Primary congenital glaucoma-associated truncation of GJA1 modeled in mice

Abstract

Purpose : We identified a heterozygous de novo mutation in gap junction alpha-1 (GJA1) in the proband of a family (trio) with presumed non-syndromic primary congenital glaucoma (PCG). The c.1014dupC (NM_000165.4, p.D339Rfs*2) mutation is predicted to result in a C-terminal truncated protein. GJA1 mutations are associated with oculodentodigital dysplasia syndrome (ODDD), a collection of systemic issues that include glaucoma as a clinical phenotype. We engineered a mouse model harboring the mutation to determine the biological mechanisms underlying glaucoma development.

Methods : CRISPR-Cas9 genome-editing was employed to incorporate a c.1014_1015insAGGT (NM_10288.3; p.D339Rfs*2) Gja1 mutation into 129S1/SvlmJ inbred mice. Heterozygous (Het) mice were compared to wild-type (WT) counterparts for all phenotyping studies. Slit-lamp gonioscopy and optical coherence tomography (OCT) were performed to assess anterior chamber morphology and structure. Ocular tissues were also assessed histologically and by transmission electron microscopy (TEM). Retinal function was tested via electroretinography. Intraocular pressure (IOP) was measured by rebound tonometry at baseline, and after provocation (intra-peritoneal saline bolus and cyclomydril pupillary dilation).

Results : Gross assessment of Het mice revealed soft tissue syndactyly in 4%. Het mice showed increased pupil irregularities (6.2%, WT 2.4%). OCT imaging identified variable narrowing of the angle in Het mice. Ultrastructural examination by TEM in the Het mice was notable for aplastic/hypoplastic Schlemm’s canal (SC), collapsed beams, collagen loss, irregularly-shaped trabecular meshwork (TM) cells, and variable ciliary clefts. Retinal function and histology were similar between genotypes. Baseline IOP was 13.54 ± 0.42 mmHg in Het vs. 14.86 ± 0.51 mmHg in WT. Provocation increased Het IOP by 4.24 ± 0.21 mmHg vs. 2.11 ± 0.24 mmHg in WT. The provoked IOP increase was significantly higher in Het (n=25) versus WT mice (n=25) (p<0.001).

Conclusions : Protein C-terminal truncation in Gja1 mutant mice results in low penetrant ODDD traits. Defects in the outflow pathway are suggested by narrowing of the drainage angle, ultrastructural abnormalities in the SC/TM, and a near 2-fold increase in IOP delta under provoked conditions. Glaucoma in individuals with GJA1 mutations may be attributable to narrow angles.

This is a 2020 ARVO Annual Meeting abstract.