Modulation of repopulating microglia in multiple sclerosis models with implication for neuroprotection

Abstract

Microglia play a critical role in CNS pathologies, including multiple sclerosis (MS), and their modulation offers therapeutic potential, especially during progressive disease courses. Using cell culture and experimental autoimmune encephalomyelitis (EAE) models, we investigated microglial dynamics during depletion and repopulation and their modulation using siponimod, an established CNS-penetrating MS medication. Repopulating microglia exhibited a transient reactive state (CD86, MHC-II, Il1b, Tnf). Siponimod modulated microglia populations, increasing CD163+ and CX3CR1+ while reducing CD86+MHC-II+ cells, accompanied by a reduction of neuronal damage. Proteomic spinal cord analysis revealed protein expression alterations by microglia repopulation and siponimod linked to inflammation, myelination, and neuronal structural organization, supported by RNA sequencing of the spinal cord. The neuroinflammation-attenuating role of siponimod could be linked to cell maintenance and myelin formation-associated processes. These findings highlight the capacity of pharmacological interventions to modulate microglia, offering new insights into therapeutic strategies targeting microglial activity in neuroinflammatory diseases.