TRANSFORMING GROWTH-FACTOR-BETA-2 IS THE PREDOMINANT ISOFORM IN THE NEURAL RETINA, RETINAL-PIGMENT EPITHELIUM-CHOROID AND VITREOUS OF THE MONKEY EYE

Several techniques were utilized to assess the levels, disposition and cellular sources of isoforms 1 and 2 of transforming growth factor beta (TGF-beta) in the posterior pole of the monkey eye. Freshly dissected tissues, as well as the saline vehicles in which dissections were performed, were analysed by sandwich enzyme-linked immunosorbent assay. In all tissues TGF-beta 2 was the predominant isoform, with beta 2:beta 1 ratios of 6:1 for neural retina (as ng g(-1)) and 425:1 for vitreous (as pmol l(-1)). Retinal pigment epithelium (RPE)-Bruch's membrane-choroid complex contained approximately 10 times the amount of both TGF-beta isoforms as neural retina. For first passage cultures of monkey RPE, TGF-beta 2, but not TGF-beta 1, accumulated over time in conditioned media samples. Immunoreactivity for TGF-beta 2 was detected both in tissue sections of posterior pole, specifically in rod outer segments and RPE, and also in the first passage cultures of RPE. Antibodies to specific peptide sequences of both isoforms localized TGF-beta to the outer segments of rod photoreceptors. The apparent sequestration of TGF-beta 2 in photoreceptor outer segments, as well as the in vitro evidence for possible synthesis and release by RPE, suggest that TGF-beta 2 is an important modulator of visual function acting at the retina-RPE interface.