Colonic MUC2 mucin regulates the expression and antimicrobial activity of β-defensin 2

Mucins as multifunctional building blocks of biomaterials

Mucins are large glycoproteins that are ubiquitous in the animal kingdom. Mucins coat the surfaces of many cell types and can be secreted to form mucus gels that assume important physiological roles in many animals. Our growing understanding of the structure and function of mucin molecules and their functionalities has sparked interest in investigating the use of mucins as building blocks for innovative functional biomaterials. These pioneering studies have explored how new biomaterials can benefit from the barrier properties, hydration and lubrication properties, unique chemical diversity, and bioactivities of mucins. Owing to their multifunctionality, mucins have been used in a wide variety of applications, including as antifouling coatings, as selective filters, and artificial tears and saliva, as basis for cosmetics, as drug delivery materials, and as natural detergents. In this review, we summarize the current knowledge regarding key mucin properties and survey how they have been put to use. We offer a vision for how mucins could be used in the near future and what challenges await the field before biomaterials made of mucins and mucin-mimics can be translated into commercial products.

The Muc2 mucin coats murine Paneth cell granules and facilitates their content release and dispersion

Paneth cells are a key subset of secretory epithelial cells found at the base of small intestinal crypts. Unlike intestinal goblet cells, which secrete the mucin Muc2, Paneth cells are best known for producing an array of antimicrobial factors. We unexpectedly identified Muc2 staining localized around Paneth cell granules. Electron microscopy (EM) confirmed an electron lucent halo around these granules, which was lost in Paneth cells from Muc2-deficient (^-/-) mice. EM and immunostaining for lysozyme revealed that Muc2^-/- Paneth cells contained larger, more densely packed granules within their cytoplasm, and we detected defects in the transcription of key antimicrobial genes in the ileal tissues of Muc2^-/- mice. Enteroids derived from the small intestine of wild-type and Muc2^-/- mice revealed phenotypic differences in Paneth cells similar to those seen in vivo. Moreover, lysozyme-containing granule release from Muc2^-/- enteroid Paneth cells was shown to be impaired. Surprisingly, Paneth cells within human ileal and duodenal tissues were found to be Muc2 negative. Thus Muc2 plays an important role in murine Paneth cells, suggesting links in function with goblet cells; however human Paneth cells lack Muc2, highlighting that caution should be applied when linking murine to human Paneth cell functions. NEW & NOTEWORTHY We demonstrate for the first time that murine Paneth cell granules possess a halo comprised of the mucin Muc2. The presence of Muc2 exerts an impact on Paneth cell granule size and number and facilitates the release and dispersal of antimicrobials into the mucus layer. Interestingly, despite the importance of Muc2 in murine Paneth cell function, our analysis of Muc2 in human intestinal tissues revealed no trace of Muc2 expression by human Paneth cells.

Entamoeba histolytica Alters Ileal Paneth Cell Functions in Intact and Muc2 Mucin Deficiency

Enteric α-defensins, termed cryptdins (Crps) in mice, and lysozymes secreted by Paneth cells contribute to innate host defense in the ileum. Antimicrobial factors, including lysozymes and β-defensins, are often embedded in luminal glycosylated colonic Muc2 mucin secreted by goblet cells that form the protective mucus layer critical for gut homeostasis and pathogen invasion. In this study, we investigated ileal innate immunity against Entamoeba histolytica, the causative agent of intestinal amebiasis, by inoculating parasites in closed ileal loops in Muc2^+/+ and Muc2^-/- littermates and quantifying Paneth cell localization (lysozyme expression) and function (Crp secretion). Relative to Muc2^+/+ littermates, Muc2^-/- littermates showed a disorganized mislocalization of Paneth cells that was diffusely distributed, with elevated lysozyme secretion in the crypts and on villi in response to E. histolytica Inhibition of E. histolytica Gal/GalNAc lectin (Gal-lectin) binding with exogenous galactose and Entamoeba histolytica cysteine proteinase 5 (EhCP5)-negative E. histolytica had no effect on parasite-induced erratic Paneth cell lysozyme synthesis. Although the basal ileal expression of Crp genes was unaffected in Muc2^-/- mice in response to E. histolytica, there was a robust release of proinflammatory cytokines and Crp peptide secretions in luminal exudates that was also present in the colon. Interestingly, E. histolytica-secreted cysteine proteinases cleaved the proregion of Crp4 but not the active form. These findings define Muc2 mucin as an essential component of ileal barrier function that regulates the localization and function of Paneth cells critical for host defense against microbes.

High MUC2 Mucin Biosynthesis in Goblet Cells Impedes Restitution and Wound Healing by Elevating Endoplasmic Reticulum Stress and Altered Production of Growth Factors

Intestinal epithelial cell wound healing involves cell migration, proliferation, and differentiation. Although numerous studies have analyzed the migration of absorptive epithelial cells during wound healing, it remains unclear how goblet cells restitute and how MUC2 mucin production affects this process. In this study, we examined the role of high MUC2 production in goblet cell migration during wound healing and demonstrated that during high MUC2 output, goblet cells migrated slower because of impaired production of wound healing factors and endoplasmic reticulum (ER) stress. Two goblet cell lines, HT29-H and HT29-L, that produced high and low MUC2 mucin, respectively, were used. HT29-L healed wounds faster than HT29-H cells by producing significantly higher amounts of fibroblast growth factor (FGF) 1, FGF2, vascular endothelial growth factor-C, and matrix metallopeptidase 1. Predictably, treatment of HT29-H cells with recombinant FGF2 significantly enhanced migration and wound healing. High MUC2 biosynthesis in HT29-H cells induced ER stress and delayed migration that was abrogated by inhibiting ER stress with tauroursodeoxycholic acid and IL-22. FGF2- and IL-22-induced wound repair was dependent on STAT1 and STAT3 signaling. During wound healing after dextran sulfate sodium-induced colitis, restitution of Math1^M1GFP+ goblet cells occurred earlier in the proximal colon, followed by the middle and then distal colon, where ulceration was severe. We conclude that high MUC2 output during colitis impairs goblet cell migration and wound healing by reducing production of growth factors critical in wound repair.

Intestinal manipulation affects mucosal antimicrobial defense in a mouse model of postoperative ileus

Aim

To explore the effects of abdominal surgery and interleukin-1 signaling on antimicrobial defense in a model of postoperative ileus.

Methods

C57BL/6 and Interleukin-1 receptor type I (IL-1R1) deficient mice underwent intestinal manipulation to induce POI. Expression of mucosal IL-1α, IL-1β and IL-1R1 and several antimicrobial peptides and enzymes were measured by quantitative PCR or ELISA, western blotting or immunohistochemistry. Bacterial overgrowth was determined by fluorescent in-situ hybridization and counting of jejunal luminal bacteria. Translocation of aerobic and anaerobic bacteria into the intestinal wall, mesenteric lymph nodes, liver and spleen was determined by counting bacterial colonies on agar plates 48h after plating of tissue homogenates. Antimicrobial activity against E. coli and B. vulgatus was analyzed in total and cationic fractions of small bowel mucosal tissue homogenates by a flow cytometry-based bacterial depolarization assay.

Results

Jejunal bacterial overgrowth was detected 24h after surgery. At the same time point, but not in the early phase 3h after surgery, bacterial translocation into the liver and mesenteric lymph nodes was observed. Increased antimicrobial activity against E. coli was induced within early phase of POI. Basal antimicrobial peptide and enzyme gene expression was higher in the ileal compared to the jejunal mucosa. The expression of lysozyme 1, cryptdin 1, cryptdin 4 and mucin 2 were reduced 24h after surgery in the ileal mucosa and mucin 2 was also reduced in the jejunum. Postoperative IL-1α and IL-1β were increased in the postoperative mucosa. Deficiency of IL-1R1 affected the expression of antimicrobial peptides during homeostasis and POI.

Conclusion

Small bowel antimicrobial capacity is disturbed during POI which is accompanied by bacterial overgrowth and translocation. IL-1R1 is partially involved in the gene expression of mucosal antimicrobial peptides. Altered small bowel antimicrobial activity may contribute also to POI development and manifestation in patients undergoing abdominal surgery.

Intestinal mucin activates human dendritic cells and IL-8 production in a glycan-specific manner

Cross-talk between different components of the intestinal barrier and the immune system may be important in maintaining gut homeostasis. A crucial part of the gut barrier is the mucus layer, a cross-linked gel on top of the intestinal epithelium that consists predominantly of the mucin glycoprotein MUC2. However, whether the mucin layer actively regulates intestinal immune cell responses is not clear. Because recent evidence suggests that intestinal dendritic cells (DCs) may be regulated by the mucus layer, we purified intestinal mucin, incubated it with human DCs, and determined the functional effects. Here we show that expression of the chemokine IL-8 and co-stimulatory DC markers CD86 and CD83 are significantly up-regulated on human DCs in the presence of intestinal mucins. Additionally, mucin-exposed DCs promoted neutrophil migration in an IL-8–dependent manner. The stimulatory effects of mucins on DCs were not due to mucin sample contaminants such as lipopolysaccharide, DNA, or contaminant proteins. Instead, mucin glycans are important for the pro-inflammatory effects on DCs. Thus, intestinal mucins are capable of inducing important pro-inflammatory functions in DCs, which could be important in driving inflammatory responses upon intestinal barrier damage.

High MUC2 Mucin Expression and Misfolding Induce Cellular Stress, Reactive Oxygen Production, and Apoptosis in Goblet Cells

MUC2 mucin is a large glycoprotein produced by goblet cells that forms the protective mucus blanket overlying the intestinal epithelium as the first line of innate host defense. High MUC2 production in inflammatory bowel disease and infectious colitis depletes goblet cells and the mucus layer by an unknown mechanism. Herein, we analyzed the effect of high MUC2 biosynthesis on endoplasmic reticulum (ER) stress and apoptosis in goblet cells using a high MUC2-producing human goblet cell line (HT29-H) and an HT29-H clone (HT29-L) silenced for MUC2 expression by lentivirus-mediated shRNA. Goblet cell ER stress and apoptosis were quantified during early onset of dextran sulfate sodium-induced colitis in C57BL/6 and Math1^M1GFP mice. Compared with HT29-L and MUC2 nonproducing Caco-2 cells, high MUC2-producing HT29-H cells had significantly increased ER stress and apoptosis after treatment with ER stress-inducing agents. Apoptosis was driven by increased misfolded MUC2 that triggered elevated levels of reactive oxygen species. Correcting MUC2 folding and inhibiting reactive oxygen species alleviated ER stress and rescued cells from apoptosis. During early-onset colitis, mucus hypersecretion caused severe ER stress and apoptosis of goblet cells that preceded absorptive epithelial cell damage. Thus, in gastrointestinal inflammation, high MUC2 biosynthesis and goblet cell apoptosis lead to a dysfunctional epithelial barrier. Enhancing MUC2 folding may help alleviate goblet cell depletion and maintain mucosal integrity.

Chronic stress promotes colitis by disturbing the gut microbiota and triggering immune system response

Chronic stress is known to promote inflammatory bowel disease (IBD), but the underlying mechanism remains largely unresolved. Here, we found chronic stress to sensitize mice to dextran sulfate sodium (DSS)-induced colitis; to increase the infiltration of B cells, neutrophils, and proinflammatory ly6C^hi macrophages in colonic lamina propria; and to present with decreased thymus and mesenteric lymph node (MLN) coefficients. Circulating total white blood cells were significantly increased after stress, and the proportion of MLN-associated immune cells were largely changed. Results showed a marked activation of IL-6/STAT3 signaling by stress. The detrimental action of stress was not terminated in IL-6^-/- mice. Interestingly, the composition of gut microbiota was dramatically changed after stress, with expansion of inflammation-promoting bacteria. Furthermore, results showed stress-induced deficient expression of mucin-2 and lysozyme, which may contribute to the disorder of gut microbiota. Of note is that, in the case of cohousing, the stress-induced immune reaction and decreased body weight were abrogated, and transferred gut microbiota from stressed mice to control mice was sufficient to facilitate DSS-induced colitis. The important role of gut microbiota was further reinforced by broad-spectrum antibiotic treatment. Taken together, our results reveal that chronic stress disturbs gut microbiota, triggering immune system response and facilitating DSS-induced colitis.

[Biologics in Rhinology - Forthcoming Personalized Concepts: the Future Starts Today]

Sinunasale Erkrankungen zählen mit zu den häufigsten chronischen Erkrankungen und führen zu einer erheblichen Störung der Lebensqualität, ein komorbides Asthma ist häufig. Trotz leitliniengerechter Therapie ist anzunehmen, dass mind. 20% der Patienten ihre Erkrankungssymptome nicht adäquat kontrollieren können. Neben den etablierten chirurgischen und konservativen Therapieoptionen finden sich nun vielversprechende Therapieansätze, die bspw. mittels therapeutischer Antikörper mechanistisch gezielt in die Pathophysiologie der Erkrankungen eingreifen können. Die Auswahl der geeigneten Patienten durch geeignete Biomarker und die richtige Therapie zum richtigen Stadium der Erkrankung anbieten zu können, ist das Ziel stratifizierter Medizin und eine wichtige Perspektive für die HNO.Chronic diseases of the nose and the paranasal sinuses are most common, frequently associated with bronchial asthma, and result in substantial reduction of quality of life. Despite optimal treatment according to guidelines, approx. 20 % of the patients will report inadequate control of symptoms. Apart from well established surgical and conservative approaches in therapy new therapeutic antibodies are available that aim specifically pathophysiological targets. The optimal allocation of effective therapy for patients using appropriate biomarkers at the most suitable timepoint is the hallmark of stratified medicine and an important perspective in ENT.

Characteristic pro-inflammatory cytokines and host defence cathelicidin peptide produced by human monocyte-derived macrophages infected withNeospora caninum

Neospora caninumis a coccidian intracellular protozoan capable of infecting a wide range of mammals, although severe disease is mostly reported in dogs and cattle. Innate defences triggered by monocytes/macrophages are key in the pathogenesis of neosporosis, as these cells are first-line defenders against intracellular infections. The aim of this study was to characterize infection and innate responses in macrophages infected withN. caninumusing a well-known cell model to study macrophage functions (human monocyte THP-1 cells). Intracellular invasion of live tachyzoites occurred as fast as 4 h (confirmed with immunofluorescence microscopy usingN. caninum-specific antibodies). Macrophages infected byN. caninumhad increased expression of pro-inflammatory cytokines (TNFα, IL-1β, IL-8, IFNγ). Interestingly,N. caninuminduced expression of host-defence peptides (cathelicidins), a mechanism of defence never reported forN. caninuminfection in macrophages. The expression of cytokines and cathelicidins in macrophages invaded byN. caninumwas mediated by mitogen-activated protein kinase (MEK 1/2). Secretion of such innate factors fromN. caninum-infected macrophages reduced parasite internalization and promoted the secretion of pro-inflammatory cytokines in naïve macrophages. We concluded that rapid invasion of macrophages byN. caninumtriggered protective innate defence mechanisms against intracellular pathogens.

Role of Soluble Innate Effector Molecules in Pulmonary Defense against Fungal Pathogens

Fungal infections of the lung are life-threatening but rarely occur in healthy, immunocompetent individuals, indicating efficient clearance by pulmonary defense mechanisms. Upon inhalation, fungi will first encounter the airway surface liquid which contains several soluble effector molecules that form the first barrier of defense against fungal infections. These include host defense peptides, like LL-37 and defensins that can neutralize fungi by direct killing of the pathogen, and collectins, such as surfactant protein A and D, that can aggregate fungi and stimulate phagocytosis. In addition, these molecules have immunomodulatory activities which can aid in fungal clearance from the lung. However, existing observations are based on in vitro studies which do not reflect the complexity of the lung and its airway surface liquid. Ionic strength, pH, and the presence of mucus can have strong detrimental effects on antifungal activity, while the potential synergistic interplay between soluble effector molecules is largely unknown. In this review, we describe the current knowledge on soluble effector molecules that contribute to antifungal activity, the importance of environmental factors and discuss the future directions required to understand the innate antifungal defense in the lung.

Direct effects of fermented cow's milk product with Lactobacillus paracasei CBA L74 on human enterocytes

Cow's milk fermented with Lactobacillus paracasei CBA L74 (FM-CBAL74) exerts a preventive effect against infectious diseases in children. We evaluated if this effect is at least in part related to a direct modulation of non-immune and immune defence mechanisms in human enterocytes. Human enterocytes (Caco-2) were stimulated for 48 h with FM-CBAL74 at different concentrations. Cell growth was assessed by colorimetric assay; cell differentiation (assessed by lactase expression), tight junction proteins (zonula occludens1 and occludin), mucin 2, and toll-like receptor (TRL) pathways were analysed by real-time PCR; innate immunity peptide synthesis, beta-defensin-2 (HBD-2) and cathelicidin (LL-37) were evaluated by ELISA. Mucus layer thickness was analysed by histochemistry. FMCBA L74 stimulated cell growth and differentiation, tight junction proteins and mucin 2 expression, and mucus layer thickness in a dose-dependent fashion. A significant stimulation of HBD-2 and LL-37 synthesis, associated with a modulation of TLR pathway, was also observed. FM-CBAL74 regulates non-immune and immune defence mechanisms through a direct interaction with the enterocytes. These effects could be involved in the preventive action against infectious diseases demonstrated by this fermented product in children.

Cysteine Protease-Dependent Mucous Disruptions and Differential Mucin Gene Expression in Giardia duodenalis Infection

The intestinal mucous layer provides a critical host defense against pathogen exposure and epithelial injury, yet little is known about how enteropathogens may circumvent this physiologic barrier. Giardia duodenalis is a small intestinal parasite responsible for diarrheal disease and chronic postinfectious illness. This study reveals a complex interaction at the surface of epithelial cells, between G. duodenalis and the intestinal mucous layer. Here, we reveal mechanisms whereby G. duodenalis evades and disrupts the first line of host defense by degrading human mucin-2 (MUC2), depleting mucin stores and inducing differential gene expression in the mouse small and large intestines. Human colonic biopsy specimens exposed to G. duodenalis were depleted of mucus, and in vivo mice infected with G. duodenalis had a thinner mucous layer and demonstrated differential Muc2 and Muc5ac mucin gene expression. Infection in Muc2^-/- mice elevated trophozoite colonization in the small intestine and impaired weight gain. In vitro, human LS174T goblet-like cells were depleted of mucus and had elevated levels of MUC2 mRNA expression after G. duodenalis exposure. Importantly, the cysteine protease inhibitor E64 prevented mucous degradation, mucin depletion, and the increase in MUC2 expression. This article describes a novel role for Giardia's cysteine proteases in pathogenesis and how Giardia's disruptions of the mucous barrier facilitate bacterial translocation that may contribute to the onset and propagation of disease.

Novel synthetic analogues of avian β-defensin-12: the role of charge, hydrophobicity, and disulfide bridges in biological functions

BACKGROUND

Avian β-defensins (AvBD) possess broad-spectrum antimicrobial, LPS neutralizing and chemotactic properties. AvBD-12 is a chemoattractant for avian immune cells and mammalian dendritic cells (JAWSII) - a unique feature that is relevant to the applications of AvBDs as chemotherapeutic agents in mammalian hosts. To identify the structural components essential to various biological functions, we have designed and evaluated seven AvBD analogues.

RESULTS

In the first group of analogues, the three conserved disulfide bridges were eliminated by replacing cysteines with alanine and serine residues, peptide hydrophobicity and charge were increased by changing negatively charged amino acid residues to hydrophobic (AvBD-12A1) or positively charged residues (AvBD-12A2 and AvBD-12A3). All three analogues in this group showed improved antimicrobial activity, though AvBD-12A3, with a net positive charge of +9, hydrophobicity of 40% and a predicted CCR2 binding domain, was the most potent antimicrobial peptide. AvBD-12A3 also retained more than 50% of wild type chemotactic activity. In the second group of analogues (AvBD-12A4 to AvBD-12A6), one to three disulfide bridges were removed via substitution of cysteines with isosteric amino acids. Their antimicrobial activity was compromised and chemotactic activity abolished. The third type of analogue was a hybrid that had the backbone of AvBD-12 and positively charged amino acid residues AvBD-6. The antimicrobial and chemotactic activities of the hybrid resembled that of AvBD-6 and AvBD-12, respectively.

CONCLUSIONS

While the net positive charge and charge distribution have a dominating effect on the antimicrobial potency of AvBDs, the three conserved disulfide bridges are essential to the chemotactic property and the maximum antimicrobial activity. Analogue AvBD-12A3 with a high net positive charge, a moderate degree of hydrophobicity and a CCR2-binding domain can serve as a template for the design of novel antimicrobial peptides with chemotactic property and salt resistance.

MUC2 Mucin and Butyrate Contribute to the Synthesis of the Antimicrobial Peptide Cathelicidin in Response to Entamoeba histolytica- and Dextran Sodium Sulfate-Induced Colitis

Embedded in the colonic mucus are cathelicidins, small cationic peptides secreted by colonic epithelial cells. Humans and mice have one cathelicidin-related antimicrobial peptide (CRAMP) each, LL-37/hCAP-18 and Cramp, respectively, with related structure and functions. Altered production of MUC2 mucin and antimicrobial peptides is characteristic of intestinal amebiasis. The interactions between MUC2 mucin and cathelicidins in conferring innate immunity against Entamoeba histolytica are not well characterized. In this study, we quantified whether MUC2 expression and release could regulate the expression and secretion of cathelicidin LL-37 in colonic epithelial cells and in the colon. The synthesis of LL-37 was enhanced with butyrate (a product of bacterial fermentation) and interleukin-1β (IL-1β) (a proinflammatory cytokine in colitis) in the presence of exogenously added purified MUC2. The LL-37 responses to butyrate and IL-1β were higher in high-MUC2-producing cells than in lentivirus short hairpin RNA (shRNA) MUC2-silenced cells. Activation of cyclic adenylyl cyclase (AMP) and mitogen-activated protein kinase (MAPK) signaling pathways was necessary for the simultaneous expression of MUC2 and cathelicidins. In Muc2 mucin-deficient (Muc2^-/-) mice, murine cathelicidin (Cramp) was significantly reduced compared to that in Muc2^+/- and Muc2^+/+ littermates. E. histolytica-induced acute inflammation in colonic loops stimulated high levels of cathelicidin in Muc2^+/+ but not in Muc2^-/- littermates. In dextran sodium sulfate (DSS)-induced colitis in Muc2^+/+ mice, which depletes the mucus barrier and goblet cell mucin, Cramp expression was significantly enhanced during restitution. These studies demonstrate regulatory mechanisms between MUC2 and cathelicidins in the colonic mucosa where an intact mucus barrier is essential for expression and secretion of cathelicidins in response to E. histolytica- and DSS-induced colitis.

Epithelial response to a high-protein diet in rat colon

Background

High-protein diets (HPD) alter the large intestine microbiota composition in association with a metabolic shift towards protein degradation. Some amino acid-derived metabolites produced by the colon bacteria are beneficial for the mucosa while others are deleterious at high concentrations. The aim of the present work was to define the colonic epithelial response to an HPD. Transcriptome profiling was performed on colonocytes of rats fed an HPD or an isocaloric normal-protein diet (NPD) for 2 weeks.

Results

The HPD downregulated the expression of genes notably implicated in pathways related to cellular metabolism, NF-κB signaling, DNA repair, glutathione metabolism and cellular adhesion in colonocytes. In contrast, the HPD upregulated the expression of genes related to cell proliferation and chemical barrier function. These changes at the mRNA level in colonocytes were not associated with detrimental effects of the HPD on DNA integrity (comet assay), epithelium renewal (quantification of proliferation and apoptosis markers by immunohistochemistry and western blot) and colonic barrier integrity (Ussing chamber experiments).

Conclusion

The modifications of the luminal environment after an HPD were associated with maintenance of the colonic homeostasis that might be the result of adaptive processes in the epithelium related to the observed transcriptional regulations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3514-z) contains supplementary material, which is available to authorized users.

Mucosal Ecological Network of Epithelium and Immune Cells for Gut Homeostasis and Tissue Healing

The intestinal epithelial barrier includes columnar epithelial, Paneth, goblet, enteroendocrine, and tuft cells as well as other cell populations, all of which contribute properties essential for gastrointestinal homeostasis. The intestinal mucosa is covered by mucin, which contains antimicrobial peptides and secretory IgA and prevents luminal bacteria, fungi, and viruses from stimulating intestinal immune responses. Conversely, the transport of luminal microorganisms-mediated by M, dendritic, and goblet cells-into intestinal tissues facilitates the harmonization of active and quiescent mucosal immune responses. The bacterial population within gut-associated lymphoid tissues creates the intratissue cohabitations for harmonized mucosal immunity. Intermolecular and intercellular communication among epithelial, immune, and mesenchymal cells creates an environment conducive for epithelial regeneration and mucosal healing. This review summarizes the so-called intestinal mucosal ecological network-the complex but vital molecular and cellular interactions of epithelial mesenchymal cells, immune cells, and commensal microbiota that achieve intestinal homeostasis, regeneration, and healing.

Functional Transcriptomics in Diverse Intestinal Epithelial Cell Types Reveals Robust MicroRNA Sensitivity in Intestinal Stem Cells to Microbial Status

Gut microbiota play an important role in regulating the development of the host immune system, metabolic rate, and at times, disease pathogenesis. The factors and mechanisms that mediate interactions between microbiota and the intestinal epithelium are not fully understood. We provide novel evidence that microbiota may control intestinal epithelial stem cell (IESC) proliferation in part through microRNAs (miRNAs). We demonstrate that miRNA profiles differ dramatically across functionally distinct cell types of the mouse jejunal intestinal epithelium and that miRNAs respond to microbiota in a highly cell type-specific manner. Importantly, we also show that miRNAs in IESCs are more prominently regulated by microbiota compared with miRNAs in any other intestinal epithelial cell subtype. We identify miR-375 as one miRNA that is significantly suppressed by the presence of microbiota in IESCs. Using a novel method to knockdown gene and miRNA expression ex vivo enteroids, we demonstrate that we can knock down gene expression in Lgr5⁺ IESCs. Furthermore, when we knock down miR-375 in IESCs, we observe significantly increased proliferative capacity. Understanding the mechanisms by which microbiota regulate miRNA expression in IESCs and other intestinal epithelial cell subtypes will elucidate a critical molecular network that controls intestinal homeostasis and, given the heightened interest in miRNA-based therapies, may offer novel therapeutic strategies in the treatment of gastrointestinal diseases associated with altered IESC function.

Innate immune defense in the inner ear - mucines are expressed by the human endolymphatic sac

The human endolymphatic sac has been shown recently to have immunological capacities and has thus been proposed as the main entity protecting the inner ear from pathogen invasion, equivalent to mucosa-associated lymphoid tissue (MALT). Although the sac expresses molecules of the innate immune system, the potential expression of members of the important mucin family has not been detailed. Thus, this paper explores endolymphatic sac expression of a number of mucins and mucin precursors. Twelve fresh tissue samples from the human endolymphatic sac were obtained during translabyrinthine surgery. The expression of Mucin 1, 2, 5B/AC and 16, as well as the core structure elements (mucin precursors) T-antigen, Tn-antigen and Sialyl-Tn-antigen was investigated by immunohistochemistry. The endolymphatic sac epithelium expressed MUC1 (both apically towards the endolymphatic sac (ES) lumen and basally towards the capillary network), MUC 16 and Tn-antigen. There was no labeling after incubation with antibodies against T-antigen, sialyl-Tn-antigen, MUC2 and MUC5B/AC. We conclude that the human endolymphatic sac epithelium expresses a number of mucin molecules, which supports the hypothesis of the sac as the primary immunological tissue structure of the inner ear, equivalent to MALT in other organs. The mucins may also play a role in the formation and continuous homeostasis of the inner ear fluids, as well as the pathogenesis of Meniere's disease.

Lactobacillus reuteri increases mucus thickness and ameliorates dextran sulphate sodium-induced colitis in mice

AIM

The aim of this study was to investigate whether two Lactobacillus reuteri strains (rat-derived R2LC and human-derived ATCC PTA 4659 (4659)) could protect mice against colitis, as well as delineate the mechanisms behind this protection.

METHODS

Mice were given L. reuteri R2LC or 4659 by gavage once daily for 14 days, and colitis was induced by addition of 3% DSS (dextran sulphate sodium) to drinking water for the last 7 days of this period. The severity of disease was assessed through clinical observations, histological evaluation and ELISA measurements of myeloperoxidase (MPO) and pro-inflammatory cytokines from colonic samples. Mucus thickness was measured in vivo with micropipettes, and tight junction protein expression was assessed using immunohistochemistry.

RESULTS

Colitis severity was significantly reduced by L. reuteri R2LC or 4659 when evaluated both clinically and histologically. The inflammation markers MPO, IL-1β, IL-6 and mKC (mouse keratinocyte chemoattractant) were increased by DSS and significantly reduced by the L. reuteri strains. The firmly adherent mucus thickness was reduced by DSS, but significantly increased by L. reuteri in both control and DSS-treated mice. Expression of the tight junction proteins occludin and ZO-1 was significantly increased in the bottom of the colonic crypts by L. reuteri R2LC.

CONCLUSION

These results demonstrate that each of the two different L. reuteri strains, one human-derived and one-rat-derived, protects against colitis in mice. Mechanisms behind this protection could at least partly be explained by the increased mucus thickness as well as a tightened epithelium in the stem cell area of the crypts.

Crosstalk between microbiota, pathogens and the innate immune responses

Research in the last decade has convincingly demonstrated that the microbiota is crucial in order to prime and orchestrate innate and adaptive immune responses of their host and influence barrier function as well as multiple developmental and metabolic parameters of the host. Reciprocally, host reactions and immune responses instruct the composition of the microbiota. This review summarizes recent evidence from experimental and human studies which supports these arms of mutual relationship and crosstalk between host and resident microbiota, with a focus on innate immune responses in the gut, the role of cell death pathways and antimicrobial peptides. We also provide some recent examples on how dysbiosis and pathogens can act in concert to promote intestinal infection, inflammatory pathologies and cancer. The future perspectives of these combined research efforts include the discovery of protective species within the microbiota and specific traits and factors of microbes that weaken or enforce host intestinal homeostasis.

Regulation of the Intestinal Barrier Function by Host Defense Peptides

Intestinal barrier function is achieved primarily through regulating the synthesis of mucins and tight junction (TJ) proteins, which are critical for maintaining optimal gut health and animal performance. An aberrant expression of TJ proteins results in increased paracellular permeability, leading to intestinal and systemic disorders. As an essential component of innate immunity, host defense peptides (HDPs) play a critical role in mucosal defense. Besides broad-spectrum antimicrobial activities, HDPs promotes inflammation resolution, endotoxin neutralization, wound healing, and the development of adaptive immune response. Accumulating evidence has also indicated an emerging role of HDPs in barrier function and intestinal homeostasis. HDP deficiency in the intestinal tract is associated with barrier dysfunction and dysbiosis. Several HDPs were recently shown to enhance mucosal barrier function by directly inducing the expression of multiple mucins and TJ proteins. Consistently, dietary supplementation of HDPs often leads to an improvement in intestinal morphology, production performance, and feed efficiency in livestock animals. This review summarizes current advances on the regulation of epithelial integrity and homeostasis by HDPs. Major signaling pathways mediating HDP-induced mucin and TJ protein synthesis are also discussed. As an alternative strategy to antibiotics, supplementation of exogenous HDPs or modulation of endogenous HDP synthesis may have potential to improve intestinal barrier function and animal health and productivity.

Rate of establishing the gut microbiota in infancy has consequences for future health

The gut of the human neonate is colonized rapidly after birth from an early sparse and highly distinct microbiota to a more adult-like and convergent state, within 1 to 3 years. The progression of colonizing bacterial species is non-random. During the first months of life several shifts commonly occur in the species prevalent in our guts. Although the sequential progression of these species is remarkably consistent across individuals and geographies, there is inter-individual variation in the rate of progression. Our study and others suggest that the rate is influenced by environmental factors, and influences our future health. In this article, we review our recent contribution to cataloging the developing infant gut microbiota alongside other important recent studies. We suggest testable hypotheses that arise from this synthesis.