Retinoid effects in purified cultures of chick embryo retina neurons and photoreceptors.

PURPOSE: To investigate the effects of retinoic acid, retinol, and 11-cis retinaldehyde on proliferation, differentiation, and survival of cultured embryonic chick neural retina cells; to describe the metabolic transformations of these retinoids by the cultured cells.
METHODS: Retinoids were added to glia-free, low-density cultures of neural retina cells, which underwent subsequent examination to determine the numbers of neurons and photoreceptors that differentiated and survived under differing conditions. Cells and conditioned medium were extracted to identify and quantify retinoid metabolic products by high pressure liquid chromatography.
RESULTS: Retinoid treatment resulted in dose-dependent increases in the number of differentiated photoreceptors present in the cultures after 6 days; smaller increases in nonphotoreceptor neurons were also observed. Retinoids were more effective when added at culture onset than at later times, but they did not stimulate cell proliferation. The order of potency was retinol > 11-cis retinaldehyde > retinoic acid. Exogenous retinoic acid was recovered unmodified after a 24-hr incubation period; retinol was also stable and unmetabolized, except for the formation of a small quantity of retinyl acetate. 11-cis retinaldehyde was less stable, and was metabolized into both retinoic acid and retinol.
CONCLUSIONS: Retinol, 11-cis retinaldehyde, and retinoic acid can promote the survival (and possibly differentiation) of cultured embryonic retina neurons and photoreceptors in the absence of glia and retinal pigment epithelium. Although retinoic acid is likely to function by interacting with one of the known nuclear receptors for this retinoid, the effectiveness of retinol in the absence of metabolic transformation into retinoic acid suggests the possible existence of a distinct, yet undiscovered receptor.