A purified diet affects intestinal epithelial proliferation and barrier functions through gut microbial alterations.

The gut microbiota plays a crucial role in maintaining epithelial barrier function. Although multiple studies have demonstrated the significance of dietary factors on the gut microbiota and mucosal barrier function, the impact of a purified diet, which has long been used in various animal experiments, on intestinal homeostasis remains to be elucidated. Here, we compared the impact of two different types of diets, a crude diet and an AIN-93G-formula purified diet, on epithelial integrity and the gut microbiota. Purified diet-fed mice exhibited shorter villi and crypt lengths and slower epithelial turnover, particularly in the ileum. In addition, antimicrobial products, including REG3γ, were substantially decreased in purified diet-fed mice. Purified diet feeding also suppressed α1,2-fucosylation on the epithelial surface. Furthermore, the purified diet induced metabolic rewiring to fatty acid oxidation and ketogenesis. 16S ribosomal RNA gene sequencing of the ileal contents and mucus layer revealed distinct gut microbiota compositions between the purified and crude diet-fed mice. Purified diet feeding reduced the abundance of segmented filamentous bacteria (SFB), which potently upregulate REG3γ and fucosyltransferase 2 (Fut2) by stimulating group 3 innate lymphoid cells (ILC3s) to produce IL-22. These observations illustrate that the intake of a crude diet secures epithelial barrier function by facilitating SFB colonization, whereas a purified diet insufficiently establishes the epithelial barrier, at least partly owing to the loss of SFB. Our data suggest that the influence of purified diets on the epithelial barrier integrity should be considered in experiments using purified diets.

MZB1-mediated IgA secretion suppresses the development and progression of colorectal cancer triggered by gut inflammation.

Colorectal cancer (CRC) ranks among the top causes of mortality globally. Gut inflammation is one crucial risk factor that augments CRC development since patients suffering from inflammatory bowel disease have an increased incidence of CRC. The role of immunoglobulin (Ig)A in maintaining gut homeostasis and preventing inflammation has been well established. Our earlier work demonstrated that the marginal zone and B1 cell-specific protein (MZB1) promotes gut IgA secretion and its absence results in pronounced dextran sulfate sodium salt (DSS)-induced colitis. In the present study, we explored the role of MZB1 in CRC development using the azoxymethane (AOM)/DSS-induced CRC model. We observed an increase in both the number and size of the tumor nodules in Mzb1-/- mice compared with Mzb1+/+ mice. The increase in CRC development and progression in Mzb1-/- mice was associated with reduced intestinal IgA levels, altered gut flora, and more severe gut and systemic inflammation. Oral administration of the monoclonal IgA, W27, alleviated both the gut inflammation and AOM/DSS-induced CRC. Notably, cohousing Mzb1+/+ and Mzb1-/- mice from the 10th day after birth led to similar CRC development. Our findings underscore the pivotal role of MZB1-mediated IgA secretion in suppressing the onset and progression of CRC triggered by gut inflammation. Moreover, our study highlights the profound impact of microbiota composition, modulated by gut IgA levels, on gut inflammation. Nonetheless, establishing a direct correlation between the severity of colitis and subsequent CRC development and the presence or absence of a particular microbiota is challenging.

α-Glucosidase inhibitors boost gut immunity by inducing IgA responses in Peyer's patches.

Peyer's patches (PPs) are specialized gut-associated lymphoid tissues that initiate follicular helper T (Tfh)-mediated immunoglobulin A (IgA) response to luminal antigens derived from commensal symbionts, pathobionts, and dietary sources. IgA-producing B cells migrate from PPs to the small intestinal lamina propria and secrete IgA across the epithelium, modulating the ecological balance of the commensal microbiota and neutralizing pathogenic microorganisms. α-glucosidase inhibitors (α-GIs) are antidiabetic drugs that inhibit carbohydrate digestion in the small intestinal epithelium, leading to alterations in the commensal microbiota composition and metabolic activity. The commensal microbiota and IgA responses exhibit bidirectional interactions that modulate intestinal homeostasis and immunity. However, the effect of α-GIs on the intestinal IgA response remains unclear. We investigated whether α-GIs affect IgA responses by administering voglibose and acarbose to mice via drinking water. We analyzed Tfh cells, germinal center (GC) B cells, and IgA-producing B cells in PPs by flow cytometry. We also assessed pathogen-specific IgA responses. We discovered that voglibose and acarbose induced Tfh cells, GCB cells, and IgA-producing B cells in the PPs of the proximal small intestine in mice. This effect was attributed to the modification of the microbiota rather than a shortage of monosaccharides. Furthermore, voglibose enhanced secretory IgA (S-IgA) production against attenuated Salmonella Typhimurium. Our findings reveal a novel mechanism by which α-GIs augment antigen-specific IgA responses by stimulating Tfh-GCB responses in PPs, and suggest a potential therapeutic application as an adjuvant for augmenting mucosal vaccines.

Safe and efficient oral allergy immunotherapy using one-pot-prepared mannan-coated allergen nanoparticles.

Allergen immunotherapy (AIT) is the only curative treatment for allergic diseases. However, AIT has many disadvantages related to efficiency, safety, long-term duration, and patient compliance. Dendritic cells (DCs) have an important role in antigen-specific tolerance induction; thus, DC-targeting strategies to treat allergies such as glutaraldehyde crosslinked antigen to mannoprotein (MAN) have been established. However, glutaraldehyde crosslinking may reduce the antigen presentation efficiency of DCs. To overcome this, we developed a MAN-coated ovalbumin (OVA) nanoparticle (MDO), which uses intermolecular disulfide bond to crosslink OVA and MAN. MDO effectively targeted DCs resulting in tolerogenic DCs, and promoted higher antigen presentation efficiency by DCs compared with OVA or glutaraldehyde crosslinked nanoparticles. In vitro and in vivo experiments showed that DCs exposed to MDO induced Treg cells. Moreover, MDO had low reactivity with anti-OVA antibodies and did not induce anaphylaxis in allergic mice, demonstrating its high safety profile. In a mouse model of allergic asthma, MDO had significant preventative and therapeutic effects when administered orally or subcutaneously. Therefore, MDO represents a promising new approach for the efficient and safe treatment of allergies.

Gut microbiota-derived lipid metabolites facilitate regulatory T cell differentiation.

Commensal bacteria-derived metabolites are critical in regulating the host immune system. Although the impact of gut microbiota-derived hydrophilic metabolites, such as short-chain fatty acids, on immune cell functions and development has been well documented, the immunomodulatory effects of gut microbiota-derived lipids are still of interest. Here, we report that lipid extracts from the feces of specific-pathogen-free (SPF), but not germ-free (GF), mice showed regulatory T (Treg)-cell-inducing activity. We conducted RP-HPLC-based fractionation and liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based lipidome profiling and identified two bioactive lipids, 9,10-dihydroxy-12Z-octadecenoic acid (9,10-DiHOME) and all-trans retinoic acid (atRA), with Treg-inducing activity in vitro. The luminal abundance of 9,10-DiHOME in the large intestine was significantly decreased by dextran sulfate sodium (DSS)-induced colitis, indicating that 9,10-DiHOME may be a potential biomarker of colitis. These observations implied that commensal bacteria-derived lipophilic metabolites might contribute to Treg development in the large intestine.

Dysfunction of Foxp3+ Regulatory T Cells Induces Dysbiosis of Gut Microbiota via Aberrant Binding of Immunoglobulins to Microbes in the Intestinal Lumen.

Foxp3+ regulatory T (Treg) cells prevent excessive immune responses against dietary antigens and commensal bacteria in the intestine. Moreover, Treg cells contribute to the establishment of a symbiotic relationship between the host and gut microbes, partly through immunoglobulin A. However, the mechanism by which Treg cell dysfunction disturbs the balanced intestinal microbiota remains unclear. In this study, we used Foxp3 conditional knockout mice to conditionally ablate the Foxp3 gene in adult mice and examine the relationship between Treg cells and intestinal bacterial communities. Deletion of Foxp3 reduced the relative abundance of Clostridia, suggesting that Treg cells have a role in maintaining Treg-inducing microbes. Additionally, the knockout increased the levels of fecal immunoglobulins and immunoglobulin-coated bacteria. This increase was due to immunoglobulin leakage into the gut lumen as a result of loss of mucosal integrity, which is dependent on the gut microbiota. Our findings suggest that Treg cell dysfunction leads to gut dysbiosis via aberrant antibody binding to the intestinal microbes.

Dietary iodine attenuates allergic rhinitis by inducing ferroptosis in activated B cells.

Iodine-containing formulations have been widely used to treat iodine deficiency and as antiseptics. Lecithin-bound iodine (LBI) has been approved to treat allergic diseases in Japan; however, its underlying mechanism remains unknown. In this study, we show that LBI ameliorated disease symptoms in an ovalbumin (OVA)-induced allergic rhinitis mouse model. LBI suppressed OVA-specific IgE production by attenuating germinal center (GC) reaction in the draining lymph nodes. The antiallergic effect of LBI is most likely attributed to increased serum iodine levels but not thyroid hormone levels. In vitro treatment of activated B cells with potassium iodide induced ferroptosis by increasing intracellular reactive oxygen species (ROS) and ferrous iron in a concentration-dependent manner. Accordingly, LBI diets increased ROS levels in GC B cells of the draining lymph nodes. This study suggests that iodine directly promotes ferroptosis in activated B cells and attenuates GC reactions, leading to the alleviation of allergic symptoms.

Medium-chain fatty acids suppress lipotoxicity-induced hepatic fibrosis via the immunomodulating receptor GPR84.

Medium-chain triglycerides (MCTs), which consist of medium-chain fatty acids (MCFAs), are unique forms of dietary fat with various health benefits. G protein-coupled 84 (GPR84) acts as a receptor for MCFAs (especially C10:0 and C12:0); however, GPR84 is still considered an orphan receptor, and the nutritional signaling of endogenous and dietary MCFAs via GPR84 remains unclear. Here, we showed that endogenous MCFA-mediated GPR84 signaling protected hepatic functions from diet-induced lipotoxicity. Under high-fat diet (HFD) conditions, GPR84-deficient mice exhibited nonalcoholic steatohepatitis (NASH) and the progression of hepatic fibrosis but not steatosis. With markedly increased hepatic MCFA levels under HFD, GPR84 suppressed lipotoxicity-induced macrophage overactivation. Thus, GPR84 is an immunomodulating receptor that suppresses excessive dietary fat intake-induced toxicity by sensing increases in MCFAs. Additionally, administering MCTs, MCFAs (C10:0 or C12:0, but not C8:0), or GPR84 agonists effectively improved NASH in mouse models. Therefore, exogenous GPR84 stimulation is a potential strategy for treating NASH.

Spi-B alleviates food allergy by securing mucosal barrier and immune tolerance in the intestine.

Food allergy is a type I allergic reaction induced by mast cells and is mainly activated by allergen-specific immunoglobulin (Ig)E. Spi-B is an E26-transformation-specific (Ets) family transcription factor essential for the differentiation and functional maturation of several immune cell subsets, including mast cells. However, the possible involvement of Spi-B in food allergy remains unclear. In this study, we found that Spi-B-deficient mice were highly susceptible to food allergy to ovalbumin (OVA), as indicated by the exacerbation of diarrhea and elevation of serum IgE levels. These pathological changes were associated with enhanced mast cell infiltration into the intestinal lamina propria. Activation of mast cells in the intestinal mucosa was observed in Spib -/- mice, even under physiological conditions. Accordingly, Spi-B deficiency increased the translocation of fluorescently labeled dextran from the lumen to the serum, suggesting increased intestinal permeability in Spib -/- mice. Moreover, Spib -/- mice showed defects in oral tolerance induction to OVA. These data illustrate that Spi-B suppresses the development of food allergies by controlling the activation of intestinal mast cells and by inducing immune tolerance to food allergens.

A Novel HDAC1-Selective Inhibitor Attenuates Autoimmune Arthritis by Inhibiting Inflammatory Cytokine Production.

Rheumatoid arthritis (RA) is systemic autoimmune arthritis that causes joint inflammation and destruction. Accumulating evidence has shown that inhibitors of class I histone deacetylases (HDACs) (i.e., HDAC1, 2, 3, and 8) are potential therapeutic candidates as targeted synthetic disease-modifying antirheumatic drugs (tsDMARDs). Nevertheless, the inhibition of class I HDACs has severe adverse effects because of their broad spectrum. We evaluated the therapeutic effect of a novel selective HDAC1 inhibitor TTA03-107 for collagen-induced arthritis (CIA) and collagen antibody-induced arthritis (CAIA) models in mice. We also examined the effect of TTA03-107 in bone marrow-derived macrophages (BMDMs) and T helper 17 (Th17) cells in vitro. Here, we delineate that TTA03-107 reduced the severity of autoimmune arthritis without obvious adverse effects in CIA and CAIA models. Moreover, TTA03-107 suppressed the production of inflammatory cytokines, such as interleukin (IL)-1ß, tumor necrosis factor (TNF)-α, and IL-17A, in serum and joint tissue. In vitro treatment of BMDMs with TTA03-107 dampened the M1 differentiation and inflammatory cytokine production. TTA03-107 also suppressed the differentiation of Th17 cells. These results demonstrate that TTA03-107 can attenuate the development of arthritis in experimental RA models by inhibiting the differentiation and activation of macrophages and Th17 cells. Therefore, TTA03-107 is a potential tsDMARD candidate.

Dietary-protein sources modulate host susceptibility to Clostridioides difficile infection through the gut microbiota.

Clostridioides difficile causes nosocomial antibiotic-associated diarrhea on a global scale. Susceptibility to C. difficile infection (CDI) is influenced by the composition and metabolism of gut microbiota, which in turn are affected by diet. However, the mechanism underlying the interplay between diet and gut microbiota that modulates susceptibility to CDI remains unclear. Here, we show that a soy protein diet increases the mortality of antibiotic-treated, C. difficile-infected mice while also enhancing the intestinal levels of amino acids (aas) and relative abundance of Lactobacillus genus. Indeed, Ligilactobacillus murinus-mediated fermentation of soy protein results in the generation of aas, thereby promoting C. difficile growth, and the process involves the anchored cell wall proteinase PrtP. Thus, mutual interaction between dietary protein and the gut microbiota is a critical factor affecting host susceptibility to CDI, suggesting that dietary protein sources can be an important determinant in controlling the disease.

D-Tryptophan suppresses enteric pathogen and pathobionts and prevents colitis by modulating microbial tryptophan metabolism.

D-Amino acids (D-AAs) have various functions in mammals and microbes. D-AAs are produced by gut microbiota and can act as potent bactericidal molecules. Thus, D-AAs regulate the ecological niche of the intestine; however, the actual impacts of D-AAs in the gut remain unknown. In this study, we show that D-Tryptophan (D-Trp) inhibits the growth of enteric pathogen and colitogenic pathobionts. The growth of Citrobacter rodentium in vitro is strongly inhibited by D-Trp treatment. Moreover, D-Trp protects mice from lethal C. rodentium infection via reduction of the pathogen. Additionally, D-Trp prevents the development of experimental colitis by the depletion of specific microbes in the intestine. D-Trp increases the intracellular level of indole acrylic acid (IA), a key molecule that determines the susceptibility of enteric microbes to D-Trp. Treatment with IA improves the survival of mice infected with C. rodentium. Hence, D-Trp could act as a gut environmental modulator that regulates intestinal homeostasis.

Cooperative action of gut-microbiota-accessible carbohydrates improves host metabolic function.

Microbiota-accessible carbohydrates (MACs) exert health-promoting effects, but how each MAC impacts gut microbiota and regulates host physiology remains unclear. Here, we show that l-arabinose and sucrose cooperatively act on gut microbiota and exert anti-obesogenic effects. Specifically, l-arabinose, a monosaccharide that is poorly absorbed in the gut and inhibits intestinal sucrase, suppresses diet-induced obesity in mice in the presence of sucrose. Additionally, the suppressive effect of l-arabinose on adiposity is abrogated in mice lacking the short-chain fatty acid (SCFA) receptors GPR43 and GPR41. Mechanistically, l-arabinose increases the relative abundance of acetate and propionate producers (e.g., Bacteroides), while sucrose enhances SCFA production. Furthermore, l-arabinose and sucrose activate the glycolytic and pentose phosphate pathways of Bacteroides, respectively, indicating that they synergistically promote acetate production through distinct pathways. These findings suggest that each MAC has a unique property and thus may serve as a precision gut-microbiota modulator to promote host homeostasis.

Thymic epithelial cells co-opt lineage-defining transcription factors to eliminate autoreactive T cells.

Medullary thymic epithelial cells (mTECs) ectopically express thousands of peripheral-tissue antigens (PTAs), which drive deletion or phenotypic diversion of self-reactive immature T cells during thymic differentiation. Failure of PTA expression causes multiorgan autoimmunity. By assaying chromatin accessibility in individual mTECs, we uncovered signatures of lineage-defining transcription factors (TFs) for skin, lung, liver, and intestinal cells-including Grhl, FoxA, FoxJ1, Hnf4, Sox8, and SpiB-in distinct mTEC subtypes. Transcriptomic and histologic analyses showed that these subtypes, which we collectively term mimetic cells, expressed PTAs in a biologically logical fashion, mirroring extra-thymic cell types while maintaining mTEC identity. Lineage-defining TFs bound to mimetic-cell open chromatin regions and were required for mimetic cell accumulation, whereas the tolerogenic factor Aire was partially and variably required. Expression of a model antigen in mimetic cells sufficed to induce cognate T cell tolerance. Thus, mTECs co-opt lineage-defining TFs to drive mimetic cell accumulation, PTA expression, and self-tolerance.

Gut microbiota reinforce host antioxidant capacity via the generation of reactive sulfur species.

Gut microbiota act beyond the gastrointestinal tract to regulate the physiology of the host. However, their contribution to the antioxidant capacity of the host remains largely understudied. In this study, we observe that gut bacteria increase the steady-state plasma levels of high-antioxidant molecules, reactive sulfur species (RSS), such as hydrogen sulfide and cysteine persulfide (CysSSH), in the host. Moreover, gut bacteria utilize cystine as a substrate to enzymatically produce CysSSH. Administration of cystine to mice increases their plasma levels of RSS and suppresses the concanavalin-A-induced oxidative stress and liver damage in a gut-microbiota-dependent manner. We find that gut bacteria belonging to the Lachnospiraceae and Ruminococcaceae families have a high capacity to produce RSS, requiring pyridoxal 5'-phosphate for their enzymatic reactions. Collectively, our data demonstrate that gut microbiota enhance the antioxidant capacity of the host through the generation of RSS.

Skate-skin mucin, rich in sulfated sugars and threonine, promotes proliferation of Akkermansia muciniphila in feeding tests in rats and in vitro fermentation using human feces.

Dietary factors, affect Akkermansia muciniphila (AM) abundance in the colon, have attracted attention, driven by the inverse correlation between AM abundance and metabolic disorders. We prepared skate-skin mucin (SM), porcine stomach mucin (PM), and rat gastrointestinal mucin (RM). SM contained more sulfated sugars and threonine than PM or RM. Rats were fed a control diet or diets including SM, PM, or RM (15 g/kg), or SM (12 g/kg) from 5 different threonine contents for 14 d. Cecal total bacteria and AM were less and more numerous, respectively, in SM-fed rats than the others, but SM did not affect microbial species richness. Low-threonine SM did not induce AM proliferation. The in vitro fermentation with human feces showed that the rate of AM increase was greater with SM than PM. Collectively, heavy SM sulfation facilitates a priority supply of SM-derived amino sugars and threonine that promotes AM proliferation in rats and human feces.

Glia maturation factor-γ is involved in S1P-induced marginal zone B-cell chemotaxis and optimal IgM production to type II T-independent antigen.

Marginal zone B cells (MZBs) represent a unique B-cell sub-population that rapidly differentiate into IgM-secreting plasma cells in response to T-independent (T-I) antigen. Sphingosine 1-phosphate (S1P) promotes MZB localization to the marginal zone. However, intracellular molecules involved in MZB localization and migration remain largely unknown. Here, we show that MZBs lacking the glia maturation factor-γ (GMFG) are impaired in chemotaxis toward S1P under both in vitro and in vivo conditions, suggesting that GMFG is an effector downstream of S1P receptors. GMFG undergoes serine phosphorylation upon S1P stimulation and is required for S1P-induced desensitization of S1P receptor 1 (S1PR1). Compared with wild-type mice, Gmfg-/- mice produce elevated levels of 4-hydroxy-3-nitrophenyl-acetyl (NP)-specific IgM against a T-I type II antigen, NP-Ficoll, accompanied by dysregulated MZB localization. These results identify GMFG as a regulator of S1P-induced MZB chemotaxis and reveal a role for MZB localization in the marginal zone for optimal IgM production against a T-I antigen.

Characterization of M Cells in Tear Duct-Associated Lymphoid Tissue of Mice: A Potential Role in Immunosurveillance on the Ocular Surface.

The ocular mucosal tissues are exposed to potentially harmful foreign antigens in the air and tear fluid. The tear duct-associated lymphoid tissue (TALT) may contribute to immune surveillance in the eye region. Follicle-associated epithelium (FAE) of TALTs is classified as stratified squamous epithelium and consists of squamous epithelial cells arranged in layers on the basement membrane. In contrast, most mucosa-associated lymphoid tissue is covered by a monolayer of epithelium containing microfold (M) cells. Therefore, antigen uptake and the presence of M cells in TALT are not fully understood. The present study found that a small population of FAE cells in the TALT expressed intestinal M-cell markers, namely Sox8, Tnfaip2, GP2, and OPG. This cell population was identified as functional M cells because of their uptake capacity of luminal nanoparticles. In addition, RANKL, which is essential for M-cell differentiation, was expressed by stroma-like cells at the subepithelial region and its receptor RANK by the FAE in the TALT. The administration of RANKL markedly increased the number of Sox8+ M cells. In contrast, deficiency in OPG, an endogenous inhibitor of RANKL, increased the number of M cells in the TALT. These data demonstrate that the RANKL-RANK axis is essential for M-cell differentiation in the TALT. Furthermore, immunization via eye drops elicited the production of antigen-specific antibodies in tears, which was enhanced by RANKL administration. Thus, TALT M cells play an important role in the immunosurveillance of the eye region.

A Retinoid X Receptor Agonist Directed to the Large Intestine Ameliorates T-Cell-Mediated Colitis in Mice.

Retinoid X receptor (RXR) is a nuclear receptor that heterodimerizes with several nuclear receptors, integrating ligand-mediated signals across the heterodimers. Synthetic RXR agonists have been developed to cure certain inflammatory diseases, including inflammatory bowel diseases (IBDs). However, pre-existing RXR agonists, which are lipophilic and readily absorbed in the upper intestine, cause considerable adverse effects such as hepatomegaly, hyperlipidemia, and hypothyroidism. To minimize these adverse effects, we have developed an RXR agonist, NEt-3IB, which has lipophilic and thus poorly absorptive properties. In this study, we evaluated the effects of NEt-3IB in an experimental murine colitis model induced through the adoptive transfer of CD45RBhighCD4+ T cells. Pharmacokinetic studies demonstrated that the major portion of NEt-3IB was successfully delivered to the large intestine after oral administration. Notably, NEt-3IB treatment suppressed the development of T cell-mediated chronic colitis, as indicated by improvement of wasting symptoms, inflammatory infiltration, and mucosal hyperplasia. The protective effect of NEt-3IB was mediated by the suppression of IFN-γ-producing Th1 cell expansion in the colon. In conclusion, NEt-3IB, a large intestine-directed RXR agonist, is a promising drug candidate for IBDs.

Commensal microbe-derived acetate suppresses NAFLD/NASH development via hepatic FFAR2 signalling in mice.

BACKGROUND: Non-alcoholic liver disease (NAFLD) is the hepatic manifestation of metabolic syndrome, and it can progress to non-alcoholic steatohepatitis (NASH). Alterations in the gut microbiome have been implicated in the development of NAFLD/NASH, although the underlying mechanisms remain unclear. RESULTS: We found that the consumption of the prebiotic inulin markedly ameliorated the phenotype of NAFLD/NASH, including hepatic steatosis and fibrosis, in mice. Inulin consumption resulted in global changes in the gut microbiome, including concomitant enrichment of the genera Bacteroides and Blautia, and increased concentrations of short-chain fatty acids, particularly acetate, in the gut lumen and portal blood. The consumption of acetate-releasing resistant starch protected against NAFLD development. Colonisation by Bacteroides acidifaciens and Blautia producta in germ-free mice resulted in synergetic effects on acetate production from inulin. Furthermore, the absence of free fatty acid receptor 2 (FFAR2), an acetate receptor, abolished the protective effect of inulin, as indicated by the more severe liver hypertrophy, hypercholesterolaemia and inflammation. These effects can be attributed to an exacerbation of insulin resistance in the liver, but not in muscle or adipose tissue. CONCLUSION: These findings demonstrated that the commensal microbiome-acetate-FFAR2 molecular circuit improves insulin sensitivity in the liver and prevents the development of NAFLD/NASH. Video abstract.