LEPTIN RECEPTOR plus BONE MARROW STROMAL CELLS REGULATE INTRAHEPATIC MIGRATION OF ANTI-INFLAMMATORY MONOCYTES IN ALCOHOLIC LIVER DISEASE

Abstract

Background: 10 % of patients with steatosis progress into alcoholic hepatitis by chronic alcohol consumption. Lines of evidence reported the existence of protective macrophages in liver, but their origins are still elusive. Here, we demonstrated that a subset of bone marrow (BM)-derived macrophages has anti-inflammatory role for alcoholic liver disease (ALD) through mesenchymal stromal cell (MSC)-mediated glutamate release and NK cell activation in BM. Methods: C57BL/6J WT and NK cell-specific mGluR5 KO (mGluR5 cKO) 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, diverse doses of ethanol, glutamate or interferon (IFN)-γ were used to treat MSCs, NK cells or macrophage. Peripheral blood mononuclear cells and plasma were collected from alcoholic patients. Flow cytometry, glutamate measurement, Western blotting, immunostaining, and qRT-PCR analysis were performed. Results: In scRNA-seq and flow cytometry analyses, chronic alcohol consumption increased a specific subtype of Ly6Clow macrophages with higher expression of interleukin-1 type II receptor (IL-1R2), a decoy receptor of IL-1β, and lower expression of CX3C chemokine receptor 1 (CX3CR1). In BM, alcohol dehydrogenase and aldehyde dehydrogenase were expressed in leptin receptor+ (LepR+) MSCs with high expression of CX3CL1. Moreover, ethanol treatment increased expression of chemokines (Cxcl9 and 10) in cultured MSCs, recruiting CXCR3+ BM NK cells. Simultaneously, glutamate was excreted from MSCs via increased expression of cystine/glutamate antiporter xCT, and it bound to mGluR5, inducing the production of IFN-γ in the neighboring BM NK cells. Furthermore, IFN-γ treatment down-regulated the expression of CX3CR1 in IL-1R2+Ly6Clow BM monocytes, releasing them from the restriction of CX3CL1+LepR+ MSCs and allowing their egress into the blood and migration to the liver. Accordingly, the migration of IL-1R2+Ly6Clow BM monocytes and IFN-γ production in BM NK cells were significantly decreased in EtOH-fed mGluR5 cKO mice compared to WT 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 CX3CR1 suppression by NK cell-derived IFN-γ, suggesting a potential inter-organ crosstalk between BM and liver in ALD.