Mucin Dynamics in Intestinal Bacterial Infection Sara K. Linde´ n1,2*, Timothy H. J. Florin1,3, Michael A. McGuckin1,3 1 Mucosal Diseases Program, Mater Medical Research Institute, Mater Health Services, South Brisbane, Queensland, Australia, 2 Mucosal Immunobiology and Vaccine Center, Sahlgrenska Academy, Gothenburg University, Gothenburg, Sweden, 3 Department of Medicine, University of Queensland, Brisbane, Queensland, Australia Abstract Background: Bacterial gastroenteritis causes morbidity and mortality in humans worldwide. Murine Citrobacter rodentium infection is a model for gastroenteritis caused by the human pathogens enteropathogenic Escherichia coli and enterohaemorrhagic E. coli. Mucin glycoproteins are the main component of the first barrier that bacteria encounter in the intestinal tract. Methodology/Principal Findings: Using Immunohistochemistry, we investigated intestinal expression of mucins (Alcian blue/PAS, Muc1, Muc2, Muc4, Muc5AC, Muc13 and Muc3/17) in healthy and C. rodentium infected mice. The majority of the C. rodentium infected mice developed systemic infection and colitis in the mid and distal colon by day 12. C. rodentium bound to the major secreted mucin, Muc2, in vitro, and high numbers of bacteria were found in secreted MUC2 in infected animals in vivo, indicating that mucins may limit bacterial access to the epithelial surface. In the small intestine, caecum and proximal colon, the mucin expression was similar in infected and non-infected animals. In the distal colonic epithelium, all secreted and cell surface mucins decreased with the exception of the Muc1 cell surface mucin which increased after infection (p,0.05). Similarly, during human infection Salmonella St Paul, Campylobacter jejuni and Clostridium difficile induced MUC1 in the colon. Conclusion: Major changes in both the cell-surface and secreted mucins occur in response to intestinal infection. Citation: Linde´n SK, Florin THJ, McGuckin MA (2008) Mucin Dynamics in Intestinal Bacterial Infection. PLoS ONE 3(12): e3952. doi:10.1371/journal.pone.0003952 Editor: Nick Gay, University of Cambridge, United Kingdom Received July 17, 2008; Accepted November 10, 2008; Published December 17, 2008 Copyright: 2008 Linden et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The work was supported by a post doctoral Fellowship from the Swedish Society for Medical Research (to S. Linden), the Swedish Reasearch Council (Vetenskapsra˚det, to S. Linden) and the Australian NHMRC Project Grant No. 382309. Competing Interests: The authors have declared that no competing interests exist. * E-mail: mmcguckin@mmri.mater.org.au Introduction Bacteria such as enteropathogenic Escherichia coli (EPEC), enterohaemorrhagic E. coli (EHEC), Salmonella enteritidis and Clostridium difficile are major causes of infectious diarrhea in humans worldwide. EPEC and EHEC develop a commensal, rather than pathogenic, interaction within the mouse host [1,2]. C. rodentium is a natural mouse pathogen that is related to, and uses the same molecular mechanisms of type III secretion and attaching and effacing lesions as human EPEC and EHEC, to colonise the epithelial cells of the gut, hence providing a good in vivo model for gastroenteritis due to these bacteria [3,4]. The gastrointestinal tract is lined by a continuously secreted mucus layer formed by high molecular mass oligomeric mucin glycoproteins. This mucus layer moves to clear trapped material. In the healthy human intestine, MUC2 is the main secreted mucin making up the mucus layer, whereas in the stomach MUC5AC and MUC6 are produced. Under the mucus layer, the cell-surface mucins are a dominant feature of the apical surface of all mucosal epithelial cells. Cell-surface mucins are likely to play an important role in mucosal defense since they may provide both a barrier and reporting function, and we have demonstrated increased pathol- ogy following gastrointestinal infection in mice lacking the Muc1 cell surface mucin [5,6]. These filamentous molecules extend further than most other cell surface structures [7]. The intestine produces the MUC1, MUC3, MUC4 MUC12, MUC13 and MUC17 cell surface mucins [8,9]. Microbial products and inflammatory cytokines stimulate increased production of mucins by mucosal epithelial cells, which can effect a massive discharge of mucin in response to stimuli [10,11,12,13,14,15,16,17,18,19,20,21]. Stimulated mucin release occurs rapidly and is accompanied by a hundredfold expansion of the secretory granules upon hydration. Several pathogens have been shown to interact with mucins [22,23,24,25,26], including EPEC and EHEC which bind to bovine mucins [27]. Upregula- tion of MUC3 expression in colonic cells has been correlated with decreased binding of EPEC [28,29]. The ability of human milk to limit gastrointestinal bacterial and viral infections has been attributed in part to the presence of large amounts of cell surface mucins, chiefly MUC1 and MUC15 [30,31,32]. Consistent with an important role for Muc1 upregulation in the intestine limiting infection, Muc12/2 mice have a higher rate of systemic infection in a murine Campylobacter jejuni model of gastroenteritis [6]. Many pathogens have evolved mechanisms to subvert the mucin barrier, for example the StcE zinc metalloprotease secreted by EHEC is a mucinase [33]. Goblet cell depletion in infection has been reported previously [34], however, no comprehensive study of expression of all mucins in an animal infection model has been performed. We map the localization along the intestinal tract of all murine mucins for which antibodies are available: Muc1, Muc2, Muc4, Muc5AC, Muc13 and Muc3 (orthologue of human MUC17, therefore hereafter referred to as Muc17. There is currently no Muc3 orthologue annotated in the mouse genome. However, a peptide PLoS ONE | www.plosone.org 1 December 2008 | Volume 3 | Issue 12 | e3952