Role of mucus layers in gut infection and inflammation

Dietary plant extracts modulate gene expression profiles in ileal mucosa of weaned pigs after an Escherichia coli infection

This study was conducted to characterize the effects of infection with a pathogenic F-18 Escherichia coli and 3 different plant extracts on gene expression of ileal mucosa in weaned pigs. Weaned pigs (total = 64, 6.3 ± 0.2 kg BW, and 21-d old) were housed in individual pens for 15 d, 4 d before and 11 d after the first inoculation (d 0). Treatments were in a 2 × 4 factorial arrangement: with or without an F-18 E. coli challenge and 4 diets (a nursery basal, control diet [CON], 10 ppm of capsicum oleoresin [CAP], garlic botanical [GAR], or turmeric oleoresin [TUR]). Results reported elsewhere showed that the plant extracts reduced diarrhea in challenged pigs. Total RNA (4 pigs/treatment) was extracted from ileal mucosa of pigs at d 5 post inoculation. Double-stranded cDNA was amplified, labeled, and further hybridized to the microarray, and data were analyzed in R. Differential gene expression was tested by fitting a mixed linear model in a 2 × 4 factorial ANOVA. Bioinformatics analysis was conducted by DAVID Bioinformatics Resources 6.7 (DAVID; National Institute of Allergy and Infectious Diseases [NIAID, NIH], http://david.abcc.ncifcrf.gov). The E. coli infection altered (P < 0.05) the expression of 240 genes in pigs fed the CON (148 up- and 92 down-regulated). Compared with the infected CON, feeding CAP, GAR, or TUR altered (P < 0.05) the expression of 52 genes (18 up, 34 down), 117 genes (34 up- and 83 down-regulated), or 84 genes (16 up- and 68 down-regulated), respectively, often counteracting the effects of E. coli. The E. coli infection up-regulated (P < 0.05) the expression of genes related to the activation of immune response and complement and coagulation cascades, but down-regulated (P < 0.05) the expression of genes involved in protein synthesis and accumulation. Compared with the CON, feeding CAP and GAR increased (P < 0.05) the expression of genes related to integrity of membranes in infected pigs, indicating enhanced gut mucosa health. Moreover, feeding all 3 plant extracts reduced (P < 0.05) the expression of genes associated with antigen presentation or other biological processes of immune responses, indicating they attenuated overstimulation of immune responses caused by E. coli. These findings may explain why diarrhea was reduced and clinical immune responses were ameliorated in infected pigs fed plant extracts. In conclusion, plant extracts altered the expression of genes in ileal mucosa of E. coli-infected pigs, perhaps leading to the reduction in diarrhea reported previously.

Inflammatory signals that regulate intestinal epithelial renewal, differentiation, migration and cell death: Implications for necrotizing enterocolitis

Necrotizing enterocolitis is a disease entity with multiple proposed pathways of pathogenesis. Various combinations of these risk factors, perhaps based on genetic predisposition, possibly lead to the mucosal and epithelial injury that is the hallmark of NEC. Intestinal epithelial integrity is controlled by a tightly regulated balance between proliferation and differentiation of epithelium from intestinal epithelial stem cells and cellular loss by apoptosis. various signaling pathways play a key role in creating and maintaining this balance. The aim of this review article is to outline intestinal epithelial barrier development and structure and the impact of these inflammatory signaling and regulatory pathways as they pertain to the pathogenesis of NEC.

Intestinal barrier in inflammatory bowel disease

A complex mucosal barrier protects as the first line of defense the surface of the healthy intestinal tract from adhesion and invasion by luminal microorganisms. In this review, we provide an overview about the major components of this protective system as for example an intact epithelium, the synthesis of various antimicrobial peptides (AMPs) and the formation of the mucus layer. We highlight the crucial importance of their correct functioning for the maintenance of a proper intestinal function and the prevention of dysbiosis and disease. Barrier disturbances including a defective production of AMPs, alterations in thickness or composition of the intestinal mucus layer, alterations of pattern-recognition receptors, defects in the process of autophagy as well as unresolved endoplasmic reticulum stress result in an inadequate host protection and are thought to play a crucial role in the pathogenesis of the inflammatory bowel diseases Crohn’s disease and ulcerative colitis.

Molecular dialogue between the human gut microbiota and the host: a Lactobacillus and Bifidobacterium perspective

The human gut represents a highly complex ecosystem, which is densely colonized by a myriad of microorganisms that influence the physiology, immune function and health status of the host. Among the many members of the human gut microbiota, there are microorganisms that have co-evolved with their host and that are believed to exert health-promoting or probiotic effects. Probiotic bacteria isolated from the gut and other environments are commercially exploited, and although there is a growing list of health benefits provided by the consumption of such probiotics, their precise mechanisms of action have essentially remained elusive. Genomics approaches have provided exciting new opportunities for the identification of probiotic effector molecules that elicit specific responses to influence the physiology and immune function of their human host. In this review, we describe the current understanding of the intriguing relationships that exist between the human gut and key members of the gut microbiota such as bifidobacteria and lactobacilli, discussed here as prototypical groups of probiotic microorganisms.

Interactions between Nod-Like Receptors and Intestinal Bacteria

Nucleotide oligomerization domain (Nod)-like Receptors (NLRs) are cytosolic sensors that mediate the activation of Caspase-1 and the subsequent processing and secretion of the pro-inflammatory cytokines IL-1β and IL-18, as well as an inflammatory cell death termed pyroptosis. While a multitude of bacteria have been shown to activate one or more NLRs under in vitro conditions, the exact impact of NLR activation during the course of colonization, both of pathogenic and commensal nature, is less understood. In this review, we will focus on the role of intestinal NLRs during the various stages of infection with common gastrointestinal bacterial pathogens, as well as NLR function in controlling and shaping the microbiota.

A refined palate: bacterial consumption of host glycans in the gut

The human intestine houses a dense microbial ecosystem in which the struggle for nutrients creates a continual and dynamic selective force. Host-produced mucus glycans provide a ubiquitous source of carbon and energy for microbial species. Not surprisingly, many gut resident bacteria have become highly adapted to efficiently consume numerous distinct structures present in host glycans. We propose that sophistication in mucus consumption is a trait most likely to be found in gut residents that have co-evolved with hosts, microbes that have adapted to the complexity associated with the host glycan landscape.

Tear film mucins: front line defenders of the ocular surface; comparison with airway and gastrointestinal tract mucins

The ocular surface including the cornea and conjunctiva and its overlying tear film are the first tissues of the eye to interact with the external environment. The tear film is complex containing multiple layers secreted by different glands and tissues. Each layer contains specific molecules and proteins that not only maintain the health of the cells on the ocular surface by providing nourishment and removal of waste products but also protect these cells from environment. A major protective mechanism that the corneal and conjunctival cells have developed is secretion of the innermost layer of the tear film, the mucous layer. Both the cornea and conjunctiva express membrane spanning mucins, whereas the conjunctiva also produces soluble mucins. The mucins present in the tear film serve to maintain the hydration of the ocular surface and to provide lubrication and anti-adhesive properties between the cells of the ocular surface and conjunctiva during the blink. A third function is to contribute to the epithelial barrier to prevent pathogens from binding to the ocular surface. This review will focus on the different types of mucins produced by the corneal and conjunctival epithelia. Also included in this review will be a presentation of the structure of mucins, regulation of mucin production, role of mucins in ocular surface diseases, and the differences in mucin production by the ocular surface, airways and gastrointestinal tract.

Toxoplasma gondii sporozoites invade host cells using two novel paralogues of RON2 and AMA1

Toxoplasma gondii is an obligate intracellular parasite of the phylum Apicomplexa. The interaction of two well-studied proteins, Apical Membrane Antigen 1 (AMA1) and Rhoptry Neck protein 2 (RON2), has been shown to be critical for invasion by the asexual tachyzoite stage. Recently, two paralogues of these proteins, dubbed sporoAMA1 and sporoRON2 (or RON2L2), respectively, have been identified but not further characterized in proteomic and transcriptomic analyses of Toxoplasma sporozoites. Here, we show that sporoAMA1 and sporoRON2 localize to the apical region of sporozoites and that, in vitro, they interact specifically and exclusively, with no detectable interaction of sporoAMA1 with generic RON2 or sporoRON2 with generic AMA1. Structural studies of the interacting domains of sporoRON2 and sporoAMA1 indicate a novel pairing that is similar in overall form but distinct in detail from the previously described interaction of the generic pairing. Most notably, binding of sporoRON2 domain 3 to domains I/II of sporoAMA1 results in major alterations in the latter protein at the site of binding and allosterically in the membrane-proximal domain III of sporoAMA1 suggesting a possible role in signaling. Lastly, pretreatment of sporozoites with domain 3 of sporoRON2 substantially impedes their invasion into host cells while having no effect on tachyzoites, and vice versa for domain 3 of generic RON2 (which inhibits tachyzoite but not sporozoite invasion). These data indicate that sporozoites and tachyzoites each use a distinct pair of paralogous AMA1 and RON2 proteins for invasion into host cells, possibly due to the very different environment in which they each must function.

Innate and acquired bacteriophage-mediated immunity

We recently described a novel, non-host-derived, phage-mediated immunity active at mucosal surfaces, the main site of pathogen entry in metazoans. In that work, we showed that phage T4 adheres to mucus glycoproteins via immunoglobulin-like domains displayed on its capsid. This adherence positions the phage in mucus surfaces where they are more likely to encounter and kill bacteria, thereby benefiting both the phage and its metazoan host. We presented this phage-metazoan symbiosis based on an exclusively lytic model of phage infection. Here we extend our bacteriophage adherence to mucus (BAM) model to consider the undoubtedly more complex dynamics in vivo. We hypothesize how mucus-adherent phages, both lytic and temperate, might impact the commensal microbiota as well as protect the metazoan epithelium from bacterial invasion. We suggest that BAM may provide both an innate and an acquired antimicrobial immunity.

Factors that explain excretion of enteric pathogens by persons without diarrhea

Excretion of enteropathogens by subjects without diarrhea influences our appreciation of the role of these pathogens as etiologic agents. Characteristics of the pathogens and host and environmental factors help explain asymptomatic excretion of diarrheal pathogens by persons without diarrhea. After causing acute diarrhea followed by clinical recovery, some enteropathogens are excreted asymptomatically for many weeks. Thus, in a prevalence survey of persons without diarrhea, some may be excreting pathogens from diarrheal episodes experienced many weeks earlier. Volunteer challenges with Vibrio cholerae O1, enterotoxigenic Escherichia coli (ETEC), enteropathogenic E. coli, Campylobacter jejuni, and Giardia lamblia document heterogeneity among enteropathogen strains, with some inexplicably not eliciting diarrhea. The immune host may not manifest diarrhea following ingestion of a pathogen but may nevertheless asymptomatically excrete. Some human genotypes render them less susceptible to symptomatic or severe diarrheal infection with certain pathogens such as Vibrio cholerae O1 and norovirus. Pathogens in stools of individuals without diarrhea may reflect recent ingestion of inocula too small to cause disease in otherwise susceptible hosts or of animal pathogens (eg, bovine or porcine ETEC) that do not cause human illness.

Comparison of the Caco-2, HT-29 and the mucus-secreting HT29-MTX intestinal cell models to investigate Salmonella adhesion and invasion

Human intestinal cell models are widely used to study host-enteric pathogen interactions, with different cell lines exhibiting specific characteristics and functions in the gut epithelium. In particular, the presence of mucus may play an important role in adhesion and invasion of pathogens. The aim of this study was to evaluate the suitability of the mucus-secreting HT29-MTX intestinal epithelial cell model to test adhesion and invasion of Salmonella strains and compare with data obtained with the more commonly used Caco-2 and HT-29 models. Adhesion of Salmonella to HT29-MTX cell model was significantly higher, likely due to high adhesiveness to mucins present in the native human mucus layer covering the whole cell surface, compared to the non- and low-mucus producing Caco-2 and HT-29 cell models, respectively. In addition, invasion percentages of some clinical Salmonella strains to HT29-MTX cultures were remarkably higher than to Caco-2 and HT-29 cells suggesting that these Salmonellae have subverted the mucus to enhance pathogenicity. The transepithelial electrical resistances of the infected HT29-MTX cell model decreased broadly and were highly correlated with invasion ability of the strain. Staining of S. Typhimurium-infected cell epithelium confirmed the higher invasion by Salmonella and subsequent disruption of tight junctions of HT29-MTX cell model compared with the Caco-2 and HT-29 cell models. Data from this study suggest that the HT29-MTX cell model, with more physiologically relevant characteristics with the mucus layer formation, could be better suited for studying cells-pathogens interactions.

Colonization resistance and microbial ecophysiology: using gnotobiotic mouse models and single-cell technology to explore the intestinal jungle

The highly diverse intestinal microbiota forms a structured community engaged in constant communication with itself and its host and is characterized by extensive ecological interactions. A key benefit that the microbiota affords its host is its ability to protect against infections in a process termed colonization resistance (CR), which remains insufficiently understood. In this review, we connect basic concepts of CR with new insights from recent years and highlight key technological advances in the field of microbial ecology. We present a selection of statistical and bioinformatics tools used to generate hypotheses about synergistic and antagonistic interactions in microbial ecosystems from metagenomic datasets. We emphasize the importance of experimentally testing these hypotheses and discuss the value of gnotobiotic mouse models for investigating specific aspects related to microbiota-host-pathogen interactions in a well-defined experimental system. We further introduce new developments in the area of single-cell analysis using fluorescence in situ hybridization in combination with metabolic stable isotope labeling technologies for studying the in vivo activities of complex community members. These approaches promise to yield novel insights into the mechanisms of CR and intestinal ecophysiology in general, and give researchers the means to experimentally test hypotheses in vivo at varying levels of biological and ecological complexity.

Physiological and molecular mechanisms of salt and water homeostasis in the nematode Caenorhabditis elegans

Intracellular salt and water homeostasis is essential for all cellular life. Extracellular salt and water homeostasis is also important for multicellular organisms. Many fundamental mechanisms of compensation for osmotic perturbations are well defined and conserved. Alternatively, molecular mechanisms of detecting salt and water imbalances and regulating compensatory responses are generally poorly defined for animals. Throughout the last century, researchers studying vertebrates and vertebrate cells made critical contributions to our understanding of osmoregulation, especially mechanisms of salt and water transport and organic osmolyte accumulation. Researchers have more recently started using invertebrate model organisms with defined genomes and well-established methods of genetic manipulation to begin defining the genes and integrated regulatory networks that respond to osmotic stress. The nematode Caenorhabditis elegans is well suited to these studies. Here, I introduce osmoregulatory mechanisms in this model, discuss experimental advantages and limitations, and review important findings. Key discoveries include defining genetic mechanisms of osmolarity sensing in neurons, identifying protein damage as a sensor and principle determinant of hypertonic stress resistance, and identification of a putative sensor for hypertonic stress associated with the extracellular matrix. Many of these processes and pathways are conserved and, therefore, provide new insights into salt and water homeostasis in other animals, including mammals.

Neonatal immune adaptation of the gut and its role during infections

The intestinal tract is engaged in a relationship with a dense and complex microbial ecosystem, the microbiota. The establishment of this symbiosis is essential for host physiology, metabolism, and immune homeostasis. Because newborns are essentially sterile, the first exposure to microorganisms and environmental endotoxins during the neonatal period is followed by a crucial sequence of active events leading to immune tolerance and homeostasis. Contact with potent immunostimulatory molecules starts immediately at birth, and the discrimination between commensal bacteria and invading pathogens is essential to avoid an inappropriate immune stimulation and/or host infection. The dysregulation of these tight interactions between host and microbiota can be responsible for important health disorders, including inflammation and sepsis. This review summarizes the molecular events leading to the establishment of postnatal immune tolerance and how pathogens can avoid host immunity and induce neonatal infections and sepsis.

The unfolded protein response and gastrointestinal disease

As the inner lining of the gastrointestinal tract, the intestinal epithelium serves an essential role in innate immune function at the interface between the host and microbiota. Given the unique environmental challenges and thus physiologic secretory functions of this surface, it is exquisitely sensitive to perturbations that affect its capacity to resolve endoplasmic reticulum (ER) stress. Genetic deletion of factors involved in the unfolded protein response (UPR), which functions in the resolution of ER stress that arises from misfolded proteins, result in spontaneous intestinal inflammation closely mimicking human inflammatory bowel disease (IBD). This is demonstrated by observations wherein deletion of genes such as Xbp1 and Agr2 profoundly affects the intestinal epithelium and results in spontaneous intestinal inflammation. Moreover, both genes, along with others (e.g., ORDML3) represent genetic risk factors for human IBD, both Crohn's disease and ulcerative colitis. Here, we review the current mechanistic understanding for how unresolved ER stress can lead to intestinal inflammation and highlight the findings that implicate ER stress as a genetically affected biological pathway in IBD. We further discuss environmental and microbial factors that might impact on the epithelium's capacity to resolve ER stress and which may constitute exogenous factors that may precipitate disease in genetically susceptible individuals.

Gate-keeper function of the intestinal epithelium

There is currently a major focus on the role of the gut barrier function in balancing mucosal immune responses. Increased epithelial permeability for exogenous antigens is a crucial primary or secondary event in the pathogenesis of several disorders affecting body surfaces and beyond. The epithelial gate-keeper function is determined by the individual's age (e.g. preterm vs. term infant), diet, genetics, mucus composition, interactions between mast cells, nerves and neuropeptides, concurrent infection, the commensal microbiota and the epithelium-shielding effect of secretory IgA (SIgA) antibodies provided by breast milk or produced in the individual's gut. The integrity of the epithelial barrier furthermore depends on homeostatic regulatory mechanisms, including mucosal induction of regulatory T cells, where commensal microbiota-host interactions apparently play decisive roles. Thus, both extrinsic and intrinsic factors have been identified that may have an impact on the dynamics of the epithelial cell-cell junctions in the gut and thereby increase or reduce paracellular permeability. Experiments have shown that SIgA normally cooperates with innate defence factors to protect the epithelium and reinforce its barrier function. In the absence of SIgA commensal gut bacteria overstimulate innate epithelial immunity at the expense of expression of genes that regulate fat and carbohydrate metabolism, resulting in an epithelial gene signature that correlates with the development of lipid malabsorption. This shows that the intestinal epithelial barrier is a cross-road between defence and nutrition, and that SIgA is essential to keep the balance between these two functions.

Goblet cells and mucins: role in innate defense in enteric infections

Goblet cells reside throughout the gastrointestinal (GI) tract and are responsible for the production and preservation of a protective mucus blanket by synthesizing and secreting high molecular weight glycoproteins known as mucins. The concept of the mucus layer functioning as a dynamic protective barrier is suggested by studies showing changes in mucins in inflammatory conditions of the GI tract, by the altered goblet cell response in germ-free animals, and by the enhanced mucus secretion seen in response to infections. The mucin-containing mucus layer coating the GI epithelium is the front line of innate host defense. Mucins are likely to be the first molecules that invading pathogens interact with at the cell surface and thus, can limit binding to other glycoproteins and neutralize the pathogen. This review will focus on what is known about goblet cell response in various GI infections and the regulatory networks that mediate goblet cell function and mucin production in response to intestinal insults. In addition, we describe the current knowledge on the role of mucins in intestinal innate defense. It is the aim of this review to provide the readers with an update on goblet cell biology and current understanding on the role of mucins in host defense in enteric infections.

Glycobiome: bacteria and mucus at the epithelial interface

The human gastrointestinal tract is colonised with a dense and diverse microbial community, that is an important player in human health and physiology. Close to the epithelial cells the mucosal microbiota is separated from the host with a thin lining of host derived glycans, including the cell surface glycocalyx and the extracellular secreted mucus. The mucosa-associated microbial composition differs from the luminal content and could be particularly important for nutrient exchange, communication with the host, development of the immune system, and resistance against invading pathogens. The mucosa-associated microbiota has adapted to the glycan rich environment by the production of mucus-degrading enzymes and mucus-binding extracellular proteins, and include mucus-degrading specialists such as Akkermansia muciniphila and Bacteroides thetaiotaomicron. This review is focussed on the host-microbe interactions within the glycan landscape at the epithelial interface and considers the spatial organisation and composition of the mucosa-associated microbiota in health and disease.

Cloning, annotation and developmental expression of the chicken intestinal MUC2 gene

Intestinal mucin 2 (MUC2) encodes a heavily glycosylated, gel-forming mucin, which creates an important protective mucosal layer along the gastrointestinal tract in humans and other species. This first line of defense guards against attacks from microorganisms and is integral to the innate immune system. As a first step towards characterizing the innate immune response of MUC2 in different species, we report the cloning of a full-length, 11,359 bp chicken MUC2 cDNA, and describe the genomic organization and functional annotation of this complex, 74.5 kb locus. MUC2 contains 64 exons and demonstrates distinct spatiotemporal expression profiles throughout development in the gastrointestinal tract; expression increases with gestational age and from anterior to posterior along the gut. The chicken protein has a similar domain organization as the human orthologue, with a signal peptide and several von Willebrand domains in the N-terminus and the characteristic cystine knot at the C-terminus. The PTS domain of the chicken MUC2 protein spans ∼1600 amino acids and is interspersed with four CysD motifs. However, the PTS domain in the chicken diverges significantly from the human orthologue; although the chicken domain is shorter, the repetitive unit is 69 amino acids in length, which is three times longer than the human. The amino acid composition shows very little similarity to the human motif, which potentially contributes to differences in the innate immune response between species, as glycosylation across this rapidly evolving domain provides much of the musical barrier. Future studies of the function of MUC2 in the innate immune response system in chicken could provide an important model organism to increase our understanding of the biological significance of MUC2 in host defense and highlight the potential of the chicken for creating new immune-based therapies.

Guarding the perimeter: protection of the mucosa by tissue-resident memory T cells

Mucosal tissues are continually bombarded with infectious agents seeking to gain entry into the body. The absence of a tough physical exterior layer surrounding these tissues creates a unique challenge for the immune system, which manages to provide broad protection against a plethora of different organisms with the aid of special adaptations that augment immunity at these vulnerable sites. For example, specialized populations of memory T lymphocytes reside at initial sites of pathogen entry into the body, where they provide an important protective barrier. Similar anatomically-confined populations of pathogen-specific CD8 T cells can be found near the outer margins of the body following recovery from a variety of local infections, where they share very similar phenotypic characteristics. How these tissue-resident T cells are retained in a single anatomic location where they can promote immunity is beginning to be defined. Here, we will review current knowledge of the mechanisms that help establish and maintain these regional lymphocytes in the mucosal tissues and discuss relevant data that enhance our understanding of the contribution of these lymphocyte populations to protective immunity against infectious diseases.

Nanoparticle toxicity by the gastrointestinal route: evidence and knowledge gaps

The increasing interest in nanoparticles for advanced technologies, consumer products, and biomedical applications has led to great excitement about potential benefits but also concern over the potential for adverse human health effects. The gastrointestinal tract represents a likely route of entry for many nanomaterials, both directly through intentional ingestion or indirectly via nanoparticle dissolution from food containers or by secondary ingestion of inhaled particles. Additionally, increased utilisation of nanoparticles may lead to increased environmental contamination and unintentional ingestion via water, food animals, or fish. The gastrointestinal tract is a site of complex, symbiotic interactions between host cells and the resident microbiome. Accordingly, evaluation of nanoparticles must take into consideration not only absorption and extraintestinal organ accumulation but also the potential for altered gut microbes and the effects of this perturbation on the host. The existing literature was evaluated for evidence of toxicity based on these considerations. Focus was placed on three categories of nanomaterials: nanometals and metal oxides, carbon-based nanoparticles, and polymer/dendrimers with emphasis on those particles of greatest relevance to gastrointestinal exposures.

Evolutionary foundations for cancer biology

New applications of evolutionary biology are transforming our understanding of cancer. The articles in this special issue provide many specific examples, such as microorganisms inducing cancers, the significance of within-tumor heterogeneity, and the possibility that lower dose chemotherapy may sometimes promote longer survival. Underlying these specific advances is a large-scale transformation, as cancer research incorporates evolutionary methods into its toolkit, and asks new evolutionary questions about why we are vulnerable to cancer. Evolution explains why cancer exists at all, how neoplasms grow, why cancer is remarkably rare, and why it occurs despite powerful cancer suppression mechanisms. Cancer exists because of somatic selection; mutations in somatic cells result in some dividing faster than others, in some cases generating neoplasms. Neoplasms grow, or do not, in complex cellular ecosystems. Cancer is relatively rare because of natural selection; our genomes were derived disproportionally from individuals with effective mechanisms for suppressing cancer. Cancer occurs nonetheless for the same six evolutionary reasons that explain why we remain vulnerable to other diseases. These four principles-cancers evolve by somatic selection, neoplasms grow in complex ecosystems, natural selection has shaped powerful cancer defenses, and the limitations of those defenses have evolutionary explanations-provide a foundation for understanding, preventing, and treating cancer.

Impaired small-bowel barrier integrity in the presence of lumenal pancreatic digestive enzymes leads to circulatory shock

In bowel ischemia, impaired mucosal integrity may allow intestinal pancreatic enzyme products to become systemic and precipitate irreversible shock and death. This can be attenuated by pancreatic enzyme inhibition in the small-bowel lumen. It is unresolved, however, whether ischemically mediated mucosal disruption is the key event allowing pancreatic enzyme products systemic access and whether intestinal digestive enzyme activity in concert with increased mucosal permeability leads to shock in the absence of ischemia. To test this possibility, the small intestinal lumen of nonischemic rats was perfused for 2 h with either digestive enzymes, a mucin disruption strategy (i.e., mucolytics) designed to increase mucosal permeability, or both, and animals were observed for shock. Digestive enzymes perfused included trypsin, chymotrypsin, elastase, amylase, and lipase. Control (n = 6) and experimental animals perfused with pancreatic enzymes only (n = 6) or single enzymes (n = 3 for each of the five enzyme groups) maintained stable hemodynamics. After mucin disruption using a combination of enteral N-acetylcysteine, atropine, and increased flow rates, rats (n = 6) developed mild hypotension (P < 0.001 compared with groups perfused with pancreatic enzymes only after 90 min) and increased intestinal permeability to intralumenally perfused fluorescein isothiocyanate-dextran 20 kd (P < 0.05) compared with control and enzyme-only groups, but there were no deaths. All animals perfused with both digestive enzymes and subjected to mucin disruption (n = 6) developed hypotension and increased intestinal permeability (P < 0.001 after 90 min). Pancreatic enzymes were measured in the intestinal wall of both groups subjected to mucin disruption, but not in the enzyme-only or control groups. Depletion of plasma protease inhibitors was found only in animals perfused with pancreatic enzymes plus mucin disruption, implicating increased permeability and intralumenal pancreatic enzyme egress in this group. These experiments demonstrate that increased bowel permeability via mucin disruption in the presence of pancreatic enzymes can induce shock and increase systemic protease activation in the absence of ischemia, implicating bowel mucin disruption as a key event in early ischemia. Digestive enzymes and their products, if allowed to penetrate the gut wall, may trigger multiorgan failure and death.

Mathematical model of colitis-associated colon cancer

As a result of chronic inflammation of their colon, patients with ulcerative colitis or Crohn's disease are at risk of developing colon cancer. In this paper, we consider the progression of colitis-associated colon cancer. Unlike normal colon mucosa, the inflammed colon mucosa undergoes genetic mutations, affecting, in particular, tumor suppressors TP53 and adenomatous polyposis coli (APC) gene. We develop a mathematical model that involves these genes, under chronic inflammation, as well as NF-κB, β-catenin, MUC1 and MUC2. The model demonstrates that increased level of cells with TP53 mutations results in abnormal growth and proliferation of the epithelium; further increase in the epithelium proliferation results from additional APC mutations. The model may serve as a conceptual framework for further data-based study of the early stage of colon cancer.

Lamellar structures of MUC2-rich mucin: a potential role in governing the barrier and lubricating functions of intestinal mucus

Mucus is a ubiquitous feature of mammalian wet epithelial surfaces, where it lubricates and forms a selective barrier that excludes a range of particulates, including pathogens, while hosting a diverse commensal microflora. The major polymeric component of mucus is mucin, a large glycoprotein formed by several MUC gene products, with MUC2 expression dominating intestinal mucus. A satisfactory answer to the question of how these molecules build a dynamic structure capable of playing such a complex role has yet to be found, as recent reports of distinct layers of chemically identical mucin in the colon and anomalously rapid transport of nanoparticles through mucus have emphasized. Here we use atomic force microscopy (AFM) to image a MUC2-rich mucus fraction isolated from pig jejunum. In the freshly isolated mucin fraction, we find direct evidence for trigonally linked structures, and their assembly into lamellar networks with a distribution of pore sizes from 20 to 200 nm. The networks are two-dimensional, with little interaction between lamellae. The existence of persistent cross-links between individual mucin polypeptides is consistent with a non-self-interacting lamellar model for intestinal mucus structure, rather than a physically entangled polymer network. We only observe collapsed entangled structures in purified mucin that has been stored in nonphysiological conditions.

Sinus hypoplasia precedes sinus infection in a porcine model of cystic fibrosis

OBJECTIVES/HYPOTHESIS

Chronic sinusitis is nearly universal in humans with cystic fibrosis (CF) and is accompanied by sinus hypoplasia (small sinuses). However, whether impaired sinus development is a primary feature of loss of the cystic fibrosis transmembrane conductance regulator (CFTR) or a secondary consequence of chronic infection remains unknown. Our objective was to study the early pathogenesis of sinus disease in CF.

STUDY DESIGN

Animal/basic science research.

METHODS

Sinus development was studied in a porcine CF model.

RESULTS

Porcine sinus epithelia expressed CFTR and exhibited transepithelial anion transport. Disruption of the CFTR gene eliminated both. Sinuses of newborn CF pigs were not infected and showed no evidence of inflammation, yet were hypoplastic at birth. Older CF pigs spontaneously developed sinus disease similar to that seen in humans with CF.

CONCLUSIONS

These results define a role for CFTR in sinus development and suggest the potential of the CF pig as a genetic model of CF-sinus disease in which to test therapeutic strategies to minimize sinus-related CF morbidity.

Innate immune signalling at the intestinal epithelium in homeostasis and disease

The intestinal epithelium--which constitutes the interface between the enteric microbiota and host tissues--actively contributes to the maintenance of mucosal homeostasis and defends against pathogenic microbes. The recognition of conserved microbial products by cytosolic or transmembrane pattern recognition receptors in epithelial cells initiates signal transduction and influences effector cell function. However, the signalling pathways, effector molecules and regulatory mechanisms involved are not yet fully understood, and the functional outcome is poorly defined. This review analyses the complex and dynamic role of intestinal epithelial innate immune recognition and signalling, on the basis of results in intestinal epithelial cell-specific transgene or gene-deficient animals. This approach identifies specific epithelial cell functions within the diverse cellular composition of the mucosal tissue, in the presence of the complex and dynamic gut microbiota. These insights have thus provided a more comprehensive understanding of the role of the intestinal epithelium in innate immunity during homeostasis and disease.

Microbial products alter the expression of membrane-associated mucin and antimicrobial peptides in a three-dimensional human endocervical epithelial cell model

Our understanding of the mechanisms that regulate tissue-specific mucosal defense can be limited by the lack of appropriate human in vitro models. The endocervix lies between the microbe-rich vaginal cavity and the relatively sterile endometrium and is a major portal of entry for Chlamydia trachomatis, Neisseria gonorrhoeae, Mycoplasma genitalium, human immunodeficiency virus (HIV), and herpes simplex virus (HSV) infection in women. The endocervix is lined with a simple epithelium, and these cells produce mucus, which plays a key role in immune defense and reproduction. Here we describe the development of a human three-dimensional endocervical epithelial cell model generated by rotating wall vessel bioreactor technology. The model is composed of cellular aggregates that recapitulate major structural and barrier properties essential for the function and protection of the endocervix, including junctional complexes, microvilli, innate immune receptors, antimicrobial peptides, and mucins, the major structural component of mucus. Using this model, we also report, for the first time, that the membrane-associated mucin genes MUC1, MUC4, and MUC16 are differentially regulated in these aggregates by different bacterial and viral products. Differential induction of antimicrobial peptides was also observed with these products. Together these data define unique and flexible innate endocervical immune signatures that follow exposure to microbial products and that likely play a critical role in the outcome of pathogen challenge at this site.

Influence of adhesion and bacteriocin production by Lactobacillus salivarius on the intestinal epithelial cell transcriptional response

Lactobacillus salivarius strain UCC118 is a human intestinal isolate that has been extensively studied for its potential probiotic effects in human and animal models. The objective of this study was to determine the effect of L. salivarius UCC118 on gene expression responses in the Caco-2 cell line to improve understanding of how the strain might modulate intestinal epithelial cell phenotypes. Exposure of Caco-2 cells to UCC118 led to the induction of several human genes (TNFAIP3, NFKBIA, and BIRC3) that are negative regulators of inflammatory signaling pathways. Induction of chemokines (CCL20, CXCL-1, and CXCL-2) with antimicrobial functions was also observed. Disruption of the UCC118 sortase gene srtA causes reduced bacterial adhesion to epithelial cells. Transcription of three mucin genes was reduced significantly when Caco-2 cells were stimulated with the ΔsrtA derivative of UCC118 compared to cells stimulated with the wild type, but there was no significant change in the transcription levels of the anti-inflammatory genes. UCC118 genes that were significantly upregulated upon exposure to Caco-2 cells were identified by bacterial genome microarray and consisted primarily of two groups of genes connected with purine metabolism and the operon for synthesis of the Abp118 bacteriocin. Following incubation with Caco-2 cells, the bacteriocin synthesis genes were transcribed at higher levels in the wild type than in the ΔsrtA derivative. These data indicate that L. salivarius UCC118 influences epithelial cells both through modulation of the inflammatory response and by modulation of intestinal cell mucin production. Sortase-anchored cell surface proteins of L. salivarius UCC118 have a central role in promoting the interaction between the bacterium and epithelial cells.