Emerging evidence suggests that innate immunity drives alcoholic liver disease (ALD) and that the interferon regulatory factor 3 (IRF3), a transcription factor regulating innate immune responses, is indispensable for the development of ALD. Here we report that IRF3 mediates ALD via linking endoplasmic reticulum (ER) stress with apoptotic signaling in hepatocytes. We found that ethanol induced ER stress and triggered the association of IRF3 with the ER adaptor, stimulator of interferon genes (STING), as well as subsequent phosphorylation of IRF3. Activated IRF3 associated with the proapoptotic molecule Bax [B-cell lymphoma 2 (Bcl2)-associated X protein] and contributed to hepatocyte apoptosis. Deficiency of STING prevented IRF3 phosphorylation by ethanol or ER stress, and absence of IRF3 prevented hepatocyte apoptosis. The pathogenic role of IRF3 in ALD was independent of inflammation or Type-I interferons. Thus, STING and IRF3 are key determinants of ALD, linking ER stress signaling with the mitochondrial pathway of hepatocyte apoptosis. A lcoholic liver disease (ALD) affects over 140 million people worldwide, and currently there is no effective treatment. Acute alcohol consumption induces fatty liver and excessive alcohol use causes progression to steatohepatitis, cirrhosis, and hepatocellular carcinoma. Dysregulation of innate immunity and liver inflammation, triggered by the translocation of gut-derived endotoxin [lipopolysaccharide (LPS)] to the liver, represent major contributors to ALD (1). The recognition of gut-derived LPS by Kupffer cells (KC) requires the Toll-like receptor 4 (TLR4), which triggers two downstream pathways. The TLR4/ myeloid differentiation primary response gene 88 (MyD88) pathway activates transcription of inflammatory cytokines, whereas TLR4/TRAM/TRIF [TIR domain-containing adaptor inducing interferon-beta (TRIF)-related adaptor molecule (TRAM)] triggers Type-I interferons (IFN) regulatory factor 3 (IRF3) to induce IFN (2). The essential role of the TLR4 signaling in ALD was demonstrated in mice lacking functional TLR4 that showed attenuation of alcoholic steatohepatitis (3, 4). In previous studies, we reported that the MyD88-dependent pathway was dispensable for ALD (4) and observed complete protection from alcohol-induced inflammation, steatosis, and injury in mice deficient in IRF3 (5), suggesting that the pathogenic effects of TLR4 in ALD were mediated via the TRAM/TRIF-dependent pathway. However, the mechanisms by which IRF3 causes ALD remain obscure.IRF3 is a constitutively expressed transcription factor that resides in the cytoplasm and dimerizes and translocates to the nucleus upon phosphorylation (6). Phosphorylated IRF3 induces IFN-β during viral infection, but may also contribute to inflammatory cytokine response to LPS (7). IRF3 also promotes apoptosis in virus-infected cells through association with proapoptotic molecule Bax [B-cell lymphoma 2 (Bcl2)-associated X protein] (8). To elucidate the mechanism by which IRF3 determines ALD, we asked three fundamental questions. F...

Background & Aims Alcoholic liver disease (ALD) ranges from fatty liver to inflammation and cirrhosis. miRNA-155 is an important regulator of inflammation. In this study, we describe the in vivo role of miR-155 in ALD. Methods Wild type, WT (C57/BL6J) or miR-155 KO and TLR4 KO mice received Lieber-DeCarli diet for 5 weeks. Some mice received corn oil or CCl4 for 2 or 9 weeks. Results We found that miR-155 KO mice are protected from alcohol-induced steatosis and inflammation. The reduction in alcohol-induced fat accumulation in miR-155 KO mice was associated with increased PPRE and PPARα (miR-155 target) binding and decreased MCP1 production. Treatment with a miR-155 inhibitor increased PPARγ expression in naive and alcohol treated RAW macrophages. Alcohol increased lipid metabolism genes (FABP4, LXRα, ACC1 and LDLR) in WT mice and this was prevented in KO mice. Alcohol diet induced increase in the number of CD163+CD206+ infiltrating macrophages and neutrophils in WT was prevented in miR-155 KO mice. Kupffer cells isolated from miR-155 KO mice exhibited predominance of M2 phenotype when exposed to M1 polarized signals and this was due to increased C/EBPβ. Profibrotic genes were attenuated in miR-155 KO mice after alcohol diet or CCl4 treatment. Compared to WT attenuation in CCl4 induced hydroxyproline and α SMA was observed in KO mice. Finally, we show TLR4 signaling regulates miR-155 as TLR4 KO mice showed no induction of miR-155 after alcohol diet. Conclusions Collectively our results demonstrated the role of miR-155 in alcohol-induced steatohepatitis and fibrosis in vivo.

BackgroundIt has been well documented that alcohol and its metabolites induce injury and inflammation in the liver. However, there is no potential biomarker to monitor the extent of liver injury in alcoholic hepatitis patients. MicroRNAs (miRNAs) are a class of non-coding RNAs that are involved in various physiologic and pathologic processes. In the circulation, a great proportion of miRNAs is associated with extracellular vesicles (EVs)/exosomes. Here, we hypothesized that the exosome-associated miRNAs can be used as potential biomarkers in alcoholic hepatitis (AH).MethodsExosomes were isolated from sera of alcohol-fed mice or pair-fed mice, and plasma of alcoholic hepatitis patients or healthy controls by ExoQuick. The exosomes were characterized by transmission electron microscopy and Western blot and enumerated with a Nanoparticle Tracking Analysis system. Firefly™ microRNA Assay was performed on miRNA extracted from mice sera. TaqMan microRNA assay was used to identify differentially expressed miRNAs in plasma of cohort of patients with AH versus controls followed by construction of receiver operating characteristic (ROC) curves to determine the sensitivity and specificity of the candidates.ResultsThe total number of circulating EVs was significantly increased in mice after alcohol feeding. Those EVs mainly consisted of exosomes, the smaller size vesicle subpopulation of EVs. By performing microarray screening on exosomes, we found nine inflammatory miRNAs which were deregulated in sera of chronic alcohol-fed mice compared to controls including upregulated miRNAs: miRNA-192, miRNA-122, miRNA-30a, miRNA-744, miRNA-1246, miRNA 30b and miRNA-130a. The ROC analyses indicated excellent diagnostic value of miRNA-192, miRNA-122, and miRNA-30a to identify alcohol-induced liver injury. We further validated findings from our animal model in human samples. Consistent with the animal model, total number of EVs, mostly exosomes, was significantly increased in human subjects with AH. Both miRNA-192 and miRNA-30a were significantly increased in the circulation of subjects with AH. miRNA-192 showed promising value for the diagnosis of AH.ConclusionElevated level of EVs/exosomes and exosome-associated miRNA signature could serve as potential diagnostic markers for AH. In addition to the biomarker diagnostic capabilities, these findings may facilitate development of novel strategies for diagnostics, monitoring, and therapeutics of AH.Electronic supplementary materialThe online version of this article (doi:10.1186/s12967-015-0623-9) contains supplementary material, which is available to authorized users.

Inflammation defines the progression of ALD from reversible to advanced stages. Translocation of bacterial LPS to the liver from the gut is necessary for alcohol-induced liver inflammation. However, it is not known whether endogenous, metabolic danger signals are required for inflammation in ALD. Uric acid and ATP, 2 major proinflammatory danger signals, were evaluated in the serum of human volunteers exposed to a single dose of ethanol or in supernatants of primary human hepatocytes exposed to ethanol. In vitro studies were used to evaluate the role of uric acid and ATP in inflammatory cross-talk between hepatocytes and immune cells. The significance of signaling downstream of uric acid and ATP in the liver was evaluated in NLRP3-deficient mice fed a Lieber-DeCarli ethanol diet. Exposure of healthy human volunteers to a single dose of ethanol resulted in increased serum levels of uric acid and ATP. In vitro, we identified hepatocytes as a significant source of these endogenous inflammatory signals. Uric acid and ATP mediated a paracrine inflammatory cross-talk between damaged hepatocytes and immune cells and significantly increased the expression of LPS-inducible cytokines, IL-1β and TNF-α, by immune cells. Deficiency of NLRP3, a ligand-sensing component of the inflammasome recognizing uric acid and ATP, prevented the development of alcohol-induced liver inflammation in mice and significantly ameliorated liver damage and steatosis. Endogenous metabolic danger signals, uric acid, and ATP are involved in inflammatory cross-talk between hepatocytes and immune cells and play a crucial role in alcohol-induced liver inflammation.

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