Obesity-mediated hypoxic stress underlies inflammation, including interferon (IFN)-γ production by natural killer (NK) cells in white adipose tissue. However, the effects of obesity on NK cell IFN-γ ...production remain obscure. Here, we show that hypoxia promotes xCT-mediated glutamate excretion and C-X-C motif chemokine ligand 12 (CXCL12) expression in white adipocytes, resulting in CXCR4+ NK cell recruitment. Interestingly, this spatial proximity between adipocytes and NK cells induces IFN-γ production in NK cells by stimulating metabotropic glutamate receptor 5 (mGluR5). IFN-γ then triggers inflammatory activation of macrophages and augments xCT and CXCL12 expression in adipocytes, forming a bidirectional pathway. Genetic or pharmacological inhibition of xCT, mGluR5, or IFN-γ receptor in adipocytes or NK cells alleviates obesity-related metabolic disorders in mice. Consistently, patients with obesity showed elevated levels of glutamate/mGluR5 and CXCL12/CXCR4 axes, suggesting that a bidirectional pathway between adipocytes and NK cells could be a viable therapeutic target in obesity-related metabolic disorders.
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•Hypoxic adipocytes recruit NK cells through CXCL12 and excrete glutamate by xCT•mGluR5 activation in CXCR4+ NK cells exerts IFN-γ production and inflammation•NK cell-derived IFN-γ augments the glutamate and CXCL12 production by adipocytes•Bidirectional crosstalk between adipocytes and NK cells mediates obesity and NAFLD
Kim et al. show that hypoxia induces xCT-mediated glutamate excretion and CXCL12 expression in adipocytes, recruiting CXCR4+ NK cells. This spatial proximity provokes IFN-γ production by NK cells via mGluR5 activation, reinforcing glutamate and CXCL12 production by adipocytes. Consequently, this bidirectional interaction between adipocytes and NK cells instigates obesity.
Chronic alcohol consumption often induces hepatic steatosis but rarely causes severe inflammation in Kupffer cells (KCs) despite the increased hepatic influx of lipopolysaccharide (LPS), suggesting ...the presence of a veiled tolerance mechanism. In addition to LPS, the liver is affected by several gut-derived neurotransmitters through the portal blood, but the effects of catecholamines on KCs have not been clearly explored in alcohol-associated liver disease (ALD). Hence, we investigated the regulatory roles of catecholamine on inflammatory KCs under chronic alcohol exposure. We discovered that catecholamine levels were significantly elevated in the cecum, portal blood, and liver tissues of chronic ethanol-fed mice. Increased catecholamines induced mitochondrial translocation of cytochrome P450 2E1 in perivenous hepatocytes expressing the β2-adrenergic receptor (ADRB2), leading to the enhanced production of growth differentiation factor 15 (GDF15). Subsequently, GDF15 profoundly increased ADRB2 expression in adjacent inflammatory KCs to facilitate catecholamine/ADRB2-mediated apoptosis. Single-cell RNA sequencing of KCs confirmed the elevated expression of Adrb2 and apoptotic genes after chronic ethanol intake. Genetic ablation of Adrb2 or hepatic Gdf15 robustly decreased the number of apoptotic KCs near perivenous areas, exacerbating alcohol-associated inflammation. Consistently, we found that blood and stool catecholamine levels and perivenous GDF15 expression were increased in patients with early-stage ALD along with an increase in apoptotic KCs. Our findings reveal a novel protective mechanism against ALD, in which the catecholamine/GDF15 axis plays a critical role in KC apoptosis, and identify a unique neuro-metabo-immune axis between the gut and liver that elicits hepatoprotection against alcohol-mediated pathogenic challenges.
Ginsenoside F2 (GF2), the protopanaxadiol-type constituent in Panax ginseng, has been reported to attenuate metabolic dysfunction-associated steatotic liver disease (MASLD). However, the mechanism of ...action is not fully understood. Here, this study investigates the molecular mechanism by which GF2 regulates MASLD progression through liver X receptor (LXR).
To demonstrate the effect of GF2 on LXR activity, computational modeling of protein-ligand binding, Time-resolved fluorescence resonance energy transfer (TR-FRET) assay for LXR cofactor recruitment, and luciferase reporter assay were performed. LXR agonist T0901317 was used for LXR activation in hepatocytes and macrophages. MASLD was induced by high-fat diet (HFD) feeding with or without GF2 administration in WT and LXRα−/− mice.
Computational modeling showed that GF2 had a high affinity with LXRα. LXRE-luciferase reporter assay with amino acid substitution at the predicted ligand binding site revealed that the S264 residue of LXRα was the crucial interaction site of GF2. TR-FRET assay demonstrated that GF2 suppressed LXRα activity by favoring the binding of corepressors to LXRα while inhibiting the accessibility of coactivators. In vitro, GF2 treatments reduced T0901317-induced fat accumulation and pro-inflammatory cytokine expression in hepatocytes and macrophages, respectively. Consistently, GF2 administration ameliorated hepatic steatohepatitis and improved glucose or insulin tolerance in WT but not in LXRα−/− mice.
GF2 alters the binding affinities of LXRα coregulators, thereby interrupting hepatic steatosis and inflammation in macrophages. Therefore, we propose that GF2 might be a potential therapeutic agent for the intervention in patients with MASLD.
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Alcohol-related liver disease (ALD) became an important health issue worldwide. Following chronic alcohol consumption, the development of ALD might be caused by metabolic and immunologic factors, ...such as reactive oxygen species (ROS) and pro-inflammatory cytokines. For example, hepatic cytochrome P450 2E1 enzyme increases ROS production and stimulates de novo lipogenesis after alcohol exposure. In addition, damage- and pathogen-associated molecular patterns stimulate their specific receptors in non-parenchymal cells, including Kupffer cells, hepatic stellate cells (HSCs), and lymphocytes, which result in hepatocyte death and infiltration of pro-inflammatory cells (e.g., neutrophils and macrophages) in the liver. Moreover, our studies have suggested the novel involvement of neurologic signaling pathways (e.g., endocannabinoid and glutamate) through the metabolic synapse between hepatocytes and HSCs in the development of alcohol-related hepatic steatosis. Additionally, agouti-related protein and beta2-adrenergic receptors aggravate hepatic steatosis. Furthermore, organ-crosstalk has emerged as a critical issue in ALD. Chronic alcohol consumption induces dysbiosis and barrier disruption in the gut, leading to endotoxin leakage into the portal circulation, or lipolysis-mediated transport of triglycerides from the adipose tissue to the liver. In summary, this review addresses multiple pathogeneses of ALD, provides novel neurologic signaling pathways, and emphasizes the importance of organ-crosstalk in the development of ALD.
In contrast to quiescent hepatic stellate cells (HSCs), activated HSCs play crucial roles in the development of liver fibrosis by producing a huge amount of extracellular matrix such as collagen ...fibers. However, recent lines of evidence have also highlighted the immunoregulatory functions of HSCs, in which they interact with diverse hepatic lymphocytes to produce cytokines and chemokines, release extracellular vesicles, or express specific ligands. Therefore, to understand the exact interactions between HSCs and lymphocyte subsets in the pathogenesis of the liver disease, it is valuable to establish experimental procedures to isolate HSC and co-culture them with lymphocytes. Here, we introduce the efficient methods to isolate and purify mouse HSCs and hepatic lymphocytes using density gradient centrifugation, microscopic observation, and flow cytometry. Moreover, we provide the direct and indirect co-culturing methods of isolated mouse HSCs and hepatic lymphocytes based upon the purpose of the study.
Background and Aims: Hepatic stellate cells (HSCs) contribute to hepatocellular carcinoma (HCC) progression by regulating multiple factors. However, the entire immunoregulatory functions of HSCs are ...still obscure. Here, we aim to investigate whether HSCs impose CX 3 CR1 + macrophages to pro-tumorigenic properties in the peritumoral area. Approach and Results: In single cell RNA-sequencing analysis of HCC patients, a subpopulation of macrophages specifically expressed Arg1 and Cx3cr1 in the peritumoral area, and were highly enriched with retinol metabolism-related genes. Flow cytometry analysis showed significantly increased frequencies of CD14 + CD11b + HLA-DR ‒ macrophages with CX 3 CR1 in the HCC adjacent region where α-SMA-expressing activated HSCs (aHSCs) showed co-localized expression of CX 3 CL1. Accordingly, in tumor-bearing mice, Cx3cl1 mRNA expression was notably increased in aHSCs within the adjacent HCC, where infiltration of CX 3 CR1 + Ly6C + macrophages was mostly observed with decreased CD8 + T cells. In adoptive transfer and in vitro co-culture of myeloid cells, we demonstrated that CX 3 CR1 + Ly6C + macrophages migrated and highly expressed arginase-1 by interacting with retinoid-enriched aHSCs in the adjacent HCC. Direct treatment of retinoids or co-culturing with retinol-storing mouse aHSCs or human LX-2 cells significantly increased arginase-1 expression in CX 3 CR1 + Ly6C + macrophages and human blood CD14 + cells, leading to the suppression of CD8 + T cell proliferation. Moreover, genetic deficiency of CX 3 CR1 in myeloid cells or pharmacological inhibition of retinol metabolism remarkably attenuated HCC development. Conclusion: We showed that CX 3 CR1 + Ly6C + macrophages migrate and interact with aHSCs in the peritumoral region where retinoids induce arginase-1 expression in CX 3 CR1 + Ly6C + macrophages, subsequently depriving CD8 + T cells of arginine and promoting HCC.
Background and Aims
The important roles of glutamate and metabotropic glutamate receptor 5 (mGluR5) in HSCs have recently been reported in various liver diseases; however, the mechanism linking the ...glutamine/glutamate metabolism and mGluR5 in liver fibrosis remains unclear. Here, we report that mGluR5 activation in natural killer (NK) cells attenuates liver fibrosis through increased cytotoxicity and interferon‐γ (IFN‐γ) production in both mice and humans.
Approach and Results
Following 2‐week injection of carbon tetrachloride (CCl4) or 5‐week methionine‐deficient and choline‐deficient diet, liver fibrosis was more aggravated in mGluR5 knockout mice with significantly decreased frequency of NK cells compared with wild‐type mice. Consistently, NK cell–specific mGluR5 knockout mice had aggravated CCl4‐induced liver fibrosis with decreased production of IFN‐γ. Conversely, in vitro activation of mGluR5 in NK cells significantly increased the expression of anti‐fibrosis‐related genes including Ifng, Prf1 (perforin), and Klrk1 (killer cell lectin like receptor K1) and the production of IFN‐γ through the mitogen‐activated extracellular signal‐regulated kinase/extracellular signal‐related kinase pathway, contributing to the increased cytotoxicity against activated HSCs. However, we found that the uptake of glutamate was increased in activated HSCs, resulting in shortage of extracellular glutamate and reduced stimulation of mGluR5 in NK cells. Consequently, this could enable HSCs to evade NK cell cytotoxicity in advanced liver fibrosis. In vivo, pharmacologic activation of mGluR5 accelerated CCl4‐induced liver fibrosis regression by restoring NK cell cytotoxicity. In humans, mGluR5 activation enhanced the cytotoxicity of NK cells isolated from healthy donors, but not from patients with cirrhosis with significantly reduced mGluR5 expression in NK cells.
Conclusions
mGluR5 plays important roles in attenuating liver fibrosis by augmenting NK cell cytotoxicity, which could be used as a potential therapeutic target for liver fibrosis.
