Peroxisome Proliferator-activated Receptor γ Ligands Regulate Myeloperoxidase Expression in Macrophages by an Estrogen-dependent Mechanism Involving the -463GA Promoter Polymorphism

Abstract

A functional myeloperoxidase (MPO) promoter polymorphism, -463GA, has been associated with incidence or severity of inflammatory diseases, including atherosclerosis and Alzheimer's disease, and some cancers. The polymorphism is within an Alu element encoding four hexamer repeats recognized by nuclear receptors (AluRRE). Here we show that peroxisome proliferator-activated receptor γ (PPARγ) agonists strongly regulate MPO gene expression through the AluRRE. Opposite effects were observed in granulocyte/macrophage colony-stimulating factor (GMCSF)-versus macrophage colony-stimulating factor (MCSF)-derived macrophages (Mφ): Expression was markedly up-regulated (mean 26-fold) in MCSF-Mφ and down-regulated (34-fold) in GMCSF-Mφ. This was observed with rosiglitazone and three other PPARγ ligands of the thiazolidinedione class, as well as the natural prostaglandin metabolite 15-deoxy-Δ12,14 prostaglandin J2. The selective PPARγ antagonist, GW9662, blocked both the positive and negative effects on MPO expression. Gel retardation assays showed PPARγ bound hexamers 3/4, and estrogen receptor-α bound hexamers 1/2, with -463A in hexamer 1 enhancing binding. Estrogen blocked PPARγ effects on MPO expression, especially for the A allele. Charcoal filtration of fetal calf serum eliminated the block of PPARγ, whereas replenishing the medium with 17β-estradiol reinstated the block. These findings suggest a model in which estrogen receptor binds the AluRRE, preventing PPARγ binding to the adjacent site. The positive and negative regulation by PPARγ ligands, and the block by estrogen, was also observed in transgenic mice expressing the G and A alleles. The mouse MPO gene, which lacks the primate-specific AluRRE, was unresponsive to PPARγ ligands, suggesting the human MPO transgenes will enhance the utility of mouse models for diseases involving MPO, such as atherosclerosis and Alzheimer's.