Multiple sclerosis (MS) is a chronic autoimmune disease that affects millions each year. It causes the body to mistakenly attack its own immune system, causing brain inflammation. One of the ways it does this is through a process called demyelination, which destroys the protective coverings of nerves called myelin sheaths. It is known that inflammation is what triggers demyelination, which is contributing to the progression of MS. Current therapies focus on targeting the inflammatory stage of the disease, but therapies targeting progressive phase of MS are not available. A previous study done in my lab, found that during demyelination, there is an increase of Interferon Stimulated Gene 15 (ISG15) expression in cortical neurons in mice demyelinating models and is elevated in postmortem tissue from the cortex of MS patients suggesting that ISG15 expression, might be a shared stress response in neurons following primary oligodendrocyte loss and inflammatory demyelination. ISG15 is known to be a key contributor to the immune system and is primarily known for its role in modulating immune cells. However, its role in demyelination and neurodegenerative disorders is still unknown. However, we hypothesize that by ablating ISG15 in all cells, as well as specifically in neurons, this will lead to a preservation of NeuN+ cells in the cortex during cuprizone induced demyelination. To test this hypothesis, two groups (A and B) were selected, each with two genotypes of mice in each group: a control, and experimental. In group A, the control group was the B6 wildtype (WT) mice with ISG15 expression in all cell types. The experimental group had the ISG15 conventional knockout (KO) mice group, that did not have ISG15 expression in any of the cell types. In group B, the regular littermate control mice group was Syn Cre-, with ISG15 expression in all cell types. The experimental mice group was the ISG15 conditional knockout (cKO; Syn Cre+ ISG15 fl/fl) group, having ISG15 present in all cell types except neurons; allowing to study its role only in neurons. Experimental design started with inducing demyelination in these mice through a cuprizone diet, starting at 6 weeks old. For the WT and KO mice, at 3, 6 and 12 weeks after starting the cuprizone diet. For the Syn Cre+ and Syn Cre- mice, they were only perfused and collected at 6 weeks after starting the cuprizone diet. Brain slices were stained with a NeuN antibody and counterstained with DAPI. Using the confocal microscope, the stained slices were imaged, and they were quantified for NeuN+ cells in the cortex using stereological sampling parameters. At 12 weeks on a cuprizone diet, preliminary results showed neuron density was preserved in the ISG15 knockout genotype compared to the wildtype control in demyelinating mouse models. In conclusion, our preliminary finding was that ISG15 deficiency protects neurons during demyelination.
