Age-Related Dysregulation of α5β1 and αvβ3 Integrin Activity Alters CONTRACTILE properties of Trabecular Meshwork Cells

Age is a major risk factor for primary open-angle glaucoma (POAG), an ocular disease associated with elevated intraocular pressure (IOP) due to the restricted outflow of aqueous humor fluid from the anterior chamber. This restriction is caused by an induction of fibrogenic pathways that increase deposition of extracellular matrix (ECM) and alter the contractile properties of trabecular meshwork (TM) cells. Integrins, a family of heterodimeric cell surface receptors that bind ECM, play a key role in regulating fibrogenic pathways. In this study, we investigated whether age-related changes in integrin subunit expression and activity signifies an early event in initiating fibrotic-like changes in the TM. TM cells were isolated from young and old human donor eyes. Flow cytometry, RT-PCR, and immunofluorescent microscopy revealed a significant decrease in α5 integrin expression in TM cells from older individuals. This loss was accompanied by an increase in activated, but not total αvβ3 integrin in focal adhesions. TM cells from older donors expressed higher levels of αSMA mRNA, assembled αSMA-containing stress fibers, and contracted collagen gels significantly more than young TM cells. TM cells from old donors also assembled higher levels of insoluble fibronectin fibrils and contained higher levels of the EDB+ isoform of fibronectin in their ECM. shRNA knockdown of α5 integrin subunits showed that the increase in αvβ3 integrin activity was due to lower levels of α5 integrin expression. These studies suggest that age-related dysregulation of α5β1 and αvβ3 integrin signaling may represent an important early molecular event in inducing fibrogenic pathways associated with POAG.