Hypercholesterolemia Negatively Regulates P2X7-Induced Cellular Function in CD4+ and CD8+ T-Cell Subsets from B6 Mice Fed a High-Fat Diet.

We have previously showed that plasma membrane cholesterol and GM1 ganglioside content are responsible for the opposite sensitivity of mouse leukemic T cells to ATP. We also reported that the sensitivity of CD4+ and CD8+ T cells to ATP depends on their stage of differentiation. Here, we show that CD4+ and CD8+ T cells from B6 mice express different levels of membrane GM1 and P2X7 but similar levels of cholesterol. Thus, in CD4+ T cells, membrane cholesterol content negatively correlated with ATP/P2X7-induced CD62L shedding but positively correlated with pore formation, phosphatidylserine externalization, and cell death. By contrast, in CD8+ T cells, cholesterol, GM1, and P2X7 levels negatively correlated with all these ATP/P2X7-induced cellular responses. The relationship between cholesterol and P2X7-induced cellular responses was confirmed by modulating cholesterol levels either ex vivo or through a high-fat diet. Membrane cholesterol enrichment ex vivo led to a significant reduction in all P2X7-induced cellular responses in T cells. Importantly, diet-induced hypercholesterolemia in B6 mice was also associated with decreased sensitivity to ATP in CD4+ and CD8+ T cells, highlighting the relationship between cholesterol intake and the amplitudes of P2X7-induced cellular responses in T cells.

Microbiota tryptophan metabolism induces aryl hydrocarbon receptor activation and improves alcohol-induced liver injury.

OBJECTIVE: Chronic alcohol consumption is an important cause of liver-related deaths. Specific intestinal microbiota profiles are associated with susceptibility or resistance to alcoholic liver disease in both mice and humans. We aimed to identify the mechanisms by which targeting intestinal microbiota can improve alcohol-induced liver lesions. DESIGN: We used human associated mice, a mouse model of alcoholic liver disease transplanted with the intestinal microbiota of alcoholic patients and used the prebiotic, pectin, to modulate the intestinal microbiota. Based on metabolomic analyses, we focused on microbiota tryptophan metabolites, which are ligands of the aryl hydrocarbon receptor (AhR). Involvement of the AhR pathway was assessed using both a pharmacological approach and AhR-deficient mice. RESULTS: Pectin treatment modified the microbiome and metabolome in human microbiota-associated alcohol-fed mice, leading to a specific faecal signature. High production of bacterial tryptophan metabolites was associated with an improvement of liver injury. The AhR agonist Ficz (6-formylindolo (3,2-b) carbazole) reduced liver lesions, similarly to prebiotic treatment. Conversely, inactivation of the ahr gene in alcohol-fed AhR knock-out mice abrogated the beneficial effects of the prebiotic. Importantly, patients with severe alcoholic hepatitis have low levels of bacterial tryptophan derivatives that are AhR agonists. CONCLUSIONS: Improvement of alcoholic liver disease by targeting the intestinal microbiota involves the AhR pathway, which should be considered as a new therapeutic target.

Overexpression of GILZ in macrophages limits systemic inflammation while increasing bacterial clearance in sepsis in mice.

Studies support the beneficial effects of glucocorticoids (GCs) during septic shock, steering research toward the potential role of GC-induced proteins in controlling excessive inflammatory responses. GILZ is a glucocorticoid-induced protein involved in the anti-inflammatory effects of GCs. We investigated whether the overexpression of GILZ specifically limited to monocytes and macrophages (M/M) alone could control inflammation, thus improving the outcome of septic shock in animal models. We also monitored the expression of GILZ in M/M from septic mice and septic-shock patients. M/M from patients and septic mice displayed significantly lower expression of GILZ than those isolated from controls. Furthermore, transgenic mice (Tg-mice) experiencing sepsis, with increased expression of GILZ restricted to M/M, showed lower frequencies of inflammatory monocytes than their littermates and lower plasma levels of inflammatory cytokines. Tg-mice also had lower blood bacterial counts. We further established that the upregulation of GILZ in M/M enhanced their phagocytic capacity in in vivo assays. The increase of GILZ in M/M was also sufficient to improve the survival rates of septic mice. These results provide evidence for a central role of both GILZ and M/M in the pathophysiology of septic shock and a possible clue for the modulation of inflammation in this disease.

Blood microbiota and metabolomic signature of major depression before and after antidepressant treatment: a prospective case-control study.

Background: The microbiota interacts with the brain through the gut-brain axis, and a distinct dysbiosis may lead to major depressive episodes. Bacteria can pass through the gut barrier and be found in the blood. Using a multiomic approach, we investigated whether a distinct blood microbiome and metabolome was associated with major depressive episodes, and how it was modulated by treatment. Methods: In this case-control multiomic study, we analyzed the blood microbiome composition, inferred bacterial functions and metabolomic profile of 56 patients experiencing a current major depressive episode and 56 matched healthy controls, before and after treatment, using 16S rDNA sequencing and liquid chromatography coupled to tandem mass spectrometry. Results: The baseline blood microbiome in patients with a major depressive episode was distinct from that of healthy controls (patients with a major depressive episode had a higher proportion of Janthinobacterium and lower levels of Neisseria) and changed after antidepressant treatment. Predicted microbiome functions confirmed by metabolomic profiling showed that patients who were experiencing a major depressive episode had alterations in the cyanoamino acid pathway at baseline. High baseline levels of Firmicutes and low proportions of Bosea and Tetrasphaera were associated with response to antidepressant treatment. Based on inferred baseline metagenomic profiles, bacterial pathways that were significantly associated with treatment response were related to xenobiotics, amino acids, and lipid and carbohydrate metabolism, including tryptophan and drug metabolism. Metabolomic analyses showed that plasma tryptophan levels are independently associated with response to antidepressant treatment. Limitations: Our study has some limitations, including a lack of information on blood microbiome origin and the lack of a validation cohort to confirm our results. Conclusion: Patients with depression have a distinct blood microbiome and metabolomic signature that changes after treatment. Dysbiosis could be a new therapeutic target and prognostic tool for the treatment of patients who are experiencing a major depressive episode.

Recovery of ethanol-induced Akkermansia muciniphila depletion ameliorates alcoholic liver disease.

OBJECTIVE: Alcoholic liver disease (ALD) is a global health problem with limited therapeutic options. Intestinal barrier integrity and the microbiota modulate susceptibility to ALD. Akkermansia muciniphila, a Gram-negative intestinal commensal, promotes barrier function partly by enhancing mucus production. The aim of this study was to investigate microbial alterations in ALD and to define the impact of A. muciniphila administration on the course of ALD. DESIGN: The intestinal microbiota was analysed in an unbiased approach by 16S ribosomal DNA (rDNA) sequencing in a Lieber-DeCarli ALD mouse model, and faecal A. muciniphila abundance was determined in a cohort of patients with alcoholic steatohepatitis (ASH). The impact of A. muciniphila on the development of experimental acute and chronic ALD was determined in a preventive and therapeutic setting, and intestinal barrier integrity was analysed. RESULTS: Patients with ASH exhibited a decreased abundance of faecal A. muciniphila when compared with healthy controls that indirectly correlated with hepatic disease severity. Ethanol feeding of wild-type mice resulted in a prominent decline in A. muciniphila abundance. Ethanol-induced intestinal A. muciniphila depletion could be restored by oral A. muciniphila supplementation. Furthermore, A. muciniphila administration when performed in a preventive setting decreased hepatic injury, steatosis and neutrophil infiltration. A. muciniphila also protected against ethanol-induced gut leakiness, enhanced mucus thickness and tight-junction expression. In already established ALD, A. muciniphila used therapeutically ameliorated hepatic injury and neutrophil infiltration. CONCLUSION: Ethanol exposure diminishes intestinal A. muciniphila abundance in both mice and humans and can be recovered in experimental ALD by oral supplementation. A. muciniphila promotes intestinal barrier integrity and ameliorates experimental ALD. Our data suggest that patients with ALD might benefit from A. muciniphila supplementation.

Fecal microbiota manipulation prevents dysbiosis and alcohol-induced liver injury in mice.

BACKGROUND & AIMS: Alcoholic liver disease (ALD) is a leading cause of liver failure and mortality. In humans, severe alcoholic hepatitis is associated with key changes to intestinal microbiota (IM), which influences individual sensitivity to develop advanced ALD. We used the different susceptibility to ALD observed in two distinct animal facilities to test the efficiency of two complementary strategies (fecal microbiota transplantation and prebiotic treatment) to reverse dysbiosis and prevent ALD. METHODS: Mice were fed alcohol in two distinct animal facilities with a Lieber DeCarli diet. Fecal microbiota transplantation was performed with fresh feces from alcohol-resistant donor mice to alcohol-sensitive receiver mice three times a week. Another group of mice received pectin during the entire alcohol consumption period. RESULTS: Ethanol induced steatosis and liver inflammation, which were associated with disruption of gut homeostasis, in alcohol-sensitive, but not alcohol resistant mice. IM analysis showed that the proportion of Bacteroides was specifically lower in alcohol-sensitive mice (p<0.05). Principal coordinate analysis showed that the IM of sensitive and resistant mice clustered differently. We targeted IM using two different strategies to prevent alcohol-induced liver lesions: (1) pectin treatment which induced major modifications of the IM, (2) fecal microbiota transplantation which resulted in an IM very close to that of resistant donor mice in the sensitive recipient mice. Both methods prevented steatosis, liver inflammation, and restored gut homeostasis. CONCLUSIONS: Manipulation of IM can prevent alcohol-induced liver injury. The IM should be considered as a new therapeutic target in ALD. LAY SUMMARY: Sensitivity to alcoholic liver disease (ALD) is driven by intestinal microbiota in alcohol fed mice. Treatment of mice with alcohol-induced liver lesions by fecal transplant from alcohol fed mice resistant to ALD or with prebiotic (pectin) prevents ALD. These findings open new possibilities for treatment of human ALD through intestinal microbiota manipulation.

Decreased expression of the glucocorticoid receptor-GILZ pathway in Kupffer cells promotes liver inflammation in obese mice.

BACKGROUND & AIMS: Kupffer cells (KC) play a key role in the onset of inflammation in non-alcoholic steatohepatitis (NASH). The glucocorticoid receptor (GR) induces glucocorticoid-induced leucine zipper (GILZ) expression in monocytes/macrophages and is involved in several inflammatory processes. We hypothesized that the GR-GILZ axis in KC may contribute to the pathophysiology of obesity-induced liver inflammation. METHODS: By using a combination of primary cell culture, pharmacological experiments, mice deficient for the Gr specifically in macrophages and transgenic mice overexpressing Gilz in macrophages, we explored the involvement of the Gr-Gilz axis in KC in the pathophysiology of obesity-induced liver inflammation. RESULTS: Obesity was associated with a downregulation of the Gr and Gilz, and an impairment of Gilz induction by lipopolysaccharide (LPS) and dexamethasone (DEX) in KC. Inhibition of Gilz expression in isolated KC transfected with Gilz siRNA demonstrated that Gilz downregulation was sufficient to sensitize KC to LPS. Conversely, liver inflammation was decreased in obese transgenic mice specifically overexpressing Gilz in macrophages. Pharmacological inhibition of the Gr showed that impairment of Gilz induction in KC by LPS and DEX in obesity was driven by a downregulation of the Gr. In mice specifically deficient for Gr in macrophages, Gilz expression was low, leading to an exacerbation of obesity-induced liver inflammation. CONCLUSIONS: Obesity is associated with a downregulation of the Gr-Gilz axis in KC, which promotes liver inflammation. The Gr-Gilz axis in KC is an important target for the regulation of liver inflammation in obesity.

Circulating microbiome analysis in patients with perioperative anaphylaxis.

Background: Perioperative anaphylaxis is a rare and acute systemic manifestation of drug-induced hypersensitivity reactions that occurs following anesthesia induction; the two main classes of drugs responsible for these reactions being neuromuscular blocking agents (NMBA) and antibiotics. The sensitization mechanisms to the drugs are not precisely known, and few risk factors have been described. A growing body of evidence underlines a link between occurrence of allergy and microbiota composition. However, no data exist on microbiota in perioperative anaphylaxis. The aim of this study was to compare circulating microbiota richness and composition between perioperative anaphylaxis patients and matched controls. Methods: Circulating 16s rDNA was quantified and sequenced in serum samples from 20 individuals with fully characterized IgE-mediated NMBA-related anaphylaxis and 20 controls matched on sex, age, NMBA received, type of surgery and infectious status. Microbiota composition was analyzed with a published bioinformatic pipeline and links with patients clinical and biological data investigated. Results: Analysis of microbiota diversity showed that anaphylaxis patients seem to have a richer circulating microbiota than controls, but no major differences of composition could be detected with global diversity indexes. Pairwise comparison showed a difference in relative abundance between patients and controls for Saprospiraceae, Enterobacteriaceae, Veillonellaceae, Escherichia-Shigella, Pseudarcicella, Rhodoferax, and Lewinella. Some taxa were associated with concentrations of mast cell tryptase and specific IgE. Conclusion: We did not find a global difference in terms of microbiota composition between anaphylaxis patient and controls. However, several taxa were associated with anaphylaxis patients and with their biological data. These findings must be further confirmed in different settings to broaden our understanding of drug anaphylaxis pathophysiology and identify predisposition markers.

Pectin in Metabolic Liver Disease.

Alterations in the composition of the gut microbiota (dysbiosis) are observed in nutritional liver diseases, including non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) and have been shown to be associated with the severity of both. Editing the composition of the microbiota by fecal microbiota transfer or by application of probiotics or prebiotics/fiber in rodent models and human proof-of-concept trials of NAFLD and ALD have demonstrated its possible contribution to reducing the progression of liver damage. In this review, we address the role of a soluble fiber, pectin, in reducing the development of liver injury in NAFLD and ALD through its impact on gut bacteria.

The unforeseen intracellular lifestyle of Enterococcus faecalis in hepatocytes.

Enterococcus faecalis is a bacterial species present at a subdominant level in the human gut microbiota. This commensal turns into an opportunistic pathogen under specific conditions involving dysbiosis and host immune deficiency. E. faecalis is one of the rare pathobionts identified to date as contributing to liver damage in alcoholic liver disease. We have previously observed that E. faecalis is internalized in hepatocytes. Here, the survival and fate of E. faecalis was examined in hepatocytes, the main epithelial cell type in the liver. Although referred to as an extracellular pathogen, we demonstrate that E. faecalis is able to survive and divide in hepatocytes, and form intracellular clusters in two distinct hepatocyte cell lines, in primary mouse hepatocytes, as well as in vivo. This novel process extends to kidney cells. Unraveling the intracellular lifestyle of E. faecalis, our findings contribute to the understanding of pathobiont-driven diseases.

Modulation of the Bile Acid Enterohepatic Cycle by Intestinal Microbiota Alleviates Alcohol Liver Disease.

Reshaping the intestinal microbiota by the ingestion of fiber, such as pectin, improves alcohol-induced liver lesions in mice by modulating bacterial metabolites, including indoles, as well as bile acids (BAs). In this context, we aimed to elucidate how oral supplementation of pectin affects BA metabolism in alcohol-challenged mice receiving feces from patients with alcoholic hepatitis. Pectin reduced alcohol liver disease. This beneficial effect correlated with lower BA levels in the plasma and liver but higher levels in the caecum, suggesting that pectin stimulated BA excretion. Pectin modified the overall BA composition, favoring an augmentation in the proportion of hydrophilic forms in the liver, plasma, and gut. This effect was linked to an imbalance between hydrophobic and hydrophilic (less toxic) BAs in the gut. Pectin induced the enrichment of intestinal bacteria harboring genes that encode BA-metabolizing enzymes. The modulation of BA content by pectin inhibited farnesoid X receptor signaling in the ileum and the subsequent upregulation of Cyp7a1 in the liver. Despite an increase in BA synthesis, pectin reduced BA serum levels by promoting their intestinal excretion. In conclusion, pectin alleviates alcohol liver disease by modifying the BA cycle through effects on the intestinal microbiota and enhanced BA excretion.

Gut Microbiota Reshaped by Pectin Treatment Improves Liver Steatosis in Obese Mice.

Pectin, a soluble fiber, improves non-alcoholic fatty-liver disease (NAFLD), but its mechanisms are unclear. We aimed to investigate the role of pectin-induced changes in intestinal microbiota (IM) in NAFLD. We recovered the IM from mice fed a high-fat diet, treated or not with pectin, to perform a fecal microbiota transfer (FMT). Mice fed a high-fat diet, which induces NAFLD, were treated with pectin or received a fecal microbiota transfer (FMT) from mice treated with pectin before (preventive FMT) or after (curative FMT) being fed a high-fat diet. Pectin prevented the development of NAFLD, induced browning of adipose tissue, and modified the IM without increasing the abundance of proteobacteria. Preventive FMT also induced browning of white adipose tissue but did not improve liver steatosis, in contrast to curative FMT, which induced an improvement in steatosis. This was associated with an increase in the concentration of short-chain fatty acids (SCFAs), in contrast to preventive FMT, which induced an increase in the concentration of branched SCFAs. Overall, we show that the effect of pectin may be partially mediated by gut bacteria.

Bile acid-receptor TGR5 deficiency worsens liver injury in alcohol-fed mice by inducing intestinal microbiota dysbiosis.

BACKGROUND & AIMS: Bile-acid metabolism and the intestinal microbiota are impaired in alcohol-related liver disease. Activation of the bile-acid receptor TGR5 (or GPBAR1) controls both biliary homeostasis and inflammatory processes. We examined the role of TGR5 in alcohol-induced liver injury in mice. METHODS: We used TGR5-deficient (TGR5-KO) and wild-type (WT) female mice, fed alcohol or not, to study the involvement of liver macrophages, the intestinal microbiota (16S sequencing), and bile-acid profiles (high-performance liquid chromatography coupled to tandem mass spectrometry). Hepatic triglyceride accumulation and inflammatory processes were assessed in parallel. RESULTS: TGR5 deficiency worsened liver injury, as shown by greater steatosis and inflammation than in WT mice. Isolation of liver macrophages from WT and TGR5-KO alcohol-fed mice showed that TGR5 deficiency did not increase the pro-inflammatory phenotype of liver macrophages but increased their recruitment to the liver. TGR5 deficiency induced dysbiosis, independently of alcohol intake, and transplantation of the TGR5-KO intestinal microbiota to WT mice was sufficient to worsen alcohol-induced liver inflammation. Secondary bile-acid levels were markedly lower in alcohol-fed TGR5-KO than normally fed WT and TGR5-KO mice. Consistent with these results, predictive analysis showed the abundance of bacterial genes involved in bile-acid transformation to be lower in alcohol-fed TGR5-KO than WT mice. This altered bile-acid profile may explain, in particular, why bile-acid synthesis was not repressed and inflammatory processes were exacerbated. CONCLUSIONS: A lack of TGR5 was associated with worsening of alcohol-induced liver injury, a phenotype mainly related to intestinal microbiota dysbiosis and an altered bile-acid profile, following the consumption of alcohol. LAY SUMMARY: Excessive chronic alcohol intake can induce liver disease. Bile acids are molecules produced by the liver and can modulate disease severity. We addressed the specific role of TGR5, a bile-acid receptor. We found that TGR5 deficiency worsened alcohol-induced liver injury and induced both intestinal microbiota dysbiosis and bile-acid pool remodelling. Our data suggest that both the intestinal microbiota and TGR5 may be targeted in the context of human alcohol-induced liver injury.

Alteration of splicing factors' expression during liver disease progression: impact on hepatocellular carcinoma outcome.

PURPOSE: Trans-acting splicing factors (SF) shape the eukaryotic transcriptome by regulating alternative splicing (AS). This process is recurrently modulated in liver cancer suggesting its direct contribution to the course of liver disease. The aim of our study was to investigate the relationship between the regulation of SFs expression and liver damage. METHODS: The expression profile of 10 liver-specific SF and the AS events of 7 genes associated with liver disorders was assessed by western-blotting in 6 murine models representing different stages of liver damage, from inflammation to hepatocellular carcinoma (HCC). Relevant SFs (PSF, SRSF3, and SRSF6) and target genes (INSR, SRSF3, and SLK) modulated in mice were investigated in a cohort of 179 HCC patients. RESULTS: Each murine model of liver disease was characterized by a unique SF expression profile. Changes in the SF profile did not affect AS events of the selected genes despite the presence of corresponding splicing sites. In human HCC expression of SFs, including the tumor-suppressor SRSF3, and AS regulation of genes studied were frequently upregulated in tumor versus non-tumor tissues. Risk of tumor recurrence positively correlated with AS isoform of the INSR gene. In contrast, increased levels of SFs expression correlated with an extended overall survival of patients. CONCLUSIONS: Dysregulation of SF expression is an early event occurring during liver injury and not just at the stage of HCC. Besides impacting on AS regulation, overexpression of SF may contribute to preserving hepatocyte homeostasis during liver pathogenesis.

Microbiota, a key player in alcoholic liver disease.

Alcoholic liver disease (ALD) is a major cause of morbidity and mortality worldwide. Only 20% of heavy alcohol consumers develop alcoholic liver cirrhosis. The intestinal microbiota (IM) has been recently identified as a key player in the severity of liver injury in ALD. Common features of ALD include a decrease of gut epithelial tight junction protein expression, mucin production, and antimicrobial peptide levels. This disruption of the gut barrier, which is a prerequisite for ALD, leads to the passage of bacterial products into the blood stream (endotoxemia). Moreover, metabolites produced by bacteria, such as short chain fatty acids, volatile organic compounds (VOS), and bile acids (BA), are involved in ALD pathology. Probiotic treatment, IM transplantation, or the consumption of dietary fiber, such as pectin, which all alter the ratio of bacterial species, have been shown to improve liver injury in animal models of ALD and to be associated with an improvement in gut barrier function. Although the connections between the microbiota and the host in ALD are well established, the underlying mechanisms are still an active area of research. Targeting the microbiome through the use of prebiotic, probiotic, and postbiotic modalities could be an attractive new approach to manage ALD.

Characterization of intestinal microbiota in alcoholic patients with and without alcoholic hepatitis or chronic alcoholic pancreatitis.

Excessive alcohol consumption leads to severe alcoholic hepatitis (sAH) or chronic alcoholic pancreatitis (CAP) only in a subset of patients. We aimed to characterize the intestinal microbiota profiles of alcoholic patients according to the presence and nature of the complications observed: sAH or CAP. Eighty two alcoholic patients were included according to their complications: CAP (N = 24), sAH (N = 13) or no complications (alcoholic controls, AC, N = 45). We analyzed the intestinal microbiota by high-throughput sequencing. Bacterial diversity was lower in patients with CAP, who had a global intestinal microbiota composition different from that of AC. The intestinal microbiota composition of these two groups differed for 17 genera, eight of which were more frequent in patients with CAP (e.g. Klebsiella, Enterococcus and Sphingomonas). There was no significant difference in bacterial diversity between the sAH and CAP groups. However, 16 taxa were more frequent in sAH patients, and 10 were more frequent in CAP patients. After adjustment for confounding factors sAH patients were found to have higher levels of Haemophilus. For alcoholic patients, specific intestinal microbiota signatures are associated with different complications. Patients with CAP and sAH also display specific dysbiosis relative to AC.

Bile acid homeostasis and intestinal dysbiosis in alcoholic hepatitis.

BACKGROUND: Intestinal microbiota plays an important role in bile acid homeostasis. AIM: To study the structure of the intestinal microbiota and its function in bile acid homeostasis in alcoholic patients based on the severity of alcoholic liver disease. METHODS: In this prospective study, we included four groups of active alcoholic patients (N = 108): two noncirrhotic, with (noCir_AH, n = 13) or without alcoholic hepatitis (noCir_noAH, n = 61), and two cirrhotic, with (Cir_sAH, n = 17) or without severe alcoholic hepatitis (Cir_noAH, n = 17). Plasma and faecal bile acid profiles and intestinal microbiota composition were assessed. RESULTS: Plasma levels of total bile acids (84.6 vs 6.8 µmol/L, P < 0.001) and total ursodeoxycholic acid (1.3 vs 0.3 µmol/L, P = 0.03) were higher in cirrhosis with severe alcoholic hepatitis (Cir_sAH) than Cir_noAH, whereas total faecal (2.4 vs 11.3, P = 0.01) and secondary bile acids (0.7 vs 10.7, P < 0.01) levels were lower. Cir_sAH patients had a different microbiota than Cir_noAH patients: at the phyla level, the abundance of Actinobacteria (9 vs 1%, P = 0.01) was higher and that of Bacteroidetes was lower (25 vs 40%, P = 0.04). Moreover, the microbiota of Cir_sAH patients showed changes in the abundance of genes involved in 15 metabolic pathways, including upregulation of glutathione metabolism, and downregulation of biotin metabolism. CONCLUSIONS: Patients with Cir_sAH show specific changes of the bile acid pool with a shift towards more hydrophobic and toxic species that may be responsible for the specific microbiota changes. Conversely, the microbiota may also alter the bile acid pool by transforming primary to secondary bile acids, leading to a vicious cycle.

Transplantation of human microbiota into conventional mice durably reshapes the gut microbiota.

Human microbiota-associated (HMA) mice are an important model to study the relationship between liver diseases and intestinal microbiota. We describe a new method to humanize conventional mice based on bowel cleansing with polyethylene glycol followed by fecal microbiota transplantation (FMT) from a human donor. Four successive bowel cleansings were sufficient to empty the intestine and decrease the microbiota by 90%. We then compared four different strategies based on the frequency of FMT over four weeks: (1) twice a week; (2) once a week; (3) two FMTs; (4) one FMT. We were able to transfer human bacteria to mice, irrespective of the strategy used. We detected human bacteria after four weeks, even if only one FMT was performed, but there was a shift of the microbiota over time. FMT twice a week for four weeks was too frequent and perturbed the stability of the newly formed ecosystem. FMT once a week appears to be the best compromise as it allowed engraftment of Faecalibacterium, and a higher diversity of bacteria belonging to the Bacteroidales order. Our easy to establish HMA mouse model could be used as an alternative to classical HMA mice to study the relationship between the liver and the microbiota.

Microbiota, Liver Diseases, and Alcohol.

Being overweight and obesity are the leading causes of liver disease in Western countries. Liver damage induced by being overweight can range from steatosis, harmless in its simple form, to steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Alcohol consumption is an additional major cause of liver disease. Not all individuals who are overweight or excessively consume alcohol develop nonalcoholic fatty liver diseases (NAFLD) or alcoholic liver disease (ALD) and advanced liver disease. The role of the intestinal microbiota (IM) in the susceptibility to liver disease in this context has been the subject of recent studies. ALD and NAFLD appear to be influenced by the composition of the IM, and dysbiosis is associated with ALD and NAFLD in rodent models and human patient cohorts. Several microbial metabolites, such as short-chain fatty acids and bile acids, are specifically associated with dysbiosis. Recent studies have highlighted the causal role of the IM in the development of liver diseases, and the use of probiotics or prebiotics improves some parameters associated with liver disease. Several studies have made progress in deciphering the mechanisms associated with the modulation of the IM. These data have demonstrated the intimate relationship between the IM and metabolic liver disease, suggesting that targeting the gut microbiota could be a new preventive or therapeutic strategy for these diseases.