INCREASED LATENT GELATINASE ACTIVITY IN THE SCLERA OF VISUALLY DEPRIVED CHICKS

Purpose. Gelatinase activity was measured in the normal chick sclera a nd in sclera of form-deprived (myopic) eyes to assess the role of this metalloproteinase in ocular elongation associated with experimental m yopia. Methods. Gelatinases were extracted from anterior and posterior regions of normal chick sclera and sclera from eyes that had been for m-vision deprived for 11 days. Gelatinase activity in the extracts was determined by measuring the digestion of H-3-gelatin after incubation with the extracts in the absence or presence of 1 mM aminophenylmercu ric acetate (APMA) to activate latent gelatinases. Scleral gelatinases were characterized by sodium dodecyl sulfate-polyacrylamide gel elect rophoresis gelatin zymography and immunoprecipitation analyses.Results . No significant differences were detected in gelatinase activity betw een normal and deprived posterior sclera in the absence of APMA. Howev er, when scleral extracts were incubated with APMA, extracts from the posterior sclera of deprived eyes contained significantly more gelatin ase activity than paired controls (+127%, P = 0.0105). In contrast, no differences in active or latent gelatinase activity were detected in extracts from the anterior sclera. Removal of tissue inhibitors of met alloproteinases (TIMP) from control scleral extracts by reduction and alkylation resulted in a 222% increase in gelatinolytic activity after APMA-activation (P less than or equal to 0.001), whereas similar trea tment of deprived scleral extracts resulted in only a 76% increase in gelatinolytic activity (P less than or equal to 0.001). A 65/58-kd dou bler was the major gelatinolytic species from control and deprived pos terior sclera that represent the proenzyme and active forms of the 72- kd gelatinase (MMP-2). Conclusions. These data indicate that visual de privation is associated with an increased amount of the 72-kd progelat inase and a decreased amount of TIMP within the posterior sclera. Ther efore, an imbalance between the levels of 72-kd progelatinase and its inhibitor may play a role in the remodeling processes of the posterior sclera during the development of form-deprivation myopia.