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A2094 - Mitochondrial Uncoupling Protein 2 (UCP2) Levels Are Modulated by Peroxisome Proliferator-Activated Receptor Gamma (PPARg) in Pulmonary Artery Smooth Muscle Cells
Author Block: E. Oommen1, B. Kang2, J. Kleinhenz1, R. L. Sutliff3, S. M. Yeligar4, C. Hart5; 1Pulmonary and Critical Care, Emory University, Atlanta, GA, United States, 2Medicine, Emory University-Atlanta VAMC, Decatur, GA, United States, 3Medicine, Emory University-Atlanta VA Medical Center, Decatur, GA, United States, 4Medicine, Emory University / Atlanta VA Medical Center, Decatur, GA, United States, 5Atlanta VA Med Ctr/Emory Univ, Decatur, GA, United States.
Rationale: Mitochondrial uncoupling protein 2 (UCP2), which is expressed in pulmonary vascular wall cells, participates in regulation of cell metabolism. UCP2 loss-of-function causes spontaneous pulmonary hypertension (PH) in mice. Previous studies demonstrated that decreases in pulmonary vascular peroxisome proliferator-activated receptor gamma (PPARg) were sufficient to promote pulmonary artery smooth muscle cell (PASMC) proliferation, vascular remodeling, and PH. Current evidence suggests that PPARg activation stimulates UCP2 expression in selected tissues. Therefore, we hypothesize that interactions between PPARg and UCP2 alter PASMC energy metabolism and affect proliferation in PH.
Methods: Human PASMC were exposed to normoxia (21% O2) or hypoxia (1% O2) for 72 hours, conditions that we previously reported were sufficient to decrease PASMC levels of PPARg and stimulate PASMC proliferation. To examine the impact of PPARg on PASMC UCP2, PASMC were transiently transfected with siPPARg, control siRNA, adenovirus expressing PPARg protein (AdPPARg), or control green fluorescent protein (AdGFP). We also examined lung tissue from littermate control and transgenic mice with inducible overexpression of constitutively activated smooth muscle PPARg (smPPARgOE). mRNA levels of PPARg and UCP2 were measured in human PASMC or mouse lung homogenates using qRT-PCR. To determine the effect of UCP2 on energy metabolism, we performed cell energy phenotype tests on PASMC transfected with siUCP2 using an extracellular flux bioanalyzer.
Results: Treatment with hypoxic conditions that reduced PASMC PPARg and stimulated proliferation caused a 25% decrease in PASMC UCP2 levels. Similarly, siPPARg (which reduced PASMC PPARg levels by 60% and increased PASMC proliferation by 60%) caused a 40% decrease in UCP2 levels. Overexpressing PPARg in PASMCs in vitro (13-fold increase in PPARg protein) and in mouse lung in vivo (2.8-fold increase in PPARg protein) increased expression of UCP2. Cell energy phenotyping studies demonstrated that siUCP2 stimulated increases in PASMC mitochondrial respiration and glycolysis.
Conclusions: Previous studies have established that decreases in PPARg are sufficient to promote PH in vivo and PASMC proliferation in vitro. However, the mechanisms by which reductions in PPARg stimulate PASMC proliferation are complex and continue to be defined. The current preliminary data suggest novel links between PPARg and the mitochondrial protein, UCP2, providing further insights into PH-associated PASMC metabolic dysregulation.