PPARγ Regulates Mitochondrial Structure and Function and HPASMC Proliferation.

Pulmonary hypertension (PH) is a progressive disorder that causes significant morbidity and mortality despite existing therapies. PH pathogenesis is characterized by metabolic derangements that increase pulmonary artery smooth muscle cell (PASMC) proliferation and vascular remodeling. PH-associated decreases in peroxisome proliferator-activated receptor gamma (PPAR gamma) stimulate PASMC proliferation, and PPAR gamma in coordination with PPAR gamma coactivator 1 alpha (PGC1 alpha) regulates mitochondrial gene expression and biogenesis. To further examine the impact of decreases inPPAR gamma expression on human PASMC (HPASMC) mitochondrial function, we hypothesized that depletion of either PPAR gamma or PGC1 alpha perturbs mitochondrial structure and function to stimulate PASMC proliferation. To test this hypothesis, HPASMCs were exposed to hypoxia and treated pharmacologically with the PPAR gamma antagonist GW9662 or with siRNA against PPAR gamma or PGC1 alpha for 72 hours. HPASMC proliferation (cell counting), target mRNA levels (qRT-PCR), target protein levels (Western blotting), mitochondria-derived H2O2 (confocal immunofluorescence), mitochondrial mass and fragmentation, and mitochondrial bioenergetic profiling were determined. Hypoxia or knockdown of either PPAR gamma or PGC1 alpha increased HPASMC proliferation, enhanced mitochondria-derived H2O2, decreased mitochondrial mass, stimulated mitochondrial fragmentation, and impaired mitochondrial bioenergetics. Taken together, these findings provide novel evidence that loss of PPAR gamma diminishes PGC1 alpha and stimulates derangements in mitochondrial structure and function that cause PASMC proliferation. Overexpression of PGC1 alpha reversed hypoxia-induced HPASMC derangements. This study identifies additional mechanistic underpinnings of PH, and provides support for the notion of activating PPAR gamma as a novel therapeutic strategy in PH.