Introduction
Experimental autoimmune encephalomyelitis (EAE), mediated by myelin-specific autoreactive T-helper cells, is a classical animal model of autoimmune encephalitis, such as anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis, which manifested with typical demyelination and neurodegeneration-associated symptoms 1. Although drugs targeting several immunological pathways have shown beneficial effects in patients with demyelinating disease, no cure is currently available 2.
Nucleotide-binding domain, leucine-rich repeat containing protein family, pyrin domain containing 3 (NLRP3) and the IL-1β pathway have show to be crucial for the development of EAE by participating in the neuroinflammation 3, 4. Activation of NLRP3 comes from two ways, in which the first way is stimulation of pathogen recognition receptors that activate the nuclear factor κB (NF-κB) pathways, and the second is activated by triggers such as lysosomal rupture, adenosine 5’-triphosphate (ATP), and reactive oxygen species (ROS)5. Upon activation, NLRP3 inflammasome led to production of cleaved caspase-1 which cleaves proIL-1β/pro-IL-18 into mature IL-1β/IL-18 that induces cell pyroptosis-related massive cytokine release and systemic inflammation 6. Potential mechanisms manipulated by NLRP3 to cause neuroinflammation include mediation of Th1 and Th17 responses 7 and induction of chemotactic immune cell migration to the CNS 8. NLRP3-depedent IL-1β maturation was reported to be detected in the lesions and cerebrospinal fluid (CSF) of MS patients9, and its presence strictly correlates with cortical lesion load 10. Conversely, mice lacking IL-1 or with damaged IL-1 signaling showed compromised development and severity of EAE 11. Only a few IL-1 targeted medicine are available for autoimmune disorders treatment 12, 13. Among these, JAK-STAT signaling is critical for T help cell polarization and autoimmune neuroinflammation 14, 15. In fact, several JAK inhibitors have been used over the past decades targeting a specific or a wide range of JAKs, providing promising alternatives to traditional biological disease modifying antirheumatic drugs in several autoimmune diseases 16, 17. Moreover, JAK mediate IL-4 receptor signals to prime Th2 response-dominant symptoms, like itch in atopic dermatitis 18, in which cytokine IL-4 production is closely regulated by function of thymic stromal lymphopoietin 19. Despite the high incidence and role of TSLP and JAK-STAT signaling, it is unclear whether TSLP functions via NLRP3 to induce autoimmune inflammation. If so, whether JAK is involved in this process is known.
Thymic stromal lymphopoietin (TSLP) is an interleukin (IL)-7 related cytokine acting on lineages, including macrophages, dendritic cells (DCs), and T cells 20. By promoting expression of major histocompatibility complex (MHC)-II and co-stimulatory molecules such as CD40, CD80, and CD86, and the production of chemokines, TSLP strongly enhances DCs maturation and function 21. MS and EAE have been associated with single nucleotide polymorphisms (SNPs) in IL-7Rαgene locus 22. Upon ligation by TSLP, TSLP receptor (TSLPR) initiates intracellular JAK/STAT signaling to induce production of IL-2, TNF and IL-6 to potentiate inflammatory responses. Targeting these cytokines has been shown to be effective in alleviating EAE or other autoimmune disease 23, 24, 25, 26. Accordingly, direct blocking JAK/STAT signaling pathways with tofacitinib inhibited NLRP3 inflammasome and IL-1β production in neutrophils 27. However, whether TSLPR signaling is capable of controlling initiates inflammation and in EAE remains unclear.
In this study we show that Tslpr -/- mice presented alleviated severity in myelin oligodendrocyte glycoprotein peptide (MOG35-55)-induced experimental autoimmune encephalitis (EAE), resulting from decreased phosphorylation of JAK2 and expression of NLRP3. Inhibition of JAK by ruxolitinib reduced NLRP3 expression in brain of EAE mouse. In addition, using JAK inhibitor ruxolitinib or NLRP3 inhibitor MCC950 all reduced inflammatory cells and CD4+ cells infiltration, NLRP3 and myelin expression, and IL-1β and TSLP in brain tissue of EAE mouse. Furthermore, patients with anti-N-methyl-D-aspartate-receptor (anti-NMDAR) encephalitis showed a significant increase inNLRP3 and IL-1βin CSF when compared with that in healthy control. These findings reveal that TSLP plays an essential role in positive regulation of JAK2-NLRP3 axis-driven neuroinflammation in autoimmune disorders.