9-Cis-retinoic acid exhibits antifibrotic activity via the induction of cyclooxygenase-2 expression and prostaglandin E2 production in scleroderma fibroblasts

Background. The pathogenesis of scleroderma (SSc) is not fully understood, and there is no effective treatment for this chronic disease. Retinoic acid (RA) can modulate connective tissue metabolism, exhibit antifibrotic activity and improve the clinical symptoms of patients with SSc. However, the mechanisms by which RA elicits its antifibrotic actions remain to be determined. Objective. To elucidate the underlying mechanisms by which retinoids exert beneficial effects on SSc. Methods. Cultured skin fibroblasts from patients with SSc were treated with retinoids (9-cis-, 13-cis- and all-trans-retinoic acid) and their effect on the expression of cyclooxygenase (COX)-2, connective tissue growth factor (CTGF) and type I and III collagen and on the production of PGE(2) was examined. COX-2 expression was analysed by western immunoblotting, PGE(2) production by enzyme immunoassay and CTGF expression, and type I and III collagen expression by reverse transcriptase PCR and western immunoblotting. Results. In cultured SSc fibroblasts, 9-cis-RA significantly increased COX-2 protein expression and PGE(2) production and inhibited the expression of CTGF and type I and III collagen. We further found that expression of CTGF and of type I and III collagen mRNA was inhibited by exogenous PGE(2) in SSc fibroblasts. Conclusion. In vitro, 9-cis-RA induced COX-2 expression and PGE(2) production in SSc fibroblasts and PGE(2) downregulated CTGF expression, leading to the inhibition of type I and III collagen synthesis. Our results indicate that the clinical effects of 9-cis-RA on SSc are, at least in part, attributable to the induction of PGE(2) and the subsequent suppression of CTGF expression that results in the blockade of collagenogenesis.