Tissue transglutaminase causes intraocular pressure elevation in mice

Purpose: The profibrotic cytokine TGF-β2 increases expression of the crosslinking enzyme tissue transglutaminase (TGM2). In the trabecular meshwork (TM), excessive crosslinking of ECM proteins mediated by TGM2 could increase extracellular matrix (ECM) protein deposition, thereby decreasing the aqueous humor outflow facility. We hypothesize that increased expression of TGM2 increased ECM crosslinking in TM cells, and increases aqueous humor outflow resistance leading to elevated intraocular pressure (IOP) in mice. Methods: MTM cells were grown to confluency and transduced with Ad5.TGM2 (MOI of 75). On Day 5, MTM cells were fixed with 4% PFA for immunocytochemistry (ICC). Ad5.TGM2 (1.28 - 106 pfu in 2ml) was injected intravitreally into the left eye of female BALBc/J retired breeder mice (n = 18). The uninjected (right) eye served as a control. Daytime conscious IOP measurements were taken twice a week using a TonoLab rebound tonometer for approximately 3 weeks. Aqueous humor outflow facilities (C) was studied on day 23 (n = 6) using our published constant flow infusion method. Results: In cultured MTM cells, treatment with Ad5.TGM2 increased immunostaining of ε-(γ-glutamyl)lysine (GGEL) bonds, demonstrating increased TGM2 crosslinking activity after treatment with Ad5.TGM2. In BALBc/J mice, injection of Ad5.TGM2 significantly increased IOP from day 14 to 22, with the maximum difference elevation at Day 19, (15.86 +/- 1.06 mmHg (injected) versus 10.7 +/- 0.48 mmHg (control) (p Conclusion: Increased expression of TGM2 in mouse TM cells increases the ECM cross-linking activity of TGM2. Increased expression of TGM2 in the TM of the living mouse increases aqueous outflow resistance and elevates IOP. In the future, we will study whether TGM2 is responsible for TGF-β2 induced ocular hypertension.