Permeability Transition Pore Closure Increases Mitochondrial Maturation and Myocyte Differentiation in the Neonatal Heart

Abstract

Background: Recent studies in embryonic mice demonstrate that mitochondrial maturation and cardiac myocyte differentiation are linked. Closure of the mitochondrial permeability transition pore (mPTP), by pharmacologically or genetically manipulating Cyclophilin D (CyPD), drives this process of differentiation. Myocytes in the neonatal heart are relatively immature, but the effects of mPTP closure have not been determined at this developmental stage.Objective: We hypothesized that closure of the mPTP in the neonatal mouse heart will increase cardiac function by increasing mitochondrial maturation and enhancing cardiac myocyte differentiation.Methods: In vitro: Cardiac myocytes cultured from the ventricles of 1-day old wild type (WT) or CyPD null mice were treated with Vehicle (Veh), 500nM Cyclosporin A (CsA), or 500nM NIM811 for 5 days. Assays to determine mitochondrial maturation, both structure and function, and cardiac myocyte differentiation were performed. In vivo: One day old WT or CyPD null mice were treated with daily intraperitoneal injections of Veh, or 10mg/kg of CsA or NIM811 for 5 days. Hearts were processed then analyzed for changes in ventricular wall thickness.Results: In vitro: WT neonatal cardiac myocytes treated with either CsA or NIM811 had more complex mitochondrial structure (P < 0.05), higher mitochondrial membrane potential (NIM811, P <0.01), and more differentiated cardiac myocytes relative to Veh (p<0.05). Deleting CyPD to close the mPTP also increased mitochondrial maturation and myocyte differentiation. In vivo: WT mice hearts treated with NIM811 had thicker left ventricular walls relative to Veh (P < 0.01).Conclusion: Closure of the mPTP using pharmacologic or genetic approaches increased mitochondrial maturation and cardiac myocyte differentiation in cultured neonatal myocytes. Early in vivo experiments demonstrate that mPTP closure in the neonatal heart increased LV wall, suggesting altered myocyte proliferation or differentiation.