Paneth cell hyperplasia and metaplasia in necrotizing enterocolitis

Interleukin-9 production by type 2 innate lymphoid cells induces Paneth cell metaplasia and small intestinal remodeling

Paneth cell metaplasia (PCM) typically arises in pre-existing gastrointestinal (GI) diseases; however, the mechanistic pathway that induces metaplasia and whether PCM is initiated exclusively by disorders intrinsic to the GI tract is not well known. Here, we describe the development of PCM in a murine model of chronic myelogenous leukemia (CML) that is driven by an inducible bcr-abl oncogene. Mechanistically, CML induces a proinflammatory state within the GI tract that results in the production of epithelial-derived IL-33. The binding of IL-33 to the decoy receptor ST2 leads to IL-9 production by type 2 innate lymphoid cells (ILC2) which is directly responsible for the induction of PCM in the colon and tissue remodeling in the small intestines, characterized by goblet and tuft cell hyperplasia along with expansion of mucosal mast cells. Thus, we demonstrate that an extra-intestinal disease can trigger an ILC2/IL-9 immune circuit, which induces PCM and regulates epithelial cell fate decisions in the GI tract.

The emerging roles of deep crypt secretory cells in colonic physiology

Deep crypt secretory (DCS) cells are a population of epithelial cells located at the colonic crypt base that share some similarities to Paneth and goblet cells. They were initially defined as c-Kit expressing cells, though subsequent work showed that they are more specifically marked by Reg4 in the murine colon. The best-understood function of DCS cells at present is supporting the stem cell niche by generating Notch and EGF ligands. However, as these cells also express immunoregulatory (e.g., Ccl6) and host defense (e.g., Retnlb) genes, it is likely they have additional functions in maintaining colonic health outside of maintenance of the stem niche. Recent advances in single-cell transcriptomic profiling hint at additional epithelial and immune roles that may exist for these cells and have aided in elucidating their developmental lineage. This review highlights the emerging evidence supporting a crucial role for DCS cells in intestinal physiology, the current understanding of how these cells are regulated, and their potential role(s) in colonic disease.

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

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

Antimicrobial Peptides in Early-Life Host Defense, Perinatal Infections, and Necrotizing Enterocolitis—An Update

Host defense against early-life infections such as chorioamnionitis, neonatal sepsis, or necrotizing enterocolitis (NEC) relies primarily on innate immunity, in which antimicrobial peptides (AMPs) play a major role. AMPs that are important for the fetus and neonate include α and β defensins, cathelicidin LL-37, antiproteases (elafin, SLPI), and hepcidin. They can be produced by the fetus or neonate, the placenta, chorioamniotic membranes, recruited neutrophils, and milk-protein ingestion or proteolysis. They possess antimicrobial, immunomodulating, inflammation-regulating, and tissue-repairing properties. AMPs are expressed as early as the 13th week and increase progressively through gestation. Limited studies are available on AMP expression and levels in the fetus and neonate. Nevertheless, existing evidence supports the role of AMPs in pathogenesis of chorioamnionitis, neonatal sepsis, and NEC, and their association with disease severity. This suggests a potential role of AMPs in diagnosis, prevention, prognosis, and treatment of sepsis and NEC. Herein, we present an overview of the antimicrobial and immunomodulating properties of human AMPs, their sources in the intrauterine environment, fetus, and neonate, and their changes during pre- and post-natal infections and NEC. We also discuss emerging data regarding the potential utility of AMPs in early-life infections, as diagnostic or predictive biomarkers and as therapeutic alternatives or adjuncts to antibiotic therapy considering the increase of antibiotic resistance in neonatal intensive care units.

Increased expression of OLFM4 and lysozyme during necrotizing enterocolitis in neonates: an observational research study

Background

In neonatal patients with necrotizing enterocolitis (NEC) the inflammatory response is mediated by a plurality of different proteins. The proteins olfactomedin 4 (OLFM4) and lysozyme (LYZ) are part of the intestinal mucosal defense and especially OLFM4 has rarely been evaluated in neonatal gastrointestinal diseases. The aim of this study was to analyze whether expression levels of both proteins of innate immunity, OLFM4 and lysozyme, were increased during NEC in neonates.

Methods

Intestinal tissues of patients with NEC were examined with immunohistochemical staining of formalin-fixed and paraffin-embedded sections of resected tissue using antibodies against OLFM4 and lysozyme. Staining-positive tissues were semi-quantitatively scored from 0 (no staining), 1 (weak staining), 2 (moderate staining) to 3 (highly intense staining) by two individual investigators. Intestinal tissue of infants with volvulus was used as a control as other intestinal tissue without major inflammation was not available.

Results

Both applied antibodies against OLFM4 showed different staining patterns with higher staining intensity of the antibody OLFM4 (D1E4M). OLFM4 (median score of the antibody OLFM4 (D1E4M): 3.0) and lysozyme (median score: 3.0) are highly expressed in intestinal and immune cells during NEC. Expression of OLFM4 and lysozyme in the control samples with volvulus was observable but significantly lower (median score of the antibody OLFM4 (D1E4M): 1.25; median score of the antibody against LYZ: 2.0; p = 0.033 and p = 0.037, respectively).

Conclusions

Both proteins, OLFM4 and lysozyme, may play a role in the pathogenesis of NEC in neonatal patients, but the exact mechanisms of OLFM4 and lysozyme function and their role in immunological responses have not yet been resolved in detail. These observations add new insights as basis for further large-scale population research.

Intestinal Epithelial Barrier Function and Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a major cause of morbidity and mortality in premature infants. NEC is characterized by intestinal tissue inflammation and necrosis. The intestinal barrier is altered in NEC, which potentially contributes to its pathogenesis by promoting intestinal bacterial translocation and stimulating the inflammatory response. In premature infants, many components of the intestinal barrier are immature. This article reviews the different components of the intestinal barrier and how their immaturity contributes to intestinal barrier dysfunction and NEC.

Expansion of Intestinal Secretory Cell Population Induced by Listeria monocytogenes Infection: Accompanied With the Inhibition of NOTCH Pathway

Listeria monocytogenes, as a model organism, is a causative agent of enteric pathogen that causes systemic infection. However, the interaction of L. monocytogenes and small intestinal epithelium has not been fully elucidated yet. In this study, mice and intestinal organoids were chosen as the models to investigate the influence of L. monocytogenes infection on the intestinal secretory cells and its differentiation-related pathways. Results confirmed the phenomenon of intestinal damage that L. monocytogenes infection could lead to villi damage in mice, which was accompanied by the increase of TNF-α production in jejunum as well as lipopolysaccharide (LPS) secretion in serum. Moreover, it was demonstrated that L. monocytogenes infection increased the number of goblet and Paneth cells in mice and intestinal organoids and upregulated the expression of Muc2 and Lyz. Furthermore, L. monocytogenes decreased the relative expression of Notch pathway-related genes (Jag1, Dll4, Notch1, and Hes1) while upregulating the relative expression of Math1 gene in mice and intestinal organoids. This indicated that L. monocytogenes infection caused the inhibition of Notch pathway, which may be the reason for the increased number of goblet and Paneth cells in the intestine. Collectively, these results are expected to provide more information on the mechanism of L. monocytogenes infection in the intestine.

Lipocalin-2 and calprotectin as stool biomarkers for predicting necrotizing enterocolitis in premature neonates

BACKGROUND

Necrotizing enterocolitis (NEC) is a major challenge for premature infants in neonatal intensive care units and efforts toward the search for indicators that could be used to predict the development of the disease have given limited results until now.

METHODS

In this study, stools from 132 very low birth weight infants were collected daily in the context of a multi-center prospective study aimed at investigating the potential of fecal biomarkers for NEC prediction. Eight infants (~6%) received a stage 3 NEC diagnosis. Their stools collected up to 10 days before diagnosis were included and matched with 14 non-NEC controls and tested by ELISA for the quantitation of eight biomarkers.

RESULTS

Biomarkers were evaluated in all available stool samples leading to the identification of lipocalin-2 and calprotectin as the two most reliable predicting markers over the 10-day period prior to NEC development. Pooling the data for each infant confirmed the significance of lipocalin-2 and calprotectin, individually and in combination 1 week in advance of the NEC clinical diagnosis.

CONCLUSIONS

The lipocalin-2 and calprotectin tandem represents a significant biomarker signature for predicting NEC development. Although not yet fulfilling the "perfect biomarker" criteria, it represents a first step toward it.

IMPACT

Stool biomarkers can be used to predict NEC development in very low birth weight infants more than a week before the diagnosis. LCN2 was identified as a new robust biomarker for predicting NEC development, which used in conjunction with CALPRO, allows the identification of more than half of the cases that will develop NEC in very low birth weight infants. Combining more stool markers with the LCN2/CALPRO tandem such as PGE2 can further improve the algorithm for the prediction of NEC development.

Breast milk nutrients driving intestinal epithelial layer maturation via Wnt and Notch signaling: Implications for necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is an often lethal, inflammatory disease of the preterm intestine. The underdeveloped immune system plays an important role; however, the initial trigger for NEC development is likely a damaged intestinal epithelial layer. We hypothesize that due to incomplete maturation of different epithelial cell lineages, nutrients and bacteria are able to damage the epithelial cells and cause the (immature) inflammatory response, food intolerance and malabsorption seen in NEC. Intestinal organoid research has shown that maturation of intestinal epithelial cell lineages is orchestrated by two key signaling pathways: Wnt and Notch. In NEC, these pathways are dysregulated by hyperactivation of Toll-like-receptor-4. Breastfeeding decreases the risk of developing NEC compared to formula milk. Here, we review the intricate link between breast milk components, Wnt and Notch signaling and intestinal epithelial maturation. We argue that (nutritional) interventions regulating these pathways may decrease the risk of NEC development in preterm infants.

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.

Intestinal SALSA/dmbt1 levels are decreased in prematurely born infants

The first months of life represent a crucial time period for an infant. Alongside establishing the early microbiome, the mucosal immunological homeostasis is being developed. Both processes may be perturbed in prematurely born infants. The glycoprotein SALSA plays a role in mucosal inflammation and microbial clearance. It is one of the most abundant molecules on the intestinal mucosal surfaces in early life. SALSA binds to many types of microbes and host defence molecules like IgA, C1q and collectin molecules. We here describe the development in faecal SALSA levels during the first three months of life. During these 90 days, the median SALSA level in full-term babies decreased from 1100 μg/mL (range 49-17 000 μg/mL) to 450 μg/mL (range 33-1000 μg/mL). Lower levels of SALSA were observed in prematurely born infants in the same time period. Our novel observation thus indicates an impact of prematurity on an important component of the infant intestinal immune system. Changes in SALSA in early life may have an effect on the early establishment of the human microbiome.

Metaplastic Paneth Cells in Extra-Intestinal Mucosal Niche Indicate a Link to Microbiome and Inflammation

Paneth cells are residents of the intestinal epithelium. Abnormal appearance of Paneth cells has been widely documented in non-intestinal tissues within the digestive tract and even observed in non-gastrointestinal organs. Although metaplastic Paneth cells are part of the overarching pathology of intestinal metaplasia (IM), only a fraction of intestinal metaplastic lesions contain Paneth cells. We survey literature documenting metaplastic Paneth cells to gain insights into mechanism underlying their etiologic development as well as their potential relevance to human health. A synthesized view from this study suggests that the emergence of metaplastic Paneth cells at extra-intestinal mucosal sites likely represents a protective, anti-bacterial, and inflammatory response evoked by an altered microbial activity.

Human Defensin-5 Blocks Ethanol and Colitis-Induced Dysbiosis, Tight Junction Disruption and Inflammation in Mouse Intestine

Alcohol consumption has been shown to cause dysbiosis, but the mechanism involved in it is unknown. Recurrent colitis is known to induce expression of α-defensins in the colon, but the effect of alcohol consumption on it is not known. We investigated the effect of ethanol on α-defensin expression in the small intestine and colitis-induced expression in colon in mice. Furthermore, we evaluated the effect of human defensin-5 (HD5) on ethanol and colitis-induced gut barrier dysfunction and mucosal damage. Recurrent colitis was induced by feeding dextran sulfate sodium (DSS), 3 cycles of 5-days each with 15 days intervals, followed by 30-days remission. Ethanol was fed during the intervals and recovery in a liquid diet with or without HD5. Expression of α-defensins, tight junction (TJ) integrity and cytokine/chemokine expression were analyzed. Chronic ethanol feeding reduced α-defensin expression in the small intestine and colitis-induced defensin expression in the colon. HD5 attenuated the growth of enterotoxigenic Bacteriodes fragilis and E. coli, but had no effect on non-toxigenic Bacteriodes fragilis or probiotics, the Lactobacilli. Ethanol and colitis elevated Enterobacteriaceae, Firmicutes and Firmicutes to Bacteriodetes ratio in colonic mucosa. HD5 feeding attenuated ethanol and colitis-induced dysbiosis, disruption of intestinal epithelial TJ, mucosal inflammation, expression of pro-inflammatory cytokines and chemokines in the small intestine and colon, and endotoxemia. These results demonstrate that ethanol suppresses intestinal α-defensin expression, leading to dysbiosis, barrier dysfunction, inflammation and endotoxemia. HD5 feeding attenuates intestinal injury caused by ethanol and colitis, indicating that defensin expression is a potential target for treatment of alcoholic tissue injury and colitis.

Diminished DEFA6 Expression in Paneth Cells Is Associated with Necrotizing Enterocolitis

Background

Necrotizing enterocolitis (NEC) is the most common gastrointestinal disorder in premature infants with a high morbidity and mortality. Paneth cell dysfunction has been suggested to be involved in the pathogenesis of NEC. Defensin alpha-6 (DEFA6) is a specific marker for Paneth cells acting as part of the innate immunity in the human intestines. The aim of this study was to investigate the expression of DEFA6 in infants with NEC.

Materials and Methods

Infants who underwent bowel resection for NEC at level III NICU in Sweden between August 2004 and September 2013 were eligible for the study. Macroscopically vital tissues were selected for histopathological evaluation. All infants in the control group underwent laparotomy and had ileostomy due to dysmotility, and samples were taken from the site of the stoma. DEFA6 expression was studied by immunohistochemistry. Digital image analysis was used for an objective and precise description of the samples.

Results

A total of 12 infants were included in the study, eight with NEC and four controls. The tissue samples were taken from the colon (n = 1), jejunum (n = 1), and ileum (n = 10). Both the NEC and control groups consisted of extremely premature and term infants (control group: 25-40 gestational weeks, NEC group: 23-39 gestational weeks). The postnatal age at the time of surgery varied in both groups (control group: 4-47 days, NEC group: 4-50 days). DEFA6 expression in the NEC group was significantly lower than that in the control group and did not correlate with gestational age.

Conclusion

The diminished DEFA6 expression in Paneth cells associated with NEC in this study supports the hypothesis that alpha-defensins are involved in the pathophysiology of NEC. Future studies are needed to elucidate the role of alpha-defensins in NEC aiming at finding preventive and therapeutic strategies against NEC.

Gastrointestinal mucosal development and injury in premature lambs supported by the artificial placenta

BACKGROUND

An Artificial Placenta (AP) utilizing extracorporeal life support (ECLS) could revolutionize care of extremely premature newborns, but its effects on gastrointestinal morphology and injury need investigation.

METHODS

Lambs (116-121days GA, term=145; n=5) were delivered by C-section, cannulated for ECLS, had total parenteral nutrition (TPN) provided, and were supported for 7days before euthanasia. Early and Late Tissue Controls (ETC, n=5 and LTC, n=5) delivered at 115-121days and 125-131days, respectively, were immediately sacrificed. Standardized jejunal samples were formalin-fixed for histology. Crypt depth (CD), villus height (VH), and VH:CD ratios were measured. Measurements also included enterocyte proliferation (Ki-67), Paneth cell count (Lysozyme), and injury scores (H&E). ANOVA and Chi Square were used with p<0.05 considered significant.

RESULTS

CD, VH, and VH:CD were similar between groups (p>0.05). AP demonstrated more enterocyte proliferation (95.7±21.8) than ETC (49.4±23.4; p=0.003) and LTC (66.1+11.8; p=0.04), and more Paneth cells (81.7±17.5) than ETC (41.6±7.0; p=0.0005) and LTC (40.7±8.2, p=0.0004). Presence of epithelial injury and congestion in the bowel of all groups were not statistically different. No villus atrophy or inflammation was present in any group.

CONCLUSIONS

This suggests preserved small bowel mucosal architecture, high cellular turnover, and minimal evidence of injury.

STUDY TYPE

Research paper/therapeutic potential.

LEVEL OF EVIDENCE

N/A.

Orai1-Mediated Antimicrobial Secretion from Pancreatic Acini Shapes the Gut Microbiome and Regulates Gut Innate Immunity

The gut microbiome participates in numerous physiologic functions and communicates intimately with the host immune system. Antimicrobial peptides are critical components of intestinal innate immunity. We report a prominent role for antimicrobials secreted by pancreatic acini in shaping the gut microbiome that is essential for intestinal innate immunity, barrier function, and survival. Deletion of the Ca²⁺ channel Orai1 in pancreatic acini of adult mice resulted in 60%-70% mortality within 3 weeks. Despite robust activation of the intestinal innate immune response, mice lacking acinar Orai1 exhibited intestinal bacterial outgrowth and dysbiosis, ultimately causing systemic translocation, inflammation, and death. While digestive enzyme supplementation was ineffective, treatments constraining bacterial outgrowth (purified liquid diet, broad-spectrum antibiotics) rescued survival, feeding, and weight gain. Pancreatic levels of cathelicidin-related antimicrobial peptide (CRAMP) were reduced, and supplement of synthetic CRAMP prevented intestinal disease. These findings reveal a critical role for antimicrobial pancreatic secretion in gut innate immunity.

Pathogenesis of NEC: Role of the innate and adaptive immune response

Necrotizing enterocolitis (NEC) is a devastating disease in premature infants with high case fatality and significant morbidity among survivors. Immaturity of intestinal host defenses predisposes the premature infant gut to injury. An abnormal bacterial colonization pattern with a deficiency of commensal bacteria may lead to a further breakdown of these host defense mechanisms, predisposing the infant to NEC. Here, we review the role of the innate and adaptive immune system in the pathophysiology of NEC.

Paneth cells in the developing gut: when do they arise and when are they immune competent?

BACKGROUND

Little is known about the perinatal development of Paneth cells (PCs) during gestation and the relation with necrotizing enterocolitis (NEC). We aimed to investigate when PCs arise and when they become immune competent during gestation.

METHODS

We included 57 samples of ileum tissue of fetuses/infants with a gestional age (GA) between 9 and 40 wk taken as part of a standard autopsy procedure. Hematoxylin-eosin staining and anti-human defensin 5 immunohistochemistry were performed. We performed a semi-quantitative assessment of (immune-competent) PC numbers per 10 crypts per tissue section per GA.

RESULTS

The number of PCs and the number of immune-competent PCs increased with increasing GA (Spearman's ρ = 0.41, P = 0.002 and ρ = 0.61, P < 0.001, respectively). Whereas significantly higher PC numbers were observed after 37 wk gestation (median 7, range 0-12) compared to preterm infants (median 0, range 0-15; P = 0.002), we counted higher numbers of immune-competent PCs already in infants with GA above 29 wk (median 6, range 0-18) compared to infants with GA under 29 wk (median 2, range 0-9; P < 0.001).

CONCLUSION

The significant increase of immune-competent PCs starting from a GA of 29 wk mimics the rise in incidence of NEC during a similar postmenstrual age in preterm infants.

Human Intestinal PEPT1 Transporter Expression and Localization in Preterm and Term Infants

The intestinal influx oligopeptide transporter peptide transporter 1 (PEPT1) (SLC15A1) is best known for nutrient-derived di- and tripeptide transport. Its role in drug absorption is increasingly recognized. To better understand the disposition of PEPT1 substrate drugs in young infants, we studied intestinal PEPT1 mRNA expression and tissue localization across the pediatric age range. PEPT1 mRNA expression was determined using real-time reverse-transcription polymerase chain reaction in small intestinal tissues collected from surgical procedures (neonates and infants) or biopsies (older children and adolescents). PEPT1 mRNA relative to villin mRNA expression was compared between neonates/infants and older children/adolescents. PEPT1 was visualized in infant tissue using immunohistochemical staining. Other transporters [multidrug resistance protein 1 (MDR1), multidrug resistance-like protein 2 (MRP2), and organic anion transporter polypeptide 2B1 (OATP2B1)] were also stained to describe the localization in relation to PEPT1. Twenty-six intestinal samples (n = 20 neonates/infants, n = 2 pediatric, n = 4 adolescents) were analyzed. The young infant samples were collected at a median (range) gestational age at birth of 29.2 weeks (24.7-40) and postnatal age of 2.4 weeks (0-16.6). The PEPT1 mRNA expression of the neonates/infants was only marginally lower (0.8-fold) than the older children (P < 0.05). Similar and clear apical PEPT1 and MRP2 staining, apical and lateral MDR1 staining, and intraepithelial OATP2B1 staining at the basolateral membrane of the enterocyte were detected in 12 infant and 2 adolescent samples. Although small intestinal PEPT1 expression tended to be lower in neonates than in older children, this difference is small and tissue distribution is similar. This finding suggests similar oral absorption of PEPT1 substrates across the pediatric age range.

Gene expression profiling in necrotizing enterocolitis reveals pathways common to those reported in Crohn's disease

BACKGROUND

Necrotizing enterocolitis (NEC) is the most frequent life-threatening gastrointestinal disease experienced by premature infants in neonatal intensive care units. The challenge for neonatologists is to detect early clinical manifestations of NEC. One strategy would be to identify specific markers that could be used as early diagnostic tools to identify preterm infants most at risk of developing NEC or in the event of a diagnostic dilemma of suspected disease. As a first step in this direction, we sought to determine the specific gene expression profile of NEC.

METHODS

Deep sequencing (RNA-Seq) was used to establish the gene expression profiles in ileal samples obtained from preterm infants diagnosed with NEC and non-NEC conditions. Data were analyzed with Ingenuity Pathway Analysis and ToppCluster softwares.

RESULTS

Data analysis indicated that the most significant functional pathways over-represented in NEC neonates were associated with immune functions, such as altered T and B cell signaling, B cell development, and the role of pattern recognition receptors for bacteria and viruses. Among the genes that were strongly modulated in neonates with NEC, we observed a significant degree of similarity when compared with those reported in Crohn's disease, a chronic inflammatory bowel disease.

CONCLUSIONS

Gene expression profile analysis revealed a predominantly altered immune response in the intestine of NEC neonates. Moreover, comparative analysis between NEC and Crohn's disease gene expression repertoires revealed a surprisingly high degree of similarity between these two conditions suggesting a new avenue for identifying NEC biomarkers.

The role of intestinal epithelial barrier function in the development of NEC

The intestinal epithelial barrier plays an important role in maintaining host health. Breakdown of intestinal barrier function is known to play a role in many diseases such as infectious enteritis, idiopathic inflammatory bowel disease, and neonatal inflammatory bowel diseases. Recently, increasing research has demonstrated the importance of understanding how intestinal epithelial barrier function develops in the premature neonate in order to develop strategies to promote its maturation. Optimizing intestinal barrier function is thought to be key to preventing neonatal inflammatory bowel diseases such as necrotizing enterocolitis. In this review, we will first summarize the key components of the intestinal epithelial barrier, what is known about its development, and how this may explain NEC pathogenesis. Finally, we will review what therapeutic strategies may be used to promote optimal development of neonatal intestinal barrier function in order to reduce the incidence and severity of NEC.

Paneth cell metaplasia in newly diagnosed inflammatory bowel disease in children

Background

Paneth cell metaplasia (PCM) is well described in adults but little is known about the distribution of colonic Paneth cells and the occurrence of PCM in a paediatric population. The aim of this study is to determine whether Paneth cell hyperplasia or metaplasia characteristically occurs in the colons of children with newly diagnosed idiopathic inflammatory bowel disease (IBD).

Methods

We retrospectively reviewed colonic series from 28 new diagnoses of paediatric IBD at a tertiary referral centre, and from a further 14 children with IBD-like symptoms whose colonic biopsies and ancillary investigations were normal. Paneth cells were counted at 6 anatomical sites in the colon, and at each site acute and chronic inflammation were assessed semi-quantitatively and the presence or absence of crypt architectural distortion and eosinophilia was documented.

Results

In control, ulcerative colitis (UC) and Crohn’s disease (CD) groups there was a gradient of decreasing Paneth cell numbers from caecum to rectum. Paneth cells were not seen in the distal colon in the control group, but they were present there in 11 of 13 patients with ulcerative colitis and 14 of 15 with Crohn’s disease. Only patients with IBD showed Paneth cell hyperplasia, assessed as more than 10 Paneth cells per 10 well-oriented crypts at any site. There was a statistically significant increase in Paneth cells in the caecum, ascending, transverse and descending colon in UC and in the ascending, transverse, descending and sigmoid colon in CD compared with controls. There was no significant difference between UC and CD. There was no correlation between the site of PCM and acute or chronic inflammation, crypt distortion or eosinophilia.

Conclusion

Paneth cells are found in the proximal but not the distal colon in otherwise normal paediatric colonic series. A high proportion of UC and CD patients show PCM in the distal colon. This is present early in the disease and does not correlate with histological features of chronicity.

Inflammatory signals that regulate intestinal epithelial renewal, differentiation, migration and cell death: Implications for necrotizing enterocolitis

Necrotizing enterocolitis is a disease entity with multiple proposed pathways of pathogenesis. Various combinations of these risk factors, perhaps based on genetic predisposition, possibly lead to the mucosal and epithelial injury that is the hallmark of NEC. Intestinal epithelial integrity is controlled by a tightly regulated balance between proliferation and differentiation of epithelium from intestinal epithelial stem cells and cellular loss by apoptosis. various signaling pathways play a key role in creating and maintaining this balance. The aim of this review article is to outline intestinal epithelial barrier development and structure and the impact of these inflammatory signaling and regulatory pathways as they pertain to the pathogenesis of NEC.

Endoplasmic reticulum stress, unfolded protein response and altered T cell differentiation in necrotizing enterocolitis

Background

Endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) play important roles in chronic intestinal inflammation. Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency in preterm infants and is characterized by acute intestinal inflammation and necrosis. The objective of the study is to investigate the role of ER stress and the UPR in NEC patients.

Methods

Ileal tissues from NEC and control patients were obtained during surgical resection and/or at stoma closure. Splicing of XBP1 was detected using PCR, and gene expression was quantified using qPCR and Western blot.

Results

Splicing of XBP1 was only detected in a subset of acute NEC (A-NEC) patients, and not in NEC patients who had undergone reanastomosis (R-NEC). The other ER stress and the UPR pathways, PERK and ATF6, were not activated in NEC patients. A-NEC patients showing XBP1 splicing (A-NEC-XBP1s) had increased mucosal expression of GRP78, CHOP, IL6 and IL8. Similar results were obtained by inducing ER stress and the UPR invitro. A-NEC-XBP1s patients showed altered T cell differentiation indicated by decreased mucosal expression of RORC, IL17A and FOXP3. A-NEC-XBP1s patients additionally showed more severe morphological damage and a worse surgical outcome. Compared with A-NEC patients, R-NEC patients showed lower mucosal IL6 and IL8 expression and higher mucosal FOXP3 expression.

Conclusions

XBP1 splicing, ER stress and the UPR in NEC are associated with increased IL6 and IL8 expression levels, altered T cell differentiation and severe epithelial injury.

Paneth cells and necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a common and devastating disease of premature infants. Immaturity of the innate immune system of the gut is central to the pathogenesis of NEC. Recent studies suggest a key role for Paneth cells in this disease. Addressing basic questions on the development and function of immature Paneth cells may shed light on the puzzling pathophysiology of NEC. Current animal models of NEC are limited in their capacity to answer these questions.

Bifidobacterium bifidum in a rat model of necrotizing enterocolitis: antimicrobial peptide and protein responses

INTRODUCTION

Necrotizing enterocolitis (NEC) is a devastating disease of premature infants. Probiotics decrease the risk of NEC in clinical and experimental studies. Antimicrobial peptides protect the gut against noxious microbes and shape the commensal microbiota, but their role in NEC remains unclear.

METHODS

To investigate the expression of antimicrobial peptides in experimental NEC and the impact of probiotics on their expression, premature rats were divided into three groups: dam fed (DF), hand fed with formula (FF), or hand fed with formula containing Bifidobacterium bifidum (FF + BIF). All groups were exposed to asphyxia and cold stress.

RESULTS

Like in human ontogeny, the rat pup has low expression of Paneth cell antimicrobials, which increases rapidly during normal development. The expression of lysozyme, secretory phospholipase A(2) (sPLA(2)), pancreatic-associated proteins 1 and 3 mRNA was elevated in the FF group with a high incidence of NEC, as compared with the DF and FF + BIF groups where the disease was attenuated.

DISCUSSION

We conclude that induction of antimicrobial peptides occurs in experimental NEC similar to that reported in human disease and is attenuated when disease is averted by probiotic B. bifidum. The induction of antimicrobial peptides is likely an adaptive mucosal response that is often not sufficient to prevent disease in the premature gut.

Paneth cell ablation in the presence of Klebsiella pneumoniae induces necrotizing enterocolitis (NEC)-like injury in the small intestine of immature mice

Necrotizing enterocolitis (NEC) is a leading cause of morbidity and mortality in premature infants. During NEC pathogenesis, bacteria are able to penetrate innate immune defenses and invade the intestinal epithelial layer, causing subsequent inflammation and tissue necrosis. Normally, Paneth cells appear in the intestinal crypts during the first trimester of human pregnancy. Paneth cells constitute a major component of the innate immune system by producing multiple antimicrobial peptides and proinflammatory mediators. To better understand the possible role of Paneth cell disruption in NEC, we quantified the number of Paneth cells present in infants with NEC and found that they were significantly decreased compared with age-matched controls. We were able to model this loss in the intestine of postnatal day (P)14-P16 (immature) mice by treating them with the zinc chelator dithizone. Intestines from dithizone-treated animals retained approximately half the number of Paneth cells compared with controls. Furthermore, by combining dithizone treatment with exposure to Klebsiella pneumoniae, we were able to induce intestinal injury and inflammatory induction that resembles human NEC. Additionally, this novel Paneth cell ablation model produces NEC-like pathology that is consistent with other currently used animal models, but this technique is simpler to use, can be used in older animals that have been dam fed, and represents a novel line of investigation to study NEC pathogenesis and treatment.

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.