Light regulates glucocorticoid receptors in mouse retinal photoreceptors

MARQUIONI RAMELLA, MD; SUBURO, AM

Córdoba

Congreso; 16th International Congress of Photobiology; 2014

International Union of Photobiology

LIGHT REGULATES GLUCOCORTICOID RECEPTORS IN MOUSE RETINAL PHOTORECEPTORS Melisa D. Marquioni-Ramella, Angela M. Suburo. Facultad de Ciencias Biomédicas. Universidad Austral. Pilar B1629AHJ, Buenos Aires, Argentina (amsuburo@cas.austral.edu.ar) Glucocorticoids are well-known retinal protectors that prevent or reduce light-induced photoreceptor damage. Most glucocorticoid effects are mediated by the nuclear receptors GRA and GRB. GRA is blocked by mifepristone (RU-486), which is the only known ligand of GRB. Since a single dose of mifepristone triggers photoreceptor death in the mouse retina, we are now studying GRA, GRB, and the phosphorylated isoforms p-Ser203-GR and p-Ser211-GR. Experimental animals (Balb-c mice) were kept under cycling illumination conditions (12 h light, ≤ 60 lux/12 h dark). Retinas were obtained at 12 a.m. or 12 p.m. Some mice were exposed to full darkness during 7 days or 1,500 lux (6 h, phototoxic conditions). We studied GRs using immunohistochemical procedures, and Western blots (WB) of extracts from whole neural retinas or isolated photoreceptor outer segments. Antibodies against GRA, GRB, and p-Ser211-GR immunostained cell nuclei in all retinal layers. Müller cell-nuclei showed the highest GRα immunoreactivity (IR) under all illumination conditions. Immunostaining was stronger in specimens obtained at noon and after exposure to 1,500 lux. Illumination had little effect on the nuclear localization of GRB and p-Ser211-GR. GRA- and GRB-IR were also present photoreceptor nerve endings in the outer plexiform layer (OPL). Specimens obtained after full darkness displayed reduced OPL immunostaining. WB indicated that GRA almost disappeared after 7 days without illumination, whereas GRB was reduced under phototoxic conditions. Retinal cell nuclei showed low p-Ser203-GR-IR. However, this antibody reacted with photoreceptor outer and inner segments. Outer segments showed this immunoreactivity at noon and after 1,500 lux, whereas inner segments were intensely immunostained after darkness. WBs demonstrated the presence of GRA, GRB, and p-Ser203-GR in outer segments isolated at noon or after 1,500 lux exposure. Our findings suggest that glucocorticoids could exert a direct action on photoreceptor outer segments, and that this effect might be mediated by GRA.