Critical roles for EGF receptor signaling during resection-induced intestinal adaptation

Generating an Artificial Intestine for the Treatment of Short Bowel Syndrome

Intestinal failure is defined as the inability to maintain fluid, nutrition, energy, and micronutrient balance that leads to the inability to gain or maintain weight, resulting in malnutrition and dehydration. Causes of intestinal failure include short bowel syndrome (ie, the physical loss of intestinal surface area and severe intestinal dysmotility). For patients with intestinal failure who fail to achieve enteral autonomy through intestinal rehabilitation programs, the current treatment options are expensive and associated with severe complications. Therefore, the need persists for next-generation therapies, including cell-based therapy, to increase intestinal regeneration, and development of the tissue-engineered small intestine.

Both epidermal growth factor and insulin-like growth factor receptors are dispensable for structural intestinal adaptation

PURPOSE

Intestinal adaptation structurally represents increases in crypt depth and villus height in response to small bowel resection (SBR). Previously, we found that neither epidermal growth factor receptor (EGFR) nor insulin-like growth factor 1 receptor (IGF1R) function was individually required for normal adaptation. In this study, we sought to determine the effect of disrupting both EGFR and IGF1R expression on resection-induced adaptation.

METHODS

Intestinal-specific EGFR and IGF1R double knockout mice (EGFR/IGF1R-IKO) (n=6) and wild-type (WT) control mice (n=7) underwent 50% proximal SBR. On postoperative day (POD) 7, structural adaptation was scored by measuring crypt depth and villus height. Rates of crypt cell proliferation, apoptosis, and submucosal capillary density were also compared.

RESULTS

After 50% SBR, normal adaptation occurred in both WT and EGFR/IGF1R-IKO. Rates of proliferation and apoptosis were no different between the two groups. The angiogenic response was less in the EGFR/IGF1R-IKO compared to WT mice.

CONCLUSION

Disrupted expression of EGFR and IGF1R in the intestinal epithelial cells does not affect resection-induced structural adaptation but attenuates angiogenesis after SBR. These findings suggest that villus growth is driven by receptors and pathways that occur outside the epithelial cell component, while angiogenic responses may be influenced by epithelial-endothelial crosstalk.

Animal models of gastrointestinal and liver diseases. Animal models of infant short bowel syndrome: translational relevance and challenges

Intestinal failure (IF), due to short bowel syndrome (SBS), results from surgical resection of a major portion of the intestine, leading to reduced nutrient absorption and need for parenteral nutrition (PN). The incidence is highest in infants and relates to preterm birth, necrotizing enterocolitis, atresia, gastroschisis, volvulus, and aganglionosis. Patient outcomes have improved, but there is a need to develop new therapies for SBS and to understand intestinal adaptation after different diseases, resection types, and nutritional and pharmacological interventions. Animal studies are needed to carefully evaluate the cellular mechanisms, safety, and translational relevance of new procedures. Distal intestinal resection, without a functioning colon, results in the most severe complications and adaptation may depend on the age at resection (preterm, term, young, adult). Clinically relevant therapies have recently been suggested from studies in preterm and term PN-dependent SBS piglets, with or without a functional colon. Studies in rats and mice have specifically addressed the fundamental physiological processes underlying adaptation at the cellular level, such as regulation of mucosal proliferation, apoptosis, transport, and digestive enzyme expression, and easily allow exogenous or genetic manipulation of growth factors and their receptors (e.g., glucagon-like peptide 2, growth hormone, insulin-like growth factor 1, epidermal growth factor, keratinocyte growth factor). The greater size of rats, and especially young pigs, is an advantage for testing surgical procedures and nutritional interventions (e.g., PN, milk diets, long-/short-chain lipids, pre- and probiotics). Conversely, newborn pigs (preterm or term) and weanling rats provide better insights into the developmental aspects of treatment for SBS in infants owing to their immature intestines. The review shows that a balance among practical, economical, experimental, and ethical constraints will determine the choice of SBS model for each clinical or basic research question.

Insulin-like growth factor 2 and its enterocyte receptor are not required for adaptation in response to massive small bowel resection

PURPOSE

Enhanced structural features of resection-induced intestinal adaptation have been demonstrated following the administration of multiple different growth factors and peptides. Among these, the insulin-like growth factor (IGF) system has been considered to be significant. In this study, we employ mutant mouse strains to directly test the contribution of IGF2 and its enterocyte receptor (IGF1R) toward the adaptation response to massive small bowel resection (SBR).

METHODS

IGF2-knockout (IGF2-KO) (n=8) and intestine specific IGF1R-knockout mice (IGF1R-IKO) (n=9) and their wild type (WT) littermates (n=5, n=7, respectively) underwent 50% proximal SBR. At post-operative day 7, structural adaptation was measured as crypt depth and villus height. Rates of enterocyte proliferation and apoptosis were also recorded.

RESULTS

The successful deletion of IGF2 and IGF1R expression in the enterocytes was confirmed by RT-PCR and Western blot, respectively. Normal adaptation occurred in both IGF2-KO and IGF1R-IKO mice after 50% SBR. Post-operative rates of proliferation and apoptosis in both IGF2-KO and IGF1R-IKO mice were no different than their respective controls.

CONCLUSION

IGF2 and functional IGF1R signaling in enterocytes are both dispensable for resection-induced adaptation responses. The mechanism for IGF-stimulation of intestinal adaptation may involve other ligands or cellular compartments within the intestine.

CXCL5 is required for angiogenesis, but not structural adaptation after small bowel resection

PURPOSE

Intestinal adaptation is the compensatory response to massive small bowel resection (SBR) and characterized by lengthening of villi and deepening of crypts, resulting in increased mucosal surface area. Previous studies have demonstrated increased villus capillary blood vessel density after SBR, suggesting a role for angiogenesis in the development of resection-induced adaptation. Since we have previously shown enhanced expression of the proangiogenic chemokine CXCL5 after SBR, the purpose of this study was to determine the effect of disrupted CXCL5 expression on intestinal adaptation.

METHODS

CXCL5 knockout (KO) and C57BL/6 wild type (WT) mice were subjected to either a 50% proximal SBR or sham operation. Ileal tissue was harvested on postoperative day 7. To assess for adaptation, villus height and crypt depth were measured. Submucosal capillary density was measured by CD31 immunohistochemistry.

RESULTS

Both CXCL5-KO and WT mice demonstrated normal structural features of adaptation. Submucosal capillary density increased in the WT but not in the KO mice following SBR.

CONCLUSION

CXCL5 is required for increased intestinal angiogenesis during resection-induced adaptation. Since adaptive villus growth occurs despite impaired CXCL5 expression and enhanced angiogenesis, this suggests that the growth of new blood vessels is not needed for resection-induced mucosal surface area expansion following massive SBR.

Intestinal mucosal atrophy and adaptation

Mucosal adaptation is an essential process in gut homeostasis. The intestinal mucosa adapts to a range of pathological conditions including starvation, short-gut syndrome, obesity, and bariatric surgery. Broadly, these adaptive functions can be grouped into proliferation and differentiation. These are influenced by diverse interactions with hormonal, immune, dietary, nervous, and mechanical stimuli. It seems likely that clinical outcomes can be improved by manipulating the physiology of adaptation. This review will summarize current understanding of the basic science surrounding adaptation, delineate the wide range of potential targets for therapeutic intervention, and discuss how these might be incorporated into an overall treatment plan. Deeper insight into the physiologic basis of adaptation will identify further targets for intervention to improve clinical outcomes.

Ret heterozygous mice have enhanced intestinal adaptation after massive small bowel resection

Intestinal adaptation is an important compensatory response to massive small bowel resection (SBR) and occurs because of a proliferative stimulus to crypt enterocytes by poorly understood mechanisms. Recent studies suggest the enteric nervous system (ENS) influences enterocyte proliferation. We, therefore, sought to determine whether ENS dysfunction alters resection-induced adaptation responses. Ret+/- mice with abnormal ENS function and wild-type (WT) littermates underwent sham surgery or 50% SBR. After 7 days, ileal morphology, enterocyte proliferation, apoptosis, and selected signaling proteins were characterized. Crypt depth and villus height were equivalent at baseline in WT and Ret+/- mice. In contrast after SBR, Ret+/- mice had longer villi (Ret+/- 426.7 ± 46.0 μm vs. WT 306.5 ± 7.7 μm, P < 0.001) and deeper crypts (Ret+/- 119 ± 3.4 μm vs. WT 82.4 ± 3.1 μm, P < 0.001) than WT. Crypt enterocyte proliferation was higher in Ret+/- (48.8 ± 1.3%) than WT (39.9 ± 2.1%; P < 0.001) after resection, but apoptosis rates were similar. Remnant bowel of Ret+/- mice also had higher levels of glucagon-like peptide 2 (6.2-fold, P = 0.005) and amphiregulin (4.6-fold, P < 0.001) mRNA after SBR, but serum glucagon-like peptide 2 protein levels were equal in WT and Ret+/- mice, and there was no evidence of increased c-Fos nuclear localization in submucosal neurons. Western blot confirmed higher crypt epidermal growth factor receptor (EGFR) protein levels (1.44-fold; P < 0.001) and more phosphorylated EGFR (2-fold; P = 0.003) in Ret+/- than WT mice after SBR. These data suggest that Ret heterozygosity enhances intestinal adaptation after massive SBR, likely via enhanced EGFR signaling. Reducing Ret activity or altering ENS function may provide a novel strategy to enhance adaptation attenuating morbidity in patients with short bowel syndrome.

Anti-inflammatory effects of epidermal growth factor on the immature human intestine

The inflammatory response of the preterm infants' intestine underlines its inability to respond to hemodynamic stress, microbes, and nutrients. Recent evidence suggests that exogenous epidermal growth factor (EGF) exerts a therapeutic influence on neonatal enteropathies. However, the molecular mechanisms underlying the beneficial effects of EGF remain to be clarified. The purpose of this study was to evaluate the impact of EGF on the gene expression profiles of the developing human small and large intestine at midgestation in serum-free organ cultures using microarrays. The gene expression profiles of cultured human fetal ileal and colonic explants were investigated in the absence or presence of a physiological concentration of 50 ng/ml EGF for 48 h. Data were analyzed with the Ingenuity Pathway Analysis (IPA) software and confirmed by qPCR. We found a total of 6,474 differentially expressed genes in the two segments in response to EGF. IPA functional analysis revealed that in addition to differentially modulating distinct cellular, molecular, and physiological functions in the small and large intestine, EGF regulated the inflammatory response in both intestinal segments in a distinct manner. For instance, several intestinal-derived chemokines such as CCL2, CCL25, CXCL5, and CXCL10 were found to be differentially regulated by EGF in the immature ileum and colon. The findings showing the anti-inflammatory influence of exogenous EGF suggests a mechanistic basis for the beneficial effects of EGF on neonatal enteropathies. These results reinforce growing evidence that by midgestation, the human small intestine and colon rely on specific and distinct regulatory pathways.

The influence of nutrients, biliary-pancreatic secretions, and systemic trophic hormones on intestinal adaptation in a Roux-en-Y bypass model

PURPOSE

The signals that govern the upregulation of nutrient absorption (adaptation) after intestinal resection are not well understood. A Gastric Roux-en-Y bypass (GRYB) model was used to isolate the relative contributions of direct mucosal stimulation by nutrients, biliary-pancreatic secretions, and systemic enteric hormones on intestinal adaptation in short bowel syndrome.

METHODS

Male rats (350-400 g; n = 8/group) underwent sham or GRYB with pair feeding and were observed for 14 days. Weight and serum hormonal levels (glucagon-like peptide-2 [GLP-2], PYY) were quantified. Adaptation was assessed by intestinal morphology and crypt cell kinetics in each intestinal limb of the bypass and the equivalent points in the sham intestine. Mucosal growth factors and expression of transporter proteins were measured in each limb of the model.

RESULTS

The GRYB animals lost weight compared to controls and exhibited significant adaptive changes with increased bowel width, villus height, crypt depth, and proliferation indices in the alimentary and common intestinal limbs. Although the biliary limb did not adapt at the mucosa, it did show an increased bowel width and crypt cell proliferation rate. The bypass animals had elevated levels of systemic PYY and GLP-2. At the mucosal level, insulin-like growth factor-1 (IGF-1) and basic fibroblast growth factor (bFGF) increased in all limbs of the bypass animals, whereas keratinocyte growth factor (KGF) and epidermal growth factor (EGF) had variable responses. The expression of the passive transporter of glucose, GLUT-2, expression was increased, whereas GLUT-5 was unchanged in all limbs of the bypass groups. Expression of the active mucosal transporter of glucose, SGLT-1 was decreased in the alimentary limb.

CONCLUSIONS

Adaptation occurred maximally in intestinal segments stimulated by nutrients. Partial adaptation in the biliary limb may reflect the effects of systemic hormones. Mucosal content of IGF-1, bFGF, and EGF appear to be stimulated by systemic hormones, potentially GLP-2, whereas KGF may be locally regulated. Further studies to examine the relationships between the factors controlling nutrient-induced adaptation are suggested. Direct contact with nutrients appears to be the most potent factor in inducing mucosal adaptation.

Epidermal growth factor in clinical practice - a review of its biological actions, clinical indications and safety implications

Chemotaxis, mitogenesis, motogenesis and cytoprotection are common cellular events involved in both tumourigenesis and tissue repair, which appear amplified upon growth factors exposure. Epidermal growth factor (EGF) promotes these events in epithelial and mesenchymal cells through the binding to a specific tyrosine kinase receptor. In experimental oncology settings, EGF does not initiate malignant transformation but exhibits 'tumour promotion'. These observations have raised doubts on the clinical use of EGF despite solid demonstrations of efficacy in experimental conditions and clinical trials. The results of a Pubmed and Bioline investigation on EGF clinical uses and preclinical safety data are presented here. EGF topical administration has been used since 1989 to enhance the healing process of a variety of peripheral tissues wounds (16 clinical reports), as well as its intravenous, oral and rectal administration for gastrointestinal damages (11 clinical reports). EGF therapeutic efficacy and excellent tolerability seem demonstrated. Lack of long-term adverse effects is highlighted in those studies with 6, 12 and 24 months of patients follow-up. Although post-treatment follow-up may fall short for malignant growth, there are no reports on evidences linking EGF clinical use with cancer. A multicentre, nationwide survey in Cuba, 15 years after randomly using silver sulphadiazine with EGF or not in burn victims yielded that cancer incidence was comparable between EGF-treated and control subjects and that such incidence rate does not differ from the age-matched national incidence for those 15-year period. All the animal species subjected to long-term EGF systemic administration exhibit dose-dependent and reversible epithelial organs hyperplasia with no changes in cells phenotypic differentiation. Histotypic pre-malignant markers were not identified. The results emerged from co-carcinogenesis studies and from transgenic mice over-expressing EGF are conflicting and indicate that EGF overexposure, either innate or postnatal, may not be sufficient to transform cells. The ability of EGF to heal injured tissues in life-threatening scenarios or to assist in preventing physical and social disability advocates for its clinical use under a rational medical risk/benefit balance.

Murine functional liver mass is reduced following partial small bowel resection

INTRODUCTION

Liver mass is regulated in precise proportion to body mass in health and is restored by regeneration following acute injury. Despite extensive experimental analyses, the mechanisms involved in this regulation have not been fully elucidated. Previous investigations suggest that signals from the bowel may play an important role. The purpose of the studies reported here was to determine the effect of proximal partial small bowel resection on liver mass in a murine model.

METHODS

Mice were subjected to a 50% proximal small bowel resection or sham surgery followed by primary anastomosis, then sacrificed at serial times for determination of liver:body mass ratio and analyses of liver tissue.

RESULTS

Liver:body weight ratio was significantly decreased 72 h after small bowel resection, and this decrease correlated with reduced functional liver mass as assessed by determination of total hepatic tissue protein and alanine transaminase (ALT) activity. Liver from bowel-resected animals demonstrated increased expression of LC3-II, a marker of autophagy, and also of pro-apoptotic Bax compared to anti-apoptotic Bcl-2.

CONCLUSION

These data support a role for signals from the intestine in liver mass regulation, and they have potential implications regarding the pathogenesis of liver injury following small bowel resection.

Dietary sulfur amino acid supplementation reduces small bowel thiol/disulfide redox state and stimulates ileal mucosal growth after massive small bowel resection in rats

Following massive small bowel resection in animal models, the remnant intestine undergoes a dynamic growth response termed intestinal adaptation. Cell growth and proliferation are intimately linked to cellular and extracellular thiol/disulfide redox states, as determined by glutathione (GSH) and GSH disulfide (GSSG) (the major cellular redox system in tissues), and cysteine (Cys) and its disulfide cystine (CySS) (the major redox system in plasma), respectively. The study was designed to determine whether dietary supplementation with sulfur amino acids (SAA) leads to a greater reduction in thiol/disulfide redox state in plasma and small bowel and colonic mucosa and alters gut mucosal growth in an established rat model of short bowel syndrome (SBS). Adult rats underwent 80% jejunal-ileal resection (RX) or small bowel transection (surgical control) and were pair-fed either isonitrogenous, isocaloric SAA-adequate (control) or SAA-supplemented diets (218% increase vs. control diet). Plasma and gut mucosal samples were obtained after 7 d and analyzed for Cys, CySS, GSH, and GSSG concentrations by HPLC. Redox status (E(h)) of the Cys/CySS and GSH/GSSG couples were calculated using the Nernst equation. SAA supplementation led to a greater reduction in E(h) GSH/GSSG in jejunal and ileal mucosa of resected rats compared with controls. Resected SAA-supplemented rats showed increased ileal adaptation (increased full-thickness wet weight, DNA, and protein content compared with RX control-fed rats; increased mucosal crypt depth and villus height compared with all other study groups). These data suggest that SAA supplementation has a trophic effect on ileal adaptation after massive small bowel resection in rats. This finding may have translational relevance as a therapeutic strategy in human SBS.

ErbB signaling is required for the proliferative actions of GLP-2 in the murine gut

BACKGROUND & AIMS

Glucagon-like peptide-2 (GLP-2) is a 33-amino acid peptide hormone secreted by enteroendocrine cells in response to nutrient ingestion. GLP-2 stimulates crypt cell proliferation leading to expansion of the mucosal epithelium; however, the mechanisms transducing the trophic effects of GLP-2 are incompletely understood.

METHODS

We examined the gene expression profiles and growth-promoting actions of GLP-2 in normal mice in the presence or absence of an inhibitor of ErbB receptor signaling, in Glp2r(-/-) mice and in Egfr(wa2) mice harboring a hypomorphic point mutation in the epidermal growth factor receptor.

RESULTS

Exogenous GLP-2 administration rapidly induced the expression of a subset of ErbB ligands including amphiregulin, epiregulin, and heparin binding (HB)-epidermal growth factor, in association with induction of immediate early gene expression in the small and large bowel. These actions of GLP-2 required a functional GLP-2 receptor because they were eliminated in Glp2r(-/-) mice. In contrast, insulin-like growth factor-I and keratinocyte growth factor, previously identified mediators of GLP-2 action, had no effect on the expression of these ErbB ligands. The GLP-2-mediated induction of ErbB ligand expression was not metalloproteinase inhibitor sensitive but was significantly diminished in Egfr(wa2) mice and completed abrogated in wild-type mice treated with the pan-ErbB inhibitor CI-1033. Furthermore, the stimulatory actions of GLP-2 on crypt cell proliferation and bowel growth were eliminated in the presence of CI-1033.

CONCLUSIONS

These findings identify the ErbB signaling network as a target for GLP-2 action leading to stimulation of growth factor-dependent signal transduction and bowel growth in vivo.

Modulation of the inflammatory response and apoptosis using epidermal growth factor and hepatocyte growth factor in a liver injury model: a potential approach to the management and treatment of cholestatic liver disease

BACKGROUND/PURPOSE

The major side effect of total parenteral nutrition is liver injury leading to liver failure. This study was designed to assess specific growth factors in modulating the hepatic response in an ANIT-induced liver-injury model.

METHODS

Sprague-Dawley rats were divided into four groups: control (n = 5), liver-injury control (alpha-naphthylisothiocyanate [ANIT], 100 mg/kg, n = 8), ANIT + epidermal growth factor (EGF, 150 mug/kg per day, n = 10), and ANIT + hepatocyte growth factor (HGF, 250 mug/kg per day, n = 9). Rats were given intraperitoneal injections of saline (control) or ANIT and implantation of an osmotic mini-pump for 7 days of continuous intravenous saline (liver injury control), EGF, or HGF. Seven and 14 days later, liver biopsies were obtained and evaluated for interleukin (IL)-6 and tumor necrosis factor alpha expression by immunofluorescent staining, and for apoptosis, by the terminal transferase dUTP nick end labeling (TUNEL) technique. All animals were euthanized at 14 days.

RESULTS

Epidermal growth factor (P < .025) and HGF (P < .001) groups induced less IL-6 expression at day 14 compared to liver-injury controls. In addition, the interval decrease in IL-6 expression between days 7 and 14 was greater in EGF (P < .001) and HGF (P < .001) groups compared to liver-injury controls. At day 14, HGF also demonstrated decreased tumor necrosis factor alpha expression (P < .005). Apoptotic activity was significantly less for the EGF (P < .011) and HGF (P < .0012) groups.

CONCLUSION

Epidermal growth factor and HGF modulated the hepatic inflammatory response and apoptotic index in this established liver-injury model and may diminish or prevent liver damage in patients with total parenteral nutrition-induced liver injury.

Resection-induced intestinal adaptation and the role of enteric smooth muscle

BACKGROUND

Intestinal adaptation after massive small bowel resection (SBR) involves all layers of the bowel wall. Most prior work has focused on changes that occur in the intestinal mucosa. However, the contribution of the underlying intestinal smooth muscle (ISM) to the overall adaptation response remains unclear.

METHODS

Male C57BL/6 or waved-2 (diminished activity of the epidermal growth factor receptor) mice underwent a 50% proximal SBR or sham operation, and the remnant ileum was harvested 3, 7, and 28 days. Markers of adaptation (villus height, bowel length, circumference, and ISM thickness) and ISM proliferation were recorded. Contractility was measured by attaching the distal ileum to strain gauge transducers and exposed to varying doses of carbachol.

RESULTS

Intestinal smooth muscle thickness was unchanged at any given time-point after resection; however, the bowel caliber and length were increased, and augmented rates of ISM proliferation were identified. Contractility was increased at 7 days after SBR. Waved-2 mice demonstrated minimal proliferation or intestinal lengthening in response to SBR.

CONCLUSION

Compared with resection-induced thickening of the mucosa, proliferative changes in the ISM are unique and primarily affect bowel caliber, length, and contractility. Epidermal growth factor receptor signaling appears to play a significant role in adaptation of the ISM cellular compartment.

Role of epidermal growth factor and other growth factors in the prevention of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) presents as the most common gastrointestinal emergency during the neonatal period and results in ulceration and necrosis of the distal small intestine and proximal colon. The etiology of NEC remains unknown. Based on the complexity of gut development, multiple growth factors and cytokines may be needed to synergistically support the developing gut. Epidermal growth factor (EGF) has been shown to play an important role in intestinal cell restitution, proliferation, and maturation. EGF is found in abundant quantities in many fluids, including the gastrointestinal tract, amniotic fluid, breast milk, and saliva. Preliminary clinical trials using EGF in neonates diagnosed with NEC have been shown to promote repair of intestinal epithelium. Additionally, other growth factors are also emerging as potential treatment modalities, including erythropoietin, granulocyte colony stimulating factor, and heparin-binding EGF. The role of EGF and other growth factors in the pathogenesis and prevention of NEC will be reviewed.

Responsiveness of intestinal epithelial cell turnover to TGF-alpha after bowel resection in a rat is correlated with EGF receptor expression along the villus-crypt axis

Recent evidence suggests that transforming growth factor alpha (TGF-alpha) enhances enterocyte proliferation and stimulates intestinal adaptation after massive bowel resection. In the present study, we evaluated the effects of TGF-alpha on enterocyte turnover and correlated it with epidermal-growth factor (EGF) receptor expression along the villus-crypt axis in a rat model of short bowel syndrome (SBS). Male rats were divided into three groups, sham rats underwent bowel transection (group A); SBS rats underwent a 75% bowel resection (group B); and SBS/TGF-alpha rats underwent bowel resection and were treated with TGF-alpha (75 microg/kg) (group C) from the seventh postoperative day. Parameters of intestinal adaptation, enterocyte proliferation and apoptosis were determined on day 15. Villus tips, lateral villi and crypts were separated using laser capture microdissection. EGF receptor expression for each compartment was assessed by quantitative real-time PCR (Taqman). Statistical analysis was performed using one-way ANOVA test, with P < 0.05 considered statistically significant. Treatment with TGF-alpha resulted in a significant increase in all parameters of intestinal adaptation. EGF receptor expression in crypts significantly increased in SBS rats (vs sham rats) (0.035 +/- 0.013 vs 0.010 +/- 0.002 Log ng Total RNA/18 s) and was accompanied by a significant increase in enterocyte proliferation (169 +/- 8 vs 138 +/- 5 BrdU positive cells/per 10 crypts, P < 0.05) and decreased apoptosis following TGF-alpha administration (group C). A significant decrease in EGF receptor expression at the tip of the villus (0.005 +/- 0.002 vs 0.029 +/- 0.014 Log ng Total RNA/18 s) and in the lateral villus (0.003 +/- 0.001 vs 0.028 +/- 0.006 Log ng Total RNA/18 s) in SBS (group B) rats (vs sham, group A) was accompanied by increased cell apoptosis in these compartments following treatment with TGF-alpha (group C). In a rat model of SBS, TGF-alpha increased enterocyte proliferation and stimulated intestinal adaptation. The effect of TGF-alpha on enterocyte turnover is correlated with EGF receptor expression along the villus-crypt axis.

Hydrocortisone and indomethacin negatively modulate EGF-R signaling in human fetal intestine

Concomitant use of hydrocortisone and the nonspecific cyclo-oxygenase (COX)-inhibitor indomethacin increases the risk for intestinal perforations in preterm infants. We determined whether this was associated with insufficient epidermal growth factor receptor (EGF-R) signaling. We tested the effect of EGF, hydrocortisone, and indomethacin on its activation, cell proliferation and migration, COX-2 expression, and prostaglandin E2 (PGE2) production. Human small intestine epithelial cell line FHsInt74 and EGF-R-deficient mice [EGF-R (-/-)] were used as models. The data revealed that EGF-R signaling had a bimodal positive effect on fetal enterocyte: 1) it increased cell proliferation and migration synergistically with hydrocortisone and 2) up-regulated COX-2 mRNA expression and subsequent PGE2 production. Correlating with this, COX-2 protein expression was down-regulated in EGF-R (-/-) intestine. Despite a positive effect on cell proliferation with EGF, hydrocortisone blunted the stimulatory effect of EGF on COX-2 expression and PGE2 production. Addition of indomethacin even further inhibited the EGF-stimulated PGE2 synthesis. The data suggest that concomitant use of indomethacin and hydrocortisone on preterm infants, who physiologically synthesize only low levels of EGF-R ligands, may lead to intestinal problems related to failure in cytoprotective and regenerative events.

New therapies and preventive approaches for necrotizing enterocolitis: report of a research planning workshop

The National Institute of Child Health and Human Development and the Digestive Diseases Interagency Coordinating Committee held a workshop, chaired by Dr. W. Allan Walker, on July 10-11, 2006, to identify promising leads in necrotizing enterocolitis (NEC) research. The goals of the workshop were to identify new approaches to the prevention and treatment of NEC, to define basic and translational mechanisms of potential approaches to NEC, and to develop recommendations for clinical studies to reduce the incidence of NEC. Workshop participants implicated prematurity, introduction of enteral feedings, gastrointestinal bacterial colonization, gut motility, proinflammatory cytokines, impaired gut blood flow, and various neonatal complications in the pathogenesis of NEC. They concluded that a unifying hypothesis encompassing these pathogenetic factors is the uncontrolled exuberant inflammatory response to bacterial colonization that characterizes the intestine of premature infants. The inflammatory cascade appears to offer multiple targets for interventions with a variety of anti-inflammatory agents, including human milk and probiotics. Because of the rapidity with which the inflammatory response gets out of control in infants with NEC, workshop participants agreed that searching for ways to prevent NEC will be more rewarding than trying to identify ways to treat the condition once it has become established.

Epidermal growth factor receptor signaling modulates apoptosis via p38alpha MAPK-dependent activation of Bax in intestinal epithelial cells

Previous studies have demonstrated that the proapoptotic protein Bax plays an important role in the elevated enterocyte apoptosis that occurs during the intestinal adaptation response to massive small bowel resection (SBR). Additionally, epidermal growth factor receptor (EGFR) activation prevents SBR-induced enterocyte apoptosis. The present study aims to delineate the relationship between EGFR activity and intestinal epithelial cell apoptosis. Treatment of model intestinal epithelial cells (RIEC-18) with both a selective EGFR inhibitor (ZD1839) and EGFR small interfering RNA knockdown resulted in a dramatic increase in apoptosis, accompanied by rapid phosphorylation of p38alpha. Concurrently, Bax underwent conformational changes consistent with activation and translocated to mitochondria. In contrast, EGF stimulation enhanced cell survival by attenuating p38alpha phosphorylation, Bax conformational change, mitochondrial trafficking, and apoptosis. These results demonstrate that that diminished EGFR activity initiates the intrinsic pathway of apoptosis through p38alpha-dependent Bax activation in intestinal epithelial cells. These finding provide mechanistic insight into the role that EGFR signaling plays in the regulation of enterocyte apoptosis following massive intestinal loss.

Epidermal growth factor receptor-directed enterocyte proliferation does not induce Wnt pathway transcription

BACKGROUND

Epidermal growth factor receptor (EGFR) stimulation enhances intestinal adaptation after massive small bowel resection (SBR), measured by taller villi, deeper crypts, and augmented enterocyte proliferation. Min mice with constitutively active beta-catenin signaling demonstrate enhanced villus growth after SBR, suggesting a role for the Wnt pathway during adaptation. Because there is crosstalk between EGFR signaling and the Wnt pathway, we hypothesized that beta-catenin is modulated by EGFR-induced enterocyte proliferation.

METHODS

Rat intestinal epithelial cells were stimulated with EGF and cytoplasmic to nuclear trafficking of beta-catenin was measured. Beta-catenin-directed transcription was also tested via transfection with a TOP/FOP luciferase reporter. Downstream transcriptional target expression was measured in murine intestine after SBR.

RESULTS

Epidermal growth factor-treated rat intestinal epithelial cells exhibited increased proliferation compared to serum-deficient cells in the face of no detectable accumulation of nuclear beta-catenin. The luciferase assay results showed minimal transcription activity in response to EGF. In vivo experiments revealed no significant difference in expression of beta-catenin targeted genes in crypt enterocytes after SBR.

CONCLUSIONS

The mechanism for EGFR-induced proliferation of enterocytes does not appear to involve a transcriptional role for beta-catenin. The effects of EGFR signaling on beta-catenin-mediated cell adhesion remain to be investigated.

Nutritional management of infants with short bowel syndrome

The prevalence of short bowel syndrome appears to be increasing because of more aggressive surgical and medical approaches to the management of neonatal intraabdominal catastrophies. Hence, a large cohort of neonates with intestinal failure occupies neonatal intensive care units, requiring chronic total parenteral nutrition (TPN) in hopes that the residual bowel will adapt, thereby permitting weaning of TPN. Alternatively, when there is no hope for adaptation, these infants are maintained on TPN in hopes that they will grow to a size and state of general health satisfactory for either isolated intestinal transplant when liver function is preserved or combined liver-intestinal transplantation when the liver is irreparably damaged. Thus, it is imperative to provide enough parenteral nutrition to facilitate growth while minimizing TPN constituents predisposing to liver damage. Liver disease associated with intestinal failure (IFALD) seems to occur due to a variety of host factors combined with deleterious components of TPN. Host factors include an immature bile secretory mechanism, bile stasis due to fasting, and repeated septic episodes resulting in endotoxemia. Many constituents of TPN are associated with liver damage. Excessive glucose may result in fatty liver and/or hepatic fibrosis, excessive protein may lead to reduced bile flow, and phytosterols present in intravenous lipid may produce direct oxidant damage to the liver or may impede cholesterol synthesis and subsequent bile acid synthesis. Parenteral strategies employed to minimize TPN damage include reducing glucose infusion rates, reducing parenteral protein load, and reducing parenteral lipid load. Furthermore, preliminary studies suggest that fish oil-based lipid solutions may have a salutary effect on IFALD. Ultimately, provision of enteral nutrition is imperative for preventing or reversing IFALD as well as facilitating bowel adaptation. While studies of trophic hormones are ongoing, the most reliable current method to facilitate adaptation is to provide enteral nutrition. Continuous enteral feeding remains the mainstay of enteral nutrition support.