PROTEOGLYCANS IN THE MOUSE INTERPHOTORECEPTOR MATRIX .4. RETINAL SYNTHESIS OF CHONDROITIN SULFATE PROTEOGLYCAN

To determine whether the mouse retina contributes chondroitin sulfate proteoglycan (CS-PG) to the interphotoreceptor matrix (IPM), 35SO42- was used as a tracer for newly synthesized proteoglycan by retinas maintained in vitro in the absence of pigment epithelium. Following incubation with the tracer for 3 hr, the 35S-labeled proteoglycans present in the incubation medium and associated with isolated photoreceptor outer segments were analyzed separately. Proteoglycan was extracted with 4 m guanidine, and then separated on a G-25 column followed by DEAE ion exchange chromatography in the presence of 8 m urea. The proteoglycan fraction was eluted with a linear NaCl gradient of 0·15-1·0 m. Eluted 35S-labeled macromolecules were susceptible to chondroitinase AC and ABC degradation, indicating that virtually all the 35S-labeled proteoglycan synthesized by the mouse retina and secreted into the incubation media is of the chondroitin sulfate type. In parallel autoradiographic analysis of retinas following 35SO42- incubation, silver grains were present over all retinal compartments, with 41-48% associated with the photoreceptor layer. Quantitative autoradiography of retinas following chondroitinase AC digestion of fixed retinas revealed significant (P < 0·025) reduction in silver grains associated with the photoreceptor outer segment layer as compared to controls. These combined biochemical and autoradiographic studies indicate that the retina, possibly the photoreceptors, synthesize at least a portion of the CS-PG present in the IPM of the mouse. © 1991.