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Original articles
Recent advances in basic science
Bacterial proteases in IBD and IBS
  1. Natalie Steck1,
  2. Kerstin Mueller2,
  3. Michael Schemann2,
  4. Dirk Haller1
  1. 1Chair for Biofunctionality, Technische Universität München, ZIEL–Research Center for Nutrition and Food Science, CDD-Center for Diet and Disease, Freising-Weihenstephan, Germany
  2. 2Department of Human Biology, Technische Universität München, Freising-Weihenstephan, Germany
  1. Correspondence to Dirk Haller, Biofunctionality, Technische Universität München, Gregor-Mendel-Str. 2, 85350 Freising-Weihenstephan, Germany; haller{at}wzw.tum.de

Abstract

Proteases play a decisive role in health and disease. They fulfil diverse functions and have been associated with the pathology of gastrointestinal disorders such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). The current knowledge focuses on host-derived proteases including matrix metalloproteinases, various serine proteases and cathepsins. The possible contribution of bacterial proteases has been largely ignored in the pathogenesis of IBD and IBS, although there is increasing evidence, especially demonstrated for proteases from pathogenic bacteria. The underlying mechanisms extend to proteases from commensal bacteria which may be relevant for disease susceptibility. The intestinal microbiota and its proteolytic capacity exhibit the potential to contribute to the pathogenesis of IBD and IBS. This review highlights the relevance of host- and bacteria-derived proteases and their signalling mechanisms.

  • Proteases in IBD and IBS
  • bacterial proteases
  • proteolytic activity in intestinal disorders
  • enteric nervous system
  • neuropharmacology
  • neurophysiology
  • nervous control of intestinal functions
  • neurogastroenterology
  • bacterial interactions
  • probiotics
  • TGF-beta
  • IBD
  • signal transduction

https://doi.org/10.1136/gutjnl-2011-300775

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    Key messages

    • Host-derived proteases are involved in the pathogenesis of IBD and IBS

    • Protease-activated receptors are specific targets for host-derived and bacteria-derived proteases

    • Proteases belong to virulence factors of intestinal pathogens and commensals

    • Mechanistically, bacterial proteases target and impair barrier function of epithelial cells and activates enteric neurons

    • Certain susceptibility is necessary for the involvement of commensal-derived proteases in IBD

    Introduction

    Inflammatory bowel disease (IBD)—including the two main distinct pathologies ulcerative colitis (UC) and Crohn's disease (CD)—and irritable bowel syndrome (IBS) are chronically relapsing diseases with an accelerating incidence, especially in developed countries.1 It is noteworthy that IBS-like symptoms such as diarrhoea or visceral pain are frequently observed in some patients with IBD in remission. Although IBD and IBS are two distinct entities, their complex pathogenesis involves common features including alterations in immune responses, altered microbiota composition with an impact on microbiota–host interactions, impaired intestinal barrier functions, altered bowel habits and changes in visceral sensitivity.2 ,3 There is increasing evidence that all of the above factors are influenced by proteases, although the particular protease involved and the pathways influenced by proteases may be different in IBD and IBS. This review focuses on the involvement of host- or bacterial-derived proteases in IBD or IBS and highlights those protease-activated pathways that may be relevant in the pathogenesis of IBD and IBS.

    Host-derived proteases in IBD and IBS

    The large group of zinc-dependent matrix metalloproteinases (MMPs) plays a central role in extracellular matrix turnover. Furthermore, MMPs proteolytically activate a variety of non-matrix substrates such as cytokines, chemokines, growth factors and junction proteins. The deregulated expression or activity of host-derived MMPs has been implicated in several diseases including arthritis, atherosclerosis and colon cancer.4 ,5 Increasing evidence suggests that MMPs are the predominant proteases involved in the pathogenesis of IBD.6 ,7 MMPs influence the disease progression in multiple ways involving the function and migration of inflammatory cells as well as matrix deposition and degradation. The expression and activity of certain MMPs is increased during acute inflammation,8 but also an imbalance between MMPs and their natural tissue inhibitors (TIMPs) has been reported for IBD.9 Besides MMPs, other proteases including trypsin, neutrophil elastase,10 mast cell tryptase,11 cathepsins12 and thrombin13 have been implicated in IBD. Supernatants of mucosal biopsy specimens from patients with IBS evoked activation of visceral nociceptive neurons14 as well as enteric neurons15 and induced hyperalgesia,16 a key feature of IBS. The responses could be attributed to serine proteases.

    Intestinal microbiota in IBD and IBS

    Changes in diversity and composition as well as functionality of the intestinal microbiota were associated with IBD17 ,18 and IBS.19 Pathogenic infections are suggested as the starting point for IBD20 and IBS,21 but further work is needed to understand the role of commensal bacteria and their possible contribution to the pathogenesis of intestinal disorders. In the context of intestinal inflammatory disease, it has to be considered that commensalism changes into a harmful situation for the host which then becomes a continuous inflammatory trigger.22

    Protease activity in the gut lumen

    Excessive concentrations of proteases have been found in the faeces of patients with UC or IBS.23–26 Consistent with these findings, secreted factors of colonic biopsy samples from patients with IBD and IBS showed increased proteolytic activity.16 Although the origin of the proteolytic activity was not elucidated, it is conceivable that proteases released from biopsy specimens are derived from the host. However, increased faecal proteolytic activity might result from colonic luminal bacteria which release serine, cysteine and metalloproteases.27 Oral antibiotic treatment of mice resulted in reduced numbers of colonic microbiota and reduced colonic luminal serine protease activity, which provides further evidence for the bacterial origin of the proteases.23 Bacterial proteolytic activity could be demonstrated even in the absence of inflammation, supporting the hypothesis that bacterial proteases are ubiquitously present in the gut lumen but only have an impact in a susceptible situation.28

    Implications for bacterial proteases in the pathology of IBD

    Role of pathogen-derived proteases

    It has been suggested that alterations in microbial diversity and composition in disease-susceptible populations may alter innate defence mechanisms leading to chronic immune-mediated activation in active IBD.29 ,30 Pathogens can be considered as the initiation step at the beginning of the disease development or during disease progression.18 ,20 ,31 Many attempts have been made to identify the bacterial structures or molecules responsible for the pathogenicity of microbes. Besides the mechanism of type-specific secretion systems which allow the infiltration of bacterial material or whole bacteria into host cells, proteases have been shown to be involved in the infectious process of pathogens. However, the pattern of different types of proteases and their expression, regulation, activation and substrate specificity is very diverse. Host tissue provides different target points for bacterial proteases. In addition to the activation of specific types of host receptors, which will be discussed later, the degradation of extracellular matrix and the disruption of epithelial barrier function exhibits the most frequently described consequence of bacterial proteases. Targeting host epithelial barrier function is a central mechanism to be considered in the complex pathogenesis of IBD. Impaired intestinal barrier function has been associated with IBD,32–34 although it is still uncertain whether the loss of barrier integrity is the cause or a consequence of chronic inflammation. Table 1 the proteases from pathogens targeting epithelial or endothelial barrier function in different organs and summarises the general mechanisms attributed to bacterial proteases which might be relevant in IBD.

    View this table:
    Table 1

    Bacterial proteases target epithelial cell barrier function

    Role of commensal-derived proteases

    The adherence junction protein E-cadherin is the best described target for bacterial proteases derived from pathogens. This might be surprising as E-cadherin provides cell–cell contact on the lateral site of epithelial cells and it remains unclear how bacterial proteases in the gut lumen get access to their cleavage sites. We have demonstrated for the first time that a commensal-derived protease plays a role in intestinal inflammation. Gelatinase (GelE), a zinc-dependent metalloproteinase from Enterococcus faecalis, disrupted the integrity of the intestinal epithelial barrier by targeting the junction proteins occludin and E-cadherin.44 The presence of disease susceptibility, but not tissue inflammation, is required for E faecalis GelE-mediated disruption of colonic barrier function (figure 1), supporting the hypothesis that commensal-derived proteases remain harmless in the healthy host. Similar to pathogens, commensal bacteria also possess a variety of virulence genes which are expressed under certain environmental conditions. E faecalis GelE can be regarded as an example in which a commensal-derived protease that has been associated with bacterial virulence plays a role in the development of intestinal inflammation. Further analysis of the structure/function interplay between bacteria and the host, including the putative role of various bacterial virulence factors in commensal bacteria, will provide important insights into the pathogenesis of IBD.

    Figure 1
    Figure 1

    Enterococcus faecalis GelE impairs barrier function in the susceptible host. To assess the impact of GelE on colonic barrier function, different susceptibility models were used for intestinal inflammation. Interleukin-10-deficient (IL-10−/−) and TNF∆ARE/Wt mice are genetically-driven spontaneous mouse models for the development of chronic inflammation in the colon and ileum, respectively. Rag2-deficient (Rag2−/−) mice lack B and T cells and develop colitis after transfer of CD4+ T cells. NOD2-deficient (NOD2−/−) mice lack the intracellular pattern recognition receptor NOD2 (nucleotide-binding oligomerisation domain 2) and are susceptible to certain bacterial infections. Appropriate wild type (Wt) counterparts 129SvEv and C57B6 were used as controls. Except for T cell transferred Rag2−/− mice, all other models did not develop histological changes with respect to inflammation in the colon after 8 weeks. Distal colon segments of the mice were apically stimulated with purified GelE (10 μg/ml) for 5 h in Ussing chamber systems. The results are expressed as the percentage change in transepithelial electrical resistance (TER) compared with the initial value of the tissue. Data are partially published44 and represent median with 25th and 75th percentiles from five animals per group; *p≤0.05.

    Bacterial mucolytic activity: an underestimated potential

    The question of how and when commensal-derived proteases are involved in IBD is clinically of great importance. Patients with IBD have an increased number of mucosa-associated bacteria and the thickness of the intestinal mucus layer is diminished.45 ,46 Mucolytic activities allow bacteria to use mucus as a carbohydrate source and enable them to survive in the niche of the intestinal outer mucus layer. Over 20 years ago, Rhodes and colleagues hypothesised that bacterial mucus degradation could be associated with IBD, but they could not correlate bacterial glycosidase activity with disease activity in patients with IBD.47 However, a recent study demonstrated a shift in the mucolytic consortium of bacteria in IBD patients. The most abundant mucolytic species in healthy controls, Akkermansia muciniphila, is reduced in IBD whereas Ruminococcus species are disproportionally increased under conditions of chronic inflammation. Ruminococcus α- and β-glycosidases remove terminal sugars from the mucus matrix that subsequently become accessible for other bacteria, providing a possible explanation for the increase in total mucosa-associated bacteria in IBD.48 Pathogens have evolved several strategies to disrupt and avoid mucosal barriers. The enzymatic degradation of mucins and the downregulation of mucin production are two of the most common mechanisms.49 The substrate specificity of bacterial proteases is often not restricted to one molecule. Proteases that have been demonstrated to digest mucins have also been shown to facilitate adherence to host cells38 or to disrupt epithelial barrier function.28 Alterations in microbial composition and mucus structure under disease-susceptible conditions might allow commensal-derived proteases to gain access to the epithelium, targeting protein substrates that would not be accessible to them under physiological conditions.

    Proteolytic activation of neurons

    The functional relevance of the elevated protease levels in patients with IBD and IBS has been demonstrated. In a rodent model, faecal supernatants of diarrhoea-predominant IBS patients with elevated serine protease contents induced visceral hypersensitivity and increased paracellular permeability via the protease-activated receptor (PAR) 2.26 However, faecal supernatants of patients with UC generated hyposensitivity to rectal distension, which was a result of PAR4 activation by cathepsin G. This anti-nociceptive action overpowered the pro-nociceptive effects of PAR2 activating proteases in the faecal supernatants.24 This study suggested that even though patients with IBD and IBS have increased faecal protease levels, the functionally active proteases must be different and, in addition, signal through distinct mechanisms. Supernatants of colonic biopsy samples of patients with IBS released proteolytic mediators that directly sensitised murine sensory neurons and generated visceral and somatic hypersensitivity through the activation of PAR2.16 Further studies showed that mucosal biopsy supernatants from patients with IBS also activated human enteric neurons15 as well as rat visceral nociceptive neurons.14 In both studies proteases have been identified as the main mediator responsible for neural excitation. Serine proteases such as thrombin, trypsin or mast cell tryptase, which are released by epithelial cells, immune cells, blood cells or even neurons, activate enteric and visceral sensory neurons as well as enteric glia by targeting PARs.50 ,51 There are four PARs (PAR1, PAR2, PAR3, PAR4), all of which are G-protein coupled tethered ligand receptors. They are activated by the proteolytic cleavage of the N-terminus which allows the tethered ligand to bind to the receptor. PAR1, PAR2 and PAR4 activate enteric neurons (see below for further details). However, PAR4 inhibits excitability of dorsal root ganglion neurons which supply the sensory innervation of the gut.52 This effect may explain the finding that PAR4 exerts analgesic effects by suppressing somatic and visceral hyperalgesia and pain.53 ,54 The functional expression of PARs in different cells may have a clinical impact in that it may open new ways to specifically target protease actions. In this context, it is important to realise that the contribution of PARs is different between rodent and human enteric neurons. While submucous neurons in the guinea pig have strong responses to PAR2 activation, PAR1 seems to be the dominant receptor in human submucous neurons.55 It needs to be considered that PARs are present on muscle cells, epithelial cells and immune cells as well as on neurons. For example, human tissue resident macrophages are activated by PAR2 ligands.55 Therefore, the disease relevant PAR signalling is a combination of several neuronal and non-neuronal pathways. It is not known whether the neural- and glia-mediated actions of proteases are part of the cascades initiating or maintaining inflammatory processes or whether they serve protective functions. In principle, bacterial proteases may also be able to activate nerves in the gastrointestinal tract but this has not yet been demonstrated. For the purpose of this review, we therefore addressed this open issue and found that the metalloproteinase GelE from commensal E faecalis activated about 20% of guinea-pig enteric neurons (figure 2). Interestingly, pretreatment of the tissue with GelE negatively influenced the ability of a selective PAR2-activating peptide to excite neurons. This suggests that GelE may signal through PAR2-expressing or dependent pathways, but further evidence for such a route is needed.

    Figure 2
    Figure 2

    Effect of the bacterial protease GelE from Enterococcus faecalis on guinea-pig submucous neurons. (A) A submucous ganglion. Individual neurons were labelled with the voltage sensitive dye Di-8-ANEPPS which allowed direct detection of action potentials. (B) Application of GelE (100 nM) for 30 s induced action potential discharge (sharp upward deflections) whereas the control buffer solution alone had no effect (C).The traces are from the neuron marked by a black cross in (A). GelE and buffer were applied shortly before the recording period as indicated by the horizontal bars. GelE significantly increased action potential discharge (D). The ability of the PAR2-AP SLIGRL-NH2 (100 μM) to evoke action potential discharge was significantly impaired by predisposing the neurons to GelE (100 nM). Symbols mark significant differences as explained in the figure. The numbers indicate numbers of tissues/ganglia/neurons studied.

    Host receptors for bacterial proteases

    Protease-activated receptors

    The potential of different bacterial proteases to target PAR as well as other host receptors has been shown for respiratory and oral epithelial cells as well as for platelets and neutrophils (table 2). However, the mode of action of bacterial proteases in the gastrointestinal tract, except for E faecalis GelE,44 is still largely unknown. In general, proteases target the G-protein coupled PAR receptors and induce activation by proteolytic cleavage of the N-terminal ligand or inactivation by disarming the receptor due to alternative cleavage of the N-terminus. The bacterial arginine-specific cysteine protease gingipain-R of the periodontitis pathogen Porphyromonas gingivalis has been shown to cleave and activate PAR2 on human neutrophils, PAR1 and PAR4 on platelets to induce platelet aggregation and PAR1 and PAR2 on an oral epithelial cell line to induce secretion of the pro-inflammatory cytokine interleukin 6 (IL-6).56–58 In addition to PARs, several other cell surface proteins such as occludin and E-cadherin were targets of gingipain in Madin-Darby canine kidney cells65 and CD14 human monocytes.66 The lung opportunistic pathogen Pseudomonas aeruginosa secreted the elastolytic metalloproteinase P aeruginosa elastase/LasB which disarmed PAR2 by proteolysis, made the receptor unresponsive to activating proteases and avoided receptor internalisation and mobilisation of intracellular pools. However, P aeruginosa elastase has also been shown to increase respiratory epithelial permeability by cleavage of tight junction proteins zonula occludens 1 and 2. Furthermore P aeruginosa released the exoprotease LepA which induced the activation of the transcription factor NF-κB via PAR1, PAR2 and PAR4 activation.60 ,61 ,67 Serratia marcescens, which is an opportunistic pathogen of the respiratory and urinary tract, produced the zinc metalloproteinase, serralysin, which has been shown to induce IL-6 and IL-8 mRNA expression in a respiratory cell line and transactivation of AP-1, C/EBP- and NF-κB-driven promotors via PAR2.62 A house dust mite cysteine protease allergen (Der p1) has been shown to target PAR2 but to inactivate PAR1 in respiratory epithelial cells and to induce release of pro-inflammatory cytokines.63 The mite allergens Der p3 and Der p9, which are serine proteases, activated lung epithelial cells by interaction with PAR2 and induced the release of pro-inflammatory cytokines.64

    View this table:
    Table 2

    Protease-activated receptors (PARs) as targets for bacterial and mite proteases

    Pattern recognition receptors

    Toll-like receptors (TLR) are part of the innate immune system and belong to the pattern recognition receptor family that identifies microbial pathogens through the recognition of pathogen- or microbial-associated molecular patterns (carbohydrates, nucleic acids, peptidoglycans, lipoteichoic acids, lipoproteins). Direct proteolytic activation of a full-length TLR has recently been described for the avian TLR15. Virulence-associated microbial-derived proteases from the fungi Candida guilliermondii, Trichosporon spp., Penecillium spp. and Mucor spp. and the Gram-negative opportunistic pathogen P aeruginosa have been shown to activate TLR15, which is a unique type of receptor that combines TLR characteristics with an activation mechanism typical of the evolutionary distinct PARs.68 Although it is still unknown which proteases activate TLR15, one could speculate that these are serine proteases as the receptor activation could be inhibited by the serine protease inhibitor phenylmethanesulfonylfluoride (PMSF). Mammalians seem to lack a TLR that is able to sense proteolytic activity, although mammalian TLR4 can be activated by elastase-activated compounds from the extracellular matrix.69 Furthermore, lipopolysaccharide (LPS) recognition by TLR4 was indirectly influenced by trypsin which is augmented in ileal inflammation and cleaved MD-2, an accessory glycoprotein essential for TLR4 signalling. The proteolysis of MD-2 provided a mechanism for intestinal epithelial LPS tolerance that helped to regulate immune responses to commensal bacteria-derived ligands.70 Recent work connected TLR and PAR signalling and described distinct features of the TLR–PAR interaction which contribute to signal diversity in inflammation and host antimicrobial responses.71 The cross-talk between different receptor signalling cascades and the recognition of diverse microbial signals provide homeostasis, but further investigations are needed to understand this complex network more fully.

    E-cadherin

    The adherence junction protein E-cadherin is a calcium-dependent single-pass transmembrane protein generally expressed in the lateral plasma membrane of epithelial cells. E-cadherin provides contact to adjacent cells and plays a major role in epithelial cell differentiation. The intracellular domain is highly conserved and signals through cytoplasmic proteins from the catenin family.72 The extracellular domain could act as a receptor for bacterial or fungal entry into epithelial cells, which so far has only been demonstrated for surface proteins. Internalin A from Listeria monocytogenes 73 and invasion Als3 from Candida albicans 74 ,75 interact with E-cadherin and mediate the internalisation of the respective microorganisms. E-cadherin is also targeted by bacterial proteases; the metalloproteinase toxin BFT from Bacteroidis fragilis was shown to induce the shedding of the E-cadherin ectodomain through an unknown intestinal epithelial cell receptor-mediated induction of γ-secretase.39 A direct E-cadherin cleavage could be demonstrated for the trypsin-like serine protease HpHtrA from Helicobacter pylori.40 We demonstrated that a commensal-derived metalloproteinase, GelE from E faecalis, was able to degrade the extracellular domain of E-cadherin in the susceptible host, suggesting that proteases from the commensal gut microbiota might play a role in the disease pathogenesis of chronic intestinal inflammation, but only if they get access to the target tissue under predisposed conditions.44 The proteolytic cleavage of E-cadherin, either direct or indirect, reflects an important mechanism for bacteria—especially pathogens—to reach the intercellular space and to translocate across the epithelium. Furthermore, E-cadherin is targeted by a number of endogenous metalloproteinases including stromelysin-1, matrilysin,76 ADAM-1077 and meprin-β.78

    Protease-dependent receptor activation

    The release of tumour necrosis factor α (TNFα) is associated with an increased permeability of the gut epithelial barrier. The blockade of TNF with anti-TNF antibodies is an established strategy in the treatment of IBD. The increase of soluble biologically active TNF arises from the conversion of membrane-bound TNF by TNF-converting enzyme (TACE).79 ,80 TACE or ADAM17 belong to the ADAM (a disintegrin and a metalloprotease) family of metal-dependent proteases and has been additionally implicated in the shedding of other membrane-bound precursors of cytokines and growth factors.81 One of these factors is transforming growth factor-α which in turn activates the epidermal growth factor receptor (EGFR). Phosphorylated EGFR induces the activation of mitogen activated protein kinases and mediates changes in intestinal permeability.82 Many of these processes and receptor activation mechanisms are described in the context of carcinogenesis,83 a frequent IBD-associated complication. In particular, the fact that numerous cytokines and growth factors are membrane-associated as precursors and require proteolytic conversion may represent a novel mechanism for bacterial-derived proteases.

    Clinical implications

    The inhibition of host-derived proteases has been discussed as a therapeutic option in IBD but there are only limited reports with inconsistent results. Studies in animal models showed that inhibition of cathepsins12 and tryptase84 ameliorates chemical-induced colitis. Furthermore, the serine protease inhibitor camostat has been reported to induce and maintain remission in patients with UC.85 Various MMP inhibitors have been shown to improve inflammation, particularly in rat models of IBD86–88 but also in dextran sodium sulfate (DSS)-induced colitis in mice. Despite the fact that MMP inhibitors showed beneficial therapeutic effects in experimental colitis models, a clinical trial investigating the beneficial potential of the MMP inhibitor prinomastat in lung cancer failed because of unacceptable adverse effects.89 In an animal model, serine protease inhibitors have been shown to be effective in inhibiting the pronociceptive effects induced by the supernatants of mucosal biopsies and faeces samples from patients with IBS.16 ,26 These results suggest the use of serine protease inhibitors in the treatment of IBS symptoms. To date, studies that use inhibitors of host-derived proteases have shown rather poor efficacy in the treatment of human IBD. Adverse side effects, presumably resulting from non-specific actions and/or broad spectrum inhibition of host proteases also affecting functions of other organs, need to be addressed before protease inhibitors become a therapeutic option. In addition, the use of endogenous protease inhibitors could be considered as a treatment option in IBD to avoid adverse side effects and to reconstitute the proteolytic balance in the gut. One example is elafin, a serine protease inhibitor, the expression of which is reduced in the gut mucosa of IBD patients.90 Furthermore, it has been demonstrated that elafin protects against DSS-induced colitis through the inhibition of pro-inflammatory mediators and the strengthening of epithelial barrier function.91

    The inhibition of PARs by PAR antagonists could be an effective strategy to suppress protease-mediated action, particularly if they specifically target a particular PAR. The use of PAR antagonists as a treatment option for IBD and IBS is supported by their involvement in the generation of pain, inflammation, increased permeability, as well as motor and secretory disorders in the intestine. In this respect it may even be beneficial to develop PAR agonists which would provide the PAR4-mediated anti-nociceptive action in humans.

    A few clinical trials have shown that the administration of probiotics such as the probiotic mixture VSL#3 improved IBS symptoms including pain/discomfort, distension/bloating and defecation92 ,93 and induced and maintained remission in patients with UC.94 ,95 Furthermore, the feeding study conducted by Kunze et al provided evidence for the interaction between the probiotic Lactobacillus reuteri and colonic enteric neurons.96 Although probiotic efficacy could be demonstrated in IBD and IBS, the active functional components/structures, the molecular mechanisms or the primary probiotic target still remain to be clarified. It may be speculated that the protective role of probiotics may be related to the release of proteases and/or protease inhibitors. Such a mechanism has recently been reported for the serine protease lactocepin from Lactobacillus paracasei which inhibited the recruitment of pro-inflammatory cells to the site of inflammation through degradation of chemokines.97 The anti-inflammatory effect of lactocepin suggested that bacterial proteases play an important role in the regulation of intestinal homeostasis.

    Summary

    We are at the very beginning of understanding the complex intestinal microbial proteolytic capacity which shows significant potential to be involved in the pathogenesis of IBD, IBS and other gastrointestinal disorders. The mechanisms so far described are mostly restricted to proteases from pathogens, whereas proteases from commensal gut bacteria have generally been ignored. As shown in figure 3, the proteolytic activity in the gut is a result of host-derived proteases expressed by a variety of different cell types, as well as bacterial proteases produced by different species. The coordinated interactions of host and bacterial-derived proteases maintain homeostasis but become relevant to disease if deregulated. GelE from E faecalis is the first example of a bacteria–host interaction involving a commensal bacterial protease that is implicated in the pathogenesis of IBD and other gut diseases associated with inflammation.

    Figure 3
    Figure 3

    Protease activity in the gut. Illustration of possible involvements of proteases in disease-related mechanisms of inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS). The role of PAR-dependent pathways and the contribution of PARs are based on data from human tissue. PAR2 would play a significant role in rodent enteric neurons. The PAR-related pathways shown in the top part may be primarily relevant in IBS while the bottom pathways prevail in IBD; however, an overlap of some mechanisms is likely. Ca, calcium; ECM, extracellular matrix; GelE, gelatinase from Enterococcus faecalis; IEC, intestinal epithelial cells; PAR, protease-activated receptor.

    References

    1. ↵
      1. Renz H,
      2. von Mutius E,
      3. Brandtzaeg P,
      4. et al
      . Gene-environment interactions in chronic inflammatory disease. Nat Immunol 2011;12:273–7.
      OpenUrlPubMed
    2. ↵
      1. Spiller RC
      . Overlap between irritable bowel syndrome and inflammatory bowel disease. Dig Dis 2009;(27 Suppl 1):48–54.
    3. ↵
      1. Ford AC,
      2. Talley NJ
      . IBS in 2010: advances in pathophysiology, diagnosis and treatment. Nat Rev Gastroenterol Hepatol 2011;8:76–8.
      OpenUrlCrossRefPubMed
    4. ↵
      1. Birkedal-Hansen H,
      2. Moore WG,
      3. Bodden MK,
      4. et al
      . Matrix metalloproteinases: a review. Crit Rev Oral Biol Med 1993;4:197–250.
      OpenUrlAbstract/FREE Full Text
    5. ↵
      1. Nelson AR,
      2. Fingleton B,
      3. Rothenberg ML,
      4. et al
      . Matrix metalloproteinases: biologic activity and clinical implications. J Clin Oncol 2000;18:1135–49.
      OpenUrlAbstract/FREE Full Text
    6. ↵
      1. Baugh MD,
      2. Perry MJ,
      3. Hollander AP,
      4. et al
      . Matrix metalloproteinase levels are elevated in inflammatory bowel disease. Gastroenterology 1999;117:814–22.
      OpenUrlCrossRefPubMedWeb of Science
    7. ↵
      1. Pedersen G,
      2. Saermark T,
      3. Kirkegaard T,
      4. et al
      . Spontaneous and cytokine induced expression and activity of matrix metalloproteinases in human colonic epithelium. Clin Exp Immunol 2009;155:257–65.
    8. ↵
      1. Ravi A,
      2. Garg P,
      3. Sitaraman SV
      . Matrix metalloproteinases in inflammatory bowel disease: boon or a bane? Inflamm Bowel Dis 2007;13:97–107.
      OpenUrlCrossRefPubMedWeb of Science
    9. ↵
      1. von Lampe B,
      2. Barthel B,
      3. Coupland SE,
      4. et al
      . Differential expression of matrix metalloproteinases and their tissue inhibitors in colon mucosa of patients with inflammatory bowel disease. Gut 2000;47:63–73.
      OpenUrlAbstract/FREE Full Text
    10. ↵
      1. Tarlton JF,
      2. Whiting CV,
      3. Tunmore D,
      4. et al
      . The role of up-regulated serine proteases and matrix metalloproteinases in the pathogenesis of a murine model of colitis. Am J Pathol 2000;157:1927–35.
      OpenUrlCrossRefPubMedWeb of Science
    11. ↵
      1. Hamilton MJ,
      2. Sinnamon MJ,
      3. Lyng GD,
      4. et al
      . Essential role for mast cell tryptase in acute experimental colitis. Proc Natl Acad Sci U S A 2011;108:290–5.
      OpenUrlAbstract/FREE Full Text
    12. ↵
      1. Menzel K,
      2. Hausmann M,
      3. Obermeier F,
      4. et al
      . Cathepsins B, L and D in inflammatory bowel disease macrophages and potential therapeutic effects of cathepsin inhibition in vivo. Clin Exp Immunol 2006;146:169–80.
      OpenUrlCrossRefPubMed
    13. ↵
      1. Saibeni S,
      2. Saladino V,
      3. Chantarangkul V,
      4. et al
      . Increased thrombin generation in inflammatory bowel diseases. Thromb Res 2010;125:278–82.
      OpenUrlCrossRefPubMed
    14. ↵
      1. Barbara G,
      2. Wang B,
      3. Stanghellini V,
      4. et al
      . Mast cell-dependent excitation of visceral-nociceptive sensory neurons in irritable bowel syndrome. Gastroenterology 2007;132:26–37.
      OpenUrlCrossRefPubMedWeb of Science
    15. ↵
      1. Buhner S,
      2. Li Q,
      3. Vignali S,
      4. et al
      . Activation of human enteric neurons by supernatants of colonic biopsy specimens from patients with irritable bowel syndrome. Gastroenterology 2009;137:1425–34.
      OpenUrlCrossRefPubMedWeb of Science
    16. ↵
      1. Cenac N,
      2. Andrews CN,
      3. Holzhausen M,
      4. et al
      . Role for protease activity in visceral pain in irritable bowel syndrome. J Clin Invest 2007;117:636–47.
      OpenUrlCrossRefPubMedWeb of Science
    17. ↵
      1. Tannock GW
      . The search for disease-associated compositional shifts in bowel bacterial communities of humans. Trends Microbiol 2008;16:488–95.
      OpenUrlCrossRefPubMedWeb of Science
    18. ↵
      1. Sartor RB
      . Microbial influences in inflammatory bowel diseases. Gastroenterology 2008;134:577–94.
      OpenUrlCrossRefPubMedWeb of Science
    19. ↵
      1. Salonen A,
      2. de Vos WM,
      3. Palva A
      . Gastrointestinal microbiota in irritable bowel syndrome: present state and perspectives. Microbiology 2010;156:3205–15.
      OpenUrlAbstract/FREE Full Text
    20. ↵
      1. Nell S,
      2. Suerbaum S,
      3. Josenhans C
      . The impact of the microbiota on the pathogenesis of IBD: lessons from mouse infection models. Nat Rev Microbiol 2010;8:564–77.
      OpenUrlCrossRefPubMed
    21. ↵
      1. Bolino CM,
      2. Bercik P
      . Pathogenic factors involved in the development of irritable bowel syndrome: focus on a microbial role. Infect Dis Clin North Am 2010;24:961–75, ix.
      OpenUrlCrossRefPubMed
    22. ↵
      1. Spor A,
      2. Koren O,
      3. Ley R
      . Unravelling the effects of the environment and host genotype on the gut microbiome. Nat Rev Microbiol 2011;9:279–90.
      OpenUrlCrossRefPubMed
    23. ↵
      1. Roka R,
      2. Rosztoczy A,
      3. Leveque M,
      4. et al
      . A pilot study of fecal serine-protease activity: a pathophysiologic factor in diarrhea-predominant irritable bowel syndrome. Clin Gastroenterol Hepatol 2007;5:550–5.
      OpenUrlCrossRefPubMed
    24. ↵
      1. Annahazi A,
      2. Gecse K,
      3. Dabek M,
      4. et al
      . Fecal proteases from diarrheic-IBS and ulcerative colitis patients exert opposite effect on visceral sensitivity in mice. Pain 2009;144:209–17.
      OpenUrlCrossRefPubMedWeb of Science
    25. ↵
      1. Bustos D,
      2. Negri G,
      3. De Paula JA,
      4. et al
      . Colonic proteinases: increased activity in patients with ulcerative colitis. Medicina (B Aires) 1998;58:262–4.
      OpenUrlPubMedWeb of Science
    26. ↵
      1. Gecse K,
      2. Roka R,
      3. Ferrier L,
      4. et al
      . Increased faecal serine protease activity in diarrhoeic IBS patients: a colonic lumenal factor impairing colonic permeability and sensitivity. Gut 2008;57:591–9.
      OpenUrlAbstract/FREE Full Text
    27. ↵
      1. Macfarlane GT,
      2. Allison C,
      3. Gibson SA,
      4. et al
      . Contribution of the microflora to proteolysis in the human large intestine. J Appl Bacteriol 1988;64:37–46.
      OpenUrlCrossRefPubMed
    28. ↵
      1. Pruteanu M,
      2. Hyland NP,
      3. Clarke DJ,
      4. et al
      . Degradation of the extracellular matrix components by bacterial-derived metalloproteases: implications for inflammatory bowel diseases. Inflamm Bowel Dis 2010;17:1189–200.
      OpenUrlPubMed
    29. ↵
      1. Qin J,
      2. Li R,
      3. Raes J,
      4. et al
      . A human gut microbial gene catalogue established by metagenomic sequencing. Nature 2010;464:59–65.
      OpenUrlCrossRefPubMedWeb of Science
    30. ↵
      1. Sokol H,
      2. Pigneur B,
      3. Watterlot L,
      4. et al
      . Faecalibacterium prausnitzii is an anti-inflammatory commensal bacterium identified by gut microbiota analysis of Crohn disease patients. Proc Natl Acad Sci U S A 2008;105:16731–6.
      OpenUrlAbstract/FREE Full Text
    31. ↵
      1. Macfarlane GT,
      2. Blackett KL,
      3. Nakayama T,
      4. et al
      . The gut microbiota in inflammatory bowel disease. Curr Pharm Des 2009;15:1528–36.
      OpenUrlCrossRefPubMedWeb of Science
    32. ↵
      1. Laukoetter MG,
      2. Nava P,
      3. Nusrat A
      . Role of the intestinal barrier in inflammatory bowel disease. World J Gastroenterol 2008;14:401–7.
      OpenUrlCrossRefPubMedWeb of Science
    33. ↵
      1. McGuckin MA,
      2. Eri R,
      3. Simms LA,
      4. et al
      . Intestinal barrier dysfunction in inflammatory bowel diseases. Inflamm Bowel Dis 2009;15:100–13.
      OpenUrlCrossRefPubMedWeb of Science
    34. ↵
      1. Su L,
      2. Shen L,
      3. Clayburgh DR,
      4. et al
      . Targeted epithelial tight junction dysfunction causes immune activation and contributes to development of experimental colitis. Gastroenterology 2009;136:551–63.
      OpenUrlCrossRefPubMedWeb of Science
      1. Warfel JM,
      2. Steele AD,
      3. D'Agnillo F
      . Anthrax lethal toxin induces endothelial barrier dysfunction. Am J Pathol 2005;166:1871–81.
      OpenUrlCrossRefPubMedWeb of Science
      1. Babbin BA,
      2. Sasaki M,
      3. Gerner-Schmidt KW,
      4. et al
      . The bacterial virulence factor lymphostatin compromises intestinal epithelial barrier function by modulating rho GTPases. Am J Pathol 2009;174:1347–57.
      OpenUrlCrossRefPubMedWeb of Science
      1. Voth DE,
      2. Ballard JD
      . Clostridium difficile toxins: mechanism of action and role in disease. Clin Microbiol Rev 2005;18:247–63.
      OpenUrlAbstract/FREE Full Text
    38. ↵
      1. Grys TE,
      2. Siegel MB,
      3. Lathem WW,
      4. et al
      . The StcE protease contributes to intimate adherence of enterohemorrhagic Escherichia coli O157:H7 to host cells. Infect Immun 2005;73:1295–303.
      OpenUrlAbstract/FREE Full Text
    39. ↵
      1. Wu S,
      2. Rhee KJ,
      3. Zhang M,
      4. et al
      . Bacteroides fragilis toxin stimulates intestinal epithelial cell shedding and gamma-secretase-dependent E-cadherin cleavage. J Cell Sci 2007;120:1944–52.
      OpenUrlAbstract/FREE Full Text
    40. ↵
      1. Hoy B,
      2. Lower M,
      3. Weydig C,
      4. et al
      . Helicobacter pylori HtrA is a new secreted virulence factor that cleaves E-cadherin to disrupt intercellular adhesion. EMBO Rep 2010;11:798–804.
      OpenUrlCrossRefPubMedWeb of Science
      1. Azghani AO,
      2. Gray LD,
      3. Johnson AR
      . A bacterial protease perturbs the paracellular barrier function of transporting epithelial monolayers in culture. Infect Immun 1993;61:2681–6.
      OpenUrlAbstract/FREE Full Text
      1. Rudack C,
      2. Sachse F,
      3. Albert N,
      4. et al
      . Immunomodulation of nasal epithelial cells by Staphylococcus aureus-derived serine proteases. J Immunol 2009;183:7592–601.
      OpenUrlAbstract/FREE Full Text
      1. Wu Z,
      2. Nybom P,
      3. Magnusson KE
      . Distinct effects of Vibrio cholerae haemagglutinin/protease on the structure and localization of the tight junction-associated proteins occludin and ZO-1. Cell Microbiol 2000;2:11–17.
      OpenUrlCrossRefPubMedWeb of Science
    44. ↵
      1. Steck N,
      2. Hoffmann M,
      3. Sava IG,
      4. et al
      . Enterococcus faecalis metalloprotease compromises epithelial barrier and contributes to intestinal inflammation. Gastroenterology 2011;141:959–71.
      OpenUrlCrossRefPubMedWeb of Science
    45. ↵
      1. Schultsz C,
      2. Van Den Berg FM,
      3. Ten Kate FW,
      4. et al
      . The intestinal mucus layer from patients with inflammatory bowel disease harbors high numbers of bacteria compared with controls. Gastroenterology 1999;117:1089–97.
      OpenUrlCrossRefPubMedWeb of Science
    46. ↵
      1. Fyderek K,
      2. Strus M,
      3. Kowalska-Duplaga K,
      4. et al
      . Mucosal bacterial microflora and mucus layer thickness in adolescents with inflammatory bowel disease. World J Gastroenterol 2009;15:5287–94.
      OpenUrlCrossRefPubMedWeb of Science
    47. ↵
      1. Rhodes JM,
      2. Gallimore R,
      3. Elias E,
      4. et al
      . Faecal mucus degrading glycosidases in ulcerative colitis and Crohn's disease. Gut 1985;26:761–5.
      OpenUrlAbstract/FREE Full Text
    48. ↵
      1. Png CW,
      2. Linden SK,
      3. Gilshenan KS,
      4. et al
      . Mucolytic bacteria with increased prevalence in IBD mucosa augment in vitro utilization of mucin by other bacteria. Am J Gastroenterol 2010;105:2420–8.
      OpenUrlCrossRefPubMed
    49. ↵
      1. McGuckin MA,
      2. Linden SK,
      3. Sutton P,
      4. et al
      . Mucin dynamics and enteric pathogens. Nat Rev Microbiol 2011;9:265–78.
      OpenUrlCrossRefPubMed
    50. ↵
      1. Vergnolle N
      . Clinical relevance of proteinase activated receptors (PARs) in the gut. Gut 2005;54:867–74.
      OpenUrlFREE Full Text
    51. ↵
      1. Amadesi S,
      2. Bunnett N
      . Protease-activated receptors: protease signaling in the gastrointestinal tract. Curr Opin Pharmacol 2004;4:551–6.
      OpenUrlCrossRefPubMedWeb of Science
    52. ↵
      1. Karanjia R,
      2. Spreadbury I,
      3. Bautista-Cruz F,
      4. et al
      . Activation of protease-activated receptor-4 inhibits the intrinsic excitability of colonic dorsal root ganglia neurons. Neurogastroenterol Motil 2009;21:1218–21.
      OpenUrlCrossRefPubMed
    53. ↵
      1. Asfaha S,
      2. Cenac N,
      3. Houle S,
      4. et al
      . Protease-activated receptor-4: a novel mechanism of inflammatory pain modulation. Br J Pharmacol 2007;150:176–85.
      OpenUrlCrossRefPubMedWeb of Science
    54. ↵
      1. Auge C,
      2. Balz-Hara D,
      3. Steinhoff M,
      4. et al
      . Protease-activated receptor-4 (PAR 4): a role as inhibitor of visceral pain and hypersensitivity. Neurogastroenterol Motil 2009;21:1189–e107.
      OpenUrlCrossRefPubMed
    55. ↵
      1. Mueller K,
      2. Michel K,
      3. Krueger D,
      4. et al
      . Activity of Protease-Activated Receptors in the Human Submucous Plexus. Gastroenterology, 2011, doi:10.1053/j.gastro.2011.08.034.
    56. ↵
      1. Lourbakos A,
      2. Chinni C,
      3. Thompson P,
      4. et al
      . Cleavage and activation of proteinase-activated receptor-2 on human neutrophils by gingipain-R from Porphyromonas gingivalis. FEBS Lett 1998;435:45–8.
      OpenUrlCrossRefPubMedWeb of Science
    57. ↵
      1. Lourbakos A,
      2. Potempa J,
      3. Travis J,
      4. et al
      . Arginine-specific protease from Porphyromonas gingivalis activates protease-activated receptors on human oral epithelial cells and induces interleukin-6 secretion. Infect Immun 2001;69:5121–30.
      OpenUrlAbstract/FREE Full Text
    58. ↵
      1. Lourbakos A,
      2. Yuan YP,
      3. Jenkins AL,
      4. et al
      . Activation of protease-activated receptors by gingipains from Porphyromonas gingivalis leads to platelet aggregation: a new trait in microbial pathogenicity. Blood 2001;97:3790–7.
      OpenUrlAbstract/FREE Full Text
      1. Holzhausen M,
      2. Spolidorio LC,
      3. Ellen RP,
      4. et al
      . Protease-activated receptor-2 activation: a major role in the pathogenesis of Porphyromonas gingivalis infection. Am J Pathol 2006;168:1189–99.
      OpenUrlCrossRefPubMedWeb of Science
    60. ↵
      1. Dulon S,
      2. Leduc D,
      3. Cottrell GS,
      4. et al
      . Pseudomonas aeruginosa elastase disables proteinase-activated receptor 2 in respiratory epithelial cells. Am J Respir Cell Mol Biol 2005;32:411–19.
      OpenUrlCrossRefPubMedWeb of Science
    61. ↵
      1. Kida Y,
      2. Higashimoto Y,
      3. Inoue H,
      4. et al
      . A novel secreted protease from Pseudomonas aeruginosa activates NF-kappaB through protease-activated receptors. Cell Microbiol 2008;10:1491–504.
      OpenUrlCrossRefPubMedWeb of Science
    62. ↵
      1. Kida Y,
      2. Inoue H,
      3. Shimizu T,
      4. et al
      . Serratia marcescens serralysin induces inflammatory responses through protease-activated receptor 2. Infect Immun 2007;75:164–74.
      OpenUrlAbstract/FREE Full Text
    63. ↵
      1. Asokananthan N,
      2. Graham PT,
      3. Stewart DJ,
      4. et al
      . House dust mite allergens induce proinflammatory cytokines from respiratory epithelial cells: the cysteine protease allergen, Der p 1, activates protease-activated receptor (PAR)-2 and inactivates PAR-1. J Immunol 2002;169:4572–8.
      OpenUrlAbstract/FREE Full Text
    64. ↵
      1. Sun G,
      2. Stacey MA,
      3. Schmidt M,
      4. et al
      . Interaction of mite allergens Der p3 and Der p9 with protease-activated receptor-2 expressed by lung epithelial cells. J Immunol 2001;167:1014–21.
      OpenUrlAbstract/FREE Full Text
    65. ↵
      1. Katz J,
      2. Sambandam V,
      3. Wu JH,
      4. et al
      . Characterization of Porphyromonas gingivalis-induced degradation of epithelial cell junctional complexes. Infect Immun 2000;68:1441–9.
      OpenUrlAbstract/FREE Full Text
    66. ↵
      1. Sugawara S,
      2. Nemoto E,
      3. Tada H,
      4. et al
      . Proteolysis of human monocyte CD14 by cysteine proteinases (gingipains) from Porphyromonas gingivalis leading to lipopolysaccharide hyporesponsiveness. J Immunol 2000;165:411–18.
      OpenUrlAbstract/FREE Full Text
    67. ↵
      1. Azghani AO
      . Pseudomonas aeruginosa and epithelial permeability: role of virulence factors elastase and exotoxin A. Am J Respir Cell Mol Biol 1996;15:132–40.
      OpenUrlCrossRefPubMedWeb of Science
    68. ↵
      1. de Zoete MR,
      2. Bouwman LI,
      3. Keestra AM,
      4. et al
      . Cleavage and activation of a Toll-like receptor by microbial proteases. Proc Natl Acad Sci U S A 2011;108:4968–73.
      OpenUrlAbstract/FREE Full Text
    69. ↵
      1. Brunn GJ,
      2. Bungum MK,
      3. Johnson GB,
      4. et al
      . Conditional signaling by Toll-like receptor 4. Faseb J 2005;19:872–4.
      OpenUrlAbstract/FREE Full Text
    70. ↵
      1. Cario E,
      2. Golenbock DT,
      3. Visintin A,
      4. et al
      . Trypsin-sensitive modulation of intestinal epithelial MD-2 as mechanism of lipopolysaccharide tolerance. J Immunol 2006;176:4258–66.
      OpenUrlAbstract/FREE Full Text
    71. ↵
      1. Moretti S,
      2. Bellocchio S,
      3. Bonifazi P,
      4. et al
      . The contribution of PARs to inflammation and immunity to fungi. Mucosal Immunol 2008;1:156–68.
      OpenUrlCrossRefPubMedWeb of Science
    72. ↵
      1. van Roy F,
      2. Berx G
      . The cell-cell adhesion molecule E-cadherin. Cell Mol Life Sci 2008;65:3756–88.
      OpenUrlCrossRefPubMedWeb of Science
    73. ↵
      1. Mengaud J,
      2. Ohayon H,
      3. Gounon P,
      4. et al
      . E-cadherin is the receptor for internalin, a surface protein required for entry of L. monocytogenes into epithelial cells. Cell 1996;84:923–32.
      OpenUrlCrossRefPubMedWeb of Science
    74. ↵
      1. Phan QT,
      2. Myers CL,
      3. Fu Y,
      4. et al
      . Als3 is a Candida albicans invasin that binds to cadherins and induces endocytosis by host cells. PLoS Biol 2007;5:e64.
      OpenUrlCrossRefPubMed
    75. ↵
      1. Moreno-Ruiz E,
      2. Galan-Diez M,
      3. Zhu W,
      4. et al
      . Candida albicans internalization by host cells is mediated by a clathrin-dependent mechanism. Cell Microbiol 2009;11:1179–89.
      OpenUrlCrossRefPubMed
    76. ↵
      1. Noe V,
      2. Fingleton B,
      3. Jacobs K,
      4. et al
      . Release of an invasion promoter E-cadherin fragment by matrilysin and stromelysin-1. J Cell Sci 2001;114:111–18.
      OpenUrlAbstract/FREE Full Text
    77. ↵
      1. Maretzky T,
      2. Reiss K,
      3. Ludwig A,
      4. et al
      . ADAM10 mediates E-cadherin shedding and regulates epithelial cell-cell adhesion, migration, and beta-catenin translocation. Proc Natl Acad Sci U S A 2005;102:9182–7.
      OpenUrlAbstract/FREE Full Text
    78. ↵
      1. Huguenin M,
      2. Muller EJ,
      3. Trachsel-Rosmann S,
      4. et al
      . The metalloprotease meprinbeta processes E-cadherin and weakens intercellular adhesion. PLoS One 2008;3:e2153.
      OpenUrlCrossRefPubMed
    79. ↵
      1. Freour T,
      2. Jarry A,
      3. Bach-Ngohou K,
      4. et al
      . TACE inhibition amplifies TNF-alpha-mediated colonic epithelial barrier disruption. Int J Mol Med 2009;23:41–8.
      OpenUrlPubMedWeb of Science
    80. ↵
      1. Kirkegaard T,
      2. Pedersen G,
      3. Saermark T,
      4. et al
      . Tumour necrosis factor-alpha converting enzyme (TACE) activity in human colonic epithelial cells. Clin Exp Immunol 2004;135:146–53.
      OpenUrlCrossRefPubMedWeb of Science
    81. ↵
      1. Peschon JJ,
      2. Slack JL,
      3. Reddy P,
      4. et al
      . An essential role for ectodomain shedding in mammalian development. Science 1998;282:1281–4.
      OpenUrlAbstract/FREE Full Text
    82. ↵
      1. Forsyth CB,
      2. Banan A,
      3. Farhadi A,
      4. et al
      . Regulation of oxidant-induced intestinal permeability by metalloprotease-dependent epidermal growth factor receptor signaling. J Pharmacol Exp Ther 2007;321:84–97.
      OpenUrlAbstract/FREE Full Text
    83. ↵
      1. Kenny PA
      . Tackling EGFR signaling with TACE antagonists: a rational target for metalloprotease inhibitors in cancer. Expert Opin Ther Targets 2007;11:1287–98.
      OpenUrlCrossRefPubMedWeb of Science
    84. ↵
      1. Isozaki Y,
      2. Yoshida N,
      3. Kuroda M,
      4. et al
      . Anti-tryptase treatment using nafamostat mesilate has a therapeutic effect on experimental colitis. Scand J Gastroenterol 2006;41:944–53.
      OpenUrlCrossRefPubMedWeb of Science
    85. ↵
      1. Senda S,
      2. Fujiyama Y,
      3. Bamba T,
      4. et al
      . Treatment of ulcerative colitis with camostat mesilate, a serine protease inhibitor. Intern Med 1993;32:350–4.
      OpenUrlCrossRefPubMed
    86. ↵
      1. Sykes AP,
      2. Bhogal R,
      3. Brampton C,
      4. et al
      . The effect of an inhibitor of matrix metalloproteinases on colonic inflammation in a trinitrobenzenesulphonic acid rat model of inflammatory bowel disease. Aliment Pharmacol Ther 1999;13:1535–42.
      OpenUrlCrossRefPubMed
    87. ↵
      1. Di Sebastiano P,
      2. di Mola FF,
      3. Artese L,
      4. et al
      . Beneficial effects of Batimastat (BB-94), a matrix metalloproteinase inhibitor, in rat experimental colitis. Digestion 2001;63:234–9.
      OpenUrlCrossRefPubMedWeb of Science
    88. ↵
      1. Medina C,
      2. Santana A,
      3. Paz MC,
      4. et al
      . Matrix metalloproteinase-9 modulates intestinal injury in rats with transmural colitis. J Leukoc Biol 2006;79:954–62.
      OpenUrlAbstract/FREE Full Text
    89. ↵
      1. Bissett D,
      2. O'Byrne KJ,
      3. von Pawel J,
      4. et al
      . Phase III study of matrix metalloproteinase inhibitor prinomastat in non-small-cell lung cancer. J Clin Oncol 2005;23:842–9.
      OpenUrlAbstract/FREE Full Text
    90. ↵
      1. Rolland C,
      2. Motta J-P,
      3. Rousset P,
      4. et al
      . Increased proteolytic activity at mucosal surfaces in IBD Patients: a possible role for elafin. Gastroenterology 2011;140:S-695.
      OpenUrl
    91. ↵
      1. Motta JP,
      2. Magne L,
      3. Descamps D,
      4. et al
      . Modifying the protease, antiprotease pattern by elafin overexpression protects mice from colitis. Gastroenterology 2011;140:1272–82.
      OpenUrlCrossRefPubMedWeb of Science
    92. ↵
      1. Kim JA,
      2. Choi SC,
      3. Yun KJ,
      4. et al
      . Expression of protease-activated receptor 2 in ulcerative colitis. Inflamm Bowel Dis 2003;9:224–9.
      OpenUrlCrossRefPubMedWeb of Science
    93. ↵
      1. Kim HJ,
      2. Vazquez Roque MI,
      3. Camilleri M,
      4. et al
      . A randomized controlled trial of a probiotic combination VSL# 3 and placebo in irritable bowel syndrome with bloating. Neurogastroenterol Motil 2005;17:687–96.
      OpenUrlCrossRefPubMedWeb of Science
    94. ↵
      1. Venturi A,
      2. Gionchetti P,
      3. Rizzello F,
      4. et al
      . Impact on the composition of the faecal flora by a new probiotic preparation: preliminary data on maintenance treatment of patients with ulcerative colitis. Aliment Pharmacol Ther 1999;13:1103–8.
      OpenUrlCrossRefPubMedWeb of Science
    95. ↵
      1. Tursi A,
      2. Brandimarte G,
      3. Giorgetti GM,
      4. et al
      . Low-dose balsalazide plus a high-potency probiotic preparation is more effective than balsalazide alone or mesalazine in the treatment of acute mild-to-moderate ulcerative colitis. Med Sci Monit 2004;10:PI126–31.
      OpenUrlPubMedWeb of Science
    96. ↵
      1. Kunze WA,
      2. Mao YK,
      3. Wang B,
      4. et al
      . Lactobacillus reuteri enhances excitability of colonic AH neurons by inhibiting calcium-dependent potassium channel opening. J Cell Mol Med 2009;13:2261–70.
      OpenUrlCrossRefPubMedWeb of Science
    97. ↵
      1. von Schillde M-A,
      2. Hãrmannsperger G,
      3. Alpert C-A,
      4. et al
      . T2025 probiotic-derived lactocepin degrades the pro-inflammatory chemokine IP-10: impact on chronic intestinal inflammation. Gastroenterology 2010;138:S-615–16.
      OpenUrl

    Footnotes

    • NS and KM are joint first authors.

    • Funding This work was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft) grant GRK 1482 and the European Union grant FP7 Intestinal Proteases: Opportunity for Drug Discovery (IPODD).

    • Competing interests None.

    • Provenance and peer review Not commissioned; externally peer reviewed.