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Expression of Collagen-Binding Integrin Receptors in the Mammalian Sclera and Their Regulation during the Development of Myopia

From the Department of Optometry and Vision Sciences, The University of Melbourne, Melbourne, Australia.

PURPOSE. The sclera has a collagen-rich extracellular matrix that undergoes significant biochemical and biomechanical remodeling during myopic eye growth. The integrin family of cell surface receptors play critical roles in extracellular matrix and biomechanical remodeling in connective tissues. This study identified the major collagen-binding integrin receptors in the mammalian sclera and investigated their mRNA expression during the development of and recovery from experimental myopia.

METHODS. The presence of the 1, 2, and ß1 integrin subunits was examined by using tree-shrew–specific primers and RT-PCR. Scleral expression of 1ß1 and 2ß1 receptor proteins was further investigated by using Western blot analysis and immunocytochemistry. Myopia was induced monocularly by occluding pattern vision and scleral tissue collected after 24 hours and 5 days. In a subset of the 5-day treatment group, vision was restored for 24 hours before tissue was isolated. Total RNA was extracted, and integrin subunit expression levels were assessed with quantitative real-time PCR.

RESULTS. The presence of the major collagen-binding integrin subunits 1, 2, and ß1 was confirmed by RT-PCR in both scleral tissue and cultured scleral fibroblasts. Both the 1 and 2 integrin subunit proteins were identified in tree shrew scleral tissues, and integrin receptor expression was localized to scleral fibroblast focal adhesions. After only 24 hours of myopia induction, a time when no structural elongation has occurred, significant decreases were observed in the expression of the 1 (–36%) and ß1 (–44%) integrin subunits. After 5 days of myopia induction, 1 integrin expression had returned to baseline levels, whereas the 2 subunit showed a significant decrease in expression (–52%). The 5-day integrin profiles were maintained during recovery from the induced myopia, with only 2 integrin showing a statistically significant relative decrease in expression (–41%).

CONCLUSIONS. The mammalian sclera expresses the major collagen-binding integrin subunits. The 1 and ß1 subunit expression was decreased early during the development of myopia, whereas the regulation of 2 integrin occurred at a later time point. The differential regulation of 1ß1 and 2ß1 during the development of myopia may reflect specific roles for these receptors in the scleral extracellular matrix and biomechanical remodeling that accompanies myopic eye growth.

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