Abstract 18191: Mitochondrial Regulation of the Hyperproliferative Vascular Smooth Muscle Cell Phenotype

Abstract

Background: During arterial restenosis and atherosclerosis, vascular smooth muscle cells (VSMCs) develop a highly proliferative and synthetic phenotype. Because such phenotypic changes are likely integrated with the energetic state of the cell, we hypothesized that changes in mitochondrial function regulate VSMC plasticity. Methods and Results: Exposure of VSMCs to platelet-derived growth factor (PDGF) promoted loss of the contractile proteins α-smooth muscle actin and calponin and was accompanied by remarkable changes in mitochondrial morphology. Confocal analysis showed that 97% of mitochondria in contractile VSMCs were filamentous; however, synthetic VSMCs showed a mitochondrial pool with >70% fragmented mitochondria (p<0.05). Mitochondrial membrane potential decreased by 86±1% with the attainment of the synthetic phenotype (p<0.01; n=3), but was not associated with mitophagy or decreases in the abundance of key proteins involved in oxidative phosphorylation. Compared with contractile VSMCs, synthetic VSMCs showed a 51±1.9% decrease in the abundance of mitofusin 2 (Mfn2; p<0.001; n=3) with no significant changes in Drp1, Fis1, or Opa1. Analysis of mitochondrial function in intact VSMCs showed a 20±3.7% decrease in glucose oxidation in synthetic cells, which was accompanied by a 17±2.6% increase in fatty acid oxidation (p<0.02; n=3). In permeabilized cells, complex II-mediated respiration was decreased by 20±2% in synthetic VSMCs (p<0.05; n=4). An inhibitor of mitochondrial fragmentation, mdivi1, decreased mitochondrial fragmentation by 50±6% (p<0.001; n=3), abolished the hyperproliferative response to PDGF (p<0.03; n=4), and reversed changes in mitochondrial respiration, yet it did not prevent PDGF-induced losses of contractile proteins. Conclusions: These results indicate that changes in mitochondrial morphology and bioenergetics contribute to the hyperproliferation of synthetic VSMCs, but do not affect the degradation of the contractile proteins. We propose that mitochondrial fragmentation that occurs during transition to the synthetic phenotype regulates mitochondrial substrate selection and bioenergetics and is a therapeutic target for vascular disorders characterized by VSMC hyperproliferation.