Inducible Nitric Oxide Synthase (NOS2) is Required for Oligodendrocyte Lineage Progression and Remyelination in Murine β-Coronavirus-Induced Neuroinflammation

Abstract Background Multiple sclerosis (MS) and post-viral demyelinating encephalomyelitis are characterized by chronic central nervous system (CNS) inflammation, myelin sheath destruction, and impaired tissue repair. While inducible nitric oxide synthase (NOS2) is traditionally viewed as a cytotoxic mediator in acute neuroinflammation, its temporal role, from myelin loss to the long-term endogenous remyelination phase, has remained controversial and poorly defined. Using a murine β-coronavirus (MHV-RSA59) model of neuroinflammation, we investigated the requirement for NOS2 during the myelin loss and repair phase (days 30 to 60 post-infection). Method Age-matched C57BL/6 wild-type (WT) and NOS2-/-mice were intracranially inoculated with 10,000 PFU of RSA59. Animals were euthanized at defined time points (day 30 and day 60 post-infection) to harvest the tissue samples. Luxal Fast Blue (LFB) staining, immunofluorescence (IF), immunoblotting, immunohistochemistry, and flow cytometry were performed on the RSA59-infected brain and spinal cord samples of NOS2-/- and WT mice. Results Our recent findings revealed that NOS2-/- mice, compared to WT mice, showed persistent demyelinating plaques, reduced myelin restoration, as indicated by the expression of myelin-forming proteins, and a diminution of oligodendrocyte precursor cells (OPCs) and mature oligodendrocytes during the remyelination phase. This delayed regenerative process in the absence of NOS2 was associated with prolonged activation of CNS-resident microglia and an infiltrated myeloid cell population, which may lead to a dysregulated inflammatory environment in the CNS. Mechanistically, loss of NOS2 led to more phagocytic activity in CNS-resident microglia and infiltrating myeloid cells. Our findings establish that NOS2-derived signals are essential for clearing inflammatory debris and transitioning myeloid cells from a pro-inflammatory state toward a pro-regenerative phenotype, thereby creating a permissive microenvironment for myelin repair. Conclusion This study elucidates how NOS2 regulates the balance between pathological damage and tissue repair. Also, our current research highlights NOS2 not merely as a marker of inflammation, but as a crucial protective factor required for effective myelin regeneration in virus-induced neuroinflammatory demyelination.