Cleavage and activation of corneal matrix metalloproteases by Pseudomonas aeruginosa proteases

Abstract

Purpose: To examine the effect of Pseudomonas aeruginosa on the expression of corneal matrix metalloproteases and the effect of its proteases on activation of corneal matrix metalloproteases in vitro.

Methods: Rat corneas and human corneal fibroblasts were co-cultivated with two different strains (RPS & 599A) of P. aeruginosa and one strain of Staphylococcus aureus, and the conditioned media were analyzed for proteolytic activity by gelatin and casein zymography. Human corneal fibroblast-conditioned medium was incubated with that from either strain of P. aeruginosa and was analyzed in a similar manner.

Results: Normal rat corneas in organ culture produce a 65 kDa gelatinase (inactive matrix metalloprotease-2), whereas thermally injured rat corneas additionally produce gelatinases with molecular masses of 92 kDa (inactive matrix metalloproteases-9) and > 200 kDa. Matrix metalloprotease-2 is also detected in human corneal fibroblast-conditioned medium. Although these matrix metalloproteases are no longer detectable when rat corneas or human corneal fibroblasts are co-cultured with two strains of P. aeruginosa for 48 hr, a 58 kDa gelatinase fragment appears in earlier stages of co-culture. In contrast, S. aureus does not affect matrix metalloprotease-2. The 58 kDa fragment is also evident by incubating human corneal fibroblast-conditioned medium with that from either strain of P. aeruginosa. Conditioned medium from the RPS strain, which produces both elastase and alkaline protease, is more effective in cleaving matrix metalloprotease-2 than that from the 599A strain, which expresses mainly alkaline protease.

Conclusion: The secreted inactive corneal matrix metalloprotease-2 is activated through limited proteolysis by pseudomonal proteases.