Increased mitochondrial accumulation in trabecular meshwork is associated with ocular hypertension in a mouse model of myocilin glaucoma

Abstract

Purpose : Mutations in myocilin (MYOC) are the leading known genetic cause of glaucoma. Here, we developed a novel Cre-inducible transgenic mice that expresses DsRed-tagged mutant of human myocilin (Tg.Cre-MYOC^Y437H). The aims of this study to characterize the glaucoma phenotypes of Tg.Cre-MYOC^Y437H mice and to further explore whether mitochondrial accumulation is associated with trabecular meshwork pathology.

Methods : We utilized a TARGATT site-specific knock in strategy to generate cre-inducible transgenic mice of carrying human Y437H mutant MYOC DsRed (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 mutant human myocilin in the TM. 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) loss of retinal ganglion cells (RGCs) and optic nerve degeneration was performed at 10 and 15 weeks. TM pathology including ER and mitochondria was analyzed by transmission electron microscopy

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. 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=12) at 10 and 15-weeks of injections. Consistent with this, we observed 30% loss of RGCs ((****P < 0.0001; n=13 two tailed) and optic nerve degeneration (30% reduction in axons; (***P=0.0002 n=13). TM outflow pathway analysis by TEM observed that increased mitochondrial accumulation and ECM deposition (n=4). TEM analysis and immunostaining of the anterior segment revealed that mutant myocilin induced chronic ER stress and mitochondrial accumulation in the TM as evident from distended ER and increased ER stress and mitochondrial markers

Conclusions : Our findings suggest that abnormal accumulation of mutant myocilin in ER may induce mitochondrial damage, which can further contribute to TM cell death and IOP elevation.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.