Peroxisome Proliferator-Activated Receptor γ Ligands Increase Release of Nitric Oxide From Endothelial Cells

Abstract

Objective-Peroxisome proliferator-activated receptor ␥ (PPAR␥) ligands reduce lesion formation in animal models of atherosclerosis by mechanisms that have not been defined completely. We hypothesized that PPAR␥ ligands stimulate endothelial-derived nitric oxide release (·NO) to protect the vascular wall. Methods and Results-The PPAR␥ ligands, 15-deoxy-⌬ 12,14 -prostaglandin J 2 (15d-PGJ 2 ) or ciglitazone, stimulated a PPAR response element-luciferase reporter construct in transfected porcine pulmonary artery endothelial cells (PAECs), demonstrating that PPAR␥ was transcriptionally functional. Treatment with 15d-PGJ 2 or ciglitazone significantly increased release of ·NO from PAECs or human aortic endothelial cells and augmented calcium ionophore-induced ·NO release from human umbilical vein endothelial cells measured by chemiluminescence analysis of culture media. Increases in ·NO release caused by treatment with 15d-PGJ 2 occurred at 24 hours, but not after 1 to 16 hours, and were abrogated by treatment with the transcriptional inhibitor ␣-amanitin. Overexpression of PPAR␥ or treatment with 9-cis retinoic acid also enhanced PAEC ·NO release. Neither 15d-PGJ 2 nor ciglitazone altered eNOS mRNA, whereas 15d-PGJ 2 , but not ciglitazone, decreased eNOS protein. Key Words: peroxisome proliferator-activated receptor ␥ Ⅲ endothelium Ⅲ nitric oxide Ⅲ nitric oxide synthase Ⅲ thiazolidinedione T he production of nitric oxide (·NO) by vascular endothelial cells is critical for maintenance of normal vascular physiology. 1 In endothelial cells (ECs), the type III endothelial nitric oxide synthase (eNOS) produces ·NO from the amino acid L-arginine. Our preliminary observations, 2 as well as reports by others, [3][4][5] indicate that exogenous fatty acids alter EC ·NO production. The molecular mechanism contributing to fatty acid-induced alterations in EC ·NO production remain unexplored. One potential mechanism for fatty acidinduced alterations in gene expression is the activation of peroxisome proliferator-activated receptors (PPARs). Originally described in 1990, PPARs belong to the nuclear hormone receptor superfamily of ligand-activated transcription factors including steroid, thyroid, and retinoid hormone receptors. 6 Structurally diverse ligands including long-chain fatty acids, eicosanoids, thiazolidinediones, and fibrates activate PPARs, which form obligate heterodimers with the 9-cis retinoic acid receptor, RXR. 7 On ligand binding, PPARs become transcriptionally active at PPAR response elements (PPRE) and alter the expression of target genes. Conclusions-TakenPPAR␥ is expressed in vascular endothelial cells 8 -11 and smooth muscle cells. 12 The expression of PPARs in vascular wall cells suggests their potential role in vascular disease. 8 -10 Some in vitro studies suggest potential atherogenic effects of PPAR␥ activation, 8,[13][14][15] whereas other studies associate PPAR␥ with potential vascular protective effects. 16 -21 Importantly, two independent in vivo studies using the LDL receptor knockout mouse demo...

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