Age-related changes of sulfated proteoglycans in the normal human trabecular meshwork

Ultrastructural changes in sulfated proteoglycans were studied in 12 pairs of normal eye-bank eyes (aged 1 day to 92 years), using the cationic dye, cuprolinic blue, in a 'critical electrolyte concentration'. Pretreatment of trabecular meshwork sections with various glycosaminoglycanases and nitrous acid served to characterize these proteoglycans. Three sizes of proteoglycan-cuprolinic blue (PG-CB) complexes were found in association with different extracellular matrix components. Small, thin PG-CB complexes were closely associated with collagen fibrils. Large, thick PG-CB complexes, although located close to collagen fibrils in a variety of places, were most commonly seen between the boundaries of the collagen bundles, where they were associated with fine filaments. Both types of collagen-associated PG-CB complexes contained chondroitin sulfate and dermatan sulfate, with dermatan sulfate predominant. Basal lamina-associated PG-CB complexes contained heparan sulfate. An age-related, progressive coalescence of collagen was found in normal trabecular meshwork in a statistically significant fashion; the regions of collagen coalescence were associated with a decrease of small, collagen-associated PG-CB complexes and an increase of a previously unrecognized matrix material. The measurement of areas of coalescence of collagen was used as an indirect indicator of small, collagen-associated PG-CB complex loss with age. Large collagen-associated PG-CB complexes and basal lamina-associated PG-CB complexes decreased from infant to young adult; no additional loss with age was found. Further studies will be needed to determine whether loss of sulfated PGs plays a role in increased aqueous outflow resistance that characterizes glaucoma.