Intravitreal administration of AAV2.soluble Fas ligand gene therapy following glaucoma injury restores retinal ganglion cell function and stops disease progression

Abstract

Purpose : In the normal eye, Fas ligand (FasL) is primarily expressed as a soluble protein (sFasL) essential in maintaining ocular immune privilege and inhibiting inflammation. In the DBA/2J mouse model of glaucoma, decreased expression of sFasL and increased expression of membrane FasL (mFasL) correlates with glial activation and the development of glaucoma. We previously demonstrated that intravitreal injection of AAV2.sFasL prior to elevation of intraocular pressure (IOP) prevents axon degeneration and death of retinal ganglion cells (RGCs) in chronic and inducible mouse models of glaucoma. We hypothesize that AAV2.sFasL promotes RGC survival in part, through inhibition of microglia activation and restoration of the neuroprotective environment of the eye. The goal of this study was to determine if treatment with AAV2.sFasL after glaucoma injury can reestablish the homeostatic phenotype of retinal microglia and restore function of dysfunctional RGCs.

Methods : Intracameral injection of microbeads (control: saline) was used to elevate IOP in WT B6 mice. IOP and RGC function were monitored by rebound tonometry and pattern ERG (pERG), respectively. At 3 wks after microbead injection, pERG was performed in all mice and two groups of mice were euthanized (pre-treatment baseline). A third group of mice received intravitreal AAV2.sFasL or control AAV2 and pERG was performed monthly until mice were euthanized at 6 months post treatment. After euthanasia, RGC survival (Brn3a staining) and microglia activation (measurement of the longest process length) were assessed. Retinal expression of sFasL and mFasL was assessed by western blot.

Results : Pre-treatment baseline pERG (3 wks post microbeads) revealed a significant loss of RGC function as compared to saline controls, which coincided with a significant (i) increase in mFasL and loss of sFasL, and (ii) increase in microglia activation. At 6 months post AAV2.sFasL treatment, RGC function by pERG was significantly restored as compared to control mice and coincided with restoration of a homeostatic microglia phenotype. Microglia remained activated in control AAV2 treated mice at 6 months.

Conclusions :
Gene therapy using AAV2.sFasL, initiated after glaucoma injury, reverts activated microglia to a homeostatic phenotype, restoring the neuroprotective environment and RGC function.

This is a 2020 ARVO Annual Meeting abstract.