Mitochondrial Superoxide Dismutase Modulates Experimental Optic Neuritis

Abstract

Abstract: : Purpose: To test whether a viral vectored ribozyme that depletes the mRNA of manganese superoxide dismutase (SOD2) aggravates optic neuritis and whether genetic augmentation of SOD2 increasing cellular defenses against reactive oxygen species (ROS) rescues optic neuritis in experimental allergic encephalomyelitis (EAE). EAE is an inflammatory autoimmune disorder of primary central nervous system demyelination that has been frequently used as an animal model for the human disease multiple sclerosis (MS). Methods:The adeno–associated vector (AAV), pTRUF12 was used to accept the hammerhead ribozyme gene designed to cleave the mRNA of SOD2 or to express the human SOD2 gene. The resulting pTR–RzSOD2 and pTR–hSOD2 were amplified and packaged into rAAV2. Two microliters of AAV–RzSOD2 or AAV–hSOD2 were injected into the right eyes of DBA/1J mice. Control left eyes received AAV containing the green fluorescent protein (gfp) gene. Six weeks after viral injection, the mice were sensitized for EAE, and then euthanized one month later for histopathologic examination. Results: Relative to controls, left eyes of animals sensitized with EAE, the AAV expressing ribozyme led to severe optic nerve head swelling by 30% (p>0.05), significant loss of retinal ganglion cells by 21.5% (p<0.0002), severe axonal destruction and demyelination in the retrobulbar optic nerve increasing demyelination by 27% (p0.05), optic nerve cell infiltration by 29% (p<0.01) and demyelination by 29.3% (p<0.01). Conclusions:Knocking down the mRNA for the SOD2 gene appeared to exacerbate optic neuritis while suppression of oxidative stress by AAV–mediated transfer of human SOD2 conferred protection in EAE mouse. These results not only implicate ROS in the pathogenesis of optic neuritis, but also suggest anti–ROS gene therapy as a new treatment avenue for patients with optic neuritis and MS. #

Keywords: gene transfer/gene therapy • oxidation/oxidative or free radical damage • neuro–ophthalmology: optic nerve