Increased synthesis and deposition of extracellular matrix proteins leads to endoplasmic reticulum stress in the trabecular meshwork

Increased synthesis and deposition of extracellular matrix (ECM) proteins in the trabecular meshwork (TM) is associated with TM dysfunction and intraocular pressure (IOP) elevation in glaucoma. However, it is not understood how ECM accumulation leads to TM dysfunction and IOP elevation. Using a mouse model of glucocorticoid (GC)-induced glaucoma, primary human TM cells and human post-mortem TM tissues, we show that increased ECM accumulation leads to endoplasmic reticulum (ER) stress in the TM. The potent GC, dexamethasone (Dex) increased the secretory protein load of ECM proteins in the ER of TM cells, inducing ER stress. Reduction of fibronectin, a major regulator of ECM structure, prevented ER stress in Dex-treated TM cells. Overexpression of fibronectin via treatment with cellular fibronectin also induced chronic ER stress in primary human TM cells. Primary human TM cells grown on ECM derived from Dex-treated TM cells induced ER stress markers. TM cells were more prone to ER stress from ECM accumulation compared to other ocular cell types. Moreover, increased co-localization of ECM proteins with ER stress markers was observed in human post-mortem glaucomatous TM tissues. These data indicate that ER stress is associated with increased ECM accumulation in mouse and human glaucomatous TM tissues.