Mechanisms and regulation of IL-22-mediated intestinal epithelial homeostasis and repair

Wogonin improves colitis by activating the AhR pathway to regulate the plasticity of ILC3/ILC1

BACKGROUND

Intestinal barrier dysfunction caused by the disrupted balance of group 3 innate lymphoid cells (ILC3)/group 1 innate lymphoid cells (ILC1) is a significant feature in the pathogenesis of inflammatory bowel disease (IBD). Activation of aryl hydrocarbon receptor (AhR) signaling contributes to the maintenance of ILC3/ILC1 balance. Wogonin, a natural flavonoid from Scutellaria baicalensis Georgi, can repair intestinal mucosal damage of IBD. However, it remains unclear if wogonin can exert a therapeutic effect by activating the AhR pathway to regulate the plasticity of ILC3/ILC1.

PURPOSE

In this study, we investigated the immunomodulatory effects of wogonin on IBD and its potential mechanisms in vitro and in vivo.

STUDY DESIGN AND METHODS

Chronic colitis was induced by four cycles of 2 % DSS treatment in mice. 20 mg kg-1/day wogonin was administrated by oral gavage and mice were treated intraperitoneally with 10 mg kg-1/2 days CH223191 to block the AhR pathway. Colon tissues were processed for histopathological examination and evaluation of the epithelial barrier function by immunohistochemistry. The activation of the AhR pathway and the plasticity of ILC3/ILC1 were determined by western blot and flow cytometry. Then, we also detected the intestinal microflora and their metabolites by 16 s sequencing and non-targeted Metabolomics analysis. Furthermore, an in vitro culture system consisting of MNK3 cells and NCM460 cells, and a CETSA assay were performed to confirm the molecular mechanism.

RESULTS

Wogonin ameliorated histological severity of the colon, decreased the secretion of inflammatory factors, and increased tight junction proteins in colitis mice. These effects are associated with the tendency of conversion from ILC3 to ILC1 prevented by wogonin, which was offset by AhR antagonist CH223191. In addition, wogonin exerted the curative effect by altering gut microbiota to produce metabolites such as Kynurenic acid, and 1H-Indole-3-carboxaldehyde as AhR endogenous ligands. In vitro data further verified that wogonin as an exogenous ligand directly binds to the structural domain of AhR by CETSA. Also, the supernatant of MNK-3 cells stimulated with wogonin enhanced expression of Occludin and Claudin1 in NCM460 cells induced by LPS.

CONCLUSION

Cumulatively, our study illustrated that wogonin improved the outcomes of DSS-induced chronic colitis via regulating the plasticity of ILC3/ILC1. Its specific mechanism is to binding to AhR directly, and to activate the AhR pathway indirectly by altering the tryptophan metabolisms of gut microbiota.

The role of goblet cells in Crohn' s disease

The prevalence of Crohn's disease (CD), a subtype of inflammatory bowel disease (IBD), is increasing worldwide. The pathogenesis of CD is hypothesized to be related to environmental, genetic, immunological, and bacterial factors. Current studies have indicated that intestinal epithelial cells, including columnar, Paneth, M, tuft, and goblet cells dysfunctions, are strongly associated with these pathogenic factors. In particular, goblet cells dysfunctions have been shown to be related to CD pathogenesis by direct or indirect ways, according to the emerging studies. The mucus barrier was established with the help of mucins secreted by goblet cells. Not only do the mucins mediate the mucus barrier permeability and bacterium selection, but also, they are closely linked with the endothelial reticulum stress during the synthesis process. Goblet cells also play a vital role in immune response. It was indicated that goblet cells take part in the antigen presentation and cytokines secretion process. Disrupted goblet cells related immune process were widely discovered in CD patients. Meanwhile, dysbiosis of commensal and pathogenic microbiota can induce myriad immune responses through mucus and goblet cell-associated antigen passage. Microbiome dysbiosis lead to inflammatory reaction against pathogenic bacteria and abnormal tolerogenic response. All these three pathways, including the loss of mucus barrier function, abnormal immune reaction, and microbiome dysbiosis, may have independent or cooperative effect on the CD pathogenesis. However, many of the specific mechanisms underlying these pathways remain unclear. Based on the current understandings of goblet cell's role in CD pathogenesis, substances including butyrate, PPARγagonist, Farnesoid X receptor agonist, nuclear factor-Kappa B, nitrate, cytokines mediators, dietary and nutrient therapies were all found to have potential therapeutic effects on CD by regulating the goblet cells mediated pathways. Several monoclonal antibodies already in use for the treatment of CD in the clinical settings were also found to have some goblet cells related therapeutic targets. In this review, we introduce the disease-related functions of goblet cells, their relationship with CD, their possible mechanisms, and current CD treatments targeting goblet cells.

Interleukin-22 Alleviates Caerulein-Induced Acute Pancreatitis by Activating AKT/mTOR Pathway

BACKGROUND

Acute pancreatitis (AP) is one of the most common acute abdominal disorders; due to the lack of specific treatment, the treatment of acute pancreatitis, especially serious acute pancreatitis (SAP), is difficult and challenging. We will observe the changes of Interleukin -22 levels in acute pancreatitis animal models, and explore the mechanism of Interleukin -22 in acute pancreatitis.

OBJECTIVE

This study aims to assess the potential protective effect of Interleukin -22 on caerulein-induced acute pancreatitis and to explore its mechanism.

METHODS

Blood levels of amylase and lipase and Interleukin -22 were assessed in mice with acute pancreatitis. In animal model and cell model of caerulein-induced acute pancreatitis, the mRNA levels of P62 and Beclin-1 were determined using PCR, and the protein expression of P62, LC3-II, mTOR, AKT, p-mTOR, and p-AKT were evaluated through Western blot analysis.

RESULTS

Interleukin -22 administration reduced blood amylase and lipase levels and mitigated tissue damage in acute pancreatitis mice model. Interleukin -22 inhibited the relative mRNA levels of P62 and Beclin-1, and the Interleukin -22 group showed a decreased protein expression of LC3-II and P62 and the phosphorylation of the AKT/mTOR pathway. Furthermore, we obtained similar results in the cell model of acute pancreatitis.

CONCLUSION

This study suggests that Interleukin -22 administration could alleviate pancreatic damage in caerulein-induced acute pancreatitis. This effect may result from the activation of the AKT/mTOR pathway, leading to the inhibition of autophagy. Consequently, Interleukin -22 shows potential as a treatment.

Interleukin-22 Contributes to Blood-Brain Barrier Disruption via STAT3/VEGFA Activation in Escherichia coli Meningitis

Escherichia coli continues to be the predominant Gram-negative pathogen causing neonatal meningitis worldwide. Inflammatory mediators have been implicated in the pathogenesis of meningitis and are key therapeutic targets. The role of interleukin-22 (IL-22) in various diseases is diverse, with both protective and pathogenic effects. However, little is understood about the mechanisms underlying the damaging effects of IL-22 on the blood-brain barrier (BBB) in E. coli meningitis. We observed that meningitic E. coli infection induced IL-22 expression in the serum and brain of mice. The tight junction proteins (TJPs) components ZO-1, Occludin, and Claudin-5 were degraded in the mouse brain and human brain microvascular endothelial cells (hBMEC) following IL-22 administration. Moreover, the meningitic E. coli-caused increase in BBB permeability in wild-type mice was restored by knocking out IL-22. Mechanistically, IL-22 activated the STAT3-VEGFA signaling cascade in E. coli meningitis, thus eliciting the degradation of TJPs to induce BBB disruption. Our data indicated that IL-22 is an essential host accomplice during E. coli-caused BBB disruption and could be targeted for the therapy of bacterial meningitis.

Remodeling of Paranasal Sinuses Mucosa Functions in Response to Biofilm-Induced Inflammation

Rhinosinusitis (RS) is an acute (ARS) or chronic (CRS) inflammatory disease of the nasal and paranasal sinus mucosa. CRS is a heterogeneous condition characterized by distinct inflammatory patterns (endotypes) and phenotypes associated with the presence (CRSwNP) or absence (CRSsNP) of nasal polyps. Mucosal barrier and mucociliary clearance dysfunction, inflammatory cell infiltration, mucus hypersecretion, and tissue remodeling are the hallmarks of CRS. However, the underlying factors, their priority, and the mechanisms of inflammatory responses remain unclear. Several hypotheses have been proposed that link CRS etiology and pathogenesis with host (eg, "immune barrier") and exogenous factors (eg, bacterial/fungal pathogens, dysbiotic microbiota/biofilms, or staphylococcal superantigens). The abnormal interplay between these factors is likely central to the pathophysiology of CRS by triggering compensatory immune responses. Here, we discuss the role of the sinonasal microbiota in CRS and its biofilms in the context of mucosal zinc (Zn) deficiency, serving as a possible unifying link between five host and "bacterial" hypotheses of CRS that lead to sinus mucosa remodeling. To date, no clear correlation between sinonasal microbiota and CRS has been established. However, the predominance of Corynebacteria and Staphylococci and their interspecies relationships likely play a vital role in the formation of the CRS-associated microbiota. Zn-mediated "nutritional immunity", exerted via calprotectin, alongside the dysregulation of Zn-dependent cellular processes, could be a crucial microbiota-shaping factor in CRS. Similar to cystic fibrosis (CF), the role of SPLUNC1-mediated regulation of mucus volume and pH in CRS has been considered. We complement the biofilms' "mechanistic" and "mucin" hypotheses behind CRS pathogenesis with the "structural" one - associated with bacterial "corncob" structures. Finally, microbiota restoration approaches for CRS prevention and treatment are reviewed, including pre- and probiotics, as well as Nasal Microbiota Transplantation (NMT).

Aryl Hydrocarbon Receptor Regulates Muc2 Production Independently of IL-22 during Colitis

We previously reported that an aryl hydrocarbon receptor (AhR) ligand, indole-3-carbinol (I3C), was effective at reducing colitis severity through immune cell-mediated interleukin-22 (IL-22) production. Intestinal epithelial cells (IECs) are also involved in regulating colitis, so we investigated their AhR-mediated mechanisms in the current report. A transcriptome analysis of IECs in wildtype (WT) mice revealed that during colitis, I3C regulated select mucin proteins, which could be attributed to goblet cell development. To address this, experiments under in vivo colitis (mice) or in vitro colon organoid conditions were undertaken to determine how select mucin proteins were altered in the absence or presence of AhR in IECs during I3C treatment. Comparing WT to IEC-specific AhR knockout mice (AhRΔIEC), the results showed that AhR expression was essential in IECs for I3C-mediated protection during colitis. AhR-deficiency also impaired mucin protein expression, particularly mucin 2 (Muc2), independently of IL-22. Collectively, this report highlights the important role of AhR in direct regulation of Muc2. These results provide justification for future studies aimed at determining how AhR might regulate select mucins through mechanisms such as direct transcription binding to enhance production.

The role of interleukin-22 in mammalian intestinal homeostasis: Friend and foe

Interleukin-22 (IL-22) is an important cytokine in the intestinal environment. IL-22 is mainly produced by immune cells and targeted at nonimmune cells such as epithelial and stromal cells in a broad array of tissues such as -but not restricted to- the liver and adipose tissue. IL-22 therefore connects immune functions with metabolic functions of the host, and since it is induced by the microbiota, connects host functioning to the outside environment. IL-22 induces epithelial cell proliferation aiding in rapid epithelium regeneration and wound healing. Additionally, IL-22 activates antiapoptotic genes and DNA damage response pathways, enhancing epithelial cell survival. Recently, it has also been shown that IL-22 induces Paneth cell differentiation in humans. However, IL-22 can also contribute to intestinal epithelium damage and reduces microbial diversity in the intestine directly or indirectly by inducing excessive antimicrobial peptide production by epithelial cells. Moreover, IL-22 enhances angiogenesis and may therefore support tumorigenesis in the intestine. In conclusion, it appears that whether IL-22 has a beneficial or harmful effect in the mammalian intestine largely depends on its regulation. This review aims to provide a comprehensive overview of the current literature and emphasizes that IL-22 signaling outcome depends on the timing and duration of IL-22 production, the presence of it regulators such as IL-22BP, and the specific location of the cytokine production in the gastrointestinal tract.

Interleukin-22 enhanced the mucosal barrier and inhibited the invasion of Salmonella enterica in human-induced pluripotent stem cell-derived small intestinal epithelial cells

Human-induced pluripotent stem cell-derived small intestinal epithelial cell (hiPSC-SIEC) monolayers are useful in vitro models for evaluating the gut mucosal barrier; however, their reactivity to cytokines, which are closely related to the regulation of mucosal barrier function, remains unclear. Interleukin (IL)-22 is a cytokine that contributes to regulate the mucosal barrier in the intestinal epithelia. Using microarray and gene set enrichment analysis, we found that hiPSC-SIEC monolayers activate the immune response and enhance the mucosal barrier in response to IL-22. Moreover, hiPSC-SIEC monolayers induced the gene expression of antimicrobials, including the regenerating islet-derived protein 3 family. Furthermore, IL-22 stimulation upregulated Mucin 2 secretion and gene expression of an enzyme that modifies sugar chains, suggesting alteration of the state of the mucus layer of hiPSC-SIEC monolayers. To evaluate its physiological significance, we measured the protective activity against Salmonella enterica subsp. enterica infection in hiPSC-SIEC monolayers and found that prestimulation with IL-22 reduced the number of viable intracellular bacteria. Collectively, these results suggest that hiPSC-SIEC monolayers enhance the mucosal barrier and inhibit infection by pathogenic bacteria in response to IL-22, as previously reported. These results can contribute to the further application of hiPSC-SIECs in evaluating mucosal barriers.

A Narrative Review of Cytokine Networks: Pathophysiological and Therapeutic Implications for Inflammatory Bowel Disease Pathogenesis

Inflammatory bowel disease (IBD) is a lifelong inflammatory immune mediated disorder, encompassing Crohn's disease (CD) and ulcerative colitis (UC); however, the cause and specific pathogenesis of IBD is yet incompletely understood. Multiple cytokines produced by different immune cell types results in complex functional networks that constitute a highly regulated messaging network of signaling pathways. Applying biological mechanisms underlying IBD at the single omic level, technologies and genetic engineering enable the quantification of the pattern of released cytokines and new insights into the cytokine landscape of IBD. We focus on the existing literature dealing with the biology of pro- or anti-inflammatory cytokines and interactions that facilitate cell-based modulation of the immune system for IBD inflammation. We summarize the main roles of substantial cytokines in IBD related to homeostatic tissue functions and the remodeling of cytokine networks in IBD, which may be specifically valuable for successful cytokine-targeted therapies via marketed products. Cytokines and their receptors are validated targets for multiple therapeutic areas, we review the current strategies for therapeutic intervention and developing cytokine-targeted therapies. New biologics have shown efficacy in the last few decades for the management of IBD; unfortunately, many patients are nonresponsive or develop therapy resistance over time, creating a need for novel therapeutics. Thus, the treatment options for IBD beyond the immune-modifying anti-TNF agents or combination therapies are expanding rapidly. Further studies are needed to fully understand the immune response, networks of cytokines, and the direct pathogenetic relevance regarding individually tailored, safe and efficient targeted-biotherapeutics.

Modulation of Zebrafish (Danio rerio) Intestinal Mucosal Barrier Function Fed Different Postbiotics and a Probiotic from Lactobacilli

It is generally accepted that microbes play a critical role in maintaining gut barrier function, making them ideal to target in order to mitigate the effects of intestinal diseases such as inflammatory bowel disease with specialist supplementations such as probiotic or postbiotic preparations. In this study, specific strains of Lactobacillus helvictus both live and inactivated and Lactobacillus plantarum inactivated were fed to zebrafish at an inclusion level of 6 × 106 cells/g in order to assess the effects on gut barrier function and protection. Taken together, our results indicate that dietary administration of pro- or postbiotics strengthens the gut barrier function and innate immunity of healthy zebrafish in a strain-specific and process-dependent way. With some differences in the response intensity, the three treatments led to increased intestinal villi length and proportion of IELs, reinforcement of the GC population and up-regulated expression of biomarkers of AMP production and tight junction zona-occludin 2a (zo-2a). In addition, LPPost had an impact on the adaptive immune response, and we hypothesized that it conferred the potential to drive Th17/ILC3 immunity, as suggested by its effect on the gene expression of il22, of different AMPs, and the expression of zo2a. Moreover, LPPost showed the potential to drive Th1/ILC1-like immunity, with a higher percentage of CD8+ cells and higher ifnγ gene expression. In summary, the use of inactivated Lactobacilli species in this study represented a promising strategy for improving barrier function and regulating the immune fate of the intestinal mucosa in a strain-specific way.

Modulation of tryptophan metabolism via AHR-IL22 pathway mediates the alleviation of DSS-induced colitis by chitooligosaccharides with different degrees of polymerization

Oral administration of chitooligosaccharides (COS) has been reported to alleviate colitis in mice. However, the mechanism of action of COS with specific polymerization degree on gut inflammation and metabolism remains unclear. This study aimed to investigate the effects of chitobiose (COS2), chitotetraose (COS4), and chitohexaose (COS6) on colitis, and to elucidate their underlying mechanisms. COS2, COS4, and COS6 were able to significantly alleviate colonic injury and inflammation levels. COS6 has the best anti-inflammatory effect. Furthermore, COS6 could down-regulate the level of indoleamine-2,3-dioxygenase1 (IDO1) and restore the levels of indole, indoleacetic-3-acid (IAA), and indole-3-carbaldehyde (I3A) in the cecum of chronic colitis mice (p < 0.05), thereby regulating tryptophan metabolism. In the aromatic hydrocarbon receptor-IL-22 (AHR-IL-22) pathway, although there were differences between chronic colitis and acute colitis mice, COS intervention could restore the AHR-IL-22 pathway to normal, promote the expression of MUC2, and repair the intestinal mucosal barrier. In conclusion, the results of this study suggested that COS had a good inhibitory effect on IDO1 under inflammation and the changes of AHR and IL-22 levels at different stages of disease development. This provides new insights into the potential use of COS as a functional food for improving intestinal inflammation and metabolism.

Colitis-associated carcinogenesis: crosstalk between tumors, immune cells and gut microbiota

Colorectal cancer (CRC) is the third most common cancer worldwide. One of the main causes of colorectal cancer is inflammatory bowel disease (IBD), which includes ulcerative colitis (UC) and Crohn's disease (CD). Intestinal epithelial cells (IECs), intestinal mesenchymal cells (IMCs), immune cells, and gut microbiota construct the main body of the colon and maintain colon homeostasis. In the development of colitis and colitis-associated carcinogenesis, the damage, disorder or excessive recruitment of different cells such as IECs, IMCs, immune cells and intestinal microbiota play different roles during these processes. This review aims to discuss the various roles of different cells and the crosstalk of these cells in transforming intestinal inflammation to cancer, which provides new therapeutic methods for chemotherapy, targeted therapy, immunotherapy and microbial therapy.

Sympathetic activity regulates epithelial proliferation and wound healing via adrenergic receptor α2A

Innervation of the intestinal mucosa by the sympathetic nervous system is well described but the effects of adrenergic receptor stimulation on the intestinal epithelium remain equivocal. We therefore investigated the effect of sympathetic neuronal activation on intestinal cells in mouse models and organoid cultures, to identify the molecular routes involved. Using publicly available single-cell RNA sequencing datasets we show that the α2A isoform is the most abundant adrenergic receptor in small intestinal epithelial cells. Stimulation of this receptor with norepinephrine or a synthetic specific α2A receptor agonist promotes epithelial proliferation and stem cell function, while reducing differentiation in vivo and in intestinal organoids. In an anastomotic healing mouse model, adrenergic receptor α2A stimulation resulted in improved anastomotic healing, while surgical sympathectomy augmented anastomotic leak. Furthermore, stimulation of this receptor led to profound changes in the microbial composition, likely because of altered epithelial antimicrobial peptide secretion. Thus, we established that adrenergic receptor α2A is the molecular delegate of intestinal epithelial sympathetic activity controlling epithelial proliferation, differentiation, and host defense. Therefore, this receptor could serve as a newly identified molecular target to improve mucosal healing in intestinal inflammation and wounding.

Responsiveness to Vedolizumab Therapy in Ulcerative Colitis is Associated With Alterations in Immune Cell-Cell Communications

BACKGROUND

Ulcerative colitis (UC) and Crohn's disease are 2 types of inflammatory bowel disease (IBD), a group of chronic digestive disorders caused by aberrant immune responses to intestinal microbes. Although changes in the composition of immune cell subsets in the context of IBD have been previously described, the interactions and communication among cells are less well understood. Moreover, the precise mechanisms of action underlying many biologic therapies, including the anti-α4β7 integrin antagonist vedolizumab, remain incompletely understood. Our study aimed to explore possible additional mechanisms through which vedolizumab acts.

METHODS

We performed cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) on peripheral blood and colon immune cells derived from patients with ulcerative colitis treated with the anti-α4β7 integrin antagonist vedolizumab. We applied a previously published computational approach, NicheNet, to predict immune cell-cell interactions, revealing putative ligand-receptor pairs and key transcriptional changes downstream of these cell-cell communications (CCC).

RESULTS

We observed decreased proportions of T helper 17 (TH17) cells in UC patients who responded to vedolizumab and therefore focused the study on identifying cell-cell communications and signals of TH17 cells with other immune cells. For example, we observed that colon TH17 cells from vedolizumab nonresponders were predicted to have a greater degree of interactions with classical monocytes compared with responders, whereas colon TH17 cells from vedolizumab responders exhibited more interactions with myeloid dendritic cells compared with nonresponders.

CONCLUSIONS

Overall, our results indicate that efforts to elucidate cell-cell communications among immune and nonimmune cell types may increase the mechanistic understanding of current and investigational therapies for IBD.

Role of MAIT cells in gastrointestinal tract bacterial infections in humans: More than a gut feeling

Mucosa-associated invariant T (MAIT) cells are the largest population of unconventional T cells in humans. These antimicrobial T cells are poised with rapid effector responses following recognition of the cognate riboflavin (vitamin B2)-like metabolite antigens derived from microbial riboflavin biosynthetic pathway. Presentation of this unique class of small molecule metabolite antigens is mediated by the highly evolutionarily conserved major histocompatibility complex class I-related protein. In humans, MAIT cells are widely found along the upper and lower gastrointestinal tracts owing to their high expression of chemokine receptors and homing molecules directing them to these tissue sites. In this review, we discuss recent findings regarding the roles MAIT cells play in various gastrointestinal bacterial infections, and how their roles appear to differ depending on the etiological agents and the anatomical location. We further discuss the potential mechanisms by which MAIT cells contribute to pathogen control, orchestrate adaptive immunity, as well as their potential contribution to inflammation and tissue damage during gastrointestinal bacterial infections, and the ensuing tissue repair following resolution. Finally, we propose and discuss the use of the emerging three-dimensional organoid technology to test different hypotheses regarding the role of MAIT cells in gastrointestinal bacterial infections, inflammation, and immunity.

Th22 cells and the intestinal mucosal barrier

T-helper 22 (Th22) cells represent a novel subset of CD4+ T cells that exhibit distinctive characteristics, namely the secretion of IL-22 while abstaining from secreting IL-17 and interferon-γ (IFN-γ). These cells serve as the primary source of IL-22, and both Th22 cells and IL-22 are believed to play a role in maintaining intestinal mucosal homeostasis in inflammatory bowel disease (IBD). However, the precise functions of Th22 cells and IL-22 in this context remain a subject of debate. In this work, we aimed to elucidate their impact on the integrity of the intestinal mucosal barrier by presenting an overview of the molecular structure characteristics and functional effects of Th22 cells and IL-22. Furthermore, we would explore targeted treatment approaches and potential therapeutic strategies focusing on the Th22 and IL-22 pathways.

Impact of Western Diet and Ultra-Processed Food on the Intestinal Mucus Barrier

The intestinal epithelial barrier plays a key role in the absorption of nutrients and water, in the regulation of the interactions between luminal contents and the underlying immune cells, and in the defense against enteric pathogens. Additionally, the intestinal mucus layer provides further protection due to mucin secretion and maturation by goblet cells, thus representing a crucial player in maintaining intestinal homeostasis. However, environmental factors, such as dietary products, can disrupt this equilibrium, leading to the development of inflammatory intestinal disorders. In particular, ultra-processed food, which is broadly present in the Western diet and includes dietary components containing food additives and/or undergoing multiple industrial processes (such as dry heating cooking), was shown to negatively impact intestinal health. In this review, we summarize and discuss current knowledge on the impact of a Western diet and, in particular, ultra-processed food on the mucus barrier and goblet cell function, as well as potential therapeutic approaches to maintain and restore the mucus layer under pathological conditions.

Inulin diet uncovers complex diet-microbiota-immune cell interactions remodeling the gut epithelium

BACKGROUND

The continuous proliferation of intestinal stem cells followed by their tightly regulated differentiation to epithelial cells is essential for the maintenance of the gut epithelial barrier and its functions. How these processes are tuned by diet and gut microbiome is an important, but poorly understood question. Dietary soluble fibers, such as inulin, are known for their ability to impact the gut bacterial community and gut epithelium, and their consumption has been usually associated with health improvement in mice and humans. In this study, we tested the hypothesis that inulin consumption modifies the composition of colonic bacteria and this impacts intestinal stem cells functions, thus affecting the epithelial structure.

METHODS

Mice were fed with a diet containing 5% of the insoluble fiber cellulose or the same diet enriched with an additional 10% of inulin. Using a combination of histochemistry, host cell transcriptomics, 16S microbiome analysis, germ-free, gnotobiotic, and genetically modified mouse models, we analyzed the impact of inulin intake on the colonic epithelium, intestinal bacteria, and the local immune compartment.

RESULTS

We show that the consumption of inulin diet alters the colon epithelium by increasing the proliferation of intestinal stem cells, leading to deeper crypts and longer colons. This effect was dependent on the inulin-altered gut microbiota, as no modulations were observed in animals deprived of microbiota, nor in mice fed cellulose-enriched diets. We also describe the pivotal role of γδ T lymphocytes and IL-22 in this microenvironment, as the inulin diet failed to induce epithelium remodeling in mice lacking this T cell population or cytokine, highlighting their importance in the diet-microbiota-epithelium-immune system crosstalk.

CONCLUSION

This study indicates that the intake of inulin affects the activity of intestinal stem cells and drives a homeostatic remodeling of the colon epithelium, an effect that requires the gut microbiota, γδ T cells, and the presence of IL-22. Our study indicates complex cross kingdom and cross cell type interactions involved in the adaptation of the colon epithelium to the luminal environment in steady state. Video Abstract.

Orchestration of MUC2 - The key regulatory target of gut barrier and homeostasis: A review

The gut mucosa of human is covered by mucus, functioning as a crucial defense line for the intestine against external stimuli and pathogens. Mucin2 (MUC2) is a subtype of secretory mucins generated by goblet cells and is the major macromolecular component of mucus. Currently, there is an increasing interest on the investigations of MUC2, noting that its function is far beyond a maintainer of the mucus barrier. Moreover, numerous gut diseases are associated with dysregulated MUC2 production. Appropriate production level of MUC2 and mucus contributes to gut barrier function and homeostasis. The production of MUC2 is regulated by a series of physiological processes, which are orchestrated by various bioactive molecules, signaling pathways and gut microbiota, etc., forming a complex regulatory network. Incorporating the latest findings, this review provided a comprehensive summary of MUC2, including its structure, significance and secretory process. Furthermore, we also summarized the molecular mechanisms of the regulation of MUC2 production aiming to provide developmental directions for future researches on MUC2, which can act as a potential prognostic indicator and targeted therapeutic manipulation for diseases. Collectively, we elucidated the micro-level mechanisms underlying MUC2-related phenotypes, hoping to offer some constructive guidance for intestinal and overall health of mankind.

Role of Interleukin-22 in ulcerative colitis

Ulcerative Colitis (UC) is a chronic disease, in the progression of which an immune overreaction may play an important role. IL-22 is a member of the IL-10 superfamily of cytokines and is pleiotropic in immune regulation and inflammatory responses. IL-22 can produce protective effects, promote wound healing and tissue regeneration, while it can also induce inflammatory reactions when it is chronically overexpressed. Extensive literatures reported that IL-22 played an essential role in the pathogenic development of UC. IL-22 participates in the whole disease process of UC involving signaling pathways, gene expression regulation, and intestinal flora imbalance, making IL-22 a possible candidate for the treatment of UC. In this paper, the latest knowledge to further elucidate the role of IL-22 in UC was summarized and analyzed.

Dendrobium fimbriatum polysaccharide ameliorates DSS-induced intestinal mucosal injury by IL-22-regulated intestinal stem cell regeneration

Ulcerative colitis (UC) is a chronic inflammatory bowel disease with unknown etiology and difficult treatment. In this study, the intervention effect of Dendrobium fimbriatum Hook polysaccharide (cDFPW1) on UC was verified by constructing a dextran sulfate sodium (DSS)-induced colitis mouse model, and the protective effect of cDFPW1 on intestinal mucosal integrity in UC was explored by the co-culture system consisting of intestinal organoids and lamina propria lymphocytes (LPLs) combined with the experiment of microbial depletion mice. Results showed that cDFPW1 significantly alleviated UC symptoms in mice and promoted the proliferation of intestinal epithelial cells. Importantly, cDFPW1 could directly improve DSS-induced morphological damage of intestinal organoids and increase the number of epithelial cells, which was validated in mice. During repair, an increase in the number of Lgr5⁺ cells in intestinal organoids and mouse intestines was promoted by cDFPW1. Meanwhile, cDFPW1 promoted intestinal stem cells (ISCs)-mediated intestinal epithelial regeneration by significantly upregulating IL-22 expression. We further confirmed that the secretion of IL-22 was mediated by LPLs. Together, these findings suggest that cDFPW1 promotes ISCs regeneration by LPLs-mediated up-regulation of IL-22 to protect the intestinal mucosal integrity, thereby playing an important role in improving UC.

Bifidobacterium bifidum FJSWX19M5 alleviated 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced chronic colitis by mitigating gut barrier injury and increasing regulatory T cells

Probiotics have been evaluated as alternative approaches for preventing the relapse of Crohn's disease (CD). Previously, we observed strain-specific anti-inflammatory properties of Bifidobacterium bifidum in 2,4,6-trinitrobenzene sulfonic acid (TNBS) acute colitis models. In this study, we further assessed the effects of several B. bifidum strains on colonic damage, fibrosis, inflammatory factors, intestinal microbial and metabolic profiles, and peripheral regulatory T cells (Tregs) in the context of TNBS chronic colitis in mice. These results indicated that B. bifidum FJSWX19M5, but not FXJWS17M4, ameliorated body weight loss, reduced colonic shortening and injury, decreased markers of gut inflammation, and rebalanced colonic metabolism in TNBS-treated mice. FJSWX19M5 supplementation also promoted Treg cell differentiation and intestinal barrier restoration compared to other strains. All living B. bifidum strains (FJSWX19M5, FXJWS17M4 and FHENJZ3M6) seemed to restore the disruption of the gut microbiota caused by TNBS. The co-culture of B. bifidum strains and mesenteric lymph node cells from TNBS-treated mice showed that those strains with anti-colitis could induce higher IL-10 levels and a lower ratio of IL-22/IL-10 and IL-17/IL-10 when compared to those strains that were not protective. Furthermore, heat-killed FJSWX19M5 exhibited a relief effect on colitis-related symptoms (including body weight loss, colonic shortening and injury). These data imply that specific B. bifidum strains or their lysates may be the current therapeutic alternatives for CD.

The intestine: A highly dynamic microenvironment for IgA plasma cells

To achieve longevity, IgA plasma cells require a sophisticated anatomical microenvironment that provides cytokines, cell-cell contacts, and nutrients as well as metabolites. The intestinal epithelium harbors cells with distinct functions and represents an important defense line. Anti-microbial peptide-producing paneth cells, mucus-secreting goblet cells and antigen-transporting microfold (M) cells cooperate to build a protective barrier against pathogens. In addition, intestinal epithelial cells are instrumental in the transcytosis of IgA to the gut lumen, and support plasma cell survival by producing the cytokines APRIL and BAFF. Moreover, nutrients are sensed through specialized receptors such as the aryl hydrocarbon receptor (AhR) by both, intestinal epithelial cells and immune cells. However, the intestinal epithelium is highly dynamic with a high cellular turn-over rate and exposure to changing microbiota and nutritional factors. In this review, we discuss the spatial interplay of the intestinal epithelium with plasma cells and its potential contribution to IgA plasma cell generation, homing, and longevity. Moreover, we describe the impact of nutritional AhR ligands on intestinal epithelial cell-IgA plasma cell interaction. Finally, we introduce spatial transcriptomics as a new technology to address open questions in intestinal IgA plasma cell biology.

Th17-Related Cytokines Involved in Fluoride-Induced Cecal and Rectal Barrier Damage of Ovariectomized Rats

To investigate fluoride (F)-induced intestine barrier damage and the role of estrogen deficiency in this progress, a rat model of estrogen deficiency was established through bilateral surgical removal of ovaries. The F exposure model was then continued by adding sodium fluoride (0, 25, 50, and 100 mg/L, calculated on a fluorine ion basis) to drinking water for 90 days. Afterward, intestinal mucosal structure, barrier function, and inflammatory cytokines were evaluated. The results showed that excessive F decreased the developmental parameters (crypt depth) of the cecum and rectum and inhibited the proliferation capacity of the intestinal epithelia, which are more obvious in the state of estrogen deficiency. The distribution of goblet cells and glycoproteins in the intestinal mucosa decreased with the increase in F concentration, and estrogen deficiency led to a further decline, especially in the rectum. Using the immunofluorescence method, the study showed that excessive F caused interleukin-17A (IL-17A) significantly decrease in the cecum and increase in the rectum. Meanwhile, F treatment remarkably upregulated the expression of intestinal IL-1β, IL-23, and IL-22, while the level of IL-6 was downregulated. In addition, estrogen deficiency increased IL-1β, IL-6, IL-23, and IL-22, but decreased IL-17A expression in the cecum and rectum. Collectively, F exposure damaged intestinal morphological structure, inhibited epithelial cell proliferation and mucus barrier function, and resulted in the disturbance of T helper (Th) 17 cell-related cytokines expression. Estrogen deficiency may further aggravate F-induced damage to the cecum and rectum.

Targeting cytokines in inflammatory bowel disease

Targeting cytokines in inflammatory bowel disease (IBD) is a useful clinical approach. Potential therapies for IBD include regulatory T cell transfer to restore cytokine balance, blocking proinflammatory cytokines (e.g., IL-12 and IL-23) or their receptors (sIL-6R and IL-36R), or inhibiting signaling kinases (e.g., JAK). An emerging trend in IBD therapy is to combine several anti-cytokine agents simultaneously.

Oleuropein Prevents OVA-Induced Food Allergy in Mice by Enhancing the Intestinal Epithelial Barrier and Remodeling the Intestinal Flora

SCOPE

This study assesses whether oleuropein prevents ovalbumin (OVA)-induced food allergy (FA) and investigates the underlying mechanisms.

METHODS AND RESULTS

A Balb/c FA mouse model is established and maintained for 7 weeks. The subjects are administered OVA by oral gavage to induce FA and supplemented with different oleuropein doses (1.00-20.00 mg kg^-1 per day) to evaluate its preventative efficacy. The results indicate that oleuropein effectively alleviates OVA-induced allergy symptoms and promotes temperature elevation in sensitized mice. The secretion of serology-specific OVA-immunoglobulin (Ig)E, OVA-IgG, and histamine is inhibited in the sensitized mice. Oleuropein dramatically upregulates the expression of intestinal tight junction (TJ) proteins, regenerating gene (Reg) IIIγ, and interleukin (IL)-22, enhancing the physical and biochemical barrier function of the intestinal epithelium. Additionally, oleuropein improves the immune homeostasis of the intestinal epithelium by affecting the function of mucosal mast cells and regulatory T (Treg) cells. The disordered intestinal flora of the sensitized mice also improves after oleuropein administration.

CONCLUSIONS

These findings suggest that oleuropein prevents FA by enhancing intestinal epithelial barrier function and improving immune homeostasis and intestinal flora in sensitized mice. Therefore, diets rich in oleuropein should be recommended for people with FA.

Promoting Effect of L-Fucose on the Regeneration of Intestinal Stem Cells through AHR/IL-22 Pathway of Intestinal Lamina Propria Monocytes

The recovery of the intestinal epithelial barrier is the goal for curing various intestinal injurious diseases, especially IBD. However, there are limited therapeutics for restoring intestinal epithelial barrier function in IBD. The stemness of intestinal stem cells (ISCs) can differentiate into various mature intestinal epithelial cells, thus playing a key role in the rapid regeneration of the intestinal epithelium. IL-22 secreted by CD4⁺ T cells and ILC3 cells was reported to maintain the stemness of ISCs. Our previous study found that L-fucose significantly ameliorated DSS-induced colonic inflammation and intestinal epithelial injury. In this study, we discovered enhanced ISC regeneration and increased intestinal IL-22 secretion and its related transcription factor AHR in colitis mice after L-fucose treatment. Further studies showed that L-fucose promoted IL-22 release from CD4⁺ T cells and intestinal lamina propria monocytes (LPMCs) via activation of nuclear AHR. The coculture system of LPMCs and intestinal organoids demonstrated that L-fucose stimulated the proliferation of ISCs through an indirect manner of IL-22 from LPMCs via the IL-22R-p-STAT3 pathway, and restored TNF-α-induced organoid damage via IL-22-IL-22R signaling. These results revealed that L-fucose helped to heal the epithelial barrier by accelerating ISC proliferation, probably through the AHR/IL-22 pathway of LPMCs, which provides a novel therapy for IBD in the clinic.

Generation of human colon organoids from healthy and inflammatory bowel disease mucosa

Ulcerative colitis and Crohn's disease are chronic inflammatory bowel diseases (IBD) of unknown cause characterized by a relapsing-remitting behavior. Growing evidence supports the idea that the epithelial barrier plays a central role in the pathogenesis of IBD as well as in its evolution over time, thus representing a potential target for novel therapeutic options. In the last decade, the introduction of 3D epithelial cultures from ex vivo-expanded intestinal adult stem cells (ASCs) has impacted our ability to study the function of the epithelium in several gastrointestinal disorders, including IBD. Here, we describe in detail a reproducible protocol to generate Matrigel-embedded epithelial organoids from ASCs of non-IBD and IBD donors using small colonic biopsies, including steps for its optimization. A slightly modified version of this protocol is also provided in case surgical samples are used. With this method, epithelial organoids can be expanded over several passages, thereby generating a large quantity of viable cells that can be used in multiple downstream analyses including genetic, transcriptional, proteomic and/or functional studies. In addition, 3D cultures generated using our protocol are suitable for the establishment of 2D cultures, which can model relevant cell-to-cell interactions that occur in IBD mucosa.

Akkermansia muciniphila Reduces Peritonitis and Improves Intestinal Tissue Wound Healing after a Colonic Transmural Defect by a MyD88-Dependent Mechanism

Anastomotic leakage is a major complication following colorectal surgery leading to peritonitis, complications, and mortality. Akkermansia muciniphila has shown beneficial effects on the gut barrier function. Whether A. muciniphila reduces peritonitis and mortality during colonic leakage is unknown. Whether A. muciniphila can directly modulate the expression of genes in the colonic mucosa in humans has never been studied. We investigated the effects of a pretreatment (14 days) with live A. muciniphila prior to surgical colonic perforation on peritonitis, mortality, and wound healing. We used mice with an inducible intestinal-epithelial-cell-specific deletion of MyD88 (IEC-MyD88 KO) to investigate the role of the innate immune system in this context. In a proof-of-concept pilot study, healthy humans were exposed to A. muciniphila for 2 h and colonic biopsies taken before and after colonic instillation for transcriptomic analysis. Seven days after colonic perforation, A.-muciniphila-treated mice had significantly lower mortality and severity of peritonitis. This effect was associated with significant improvements of wound histological healing scores, higher production of IL22, but no changes in the mucus layer thickness or genes involved in cell renewal, proliferation, or differentiation. All these effects were abolished in IEC-MyD88 KO mice. Finally, human subjects exposed to A. muciniphila exhibited an increased level of the bacterium at the mucus level 2 h after instillation and significant changes in the expression of different genes involved in the regulation of cell cycling, gene transcription, immunity, and inflammation in their colonic mucosa. A. muciniphila improves wound healing during transmural colonic wall defect through mechanisms possibly involving IL22 signaling and requiring MyD88 in the intestinal cells. In healthy humans, colonic administration of A. muciniphila is well tolerated and changes the expression of genes involved in the immune pathways.

Acinetobacter baumannii Outer Membrane Protein A Induces Pulmonary Epithelial Barrier Dysfunction and Bacterial Translocation Through The TLR2/IQGAP1 Axis

Pulmonary epithelial barrier dysfunction is a critical pathophysiological process in pneumonia and associated invasive infections, such as those caused by Acinetobacter baumannii. However, the mechanisms underlying A. baumannii-induced pulmonary epithelial barrier dysfunction and bacterial translocation remain unclear. In this study, lungs of mice and A549 human epithelial cell monolayers were challenged with the A. baumannii wild-type strain and an outer membrane protein A (ompA) deletion strain. In addition, epithelial cells in culture were treated with purified OmpA protein or transfected with a eukaryotic expression vector encoding ompA (pCMV-ompA). Bacterial translocation across cell monolayers and intrapulmonary burden were measured, barrier function was evaluated in vivo and in vitro; cell migration ability was determined. The specific inhibitors C29 and JSH-23 were used to suppress the activity of Toll-like receptor 2 (TLR2) and of NF-κB, respectively. IQ-GTPase-activating protein 1 (IQGAP1) small interfering RNA was used to knock down endogenous IQGAP1 expression. In this work, we show that OmpA from A. baumannii increased the production of pro-inflammatory cytokines, remodeled the cytoskeleton, and internalized intercellular adherens junctions (AJs); these changes eventually induced pulmonary epithelial barrier dysfunction to promote bacterial translocation. IQGAP1-targeting small interfering RNA and chemical inhibition of TLR2 or NF-κB prevented high permeability of the pulmonary epithelial barrier. TLR2/NF-κB signaling was involved in OmpA-induced inflammation, IQGAP1-mediated OmpA-induced opening of the pulmonary epithelial barrier via cytoskeleton dynamic remodeling, and cellular redistribution of the major AJ protein, E-cadherin. These observations indicate that A. baumannii uses OmpA to overcome epithelial defences and cross the pulmonary epithelial barrier.

The role of γδ T cells in the interaction between commensal and pathogenic bacteria in the intestinal mucosa

The intestinal mucosa is an important structure involved in resistance to pathogen infection. It is mainly composed of four barriers, which have different but interrelated functions. Pathogenic bacteria can damage these intestinal mucosal barriers. Here, we mainly review the mechanisms of pathogen damage to biological barriers. Most γδ T cells are located on the surface of the intestinal mucosa, with the ability to migrate and engage in crosstalk with microorganisms. Commensal bacteria are involved in the activation and migration of γδ T cells to monitor the invasion of pathogens. Pathogen invasion alters the migration pattern of γδ T cells. γδ T cells accelerate pathogen clearance and limit opportunistic invasion of commensal bacteria. By discussing these interactions among γδ T cells, commensal bacteria and pathogenic bacteria, we suggest that γδ T cells may link the interactions between commensal bacteria and pathogenic bacteria.

A novel ladderlectin from hybrid crucian carp possesses antimicrobial activity and protects intestinal mucosal barrier against Aeromonas hydrophila infection

Ladderlectin is a pattern recognition receptor (PRR) in fish that is critical for rapid detection of bacteria in vitro, but the immunological function of ladderlectin in vivo is essentially unknown. In this study, we examined the expression and function of a ladderlectin homologue (WR-ladderlectin) from hybrid crucian carp. WR-ladderlectin contains 157 amino acids and possesses the conserved C-type lectin domain. WR-ladderlectin is mainly expressed in the intestine and is upregulated by bacterial infection. Recombinant WR-ladderlectin (rWR-ladderlectin) agglutinated Aeromonas hydrophila and Escherichia coli. rWR-ladderlectin also bound the A. hydrophila and E. coli in a protein dose-dependent manner. As well as its ability to bind bacterial cells, rWR-ladderlectin displayed apparent bactericidal activity against A. hydrophila and E. coli in vitro. When introduced in vivo, rWR-ladderlectin induced significant expression of the antimicrobial molecules and tight junctions in the intestine. In addition, rWR-ladderlectin prevented significant decrease in the length of intestine villus and enhanced the host's resistance to bacterial infection. These results indicate that WR-ladderlectin is a classic pattern recognition molecule that protects intestinal mucosal barrier against bacterial infection.

KLF5 protects the intestinal epithelium against Th17 immune response in a murine colitis model

Inflammatory bowel disease (IBD) is a chronic illness characterized by dysregulated immune cascades in the intestines, in which the Th17 immune response plays an important role. We demonstrated that mice with intestinal epithelium–specific deletion of Krüppel-like factor 5 (Klf5) developed Th17-dependent colonic inflammation. In the absence of KLF5, there was aberrant cellular localization of phosphorylated STAT3, an essential mediator of the Th17-associated cytokine, IL-22, which is required for epithelial tissue regeneration. In contrast, mitigation of IL-17A with anti–IL-17A neutralizing antibody attenuated colitis in Klf5-deficient mice. There was also a considerable shift in the colonic microbiota of Klf5-deficient mice that phenocopied human IBD. Notably, the inflammatory response due to Klf5 deletion was alleviated by antibiotic treatment, implicating the role of microbiota in pathogenesis. Finally, human colitic tissues had reduced KLF5 levels when compared with healthy tissues. Together, these findings demonstrated the importance of KLF5 in protecting the intestinal epithelium against Th17-mediated immune and inflammatory responses. The mice described herein may serve as a potential model for human IBD.

WR-GLP2, a glucagon-like peptide 2 from hybrid crucian carp that protects intestinal mucosal barrier and inhibits bacterial infection

Glucagon-like peptide 2 (GLP2) is a proglucagon-derived peptide produced by intestinal enteroendocrine L-cells. The main biological actions of GLP2 in mammals are related to regulating energy absorption and maintaining the morphology, integrity of intestinal mucosa. However, the in vivo function of fish GLP2 in intestinal barrier and immune defense is essentially unknown. With an aim to elucidate the antimicrobial mechanism of GLP2 in fish, we in this study examined the function of GLP2 from hybrid crucian carp. Hybrid crucian carp GLP2 (WR-GLP2) possesses the conserved glucagon like hormones 2 domain. WR-GLP2 is mainly expressed in the intestine and is significantly upregulated after Aeromonas hydrophila infection. AB-PAS staining analysis showed WR-GLP2 significantly increased the number of goblet cells in intestine. WR-GLP2 induced significant inductions in the expression of the antimicrobial molecules (MUC2, Lyzl-1, Hepcidin-1 and LEAP-2) and tight junctions (ZO-1, Occludin and Claudin-4). In addition, WR-GLP2 significantly alleviated the intestinal apoptosis, thereby enhancing host's resistance against Aeromonas hydrophila infection. Together these results indicate that WR-GLP2 is involved in intestinal mucosal barrier and immune defense against pathogen infection.

The Roles of IL-22 and Its Receptor in the Regulation of Inflammatory Responses in the Brain

Interleukin (IL)-22 is a potent mediator of inflammatory responses. The IL-22 receptor consists of the IL-22Rα and IL-10Rβ subunits. Previous studies have shown that IL-22Rα expression is restricted to non-hematopoietic cells in the skin, pancreas, intestine, liver, lung, and kidney. Although IL-22 is involved in the development of inflammatory responses, there have been no reports of its role in brain inflammation. Here, we used RT-PCR, Western blotting, flow cytometry, immunohistochemical, and microarray analyses to examine the role of IL-22 and expression of IL-22Rα in the brain, using the microglial cell line, hippocampal neuronal cell line, and inflamed mouse brain tissue. Treatment of BV2 and HT22 cells with recombinant IL-22 increased the expression levels of the pro-inflammatory cytokines IL-6 and TNF-α, as well as cyclooxygenase (COX)-2 and prostaglandin E2. We also found that the JNK and STAT3 signaling pathways play an important role in IL-22-mediated increases in inflammatory mediators. Microarray analyses revealed upregulated expression of inflammation-related genes in IL-22-treated HT22 cells. Finally, we found that IL-22Rα is spontaneously expressed in the brain and is upregulated in inflamed mouse brain. Overall, our results demonstrate that interaction of IL-22 with IL-22Rα plays a role in the development of inflammatory responses in the brain.

Intestinal mucus barrier: a missing piece of the puzzle in food allergy

The prevalence of food allergies has reached epidemic levels but the cause remains largely unknown. We discuss the clinical relevance of the gut mucosal barrier as a site for allergic sensitization to food. In this context, we focus on an important but overlooked part of the mucosal barrier in pathogenesis, the glycoprotein-rich mucus layer, and call attention to both beneficial and detrimental aspects of mucus-gut microbiome interactions. Studying the intricate links between the mucus barrier, the associated bacteria, and the mucosal immune system may advance our understanding of the mechanisms and inform prevention and treatment strategies in food allergy.

Probiotics-Based Treatment as an Integral Approach for Alcohol Use Disorder in Alcoholic Liver Disease

Alcoholic liver disease (ALD) is one of the leading causes of morbidity among adults with alcohol use disorder (AUD) worldwide. Its clinical course ranges from steatosis to alcoholic hepatitis, progressing to more severe forms of liver damage, such as cirrhosis and hepatocellular carcinoma. The pathogenesis of ALD is complex and diverse elements are involved in its development, including environmental factors, genetic predisposition, the immune response, and the gut-liver axis interaction. Chronic alcohol consumption induces changes in gut microbiota that are associated with a loss of intestinal barrier function and inflammatory responses which reinforce a liver damage progression triggered by alcohol. Alcohol metabolites such as acetaldehyde, lipid peroxidation-derived aldehyde malondialdehyde (MDA), and protein-adducts act as liver-damaging hepatotoxins and potentiate systemic inflammation. Additionally, ethanol causes direct damage to the central nervous system (CNS) by crossing the blood-brain barrier (BBB), provoking oxidative stress contributing to neuroinflammation. Overall, these processes have been associated with susceptibility to depression, anxiety, and alcohol craving in ALD. Recent evidence has shown that probiotics can reverse alcohol-induced changes of the microbiota and prevent ALD progression by restoring gut microbial composition. However, the impact of probiotics on alcohol consumption behavior has been less explored. Probiotics have been used to treat various conditions by restoring microbiota and decreasing systemic and CNS inflammation. The results of some studies suggest that probiotics might improve mental function in Alzheimer’s, autism spectrum disorder, and attenuated morphine analgesic tolerance. In this sense, it has been observed that gut microbiota composition alterations, as well as its modulation using probiotics, elicit changes in neurotransmitter signals in the brain, especially in the dopamine reward circuit. Consequently, it is not difficult to imagine that a probiotics-based complementary treatment to ALD might reduce disease progression mediated by lower alcohol consumption. This review aims to present an update of the pathophysiologic mechanism underlying the microbiota-gut-liver-brain axis in ALD, as well as to provide evidence supporting probiotic use as a complementary therapy to address alcohol consumption disorder and its consequences on liver damage.

Bacterial Translocation as Inflammatory Driver in Crohn's Disease

Crohn’s disease (CD) is a chronic inflammatory disorder of the gastrointestinal tract responsible for intestinal lesions. The multifactorial etiology attributed to CD includes a combination of environmental and host susceptibility factors, which result in an impaired host–microbe gut interaction. Bacterial overgrowth and dysbiosis, increased intestinal barrier permeability, and altered inflammatory responses in patients with CD have been described in the past. Those events explain the pathogenesis of luminal translocation of bacteria or its products into the blood, a frequent event in CD, which, in turn, favors a sustained inflammatory response in these patients. In this review, we navigate through the interaction between bacterial antigen translocation, permeability of the intestinal barrier, immunologic response of the host, and genetic predisposition as a combined effect on the inflammatory response observed in CD. Several lines of evidence support that translocation of bacterial products leads to uncontrolled inflammation in CD patients, and as a matter of fact, the presence of gut bacterial genomic fragments at a systemic level constitutes a marker for increased risk of relapse among CD patients. Also, the significant percentage of CD patients who lose response to biologic therapies may be influenced by the translocation of bacterial products, which are well-known drivers of proinflammatory cytokine production by host immune cells. Further mechanistic studies evaluating cellular and humoral immune responses, gut microbiota alterations, and genetic predisposition will help clinicians to better control and personalize the management of CD patients in the future.

Sodium butyrate converts Caco-2 monolayers into a leaky but healthy intestinal barrier resembling that of a newborn infant

A simple and reliable in vitro model of the infant intestinal barrier is needed to study nutrient absorption and drug permeability specifically for this life stage. This study investigated the treatment of 20 day old differentiated Caco-2 monolayers with sodium butyrate at various concentrations (0-250 mM). Monolayer integrity, cytotoxicity, permeability and inflammatory response were tracked. An intestinal barrier model, with infant gut characteristics, was developed based on the treatment of mature monolayers with 125 mM sodium butyrate for 24 h. Such treatment was not cytotoxic but caused a stable transepithelial electrical resistance value of 408 ± 52 Ω cm2. The ratio of lactulose to mannitol transport across the intestinal barrier increased 1.79-fold. Redistribution of the tight junction proteins, occludin and ZO-1, in response to sodium butyrate treatment was visualized with immunofluorescence. Levels of the cytokines, TNF-α and IL-6, although modestly increased did not indicate an inflammatory response by Caco-2 to sodium butyrate. This intestinal barrier demonstrated physiologically relevant transport rates for dairy protein of 0.01-0.06%, suggesting it may be used to track permeability of proteins in infant nutritional products.