Pioglitazone Inhibits LOX-1 Expression in Human Coronary Artery Endothelial Cells by Reducing Intracellular Superoxide Radical Generation

Abstract

Objective-LOX-1, a novel lectin-like receptor for oxidized LDL (ox-LDL), is expressed in response to ox-LDL, angiotensin II (Ang II), tumor necrosis factor (TNF)-α, and other stress stimuli. It is highly expressed in atherosclerotic tissues. Peroxisome proliferator-activated receptor (PPAR)-γ ligands, such as pioglitazone, exert antiatherosclerotic effects. This study examined the regulation of LOX-1 expression in human coronary artery endothelial cells (HCAECs) by pioglitazone. Methods and Results-Fourth generation HCAECs were treated with ox-LDL, Ang II, or TNF-α with or without pioglitazone pretreatment. All 3 stimuli upregulated LOX-1 expression (mRNA and protein). Pioglitazone, in a concentration-dependent manner, reduced LOX-1 expression (P<0.01 versus ox-LDL, Ang II, or TNF-α alone). Ox-LDL, Ang II, and TNF-α each enhanced intracellular superoxide radical generation, and pioglitazone pretreatment reduced superoxide generation (P<0.01 versus ox-LDL, Ang II, or TNF-α). Furthermore, all 3 stimuli upregulated the expression of the transcription factors nuclear factor-κB and activator protein-1 (determined by electrophoretic mobility shift assay), and pioglitazone pretreatment reduced this expression (P<0.01 versus ox-LDL, Ang II, or TNF-α). To determine the biological significance of pioglitazone-mediated downregulation of LOX-1, we studied monocyte adhesion to ox-LDL-treated HCAECs. Pioglitazone reduced the adhesion of monocytes to activated HCAECs in a fashion similar to that produced by antisense to LOX-1 mRNA. Conclusions-These observations suggest that the PPAR-γ ligand pioglitazone reduces intracellular superoxide radical generation and subsequently reduces the expression of transcription factors, expression of the LOX-1 gene, and monocyte adhesion to activated endothelium. The salutary effect of PPAR-γ ligands in atherogenesis may involve the inhibition of LOX-1 and the adhesion of monocytes to endothelium.