Abstract
Purpose :
Uncovering the pathogenesis of human POAG has been hindered by a paucity of appropriate animal models. POAG is an idiopathic and leading cause of irreversible blindness. A progressive optic neuropathy develops in association with major risk factors of central corneal thickness(CCT) and increasing age and IOP in the presence of open angles. Elevated aqueous humor TGFβ2 is common to many populations with POAG. Fibrillin–1 is a major extracelullar matrix protein that serves as a repository for TGFβ. We sought to determine if spontaneously occurring tight skin fibrillin–1 mutant mice(Tsk) develop abnormal aqueous TGFβ2 and phenotypic features resembling human POAG.
Methods :
The following studies were performed in Tsk and wild–type(WT) mice: TGFβ2 levels in aqueous humor by ELISA; TGFβ2 activity by MINK epithelial cell–based luciferase assay; IOP measurement and validation by TonoLab and manometry; central corneal thickness(CCT) and angle morphology by OCT; analysis for retinal ganglion cells(RGC) loss, glial reactivity, and apoptosis by immunohistochemistry; optic nerve degeneration by paraphenylenediamine(PPD) and transmission electron microscopy(TEM); RGC function by testing scotopic threshold response(STR) and pattern electroretinogram(PERG).
Results :
Aqueous TGFβ2 levels and activity were significantly higher in Tsk than WT mice(p<0.0004), mirroring human findings in POAG and normal control eyes(p<0.00005). CCT was 20% lower in Tsk than WT mice(p<0.003). Tonometric IOP was systematically underestimated in Tsk relative to WT mice based on intraocular manometry reference measurements and this difference was adjusted for. Tsk IOP was higher than WT(p<0.0001) and rose with age(p=0.04) in the presence of open anterior chamber angles. RGC counts were fewer in Tsk than WT mice(p<0.05) and associated with increased glial reactivity, apoptosis, and axon loss in superotemporal and temporal optic nerve regions(p<0.03). TEM showed axonal enlargement with disordered axoplasm, neurofilaments, and astrocyte processes. Visual STR(p<0.002) and PERG(p<0.007) responses were reduced in Tsk mice indicating RGC dysfunction.
Conclusions :
We have uncovered defining features of human POAG in Tsk mice. Our data implicates altered fibrillin–1 homeostasis as a candidate pathogenic mechanism underlying aqueous humor TGFβ2 dysregulation and a POAG phenotype.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.