AAV2-mediated GRP78 Transfer Alleviates Retinal Neuronal Injury by Downregulating ER Stress and Tau Oligomer Formation

Abstract

PurposeRetinal ganglion cell (RGC) death following axonal injury occurring in traumatic optic neuropathy (TON) causes irreversible vision loss. GRP78 is a molecular chaperone that enhances protein folding and controls activation of endoplasmic reticulum (ER) stress pathways. This study determined whether adeno-associated virus (AAV)-mediated gene transfer of GRP78 protected RGCs from death in a mouse model of TON induced by optic nerve crush (ONC).MethodsONC was induced by a transient crush of optic nerve behind the eye globe. AAV was used to deliver genes into retina. Molecules in the ER stress branches, tau oligomers, and RGC injury were determined by immunohistochemistry or Western blot.ResultsAmong tested AAV serotypes, AAV2 was the most efficient for delivering genes to RGCs. Intravitreal delivery of AAV2-GRP78 markedly attenuated ER stress and RGC death 3 days after ONC, and significantly improved RGC survival and function 7 days after ONC. Protein aggregation is increased during ER stress and aggregated proteins such as tau oligomers are key players in neurodegenerative diseases. AAV2-GRP78 alleviated ONC-induced increases in tau phosphorylation and oligomerization. Furthermore, tau oligomers directly induced RGC death, and blocking tau oligomers with tau oligomer monoclonal antibody (TOMA) attenuated ONC-induced RGC loss.ConclusionThese data indicate that the beneficial effect of AAV2-GRP78 is partially mediated by the reduction of misfolded tau, and provide compelling evidence that gene therapy with AAV2-GRP78 or immunotherapy with TOMA offers novel therapeutic approaches to alleviate RGC loss in TON.

Neuronal Epac1 mediates retinal neurodegeneration in mouse models of ocular hypertension

“…injection of a mixture of 100 mg/kg ketamine and 10 mg/kg xylazine. After pupils were dilated with tropicamide and phenylephrine, mice were positioned on the imaging platform for radial and annular scans with a Spectral Domain Ophthalmical Imaging System (Envisu R2200, Bioptigen; Ha et al, 2018;Liu et al, 2017;Yang et al, 2012a). A representative radial B-scan from the same location of the retina was selected for illustrative purposes only.…”

The Susceptibility of Retinal Ganglion Cells to Optic Nerve Injury is Type Specific

“…ONC is a commonly used model for RGC injury due to TON or glaucoma. Although most of the experiments were performed using similar cross-action forceps, which apply a constant and consistent force to press on the optic nerve by the pressure from the self-clamping action of the forceps, different studies clamped the optic nerve for a different length of time (from 3 s to 60 s) [52][53][54][55][56][57][58]. To determine the potential variation by the ONC procedure on RGC death, we first tested whether various durations of clamping cause RGCs to die to a different extent.…”

Endoplasmic reticulum stress and the protein degradation system in ophthalmic diseases

“…The ER is an important site for protein synthesis, and therefore, if the function of the ER is disrupted by various pathological factors, the excessive accumulation of unfolded or misfolded proteins in the ER may eventually lead to ER stress. Many pathological conditions can lead to ER stress, such as hypoxia, oxidative stress, aging, or metabolic disorders (Lenox et al, 2015;Rozpedek et al, 2016;Rutkowski & Hegde, 2010;Zhu et al, 2018). When ER stress happens, the UPR is activated as a protective mechanism to restore the balance of the ER environment.…”

“…For example, a recent study indicated that ER stress is detrimental for retinas in the early stages of DR, and suppressing ER stress may protect retinas against visual deficits caused by hyperglycemia (Raji et al, 2018). Moreover, in a mice model of TON induced by optic nerve crush (ONC), ER stress results in RGC death, however suppressing ER stress through GRP78 overexpression is an effective way to protect RGC from death (Ha et al, 2018). This suggests that reducing the pathological factors that result in ER stress and maintaining cell homeostasis are key factors in sustaining cell physiological functions.…”