Spinal Cord Microglia Exhibit Impaired Repair Responses to Myelin Damage

BackgroundMultiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS) that affects both the brain and spinal cord, although the brain has historically received greater attention. In the inducible, oligodendrocyte-specific knockout model of Myrf, which results in white matter damage to both the brain and spinal cord, our laboratory previously demonstrated that the brain undergoes partial remyelination following white matter damage, whereas the spinal cord fails to do so. We also observed that brain microglia display a much stronger activation than spinal cord microglia in this model. Microglia regulate remyelination by clearing myelin debris, processing resulting lipids, and modulating an inflammation response. ResultsHere, to test our hypothesis, we characterized microglial phenotypes during demyelination in both tissues. The brain exhibited greater early microglial recruitment and higher baseline expression of activation and phagocytic markers, suggesting a primed state for responding to damage. In contrast, spinal cord microglia showed delayed phagocytic marker expression, sustained inflammation, and a predominately amoeboid morphology during demyelination. ConclusionsTogether, these findings indicate that brain microglia mount a timely and coordinated response to demyelination that supports remyelination, whereas spinal cord microglia adopt a dysfunctional phenotype that may contribute to impaired myelin repair.