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 immunocytochemical, biochemical and autoradiographic techniques. Immunostaining with specific antibodies indicated that decorin is present in both the fibrous and cartilaginous layers of chick sclera, while aggrecan localizes only to the cartilaginous layer. For biochemical analyses of proteoglycan synthesis, sclera were isolated from control and 10-day-form-vision-deprived eyes and radiolabeled in organ culture with 35SO4. Proteoglycan synthesis was significantly increased only within a 6.5-mm-diameter button from the posterior pole of deprived eyes (+113%, P = 0.04), while no significant differences were detected in anterior and equatorial regions of control and deprived eyes. Chromatographic analyses of newly synthesized proteoglycans indicated that form-deprivation stimulates the synthesis of a large chondroitin/keratan sulfate proteoglycan (+77.47%), eluting at the position of aggrecan, as well as smaller chondroitin sulfate and keratan sulfate proteoglycans (+91.05%), which coelute with decorin. Autoradiographic analysis of incorporated sulfate indicated that the increase in proteoglycan synthesis observed in the posterior pole of deprived eyes occurs only in the cartilaginous scleral layer. The distribution of incorporated 35SO4, present over the cartilaginous layer of deprived sclera indicates that proteoglycan synthesis is lowest in scleral cartilage adjacent to the choroid and higher in interstitial regions of posterior cartilaginous sclera as well as in regions near the outer fibrous perichondrium. These results suggest that form-deprivation induced scleral growth in chicks can be attributed to growth and differentiation of scleral cartilage in the posterior pole.