Inhibition of Transforming Growth Factor-β2 Signaling Prevents ECM Remodeling, Endoplasmic Reticulum Stress and Ocular Hypertension in Steroid-induced Glaucoma

Purpose: Ocular hypertension is a serious side effect of glucocorticoid (GC) therapy. Abnormal accumulation of extracellular matrix (ECM) and chronic endoplasmic reticulum (ER) stress in the trabecular meshwork (TM) is associated with GC-induced ocular hypertension. In the present study, we examined the role of TGFβ2 signaling in dexamethasone (Dex)-induced ECM remodeling, ER stress and ocular hypertension. Methods: Conscious IOP and outflow facility was measured in C57 mice treated with vehicle or Dex eye drops up to 7-weeks. TGFβ2 & fibronectin levels in the aqueous humor (AH) were analyzed by Western blotting. Effect of inhibition of TGFβ signaling on Dex-induced ER stress and ECM accumulation was examined by Western blot, immunostaining & Smad reporter assay in TM cells treated with or without TGFβ signaling inhibitors (SIS3 and LY364947). To further examine the role of TGF-β2 signaling, IOP, ECM and ER stress was examined in WT or Smad3-/- mice treated with Dex. Results: Dexamethasone (Dex) mediated reduction of outflow facility and IOP elevation is associated with increased abnormal extracellular matrix (ECM) accumulation in the TM, inducing ER stress. Biochemical analysis of the aqueous humor samples from Dex-treated eyes revealed significantly increased bioactive form of transforming growth factor-β2 (TGF-β2), a major regulator of ECM in the TM. Dex treatment increased both precursor and bioactive form of TGF-β2 in the conditioned medium and activated TGF-β2-induced Smad signaling pathway in primary human TM cells as evident from increased phosphorylation of Smad3 and increased Smad luciferase activity. Inhibition of TGF-β2 signaling significantly reduced Dex-induced abnormal intracellular ECM accumulation and ER stress in human TM cells. Smad3-/- mice, which are required for TGF-β2 signaling, protected from Dex-induced ocular hypertension, ER stress and abnormal ECM accumulation further indicating the role of TGF-β2 signaling in GC-induced glaucoma. Interestingly, knock out of ER stress-induced transcriptional factors, ATF4 and CHOP prevented activation of TGF-β2 signaling and also reduced intracellular ECM accumulation in the TM, thus preventing Dex-induced ER stress and IOP elevation. Conclusions: These studies indicate that Dex-induced TGF-β2 signaling is responsible for ECM remodeling, ER stress and elevation of IOP in GC-induced glaucoma.