Mutant human myocilin induces strain specific differences in ocular hypertension and optic nerve damage in mice

Abstract

Elevated intraocular pressure (IOP) is a causative risk factor for the development and progression of glaucoma. Glaucomatous mutations in myocilin (MYOC) damage the trabecular meshwork and elevate IOP in humans and in mice. Animal models of glaucoma are important to discover and better understand molecular pathogenic pathways and to test new glaucoma therapeutics. Although a number of different animal models of glaucoma have been developed and characterized, there are no true models of human primary open angle glaucoma (POAG). The overall goal of this work is to develop the first inducible mouse model of POAG using a human POAG relevant transgene (i.e. mutant MYOC) expression in mouse eyes to elevate IOP and cause pressure induced damage to the optic nerve. Four mouse strains (A/J, BALB/cJ, C57BL/6J, and C3H/HeJ) were used in this study. Ad5.MYOC.Y437H (5 × 107 pfu) was injected intravitreally into one eye, with the uninjected contralateral eye serving as the control eye. Conscious IOP measurements were taken using a TonoLab rebound tonometer. Optic nerve damage was determined by scoring PPD stained optic nerve cross sections. Retinal ganglion cell and superior colliculus damage was assessed by Nissl stain cell counts. Intravitreal administration of viral vector Ad5.MYOC.Y437H caused a prolonged, reproducible, and statistically significant IOP elevation in BALB/cJ, A/J, and C57BL/6J mice. IOPs increased to approximately 25 mm Hg for 8 weeks (p<0.0001). In contrast, the C3H/HeJ mouse strain was resistant to Ad5.MYOC.Y437H induced IOP elevation for the 8-week time period. IOPs were stable (12–15 mm Hg) in the uninjected control eyes. We also determined whether there were any strain differences in pressure-induced optic nerve damage. Even though IOP was similarly elevated in three of the strains tested (BALB/cJ, C57BL/6J, and A/J ) only the A/J strain had considerable and significant optic nerve damage at the end of 8 weeks with optic nerve damage score of 2.64 +/− 0.19 (n=18, p<0.001) in the injected eye. There was no statistical difference in retinal ganglion cell death or superior colliculus damage at the 8-week time point in any of the strains tested. These results demonstrate strain dependent responses to Ad5.MYOC.Y437H-induced ocular hypertension and pressure-induced optic nerve damage.

Dexamethasone-Induced Ocular Hypertension in Mice

“…Our findings agree with daytime/nighttime IOPs in POAG transgenic MYOC Y437H mice. 37 This diurnal IOP variation in mice has been reported previously.…”

The Olfactomedin Domain from Gliomedin Is a β-Propeller with Unique Structural Properties

“…Another human glaucoma mutation is Y437H, which also can induce disease when injected into mice (68). The corresponding residue in gliomedin (Tyr-480) lies in the middle of ␤-strand 4b, surrounded by many hydrophobic residues.…”

Gremlin Induces Ocular Hypertension in Mice Through Smad3-Dependent Signaling

“…Previously we have shown that intravitreal injections of Ad5 transgenes produce a more pronounced and consistent IOP response compared with intracameral injections in mouse eyes. 16,21,25,26 We have also demonstrated that Ad5.null, Ad5.GFP, and transgenes not associated with glaucomatous phenotypes have no effect on ocular hypertension. 16,21,25,26 …”

“…21,27 In all experiments involving A/J mice, IOP was measured using a noninvasive method in conscious mice with the TonoLab tonometer (Colonial Medical Supply, Franconia, NH, USA). In all experiments involving 129-Smad3 tm1Par /J mice, IOP was measured after anesthesia with 2.5% isoflurane þ 100% oxygen with the TonoLab tonometer.…”

“…5,7 We have also determined that TGFb2 signaling through the canonical Smad pathway is essential for TGFb2-induced ocular hypertension in mice. 21 Transforming growth factor-b2 signaling is regulated by bone morphogenetic proteins (BMPs) that control a variety of functions in different cell types, and are present in the TM. 9,22 Bone morphogenetic proteins are regulated by BMP antagonists, such as gremlin, which bind BMP ligands and block BMP binding to their receptors.…”