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

Abstract

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. 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. 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. 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.