NLRX1 Limits Inflammatory Neurodegeneration in the Anterior Visual Pathway

Chronic innate immune activation in the central nervous system (CNS) significantly contributes to neurodegeneration in progressive multiple sclerosis (MS). Using multiple EAE models, we explored the potential of the innate immune sensor NLRX1 to protect neurons in the anterior visual pathway from inflammatory neurodegeneration. To do this, we assessed retinal ganglion cell (RGC) density and optic nerve axonal degeneration, gliosis, and T-cell infiltration in Nlrx1-/- and wild-type (WT) EAE mice. Our results indicate that Nlrx1-/- mice exhibit significantly increased RGC loss and axonal injury compared to WT mice in both active immunization EAE and spontaneous opticospinal encephalomyelitis models. Adoptive transfer experiments, in which wild type T cells were transferred into lymphocyte-deficient Rag-/- mice to minimize the effects of Nlrx1 knockout on peripheral lymphocyte priming, revealed more severe microgliosis and astrogliosis in the optic nerve of Nlrx1-/-Rag-/- mice compared to Rag-/- mice, suggesting a regulatory role of NLRX1 in innate immune compartments. Transcriptome analysis in primary astrocytes demonstrated that NLRX1 negatively regulates TLR-mediated NF-κB activation. The novel pharmacologic NLRX1 activator LABP-66 decreased LPS-mediated gene expression of inflammatory cytokines and chemokines in mixed glial cultures. Moreover, treating EAE mice with oral LABP-66 after the onset of paralysis resulted in less anterior visual pathway neurodegeneration compared to vehicle. These data suggest that a pharmacologic NLRX1 activators attenuates glial immune activation and has the potential to limit inflammatory neurodegeneration in diseases, such as MS, where chronic CNS-compartmentalized inflammation may drive neurodegenerative pathology. This study highlights that NLRX1 could serve as a promising target for neuroprotection in progressive MS and other neurodegenerative diseases where chronic compartmentalized innate immune activation and neuroinflammation play a role.