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Urmimala Raychaudhuri, J Cameron Millar, Colleen M McDowell, Abbot F Clark; Tissue transglutaminase causes intraocular pressure elevation in mice. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4683.
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© ARVO (1962-2015); The Authors (2016-present)
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 increases ECM crosslinking in TM, and increases aqueous humor outflow resistance leading to elevated intraocular pressure (IOP) in mice.
Mouse trabecular meshwork (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 2μl) was injected intravitreally into the left eye of female BALB/cJ 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 facility (C) was measured on day 23 (n = 6) using our published constant flow infusion method.
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 BALB/cJ 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<0.0001, ANOVA)). Mean C in injected eyes was significantly lower than uninjected eyes (0.013 μl/min/mmHg (injected) versus 0.021 μl/min/mmHg (control) (p = 0.01, paired t-test)), and correlated with the associated increase in IOP. The decrease in C supports our hypothesis that increased crosslinking in the TM can increase aqueous humor outflow resistance thereby leading to increased IOP.
Increased expression of TGM2 in mouse TM cells increases the ECM crosslinking 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.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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