Role of Dynamin-Related Protein 1 (Drp1)-Mediated Mitochondrial Fission in Oxygen Sensing and Constriction of the Ductus Arteriosus

Rationale: Closure of the ductus arteriosus (DA) is essential for the transition from fetal to neonatal patterns of circulation. Initial PO2-dependent vasoconstriction causes functional DA closure within minutes. Within days a fibrogenic, proliferative mechanism causes anatomic closure. Though modulated by endothelial-derived vasodilators and constrictors, O-2 sensing is intrinsic to ductal smooth muscle cells and oxygen-induced DA constriction persists in the absence of endothelium, endothelin, and cyclooxygenase mediators. O-2 increases mitochondrial-derived H2O2, which constricts ductal smooth muscle cells by raising intracellular calcium and activating rho kinase. However, the mechanism by which oxygen changes mitochondrial function is unknown. Objective: The purpose of this study was to determine whether mitochondrial fission is crucial for O-2-induced DA constriction and closure. Methods and Results: Using DA harvested from 30 term infants during correction of congenital heart disease, as well as DA from term rabbits, we demonstrate that mitochondrial fission is crucial for O-2-induced constriction and closure. O-2 rapidly (<5 minutes) causes mitochondrial fission by a cyclin-dependent kinase-mediated phosphorylation of dynamin-related protein 1 (Drp1) at serine 616. Fission triggers a metabolic shift in the ductal smooth muscle cells that activates pyruvate dehydrogenase and increases mitochondrial H2O2 production. Subsequently, fission increases complex I activity. Mitochondrial-targeted catalase overexpression eliminates PO2-induced increases in mitochondrial-derived H2O2 and cytosolic calcium. The small molecule Drp1 inhibitor, Mdivi-1, and siDRP1 yield concordant results, inhibiting O-2-induced constriction (without altering the response to phenylephrine or KCl) and preventing O-2-induced increases in oxidative metabolism, cytosolic calcium, and ductal smooth muscle cells proliferation. Prolonged Drp1 inhibition reduces DA closure in a tissue culture model. Conclusions: Mitochondrial fission is an obligatory, early step in mammalian O-2 sensing and offers a promising target for modulating DA patency. (Circ Res. 2013;112:802-815.)