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.