Abstract 14193: Dynamin-Related Protein 1 (DRP1)-Mediated Mitochondrial Fission Promotes Smooth Muscle Cell Hyperproliferation in Human and Experimental Pulmonary Hypertension Which Can be Therapeutically Targeted by the Fission Inhibitor MDIVI-1
Introduction: Pulmonary arterial hypertension (PAH) is an obstructive, proliferative vasculopathy. Mortality remains high despite current vasodilator therapies. Mitochondrial fragmentation and normoxic hypoxia-inducible factor-1α (HIF-1α) activation accompany pulmonary artery smooth muscle cell (PASMC) proliferation in PAH. However, the molecular basis for mitochondrial fragmentation, and its relationship to HIF-1α and proliferation are unknown.
Methods and Results: Studies were performed in human control and PAH PASMC and lungs, as well as in a new rat model of PAH. Compared to controls, PAH PASMCs have fragmented mitochondria and increased expression of dynamin-related protein-1 (DRP1), a major mitochondrial fission regulator. In PAH PASMC, DRP1 is activated (evident as increased phosphorylation of serine 616). This reflects increased activation of cyclin B1- cyclin dependent kinase 1 (CDK1) complex, which also regulates mitotic entry. DRP1-Ser616 phosphorylation and cyclin B1 expression are 10- and 4-fold upregulated in PAH vs control lungs, respectively (p<0.05, n=5 each). The DRP1 inhibitor, Mdivi-1, reverses fission and causes a dose dependent reduction in proliferation by arresting cells in G2/M phase. To establish the relationship between HIF-1α and fission we used 2 well-established HIF-1α activators, cobalt and desferrioxamine, to activate HIF-1α in normal PASMC. HIF-1α activators caused DRP1-mediated mitochondrial fission within 2 hours. In vivo, cobalt (8mg/day/kg ip x 4 weeks) leads to PAH in rats (increasing pulmonary vascular resistance, PVR, from 0.14±0.02 to 0.28±0.02 mmHg x min/L, n=8, P<0.01). Mdivi-1 (50mg/kg/week) regressed PAH in this model (improving walking distance and decreasing PVR and medial hypertrophy of PAs). Electron microscopy confirms that Mdivi-1 reverses mitochondrial fission in PASMC in vivo.
Conclusion: HIF-1α induces DRP1-mediated mitochondrial fission and promotes PASMC hyperproliferation and PAH. DRP1 inhibition slows proliferation and regresses experimental PAH. This is the first report to establish a link between mitochondrial fission and the cell cycle in human vascular disease and suggests DRP-1 inhibition as a new antiproliferative therapeutic strategy for PAH.
- © 2011 by American Heart Association, Inc.