Professor Golisano Children's Hospital at The University of Rochester Medical Center Rochester, New York, United States
Background: During birth, demands on the heart increase when exposed to high oxidative stress. Cardiac myocyte differentiation is dependent on changes in mitochondrial function that regulate cell stress pathways to enhance differentiation. We have shown these changes are dependent on closure of the mitochondrial permeability transition pore (mPTP) controlled by the protein cyclophilin D (CypD). Objective: These studies aim to determine the effects of independently manipulating CypD, mitochondrial membrane potential, and reactive oxygen species (ROS) production on mitochondrial function, myocyte differentiation, and cardiac function in the neonate. Design/Methods: Neonatal C57Bl6 mice were intraperitoneally injected on postnatal day 1-6 of with mitoparaquat (0.025-0.05 mg/kg), Tempol (0.7 mg/kg), mitoTempo (0.7 mg/kg), 2,4-dinitrophenol (2 mg/kg), or vehicle. Hearts were harvested at P7 and mitochondrial respiration, enzymatic activity of the electron transport chain (ETC) complex (Cx) I and 2, protein oxidation and assembly of mitochondrial supercomplexes were measured by native gel electrophoresis. Heart and body weight were also measured. Results: Treatment with mitoparaquat to increase mitochondrial ROS caused a dose-dependent decrease of Cx I activity measured by oxygen consumption and enzyme assays. This corresponded to decrease in assembly of Cx-I containing supercomplexes. Decreasing mitochondrial ROS using mitoTempo had no effect on Cx I activity but increased assembly of Cx-III containing supercomplexes. Decreasing ROS in the cell with Tempol decreased Cx-I activity but had no effect on supercomplex assembly. Uncoupling at the mitochondrial membrane using 2,4-dinitrophenol increased electron flux from Cx I to Cx III but may decrease supercomplex assembly. Treatment of isolated mitochondria with cyclosporin A to inhibit CypD had no effects on these measures. There is a larger heart weight to body weight ratio in mitoparaquat treated mice compared with controls.
Conclusion(s): Changes in ROS and mitochondrial membrane potential have selective effects on ETC assembly, activity in the neonatal period, and are not inhibited by closure of the mPTP. This data suggests a pathway where CypD regulates the mPTP to regulate the ETC, membrane potential, and ROS production to regulate myocyte differentiation; such a pathway could be targeted to increase cardiac maturation in infants with poor cardiac function.
