HYALOCYTES SYNTHESIZE AND SECRETE INHIBITORS OF RETINAL-PIGMENT EPITHELIAL-CELL PROLIFERATION IN-VITRO

Background: Retinal pigment epithelial (RPE) cells that enter the vitr eous in pathologic conditions, such as retinal detachment, may prolife rate and contribute to the formation of epiretinal membranes. Objectiv e: To study whether hyalocytes, endogenous vitreous cells, play a role in modulating the proliferation of RPE cells. Methods: Cell prolifera tion was measured by tritiated thymidine incorporation in density-arre sted human RPE cells after incubation with media that had been conditi oned by cultured bovine hyalocytes. Preliminary characterization of in hibitory activity in hyalocyte-conditioned medium was performed, inclu ding blocking experiments with a neutralizing antibody to transforming growth factor-beta(2) (TGF-beta) and proliferation assays that used M V-1-Lu mink lung epithelial cells. Northern blots were done to assess hyalocyte expression of TGF-beta messenger RNA. Results: Hyalocyte-con ditioned medium inhibited tritiated thymidine incorporation in RPE cel ls and MV-1-Lu mink lung epithelial cells in the presence or absence o f serum or protease inhibitors. A portion of the inhibitory activity w as neutralized by an antibody directed against TGF-beta. Northern blot s of hyalocyte RNA demonstrated the presence of messenger RNA for TGF- beta(2). These data suggest that TGF-beta is responsible for a portion of the inhibitory activity secreted by hyalocytes. Additional inhibit ory activity is attributable to one or more low-molecular-weight molec ules distinct from TGF-beta. Conclusion: Hyalocyte-conditioned medium inhibits RPE cell proliferation in vitro through TGF-beta and at least one other molecule. Production of these factors by hyalocytes in vivo could provide a deterrent for epiretinal membrane formation that may be perturbed under pathologic conditions.