Selective Upregulation of SIRT1 Expression in Retinal Ganglion Cells by AAV-Mediated Gene Delivery Increases Neuronal Cell Survival and Alleviates Axon Demyelination Associated with Optic Neuritis

Abstract

Optic neuritis (ON), the most common ocular manifestation of multiple sclerosis, is an autoimmune inflammatory demyelinating disease also characterized by degeneration of retinal ganglion cells (RGCs) and their axons, which commonly leads to visual impairment despite attempted treatments. Although ON disease etiology is not known, changes in the redox system and exacerbated optic nerve inflammation play a major role in the pathogenesis of the disease. Silent information regulator 1 (sirtuin-1/SIRT1) is a ubiquitously expressed NAD+-dependent deacetylase, which functions to reduce/prevent both oxidative stress and inflammation in various tissues. Non-specific upregulation of SIRT1 by pharmacologic and genetic approaches attenuates RGC loss in experimental ON. Herein, we hypothesized that targeted expression of SIRT1 selectively in RGCs using an adeno-associated virus (AAV) vector as a delivery vehicle is an effective approach to reducing neurodegeneration and preserving vision in ON. We tested this hypothesis through intravitreal injection of AAV7m8.SNCG.SIRT1, an AAV2-derived vector optimized for highly efficient SIRT1 transgene transfer and protein expression into RGCs in mice with experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis that recapitulates optic neuritis RGC loss and axon demyelination. Our data show that EAE mice injected with a control vehicle exhibit progressive alteration of visual function reflected by decreasing optokinetic response (OKR) scores, whereas comparatively, AAV7m8.SNCG.SIRT1-injected EAE mice maintain higher OKR scores, suggesting that SIRT1 reduces the visual deficit imparted by EAE. Consistent with this, RGC survival determined by immunolabeling is increased and axon demyelination is decreased in the AAV7m8.SNCG.SIRT1 RGC-injected group of EAE mice compared to the mouse EAE counterpart injected with a vehicle or with control vector AAV7m8.SNCG.eGFP. However, immune cell infiltration of the optic nerve is not significantly different among all EAE groups of mice injected with either vehicle or AAV7m8.SNCG.SIRT1. We conclude that despite minimally affecting the inflammatory response in the optic nerve, AAV7m8-mediated SIRT1 transfer into RGCs has a neuroprotective potential against RGC loss, axon demyelination and vison deficits associated with EAE. Together, these data suggest that SIRT1 exerts direct effects on RGC survival and function.

Treatment with MDL 72527 Ameliorated Clinical Symptoms, Retinal Ganglion Cell Loss, Optic Nerve Inflammation, and Improved Visual Acuity in an Experimental Model of Multiple Sclerosis

“…The loss of RGCs is a major characteristic feature of MS and EAE [ 20 , 21 , 67 , 68 ] and is recognized as a major cause of visual dysfunction in MS patients [ 69 , 70 ]. Similar to the findings from other laboratories, a significant reduction in RGCs was observed in the EAE retina in our studies.…”

“…The clinical disease was monitored daily in a blinded fashion by measuring the progression of paralysis as per the conventional grading system: 0, no disease; 1, complete loss of tail tonicity; 2, partial hind limb paralysis (uneven gate of hind limb); 3, complete hind limb paralysis; 4, complete hind and forelimb paralysis; and 5, moribund or dead [ 20 , 43 ]. Animals displaying paralysis on all four limbs and/or weight loss of more than 15% were sacrificed immediately.…”

“…ON is characterized by the acute development of visual field defects or visual acuity loss, with evidence of retinal ganglion cell (RGC) degeneration [ 17 , 18 , 19 ]. Experimental autoimmune encephalomyelitis (EAE) is a widely used rodent model to study MS-associated pathophysiology, including ON [ 20 , 21 , 22 ]. Earlier studies have shown that EAE mice develop retinal inflammation, RGC loss, Müller cell activation, infiltration of macrophages, and visual acuity changes [ 23 , 24 , 25 , 26 ].…”

Research Progress of Bioinspired Nanostructured Systems for the Treatment of Ocular Disorders

“…This study may revolutionize the therapeutic effect and accessibility of gene therapy for acquired retinal dystrophies or IRDs. Recently, the engineered AAV was also used to selectively upregulate the expression of silent information regulator 1 (SIRT1) in retinal ganglion cells of mice with experimental autoimmune encephalomyelitis (EAE) to increase neuronal cell survival and alleviate axon demyelination associated with optic neuritis [ 102 ]. The above data suggests a wide applicability and utility of gene therapy based on the recombinant AAV vector for retinal disorders occurring in the retinal pigment epithelium, photoreceptors, or ganglion cells.…”

Emerging Gene Therapy Technologies for Retinal Ganglion Cell Neuroprotection

“…116,117 Further studies delivered SIRT1 as a gene therapy and demonstrated its efficacy in reducing RGC death in traumatic optic neuropathy, optic neuritis, and glaucoma. 26,29,118,119 Other work with experimental models of glaucoma and traumatic optic neuropathy highlighted the significance of declining redox factors, linked to decreased expression of NAD+-synthetic enzyme, NMNAT2. Notably, levels of NAD+ were decreased, and supplementation with NAD+ and its precursors increased RGC survival.…”