Background Neuronal loss in multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), correlates with permanent neurological dysfunction. Current MS therapies have limited ability to prevent neuronal damage. Methods We examined whether oral therapy with SRT501, a pharmaceutical-grade formulation of resveratrol, reduces neuronal loss during relapsing/remitting EAE. Resveratrol activates SIRT1, an NAD+-dependent deacetylase that promotes mitochondrial function. Results Oral SRT501 prevented neuronal loss during optic neuritis, an inflammatory optic nerve lesion in MS and EAE. SRT501 also suppressed neurological dysfunction during EAE remission, and spinal cords from SRT501-treated mice had significantly higher axonal density than vehicle-treated mice. Similar neuroprotection was mediated by SRT1720, another SIRT1-activating compound; and sirtinol, a SIRT1 inhibitor, attenuated SRT501 neuroprotective effects. SIRT1 activators did not prevent inflammation. Conclusions These studies demonstrate SRT501 attenuates neuronal damage and neurological dysfunction in EAE by a mechanism involving SIRT1 activation. SIRT1 activators are a potential oral therapy in MS.

Optic neuritis is an inflammatory disease of the optic nerve that often occurs in patients with multiple sclerosis and leads to permanent visual loss mediated by retinal ganglion cell (RGC) damage. Optic neuritis occurs with high frequency in relapsing-remitting experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, with significant loss of RGCs. In the current study, mechanisms of RGC loss in this model were examined to determine whether inflammation-induced axonal injury mediates apoptotic death of RGCs. RGCs were retrogradely labeled by injection of fluorogold into superior colliculi of 6-7 week old female SJL/J mice. EAE was induced one week later by immunization with proteolipid protein peptide. Optic neuritis was detected by inflammatory cell infiltration on histological examination as early as 9 days after immunization, with peak incidence by day 12. Demyelination occurred 1-2 days after inflammation began. Loss of RGC axons was detected following demyelination, with significant axonal loss occurring by day 13 post-immunization. Axonal loss occurred prior to loss of RGC bodies at day 14. Apoptotic cells were also observed at day 14 in the ganglion cell layer of eyes with optic neuritis, but not control eyes. Together these results suggest that inflammatory cell infiltration mediates demyelination and leads to direct axonal injury in this model of experimental optic neuritis. RGCs die by an apoptotic mechanism triggered by axonal injury. Potential neuroprotective therapies to prevent permanent RGC loss from optic neuritis will likely need to be initiated prior to axonal injury to preserve neuronal function.

Multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE) are neurodegenerative diseases with characteristic inflammatory demyelination in the central nervous system, including the optic nerve. Neuronal and axonal damage is considered to be the main cause of long-term disability in patients with MS. Neuronal loss, including retinal ganglion cell (RGC) apoptosis in eyes with optic neuritis (ON), also occurs in EAE. However, there is significant variability in the clinical course and level of neuronal damage in MS and EAE. The current studies examine the mechanisms and kinetics of RGC loss in C57/BL6 mice immunized with myelin oligodendrocyte glycoprotein to induce a chronic EAE disease. Clinical progression of EAE was scored daily and vision was assessed by optokinetic responses. At various time points, RGCs were counted and optic nerves were examined for inflammatory cell infiltration. Almost all EAE mice develop ON by day 15 post-immunization; however, RGC loss is delayed in these mice. No RGC loss is detected 25 days post-immunization, whereas RGC numbers in EAE mice significantly and progressively decrease compared to controls from 35 to 50 days post-immunization. The delayed time course of RGC loss is in stark contrast to that reported in relapsing EAE, as well as in rats with chronic EAE. Results suggest that different clinical disease courses of optic nerve inflammation may trigger distinct mechanisms of neuronal damage, or RGCs in different rodent strains may have variable resistance to neuronal degeneration.

Resveratrol is a naturally occurring polyphenol that activates SIRT1, an NAD-dependent deacetylase. SRT501, a pharmaceutical formulation of resveratrol with enhanced systemic absorption, prevents neuronal loss without suppressing inflammation in mice with relapsing experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS). In contrast, resveratrol has been reported to suppress inflammation in chronic EAE, although neuroprotective effects were not evaluated. The current studies examine potential neuroprotective and immunomodulatory effects of resveratrol in chronic EAE induced by immunization with myelin oligodendroglial glycoprotein peptide in C57/Bl6 mice. Effects of two distinct formulations of resveratrol administered daily orally were compared. Resveratrol delayed the onset of EAE compared to vehicle-treated EAE mice, but did not prevent or alter the phenotype of inflammation in spinal cords or optic nerves. Significant neuroprotective effects were observed, with higher numbers of retinal ganglion cells found in eyes of resveratrol-treated EAE mice with optic nerve inflammation. Results demonstrate that resveratrol prevents neuronal loss in this chronic demyelinating disease model, similar to its effects in relapsing EAE. Differences in immunosuppression compared with prior studies suggest that immunomodulatory effects may be limited and may depend on specific immunization parameters or timing of treatment. Importantly, neuroprotective effects can occur without immunosuppression, suggesting a potential additive benefit of resveratrol in combination with anti-inflammatory therapies for MS.

Optic neuritis (ON), an inflammatory demyelinating optic nerve disease, occurs in multiple sclerosis (MS).Pathological mechanisms and potential treatments for ON have been studied via experimental autoimmune MS models. However, evidence suggests that virus-induced inflammation is a likely etiology triggering MS and ON; experimental virus-induced ON models are therefore required. We demonstrate that MHV-A59, a mouse hepatitis virus (MHV) strain that causes brain and spinal cord inflammation and demyelination, induces ON by promoting mixed inflammatory cell infiltration. In contrast, MHV-2, a nondemyelinating MHV strain, does not induce ON. Results reveal a reproducible virus-induced ON model important for the evaluation of novel therapies.Significant neuronal damage, with loss of retinal ganglion cell (RGC) axons that comprise the optic nerve, occurs following inflammatory optic neuritis (ON) and correlates with permanent vision loss (2,6,28). Experimental ON is a useful model to examine mechanisms of neuronal damage in multiple sclerosis (MS) because RGCs can readily be labeled and quantified (23). Rodents immunized with myelin proteins develop experimental autoimmune encephalomyelitis (EAE), a model of MS with inflammation in the brain, spinal cord, and optic nerves (12). Mechanisms of neuronal damage during ON in EAE have been examined but vary between chronic (16, 19) and relapsing (23) EAE models, suggesting that different causes of ON may mediate vision-threatening neuronal damage by distinct mechanisms.MS may be caused by a viral infection triggering an immune response against myelin (1, 26). Studies of virus-mediated models of MS are therefore important for our understanding of disease mechanisms and the development of novel therapies. While virus-induced models of MS exist (15, 26), the incidence of ON has not been characterized.Mouse hepatitis virus (MHV) infection in mice has been used as a model for virus-induced demyelination that mimics many pathological features of MS (9,13,15,27,29). Some neurotropic strains of MHV induce a biphasic neurological disease with acute meningoencephalitis, followed by chronic demyelination (15). Similarly to results for autoimmune mod- els of MS, Dandekar et al. recently demonstrated that axonal damage occurs in mice with MHV-induced demyelination (3).It is not known whether the inflammatory demyelination and axonal loss observed to occur in the MHV-infected mouse brain and spinal cord also affect the optic nerve.In the current study, we inoculated mice with plaque-purified demyelinating strain MHV-A59 (14, 15) and nondemyelinating strain MHV-2 (10). MHV-A59 infects a variety of cell types, including neurons, astrocytes, oligodendrocytes, microglia, and ependymal cells (11,13,15,30), in the central nervous system (CNS) and causes acute encephalitis, meningitis, hepatitis, and chronic demyelination. In contrast, MHV-2, a strain closely related to MHV-A59, has a limited ability to invade the brain and spinal cord, causing meningitis without encephalitis or demyelination ...

Following intracranial inoculation, neurovirulent mouse hepatitis virus (MHV) strains induce acute inflammation, demyelination and axonal loss in the CNS. Prior studies using recombinant MHV strains that differ only in the spike gene, which encodes a glycoprotein involved in virus-host cell attachment, demonstrated that spike mediates anterograde axonal transport of virus to the spinal cord. A demyelinating MHV strain induces optic neuritis, but whether this is due to retrograde axonal transport of viral particles to the retina, or if it is due to traumatic disruption of retinal ganglion cell axons during intracranial inoculation is not known. Using recombinant isogenic MHV strains, we examined the ability of recombinant MHV to induce optic neuritis by retrograde spread from the brain through the optic nerve into the eye following intracranial inoculation. Recombinant demyelinating MHV induced macrophage infiltration of optic nerves, demyelination and axonal loss whereas optic neuritis and axonal injury were minimal in mice infected with the non-demyelinating MHV strain that differs in the spike gene. Thus, optic neuritis was dependent on a spike glycoprotein-mediated mechanism of viral antigen transport along retinal ganglion cell axons. These data indicate that MHV spreads by retrograde axonal transport to the eye and that targeting spike protein interactions with axonal transport machinery is a potential therapeutic strategy for CNS viral infections and associated diseases.

Corticosteroids can suppress optic neuritis and prevent RGC loss if treatment is initiated before optic nerve inflammation onset. Treatment is less effective after inflammation begins. Results suggest that chronic immunomodulation may prevent recurrent optic neuritis and RGC damage.

Optic neuritis is an inflammatory demyelination of optic nerve often occurring in multiple sclerosis (MS) patients. Mice with experimental autoimmune encephalomyelitis (EAE), an MS model, develop optic neuritis, but it is detected histologically after sacrifice, limiting the ability to monitor progression or treatment in vivo. We examined whether pupillary light responses measured by pupillometry can identify eyes with optic neuritis in EAE mice. C57BL/6 mice were exposed to unilateral light flashes of increasing intensity at 10 second intervals (4.7, 37, and 300 μW/cm2). Pupillary responses were recorded with a commercially available pupillometer. EAE was then induced by immunization with myelin oligodendrocyte glycoprotein. Pupillometry was repeated up to 17 days post-immunization, and responses were correlated with optic nerve inflammation. By day 17 post-immunization, 90% of EAE eyes had optic nerve inflammation. EAE eyes had significantly reduced pupillary constriction compared to control eyes. Mice exhibited more than a 25% decrease in pupillary constriction in at least one eye by days 13-15 post-immunization. In some eyes, pupil responses decreased prior to onset of detectable inflammation. Results show that pupillometry detects decreased optic nerve function in experimental optic neuritis, even in the absence of histological detection. Measuring pupillary constriction allows in vivo identification and functional assessment of eyes with optic neuritis that will be useful in evaluating potential therapies over time. Furthermore, results demonstrate that decreased visual function occurs early in optic neuritis, before optic nerve inflammation reaches its peak level.