Epidermal growth factor promotes intestinal secretory cell differentiation in weaning piglets via Wnt/β-catenin signalling

Role of trefoil factors in maintaining gut health in food animals

It is imperative to preserve the integrity of the gastrointestinal system in spite of the persistent existence of harmful chemicals and microbial flora in the gut. This is made possible by essential healing initiators called Trefoil factors which helps in mucosal reconstitution and tissue development on the gastrointestinal surface. The trefoil factors are a class of abundant secreted proteins that are essential for epithelial continuity (TFFs). Trefoil factor family (TFF) proteins are biologically active peptides that play significant role in safeguarding, restoring and continuity of the gastrointestinal tract (GIT) epithelium, through collaborative modulations with mucins in the mucosal layer. These peptides are readily produced in reaction to epithelial damage in the digestive tract, thereby contributing to the healing and restituting of the epithelial layers of the intestine. In addition, considerable evidence indicated that TFF peptides trigger proliferation, migration and angiogenesis, all which are crucial processes for wound healing. There is also increasing evidence that TFF peptides modulate the mucosal immune system. These protective properties, suggest that dietary manipulation strategies targeted at enhancing the expression and synthesis of TFF peptides at optimal levels in the GIT epithelium, may constitute a plausible alternative strategy to the use of in-feed antibiotic growth promoters to maintain epithelial integrity and promote resistance to enteric pathogens. This review describes TFF peptides, with importance to their biological functions and involvement in gastrointestinal mucosal protection and repair in food animals.

The Mechanism of Zinc Oxide in Alleviating Diarrhea in Piglets after Weaning: A Review from the Perspective of Intestinal Barrier Function

Weaning is one of the most challenging phases for piglets, and it is also the time when piglets are the most susceptible to diarrhea, which may result in significant economic losses for pig production. One of the dietary strategies for reducing post-weaning diarrhea (PWD) in piglets is to provide them with a pharmacological dose of zinc oxide (ZnO). However, excessive or long-term usage of high-dose ZnO has significant impacts on pig health and the ecological environment. Therefore, caution should be exercised when considering the use of high-dose ZnO for the prevention or treatment of PWD in piglets. In this paper, the significant role of zinc in animal health, the potential mode of action of ZnO in alleviating diarrhea, and the impact of innovative, highly efficient ZnO alternatives on the regulation of piglet diarrhea were reviewed to offer insights into the application of novel ZnO in pig production.

Dietary nutrition, intestinal microbiota dysbiosis and post-weaning diarrhea in piglets

Weaning is a critical transitional point in the life cycle of piglets. Early weaning can lead to post-weaning syndrome, destroy the intestinal barrier function and microbiota homeostasis, cause diarrhea and threaten the health of piglets. The nutritional components of milk and solid foods consumed by newborn animals can affect the diversity and structure of their intestinal microbiota, and regulate post-weaning diarrhea in piglets. Therefore, this paper reviews the effects and mechanisms of different nutrients, including protein, dietary fiber, dietary fatty acids and dietary electrolyte balance, on diarrhea and health of piglets by regulating intestinal function. Protein is an essential nutrient for the growth of piglets; however, excessive intake will cause many harmful effects, such as allergic reactions, intestinal barrier dysfunction and pathogenic growth, eventually aggravating piglet diarrhea. Dietary fiber is a nutrient that alleviates post-weaning diarrhea in piglets, which is related to its promotion of intestinal epithelial integrity, microbial homeostasis and the production of short-chain fatty acids. In addition, dietary fatty acids and dietary electrolyte balance can also facilitate the growth, function and health of piglets by regulating intestinal epithelial function, immune system and microbiota. Thus, a targeted control of dietary components to promote the establishment of a healthy bacterial community is a significant method for preventing nutritional diarrhea in weaned piglets.

New insights into the unfolded protein response (UPR)-anterior gradient 2 (AGR2) pathway in the regulation of intestinal barrier function in weaned piglets

Sustained dysfunction of the intestinal barrier caused by early weaning is a major factor that induces postweaning diarrhea in weaned piglets. In both healthy and diseased states, the intestinal barrier is regulated by goblet cells. Alterations in the characteristics of goblet cells are linked to intestinal barrier dysfunction and inflammatory conditions during pathogenic infections. In this review, we summarize the current understanding of the mechanisms of the unfolded protein response (UPR) and anterior gradient 2 (AGR2) in maintaining intestinal barrier function and how modifications to these systems affect mucus barrier characteristics and goblet cell dysregulation. We highlight a novel mechanism underlying the UPR-AGR2 pathway, which affects goblet cell differentiation and maturation and the synthesis and secretion of mucin by regulating epidermal growth factor receptor and mucin 2. This study provides a theoretical basis and new insights into the regulation of intestinal health in weaned piglets.

Human breast milk: A promising treatment for necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a severe gastrointestinal disorder occurring in newborns, with a mortality rate ranging from 20 % to 30 %. The existing therapeutic approaches for NEC are limited in their effectiveness. Various factors contribute to the development of NEC, including disruption of barrier function, dysregulation of the intestinal immune system, and abnormal colonization of the intestinal microbiota. Researchers have shown considerable interest in exploring the therapeutic potential of the constituents present in human breast milk (HBM) for treating NEC. HBM contains numerous bioactive components, such as exosomes, growth factors, and oligosaccharides. However, the precise mechanisms by which HBM exerts its protective effects against NEC remain incompletely understood. In this study, our objective was to comprehensively review the bioactive substances present in HBM, aiming to facilitate the development of novel therapeutic strategies for NEC.

Paneth cells in farm animals: current status and future direction

A healthy intestine plays an important role in the growth and development of farm animals. In small intestine, Paneth cells are well known for their regulation of intestinal microbiota and intestinal stem cells (ISCs). Although there has been a lot of studies and reviews on human and murine Paneth cells under intestinal homeostasis or disorders, little is known about Paneth cells in farm animals. Most farm animals possess Paneth cells in their small intestine, as identified by various staining methods, and Paneth cells of various livestock species exhibit noticeable differences in cell shape, granule number, and intestinal distribution. Paneth cells in farm animals and their antimicrobial peptides (AMPs) are susceptible to multiple factors such as dietary nutrients and intestinal infection. Thus, the comprehensive understanding of Paneth cells in different livestock species will contribute to the improvement of intestinal health. This review first summarizes the current status of Paneth cells in pig, cattle, sheep, horse, chicken and rabbit, and points out future directions for the investigation of Paneth cells in the reviewed animals.

Expression Profile of miR-199a and Its Role in the Regulation of Intestinal Inflammation

Early weaning stress impairs intestinal health in piglets. miRNAs are crucial for maintaining host homeostasis, while their implication for animal health remains unclear. To identify weaning-associated miRNAs, piglets were sampled at day 0, 1, 3, 7 and 14 after weaning. The data indicated that the highest levels of miR-199a-5p in jejunal villus upper cells were observed on day 14 after weaning, while the lowest levels in crypt cells were noted on day 7 and 14. In contrast, miR-199a-3p was down-regulated in both of these two cells on day 7 after weaning compared with day 0. Both miR-199a-5p and -3p were differently expressed along the villus-crypt axis. To further clarify the function of miR-199a, mice deficient in miR-199a were exposed to dextran sulfate sodium (DSS) to induce colitis. Results revealed that silencing of miR-199a enhanced sensitivity to DSS-induced colitis. Moreover, the increased morbidity and mortality were correlated with enhanced inflammatory cell infiltration, elevated pro-inflammatory cytokine expression, impaired barrier function, and a concomitant increase in permeability-related parameters. Bioinformatic analysis further demonstrated that lipid metabolism-related pathways were significantly enriched and Ndrg1 was verified as a target of miR-199a-3p. These findings indicate that miR-199a may be important for animal health management.

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.

Comparison of the Pig Breeds in the Small Intestinal Morphology and Digestive Functions at Different Ages

The small intestine is the main site for digestion and absorption of nutrients, and the development of the small intestine can be affected by several factors, such as diet composition, age, and genotype. Thus, this study aimed to compare the small intestinal morphology and digestive function differences at different ages of three pig breeds. Thirty litters of newborn Taoyuan black (TB), Xiangcun black (XB), and Duroc (DR) piglets (ten litters per breed) were selected for this study. Ten piglets from each breed were selected and sampled at 1, 10, 21, and 24 days old. The results showed that the TB and XB piglets had lower growth but had higher lactase and maltase activities in the jejunum compared with the DR piglets, while most of the digestive enzyme activities in the ileum were higher in the DR piglets at different ages. The expression levels of nutrient transporters, mainly including amino acids, glucose, and fatty acids transporters, differed in the jejunum at different ages among three pig breeds and were higher in the DR piglets at 1 day old and XB piglets at 24 days old. Collectively, these findings suggest that the phenotypic differences in the growth, intestinal morphology, and digestive function among the three pig breeds mainly resulted from the differences in digestive enzymes and nutrient transporters in the intestine.

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.

Weaning stress and intestinal health of piglets: A review

Weaning is considered to be one of the most critical periods in pig production, which is related to the economic benefits of pig farms. However, in actual production, many piglets are often subjected to weaning stress due to the sudden separation from the sow, the changes in diet and living environment, and other social challenges. Weaning stress often causes changes in the morphology and function of the small intestine of piglets, disrupts digestion and absorption capacity, destroys intestinal barrier function, and ultimately leads to reduced feed intake, increased diarrhea rate, and growth retardation. Therefore, correctly understanding the effects of weaning stress on intestinal health have important guiding significance for nutritional regulation of intestinal injury caused by weaning stress. In this review, we mainly reviewed the effects of weaning stress on the intestinal health of piglets, from the aspects of intestinal development, and intestinal barrier function, thereby providing a theoretical basis for nutritional strategies to alleviate weaning stress in mammals in future studies.

Dietary Epidermal Growth Factor Supplementation Alleviates Intestinal Injury in Piglets with Intrauterine Growth Retardation via Reducing Oxidative Stress and Enhancing Intestinal Glucose Transport and Barrier Function

EGF plays an important role in the intestinal repair and nutrients transport of animals. However, the effect of EGF on the intestinal health of piglets with IUGR has not been reported. Thus, the present study was performed to investigate the effects of EGF on the intestinal morphology, glucose absorption, antioxidant capacity, and barrier function of piglets with IUGR. A total of 6 NBW piglets and 12 IUGR piglets were randomly divided into three treatments: NC group (NBW piglets fed with basal diet, n = 6), IC group (IUGR piglets fed with basal diet, n = 6), and IE group (IUGR piglets fed with basal diet supplemented with 2 mg/kg EGF, n = 6). Growth performance, serum biochemical profile, jejunum histomorphology, jejunum glucose absorption and antioxidant capacity, and jejunal barrier function were measured. The results showed that EGF supplementation significantly increased the final body weight (FBW), average daily gain (ADG), and average daily feed intake (ADFI) of piglets with IUGR; EGF supplementation significantly increased the total protein (TP), glucose (GLU), and immunoglobulin G (IgG) levels compared with the IUGR piglets in the IC group; EGF administration effectively exhibited an increased jejunum villus height (VH) and the villus-height-to-crypt-depth ratio (V/C) of IUGR piglets compared with the IC group; EGF supplementation significantly increased sodium/potassium-transporting adenosine triphosphatase (Na+/K+-ATPase) activity, intestinal alkaline phosphatase (AKP) activity, glucose transporter sodium/glucose cotransporter 1 (SGLT1), glucose transporter 2 (GLUT2), and AMP-activated protein kinase α1 (AMPK-α1) mRNA expressions in the jejunum of IUGR piglets compared with the IC group; EGF supplementation exhibited increased superoxide dismutase (SOD) activity and total antioxidant capacity (T-AOC) levels, tended to increase glutathione peroxidase (GSH-Px) and catalase (CAT) activities, and tended to decrease the malondialdehyde (MDA) level in the jejunum of IUGR piglets compared with the IC group; EGF supplementation significantly increased ZO-1, Claudin-1, Occludin, and MUC2 mRNA expressions and improved secreted immunoglobulin A (sIgA) secretion in the jejunum of IUGR piglets compared with the IC group and tended to decrease the interleukin 1β (IL-1β), IL-6, and tumor necrosis factor α (TNF-α) levels in the jejunum of IUGR piglets compared with the IC group. Pearson’s correlation analysis further showed that EGF can promote intestinal development and nutrient absorption by promoting intestinal barrier function, thus improving the growth performance of IUGR piglets.

Sodium/hydrogen-exchanger-2 modulates colonocyte lineage differentiation

AIM

The sodium/hydrogen exchanger 2 (NHE2) is an intestinal acid extruder with crypt-predominant localization and unresolved physiological significance. Our aim was to decipher its role in colonic epithelial cell proliferation, differentiation and electrolyte transport.

METHODS

Alterations induced by NHE2-deficiency were addressed in murine nhe2^-/- and nhe2^+/+ colonic crypts and colonoids, and NHE2-knockdown and control Caco2Bbe cells using pH-fluorometry, gene expression analysis and immunofluorescence.

RESULTS

pH_i -measurements along the colonic cryptal axis revealed significantly decreased intracellular pH (pH_i ) in the middle segment of nhe2^-/- compared to nhe2^+/+ crypts. Increased Nhe2 mRNA expression was detected in murine colonoids in the transiently amplifying/progenitor cell stage (TA/PE). Lack of Nhe2 altered the differentiation programme of colonic epithelial cells with reduced expression of absorptive lineage markers alkaline phosphatase (iAlp), Slc26a3 and transcription factor hairy and enhancer-of-split 1 (Hes1), but increased expression of secretory lineage markers Mucin 2, trefoil factor 3 (Tff3), enteroendocrine marker chromogranin A and murine atonal homolog 1 (Math1). Enterocyte differentiation was found to be pH_i dependent with acidic pH_i reducing, and alkaline pH_i stimulating the expression of enterocyte differentiation markers in Caco2Bbe cells. A thicker mucus layer, longer crypts and an expanded brush border membrane zone of sodium/hydrogen exchanger 3 (NHE3) abundance may explain the lack of inflammation and the normal fluid absorptive rate in nhe2^-/- colon.

CONCLUSIONS

The results suggest that NHE2 expression is activated when colonocytes emerge from the stem cell niche. Its activity increases progenitor cell pH_i and thereby supports absorptive enterocyte differentiation.

Changes in progenitors and differentiated epithelial cells of neonatal piglets

This study aimed to assess the changes of small intestinal morphology, progenitors, differentiated epithelial cells, and potential mechanisms in neonatal piglets. Hematoxylin and eosin staining of samples from 36 piglets suggested that dramatic changes were observed in the jejunum crypts depth and crypt fission index of neonatal piglets (P < 0.001). The number of intestinal stem cells (ISC) tended to increase (P < 0.10), and a decreased number of enteroendocrine cells appeared in the jejunal crypt on d 7 (P < 0.05). Furthermore, the mRNA expression of jejunal chromogranin A (ChgA) was down-regulated in d 7 piglets (P < 0.05). There was an up-regulation of the adult ISC marker gene of SPARC related modular calcium binding 2 (Smoc2), and Wnt/β-catenin target genes on d 7 (P < 0.05). These results were further verified in vitro enteroid culture experiments. A mass of hollow spheroids was cultured from the fetal intestine of 0-d-old piglets (P < 0.001), whereas substantial organoids with budding and branching structures were cultured from the intestine of 7-d-old piglets (P < 0.001). The difference was reflected by the organoid budding efficiency, crypt domains per organoid, and the surface area of the organoid. Furthermore, spheroids on d 0 had more Ki67-positive cells and enteroendocrine cells (P < 0.05) and showed a decreasing trend in the ISC and goblet cells (P < 0.10). Moreover, the mRNA expression of spheroids differed markedly from that of organoids, with low expression of intestinal differentiation gene (Lysozyme; P < 0.05), epithelial-specific markers (Villin, E-cadherin; P < 0.05), and adult ISC markers (leucine-rich repeat-containing G protein-coupled receptor 5 [Lgr5], Smoc2; P < 0.001), and up-regulation of fetal marker (connexin 43 [Cnx43]; P < 0.05). The mRNA expression of relevant genes was up-regulated, and involved in Wnt/β-catenin, epidermal growth factor (EGF), Notch, and bone morphogenetic protein (BMP) signaling on d 7 organoids (P < 0.05). Spheroids displayed low differentiated phenotype and high proliferation, while organoids exhibited strong differentiation potential. These results indicated that the conversion from the fetal progenitors (spheroids) to adult ISC (normal organoids) might largely be responsible for the fast development of intestinal epithelial cells in neonatal piglets.

Dietary high protein-induced diarrhea and intestinal inflammation by activation of NF-κB signaling in piglets

The present study aimed to investigate whether inflammation-associated responses in piglets are induced by high protein (HP) through activating nuclear factor kappa B (NF-κB) signaling. Sixteen piglets (35 d of age, Duroc × [Landrace × Yorkshire], weaned at d 21, initial BW = 9.70 ± 0.11 kg) were allocated to 18% and 26% CP (HP group) at random, comprising 8 replicate pens per treatment. The piglets were slaughtered to collect intestinal tissues when apparent, persistent, and stable diarrhea syndromes happened (on d 12). No significant differences were observed in their growth performance (P > 0.05), but reduction by 19.11%, 25.31%, 23.64% of ADFI, ADG, and G:F, respectively was detected in the HP group. The HP group had greater (P = 0.002) diarrhea rates. Furthermore, dietary HP had lower ileal villus height (VH; P = 0.048), ratio of villus height to crypt depth (VH/CD ratio; P = 0.016), and colonic CD (P = 0.034), as well as had the trend (P = 0.075) to reduce the ileal villus absorptive area. Moreover, HP diets significantly elevated the goblet cell numbers in the ileal villi (P = 0.016) and colonic crypts (P < 0.001) and up-regulated (P = 0.012) the mRNA expression of mucin2 (Muc2) in the ileum. In addition, HP diets increased the myeloperoxidase concentration in the ileum (P = 0.002) and colon (P = 0.007) of piglets. Dietary HP significantly down-regulated the mRNA expression of tumor necrosis factor-α (TNF-α; P < 0.001) in the ileum, induced nitric oxide synthase (iNOS; P = 0.040) and interleukin-22 (IL-22; P = 0.008) in the colon, and inclined to down-regulate interleukin-1β (IL-1β; P = 0.076) expression in the colon. The relative protein abundance of Galectin-3 (P = 0.046) in the colon and the ratio of phosphorylation NF-κB to NF-κB (p-NF-κB/NF-κB ratio) in the ileum of HP piglets were also greater (P = 0.038). These results suggest that dietary HP may cause diarrhea in piglets by activating NF-κB signaling induced intestinal inflammation.

Unveiling the Roles of Low-Density Lipoprotein Receptor-Related Protein 6 in Intestinal Homeostasis, Regeneration and Oncogenesis

Intestinal epithelial self-renewal is tightly regulated by signaling pathways controlling stem cell proliferation, determination and differentiation. In particular, Wnt/β-catenin signaling controls intestinal crypt cell division, survival and maintenance of the stem cell niche. Most colorectal cancers are initiated by mutations activating the Wnt/β-catenin pathway. Wnt signals are transduced through Frizzled receptors and LRP5/LRP6 coreceptors to downregulate GSK3β activity, resulting in increased nuclear β-catenin. Herein, we explored if LRP6 expression is required for maintenance of intestinal homeostasis, regeneration and oncogenesis. Mice with an intestinal epithelial cell-specific deletion of Lrp6 (Lrp6^IEC-KO) were generated and their phenotype analyzed. No difference in intestinal architecture nor in proliferative and stem cell numbers was found in Lrp6^IEC-KO mice in comparison to controls. Nevertheless, using ex vivo intestinal organoid cultures, we found that LRP6 expression was critical for crypt cell proliferation and stem cell maintenance. When exposed to dextran sodium sulfate, Lrp6^IEC-KO mice developed more severe colitis than control mice. However, loss of LRP6 did not affect tumorigenesis in Apc^Min/+ mice nor growth of human colorectal cancer cells. By contrast, Lrp6 silencing diminished anchorage-independent growth of BRaf^V600E-transformed intestinal epithelial cells (IEC). Thus, LRP6 controls intestinal stem cell functionality and is necessary for BRAF-induced IEC oncogenesis.

Mechanisms of Epidermal Growth Factor Effect on Animal Intestinal Phosphate Absorption: A Review

Phosphorus is one of the essential mineral elements of animals that plays an important role in animal growth and development, bone formation, energy metabolism, nucleic acid synthesis, cell signal transduction, and blood acid–base balance. It has been established that the Type IIb sodium-dependent phosphate cotransporters (NaPi-IIb) protein is the major sodium-dependent phosphate (Pi) transporter, which plays an important role in Pi uptake across the apical membrane of epithelial cells in the small intestine. Previous studies have demonstrated that epidermal growth factor (EGF) is involved in regulating intestinal Pi absorption. Here we summarize the effects of EGF on active Pi transport of NaPi-IIb under different conditions. Under normal conditions, EGF inhibits the active transport of Pi by inhibiting the expression of NaPi-IIb, while, under intestinal injury condition, EGF promotes the active absorption of Pi through upregulating the expression of NaPi-IIb. This review provides a reference for information about EGF-regulatory functions in Pi absorption in the animal intestine.

Effects of Dietary Supplementation of gEGF on the Growth Performance and Immunity of Broilers

EGF has been shown to stimulate the growth of animals. In this study, the content of EGF in chicken embryos (gallus EGF, gEGF) aged from 1 to 20 days of incubation were determined by ELISA kit, and the 5-day-old chicken embryos with the highest content of 5593 pg/g were selected to make gEGF crude extracts. A total of 1500 1-day-old Xianju chickens were randomly divided into five groups with six replicates of 50 chickens each. The control group was fed a basal diet, and other treatment diets were supplemented with 4, 8, 16 and 32 ng/kg gEGF crude extract, respectively. The experiment lasted for 30 days. Chicks were harvested at the end of the experiment, and liver, spleen, thymus, bursa and serum samples were collected. Results showed that average daily gain (ADG) and average daily feed intake (ADFI) of 16 ng/kg group were higher than those in the control group (p < 0.05). The serum uric acid (UA) of the 16 ng/kg group was reduced (p < 0.01), and the serum alkaline phosphatase (AKP) of the 16 ng/kg group increased (p < 0.01). The gEGF extract also increased chick's antioxidant capacity, decreased malondialdehyde (MDA) and increased catalase (CAT) in the liver and serum of 16 ng/kg groups in compared to the control group (p < 0.01). Furthermore, immunity was improved by the addition of gEGF to broiler diets. The serum immunoglobin A (IgA) content of 8 and 16 ng/kg groups and the serum immunoglobin M (IgM) content of 4 and 8 ng/kg groups were increased (p < 0.05) compared to the control group. The bursa index of each experimental group was higher than the control group (p < 0.01). These findings demonstrate that the crude extract of gEGF prepared in this experiment could improve the growth performance, antioxidant capacity and immunity of broilers.