Integrative roles of transforming growth factor-alpha in the cytoprotection mechanisms of gastric mucosal injury

Gut homeostasis, injury, and healing: New therapeutic targets

The integrity of the gastrointestinal mucosa plays a crucial role in gut homeostasis, which depends upon the balance between mucosal injury by destructive factors and healing via protective factors. The persistence of noxious agents such as acid, pepsin, nonsteroidal anti-inflammatory drugs, or Helicobacter pylori breaks down the mucosal barrier and injury occurs. Depending upon the size and site of the wound, it is healed by complex and overlapping processes involving membrane resealing, cell spreading, purse-string contraction, restitution, differentiation, angiogenesis, and vasculogenesis, each modulated by extracellular regulators. Unfortunately, the gut does not always heal, leading to such pathology as peptic ulcers or inflammatory bowel disease. Currently available therapeutics such as proton pump inhibitors, histamine-2 receptor antagonists, sucralfate, 5-aminosalicylate, antibiotics, corticosteroids, and immunosuppressants all attempt to minimize or reduce injury to the gastrointestinal tract. More recent studies have focused on improving mucosal defense or directly promoting mucosal repair. Many investigations have sought to enhance mucosal defense by stimulating mucus secretion, mucosal blood flow, or tight junction function. Conversely, new attempts to directly promote mucosal repair target proteins that modulate cytoskeleton dynamics such as tubulin, talin, Ehm², filamin-a, gelsolin, and flightless I or that proteins regulate focal adhesions dynamics such as focal adhesion kinase. This article summarizes the pathobiology of gastrointestinal mucosal healing and reviews potential new therapeutic targets.

Annexin A1, formyl peptide receptor, and NOX1 orchestrate epithelial repair

N-formyl peptide receptors (FPRs) are critical regulators of host defense in phagocytes and are also expressed in epithelia. FPR signaling and function have been extensively studied in phagocytes, yet their functional biology in epithelia is poorly understood. We describe a novel intestinal epithelial FPR signaling pathway that is activated by an endogenous FPR ligand, annexin A1 (ANXA1), and its cleavage product Ac2-26, which mediate activation of ROS by an epithelial NADPH oxidase, NOX1. We show that epithelial cell migration was regulated by this signaling cascade through oxidative inactivation of the regulatory phosphatases PTEN and PTP-PEST, with consequent activation of focal adhesion kinase (FAK) and paxillin. In vivo studies using intestinal epithelial specific Nox1(-/-IEC) and AnxA1(-/-) mice demonstrated defects in intestinal mucosal wound repair, while systemic administration of ANXA1 promoted wound recovery in a NOX1-dependent fashion. Additionally, increased ANXA1 expression was observed in the intestinal epithelium and infiltrating leukocytes in the mucosa of ulcerative colitis patients compared with normal intestinal mucosa. Our findings delineate a novel epithelial FPR1/NOX1-dependent redox signaling pathway that promotes mucosal wound repair.

Review article: cellular and molecular mechanisms of NSAID-induced peptic ulcers

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) are some of the most prescribed drugs worldwide and have now probably overtaken Helicobacter pylori as the most common cause of gastrointestinal injury in Western countries. Further understanding of the pathogenesis of NSAID-induced ulcers is important to enable the development of novel and effective preventive strategies.

AIMS

To provide an update on recent advances in our understanding of the cellular and molecular mechanisms involved in the development of NSAID-induced ulcers.

METHODS

A Medline search was performed to identify relevant literature using search terms including 'nonsteroidal anti-inflammatory drugs, aspirin, gastric ulcer, duodenal ulcer, pathogenesis, pharmacogenetics'.

RESULTS

The mechanisms of NSAID-induced ulcers can be divided into topical and systemic effects and the latter may be prostaglandin-dependent (through COX inhibition) or prostaglandin-independent. Genetic factors may play an important role in determining individual predisposition.

CONCLUSIONS

The pathogenesis of NSAID-induced peptic ulcers is complex and multifactorial. Recent advances in cellular and molecular biology have highlighted the importance of various prostaglandin-independent mechanisms. Pharmacogenetic studies may provide further insights into the pathogenetic mechanisms of NSAID-induced ulcers and help identify patients at increased risk.

Expression of transforming growth factor α and Cyclin E and their correlation in chronic gastric lesion tissues from patients with different TCM types

AIM: To explore the expression of transforming growth factor α (TGF-α) and Cyclin E in chronic gastric lesion tissues from patients with different types of traditional Chinese medicine (TCM), and analyze the correlation between TGF-α and Cyclin E expression.

METHODS: The patients (n = 135) with chronic gastric diseases were classified to 4 groups according to different TCM types such as disharmony between liver and stomach (group A), spleen-stomach cold deficiency (group B), stomach-yin deficiency (group C), and mixed cold and heat (group D). Immunohistochemical staining was used to examine the expression of TGF-α and Cyclin E in the lesion tissues and the correlation between TGF-α and Cyclin E expression was also ssessed.

RESULTS: The positive rates of TGF-α expression in the lesion tissues of group A, B, C and D were 25.0%, 18.6%, 47.1% and 42.1%, respectively, and there was significant difference between group B and C (P < 0.05). The positive rates of Cyclin E expression were 20.0%, 7.0%, 26.5% and 31.6%, respectively, and there was marked difference between group B and D (P < 0.05). Both TGF-α and Cyclin E expression were the lowest in group B, and there existed a positive correlation between the expression of TGF-α and Cyclin E.

CONCLUSION: TGF-α and Cyclin E are differentially expressed in chronic gastric lesion tissues of patients with different TCM types, and the expression of TGF-α and Cyclin E are positively correlated.

Transforming growth factor-alpha accelerates hepatocyte repopulation after hepatocyte transplantation

BACKGROUND AND AIM

Although hepatocyte transplantation could be an alternative to orthotopic liver transplantation, many problems, such as rejection, location, required volume, and hepatocyte activity are currently unresolved. We previously demonstrated an anti-apoptotic effect in transgenic mice overexpressing transforming growth factor (TGF)-alpha. We herein present the details of a successful hepatocyte transplantation using TGF-alpha transgenic mice.

METHODS

We used transgenic (TG) mice which overexpressed human TGF-alpha controlled by the metallothionein promoter. Wild-type mice were used as the controls (WT). Parenchymal hepatocytes were isolated from an adult mouse by the modified in situ perfusion method. The proliferation and resistance to Fas-induced apoptosis were examined in vitro. In addition, we transplanted the parenchymal hepatocytes into the peritoneal cavity of the WT mice.

RESULTS

The TG hepatocytes showed higher proliferative activity and more resistance to Fas-induced apoptosis in comparison to the WT hepatocytes. Moreover, an immunohistochemical analysis demonstrated that the transplanted TG hepatocytes increased more in size and showed a higher expression of CD31 and vascular endothelial growth factor in comparison to the WT hepatocytes. We also observed that albumin was expressed in equal amounts in both types of transplanted hepatocytes.

CONCLUSION

Cell transplantation with TGF-alpha overexpressing hepatocytes could preserve hepatocyte function.

Overexpression of NK2 promotes liver fibrosis in carbon tetrachloride-induced chronic liver injury

BACKGROUND/AIMS

Hepatocyte growth factor (HGF) inhibits liver fibrosis induced by carbon tetrachloride (CCl4) in animal models. NK2 is a natural splice variant of HGF, but its in vivo function remains to be elucidated. We investigated the in vivo effects of NK2 on CCl4-induced liver fibrosis.

METHODS

NK2 transgenic mice and wild-type (WT) mice were injected intraperitoneally with CCl4 twice a week. The extent of hepatic fibrosis was evaluated by Azan-Mallory staining. Expression levels of mRNAs of transforming growth factor-beta1 (TGF-beta1) and matrix metalloproteinase-13 (MMP-13) were examined by real-time polymerase chain reaction. The protein levels of alpha-smooth muscle actin (alpha-SMA), c-Met and its phosphorylation were determined by Western blot analysis.

RESULTS

Liver fibrosis was significantly more severe in NK2 transgenic mice than in WT mice. CCl4 administration increased the expression levels of TGF-beta1 mRNA and alpha-SMA protein, and decreased the expression of MMP-13 mRNA in livers of NK2 transgenic mice compared with those of WT mice. c-Met protein expression in the liver was compatible with the degree of fibrosis. As for c-Met activation, no difference was found between NK2 and WT livers.

CONCLUSION

Overexpression of NK2 acts as an antagonist of HGF and promotes liver fibrosis in CCl4-induced chronic liver injury.

Gastroduodenal defense

PURPOSE OF REVIEW

The gastroduodenum resists mucosal injury despite continuous exposure to concentrated gastric acid. The mucosal barrier consists of a preepithelial mucus HCO3- layer, intercellular tight junctions connecting the epithelial cells, and submucosal acid sensors, prostaglandins, cytokines, enteric nerves and blood flow. In the past year, study of these defensive mechanisms has revealed new insight into the observed sex differences in ulcer prevalence, the protective role of transforming growth factor, the role of serotonin in regulating HCO3- secretion, the role of mechanisms in ulcer healing, the interaction of trefoil factors with the mucus gel, the interaction of glucocorticoids with cyclooxygenase and the characterization of novel, mucosal sparing antiinflammatory agents.

RECENT FINDINGS

Transforming growth factor, melatonin, serotonin, trefoil factors and H2S all enhance mucosal barrier function or accelerate ulcer healing. Newer coxibs may have safety and advantages over existing compounds. Existing nonsteroidal antiinflammatory drugs may be safer than originally thought.

SUMMARY

The continued elucidation of basic defense mechanisms has led to the development of several new compounds designed to enhance barrier function and repair mechanisms.

HGF ameliorates a high-fat diet-induced fatty liver

Hepatocyte growth factor (HGF) has various effects especially on epithelial cells. However, the precise role of HGF on lipogenesis is still not fully understood. A high-fat diet was administered to HGF transgenic mice and wild-type control mice in vivo. Furthermore, recombinant human HGF (rhHGF) was administered to HepG2 cell line in vitro. We performed an analysis regarding the factors relating to lipid metabolism. An overexpression of HGF dramatically ameliorates a high-fat diet-induced fatty liver. HGF transgenic mice showed an apparently reduced lipid accumulation in the liver. The activation of microsomal triglyceride transfer protein (MTP) and apolipoprotein B (ApoB) accompanying higher triglyceride levels in the serum were found in HGF transgenic mice on a normal diet. Interestingly, this upregulation of the MTP activation became more apparent in the high-fat diet. In addition, the administration of rhHGF stimulated MTP and ApoB expression while reducing reduced the intracellular lipid content in HepG2 cell line. However, this induction of MTP and ApoB by HGF was clearly inhibited by PD98059 (MAPK inhibitor). In conclusion, the data presented in this study indicated that HGF ameliorates a high-fat diet-induced fatty liver via the activation of MTP and ApoB.

Ménétrier disease and gastrointestinal stromal tumors: hyperproliferative disorders of the stomach

Ménétrier disease and gastrointestinal stromal tumors (GISTs) are hyperproliferative disorders of the stomach caused by dysregulated receptor tyrosine kinases (RTKs). In Ménétrier disease, overexpression of TGF-alpha, a ligand for the RTK EGFR, results in selective expansion of surface mucous cells in the body and fundus of the stomach. In GISTs, somatic mutations of the genes encoding the RTK KIT (or PDGFRA in a minority of cases) result in constitutive kinase activity and neoplastic transformation of gut pacemaker cells (interstitial cells of Cajal). On the basis of the involvement of these RTKs in the pathogenesis of these disorders, Ménétrier disease patients have been effectively treated with a blocking monoclonal antibody specific for EGFR and GIST patients with KIT and PDGFRA tyrosine kinase inhibitors.