Ceramide inhibits connective tissue growth factor expression by human retinal pigment epithelial cells

Connective tissue growth factor (CTGF) is known to be involved in retinal fibrotic disorders. We used human retinal pigment epithelial cells (HRPE), which play critical roles in retinal fibrosis, to examine the expression of CTGF and its regulation by ceramide and TGF-β. Real-time PCR analysis showed downregulation of CTGF mRNA by C2 ceramide and upregulation by TGF-β. C2 ceramide also inhibited constitutive and TGF-β-enhanced CTGF secretion by HRPE cells. Predominant secretion (>80% of total) of CTGF from the apical side was observed in highly polarized HRPE cells. Fumonosin, an inhibitor of ceramide synthesis, stimulated CTGF secretion while 4HPR, an activator of ceramide synthesis, downregulated CTGF secretion. Based on these results demonstrating ceramide regulation of CTGF secretion by HRPE, we suggest that ceramide may have therapeutic potential for the treatment of retinal fibrotic diseases by inhibiting CTGF production.