Transforming growth factor alpha inhibits secretion of gastric acid

The Gastrointestinal Tract Is an Alternative Route for SARS-CoV-2 Infection in a Nonhuman Primate Model

BACKGROUND & AIMS

Gastrointestinal (GI) manifestations have been increasingly reported in patients with coronavirus disease 2019 (COVID-19). However, the roles of the GI tract in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection are not fully understood. We investigated how the GI tract is involved in SARS-CoV-2 infection to elucidate the pathogenesis of COVID-19.

METHODS

Our previously established nonhuman primate (NHP) model of COVID-19 was modified in this study to test our hypothesis. Rhesus monkeys were infected with an intragastric or intranasal challenge with SARS-CoV-2. Clinical signs were recorded after infection. Viral genomic RNA was quantified by quantitative reverse transcription polymerase chain reaction. Host responses to SARS-CoV-2 infection were evaluated by examining inflammatory cytokines, macrophages, histopathology, and mucin barrier integrity.

RESULTS

Intranasal inoculation with SARS-CoV-2 led to infections and pathologic changes not only in respiratory tissues but also in digestive tissues. Expectedly, intragastric inoculation with SARS-CoV-2 resulted in the productive infection of digestive tissues and inflammation in both the lung and digestive tissues. Inflammatory cytokines were induced by both types of inoculation with SARS-CoV-2, consistent with the increased expression of CD68. Immunohistochemistry and Alcian blue/periodic acid-Schiff staining showed decreased Ki67, increased cleaved caspase 3, and decreased numbers of mucin-containing goblet cells, suggesting that the inflammation induced by these 2 types of inoculation with SARS-CoV-2 impaired the GI barrier and caused severe infections.

CONCLUSIONS

Both intranasal and intragastric inoculation with SARS-CoV-2 caused pneumonia and GI dysfunction in our rhesus monkey model. Inflammatory cytokines are possible connections for the pathogenesis of SARS-CoV-2 between the respiratory and digestive systems.

Contribution of Wound-Associated Cells and Mediators in Orchestrating Gastrointestinal Mucosal Wound Repair

The gastrointestinal mucosa, structurally formed by the epithelium and lamina propria, serves as a selective barrier that separates luminal contents from the underlying tissues. Gastrointestinal mucosal wound repair is orchestrated by a series of spatial and temporal events that involve the epithelium, recruited immune cells, resident stromal cells, and the microbiota present in the wound bed. Upon injury, repair of the gastrointestinal barrier is mediated by collective migration, proliferation, and subsequent differentiation of epithelial cells. Epithelial repair is intimately regulated by a number of wound-associated cells that include immune cells and stromal cells in addition to mediators released by luminal microbiota. The highly regulated interaction of these cell types is perturbed in chronic inflammatory diseases that are associated with impaired wound healing. An improved understanding of prorepair mechanisms in the gastrointestinal mucosa will aid in the development of novel therapeutics that promote mucosal healing and reestablish the critical epithelial barrier function.

Ménétrier's disease of the stomach: a clinical challenge

Ménétrier's disease is a rare hyperproliferative protein-losing gastropathy of the gastric foveolar epithelium. Most common symptoms include epigastric pain with fullness and vomiting, and generalized peripheral edema with hypoalbuminemia. Radiologically, the wall of the gastric body and fundus is diffusely thickened, often with antral sparing. Giant rugal edematous folds are seen on gastroscopy, and histology of biopsy material shows diffuse foveolar hyperplasia with cystic dilatation of the glandular portion of the gastric mucosa in the absence of significant inflammatory infiltrate. The recent discovery of transforming growth factor α overexpression opens the way of epidermal growth factor receptor blockade with cetuximab as first-line treatment modality in severe cases of Ménétrier's disease.

EGFR is involved in control of gastric cell proliferation through activation of MAPK and Src signalling pathways in early-weaned rats

OBJECTIVES

Early weaning (EW) increases proliferation of the gastric epithelium in parallel with higher expression of transforming growth factor alpha and its receptor epidermal growth factor receptor (EGFR). The primary objective of the present study was to examine involvement of EGFR signalling in regulating mucosal cell proliferation during the early weaning period.

MATERIALS AND METHODS

Fifteen-day-old rats were split into two groups: suckling (control) and EW, in which pups were separated from the dam. Animals were killed daily until the 18th day, 3 days after onset of treatment. To investigate the role of EGFR in proliferation control, EW pups were injected with AG1478, an EGFR inhibitor; signalling molecules, proliferative indices and cell cycle-related proteins were evaluated.

RESULTS

EW increased ERK1/2 and Src phosphorylation at 17 days, but p-Akt levels were unchanged. Moreover, at 17 days, AG1478 administration impaired ERK phosphorylation, whereas p-Src and p-Akt were not altered. AG1478 treatment reduced mitotic and DNA synthesis indices, which were determined on HE-stained and BrdU-labelled sections. Finally, AG1478 injection decreased p21 levels in the gastric mucosa at 17 days, while no changes were detected in p27, cyclin E, CDK2, cyclin D1 and CDK4 concentrations.

CONCLUSIONS

EGFR is part of the mechanism that regulates cell proliferation in rat gastric mucosa during early weaning. We suggest that such responses might depend on activation of MAPK and/or Src signalling pathways and regulation of p21 levels.

Carbachol induces TGF-alpha expression and colonic epithelial cell proliferation in sensory-desensitised rats

OBJECTIVE/BACKGROUND

Signals for the expression of the peptide growth factors epidermal growth factor and transforming growth factor-alpha (TGFalpha) in the gastrointestinal mucosa are largely unknown. We have shown earlier that extrinsic afferents in the gastrointestinal tract induce TGFalpha expression in colonic mucosa via the deliberation of neurotransmitters substance P and calcitonin gene-related peptide. The aim of our present study was to determine the effects of carbachol on mucosal TGFalpha expression and epithelial cell proliferation in vivo.

DESIGN/METHODS

Rats were divided in three groups. Group 1 was treated with vehicle only, group 2 received one single subcutaneous injection of 250 microg/kg of carbachol and animals in group 3 were sensory-desensitised prior to the injection of 250 microg/kg carbachol. TGFalpha expression and epithelial cell proliferation was evaluated by polymerase chain reaction, Western blot analysis and bromodeoxyuridine staining.

RESULTS

Carbachol induced a significant increase in mucosal epithelial cell proliferation and TGFalpha expression. Sensory desensitisation did neither abolish the increased TGFalpha expression nor the increase in epithelial cell proliferation.

CONCLUSION

Parasympathetic pathways are involved in the control of TGFalpha expression in gastrointestinal mucosa as well as in epithelial cell proliferation.

Increased duodenal expression of transforming growth factor-alpha and epidermal growth factor during experimental colitis in rats

OBJECTIVE/BACKGROUND

Epidermal growth factor (EGF) and transforming growth factor alpha (TGFalpha) protect gastrointestinal mucosa against injury. Having shown earlier, that TGFalpha but not EGF is locally increasingly expressed after mucosal injury in the colon, we now wanted to explore the pattern of expression of EGF and TGFalpha in the remaining gastrointestinal tract and to infer from the pattern of expression, to possible signals for the induction of the growth factor expression and further mechanisms for mucosal protection.

DESIGN/METHODS

The trinitrobenzene sulfonic acid/ethanol-induced model of colitis in rats was used. TGFalpha-mRNA and EGF-mRNA expression was evaluated in inflamed and noninflamed colon, in the ileum, jejunum, duodenum, stomach, and in the submandibulary glands.

RESULTS

A significant increase of TGFalpha-mRNA and EGF-mRNA expressions was detected in the duodenal mucosa and a significant increase in TGFalpha-mRNA expression was observed in the inflamed colonic mucosa after mucosal injury in the colon within the first hours of colitis.

CONCLUSION

The increased expression of EGF and TGFalpha in the duodenum may lead to neutralization of gastric acid and proteolytic enzymes in the upper gastrointestinal tract during the course of colitis. Possible signals for the increased expression of EGF and TGFalpha presumably are fasting, parasympathetic, or adrenergic parts of the enteric nervous system or yet unknown mechanisms.

Histamine stimulation of MMP-1(collagenase-1) secretion and gene expression in gastric epithelial cells: role of EGFR transactivation and the MAP kinase pathway

BACKGROUND AND AIMS

GPCR stimulation by various ligands including histamine has been shown to transactivate the epidermal growth factor receptor (EGFR). This study examines the functional interactions between the H2 receptor and the EGFR in the regulation of matrix metalloproteinase-1 (MMP-1) secretion and gene expressions in cultured gastric epithelial cells.

METHODS

AGS cells were incubated for up to 24 h with either histamine or heparin binding-epidermal growth factor (HB-EGF) and MMP-1 release was determined by immunoassay. MMP-1 responses to histamine and HB-EGF were further tested by the use of H2 receptor antagonist, EGFR inhibitor and mitogen activator protein kinase (MAPK) inhibitor. The role of EGFR in MMP-1 release was further tested in cells transfected with specific EGFR siRNA. EGFR and ERK1/2 phosphorylation was determined by Western blot analysis. MMP-1 gene expression was determined by RNase protection assay (RPA).

RESULTS

Histamine and HB-EGF caused a dose-dependent release of MMP-1 with maximal responses that were 2.7- and 4.5-fold greater, respectively, than control, P<0.001. Famotidine prevented histamine-mediated MMP-1 release and AG1478 and EGFR siRNA completely inhibited MMP-1 secretion stimulated by both histamine and HB-EGF. Both histamine and HB-EGF stimulation of MMP-1 release was associated with activation of ERK1/2. MAPK inhibition also prevented histamine-and HB-EGF-induced MMP-1 secretion. Results of MMP-1 gene expression, either stimulatory or inhibitory, paralleled responses to MMP-1 secretion.

CONCLUSION

Histamine stimulation of the H2 receptor on AGS cells evoked MMP-1 secretion and gene up regulation that was dependent on transactivation of the EGFR and downstream activation of MAPK.

Potentiation of oxyntic atrophy-induced gastric metaplasia in amphiregulin-deficient mice

BACKGROUND & AIMS

The loss of parietal cells from the gastric mucosa (oxyntic atrophy) is a critical step in the pathogenesis of chronic gastritis and gastric adenocarcinoma. Parietal cells are known to secrete epidermal growth factor receptor (EGFR) ligands, which are critical regulators of differentiation in the gastric mucosa. Although all of the actions of EGFR ligands are mediated through a common EGFR protein, individual ligands may produce different physiologic responses. Previous investigations have suggested that a deficit in EGFR signaling in waved-2 mice accelerates the emergence of metaplasia after induction of acute oxyntic atrophy. We sought to determine whether specific EGFR ligands regulate the metaplastic response to oxyntic atrophy.

METHODS

To induce spasmolytic polypeptide-expressing metaplasia (SPEM), amphiregulin (AR) and transforming growth factor-alpha-deficient mice and their wild-type littermates were treated with DMP-777 for 0-14 days and for 14 days followed by 14 days of recovery off drug. We evaluated the gastric mucosal response to oxyntic atrophy using cell lineage-specific markers.

RESULTS

Although loss of transforming growth factor-alpha did not influence the induction of SPEM, loss of AR caused an acceleration and amplification in the induction of SPEM after acute oxyntic atrophy. Trefoil factor family 2/spasmolytic polypeptide and intrinsic factor dual-immunostaining cells significantly increased in the SPEM of AR-deficient mice. At the bases of glands, intrinsic factor immunoreactive cells also were costained for 5-bromo-2'-deoxyuridine, suggesting their re-entry into the cell cycle.

CONCLUSIONS

The absence of AR promoted the rapid emergence of SPEM in response to oxyntic atrophy.

Inhibition of epidermal growth factor receptor activation enhances in vivo histamine-stimulated gastric acid secretion in the rat

Epidermal growth factor (EGF) and transforming growth factor alpha (TGFalpha) have been shown to inhibit gastric acid secretion through stimulation of the EGF receptor (EGFR). In this study we examined in vivo the effects of inhibition of the EGFR on histamine-stimulated acid secretion in the rat. Submaximal (1.5 mg/kg/hr) histamine-stimulated acid secretion was measured (microEq H(+)/2 hr) during infusion of EGFRtk inhibitors and ranitidine in anesthetized rats. EGFR phosphorylation in gastric mucosal tissue lysates was measured by Western blot analysis. Submaximal histamine-stimulated acid secretion was increased significantly by the EGFR inhibitors tyrphostin (Tyr) A46 and Tyr AG1478. Tyr A46 prevented TGFalpha (10 microg/kg/hr)-mediated inhibition of maximal (5.0 microg/kg/hr) histamine-stimulated acid output. Histamine caused a fourfold increase in EGFR phosphorylation which was inhibited by both Tyr and ranitidine. We conclude that the EGFRtk inhibitors, Tyr A46 and Tyr AG1478, significantly increased submaximal histamine-stimulated acid output and Tyr A46 prevented TGFalpha inhibition of histamine-stimulated acid secretion. These observations suggest that the EGFR is involved, in vivo, in the regulation of gastric acid secretion.

Functional interaction between transforming growth factor α and capsaicin-sensitive sensory neurons in the rat stomach

BACKGROUND AND AIMS

Transforming growth alpha (TGFalpha) and sensory neurons have been shown to promote gastric mucosal protection and healing. Aims were to examine in vitro interactions between gastric sensory neurons, the sensory neuropeptide calcitonin gene-related peptide (CGRP), and TGFalpha.

METHODS

Gastric mucosal/submucosal tissue fragments from Sprague-Dawley (SD) rats were incubated in short-term (30 min) culture. Peptide release into media and TGFalpha tissue content were measured by radioimmunoassay.

RESULTS

TGFalpha (1 x 10(-8) to 1 x 10(-6) M) caused dose-dependent stimulation of CGRP release. Maximal CGRP release (+87%) was observed with 1 x 10(-6) M TGFalpha: 28.6+/-3.8 vs. control of 15.5+/-2.7 pg/g tissue; P<0.05. Both CGRP (1 x 10(-7) to 1 x 10(-5) M) and capsaicin (1 x 10-(8) to 1 x 10(-6)M) significantly inhibited basal TGFalpha release in a dose-dependent fashion that ranged from -20% to -39%. In contrast, capsaicin-induced sensory denervation caused significant increases in both basal TGFalpha release and TGFalpha tissue content.

CONCLUSION

Function interactions between TGFalpha and gastric sensory neurons are suggested by the observations that (1) TGFalpha stimulated CGRP release from gastric sensory neurons; (2) CGRP and acute capsaicin treatment inhibited TGFalpha release and; (3) capsaicin-induced sensory denervation caused significant increases in both gastric TGFalpha basal release and tissue content.

Transforming growth factor-alpha directly augments histidine decarboxylase and vesicular monoamine transporter 2 production in rat enterochromaffin-like cells

For the production and vesicle storage of histamine, Enterochromaffin-like (ECL) cells express histidine decarboxylase (HDC) and vesicular monoamine transporter 2 (VMAT2). Although HDC and VMAT2 show dynamic changes during gastric ulcer healing, the control system of their expression has not been fully investigated. In the present study, we investigated the effect of transforming growth factor-alpha (TGF-alpha) and proinflammatory cytokines on HDC and VMAT2 expression in rat ECL cells. Time course changes in the expression of TGF-alpha during the healing of acetic acid-induced ulcers were studied. EGF receptor (EGFR) expression was also examined in ECL cells, whereas the direct effects of TGF-alpha and proinflammatory cytokines on HDC and VMAT2 expression in ECL cells were investigated using in vivo and in vitro models. During the process of ulcer healing, expression of TGF-alpha mRNA was markedly augmented. Furthermore, EGFR was identified in isolated ECL cells. TGF-alpha stimulated HDC and VMAT2 mRNA expression and protein production and also increased histamine release from ECL cells. Selective EGFR tyrosine kinase inhibitor tyrphostin AG1478 almost completely inhibited HDC and VMAT2 gene expression induced by TGF-alpha in vivo and in vitro. During gastric mucosal injury, TGF-alpha was found to stimulate ECL cell functions by increasing HDC and VMAT2 expression.

Involvement of the signal transduction pathway mediated by epidermal growth factor receptor in the differentiation of chicken glandular stomach

During the development of the chicken proventriculus (glandular stomach), the initially undifferentiated epithelium differentiates into two distinct cell populations: the glandular epithelium, cells of which secrete embryonic chicken pepsinogen (ECPg), and luminal epithelial cells, which express the chicken spasmolytic polypeptide gene (cSP). Based on knowledge of the adult mouse stomach, the ligands of epidermal growth factor (EGF) receptor (EGFR) were expected to affect differentiation of the proventricular epithelium. When EGF was added to the medium in which proventriculi were cultured in vitro, gland formation was suppressed in a dose-dependent manner and the amount of ECPg mRNA decreased, whereas morphological differentiation of luminal epithelium was stimulated. Simultaneous treatment of the proventriculus with EGF and tyrphostin 47 resulted in the attenuation of the effect of EGF, suggesting that EGF, or other ligands of EGFR, may actually be involved in the normal course of development of the proventricular epithelium.

Influence of epidermal growth factor on bovine pancreatic duct cell bicarbonate

BACKGROUND AND AIMS

Epidermal growth factor (EGF) is secreted in pancreatic juice and its receptor is expressed on pancreatic duct cells (PDCs), suggesting a physiological role which has yet to be defined. Here we examined the effects of EGF on bicarbonate production and carbonic anhydrase (CA) activity in a PDC explant model.

METHODS

Bovine main PDCs were prepared and maintained in culture as explants. Levels of CA expression, phosphorylation, and enzymatic activity were measured in resting cells and compared to that of cells exposed to 10 nM secretin, 10 nM EGF, or both. Bicarbonate production was measured using the autoburette pH titration technique.

RESULTS

CA protein levels were unchanged with any treatment, but enzyme activity increased by 180% with secretin treatment and was reduced by 54% with EGF. The combination treatment led to a synergistic increase 240% above basal. EGF alone did not affect bicarbonate secretion, but the normal increase observed with secretin stimulation (1.3 +/- 0.4 to 2.9 +/- 0.6 micromol/h/cm(2)) was abolished by acute EGF pretreatment. On the other hand, EGF pretreatment for 24 h significantly increased basal and stimulated secretion (2.2 +/- 0.5 and 3.8 +/- 0.5, respectively) compared to controls.

CONCLUSIONS

EGF exerts a regulatory role on bicarbonate secretion by the pancreatic duct epithelium, independent of its effect on CA activity. Its inhibition of stimulated bicarbonate secretion could play a protective role in the setting of pancreatic inflammation, where increased levels of EGF are associated with reduced pancreatic juice production.

Comparison of the antisecretory and antiulcer activity of epidermal growth factor, urogastrone and transforming growth factor alpha and its derivative in rodents in vivo

This study investigates the effects of epidermal growth factor (EGF), urogastrone (UG) and transforming growth factor-alpha (TGFalpha) and its derivative on dimaprit- and pentagastrin-induced gastric acid secretion and on acidified ethanol (AE)-evoked ulcer formation in anaesthetized rats. EGF, TGFalpha and UG administered subcutaneously (s.c.) 30 min before dimaprit inhibited gastric acid secretion. Against pentagastrin-stimulated secretion, TGFalpha inhibited, while EGF and UG potentiated, acid secretion dose-dependently. Intraduodenal (i.d.) administration of TGFalpha and UG had no effect, while EGF potentiated, both secretagogue-induced acid secretion in the same dosage schedule. Administration of either EGF, UG or TGFalpha i.v. bolus, in response to continuous infusion of dimaprit resulted in a significant (p < 0.05-p < 0.001) inhibition of acid secretion which was transient and returned to normal within 30-45 min for UG while it slowly returned to normal for EGF and TGFalpha. The truncated form of TGFa (amino acids 34-43) did not show any antisecretory effect when administered parenterally. Acidified ethanol produced gastric haemorrhagic lesions in the rat 1 h after oral administration. The gastric mucosal protective effects of TGFalpha, EGF and UG administered either orally or s.c. 30 min before the administration of AE were dose-dependent against this model of ulcer induction. Indomethacin (Indo), administered 15 min before AE to inhibit prostanoids biosynthesis, significantly (p < 0.001) reduced the cytoprotective effects of TGFalpha, EGF and UG and aggravated the ulcer index when administered s.c. The results show that PGs may be involved in mediating the protective effects of the three growth factors. Administration of NG-nitro-L argininemethylester (L-NAME) 15 min prior to TGFa, EGF and UG s.c. or orally, significantly (p < 0.001) decreased the degree of ulcer indices and was able to reduce the protective effects of TGFalpha, EGF and UG, thus including the role of NO in mediating the protective effects of these growth factors. In conclusion, these results have demonstrated that EGF, UG and TGFalpha have a short and reversible inhibitory effect on dimaprit-stimulated gastric acid secretion and each is effective parenterally but not orally. UG and EGF potentiated, while, TGFa inhibited pentagastrin-stimulated acid secretion. In addition, TGFalpha seems to lose its activity when it is truncated from the C terminus. The present study also suggests that EGF, UG and TGFalpha are equally effective against AE-induced gastric ulcer and bring about their cytoprotective action through their reduction of acid secretion and through PG and NO pathways.

Immunolocalization of transforming growth factor-alpha and epidermal growth factor receptor in the rat gastroduodenal area

The maintenance of gastrointestinal epithelium integrity requires a fine balance between proliferation and differentiation as well as protection against gastric acid secretion. Transforming growth factor-alpha (TGF-alpha) regulates these functions by binding to epidermal growth factor receptor (EGF-R). This study was designed to identify the localization of TGF-alpha and EGF-R in the rat gastroduodenal region. In the stomach, the surface and gastric pit cells showed staining for TGF-alpha antibodies in the cytoplasm and basolateral and apical membranes. TGF-alpha and EGF-R were observed in the supranuclear region of the cells lining the gland. In the duodenum, the enterocytes coexpressed both TGF-alpha and EGF-R in the supranuclear area. The EGF-R was also observed in the apical membrane. Brunner's glands were positive for both TGF-alpha and EGF-R antibodies. Our results demonstrate the coexpression of TGF-alpha and EGF-R in the rat gastroduodenal area, which suggests a functional role for them in the establishment and maintenance of the epithelial renewal.

Kex2 family endoprotease furin is expressed specifically in pit-region parietal cells of the rat gastric mucosa

The proprotein-processing endoprotease furin is localized in the gastric epithelial cells of the pit region in the rat gastric gland. The gastric pit is composed of several cell types, including gastric surface mucosal (GSM) cells and parietal cells. Furin converts many growth- or differentiation-related proproteins to their active forms. We examined identification of furin-positive cells by immunostaining of rat gastric mucosa and regulators of the furin expression by measuring the furin promoter activity by luciferase assay. Furin-positive cells were stained for H(+)-K(+)-ATPase, indicating that they are parietal cells. Furin-positive parietal cells were not stained for transforming growth factor-alpha (TGF-alpha) but were surrounded by TGF-alpha-positive GSM cells. In contrast, parietal cells below the proliferative zone were positive for TGF-alpha but not for furin. Furin-positive parietal cells expressed a high level of epidermal growth factor receptor (EGFR). TGF-alpha stimulated the furin promoter activity highly in a mouse GSM cell line GSM06. Thus we suggest that the parietal cells of the pit region have furin-mediated functions that can be stimulated by EGFR signaling.

TGF-alpha reduces bradykinin-stimulated ion transport and prostaglandin release in human colonic epithelial cells

The effect of chronic exposure to transforming growth factor-alpha (TGF-alpha) on bradykinin-stimulated acute prostanoid production and ion secretion in monolayers of HCA-7 colony 29 colonic epithelial cells has been studied. Monolayers synthesized prostaglandin E2 (PGE2) at a basal rate of 2.10 +/- 0.31 pg. monolayer-1. min-1 over 24 h. Bradykinin (10(-8)-10(-5) M) dose dependently increased acute PGE2 release by three orders of magnitude. This was associated with a rise in cAMP from 1.60 +/- 0.14 to 2.90 +/- 0.1 pmol/monolayer (P < 0.02) and a dose-dependent increase in short-circuit current (SCC). When monolayers were primed by a 24-h exposure to TGF-alpha, basal PGE2 release rose to 6.31 +/- 0.38 pg. monolayer-1. min-1 (TGF-alpha concn 10 ng/ml; P = 0.001). However, the stimulation of acute prostaglandin release, intracellular cAMP, and increased SCC by bradykinin was significantly reduced by preincubation with TGF-alpha. Priming with PGE2 (10(-8)-10(-6) M) over 24 h mimicked the effect of TGF-alpha on bradykinin-induced changes in cAMP and SCC. These data suggest that enhanced chronic release of prostaglandins in response to stimulation with TGF-alpha may downregulate acute responses to bradykinin. In vivo, TGF-alpha could have an important modulatory function in regulating secretion under inflammatory conditions.

Changes in mucosal levels of transforming growth factor-alpha from the oxyntic region and ulcer site during duodenal ulcer healing with ranitidine or sucralfate

Changes in the levels of transforming growth factor-alpha (TGF-alpha) in gastric mucosa during ulcer healing were studied in 24 patients with endoscopically confirmed duodenal ulcers, treated either with ranitidine (300 mg daily, at night) or with sucralfate (2 g twice daily). Endoscopic biopsies were taken from the gastric fundus and from the ulcer margin at baseline and after 7-10 days of treatment. TGF-alpha levels were determined by radioimmunoassay in paired samples from 22 patients (fundal) and 18 patients (duodenal). There were no significant changes in TGF-alpha levels in the fundus of the whole group or of either treatment group. At the ulcer site, however, there was a significant increase in TGF-alpha levels in the whole group (from 16.4 to 33 pg/mg protein (medians); P < 0.005), and an increasing trend was seen in both treatment groups but was statistically significantly only in the group treated with sucralfate (P < 0.03).

Increased expression of transforming growth factor alpha precursors in acute experimental colitis in rats

BACKGROUND AND AIM

Epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha), members of the EGF family of growth factors, protect rat gastric and colonic mucosa against injury. Having shown previously that exogenously applied EGF protects rat colonic mucosa against injury, the aim of the present study was to evaluate the endogenously expressed ligand mediating the protective effect of EGF/TGF-alpha in vivo.

METHODS

In an experimental model of trinitrobenzene sulphonic acid (TNBS)/ethanol induced colitis in rats EGF and TGF-alpha expression was evaluated using a ribonuclease protection assay, northern blot analysis, western blot analysis, and immunohistochemistry.

RESULTS

TGF-alpha mRNA increased 3-4 times at 4-8 hours after induction of colitis and returned to control levels within 24 hours. TGF-alpha immunoreactive protein with a molecular size of about 28 kDa representing TGF-alpha precursors increased markedly after induction of colitis with a peak at 8-12 hours. No fully processed 5.6 kDa TGF-alpha protein was detected in normal or inflamed colon tissue. Only a weak signal for EGF mRNA expression was detected in the rat colon and no EGF protein was observed by immunohistochemistry or western blot analysis.

CONCLUSIONS

TGF-alpha precursors are the main ligands for the EGF receptor in acute colitis. It is hypothesised that TGF-alpha precursors convey the biological activity of endogenous TGF-alpha peptides during mucosal defence and repair.

Inhibition of parietal cell acid secretion is mediated by the classical epidermal growth factor receptor

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) inhibit gastric acid secretion both in vivo and in vitro. Previous studies have indicated that EGF and TGF-alpha bind to the same EGF/TGF-alpha receptor. Nevertheless, we and others have previously demonstrated that inhibition of acid secretion by these growth factors requires concentrations of the peptides that are 10-fold higher than those necessary for induction of mitogenesis. Therefore, we have sought to investigate whether gastric parietal cells may possess a second EGF/TGF-alpha receptor class. Two systems were studied: First, [125I]TGF-alpha was cross-linked to the receptor in isolated rabbit parietal cell membranes, and labeled species were resolved on SDS-PAGE. Second, acid secretion was evaluated in pylorus-ligated waved-2 mutant mice, which carry a disabling point mutation in their classical EGF/TGF-alpha receptor. In isolated parietal cells, [125I]TGF-alpha was cross-linked into a single species of 170 kDa. Cross-linking was inhibited in the presence of unlabeled TGF-alpha with an IC50 of 80 nM. In the pylorus-ligated mice, control littermate mice demonstrated a dose-dependent inhibition of acid secretion by EGF with an IC50 of 20 micrograms/kg. In contrast, EGF had no inhibitory effect on acid secretion in waved-2 mice at concentrations up to 100 micrograms/kg. No alterations in parietal cell or gastrin cell numbers were observed. These results in both isolated rabbit parietal cells and waved-2 mice support the existence of only a single class of EGF/TGF-alpha receptors in parietal cells. Differences in growth factor affinity are likely due to the modification of the receptor or one of its coordinate regulators.

Transforming growth factor alpha-immunoreactivity in neural tissues of the rat stomach

We report TGF alpha immunoreactivity in neurons of the myenteric plexus and in nerve fibers in the muscle and submucosal layers of the rat stomach. Association of TGF alpha staining nerve fibers to vessels and smooth muscle cells gives morphological evidence that EGF/TGF alpha's actions to increase mucosal blood flow and gastric motility may be mediated by TGF alpha derived from neural structures. These data suggest that TGF alpha plays a role in the neural control of the gastric function.

Cytokine effects on pepsinogen secretion from human peptic cells

BACKGROUND

Different cytokines, including epidermal growth factor (EGF) and interleukin 1 beta (IL 1 beta), participate in the pathogenesis of gastric mucosal damage and repair by means of different mechanisms that are either paracrine or autocrine in nature.

AIMS

To study whether EGF and IL 1 beta affect pepsinogen secretion in vitro.

METHODS

Dispersed human peptic cells were prepared from endoscopically obtained biopsy specimens after collagenase digestion, mechanical disruption, and density gradient centrifugation.

RESULTS

EGF dose dependently increased basal pepsinogen secretion and mitogenic concentrations (0.1 nM) of EGF induced submaximal stimulation. Similar effects were observed with transforming growth factor alpha. EGF effects on pepsinogen secretion were in addition to that induced by CCK-OP and db-cAMP stimulated pepsinogen secretion. EGF stimulated pepsinogen secretion was completely inhibited by a human immunospecific EGF receptor antibody and reduced by both genistein and tyrphostin-25, two different tyrosine kinase inhibitors. IL 1 beta does not affect basal, CCK-OP or acetylcholine stimulated pepsinogen secretion. However, IL 1 beta dose dependently inhibited db-cAMP and histamine stimulated pepsinogen secretion.

CONCLUSIONS

These results show that both EGF and IL 1 beta modulate human pepsinogen secretion in vitro and suggest that the paracrine effects of these cytokines on pepsinogen secretion might be involved in some pathological conditions of damage and inflammation of the gastric mucosa.

Histochemical analysis of hyperplastic stomach of TGF-alpha transgenic mice

Hypertrophic gastric mucosa in transgenic mice overexpressing transforming growth factor (TGF)-alpha showed mucosal cellular hyperplasia with dysplasia, suppression of gastric acid secretion, and chief and parietal cell depletion. In order to clarify the effects of TGF-alpha on the gastric mucosa, we analyzed the stomach of TGF-alpha transgenic mice by mucin histochemical staining and immunohistochemical analysis of TGF-alpha. In transgenic mice, especially those older than 3 months, the fundic gland was notably atrophic but the total mucosa was thickened. The mucous neck cells were hypersecretory and associated with abnormal sulfation. Mucosal hyperplasia was caused by proliferation of surface epithelial cells, associated with formation of intracytoplasmic lumina. The hyperplastic foveolar cells revealed production of a high amount of sialomucin. In addition, the involved stomach regionally revealed collagenous fibrosis in the submucosal layer. The wide distribution of TGF-alpha in the hyperplastic foveolar cells was in sharp contrast to negative expression in the foveolar cells in the control mice. These findings demonstrated the various regulatory functions of TGF-alpha in mucin production, fibrogenesis, and neck cell proliferation in the stomach.

Expression of epidermal growth factor and transforming growth factor alpha during ulcer healing. Time sequence study

BACKGROUND

Growth factors such as epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) have been shown to share common receptor (EGFR) and to accelerate ulcer healing due to stimulation of cell proliferation, but the time sequence of expression of EGF and TGF alpha during ulcer healing has not been investigated. In this study the rate of cell proliferation and the gastric secretion and gene expression of mRNA for EGF and TGF alpha were determined during ulcer healing.

METHODS

Gastric ulcers were induced in 150 Wistar rats by serosal application of 100% acetic acid (ulcer area, 14 mm2). Some of these animals were also equipped with a gastric fistula for the assessment of gastric secretion during ulcer healing. The animals were killed 0, 2, 4, 6, or 8 days after ulcer induction, and the ulcer area was determined. The mucosal sections with gastric ulcer were immunostained for proliferating cell nuclear antigen (PCNA) and for immunoexpression of EGF, TGF alpha, and EGFR. The expression of mRNA EGF and mRNA TGF alpha was also determined in the ulcer margin by reverse transcriptase (RT) polymerase chain reaction (PCR) using specific primers.

RESULTS

Two, 4, 6, and 8 days after ulcer induction the gastric ulcer area was gradually reduced from the initial size (day 0) by 47%, 70%, 80%, and 87%, respectively, and this was accompanied by an increase in PCNA with its maximum on day 4. The gastric acid and pepsin secretion was significantly reduced by 75% and 79%, respectively, on day 2 after ulcer induction but then the secretion tended to return to normal value by day 8. The expression of EGF, TGF alpha, and EGFR was negligible on day 0 but increased significantly during the healing, reaching maximum on day 4. Expression of EGF mRNA was detected on days 2, 4, and 6, and that of TGF alpha mRNA on days 2, 4, 6, and 8 after ulcer induction, with the most intense signals for both transcripts observed on day 2.

CONCLUSIONS

1) The enhancement in cell proliferation during ulcer healing may be mediated by increased release of EGF and TGF alpha; 2) the expression of EGF and TGF alpha mRNA precedes the overexpression of these growth factors at the ulcer margin during ulcer healing; and 3) the overexpression of growth factors coincides with the inhibition of gastric secretion and increased blood flow at the ulcer margin, indicating that these factors affect gastric secretion and blood flow in the course of ulcer healing.

Transforming growth factor-alpha in vivo stimulates epithelial cell proliferation in digestive tissues of suckling rats

BACKGROUND

The role that exogenous transforming growth factor-alpha (TGF-alpha) may exert on cell proliferation in vivo is poorly understood.

AIM

To investigate the effect of rat TGF-alpha on epithelial cell proliferation in all suckling rat digestive tissues and to compare it with that of rat epidermal growth factor (EGF). ANIMAL AND METHODS: TGF-alpha and EGF were given three times daily either subcutaneously (10 or 20 micrograms/kg) or intraperitoneally (100 micrograms/kg) to rats from the ninth postnatal day. Cell proliferation was assessed through 5-bromo- 2-deoxyuridine incorporation and estimation of labelling indices.

RESULTS

For both growth factors, the highest dose given for only two days significantly increased stomach and intestinal weights compared with controls (p < 0.05 to p < 0.001). The proliferative responded depended on the dose given, colonic mucosa being the most sensitive whereas oxyntic mucosa remained unresponsive. TGF-alpha was as potent as EGF in stimulating epithelial cell proliferation in antral, duodenal, and colonic mucosae. However, EGF was more active on oesophageal and jejunal cell proliferation whereas TGF-alpha was more active on pancreatic exocrine cell proliferation and the differences between the two growth factor treated groups were significant.

CONCLUSIONS

These results prove for the first time the stimulating effect in vivo of exogenous rat TGF-alpha on epithelial cell proliferation in rat digestive tissues during the developmental period and support a functional role for TGF-alpha at that time.

Epidermal growth factor inhibits Ca(2+)-dependent Cl- transport in T84 human colonic epithelial cells

This study examined whether epidermal growth factor (EGF) inhibits Ca(2+)-dependent Cl- secretion by T84 cells. Basolateral EGF inhibited Cl- secretion induced by carbachol or thapsigargin, without blocking the rise in intracellular Ca2+. Studies have shown that carbachol renders T84 cells refractory to subsequent stimulation by thapsigargin, an effect ascribed to D-myo-inositol 3,4,5,6-tetrakisphosphate [D-Ins(3,4,5,6)P4]. EGF also increased DL-Ins(3,4,5,6)P4 to a maximum of 170% above control. However, despite the fact that EGF inhibited Cl- secretion at 1 min, DL-Ins(3,4,5,6)P4 was not elevated at this time point. EGF plus carbachol had a greater inhibitory effect on Cl- secretion than either alone, indicating the likely involvement of an additional inhibitory pathway activated by EGF. Staurosporine did not alter the ability of EGF to inhibit Cl- secretion or increase DL-Ins(3,4,5,6)P4. In contrast, genistein inhibited the rise in DL-Ins(3,4,5,6)P4 and partially reversed EGF's inhibitory effect on Cl- secretion. In conclusion, EGF and carbachol can both inhibit Cl- secretion via D-Ins(3,4,5,6)P4, whereas EGF also generates an additional inhibitory signal.

Simian virus 40 T antigen-induced amplification of pre-parietal cells in transgenic mice. Effects on other gastric epithelial cell lineages and evidence for a p53-independent apoptotic mechanism that operates in a committed progenitor

Gastric units in the glandular epithelium of the mouse stomach contain several types of continuously renewing epithelial cells. Acid-producing parietal cells are derived from a multipotent stem cell that also gives rise to mucus-producing pit cells and pepsinogen- and intrinsic factor-producing zymogenic cells. We used nucleotides -1035 to +24 of the mouse H+/K(+)-ATPase beta subunit gene (H+/K(+)-ATPase beta subunit-1035 to +24) to examine the consequences of expressing simian virus 40 T antigen (SV 40 TAg) in the normally rare, nonproliferating, short-lived pre-parietal cell progenitor. Light and electron microscopic morphologic studies plus multilabel immunohistochemical analyses of postnatal day (P) 14-80-day transgenic mice revealed that SV40 TAg produces a 50-70-fold amplification of pre-parietal cells which become the predominant cell type in gastric units. Differentiation to mature parietal cells is blocked, resulting in hypochlorhydria and an associated systemic iron deficiency. SV40 TAg-induced pre-parietal proliferation is accompanied by apoptosis. Examination of adult transgenic mice homozygous for p53 wild type or p53 null alleles established that the apoptosis occurs through a p53-independent pathway. H+/K(+)-ATPase beta subunit -1035 to +24/SV40 Tag is not expressed during differentiation of the zymogenic lineage. Nonetheless, P28-P80 transgenic mice exhibit an apparent block in the conversion of pre-zymogenic to zymogenic cells. This block appears to be quite specific: conversion of preneck to neck cells and neck to pre-zymogenic cells is not affected. Comparison of normal and transgenic mice that are p53+/+ or p53-/- confirmed that the loss of mature zymogenic cells is not dependent upon p53. Although H+/K(+)-ATPase beta subunit -1035 to +24 is not active in pit cell progenitors or their differentiated descendants, there is a 2-3-fold increase in mature pit cells in transgenic animals. Our findings (i) demonstrate an approach for amplifying and characterizing pre-parietal or other progenitor cell populations in gastric units, (ii) reveal an SV40 TAg-inducible, p53-independent apoptotic mechanism that operates in a committed epithelial progenitor cell, and (iii) provide a transgenic mouse model for defining factors that may mediate progression through specific points in the differentiation programs of the parietal and zymogenic cell lineages or that may influence decisions about allocation to the pit cell lineage.

Experimental ulceration leads to sequential expression of spasmolytic polypeptide, intestinal trefoil factor, epidermal growth factor and transforming growth factor alpha mRNAs in rat stomach

A model of gastric ulceration in the rat has been used to determine the expression of four messenger RNAs (mRNAs) encoding peptides considered to play active parts in the healing response. The trefoil peptides, rat spasmolytic polypeptide (rSP) and rat intestinal trefoil factor (rITF), along with epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) were the molecules studied. Ulceration was caused under anaesthesia by brief application of a liquid nitrogen-filled cryoprobe to the gastric serosal surface and RNA expression was monitored over the next 10 days. Each mRNA was quantified by ribonuclease protection assay, and mRNAs encoding rSP and rITF were localized within tissue sections by hybridization in situ with 35S antisense riboprobes. Ulceration induced the very rapid expression of first rSP and then rITF mRNA, whereas the mRNAs encoding EGF and TGF alpha increased at later times, with maxima recorded at 3 and 6 days, respectively. Hybridization in situ detected extensive rSP mRNA expression in the regenerative epithelia. The pronounced, but temporally different patterns of mRNA induction after ulceration suggest that the trefoil peptides may fulfil different and more immediate roles than the more 'traditional' healing proteins EGF and TGF alpha.

Effects of hypochlorhydria and hypergastrinemia on structure and function of gastrointestinal cells. A review and analysis

Since hypochlorhydria can induce hypergastrinemia, and gastrin has a trophic effect on some gastrointestinal cells, states that cause elevated plasma gastrin levels are of interest in terms of effects on cell growth and function. This article reviews the relationship between gastric mucosal cells during periods of acid stimulation and inhibition and analyses the effects of hypochlorhydria and hypergastrinemia on gastric and colonic cells and tumors. Hypochlorhydria releases the inhibitory effect of antral gastrin cells, inducing them to release gastrin in the presence of peptides or amino acids in the gastric lumen or in response to antral distension. Gastrin stimulates the oxyntic mucosa, which may lead to hyperplasia of enterochromaffin-like cells, resulting in enterochromaffin-like carcinoid tumors in aged rats and, rarely, in patients with chronic atrophic gastritis or gastrinomas. In addition to hypergastrinemia, other factors appear to be required for the progression of enterochromaffin-like hyperplasia to carcinoids; genetic factors may be involved. Gastrin elevations due to antisecretory drug therapy are indirectly proportional to the degree of acid inhibition and are reversible upon cessation of therapy. The gastrin levels during omeprazole therapy are similar to those caused by gastric vagotomy. Available evidence does not support a relationship between hypergastrinemia and the occurrence or growth of gastric carcinoma or colonic tumors.

Transforming growth factor alpha disrupts the normal program of cellular differentiation in the gastric mucosa of transgenic mice

Transforming growth factor alpha (TGF alpha) evokes diverse responses in transgenic mouse tissues in which it is over-expressed, including the gastric mucosa, which experiences aberrant growth and a coincident repression of hydrochloric acid production. Here we show that ectopically expressed TGF alpha induces an age-dependent cellular reorganization of the transgenic stomach, in which the surface mucous cell population in the gastric pit is greatly expanded at the expense of cells in the glandular base. Immunohistochemical analysis of BrdU incorporation into DNA demonstrated that although mature surface mucous cells were not proliferating, DNA synthesis was enhanced by approximately 67% in the glandular base and isthmus, where progenitor cells reside. RNA blot and in situ hybridization were employed to determine temporal and spatial expression patterns of specific markers representing a variety of exocrine and endocrine gastric cell types. Mature parietal and chief cells were specifically depleted from the glandular mucosa, as judged by a 6- to 7-fold decrease in the expression of genes encoding H+,K(+)-ATPase, which is required for acid secretion, and pepsinogen C, respectively. The reduction of these markers coincided in time with the activation of TGF alpha transgene expression in the neonatal stomach. The rate of cell death in the glandular region was not overtly different. Significantly, the loss of parietal and chief cells occurred without a concomitant loss of their respective cellular precursors. In contrast to exocrine cells, D and G endocrine cells were much less severely affected, based on analysis of somatostatin and gastrin expression. Analysis of these dynamic changes indicates that TGF alpha can induce selective alterations in terminal differentiation and proliferation in the gastric mucosa, and suggests that TGF alpha plays an important physiological role in the normal regulation of epithelial cell renewal.

EGF and TGF-alpha in the human kidney: identification of octopal cells in the collecting duct

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) are well-known mitogens expressed in the kidney. Their human renal cell origin has not been conclusively identified. The distribution of EGF and TGF-alpha was investigated immunohistochemically in the adult human kidney in comparison with the monkey and rodent kidney. In humans, as in the monkey, two variants of EGF immunoreactivity were detected. One was present along the apical cell surfaces and diffusely in the cytoplasm of the thick ascending limb (TAL), co-localizing with Tamm-Horsfall protein, and in the distal convoluted tubule (DCT). The other occurred as overall membranous staining in the connecting tubule and cortical collecting duct (CD), and mainly as basal staining in the rest of the CD. The EGF stained cells in the cortical and outer medullary CD reached a diameter of 40 mu and were identified as intercalated or dark cells; they displayed a peculiar octopus-like shape, bearing long lateral extensions that stretched underneath and between 20 surrounding smaller negative cells. Cytoplasmic TGF-alpha staining appeared in the DCT and decreased further on.

IN CONCLUSION

(1) the normal human distal nephron displayed EGF and TGF-alpha immunoreactivity in a partly complementary segmental and subcellular distribution pattern, partly differing from that in rodents. (2) EGF immunostaining revealed the presence of long lateral projections on CD intercalated cells; this peculiar morphology suggests a modulatory role within the CD epithelium, possibly involving the EGF immunoreactivity on their surface.

Effect of transforming growth factor-alpha on gastric acid secretion in rats and monkeys

The effect of transforming growth factor-alpha was studied in histamine-stimulated gastric acid secretion in monkeys and in pylorus-ligated rats. In monkeys, transforming growth factor-alpha given intravenously in a stepwise manner gradually reduced gastric acid secretion. A dose of 0.1 mmol/kg induced about a 50% inhibition of gastric acid output, while about 100% inhibition of the same parameter, was observed after a dose of 1 nmol/kg. Following a single administration of 1 nmol/kg intravenously in monkey, the maximum inhibitory effect on gastric acid output was reached 60 min after the administration of the drug, when a 91.8% inhibition was observed. Pretreatment values were reached 210-240 min after transforming growth factor-alpha administration. In pylorus-ligated rats, transforming growth factor-alpha, at doses of 9 and 18 nmol/kg produced an almost complete inhibition of gastric acid secretion. In this model, the ED50 was calculated to be 4.5 nmol/kg. Comparison with epidermal growth factor on the same models of gastric acid secretion showed that these two compounds have similar inhibitory potency. However, the effect of transforming growth factor-alpha on gastric acid secretion in monkeys was shorter lasting than that of epidermal growth factor.

Inflammation, acid and ulcers

Chronic active type B gastritis is invariably the result of Helicobacter pylori infection and is an important factor in duodenal ulcer disease. The actions of mediators produced (a protein factor, a lipid soluble "pore-forming factor" and urease) or induced (immune/inflammatory cell mediators) by this bacterium on the control of gastric acid secretion are currently being investigated. These studies are reviewed in light of our current knowledge of the physiological control of gastric acid secretion.

Negative feedback regulation of acid secretion: linkage of acid secretion and mucosal defense

To regulate inappropriate or excessive acid secretion that may be harmful not only to surrounding mucosal cells but also parietal cells themselves, versatile mechanisms operate to control acid secretion. In this article elaborate mechanisms that participate in the control of acid secretion are described with our data and a review of relevant findings in the literature concerning the action or secretion of key regulatory molecules. The analysis of the regulatory mechanisms revealed that appropriate secretory control can be achieved by multiple feedback regulations, which are closely coordinated with mucosal defense. In the feedback circuits, the regulatory factors cannot be simply categorized into either aggressive or defensive factors. Therefore we propose that the mucosal integrity and tissue homeostasis would be better understood by a feedback loop model rather than by a dualistic balance model.

Localization of epidermal growth factor/transforming growth factor-alpha receptor in the human gastric mucosa. An immunohistochemical and in situ hybridization study

Current evidence indicates that epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) play a pivotal role in the maintenance of gastric mucosal integrity, via binding to a common cell-surface receptor (EGF/TGF-alpha receptor). We examined the distribution and cellular sites of synthesis of EGF/TGF-alpha receptor in normal human gastric mucosa by immunohistochemical and in situ hybridization techniques. Intense EGF/TGF-alpha receptor immunoreactivity was observed in the basal cytoplasm and along basolateral membranes of mucus neck cells, foveolar columnar cells, and surface epithelial cells facing the gastric lumen. Parietal cells and mucus-secreting pyloric gland cells displayed a distinct basolateral immunostaining, whereas the luminal membrane was unstained. Immunoreactivity was also noted in spindle-shaped cells of the lamina propria and in smooth muscle cells of the muscularis mucosae and muscularis propria. In situ hybridization revealed EGF/TGF-alpha receptor RNA transcripts in all cell types displaying positive immunoreaction. These results suggest a physiological role for EGF/TGF-alpha in the regulation of multiple gastric functions. The receptor distribution at the luminal aspect of the gastric mucosa provides the anatomical basis for a possible interaction of gastric juice EGF (or TGF-alpha) with cells of the mucosal surface, whereas the expression of EGF/TGF-alpha receptor in cells which are not in direct contact with the gastric lumen is consistent with blood-mediated or paracrine/autocrine mechanisms of EGF/TGF-alpha action on these cells.

Transforming growth factor alpha protection against drug-induced injury to the rat gastric mucosa in vivo

This study was designed to determine whether transforming growth factor alpha (TGF alpha) protects rat gastric mucosa against ethanol- and aspirin-induced injury. Systemic administration of TGF alpha dose-dependently decreased 100% ethanol-induced gastric mucosal injury; a dose of 50 micrograms/kg delivered intraperitoneally 15 min before ethanol decreased macroscopic mucosal injury by > 90%. At the microscopic level, TGF alpha prevented deep gastric necrotic lesions and reduced disruption of surface epithelium. Pretreatment with orogastric TGF alpha (200 micrograms/kg) only partially (40%) decreased macroscopic ethanol damage. Intraperitoneal administration of TGF alpha at a dose of 10 micrograms/kg, which does not significantly inhibit gastric acid secretion, decreased aspirin-induced macroscopic damage by > 80%. TGF alpha protection does not seem to be mediated by prostaglandin, glutathione, or ornithine decarboxylase-related events, as evidenced by lack of influence of the inhibition of their production. Pretreatment with the sulfhydryl blocking agent N-ethylmaleimide partially abolished (40%) the protective effect of TGF alpha. In addition, systemic administration of TGF alpha resulted in a two-fold increase in tyrosine phosphorylation of phospholipase C-gamma 1 and in a time- and dose-dependent increase in levels of immunoreactive insoluble gastric mucin; these events occurred in a time frame consistent with their participation in the protective effect of TGF alpha.

Hypertrophic gastropathy resembling Ménétrier's disease in transgenic mice overexpressing transforming growth factor alpha in the stomach

Transforming growth factor alpha (TGF alpha) is thought to participate in the normal and pathologic processes of numerous tissues, including the gastric mucosa. To explore its role in vivo, transgenic mice were generated overexpressing TGF alpha in the stomach. TGF alpha induced dramatic structural and functional lesions of the glandular stomach that were similar to Ménétrier's disease in humans. Transgenic mice developed severe adenomatous hyperplasia that resulted in a striking nodular thickening or hypertrophy of the gastric mucosa. Secretions obtained from affected stomachs contained no detectable gastric acid, suggesting that parietal cell function had been greatly impaired. These findings demonstrate that overproduction of TGF alpha can stimulate cellular proliferation, suppress acid secretion, and perturb organogenesis of the stomach of transgenic mice. Moreover, TGF alpha may contribute to the pathogenesis of related human hypertrophic gastropathies, such as Ménétrier's disease.

Immunoreactivity of transforming growth factor alpha in the normal adult gastrointestinal tract

The immunolocalisation of transforming growth factor alpha (TGF alpha) in the normal human oesophagus and the gastrointestinal tract was elucidated using two different antibodies - Ab2, a monoclonal antibody reacting with part of the human TGF alpha molecule, and 26T a rabbit affinity purified polyclonal antibody raised against part of the rat TGF alpha peptide. There have been conflicting reports on the distribution of this growth factor in the gut. The results clearly showed that this peptide regulatory factor is confined to the luminal surface and foveolae in the stomach, restricted to the villous epithelium in the small intestine, and in the colon was seen in the upper one third of the crypt. This pattern indicates that the distribution of this peptide regulatory factor is within the differentiated compartment and indicates a role in differentiation besides its well known proliferative effects.

Roles for transforming growth factor-alpha in gastric physiology and pathophysiology

Transforming growth factor alpha (TGF alpha) is a 5.6 kd single-chain polypeptide that acts through binding to the epidermal growth factor receptor (EGFR). TGF alpha is produced in a wide range of normal as well as embryonic and neoplastic cells and tissues. TGF alpha and EGFR, but not EGF, are expressed in normal gastric mucosa. We have identified the following biological roles for TGF alpha in the stomach, using a variety of primate and rodent models: inhibition of acid secretion; stimulation of mucous cell growth; protection against ethanol- and aspirin-induced injury. This last effect is associated with a time- and dose-dependent increase in levels of insoluble gastric mucin. Based on these known biological actions of TGF alpha, we have examined TGF alpha production in Ménétrier's disease, a disorder characterized by foveolar hyperplasia, hypochlorhydria, and increased gastric mucin content. In four patients with Ménétrier's disease, there was enhanced TGF alpha immunostaining throughout the gastric mucosa. Furthermore, metallothionein (MT)-TGF alpha transgenic mice which overproduce TGF alpha in the stomach exhibit histopathological and biochemical features characteristic of and consistent with the diagnosis of Ménétrier's disease. Thus locally produced TGF alpha may mediate a number of biological processes in the stomach, and its altered production may participate in the pathogenesis of selected pathological states.

Transforming growth factor-alpha and epidermal growth factor messenger ribonucleic acid and protein levels in human placentas from early, mid, and late gestation

OBJECTIVE

Human placenta expresses receptors for transforming growth factor-alpha and epidermal growth factor throughout pregnancy. Experiments were performed to determine whether epidermal growth factor or transforming growth factor-alpha might be synthesized by placental cells and act through an autocrine mechanism to influence functioning of placental cells in vivo.

STUDY DESIGN

Human placentas from early, mid, and late gestations were analyzed for transforming growth factor-alpha and epidermal growth factor messenger ribonucleic acid and proteins. Polyadenylic acid-positive ribonucleic acid was isolated from placentas from 10, 11, 13, 21, 32, 38, 39, and 40 weeks of gestation and analyzed by Northern analysis for hybridization with complementary deoxyribonucleic acid probes specific for epidermal growth factor or transforming growth factor-alpha. Levels of immunoreactive epidermal growth factor and transforming growth factor-alpha were measured by specific radioimmunoassays in pools of placentas from early, mid, and late gestations, and levels of epidermal growth factor and transforming growth factor-alpha receptor-active protein were measured by radioreceptor assay.

RESULTS

All placentas had a strong transforming growth factor-alpha hybridization band at 4.5 kb and a weak epidermal growth factor hybridization band at 5.2 kb. High levels of transforming growth factor-alpha immunoreactive protein (90 to 180 ng/mg protein) and low levels of immunoreactive epidermal growth factor (3 to 9 pg/mg protein) were detected in pools of placentas from early, mid, and late gestations. High levels of epidermal growth factor and transforming growth factor-alpha receptor-active protein (250 ng/mg protein) were also detected.

CONCLUSION

Human placentas contain relatively high levels of immunoreactive and receptor-active transforming growth factor-alpha, as well as transforming growth factor-alpha messenger ribonucleic acid, throughout gestation. This finding suggests that transforming growth factor-alpha may act by an autocrine system to influence human placental cell function in vivo.

Production of transforming growth factor-alpha by normal rat small intestine

Transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF) are similar in structure and biological activity. In the present study, the distributions of TGF-alpha mRNA, TGF-alpha immunoreactivity, and TGF-alpha-EGF receptor mRNA were examined in epithelial and nonepithelial compartments of the jejunum, and the effect of TGF-alpha on growth of a jejunal crypt cell line (IEC-6) was determined. Epithelial cells eluted from the rat jejunal cryptvillus axis expressed TGF-alpha mRNA at twofold higher levels in the villus tip than in the crypt and EGF receptor mRNA at sevenfold higher levels in the villus tip. Expression of these two mRNA transcripts in the subepithelium was low. Immunohistochemical staining showed TGF-alpha immunoreactivity predominantly in the epithelium and muscularis. Immunostaining of villus cells was uniform, whereas crypt cells did not stain. IEC-6 cells bound 125I-EGF to a single class of high-affinity (dissociation constant = 833 pM) receptors. EGF and TGF-alpha (10 ng/ml) only modestly stimulated IEC-6 cell growth in the presence of 5% serum but increased expression of the protooncogenes c-jun and c-myc threefold over control cells. These findings suggest that, among the potential physiological roles for TGF-alpha produced by the jejunal epithelium, promotion of cell migration and modulation of fluid and electrolyte transport may be as relatively important as stimulation of cell proliferation.

Duodenal ulcer. Discovery of a new mechanism and development of angiogenic therapy that accelerates healing

The complete purification of the first angiogenic molecule, basic fibroblast growth factor (bFGF), was carried out in the authors' laboratory in 1983. Application of this peptide to chronic wounds enhances angiogenesis and accelerates wound healing. The authors showed that an acid-stable form of bFGF (i.e., bFGF-CS23) could be administered orally to rats with duodenal ulcers. The peptide promoted a ninefold increase of angiogenesis in the ulcer bed and accelerated ulcer healing more potently than cimetidine. Basic fibroblast growth factor did not reduce gastric acid. The authors now show that bFGF exists as a naturally occurring peptide in rat and human gastric and duodenal mucosa. This endogenous bFGF is present also in the bed of chronic ulcers in rats. Sucralfate binds bFGF and protects it from acid degradation. The sucralfate is angiogenic, based on its affinity for bFGF. When sucralfate is administered orally to rats, it significantly elevates the level of bFGF in the ulcer bed. Cimetidine, by its capacity to reduce gastric acid, also elevates bFGF in the ulcer bed. A hypothetical model is proposed in which prevention of ulcer formation or accelerated healing of ulcers by conventional therapies may be FGF dependent. Acid-stable bFGF-CS23 may be considered as a form of replacement therapy in the treatment of duodenal ulcers.

Mapping the receptor-recognition site of human transforming growth factor-alpha

The receptor-recognition site human transforming growth factor-alpha (TGF alpha), a 50-residue tricyclic peptide with three disulfide bonds, was mapped by a set of 46 peptide analogs consisting of linear, monocyclic, bicyclic, and tricyclic structures representing individual and overlapping subdomains of human TGF alpha. Linear overlapping fragments ranging from 7 to 18 residues and spanning the entire length of TGF alpha as well as monocyclic analogs with one disulfide linkage were found to be inactive in both receptor-binding and mitogenic assays. Bicyclic analogs with two disulfide linkage and representing either the amino or carboxyl two-thirds of TGF alpha showed low activity at 0.1-0.9 mM concentrations. Tricyclic analogs containing all three disulfide linkages but lacking either the amino or carboxyl terminal heptapeptide was, respectively, 3% and 0.1% as active as TGF alpha. These results show that determinants for the receptor binding cannot be represented by a short continuous fragment or a single subdomain, but are located on a discontinuous surface on a folded structure with disulfide restraints. Furthermore, these results when combined with our previous results which shows that the middle subdomain (second disulfide loop) is not involved in the receptor binding suggest that the receptor-binding residues are constituted of three fragments located at the first and third subdomains as well as the external carboxyl peptide.

Growth factors and pancreatic cancer

Cultured human pancreatic cancer cells produce a number of growth factors, including transforming growth factor-alpha (TGF-alpha). These cells also overexpress the epidermal growth factor (EGF) receptor and exhibit a parallel increase in EGF receptor mRNA levels. TGF-alpha, which binds to the EGF receptor, is more potent than EGF in enhancing the anchorage-independent growth of several pancreatic cancer cell lines, including T3M4 cells. In contrast, EGF is more efficient than TGF-alpha with respect to EGF receptor downregulation and tyrosine phosphorylation in T3M4 cells. Further, T3M4 cells recycle EGF, but markedly degrade TGF-alpha. It is suggested that the production of multiple growth factors, the overexpression of the EGF receptor, the recycling of EGF, and the attenuated ability of TGF-alpha to downregulate the EGF receptor combine to enhance the growth advantage of human pancreatic cancer cells.

A GC-rich element confers epidermal growth factor responsiveness to transcription from the gastrin promoter

Epidermal growth factor (EGF) and transforming growth factor alpha are important determinants of mucosal integrity in the gastrointestinal tract, and they act both directly and indirectly to prevent ulceration in the stomach. Consistent with this physiological role, EGF stimulates transcription of gastrin, a peptide hormone which regulates gastric acid secretion and mucosal growth. EGF stimulation of gastrin transcription is mediated by a GC-rich gastrin EGF response element (gERE) (GGGGCGGGGTGGGGGG) which lies between -54 and -68 in the human gastrin promoter. The gERE sequence also confers weaker responsiveness to phorbol ester stimulation. The gERE sequence differs from previously described EGF response elements. The gERE DNA sequence specifically interacts with a GH4 DNA-binding protein distinct from previously described transcription factors (Egr-1 and AP2) which bind GC-rich sequences and mediate transcriptional activation by growth factors. Furthermore, the gERE element does not bind the Sp1 transcription factor even though the gERE sequence contains a high-affinity Sp1-binding site (GGCGGG).

A GC-rich element confers epidermal growth factor responsiveness to transcription from the gastrin promoter

Epidermal growth factor (EGF) and transforming growth factor alpha are important determinants of mucosal integrity in the gastrointestinal tract, and they act both directly and indirectly to prevent ulceration in the stomach. Consistent with this physiological role, EGF stimulates transcription of gastrin, a peptide hormone which regulates gastric acid secretion and mucosal growth. EGF stimulation of gastrin transcription is mediated by a GC-rich gastrin EGF response element (gERE) (GGGGCGGGGTGGGGGG) which lies between -54 and -68 in the human gastrin promoter. The gERE sequence also confers weaker responsiveness to phorbol ester stimulation. The gERE sequence differs from previously described EGF response elements. The gERE DNA sequence specifically interacts with a GH4 DNA-binding protein distinct from previously described transcription factors (Egr-1 and AP2) which bind GC-rich sequences and mediate transcriptional activation by growth factors. Furthermore, the gERE element does not bind the Sp1 transcription factor even though the gERE sequence contains a high-affinity Sp1-binding site (GGCGGG).

Potential role of the epidermal growth factor receptor in human pancreatic cancer

The epidermal growth factor (EGF) receptor is a transmembrane protein that has tyrosine kinase activity. It is activated by both EGF and transforming growth factor-alpha (TGF-alpha). Human pancreatic cancer cells overexpress the EGF receptor and exhibit a parallel increase in EGF receptor mRNA without a detectable increase in the number of gene copies coding for the receptor. These cells also produce TGF-alpha and are capable of binding exogenous TGF-alpha. They often recycle EGF, but markedly and rapidly degrade TGF-alpha. However, TGF-alpha is 10-100-fold more potent than EGF in enhancing their anchorage-independent growth. Both growth factors induce EGF receptor down-regulation, but EGF is more efficient than TGF-alpha in this regard. The concomitant overexpression of the EGF receptor and production of TGF-alpha, the recycling of EGF, and the attenuated ability of TGF-alpha to down-regulate the EGF receptor may combine to provide a distinct growth advantage to human pancreatic cancer cells.