The peroxisome proliferator-activated receptor-γ is a negative regulator of macrophage activation

Abstract

The peroxisome proliferator-activated receptor-γ (PPAR-γ) is a member of the nuclear receptor superfamily of ligand-dependent transcription factors that is predominantly expressed in adipose tissue, adrenal gland and spleen. PPAR-γ has been demonstrated to regulate adipocyte differentiation and glucose homeostasis in response to several structurally distinct compounds, including thiazolidinediones and fibrates. Naturally occurring compounds such as fatty acids and the prostaglandin D2 metabolite 15-deoxy-Δ prostaglandin J2 (15d-PGJ2) bind to PPAR-γ and stimulate transcription of target genes. Prostaglandin D2 metabolites have not yet been identified in adipose tissue, but are major products of arachidonic-acid metabolism in macrophages, raising the possibility that they might serve as endogenous PPAR-γ ligands in this cell type. Here we show that PPAR-γ is markedly upregulated in activated macrophages and inhibits the expression of the inducible nitric oxide synthase, gelatinase B and scavenger receptor A genes in response to 15d- PGJ2 and synthetic PPAR-γ ligands. PPAR-γ inhibits gene expression in part by antagonizing the activities of the transcription factors AP-1, STAT and NF-κB. These observations suggest that PPAR-γ and locally produced prostaglandin D2 metabolites are involved in the regulation of inflammatory responses, and raise the possibility that synthetic PPAR-γ ligands may be of therapeutic value in human diseases such as atherosclerosis and rheumatoid arthritis in which activated macrophages exert pathogenic effects.