Gastric Mucosal Repair Research Articles

Helicobacter suis affects the health and function of porcine gastric parietal cells.

The stomach of pigs at slaughter age is often colonized by Helicobacter (H.) suis, which is also the most prevalent gastric non-H. pylori Helicobacter (NHPH) species in humans. It is associated with chronic gastritis, gastric ulceration and other gastric pathological changes in both hosts. Parietal cells are highly specialized, terminally differentiated epithelial cells responsible for gastric acid secretion and regulation. Dysfunction of these cells is closely associated with gastric pathology and disease. Here we describe a method for isolation and culture of viable and responsive parietal cells from slaughterhouse pigs. In addition, we investigated the interactions between H. suis and gastric parietal cells both in H. suis-infected six-month-old slaughter pigs, as well as in our in vitro parietal cell model. A close interaction of H. suis and parietal cells was observed in the fundic region of stomachs from H. suis positive pigs. The bacterium was shown to be able to directly interfere with cultured porcine parietal cells, causing a significant impairment of cell viability. Transcriptional levels of Atp4a, essential for gastric acid secretion, showed a trend towards an up-regulation in H. suis positive pigs compared to H. suis-negative pigs. In addition, sonic hedgehog, an important factor involved in gastric epithelial differentiation, gastric mucosal repair, and stomach homeostasis, was also significantly up-regulated in H. suis positive pigs. In conclusion, this study describes a successful approach for the isolation and culture of porcine gastric parietal cells. The results indicate that H. suis affects the viability and function of this cell type.

Caveolin-1 enhances rapid mucosal restitution by activating TRPC1-mediated Ca2+ signaling.

Early rapid mucosal restitution occurs as a consequence of epithelial cell migration to reseal superficial wounds, a process independent of cell proliferation. Our previous studies revealed that the canonical transient receptor potential‐1 (TRPC1) functions as a store‐operated Ca2+ channel (SOCs) in intestinal epithelial cells (IECs) and regulates epithelial restitution after wounding, but the exact mechanism underlying TRPC1 activation remains elusive. Caveolin‐1 (Cav1) is a major component protein that is associated with caveolar lipid rafts in the plasma membrane and was recently identified as a regulator of store‐operated Ca2+ entry (SOCE). Here, we showed that Cav1 plays an important role in the regulation of mucosal restitution by activating TRPC1‐mediated Ca2+ signaling. Target deletion of Cav1 delayed gastric mucosal repair after exposure to hypertonic NaCl in mice, although it did not affect total levels of TRPC1 protein. In cultured IECs, Cav1 directly interacted with TRPC1 and formed Cav1/TRPC1 complex as measured by immunoprecipitation assays. Cav1 silencing in stable TRPC1‐transfected cells by transfection with siCav1 reduced SOCE without effect on the level of resting [Ca2+]cyt. Inhibition of Cav1 expression by siCav1 and subsequent decrease in Ca2+ influx repressed epithelial restitution, as indicated by a decrease in cell migration over the wounded area, whereas stable ectopic overexpression of Cav1 increased Cav1/TRPC1 complex, induced SOCE, and enhanced cell migration after wounding. These results indicate that Cav1 physically interacts with and activates TRPC1, thus stimulating TRPC1‐mediated Ca2+ signaling and rapid mucosal restitution after injury.

Cytoprotective effects of hydrogen sulfide in novel rat models of non-erosive esophagitis.

Non-erosive esophagitis is a chronic inflammatory condition of the esophagus and is a form of gastroesophageal reflux disease. There are limited treatment options for non-erosive esophagitis, and it often progresses to Barrett’s esophagus and esophageal carcinoma. Hydrogen sulfide has been demonstrated to be a critical mediator of gastric and intestinal mucosal protection and repair. However, roles for H2S in esophageal mucosal defence, inflammation and responses to injury have not been reported. We therefore examined the effects of endogenous and exogenous H2S in rat models of non-erosive esophagitis. Mild- and moderate-severity non-erosive esophagitis was induced in rats through supplementation of drinking water with fructose, plus or minus exposure to water-immersion stress. The effects of inhibitors of H2S synthesis or of an H2S donor on severity of esophagitis was then examined, along with changes in serum levels of a pro- and an anti-inflammatory cytokine (IL-17 and IL-10, respectively). Exposure to water-immersion stress after consumption of the fructose-supplemented water for 28 days resulted in submucosal esophageal edema and neutrophil infiltration and the development of lesions in the muscular lamina and basal cell hyperplasia. Inhibition of H2S synthesis resulted in significant exacerbation of inflammation and injury. Serum levels of IL-17 were significantly elevated, while serum IL-10 levels were reduced. Treatment with an H2S donor significantly reduced the severity of esophageal injury and inflammation and normalized the serum cytokine levels. The rat models used in this study provide novel tools for studying non-erosive esophagitis with a range of severity. H2S contributes significantly to mucosal defence in the esophagus, and H2S donors may have therapeutic value in treating esophageal inflammation and injury.

IL-11 is a parietal cell cytokine that induces atrophic gastritis

Background and AimsIL-is important in gastric damage, mucosal repair and gastric cancer progression. We analysed IL-11 expression in H.pylori infected mouse stomach, the site of gastric IL-11 expression in mice...

Sulforaphane Enhances Protection and Repair of Gastric Mucosa Against Oxidative stress In Vitro, and Demonstrates Anti-inflammatory Effects on Helicobacter pyloriInfected Gastric Mucosae in Mice and Human Subjects

Helicobacter pylori infection induces oxidative stress on gastric mucosa, thereby causing mucosal damage, retarding mucosal repair, and eventually inducing gastric cancer. Cells can survive against chronic oxidative stress by enhancing activities of antioxidant enzymes, thereby protecting cells from DNA damage. Recent studies have clearly shown that the genes encoding nrf2 (NF-E2 p45-related factor-2) and keap1 (Kelch-like ECH-associated protein 1) play an important role in the induction of antioxidant enzymes against oxidative stress. In this paper, we will first describe the cellular mechanisms by which the nrf2-keap1 system contributes to induction of a variety of antioxidant enzymes during exposure to oxidative stress. Secondly, we will also mention beneficial effects of a natural compound sulforaphane, an isothiocyanate family, rich in broccoli sprouts, on gastric mucosa. Sulforaphane stimulates nrf2 gene-dependent antioxidant enzyme activities, thereby protecting cells from oxidative injury. Finally, we will show our data on the effect of sulforaphane, a natural chemical compound rich in broccoli sprouts, on protection and repair of gastric mucosa against oxidative stress, and anti-inflammatory effects on gastric mucosa during H. pylori infection, which appears to be closely related to chemoprotection against gastric cancer induced by .H. pylori-infection.

Gastric mucosal injury activates bFGF gene expression and triggers preferential translation of high molecular weight bFGF isoforms through CUG-initiated, non-canonical codons

Basic fibroblast growth factor (bFGF or FGF-2) is a pleiotropic growth factor that promotes growth of mesenchymal and epithelial cells, stimulates angiogenesis and neuroprotection. Moreover, exogenous bFGF by stimulating angiogenesis promotes healing of gastroduodenal ulcers and cardiac and brain injury. All these actions were demonstrated in regard to 18kDa bFGF isoform that is secreted by cells via an ER/Golgi-independent pathway and activates FGF receptors. However in some transformed and stressed cells and in some tissues (e.g. brain) the single copy bFGF gene encodes multiple gene products: 18kDa and also higher molecular weight (HMW) bFGF isoforms: ∼21 and ∼22kDa in rodents, and ∼22, ∼23 and ∼24kDa in humans. The biologic roles of these HMW bFGF isoforms in vivo remain unknown. In this study we demonstrated that in normal, uninjured gastric mucosa, bFGF is almost exclusively expressed as 18kDa isoform translated through a classical AUG (methionine) codon. In contrast, in injured gastric mucosa of rat, bFGF gene is preferentially translated to HMW bFGF isoforms through alternative CUG (leucine) initiation codon. Gastric mucosal injury caused in rats a significant increase in bFGF mRNA at 8 and 24h vs. normal mucosa and a significant increase in bFGF protein at 24–72h, mainly due to increased expression of ∼21 and ∼22kDa HMW bFGF isoforms. This is first demonstration that gastric mucosal injury and repair triggers local activation of bFGF gene with preferential translation of HMW bFGF isoforms through a non-canonical CUG codon. This study uncovered CUG-initiated HMW bFGF translation as a novel regulatory mechanism operating in vivo during gastric injury repair.

Muc-2–Deficient Mice Display a Sex-Specific, COX-2–Related Impairment of Gastric Mucosal Repair

Mucus is known to contribute significantly to the prevention and repair of mucosal damage throughout the gastrointestinal tract. Although not normally expressed in the stomach, mucin-2 (MUC-2, encoded by the MUC2 gene) is expressed in certain disease states. The aim of this study was to determine in a mouse model whether the absence of Muc-2 would result in impaired susceptibility to and healing of gastric mucosal injury. Acute gastric damage was induced in mice deficient in Muc-2 and in wild-type controls, through oral administration of indomethacin. Chronic gastric ulcers were induced by serosal application of acetic acid. The extent of injury and the extent of healing of the damage over time were examined in both models. Indomethacin administration caused similar levels of gastric damage in Muc-2-deficient and wild-type mice, but the erosions healed more slowly in the former. Acetic acid-induced gastric ulcers were initially similar in size in Muc-2-deficient and wild-type mice of both sexes, but ulcer healing was significantly impaired in male Muc-2-deficient mice. Induction of cyclooxygenase-2 in the stomach, in response to indomethacin- or acetic acid-induced ulceration, was significantly reduced in male Muc-2-deficient mice. This phenomenon, and the sex specificity, was also apparent in bone marrow-derived macrophages stimulated with endotoxin. These results demonstrate a marked impairment of gastric mucosal repair in male Muc-2-deficient mice that may be related to an insufficient induction of cyclooxygenase-2, an enzyme known to contribute to mucosal repair.

Pathogenetic effects of salted pork in an area of China with high-risk for stomach cancer.

To study the pathogenetic effects of salted pork (SP) (a special food in Zhuanghe City, a region of northern China that is a high-risk area for stomach cancer) on stomach cancer, and a provide scientific basis for the primary prevention of stomach cancer in this high-risk region. This study consisted of three distinct parts. The first part involved a study of SP mutagenicity and employed both the Ames test and micronuclei assay using V79 cells. The second part included a study of SP's effect on the gastric mucosa of residents in the Zhuanghe area who had consumed SP for more than ten years. Additionally, these studies involved an analysis of the dose effect relationship between SP and pathological changes in gastric mucosa, with a total of 300 cases analyzed. The third part of this study involved an observation of the mucosal lesions from experimental dogs by both gastroscopy and mucosal biopsy. Six healthy male dogs were selected, three were fed with SP, and the others served as controls. This study revealed that SP extract could mutate Salmonella typhimurium TA98 and induce an increase in both the micro nuclei rate (MNR) and micro nuclei cell rate (MNCR) of V79 at a dose range of 20-80 μL/mL. There were significant dose-effect relations between SP and either MNR or MNCR. Pathological changes in the gastric mucosa of local residents who had consumed SP were significantly different from those of the control group. In people who had consumed SP for ten years, mucosal lesions were found that contained evidence of necrosis and erosion; In those who consumed SP for ten-20 years, both hyperplasia and dysplasia were seen in addition to the above lesions. In individuals who had consumed SP for 20-30 years, severe dysplasia and malignant changes were found. Furthermore, SP had damaging effect on the gastric mucosa of dogs that were fed SP. The mucosal lesions became more severe with increased feeding time. SP is a strong mutagen and long-term SP exposure may result in repeated gastric mucosal damage and repair, ultimately leading to severe dysplasia and malignancy.

Tocotrienol and Growth Factors In Acute Gasrtic Mucosal Injury

Gastric mucosal damage caused by nonsteroidal anti‐inflammatory drugs is recognized as the most serious adverse reaction for this drug class and has been the stimulus for research aimed at developing more effective gastroprotective drugs. Transforming growth factor alpha (TGFa) and epidermal growth factor (EGF), basic fibroblast growth factor (bFGF) are crucial in the regulation for reconstruction of damaged mucosal structures. We have previously shown that tocotrienol (T3) improved NSAID‐induced AGML. The present study aims to assess the effect of pretreatment of rats, exposed to a single dose of NSAID on the expression of growth factors, with T3. After 8 weeks, they were administered with a single dose of indomethacin. Six hours post insult, measurements of TGF‐α, bFGF, EGF‐R and ERK‐1 were done. There was a significant increase in the TGF‐α, bFGF, EGF‐R and ERK‐1 content the gastric mucosa of rats treated with T3 but not in rats without T3. This findings demonstrated that T3 rapidly stimulated the growth factors involved in cell proliferation and migration through involvement of EGF‐R‐ MAP and Erk1 kinase. We conclude T3 may potentially accelerate healing of AGML through higher expression of growth factors, related receptor and kinase involved in gastric mucosal repair. Source of research fund: Ministry of Science, Technology and Innovation, Malaysia IRPA 06‐02‐02‐0052‐ EA246.

Investigation of doublecortin and calcium/calmodulin‐dependent protein kinase‐like‐1‐expressing cells in the mouse stomach

For lack of a definite stem cell marker, there is limited knowledge of the precise location and fate of stem cells after injury. Doublecortin and calcium/calmodulin-dependent protein kinase-like-1 (DCAMKL-1) is a putative intestinal and colon stem cell marker. Our aim was to identify DCAMKL-1-expressing cells in the gastric epithelium and to analyze the fate of DCAMKL-1-expressing cells during gastric mucosal injury and repair. Acidified ethanol was administered to wild-type mice. DCAMKL-1 expression were detected by immunohistochemistry and western blotting. There were some DCAMKL-1-expressing cells in normal mouse stomachs. All the cells were located in the gastric isthmus region. All DCAMKL-1-expressing cells were double stained with Dolichos biflorus lectin-expressing parietal cells and Musashi-1-expressing cells. The DCAMKL-1 antigen expression decreased 12 h after injury and gradually increased to normal 4 d after injury. Using DCAMKL-1 as a marker for stomach stem cells, we could describe the expression pattern of stomach stem cells during mucosal injury.

Burdock Essence Promotes Gastrointestinal Mucosal Repair in Ulcer Patients

Peptic ulcer is a common gastrointestinal disease and produces mucosa erosion. The current study assessed the ability of burdock essence to repair gastrointestinal mucosa in clinical trials. In the experimental group, two tablets of burdock essence (500 mg/tablet) were administered three times a day after meals and a placebo was administered in controls. Four weeks after drug administration, the subjects in the study underwent an assessment for the efficacy of burdock essence as health supplements before and after administration of the drug. The presence of gastric mucosal lesions was determined in all of the peptic ulcer patients using electronic endoscopy before and after taking burdock essence. A rapid urease test on tissue samples from ulcers was conducted to verify Helicobacter pylori infection. Endoscopy confirmed gastric or duodenal ulcers in 30 patients. In clinical trials of 27 patients, 20 patients took burdock essence; 17 (85%) recovered completely and three (15%) did not. Of the seven patients who took placebos, five (71%) did not completely recover and two (29%) recovered. In the experimental group, the ulcer wounds of the three patients who had taken burdock essence did not completely heal, but wounds were reduced in size by 30%, 75%, and 33%. Moreover, 10 out of 11 patients who originally were positive for H. pylori infections no longer had the pathogen by the end of the trial. These results indicate that burdock essence has an inhibitory effect on H. pylori . This study confirms that two tablets (500 mg/tablet) of burdock essence taken orally three times a day after meals can help abolish H. pylori infection and promote the therapeutic effect of conventional medication on gastric mucosal repair in gastrointestinal ulcer patients.

Involvement of constitutive nitric oxide synthase in ghrelin-induced cytosolic phospholipase A2 activation in gastric mucosal cell protection against ethanol cytotoxicity

Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, is an important regulator of nitric oxide synthase (NOS) and cyclooxygenase (COX) enzyme systems, the products of which are of major significance to the processes of gastric mucosal defense and repair. Here, using primary culture of rat gastric mucosal cells, we report on the mechanism of ghrelin protection against ethanol cytotoxicity. We show that the protective effect of ghrelin was associated with the increase in NO and PGE2 production, and characterized by a marked up-regulation in cytosolic phospholipase A(2) (cPLA(2)) activity and arachidonic acid (AA) release. The loss in countering effect of ghrelin on the ethanol cytotoxicity was attained with constitutive NOS (cNOS) inhibitor, L-NAME, as well as indomethacin and a specific COX-1 inhibitor, SC-560, while specific COX-2 inhibitor, NS-398, and a selective inducible NOS (iNOS) inhibitor, 1400W, had no effect. The effect of L-NAME was reflected in the inhibition of ghrelin-induced mucosal cell capacity for NO production, cPLA(2) activation, and PGE2 generation, whereas indomethacin caused only the inhibition in PGE2 generation. Moreover, the ghrelin-induced up-regulation in AA release was reflected in the cPLA(2) enzyme protein phosphorylation and S-nitrosylation. Preincubation with L-NAME resulted in the inhibition of the ghrelin-induced S-nitrosylation, whereas the ERK inhibitor, PD98059, caused the blockage in cPLA(2) protein phosphorylation as well as S-nitrosylation. The findings demonstrate that ghrelin protection of gastric mucosa against ethanol cytotoxicity involves cNOS-derived NO induction of cPLA(2) activation for the increase in PGE2 synthesis. This activation process apparently includes the cPLA(2) phosphorylation followed by S-nitrosylation.

Roles of NADPH Oxidase in Occurrence of Gastric Damage and Expression of Cyclooxygenase-2 During Ischemia/Reperfusion in Rat Stomachs

NADPH oxidase is an enzyme that converts molecular oxygen into reactive oxygen species, which cause severe damage in several organs. Cyclooxygenase (COX)-2 is an inducible enzyme that is important in gastric mucosal defense and repair processes. It is unclear whether NADPH oxidase is related to COX expression in the gastric mucosa, so we investigated the correlation. Under urethane anesthesia, a male Sprague Dawley rat stomach was mounted in an ex-vivo chamber, and ischemia/reperfusion (I/R) was performed through a cannula in the femoral vein. I/R significantly increased NADPH oxidase activity, H2O2 production, and myeloperoxidase (MPO) activity. In contrast, ischemia alone clearly enhanced both NADPH oxidase activity and H2O2 production but not MPO activity. Pretreatment with the NADPH oxidase inhibitor diphenylene iodonium (DPI) suppressed I/R-induced mucosal damage. On the other hand, the selective COX-2 inhibitor rofecoxib exhibited a tendency to enhance the severity of gastric damage induced by I/R, although the selective COX-1 inhibitor SC-560 and the nonselective COX inhibitor indomethacin had no effect. I/R also increased the expression of COX-2, and this increase was suppressed by pretreatment with DPI. These findings suggest that the increase in NADPH oxidase activity is involved in the occurrence of gastric mucosal damage induced by I/R and that this enzyme activity may be causally related to the upregulation of COX-2 during I/R.

Leptin-induced cytosolic phospholipase A2 activation in gastric mucosal protection against ethanol cytotoxicity involves epidermal growth factor receptor transactivation

A pluripotent cytokine, leptin, released locally within the mucosal tissue is an important mediator of the processes of gastric mucosal defense and repair. Here, we report that leptin protection of gastric mucosal cells against ethanol cytotoxicity requires epidermal growth factor receptor (EGFR) participation. We show that the protective effect of leptin against ethanol cytotoxicity was associated with the increased EGFR and cPLA(2) phosphorylation, and characterized by a marked increase in arachidonic acid (AA) release and prostaglandin (PGE(2)) generation. The loss in countering capacity of leptin on the ethanol-induced cytotoxicity was attained with Src kinase inhibitor, PP2, and EGFR kinase inhibitor, AG1478, as well as ERK inhibitor, PD98059. Moreover, all three agents evoked also the inhibition in leptin-induced upregulation in cPLA(2) activity, AA release, and PGE(2) generation. Furthermore, changes caused by leptin in EGFR phosphorylation and cPLA(2) activation were susceptible to suppression by GM6001, a metalloprotease inhibitor of membrane-anchored EGFR ligand cleavage. These findings disclose an important link between leptin-induced and Src kinase-mediated EGFR transactivation and the activation of cytosolic phospholipase A(2) that leads to up-regulation in PGE2 production, thus providing new insights into the mechanism of gastric mucosal protection by leptin.

Dynamic physiological and molecular changes in gastric ulcer healing achieved by melatonin and its precursor L‐tryptophan in rats

Following induction of gastric ulcer in rats by serosal application of acetic acid, local mucosal necrosis ensues accompanied by a reduction in mucosal microcirculation and by almost immediate expression of inducible nitric oxide (NO) synthase (iNOS) and proinflammatory cytokines. Daily application of melatonin (20 mg/kg) or l-tryptophan (100 mg/kg) accelerates ulcer healing by affecting the cyclooxygenase-2 (COX-2)-prostaglandin (PG) system with excessive production of protective PG, especially in later period of ulcer healing. Furthermore, expression of hypoxia inducible factor, vascular-endothelial growth factor, an activation of cNOS-NO system and the stimulation of sensory nerves with the expression and release of calcitonin gene related peptide (CGRP) appear to aid the restoration of mucosal repair and microcirculation in the ulcer bed. The enhanced expression of the melatonin MT(2) receptors (MT(2)-R) combined with overexpression of key enzymes involved in biosynthesis of melatonin such as N-acetyltransferase and hydroxyindole-O-methyltransferase contribute to the acceleration of ulcer healing by this indole. Melatonin-induced acceleration of ulcer healing is also mediated by release of gastrin and ghrelin, the most potent stimulants of gastric mucosal cell proliferation and mucosal repair. These sequential steps in ulcer healing accelerated by melatonin can be interfered with by the blockade of MT(2)R, COX-2/PG and cNOS/NO systems, and by reduction in the inflammatory iNOS/NO system. Thus, melatonin and its precursor l-tryptophan, trigger the cascade of molecular events leading to the functional improvement in ulcer healing.

S1651 IL-6 Signalling Plays a Crucial Role in Repair of Gastric Mucosa After Ulceration By Regulation of the Reg and MMP Gene Families

S1651 IL-6 Signalling Plays a Crucial Role in Repair of Gastric Mucosa After Ulceration By Regulation of the Reg and MMP Gene Families

S1624 Mesenchymal Stem Cells Transplantation Accelerates Gastric Ulcer Healing in Rats

of MT and Trp. Furthermore, treatment with MT and Trp suppressed the expression of mRNAs for proinflammatory cytokines in ulcer area, but failed to affect the expression of HIF-1α and VEGF. Conclusions: MT promotes ulcer healing. This effect is mediated by suppression of proinflammatory cytokines and release of gastrin and PGE2 , the most potent stimulants of gastric mucosal cell proliferation and mucosal repair. Ulcer healing effects of MT can be interfered by the inhibition of MT2R and COX-2-PG or NOS-NO system.

Extracellular signal-regulated kinase 1- and 2-mediated gastric mucosal injury and repair in gastric ischemia–reperfusion of rats

The current study was undertaken to investigate the time course of gastric ischemia-reperfusion (GI-R)-induced gastric mucosal injury and repair and whether extracellular signal-regulated kinase 1/2 (ERK1/2) were involved in GI-R-induced gastric mucosal injury and repair. Immunohistochemistry and Western blot analyses were used. Gastric mucosal injury induced by ischemia alone was mild. However, the injury worsened after reperfusion, reaching a maximum at 1 h, and was accompanied by increased apoptotic cells and decreased proliferative cells. Then, the gastric mucosal cells began to repair the injury by enhanced proliferation, which peaked at 24 h after reperfusion, and by 72 h the damaged gastric mucosa was mostly repaired. The ERK1/2 (nonactivated ERK1/2) protein expression level and distribution profile showed no significant changes during the entire reperfusion phase, but the p-ERK1/2 (activated ERK1/2) level changed dramatically. The p-ERK1/2 protein level was decreased at 0.5 h after reperfusion began, and then gradually increased, peaking after 3 h of reperfusion; these changes in p-ERK1/2 occurred simultaneously in the cytoplasm and nucleus. On the other hand, inhibition of the activation of ERK1/2, induced by PD98059, a specific ERK1/2 upstream inhibitor, aggravated the gastric mucosal injury, and apoptosis was increased and proliferation was reduced in the gastric mucosal cells after the same duration of reperfusion. Serious gastric mucosal damage involving apoptotic cells occurred rapidly at an early stage of reperfusion and was closely related to the suppression of ERK1/2 activation. The activated ERK1/2 signaling transduction pathway played an important role. Activated ERK1/2 participated in the regulation of gastric mucosal injury and repair induced by GI-R, and might be mediated by the inhibition of apoptosis and the promotion of proliferation in gastric mucosal cells.

Hedgehog signaling pathway and gastrointestinal stem cell signaling network (Review)

Hedgehog, BMP/TGFbeta, FGF, WNT and Notch signaling pathways constitute the stem cell signaling network, which plays a key role in a variety of processes, such as embryogenesis, maintenance of adult tissue homeostasis, tissue repair during chronic persistent inflammation, and carcinogenesis. Sonic hedgehog (SHH), Indian hedgehog (IHH) and Desert hedgehog (DHH) bind to PTCH1/PTCH or PTCH2 receptor to release Smoothened (SMO) signal transducer from Patched-dependent suppression. SMO then activates STK36 serine/threonine kinase to stabilize GLI family members and to phosphorylate SUFU for nuclear accumulation of GLI. Hedgehog signaling activation leads to GLI-dependent transcriptional activation of target genes, such as GLI1, PTCH1, CCND2, FOXL1, JAG2 and SFRP1. GLI1-dependent positive feedback loop combined with PTCH1-dependent negative feedback loop gives rise to transient proliferation of Hedgehog target cells. Iguana homologs (DZIP1 and DZIP1L) and Costal-2 homologs (KIF7 and KIF27) are identified by comparative integromics. SHH-dependent parietal cell proliferation is implicated in gastric mucosal repair during chronic Helicobacter pylori infection. BMP-RUNX3 signaling induces IHH expression in surface differentiated epithelial cells of stomach and intestine. Hedgehog signals from epithelial cells then induces FOXL1-mediated BMP4 upregulation in mesenchymal cells. Hedgehog signaling is frequently activated in esophageal cancer, gastric cancer and pancreatic cancer due to transcriptional upregulation of Hedgehog ligands and epigenetic silencing of HHIP1/HHIP gene, encoding the Hedgehog inhibitor. However, Hedgehog signaling is rarely activated in colorectal cancer due to negative regulation by the canonical WNT signaling pathway. Hedgehog signaling molecules or targets, such as SHH, IHH, HHIP1, PTCH1 and GLI1, are applied as biomarkers for cancer diagnostics, prognostics and therapeutics. Small-molecule inhibitors for SMO or STK36 are suitable to be used for treatment of Hedgehog-dependent cancer.

Peroxisome proliferator-activated receptor γ (PPARγ) regulates trefoil factor family 2 (TFF2) expression in gastric epithelial cells

Although trefoil factor family 2 (TFF2) plays a critical role in the defense and repair of gastric mucosa, the regulatory mechanism of TFF2 expression is not fully understood. In this study, we investigated the regulation of TFF2 expression by peroxisome proliferator-activated receptor γ (PPARγ) in gastric epithelial cells. MKN45 gastric cells were used. TFF2 mRNA expression was analyzed by real-time quantitative RT-PCR. The promoter sequence of the human TFF2 gene was cloned into pGL3-basic vector for reporter gene assays. Ciglitazone was mainly used as a specific PPARγ ligand. MKN45 cells expressed functional PPARγ proteins. Endogenous TFF2 mRNA expression and TFF2 reporter gene transcription was significantly up-regulated by ciglitazone in a dose-dependent manner. Reporter gene assays showed that two distinct cis-elements are involved in the response to PAPRγ activation. Within one of these element (nucleotides −558 to −507), we identified a functional peroxisome proliferator responsive element (PPRE) at −522 (5′-GGGACAAAGGGCA-3′). Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assay confirmed the binding of PPARγ to this sequence. Another element (nucleotides −407 to −358) appeared to be a composite enhancer element indirectly regulated by PPARγ and a combination of these two cis-elements was required for the full response of the human TFF2 gene expression to PPARγ. These data demonstrate that human TFF2 gene is a direct target of PPARγ in gastric epithelial cells. Since TFF2 is a critical gastroprotective agent, PPARγ may be involved in the gastric mucosal defense through regulating TFF2 expression in humans.