PPARγ Inhibition of Cyclooxygenase-2, PGE 2 Synthase, and Inducible Nitric Oxide Synthase in Cardiac Myocytes

Abstract

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear receptor superfamily. They regulate lipid metabolism, glucose homeostasis, cell proliferation, and differentiation and modulate inflammatory responses. We examined whether PPARγ is functional in cultured neonatal ventricular myocytes and studied its role in inflammation. Western blots revealed PPARγ in myocytes. When myocytes were transfected with a PPAR response element reporter plasmid (PPRE-TK-luciferase), the PPARγ activator 15-deoxy-Δ^12,14-prostaglandin J₂ (15dPGJ₂) increased promoter activity, whereas cotransfection of a dominant negative PPARγ inhibited it. To determine the role of 15dPGJ₂ in expression of proinflammatory genes, we tested its effect on interleukin-1β induction of cyclooxygenase-2 (COX-2). 15dPGJ₂ decreased interleukin-1β stimulation of COX-2 by 40% and PGE₂ production by 73%. We next questioned whether 15dPGJ₂ was modulating the expression of inducible prostaglandin E₂ synthase (PGES) and found that it completely blocked interleukin-1β induction of PGES. Use of a second PPARγ agonist, troglitazone, and the selective PPARγ antagonist GW9662 demonstrated that the effects seen were PPARγ-dependent. In addition, we found that 15dPGJ₂ blocked interleukin-1β stimulation of inducible nitric oxide synthase (iNOS). We concluded that 15dPGJ₂ may play an anti-inflammatory role in a PPARγ-dependent manner, decreasing COX-2, PGES, and PGE₂ production, as well as iNOS expression.