| 1. |
- Hansson, Gunnar C., 1951, et al.
(författare)
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Biosynthesis and Secretion of Mucins, Especially the MUC2 Mucin, in Relation to Cystic Fibrosis
- 2005
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Ingår i: Advances in Experimental Medicine and Biology. - Göteborg : Springer US. - 9780387230764 ; , s. 169-178
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The typical CF symptoms with viscous and trapped mucus are still lacking a full explanation. Here we suggest that the CF mucus become sticky and adherent to the epithelial cells by a covalent attachment of MUC2 and MUC5AC. We also suggest that the expression of MUC2 in the lungs could contribute to the CF phenotype. However, there are several unanswered questions before these suggestions can be proved. Among the most urgent ones are to show to what molecules the generated anhydride can attach or if the anhydride only has been hydrolyzed. Once this and other questions have been answered, one can start to address potential therapeutic approaches using recent advances in mucin knowledge.
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| 2. |
- Johansson, Malin E V, 1971, et al.
(författare)
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Proteomic analyses of the two mucus layers of the colon barrier reveal that their main component, the Muc2 mucin, is strongly bound to the Fcgbp protein.
- 2009
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Ingår i: Journal of proteome research. - : American Chemical Society (ACS). - 1535-3893 .- 1535-3907. ; 8:7, s. 3549-57
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Tidskriftsartikel (refereegranskat)abstract
- The colon epithelium is protected from the luminal microbes as recently revealed by an inner firmly attached mucus layer impervious to bacteria and an outer loose mucus layer that is the habitat of bacteria. For an additional understanding of these layers, we analyzed the protein composition of these two mucus layers from the mouse colon. Proteomics using nano-LC-MS and MS/MS revealed more than 1000 protein entries. As the mucus layers contain detached cells, a majority of the proteins had an intracellular origin. However, at least 44 entries were described as secreted proteins and predicted to be mucus constituents together with extracellular/plasma and bacterial proteins, the latter largely in the loose mucus layer. A major protein was the Muc2 mucin that by its net-like disulfide-bonded polymer structure builds the mucus. When guanidinium chloride insoluble Muc2 units were analyzed, N-terminal parts of the Fc-gamma binding protein (Fcgbp) was found to be covalently attached in mouse and human colon, whereas its C-terminus was lost by reducing the disulfide bonds. In conclusion, the Fcgbp protein is probably cleaved at GD/PH and covalently attached to Muc2 via one or several of its von Willebrand D domains.
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| 3. |
- Johansson, Malin E V, 1971, et al.
(författare)
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The inner of the two Muc2 mucin-dependent mucus layers in colon is devoid of bacteria.
- 2008
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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. ; 105:39, s. 15064-9
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Johansson, Malin E V, 1971
(författare)
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The MUC2 mucin -A network in the intestinal protective mucus
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The intestine is covered by mucus that is the first line of defence of the epithelium. The main structural component of the intestinal mucus is the MUC2 mucin. This is a large glycoprotein with two long and heavily O-glycosylated mucin domains. Our studies of the biosynthesis have revealed that MUC2 forms large disulphide linked networks starting with C-C terminal dimers. In the late secretory pathway the N-terminal of MUC2 forms trimers within a core fragment resistant to trypsin cleavage. The MUC2 assembly creates an enormous network with an ability to resist protease degradation. It is important that the mucus is resistant to the intestinal digestive enzymes. In colon, the real challenge is to wield the large number of bacteria in the normal flora. Immune tolerance has been studied intensely, but the contribution of the mucus in the protective function has been neglected largely due to the technical difficulties to work with the large mucin glycoproteins. The mucus in colon is made up of two mucus layers. In mouse the inner mucus layer is 50 µm thick and firmly attached to the epithelium. This is a compact, insoluble and stratified mucus layer with a high Muc2 concentration. The firm layer is converted to a 100 µm, soluble, loose overlaying mucus layer that is expanded in volume by proteolysis. The mucus turnover is fast and in colon the luminal mucus layers are renewed in hours. The composition of the mucus was investigated by proteomics and was found to be similar in the two mucus layers, indicating a common source. One of the components identified, Fc gamma binding protein (Fcgbp) was shown by purification of the mucus in guanidinium chloride to be covalently attached to Muc2. The binding may be mediated by potential autocatalytic cleavage sites that generate new reactive C-termini in Fcgbp. The disulphide stabilized Fcgbp could thus be a cross-linker of the Muc2 network. Bacteria in colon were detected in the outer loose mucus layer by in-situ hybridization using a 16S rRNA general bacterial probe. This mucus is likely to be a good habitat for bacteria providing binding sites and energy. The inner compact firm mucus is impervious to bacteria, making it a protective barrier for the enormous bacterial load. The mucus is through this mechanism a part of the innate immunity to keep the homeostasis in colon. The protective function of mucus argues for that defects in the mucus can be a cause of inflammation. In fact, mice with the Muc2 gene disrupted do not produce mucus and develop spontaneous colitis. In these animals the epithelium is in direct contact with the colonic flora, bacteria enter deep into the normally sterile crypts and penetrate the epithelial cells. An overt immune reaction to the bacteria is an obvious cause of the inflammation. In wild type mice Dextran sulphate (DSS), a highly sulphated glucose polymer, is used to induce colitis and is the most common UC model. DSS exposure resulted in alterations in the mucus long before any signs of inflammation were observed. The inner mucus allowed bacteria to penetrate as early as after 4 h of exposure, with a massive bacterial penetration into the inner mucus after 12 h. The mechanisms behind this colitis model were not known until now when our observations suggest that a defect mucus layer is likely to have triggered the inflammation. The importance of the inner mucus for epithelial protection argues for defective mucus as a possible cause of ulcerative colitis.
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| 5. |
- Malmberg, Emily, 1978, et al.
(författare)
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Increased levels of mucins in the cystic fibrosis mouse small intestine, and modulator effects of the Muc1 mucin expression.
- 2006
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Ingår i: American journal of physiology. Gastrointestinal and liver physiology. - : American Physiological Society. - 0193-1857 .- 1522-1547. ; 291:2
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Tidskriftsartikel (refereegranskat)abstract
- The mouse model (Cftr(tm1UNC)/Cftr(tm1UNC)) for cystic fibrosis (CF) shows mucus accumulation and increased Muc1 mucin mRNA levels due to altered splicing (Hinojosa-Kurtzberg AM, Johansson MEV, Madsen CS, Hansson GC, and Gendler SJ. Am J Physiol Gastrointest Liver Physiol 284: G853-G862, 2003). However, it is not known whether Muc1 is a major mucin contributing to the increased mucus and why CF/Muc1-/- mice show lower mucus accumulation. To address this, we have purified mucins from the small intestine of CF mice using guanidinium chloride extraction, ultracentrifugation, and gel filtration and analyzed them by slot blot, gel electrophoresis, proteomics, and immunoblotting. Normal and CF mice with wild-type (WT) Muc1 or Muc1-/- or that are transgenic for human MUC1 (MUC1.Tg, on a Muc1-/- background) were analyzed. The total amount of mucins, both soluble and insoluble in guanidinium chloride, increased up to 10-fold in the CF mice compared with non-CF animals, whereas the CF mice lacking Muc1 showed intermediate levels between the CF and non-CF mice. However, the levels of Muc3 (orthologue of human MUC17) were increased in the CF/Muc1-/- mice compared with the CF/MUC1.Tg animals. The amount of MUC1 mucin was increased several magnitudes in the CF mice, but MUC1 did still not appear to be a major mucin. The amount of insoluble mucus of the large intestine was also increased in the CF mice, an effect that was partially restored in the CF/Muc1-/- mice. The thickness of the firmly adherent mucus layer of colon in the Muc1-/- mice was significantly lower than that of WT mice. The results suggest that MUC1 is not a major component in the accumulated mucus of CF mice and that MUC1 can influence the amount of other mucins in a still unknown way.
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| 6. |
- Phillipson, Mia, et al.
(författare)
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The gastric mucus layers: constituents and regulation of accumulation.
- 2008
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Ingår i: American journal of physiology. Gastrointestinal and liver physiology. - : American Physiological Society. - 0193-1857 .- 1522-1547. ; 295:4
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Tidskriftsartikel (refereegranskat)abstract
- The mucus layer continuously covering the gastric mucosa consists of a loosely adherent layer that can be easily removed by suction, leaving a firmly adherent mucus layer attached to the epithelium. These two layers exhibit different gastroprotective roles; therefore, individual regulation of thickness and mucin composition were studied. Mucus thickness was measured in vivo with micropipettes in anesthetized mice [isoflurane; C57BL/6, Muc1-/-, inducible nitric oxide synthase (iNOS)-/-, and neuronal NOS (nNOS)-/-] and rats (inactin) after surgical exposure of the gastric mucosa. The two mucus layers covering the gastric mucosa were differently regulated. Luminal administration of PGE(2) increased the thickness of both layers, whereas luminal NO stimulated only firmly adherent mucus accumulation. A new gastroprotective role for iNOS was indicated since iNOS-deficient mice had thinner firmly adherent mucus layers and a lower mucus accumulation rate, whereas nNOS did not appear to be involved in mucus secretion. Downregulation of gastric mucus accumulation was observed in Muc1-/- mice. Both the firmly and loosely adherent mucus layers consisted of Muc5ac mucins. In conclusion, this study showed that, even though both the two mucus layers covering the gastric mucosa consist of Muc5ac, they are differently regulated by luminal PGE(2) and NO. A new gastroprotective role for iNOS was indicated since iNOS-/- mice had a thinner firmly adherent mucus layer. In addition, a regulatory role of Muc1 was demonstrated since downregulation of gastric mucus accumulation was observed in Muc1-/- mice.
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