Studies of mucus in mouse stomach, small intestine, and colon. I. Gastrointestinal mucus layers have different properties depending on location as well as over the Peyer's patches.
01 Sep 2013-American Journal of Physiology-gastrointestinal and Liver Physiology (American Physiological Society)-Vol. 305, Iss: 5
TL;DR: Mulus release, thickness, growth over time, adhesive properties, and penetrability to fluorescent beads from stomach to distal colon are characterized and suggest a functional organization of the intestinal mucus system, where the small intestine has loose and penetraterable mucus that may allow easy penetration of nutrients.
Abstract: Colon has been shown to have a two-layered mucus system where the inner layer is devoid of bacteria. However, a complete overview of the mouse gastrointestinal mucus system is lacking. We now characterize mucus release, thickness, growth over time, adhesive properties, and penetrability to fluorescent beads from stomach to distal colon. Colon displayed spontaneous mucus release and all regions released mucus in response to carbachol and PGE2, except the distal colon and domes of Peyer's patches. Stomach and colon had an inner mucus layer that was adherent to the epithelium. In contrast, the small intestine and Peyer's patches had a single mucus layer that was easily aspirated. The inner mucus layer of the distal colon was not penetrable to beads the size of bacteria and the inner layer of the proximal colon was only partly penetrable. In contrast, the inner mucus layer of stomach was fully penetrable, as was the small intestinal mucus. This suggests a functional organization of the intestinal mucus system, where the small intestine has loose and penetrable mucus that may allow easy penetration of nutrients, in contrast to the stomach, where the mucus provides physical protection, and the colon, where the mucus separates bacteria from the epithelium. This knowledge of the mucus system and its organization improves our understanding of the gastrointestinal tract physiology.
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TL;DR: The mucus and epithelial cells of the gastrointestinal tract are the primary gate keepers and controllers of bacterial interactions with the host immune system, but the understanding of this relationship is still in its infancy.
Abstract: The gastrointestinal tract is covered by mucus that has different properties in the stomach, small intestine, and colon. The large highly glycosylated gel-forming mucins MUC2 and MUC5AC are the major components of the mucus in the intestine and stomach, respectively. In the small intestine, mucus limits the number of bacteria that can reach the epithelium and the Peyer's patches. In the large intestine, the inner mucus layer separates the commensal bacteria from the host epithelium. The outer colonic mucus layer is the natural habitat for the commensal bacteria. The intestinal goblet cells secrete not only the MUC2 mucin but also a number of typical mucus components: CLCA1, FCGBP, AGR2, ZG16, and TFF3. The goblet cells have recently been shown to have a novel gate-keeping role for the presentation of oral antigens to the immune system. Goblet cells deliver small intestinal luminal material to the lamina propria dendritic cells of the tolerogenic CD103+ type. In addition to the gel-forming mucins, the transmembrane mucins MUC3, MUC12, and MUC17 form the enterocyte glycocalyx that can reach about a micrometer out from the brush border. The MUC17 mucin can shuttle from a surface to an intracellular vesicle localization, suggesting that enterocytes might control and report epithelial microbial challenge. There is communication not only from the epithelial cells to the immune system but also in the opposite direction. One example of this is IL10 that can affect and improve the properties of the inner colonic mucus layer. The mucus and epithelial cells of the gastrointestinal tract are the primary gate keepers and controllers of bacterial interactions with the host immune system, but our understanding of this relationship is still in its infancy.
846 citations
Cites background from "Studies of mucus in mouse stomach, ..."
...The uptake of luminal material by goblet cells is stimulated by acetyl choline analogs that are effective stimulators of small intestinal mucus secretion (8, 77)....
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...The axis to the left shows the thickness of the mucus as measured in mice (8)....
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...The glandular stomach and colon have a two-layered system with an inner and an outer mucus layer, whereas the small intestine has only a single layer (6, 8)....
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...Fresh mucus is constantly secreted from the goblet cells, especially from the crypt openings (8)....
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...1 with the mucus illustrated in different shades of green depending on mucus density and the bacteria shown in red (8)....
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TL;DR: This review focuses on recent findings unraveling the molecular strategies used by mucin-degrading bacteria to utilize host glycans, adapt to the mucosal environment, and influence human health.
Abstract: The availability of host and dietary carbohydrates in the gastrointestinal (GI) tract plays a key role in shaping the structure-function of the microbiota. In particular, some gut bacteria have the ability to forage on glycans provided by the mucus layer covering the GI tract. The O-glycan structures present in mucin are diverse and complex, consisting predominantly of core 1-4 mucin-type O-glycans containing α- and β- linked N-acetyl-galactosamine, galactose and N-acetyl-glucosamine. These core structures are further elongated and frequently modified by fucose and sialic acid sugar residues via α1,2/3/4 and α2,3/6 linkages, respectively. The ability to metabolize these mucin O-linked oligosaccharides is likely to be a key factor in determining which bacterial species colonise the mucosal surface. Due to their proximity to the immune system, mucin-degrading bacteria are in a prime location to influence the host response. However, despite the growing number of bacterial genome sequences available from mucin degraders, our knowledge on the structural requirements for mucin degradation by gut bacteria remains fragmented. This is largely due to the limited number of functionally characterized enzymes and the lack of studies correlating the specificity of these enzymes with the ability of the strain to degrade and utilize mucin and mucin glycans. This review focuses on recent findings unravelling the molecular strategies used by mucin-degrading bacteria to utilise host glycans, adapt to the mucosal environment, and influence human health.
602 citations
TL;DR: This Review will give a basic overview of mucus, mucins and goblet cells, and explain how each of these contributes to immune regulation in the intestine.
Abstract: A number of mechanisms ensure that the intestine is protected from pathogens and also against our own intestinal microbiota. The outermost of these is the secreted mucus, which entraps bacteria and prevents their translocation into the tissue. Mucus contains many immunomodulatory molecules and is largely produced by the goblet cells. These cells are highly responsive to the signals they receive from the immune system and are also able to deliver antigens from the lumen to dendritic cells in the lamina propria. In this Review, we will give a basic overview of mucus, mucins and goblet cells, and explain how each of these contributes to immune regulation in the intestine.
544 citations
TL;DR: Different aspects of the mucus layer are debated by focusing on its chemical composition, regulation of synthesis and degradation by the microbiota as well as some characteristics of the slime layer in both physiological and pathological situations.
Abstract: The gastrointestinal tract is often considered as a key organ involved in the digestion of food and providing nutrients to the body for proper maintenance. However, this system is composed of organs that are extremely complex. Among the different parts, the intestine is viewed as an incredible surface of contact with the environment and is colonised by hundreds of trillions of gut microbes. The role of the gut barrier has been studied for decades, but the exact mechanisms involved in the protection of the gut barrier are various and complementary. Among them, the integrity of the mucus barrier is one of the first lines of protection of the gastrointestinal tract. In the past, this ‘slimy’ partner was mostly considered a simple lubricant for facilitating the progression of the food bolus and the stools in the gut. Since then, different researchers have made important progress, and currently, the regulation of this mucus barrier is gaining increasing attention from the scientific community. Among the factors influencing the mucus barrier, the microbiome plays a major role in driving mucus changes. Additionally, our dietary habits (ie, high-fat diet, low-fibre/high-fibre diet, food additives, pre- probiotics) influence the mucus at different levels. Given that the mucus layer has been linked with the appearance of diseases, proper knowledge is highly warranted. Here, we debate different aspects of the mucus layer by focusing on its chemical composition, regulation of synthesis and degradation by the microbiota as well as some characteristics of the mucus layer in both physiological and pathological situations.
513 citations
TL;DR: The study shows that bacteria and their community structure affect mucus barrier properties in ways that can have implications for health and disease and highlights that genetically identical animals housed in the same facility can have rather distinct microbiotas and barrier structures.
Abstract: Two C57BL/6 mice colonies maintained in two rooms of the same specific pathogen-free (SPF) facility were found to have different gut microbiota and a mucus phenotype that was specific for each colony. The thickness and growth of the colon mucus were similar in the two colonies. However, one colony had mucus that was impenetrable to bacteria or beads the size of bacteria—which is comparable to what we observed in free-living wild mice—whereas the other colony had an inner mucus layer penetrable to bacteria and beads. The different properties of the mucus depended on the microbiota, as they were transmissible by transfer of caecal microbiota to germ-free mice. Mice with an impenetrable mucus layer had increased amounts of Erysipelotrichi, whereas mice with a penetrable mucus layer had higher levels of Proteobacteria and TM7 bacteria in the distal colon mucus. Thus, our study shows that bacteria and their community structure affect mucus barrier properties in ways that can have implications for health and disease. It also highlights that genetically identical animals housed in the same facility can have rather distinct microbiotas and barrier structures.
499 citations
Cites background from "Studies of mucus in mouse stomach, ..."
...The mucus in the small intestine fills up the space between the villi and covers these, but is not attached to the epithelium and has a structure that can allow particles as large as bacteria to penetrate [8]....
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References
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TL;DR: New studies are revealing how the gut microbiota has coevolved with us and how it manipulates and complements the authors' biology in ways that are mutually beneficial.
Abstract: The distal human intestine represents an anaerobic bioreactor programmed with an enormous population of bacteria, dominated by relatively few divisions that are highly diverse at the strain/subspecies level. This microbiota and its collective genomes (microbiome) provide us with genetic and metabolic attributes we have not been required to evolve on our own, including the ability to harvest otherwise inaccessible nutrients. New studies are revealing how the gut microbiota has coevolved with us and how it manipulates and complements our biology in ways that are mutually beneficial. We are also starting to understand how certain keystone members of the microbiota operate to maintain the stability and functional adaptability of this microbial organ.
4,526 citations
"Studies of mucus in mouse stomach, ..." refers background or methods in this paper
...1, E and F: unstimulated tissue (1), tissue stimulated for 20 min with carbachol and PGE2 (10 M of each) (2), mucus secreted after 10 min stimulation into an apical pH 3 buffer (3)....
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...2D, duodenum (1), jejunum (2), and ileum (3)]....
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...The host benefits from harboring bacteria since they degrade the mucins and ingested complex carbohydrates from the food into simple sugars that are converted into butyrate, propionate, and acetate supplied to the host (3)....
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TL;DR: Advances in understanding of the interactions between resident microbes and the immune system are reviewed and the implications for human health are reviewed.
Abstract: The large numbers of microorganisms that inhabit mammalian body surfaces have a highly coevolved relationship with the immune system. Although many of these microbes carry out functions that are critical for host physiology, they nevertheless pose the threat of breach with ensuing pathologies. The mammalian immune system plays an essential role in maintaining homeostasis with resident microbial communities, thus ensuring that the mutualistic nature of the host-microbial relationship is maintained. At the same time, resident bacteria profoundly shape mammalian immunity. Here, we review advances in our understanding of the interactions between resident microbes and the immune system and the implications of these findings for human health.
3,330 citations
"Studies of mucus in mouse stomach, ..." refers background in this paper
...Antigens in the bowel content are sampled by lymphoid follicles, which are part of the gut-associated lymphoid tissues of the adaptive immune system (12)....
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...Although this varies by region, food and luminal contents contain large numbers of diverse microorganisms that can be potentially harmful if they breach the mucus or epithelial barrier (12)....
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TL;DR: Findings show that the Muc2 mucin can build a mucus barrier that separates bacteria from the colon epithelia and suggest that defects in this mucus can cause colon inflammation.
Abstract: We normally live in symbiosis with approximately 10(13) bacteria present in the colon. Among the several mechanisms maintaining the bacteria/host balance, there is limited understanding of the structure, function, and properties of intestinal mucus. We now demonstrate that the mouse colonic mucus consists of two layers extending 150 mum above the epithelial cells. Proteomics revealed that both of these layers have similar protein composition, with the large gel-forming mucin Muc2 as the major structural component. The inner layer is densely packed, firmly attached to the epithelium, and devoid of bacteria. In contrast, the outer layer is movable, has an expanded volume due to proteolytic cleavages of the Muc2 mucin, and is colonized by bacteria. Muc2(-/-) mice have bacteria in direct contact with the epithelial cells and far down in the crypts, explaining the inflammation and cancer development observed in these animals. These findings show that the Muc2 mucin can build a mucus barrier that separates bacteria from the colon epithelia and suggest that defects in this mucus can cause colon inflammation.
1,868 citations
"Studies of mucus in mouse stomach, ..." refers background or methods in this paper
...This large amount of bacteria is kept separated from the epithelium by an inner mucus layer physically impenetrable to bacteria (16)....
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...The two-layered mucus system of colon is also present in germ-free mice (16), but less developed with thinner thickness....
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...We have developed a methodology and performed studies on the mucus system of the distal colon (10, 16, 17), but to provide a more complete picture of gastrointestinal mucus we are now characterizing the normal mucus system of the whole GIT....
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...Although it is not fully understood how the inner mucus layer of the colon becomes impenetrable to bacteria (16), our studies using fluorescent beads with sizes typical for bacteria suggest that the inner mucus layer is acting as a molecular sieve (10, 13)....
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...Whole tissue from stomach, duodenum, jejunum, ileum, and proximal and distal colon with content was fixed in methanol-Carnoy’s fixative and stained after antigen retrieval (16) with the anti-MUC2C3 antiserum raised against a peptide from a nonglycosylated region (1:500) (16) or mouse monoclonal anti-MUC5AC (45M1, 1:2,000; Invitrogen)....
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TL;DR: The components of the secreted and cell surface mucosal barriers and the evidence that they form an effective barricade against potential pathogens are described and dynamic alterations in the mucin barrier are described driven by host innate and adaptive immune responses to infection.
Abstract: The extracellular secreted mucus and the cell surface glycocalyx prevent infection by the vast numbers of microorganisms that live in the healthy gut. Mucin glycoproteins are the major component of these barriers. In this Review, we describe the components of the secreted and cell surface mucosal barriers and the evidence that they form an effective barricade against potential pathogens. However, successful enteric pathogens have evolved strategies to circumvent these barriers. We discuss the interactions between enteric pathogens and mucins, and the mechanisms that these pathogens use to disrupt and avoid mucosal barriers. In addition, we describe dynamic alterations in the mucin barrier that are driven by host innate and adaptive immune responses to infection.
1,166 citations
"Studies of mucus in mouse stomach, ..." refers background in this paper
...Although much is known about the immune cells in the Peyer’s patches, it is debated whether the domes of Peyer’s patches are covered by mucus (21, 24)....
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TL;DR: The colon mucus is organized in two layers: an inner, stratified mucus layer that is firmly adherent to the epithelial cells and approximately 50 μm thick; and an outer, nonattached layer, usually approximately 100 μm thickness as measured in mouse.
Abstract: The normal intestinal microbiota inhabits the colon mucus without triggering an inflammatory response. The reason for this and how the intestinal mucus of the colon is organized have begun to be unraveled. The mucus is organized in two layers: an inner, stratified mucus layer that is firmly adherent to the epithelial cells and approximately 50 μm thick; and an outer, nonattached layer that is usually approximately 100 μm thick as measured in mouse. These mucus layers are organized around the highly glycosylated MUC2 mucin, forming a large, net-like polymer that is secreted by the goblet cells. The inner mucus layer is dense and does not allow bacteria to penetrate, thus keeping the epithelial cell surface free from bacteria. The inner mucus layer is converted into the outer layer, which is the habitat of the commensal flora. The outer mucus layer has an expanded volume due to proteolytic activities provided by the host but probably also caused by commensal bacterial proteases and glycosidases. The numerous O-glycans on the MUC2 mucin not only serve as nutrients for the bacteria but also as attachment sites and, as such, probably contribute to the selection of the species-specific colon flora. This observation that normal human individuals carry a uniform MUC2 mucin glycan array in colon may indicate such a specific selection.
1,140 citations