Increased latent gelatinase activity in the sclera of visually deprived chicks.

PURPOSE

Gelatinase activity was measured in the normal chick sclera and in sclera of form-deprived (myopic) eyes to assess the role of this metalloproteinase in ocular elongation associated with experimental myopia.

METHODS

Gelatinases were extracted from anterior and posterior regions of normal chick sclera and sclera from eyes that had been form-vision deprived for 11 days. Gelatinase activity in the extracts was determined by measuring the digestion of 3H-gelatin after incubation with the extracts in the absence or presence of 1 mM aminophenylmercuric acetate (APMA) to activate latent gelatinases. Scleral gelatinases were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis gelatin zymography and immunoprecipitation analyses.

RESULTS

No significant differences were detected in gelatinase activity between normal and deprived posterior sclera in the absence of APMA. However, when scleral extracts were incubated with APMA, extracts from the posterior sclera of deprived eyes contained significantly more gelatinase 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 metalloproteinases (TIMP) from control scleral extracts by reduction and alkylation resulted in a 222% increase in gelatinolytic activity after APMA-activation (P < or = 0.001), whereas similar treatment of deprived scleral extracts resulted in only a 76% increase in gelatinolytic activity (P < or = 0.001). A 65/58-kd doublet was the major gelatinolytic species from control and deprived posterior sclera that represent the proenzyme and active forms of the 72-kd gelatinase (MMP-2).

CONCLUSIONS

These data indicate that visual deprivation is associated with an increased amount of the 72-kd progelatinase and a decreased amount of TIMP within the posterior sclera. Therefore, 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.