Retinoic Acid Induces Corneal Epithelial CYP4B1 Gene Expression and Stimulates the Synthesis of Inflammatory 12-Hydroxyeicosanoids

Abstract

Abstract: : Purpose: Injury to the ocular surface provokes an inflammatory response that is mediated, at least in part, by corneal epithelial derived 12-hydroxyeicosanoids (HETE) including 12-HETE and 12-HETrE; both metabolites exhibit potent inflammatory and angiogenic properties and are formed by a cytochrome P450 enzyme, namely CYP4B1. Retinoids are known to mediate wound healing processes in many tissues and as such are integral components of the inflammatory response. We studied the effect of various retinoids on corneal synthesis of 12-hydroxyeicosanoids and on activation of CYP4B1 gene expression. Methods: Corneal organ cultures were used to assess the effect of retinoic acid on epithelial metabolism of arachidonic acid to 12-hydroxyeicosanoids. Lucifrease reporter vectors containing different lengths of the CYP4B1 3.4 kb-5'-untranslated region were used to examine the effect of retinoids (vitamin D, 9-cis-retinoic acid and all trans retinoic acid) on transcriptional activation of CYP4B1 in transient transfection experiments with HepG2 cells. Results: Vitamin D had no effect on CYP4B1 promoter activity, whereas, 9-cis and all trans retinoic acids increased promoter activity by up to 70% over control. Addition of both 9-cis and all trans retinoic acids resulted in an additive effect increasing promoter activity by 2-fold. The increased promoter activity correlated with the presence of RXR/RAR binding motifs RXR/RAR. Incubation of corneal organ culture for 24 h in the presence of 9-cis and all trans retinoic acids increased the synthesis of 12-HETE and 12-HETrE by 2 fold. Conclusions:The finding that retinoic acid increases the expression of the CYP4B1 gene and enhances production of the inflammatory 12-hydroxyeicosanoids in the corneal epithelium may provide a linkage between wound healing and inflammation in the ocular surface.

Keywords: eicosanoids • retinoids/retinoid binding proteins • inflammation