Helper Ad5.Cre-induced mutant myocilin expression in trabecular meshwork develops glaucoma in an inducible transgenic mouse model of myocilin glaucoma

Abstract

Purpose : The pathological mechanisms of glaucomatous damage to trabecular meshwork (TM) leading to elevation of intraocular pressure (IOP) are poorly understood due to lack of reproducible mouse model of Primary Open Angle Glaucoma (POAG). Mutations in myocilin (MYOC) gene are the most common genetic cause of POAG. Using site-specific knock in strategy, we developed a Cre-inducible transgenic mice that expresses DsRed-tagged Y437H mutant of human myocilin (Tg. Cre-MYOC^Y437H). The aim of this study to characterize the glaucoma phenotypes of Tg. Cre-MYOC^Y437H mice.

Methods : We utilized a TARGATT site-specific knock in strategy to generate cre-inducible transgenic mice of carrying human mutant MYOC with a tyrosine to histidine substitution at codon 437 tagged with DsRed fluorescent protein (C57BL/6J background). An intravitreal injection of helper adenovirus (HAd) 5 expressing Cre was performed in adult Tg.Cre-MYOC^Y437H mice to induce the expression of DsRed tagged mutant human myocilin. Myocilin expression in various ocular tissues was analyzed using qPCR, Western blotting, and immuno-staining. Glaucoma phenotypes including IOP, outflow facility, functional (PERG and VEP) and structural (RBPMS staining) loss of retinal ganglion cells (RGCs) and optic nerve degeneration (PPD staining) was performed at 10 and 15 weeks of injections.

Results : A single intravitreal injection of HAd 5 expressing Cre selectively induced human mutant myocilin protein in mouse TM. Importantly, HAd5.Cre injection resulted in significant and sustained IOP elevation in Tg.Cre-MYOC^Y437H mice starting from 2-weeks of injection. This IOP elevation was associated with reduced outflow facility and expression of mutant myocilin in TM. Remarkably, pattern ERG and VEP demonstrated a significant RGC functional loss and damage to the visual centers of the brain respectively (****P < 0.0001; n=10) at 10 and 15-weeks of injections. Consistent with this, we observed 15% loss of RGCs (p=0.000027 ***two tailed; n=5)) and optic nerve degeneration (15% reduction in axons; (_*P=0.0180 n=5).

Conclusions : Our findings suggest that Tg. Cre-MYOC^Y437H mice recapitulates clinical features of POAG patients with Y437H mutation and this model may be useful in studying pathological mechanisms of glaucomatous TM damage.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.