Localization of human intestinal defensin 5 in Paneth cell granules

Anti-DEFA5 Monoclonal Antibody Clones 1A8 and 4F5 Immunoreactive Bioassay for Diagnosing Inflammatory Bowel Disease

Background

Robust evidence suggests that the aberrant expression of α defensin 5 protein (DEFA5) in colon inflammatory bowel diseases (IBDs) underlies the distinct pathogenesis of Crohn's colitis, can be exploited as a reliable diagnostic biomarker to differential diagnosis of Crohn's colitis (CC) from Ulcerative colitis (UC) in otherwise indeterminate colitis (IC). We evaluated the specificity of the commercially available anti-DEFA5 antibodies and showed further validation of their appropriateness for a given application is required.

Methods

We established two mouse monoclonal DEFA5 antibody clones 1A8 and 4F5 by immunizing the mice with purified recombinant protein and validated the specificity, selectivity and cross reactivity in recognizing the endogenous and recombinant DEFA5 protein, especially for Immunohistochemistry, Western blot, Immunoprecipitation, or enzyme-linked immunosorbent assay.

Results

Clones 1A8 and 4F5 recognized effectively the endogenous DEFA5 in active human diverticulitis (DV), UC, CC or IC disease samples, including transiently transfected HEK293T cells expressing DEFA5 with high degree of specificity and minimal non-confounding cross reactivity.

Conclusions

1A8 and 4F5 clones are worth studying in larger IBD cohorts to fully address whether DEFA5 expression may be used as a diagnostic biomarker to discrimination of the diagnosis of UC from CC or IC into authentic CC or UC or a colitis with different pathological characteristics.

Application of enzyme-linked immunosorbent assay to detect antimicrobial peptides in human intestinal lumen

Intestinal transplantation is the definitive treatment for intestinal failure. However, tissue rejection and graft-versus-host disease are relatively common complications, necessitating aggressive immunosuppression that can itself pose further complications. Tracking intraluminal markers in ileal effluent from standard ileostomies may present a noninvasive and sensitive way to detect developing pathology within the intestinal graft. This would be an improvement compared to current assessments, which are limited by poor sensitivity and specificity, contributing to under or over-immunosuppression, respectively, and by the need for invasive biopsies. Herein, we report an approach to reproducibly analyze ileal fluid obtained through stoma sampling for antimicrobial peptide/protein concentrations, reasoning that these molecules may provide an assessment of intestinal homeostasis and levels of intestinal inflammation over time. Concentrations of lysozyme (LYZ), myeloperoxidase (MPO), calprotectin (S100A8/A9) and β-defensin 2 (DEFB2) were assessed using adaptations of commercially available enzyme-linked immunosorbent assays (ELISAs). The concentration of α-defensin 5 (DEFA5) was assessed using a newly developed sandwich ELISA. Our data support that with proper preparation of ileal effluent specimens, precise and replicable determination of antimicrobial peptide/protein concentrations can be achieved for each of these target molecules via ELISA. This approach may prove to be reliable as a clinically useful assessment of intestinal homeostasis over time for patients with ileostomies.

Infection and inflammation stimulate expansion of a CD74+ Paneth cell subset to regulate disease progression

Paneth cells (PCs), a specialized secretory cell type in the small intestine, are increasingly recognized as having an essential role in host responses to microbiome and environmental stresses. Whether and how commensal and pathogenic microbes modify PC composition to modulate inflammation remain unclear. Using newly developed PC-reporter mice under conventional and gnotobiotic conditions, we determined PC transcriptomic heterogeneity in response to commensal and invasive microbes at single cell level. Infection expands the pool of CD74+ PCs, whose number correlates with auto or allogeneic inflammatory disease progressions in mice. Similar correlation was found in human inflammatory disease tissues. Infection-stimulated cytokines increase production of reactive oxygen species (ROS) and expression of a PC-specific mucosal pentraxin (Mptx2) in activated PCs. A PC-specific ablation of MyD88 reduced CD74+ PC population, thus ameliorating pathogen-induced systemic disease. A similar phenotype was also observed in mice lacking Mptx2. Thus, infection stimulates expansion of a PC subset that influences disease progression.

Antimicrobial Peptide Synergies for Fighting Infectious Diseases

Antimicrobial peptides (AMPs) are essential elements of thehost defense system. Characterized by heterogenous structures and broad-spectrumaction, they are promising candidates for combating multidrug resistance. Thecombined use of AMPs with other antimicrobial agents provides a new arsenal ofdrugs with synergistic action, thereby overcoming the drawback of monotherapiesduring infections. AMPs kill microbes via pore formation, thus inhibitingintracellular functions. This mechanism of action by AMPs is an advantage overantibiotics as it hinders the development of drug resistance. The synergisticeffect of AMPs will allow the repurposing of conventional antimicrobials andenhance their clinical outcomes, reduce toxicity, and, most significantly,prevent the development of resistance. In this review, various synergies ofAMPs with antimicrobials and miscellaneous agents are discussed. The effect ofstructural diversity and chemical modification on AMP properties is firstaddressed and then different combinations that can lead to synergistic action,whether this combination is between AMPs and antimicrobials, or AMPs andmiscellaneous compounds, are attended. This review can serve as guidance whenredesigning and repurposing the use of AMPs in combination with other antimicrobialagents for enhanced clinical outcomes.

Evolutionary diversification of defensins and cathelicidins in birds and primates

Divergent evolution for more than 310 million years has resulted in an avian immune system that is complex and more compact than that of primates, sharing much of its structure and functions. Not surprisingly, well conserved ancient host defense molecules, such as defensins and cathelicidins, have diversified over time. In this review, we describe how evolution influenced the host defense peptides repertoire, its distribution, and the relationship between structure and biological functions. Marked features of primate and avian HDPs are linked to species-specific characteristics, biological requirements, and environmental challenge.

Human intelectin-2 (ITLN2) is selectively expressed by secretory Paneth cells

Intelectins (intestinal lectins) are highly conserved across chordate evolution and have been implicated in various human diseases, including Crohn's disease (CD). The human genome encodes two intelectin genes, intelectin-1 (ITLN1) and intelectin-2 (ITLN2). Other than its high sequence similarity with ITLN1, little is known about ITLN2. To address this void in knowledge, we report that ITLN2 exhibits discrete, yet notable differences from ITLN1 in primary structure, including a unique amino terminus, as well as changes in amino acid residues associated with the glycan-binding activity of ITLN1. We identified that ITLN2 is a highly abundant Paneth cell-specific product, which localizes to secretory granules, and is expressed as a multimeric protein in the small intestine. In surgical specimens of ileal CD, ITLN2 mRNA levels were reduced approximately five-fold compared to control specimens. The ileal expression of ITLN2 was unaffected by previously reported disease-associated variants in ITLN2 and CD-associated variants in neighboring ITLN1 as well as NOD2 and ATG16L1. ITLN2 mRNA expression was undetectable in control colon tissue; however, in both ulcerative colitis (UC) and colonic CD, metaplastic Paneth cells were found to express ITLN2. Together, the data reported establish the groundwork for understanding ITLN2 function(s) in the intestine, including its possible role in CD.

Regulation of Paneth Cell Function by RNA-Binding Proteins and Noncoding RNAs

Paneth cells are specialized intestinal epithelial cells that are located at the base of small intestinal crypts and play a vital role in preserving the gut epithelium homeostasis. Paneth cells act as a safeguard from bacterial translocation across the epithelium and constitute the niche for intestinal stem cells in the small intestine by providing multiple niche signals. Recently, Paneth cells have become the focal point of investigations defining the mechanisms underlying the epithelium-microbiome interactions and pathogenesis of chronic gut mucosal inflammation and bacterial infection. Function of Paneth cells is tightly regulated by numerous factors at different levels, while Paneth cell defects have been widely documented in various gut mucosal diseases in humans. The post-transcription events, specific change in mRNA stability and translation by RNA-binding proteins (RBPs) and noncoding RNAs (ncRNAs) are implicated in many aspects of gut mucosal physiology by modulating Paneth cell function. Deregulation of RBPs and ncRNAs and subsequent Paneth cell defects are identified as crucial elements of gut mucosal pathologies. Here, we overview the posttranscriptional regulation of Paneth cells by RBPs and ncRNAs, with a particular focus on the increasing evidence of RBP HuR and long ncRNA H19 in this process. We also discuss the involvement of Paneth cell dysfunction in altered susceptibility of the intestinal epithelium to chronic inflammation and bacterial infection following disrupted expression of HuR and H19.

Human Defensins Inhibit SARS-CoV-2 Infection by Blocking Viral Entry

Innate immunity during acute infection plays a critical role in the disease severity of severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), and is likely to contribute to COVID-19 disease outcomes. Defensins are highly abundant innate immune factors in neutrophils and epithelial cells, including intestinal Paneth cells, and exhibit antimicrobial and immune-modulatory activities. In this study, we investigated the effects of human α- and β-defensins and RC101, a θ-defensin analog, on SARS-CoV-2 infection. We found that human neutrophil peptides (HNPs) 1-3, human defensin (HD) 5 and RC101 exhibited potent antiviral activity against pseudotyped viruses expressing SARS-CoV-2 spike proteins. HNP4 and HD6 had weak anti-SARS-CoV-2 activity, whereas human β-defensins (HBD2, HBD5 and HBD6) had no effect. HNP1, HD5 and RC101 also inhibited infection by replication-competent SARS-CoV-2 viruses and SARS-CoV-2 variants. Pretreatment of cells with HNP1, HD5 or RC101 provided some protection against viral infection. These defensins did not have an effect when provided post-infection, indicating their effect was directed towards viral entry. Indeed, HNP1 inhibited viral fusion but not the binding of the spike receptor-binding domain to hACE2. The anti-SARS-CoV-2 effect of defensins was influenced by the structure of the peptides, as linear unstructured forms of HNP1 and HD5 lost their antiviral function. Pro-HD5, the precursor of HD5, did not block infection by SARS-CoV-2. High virus titers overcame the effect of low levels of HNP1, indicating that defensins act on the virion. HNP1, HD5 and RC101 also blocked viral infection of intestinal and lung epithelial cells. The protective effects of defensins reported here suggest that they may be useful additives to the antivirus arsenal and should be thoroughly studied.

Secretory Sorcery: Paneth Cell Control of Intestinal Repair and Homeostasis

Paneth cells are professional secretory cells that classically play a role in the innate immune system by secreting antimicrobial factors into the lumen to control enteric bacteria. In this role, Paneth cells are able to sense cues from luminal bacteria and respond by changing production of these factors to protect the epithelial barrier. Paneth cells rely on autophagy to regulate their secretory capability and capacity. Disruption of this pathway through mutation of genes, such as Atg16L1, results in decreased Paneth cell function, dysregulated enteric microbiota, decreased barrier integrity, and increased risk of diseases such as Crohn's disease in humans. Upon differentiation Paneth cells migrate downward and intercalate among active intestinal stem cells at the base of small intestinal crypts. This localization puts them in a unique position to interact with active intestinal stem cells, and recent work shows that Paneth cells play a critical role in influencing the intestinal stem cell niche. This review discusses the numerous ways Paneth cells can influence intestinal stem cells and their niche. We also highlight the ways in which Paneth cells can alter cells and other organ systems.

Lower human defensin 5 in elderly people compared to middle-aged is associated with differences in the intestinal microbiota composition: the DOSANCO Health Study

Recently, aging is considered a risk factor for various diseases. Although changes in the intestinal microbiota along with aging are thought to associate with the increased disease risk, mechanisms that cause age-related transition of the intestinal microbiota remain unknown. This study aims to clarify relationships between the amount of human defensin 5 (HD5), a Paneth cell α-defensin, which is known to regulate the intestinal microbiota, and age-related differences of the intestinal microbiota composition. Fecal samples from 196 healthy Japanese (35 to 81 years old) were collected and measured HD5 concentration. HD5 concentration in the elderly group (age > 70 years old) was significantly lower than the middle-aged group (age ≤ 70 years old). Furthermore, individual age was negatively correlated with HD5 concentration (r =  - 0.307, p < 0.001). In β-diversity, the intestinal microbiota of the elderly showed a significantly different composition compared to the middle-aged. At the genus level, relative abundance of Collinsella, Alistipes, Peptococcaceae; unassigned, Lactobacillus, Lactococcus, Weissella, Christensenellaceae R-7 group, Megasphaera, and [Eubacterium] eligens group was significantly higher, and Lachnospiraceae; unassigned, Blautia, Anaerostipes, Fusicatenibacter, Dorea, and Faecalibacterium was significantly lower in the elderly compared to the middle-aged. In addition, HD5 concentration was negatively correlated with Alistipes, Peptococcaceae; unassigned, and Christensenellaceae R-7 group and positively correlated with Lachnospiraceae; unassigned and Dorea. These results provide novel insights into the immunosenescence of enteric innate immunity, indicating low HD5 is suggested to contribute to the age-related differences in the intestinal microbiota and may relate to increased risk of diseases in elderly people.

An intercrypt subpopulation of goblet cells is essential for colonic mucus barrier function

The intestinal mucus layer, an important element of epithelial protection, is produced by goblet cells. Intestinal goblet cells are assumed to be a homogeneous cell type. In this study, however, we delineated their specific gene and protein expression profiles and identified several distinct goblet cell populations that form two differentiation trajectories. One distinct subtype, the intercrypt goblet cells (icGCs), located at the colonic luminal surface, produced mucus with properties that differed from the mucus secreted by crypt-residing goblet cells. Mice with defective icGCs had increased sensitivity to chemically induced colitis and manifested spontaneous colitis with age. Furthermore, alterations in mucus and reduced numbers of icGCs were observed in patients with both active and remissive ulcerative colitis, which highlights the importance of icGCs in maintaining functional protection of the epithelium.

Synergism between Host Defence Peptides and Antibiotics Against Bacterial Infections

Background:

Antimicrobial resistance (AMR) to conventional antibiotics is becoming one of the main global health threats and novel alternative strategies are urging. Antimicrobial peptides (AMPs), once forgotten, are coming back into the scene as promising tools to overcome bacterial resistance. Recent findings have attracted attention to the potentiality of AMPs to work as antibiotic adjuvants.

Methods:

In this review, we have tried to collect the currently available information on the mechanism of action of AMPs in synergy with other antimicrobial agents. In particular, we have focused on the mechanisms of action that mediate the inhibition of the emergence of bacterial resistance by AMPs.

Results and Conclusion:

We find in the literature many examples where AMPs can significantly reduce the antibiotic effective concentration. Mainly, the peptides work at the bacterial cell wall and thereby facilitate the drug access to its intracellular target. Complementarily, AMPs can also contribute to permeate the exopolysaccharide layer of biofilm communities, or even prevent bacterial adhesion and biofilm growth. Secondly, we find other peptides that can directly block the emergence of bacterial resistance mechanisms or interfere with the community quorum-sensing systems. Interestingly, the effective peptide concentrations for adjuvant activity and inhibition of bacterial resistance are much lower than the required for direct antimicrobial action. Finally, many AMPs expressed by innate immune cells are endowed with immunomodulatory properties and can participate in the host response against infection. Recent studies in animal models confirm that AMPs work as adjuvants at non-toxic concentrations and can be safely administrated for novel combined chemotherapies.

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.

The Paneth Cell: The Curator and Defender of the Immature Small Intestine

Paneth cells were first described in the late 19th century by Gustav Schwalbe and Josef Paneth as columnar epithelial cells possessing prominent eosinophilic granules in their cytoplasm. Decades later there is continued interest in Paneth cells as they play an integral role in maintaining intestinal homeostasis and modulating the physiology of the small intestine and its associated microbial flora. Paneth cells are highly specialized secretory epithelial cells located in the small intestinal crypts of Lieberkühn. The dense granules produced by Paneth cells contain an abundance of antimicrobial peptides and immunomodulating proteins that function to regulate the composition of the intestinal flora. This in turn plays a significant role in secondary regulation of the host microvasculature, the normal injury and repair mechanisms of the intestinal epithelial layer, and the levels of intestinal inflammation. These critical functions may have even more importance in the immature intestine of premature infants. While Paneth cells begin to develop in the middle of human gestation, they do not become immune competent or reach their adult density until closer to term gestation. This leaves preterm infants deficient in normal Paneth cell biology during the greatest window of susceptibility to develop intestinal pathology such as necrotizing enterocolitis (NEC). As 10% of infants worldwide are currently born prematurely, there is a significant population of infants contending with an inadequate cohort of Paneth cells. Infants who have developed NEC have decreased Paneth cell numbers compared to age-matched controls, and ablation of murine Paneth cells results in a NEC-like phenotype suggesting again that Paneth cell function is critical to homeostasis to the immature intestine. This review will provide an up to date and comprehensive look at Paneth cell ontogeny, the impact Paneth cells have on the host-microbial axis in the immature intestine, and the repercussions of Paneth cell dysfunction or loss on injury and repair mechanisms in the immature gut.

Single-Cell Studies of Intestinal Stem Cell Heterogeneity During Homeostasis and Regeneration

Single-cell RNA-sequencing (scRNA-seq) provides a unique opportunity to study heterogeneous cell populations within tissues, including the intestinal epithelium, to gain detailed molecular insights into their biology. Many new putative markers of intestinal stem cells and their progeny have been described using single-cell transcriptomics, which has contributed to the identification of novel subpopulations of mature cell types and insight into their developmental trajectories. This approach has revealed tremendous cellular heterogeneity within the intestinal epithelium that is concordant with its diverse and multifaceted functions. We discuss the function of these subpopulations during tissue homeostasis, as well as putative subpopulations with inducible regenerative potential following tissue injury.

"Candida Albicans Interactions With The Host: Crossing The Intestinal Epithelial Barrier"

Formerly a commensal organism of the mucosal surfaces of most healthy individuals, Candida albicans is an opportunistic pathogen that causes infections ranging from superficial to the more life-threatening disseminated infections, especially in the ever-growing population of vulnerable patients in the hospital setting. In these situations, the fungus takes advantage of its host following a disturbance in the host defense system and/or the mucosal microbiota. Overwhelming evidence suggests that the gastrointestinal tract is the main source of disseminated C. albicans infections. Major risk factors for disseminated candidiasis include damage to the mucosal intestinal barrier, immune dysfunction, and dysbiosis of the resident microbiota. A better understanding of C. albicans' interaction with the intestinal epithelial barrier will be useful for designing future therapies to avoid systemic candidiasis. In this review, we provide an overview of the current knowledge regarding the mechanisms of pathogenicity that allow the fungus to reach and translocate the gut barrier.

Alarin in different human intestinal epithelial cell types

Alarin (AL), a new member of the galanin family, has been localized in various CNS regions, mainly in rodents. Among other effects, it modulates food intake. Therefore, we analyzed the immunohistochemical distribution pattern of AL in human intestinal epithelia. Cryosections of 12 human bowel samples were immunohistochemically double-stained for AL and α-defensin 5 (αD; first set). Two further sets of sections were quadruple-stained either (second set) for AL, chromogranin (CG), synaptophysin (SY), and somatostatin (SO) or (third set) for AL, CG, Peptide Y (PY), and 5-hydroxytryptamine (5-HT). Slides were digitized and quantitative analysis of co-localization rates was undertaken. Small bowel: most of AL-positive cells (56%) were αD-positive Paneth cells located within the base of the crypts (first set). In the second set, about 27% of AL-labeled cells were co-reactive for SY and CG, likely representing entero-endocrine cells. In the third set, the largest subpopulation of AL-positive cells was not co-reactive for other markers applied (89%); most of them were likely Paneth cells. Large bowel: co-localization of AL with αD was not detected (first set). In the second set, AL was frequently co-localized with the other three markers applied (68%). In the third set, AL was frequently co-localized with 5-HT and CG (31%) as well as with PY and 5-HT (22%). Due to its presence in various enteroendocrine as well as Paneth cells, AL may be involved in different physiological and pathological processes.

Expression of α-Defensins, CD20+ B-lymphocytes, and Intraepithelial CD3+ T-lymphocytes in the Intestinal Mucosa of Patients with Liver Cirrhosis: Emerging Mediators of Intestinal Barrier Function

AIM

The present study investigates the role of innate and adaptive immune system of intestinal mucosal barrier function in cirrhosis.

METHODS

Forty patients with decompensated (n = 40, group A), 27 with compensated cirrhosis (n = 27, group B), and 27 controls (n = 27, group C) were subjected to duodenal biopsy. Expression of α-defensins 5 and 6 at the intestinal crypts was evaluated by immunohistochemistry and immunofluorescence. Serum endotoxin, intestinal T-intraepithelial, and lamina propria B-lymphocytes were quantified.

RESULTS

Cirrhotic patients presented higher endotoxin concentrations (p < 0.0001) and diminished HD5 and HD6 expression compared to healthy controls (p = 0.000287, p = 0.000314, respectively). The diminished HD5 and HD6 expressions were also apparent among the decompensated patients compared to compensated group (p = 0.025, p = 0.041, respectively). HD5 and HD6 expressions were correlated with endotoxin levels (r = -0.790, p < 0.0001, r = - 0.777, p < 0.0001, respectively). Although intraepithelial T-lymphocytes were decreased in group A compared to group C (p = 0.002), no notable alterations between groups B and C were observed. The B-lymphocytic infiltrate did not differ among the investigated groups.

CONCLUSIONS

These data demonstrate that decreased expression of antimicrobial peptides may be considered as a potential pathophysiological mechanism of intestinal barrier dysfunction in liver cirrhosis, while remodeling of gut-associated lymphoid tissue as an acquired immune response to bio-pathogens remains an open field to illuminate.

Human β-defensin-1: A natural antimicrobial peptide present in amniotic fluid that is increased in spontaneous preterm labor with intra-amniotic infection

PROBLEM

Human β-defensins (HBDs) are antimicrobial peptides that participate in the soluble innate immune mechanisms against infection. Herein, we determined whether HBD-1 was present in amniotic fluid during normal pregnancy and whether its concentrations change with intra-amniotic inflammation and/or infection.

METHOD OF STUDY

Amniotic fluid was collected from 219 women in the following groups: (a) midtrimester who delivered at term (n = 35); (b) term with (n = 33) or without (n = 17) labor; (c) preterm labor with intact membranes who delivered at term (n = 29) or who delivered preterm with (n = 19) and without (n = 29) intra-amniotic inflammation and infection or with intra-amniotic inflammation but without infection (n = 21); and (d) preterm prelabor rupture of membranes (pPROM) with (n = 19) and without (n = 17) intra-amniotic inflammation/infection. Amniotic fluid HBD-1 concentrations were determined using a sensitive and specific ELISA kit.

RESULTS

(a) HBD-1 was detectable in all amniotic fluid samples; (b) amniotic fluid concentrations of HBD-1 were changed with gestational age (midtrimester vs term no labor), being higher in midtrimester; (c) amniotic fluid concentrations of HBD-1 were similar between women with and without spontaneous labor at term; (d) among patients with spontaneous preterm labor, amniotic fluid concentrations of HBD-1 in women with intra-amniotic inflammation/infection and in those with intra-amniotic inflammation without infection were greater than in women without intra-amniotic inflammation or infection who delivered preterm or at term; and (e) the presence of intra-amniotic inflammation and infection in patients with pPROM did not change amniotic fluid concentrations of HBD-1.

CONCLUSION

HBD-1 is a physiological constituent of amniotic fluid that is increased in midtrimester during normal pregnancy and in the presence of culturable microorganisms in the amniotic cavity. These findings provide insight into the soluble host defense mechanisms against intra-amniotic infection.

Entamoeba histolytica Alters Ileal Paneth Cell Functions in Intact and Muc2 Mucin Deficiency

Enteric α-defensins, termed cryptdins (Crps) in mice, and lysozymes secreted by Paneth cells contribute to innate host defense in the ileum. Antimicrobial factors, including lysozymes and β-defensins, are often embedded in luminal glycosylated colonic Muc2 mucin secreted by goblet cells that form the protective mucus layer critical for gut homeostasis and pathogen invasion. In this study, we investigated ileal innate immunity against Entamoeba histolytica, the causative agent of intestinal amebiasis, by inoculating parasites in closed ileal loops in Muc2^+/+ and Muc2^-/- littermates and quantifying Paneth cell localization (lysozyme expression) and function (Crp secretion). Relative to Muc2^+/+ littermates, Muc2^-/- littermates showed a disorganized mislocalization of Paneth cells that was diffusely distributed, with elevated lysozyme secretion in the crypts and on villi in response to E. histolytica Inhibition of E. histolytica Gal/GalNAc lectin (Gal-lectin) binding with exogenous galactose and Entamoeba histolytica cysteine proteinase 5 (EhCP5)-negative E. histolytica had no effect on parasite-induced erratic Paneth cell lysozyme synthesis. Although the basal ileal expression of Crp genes was unaffected in Muc2^-/- mice in response to E. histolytica, there was a robust release of proinflammatory cytokines and Crp peptide secretions in luminal exudates that was also present in the colon. Interestingly, E. histolytica-secreted cysteine proteinases cleaved the proregion of Crp4 but not the active form. These findings define Muc2 mucin as an essential component of ileal barrier function that regulates the localization and function of Paneth cells critical for host defense against microbes.

Paneth Cells during Viral Infection and Pathogenesis

Paneth cells are major secretory cells located in the crypts of Lieberk&uuml;hn in the small intestine. Our understanding of the diverse roles that Paneth cells play in homeostasis and disease has grown substantially since their discovery over a hundred years ago. Classically, Paneth cells have been characterized as a significant source of antimicrobial peptides and proteins important in host defense and shaping the composition of the commensal microbiota. More recently, Paneth cells have been shown to supply key developmental and homeostatic signals to intestinal stem cells in the crypt base. Paneth cell dysfunction leading to dysbiosis and a compromised epithelial barrier have been implicated in the etiology of Crohn&rsquo;s disease and susceptibility to enteric bacterial infection. Our understanding of the impact of Paneth cells on viral infection is incomplete. Enteric &alpha;-defensins, produced by Paneth cells, can directly alter viral infection. In addition, &alpha;-defensins and other antimicrobial Paneth cell products may modulate viral infection indirectly by impacting the microbiome. Here, we discuss recent insights into Paneth cell biology, models to study their function, and the impact, both direct and indirect, of Paneth cells on enteric viral infection.

Cytotoxic and biological effects of bulk fill composites on rat cortical neuron cells

The aim of this study was to investigate potential cellular responses and biological effects of new generation dental composites on cortical neuron cells in two different exposure times. The study group included five different bulk-fill flow able composites; Surefil SDR Flow, X-tra Base Flow, Venus Bulk Flow, Filtek Bulk Flow and Tetric-Evo Flow. They were filled in Teflon molds (Height: 4 mm, Width: 6 mm) and irradiated for 20 s. Cortical neuron cells were inoculated into 24-well plates. After 80% of the wells were coated, the 3 µm membrane was inserted and dental filling materials were added. The experiment was continued for 24 and 72 h. Cell viability measured by MTT assay test, total antioxidant and total oxidant status were examined using real assay diagnostic kits. The patterns of cell death (apoptosis) were analyzed using annexin V-FITC staining with flow cytometry. Β-defensins were quantitatively assessed by RT-PCR. IL-6, IL-8 and IL-10 cytokines were measured from the supernatants. All composites significantly affected analyses parameters during the exposure durations. Our data provide evidence that all dental materials tested are cytotoxic in acute phase and these effects are induced cellular death after different exposure periods. Significant cytotoxicity was detected in TE, XB, SS, FBF and VBF groups at 24 and 72 h, respectively.

Human α-Defensin 6: A Small Peptide That Self-Assembles and Protects the Host by Entangling Microbes

Human α-defensin 6 (HD6) is a 32-residue cysteine-rich peptide that contributes to innate immunity by protecting the host at mucosal sites. This peptide is produced in small intestinal Paneth cells, stored as an 81-residue precursor peptide named proHD6 in granules, and released into the lumen. One unusual feature of HD6 is that it lacks the broad-spectrum antimicrobial activity observed for other human α-defensins, including the Paneth cell peptide human α-defensin 5 (HD5). HD6 exhibits unprecedented self-assembly properties, which confer an unusual host-defense function. HD6 monomers self-assemble into higher-order oligomers termed "nanonets", which entrap microbes and prevent invasive gastrointestinal pathogens such as Salmonella enterica serovar Typhimurium and Listeria monocytogenes from entering host cells. One possible advantage of this host-defense mechanism is that HD6 helps to keep microbes in the lumen such that they can be excreted or attacked by other components of the immune system, such as recruited neutrophils. In this Account, we report our current understanding of HD6 and focus on work published since 2012 when Bevins and co-workers described the discovery of HD6 nanonets in the literature. First, we present studies that address the biosynthesis, storage, and maturation of HD6, which demonstrate that nature uses a propeptide strategy to spatially and temporally control the formation of HD6 nanonets in the small intestine. The propeptide is stored in Paneth cell granules, and proteolysis occurs during or following release into the lumen, which affords the 32-residue mature peptide that self-assembles. We subsequently highlight structure-function studies that provide a foundation for understanding the molecular basis for why HD6 exhibits unusual self-assembly properties compared with other characterized defensins. The disposition of hydrophobic residues in the HD6 primary structure differs from that of other human α-defensins and is an important structural determinant for oligomerization. Lastly, we consider functional studies that illuminate how HD6 contributes to mucosal immunity. We recently discovered that in addition to blocking bacterial invasion into host epithelial cells by Gram-negative and Gram-positive gastrointestinal pathogens, HD6 suppresses virulence traits displayed by the opportunistic human fungal pathogen Candida albicans. In particular, we found that C. albicans biofilm formation, which causes complications in the treatment of candidiasis, is inhibited by HD6. This observation suggests that HD6 may contribute to intestinal homeostasis by helping to keep C. albicans in its commensal state. We intend for this Account to inspire further biochemical, biophysical, and biological investigations that will advance our understanding of HD6 in mucosal immunity and the host-microbe interaction.

Convergent evolution of defensin sequence, structure and function

Defensins are a well-characterised group of small, disulphide-rich, cationic peptides that are produced by essentially all eukaryotes and are highly diverse in their sequences and structures. Most display broad range antimicrobial activity at low micromolar concentrations, whereas others have other diverse roles, including cell signalling (e.g. immune cell recruitment, self/non-self-recognition), ion channel perturbation, toxic functions, and enzyme inhibition. The defensins consist of two superfamilies, each derived from an independent evolutionary origin, which have subsequently undergone extensive divergent evolution in their sequence, structure and function. Referred to as the cis- and trans-defensin superfamilies, they are classified based on their secondary structure orientation, cysteine motifs and disulphide bond connectivities, tertiary structure similarities and precursor gene sequence. The utility of displaying loops on a stable, compact, disulphide-rich core has been exploited by evolution on multiple occasions. The defensin superfamilies represent a case where the ensuing convergent evolution of sequence, structure and function has been particularly extreme. Here, we discuss the extent, causes and significance of these convergent features, drawing examples from across the eukaryotes.

Defensins, lectins, mucins, and secretory immunoglobulin A: microbe-binding biomolecules that contribute to mucosal immunity in the human gut

In the intestine, the mucosal immune system plays essential roles in maintaining homeostasis between the host and microorganisms, and protecting the host from pathogenic invaders. Epithelial cells produce and release a variety of biomolecules into the mucosa and lumen that contribute to immunity. In this review, we focus on a subset of these remarkable host-defense factors - enteric α-defensins, select lectins, mucins, and secretory immunoglobulin A - that have the capacity to bind microbes and thereby contribute to barrier function in the human gut. We provide an overview of the intestinal epithelium, describe specialized secretory cells named Paneth cells, and summarize our current understanding of the biophysical and functional properties of these select microbe-binding biomolecules. We intend for this compilation to complement prior reviews on intestinal host-defense factors, highlight recent advances in the field, and motivate investigations that further illuminate molecular mechanisms as well as the interplay between these molecules and microbes.

Defensins, lectins, mucins, and secretory immunoglobulin A: microbe-binding biomolecules that contribute to mucosal immunity in the human gut

In the intestine, the mucosal immune system plays essential roles in maintaining homeostasis between the host and microorganisms, and protecting the host from pathogenic invaders. Epithelial cells produce and release a variety of biomolecules into the mucosa and lumen that contribute to immunity. In this review, we focus on a subset of these remarkable host-defense factors - enteric α-defensins, select lectins, mucins, and secretory immunoglobulin A - that have the capacity to bind microbes and thereby contribute to barrier function in the human gut. We provide an overview of the intestinal epithelium, describe specialized secretory cells named Paneth cells, and summarize our current understanding of the biophysical and functional properties of these select microbe-binding biomolecules. We intend for this compilation to complement prior reviews on intestinal host-defense factors, highlight recent advances in the field, and motivate investigations that further illuminate molecular mechanisms as well as the interplay between these molecules and microbes.

Defensins: The Case for Their Use against Mycobacterial Infections

Human tuberculosis remains a huge global public health problem with an estimated 1/3rd of the population being infected. Defensins are antibacterial cationic peptides produced by a number of cell types, most notably neutrophil granulocytes and epithelial cells. All three defensin types (α-, β-, and θ-defensins) have antibacterial activities, mainly through bacterial membrane permeabilization. Defensins are effective against Gram-negative and Gram-positive bacteria including mycobacteria and are active both intra- and extracellularly. Mycobacterial resistance has never been demonstrated although the mprF gene encoding resistance in Staphylococcus aureus is present in the Mycobacterium tuberculosis genome. In addition to their antibacterial effect, defensins are chemoattractants for macrophages and neutrophils. There are many cases for their use for therapy or prophylaxis in tuberculosis as well. In conclusion, we propose that there is considerable scope and potential for exploring their use as therapeutic/prophylactic agents and more comprehensive survey of defensins from different species and their bioactivity is timely.

Characterization of paneth cells in alpacas (Vicugna pacos, Mammalia, Camelidae)

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We determinated Paneth Cells in fetus, offspring and adults alpacas.

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Studies of Paneth cells were done by cytochemistry, immunohistochemistry and lectinhistochemistry techniques.

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We describe Paneth Cell morphometry in fetal, young and adult alpacas.

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We founded Paneth cells in all the small intestinal sections from mid-gestation.

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PC location was similar to that described in other mammals, however they were more columnar than the conventional pyramidal shape.

Paneth cells are secretory epithelial cells of the innate immune system of the intestine of several mammals, including alpacas. Little is known about the latter; thus, in the present study we described the morphology and histochemical characteristics of Paneth cells in healthy fetuses, and young and adult alpacas. For this purpose, samples of duodenum, jejunum and ileum were taken from 6 fetuses at different days of pregnancy (between days 221–330), 66 offsprings (between 0 and 45-days-old) and 5 adult alpacas (>2-years-old). Samples were fixed in 10% buffered formalin and processed for histological and morphometrical analysis using HE and Masson Trichomićs technique. Immunohistochemistry was used to identify Paneth cells using anti-lysozyme antibody. In addition, the lectinhistochemichal binding-pattern of Paneth celĺs granules was evaluated. Lyzozyme was immunohistochemically detected in the granules of Paneth cells from day 283 of pregnancy in all the small intestinal sections of the studied fetuses. In newborn alpacas Paneth cells were initially found in the duodenum, but the following days (days 18–21 after birth) they were also found in the ileum. Their size gradually increased after birth, but then no significant differences were found. In adult alpacas the number was lower than offsprings. We suggest that Paneth cells early differentiate in the small intestine of alpacas, and the increase in their number during the first two weeks of life strongly support their possible involvement in the intestinal defensive functions against the enteric diseases that occur during the lactancy stage.

Proteolysis Triggers Self-Assembly and Unmasks Innate Immune Function of a Human α-Defensin Peptide

Human α-defensin 6 (HD6) is a unique peptide of the defensin family that provides innate immunity in the intestine by self-assembling to form high-order oligomers that entrap bacteria and prevent host cell invasion. Here, we report critical steps in the self-assembly pathway of HD6. We demonstrate that HD6 is localized in secretory granules of small intestinal Paneth cells. HD6 is stored in these granules as an 81-residue propeptide (proHD6), and is recovered from ileal lumen as a 32-residue mature peptide. The propeptide neither forms higher-order oligomers, nor agglutinates bacteria, nor prevents Listeria monocytogenes invasion into epithelial cells. The Paneth cell granules also contain the protease trypsin, and trypsin-catalyzed hydrolysis of proHD6 liberates mature HD6, unmasking its latent activities. This work illustrates a remarkable example of how nature utilizes a propeptide strategy to spatially and temporally control peptide self-assembly, and thereby initiates innate immune function in the human intestine.

Visualizing attack of Escherichia coli by the antimicrobial peptide human defensin 5

Human α-defensin 5 (HD5) is a 32-residue cysteine-rich host-defense peptide that exhibits broad-spectrum antimicrobial activity and contributes to innate immunity in the human gut and other organ systems. Despite many years of investigation, its antimicrobial mechanism of action remains unclear. In this work, we report that HD5ox, the oxidized form of this peptide that exhibits three regiospecific disulfide bonds, causes distinct morphological changes to Escherichia coli and other Gram-negative microbes. These morphologies include bleb formation, cellular elongation, and clumping. The blebs are up to ∼1 μm wide and typically form at the site of cell division or cell poles. Studies with E. coli expressing cytoplasmic GFP reveal that HD5ox treatment causes GFP emission to localize in the bleb. To probe the cellular uptake of HD5ox and subsequent localization, we describe the design and characterization of a fluorophore-HD5 conjugate family. By employing these peptides, we demonstrate that fluorophore-HD5ox conjugates harboring the rhodamine and coumarin fluorophores enter the E. coli cytoplasm. On the basis of the fluorescence profiles, each of these fluorophore-HD5ox conjugates localizes to the site of cell division and cell poles. These studies support the notion that HD5ox, at least in part, exerts its antibacterial activity against E. coli and other Gram-negative microbes in the cytoplasm.

A small intestinal organoid model of non-invasive enteric pathogen-epithelial cell interactions

Organoids mirror in vivo tissue organization and are powerful tools to investigate the development and cell biology of the small intestine. However, their application for the study of host-pathogen interactions has been largely unexplored. We have established a model using microinjection of organoids to mimic enteric infection, allowing for direct examination of pathogen interactions with primary epithelial cells in the absence of confounding variables introduced by immune cells or the commensal microbiota. We investigated the impact of Paneth cell α-defensin antimicrobial peptides on bacterial growth. We demonstrate that organoids form a sealed lumen, which contains concentrations of α-defensins capable of restricting growth of multiple strains of Salmonella enterica serovar Typhimurium for at least 20 h postinfection. Transgenic expression of human defensin 5 in mouse organoids lacking functional murine α-defensins partially restored bacterial killing. We also found that organoids from NOD2(-/-) mice were not impaired in α-defensin expression or antibacterial activity. This model is optimized for the study of non-invasive bacteria but can be extended to other enteric pathogens and is amenable to further genetic manipulation of both the host and microbe to dissect this critical interface of host defense.

Molecular basis for self-assembly of a human host-defense peptide that entraps bacterial pathogens

Human α-defensin 6 (HD6) is a 32-aa cysteine-rich peptide of the innate immune system. Although HD6 is a member of an antimicrobial peptide family, it exhibits negligible antibacterial activity in vitro. Rather, HD6 possesses a unique innate immune mechanism whereby it self-assembles into oligomers that capture pathogens to prevent microbial invasion of the intestinal epithelium and subsequent dissemination. Molecular-level understanding for why HD6 functions differently from other human defensins remains unclear. To further elucidate the HD6 self-assembly process and its biological activity, we developed robust protocols for obtaining native and mutant HD6 in high purity from overexpression in Escherichia coli. We combined biophysical characterization with biological assays to probe HD6 structure and function. We report that native HD6 readily self-assembles into elongated fibrils observable by transmission electron microscopy, agglutinates both Gram-negative and -positive bacteria, and prevents the human gastrointestinal pathogen Listeria monocytogenes from invading cultured mammalian cells. Mutation of hydrophobic residues (F2A, I22T, V25T, F29A) perturbs self-assembly and results in attenuated biological activity. In particular, the F2A and F29A mutants do not form fibrils under our experimental conditions and neither agglutinate bacteria nor prevent L. monocytogenes invasion. In total, our results demonstrate that the hydrophobic effect is essential for promoting HD6 self-assembly and innate immune function, and indicate that HD6 may provide host defense against Listeria in the gut. This investigation provides a timely description of how variations in amino acid sequence confer diverse physiological functions to members of the defensin family.

Molecular evolution of the primate α-/θ-defensin multigene family

The primate α-/θ-defensin multigene family encodes versatile endogenous cationic and amphipathic peptides that have broad-spectrum antibacterial, antifungal and antiviral activity. Although previous studies have reported that α-/θ-defensin (DEFA/DEFT) genes are under birth-and-death evolution with frequent duplication and rapid evolution, the phylogenetic relationships of the primate DEFA/DEFT genes; the genetic bases for the existence of similar antimicrobial spectra among closely related species; and the evolutionary processes involved in the emergence of cyclic θ-defensins in Old World monkeys and their subsequent loss of function in humans, chimpanzees and gorillas require further investigation. In this study, the DEFA/DEFT gene repertoires from primate and treeshrew were collected, followed by detailed phylogenetic, sequence and structure, selection pressure and comparative genomics analyses. All treeshrew, prosimian and simian DEFA/DEFT genes are grouped into two major clades, which are tissue-specific for enteric and myeloid defensins in simians. The simian enteric and myeloid α-defensins are classified into six functional gene clusters with diverged sequences, variable structures, altered functional constraints and different selection pressures, which likely reflect the antimicrobial spectra among closely related species. Species-specific duplication or pseudogenization within each simian cluster implies that the antimicrobial spectrum is ever-shifting, most likely challenged by the ever-changing pathogen environment. The DEFT evolved from the myeloid DEFA8. The prosegment of θ-defensin is detected with adaptive changes coevolving with the new protein fold of mature peptide, coincident with the importance of the prosegment for the correct folding of the mature peptide. Lastly, a less-is-hitchhiking hypothesis was proposed as a possible explanation for the expansion of pseudogene DEFTP and the loss of functional DEFT, where the gain or loss of the hitchhiker is determined by its adjacent driver gene during the birth-and-death evolutionary process.

Anti-HIV activity of human defensin 5 in primary CD4+ T cells under serum-deprived conditions is a consequence of defensin-mediated cytotoxicity

BACKGROUND

We have previously shown that human defensin 5 (HD5) promotes HIV infectivity in both primary CD4+ T cells and HeLa cells expressing CD4 and CCR5. HD5 is induced in response to sexually transmitted infections (STIs) such as Chlamydia trachomatis and Neisseria gonorrhoeae, suggesting it plays a role in STI-mediated enhancement of HIV transmission. In contrast to our findings, a recent study reports that HD5 has an anti-HIV effect in primary CD4+ T cells under serum-deprived conditions. To resolve these apparently contradictory observations, we investigated experimental parameters that might contribute to contrasting effects of HD5.

RESULTS

Serum-deprived culture conditions were associated with anti-HIV activity. In contrast to the dependence of the HIV enhancing effect on HD5 structure, the anti-HIV activity in serum-deprived primary CD4+ T cells was independent of HD5 structure as the linear peptide [Abu] HD5 exhibited similar anti-HIV activity. Under serum deprived conditions, HD5 blocked CD4-receptor-independent HIV-1vsv infection before or after viral entry. We found that HD5 and its linear form induced significant cell death in primary CD4+ T cells under serum-deprived culture conditions. HD5-mediated apoptosis was observed as early as 2 h after addition of defensins to serum-deprived primary CD4+ T cells. In contrast to primary CD4+ T cells, HD5 did not induce cytotoxicity and promote HIV infectivity of HeLa-CD4-CCR5 cells under serum-deprived conditions.

CONCLUSIONS

These results indicate that under serum-deprived culture conditions HD5 is toxic for primary CD4+ T cells, warranting caution in data interpretation.

Reduction of human defensin 5 affords a high-affinity zinc-chelating peptide

Human defensin 5 (HD5) is a 32-residue cysteine-rich host-defense peptide that exhibits three disulfide bonds in the oxidized form (HD5ox). It is abundant in small intestinal Paneth cells, which release HD5 into the intestinal lumen and house a labile Zn(II) store of unknown function. Here, we consider the redox properties of HD5 and report that the reduced form, HD5red, is a metal-ion chelator. HD5 has a midpoint potential of -257 mV at pH 7.0. HD5red utilizes its cysteine residues to coordinate one equivalent of Zn(II) with an apparent Kd1 value in the midpicomolar range. Zn(II) or Cd(II) binding perturbs the oxidative folding pathway of HD5red to HD5ox. Whereas HD5red is highly susceptible to proteolytic degradation, the Zn(II)-bound form displays resistance to hydrolytic breakdown by trypsin and other proteases. The ability of a reduced defensin peptide to coordinate Zn(II) provides a putative mechanism for how these peptides persist in vivo.

Human β-defensin 3 peptide is increased and redistributed in Crohn's ileitis

BACKGROUND

Antimicrobial peptides (AMPs) maintain a sterile environment in intestinal crypts, limiting microbial colonization and invasion. Decreased AMP expression is proposed to increase the risk for inflammatory bowel disease. Expression and function of inducible AMPs, human β-defensin 2 and 3 (hBD-2 and hBD-3), remain poorly characterized in healthy and chronically inflamed intestine.

METHODS

Peptide concentrations of hBD-2 and hBD-3 in serum and intestinal biopsies of subjects with ulcerative colitis and Crohn's disease (CD), and those of healthy subjects were measured by ELISA. Messenger RNA of hBD-2 and hBD-3 was quantified by quantitative PCR in biopsies from the terminal ileum (TI) of patients with CD and healthy controls. Peptide localization of hBD-3 in the TI was visualized by confocal microscopy.

RESULTS

Immunoreactive hBD-3 peptide is present in the TI and colon in healthy subjects. In the TI of patients with CD, hBD-3, but not hBD-2 peptide, is increased 4-fold, whereas hBD-2 peptide is elevated in the serum. Messenger RNA of hBD-3 in the CD TI remains unchanged and does not correlate with hBD-3 peptide expression. However, hBD-3 is localized to Paneth cell granules and the apical surface of the healthy columnar epithelium. In CD, hBD-3 peptide location switches to the basolateral surface of the columnar epithelium and is diffusely distributed within the lamina propria.

CONCLUSION

The peptide hBD-3 throughout the healthy gastrointestinal tract suggests a role in maintaining balance between host defenses and commensal microbiota. Increased and relocalized secretion of hBD-3 toward the lamina propria in the CD TI indicates possible local immunomodulation during chronic inflammation, whereas increased serum hBD-2 in CD implicates its systemic antimicrobial and immunomodulatory role.

Expression of human beta defensins (HBDs) 1, 2 and 3 in gingival crevicular fluid of patients affected by localized aggressive periodontitis

AIM

To study the effect of nonsurgical periodontal therapy on the expression frequencies of human beta-defensin (HBD)-1, -2, and -3 in the gingival crevicular fluid (GCF) of patients affected by localized aggressive periodontitis.

MATERIALS AND METHODS

Twenty patients affected by localized aggressive periodontitis (age range, 20-35 years) and 20 healthy subjects (age range, 21-37 years) were examined with clinical periodontal parameters and radiographic examination with the long-cone parallel technique. All periodontitis patients underwent nonsurgical periodontal therapy combined with doxycycline treatment and a maintenance program (including brushing with regular toothpaste). GCF samples were collected from patients and healthy control subjects at baseline as well as 3 months after periodontal therapy for the patient group.

RESULTS

In the patient group, the expression frequencies of HBD-1, -2, and -3 mRNA at baseline were 30%, 85%, and 35%, respectively, which changed after periodontal therapy to 80%, 45%, and 85%, respectively (all P < 0.001). In the healthy control subjects, the expression frequencies were 95%, 40%, and 95% for HBD-1, -2, and -3, respectively, which were different from those of diseased patients at baseline (all P < 0.001).

CONCLUSIONS

The appropriate expression of HBD peptides in health and disease may contribute to the maintenance of periodontal homeostasis, possibly through its antimicrobial effects and the promotion of adaptive immune responses.

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.

Functional determinants of human enteric α-defensin HD5: crucial role for hydrophobicity at dimer interface

Human α-defensins are cationic peptides that self-associate into dimers and higher-order oligomers. They bind protein toxins, such as anthrax lethal factor (LF), and kill bacteria, including Escherichia coli and Staphylococcus aureus, among other functions. There are six members of the human α-defensin family: four human neutrophil peptides, including HNP1, and two enteric human defensins, including HD5. We subjected HD5 to comprehensive alanine scanning mutagenesis. We then assayed LF binding by surface plasmon resonance, LF activity by enzyme kinetic inhibition, and antibacterial activity by the virtual colony count assay. Most mutations could be tolerated, resulting in activity comparable with that of wild type HD5. However, the L29A mutation decimated LF binding and bactericidal activity against Escherichia coli and Staphylococcus aureus. A series of unnatural aliphatic and aromatic substitutions at position 29, including aminobutyric acid (Abu) and norleucine (Nle) correlated hydrophobicity with HD5 function. The crystal structure of L29Abu-HD5 depicted decreased hydrophobic contacts at the dimer interface, whereas the Nle-29-HD5 crystal structure depicted a novel mode of dimerization with parallel β strands. The effect of mutating Leu(29) is similar to that of a C-terminal hydrophobic residue of HNP1, Trp(26). In addition, in order to further clarify the role of dimerization in HD5 function, an obligate monomer was generated by N-methylation of the Glu(21) residue, decreasing LF binding and antibacterial activity against S. aureus. These results further characterize the dimer interface of the α-defensins, revealing a crucial role of hydrophobicity-mediated dimerization.

Expansion of Paneth cell population in response to enteric Salmonella enterica serovar Typhimurium infection

Paneth cells residing at the base of the small intestinal crypts contribute to the mucosal intestinal first line defense by secreting granules filled with antimicrobial polypeptides including lysozyme. These cells derive from the columnar intestinal stem cell located at position 0 and the transit amplifying cell located at position +4 in the crypts. We have previously shown that Salmonella enterica serovar Typhimurium (ST), a leading cause of gastrointestinal infections in humans, effects an overall reduction of lysozyme in the small intestine. To extend this work, we examined small-intestinal tissue sections at various time points after ST infection to quantify and localize expression of lysozyme and assess Paneth cell abundance, apoptosis, and the expression of Paneth cell differentiation markers. In response to infection with ST, the intestinal Paneth cell-specific lysozyme content, the number of lysozyme-positive Paneth cells, and the number of granules per Paneth cell decreased. However, this was accompanied by increases in the total number of Paneth cells and the frequency of mitotic events in crypts, by increased staining for the proliferation marker PCNA, primarily at the crypt side walls where the transit amplifying cell resides and not at the crypt base, and by apoptotic events in villi. Furthermore, we found a time-dependent upregulation of first β-catenin, followed by EphB3, and lastly Sox9 in response to ST, which was not observed after infection with a Salmonella pathogenicity island 1 mutant deficient in type III secretion. Our data strongly suggest that, in response to ST infection, a Paneth cell differentiation program is initiated that leads to an expansion of the Paneth cell population and that the transit amplifying cell is likely the main progenitor responder. Infection-induced expansion of the Paneth cell population may represent an acute intestinal inflammatory response similar to neutrophilia in systemic infection.

α-Defensins and hsCRP levels in inflammatory response of standard and laparoendoscopic single-site cholecystectomy

BACKGROUND

Laparoendoscopic single-site (LESS) surgery is an evolution of laparoscopic surgery aiming at decreasing the patient's parietal trauma associated with abdominal operations. LESS has been found so far to be efficient and have the same good results as the standard four-port laparoscopic cholecystectomy. α-Defensins are antimicrobial peptides of the organism. They are the first cell components against pathogens. Cytokines are also mediators in the response to trauma. The aim of this study was to compare the inflammatory reaction in LESS and four-port laparoscopic cholecystectomy.

METHODS

Forty patients with noncomplicated cholelithiasis were randomly assigned into one of two groups. Group A included the patients who would undergo four-port laparoscopic cholecystectomy and group B included the patients who would undergo LESS cholecystectomy. These patients had a BMI < 30, were ASA I or II, and had no previous upper-GI surgery. Blood was taken preoperatively and 6 and 24 h postoperatively. hsCRP (with automated analyzer) and α-defensins (using ELISA) were calculated for each sample. The same postoperative protocol was followed for both groups. Mann-Whitney U test was used to analyze the results. Pain was calculated with a visual analog scale (VAS) for shoulder and abdomen at 6 and 24 h. Hospital stay, nausea, and pain medication needed was noted.

RESULTS

The α-defensins value was statistically significantly higher in the 24-h samples (P < 0.001) for LESS cholecystectomy. No statistically significant difference was shown for hsCRP, even though P = 0.05 for the 24-h samples with the values of LESS higher. No LESS was converted to a classical laparoscopic cholecystectomy, and none of the patients of either group needed conversion to open cholecystectomy. Pain was statistically significantly less for the LESS group at the 24-h interval (P < 0.0001). Less medication was needed for LESS patients after the 6th postoperative hour (P = 0.007).

CONCLUSION

Higher inflammatory reaction in LESS cholecystectomy could be the result of greater tension on the tissues. More studies are needed to conclude if this has a significant clinical expression.

Human defensin 5 disulfide array mutants: disulfide bond deletion attenuates antibacterial activity against Staphylococcus aureus

Human α-defensin 5 (HD5, HD5(ox) to specify the oxidized and disulfide linked form) is a 32-residue cysteine-rich host-defense peptide, expressed and released by small intestinal Paneth cells, that exhibits antibacterial activity against a number of Gram-negative and -positive bacterial strains. To ascertain the contributions of its disulfide array to structure, antimicrobial activity, and proteolytic stability, a series of HD5 double mutant peptides where pairs of cysteine residues corresponding to native disulfide linkages (Cys(3)-Cys(31), Cys(5)-Cys(20), Cys(10)-Cys(30)) were mutated to Ser or Ala residues, overexpressed in E. coli, purified, and characterized. A hexa mutant peptide, HD5[Ser(hexa)], where all six native Cys residues are replaced by Ser residues, was also evaluated. Removal of a single native S-S linkage influences oxidative folding and regioisomerization, antibacterial activity, Gram-negative bacterial membrane permeabilization, and proteolytic stability. Whereas the majority of the HD5 mutant peptides show low micromolar activity against Gram-negative E. coli ATCC 25922 in colony counting assays, the wild-type disulfide array is essential for low micromolar activity against Gram-positive S. aureus ATCC 25923. Removal of a single disulfide bond attenuates the activity observed for HD5(ox) against this Gram-positive bacterial strain. This observation supports the notion that the HD5(ox) mechanism of antibacterial action differs for Gram-negative and Gram-positive species [Wei et al. (2009) J. Biol. Chem. 284, 29180-29192] and that the native disulfide array is a requirement for its activity against S. aureus.

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.

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.