Effects of TGF-β2 on Cadherins and β-Catenin in Human Trabecular Meshwork Cells

Purpose.: The effects of TGF-β2 on cadherin-mediated cell–cell adhesion in human trabecular meshwork (HTM) cells were characterized, since TGF-β–induced changes in the cytoskeleton, cell–cell, and cell–matrix interactions of HTM cells are suggested to have a significant role in primary open angle glaucoma. Methods.: The HTM cells were derived from donor cornea rings and treated with TGF-β2 or vehicle, and protein expression was studied by Western Blot, while protein localization was studied by fractionation of lysates and by confocal immunofluorescence microscopy. Cell–cell adhesion was assessed functionally in dissociation experiments and N-cadherin–mediated cell contact formation in cell spreading experiments on cadherin-coated substrates. A rho-associated protein kinase (ROCK) inhibitor was used to evaluate the contribution of cytoskeletal tension to TGF-β2–induced changes in protein expression and localization. Results.: TGF-β2 activated Smad-2/3, serine–threonine kinase (AKT), and extracellular signal-regulated kinase (ERK) signaling, and enhanced expression of β-catenin as well as N- and OB-cadherin. The nuclear fraction of β-catenin was not enhanced by TGF-β2. Immunofluorescence microscopy revealed an increased localization of N-cadherin and β-catenin to cell–cell adhesions, and an increase in F-actin. The TGF-β2 increased cell–cell adhesion strength and enhanced N-cadherin–mediated cell contact formation. This effect was blocked by inhibition of mitogen-activated protein kinase kinase (MEK) or AKT. Cytoskeletal relaxation by a ROCK inhibitor did not prevent a TGF-β2–induced increase in cadherin and β-catenin expression. Conclusions.: The cytokine TGF-β2 enhances cadherin-mediated cell–cell adhesion and β-catenin expression in HTM cells. Increased cell–cell adhesion may contribute to biomechanical alterations in glaucomatous trabecular meshwork (TM), and changes in β-catenin levels and its possible sequestration to cell adhesion sites may affect Wnt signaling. Thus, the crosstalk of TGF-β2 and Wnt signaling in TM may deserve further investigation.