Integrin α2 Level is a Critical Determinant for Mesenchymal to Endothelial Phenotype Transition of Trabecular Meshwork Cells

PURPOSE: Trabecular meshwork (TM) cells play a role in the regulation of aqueous humor outflow. In glaucoma, a large number of TM cells exhibiting mesenchymal phenotypes is associated with abnormal turnover of extracellular matrix components including collagen, leading to high intraocular pressure (IOP). Integrin α2 is a collagen receptor, although its role in TM cells is unknown. In this study, we assessed the role of integrin α2 in TM cells. METHODS: We assessed the expression of integrin α2 and cell phenotypes in human TM cells using western blot analysis, immunohistochemistry and collagen contraction assays. The integrin α2 inhibitor BTT3033 and an integrin α2-targeting small interfering RNA (siRNA) were used to assess the roles of integrin α2 in TM cells. RESULTS: Transforming growth factor (TGF)-β2 stimulation decreased integrin α2 expression, and transfection of cells with integrin α2 siRNA enhanced mesenchymal phenotypes. In contrast, cells treated with the integrin α2 inhibitor BTT3033 tended to exhibit more endothelial features than mesenchymal features, and BTT3033 increased integrin α2 expression due to the accumulation of integrin α2 at the plasma membrane. BTT3033 also attenuated mesenchymal characteristics, along with decreasing Smad2 phosphorylation and reducing collagen contraction. The induction of endothelial characteristics by BTT3033 was observed even in the presence of TGF-β2. CONCLUSION: The expression level of integrin α2 is a determinant of endothelial characteristics in TM cells, and pharmacological modulation of integrin α2 by BTT3033 promotes an endothelial phenotype, thus offering a novel therapeutic strategy for IOP regulation.