SIRT1-Based Gene Therapy Targets a Gene Program Involved in Mitochondrial Turnover in Experimental Autoimmune Encephalomyelitis

Abstract

Purpose : Retinal ganglion cell (RGC) loss and damage to their axons cause irreversible blindness in optic neuropathies. Experimentally tested, pharmacologically- or adeno-associated virus (AAV)-based interventions enhancing expression or activity of SIRT1, an NAD⁺-dependent deacetylase, have proven to promote, at least in part, survival of RGCs following injury. Herein, we used transcriptomic profiling and a mouse model of optic neuritis to determine the molecular signatures of RGC death and SIRT1-mediated neuroprotection.

Methods : Eight-week-old C57BL/6 mice (3 animals/group) are intravitreally injected with either control or therapeutic AAV expressing a γ-synuclein promoter-driven human SIRT1 cDNA (AAV-SIRT1) targeting SIRT1 expression to RGCs. Thereafter, mice are immunized with 300 μg of MOG_35-55 (myelin oligodendrocyte glycoprotein) to induce optic neuritis characteristic of this experimental autoimmune encephalomyelitis (EAE) model. Control mice are immunized with a MOG_35-55-free emulsion. RNA sequencing and pathway enrichment analyses are performed to determine transcriptomic changes among retinas from control and EAE mice with and without AAV-SIRT1 treatments, 8 weeks after the onset of EAE.

Results : The most upregulated retinal genes in EAE mice include those involved in inflammation and immune responses as well as apoptotic mitochondrion changes. EAE upregulated the expression of genes affecting mitophagy (e.g., ATG4), mitochondrial transport (e.g., IPO-6, XPO-6), monocarboxylic acid transport (e.g., ABCG2) and mitochondrial localization (e.g., Chrna4, Scn9a). SIRT1 treatment reversed the changes of numerous gene programs associated with EAE. Phagocytosis, inflammatory, and metabolic processes are among the functional pathways affected by AAV-mediated SIRT1 expression in RGCs in EAE mice. Targeted expression of SIRT1 to RGCs downregulated the expression of SIRT1 target and mitophagy genes (e.g., ATG2B, Arifip1) which were upregulated by EAE alone.

Conclusions : AAV-mediated SIRT1 expression in RGCs reverses the effects of EAE on numerous SIRT1 target genes and downregulates a gene program associated with cell death and mitochondrial turnover. SIRT1 expression likely enhances RGC survival by preserving mitochondrial function and increasing the bioenergetic capacity of RGCs in the face of injury.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.