Hyalocytes synthesize and secrete inhibitors of retinal pigment epithelial cell proliferation in vitro
H. S. Lazarus, C. L. Schoenfeld, S. Fekrat, S. Cohen, A. Carol, G. S. Hageman, S. Hackett, Y. S. Chen, S. A. Vinores and P. A. Campochiaro
Wilmer Ophthalmological Institute, Johns Hopkins Hospital, Baltimore, Md, USA.
BACKGROUND: Retinal pigment epithelial (RPE) cells that enter the vitreous
in pathologic conditions, such as retinal detachment, may proliferate and
contribute to the formation of epiretinal membranes. OBJECTIVE: To study
whether hyalocytes, endogenous vitreous cells, play a role in modulating
the proliferation of RPE cells. METHODS: Cell proliferation was measured by
tritiated thymidine incorporation in density-arrested human RPE cells after
incubation with media that had been conditioned by cultured bovine
hyalocytes. Preliminary characterization of inhibitory activity in
hyalocyte-conditioned medium was performed, including blocking experiments
with a neutralizing antibody to transforming growth factor-beta 2
(TGF-beta) and proliferation assays that used MV-1-Lu mink lung epithelial
cells. Northern blots were done to asses hyalocyte expression of TGF-beta
messenger RNA. RESULTS: Hyalocyte-conditioned medium inhibited tritiated
thymidine incorporation in RPE cells and MV-1-Lu mink lung epithelial cells
in the presence or absence of serum or protease inhibitors. A portion of
the inhibitory activity was neutralized by an antibody directed against
TGF-beta. Northern blots 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 inhibitory activity is attributable to one or more
low-molecular-weight molecules distinct from TGF-beta. CONCLUSIONS:
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.
