Objective: Antimicrobial C-type lectin regenerating islet-derived 3 gamma (REG3G) is suppressed in the small intestine during chronic ethanol feeding. Our aim was to determine the mechanism that underlies REG3G suppression during experimental alcoholic liver disease.Design: Interleukin 22 (IL-22) regulates expression of REG3G. Therefore, we investigated the role of IL-22 in mice subjected to chronic-binge ethanol feeding (NIAAA model).Results: In a mouse model of alcoholic liver disease, we found that type 3 innate lymphoid cells produce lower levels of IL-22. Reduced IL-22 production was the result of ethanol-induced dysbiosis and lower intestinal levels of indole-3-acetic acid (IAA), a microbiota-derived ligand of the aryl hydrocarbon receptor (AHR), which regulates expression of IL-22. Importantly, faecal levels of IAA were also found to be lower in patients with alcoholic hepatitis compared with healthy controls. Supplementation to restore intestinal levels of IAA protected mice from ethanol-induced steatohepatitis by inducing intestinal expression of IL-22 and REG3G, which prevented translocation of bacteria to liver. We engineeredLactobacillus reuterito produce IL-22 (L. reuteri/IL-22) and fed them to mice along with the ethanol diet; these mice had reduced liver damage, inflammation and bacterial translocation to the liver compared with mice fed an isogenic control strain and upregulated expression of REG3G in intestine. However,L. reuteri/IL-22 did not reduce ethanol-induced liver disease inReg3g^–/–mice.Conclusion: Ethanol-associated dysbiosis reduces levels of IAA and activation of the AHR to decrease expression of IL-22 in the intestine, leading to reduced expression of REG3G; this results in bacterial translocation to the liver and steatohepatitis. Bacteria engineered to produce IL-22 induce expression of REG3G to reduce ethanol-induced steatohepatitis.

Gut dysbiosis is commonly observed in patients with cirrhosis and chronic gastrointestinal disorders; however, its effect on antitumor immunity in the liver is largely unknown. Here we studied how the gut microbiome affects antitumor immunity in cholangiocarcinoma. Primary sclerosing cholangitis (PSC) or colitis, two known risk factors for cholangiocarcinoma which promote tumor development in mice, caused an accumulation of CXCR2+ polymorphonuclear myeloid-derived suppressor cells (PMN-MDSC). A decrease in gut barrier function observed in mice with PSC and colitis allowed gut-derived bacteria and lipopolysaccharide to appear in the liver and induced CXCL1 expression in hepatocytes through a TLR4-dependent mechanism and an accumulation of CXCR2+ PMN-MDSCs. In contrast, neomycin treatment blocked CXCL1 expression and PMN-MDSC accumulation and inhibited tumor growth even in the absence of liver disease or colitis. Our study demonstrates that the gut microbiome controls hepatocytes to form an immunosuppressive environment by increasing PMN-MDSCs to promote liver cancer.Significance: MDSCs have been shown to be induced by tumors and suppress antitumor immunity. Here we show that the gut microbiome can control accumulation of MDSCs in the liver in the context of a benign liver disease or colitis.See related commentary by Chagani and Kwong, p. 1014.This article is highlighted in the In This Issue feature, p. 995

Objective: The pathogenesis of sepsis is complex, and the sepsis-induced systemic proinflammatory phase is one of the key drivers of organ failure and consequent mortality. Akkermansia muciniphila (AKK) is recognised as a functional probiotic strain that exerts beneficial effects on the progression of many diseases; however, whether AKK participates in sepsis pathogenesis is still unclear. Here, we evaluated the potential contribution of AKK to lethal sepsis development. Design: Relative abundance of gut microbial AKK in septic patients was evaluated. Cecal ligation and puncture (CLP) surgery and lipopolysaccharide (LPS) injection were employed to establish sepsis in mice. Non-targeted and targeted metabolomics analysis were used for metabolites analysis. Results: We first found that the relative abundance of gut microbial AKK in septic patients was significantly reduced compared with that in non-septic controls. Live AKK supplementation, as well as supplementation with its culture supernatant, remarkably reduced sepsis-induced mortality in sepsis models. Metabolomics analysis and germ-free mouse validation experiments revealed that live AKK was able to generate a novel tripeptide Arg-Lys-His (RKH). RKH exerted protective effects against sepsis-induced death and organ damage. Furthermore, RKH markedly reduced sepsis-induced inflammatory cell activation and proinflammatory factor overproduction. A mechanistic study revealed that RKH could directly bind to Toll-like receptor 4 (TLR4) and block TLR4 signal transduction in immune cells. Finally, we validated the preventive effects of RKH against sepsis-induced systemic inflammation and organ damage in a piglet model. Conclusion: We revealed that a novel tripeptide, RKH, derived from live AKK, may act as a novel endogenous antagonist for TLR4. RKH may serve as a novel potential therapeutic approach to combat lethal sepsis after successfully translating its efficacy into clinical practice.

The intestinal microbiome plays a major role in the pathogenesis of liver disease, with a hallmark event being dysbiosis, or an imbalance of pathobionts and beneficial bacteria with the associated deleterious effects on their host. Reducing the number of intestinal bacteria with antibiotic treatment is generally advantageous in experimental liver diseases. Complete absence of intestinal microbiota as in germ-free rodents can be protective in autoimmune hepatitis and hepatic tumors induced by chemicals, or it can exacerbate disease as in acute toxic liver injury and liver fibrosis/cirrhosis. In alcoholic liver disease, nonalcoholic fatty liver disease, and autoimmune cholangiopathies, germ-free status can be associated with worsened or improved hepatic phenotype depending on the experimental model and type of rodent. Some of the unexpected outcomes can be explained by the limitations of rodents raised in a germ-free environment including a deficient immune system and an altered metabolism of lipids, cholesterol, xenobiotics/toxins, and bile acids. Given these limitations and to advance understanding of the interactions between host and intestinal microbiota, simplified model systems such as humanized gnotobiotic mice, or gnotobiotic mice monoassociated with a single bacterial strain or colonized with a defined set of microbes, are unique and useful models for investigation of liver disease in a complex ecosystem.