Aqueous humor-borne factor upregulates Bcl-2 expression in corneal endothelial cells.

PURPOSE: To determine if factors present in the aqueous humor (AH) protect the corneal endothelium from apoptosis.

METHODS: Mouse and human corneal endothelial cells were cultured in vitro, and apoptosis was induced by nutrient deprivation. AH and supernatant from iris/ciliary body (I/CB) cell cultures were tested for their effect on corneal endothelial cell apoptosis. The effect of I/CB supernatant on Fas, Bax, and Bcl-2 gene transcription was evaluated by Northern blotting. I/CB supernatant was subjected to proteinase analysis to identify the apoptosis inhibitory factor(s).

RESULTS: Rabbit AH and supernatant from mouse I/CB cell cultures inhibited the apoptosis of mouse and human immortalized corneal endothelial cell lines. The inhibition of apoptosis was associated with an upregulation of Bcl-2 gene transcription and Bcl-2 protein expression. Bax gene expression was not significantly affected by I/CB cell supernatant. Induction of apoptosis by stimulation of the Fas receptor was unaffected by I/CB cell supernatant. Protease analyses indicated that the apoptosis inhibitory factor was a protein.

CONCLUSIONS: The inability of corneal endothelial cells to undergo mitosis renders the corneal endothelium vulnerable to loss of physiological function through cellular attrition. However, a protein(s) produced by I/CB cells and present in the AH, upregulates Bcl-2 gene transcription and protects the corneal endothelial cells from apoptosis.