Abstract

SIRT1 prevents retinal ganglion cell (RGC) loss in models of optic neuropathy following pharmacologic activation or genetic overexpression. The exact mechanism of loss is not known, prior evidence suggests this is through oxidative stress to either neighboring cells or RGC specifically. We investigated the neuroprotective potential of RGC-selective SIRT1 gene therapy in the optic nerve crush (ONC) model. We hypothesized that AAV-mediated overexpression of SIRT1 in RGCs reduces RGC loss, thereby preserving visual function. Cohorts of C57Bl/6J mice received intravitreal injection of experimental or control AAVs using either a ganglion cell promoter or a constitutive promoter and ONC was performed. Visual function was examined by optokinetic response (OKR) for 7 days following ONC. Retina and optic nerves were harvested to investigate RGC survival by immunolabeling. The AAV7m8-SNCG.SIRT1 vector showed 44% transduction efficiency for RGCs compared with 25% (P > 0.05) by AAV2-CAG.SIRT1, and AAV7m8-SNCG.SIRT1 drives expression selectively in RGCs in vivo. Animals modeling ONC demonstrated reduced visual acuity compared to controls. Intravitreal delivery of AAV7m8-SNCG.SIRT1 mediated significant preservation of the OKR and RGC survival compared to AAV7m8-SNCG.eGFP controls, an effect not seen with the AAV2 vector. RGC-selective expression of SIRT1 offers a targeted therapy for an animal model with significant ganglion cell loss. Over-expression of SIRT1 through AAV-mediated gene transduction suggests a RGC selective component of neuro-protection using the ONC model. This study expands our understanding of SIRT1 mediated neuroprotection in the context of compressive or traumatic optic neuropathy, making it a strong therapeutic candidate for testing in all optic neuropathies.

Highlights

  • The irreversible effects of traumatic optic neuropathy (TON) can result from direct impulse or indirectly by shearing or stretch of the optic nerve [1]

  • Compared with the 25% retinal ganglion cell (RGC) transduction displayed by the AAV2-CAG.enhanced green fluorescent protein (eGFP) vector, AAV7m8-SNCG.eGFP achieved ~44% RGC transduction by quantifying the number of eGFP positive RGCs labeled with BRN3A antibody in retinal whole mounts (Fig. 2A1, A2)

  • Our results suggest that SIRT1 driven by a RGC specific promoter delayed loss of visual acuity and enhanced RGC survival in Optic nerve crush (ONC)

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Summary

Introduction

The irreversible effects of traumatic optic neuropathy (TON) can result from direct impulse or indirectly by shearing or stretch of the optic nerve [1] The damage occurs at the level of axons, disrupting critical connections needed to maintain retinal ganglion cell (RGC) function. Mechanisms such as vascular and inflammatory mediators of RGC death have been implicated in perpetuating the process of RGC death, the true pathophysiology is likely direct cell death [2]. Optic nerve crush (ONC) induces axonal degeneration, followed by a gradual death of RGCs, which results in irreversible vision loss [3], providing a fast, reproducible technique to observe RGC decline, as well as observe effects of novel neuroprotective therapeutic approaches [4]

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