Purpose: Scleral proteoglycans were characterized from human donor eyes aged 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 35SO4) 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 total accumulated proteoglycans were determined by assaying each fraction for radioactivity and glycosaminoglycans, respectively. Regression analyses were performed on the three major proteoglycan peaks to identify age-related changes in scleral proteoglycan composition. Scleral proteoglycans were further purified by anion-exchange chromatography and characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analyses.
Results: Human scleral proteoglycans were apparent as three major peaks after chromatography on Sepharose CL-4B. The two faster eluting peaks contained alternative forms of the cartilage proteoglycan, aggrecan, whereas the third peak contained the small proteoglycans biglycan and decorin. The relative percentage of newly synthesized and total accumulated aggrecan increased approximately two- to sixfold from infancy to 94 years. In contrast, the relative percentage of newly synthesized and total accumulated biglycan and decorin decreased by approximately 25%. Chromatography and Western blot results indicated that the absolute amounts of all three proteoglycans significantly increased in concentration within the sclera from birth to the fourth decade. Beyond the fourth decade, decorin and biglycan decreased in all scleral regions and were present in lowest concentrations by the ninth decade. 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 observed in the present study are likely to contribute to the regional alterations in biomechanical properties of the sclera associated with growth and aging.