Human defensin 5 is stored in precursor form in normal Paneth cells and is expressed by some villous epithelial cells and by metaplastic Paneth cells in the colon in inflammatory bowel disease

Relationship between pouch microbiota and pouchitis following restorative proctocolectomy for ulcerative colitis

Restorative proctocolectomy with ileal pouch-anal anastomosis (IPAA) has become the surgical treatment of choice for many patients with medically refractory ulcerative colitis (UC) and familial adenomatous polyposis (FAP). UC patients with IPAA (UC-IPAA) are, nevertheless, susceptible to inflammatory and noninflammatory sequelae such as pouchitis, which is only rarely noted in FAP patients with IPAA. Pouchitis is the most frequent long-term complication of UC-IPAA patients, with a cumulative prevalence of up to 50%. Although the aetiology of pouchitis remains unclear, accumulating evidence suggests that a dysbiosis of the pouch microbiota and an abnormal mucosal immune response are implicated in its pathogenesis. Studies using culture and molecular techniques have detected a dysbiosis of the pouch microbiota in patients with pouchitis. Risk factors, genetic associations, and serological markers suggest that interactions between the host immune response and the pouch microbiota underlie the aetiology of this idiopathic inflammatory condition. This systematic review focuses on the dysbiosis of the microbiota that inhabit the pouch in UC and FAP patients and its interaction with the mucosal immune system. A meta-analysis was not attempted due to the highly heterogeneous microbiota composition and the different detection methods used by the various studies. Although no specific bacterial species, genus, or family has as yet been identified as pathogenic, there is evidence that a dysbiosis characterized by decreased gut microbiota diversity in UC-IPAA patients may, in genetically predisposed subjects, lead to aberrant mucosal immune regulation triggering an inflammatory process.

In vitro studies on the antimicrobial peptide human beta-defensin 9 (HBD9): signalling pathways and pathogen-related response (an American Ophthalmological Society thesis)

PURPOSE

Human β-defensins (HBDs) are an important part of the innate immune host defense at the ocular surface. Unlike other defensins, expression of HBD9 at the ocular surface is reduced during microbial infection, but activation of toll-like receptor 2 (TLR2) in corneal epithelial cells has been shown to up-regulate HBD9. Our purpose was to test the hypothesis that TLR2 has a key role in the signalling pathway(s) involved in the overexpression or underexpression of HBD9, and accordingly, different pathogens would induce a different expression pattern of HBD9.

METHODS

The in vitro RNAi silencing method and response to dexamethasone were used to determine key molecules involved in signalling pathways of HBD9 in immortalized human corneal epithelial cells. The techniques included cell culture with exposure to specific transcription factor inhibitors and bacteria, RNA extraction and cDNA synthesis, quantitative real-time polymerase chain reaction, and immunohistology.

RESULTS

This study demonstrates that TLR2 induces HBD9 mRNA and protein expression in a time- and dose-dependent manner. Transforming growth factor-β-activated kinase 1 (TAK1) plays a central role in HBD9 induction by TLR2, and transcription factors c-JUN and activating transcription factor 2 are also involved. Dexamethasone reduces TLR2-mediated up-regulation of HBD9 mRNA and protein levels in mitogen-activated protein kinase phosphatase 1 (MKP1)-dependent and c-JUN-independent manner. HBD9 expression differs with gram-negative and gram-positive bacteria.

CONCLUSIONS

TLR2-mediated MKPs and nuclear factor-κB signalling pathways are involved in HBD9 expression. TAK-1 is a key molecule. These molecules can be potentially targeted to modulate HBD9 expression. Differential expression of HBD9 with different bacteria could be related to differences in pathogen-associated molecular patterns of these organisms.

Intestinal barrier in inflammatory bowel disease

A complex mucosal barrier protects as the first line of defense the surface of the healthy intestinal tract from adhesion and invasion by luminal microorganisms. In this review, we provide an overview about the major components of this protective system as for example an intact epithelium, the synthesis of various antimicrobial peptides (AMPs) and the formation of the mucus layer. We highlight the crucial importance of their correct functioning for the maintenance of a proper intestinal function and the prevention of dysbiosis and disease. Barrier disturbances including a defective production of AMPs, alterations in thickness or composition of the intestinal mucus layer, alterations of pattern-recognition receptors, defects in the process of autophagy as well as unresolved endoplasmic reticulum stress result in an inadequate host protection and are thought to play a crucial role in the pathogenesis of the inflammatory bowel diseases Crohn’s disease and ulcerative colitis.

Antimicrobial proteins in intestine and inflammatory bowel diseases

Mucosal surface of the intestinal tract is continuously exposed to a large number of microorganisms. To manage the substantial microbial exposure, epithelial surfaces produce a diverse arsenal of antimicrobial proteins (AMPs) that directly kill or inhibit the growth of microorganisms. Thus, AMPs are important components of innate immunity in the gut mucosa. They are frequently expressed in response to colonic inflammation and infection. Expression of many AMPs, including human β-defensin 2-4 and cathelicidin, is induced in response to invasion of pathogens or enteric microbiota into the mucosal barrier. In contrast, some AMPs, including human α-defensin 5-6 and human β-defensin 1, are constitutively expressed without microbial contact or invasion. In addition, specific AMPs are reported to be associated with inflammatory bowel disease (IBD) due to altered expression of AMPs or development of autoantibodies against AMPs. The advanced knowledge for AMPs expression in IBD can lead to its potential use as biomarkers for disease activity. Although the administration of exogenous AMPs as therapeutic strategies against IBD is still at an early stage of development, augmented induction of endogenous AMPs may be another interesting future research direction for the protective and therapeutic purposes. This review discusses new advances in our understanding of how intestinal AMPs protect against pathogens and contribute to pathophysiology of IBD.

Antimicrobial peptides and colitis

Antimicrobial peptides (AMPs) are important components of innate immunity. They are often expressed in response to colonic inflammation and infection. Over the last several years, the roles of several antimicrobial peptides have been explored. Gene expression of many AMPs (beta defensin HBD2-4 and cathelicidin) is induced in response to invasion of gut microbes into the mucosal barrier. Some AMPs are expressed in a constitutive manner (alpha defensin HD 5-6 and beta defensin HBD1), while others (defensin and bactericidal/ permeability increasing protein BPI) are particularly associated with Inflammatory Bowel Disease (IBD) due to altered defensin expression or development of autoantibodies against Bactericidal/permeability increasing protein (BPI). Various AMPs have different spectrum and strength of antimicrobial effects. Some may play important roles in modulating the colitis (cathelicidin) while others (lactoferrin, hepcidin) may represent biomarkers of disease activity. The use of AMPs for therapeutic purposes is still at an early stage of development. A few natural AMPs were shown to be able to modulate colitis when delivered intravenously or intracolonically (cathelicidin, elafin and SLPI) in mouse colitis models. New AMPs (synthetic or artificial non-human peptides) are being developed and may represent new therapeutic approaches against colitis. This review discusses the latest research developments in the AMP field with emphasis in innate immunity and pathophysiology of colitis.

REG gene expression in inflamed and healthy colon mucosa explored by in situ hybridisation

The regenerating islet-derived (REG) gene family encodes a group of proteins highly expressed in several human pathologies, many of which are associated with epithelial inflammation. All human family members, namely REG1A, REG1B, REG3A and REG4, are closely related in genomic sequence and all are part of the c-type lectin superfamily. REGs are highly expressed during inflammatory bowel disease (IBD)-related colonic inflammation and the in vivo expression pattern of REG1A and REG4 has been localised by using immunohistochemistry. However, the function of the encoded proteins is largely unknown and the cellular localisation of REG expression during colonic inflammation has not been described. Therefore, we have used in situ hybridisation to demonstrate the cellular localisation of REG expression in healthy and diseased colonic mucosa. Samples drawn from an IBD cohort including both inflamed and un-inflamed colonic mucosa are described, as are samples from non-IBD inflammation and healthy controls. Immunohistochemistry against known cell-type markers on serial sections has localised the expression of REGs to metaplastic Paneth cells (REG1A, REG1B and REG3A) and enteroendocrine cells (REG4), with a marked expansion of expression during inflammation. The group of REGs can, based on gene expression patterns, be divided into at least two groups; REG1A, REG1B and REG3A with their expression focused in the crypt base spreading from Paneth cells and REG4 being more highly expressed towards the luminal face. This exploration of expression pattern forms provides the background for further exploration of REG function in the intestine.

Epithelial cells augment barrier function via activation of the Toll-like receptor 2/phosphatidylinositol 3-kinase pathway upon recognition of Salmonella enterica serovar Typhimurium curli fibrils in the gut

Curli fibrils, the best-characterized functional bacterial amyloids, are an important component of enterobacterial biofilms. We have previously shown that curli fibrils are recognized by the Toll-like receptor 2 (TLR2)/TLR1 heterodimer complex. Utilizing polarized T-84 cells, an intestinal epithelial cell line derived from colon carcinoma grown on semipermeable tissue culture inserts, we determined that infection with a Salmonella enterica serovar Typhimurium csgBA mutant, which does not express curli, resulted in an increase in intestinal barrier permeability and an increase in bacterial translocation compared to infection with curliated wild-type S. Typhimurium. When the TLR2 downstream signaling molecule phosphatidylinositol 3-kinase (PI3K) was blocked using wortmannin or LY294002, the difference in disruption of the intestinal epithelium and bacterial translocation was no longer observed. Additionally, disruption of polarized T-84 cells treated basolaterally with the TLR5 ligand flagellin was prevented when the polarized cells were simultaneously treated with the synthetic TLR2/TLR1 ligand Pam(3)CSK(4) or with purified curli fibrils in the apical compartment. Similar to in vitro observations, C57BL/6 mice infected with the csgBA mutant suffered increased disruption of the intestinal epithelium and therefore greater dissemination of the bacteria to the mesenteric lymph nodes than mice infected with wild-type S. Typhimurium. The differences in disruption of the intestinal epithelium and bacterial dissemination in the mice infected with csgBA mutant or wild-type S. Typhimurium were not apparent in TLR2-deficient mice. Overall, these studies report for the first time that activation of the TLR2/PI3K pathway by microbial amyloids plays a critical role in regulating the intestinal epithelial barrier as well as monitoring bacterial translocation during infection.

Heterogeneity in histone 2B-green fluorescent protein-retaining putative small intestinal stem cells at cell position 4 and their absence in the colon

Stem cells have been identified in two locations in small intestinal crypts; those intercalated between Paneth cells and another population (which retains DNA label) are located above the Paneth cell zone, at cell position 4. Because of disadvantages associated with the use of DNA label, doxycycline-induced transient transgenic expression of histone 2B (H2B)-green fluorescent protein (GFP) was investigated. H2B-GFP-retaining putative stem cells were consistently seen, with a peak at cell position 4, over chase periods of up to 112 days. After a 28-day chase, a subpopulation of the H2B-GFP-retaining cells was cycling, but the slow cycling status of the majority was illustrated by lack of expression of pHistone H3 and Ki67. Although some H2B-GFP-retaining cells were sensitive to low-dose radiation, the majority was resistant to low- and high-dose radiation-induced cell death, and a proportion of the surviving cells proliferated during subsequent epithelial regeneration. Long-term retention of H2B-GFP in a subpopulation of small intestinal Paneth cells was also seen, implying that they are long lived. In contrast to the small intestine, H2B-GFP-retaining epithelial cells were not seen in the colon from 28-day chase onward. This implies important differences in stem cell function between these two regions of the gastrointestinal tract, which may have implications for region-specific susceptibility to diseases (such as cancer and ulcerative colitis), in which epithelial stem cells and their progeny are involved.

Temporal colonic gene expression profiling in the recurrent colitis model identifies early and chronic inflammatory processes

The recurrent TNBS-colitis model in BALB/c mice has been proposed as a model of Inflammatory Bowel Disease with a shifting pattern of local cytokines with the expression of Th1 cytokines during the early phase, Th17 cytokines during the intermediate phase and Th2 cytokines during late fibrotic stages. In this study, we evaluated the development of pathology in time–in conjunction with genome-wide gene expression in the colons–in response to three weekly intrarectal instillations of TNBS. During this time-frame mice develop colitis with extensive cellular infiltration of (sub)mucosa and mildly to moderately affected crypt architecture. These pathological processes were sensitive to local treatment with budesonide. Gene expression profiling confirmed an acute phase response after each intrarectal TNBS-challenge. In addition, a chronic inflammatory process developed over time particularly evident from a gradual increase in expression of mast cell related genes. The changes in pathological hallmarks were consistent with a temporal expression of mRNA encoding a selection of chemokines. In conclusion, the early stages of the recurrent TNBS-colitis model reflect several aspects of inflammatory bowel disease which are sensitive to immunomodulation.

NMR solution structure and condition-dependent oligomerization of the antimicrobial peptide human defensin 5

Human defensin 5 (HD5) is a 32-residue host-defense peptide expressed in the gastrointestinal, reproductive, and urinary tracts that has antimicrobial activity. It exhibits six cysteine residues that are regiospecifically oxidized to form three disulfide bonds (Cys(3)-Cys(31), Cys(5)-Cys(20), and Cys(10)-Cys(30)) in the oxidized form (HD5(ox)). To probe the solution structure and oligomerization properties of HD5(ox), and select mutant peptides lacking one or more disulfide bonds, NMR solution studies and analytical ultracentrifugation experiments are reported in addition to in vitro peptide stability assays. The NMR solution structure of HD5(ox), solved at pH 4.0 in 90:10 H(2)O/D(2)O, is presented (PDB: 2LXZ ). Relaxation T(1)/T(2) measurements and the rotational correlation time (τ(c)) estimated from a (15)N-TRACT experiment demonstrate that HD5(ox) is dimeric under these experimental conditions. Exchange broadening of the Hα signals in the NMR spectra suggests that residues 19-21 (Val(19)-Cys(20)-Glu(21)) contribute to the dimer interface in solution. Exchange broadening is also observed for residues 7-14 comprising the loop. Sedimentation velocity and equilibrium studies conducted in buffered aqueous solution reveal that the oligomerization state of HD5(ox) is pH-dependent. Sedimentation coefficients of ca. 1.8 S and a molecular weight of 14 363 Da were determined for HD5(ox) at pH 7.0, supporting a tetrameric form ([HD5(ox)] ≥ 30 μM). At pH 2.0, a sedimentation coefficient of ca. 1.0 S and a molecular weight of 7079 Da, corresponding to a HD5(ox) dimer, were obtained. Millimolar concentrations of NaCl, CaCl(2), and MgCl(2) have a negligible effect on the HD5(ox) sedimentation coefficients in buffered aqueous solution at neutral pH. Removal of a single disulfide bond results in a loss of peptide fold and quaternary structure. These biophysical investigations highlight the dynamic and environmentally sensitive behavior of HD5(ox) in solution, and provide important insights into HD5(ox) structure/activity relationships and the requirements for antimicrobial action.

Inflammatory bowel disease: an impaired barrier disease

BACKGROUND

The intestinal barrier is a delicate structure composed of a single layer of epithelial cells, the mucus, commensal bacteria, immune cells, and antibodies. Furthermore, a wealth of antimicrobial peptides (AMPs) can be found in the mucus and defend the mucosa. Different lines of investigations now point to a prominent pathophysiological role of defensins, an important family of AMPs, in the pathogenesis of inflammatory bowel disease and, particularly, in small intestinal Crohn's disease.

PURPOSE

In this review, we introduce the different antimicrobial peptides of the intestinal mucosa and describe their function, their expression pattern along the gastrointestinal tract, and their spatial relationship to the mucus layer. We then focus on the alterations found in inflammatory bowel disease. Small intestinal Crohn's disease (CD) is closely linked to defects in Paneth cells (specialized secretory epithelial cells at the bottom crypts) which secrete α-defensin human defensin (HD)-5 in huge quantities in healthy individuals. Decreased expression of these antimicrobial peptides is found in ileal CD, and single nucleotide polymorphisms with the highest linkage to CD affect genes involved in Paneth cell biology and defensin secretion. Additionally, antimicrobial peptides have a role in ulcerative colitis, where the depleted mucus layer cannot fulfill its crucial function of binding defensins and other AMPs to their proper site of action.

CONCLUSION

Inflammatory bowel disease arises when the mucosal barrier is compromised in its defense against challenges from the intestinal microbiota. In ileal CD, a strong association can be found between diminished expression or defective function of defensins and the advent of intestinal inflammation.

CD24 can be used to isolate Lgr5+ putative colonic epithelial stem cells in mice

A growing body of evidence has implicated CD24, a cell-surface protein, as a marker of colorectal cancer stem cells and target for antitumor therapy, although its presence in normal colonic epithelium has not been fully characterized. Previously, our group showed that CD24-based cell sorting can be used to isolate a fraction of murine small intestinal epithelial cells enriched in actively cycling stem cells. Similarly, we hypothesized that CD24-based isolation of colonic epithelial cells would generate a fraction enriched in actively cycling colonic epithelial stem cells (CESCs). Immunohistochemistry performed on mouse colonic tissue showed CD24 expression in the bottom half of proximal colon crypts and the crypt base in the distal colon. This pattern of distribution was similar to enhanced green fluorescent protein (EGFP) expression in Lgr5-EGFP mice. Areas expressing CD24 contained actively proliferating cells as determined by ethynyl deoxyuridine (EdU) incorporation, with a distinct difference between the proximal colon, where EdU-labeled cells were most frequent in the midcrypt, and the distal colon, where they were primarily at the crypt base. Flow cytometric analyses of single epithelial cells, identified by epithelial cell adhesion molecule (EpCAM) positivity, from mouse colon revealed an actively cycling CD24(+) fraction that contained the majority of Lgr5-EGFP(+) putative CESCs. Transcript analysis by quantitative RT-PCR confirmed enrichment of active CESC markers [leucine-rich-repeat-containing G protein-coupled receptor 5 (Lgr5), ephrin type B receptor 2 (EphB2), and CD166] in the CD24(+)EpCAM(+) fraction but also showed enrichment of quiescent CESC markers [leucine-rich repeats and immunoglobin domains (Lrig), doublecortin and calmodulin kinase-like 1 (DCAMKL-1), and murine telomerase reverse transcriptase (mTert)]. We conclude that CD24-based sorting in wild-type mice isolates a colonic epithelial fraction highly enriched in actively cycling and quiescent putative CESCs. Furthermore, the presence of CD24 expression in normal colonic epithelium may have important implications for the use of anti-CD24-based colorectal cancer therapies.

Parenteral nutrition suppresses the bactericidal response of the small intestine

BACKGROUND

Parenteral nutrition (PN) increases infectious risk in critically ill patients compared with enteral feeding. Previously, we demonstrated that PN feeding suppresses the concentration of the Paneth cell antimicrobial protein secretory phospholipase A2 (sPLA2) in the gut lumen. sPLA2 and other Paneth cell proteins are released in response to bacterial components, such as lipopolysaccharide (LPS), and they modulate the intestinal microbiome. Because the Paneth cell protein sPLA2 was suppressed with PN feeding, we hypothesized PN would diminish the responsiveness of the small bowel to LPS through reduced secretions and as a result exhibit less bactericidal activity.

METHODS

The distal ileum was harvested from Institute of Cancer Research mice, washed, and randomized for incubation with LPS (0, 1, or 10 μg/mL). Culture supernatant was collected and sPLA2 activity was measured. Bactericidal activity of the ileum segment secretions was assessed against Pseudomonas aeruginosa with and without an sPLA2 inhibitor at 2 concentrations, 100 nmol/L and 1 μmol/L. Institute of Cancer Research mice were randomized to chow or PN for 5 days. Tissue was collected for immunohistochemistry (IHC) and ileal segments were incubated with LPS (0 or 10 μg/mL). sPLA2 activity and bactericidal activity were measured in secretions from ileal segments.

RESULTS

Ileal segments responded to 10 μg/mL LPS with significantly greater sPLA2 activity and bactericidal activity. The bactericidal activity of secretions from LPS stimulated tissue was suppressed 50% and 70%, respectively, with the addition of the sPLA2-inhibitor. Chow displayed greater sPLA2 in the Paneth cell granules and secreted higher levels of sPLA2 than PN before and after LPS. Accordingly, media collected from chow was more bactericidal than PN. IHC confirmed a reduction in Paneth cell granules after PN.

CONCLUSION

This work demonstrates that ileal segments secrete bactericidal secretions after LPS exposure and the inhibition of the Paneth cell antimicrobial protein sPLA2 significantly diminishes this. PN feeding resulted in suppressed secretion of the sPLA2 and resulted in increased bacterial survival. This demonstrates that PN significantly impairs the innate immune response by suppressing Paneth cell function.

Cdc42 and Rab8a are critical for intestinal stem cell division, survival, and differentiation in mice

The constant self renewal and differentiation of adult intestinal stem cells maintains a functional intestinal mucosa for a lifetime. However, the molecular mechanisms that regulate intestinal stem cell division and epithelial homeostasis are largely undefined. We report here that the small GTPases Cdc42 and Rab8a are critical regulators of these processes in mice. Conditional ablation of Cdc42 in the mouse intestinal epithelium resulted in the formation of large intracellular vacuolar structures containing microvilli (microvillus inclusion bodies) in epithelial enterocytes, a phenotype reminiscent of human microvillus inclusion disease (MVID), a devastating congenital intestinal disorder that results in severe nutrient deprivation. Further analysis revealed that Cdc42-deficient stem cells had cell division defects, reduced capacity for clonal expansion and differentiation into Paneth cells, and increased apoptosis. Cdc42 deficiency impaired Rab8a activation and its association with multiple effectors, and prevented trafficking of Rab8a vesicles to the midbody. This impeded cytokinesis, triggering crypt apoptosis and disrupting epithelial morphogenesis. Rab8a was also required for Cdc42-GTP activity in the intestinal epithelium, where continued cell division takes place. Furthermore, mice haploinsufficient for both Cdc42 and Rab8a in the intestine demonstrated abnormal crypt morphogenesis and epithelial transporter physiology, further supporting their functional interaction. These data suggest that defects of the stem cell niche can cause MVID. This hypothesis represents a conceptual departure from the conventional view of this disease, which has focused on the affected enterocytes, and suggests stem cell-based approaches could be beneficial to infants with this often lethal condition.

Innate immune environment in ileal pouch mucosa: α5 defensin up-regulation as predictor of chronic/relapsing pouchitis

Defensins are small cationic peptides with antibacterial activity expressed in Paneth cells (α-defensins) or generally in intestinal epithelial cells (β-defensins) that have a profound effect on gut microbiota. Chronic pouchitis, which occurs in 5% of patients after restorative proctocolectomy and can cause pouch failure, is associated to a significant increase of Clostridiaceae spp. The aim of this study was to gain further insight in the pathogenesis of pouch dysbiosis by exploring defensin expression. Thirty-two consecutive patients coming for follow-up endoscopy were recruited. On pouch biopsies, we cultured bacteria adherent to the mucosa and determined α- and β-defensins and toll-like receptor-4 and -2 mRNA by quantitative real-time RT-PCR. Serum and mucosal levels of IL-1β, IL-6 and TNF-α were measured with immunometric assays. Faecal lactoferrin was analysed by quantitative ELISA. After a median follow-up of 23 (IQR 20-24) months, the patients were contacted for a reassessment of current and past disease activity. During the follow-up, chronic/relapsing pouchitis was diagnosed in six patients. The mucosal level of α-5 and α-6 defensins correlated with chronic/relapsing pouchitis onset (τ = 0.30, p = 0.034 and τ = 0.28, p = 0.053, respectively). High levels of α-5 defensin resulted to be predictive of chronic/relapsing pouchitis [AUC = 74% (95% CI = 53-89%), p = 0.052]. Patients with high levels of α-5 and α-6 defensins had earlier pouchitis relapses (p = 0.009 and p = 0.034, respectively). High levels of α-5 defensin were associated to a significant risk of chronic/relapsing pouchitis [OR = 10.6 (95% CI = 1.2-97.6), p = 0.027]. At multivariate analysis, the mucosal levels of α-5 defensin and the number of CFU of mucosa-associated Clostridiaceae spp resulted to be independent predictors of chronic/relapsing pouchitis [β = 0.46 (0.18), p = 0.024 and β = 0.44 (0.18), p = 0.027, respectively]. In conclusion, chronic/relapsing pouchitis is associated to increased expression of mucosal HD-5 and to increased antimicrobial activity against Escherichia coli. In patients with chronic/relapsing pouchitis, HD-5 and TLR-4 over-expression is likely to create a hostile environment against Enterobacteriaceae, thus favouring Clostridiaceae spp by decreasing competing bacteria families.

Alteration of local microflora and α-defensins hyper-production in colonic adenoma mucosa

BACKGROUND AND AIM

Gut flora/host interactions are fundamental for the maintenance of homeostasis. Evidence of possible regulatory effect of commensal bacteria on proliferative disorders of the colon is mounting. In this study, we explored the hypothesis that precancerous lesions, such as adenomas, present alteration of the local microflora and lead to an overproduction of antibacterial molecules of the innate immunity, namely α-defensins. Thus, the host-bacteria misbalance could represent a potential procarcinogenic factor.

METHODS

Biopsies from adenomatous polyps and normal mucosa, in the rectum-sigmoid colon, were collected from 51 patients. Concentration of mucosal bacteria was evaluated by real-time polymerase chain reaction after extraction of total DNA. Total RNA was also extracted, and the defensin α-1, defensin-5, and defensin-6 gene expressions were evaluated by real-time polymerase chain reaction. Immunohistochemical study has been carried out to evaluate protein production and location. Antibacterial activity of adenomatous polyps mucosa was evaluated in vitro.

RESULTS

Biopsies from adenomatous polyps had a significant relative reduction of mucosa adherent bacteria compared with normal tissue (20-fold relative reduction, P<0.05). Concomitantly, α-defensin expression and production were significantly increased in adenomas. Adenoma mucosa showed increased antibacterial activity in vitro compared with normal mucosa.

CONCLUSIONS

Microflora dysbiosis occurs at the mucosal surface in colonic adenomas, and may represent a potential factor for dysplastic cell proliferation. Further studies are needed to confirm and define the role of this mechanism in colon carcinogenesis and the potential applications in the clinical setting.

Antimicrobial peptides in the duodenum at the acute and convalescent stages in patients with diarrhea due to Vibrio cholerae O1 or enterotoxigenic Escherichia coli infection

Patients with acute watery diarrhea caused by Vibrio cholerae O1 or enterotoxigenic Escherichia coli (ETEC) were analyzed for innate immune factors produced by the epithelium during the disease process. Duodenal biopsies were obtained from study participants at the acute (day 2) and convalescent (day 21) stages of disease. Levels of α-defensin (HD-5 and -6), β-defensin (hBD-1-4), and cathelicidin (LL-37) mRNAs were determined by real-time qRT-PCR. hBD-2, HD-5, LL-37 peptides were analyzed in duodenal epithelium by immunomorphometry. Concentration of hBD-2 in stool was determined by ELISA. Specimens from healthy controls were also analyzed. hBD-2 mRNA levels were significantly increased at acute stage of diarrhea; hBD-2 peptide was detected in fecal specimens but barely in duodenal epithelium at acute stage. Immunomorphometry analysis showed that Paneth cells contain significantly higher amounts of HD-5 pre/propeptide at convalescence (P<0.01) and in healthy controls (P<0.001) compared to acute stage, LL-37 peptide levels also decreased at acute stage while mRNA levels remained unchanged. mRNA expression levels of the other antimicrobial peptides remained unchanged with higher levels of α-defensins than β-defensins. V. cholerae induced an innate immune response at the acute stage of disease characterized by increased expression of hBD-2, and continued expression of hBD-1, HD-5-6, and LL-37.

Paneth cell α-defensins in enteric innate immunity

Paneth cells at the base of small intestinal crypts of Lieberkühn secrete high levels of α-defensins in response to cholinergic and microbial stimuli. Paneth cell α-defensins are broad spectrum microbicides that function in the extracellular environment of the intestinal lumen, and they are responsible for the majority of secreted bactericidal peptide activity. Paneth cell α-defensins confer immunity to oral infection by Salmonella enterica serovar Typhimurium, and they are major determinants of the composition of the small intestinal microbiome. In addition to host defense molecules such as α-defensins, lysozyme, and Pla2g2a, Paneth cells also produce and release proinflammatory mediators as components of secretory granules. Disruption of Paneth cell homeostasis, with subsequent induction of endoplasmic reticulum stress, autophagy, or apoptosis, contributes to inflammation in diverse genetic and experimental mouse models.

Paneth cells, antimicrobial peptides and maintenance of intestinal homeostasis

Building and maintaining a homeostatic relationship between a host and its colonizing microbiota entails ongoing complex interactions between the host and the microorganisms. The mucosal immune system, including epithelial cells, plays an essential part in negotiating this equilibrium. Paneth cells (specialized cells in the epithelium of the small intestine) are an important source of antimicrobial peptides in the intestine. These cells have become the focus of investigations that explore the mechanisms of host-microorganism homeostasis in the small intestine and its collapse in the processes of infection and chronic inflammation. In this Review, we provide an overview of the intestinal microbiota and describe the cell biology of Paneth cells, emphasizing the composition of their secretions and the roles of these cells in intestinal host defence and homeostasis. We also highlight the implications of Paneth cell dysfunction in susceptibility to chronic inflammatory bowel disease.

Paneth cells, antimicrobial peptides and maintenance of intestinal homeostasis

Building and maintaining a homeostatic relationship between a host and its colonizing microbiota entails ongoing complex interactions between the host and the microorganisms. The mucosal immune system, including epithelial cells, plays an essential part in negotiating this equilibrium. Paneth cells (specialized cells in the epithelium of the small intestine) are an important source of antimicrobial peptides in the intestine. These cells have become the focus of investigations that explore the mechanisms of host-microorganism homeostasis in the small intestine and its collapse in the processes of infection and chronic inflammation. In this Review, we provide an overview of the intestinal microbiota and describe the cell biology of Paneth cells, emphasizing the composition of their secretions and the roles of these cells in intestinal host defence and homeostasis. We also highlight the implications of Paneth cell dysfunction in susceptibility to chronic inflammatory bowel disease.

Fibroblast growth factor receptor-3 (FGFR-3) regulates expression of paneth cell lineage-specific genes in intestinal epithelial cells through both TCF4/beta-catenin-dependent and -independent signaling pathways

Fibroblast growth factor receptor-3 (FGFR-3) expression in the developing intestine is restricted to the undifferentiated epithelial cells within the lower portion of the crypt. We previously showed that mice lacking functional FGFR-3 have a significant decrease in the number of Paneth cells in the small intestine. Here, we used Caco2 cells to investigate whether FGFR-3 signaling can directly modulate expression of Paneth cell differentiation markers through its effects on TCF4/β-catenin or through other signaling pathways downstream of this receptor. Caco2 cells treated with FGFR-3 ligands or expressing FGFR-3(K650E), a constitutively active mutant, resulted in a significantly increased expression of genes characteristic of mature Paneth cells, including human α-defensins 5 and 6 (HD5 and HD6) and Paneth cell lysozyme, whereas enterocytic differentiation markers were reduced. Activation of FGFR-3 signaling sustained high levels of β-catenin mRNA expression, leading to increased TCF4/β-catenin-regulated transcriptional activity in Caco2 cells. Sustained activity of the TCF4/β-catenin pathway was required for the induction of Paneth cell markers. Activation of the MAPK pathway by FGFR-3 is also required for the induction of Paneth cell markers in addition to and independent of the effect of FGFR-3 on TCF4/β-catenin activity. These studies suggest that coordinate activation of multiple independent signaling pathways downstream of FGFR-3 is involved in regulation of Paneth cell differentiation.

Expression profiling of Wnt family of genes in normal and inflammatory bowel disease primary human intestinal myofibroblasts and normal human colonic crypt epithelial cells

BACKGROUND

Wnt signaling regulates intestinal epithelial stem cell function. Wnt ligands bind Frizzled (Fz) receptors and low-density lipoprotein-receptor-related protein (LRP) 5 and 6. Secreted Frizzled-related protein (SFRP) and Dickkopf families inhibit Wnt signaling. Our aim was to study expression of Wnt family of genes in isolated intestinal myofibroblasts and crypt epithelial cells.

METHODS

Myofibroblasts were isolated from normal colonic and small intestinal mucosal samples and those affected by ulcerative colitis (UC) and Crohn's disease. Expression of the Wnt family of genes was studied by polymerase chain reaction (PCR) array. Epithelial proliferation was studied using IEC-6 cells.

RESULTS

Most of the myofibroblast isolates expressed Wnt2, Wnt5A, Wnt5B, Fzd1, Fzd2, Fzd4, Fzd6, Fzd7, Fzd8, LRP6, Dickkopf1, and SFRP1. Compared to myofibroblasts isolated from normal colonic mucosal samples, real-time reverse transcription-PCR studies (using additional isolates) showed significantly reduced expression of SFRP1 in UC myofibroblasts (3.34-fold reduction, P < 0.01). Recombinant SFRP1 inhibited proliferation of IEC-6 epithelial cells. In colonic crypt epithelial cells, expression of Wnt ligands and their inhibitors was generally either absent or very weak. By contrast, all the crypt epithelial preparations expressed Fzd1, Fzd5, Fzd7, Fzd8, and LRP6.

CONCLUSIONS

Human intestinal myofibroblasts expressed a number of Wnt ligands, their receptors, and inhibitors. In contrast, colonic crypt epithelial cells predominantly expressed Wnt receptors. Compared to myofibroblasts isolated from normal colonic mucosa, those affected by UC showed significantly reduced expression of SFRP1. Since reduced SFRP1 expression has been associated with malignancy, low myofibroblast expression of this Wnt inhibitor may be implicated in increased risk of cancer in UC.

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.

Altered expression of innate immunity genes in different intestinal sites of children with ulcerative colitis

BACKGROUND

Innate immunity has been very rarely investigated in ulcerative colitis and never in paediatrics. The present study was aimed at describing expression of innate immunity genes (NOD2, RIP2, α-defensins HD5 and HD6) in inflamed colon and in ileum of children with ulcerative colitis. Expression of TNFα and IL-1β was also analyzed.

METHODS

15 children with ulcerative colitis (9 pancolitis, 6 left-sided colitis) and 10 control children were enrolled. mRNA and protein expressions were detected by real time PCR and western blot assays.

RESULTS

NOD2, RIP2, IL-1β, TNFα expression levels were significantly increased in colonic mucosa of patients compared to controls (p<0.01). These genes were also upregulated (p<0.01) in the ileum of both pancolitis and left-sided colitis children. HD5 and HD6 were significantly upregulated (p<0.01) in the inflamed colon of patients as well as in the ileum of those with pancolitis.

CONCLUSIONS

An increased mucosal expression of innate immunity genes was found in the inflamed colon of children with ulcerative colitis, outlining the role of the innate immune response in disease pathogenesis. Involvement of the ileum in ulcerative colitis suggests that an immune activation can also be established in intestinal sites classically uninvolved by the inflammation, carrying implications for the treatment and course of the disease.

Antimicrobial peptides in gastrointestinal inflammation

Acute and chronic inflammations of mucosal surfaces are complex events in which the effector mechanisms of innate and adaptive immune systems interact with pathogenic and commensal bacteria. The role of constitutive and inducible antimicrobial peptides in intestinal inflammation has been investigated thoroughly over the recent years, and their involvement in various disease states is expanded ever more. Especially in the intestines, a critical balance between luminal bacteria and the antimicrobial peptides is essential, and a breakdown in barrier function by impaired production of defensins is already implicated in Crohn's disease. In this paper, we focus on the role of antimicrobial peptides in inflammatory processes along the gastrointestinal tract, while considering the resident and pathogenic flora encountered at the specific sites. The role of antimicrobial peptides in the primary events of inflammatory bowel diseases receives special attention.

Paneth cells and innate mucosal immunity

PURPOSE OF REVIEW

Recent evidence shows that disruption of Paneth cell homeostasis by induction of endoplasmic reticulum stress or autophagy, with consequent apoptosis, contributes to inflammation and morbidity in a variety of experimental mouse models.

RECENT FINDINGS

Recent advances show that proinflammatory mediators in Paneth cell dense core secretory granules mediate tumor necrosis factor-α-induced shock, that Paneth cell α-defensins modulate the composition of the small intestinal microflora, that development of crypt organoid culture systems provides a novel means for investigating the crypt microenvironment, and that varied genetic defects that disrupt Paneth cell homeostasis are emergent as risk factors in inflammatory bowel disease.

SUMMARY

This recent literature identifies Paneth cells as particularly sensitive targets of endoplasmic reticulum stress responses and implicates this unique small intestinal lineage in inflammatory bowel disease pathogenesis resulting from diverse heritable and environmental causes.

Intestinal metaplasia -the effect of Acid on the gastric mucosa and gastric carcinogenesis-

This review concerns stem cells and their relation to intestinal metaplasia. When gastric regions of mice, Mongolian gerbils or several strains of rats were irradiated with a total dose of 20 Gy of X-rays given in two fractions, intestinal metaplasia was only induced in rats. In addition, it was greatly influenced by rat strain and sex. Alkaline phosphatase (ALP) positive metaplastic foci were increased by administration of ranitidine (H₂ receptor antagonist), crude stomach antigens or subtotal resection of the fundus and decreased by cysteamine (gastric acid secretion stimulator), histamine or removal of the submandibular glands. Recent studies have shown that Cdx2 transgenic mice with gastric achlorhydria develop intestinal metaplasia and that in men and animals, Helicobacterpylori (H. pyrlori) infection can cause intestinal metaplasias that are reversible on eradication. Our results combined with findings for H. pylori infection or eradication and transgenic mice suggest that an elevation in the pH of the gastric juice due to disappearance of parietal cells is one of the principal factors for development of reversible intestinal metaplasia. When different organs were transplanted into the stomach or duodenum, they were found to transdifferentiate into gastric or duodenal mucosae, respectively. Organ-specific stem cells in normal non-liver tissues (heart, kidney, brain and skin) also differentiate into hepatocytes when transplanted into an injured liver. Therefore, stem cells have a multipotential ability, transdifferentiating into different organs when transplanted into different environments. Finally, intestinal metaplasia has been found to possibly increase sensitivity to the induction of tumors by colon carcinogens of the 1,2-dimethylhydrazine (DMH), azoxymethane (AOM) or 2-amino-1-methyl-6-phenylimidazo[4.5-b]pyridine (PhIP) type. This carcinogenic process, however, may be relatively minor compared with the main gastric carcinogenesis process induced by N-methy1-N’-nitro-N-nitrosoguanidine (MMNG) or N-methylnitrosourea (MNU), which is not affected by the presence of intestinal metaplasia. The protocol used in these experiments may provide a new approach to help distinguish between developmental events associated with intestinal metaplasia and gastric tumors.

Defective paneth cell-mediated host defense in pediatric ileal Crohn's disease

OBJECTIVES

Adult ileal Crohn's disease (CD) is characterized by a specific decrease in ileal Paneth cell alpha-defensins. In addition to NOD2, we previously identified a disturbance of the Wnt-signaling transcription factor TCF-4 as a major mechanism for this deficiency. The aim of this study was to evaluate human alpha-defensin-5 (HD-5) and TCF-4 in an independent cohort of pediatric CD patients.

METHODS

Expression levels of HD-5 and TCF-4 mRNA were quantified by real-time PCR in biopsies from newly diagnosed untreated pediatric CD patients (<18 years, n=36) and age-matched symptomatic non-inflammatory bowel disease controls with a histologically normal gut (n=29). To assess the influence of current inflammation, mucosal interleukin-8 (IL-8) and fecal calprotectin levels were determined.

RESULTS

Small intestinal HD-5 and TCF-4 mRNA were significantly reduced in pediatric ileal CD (L1+L3) (P=0.022 and P=0.0005, respectively) and were significantly correlated (r=0.499; P=0.0001). In ileal but not colonic CD, TCF-4 was also reduced in the colon (P=0.005). Importantly, both HD-5 and TCF-4 were independent of inflammation, as measured by IL-8 expression or fecal calprotectin. In contrast to the small intestine, colonic Paneth cell HD-5 mRNA was significantly elevated in colonic CD (L2) (P=0.026) and was correlated with fecal calprotectin levels (r=0.481; P=0.020).

CONCLUSIONS

In this study, we describe a specific decrease in HD-5 and TCF-4 mRNA expression levels in children with ileal CD. In the small intestine, this decrease was independent of current inflammation, whereas inflammation seems to induce Paneth cell metaplasia in the colon. Our data extend the hypothesis of an important role of antimicrobial host defense in pediatric CD patients.

Hepcidin and inflammatory bowel disease: dual role in host defence and iron homoeostasis

OBJECTIVE

Hepcidin is an endogenous antimicrobial peptide with a key role in iron homoeostasis. Hepcidin is similar to defensin, the deficiency of which is associated with Crohn's disease. To date there has been no validated method to reliably assay serum hepcidin. We studied iron indices in inflammatory bowel disease (IBD) including hepcidin.

DESIGN

We assessed serum hepcidin concentrations (using a newly developed competitive radioimmunoassay) and ferritin in patients with IBD. Haematinics including serum soluble transferrin receptor, serum iron, serum vitamin B12 and red cell folate levels were also measured. The hepcidin results were compared with a control group of healthy volunteers from the local community.

SETTING

This study was based in a hospital.

PATIENTS

Sixty-one patients with IBD (51 patients with ulcerative colitis and 10 with Crohn's disease). Their mean hepcidin results were compared with 25 healthy controls.

MAIN OUTCOME MEASURE

hepcidin concentration in serum samples in IBD patients compared with normal volunteers.

RESULTS

We found significantly low serum hepcidin levels in patients with IBD. The hepcidin levels were low in IBD patients without iron deficiency anaemia as evidenced by normal ferritin and serum iron levels (n=41, mean hepcidin 6.81 ng/ml, SEM 1.2) and in IBD patients with iron deficiency anaemia (n=18, mean hepcidin 4.14 ng/ml, SEM 0.72) compared with healthy controls (n=25, mean hepcidin 15.3 ng/ml, SEM 3.14) (P=0.0045 and P=0.0050 on unpaired t-tests, respectively). We also measured IL-6 (enzyme-linked immunosorbent assay method, Abcam plc) in 21 of the 61 patients with IBD and compared the results with samples from 10 healthy volunteers. The IL-6 level was significantly higher (P=0.0222 on unpaired t-tests) in this group of IBD patients (n=21, IL-6 mean 2.94 pg/ml, SEM 0.64) compared with controls (n=10, IL-6 mean 0.663 pg/ml SEM 0.14). A significant positive correlation (Pearson's correlation coefficient r=0.6331) was present between hepcidin and IL-6, but not between hepcidin and serum soluble transferrin receptor (r=-0.235).

CONCLUSION

The low hepcidin results in IBD patients may reflect a causal or perpetuator effect on intestinal inflammation.

Differential Processing of {alpha}- and {beta}-Defensin Precursors by Matrix Metalloproteinase-7 (MMP-7)

Proteolytic processing of defensins is a critical mode of posttranslational regulation of peptide activity. Because mouse alpha-defensin precursors are cleaved and activated by matrix metalloproteinase-7 (MMP-7), we determined if additional defensin molecules, namely human neutrophil defensin pro-HNP-1 and beta-defensins, are targets for MMP-7. We found that MMP-7 cleaves within the pro-domain of the HNP-1 precursor, a reaction that does not generate the mature peptide but produces a 59-amino acid intermediate. This intermediate, which retains the carboxyl-terminal end of the pro-domain, had antimicrobial activity, indicating that the residues important for masking defensin activity reside in the amino terminus of this domain. Mature HNP-1 was resistant to processing by MMP-7 unless the peptide was reduced and alkylated, demonstrating that only the pro-domain of alpha-defensins is normally accessible for cleavage by this enzyme. From the 47-residue HBD-1 precursor, MMP-7 catalyzed removal of 6 amino acids from the amino terminus. Neither a 39-residue intermediate form of HBD-1 nor the mature 36-residue form of HBD-1 was cleaved by MMP-7. In addition, both pro-HBD-2, with its shorter amino-terminal extension, and pro-HBD-3 were resistant to MMP-7. However, human and mouse beta-defensin precursors that lack disulfide bonding contain a cryptic MMP-7-sensitive site within the mature peptide moiety. These findings support and extend accumulating evidence that the native three-dimensional structure of both alpha- and beta-defensins protects the mature peptides against proteolytic processing by MMP-7. We also conclude that sites for MMP-7 cleavage are more common at the amino termini of alpha-defensin rather than beta-defensin precursors, and that catalysis at these sites in alpha-defensin pro-domains results in acquisition of defensin activity.

Paneth cell differentiation in colonic epithelial neoplasms: evidence for the role of the Apc/beta-catenin/Tcf pathway

Paneth cell differentiation may occur in colonic epithelial neoplasms. However, its significance and mechanism of development remains unclear. Human defensin 5 is a specific marker of Paneth cells and has been shown to represent one of the target genes of the Apc/beta-catenin/Tcf pathway. The aim of this study was to evaluate the frequency of Paneth cell differentiation in a variety of colonic neoplasms, and to investigate the role of human defensin 5 and beta-catenin in this process. The clinical and pathologic findings, including histologic evidence of Paneth cell differentiation and immunostaining for human defensin 5 and beta-catenin, were evaluated in 29 samples of nonneoplastic colonic mucosa, 18 hyperplastic polyps, 10 sessile serrated adenomas, 12 traditional serrated adenomas, 21 mixed polyps, 39 conventional adenomas, and 40 adenocarcinomas. Human defensin-5 and beta-catenin expression were evaluated for the location and degree of staining in all cell types (dysplastic and nondysplastic) and correlated with histologic areas of Paneth cell differentiation in all types of polyps. Histologic evidence of Paneth cell differentiation was observed in 15 conventional adenomas (38.5%) and 1 adenocarcinoma (2.5%) but not in other types of polyps. Human defensin-5 immunostaining was positive in the cytoplasm of all nonneoplastic Paneth cells and all neoplastic cells with Paneth cell differentiation. Human defensin-5 expression was noted in 0% of hyperplastic polyps, 10% of sessile serrated adenomas, 25% of traditional serrated adenomas, 33.3% of mixed polyps, 82.1% of conventional adenomas, and 17.5% of adenocarcinomas: human defensin 5 expression was significantly higher in conventional adenomas compared to all other groups (P < .01). Seventeen (53.1%) of 32 human defensin 5 positive conventional adenomas, 6 (86%) of 7 of human defensin 5 positive adenocarcinomas, and all human defensin 5-positive sessile serrated adenomas, traditional serrated adenomas, and mixed polyps did not show histologic evidence of Paneth cell differentiation. All mixed polyps (100%) that revealed human defensin 5 expression (7; 33.3%) revealed conventional dysplasia. In the positive mixed polyp cases, human defensin 5 was only positive in areas of conventional dysplasia. Of the 31 conventional adenomas with nuclear beta-catenin staining, 15 (48.4%) revealed histologic evidence of Paneth cell differentiation, and all of the neoplastic cells with Paneth cell differentiation showed nuclear beta-catenin staining, whereas nonneoplastic Paneth cells consistently showed a normal pattern of membranous beta-catenin staining. A strong topographical correlation was noted between human defensin 5 expression and nuclear beta-catenin expression in conventional adenomas and in conventional dysplastic epithelium of mixed polyps. Paneth cell differentiation is common in early colonic neoplasms that develop via the conventional adenoma-carcinoma carcinogenic pathway. Activation of Apc/beta-catenin/Tcf pathway may play a role in Paneth cell differentiation in human colonic neoplasms.

Contribution of intestinal epithelial cells to innate immunity of the human gut--studies on polarized monolayers of colon carcinoma cells

The aim was to establish an in vitro model for studies of innate defence mechanisms of human intestinal epithelium. Ultrastructural characterization and determination of mRNA expression levels for apical glycocalyx and mucous components showed that polarized, tight monolayers of the colon carcinoma cell lines T84 and Caco2 acquire the features of mature- and immature columnar epithelial cells, respectively. Polarized monolayers were challenged with non-pathogenic Gram+ and Gram- bacteria from the apical side and the proinflammatory cytokines interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) from the basolateral side. Immune responses were estimated as changes in mRNA expression levels for the mucous component mucin-2 (MUC2), the glycocalyx components carcinoembryonic antigen (CEA), CEA-related cell adhesion molecule-1 (CEACAM1), CEACAM6, CEACAM7 and MUC3, the antimicrobial factors human beta-defensin-1 (hBD1), hBD2, hBD3 and lysozyme, the chemokine IL-8 and the cytokines IL-6 and TNF-alpha. Tight monolayer cells were generally unresponsive to bacterial challenge, but increased their hBD2 levels when challenged with Bacillus megaterium. T84 cells also increased their TNF-alpha levels upon bacterial challenge. Tight monolayer cells responded to cytokine challenge suggesting awareness of basolateral attack. TNF-alpha induced significantly increased levels of IL-8 and TNF-alpha itself in both cell lines suggesting recruitment and activation of immune cells in the underlying mucosa in vivo. Cytokine challenge also increased levels of CEACAM1, which includes two functionally different forms, CEACAM1-L and CEACAM1-S. In T84 cells, IFN-gamma was selective for CEACAM1-L while TNF-alpha upregulated both forms. Increased CEACAM1 expression may influence epithelial function and communication between epithelial cells and intraepithelial lymphocytes.

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.

Characterization of putative stem cells in isolated human colonic crypt epithelial cells and their interactions with myofibroblasts

Colonic epithelial stem cells are believed to be located at the crypt base where they have previously been shown to express musashi-1. The colonic stem cell niche, which includes extracellular matrix and myofibroblasts (together with other cell types), is likely to be important in maintaining the function of the progenitor cells. The aims of our studies were to characterize stem cells in isolated and disaggregated human colonic crypt epithelial cells and investigate their interactions with monolayers of primary human colonic myofibroblasts. In unfractionated preparations of disaggregated colonic crypts, musashi-1 positive cells preferentially adhered to colonic myofibroblasts, despite the presence of excess blocking anti-beta(1)-integrin antibody. These adherent epithelial cells remained viable for a number of days and developed slender processes. Cells with side population characteristics (as demonstrated by ability to expel the dye Hoechst 33342) were consistently seen in the isolated colonic crypt epithelial cells. These side population cells expressed musashi-1, beta(1)-integrin, BerEP4, and CD133. Sorted side population crypt epithelial cells also rapidly adhered to primary colonic myofibroblasts. In conclusion, in preparation of isolated and disaggregated human colonic crypts, cells with stem cell characteristics preferentially adhere to primary human colonic myofibroblasts in a beta(1)-integrin-independent fashion.

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.

Molecular determinants for the interaction of human neutrophil alpha defensin 1 with its propeptide

Human neutrophil alpha-defensins (HNPs) are cationic antimicrobial peptides that are synthesized in vivo as inactive precursors (proHNPs). Activation requires proteolytic excision of their anionic N-terminal inhibitory pro peptide. The pro peptide of proHNP1 also interacts specifically with and inhibits the antimicrobial activity of HNP1 inter-molecularly. In the light of the opposite net charges segregated in proHNP1, functional inhibition of the C-terminal defensin domain by its propeptide is generally thought to be of electrostatic nature. Using a battery of analogs of the propeptide and of proHNP1, we identified residues in the propeptide region important for HNP1 binding and inhibition. Only three anionic residues in the propeptide, Glu(15), Asp(20) and Glu(23), were modestly important for interactions with HNP1. By contrast, the hydrophobic residues in the central part of the propeptide, and the conserved hydrophobic motif Val(24)Val(25)Val(26)Leu(28) in particular, were critical for HNP1 binding and inhibition. Neutralization of all negative charges in the propeptide only partially activated the bactericidal activity of proHNP1. Our data indicate that hydrophobic forces have a dominant role in mediating the interactions between HNP1 and its propeptide--a finding largely contrasting the commonly held view that the interactions are of an electrostatic nature.

Stem cells might participate in the cell turnover of duodenal adenomas

Eighty-three duodenal adenomas were stained with hematoxylin-eosin (H&E) and with anti-lysozyme immunostain. Mature Paneth cells were those showing coarse brightly red cytoplasmic granules in H&E stain and Paneth cell precursors were those lysozyme-expressing cells that had remained undetected in H&E stain. In the adenomas, the number of mature Paneth cells/high power field varied from 4 to 12 (mean 6.5) in H&E stain, and of lysozyme-expressing cells from 32 to 62 (mean 46.5) (p<0.05). Lysozyme-expressing cells were found haphazardly distributed within the histological profile of the lesion, even in the most superficial cell layer of the dysplastic glands. The latter suggests that if the innate programmed vector of cell migration were valid for duodenal adenomas (from stem cells towards the bottom of the crypts for Paneth cells) the stem cells, normally overlaying Paneth cells, would have been exfoliated into the lumen. Another, less likely option, is that mutated stem cells at the bottom of duodenal adenomas translocate, in an unprecedented manner, the ontogenic signals of migration for Paneth cells. This stochastic molecular option would imply a total reversal of the normal migratory vector for Paneth cells, to a more aberrant, paradoxical migration flow, from stem cells to the villus domain, before exfoliation. Because of the unique migratory direction of the Paneth cells in the crypts of Lieberkühn, the duodenal adenoma emerges as a suitable histo-biological model to monitor the fate of stem cells. It is suggested that stem cells, together with the other recordable mature cells, namely dysplastic enterocytes, Paneth cells and goblet cells, participate in the cell turnover of duodenal adenomas. Further studies are necessary to definitively validate the abovementioned suggested hypothesis.

The mucosal immune system at the gastrointestinal barrier

The immune system faces a considerable challenge in its efforts to maintain tissue homeostasis in the intestinal mucosa. It is constantly confronted with a large array of antigens, and has to prevent the dissemination and proliferation of potentially harmful agents while sparing the vital structures of the intestine from immune-mediated destruction. Complex interactions between the highly adapted effector cells and mechanisms of the innate and adaptive immune system generally prevent the luminal microflora from penetrating the intestinal mucosa and from spreading systemically. Non-haematopoietic cells critically contribute to the maintenance of local tissue homeostasis in an antigen-rich environment by producing protective factors (e.g. production of mucus by goblet cells, or secretion of microbicidal defensins by Paneth cells) and also through interactions with the adaptive and innate immune system (such as the production of chemotactic factors that lead to the selective recruitment of immune cell subsets). The complexity of the regulatory mechanisms that control the local immune response to luminal antigens is also reflected in the observation that mutations in immunologically relevant genes often lead to the development of uncontrolled inflammatory reactions in the microbially colonized intestine of experimental animals.

Neisseria gonorrhoeae-induced human defensins 5 and 6 increase HIV infectivity: role in enhanced transmission

Sexually transmitted infections (STIs) increase the likelihood of HIV transmission. Defensins are part of the innate mucosal immune response to STIs and therefore we investigated their role in HIV infection. We found that human defensins 5 and 6 (HD5 and HD6) promoted HIV infection, and this effect was primarily during viral entry. Enhancement was seen with primary viral isolates in primary CD4(+) T cells and the effect was more pronounced with R5 virus compared with X4 virus. HD5 and HD6 promoted HIV reporter viruses pseudotyped with vesicular stomatitis virus and murine leukemia virus envelopes, indicating that defensin-mediated enhancement was not dependent on CD4 and coreceptors. Enhancement of HIV by HD5 and HD6 was influenced by the structure of the peptides, as loss of the intramolecular cysteine bonds was associated with loss of the HIV-enhancing effect. Pro-HD5, the precursor and intracellular form of HD5, also exhibited HIV-enhancing effect. Using a cervicovaginal tissue culture system, we found that expression of HD5 and HD6 was induced in response to Neisseria gonorrhoeae (GC, for gonococcus) infection and that conditioned medium from GC-exposed cervicovaginal epithelial cells with elevated levels of HD5 also enhanced HIV infection. Introduction of small interfering RNAs for HD5 or HD6 abolished the HIV-enhancing effect mediated by GC. Thus, the induction of these defensins in the mucosa in the setting of GC infection could facilitate HIV infection. Furthermore, this study demonstrates the complexity of defensins as innate immune mediators in HIV transmission and warrants further investigation of the mechanism by which defensins modulate HIV infection.

An anti-adenoma antibody, Adnab-9, may reflect the risk for neoplastic progression in familial hamartomatous polyposis syndromes

Patients with the hamartomatous polyposis Peutz-Jeghers and familial juvenile polyposis syndromes are predisposed to colorectal cancer but lack early genetic alterations found in adenomatous premalignant lesions. We studied hamartomatous polyps for the expression of an early preneoplastic colorectal neoplasia risk marker also found in familial adenomatous polyposis patients. Retrospective, genetic, and hospital archival tissue immunohistochemistry using Adnab-9, a premalignant marker often found in Paneth-like cells (PCs), was performed on sections of polyps from eight patients with Peutz-Jeghers syndrome, eight patients with familial juvenile polyposis, and 36 hyperplastic polyp control sections. Anti-alpha-defensin 5 (AD5), a universal PC marker, was also used to label a subgroup of sections. Hamartomatous polyposis patients also underwent specific genetic analysis. Eighty-nine percent of Peutz-Jeghers syndrome polyps labeled with Adnab-9 compared with 63% for AD5; 88% of familial juvenile polyposis sections also labeled with Adnab-9. Of the 36 hyperplastic polyp sections, only four (11%) labeled with Adnab-9 and one (3%) with AD5. Adnab-9 labeling of PCs in the epithelial elements of hamartomatous colonic lesions of hereditary hamartomatous syndrome patients reflects the predisposition to colorectal cancer, further justifying early intervention strategies.

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.

Defensins and Paneth cells in inflammatory bowel disease

Defensins are antimicrobial peptides produced by professional phagocytes, Paneth cells, and intestinal epithelial cells. In addition to their potent antimicrobial activity, defensins can also modulate the function and movement of neutrophils, monocytes, T-lymphocytes, dendritic cells, and epithelial cells. Paneth cells are equipped with multiple defensins and antimicrobial proteins and usually reside in the small intestine. This review highlights the diverse functions of defensins and changes in defensin expression and Paneth cell proliferation in Crohn's disease, ulcerative colitis, and animal models of inflammatory bowel disease. Current data favor the hypothesis that defensins and Paneth cells may play important roles in the maintenance of intestinal immune homeostasis through 2 distinct mechanisms. The first mechanism is to act as effector molecules and cells against pathogenic microbes, while the second is to regulate host immune cell functions.

Probiotics for preventing relapse or recurrence in Crohn's disease involving the ileum: Are there reasons for failure?

In contrast to ulcerative colitis and pouchitis, benefits of probiotic therapy in preventing recurrence/relapse in Crohn's disease (mostly involving the ileum) are far from being proven. The lack of response in this setting does not seem attributable to a lower relevance of dysbiosis in ileal Crohn's disease, since this - or at least the presence of increased mucosal amounts of potentially pathogen bacteria - has been proven to occur in the ileum of Crohn's disease patients. Available data indicate that whereas in ulcerative colitis (and to a lesser extent in colonic Crohn's disease) the innate immune response is enhanced, it is constitutively depressed in ileal Crohn's disease. Therefore, attempts to modify the composition of intestinal microflora in colonic IBD or pouchitis by means of probiotics do make sense. In contrast, supplying additional bacteria (even being probiotics) to an ileum with decreased antibacterial defence does not seem reasonable. In fact, the presence of intestinal contents has been reported to be related to postoperative recurrence in ileo-caecal Crohn's disease, and antibiotic treatment in effective to prevent its development.

Alteration in human defensin-5 expression following gastric bypass surgery

BACKGROUND

Roux-en-Y gastric bypass surgery provides a novel human model to investigate small bowel mucosal innate immunity, in which there is loss of gastric acid-mediated protection against orally-acquired microorganisms.

AIM

To study changes in jejunal mucosal immunoreactivity of human defensin (HD)-5, an antimicrobial peptide normally produced by Paneth cells.

METHODS

Mucosal samples were obtained from 18 female patients (24-54 years), from the same segment of jejunum during and after gastric bypass surgery. Samples were used for bacterial culture and immunohistochemistry using anti-HD-5 antibody. The number of immunoreactive cells per crypt and villus were determined and expressed as mean (SD).

RESULTS

No bacteria were cultured from any of the perioperative jejunal samples but colonies of bacteria normally present in the pharynx were identified during culture of all postoperative jejunal biopsy specimens (1->100 colonies). Paneth cell numbers per crypt were unchanged after gastric bypass (4.16 (0.71) vs 4.24 (0.78)). However, following surgery, there was an increase in HD-5-positive intermediate cells per crypt (0.25 (0.41) vs 1.12 (0.66), p<0.01), HD-5 staining enterocytes per crypt (0.03 (0.09) vs 1.38 (1.10), p<0.01), HD-5 staining material in the crypt lumen (crypt lumens: 5.0% (10.9%) vs 68.1% (27.9%), p<0.01) and HD-5 immunoreactivity coating the luminal surface of villus enterocytes (villi sampled: 15.0% (31.0%) vs 67.5% (42.0%), p<0.01).

CONCLUSIONS

Bacteria normally resident in the pharynx were present in the proximal jejunal mucosa following Roux-en-Y gastric bypass surgery. After gastric bypass, there was increased secretion of HD-5 and an increase in HD-5 expressing intermediate cells and enterocytes in the crypt. The increase in HD-5 expression in the jejunal mucosa following gastric bypass surgery is likely to be secondary to exposure to orally-acquired microorganisms.