A direct comparison of mouse and human intestinal development using epithelial gene expression patterns

Refining the gut colonization Zophobas morio larvae model using an oral administration of multidrug-resistant Escherichia coli

BACKGROUND

The darkling beetle Zophobas morio can be implemented as an alternative in vivo model to study different intestinal colonization aspects. Recently, we showed that its larvae can be colonized by multidrug-resistant Escherichia coli strains administered via contaminated food (for 7 days) for a total experimental duration of 28 days.

METHOD

In the present work, we aimed to shorten the model to 14 days (T14) by administering the previously used CTX-M-15 ESBL-producing ST131 Escherichia coli strain Ec-4901.28 via a single oral administration (5 µL dose of 108 CFU/mL) , using a blunt 26s-gauge needle connected to a 250 μL gastight syringe. Force-feeding was performed either without or with (larvae placed on ice for 10 minutes before injection) anesthesia. In addition, phage-treated larvae were orally injected with 10 µL of INTESTI bacteriophage cocktail (∼105-6 PFU/mL) on days 4 (T4) and 7 (T7) .

RESULTS

Growth curve analyses showed that, while larvae rapidly became colonized with Ec-4901.28 (T1, ∼106-7 CFU/mL) , only those anesthetized maintained a high bacterial load (∼102-3vs. ∼105-6 CFU/mL) and survival rate (76% vs. 99%; P<0.001) by T14. Moreover, bacteriophage administration to anesthetized larvae significantly reduced the bacterial count of INTESTI-susceptible Ec-4901.28 at T14 (5.17 × 105vs. 2.26 × 104, for non-treated and phage-treated larvae, respectively; P=0.04) .

CONCLUSION

The methodological refinements applied to establish the intestinal colonization model simplify the use of Z. morio larvae, facilitate prompt evaluation of novel decolonization approaches and reduce experiments involving vertebrate animals in accordance with the Replacement, Reduction and Refinement principles.

Nur77 as a novel regulator of Paneth cell differentiation and function

Serving as a part of intestinal innate immunity, Paneth cells play an important role in intestinal homeostasis maintenance via their multiple functions. However, the regulation of Paneth cells has been proven to be complex and diverse. Here, we identified nuclear receptor Nur77 as a novel regulator of Paneth cell differentiation and function. Nur77 deficiency led to the loss of Paneth cells in murine ileal crypts. Intestinal tissues or organoids with Nur77 deficiency exhibited the impaired intestinal stem cell niche and failed to enhance antimicrobial peptide expression after Paneth cell degranulation. The defects in Paneth cells and antimicrobial peptides in Nur7-/- mice led to intestinal microbiota disorders. Nur77 deficiency rendered postnatal mice susceptible to necrotizing enterocolitis. Mechanistically, Nur77 transcriptionally inhibited Dact1 expression to activate Wnt signaling activity, thus promoting Paneth cell differentiation and function. Taken together, our data suggest the regulatory role of Nur77 in Paneth cell differentiation and function and reveal a novel Dact1-mediated Wnt inhibition mechanism in Paneth cell development.

Immunological aspects of necrotizing enterocolitis models: a review

Necrotizing enterocolitis (NEC) is one of the most devasting diseases affecting preterm neonates. However, despite a lot of research, NEC's pathogenesis remains unclear. It is known that the pathogenesis is a multifactorial process, including (1) a pathological microbiome with abnormal bacterial colonization, (2) an immature immune system, (3) enteral feeding, (3) an impairment of microcirculation, and (4) possibly ischemia-reperfusion damage to the intestine. Overall, the immaturity of the mucosal barrier and the increased expression of Toll-like receptor 4 (TLR4) within the intestinal epithelium result in an intestinal hyperinflammation reaction. Concurrently, a deficiency in counter-regulatory mediators can be seen. The sum of these processes can ultimately result in intestinal necrosis leading to very high mortality rates of the affected neonates. In the last decade no substantial advances in the treatment of NEC have been made. Thus, NEC animal models as well as in vitro models have been employed to better understand NEC's pathogenesis on a cellular and molecular level. This review will highlight the different models currently in use to study immunological aspects of NEC.

Endogenous Hyaluronan Promotes Intestinal Homeostasis and Protects against Murine Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a complex, multifactorial gastrointestinal disorder predominantly affecting preterm infants. The pathogenesis of this condition involves a complex interplay between intestinal barrier dysfunction, microbial dysbiosis, and an altered immune response. This study investigates the potential role of endogenous hyaluronan (HA) in both the early phases of intestinal development and in the context of NEC-like intestinal injury. We treated neonatal CD-1 mouse pups with PEP1, a peptide inhibiting HA receptor interactions, from postnatal days 8 to 12. We evaluated postnatal intestinal developmental indicators, such as villi length, crypt depth, epithelial cell proliferation, crypt fission, and differentiation of goblet and Paneth cells, in PEP1-treated animals compared with those treated with scrambled peptide. PEP1 treatment significantly impaired intestinal development, as evidenced by reductions in villi length, crypt depth, and epithelial cell proliferation, along with a decrease in crypt fission activity. These deficits in PEP1-treated animals correlated with increased susceptibility to NEC-like injuries, including higher mortality rates, and worsened histological intestinal injury. These findings highlight the role of endogenous HA in supporting intestinal development and protecting against NEC.

Worming into infancy: Exploring helminth-microbiome interactions in early life

There is rapidly growing awareness of microbiome assembly and function in early-life gut health. Although many factors, such as antibiotic use and highly processed diets, impinge on this process, most research has focused on people residing in high-income countries. However, much of the world's population lives in low- and middle-income countries (LMICs), where, in addition to erratic antibiotic use and suboptimal diets, these groups experience unique challenges. Indeed, many children in LMICs are infected with intestinal helminths. Although helminth infections are strongly associated with diverse developmental co-morbidities and induce profound microbiome changes, few studies have directly examined whether intersecting pathways between these components of the holobiont shape health outcomes in early life. Here, we summarize microbial colonization within the first years of human life, how helminth-mediated changes to the gut microbiome may affect postnatal growth, and why more research on this relationship may improve health across the lifespan.

An engineered Escherichia coli Nissle strain prevents lethal liver injury in a mouse model of tyrosinemia type 1

BACKGROUND & AIMS

Hereditary tyrosinemia type 1 (HT1) results from the loss of fumarylacetoacetate hydrolase (FAH) activity and can lead to lethal liver injury. Therapeutic options for HT1 remain limited. In this study, we aimed to construct an engineered bacterium capable of reprogramming host metabolism and thereby provide a potential alternative approach for the treatment of HT1.

METHODS

Escherichia coli Nissle 1917 (EcN) was engineered to express genes involved in tyrosine metabolism in the anoxic conditions that are characteristic of the intestine (EcN-HT). Bodyweight, survival rate, plasma (tyrosine/liver function), H&E staining and RNA sequencing were used to assess its ability to degrade tyrosine and protect against lethal liver injury in Fah-knockout (KO) mice, a well-accepted model of HT1.

RESULTS

EcN-HT consumed tyrosine and produced L-DOPA (levodopa) in an in vitro system. Importantly, in Fah-KO mice, the oral administration of EcN-HT enhanced tyrosine degradation, reduced the accumulation of toxic metabolites, and protected against lethal liver injury. RNA sequencing analysis revealed that EcN-HT rescued the global gene expression pattern in the livers of Fah-KO mice, particularly of genes involved in metabolic signaling and liver homeostasis. Moreover, EcN-HT treatment was found to be safe and well-tolerated in the mouse intestine.

CONCLUSIONS

This is the first report of an engineered live bacterium that can degrade tyrosine and alleviate lethal liver injury in mice with HT1. EcN-HT represents a novel engineered probiotic with the potential to treat this condition.

IMPACT AND IMPLICATIONS

Patients with hereditary tyrosinemia type 1 (HT1) are characterized by an inability to metabolize tyrosine normally and suffer from liver failure, renal dysfunction, neurological impairments, and cancer. Given the overlap and complementarity between the host and microbial metabolic pathways, the gut microbiome provides a potential chance to regulate host metabolism through degradation of tyrosine and reduction of byproducts that might be toxic. Herein, we demonstrated that an engineered live bacterium, EcN-HT, could enhance tyrosine breakdown, reduce the accumulation of toxic tyrosine byproducts, and protect against lethal liver injury in Fah-knockout mice. These findings suggested that engineered live biotherapeutics that can degrade tyrosine in the gut may represent a viable and safe strategy for the prevention of lethal liver injury in HT1 as well as the mitigation of its associated pathologies.

Paneth cell ontogeny in term and preterm ovine models

Introduction

Paneth cells are critically important to intestinal health, including protecting intestinal stem cells, shaping the intestinal microbiome, and regulating host immunity. Understanding Paneth cell biology in the immature intestine is often modeled in rodents with little information in larger mammals such as sheep. Previous studies have only established the distribution pattern of Paneth cells in healthy adult sheep. Our study aimed to examine the ontogeny, quantification, and localization of Paneth cells in fetal and newborn lambs at different gestational ages and with perinatal transient asphyxia. We hypothesized that ovine Paneth cell distribution at birth resembles the pattern seen in humans (highest concentrations in the ileum) and that ovine Paneth cell density is gestation-dependent.

Methods

Intestinal samples were obtained from 126-127 (preterm, with and without perinatal transient asphyxia) and 140-141 (term) days gestation sheep. Samples were quantified per crypt in at least 100 crypts per animal and confirmed as Paneth cells through in immunohistochemistry.

Results

Paneth cells had significantly higher density in the ileum compared to the jejunum and were absent in the colon.

Discussion

Exposure to perinatal transient asphyxia acutely decreased Paneth cell numbers. These novel data support the possibility of utilizing ovine models for understanding Paneth cell biology in the fetus and neonate.

The case for microbial intervention at weaning

Weaning, the transition from a milk-based diet to solid food, coincides with the most significant shift in gut microbiome composition in the lifetime of most mammals. Notably, this period also marks a "window of opportunity" where key components of the immune system develop, and host-microbe interactions shape long-term immune homeostasis thereby influencing the risk of autoimmune and inflammatory diseases. This review provides a comprehensive analysis of the changes in nutrition, microbiota, and host physiology that occur during weaning. We explore how these weaning-associated processes differ across species, lifestyles, and regions of the intestine. Using prinicples of microbial ecology, we propose that the weaning transition is an optimal period for microbiome-targeted therapeutic interventions. Additionally, we suggest that replicating features of the weaning microbiome in adults could promote the successful engraftment of probiotics. Finally, we highlight key research areas that could deepen our understanding of the complex relationships between diet, commensal microbes, and the host, informing the development of more effective microbial therapies.

Animal and In Vitro Models as Powerful Tools to Decipher the Effects of Enteric Pathogens on the Human Gut Microbiota

Examining the interplay between intestinal pathogens and the gut microbiota is crucial to fully comprehend the pathogenic role of enteropathogens and their broader impact on human health. Valid alternatives to human studies have been introduced in laboratory practice to evaluate the effects of infectious agents on the gut microbiota, thereby exploring their translational implications in intestinal functionality and overall health. Different animal species are currently used as valuable models for intestinal infections. In addition, considering the recent advances in bioengineering, futuristic in vitro models resembling the intestinal environment are also available for this purpose. In this review, the impact of the main human enteropathogens (i.e., Clostridioides difficile, Campylobacter jejuni, diarrheagenic Escherichia coli, non-typhoidal Salmonella enterica, Shigella flexneri and Shigella sonnei, Vibrio cholerae, and Bacillus cereus) on intestinal microbial communities is summarized, with specific emphasis on results derived from investigations employing animal and in vitro models.

Single-cell map of dynamic cellular microenvironment of radiation-induced intestinal injury

Intestine is a highly radiation-sensitive organ that could be injured during the radiotherapy for pelvic, abdominal, and retroperitoneal tumors. However, the dynamic change of the intestinal microenvironment related to radiation-induced intestine injury (RIII) is still unclear. Using single-cell RNA sequencing, we pictured a dynamic landscape of the intestinal microenvironment during RIII and regeneration. We showed that the various cell types of intestine exhibited heterogeneous radiosensitivities. We revealed the distinct dynamic patterns of three subtypes of intestinal stem cells (ISCs), and the cellular trajectory analysis suggested a complex interconversion pattern among them. For the immune cells, we found that Ly6c+ monocytes can give rise to both pro-inflammatory macrophages and resident macrophages after RIII. Through cellular communication analysis, we identified a positive feedback loop between the macrophages and endothelial cells, which could amplify the inflammatory response induced by radiation. Besides, we identified different T cell subtypes and revealed their role in immunomodulation during the early stage of RIII through inflammation and defense response relevant signaling pathways. Overall, our study provides a valuable single-cell map of the multicellular dynamics during RIII and regeneration, which may facilitate the understanding of the mechanism of RIII.

Lrig1 drives cryptogenesis and restrains proliferation during colon development

Growth and specification of the mouse intestine occurs in utero and concludes after birth. Although numerous studies have examined this developmental process in the small intestine, far less is known about the cellular and molecular cues required for colon development. In this study, we examine the morphological events leading to crypt formation, epithelial cell differentiation, proliferation, and the emergence and expression of a stem and progenitor cell marker Lrig1. Through multicolor lineage tracing, we show Lrig1-expressing cells are present at birth and behave as stem cells to establish clonal crypts within 3 wk of life. In addition, we use an inducible knockout mouse to eliminate Lrig1 and show Lrig1 restrains proliferation within a critical developmental time window, without impacting colonic epithelial cell differentiation. Our study illustrates morphological changes during crypt development and the importance of Lrig1 in the developing colon.NEW & NOTEWORTHY Our studies define the importance of studying Lrig1 in colon development. We address a critical gap in the intestinal development literature and provide new information about the molecular cues that guide colon development. Using a novel, inducible knockout of Lrig1, we show Lrig1 is required for appropriate colon epithelial growth and illustrate the importance of Lrig1-expressing cells in the establishment of colonic crypts.

Polar lipid-enriched milk fat globule membrane supplementation in maternal high-fat diet promotes intestinal barrier function and modulates gut microbiota in male offspring

Intestinal development plays a critical role in physiology and disease in early life and has long-term effects on the health status throughout the lifespan. Maternal high-fat diet (HFD) fuels the inflammatory reaction and metabolic syndrome, disrupts intestinal barrier function, and alters gut microbiota in offspring. The aim of this study was to evaluate whether polar lipid-enriched milk fat globule membrane (MFGM-PL) supplementation in maternal HFD could promote intestinal barrier function and modulate gut microbiota in male offspring. Obese female rats induced by HFD were supplemented with MFGM-PL during pregnancy and lactation. The offspring were fed HFD for 11 weeks after weaning. MFGM-PL supplementation to dams fed HFD decreased the body weight gain and ameliorated abnormalities of serum insulin, lipids, and inflammatory cytokines in offspring at weaning. Maternal MFGM-PL supplementation promoted the intestinal barrier by increasing the expression of Ki-67, lysozyme, mucin 2, zonula occludens-1, claudin-3, and occludin. Additionally, MFGM-PL supplementation to HFD dams improved gut dysbiosis in offspring. MFGM-PL increased the relative abundance of Akkermansiaceae, Ruminococcaceae, and Blautia. Concomitantly, maternal MFGM-PL treatment increased short-chain fatty acids of colonic contents and G-protein-coupled receptor (GPR) 41 and GPR 43 expressions in the colon of offspring. Importantly, the beneficial effects of maternal MFGM-PL intervention persisted to offspring's adulthood, as evidenced by increased relative abundance of norank_f_Muribaculaceae, Peptostreptococcaceae and Romboutsia and modulated the taxonomic diversity of gut microbiota in adult offspring. In summary, maternal MFGM-PL supplementation improved intestinal development in the offspring of dams fed with HFD, which exerted long-term beneficial effects on offspring intestinal health.

Small intestine vs. colon ecology and physiology: Why it matters in probiotic administration

Research on gut microbiota has generally focused on fecal samples, representing luminal content of the large intestine. However, nutrient uptake is restricted to the small intestine. Abundant immune cell populations at this anatomical site combined with diminished mucus secretion and looser junctions (partly to allow for more efficient fluid and nutrient absorption) also results in intimate host-microbe interactions despite more rapid transit. It is thus crucial to dissect key differences in both ecology and physiology between small and large intestine to better leverage the immense potential of human gut microbiota imprinting, including probiotic engraftment at biological sensible niches. Here, we provide a detailed review unfolding how the physiological and anatomical differences between the small and large intestine affect gut microbiota composition, function, and plasticity. This information is key to understanding how gut microbiota manipulation, including probiotic administration, may strain-dependently transform host-microbe interactions at defined locations.

Microfluidic Model of Necrotizing Enterocolitis Incorporating Human Neonatal Intestinal Enteroids and a Dysbiotic Microbiome

Necrotizing enterocolitis (NEC) is a severe and potentially fatal intestinal disease that has been difficult to study due to its complex pathogenesis, which remains incompletely understood. The pathophysiology of NEC includes disruption of intestinal tight junctions, increased gut barrier permeability, epithelial cell death, microbial dysbiosis, and dysregulated inflammation. Traditional tools to study NEC include animal models, cell lines, and human or mouse intestinal organoids. While studies using those model systems have improved the field's understanding of disease pathophysiology, their ability to recapitulate the complexity of human NEC is limited. An improved in vitro model of NEC using microfluidic technology, named NEC-on-a-chip, has now been developed. The NEC-on-a-chip model consists of a microfluidic device seeded with intestinal enteroids derived from a preterm neonate, co-cultured with human endothelial cells and the microbiome from an infant with severe NEC. This model is a valuable tool for mechanistic studies into the pathophysiology of NEC and a new resource for drug discovery testing for neonatal intestinal diseases. In this manuscript, a detailed description of the NEC-on-a-chip model will be provided.

Human milk oligosaccharides reduce necrotizing enterocolitis-induced neuroinflammation and cognitive impairment in mice

Necrotizing enterocolitis (NEC) is the leading cause of morbidity and mortality in premature infants. One of the most devastating complications of NEC is the development of NEC-induced brain injury, which manifests as impaired cognition that persists beyond infancy and which represents a proinflammatory activation of the gut-brain axis. Given that oral administration of the human milk oligosaccharides (HMOs) 2'-fucosyllactose (2'-FL) and 6'-sialyslactose (6'-SL) significantly reduced intestinal inflammation in mice, we hypothesized that oral administration of these HMOs would reduce NEC-induced brain injury and sought to determine the mechanisms involved. We now show that the administration of either 2'-FL or 6'-SL significantly attenuated NEC-induced brain injury, reversed myelin loss in the corpus callosum and midbrain of newborn mice, and prevented the impaired cognition observed in mice with NEC-induced brain injury. In seeking to define the mechanisms involved, 2'-FL or 6'-SL administration resulted in a restoration of the blood-brain barrier in newborn mice and also had a direct anti-inflammatory effect on the brain as revealed through the study of brain organoids. Metabolites of 2'-FL were detected in the infant mouse brain by nuclear magnetic resonance (NMR), whereas intact 2'-FL was not. Strikingly, the beneficial effects of 2'-FL or 6'-SL against NEC-induced brain injury required the release of the neurotrophic factor brain-derived neurotrophic factor (BDNF), as mice lacking BDNF were not protected by these HMOs from the development of NEC-induced brain injury. Taken in aggregate, these findings reveal that the HMOs 2'-FL and 6'-SL interrupt the gut-brain inflammatory axis and reduce the risk of NEC-induced brain injury.NEW & NOTEWORTHY This study reveals that the administration of human milk oligosaccharides, which are present in human breast milk, can interfere with the proinflammatory gut-brain axis and prevent neuroinflammation in the setting of necrotizing enterocolitis, a major intestinal disorder seen in premature infants.

Impact of neonatal nutrition on necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading cause of morbidity and mortality in preterm infants. NEC is multifactorial and the result of a complex interaction of feeding, dysbiosis, and exaggerated inflammatory response. Feeding practices in the neonatal intensive care units (NICUs) can vary among institutions and have significant impact on the vulnerable gastointestinal tract of preterm infants. . These practices encompass factors such as the type of feeding and fortification, duration of feeding, and rate of advancement, among others. The purpose of this article is to review the data on some of the most common feeding practices in the NICU and their impact on the development of NEC in preterm infants. Data on the human milk bioactive component glycosaminoglycans, specifically hyaluronan, will also be discussed in the context of postnatal intestinal development and NEC prevention.

Paneth cell development in the neonatal gut: pathway regulation, development, and relevance to necrotizing enterocolitis

Paneth cells (PCs) are intestinal epithelial cells (IECs) that contain eosinophilic granules, which are located in Lieberkühn crypts. An increasing number of animal and human experiments have indicated that PCs are involved in the progression of a variety of intestinal as well as systemic inflammatory responses including necrotizing enterocolitis (NEC). NEC is an enteric acquired disease with high mortality that usually occurs in premature infants and neonates, however the underlying mechanisms remain unclear. In this review, we summarize the features of PCs, including their immune function, association with gut microbiota and intestinal stem cells, and their mechanism of regulating IEC death to explore the possible mechanisms by which PCs affect NEC.

The Impact of Maternal Probiotics on Intestinal Vitamin D Receptor Expression in Early Life

Vitamin D signaling via the Vitamin D Receptor (VDR) has been shown to protect against intestinal inflammation. Previous studies have also reported the mutual interactions of intestinal VDR and the microbiome, indicating a potential role of probiotics in modulating VDR expression. In preterm infants, although probiotics have been shown to reduce the incidence of necrotizing enterocolitis (NEC), they are not currently recommended by the FDA due to potential risks in this population. No previous studies have delved into the effect of maternally administered probiotics on intestinal VDR expression in early life. Using an infancy mouse model, we found that young mice exposed to maternally administered probiotics (SPF/LB) maintained higher colonic VDR expression than our unexposed mice (SPF) in the face of a systemic inflammatory stimulus. These findings indicate a potential role for microbiome-modulating therapies in preventing diseases such as NEC through the enhancement of VDR signaling.

Postnatal 14D is the Key Window for Mice Intestinal Development- An Insight from Age-Dependent Antibiotic-Mediated Gut Microbial Dysbiosis Study

The postnatal period is one of the critical windows for the structure-function development of the gastrointestinal tract and associated mucosal immunity. Along with other constituent members, recent studies suggest the contribution of gut microbiota in maintaining host health, immunity, and development. Although the gut microbiota's role in maintaining barrier integrity is known, its function in early life development still needs to be better understood. To understand the details of gut microbiota's effects on intestinal integrity, epithelium development, and immune profile, the route of antibiotic-mediated perturbation is taken. Mice on days 7(P7D), 14(P14D), 21(P21D) and 28(P28D) are sacrificed and 16S rRNA metagenomic analysis is performed. The barrier integrity, tight junction proteins (TJPs) expression, intestinal epithelial cell (IEC) markers, and inflammatory cytokines are analyzed. Results reveal a postnatal age-related impact of gut microbiota perturbation, with a gradual increase in the relative abundance of Proteobacteria and a reduction in Bacteroidetes and Firmicutes. Significant barrier integrity disruption, reduced TJPs and IECs marker expression, and increased systemic inflammation at P14D of AVNM-treated mice are found. Moreover, the microbiota transplantation shows recolonization of Verrucomicrobia, proving a causal role in barrier functions. The investigation reveals P14D as a critical period for neonatal intestinal development, regulated by specific microbiota composition.

The Role of Lrig1 in the Development of the Colonic Epithelium

Growth and specification of the mouse intestine occurs in utero and concludes after birth. While numerous studies have examined this developmental process in the small intestine, far less is known about the cellular and molecular cues required for colon development. In this study, we examine the morphological events leading to crypt formation, epithelial cell differentiation, areas of proliferation, and the emergence and expression of a stem and progenitor cell marker Lrig1. Through multicolor lineage tracing, we show Lrig1 expressing cells are present at birth and behave as stem cells to establish clonal crypts within three weeks after birth. In addition, we use an inducible knockout mouse to eliminate Lrig1 during colon development and show loss of Lrig1 restrains proliferation within a critical developmental time window, without impacting colonic epithelial cell differentiation. Our study illustrates the morphological changes that occur during crypt development and the importance of Lrig1 in the developing colon.

State-of-the-art review and update of in vivo models of necrotizing enterocolitis

NEC remains one of the most common causes of mortality and morbidity in preterm infants. Animal models of necrotizing enterocolitis (NEC) have been crucial in improving our understanding of this devastating disease and identifying biochemical pathways with therapeutic potential. The pathogenesis of NEC remains incompletely understood, with no specific entity that unifies all infants that develop NEC. Therefore, investigators rely on animal models to manipulate variables and provide a means to test interventions, making them valuable tools to enhance our understanding and prevent and treat NEC. The advancements in molecular analytic tools, genetic manipulation, and imaging modalities and the emergence of scientific collaborations have given rise to unique perspectives and disease correlates, creating novel pathways of investigation. A critical review and understanding of the current phenotypic considerations of the highly relevant animal models of NEC are crucial to developing novel therapeutic and preventative strategies for NEC.

From birth to death: The hardworking life of Paneth cell in the small intestine

Paneth cells are a group of unique intestinal epithelial cells, and they play an important role in host-microbiota interactions. At the origin of Paneth cell life, several pathways such as Wnt, Notch, and BMP signaling, affect the differentiation of Paneth cells. After lineage commitment, Paneth cells migrate downward and reside in the base of crypts, and they possess abundant granules in their apical cytoplasm. These granules contain some important substances such as antimicrobial peptides and growth factors. Antimicrobial peptides can regulate the composition of microbiota and defend against mucosal penetration by commensal and pathogenic bacteria to protect the intestinal epithelia. The growth factors derived from Paneth cells contribute to the maintenance of the normal functions of intestinal stem cells. The presence of Paneth cells ensures the sterile environment and clearance of apoptotic cells from crypts to maintain the intestinal homeostasis. At the end of their lives, Paneth cells experience different types of programmed cell death such as apoptosis and necroptosis. During intestinal injury, Paneth cells can acquire stem cell features to restore the intestinal epithelial integrity. In view of the crucial roles of Paneth cells in the intestinal homeostasis, research on Paneth cells has rapidly developed in recent years, and the existing reviews on Paneth cells have mainly focused on their functions of antimicrobial peptide secretion and intestinal stem cell support. This review aims to summarize the approaches to studying Paneth cells and introduce the whole life experience of Paneth cells from birth to death.

Towards early detection of neurodegenerative diseases: A gut feeling

The gastrointestinal tract communicates with the nervous system through a bidirectional network of signaling pathways called the gut-brain axis, which consists of multiple connections, including the enteric nervous system, the vagus nerve, the immune system, endocrine signals, the microbiota, and its metabolites. Alteration of communications in the gut-brain axis is emerging as an overlooked cause of neuroinflammation. Neuroinflammation is a common feature of the pathogenic mechanisms involved in various neurodegenerative diseases (NDs) that are incurable and debilitating conditions resulting in progressive degeneration and death of neurons, such as in Alzheimer and Parkinson diseases. NDs are a leading cause of global death and disability, and the incidences are expected to increase in the following decades if prevention strategies and successful treatment remain elusive. To date, the etiology of NDs is unclear due to the complexity of the mechanisms of diseases involving genetic and environmental factors, including diet and microbiota. Emerging evidence suggests that changes in diet, alteration of the microbiota, and deregulation of metabolism in the intestinal epithelium influence the inflammatory status of the neurons linked to disease insurgence and progression. This review will describe the leading players of the so-called diet-microbiota-gut-brain (DMGB) axis in the context of NDs. We will report recent findings from studies in model organisms such as rodents and fruit flies that support the role of diets, commensals, and intestinal epithelial functions as an overlooked primary regulator of brain health. We will finish discussing the pivotal role of metabolisms of cellular organelles such as mitochondria and peroxisomes in maintaining the DMGB axis and how alteration of the latter can be used as early disease makers and novel therapeutic targets.

Regulation and functions of cell division in the intestinal tissue

In multicellular organisms, epithelial cells are key elements of tissue organization. In developing epithelial tissues, cellular proliferation and differentiation are under the tight regulation of morphogenetic programs to ensure correct organ formation and functioning. In these processes, proliferation rates and division orientation regulate the speed, timing and direction of tissue expansion but also its proper patterning. Moreover, tissue homeostasis relies on spatio-temporal modulations of daughter cell behavior and arrangement. These aspects are particularly crucial in the intestine, which is one of the most proliferative tissues in adults, making it a very attractive adult organ system to study the role of cell division on epithelial morphogenesis and organ function. Although epithelial cell division has been the subject of intense research for many years in multiple models, it still remains in its infancy in the context of the intestinal tissue. In this review, we focus on the current knowledge on cell division and regulatory mechanisms at play in the intestinal epithelial tissue, as well as their importance in developmental biology and physiopathology.

Neonatal development of intestinal neuroimmune interactions

Interactions between the enteric nervous system (ENS), immune system, and gut microbiota regulate intestinal homeostasis in adults, but their development and role(s) in early life are relatively underexplored. In early life, these interactions are dynamic, because the mucosal immune system, microbiota, and the ENS are developing and influencing each other. Moreover, disrupting gut microbiota and gut immune system development, and potentially ENS development, by early-life antibiotic exposure increases the risk of diseases affecting the gut. Here, we review the development of the ENS and immune/epithelial cells, and identify potential critical periods for their interactions and development. We also highlight knowledge gaps that, when addressed, may help promote intestinal homeostasis, including in the settings of early-life antibiotic exposure.

The role of goblet cells and mucus in intestinal homeostasis

The intestinal tract faces numerous challenges that require several layers of defence. The tight epithelium forms a physical barrier that is further protected by a mucus layer, which provides various site-specific protective functions. Mucus is produced by goblet cells, and as a result of single-cell RNA sequencing identifying novel goblet cell subpopulations, our understanding of their various contributions to intestinal homeostasis has improved. Goblet cells not only produce mucus but also are intimately linked to the immune system. Mucus and goblet cell development is tightly regulated during early life and synchronized with microbial colonization. Dysregulation of the developing mucus systems and goblet cells has been associated with infectious and inflammatory conditions and predisposition to chronic disease later in life. Dysfunctional mucus and altered goblet cell profiles are associated with inflammatory conditions in which some mucus system impairments precede inflammation, indicating a role in pathogenesis. In this Review, we present an overview of the current understanding of the role of goblet cells and the mucus layer in maintaining intestinal health during steady-state and how alterations to these systems contribute to inflammatory and infectious disease.

Microbial bile salt hydrolase activity influences gene expression profiles and gastrointestinal maturation in infant mice

The mechanisms by which early microbial colonizers of the neonate influence gut development are poorly understood. Bacterial bile salt hydrolase (BSH) acts as a putative colonization factor that influences bile acid signatures and microbe-host signaling pathways and we considered whether this activity can influence infant gut development. In silico analysis of the human neonatal gut metagenome confirmed that BSH enzyme sequences are present as early as one day postpartum. Gastrointestinal delivery of cloned BSH to immature gnotobiotic mice accelerated shortening of the colon and regularized gene expression profiles, with monocolonised mice more closely resembling conventionally raised animals. In situ expression of BSH decreased markers of cell proliferation (Ki67, Hes2 and Ascl2) and strongly increased expression of ALPI, a marker of cell differentiation and barrier function. These data suggest an evolutionary paradigm whereby microbial BSH activity potentially influences bacterial colonization and in-turn benefits host gastrointestinal maturation.

DNA Methylome Mapping Identifies Epigenetic Abnormalities in Intestinal Lymphocyte Regulation in Human Necrotizing Enterocolitis

BACKGROUND

Epigenetic changes occur in response to environmental factors during the pathogenesis of necrotizing enterocolitis (NEC) in animal models, but the DNA methylation signature in human patients with NEC has not been examined.

AIM

To illustrate the signature and function of DNA methylation in the intestine of human NEC.

METHODS

DNA methyltransferases (DNMTs) were compared between intestinal tissue with NEC and control. Genome-wide DNA methylation was analyzed by reduced representation bisulfite sequencing (RRBS). The biological functions of the potential methylation regulated genes were analyzed by Gene Ontology. Gene methylation and expression were confirmed by bisulfite genomic sequencing (BGS) and RT-qPCR.

RESULTS

By screening the expression of DNMTs, we identified a marked reduction in DNMT3A at both the mRNA and protein levels in NEC. Genome-wide variation of DNA methylation was detected in NEC lesions. The CG methylation level in almost all unique regions except CpG islands (CGIs) was lower in NEC compared with control. A total of 287 differentially methylated regions (DMRs) were identified across the whole genome in NEC, 123 of them are located on the CGI in the promoter. The DMR-associated genes were linked to intestinal epithelial permeability, platelet aggregation, and lymphocyte proliferation. Four genes (ZNF335, MPL, RASAL3, and KDM6A) with roles in the regulation of lymphocytes that may predispose the intestine to imbalanced immune processes were further confirmed to be hypermethylated and transcriptionally downregulated.

CONCLUSIONS

These findings underscore the novel relationship between epigenetic changes and lymphocyte regulation in human NEC, which may have potential diagnostic and therapeutic relevance for NEC.

The administration of amnion-derived multipotent cell secretome ST266 protects against necrotizing enterocolitis in mice and piglets

Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal disease in premature infants and is steadily rising in frequency. Patients who develop NEC have a very high mortality, illustrating the importance of developing novel prevention or treatment approaches. We and others have shown that NEC arises in part from exaggerated signaling via the bacterial receptor, Toll-like receptor 4 (TLR4) on the intestinal epithelium, leading to widespread intestinal inflammation and intestinal ischemia. Strategies that limit the extent of TLR4 signaling, including the administration of amniotic fluid, can reduce NEC development in mouse and piglet models. We now seek to test the hypothesis that a secretome derived from amnion-derived cells can prevent or treat NEC in preclinical models of this disease via a process involving TLR4 inhibition. In support of this hypothesis, we show that the administration of this secretome, named ST266, to mice or piglets can prevent and treat experimental NEC. The protective effects of ST266 occurred in the presence of marked TLR4 inhibition in the intestinal epithelium of cultured epithelial cells, intestinal organoids, and human intestinal samples ex vivo, independent of epidermal growth factor. Strikingly, RNA-seq analysis of the intestinal epithelium in mice reveals that the ST266 upregulates critical genes associated with gut remodeling, intestinal immunity, gut differentiation. and energy metabolism. These findings show that the amnion-derived secretome ST266 can prevent and treat NEC, suggesting the possibility of novel therapeutic approaches for patients with this devastating disease.NEW & NOTEWORTHY This work provides hope for children who develop NEC, a devastating disease of premature infants that is often fatal, by revealing that the secreted product of amniotic progenitor cells (called ST266) can prevent or treat NEC in mice, piglet, and "NEC-in-a-dish" models of this disease. Mechanistically, ST266 prevented bacterial signaling, and a detailed transcriptomic analysis revealed effects on gut differentiation, immunity, and metabolism. Thus, an amniotic secretome may offer novel approaches for NEC.

Impact of Age, Sex, and Genetic Diversity in Murine Models of the Hematopoietic Acute Radiation Syndrome (H-ARS) and the Delayed Effects of Acute Radiation Exposure (DEARE)

Purpose of review

Malicious or accidental radiation exposure increases risk for the hematopoietic acute radiation syndrome (H-ARS) and the delayed effects of acute radiation exposure (DEARE). Radiation medical countermeasure (MCM) development relies on robust animal models reflective of all age groups and both sexes. This review details critical considerations in murine H-ARS and DEARE model development including divergent radiation responses dependent on age, sex, and genetic diversity.

Recent findings

Radioresistance increases with murine age from pediatrics through geriatrics. Between sexes, radioresistance is higher in male weanlings, pubescent females, and aged males, corresponding with accelerated myelopoiesis. Jackson diversity outbred (JDO) mice resemble non-human primates in radiation response for modeling human diversity. Weanlings and JDO models exhibit less DEARE than other models.

Summary

Highly characterized age-, sex- and diversity-conscious murine models of H-ARS and DEARE provide powerful and essential tools in MCM development for all radiation victims.

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.

Impact of Surfactant Protein-A on Immunomodulatory Properties of Murine and Human Breast Milk

OBJECTIVES

Human milk reduces the incidence of necrotizing enterocolitis (NEC). Prior studies have demonstrated that exogenous surfactant protein-A (SP-A) modulates intestinal inflammation, reduces NEC-like pathology in SP-A-deficient (SPAKO) pups, and may contribute to breast milk's immunomodulatory potential. We hypothesize that SP-A is present in milk and impacts inflammatory responses in the terminal ileum of neonatal mice.

METHODS

Human milk was collected at postpartum days 1-3 and 28. Mouse milk was collected at postpartum days 1-10. SP-A was detected in milk through immunoprecipitation and western blot analysis. The impact of murine wild-type (WT) milk on SPAKO pup ileum was evaluated in a model of intestinal inflammation via cross-rearing experiments. Terminal ileum was evaluated for inflammatory cytokine and toll-like receptor 4 (TLR4) mRNA expression via quantitative real-time RT-PCR.

RESULTS

SP-A was detected in human milk and wild type (WT) mouse milk, but not in SPAKO mouse milk. Expression of TLR4, interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α was decreased in SPAKO pups reared with WT dams compared to SPAKO pups reared with SPAKO dams, with a peak effect at day of life 14. When inflammation was induced using a lipopolysaccharide-induced model of inflammation, expression of TLR4, IL-1β, IL-6, CXCL-1, and TNF-α was significantly lower in SPAKO pups reared with WT dams compared to SPAKO pups reared with SPAKO dams.

CONCLUSIONS

SP-A is present in human and murine milk and plays a role in lowering inflammation in murine pup terminal ileum. Both baseline inflammation and induced inflammatory responses are reduced via exposure to SP-A in milk with the effect amplified in inflammatory conditions.

Intestinal epithelium in early life

Rapid development of the fetal and neonatal intestine is required to meet the growth requirements of early life and form a protective barrier against external insults encountered by the intestinal mucosa. The fetus receives nutrition via the placenta and is protected from harmful pathogens in utero, which leads to intestinal development in a relatively quiescent environment. Upon delivery, the intestinal mucosa is suddenly tasked with providing host defense and meeting nutritional demands. To serve these functions, an array of specialized epithelial cells develop from intestinal stem cells starting in utero and continuing postnatally. Intestinal disease results when these homeostatic processes are interrupted. For preterm neonates, the most common pathology resulting from epithelial barrier dysfunction is necrotizing enterocolitis (NEC). In this review, we discuss the normal development and function of the intestinal epithelium in early life as well as how disruption of these processes can lead to NEC.

Hyaluronic Acid 35 kDa Protects against a Hyperosmotic, Formula Feeding Model of Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC), an inflammatory disease of the intestine, is a common gastrointestinal emergency among preterm infants. Intestinal barrier dysfunction, hyperactivation of the premature immune system, and dysbiosis are thought to play major roles in the disease. Human milk (HM) is protective, but the mechanisms underpinning formula feeding as a risk factor in the development of NEC are incompletely understood. Hyaluronic acid 35 kDa (HA35), a bioactive glycosaminoglycan of HM, accelerates intestinal development in murine pups during homeostasis. In addition, HA35 prevents inflammation-induced tissue damage in pups subjected to murine NEC, incorporating Paneth cell dysfunction and dysbiosis. We hypothesized HA35 treatment would reduce histological injury and mortality in a secondary mouse model of NEC incorporating formula feeding. NEC-like injury was induced in 14-day mice by dithizone-induced disruption of Paneth cells and oral gavage of rodent milk substitute. Mortality and histological injury, serum and tissue cytokine levels, stool bacterial sequencing, and bulk RNA-Seq comparisons were analyzed. HA35 significantly reduced the severity of illness in this model, with a trend toward reduced mortality, while RNA-Seq analysis demonstrated HA35 upregulated genes associated with goblet cell function and innate immunity. Activation of these critical protective and reparative mechanisms of the small intestine likely play a role in the reduced pathology and enhanced survival trends of HA-treated pups subjected to intestinal inflammation in this secondary model of NEC, providing potentially interesting translational targets for the human preterm disease.

Bifidobacterium longum Subspecies infantis Strain EVC001 Decreases Neonatal Murine Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a disease mainly of preterm infants with a 30-50% mortality rate and long-term morbidities for survivors. Treatment strategies are limited and have not improved in decades, prompting research into prevention strategies, particularly with probiotics. Recent work with the probiotic B. infantis EVC001 suggests that this organism may generate a more appropriate microbiome for preterm infants who generally have inappropriate gut colonization and inflammation, both risk factors for NEC. Experimental NEC involving Paneth cell disruption in combination with bacterial dysbiosis or formula feeding was induced in P14-16 C57Bl/6 mice with or without gavaged B. infantis. Following completion of the model, serum, small intestinal tissue, the cecum, and colon were harvested to examine inflammatory cytokines, injury, and the microbiome, respectively. EVC001 treatment significantly decreased NEC in a bacterial dysbiosis dependent model, but this decrease was model-dependent. In the NEC model dependent on formula feeding, no difference in injury was observed, but trending to significant differences was observed in serum cytokines. EVC001 also improved wound closure at six and twelve hours compared to the sham control in intestinal epithelial monolayers. These findings suggest that B. infantis EVC001 can prevent experimental NEC through anti-inflammatory and epithelial barrier restoration properties.

Neutrophil extracellular trap inhibition increases inflammation, bacteraemia and mortality in murine necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal disease affecting primarily premature infants. The disease is characterized by intestinal inflammation and leucocyte infiltration, often progressing to necrosis, perforation, systemic inflammatory response and death. Neutrophil extracellular traps (NETs), denoting nuclear DNA, histone and antimicrobial protein release, have been suggested to play a role in NEC. This study aimed to determine the role of NETs in NEC and explore the effect of chloramidine, a NET inhibitor, on a murine NEC-like intestinal injury model. Blood and intestinal tissues were collected from infants diagnosed with ≥ Stage II NEC, and levels of nucleosomes and NETs, respectively, were compared with those of case-matched controls. In mice, NEC was induced with dithizone/Klebsiella, and mice in the treatment group received 40 mg/kg chloramidine. Bacterial load, intestinal histology, plasma myeloperoxidase and cytokine levels, and immunofluorescent staining were compared with controls. Nucleosomes were significantly elevated in both human and mouse NEC plasma, whereas NET staining was only present in NEC tissue in both species. Chloramidine treatment increased systemic inflammation, bacterial load, organ injury and mortality in murine NEC. Taken together, our findings suggest that NETs are critical in the innate immune defence during NEC in preventing systemic bacteraemia.

Innate immune sensing by epithelial barriers

Epithelial cells in barrier tissues perform a critical immune function by detecting, restricting, and often directly eliminating extrinsic pathogens. Membrane-bound and cytosolic pattern recognition receptors in epithelial cells bind to diverse ligands, detecting pathogen components and behaviors and stimulating cell-autonomous immunity. In addition to directly acting as first-responders to pathogens, epithelial cells detect commensal-derived and diet-derived products to promote homeostasis. Recent advances have clarified the array of molecular sensors expressed by epithelial cells, and how epithelial cells responses are wired to promote homeostatic balance while simultaneously allowing elimination of pathogens. These new studies emphatically position epithelial cells as central to an effective innate immune response.

Human Breast Milk Enhances Intestinal Mucosal Barrier Function and Innate Immunity in a Healthy Pediatric Human Enteroid Model

Breastfeeding has been associated with long lasting health benefits. Nutrients and bioactive components of human breast milk promote cell growth, immune development, and shield the infant gut from insults and microbial threats. The molecular and cellular events involved in these processes are ill defined. We have established human pediatric enteroids and interrogated maternal milk's impact on epithelial cell maturation and function in comparison with commercial infant formula. Colostrum applied apically to pediatric enteroid monolayers reduced ion permeability, stimulated epithelial cell differentiation, and enhanced tight junction function by upregulating occludin. Breast milk heightened the production of antimicrobial peptide α-defensin 5 by goblet and Paneth cells, and modulated cytokine production, which abolished apical release of pro-inflammatory GM-CSF. These attributes were not found in commercial infant formula. Epithelial cells exposed to breast milk elevated apical and intracellular pIgR and enabled maternal IgA translocation. Proteomic data revealed a breast milk-induced molecular pattern associated with tissue remodeling and homeostasis. Using a novel ex vivo pediatric enteroid model, we have identified distinct cellular and molecular events involved in human milk-mediated improvement of human intestinal physiology and immunity.

Acceleration of Small Intestine Development and Remodeling of the Microbiome Following Hyaluronan 35 kDa Treatment in Neonatal Mice

The beneficial effects of human milk suppressing the development of intestinal pathologies such as necrotizing enterocolitis in preterm infants are widely known. Human milk (HM) is rich in a multitude of bioactive factors that play major roles in promoting postnatal maturation, differentiation, and the development of the microbiome. Previous studies showed that HM is rich in hyaluronan (HA) especially in colostrum and early milk. This study aims to determine the role of HA 35 KDa, a HM HA mimic, on intestinal proliferation, differentiation, and the development of the intestinal microbiome. We show that oral HA 35 KDa supplementation for 7 days in mouse pups leads to increased villus length and crypt depth, and increased goblet and Paneth cells, compared to controls. We also show that HA 35 KDa leads to an increased predominance of Clostridiales Ruminococcaceae, Lactobacillales Lactobacillaceae, and Clostridiales Lachnospiraceae. In seeking the mechanisms involved in the changes, bulk RNA seq was performed on samples from the terminal ileum and identified upregulation in several genes essential for cellular growth, proliferation, and survival. Taken together, this study shows that HA 35 KDa supplemented to mouse pups promotes intestinal epithelial cell proliferation, as well as the development of Paneth cells and goblet cell subsets. HA 35 KDa also impacted the intestinal microbiota; the implications of these responses need to be determined.

Early Life Antibiotics Influence In Vivo and In Vitro Mouse Intestinal Epithelium Maturation and Functioning

BACKGROUND & AIMS

The use of antibiotics (ABs) is a common practice during the first months of life. ABs can perturb the intestinal microbiota, indirectly influencing the intestinal epithelial cells (IECs), but can also directly affect IECs independent of the microbiota. Previous studies have focused mostly on the impact of AB treatment during adulthood. However, the difference between the adult and neonatal intestine warrants careful investigation of AB effects in early life.

METHODS

Neonatal mice were treated with a combination of amoxicillin, vancomycin, and metronidazole from postnatal day 10 to 20. Intestinal permeability and whole-intestine gene and protein expression were analyzed. IECs were sorted by a fluorescence-activated cell sorter and their genome-wide gene expression was analyzed. Mouse fetal intestinal organoids were treated with the same AB combination and their gene and protein expression and metabolic capacity were determined.

RESULTS

We found that in vivo treatment of neonatal mice led to decreased intestinal permeability and a reduced number of specialized vacuolated cells, characteristic of the neonatal period and necessary for absorption of milk macromolecules. In addition, the expression of genes typically present in the neonatal intestinal epithelium was lower, whereas the adult gene expression signature was higher. Moreover, we found altered epithelial defense and transepithelial-sensing capacity. In vitro treatment of intestinal fetal organoids with AB showed that part of the consequences observed in vivo is a result of the direct action of the ABs on IECs. Lastly, ABs reduced the metabolic capacity of intestinal fetal organoids.

CONCLUSIONS

Our results show that early life AB treatment induces direct and indirect effects on IECs, influencing their maturation and functioning.

Establishing Pediatric Mouse Models of the Hematopoietic Acute Radiation Syndrome and the Delayed Effects of Acute Radiation Exposure

Medical countermeasures (MCMs) for hematopoietic acute radiation syndrome (H-ARS) should be evaluated in well-characterized animal models, with consideration of at-risk populations such as pediatrics. We have developed pediatric mouse models of H-ARS and delayed effects of acute radiation exposure (DEARE) for efficacy testing of MCMs against radiation. Male and female C57BL/6J mice aged 3, 4, 5, 6, 7 and 8 weeks old (±1 day) were characterized for baseline hematopoietic and gastrointestinal parameters, radiation response, efficacy of a known MCM, and DEARE at six and 12 months after total-body irradiation (TBI). Weanlings (age 3 weeks) were the most radiosensitive age group with an estimated LD50/30 of 712 cGy, while mice aged 4 to 8 weeks were more radioresistant with an estimated LD50/30 of 767-787 cGy. Female weanlings were more radiosensitive than males at 3 and 4 weeks old but became significantly more radioresistant after the pubertal age of 5 weeks. The most dramatic increase in body weight, RBC counts and intestinal circumference length occurred from 3 to 5 weeks of age. The established radiomitigator Neulasta® (pegfilgrastim) significantly increased 30-day survival in all age groups, validating these models for MCM efficacy testing. Analyses of DEARE among pediatric survivors revealed depressed weight gain in males six months post-TBI, and increased blood urea nitrogen at 12 months post-TBI which was more severe in females. Hematopoietic DEARE at six months post-TBI appeared to be less severe in survivors from the 3- and 4-week-old groups but was equally severe in all age groups by 12 months of age. Similar to our other acute radiation mouse models, there was no appreciable effect of Neulasta used as an H-ARS MCM on the severity of DEARE. In summary, these data characterize a pediatric mouse model useful for assessing the efficacy of MCMs against ARS and DEARE in children.

Global hypermethylation of intestinal epithelial cells is a hallmark feature of neonatal surgical necrotizing enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) remains one of the overall leading causes of death in premature infants, and the pathogenesis is unpredictable and not well characterized. The aim of our study was to determine the molecular phenotype of NEC via transcriptomic and epithelial cell-specific epigenomic analysis, with a specific focus on DNA methylation.

METHODS

Using laser capture microdissection, epithelial cell-specific methylation signatures were characterized by whole-genome bisulfite sequencing of ileal and colonic samples at the time of surgery for NEC and after NEC had healed at reanastomosis (n = 40). RNA sequencing was also performed to determine the transcriptomic profile of these samples, and a comparison was made to the methylome data.

RESULTS

We found that surgical NEC has a considerable impact on the epigenome by broadly increasing DNA methylation levels, although these effects are less pronounced in genomic regions associated with the regulation of gene expression. Furthermore, NEC-related DNA methylation signatures were influenced by tissue of origin, with significant differences being noted between colon and ileum. We also identified numerous transcriptional changes in NEC and clear associations between gene expression and DNA methylation.

CONCLUSIONS

We have defined the intestinal epigenomic and transcriptomic signatures during surgical NEC, which will advance our understanding of disease pathogenesis and may enable the development of novel precision medicine approaches for NEC prediction, diagnosis and phenotyping.

Maternal administration of probiotics promotes gut development in mouse offsprings

Necrotizing enterocolitis is the most common gastrointestinal disorder in premature neonates. This disease is characterized by massive epithelial necrosis, gut barrier dysfunction and improper mucosal defense development. Studies have shown that probiotic administration can decrease NEC incidence and mortality. The proposed mechanisms of probiotics for the prevention of NEC are: promotion of intestinal development; improved barrier function through decreased apoptosis and improved mucin production; decreased expression of proinflammatory cytokines IL6, IL8, and TNFα, and modulation of microbiota dysbiosis in preterm infants. However, reported sepsis in the immunocompromised preterm host has deterred routine prophylactic administration of probiotics in the neonatal intensive care unit. We hypothesize that maternal administration of probiotics to pregnant mouse dams can recapitulate the beneficial effects observed in neonates fed with probiotics directly. We exposed pregnant mice to the probiotics and monitored the changes in the developing intestines of the offspring. Pregnant mice were fed daily with the probiotics Lactobacillus acidophilus and Bifidobacterium infantis (LB) from embryonic day15 to 2-week-old postnatally. Intraperitoneal administration of IL-1β in the pups was used to model proinflammatory insults. Sera were collected at 2 weeks of age and evaluated for inflammatory cytokines by enzyme-linked-immunosorbent-assay and gut permeability by Fluorescein isothiocyanate-dextran tracer assay. Ileal tissues were collected for the evaluation of apoptosis and proliferation of the intestinal epithelium; as well as mucin and tight junction integrity at mucosal surface by immunofluorescent staining. We find that maternal LB exposure facilitated intestinal epithelial cell differentiation, prevented loss of mucin and preserved the intestinal integrity and barrier function and decreased serum levels of IL-1β, TNF-α and IL-6 in the preweaned offsprings. in LB exposed pups. We demonstrate that maternal probiotic supplementation promotes gut maturation in developing offspring. This is potentially a safe alternative therapy to induce intestinal maturation and prevent prematurity-associated neonatal disorders.

Hyaluronan 35 kDa enhances epithelial barrier function and protects against the development of murine necrotizing enterocolitis

BACKGROUND

Disruption of tight junctions (TJs) predisposes to bacterial translocation, intestinal inflammation, and necrotizing enterocolitis (NEC). Previously, studies showed that hyaluronan (HA), a glycosaminoglycan in human milk, maintains intestinal permeability, enhances intestinal immunity, and reduces intestinal infections. In this study, we investigated the effects of HA 35 kDa on a NEC-like murine model.

METHODS

Pups were divided into Sham, NEC, NEC+HA 35, and HA 35. Severity of intestinal injury was compared using a modified macroscopic gut scoring and histologic injury grading. The effect of HA 35 on intestinal permeability was determined by measuring FITC dextran and bacterial translocation. RNA and protein expression of TJ proteins (claudin-2, -3, -4, occludin, and ZO-1) were compared between the groups.

RESULTS

Pups in the NEC+HA 35 group had increased survival and lower intestinal injury compared to untreated NEC. In addition, HA 35 reduced intestinal permeability, bacterial translocation, and proinflammatory cytokine release. Ileal expression of claudin-2, -3, -4, occludin, and ZO-1 was upregulated in NEC+HA 35 and HA 35 compared to untreated NEC and shams.

CONCLUSION

These findings suggest that HA 35 protects against NEC partly by upregulating intestinal TJs and enhancing intestinal barrier function.

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.

Feeding Formula Eliminates the Necessity of Bacterial Dysbiosis and Induces Inflammation and Injury in the Paneth Cell Disruption Murine NEC Model in an Osmolality-Dependent Manner

Necrotizing enterocolitis (NEC) remains a significant cause of morbidity and mortality in preterm infants. Formula feeding is a risk factor for NEC and osmolality, which is increased by the fortification that is required for adequate growth of the infant, has been suggested as a potential cause. Our laboratory has shown that Paneth cell disruption followed by induction of dysbiosis can induce NEC-like pathology in the absence of feeds. We hypothesized adding formula feeds to the model would exacerbate intestinal injury and inflammation in an osmolality-dependent manner. NEC-like injury was induced in 14-16 day-old C57Bl/6J mice by Paneth cell disruption with dithizone or diphtheria toxin, followed by feeding rodent milk substitute with varying osmolality (250-1491 mOsm/kg H₂O). Animal weight, serum cytokines and osmolality, small intestinal injury, and cecal microbial composition were quantified. Paneth cell-disrupted mice fed formula had significant NEC scores compared to controls and no longer required induction of bacterial dysbiosis. Significant increases in serum inflammatory markers, small intestinal damage, and overall mortality were osmolality-dependent and not related to microbial changes. Overall, formula feeding in combination with Paneth cell disruption induced NEC-like injury in an osmolality-dependent manner, emphasizing the importance of vigilance in designing preterm infant feeds.

An Experimental Approach to Rigorously Assess Paneth Cell α-Defensin (Defa) mRNA Expression in C57BL/6 Mice

Abundant evidence from many laboratories supports the premise that α-defensin peptides secreted from Paneth cells are key mediators of host-microbe interactions in the small intestine that contribute to host defense and homeostasis. α-defensins are among the most highly expressed antimicrobial peptides at this mucosal surface in many mammals, including humans and mice; however, there is striking variation among species in the number and primary structure of α-defensin paralogs. Studies of these biomolecules in vivo are further complicated by striking variations between laboratory mouse strains. Herein, we report an experimental approach to determine with precision and specificity expression levels of α-defensin (Defa) mRNA in the small intestine of C57BL/6 mice through an optimized set of oligonucleotide primers for qRT-PCR assays and cloned cDNA plasmids corresponding to the Defa paralogs. This approach demonstrated marked differences in α-defensin expression in C57BL/6 mice with respect to proximal/distal anatomical location and developmental stage, which have not been described previously. These data underscore the importance of careful attention to method (primer choice, proximal vs. distal location, and developmental stage) in analysis of antimicrobial peptide expression and their impact.