Matriptase protects against experimental colitis and promotes intestinal barrier recovery

The proteolytic activity in inflammatory bowel disease: insight from gut microbiota

Inflammatory bowel disease (IBD) is a chronic, recurrent inflammatory disease caused by the destruction of the intestinal mucosal epithelium that affects a growing number of people worldwide. Although the etiology of IBD is complex and still elucidated, the role of dysbiosis and dysregulated proteolysis is well recognized. Various studies observed altered composition and diversity of gut microbiota, as well as increased proteolytic activity (PA) in serum, plasma, colonic mucosa, and fecal supernatant of IBD compared to healthy individuals. The imbalance of intestinal microecology and intestinal protein hydrolysis were gradually considered to be closely related to IBD. Notably, the pivotal role of intestinal microbiota in maintaining proteolytic balance received increasing attention. In summary, we have speculated a mesmerizing story, regarding the hidden role of PA and microbiota-derived PA hidden in IBD. Most importantly, we provided the diagnosis and therapeutic targets for IBD as well as the formulation of new treatment strategies for other digestive diseases and protease-related diseases.

M2a macrophages facilitate resolution of chemically-induced colitis in TLR4-SNP mice

IMPORTANCE

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, impacts millions of individuals worldwide and severely impairs the quality of life for patients. Dysregulation of innate immune signaling pathways reduces barrier function and exacerbates disease progression. Macrophage (Mφ) signaling pathways are potential targets for IBD therapies. While multiple treatments are available for IBD, (i) not all patients respond, (ii) responses may diminish over time, and (iii) treatments often have undesirable side effects. Genetic studies have shown that the inheritance of two co-segregating SNPs expressed in the innate immune receptor, TLR4, is associated with human IBD. Mice expressing homologous SNPs ("TLR4-SNP" mice) exhibited more severe colitis than WT mice in a DSS-induced colonic inflammation/repair model. We identified a critical role for M2a "tissue repair" Mφ in the resolution of colitis. Our findings provide insight into potential development of novel therapies targeting Mφ signaling pathways that aim to alleviate the debilitating symptoms experienced by individuals with IBD.

The Effect of Serine Protease Inhibitors on Visceral Pain in Different Rodent Models With an Intestinal Insult

Background: Serine proteases are believed to play a key role in the origin of abdominal pain in IBD and IBS. We previously demonstrated a reduction of visceral pain in a post-inflammatory IBS rat model after a single intraperitoneal or intracolonic administration of a serine protease inhibitor. The aim of this study was to investigate the efficacy of serine protease inhibition on visceral pain in two different animal models involving a colonic insult based either on acute inflammation or on neonatal irritation. Moreover, protease profiling was explored in the acute colitis model. Methods: An acute 2,4,6-trinitrobenzenesulphonic acid (TNBS) colitis rat model and a chronic neonatal acetic acid mouse model were used in this study. Visceral sensitivity was quantified by visceromotor responses (VMRs) to colorectal distension, 30 min after intraperitoneal administration of the serine protease inhibitors nafamostat, UAMC-00050 or their vehicles. Colonic samples from acute colitis rats were used to quantify the mRNA expression of a panel of serine proteases and mast cell tryptase by immunohistochemistry. Finally, proteolytic activities in colonic and fecal samples were characterized using fluorogenic substrates. Key Results: We showed a significant and pressure-dependent increase in visceral hypersensitivity in acute colitis and neonatal acetic acid models. UAMC-00050 and nafamostat significantly reduced VMRs in both animal models. In acute colitis rats, the administration of a serine protease inhibitor did not affect the inflammatory parameters. Protease profiling of these acute colitis animals revealed an increased tryptase immunoreactivity and a downregulation of matriptase at the mRNA level after inflammation. The administration of UAMC-00050 resulted in a decreased elastase-like activity in the colon associated with a significantly increased elastase-like activity in fecal samples of acute colitis animals. Conclusion: In conclusion, our results suggest that serine proteases play an important role in visceral hypersensitivity in an acute TNBS colitis model in rats and a neonatal acetic acid model in mice. Moreover, we hypothesize a potential mechanism of action of UAMC-00050 via the alteration of elastase-like proteolytic activity in acute inflammation. Taken together, we provided fundamental evidence for serine protease inhibitors as a promising new therapeutic strategy for abdominal pain in gastrointestinal diseases.

Angelica sinensis polysaccharide improves rheumatoid arthritis by modifying the expression of intestinal Cldn5, Slit3 and Rgs18 through gut microbiota

Rheumatoid arthritis (RA) is an autoimmune disease with a high incidence. Recent studies have demonstrated that diet can contribute to the development and progression of RA. Indeed, non-starch polysaccharides (NSPs) were known to be related to the improvement of RA. In this study, the collagen-induced rats were administrated with Angelica sinensis polysaccharide (ASP) at 200 mg/kg (L), 400 mg/kg (M), or 800 mg/kg (H). Results showed that ASP could reduce joint swelling and significantly inhibit anti-CII-antibodies and pro-inflammatory factors in RA, H group showed the best treatment among them. Further analysis using 16S rDNA sequencing suggested that ASP could shape the gut microbiota composition. Several key bacteria, including norank_f__norank_o__Clostridia_UCG-014, Lactobacillus, norank_f__Oscillospiraceae, and norank_f__Desulfovibrionaceae, were found to be related to the development of RA. The colonic transcriptome showed that ASP could restore RA-induced intestinal dysfunction, such as tight junction disarrangement, by upregulating Cldn5. The balance between osteoblasts and osteoclasts might be modified by regulating the expression of Slit3 and Rgs18 to alleviate RA, which may be correlated with gut microbiota. Our results suggested that ASP improved RA by regulating gut microbiota and gene expression, revealing a positive relationship between dietary patterns and RA.

T cell protein tyrosine phosphatase protects intestinal barrier function by restricting epithelial tight junction remodeling

Genome-wide association studies revealed that loss-of-function mutations in protein tyrosine phosphatase non-receptor type 2 (PTPN2) increase the risk of developing chronic immune diseases, such as inflammatory bowel disease (IBD) and celiac disease. These conditions are associated with increased intestinal permeability as an early etiological event. The aim of this study was to examine the consequences of deficient activity of the PTPN2 gene product, T cell protein tyrosine phosphatase (TCPTP), on intestinal barrier function and tight junction organization in vivo and in vitro. Here, we demonstrate that TCPTP protected against intestinal barrier dysfunction induced by the inflammatory cytokine IFN-γ by 2 mechanisms: it maintained localization of zonula occludens 1 and occludin at apical tight junctions and restricted both expression and insertion of the cation pore-forming transmembrane protein, claudin-2, at tight junctions through upregulation of the inhibitory cysteine protease, matriptase. We also confirmed that the loss-of-function PTPN2 rs1893217 SNP was associated with increased intestinal claudin-2 expression in patients with IBD. Moreover, elevated claudin-2 levels and paracellular electrolyte flux in TCPTP-deficient intestinal epithelial cells were normalized by recombinant matriptase. Our findings uncover distinct and critical roles for epithelial TCPTP in preserving intestinal barrier integrity, thereby proposing a mechanism by which PTPN2 mutations contribute to IBD.

The Effects of Matriptase Inhibition on the Inflammatory and Redox Homeostasis of Chicken Hepatic Cell Culture Models

The function of the transmembrane serine protease matriptase is well described in mammals, but it has not been elucidated in avian species yet. Hence, the aim of the present study was to assess the effects of the 3-amidinophenylalanine (3-AphA)-type matriptase inhibitors MI432 and MI460 on the inflammatory and oxidative state of chicken primary hepatocyte mono-cultures and hepatocyte-nonparenchymal cell co-cultures, the latter serving as a proper model of hepatic inflammation in birds. Cell cultures were exposed to MI432 and MI460 for 4 and 24 h at 10, 25, and 50 µM concentrations, and thereafter the cellular metabolic activity, extracellular interleukin (IL-)6, IL-8, H₂O₂ and malondialdehyde concentrations were monitored. Both inhibitors caused a transient moderate reduction in the metabolic activity following 4 h exposure, which was restored after 24 h, reflecting the fast hepatic adaptation potential to matriptase inhibitor administration. Furthermore, MI432 triggered an intense elevation in the cellular proinflammatory IL-6 and IL-8 production after both incubation times in all concentrations, which was not coupled to enhanced oxidative stress and lipid peroxidation based on unchanged H₂O₂ production, malondialdehyde levels and glutathione peroxidase activity. These data suggest that physiological matriptase activities might have a key function in retaining the metabolic and inflammatory homeostasis of the liver in chicken, without being a major modulator of the hepatocellular redox state.

Exposure of human intestinal epithelial cells and primary human hepatocytes to trypsin-like serine protease inhibitors with potential antiviral effect

Human intestinal epithelial cell line-6 (HIEC-6) cells and primary human hepatocytes (PHHs) were treated with 3-amidinophenylalanine-derived inhibitors of trypsin-like serine proteases for 24 hours. It was proven that treatment with MI-1900 and MI-1907 was tolerated up to 50 μM in HIEC-6. These inhibitors did not cause elevations in extracellular H₂O₂ levels and in the concentrations of interleukin (IL)-6 and IL-8 and did not alter occludin distribution in HIEC-6. It was also found that MI-1900 and MI-1907 up to 50 μM did not affect cell viability, IL-6 and IL-8 and occludin levels of PHH. Based on our findings, these inhibitors could be safely applicable at 50 μM in HIEC-6 and in PHH; however, redox status was disturbed in case of PHH. Moreover, it has recently been demonstrated that MI-1900 prevents the replication and spread of the new SARS-CoV-2 in infected Calu-3 cells, most-likely via an inhibition of the membrane-bound host protease TMPRSS2.

Inflammatory bowel disease: tri-directional relationship between microbiota, immune system and intestinal epithelium

Human gut microbiota contributes to host nutrition and metabolism, sustains intestinal cell proliferation and differentiation, and modulates host immune system. The alterations in their composition lead to severe gut disorders, including inflammatory bowel disease (IBD) or inflammatory bowel syndrome (IBS). IBD including ulcerative colitis (UC) and Crohn's disease (CD) are gamut of chronic inflammatory disorders of gut, mediated by complex interrelations among genetic, environmental, and internal factors. IBD has debateable aetiology, however in recent years, exploring the central role of a tri-directional relationship between gut microbiota, mucosal immune system, and intestinal epithelium in pathogenesis is getting the most attention. Increasing incidences and early onset explains the exponential rise in IBD burden on health-care systems. Industrialization, hypersensitivity to allergens, lifestyle, hygiene hypothesis, loss of intestinal worms, and gut microbial composition, explains this shifted rise. Hitherto, the interventions modulating gut microbiota composition, microfluidics-based in vitro gastrointestinal models, non-allergic functional foods, nutraceuticals, and faecal microbiota transplantation (FMT) from healthy donors are some of the futuristic approaches for the disease management.

The Interplay Between Genetic Risk Factors and Proteolytic Dysregulation in the Pathophysiology of Inflammatory Bowel Disease

Crohn's disease [CD] and ulcerative colitis [UC] are the two main forms of inflammatory bowel disease [IBD]. Previous studies reported increased levels of proteolytic activity in stool and tissue samples from IBD patients, whereas the re-establishment of the proteolytic balance abrogates the development of experimental colitis. Furthermore, recent data suggest that IBD occurs in genetically predisposed individuals who develop an abnormal immune response to intestinal microbes once exposed to environmental triggers. In this review, we highlight the role of proteases in IBD pathophysiology, and we showcase how the main cellular pathways associated with IBD influence proteolytic unbalance and how functional proteomics are allowing the unambiguous identification of dysregulated proteases in IBD, paving the way to the development of new protease inhibitors as a new potential treatment.

Relevance of physicochemical properties and functional pharmacology data to predict the clinical safety profile of direct oral anticoagulants

Direct oral anticoagulants (DOACs) have rapidly become the drug class of choice for anticoagulation therapy in secondary care. It is known that gastrointestinal hemorrhage are potential side effects of the DOAC drug class. In this study we have investigated the relevance of molecular structure and on/off-target pharmacology as a predictor of adverse drug reactions (ADRs) for the DOAC drug class. Use of the Reaxys MedChem module allowed for data mining of all possible reported off-target effects of the DOAC class members. For the first time, the MHRA Yellow card database in combination with prescribing rates in the United Kingdom (data for n = 30 566 936 DOAC Rx (up to 2017) and ADR data n = 22 275 (up to 2018)) were used for our data comparison of DOACs. From the underlying reported data, we were able to rank the DOACs in terms of the likely adverse events we would expect to observe. We identified potential risks of ADRs based on the DOACs pharmacology including the expected GI hemorrhage, but also the unexpected risk of stroke, pulmonary embolism and kidney injury. Statistically significant (P < .001) differences were found between all DOACs and their total number of ADRs. Although the risks are small, strong statistical correlation between observed pharmacology and national ADR data is observed in three out of the five areas of concern.

Serine proteases at the cutting edge of IBD: Focus on gastrointestinal inflammation

Serine proteases have been long recognized to coordinate many physiological processes and play key roles in regulating the inflammatory response. Accordingly, their dysregulation has been regularly associated with several inflammatory disorders and suggested as a central mechanism in the pathophysiology of digestive inflammation. So far, studies addressing the proteolytic homeostasis in the gut have mainly focused on host serine proteases as candidates of interest, while largely ignoring the potential contribution of their bacterial counterparts. The human gut microbiota comprises a complex ecosystem that contributes to host health and disease. Yet, our understanding of microbially produced serine proteases and investigation of whether they are causally linked to IBD is still in its infancy. In this review, we highlight recent advances in the emerging roles of host and bacterial serine proteases in digestive inflammation. We also discuss the application of available tools in the gut to monitor disease-related serine proteases. An exhaustive representation and understanding of such functional potential would help in closing existing gaps in mechanistic knowledge.

High-resolution MS/MS metabolomics by data-independent acquisition reveals urinary metabolic alteration in experimental colitis

INTRODUCTION

Traditional high-resolution MS1 based untargeted metabolomics suffers from low sensitivity, while low-resolution MS/MS based multiple reaction monitoring increases sensitivity at the cost of metabolite coverage and the mass accuracy.

OBJECTIVES

To evaluate and apply the high-resolution MS/MS level untargeted metabolomics.

METHODS

SWATH based data-independent acquisition (DIA) was optimized to obtain MS/MS of all precursor ions.

RESULTS

SWATH-MS/MS could rescue MS1 obscured or saturated metabolites and potentially provide diagnostic fragments to differentiate isomers. For SWATH-MS/MS, 4944 out of 21492 (23.0%) and 2289 out of 12831 (17.8%) fragment ion features significantly changed (Fold change > 1.5, P < 0.05) between Normal and experimental acute ulcerative colitis (UC) groups in positive and negative ion mode, respectively. For SWATH-MS1, 1022 out of 4818 (21.2%) and 353 out of 2266 (15.6%) features significantly changed in positive and negative ion mode, respectively. By deciphering the metabolite profiles with high-resolution MS/MS, it allows versatile post-acquisition data mining such as open detection of different sub-metabolome. The method revealed a global urinary metabolic alteration and increased glucuronide and sulfate sub-metabolome in UC. The major limitation of untargeted SWATH-MS/MS is increased interferences derived from wider Q1 isolation window.

CONCLUSIONS

SWATH-MS/MS is a versatile metabolomics strategy, merging the coverage of high-resolution untargeted metabolomics and the sensitivity of MS/MS.

Membrane-Anchored Serine Proteases and Protease-Activated Receptor-2-Mediated Signaling: Co-Conspirators in Cancer Progression

Pericellular proteolysis provides a significant advantage to developing tumors through the ability to remodel the extracellular matrix, promote cell invasion and migration, and facilitate angiogenesis. Recent advances demonstrate that pericellular proteases can also communicate directly to cells by activation of a unique group of transmembrane G-protein-coupled receptors (GPCR) known as protease-activated receptors (PAR). In this review, we discuss the specific roles of one of four mammalian PARs, namely PAR-2, which is overexpressed in advanced stage tumors and is activated by trypsin-like serine proteases that are highly expressed or otherwise dysregulated in many cancers. We highlight recent insights into the ability of different protease agonists to bias PAR-2 signaling and the newly emerging evidence for an interplay between PAR-2 and membrane-anchored serine proteases, which may co-conspire to promote tumor progression and metastasis. Interfering with these pathways might provide unique opportunities for the development of new mechanism-based strategies for the treatment of advanced and metastatic cancers.

Intestinal regulation of suppression of tumorigenicity 14 (ST14) and serine peptidase inhibitor, Kunitz type -1 (SPINT1) by transcription factor CDX2

The type II membrane-anchored serine protease, matriptase, encoded by suppression of tumorgenicity-14 (ST14) regulates the integrity of the intestinal epithelial barrier in concert with its inhibitor, HAI-1 encoded by serine peptidase inhibitor, Kunitz type -1 (SPINT1). The balance of the protease/inhibitor gene expression ratio is vital in preventing the oncogenic potential of matriptase. The intestinal cell lineage is regulated by a transcriptional regulatory network where the tumor suppressor, Caudal homeobox 2 (CDX2) is considered to be an intestinal master transcription factor. In this study, we show that CDX2 has a dual function in regulating both ST14 and SPINT1, gene expression in intestinal cells. We find that CDX2 is not required for the basal ST14 and SPINT1 gene expression; however changes in CDX2 expression affects the ST14/SPINT1 mRNA ratio. Exploring CDX2 ChIP-seq data from intestinal cell lines, we identified genomic CDX2-enriched enhancer elements for both ST14 and SPINT1, which regulate their corresponding gene promoter activity. We show that CDX2 displays both repressive and enhancing regulatory abilities in a cell specific manner. Together, these data reveal new insight into transcriptional mechanisms controlling the intestinal matriptase/inhibitor balance.

Fecal Microbiota Transplantation in Experimental Ulcerative Colitis Reveals Associated Gut Microbial and Host Metabolic Reprogramming

Fecal microbiota transplantation (FMT) is gaining attention for the treatment of ulcerative colitis (UC). Data from individual case studies have suggested that FMT may be beneficial for UC, but the detailed microbial and molecular basis remains unknown. Here, we employ 16S rRNA gene sequencing and metabolomics to investigate the influence of FMT on gut microbial community composition and host metabolism in the dextran sulfate sodium-induced UC rat model. The findings from this pilot study suggest that FMT from normal donors to UC recipients could alleviate UC symptoms without close resemblance of donor's gut microbial and metabolic pattern. Meanwhile, FMT from UC donors to normal recipient rats triggered UC symptoms, UC-prone microbial shift, and host metabolic adaption. Gut microbiota under normal conditions could maintain stable species richness and diversity upon FMT intervention, but the disturbed gut microbiota under UC conditions could not maintain such homeostasis. Significant correlations between altered bacterial composition and host metabolism could be assigned to the pathological effects of UC (accounting for 8.0 to 16.2% of total variance) and/or the FMT intervention effects (3.9 to 7.0% of total variance). Overall, our study reveals diverse gut microbial shifts in UC related FMT and their association with host metabolic reprogramming.IMPORTANCE This study combined clinical symptoms measurement, 16S rRNA gene microbial profiling and metabolomics to comprehensively investigate the gut bacterial and host metabolic association and reprogramming in FMT-treated experimental UC. These data can advance our understanding of the effect of FMT on UC and the involvement of gut microbial dysbiosis in the development of UC.

Membrane-Anchored Serine Proteases: Host Cell Factors in Proteolytic Activation of Viral Glycoproteins

Over one third of all known proteolytic enzymes are serine proteases. Among these, the trypsin-like serine proteases comprise one of the best characterized subfamilies due to their essential roles in blood coagulation, food digestion, fibrinolysis, or immunity. Trypsin-like serine proteases possess primary substrate specificity for basic amino acids. Most of the well-characterized trypsin-like proteases such as trypsin, plasmin, or urokinase are soluble proteases that are secreted into the extracellular environment. At the turn of the millennium, a number of novel trypsin-like serine proteases have been identified that are anchored in the cell membrane, either by a transmembrane domain at the N- or C-terminus or via a glycosylphosphatidylinositol (GPI) linkage. Meanwhile more than 20 membrane-anchored serine proteases (MASPs) have been identified in human and mouse, and some of them have emerged as key regulators of mammalian development and homeostasis. Thus, the MASP corin and TMPRSS6/matriptase-2 have been demonstrated to be the activators of the atrial natriuretic peptide (ANP) and key regulator of hepcidin expression, respectively. Furthermore, MASPs have been recognized as host cell factors activating respiratory viruses including influenza virus as well as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) coronaviruses. In particular, transmembrane protease serine S1 member 2 (TMPRSS2) has been shown to be essential for proteolytic activation and consequently spread and pathogenesis of a number of influenza A viruses in mice and as a factor associated with severe influenza virus infection in humans.

This review gives an overview on the physiological functions of the fascinating and rapidly evolving group of MASPs and a summary of the current knowledge on their role in proteolytic activation of viral fusion proteins.

Panax notoginseng Promotes Repair of Colonic Microvascular Injury in Sprague-Dawley Rats with Experimental Colitis

To investigate the therapeutic effects of PN on intestinal inflammation and microvascular injury and its mechanisms, dextran sodium sulfate- (DSS-) or iodoacetamide- (IA-) induced rat colitis models were used. After colitis model was established, PN was orally administered for 7 days at daily dosage of 1.0 g/kg. Obvious colonic inflammation and mucosal injuries and microvessels were observed in DSS- and IA-induced colitis groups. DAI scores, serum concentrations of VEGFA121, VEGFA165, VEGFA165/VEGFA121, IL-6, and TNF-α, and expression of Rap1GAP and TSP1 proteins in the colon were significantly higher while serum concentrations of IL-4 and IL-10 and MVD in colon were significantly lower in the colitis model groups than in the normal control group. PN promoted repair of colonic mucosal injury and microvessels, attenuated inflammation, and decreased DAI scores in rats with colitis. PN also decreased the serum concentrations of VEGFA121, VEGFA165, VEGFA165/VEGFA121, IL-6, and TNF-α and increased the serum concentrations of IL-4 and IL-10, with the expression of Rap1GAP and TSP1 proteins in colonic mucosa being downregulated. The constituents of PN were identified with HPLC-DAD. To sum up, PN could promote repair of injuries of colonic mucosa and microvessels via downregulating VEGFA isoforms and inhibiting Rap1GAP/TSP1 signaling pathway.

Type II transmembrane serine proteases as potential targets for cancer therapy

Carcinogenesis is accompanied by increased protein and activity levels of extracellular cell-surface proteases that are capable of modifying the tumor microenvironment by directly cleaving the extracellular matrix, as well as activating growth factors and proinflammatory mediators involved in proliferation and invasion of cancer cells, and recruitment of inflammatory cells. These complex processes ultimately potentiate neoplastic progression leading to local tumor cell invasion, entry into the vasculature, and metastasis to distal sites. Several members of the type II transmembrane serine protease (TTSP) family have been shown to play critical roles in cancer progression. In this review the knowledge collected over the past two decades about the molecular mechanisms underlying the pro-cancerous properties of selected TTSPs will be summarized. Furthermore, we will discuss how these insights may facilitate the translation into clinical settings in the future by specifically targeting TTSPs as part of novel cancer treatment regimens.

Signaling pathways induced by serine proteases to increase intestinal epithelial barrier function

Changes in barrier function of the gastrointestinal tract are thought to contribute to the inflammatory bowel diseases Crohn's disease and ulcerative colitis. Previous work in our lab demonstrated that apical exposure of intestinal epithelial cell lines to serine proteases results in an increase in transepithelial electrical resistance (TER). However, the underlying mechanisms governing this response are unclear. We aimed to determine the requirement for proteolytic activity, epidermal growth factor receptor (EGFR) activation, and downstream intracellular signaling in initiating and maintaining enhanced barrier function following protease treatment using a canine intestinal epithelial cell line (SCBN). We also examined the role of phosphorylation of myosin regulatory light chain on the serine protease-induced increase in TER through. It was found that proteolytic activity of the serine proteases trypsin and matriptase is required to initiate and maintain the protease-mediated increase in TER. We also show that MMP-independent EGFR activation is essential to the sustained phase of the protease response, and that Src kinases may mediate EGFR transactivation. PI3-K and ERK1/2 signaling were important in reaching a maximal increase in TER following protease stimulation; however, their upstream activators are yet to be determined. CK2 inhibition prevented the increase in TER induced by serine proteases. The bradykinin B(2) receptor was not involved in the change in TER in response to serine proteases, and no change in phosphorylation of MLC was observed after trypsin or matriptase treatment. Taken together, our data show a requirement for ongoing proteolytic activity, EGFR transactivation, as well as downstream PI3-K, ERK1/2, and CK2 signaling in protease-mediated barrier enhancement of intestinal epithelial cells. The pathways mediating enhanced barrier function by proteases may be novel therapeutic targets for intestinal disorders characterized by disrupted epithelial barrier function.

Matriptase zymogen supports epithelial development, homeostasis and regeneration

Background

Matriptase is a membrane serine protease essential for epithelial development, homeostasis, and regeneration, as well as a central orchestrator of pathogenic pericellular signaling in the context of inflammatory and proliferative diseases. Matriptase is an unusual protease in that its zymogen displays measurable enzymatic activity.

Results

Here, we used gain and loss of function genetics to investigate the possible biological functions of zymogen matriptase. Unexpectedly, transgenic mice mis-expressing a zymogen-locked version of matriptase in the epidermis displayed pathologies previously reported for transgenic mice mis-expressing wildtype epidermal matriptase. Equally surprising, mice engineered to express only zymogen-locked endogenous matriptase, unlike matriptase null mice, were viable, developed epithelial barrier function, and regenerated the injured epithelium. Compatible with these observations, wildtype and zymogen-locked matriptase were equipotent activators of PAR-2 inflammatory signaling.

Conclusion

The study demonstrates that the matriptase zymogen is biologically active and is capable of executing developmental and homeostatic functions of the protease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-017-0384-4) contains supplementary material, which is available to authorized users.

Inflammatory cytokines down-regulate the barrier-protective prostasin-matriptase proteolytic cascade early in experimental colitis

Compromised gastrointestinal barrier function is strongly associated with the progressive and destructive pathologies of the two main forms of irritable bowel disease (IBD), ulcerative colitis (UC), and Crohn's disease (CD). Matriptase is a membrane-anchored serine protease encoded by suppression of tumorigenicity-14 (ST14) gene, which is critical for epithelial barrier development and homeostasis. Matriptase barrier-protective activity is linked with the glycosylphosphatidylinositol (GPI)-anchored serine protease prostasin, which is a co-factor for matriptase zymogen activation. Here we show that mRNA and protein expression of both matriptase and prostasin are rapidly down-regulated in the initiating inflammatory phases of dextran sulfate sodium (DSS)-induced experimental colitis in mice, and, significantly, the loss of these proteases precedes the appearance of clinical symptoms, suggesting their loss may contribute to disease susceptibility. We used heterozygous St14 hypomorphic mice expressing a promoter-linked β-gal reporter to show that inflammatory colitis suppresses the activity of the St14 gene promoter. Studies in colonic T84 cell monolayers revealed that barrier disruption by the colitis-associated Th2-type cytokines, IL-4 and IL-13, down-regulates matriptase as well as prostasin through phosphorylation of the transcriptional regulator STAT6 and that inhibition of STAT6 with suberoylanilide hydroxamic acid (SAHA) restores protease expression and reverses cytokine-induced barrier dysfunction. Both matriptase and prostasin are significantly down-regulated in colonic tissues from human subjects with active ulcerative colitis or Crohn's disease, implicating the loss of this barrier-protective protease pathway in the pathogenesis of irritable bowel disease.

Regulation of intestinal permeability: The role of proteases

The gastrointestinal barrier is - with approximately 400 m² - the human body’s largest surface separating the external environment from the internal milieu. This barrier serves a dual function: permitting the absorption of nutrients, water and electrolytes on the one hand, while limiting host contact with noxious luminal antigens on the other hand. To maintain this selective barrier, junction protein complexes seal the intercellular space between adjacent epithelial cells and regulate the paracellular transport. Increased intestinal permeability is associated with and suggested as a player in the pathophysiology of various gastrointestinal and extra-intestinal diseases such as inflammatory bowel disease, celiac disease and type 1 diabetes. The gastrointestinal tract is exposed to high levels of endogenous and exogenous proteases, both in the lumen and in the mucosa. There is increasing evidence to suggest that a dysregulation of the protease/antiprotease balance in the gut contributes to epithelial damage and increased permeability. Excessive proteolysis leads to direct cleavage of intercellular junction proteins, or to opening of the junction proteins via activation of protease activated receptors. In addition, proteases regulate the activity and availability of cytokines and growth factors, which are also known modulators of intestinal permeability. This review aims at outlining the mechanisms by which proteases alter the intestinal permeability. More knowledge on the role of proteases in mucosal homeostasis and gastrointestinal barrier function will definitely contribute to the identification of new therapeutic targets for permeability-related diseases.

The Transmembrane Serine Protease HAT-like 4 Is Important for Epidermal Barrier Function to Prevent Body Fluid Loss

Membrane-bound proteases are essential for epidermal integrity. Human airway trypsin-like protease 4 (HAT-L4) is a type II transmembrane serine protease. Currently, its biochemical property, cellular distribution and physiological function remain unknown. Here we examined HAT-L4 expression and function in vitro and in vivo. In Western analysis, HAT-L4 expressed in transfected CHO cells appeared as a 48-kDa protein. Flow cytometry confirmed HAT-L4 expression on the cell surface with the expected membrane topology. RT-PCR and immunostaining experiments indicated that HAT-L4 was expressed in epithelial cells and exocrine glands in tissues including skin, esophagus, trachea, tongue, eye, bladder, testis and uterus. In the skin, HAT-L4 expression was abundant in keratinocytes and sebaceous glands. We generated HAT-L4 knockout mice by disrupting the Tmprss11f gene encoding HAT-L4. HAT-L4 knockout mice were viable and fertile. No defects were found in HAT-L4 knockout mice in hair growth, wound healing, water repulsion and body temperature regulation. Compared with wild-type controls, HAT-L4-deficient newborn mice had greater body fluid loss and higher mortality in a trans-epidermal body fluid loss test. In metabolic studies, HAT-L4-deficient adult mice drank water more frequently than wild-type controls did. These results indicate that HAT-L4 is important in epidermal barrier function to prevent body fluid loss.

Matriptase-mediated cleavage of EpCAM destabilizes claudins and dysregulates intestinal epithelial homeostasis

Congenital tufting enteropathy (CTE) is a severe autosomal recessive human diarrheal disorder with characteristic intestinal epithelial dysplasia. CTE can be caused by mutations in genes encoding EpCAM, a putative adhesion molecule, and HAI-2, a cell surface protease inhibitor. A similar phenotype occurs in mice whose intestinal epithelial cells (IECs) fail to express the tight junction-associated protein claudin-7. EpCAM stabilizes claudin-7 in IECs, and HAI-2 regulates the cell surface serine protease matriptase, a known modifier of intestinal epithelial physiology. Therefore, we hypothesized that HAI-2, matriptase, EpCAM, and claudin-7 were functionally linked. Herein we have demonstrated that active matriptase cleaves EpCAM after Arg80 and that loss of HAI-2 in IECs led to unrestrained matriptase activity and efficient cleavage of EpCAM. Cleavage of EpCAM decreased its ability to associate with claudin-7 and targeted it for internalization and lysosomal degradation in conjunction with claudin-7. CTE-associated HAI-2 mutant proteins exhibited reduced ability to inhibit matriptase and also failed to efficiently stabilize claudin-7 in IECs. These results identify EpCAM as a substrate of matriptase and link HAI-2, matriptase, EpCAM, and claudin-7 in a functionally important pathway that causes disease when it is dysregulated.

Altered Prostasin (CAP1/Prss8) Expression Favors Inflammation and Tissue Remodeling in DSS-induced Colitis

BACKGROUND

Inflammatory bowel diseases (IBD) including ulcerative colitis and Crohn's disease are diseases with impaired epithelial barrier function. We aimed to investigate whether mutated prostasin and thus, reduced colonic epithelial sodium channel activity predisposes to develop an experimentally dextran sodium sulfate (DSS)-induced colitis.

METHODS

Wildtype, heterozygous (fr/+), and homozygous (fr/fr) prostasin-mutant rats were treated 7 days with DSS followed by 7 days of recovery and analyzed with respect to histology, clinicopathological parameters, inflammatory marker mRNA transcript expression, and sodium transporter protein expression.

RESULTS

In this study, a more detailed analysis on rat fr/fr colons revealed reduced numbers of crypt and goblet cells, and local angiodysplasia, as compared with heterozygous (fr/+) and wildtype littermates. Following 2% DSS treatment for 7 days followed by 7 days recovery, fr/fr animals lost body weight, and reached maximal diarrhea score and highest disease activity after only 3 days, and strongly increased cytokine levels. The histology score significantly increased in all groups, but fr/fr colons further displayed pronounced histological alterations with near absence of goblet cells, rearrangement of the lamina propria, and presence of neutrophils, eosinophils, and macrophages. Additionally, fr/fr colons showed ulcerations and edemas that were absent in fr/+ and wildtype littermates. Following recovery, fr/fr rats reached, although significantly delayed, near-normal diarrhea score and disease activity, but exhibited severe architectural remodeling, despite unchanged sodium transporter protein expression.

CONCLUSIONS

In summary, our results demonstrate a protective role of colonic prostasin expression against experimental colitis, and thus represent a susceptibility gene in the development of inflammatory bowel disease.

The serine protease-mediated increase in intestinal epithelial barrier function is dependent on occludin and requires an intact tight junction

Barrier dysfunction is a characteristic of the inflammatory bowel diseases (IBD), Crohn's disease and ulcerative colitis. Understanding how the tight junction is modified to maintain barrier function may provide avenues for treatment of IBD. We have previously shown that the apical addition of serine proteases to intestinal epithelial cell lines causes a rapid and sustained increase in transepithelial electrical resistance (TER), but the mechanisms are unknown. We hypothesized that serine proteases increase barrier function through trafficking and insertion of tight junction proteins into the membrane, and this could enhance recovery of a disrupted monolayer after calcium switch or cytokine treatment. In the canine epithelial cell line, SCBN, we showed that matriptase, an endogenous serine protease, could potently increase TER. Using detergent solubility-based cell fractionation, we found that neither trypsin nor matriptase treatment changed levels of tight junction proteins at the membrane. In a fast calcium switch assay, serine proteases did not enhance the rate of recovery of the junction. In addition, serine proteases could not reverse barrier disruption induced by IFNγ and TNFα. We knocked down occludin in our cells using siRNA and found this prevented the serine protease-induced increase in TER. Using fluorescence recovery after photobleaching (FRAP), we found serine proteases induce a greater mobile fraction of occludin in the membrane. These data suggest that a functional tight junction is needed for serine proteases to have an effect on TER, and that occludin is a crucial tight junction protein in this mechanism.

Protease inhibition as new therapeutic strategy for GI diseases

The GI tract is the most exposed organ to proteases, both in physiological and pathophysiological conditions. For digestive purposes, the lumen of the upper GI tract contains large amounts of pancreatic proteases, but studies have also demonstrated increased proteolytic activity into mucosal tissues (both in the upper and lower GI tract), associated with pathological conditions. This review aims at outlining the evidences for dysregulated proteolytic homeostasis in GI diseases and the pathogenic mechanisms of increased proteolytic activity. The therapeutic potential of protease inhibition in GI diseases is discussed, with a particular focus on IBDs, functional GI disorders and colorectal cancer.

Pathophysiological roles of proteases in gastrointestinal disease

Gastrointestinal diseases, such as irritable bowel syndrome, inflammatory bowel disease, and colorectal cancer, affect a large proportion of the population and are associated with many unpleasant symptoms. Although the causes of these diseases remain largely unknown, there is increasing evidence to suggest that dysregulated protease activity may be a contributing factor. Proteases are enzymes that cleave other proteins, and their activity is normally very tightly regulated. During disease, however, the balance between proteases and their inhibitors is often shifted, leading to altered spatial and temporal control of substrate cleavage. Evaluating protease levels in normal physiology and disease has relied heavily on the use of chemical tools. Although these tools have greatly advanced the field, they are not without caveats. This review provides an introduction to these tools, their application in the gut, and a summary of the current knowledge on the contribution of protease activity to gastrointestinal disease.

Extracellular: Plasma Membrane Proteases – Serine Proteases

Membrane-anchored serine proteases are a group of extracellular serine proteases tethered directly to plasma membranes, via a C-terminal glycosylphosphatidylinositol linkage (GPI-anchored), a C-terminal transmembrane domain (Type I), or an N-terminal transmembrane domain (Type II). A variety of biochemical, cellular, and in vivo studies have established that these proteases are important pericellular contributors to processes vital for the maintenance of homeostasis, including food digestion, blood pressure regulation, hearing, epithelial permeability, sperm maturation, and iron homeostasis. These enzymes are hijacked by viruses to facilitate infection and propagation, and their misregulation is associated with a wide range of diseases, including cancer malignancy.

Reinforced Epithelial Barrier Integrity via Matriptase Induction with Sphingosine-1-Phosphate Did Not Result in Disturbances in Physiological Redox Status

Objectives. The relationship among matriptase function, cellular redox status, and maintenance of intestinal barrier integrity has not been established yet. The aim of this study is to reveal if the crosstalk between matriptase activators and intestinal epithelial monolayers can lead to perturbations in physiological redox regulation in vitro. Methods. The effects of suramin and sphingosine-1-phosphate (S1P) were tested on viability of intestinal porcine epithelial IPEC-J2 cells using MTS assay. Measurements of transepithelial electrical resistance (TER) were performed to determine changes in barrier integrity of cell monolayers. Amplex Red assay was used to monitor extracellular hydrogen peroxide production. Occludin distribution pattern was detected prior to and after matriptase activation using immunofluorescent staining technique. Results. TER reduction was observed in suramin-treated IPEC-J2 cell monolayers, which could be attributed to cell cytotoxic properties of 48 hr 50 μM suramin administration. In contrast, S1P treatment increased TER significantly and elevated occludin accumulation in tight junctions. It was also found that extracellular hydrogen peroxide levels were maintained in IPEC-J2 cells exposed to matriptase activators. Discussion. S1P administration not accompanied by redox imbalance might be one of the key strategies in the improvement of barrier function and consequently in the therapy of intestinal inflammations.

Inhibition of Matriptase Activity Results in Decreased Intestinal Epithelial Monolayer Integrity In Vitro

Barrier dysfunction in inflammatory bowel diseases implies enhanced paracellular flux and lowered transepithelial electrical resistance (TER) causing effective invasion of enteropathogens or altered intestinal absorption of toxins and drug compounds. To elucidate the role of matriptase-driven cell surface proteolysis in the maintenance of intestinal barrier function, the 3-amidinophenylalanine-derived matriptase inhibitor, MI-432 was used on porcine IPEC-J2 cell monolayer. Studies with two fluorescent probes revealed that short (2 h) treatment with MI-432 caused an altered distribution of oxidative species between intracellular and extracellular spaces in IPEC-J2 cells. This perturbation was partially compensated when administration of inhibitor continued for up to 48 h. Significant decrease in TER between apical and basolateral compartments of MI-432-treated IPEC-J2 cell monolayers proved that matriptase is one of the key effectors in the maintenance of barrier integrity. Changes in staining pattern of matriptase and in localization of the junctional protein occludin were observed suggesting that inhibition of matriptase by MI-432 can also exert an effect on paracellular gate opening via modulation of tight junctional protein assembly. This study confirms that non-tumorigenic IPEC-J2 cells can be used as an appropriate small intestinal model for the in vitro characterization of matriptase-related effects on intestinal epithelium. These findings demonstrate indirectly that matriptase plays a pivotal role in the development of barrier integrity; thus matriptase dysfunction can facilitate the occurence of leaky gut syndrome observed in intestinal inflammatory diseases.

Divergent Inhibitor Susceptibility among Airway Lumen-Accessible Tryptic Proteases

Tryptic serine proteases of bronchial epithelium regulate ion flux, barrier integrity, and allergic inflammation. Inhibition of some of these proteases is a strategy to improve mucociliary function in cystic fibrosis and asthmatic inflammation. Several inhibitors have been tested in pre-clinical animal models and humans. We hypothesized that these inhibitors inactivate a variety of airway protease targets, potentially with bystander effects. To establish relative potencies and modes of action, we compared inactivation of human prostasin, matriptase, airway trypsin-like protease (HAT), and β-tryptase by nafamostat, camostat, bis(5-amidino-2-benzimidazolyl)methane (BABIM), aprotinin, and benzamidine. Nafamostat achieved complete, nearly stoichiometric and very slowly reversible inhibition of matriptase and tryptase, but inhibited prostasin less potently and was weakest versus HAT. The IC₅₀ of nafamostat’s leaving group, 6-amidino-2-naphthol, was >10⁴-fold higher than that of nafamostat itself, consistent with suicide rather than product inhibition as mechanisms of prolonged inactivation. Stoichiometric release of 6-amidino-2-naphthol allowed highly sensitive fluorometric estimation of active-site concentration in preparations of matriptase and tryptase. Camostat inactivated all enzymes but was less potent overall and weakest towards matriptase, which, however was strongly inhibited by BABIM. Aprotinin exhibited nearly stoichiometric inhibition of prostasin and matriptase, but was much weaker towards HAT and was completely ineffective versus tryptase. Benzamidine was universally weak. Thus, each inhibitor profile was distinct. Nafamostat, camostat and aprotinin markedly reduced tryptic activity on the apical surface of cystic fibrosis airway epithelial monolayers, suggesting prostasin as the major source of such activity and supporting strategies targeting prostasin for inactivation.

Targeting matriptase in breast cancer abrogates tumour progression via impairment of stromal-epithelial growth factor signalling

Matriptase is an epithelia-specific membrane-anchored serine protease that has received considerable attention in recent years due to its consistent dysregulation in human epithelial tumors, including breast cancer. Mice with reduced levels of matriptase display a significant delay in oncogene-induced mammary tumor formation and blunted tumor growth. The abated tumor growth is associated with a decrease in cancer cell proliferation. Here we demonstrate by genetic deletion and silencing that the proliferation impairment in matriptase deficient breast cancer cells is caused by their inability to initiate activation of the c-Met signaling pathway in response to fibroblast-secreted pro-HGF. Similarly, inhibition of matriptase catalytic activity using a selective small-molecule inhibitor abrogates the activation of c-Met, Gab1 and AKT, in response to pro-HGF, which functionally leads to attenuated proliferation in breast carcinoma cells. We conclude that matriptase is critically involved in breast cancer progression and represents a potential therapeutic target in breast cancer.

Regulation of Trek1 expression in nasal mucosa with allergic rhinitis by specific immunotherapy

Epithelial barrier dysfunction is involved in the pathogenesis of allergic disorders, such as nasal allergy. TWIK-related K(+) 1 (Trek1) potassium channels are required in the maintenance of the epithelial barrier function. This study aims to investigate the role of antigen-specific immunotherapy (SIT) in the regulation of Trek1 expression in the nasal mucosa. In this study, patients with nasal allergy were treated with SIT and/or Clostridium butyricum. The expression of Trek1 and histone demethylase 1 (HDAC1) in the nasal epithelia was assessed by real-time reverse transcription polymerase chain reaction and Western blotting. Serum cytokines were assessed by enzyme-linked immunosorbent assay. The results showed that Trek1 and HDAC1 were detected in the nasal epithelia. Trek1 was lower, whereas HDAC1 was higher in patients with allergic rhinitis as compared with healthy controls. Trek1-null RPMI2650 monolayers showed a markedly compromised epithelial barrier function. Treatment with SIT significantly increased the Trek1 levels in the nasal epithelia of allergic rhinitis patients that were further improved in conjunction of SIT and administration of probiotic C. butyricum. In conclusion, nasal epithelia express Trek1 that can be suppressed by allergic response. SIT can restore the expression of Trek1 in the nasal epithelia and can be further improved by conjunction with administration of C. butyricum.

The in vivo and in vitro study of polysaccharides from a two-herb formula on ulcerative colitis and potential mechanism of action

ETHNOPHARMACOLOGICAL RELEVANCE

Lycium barbarum and Astragalus membranaceus are two traditional medicinal herbs widely used in China for nourishing Yin and reinforcing Qi. The purpose of the study was to investigate the prophylactic and curative effects of crude polysaccharides (QHPS) extracted from a two-herb formula composed of Lycium barbarum and Astragalus membranaceus at a ratio of 2:3 in colitis rats, and to further elucidate the potential mechanism of action in epithelial cell proliferation in vitro.

MATERIALS AND METHODS

An acetic acid (AA)-induced ulcerative colitis rat model was applied in the study. Two independent protocols were used to assess the prophylactic and curative effects of QHPS, respectively, in which rats were either pre-treated with QHPS (0.18g/kg) for 14 days prior to AA induction, or post-treated with QHPS for 7 days after AA induction. The stool consistency and weight loss were used to evaluate disease activity. The morphological changes in intestinal mucosa at the end of the experiments were observed. The serum levels of endotoxin (EDT), diamine oxidase (DAO) and d-lactate (DLA), important biochemical markers for evaluating intestinal mucosal structure and function, were measured. In the in vitro mechanistic studies, rat intestinal epithelial cells (IEC-6) were used to access for epithelium regeneration.

RESULTS

The intra-colonic instillation of AA induced ulcerative colitis in rat, as indicated by diarrhea, weight loss, and colonic mucosal damage. Both prophylactic and curative treatments effectively reduced the weight loss and diarrhea and attenuated the colonic mucosal damage associated with inducible colitis. The significant increase in serum levels of DAO, DLA and EDT was induced by AA and inhibited by QHPS treatment. Moreover, QHPS could significantly stimulate IEC-6 proliferation in a dose-dependent manner (p<0.05).

CONCLUSION

The present study indicated for the first time that polysaccharides extracted from this two-herb formula can protect against experimental ulcerative colitis, presumably by promoting the recovery of the intestinal barrier.

Proteases and small intestinal barrier function in health and disease

PURPOSE OF REVIEW

To summarize the recent knowledge regarding intestinal proteases and the gut barrier.

RECENT FINDINGS

It is now well established that intestinal proteases, such as matrix metalloproteinase (MMP)-1, MMP-3, MMP-10 and MMP-12, are key players in the development of ulcers in inflammatory bowel disease, have direct effects on epithelial barrier function and are involved in epithelial restitution. However, more recent work has suggested that the membrane-anchored epithelial cell serine protease matriptase is critical in maintaining the gut barrier, and roles have also been described for elastase, MMP-13, gelatinases, mast cell proteases and proteases derived from parasites and gut bacteria. Interestingly, epithelial proteases often co-localize with epithelial adherens junctions, and nonepithelial-derived proteases have junctional proteins as targets.

SUMMARY

The role of proteases in controlling normal barrier function in the gut is now becoming very clear, to go alongside their role in intestinal inflammation.

Discovery of Pyridyl Bis(oxy)dibenzimidamide Derivatives as Selective Matriptase Inhibitors

Matriptase belongs to trypsin-like serine proteases involved in matrix remodeling/degradation, growth regulation, survival, motility, and cell morphogenesis. Herein, we report a structure-based approach, which led to the discovery of sulfonamide and amide derivatives of pyridyl bis(oxy)benzamidine as potent and selective matriptase inhibitors. Co-crystal structures of selected compounds in complex with matriptase supported compound designing. Additionally, WaterMap analyses indicated the possibility of occupying a distinct pocket within the catalytic domain, exploration of which resulted in >100-fold improvement in potency. Co-crystal structure of 10 with matriptase revealed critical interactions leading to potent target inhibition and selectivity against other serine proteases.

Claudins in intestines: Distribution and functional significance in health and diseases

Intestines are organs that not only digest food and absorb nutrients, but also provide a defense barrier against pathogens and noxious agents ingested. Tight junctions (TJs) are the most apical component of the junctional complex, providing one form of cell-cell adhesion in enterocytes and playing a critical role in regulating paracellular barrier permeability. Alteration of TJs leads to a number of pathophysiological diseases causing malabsorption of nutrition and intestinal structure disruption, which may even contribute to systemic organ failure. Claudins are the major structural and functional components of TJs with at least 24 members in mammals. Claudins have distinct charge-selectivity, either by tightening the paracellular pathway or functioning as paracellular channels, regulating ions and small molecules passing through the paracellular pathway. In this review, we have discussed the functions of claudin family members, their distribution and localization in the intestinal tract of mammals, their alterations in intestine-related diseases and chemicals/agents that regulate the expression and localization of claudins as well as the intestinal permeability, which provide a therapeutic view for treating intestinal diseases.

Hepatocyte growth factor activator inhibitor type 1 is a suppressor of intestinal tumorigenesis

Hepatocyte growth factor activator inhibitor type 1 (HAI-1/SPINT1) is a membrane-bound serine protease inhibitor expressed on the surface of epithelial cells. Although HAI-1/SPINT1 is abundantly expressed in the intestinal epithelium, its role in intestinal tumorigenesis is not known. In this study, we investigated the role of Hai-1/Spint1 in intestinal tumorigenesis using mouse models. The membranous Hai-1/Spint1 immunoreactivity was decreased in murine Apc(Min/+) tumors and also in carcinogen (azoxymethane treatment followed by dextran sodium sulfate administration)-induced colon tumors compared with the adjacent non-neoplastic epithelium. The decreased immunoreactivity appeared to be due to sheddase activity of membrane-type 1 matrix metalloprotease. Then, we examined the effect of intestine-specific deletion of Spint1 gene on Apc(Min/+) mice. The loss of Hai-1/Spint1 significantly accelerated tumor formation in Apc(Min/+) mice and shortened their survival periods. Activation of HGF was enhanced in Hai-1/Spint1-deficient Apc(Min/+) intestine. Gene expression profiling revealed upregulation of the Wnt/β-catenin signaling circuit, claudin-2 expression, and angiogenesis not only in tumor tissue but also in the background mucosa without macroscopic tumors in Hai-1/Spint1-deficient Apc(Min/+) intestine. Intestinal deletion of Spint1 also enhanced the susceptibility to carcinogen-induced colon tumorigenicity of wild-type Apc mice. Our findings suggest that HAI-1/SPINT1 has a crucial role in suppressing intestinal tumorigenesis, which implies a novel link between epithelial cell surface serine protease inhibitors and protection from carcinogenic stimuli.

Prostasin is required for matriptase activation in intestinal epithelial cells to regulate closure of the paracellular pathway

The type II transmembrane serine protease matriptase is a key regulator of epithelial barriers in skin and intestine. In skin, matriptase acts upstream of the glycosylphosphatidylinositol-anchored serine protease, prostasin, to activate the prostasin zymogen and initiate a proteolytic cascade that is required for stratum corneum barrier functionality. Here, we have investigated the relationship between prostasin and matriptase in intestinal epithelial barrier function. We find that similar to skin, matriptase and prostasin are components of a common intestinal epithelial barrier-forming pathway. Depletion of prostasin by siRNA silencing in Caco-2 intestinal epithelium inhibits barrier development similar to loss of matriptase, and the addition of recombinant prostasin to the basal side of polarized Caco-2 epithelium stimulates barrier forming changes similar to the addition of recombinant matriptase. However, in contrast to the proteolytic cascade in skin, prostasin functions upstream of matriptase to activate the endogenous matriptase zymogen. Prostasin is unable to proteolytically activate the matriptase zymogen directly but induces matriptase activation indirectly. Prostasin requires expression of endogenous matriptase to stimulate barrier formation since matriptase depletion by siRNA silencing abrogates prostasin barrier-forming activity. Active recombinant matriptase, however, does not require the expression of endogenous prostasin for barrier-forming activity. Together, these data show that matriptase and not prostasin is the primary effector protease of tight junction assembly in simple columnar epithelia and further highlight a spatial and tissue-specific aspect of cell surface proteolytic cascades.

Design and synthesis of potent, selective inhibitors of matriptase

Matriptase is a member of the type II transmembrane serine protease family. Several studies have reported deregulated matriptase expression in several types of epithelial cancers, suggesting that matriptase constitutes a potential target for cancer therapy. We report herein a new series of slow, tight-binding inhibitors of matriptase, which mimic the P1-P4 substrate recognition sequence of the enzyme. Preliminary structure-activity relationships indicate that this benzothiazole-containing RQAR-peptidomimetic is a very potent inhibitor and possesses a good selectivity for matriptase versus other serine proteases. A molecular model was generated to elucidate the key contacts between inhibitor 1 and matriptase.