Proteoglycan composition in the human sclera during growth and aging

PURPOSE. Scleral proteoglycans were characterized from human donor eyes age d 2 months to 94 years to identify age-related changes in the synthesis and /or accumulation of these extracellular matrix components. METHODS. Newly synthesized proteoglycans (previously radiolabeled with (SO4 )-S-35) and total accumulated scleral proteoglycans were extracted with 4 M guanidine hydrochloride and separated by molecular sieve chromatography on a Sepharose CL-4B column. The elution positions of newly synthesized and t otal accumulated proteoglycans were determined by assaying each fraction fo r radioactivity and glycosaminoglycans, respectively Regression analyses we re performed on the three major proteoglycan peaks to identify age-related changes in scleral proteoglycan composition. Scleral proteoglycans were fur ther purified by anion-exchange chromatography and characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analyse s. RESULTS. Human scleral proteoglycans were apparent as three major peaks aft er chromatography on Sepharose CL-4B. The two faster eluting peaks containe d alternative forms of the cartilage proteoglycan, aggrecan, whereas the th ird peak contained the small proteoglycans biglycan and decorin. The relati ve percentage of newly synthesized and total accumulated aggrecan increased approximately two- to sixfold from infancy to 94 years. In contrast, the r elative percentage of newly synthesized and total accumulated biglycan and decorin decreased by approximately 25%. Chromatography and Western blot res ults indicated that the absolute amounts of all three proteoglycans signifi cantly increased in concentration within the sclera from birth to the fourt h decade. Beyond the fourth decade, decorin and biglycan decreased in all s cleral regions and were present in lowest concentrations by the ninth decad e. In contrast, aggrecan, which was present in highest concentration in the posterior sclera, was not significantly reduced with increasing age. CONCLUSIONS. The age-related changes in scleral proteoglycan composition ob served in the present study are likely to contribute to the regional altera tions in biomechanical properties of the sclera associated with growth and aging.