Dynamin-Related Protein 1-Mediated Mitochondrial Mitotic Fission Permits Hyperproliferation of Vascular Smooth Muscle Cells and Offers a Novel Therapeutic Target in Pulmonary Hypertension

Rationale: Pulmonary arterial hypertension (PAH) is a lethal syndrome characterized by pulmonary vascular obstruction caused, in part, by pulmonary artery smooth muscle cell (PASMC) hyperproliferation. Mitochondrial fragmentation and normoxic activation of hypoxia-inducible factor-1 alpha (HIF-1 alpha) have been observed in PAH PASMCs; however, their relationship and relevance to the development of PAH are unknown. Dynamin-related protein-1 (DRP1) is a GTPase that, when activated by kinases that phosphorylate serine 616, causes mitochondrial fission. It is, however, unknown whether mitochondrial fission is a prerequisite for proliferation. Objective: We hypothesize that DRP1 activation is responsible for increased mitochondrial fission in PAH PASMCs and that DRP1 inhibition may slow proliferation and have therapeutic potential. Methods and Results: Experiments were conducted using human control and PAH lungs (n = 5) and PASMCs in culture. Parallel experiments were performed in rat lung sections and PASMCs and in rodent PAH models induced by the HIF-1 alpha activator, cobalt, chronic hypoxia, and monocrotaline. HIF-1 alpha activation in human PAH leads to mitochondrial fission by cyclin B1/CDK1-dependent phosphorylation of DRP1 at serine 616. In normal PASMCs, HIF-1 alpha activation by CoCl2 or desferrioxamine causes DRP1-mediated fission. HIF-1 alpha inhibition reduces DRP1 activation, prevents fission, and reduces PASMC proliferation. Both the DRP1 inhibitor Mdivi-1 and siDRP1 prevent mitotic fission and arrest PAH PASMCs at the G2/M interphase. Mdivi-1 is antiproliferative in human PAH PASMCs and in rodent models. Mdivi-1 improves exercise capacity, right ventricular function, and hemodynamics in experimental PAH. Conclusions: DRP-1-mediated mitotic fission is a cell-cycle checkpoint that can be therapeutically targeted in hyperproliferative disorders such as PAH. (Circ Res. 2012;110:1484-1497.)