Effect of BAMBI expression on intraocular pressure and aqueous humor outflow facility in mice

Abstract

Purpose : Elevated intraocular pressure (IOP) is an important risk factor in the development of glaucoma. TGFβ2 is well known to be involved in regulating both the extracellular matrix in the trabecular meshwork (TM) as well as ocular hypertension. BAMBI (BMP and activin membrane-bound inhibitor) has been shown to be a negative regulator of TGF-β2. However, the role of BAMBI in regulating IOP is unknown. We investigated whether knockdown of BAMBI results in ocular hypertension in mice due to uninhibited TGFβ2 signaling.

Methods : B6;129S1-Bambi^tm1Jian/J mice were injected intravitreally with 2.5x10⁷ pfu of either Ad5.Cre (n=9), Ad5.TGFβ2 (n=10), or Ad5.TGFβ2 + Ad5.Cre (n=10), in one eye of each animal. The contralateral uninjected eyes were used as negative controls. IOP was measured using a TonoLab rebound tonometer. Aqueous humor outflow facility was assessed using a constant flow infusion method. Student’s t-test was used to compare between vector-treated and control uninjected eyes.

Results : Injection with either Ad5.Cre, Ad5.TGFβ2, or Ad5.TGFβ2 + Ad5.Cre each induced ocular hypertension starting at day 7 post-injection and maintained significant IOP elevation throughout the 56 day time course compared to uninjected control eyes (p<0.01, days 7-56). At day 56 post-injection IOP increased to 29.8 +/- 3.2 mmHg in Ad5.Cre injected eyes compared to 14.2 +/- 0.3 mmHg in contralateral uninjected eyes (p<0.001). Ad5.TGFβ2 (32.3 +/- 2.6 mm Hg) and Ad5.TGFβ2 + Ad5.Cre (32.4 +/- 3.9 mmHg) also had significant IOP elevation at 56 days post-injection compared to uninjected control eyes (14.2 +/- 0.3 mmHg), p<0.001. Aqueous humor outflow facility was also significantly lower in vector-treated eyes compared to control uninjected eyes: Ad5.Cre (uninjected 0.022 +/- 0.004 ul/min/mmHg, injected 0.012 +/- 0.004 ul/min/mmHg; p=0.012, n=5), Ad5.TGFβ2 (uninjected 0.016 +/- 0.002 ul/min/mmHg, injected 0.0096 +/- 0.0004 ul/min/mmHg; p=0.011, n=3), Ad5.TGFβ2 + Ad5.Cre (uninjected 0.022 +/- 0.003 ul/min/mmHg, injected 0.0093 +/- 0.0009 ul/min/mmHg; p=0.02, n=3).

Conclusions : We show for the first time that conditional knockdown of BAMBI in the TM with Ad5.Cre induces ocular hypertension by reducing aqueous humor outflow facility. These data further explain the molecular mechanisms involved in the development of glaucomatous TM damage and provide potential new targets to lower IOP.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.