TRANSFORMING GROWTH-FACTOR-BETA REGULATES HUMAN RETINAL-PIGMENT EPITHELIAL-CELL PHAGOCYTOSIS BY INFLUENCING A PROTEIN KINASE-C-DEPENDENT PATHWAY

Background: Transforming growth factor-beta (TGF-beta) plays an import ant role in the pathogenesis of many ocular diseases, including prolif erative vitreoretinopathy. We examined the effect of TGF-beta on the p hagocytosis of rod outer segments by retinal pigment epithelium (RPE), which is a major function of RPE, and investigated the dependence of this effect on the protein kinase C (PKC) pathway. Methods: Phagocytot ic uptake of fluoresceinated bovine rod outer segments was determined by flow cytometry. RPE cells were treated with TGF-beta1 or TGF-beta2 and their effects on phagocytosis were examined. The effects of variou s PKC inhibitors (calphostin C, staurosporine, and extended exposure t o phorbol 12-myristate 13-acetate, PMA) and a stimulator (brief exposu re to PMA) on RPE phagocytosis was evaluated. Results: Both TGF-beta1 and TGF-beta2 up-regulated RPE phagocytosis and PMA abolished the up-r egulating effect of TGF-beta. In contrast, PKC inhibition by staurospo rine and calphostin C resulted in increased phagocytosis. A combinatio n of TGF-beta and PKC inhibitor treatment did not produced any additiv e effect on phagocytosis. Conclusion: We concluded that TGF-beta up-re gulates human RPE phagocytosis, but that this effect is counteracted b y PKC activation. It is possible that this TGF-beta-induced effect is due, in part, to a negative modulation of the PKC-dependent pathway.