Pathogenic Microglia Orchestrate Neurotoxic Properties of Eomes-Expressing Helper T Cells

In addition to disease-associated microglia (DAM), microglia with MHC-II and/or IFN-I signatures may form additional pathogenic subsets that are relevant to neurodegeneration. However, the significance of such MHC-II and IFN-I signatures remains elusive. We demonstrate here that these microglial subsets play intrinsic roles in orchestrating neurotoxic properties of neurotoxic Eomes+ Th cells under the neurodegeneration-associated phase of experimental autoimmune encephalomyelitis (EAE) that corresponds to progressive multiple sclerosis (MS). Microglia acquire IFN-signature after sensing ectopically expressed long interspersed nuclear element-1 (L1) gene. Furthermore, ORF1, an L1-encoded protein aberrantly expressed in the diseased central nervous system (CNS), stimulated Eomes+ Th cells after Trem2-dependent ingestion and presentation in MHC-II context by microglia. Interestingly, administration of an L1 inhibitor significantly ameliorated neurodegenerative symptoms of EAE concomitant with reduced accumulation of Eomes+ Th cells in the CNS. Collectively, our data highlight a critical contribution of new microglia subsets as a neuroinflammatory hub in immune-mediated neurodegeneration.

Immune-mediated neurodegenerative trait provoked by multimodal derepression of long-interspersed nuclear element-1

Neurodegeneration is a process involving both cell autonomous and non-cell autonomous neuron loss, followed by a collapse of neural networks, but its pathogenesis is poorly understood. We have previously demonstrated that Eomes-positive helper T (Eomes + Th) cells recognizing LINE-1(L1)-derived prototypic antigen ORF1 mediate neurotoxicity associated with the neurodegenerative pathology of experimental autoimmune encephalomyelitis (EAE). Here, we show that Eomes + Th cells accumulate in the CNS of mouse models of authentic neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease (AD), and secrete the neurotoxic granzyme B after encounter with ORF1 antigen. Multimodal derepression of neuronal L1 transcription is observed in EAE and ALS/AD models during neurodegeneration in active and cell cycle-mediated manner, respectively. These data suggest that the adventitious concurrence of immune-mediated neurodegenerative traits by Eomes + Th cells and ectopic expression of L1-derived antigen(s) in the inflamed CNS may materialize a communal and previously unappreciated pathogenesis of neurodegeneration.

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Eomes + Th cells accumulate in the CNS with undergoing neurodegeneration in common

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Multimodal L1 derepression is emerged in neuron cells under neurodegeneration

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Eomes + Th cells recognize L1-ORF1 antigen to exert neurotoxicity via granzyme B

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Immune-mediated neurotoxicity may embody a novel pathogenesis of neurodegeneration

Expression of the orphan nuclear receptor NR4A2 is required for IL-17 production by Th17 cells and the induction of Th17-mediated autoimmunity (93.14)

Previously, we reported that NR4A2, an orphan nuclear receptor, is upregulated by peripheral blood cells during the human autoimmune disease multiple sclerosis (MS), as well as by peripheral blood cells and leukocytes infiltrating the central nervous system (CNS) during experimental autoimmune encecephalomyelitis (EAE). The pathology of MS and EAE is mediated by infiltration of both Th1 and Th17 cells into the CNS, but we reveal that upregulation of NR4A2 observed in CNS-infiltrating leukocytes and peripheral blood cells is most apparent amongst IL-17-secreting CD4+ T cells. Therefore, we examined the role of NR4A2 in the differentiation of these Th17 cells: transfection of naïve T cells with NR4A2 siRNA precludes IL-17 secretion when cultured under Th17 polarising conditions. However, such cells do proliferate and upregulate RORγt to the same extent as fully functional Th17 cells. IL-23 stimulation is critical in licensing IL-17 production by Th17 cells and that this depends on the upregulation of IL-23R by Th17 cells subsequent to autocrine IL-21 signalling. NR4A2 siRNA knock-down in CD4+ T cells prevents IL-21 production under Th17 polarising conditions and consequently such cells do not upregulate IL-23R. Addition of exogenous IL-21 circumvented NR4A2 knock-down, leading to IL-23R upregulation and IL-17 production. Furthermore, NR4A2 appears to be critical in generating Th17-mediated autoimmunity as systemic administration of NR4A2 siRNA prevented EAE induction.