Westphal, Maria

Neurons upregulate major histocompatibility complex class I (MHC I) during demyelination, enabling the presentation of self-antigens to cytotoxic CD8 + T cells. While this phenomenon is well described in multiple sclerosis lesions, its functional significance for disease progression remains poorly understood. Here, we test the hypothesis that neuronal MHC I expression promotes CD8 + T cell-mediated neurodegeneration in demyelinating disease. Using genetic and viral approaches to selectively ablate β ₂-microglobulin (β₂M) in neurons, we demonstrate that the loss of neuronal MHC I limits antigen presentation, attenuates the activation of neuron-antigen–specific CD8 + T cells, and reduces the recruitment of these cells to the demyelinated central nervous system (CNS). In myelin oligodendrocyte glycoprotein (MOG₃₅–₅₅)-induced experimental autoimmune encephalomyelitis, CD8 + T cell ablation during active disease limited neuronal injury and improved clinical recovery. Similarly, neuronal β ₂M ablation decreased clinical disease burden without affecting CNS T cell infiltration. Likewise, in the context of cuprizone intoxication, neuronal β ₂M deletion reduced peripheral activation and CNS recruitment of CD8 + T cells recognizing a neuron-restricted neoantigen. It protected neoantigen-expressing neurons from cognate CD8 + T cell-mediated cytotoxicity. Collectively, these findings identify neuronal MHC I–dependent antigen presentation as a driver of both the immune surveillance of neuronal antigens and neuronal injury during demyelination.

Abstract Background Significant proportion of inflammatory bowel disease (IBD) patients respond inconsistently to therapies, underscoring disease complexity. Interleukin 21 (IL21) is highly expressed during IBD. In addition to T helper (Th) cells, inflammatory regulatory T cells (Tregs) have been linked to refractory IBD. Thus, we explored the metabolic role of IL21 in inducing Treg dysfunction and IBD. Methods Human Tregs and Th cells were subjected to transcriptional profiling and metabolic phenotyping. Colitis was induced in Rag1−/− mice by naïve CD4 T cell adoptive transfer. Results IL21 stimulation of human Tregs induced glycolysis and OXPHOS. In agreement, IL21 enhanced the expression of genes associated with glycolysis, anabolism, and OXPHOS, leading to inflammatory cytokine production. Mechanistically, we found disruption to mitochondrial integrity with concomitant activation of glycogen synthase kinase 3 (GSK3) β, a kinase known to prevent mitochondrial pyruvate metabolism. IL21-induced GSK3β activation was accompanied by pyruvate and lactate buildup. Notably, GSK3 inhibition or supplementation with membrane-permeable methyl pyruvate abrogated metabolic wiring of and inflammatory responses by IL21-stimulated Tregs and effector Th cells. These results suggest that impaired mitochondrial pyruvate metabolism is a feature of inflammatory CD4 T cells. Lastly, GSK3 inhibition prevented pathogenic CD4 T cell-induced colitis in mice, as evidenced by reduced Mouse Colon Histology Index and serum inflammatory cytokines. Conclusions IL21 engages Tregs in a hypermetabolic state that augments inflammatory cytokine production. Therefore, desensitizing CD4 T cells to IL21 may also augment Treg function during IBD. Supported by NIDDK award K01DK124358, the Center for Cell Signaling in Gastroenterology (P30DK084567), and the Mayo Clinic Center for Biomedical Discovery.

Background Significant proportion of inflammatory bowel disease (IBD) patients continue to respond inconsistently to therapies, underscoring disease complexity and the need for efficacious treatment. Interleukin 21 (IL‐21), which is known to support T helper (Th) cell function, is highly expressed within inflamed intestinal tissues of IBD patients compared to healthy controls. In addition, inflammatory regulatory T cells (Tregs) have been linked to refractory human IBD. Given that healthy Tregs are critical for self‐tolerance and prevention of IBD, we investigated the metabolic role of IL‐21 in instigating Treg dysfunction and the therapeutic ramifications of targeting metabolism pathways during IBD pathogenesis. Methods Human Tregs as well as relevant control effector Th cells were generated from naïve CD4 + T cells isolated from healthy blood donors. Microarray analysis was utilized for targeted metabolic transcriptional profiling. Immune phenotyping was assessed by fluorescence‐activated cell sorting. Metabolic phenotyping of cells was assessed by Seahorse flux analysis and mass spectrometry‐based metabolomics. Ultrastructural analysis of mitochondria was performed by confocal and transmission electron microscopy. Intestinal inflammation was induced in Rag1 ‐/‐ (T and B cell deficient) mice by the adoptive transfer of pathogenic naïve CD4 + T cells. Results Acute IL‐21 stimulation of human Tregs induced glycolysis and fluctuations in mitochondrial respiration (i.e. oxidative phosphorylation – OXPHOS), as assessed by Seahorse flux analysis. In agreement, microarray analysis, validated by qPCR, revealed an IL‐21‐mediated increase in the expression of genes associated with glycolysis and pathways known to support anabolic and OXPHOS metabolism, thus resembling a hypermetabolic state. Furthermore, IL‐21 stimulation rendered Tregs susceptible to inflammatory response, as evidenced by the production of effector Th cell‐associated cytokines such as interferon γ, tumor necrosis factor, IL‐17A, and IL‐17F. Exploring the mechanisms underlying IL‐21‐induced effects, we found significant disruption of mitochondrial integrity with concomitant activation of glycogen synthase kinase 3 (GSK3) β, a kinase known to prevent pyruvate entry into the mitochondria. IL‐21‐induced GSK3β activation was accompanied by a marked increase in intracellular and extracellular metabolites such as pyruvate and lactate, as assessed by metabolomics. Importantly, GSK3 inhibition or supplementation with mitochondrial membrane‐permeable methyl pyruvate broadly abrogated metabolic wiring of and inflammatory responses by IL‐21‐stimulated Tregs and effector Th cells. Collectively, these results suggest that impaired mitochondrial pyruvate metabolism is a feature of inflammatory CD4 + T cells. Lastly, GSK3 inhibition prevented pathogenic CD4 + T cell‐induced colitis in mice as evidenced by reduced Disease Activity Index, Mouse Colon Histology Index, and serum inflammatory cytokines. Conclusions IL‐21 potently engages human Tregs in a hypermetabolic state that augments inflammatory cytokine production via induction of mitochondrial dysfunction. Therefore desensitizing CD4 + T cells to detrimental cues, such as IL‐21, may also augment Treg function during human IBD.