REGIONAL PROTEOGLYCAN SYNTHESIS IN THE SCLERA OF EXPERIMENTALLY MYOPIC CHICKS

Proteoglycan distribution and synthesis were compared in the sclera of normal and 10-day-form-vision-deprived (myopic) chick eyes using immu nocytochemical, biochemical and autoradiographic techniques. Immunosta ining with specific antibodies indicated that decorin is present in bo th the fibrous and cartilaginous layers of chick sclera, while aggreca n localizes only to the cartilaginous layer. For biochemical analyses of proteoglycan synthesis, sclera were isolated from control and 10-da y-formvision-deprived eyes and radiolabeled in organ culture with (SO4 )-S-35. Proteoglycan synthesis was significantly increased only within a 6.5-mm-diameter button from the posterior pole of deprived eyes (+1 13%, P = 004), while no significant differences were detected in anter ior and equatorial regions of control and deprived eyes. Chromatograph ic analyses of newly synthesized proteoglycans indicated that form-dep rivation stimulates the synthesis of a large chondroitin/keratan sulfa te proteoglycan (+77.47%), eluting at the position of aggrecan, as wel l as smaller chondroitin sulfate and keratan sulfate proteoglycans (+9 1.05%), which coelute with decorin. Autoradiographic analysis of incor porated sulfate indicated that the increase in proteoglycan synthesis observed in the posterior pole of deprived eyes occurs only in the car tilaginous scleral layer. The distribution of incorporated (SO4)-S-35, present over the cartilaginous layer of deprived sclera indicates tha t proteoglycan synthesis is lowest in scleral cartilage adjacent to th e choroid and higher in interstitial regions of posterior cartilaginou s sclera as well as in regions near the outer fibrous perichondrium. T hese results suggest that form-deprivation induced scleral growth in c hicks can be attributed to growth and differentiation of scleral carti lage in the posterior pole.