| 1. |
- Johansson, Malin E V, 1971, et al.
(författare)
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Composition and functional role of the mucus layers in the intestine.
- 2011
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Ingår i: Cellular and Molecular Life Sciences. - : Springer Science and Business Media LLC. - 1420-682X .- 1420-9071. ; 68, s. 3635-3641
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Forskningsöversikt (refereegranskat)abstract
- In discussions on intestinal protection, the protective capacity of mucus has not been very much considered. The progress in the last years in understanding the molecular nature of mucins, the main building blocks of mucus, has, however, changed this. The intestinal enterocytes have their apical surfaces covered by transmembrane mucins and the whole intestinal surface is further covered by mucus, built around the gel-forming mucin MUC2. The mucus of the small intestine has only one layer, whereas the large intestine has a two-layered mucus where the inner, attached layer has a protective function for the intestine, as it is impermeable to the luminal bacteria.
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| 2. |
- Ambort, Daniel, 1978, et al.
(författare)
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Calcium and pH-dependent packing and release of the gel-forming MUC2 mucin.
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 109:15, s. 5645-50
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Tidskriftsartikel (refereegranskat)abstract
- MUC2, the major colonic mucin, forms large polymers by N-terminal trimerization and C-terminal dimerization. Although the assembly process for MUC2 is established, it is not known how MUC2 is packed in the regulated secretory granulae of the goblet cell. When the N-terminal VWD1-D2-D'D3 domains (MUC2-N) were expressed in a goblet-like cell line, the protein was stored together with full-length MUC2. By mimicking the pH and calcium conditions of the secretory pathway we analyzed purified MUC2-N by gel filtration, density gradient centrifugation, and transmission electron microscopy. At pH 7.4 the MUC2-N trimer eluted as a single peak by gel filtration. At pH 6.2 with Ca(2+) it formed large aggregates that did not enter the gel filtration column but were made visible after density gradient centrifugation. Electron microscopy studies revealed that the aggregates were composed of rings also observed in secretory granulae of colon tissue sections. The MUC2-N aggregates were dissolved by removing Ca(2+) and raising pH. After release from goblet cells, the unfolded full-length MUC2 formed stratified layers. These findings suggest a model for mucin packing in the granulae and the mechanism for mucin release, unfolding, and expansion.
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| 3. |
- Bäckström, Malin, 1967, et al.
(författare)
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Increased understanding of the biochemistry and biosynthesis of MUC2 and other gel-forming mucins through the recombinant expression of their protein domains.
- 2013
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Ingår i: Molecular biotechnology. - : Springer Science and Business Media LLC. - 1559-0305 .- 1073-6085. ; 54:2, s. 250-6
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Tidskriftsartikel (refereegranskat)abstract
- The gel-forming mucins are large and heavily O-glycosylated proteins which build up mucus gels. The recombinant production of full-length gel-forming mucins has not been possible to date. In order to study mucin biosynthesis and biochemistry, we and others have taken the alternative approach of constructing different recombinant proteins consisting of one or several domains of these large proteins and expressing them separately in different cell lines. Using this approach, we have determined that MUC2, the intestinal gel-forming mucin, dimerizes via its C-terminal cysteine-knot domain and also trimerizes via one of the N-terminal von Willebrand D domains. Both of these interactions are disulfide bond mediated. Via this assembly, a molecular network is built by which the mucus gel is formed. Here we discuss not only the functional understanding obtained from studies of the recombinant proteins, but also highlight the difficulties encountered when these proteins were produced recombinantly. We often found an accumulation of the proteins in the ER and consequently no secretion. This was especially apparent when the cysteine-rich domains of the N- and C-terminal parts of the mucins were expressed. Other proteins that we constructed were either not secreted or not expressed at all. Despite these problems, the knowledge of mucin biosynthesis and assembly has advanced considerably through the studies of these recombinant proteins.
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| 4. |
- Carvalho, F. A., et al.
(författare)
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Transient Inability to Manage Proteobacteria Promotes Chronic Gut Inflammation in TLR5-Deficient Mice
- 2012
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Ingår i: Cell Host & Microbe. - : Elsevier BV. - 1931-3128. ; 12:2, s. 139-152
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Tidskriftsartikel (refereegranskat)abstract
- Colitis results from breakdown of homeostasis between intestinal microbiota and the mucosal immune system, with both environmental and genetic influencing factors. Flagellin receptor TLR5-deficient mice (T5KO) display elevated intestinal proinflammatory gene expression and colitis with incomplete penetrance, providing a genetically sensitized system to study the contribution of microbiota to driving colitis. Both colitic and noncolitic T5KO exhibited transiently unstable microbiotas, with lasting differences in colitic T5KO, while their noncolitic siblings stabilized their microbiotas to resemble wild-type mice. Transient high levels of proteobacteria, especially enterobacteria species including E. coli, observed in close proximity to the gut epithelium were a striking feature of colitic microbiota. A Crohn's disease-associated E. coli strain induced chronic colitis in T5KO, which persisted well after the exogenously introduced bacterial species had been eliminated. Thus, an innate immune deficiency can result in unstable gut microbiota associated with low-grade inflammation, and harboring proteobacteria can drive and/or instigate chronic colitis.
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| 5. |
- Holmén Larsson, Jessica, 1971, et al.
(författare)
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Altered O-glycosylation profile of MUC2 mucin occurs in active ulcerative colitis and is associated with increased inflammation.
- 2011
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Ingår i: Inflammatory bowel diseases. - : Oxford University Press (OUP). - 1536-4844 .- 1078-0998.
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The MUC2 mucin organizes the two mucus layers in the colon. This mucin carries a large number of O-glycans that are assumed to be attachment sites for the commensal flora found in the outer mucus layer. METHODS: Single biopsies from the sigmoid colon of controls (25) and patients with inactive (13) or active (15) ulcerative colitis (UC) were collected during routine colonoscopy. The insoluble MUC2 mucin was prepared and separated by gel electrophoresis, its relative amount estimated, its O-glycans released, and glycans analyzed by novel sensitive glycomics chromatography / mass spectrometry providing information on glycan structures and relative abundances. The glycosylation pattern was related to the degree of mucosal inflammation and clinical severity of the disease. RESULTS: The relative abundance of MUC2 showed high individual variability. Two major glycan profiles were found; a normal pattern in the control and inactive UC patients and an aberrant profile in patients with active colitis with an increase in a subset of the smaller glycans and a decrease of several complex glycans. The magnitude of this phenomenon was significantly related to both the degree of inflammation in the biopsies and also to some extent the severity of disease course. The aberrant profile was further shown to be reversible upon remission. CONCLUSIONS: In the majority of the active UC patients MUC2 mucin has an altered glycan profile as compared to inactive UC and control patients. Patients with strong alterations in the glycan pattern tended to have a more severe disease course. (Inflamm Bowel Dis 2011).
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| 6. |
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| 7. |
- Johansson, Malin E V, 1971, et al.
(författare)
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Bacteria penetrate the inner mucus layer before inflammation in the dextran sulfate colitis model.
- 2010
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Ingår i: PloS one. - : Public Library of Science (PLoS). - 1932-6203. ; 5:8
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Tidskriftsartikel (refereegranskat)abstract
- Protection of the large intestine with its enormous amount of commensal bacteria is a challenge that became easier to understand when we recently could describe that colon has an inner attached mucus layer devoid of bacteria (Johansson et al. (2008) Proc. Natl. Acad. Sci. USA 105, 15064-15069). The bacteria are thus kept at a distance from the epithelial cells and lack of this layer, as in Muc2-null mice, allow bacteria to contact the epithelium. This causes colitis and later on colon cancer, similar to the human disease Ulcerative Colitis, a disease that still lacks a pathogenetic explanation. Dextran Sulfate (DSS) in the drinking water is the most widely used animal model for experimental colitis. In this model, the inflammation is observed after 3-5 days, but early events explaining why DSS causes this has not been described.
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| 8. |
- Johansson, Malin E V, 1971, et al.
(författare)
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Bacteria penetrate the normally impenetrable inner colon mucus layer in both murine colitis models and patients with ulcerative colitis.
- 2014
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Ingår i: Gut. - : BMJ. - 1468-3288 .- 0017-5749. ; 63:2, s. 281-291
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: The inner mucus layer in mouse colon normally separates bacteria from the epithelium. Do humans have a similar inner mucus layer and are defects in this mucus layer a common denominator for spontaneous colitis in mice models and ulcerative colitis (UC)? METHODS AND RESULTS: The colon mucus layer from mice deficient in Muc2 mucin, Core 1 O-glycans, Tlr5, interleukin 10 (IL-10) and Slc9a3 (Nhe3) together with that from dextran sodium sulfate-treated mice was immunostained for Muc2, and bacterial localisation in the mucus was analysed. All murine colitis models revealed bacteria in contact with the epithelium. Additional analysis of the less inflamed IL-10(-/-) mice revealed a thicker mucus layer than wild-type, but the properties were different, as the inner mucus layer could be penetrated both by bacteria in vivo and by fluorescent beads the size of bacteria ex vivo. Clear separation between bacteria or fluorescent beads and the epithelium mediated by the inner mucus layer was also evident in normal human sigmoid colon biopsy samples. In contrast, mucus on colon biopsy specimens from patients with UC with acute inflammation was highly penetrable. Most patients with UC in remission had an impenetrable mucus layer similar to that of controls. CONCLUSIONS: Normal human sigmoid colon has an inner mucus layer that is impenetrable to bacteria. The colon mucus in animal models that spontaneously develop colitis and in patients with active UC allows bacteria to penetrate and reach the epithelium. Thus colon mucus properties can be modulated, and this suggests a novel model of UC pathophysiology.
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| 9. |
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| 10. |
- Johansson, Malin E V, 1971, et al.
(författare)
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The two mucus layers of colon are organized by the MUC2 mucin, whereas the outer layer is a legislator of host-microbial interactions.
- 2011
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 1091-6490. ; 108 Suppl 1, s. 4659-65
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Tidskriftsartikel (refereegranskat)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.
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