Protease Inhibition As New Therapeutic Strategy for GI Diseases Gut: First Published As 10.1136/Gutjnl-2015-309147 on 12 April 2016
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Recent advances in basic science Protease inhibition as new therapeutic strategy for GI diseases Gut: first published as 10.1136/gutjnl-2015-309147 on 12 April 2016. Downloaded from Nathalie Vergnolle1,2,3,4,5 1Inserm, U1220, Toulouse, ABSTRACT France The GI tract is the most exposed organ to proteases, Key messages 2Université de Toulouse, Université Paul Sabatier, both in physiological and pathophysiological conditions. For digestive purposes, the lumen of the upper GI tract Institut de Recherche en Santé ▸ Protease inhibition as therapeutic approach in Digestive (IRSD), Toulouse, contains large amounts of pancreatic proteases, but intestinal pathologies: what should we France studies have also demonstrated increased proteolytic 3 consider? Inra, U1416, Toulouse, France activity into mucosal tissues (both in the upper and 4Ecole Nationale Vétérinaire de – Profiles of active proteases have to be lower GI tract), associated with pathological conditions. Toulouse (ENVT), France performed in pathological tissues in order to 5 This review aims at outlining the evidences for Department of Pharmacology define the best molecular targets for and Physiology, University of dysregulated proteolytic homeostasis in GI diseases and therapeutic intervention Calgary, Calgary, Alberta, the pathogenic mechanisms of increased proteolytic – Large spectrum inhibitors might have severe Canada activity. The therapeutic potential of protease inhibition side effects in GI diseases is discussed, with a particular focus on Correspondence to – Promote the expression or delivery of natural Dr Nathalie Vergnolle, INSERM, IBDs, functional GI disorders and colorectal cancer. UMR-1220, IRSD, Place du endogenous inhibitors could be a safe Dr. Baylac, CHU Purpan, therapeutic option CS 60039, Toulouse 31024, – Local versus systemic delivery would have to Cedex 3, France; be considered [email protected] INTRODUCTION – The use of food-grade bacteria as carrier for Proteases represent up to 2% of the human the delivery of therapeutic proteins has been Received 3 April 2015 genome, with 500–600 different proteases that Revised 5 February 2016 proposed fi Accepted 12 February 2016 have been identi ed. Through the evolution, pro- ▸ Protease targets for IBD Published Online First teases have adapted to the different conditions that – MMPs inhibitors have been abandoned 12 April 2016 characterise complex organisms: pH variation, – Serine proteases are considered oxydo-reduction environment, temperature, etc. – Ubiquitin–proteasome system inhibitors are fi Proteases speci cally cleave proteins at their considered extremities (N-terminal or C-terminal regions) and ▸ Protease targets for IBS http://gut.bmj.com/ are then called exopeptidases, or in the middle of – Trypsin inhibition fi the proteins, being quali ed then as endopepti- – Tryptase inhibitors dases. Depending on their proteolytic mechanism, – Protease-Activated Receptor (PAR )/PAR fi 1 2 human proteases are classi ed as serine, threonine, antagonists cysteine, aspartic or metalloproteases (figure 1 and table 1). Some of them are secreted and released in the extracellular milieu, while others have intracel- on September 27, 2021 by guest. Protected copyright. lular functions and exclusively remain inside the identified. These findings could question the contri- fi cells ( gure 1). bution of microbial proteases, to overall luminal proteolytic activity in the gut. Another study has PROTEASES AND PROTEASE INHIBITORS OF established significant associations between specific THE GI TRACT bacterial subgroups and faecal protease activity, sug- Proteases gesting that microbiota composition could affect In the GI tract, proteases are heavily present, both intestinal proteolytic homeostasis. More recently, in the lumen and deeply into the tissues.1 forms of secreted proteases have been identified in Pancreatic proteases (trypsins, chymotrypsin, elas- intestinal epithelium: mesotrypsin mRNA is found tase, etc) are released into the lumen of the upper in human intestinal epithelial cells3 and trypsin GI tract, where they exert digestive functions. The activity is released by cultures of those cells Open Access Scan to access more microbiota constitutes also an important source of (Vergnolle, personal communication). Other resi- free content proteases (figure 2). Bacteria, yeasts and helminths dent cells of the intestinal mucosa produce and potentially present in the intestinal lumen produce release proteases (figure 2). For instance, the major and release proteases.2 For some pathogens such as protein content of mucosal mast cells is proteases. pathogenic forms of Escherichia coli or the entero- Mast cells release different forms of proteases: toxigenic Bacteroides fragilis, their ability to release tryptase and chymase for the vast majority, and also proteases is crucial for their pathogenicity. Serine, cathepsin G and granzyme B. Resident macro- cysteine, aspartic and metalloproteases are phages also produce and/or release different forms expressed and released by the microbiota (table 2).2 of proteases: matrix metalloproteinases (MMPs) However, it is interesting to note that when the (MMP-12 among other MMPs), caspase, cathepsins To cite: Vergnolle N. Gut nature of the proteases present in human faeces L and D.1 In the inflamed gut, inflammatory cells – 2016;65:1215 1224. was investigated, only host proteases were are another major source of proteases, which they Vergnolle N. Gut 2016;65:1215–1224. doi:10.1136/gutjnl-2015-309147 1215 Recent advances in basic science Although specific proteases can be detected in tissues, the cel- lular origin of most proteases is quite difficult to define, and no study so far has determined the origin of proteases detected in Gut: first published as 10.1136/gutjnl-2015-309147 on 12 April 2016. Downloaded from intestinal tissues. The site of action of a given protease is also debated. As of today, one can only specify the possible site of action of a given protease. Another level of difficulty in studying proteases is that for activity tests, substrates are never fully specific of one protease, neither are their inhibitors. Therefore, the proteolytic activity that is measured is possibly due to a mix of proteases and cannot be attributed to one specific protease. Protease inhibitors Protease inhibitors have coevolved with proteases, in order to control their destructive nature. Natural endogenous protease inhibitors are particularly present in the GI tract.1 They are either circulating inhibitors produced at distance from the GI tract (mostly in the liver), or are produced on site, by intestinal Figure 1 Representation of human cell proteases according to their epithelial cells or infiltrated inflammatory cells (table 3). Serpins catalytic mechanism and their intracellular or extracellular representation. MMPs, matrix metalloproteinases. A1, A3, A4, E1 and C1 are circulating protease inhibitors inhi- biting serine proteases such as trypsins, chymase, tryptase, elas- tases, kallikreins and cathepsin G (table 3). Secretory leucocyte use to degrade extracellular tissues and intracellular particles, protease inhibitor (SLPI) and elafin are produced in situ by thereby increasing their phagocytic properties.4 Upon inflamma- intestinal epithelial cells or leucocytes. Both inhibit elastase and tory cell infiltration and activation, tissue proteolytic activity is proteinase-3, while SLPI also inhibits trypsin, chymotrypsin, considerably increased. Neutrophils in particular release massive cathepsin G, tryptase and chymase7 (table 3). Tissue inhibitors amounts of elastase, proteinase-3 and cathepsin G5 (figure 2). of metalloproteinases (TIMPs) are ubiquitously produced, Finally, all resident cells of the GI tract express intracellular pro- TIMP-1, TIMP-2, TIMP-3 and TIMP-4 are present in the GI teases: caspases, which have fundamental roles in cell apoptosis, tract, where they inhibit a number of different MMPs8 (table 3). and autophagins, which are the proteolytic enzymes responsible The caspase-9 inhibitor, which is a cellular inhibitor of apop- of autophagy processes6 (table 1). A special case can be made tosis protein-2 (c-IAP2) is also ubiquitously produced by cells for deubiquitylases, which are crucial regulators of intracellular present in intestinal tissues. protein turnover through the proteasome system. These enzymes present in all cell types, are either cysteines or metallo- PROTEASES AND INTESTINAL PHYSIOLOGY http://gut.bmj.com/ proteinases and target ubiquitinylated proteins, thereby chan- The roles and functions of proteases and their inhibitors under ging their degradation fate inside the cell. physiological conditions have been poorly investigated. While Table 1 Proteases identified in GI tissues and cells, and disease-associated upregulation Upregulated expression in on September 27, 2021 by guest. Protected copyright. Family Proteases Cellular location Possible sites of action CD UC IBS CRC Serine proteases Elastases Intra/extra L, M, P, I + + + + Proteinase-3 Intra/extra L, M, P, I + + Chymase Extra L, M, P + + + Kallikreins Extra L, M, P + + + Granzymes Intra/extra L, M, I + + + Tryptase Extra L, M, P + + + + Plasminogen Extra M, P + Activator Trypsins Extra L, M, P + + + Cathepsin G Intra/extra L, M, P, I + + Thrombin L, M, P + + Factors V and VIII L, M, P + Matriptase Membrane-bound M, I + Cysteine proteases Caspases Intra I + + Cathepsins (B, L) Extra M, P + + Autophagins Intra I Calpains Intra I + + Deubiquitinases Intra I + + + + Aspartate proteases Cathepsin D Intra I + + + Renin