141 - Redox Balance Effects Neonatal Heart Mitochondrial Function

Publication Number: 141.6495

Hope Kile, Golisano Children's Hospital at The University of Rochester Medical Center, Rochester, NY, United States; Gisela Beutner, University of Rochester, Golisano Children’s Hospital, Rochester, NY, United States; George A. Porter, Golisano Children's Hospital at The University of Rochester Medical Center, Rochester, NY, United States

Background: During birth, demands on the heart increase when exposed to oxygen, and ultimately set into motion final cardiac myocyte differentiation. We have shown that cardiac myocyte differentiation is dependent on mitochondrial function, which is dependent on closure of the mitochondrial permeability transition pore.

Objective: These studies aim to determine the effects of manipulating the cellular and mitochondrial redox environment on mitochondrial and cardiac function in the neonate.

Design/Methods: Neonatal C57Bl6 mice were intraperitoneally injected on postnatal (P) day 1-6 of with mitoparaquat (0.025-0.05 mg/kg), paraquat (2.5 mg/kg), Tempol (0.7 mg/kg), mitoTempo (0.7 mg/kg), 2,4-dinitrophenol (2 mg/kg), or equivalent volume of vehicle. Hearts were harvested at P7 after performing an echocardiogram to assess heart function and mitochondrial respiration. Enzymatic activity of the electron transport chain (ETC) complexes (Cx) I , II and III was measured. Mitochondrial supercomplexes were visualized by in-gel assays after native gel electrophoresis. Oxidative stress was accessed by Oxyblot and measuring reactive oxygen species (ROS) with Amplex Red.

Results: Injecting ROS modifying drugs mitoparaquat and dinitrophenol increased the ratio of heart to body weight. Mitoparaquat caused an increase of ROS at baseline, and a dose-dependent decrease of mitochondrial function due to a decrease of Cx I. This corresponded to a decrease of Cx-I containing supercomplexes. Injecting Tempol decreased Cx I activity and mitochondrial oxygen consumption but had no effect on mitochondrial supercomplexes. MitoTempo had no effect on Cx I activity and stabilized Cx I and III containing supercomplexes. Dinitrophenol uncoupled the mitochondrial membrane potential but had no direct effect on the enzymatic activity of Cx I or supercomplex detection. All treatments decreased ejection fraction and shortening fraction of the heart compared with vehicle.

Conclusion(s): Changes in ROS and mitochondrial membrane potential have selective effects on ETC assembly and activity in the neonatal period. Our data suggest that modifying ROS generation to regulate mitochondrial and cardiomyocyte functionality could be targeted to develop treatment options to delay cardiac maturation in order to increase a time window for surgical intervention in infants with congenital heart disease.