Abstract 251: Regulator of G Protein Signaling 5 is a Novel Peroxisome Proliferator-Activated Receptor (PPAR)-gamma and PPAR-delta Target Gene and Regulator of Resistance Vessel Tone

Abstract

PPARγ is a ligand-activated transcription factor expressed in the vasculature. Targeted expression of dominant negative (DN) PPARγ to vascular muscle of transgenic mice (S-P467L) caused hypertension and aortic dysfunction. Recently, we demonstrated a robust increase in myogenic tone in S-P467L resistance artery and a reduced large conductance Ca 2+ -activated K + (BKCa) current in S-P467L smooth muscle cells (SMC). Inhibition of protein kinase C (PKC) corrected enhanced myogenic constriction and impaired BKCa channel function. Here, we tested the hypothesis that altered expression of PPARγ target genes in S-P467L resistance artery contributes to increased vessel tone. Gene expression profiling in mesenteric artery revealed a marked loss of the regulator of G protein signaling 5 (RGS5) in S-P467L compared to non-transgenic (NT) (fold change compared to NT; 0.18±0.03, p<0.05). Knock down of RGS5 by siRNA in SMC cultures enhanced PKC activity. Consistent with the function of RGS5 as a negative regulator of angiotensin (Ang) II signaling, S-P467L mesenteric artery exhibited an increased Ang II-induced constriction (at 3 nM: 31.4±4% in S-P467L vs 12.9±2% in NT, p<0.05). Pre-incubation of the artery for 30 minutes with the AT1 receptor (AT1R) antagonist losartan completely abolished Ang II-induced vasoconstriction. Neither AT1aR nor AT1bR mRNA expression was different between the groups, implicating a post-receptor mechanism in response to Ang II. Using a sequence-based model, we identified potential PPAR response elements (PPREs) close to the RGS5 promoter. Electrophoretic mobility shift assays showed that both PPARγ and PPARδ can bind at one of the identified PPREs, suggesting that RGS5 might be a direct target of both PPARs. Whereas a significant induction of RGS5 expression was observed in normal mesenteric artery following PPARγ (3.3±0.4 fold) or PPARδ (3.5±0.3 fold) agonist treatment, these inductions were completely lost in S-P467L. We conclude that PPARγ is required for normal resistance vessel tone and have identified RGS5 as a functionally important PPAR target gene.