FGF2-STIMULATED RELEASE OF ENDOGENOUS FGF1 IS ASSOCIATED WITH REDUCEDAPOPTOSIS IN RETINAL PIGMENTED EPITHELIAL-CELLS

Both inhibition of endogenous fibroblast growth factor (FGF) synthesis on nondividing lens epithelial cells and inhibition of secreted FGF1 in confluent quiescent retinal pigmented epithelial (RPE) cells induce rapid cell apoptosis (Renaud et al., 1996, J. Biol. Chem., 271, 2801- 2811). In addition several studies demonstrate that exogenous FGF2 can promote retinal cell survival in vitro and in vivo. To determine the possible relationship between exogenous FGF2, endogenous FGF1, and cel l survival, we examined the protective effect of a single dose of exog enous FGF2 on long-term culture of quiescent RPE cells after serum wit hdrawal. After 4 days of culture, a dramatic and sustained upregulatio n of FGF1 protein expression occurs specifically in response to exogen ous FGF2. After addition of FGF2 (20 ng/ml), RPE cells express fourfol d more FGF1 after Day 7 than after Day 1 of culture. This phenomenon i s FGF2 dose-dependent. In contrast, neither serum nor FGF2 have an eff ect on total endogenous FGF2 expression. In addition, in response to e xogenous FGF, FGF1 is secreted in significant amounts into the extrace llular medium at a rate comparable to FGF1 accumulation within the cel l. Furthermore, in the absence of serum, significant increase in cell death occurs on Day 6 of culture, whereas addition of exogenous FGF2 i nduces a twofold decrease of RPE cell apoptosis. In the presence of ex ogenous FGF2, addition of a specific anti-FGF1 neutralizing antibody i nduces a rapid apoptosis of RPE cell cultures. Thus, we speculate that exogenous FGF2 may indirectly prolong cell survival by increasing syn thesis and secretion of endogenous FGF1 and that endogenous FGF1, dire ctly in response to exogenous FGF2, may function as an autocrine troph ic factor in RPE cells. (C) 1997 Academic Press.