help develop therapies to treat cardiomyopathies and the effects of hypoxia on the neonatal heart.