Elevation of transforming growth factor alpha in cat aqueous humor after corneal endothelial injury.

PURPOSE

To determine if a scrape injury to cat corneal endothelial cells increases the level of mitogenic proteins such as transforming growth factor alpha (TGF alpha) in aqueous humor.

METHODS

Aqueous humor of cats was collected at 0, 2, 6, and 24 hours after wounding the endothelium by contact with a cannula tip. Aqueous humor samples collected from sham-wounded cats served as controls. Aqueous humor samples were analyzed for levels of protein, for mitogenic activity using incorporation of tritiated thymidine by cultures of bovine corneal endothelial cells, and for immunoreactive TGF alpha protein using a specific radioimmunoassay.

RESULTS

The average protein level in aqueous humor obtained before wounding was low (0.5 mg/ml), increased 26-fold at 2 hours after injury (13 mg/ml), then progressively decreased at 6 hours (8 mg/ml) and 24 hours (2 mg/ml). Levels of mitogenic activity of aqueous humor samples collected 2, 6, and 24 hours after wounding were 2-fold, 2.5-fold, and 0.6-fold higher, respectively, compared to the level of mitogenic activity measured in aqueous humor collected before wounding (0 hours) or in aqueous humor collected from sham-wounded eyes. TGF alpha concentration in aqueous humor collected before endothelial wounding was low (6.8 ng/ml), increased 14-fold 2 hours after wounding (97.4 ng/ml), then progressively decreased at 6 hours (63.3 ng/ml) and 24 hours (35.5 ng/ml) after wounding. TGF alpha concentrations in aqueous humor collected from sham-wounded eyes at 2 hours (9.5 ng/ml) and 6 hours (5.3 ng/ml) were not significantly different from prewound levels. Detergent extracts of bovine corneal endothelial cells contained substantial levels of TGF alpha immunoreactive protein (20 ng/mg protein).

CONCLUSIONS

Wounding of cat endothelium causes a rapid increase in mitogenic proteins in aqueous humor including TGF alpha, which may act by an autocrine mechanism to stimulate endothelial wound healing.