LEPTINR plus BONE MARROW STROMAL CELLS DERIVE THE MIGRATION OF IL-1R2+MACROPHAGES THROUGH THE mGluR5 ACTIVATION IN NK CELLS

초록

Background: Although chronic alcohol consumption induces hepatic steatosis and mild inflammatory responses, severe alcoholic hepatitis rarely occurs, suggesting that unknown anti-inflammatory mechanisms exist against alcoholic injury. Recently, some macrophages are known to have anti-inflammatory roles, but their phenotypes and origins are unveiled. Here, we demonstrated that a subset of bone marrow (BM)-derived macrophages has an anti-inflammatory role in alcohol-associated liver disease (ALD) through the mesenchymal stromal cell (MSC)-mediated glutamate release and NK cell activation in BM. Methods: C57BL/6J WT, NK cell-specific Grm5 KO (Grm5NK), leptin receptor+ (LepR+) cell-specific Slc7a11 KO (Slc7a11LepR) mice were fed with liquid ethanol for 8 weeks. To identify a novel phenotype, single-cell RNA analysis was performed using hepatic macrophages. In vitro, ethanol, glutamate or interferon (IFN)-γ were used to treat MSCs, NK cells or monocytes. Human cells and plasma were collected from alcoholic patients. Flow cytometry, glutamate measurement, Western blotting, immunostaining, and qRT-PCR analysis were performed. Results: In ethanol-fed mouse liver, scRNA-Seq revealed high expression of interleukin-1 type II receptor (IL-1R2), decoy receptor of IL-1β in Ly6Clow macrophages. Besides, alcohol dehydrogenase and aldehyde dehydrogenase were expressed in LepR+ MSCs and increased after ethanol intake, whereas ethanol treatment increased the expression of chemokines (Cxcl9 and 10) and cystine/glutamate antiporter xCT (Slc7a11) in cultured MSCs, thereby recruiting CXCR3+ BM NK cells. Moreover, excreted glutamate via xCT in LepR+ MSCs stimulated metabotropic glutamate receptor 5 (mGluR5) in NK cells, leading to enhanced production of IFN-γ. Furthermore, IFN-γ treatment down-regulated the expression of CX3CR1 in IL-1R2+Ly6Clow BM monocytes, bound to CX3CL1+ MSCs, consequently inducing egress of Ly6Clow monocytes into the blood. Accordingly, IFN-γ production in BM NK cells and the migration of IL-1R2+Ly6Clow BM monocytes were decreased in EtOH-fed Grm5NK mice and Slc7a11LepR mice. In humans, plasma levels of soluble IL-1R2 and blood frequency of IL-1R2+CD14+CD16+ monocytes were elevated in patients with ALD compared to healthy controls. Conclusion: Glutamate of LepR+ MSCs granted egress license on anti-inflammatory IL-1R2+Ly6Clow monocytes through mGluR5-mediated IFN-γ by NK cell, suggesting a potential inter-organ crosstalk between BM and liver in ALD.