Astrocyte-intrinsic signaling of chitinase-like protein CHI3L1 drives inflammation and amplifies demyelination in neuromyelitis optica
Huiming Xu, Wei Jiang, Li Xu, Haoyang Li, Xin Yang, Fan Zhu, Pengyan He, Yanna Song, Yuhan Li, Yu-Wen Alvin Huang, Wei Qiu, Changyong Tang
Huiming Xu, Wei Jiang, Li Xu, Haoyang Li, Xin Yang, Fan Zhu, Pengyan He, Yanna Song, Yuhan Li, Yu-Wen Alvin Huang, Wei Qiu, Changyong Tang
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Research Article Autoimmunity Neuroscience

Astrocyte-intrinsic signaling of chitinase-like protein CHI3L1 drives inflammation and amplifies demyelination in neuromyelitis optica

Abstract

Neuromyelitis optica (NMO) is an autoimmune disorder characterized by autoantibodies against the astrocyte water channel aquaporin-4 (AQP4) that cause demyelination in the optic nerves and spinal cord. How astrocytopathy leads to myelination deficits remains unclear. Chitinase-3–like protein 1 (CHI3L1, also known as YKL-40) is predominantly secreted by activated astrocytes, serves as a robust NMO biomarker, and plays a role in immune responses, but how it is induced and shapes astrocyte activation in NMO is not well defined. Using ex vivo and in vivo NMO mouse models together with mice with astrocyte-specific CHI3L1 knockout, we demonstrated that CHI3L1 directly contributed to demyelinating lesions elicited by AQP4 autoantibody–activated astrocytes. With complementary in vitro assays and inducible transgenic lines, we uncovered an astrocyte-intrinsic cascade in which AQP4 autoantibody exposure activated STAT3, which in turn drove CHI3L1 expression and secretion. Secreted CHI3L1 then engaged the astrocytic receptor RAGE in an autocrine manner, activating downstream NF-κB signaling that drove proinflammatory gliosis and damaged myelination. Pharmacological blockade of this pathway in NMO models rescued demyelinating pathology and improved motor function. These findings reveal an astrocyte-intrinsic CHI3L1 pathway that contributed to demyelination in NMO and identify actionable therapeutic targets.

Authors

Huiming Xu, Wei Jiang, Li Xu, Haoyang Li, Xin Yang, Fan Zhu, Pengyan He, Yanna Song, Yuhan Li, Yu-Wen Alvin Huang, Wei Qiu, Changyong Tang

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Figure 3

CHI3L1 activates astrocytic NF-κB and potentiates AQP4-IgG–evoked proinflammatory responses.

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CHI3L1 activates astrocytic NF-κB and potentiates AQP4-IgG–evoked proinf...
(A) In vitro paradigm: primary mouse astrocytes exposed to recombinant human CHI3L1 at graded doses to assess cell-intrinsic signaling. (B) CHI3L1 (10–200 ng/mL, 4 hours) selectively increases NF-κB p65 phosphorylation without activating ERK, AKT, or β-catenin; immunoblot densitometry shown as phospho/total ratios (n = 3 experiments). (C) CHI3L1 dose-dependently induces NF-κB target transcripts (TNF-α, IL-1β, IL-6, IL-1α, CCL5, CCL7, C3) at 24 hours; heatmap normalized to vehicle (0 ng/mL) (n = 3). (D) Corresponding cytokine secretion (TNF-α, IL-1β, IL-6, C3) measured by ELISA from conditioned media after 24 hours of CHI3L1 (10–200 ng/mL) (n = 3). (E) Costimulation design: astrocytes treated with Ctrl-IgG or AQP4-IgG (100 ng/mL) with or without CHI3L1 (100 ng/mL) to test pathway convergence. (F) AQP4-IgG and CHI3L1 each increase p65 phosphorylation at 6 hours; combined treatment further augments p65 activation (immunoblot phospho/total p65; n = 3). (G) Immunofluorescence at 24 hours shows increased nuclear p65, GFAP upregulation, and AQP4 internalization in response to AQP4-IgG; these effects are enhanced by CHI3L1 cotreatment. Scale bars: 20 μm; n = 5 slides (6 fields per slide). (H) qPCR confirms amplification of NF-κB–regulated cytokine mRNAs by CHI3L1 in the AQP4-IgG condition; heatmap normalized to Ctrl-IgG + vehicle (n = 3). (I) ELISA detects higher secreted TNF-α, IL-1β, IL-6, and C3 with AQP4-IgG + CHI3L1 versus either alone (24 hours; n = 3). Statistics: Data are mean ± SEM. Bar graph comparisons used 1-way ANOVA with Tukey’s post hoc test or Welch’s ANOVA with Dunnett’s T3 test for unequal variances. Non-significant comparisons are not shown. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001.