Gelatinase A and TIMP-2 expression in the fibrous sclera of myopic and recovering chick eyes

PURPOSE. Myopia, or nearsightedness, is characterized by excessive lengthen ing of the ocular globe and is associated with extracellular matrix remodel ing in the posterior sclera. The activity of gelatinase A, a member of the matrix metalloproteinase family, has been shown to increase in the posterio r sclera during the development of induced myopia in several species. In. t he present study, the distribution and relative expression of gelatinase A and its associated inhibitor, tissue inhibitor of metalloproteinases (TIMP) -2, were measured within the fibrous scleras of experimentally myopic (form -deprived) eyes, control eyes, and eyes recovering from form deprivation to better understand the mechanisms that regulate scleral remodeling and the I-ate of ocular elongation. METHODS. Total RNA was extracted from the posterior scleras of form-deprive d chick eyes, eyes recovering from deprivation myopia, and paired contralat eral control eyes, and subjected to northern blot analysis analyses using c DNA probes to chicken gelatinase A and TIMP-2. The distribution of gelatina se A and TIMP-2 mRNAs was evaluated by in situ hybridization on frozen sect ions of chick scleras using P-33-labeled RNA probes. Gelatinase A activity within the fibrous scleras of form-deprived eyes and paired contralateral r ecovering eyes was evaluated by gelatin zymography. RESULTS. Northern blot analysis indicated that the relative expression of g elatinase A was increased by 128% in deprived eyes (P = 0.009), whereas aft er 1 day of recovery, levels were decreased by 80% in scleras from recoveri ng eyes (P = 0.005). In contrast, TIMP-2 expression was significantly decre ased (-53%, P = 0.027) in the posterior scleras of for-deprived eyes. No si gnificant differences were detected in levels of TIMP-2 expression between recovering eyes and paired control eyes. In situ hybridization indicated th at most of the gelatinase A transcripts were present in the fibrous layer o f the posterior scleras from form-deprived and recovering eyes. CONCLUSIONS. Changes in the steady state levels of gelatinase A and TIMP-2 mRNA lead to changes in gelatinase activity within the fibrous sclera and m ediate, at least in part, the process of visually regulated ocular growth a nd scleral remodeling.