RETINAL PIGMENT EPITHELIAL CELLS AND DOCOSAHEXAENOIC ACID DIRECT SURVIVAL AND SPATIAL REORGANIZATION OF PHOTORECEPTORS IN VITRO

GERMAN L; BUZZI E.; ROTSTEIN N.; RODRÍGUEZ BOULAN E; POLITI L.

Buenos Aires, Argentina

Congreso; XVII International congress of eye research. (ICER).; 2006

RETINAL PIGMENT EPITHELIAL CELLS AND DOCOSAHEXAENOIC ACID DIRECT SURVIVAL AND SPATIAL REORGANIZATION OF PHOTORECEPTORS IN VITRO  *German L., * Buzzi E., * Rotstein N., # Rodríguez Boulan E. and *Politi L.*Instituto de Investigaciones Bioquímicas, 8000 Bahía Blanca, Argentina and  #M. Dyson Vision Research Inst. & Dept. of Cell Biol. and Anatomy, Weill Medical College of Cornell Univ., New York, NY 10021, USA.   Retinal pigment epithelial (RPE) cells contribute to maintain the structural and functional properties of photoreceptor cells; however, the precise role of RPE cells during photoreceptor development and the relationship between these cells and photoreceptor survival factors, such as docosahexaenoic acid (DHA) remains unsolved. Interactions between RPE cells and photoreceptors were investigated using cocultures of rat retinal neurons and the retinal pigment epithelial cell line ARPE-19. RPE cells partially prevented photoreceptor apoptosis in neuron-ARPE-19 cocultures lacking photoreceptor trophic factors; addition of DHA showed no additive protective effect. RPE cells and DHA enhanced photoreceptor differentiation, promoting the development of apical processes and opsin localization in these processes. DHA increased opsin expression in cocultures, while RPE cells did not. When retinal neurons were seeded over RPE monolayers, photoreceptors attached to the apical surface of the epithelial cells, mimicking the spatial organization found in the retina in vivo. On the other hand, when RPE cells were seeded over neurons, a spatial arrangement opposite to that found in vivo, a remarkable spatial reorganization took place: nearly all RPE cells switched their positions, and 6 hs later, no neurons remained beneath RPE cells. This reorganization appeared to be specific for RPE and neuronal cells, since it was not observed in cocultures of neurons with the muscle cell line, BC3H1. Addition of a metalloproteinase inhibitor (TIMP-1) blocked the ability of epithelial cells to detach neurons from their substrate, without affecting the outgrowth of lamellipodia, suggesting that metalloproteinases were involved in the reorganization process. RPE cells also regulated neurite orientation: when neurons were nearer than 50 µm from the epithelium, most developing axons grew parallel to, or away from the RPE cells, again resembling the organization found in the in vivo retina. These results show that RPE cells and DHA stimulated survival and differentiation of photoreceptors and suggest that RPE cells might play a key role in building the spatial organization of photoreceptor cells in the developing retina.