CUR - The Council on Undergraduate Research

Demyelination and Interferon Signaling in Axons Cause Retrograde Upregulation of ISGylation Pathway Genes

Kenneth R. David, Benjamin D. S. Clarkson, Ph.D., Charles Howe, Ph.D., Department of Neurology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905

Cognitive impairment in Multiple Sclerosis (MS), an autoimmune disease of the central nervous system, is associated with diffuse gray matter injury but remains poorly understood. Given that axons span both white and gray matter regions, signals within these axons may contribute to the spread of diffuse injury in the brain. We show that retrograde interferon-gamma (IFNg) signaling in axons (in vitro human and mouse) and demyelination (mouse in vivo) cause transcriptional and translational changes in neuronal cell bodies. Chief among the candidate signaling pathways identified is ISGylation, a process whereby a multitude of cellular proteins are modified by the attachment of one or more ISG15 molecules. Using custom adeno-associated viral vectors, we tested how altering ISGylation in neurons affects neuronal synaptic function and how it affects neuronal responsiveness to specific inflammatory factors in cell cultures. We also measured ISGylation in human MS brain tissues to see if neuronal ISGylation correlates with gray matter injury in MS. We report early evidence that increased neuron ISGylation alters the composition of neuron-derived extracellular vesicles. Microglia treated with extracellular vesicles from neurons overexpressing ISGylation pathway genes exhibited morphology consistent with increased phagocytic activity and increased mRNA expression of inflammatory cytokines including: CCL2, IL1b, TNFa, iNOS, CXCL10, CCL5, and IL6. At this point, it is still unclear how these changes are related to gray matter pathology; however, microglial activation by these vesicles may be involved in driving synapse loss as activated microglia are capable of stripping neuronal synapses.

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