FGF19 exhibits neuroprotective effects on adult mammalian photoreceptors in vitro.

PURPOSE Several fibroblast growth factors (FGFs) exhibit neuroprotective influences against retinal photoreceptor degeneration. The expression of FGF receptor (FGFR) 4 on photoreceptors suggests a specific ligand, FGF-19, might also be beneficial. The authors hence examined the potential role of FGF-19 in this regard. METHODS Adult human retinal sections were processed for anti-FGFR-4 immunohistochemistry. Total RNA and proteins were extracted from parallel cultures of human Y79 retinoblastoma and primary adult pig photoreceptors; RNA samples were used for RT-PCR analysis of FGF-19, and proteins were subjected to immunoprecipitation for FGFR-1 and FGFR-4 or to Western blotting of FGF-19. Cultures were incubated with increasing concentrations of FGF-19 before extraction and Western blotting for phosphotyrosine. Photoreceptor cultures were screened for cell survival and processed for immunocytochemistry using anti-neural retina leucine zipper (Nrl) antibody. RESULTS FGF-19 mRNA was detected in adult pig retinal pigment epithelial cells, and FGF-19 protein was found in cell extracts and conditioned medium prepared from retinal pigment epithelium. The addition of FGF-19 to Y79 retinoblastoma or primary adult pig photoreceptor cultures led to time- and dose-dependent changes in proliferation (for Y79) or survival (for primary photoreceptors). FGF-19 induced the phosphorylation of an FGFR-4-immunoreactive band of approximately 80 kDa and led to the heterodimerization of FGFR-1 and FGFR-4. Y79 and primary photoreceptor cells maintained in serum-supplemented media exhibited Nrl immunoreactivity by Western blotting, which decreased after serum deprivation. The addition of FGF-19 led to the reexpression of Nrl immunoreactivity in both culture models. CONCLUSIONS These data indicate a physiological role for FGF-19 in adult photoreceptor phenotypic maintenance and survival and argue in favor of its use as a neuroprotectant.