Inhibition of transforming growth factor-beta-induced cataractous changes in lens explants by ocular media and alpha 2-macroglobulin.

PURPOSE

To investigate the ocular media for the presence of inhibitors of transforming growth factor-beta (TGF beta) using a lens epithelial explant system in which TGF beta induces cataractous changes. The effect of alpha 2-macroglobulin, an inhibitor of TGF beta in other systems, also was assessed.

METHODS

Explants prepared from 21-day-old rats were cultured with TGF beta 2 with and without 50% bovine aqueous or vitreous or alpha 2-macroglobulin. alpha 2-macroglobulin was added to an aqueous concentrate, shown to contain endogenous TGF beta activity by blocking with anti-TGF beta. Explants were monitored by phase-contrast microscopy for 5 days and assessed in terms of capsule wrinkling, spindle-cell formation, blebbing, and cell loss. alpha 2-macroglobulin in the ocular media was assessed by enzyme-linked immunosorbent assay and Western blot analysis.

RESULTS

At 50% strength, neither aqueous nor vitreous demonstrated TGF beta-like activity; however, aqueous partially and vitreous completely prevented cataractous changes induced by 25 and 100 pg/ml TGF beta 2, respectively. alpha 2-macroglobulin (50 to 200 micrograms/ml) also protected against these changes, with complete inhibition of TGF beta 2 or aqueous-derived TGF beta activity at the highest concentration. A threefold higher concentration of alpha 2-macroglobulin was detected in vitreous than aqueous.

CONCLUSIONS

Both aqueous and vitreous contain molecule(s) that inhibit TGF beta 2 activity. alpha 2-macroglobulin has been identified in the ocular media and shown to block cataractous changes induced by TGF beta. Maintaining appropriate levels of alpha 2-macroglobulin or similar molecules in the ocular media may protect lens cells from the damaging effects of TGF beta, and reduced levels may predispose to cataract.