Denatured human alpha-defensin attenuates the bactericidal activity and the stability against enzymatic digestion

HNP-1: From Structure to Application Thanks to Multifaceted Functions

Antimicrobial peptides (AMPs) are critical components of innate immunity in animals and plants, exhibiting thrilling prospectives as alternatives to traditional antibiotics due to their ability to combat pathogens without leading to resistance. Among these, Human Neutrophil Peptide-1 (HNP-1), primarily produced by human neutrophils, exhibits broad-spectrum antimicrobial activity against bacteria and viruses. However, the clinical application of HNP-1 has been hampered by challenges associated with mass production and inconsistent understanding of its bactericidal mechanisms. This review explores the structure and function of HNP-1, discussing its gene expression, distribution, immune functions and the regulatory elements controlling its production, alongside insights into its antimicrobial mechanisms and potential clinical applications as an antimicrobial agent. Furthermore, the review highlights the biosynthesis of HNP-1 using microbial systems as a cost-effective alternative to human extraction and recent studies revealing HNP-1's endogenous bactericidal mechanism. A comprehensive understanding of HNP-1's working mechanisms and production methods will pave the way for its effective clinical utilization in combating antibiotic-resistant infections.

Shorter sleep time relates to lower human defensin 5 secretion and compositional disturbance of the intestinal microbiota accompanied by decreased short-chain fatty acid production

Sleep is essential for our health. Short sleep is known to increase disease risks via imbalance of intestinal microbiota, dysbiosis. However, mechanisms by which short sleep induces dysbiosis remain unknown. Small intestinal Paneth cell regulates the intestinal microbiota by secreting antimicrobial peptides including α-defensin, human defensin 5 (HD5). Disruption of circadian rhythm mediating sleep-wake cycle induces Paneth cell failure. We aim to clarify effects of short sleep on HD5 secretion and the intestinal microbiota. Fecal samples and self-reported sleep time were obtained from 35 healthy middle-aged Japanese (41 to 60-year-old). Shorter sleep time was associated with lower fecal HD5 concentration (r = 0.354, p = 0.037), lower centered log ratio (CLR)-transformed abundance of short-chain fatty acid (SCFA) producers in the intestinal microbiota such as [Ruminococcus] gnavus group (r = 0.504, p = 0.002) and Butyricicoccus (r = 0.484, p = 0.003), and lower fecal SCFA concentration. Furthermore, fecal HD5 positively correlated with the abundance of these genera and SCFA concentration. These findings suggest that short sleep relates to disturbance of the intestinal microbiota via decreased HD5 secretion.

Paneth cells as the cornerstones of intestinal and organismal health: a primer

Paneth cells are versatile secretory cells located in the crypts of Lieberkühn of the small intestine. In normal conditions, they function as the cornerstones of intestinal health by preserving homeostasis. They perform this function by providing niche factors to the intestinal stem cell compartment, regulating the composition of the microbiome through the production and secretion of antimicrobial peptides, performing phagocytosis and efferocytosis, taking up heavy metals, and preserving barrier integrity. Disturbances in one or more of these functions can lead to intestinal as well as systemic inflammatory and infectious diseases. This review discusses the multiple functions of Paneth cells, and the mechanisms and consequences of Paneth cell dysfunction. It also provides an overview of the tools available for studying Paneth cells.

Antimicrobial peptide production in response to gut microbiota imbalance

The gut microbiota presents essential functions in the immune response. The gut epithelium acts as a protective barrier and, therefore, can produce several antimicrobial peptides (AMPs) that can act against pathogenic microorganisms, including bacteria. Several factors cause a disturbance in gut microbiota, including the exacerbated and erroneous use of antibiotics. Antibiotic therapy has been closely related to bacterial resistance and is also correlated with undesired side-effects to the host, including the eradication of commensal bacteria. Consequently, this results in gut microbiota imbalance and inflammatory bowel diseases (IBD) development. In this context, AMPs in the gut epithelium play a restructuring role for gut microbiota. Some naturally occurring AMPs are selective for pathogenic bacteria, thus preserving the health microbiota. Therefore, AMPs produced by the host's epithelial cells represent effective molecules in treating gut bacterial infections. Bearing this in mind, this review focused on describing the importance of the host's AMPs in gut microbiota modulation and their role as anti-infective agents against pathogenic bacteria.

Exploring the impact of the recombinant Escherichia coli strain on defensins antimicrobial activity: BL21 versus Origami strain

The growing emergence of microorganisms resistant to antibiotics has prompted the development of alternative antimicrobial therapies. Among them, the antimicrobial peptides produced by innate immunity, which are also known as host defense peptides (HDPs), hold great potential. They have been shown to exert activity against both Gram-positive and Gram-negative bacteria, including those resistant to antibiotics. These HDPs are classified into three categories: defensins, cathelicidins, and histatins. Traditionally, HDPs have been chemically synthesized, but this strategy often limits their application due to the high associated production costs. Alternatively, some HDPs have been recombinantly produced, but little is known about the impact of the bacterial strain in the recombinant product. This work aimed to assess the influence of the Escherichia coli strain used as cell factory to determine the activity and stability of recombinant defensins, which have 3 disulfide bonds. For that, an α-defensin [human α-defensin 5 (HD5)] and a β-defensin [bovine lingual antimicrobial peptide (LAP)] were produced in two recombinant backgrounds. The first one was an E. coli BL21 strain, which has a reducing cytoplasm, whereas the second was an E. coli Origami B, that is a strain with a more oxidizing cytoplasm. The results showed that both HD5 and LAP, fused to Green Fluorescent Protein (GFP), were successfully produced in both BL21 and Origami B strains. However, differences were observed in the HDP production yield and bactericidal activity, especially for the HD5-based protein. The HD5 protein fused to GFP was not only produced at higher yields in the E. coli BL21 strain, but it also showed a higher quality and stability than that produced in the Origami B strain. Hence, this data showed that the strain had a clear impact on both HDPs quantity and quality.

Structure-activity trend analysis between amino-acids and minimal inhibitory concentration of antimicrobial peptides

Antimicrobial peptides (AMPs) provide large structural libraries of molecules with high variability of constitutional amino-acids (AAs). Highlighting structural organization and structure-activity trends in such molecular systems provide key information on structural associations and functional conditions that could usefully help for drug design. This work presents link analyses between minimal inhibitory concentration (MIC) and different types of constitutional AAs of anti-Pseudomonas aeruginosa AMPs. This scope was based on a dataset of 328 published molecules. Regulation levels of AAs in AMPs were statistically ordinated by correspondence analysis helping for classification of the 328 AMPs into nine structurally homogeneous peptide clusters (PCs 1-9) characterized by high/low relative occurrences of different AAs. Within each PC, negative trends between MIC and AAs were highlighted by iterated multiple linear regression models built by bootstrap processes (bagging). MIC-decrease was linked to different AAs that varied with PCs: alcohol type AAs (Thr, Ser) in Cys-rich and low Arg PCs (PCs 1-3); basic AAs (Lys, Arg) in Pro-rich and low Val PCs (PCs 4-8); Trp (heterocyclic AA) in Arg-rich PCs (PCs 6, 7, 9). Aliphatic AAs (more particularly Gly) showed MIC-reduction effects in different PCs essentially under interactive forms.

Location is important: differentiation between ileal and colonic Crohn's disease

Crohn's disease can affect any part of the gastrointestinal tract; however, current European and national guidelines worldwide do not differentiate between small-intestinal and colonic Crohn's disease for medical treatment. Data from the past decade provide evidence that ileal Crohn's disease is distinct from colonic Crohn's disease in several intestinal layers. Remarkably, colonic Crohn's disease shows an overlap with regard to disease behaviour with ulcerative colitis, underlining the fact that there is more to inflammatory bowel disease than just Crohn's disease and ulcerative colitis, and that subtypes, possibly defined by location and shared pathophysiology, are also important. This Review provides a structured overview of the differentiation between ileal and colonic Crohn's disease using data in the context of epidemiology, genetics, macroscopic differences such as creeping fat and histological findings, as well as differences in regard to the intestinal barrier including gut microbiota, mucus layer, epithelial cells and infiltrating immune cell populations. We also discuss the translation of these basic findings to the clinic, emphasizing the important role of treatment decisions. Thus, this Review provides a conceptual outlook on a new mechanism-driven classification of Crohn's disease.

Paneth cell α-defensin misfolding correlates with dysbiosis and ileitis in Crohn's disease model mice

This study provides novel insight into Crohn’s disease where α-defensin misfolding resulting from excessive ER stress in Paneth cells induces dysbiosis and disease progression.

Crohn’s disease (CD) is an intractable inflammatory bowel disease, and dysbiosis, disruption of the intestinal microbiota, is associated with CD pathophysiology. ER stress, disruption of ER homeostasis in Paneth cells of the small intestine, and α-defensin misfolding have been reported in CD patients. Because α-defensins regulate the composition of the intestinal microbiota, their misfolding may cause dysbiosis. However, whether ER stress, α-defensin misfolding, and dysbiosis contribute to the pathophysiology of CD remains unknown. Here, we show that abnormal Paneth cells with markers of ER stress appear in SAMP1/YitFc, a mouse model of CD, along with disease progression. Those mice secrete reduced-form α-defensins that lack disulfide bonds into the intestinal lumen, a condition not found in normal mice, and reduced-form α-defensins correlate with dysbiosis during disease progression. Moreover, administration of reduced-form α-defensins to wild-type mice induces the dysbiosis. These data provide novel insights into CD pathogenesis induced by dysbiosis resulting from Paneth cell α-defensin misfolding and they suggest further that Paneth cells may be potential therapeutic targets.

Microbiota and mucosal defense in IBD: an update

Introduction: Inflammatory bowel diseases (IBD) are on the rise worldwide. This review covers the current concepts of the etiology of Crohn´s disease and ulcerative colitis by focusing on an unbalanced interaction between the intestinal microbiota and the mucosal barrier. Understanding these issues is of paramount importance for the development of targeted therapies aiming at the disease cause.Area covered: Gut microbiota alterations and a dysfunctional intestinal mucosa are associated with IBD. Here we focus on specific defense structures of the mucosal barrier, namely antimicrobial peptides and the mucus layer, which keep the gut microbiota at a distance under healthy conditions and are defective in IBD.Expert commentary: The microbiology of both forms of IBD is different but characterized by a reduced bacterial diversity and richness. Abundance of certain bacterial species is altered, and the compositional changes are related to disease activity. In IBD the mucus layer above the epithelium is contaminated by bacteria and the immune reaction is dominated by the antibacterial response. Human genetics suggest that many of the basic deficiencies in the mucosal response, due to Paneth cell, defensin and mucus defects, are primary. Nutrition may also be important but so far there is no therapy targeting the mucosal barrier.

ACPred: A Computational Tool for the Prediction and Analysis of Anticancer Peptides

Anticancer peptides (ACPs) have emerged as a new class of therapeutic agent for cancer treatment due to their lower toxicity as well as greater efficacy, selectivity and specificity when compared to conventional small molecule drugs. However, the experimental identification of ACPs still remains a time-consuming and expensive endeavor. Therefore, it is desirable to develop and improve upon existing computational models for predicting and characterizing ACPs. In this study, we present a bioinformatics tool called the ACPred, which is an interpretable tool for the prediction and characterization of the anticancer activities of peptides. ACPred was developed by utilizing powerful machine learning models (support vector machine and random forest) and various classes of peptide features. It was observed by a jackknife cross-validation test that ACPred can achieve an overall accuracy of 95.61% in identifying ACPs. In addition, analysis revealed the following distinguishing characteristics that ACPs possess: (i) hydrophobic residue enhances the cationic properties of α-helical ACPs resulting in better cell penetration; (ii) the amphipathic nature of the α-helical structure plays a crucial role in its mechanism of cytotoxicity; and (iii) the formation of disulfide bridges on β-sheets is vital for structural maintenance which correlates with its ability to kill cancer cells. Finally, for the convenience of experimental scientists, the ACPred web server was established and made freely available online.

Different dynamics and pathway of disulfide bonds reduction of two human defensins, a molecular dynamics simulation study

Human defensins are a class of antimicrobial peptides that are crucial components of the innate immune system. Both human α defensin type 5 (HD5) and human β defensin type 3 (hBD-3) have 6 cysteine residues which form 3 pairs of disulfide bonds in oxidizing condition. Disulfide bond linking is important to the protein structure stabilization, and the disulfide bond linking and breaking order have been shown to influence protein function. In this project, microsecond long molecular dynamics simulations were performed to study the structure and dynamics of HD5 and hBD-3 wildtype and analogs which have all 3 disulfide bonds released in reducing condition. The structure of hBD-3 was found to be more dynamic and flexible than HD5, based on RMSD, RMSF, and radius of gyration calculations. The disulfide bridge breaking order of HD5 and hBD-3 in reducing condition was predicted by two kinds of methods, which gave consistent results. It was found that the disulfide bonds breaking pathways for HD5 and hBD-3 are very different. The breaking of disulfide bonds can influence the dimer interface by making the dimer structure less stable for both kinds of defensin. In order to understand the difference in dynamics and disulfide bond breaking pathway, hydrophilic and hydrophobic accessible surface areas (ASA), buried surface area between cysteine pairs, entropy of cysteine pairs, and internal energy were calculated. Comparing to the wildtype, hBD-3 analog is more hydrophobic, while HD5 is more hydrophilic. For hBD-3, the disulfide breaking is mainly entropy driven, while other factors such as the solvation effects may take the major role in controlling HD5 disulfide breaking pathway. Proteins 2017; 85:665-681. © 2016 Wiley Periodicals, Inc.

Paneth cell α-defensins and enteric microbiota in health and disease

Antimicrobial peptides are major effectors of innate immunity of multicellular organisms including humans and play a critical role in host defense, and their importance is widely recognized. The epithelium of the intestine is the largest surface area exposed to the outer environment, including pathogens, toxins and foods. The Paneth cell lineage of intestinal epithelial cells produces and secretes α-defensin antimicrobial peptides and functions in innate enteric immunity by removing pathogens and living symbiotically with commensal microbiota to contribute to intestinal homeostasis. Paneth cells secrete α-defensins, HD5 and HD6 in humans and cryptdins in mice, in response to bacterial, cholinergic and other stimuli. The α-defensins have selective activities against bacteria, eliciting potent microbicidal activities against pathogenic bacteria but minimal or no bactericidal activity against commensal bacteria. Therefore, α-defensins regulate the composition of the intestinal microbiota in vivo and play a role in homeostasis of the entire intestine. Recently, relationships between dysbiosis, or abnormal composition of the intestinal microbiota, and diseases such as inflammatory bowel disease and lifestyle diseases including obesity and atherosclerosis have been reported. Because α-defensins regulate the composition of the intestinal microbiota, Paneth cells and their α-defensins may have a key role as one mechanism linking the microbiota and disease.

Peptides and Peptidomimetics for Antimicrobial Drug Design

The purpose of this paper is to introduce and highlight a few classes of traditional antimicrobial peptides with a focus on structure-activity relationship studies. After first dissecting the important physiochemical properties that influence the antimicrobial and toxic properties of antimicrobial peptides, the contributions of individual amino acids with respect to the peptides antibacterial properties are presented. A brief discussion of the mechanisms of action of different antimicrobials as well as the development of bacterial resistance towards antimicrobial peptides follows. Finally, current efforts on novel design strategies and peptidomimetics are introduced to illustrate the importance of antimicrobial peptide research in the development of future antibiotics.

Conformational landscape and pathway of disulfide bond reduction of human alpha defensin

Human alpha defensins are a class of antimicrobial peptides with additional antiviral activity. Such antimicrobial peptides constitute a major part of mammalian innate immunity. Alpha defensins contain six cysteines, which form three well defined disulfide bridges under oxidizing conditions. Residues C3-C31, C5-C20, and C10-C30 form disulfide pairs in the native structure of the peptide. The major tissue in which HD5 is expressed is the crypt of the small intestine, an anaerobic niche that should allow for substantial pools of both oxidized and (partly) reduced HD5. We used ion mobility coupled to mass spectrometry to track the structural changes in HD5 upon disulfide bond reduction. We found evidence of stepwise unfolding of HD5 with sequential reduction of the three disulfide bonds. Alkylation of free cysteines followed by tandem mass spectrometry of the corresponding partially reduced states revealed a dominant pathway of reductive unfolding. The majority of HD5 unfolds by initial reduction of C5-C20, followed by C10-C30 and C3-C31. We find additional evidence for a minor pathway that starts with reduction of C3-C31, followed by C5-C20 and C10-C30. Our results provide insight into the pathway and conformational landscape of disulfide bond reduction in HD5.

Immune aspects of the pathogenesis of inflammatory bowel disease

Although the precise etiologies of inflammatory bowel disease (IBD) (ulcerative colitis and Crohn's disease) remain obscure, several reports have indicated that dysfunction of the mucosal immune system plays an important role in its pathogenesis. Recent progress with genome-wide association studies has identified many IBD susceptibility genes. In individuals with genetic risk, abnormal interactions between the host immune system and gut flora, and dysregulation of cellular responses such as autophagy and ER stress, induce an abnormal host immune response in the gut resulting in intestinal inflammation. Research progress animal models in IBD, and in human IBD, has identified several key molecules in IBD pathogenesis such as TNFα and adhesion molecules, and molecular targeting therapies based on these molecules have been developed. Here, we review immunological aspects in IBD pathogenesis and the development of immunoregulatory therapy.

Host defense peptides: an alternative as antiinfective and immunomodulatory therapeutics

Host defense peptides are conserved components of innate immune response present among all classes of life. These peptides are potent, broad spectrum antimicrobial agents with potential as novel therapeutic compounds. Also, the ability of host defense peptides to modulate immunity is an emerging therapeutic concept since its selective modulation is a novel antiinfective strategy. Their mechanisms of action and the fundamental differences between pathogens and host cells surfaces mostly lead to a not widely extended microbial resistance and to a lower toxicity toward host cells. Biological libraries and rational design are novel tools for developing such molecules with promising applications as therapeutic drugs.

α-Defensins in human innate immunity

Defensins are small, multifunctional cationic peptides. They typically contain six conserved cysteines whose three intramolecular disulfides stabilize a largely β-sheet structure. This review of human α-defensins begins by describing their evolution, including their likely relationship to the Big Defensins of invertebrates, and their kinship to the β-defensin peptides of many if not all vertebrates, and the θ-defensins found in certain non-human primates. We provide a short history of the search for leukocyte-derived microbicidal molecules, emphasizing the roles played by luck (good), preconceived notions (mostly bad), and proper timing (essential). The antimicrobial, antiviral, antitoxic, and binding properties of human α-defensins are summarized. The structural features of α-defensins are described extensively and their functional contributions are assessed. The properties of HD6, an enigmatic Paneth cell α-defensin, are contrasted with those of the four myeloid α-defensins (HNP1-4) and of HD5, the other α-defensin of human Paneth cells. The review ends with a decalogue that may assist researchers or students interested in α-defensins and related aspects of neutrophil function.

Alternative luminal activation mechanisms for paneth cell α-defensins

Paneth cell α-defensins mediate host defense and homeostasis at the intestinal mucosal surface. In mice, matrix metalloproteinase-7 (MMP7) converts inactive pro-α-defensins (proCrps) to bactericidal forms by proteolysis at specific proregion cleavage sites. MMP7(-/-) mice lack mature α-defensins in Paneth cells, accumulating unprocessed precursors for secretion. To test for activation of secreted pro-α-defensins by host and microbial proteinases in the absence of MMP7, we characterized colonic luminal α-defensins. Protein extracts of complete (organ plus luminal contents) ileum, cecum, and colon of MMP7-null and wild-type mice were analyzed by sequential gel permeation chromatography/acid-urea polyacrylamide gel analyses. Mature α-defensins were identified by N-terminal sequencing and mass spectrometry and characterized in bactericidal assays. Abundance of specific bacterial groups was measured by qPCR using group specific 16 S rDNA primers. Intact, native α-defensins, N-terminally truncated α-defensins, and α-defensin variants with novel N termini due to alternative processing were identified in MMP7(-/-) cecum and colon, and proteinases of host and microbial origin catalyzed proCrp4 activation in vitro. Although Paneth cell α-defensin deficiency is associated with ileal microbiota alterations, the cecal and colonic microbiota of MMP7(-/-) and wild-type mice were not significantly different. Thus, despite the absence of MMP7, mature α-defensins are abundant in MMP7(-/-) cecum and colon due to luminal proteolytic activation by alternative host and microbial proteinases. MMP7(-/-) mice only lack processed α-defensins in the small intestine, and the model is not appropriate for studying effects of α-defensin deficiency in cecal or colonic infection or disease.

Expression of plectasin in Pichia pastoris and its characterization as a new antimicrobial peptide against Staphyloccocus and Streptococcus

Recombinant plectasin, the first fungus defensin, was expressed in Pichia pastoris and purified, and its physical, chemical and antimicrobial characteristics were studied. Following a 120 h induction of recombinant yeast, the amount of total secreted protein reached 748.63 μg/ml. The percentage of recombinant plectasin was estimated to be 71.79% of the total protein. After purification with a Sephadex G-25 column and RP-HPLC, the identity of plectasin was verified by MALDI-TOF MS. Plectasin exhibited strong antimicrobial activity against the Gram-positive bacteria Staphyloccocusaureus, Staphylococcus epidermidis, Streptococcus pneumoniae, and Streptococcus suis. At a concentration of 2560 μg/ml, this peptide showed approximately equal activity against S. aureus, S. epidermidis, S. suis, and S. pneumoniae, when compared to 320 μg/ml vancomycin, 640 μg/ml penicillin, 320 μg/ml vancomycin and 160 μg/ml vancomycin, respectively. In addition, plectasin showed anti-S. aureus activity over a wide pH range of 2.0 and 10.0, a high thermal stability at 100 °C for 1h and remarkable resistance to papain and pepsin. The expression and characterization of recombinant plectasin in P. pastoris has potential to treat Streptococcus and Staphyloccocus infections when most traditional antibiotics show no effect on them. Our results indicate that plectasin can be produced in large quantities, and that it has pharmaceutical importance for the prevention and clinical treatment of Staphyloccocus and Streptococcus infections.

Defensin-immunology in inflammatory bowel disease

Defensins are endogenous antibiotics with microbicidal activity against Gram-negative and Gram-positive bacteria, fungi, enveloped viruses and protozoa. A disturbed antimicrobial defense, as provided by Paneth- and other epithelial cell defensins, seems to be a critical factor in the pathogenesis of inflammatory bowel diseases. Conspicuously, there is a relative lack of Paneth cell beta-defensins HD-5 and HD-6 in ileal Crohn's disease, both in the absence of a pattern recognition receptor NOD2 mutation and, even more pronounced, in its presence. This deficit is independent of concurrent active inflammation and results in a diminished antibacterial killing by the mucosa. The Crohn's disease mucosa has not only a significant lack in killing different Escherichia coli but also an impaired ability in clearing Staphylococcus aureus as well as anaerobic micro-organisms. Thus, this dysfunction in antibacterial barrier seems to be broad and is not restricted to a single bacterial strain. In addition to directly controlling barrier function, Paneth cell defensins also regulate the composition of the bacterial stool flora. In the majority of patients, the Paneth cell deficiency is mediated by WNT signalling which suggests a disturbed Paneth cell differentiation in ileal Crohn's disease. In contrast, colonic Crohn's disease is characterised by an impaired induction of mucosal beta-defensins, partly due to a low copy number of the beta-defensin gene cluster. Therefore it seems plausible that bacteria take advantage of a niche formed by defensin deficiency. This would represent a paradigm shift in understanding Crohn's disease and provides a target for future therapeutic strategies.

Bactericidal activity of mouse α-defensin cryptdin-4 predominantly affects noncommensal bacteria

Mouse Paneth cell α-defensins, termed cryptdins, are secreted into the intestinal lumen, have microbicidal activity, and contribute to intestinal innate immunity. Among them, cryptdin-4 (Crp4) has the most potent microbicidal activity. In the intestinal lumen, commensal bacteria colonize and elicit beneficial effects in the host. However, the effects of Crp4 against commensal bacteria are poorly understood. Thus, we investigated the bactericidal activities of Crp4 against commensal bacteria compared to noncommensal bacteria. Oxidized Crp4 showed only minimal or no bactericidal activity against 8 out of 12 commensal bacterial species, including Bifidobacterium bifidum and Lactobacillus casei. We further addressed a role of the conserved disulfide bonds of Crp4 by analyzing reduced Crp4 (r-Crp4). r-Crp4 demonstrated significantly greater bactericidal activities against 7 of 12 commensal bacteria than did oxidized Crp4. Oxidized Crp4 and r-Crp4 elicited equivalently potent bactericidal activities against 11 of the 11 noncommensal bacteria tested, such as Salmonella enterica serovar Typhimurium,and against 5 of 12 commensal bacteria. Furthermore, when r-Crp4 was exposed to a processing enzyme of cryptdins, i.e. MMP-7, r-Crp4 was degraded and the bactericidal activities disappeared. These findings suggest that Crp4 has selective bactericidal activities against intestinal microbiota and that the activities are dependent on the disulfide bonds.

Intestinal epithelial cells in inflammatory bowel diseases

The pathogenesis of inflammatory bowel diseases (IBDs) seems to involve a primary defect in one or more of the elements responsible for the maintenance of intestinal homeostasis and oral tolerance. The most important element is represented by the intestinal barrier, a complex system formed mostly by intestinal epithelial cells (IECs). IECs have an active role in producing mucus and regulating its composition; they provide a physical barrier capable of controlling antigen traffic through the intestinal mucosa. At the same time, they are able to play the role of non-professional antigen presenting cells, by processing and presenting antigens directly to the cells of the intestinal immune system. On the other hand, immune cells regulate epithelial growth and differentiation, producing a continuous bi-directional cross-talk within the barrier. Several alterations of the barrier function have been identified in IBD, starting from mucus features up to its components, from epithelial junctions up to the Toll-like receptors, and altered immune responses. It remains to be understood whether these defects are primary causes of epithelial damage or secondary effects. We review the possible role of the epithelial barrier and particularly describe the role of IECs in the pathogenesis of IBD.

Constructing bioactive peptides with pH-dependent activities

Many bioactive peptides are featured by their arginine and lysine rich contents. In this study, lysine and arginine residues in lytic peptides were selectively replaced by histidines. Although resulting histidine-containing lytic peptides had decreased activity, they did show pH-dependent cytotoxicity. The activity of the constructed histidine-containing lytic peptides increased 2-8 times as the solution pH changed from 7.4 to 5.5. More importantly, these histidine-containing peptides maintain the same cell killing mechanism as their parent peptides by causing cell lysis. Both the activity and pH-sensitivity of histidine-containing peptides are tunable by adjusting histidine substitution numbers and positions. This study has presented a general strategy to create bioactive peptides with desired pH-sensitivity to meet the needs of various applications such as cancer treatments.

Defensins and inflammation: the role of defensins in inflammatory bowel disease

Defensins are antimicrobial peptides produced at a variety of epithelial surfaces. In the intestinal tract, they contribute to host immunity and assist in maintaining the balance between protection from pathogens and tolerance to normal flora. However, attenuated expression of defensins compromises host immunity and hence may alter the balance toward inflammation. Altered defensin production is suggested to be an integral element in the pathogenesis of inflammatory bowel disease (IBD). Evidence for this is shown in Crohn's disease where reduced alpha-defensin levels are seen in patients with ileal disease and reduced beta-defensin levels in those with colonic involvement. Further evidence is provided by research linking nucleotide oligomerization domain 2 (NOD2) mutations and deficient defensin expression. However, alternate studies suggest that NOD2 status and defensin expression are independent, and that defensin deficiency is due to mucosal surface destruction as a result of inflammatory changes, indicating that reduced defensin expression is a symptom of the disease and not the cause. Although it is clear that defensin expression is altered in IBD, it is less clear whether defensin deficiency is implicated in the pathogenesis of IBD or is a consequence of the disease process. The aim of this article is to review the current knowledge of defensins in IBD and discuss their potential role in IBD pathogenesis.

Barrier dysfunction due to distinct defensin deficiencies in small intestinal and colonic Crohn's disease

Defensins are endogenous antibiotics with broad microbicidal activity. A disturbed antimicrobial defense, as provided by Paneth and other epithelial defensins, seems to be a critical factor in the pathogenesis of inflammatory bowel diseases. Conspicuously, there is a relative lack of Paneth-cell alpha-defensins in ileal Crohn's disease (CD), both in the absence of a pattern recognition receptor nucleotide-binding oligomerization domain 2 (NOD2) frameshift mutation and, even more pronounced, in its presence. This deficit is independent of concurrent active inflammation and cannot be seen in active small intestinal ulcerative colitis (UC; pouchitis) as well as NOD2 wild-type graft vs. host ileitis. After intestinal transplantation, in case of NOD2 mutation, defensins are decreased before the onset of inflammation. In the majority of patients, the Paneth-cell deficiency is mediated by Wnt-TCF4, which suggests a disturbed Paneth-cell differentiation. In contrast, colonic CD is characterized by an impaired induction of mucosal beta-defensins, partly because of a low copy number of the beta-defensin gene cluster. In both ileal and colonic CD, the lack in defensins results in a broadly diminished antibacterial killing by the mucosa, which can also be found independent of inflammation. In summary, the main disease locations can be linked to distinct mechanisms of epithelial barrier dysfunction.

Functional role of metaplastic paneth cell defensins in Helicobacter pylori-infected stomach

BACKGROUND AND AIMS

Chronic gastritis is caused by Helicobacter pylori infection, and gastritis is classified as inflammation, atrophy, and intestinal metaplasia. Detailed pathologic studies have shown that H. pylori settles on the surface of gastric mucosa, and that it is eliminated from metaplastic mucosa. However, its mechanism of natural protection is not well known.

METHODS

Antimicrobial human enteric defensin expression was determined in the RNA and protein levels. Recombinant enteric defensins were produced with a bacterial expression system and their anti-H. pylori activities were assessed by bactericidal assay.

RESULTS

Human enteric defensin (HD)-5 and HD-6 were detected in Paneth cells, which are observed in the gastric metaplastic mucosa as well as small intestinal epithelia. HD-5 protein was coexpressed with trypsin, which is considered to be an activating enzyme of HD-5. Less H. pylori was observed in the intestinal metaplasia with HD-5 expressing Paneth cells. The recombinant defensins showed killing activity against H. pylori at a low concentration in vitro.

CONCLUSIONS

The human defensins that are expressed in the metaplastic Paneth cells eliminate H. pylori. Metaplastic change may be a purposive development of the human stomach.

Innate immunity in inflammatory bowel disease: state of the art

PURPOSE OF REVIEW

Gut is exposed to enteric bacteria and food antigens but maintains its homeostasis without the development of acute or chronic inflammation in normal situations. Abnormal innate immunity to enteric flora may develop into intestinal inflammation such as inflammatory bowel disease. This paper reviews recent studies on innate immunity in gut homeostasis and inflammation, identifying novel susceptible genes and clarifying the interaction between epithelial cells and immune cells such as intestinal macrophages and dendritic cells, as well as the interaction between NOD2 and toll-like receptor.

RECENT FINDINGS

Crosstalk between epithelial cells and monocytic cells such as macrophages and dendritic cells plays an important role in gut homeostasis. Dysregulation of this crosstalk leads to decreased epithelial integrity and chronic intestinal inflammation. Macrophages and dendritic cells also regulate bacterial flora for the maintenance of intestinal homeostasis. Interleukin-23 derived from these cells is a key cytokine in inflammatory bowel disease pathogenesis. Interactions between NOD2 and toll-like receptor signaling pathways may cause abnormal immune responses and decreased bacterial clearance. Genome-wide scanning has identified innate immunity-related genes as inflammatory bowel disease susceptibility genes.

SUMMARY

Recent studies on gut innate immunity in animal models have greatly advanced our knowledge of inflammatory bowel disease pathogenesis. For further progress, human studies and clarification of the functions of the identified susceptibility genes are needed.

The conserved salt bridge in human alpha-defensin 5 is required for its precursor processing and proteolytic stability

Mammalian alpha-defensins, expressed primarily in leukocytes and epithelia, play important roles in innate and adaptive immune responses to microbial infection. Six invariant cysteine residues forming three indispensable disulfide bonds and one Gly residue required structurally for an atypical beta-bulge are totally conserved in the otherwise diverse sequences of all known mammalian alpha-defensins. In addition, a pair of oppositely charged residues (Arg/Glu), forming a salt bridge across a protruding loop in the molecule, is highly conserved. To investigate the structural and functional roles of the conserved Arg(6)-Glu(14) salt bridge in human alpha-defensin 5 (HD5), we chemically prepared HD5 and its precursor proHD5 as well as their corresponding salt bridge-destabilizing analogs E14Q-HD5 and E57Q-proHD5. The Glu-to-Gln mutation, whereas significantly reducing the oxidative folding efficiency of HD5, had no effect on the folding of proHD5. Bovine trypsin productively and correctly processed proHD5 in vitro but spontaneously degraded E57Q-proHD5. Significantly, HD5 was resistant to trypsin treatment, whereas E14Q-HD5 was highly susceptible. Further, degradation of E14Q-HD5 by trypsin was initiated by the cleavage of the Arg(13)-Gln(14) peptide bond in the loop region, a catastrophic proteolytic event resulting directly in quick digestion of the whole defensin molecule. The E14Q mutation did not alter the bactericidal activity of HD5 against Staphylococcus aureus but substantially enhanced the killing of Escherichia coli. By contrast, proHD5 and E57Q-proHD5 were largely inactive against both strains at the concentrations tested. Our results confirm that the primary function of the conserved salt bridge in HD5 is to ensure correct processing of proHD5 and subsequent stabilization of mature alpha-defensin in vivo.

Impaired luminal processing of human defensin-5 in Crohn's disease: persistence in a complex with chymotrypsinogen and trypsin

Human defensin (HD)-5 is an antimicrobial peptide expressed in small intestinal Paneth cells, and alterations in HD-5 expression may be important in Crohn's disease (CD) pathogenesis. Levels of HD-5 in Paneth cells and ileostomy fluid from control and CD patients were studied by quantitative immunodot analysis, immunohistochemistry, acid urea-polyacrylamide gel electrophoresis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis Western blotting, reverse phase-high performance liquid chromatography, N-terminal amino acid sequencing, and ES-QToF mass spectrometry. In both control and CD patients, HD-5 in Paneth cell extracts was present almost exclusively in the precursor form. HD-5 levels in ileostomy fluid were lower in CD patients (n = 51) than in controls (n = 20): median (range), 7.9 (5.5 to 35.0) microg/ml versus 10.5 (6.0 to 30.4) microg/ml; P = 0.05; this difference was most marked in CD patients with homozygous/compound heterozygous mutations in NOD2 (P = 0.03). In control ileostomy fluid, HD-5 was present in the mature form only. In contrast, CD patient ileostomy fluid contained both precursor and mature forms of HD-5, with the majority present in a complex with trypsin, chymotrypsinogen/chymotrypsin, and alpha1-anti-trypsin. Pro-HD-5 was not associated with trypsin or chymotrypsinogen in Paneth cell extracts. In conclusion, pro-HD-5 in the intestinal lumen is processed by trypsin in a complex in which chymotrypsinogen is also cleaved for activation. The persistence of this complex in CD may be attributable to increased luminal levels of proteinase inhibitors such as alpha1-anti-trypsin.

Host-microbe interaction: mechanisms of defensin deficiency in Crohn's disease

Defensins are endogenous antibiotics with microbicidal activity against Gram-negative and -positive bacteria, fungi, enveloped viruses and protozoa. A disturbed antimicrobial defense, as provided by Paneth and other epithelial cell defensins, seems to be a critical factor in the pathogenesis of Crohn's disease, an inflammatory disease of the intestinal tract. Different direct and indirect mechanisms leading to a breakdown of antimicrobial barrier function include direct changes in defensin gene numbers (e.g., copy number polymorphism), genetic mutations in pattern-recognition receptors (e.g., nucleotide-binding oligomerization domain 2) and, as described recently, a differentiation problem of epithelial stem cells mediated by the wingless type (Wnt) pathway. Knowledge regarding the regulation and biology of defensins provides an attractive target to open up new therapeutic avenues.