INCREASED GELATINOLYTIC AND CASEINOLYTIC ACTIVITY IN THE THERMALLY INJURED, NUTRITIONALLY COMPROMISED RAT CORNEA - DETECTION OF A 27-KDA LYMPHORETICULAR CELL-ASSOCIATED CASEINASE

This study assesses the impact of various forms of injury on matrix degrading enzymes in nutritionally compromised rat corneas. In vitamin A-deficient (nutritionally compromised) and normal control corneas, in vivo or ex vivo mild mechanical abrasion did not appreciably alter the activity of either the 65-kDa or the 92-kDa gelatinases. In contrast, after thermal injury, while no appreciable change was detected in activity associated with the 65-kDa gelatinase in either vitamin A-deficient or normal control corneas, 92-kDa gelatinolytic activity was consistently higher in corneas from both groups, although activity associated with nutritionally compromised corneas was much higher. In these corneas, thermal injury also induced the expression of two high molecular weight (approximately 130-kDa and 225-kDa) gelatinases and a 27-kDa caseinase. While gelatinases were totally inactivated by inhibitors of metalloproteinases such as 1,10-phenanthroline and Galardin(TM) MPI, the 27-kDa caseinase showed considerable susceptibility to a mixture of serine protease inhibitors {aprotinin, dichloro-isocoumarin and pA-PMSF [(4-amidino-phenyl)-methane-sulphonyl fluoride]. Furthermore, unactivated-lymphoreticular cells from either nutritionally compromised or normal control animals contained a 24- and 27-kDa caseinase, however most of the activity was due to the 24-kDa caseinase. In contrast, glycogen-activated lymphoreticular cells contained a preponderance of the 27-kDa caseinase. Activated-lymphoreticular cells also expressed 92-kDa, 130-kDa and 225-kDa gelatinases. The presence of low molecular weight caseinases in lymphoreticular cells implicates them as the source of these enzymes. To the best of our knowledge, this is the first report of a 27-kDa caseinase in thermally injured, nutritionally compromised corneas. In both nutritionally compromised and normal corneas, the type of injury appears to be an important regulator of gelatinolytic and caseinolytic activities. These results suggest a major role for lymphoreticular cell-associated caseinases in corneal ulceration and keratomalacia.