Augmented leptin-induced trefoil factor 3 expression and epidermal growth factor receptor transactivation differentially influences neoplasia progression in the stomach and colorectum of dietary fat-induced obese mice.

Obesity is a risk factor for gastrointestinal malignancies and tumors. However, which factors either protect or predispose the gastrointestinal organs to high-fat diet (HFD)-induced neoplasia remains unclear. Here, we demonstrate that HFD impacts the stomach to a greater extent as compared to the colorectum, resulting in leptin receptor (LepR) signaling-mediated neoplasia in the tissues. HFD activated leptin signaling, which in turn, accelerates the pathogenesis in the gastric mucosa more than that in the colorectum along with ectopic TFF3 expression. Moreover, in the stomach, higher levels of phosphorylated epidermal growth factor receptor (EGFR) in addition to the activation of STAT3 and Akt were observed as compared to the colorectum. The mice with LepR deletion in the gastrointestinal epithelium exhibited a suppressed induction of leptin, TFF3, and phosphorylated EGFR in the stomach, whereas the levels in the colorectum were insignificant. In co-transfected COS-7 cells with LepR and EGFR plasmid DNA, leptin transactivated EGFR to accelerate TFF3 induction along with activation of STAT3, ERK1/2, Akt, and PI3K p85/p55. Furthermore, TFF3 could bind to EGFR but did not transactivate LepR. Leptin-induced TFF3 induction was markedly suppressed by inhibitors of PI3K (LY294002) and EGFR (Erlotinib). Together, these results suggest a novel role of LepR-mediated signaling in transactivating EGFR that leads to TFF3 expression via the PI3K-Akt pathway. Therefore, this study sheds light on the identification of potentially new therapeutic targets for the treatment of pre-cancerous symptoms in stomach and colorectum.

Gastric Leptin and Tumorigenesis: Beyond Obesity.

Leptin, an adipocyte-derived hormone and its receptor (ObR) expressed in the hypothalamus are well known as an essential regulator of appetite and energy expenditure. Obesity induces abundant leptin production, however, reduced sensitivity to leptin leads to the development of metabolic disorders, so called leptin resistance. The stomach has been identified as an organ that simultaneously expresses leptin and ObR. Accumulating evidence has shown gastric leptin to perform diverse functions, such as those in nutrient absorption and carcinogenesis in the gastrointestinal system, independent of its well-known role in appetite regulation and obesity. Overexpression of leptin and phosphorylated ObR is implicated in gastric cancer in humans and in murine model, and diet-induced obesity causes precancerous lesions in the stomach in mice. While the underlying pathomechanisms remain unclear, leptin signaling can affect gastric mucosal milieu. In this review, we focus on the significant role of the gastric leptin signaling in neoplasia and tumorigenesis in stomach in the context of hereditary and diet-induced obesity.

Antagonizing effect of CLPABP on the function of HuR as a regulator of ARE-containing leptin mRNA stability and the effect of its depletion on obesity in old male mouse.

Cardiolipin and phosphatidic acid-binding protein (CLPABP) is a pleckstrin homology domain-containing protein and is localized on the surface of mitochondria of cultured cells as a large protein-RNA complex. To analyze the physiological functions of CLPABP, we established and characterized a CLPABP knockout (KO) mouse. Although expression levels of CLPABP transcripts in the developmental organs were high, CLPABP KO mice were normal at birth and grew normally when young. However, old male mice presented a fatty phenotype, similar to that seen in metabolic syndrome, in parallel with elevated male- and age-dependent CLPABP gene expression. One of the reasons for this obesity in CLPABP KO mice is dependence on increases in leptin concentration in plasma. The leptin transcripts were also upregulated in the adipose tissue of KO mice compared with wild-type (WT) mice. To understand the difference in levels of the transcriptional product, we focused on the effect of CLPABP on the stability of mRNA involving an AU-rich element (ARE) in its 3'UTR dependence on the RNA stabilizer, human antigen R (HuR), which is one of the CLPABP-binding proteins. Increase in stability of ARE-containing mRNAs of leptin by HuR was antagonized by the expression of CLPABP in cultured cells. Depletion of CLPABP disturbed the normal subcellular localization of HuR to stress granules, and overexpression of CLPABP induced instability of leptin mRNA by inhibiting HuR function. Consequently, leptin levels in old male mice might be regulated by CLPABP expression, which might lead to body weight control.

High-fat diet feeding promotes stemness and precancerous changes in murine gastric mucosa mediated by leptin receptor signaling pathway.

Obesity increases the risk for gastric cancers. However, the occurrence and mechanisms of precancerous atrophic gastritis induced by high-fat diet (HFD) remain unclear. Here, we show that HFD-associated lipotoxicity induces precancerous lesions that are accompanied by the disruption of organelle homeostasis, tissue integrity, and deregulated expression of stemness genes in the gastric epithelium mediated by leptin receptor (ObR) signaling. Following HFD feeding, ectopic fat accumulated and expression of LAMP2A in lysosome and COX IV in mitochondria increased in the gastric mucosa. HFD feeding also led to enhanced expression of activated-Notch1 and stem cell markers Lgr5, CD44, and EpCAM. In addition, HFD-fed mice showed intracellular ß-catenin accumulation in the gastric mucosa with increased expression of its target genes, Nanog, Oct4, and c-Myc. These observations were abrogated in the leptin-deficient ob/ob mice and ObR-mutated db/db mice, indicating that these HFD-induced changes were responsible for effects downstream of the ObR. Consistent with this, the expression of the Class IA and III PI3Ks was increased following ObR activation in the gastric mucosa of HFD-fed mice. Together, these results suggest that HFD-induced lipotoxicity and deregulated organelle biosynthesis confer cancer stem cell-like properties to the gastric mucosa via signaling pathway mediated by leptin, PI3K and ß-catenin.

Interleukin-13 damages intestinal mucosa via TWEAK and Fn14 in mice-a pathway associated with ulcerative colitis.

BACKGROUND & AIMS: TWEAK, a member of the tumor necrosis factor (TNF) superfamily, promotes intestinal epithelial cell injury and signals through the receptor Fn14 following irradiation-induced tissue damage and during development of colitis in mice. Interleukin (IL)-13, an effector of tissue damage in similar models, has been associated with the pathogenesis of ulcerative colitis (UC). We investigated interactions between TWEAK and IL-13 following mucosal damage in mice. METHODS: We compared patterns of gene expression in intestinal tissues from wild-type and TWEAK knockout mice following γ-irradiation. Intestinal explants from these mice were used to detect cell damage induced by IL-13 and TNF-α. Levels of messenger RNA for IL-13, TWEAK, and Fn14 were measured in mucosal samples from patients with UC. RESULTS: Based on gene expression analysis, TWEAK mediates γ-irradiation-induced epithelial cell cycle arrest and apoptosis. However, TWEAK alone did not induce damage or apoptosis of primary intestinal epithelial cells. On the other hand, exogenous IL-13 activated caspase-3 in naïve intestinal explants; this process required TWEAK, Fn14, and secretion of endogenous TNF-α which was mediated by ADAM17. Conversely, activation of caspase by exogenous TNF-α required IL-13, TWEAK, and Fn14. In mucosa from patients with UC, messenger RNA levels of IL-13, TWEAK, and Fn14 increased with level of disease severity. CONCLUSIONS: IL-13-induced damage of intestinal epithelial cells requires TWEAK, its receptor (Fn14), and TNF-α. IL-13, TNF-α, TWEAK, and Fn14 could perpetuate and aggravate intestinal inflammation in patients with UC.

γδ T cells play a protective role during infection with Nippostrongylus brasiliensis by promoting goblet cell function in the small intestine.

The intestinal epithelium is rich in γδ T cells and the gut is a site of residence for a wide variety of pathogens, including nematodes. Although CD4+ T-cell receptor (TCR) -αß+ T helper type 2 T cells are essential for the expulsion of intestinal nematodes, little information is available on the function of γδ T cells in this type of infection. Here, we demonstrate two major functions of γδ T cells as a potently protective T-cell population against Nippostrongylus brasiliensis infection using γδ T-cell-deficient (TCR-δ(-/-) ) mice. First, γδ T cells are required to initiate rapid expulsion of adult worms from the intestine and to limit egg production. Second, γδ T cells prevent the pathological intestinal damage associated with nematode infection, evident by increased clinical disease and more severe microscopic lesions in infected TCR-δ(-/-) mice. γδ T-cell deficiency led to delayed goblet cell hyperplasia in association with reduced expression of phosphorylated STAT6, MUC2, Trefoil factor-3 (TFF3) and T helper type 2 cytokines including interleukin-13 (IL-13). TCR-δ(-/-) mice also produced more interferon-γ than wild-type mice. Within the intraepithelial lymphocyte compartment, γδ T cells produced IL-13. Adoptive transfer of γδ T cells or administration of recombinant IL-13 to TCR-δ(-/-) mice successfully reduced the egg production by N. brasiliensis. Collectively, these data provide strong evidence that γδ T cells play an important role in controlling infection with intestinal nematodes and limiting infection-induced pathology.

An enzymatic photometric assay for 2-deoxyglucose uptake in insulin-responsive tissues and 3T3-L1 adipocytes.

An enzymatic assay adapted to photometric analysis with 96-well microplates was evaluated for the measurement of 2-deoxyglucose (2DG) uptake in insulin-responsive tissues and differentiated 3T3-L1 adipocytes. For in vivo measurements, a small amount of nonradiolabeled 2DG was injected into mice without affecting glucose metabolism. For photometric quantification of the small amount of 2-deoxyglucose 6-phosphate (2DG6P) that accumulates in cells, we introduced glucose-6-phosphate dehydrogenase, glutathione reductase, and 5,5'-dithiobis(2-nitrobenzoic acid) to the recycling amplification reaction of NADPH. We optimized the enzyme reaction for complete oxidation of endogenous glucose 6-phosphate (G6P) and glucose in mouse tissues in vivo and serum as well as in 3T3-L1 adipocytes in vitro. All reactions are performed in one 96-well microplate by consecutive addition of reagents, and the assay is able to quantify 2DG and 2DG6P in the range of 5-80 pmol. The results obtained with the assay for 2DG uptake in vitro and in vivo in the absence or presence of insulin stimulation was similar to those obtained with the standard radioisotopic method. Thus, the enzymatic assay should prove to be useful for measurement of 2DG uptake in insulin-responsive tissues in vivo as well as in cultured cells.

SOCS-3 regulates onset and maintenance of T(H)2-mediated allergic responses.

Members of the suppressor of cytokine signaling (SOCS) family are involved in the pathogenesis of many inflammatory diseases. SOCS-3 is predominantly expressed in T-helper type 2 (T(H)2) cells, but its role in T(H)2-related allergic diseases remains to be investigated. In this study we provide a strong correlation between SOCS-3 expression and the pathology of asthma and atopic dermatitis, as well as serum IgE levels in allergic human patients. SOCS-3 transgenic mice showed increased T(H)2 responses and multiple pathological features characteristic of asthma in an airway hypersensitivity model system. In contrast, dominant-negative mutant SOCS-3 transgenic mice, as well as mice with a heterozygous deletion of Socs3, had decreased T(H)2 development. These data indicate that SOCS-3 has an important role in regulating the onset and maintenance of T(H)2-mediated allergic immune disease, and suggest that SOCS-3 may be a new therapeutic target for the development of antiallergic drugs.

Interleukin-17A is required to suppress invasion of Salmonella enterica serovar Typhimurium to enteric mucosa.

Salmonella enterica serovar Typhimurium (S. typhimurium) causes a localized enteric infection and its elimination is dependent on a T helper type 1 immune response. However, the mechanism of the protective immune response against the pathogen in gut-associated lymphoid tissue (GALT) at an early stage of the infection is not yet clarified. Here, we show that interleukin-17A (IL-17A) was constitutively expressed in GALT; it was also detected on crypt and epithelial cells of the small intestine. Neutralization of the IL-17A in the intestinal lumen exacerbated epithelial damage induced by intestinal S. typhimurium infection at an early stage of the infection. The result suggests that IL-17A has a pivotal role in the immediate early stage of protection against bacterial infection at the intestinal mucosa. As IL-17A neutralization also suppressed the constitutive localization of ß-defensin 3 (BD3), an IL-17A-induced antimicrobial peptide, at the apical site of the intestinal mucosa, it is estimated that IL-17A constitutively induces the expression of the antimicrobial peptide to kill invading pathogens at the epithelial surface immediately after the infection. In contrast, interferon-γ is induced around 3 days after S. typhimurium infection, and its expression level increases thereafter. Taken together, the findings lead to the hypothesis that IL-17A participates in the immediate early stage of protection against S. typhimurium intestinal infection whereas interferon-γ is important at a later stage of the infection.

High-fat-diet-induced modulations of leptin signaling and gastric microbiota drive precancerous lesions in the stomach.

OBJECTIVES: Obesity is a risk factor for malignancy in various tissues, and has been associated with gut microbiota alterations. However, the link between obesity-associated microbiota and gastric pathogenesis has not been clarified. We demonstrated that high-fat-diet (HFD) feeding causes intestinal metaplasia, which are precancerous lesions of the stomach, with augmented gastric leptin signaling. The aim of this study was to investigate the precise role of leptin signaling in the altered microbiota composition and pathogenesis in the stomach during diet-induced obesity. METHODS: Male C57 BL/6 J, leptin receptor (Lepr)-mutated db/db, and gastrointestinal epithelium-specific Lepr conditional knockout (T3 b-Lepr cKO) mice were fed a HFD or control diet. Gastrointestinal microbiota was analyzed by 16 S rRNA gene sequences and quantitative polymerase chain reaction. Transplantation of gastric microbiota of HFD-fed mice was performed to evaluate metaplasia onset in recipient mice. RESULTS: One week of HFD caused severe microbial dysbiosis in the stomach. The microbiota changes were accompanied by increased gastric leptin, leading to the consequent development of intestinal metaplasia. Transplantation of gastric microbiota from HFD-fed mice induced intestinal metaplasia in recipient mice; however, only a limited effect on pathogenesis was noted. HFD-fed db/db mice did not show a decrease in microbial abundance. Moreover, T3 b-Lepr cKO mice failed spontaneous obesity, and suppressed decreased abundance of gastric microbiota and occurrence of intestinal metaplasia during HFD feeding similar to db/db mice. CONCLUSIONS: Gastric leptin signaling modulates the gastric microbiota community and regulates the pathogenesis in the gastric mucosa.

Dietary Fat-Accelerating Leptin Signaling Promotes Protumorigenic Gastric Environment in Mice.

Excess of fat intake leads to obesity and causes a variety of metabolic diseases and cancer. We previously demonstrated that high-lard diet induces intestinal metaplasia, a precancerous lesion of the stomach mediated by leptin signaling. This study aims to investigate which kinds of dietary fat cause the intestinal metaplasia onset. We fed eight kinds of high-fat diets (HFDs) of animal or plant origin to mice evaluated their effect on gastric pathogenesis. Five types of dietary fat were divided according to their observed effects: Obese with high metaplasia (group I; beef tallow, lard, and hydrogenated coconut oil), non-obese with high metaplasia (group II; linseed oil), obese without metaplasia (group III; corn oil and olive oil), non-obese without metaplasia (group IV, soybean oil) and lean without metaplasia (group V; cocoa butter). The group I and II diets induced leptin, phosphorylated leptin receptor (ObR), signal transducer and activator 3 (STAT3), and increased intracellular ß-catenin accumulation in the stomach. Moreover, mice fed these HFDs with 1-methyl-3-nitro-1-nitrosoguanidine (MNNG), a gastric carcinogen, and further accelerated dysplasia in the stomach. Lactobacillus occupancy in the stomach increased in all HFDs except hydrogenated coconut oil. Our findings suggest that HFDs inducing leptin signaling accelerate the enhancement of protumorigenic gastric microenvironment independent of body mass gain or microbiome changes.

Subcutaneously administered adrenomedullin exerts a potent therapeutic effect in a murine model of ulcerative colitis.

Adrenomedullin (AM) exerts a potent anti-inflammatory effect. Intrarectal or consecutive intravenous administrations of AM reduce pathological manifestations in rodent colitis models. However, in clinical applications, a safer administration route that provides stronger alleviation of patient burden is preferred. We investigated whether subcutaneously administered AM is effective against dextran sulfate sodium (DSS)-induced colitis. C57BL/6J mice were administered 1% DSS in drinking water and received AM at 8, 40 or 80 nmol/kg subcutaneously once a day for 7 consecutive days. Subcutaneously administered AM significantly and dose-dependently ameliorated body weight loss, diarrhea, and histological severity of colonic inflammation in DSS-treated mice. The AM therapeutic effect was associated with the upregulation of the production of autocrine AM, and expression of cAMP, c-fos, KLF4, and downregulation of STAT3 and NF-κB p65 phosphorylation, as well as a decrease in proinflammatory cytokine expression in the colon. Subcutaneous AM treatment potently attenuated DSS-induced colitis, which suggests that AM administered subcutaneously in ulcerative colitis (UC) patients may decrease diseases burden and improve quality of life.

Increased intestinal endotoxin absorption during enteric nematode but not protozoal infections through a mast cell-mediated mechanism.

It is known that hypersensitivity reactions in the gastrointestinal tract, which are primarily mediated by mast cells, are associated with a secretory response of the epithelium and often increased permeability to macromolecules. Studies to date have not examined the effects of hyperpermeability on the absorption of toxic substances normally present in the intestinal lumen such as bacterial LPS. In the present study, we observed that Strongyloides venezuelensis infection in mice decreases the mRNA expression of intestinal epithelial cell junctional molecules (occludin and zonula occludens 1) and increases portal endotoxin levels 4 h after intragastric administration of LPS (20 mg/kg body weight). Furthermore, an increase in the flux of immunoglobulin G into the intestinal lumen was observed 10 days postinfection (PI). An increased rate of LPS absorption was also seen in mice infected with Nippostrongylus brasiliensis on day 14 PI and rats concurrently infected with S. venezuelensis and N. brasiliensis on day 20 PI. On the other hand, infection with Eimeria vermiformis and Eimeria pragensis was not observed to enhance LPS absorption 4 h after intragastric administration of LPS (20 mg/kg body weight), although E. vermiformis infection did inhibit the epithelial cell mRNA expression of zonula occludens 1, but not occludin, on day 9 PI, resulting in a reduced immunoglobulin G flux than that produced by S. venezuelensis infection. Our results suggest that mastocytosis accompanying intestinal nematode infection increases the intestinal absorption of LPS into the portal circulation by suppressing the expression of tight junction molecules.

Leptin receptor signaling is required for high-fat diet-induced atrophic gastritis in mice.

BACKGROUND: Obesity increases the risk for malignancies in various tissues including the stomach. Atrophic gastritis with precancerous lesions is an obesity-associated disease; however, the mechanisms that underlie the development of obesity-associated atrophic gastritis are unknown. Leptin is a hormone derived from stomach as well as adipose tissue and gastric leptin is involved in the development of gastric cancer. The aim of the current study is to investigate the involvement of leptin receptor signaling in the development of atrophic gastritis during diet-induced obesity. METHODS: Male C57BL/6, ob/ob and db/db mice were fed a high-fat diet (HFD) or a control diet (CD) from 1 week to 5 months. Pathological changes of the gastric mucosa and the expression of molecules associated with atrophic gastritis were evaluated in these mice. RESULTS: HFD feeding induced gastric mucosal hyperplasia with increased gastric leptin expression. Mucosal hyperplasia was accompanied by a higher frequency of Ki67-positive proliferating cells and atrophy of the gastric glands in the presence of inflammation, which increased following HFD feeding. Activation of ObR signaling-associated molecules such as ObR, STAT3, Akt, and ERK was detected in the gastric mucosa of mice fed the HFD for 1 week. The morphological alterations associated with gastric mucosal atrophy and the expression of Muc2 and Cdx2 resemble those associated with human intestinal metaplasia. In contrast to wild-type mice, leptin-deficient ob/ob mice and leptin receptor-mutated db/db mice did not show increased Cdx2 expression in response to HFD feeding. CONCLUSION: Together, these results suggest that activation of the leptin signaling pathway in the stomach is required to develop obesity-associated atrophic gastritis.

Negative regulation of cytokine signaling and inflammatory diseases.

Immune and inflammatory systems are controlled by multiple cytokines, including interleukins and interferons. These cytokines exert their biological functions through Janus tyrosine kinases and signal transducer and activators of transcription (STATs). The cytokine-inducible SH2 proteins (CIS) and suppressors of cytokine signaling (SOCS) are a family of intracellular proteins, several of which have emerged as key physiological regulators of cytokine responses, including those that regulate the inflammatory system. Several recent advances have been made in this field, including treatment of inflammatory diseases by modulating extracellular and intracellular signaling pathways.

Chemokine receptor CCR8 is required for lipopolysaccharide-triggered cytokine production in mouse peritoneal macrophages.

Chemokine (C-C motif) receptor 8 (CCR8), the chemokine receptor for chemokine (C-C motif) ligand 1 (CCL1), is expressed in T-helper type-2 lymphocytes and peritoneal macrophages (PMφ) and is involved in various pathological conditions, including peritoneal adhesions. However, the role of CCR8 in inflammatory responses is not fully elucidated. To investigate the function of CCR8 in macrophages, we compared cytokine secretion from mouse PMφ or bone marrow-derived macrophages (BMMφ) stimulated with various Toll-like receptor (TLR) ligands in CCR8 deficient (CCR8-/-) and wild-type (WT) mice. We found that CCR8-/- PMφ demonstrated attenuated secretion of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-10 when stimulated with lipopolysaccharide (LPS). In particular, LPS-induced IL-10 production absolutely required CCR8. CCR8-dependent cytokine secretion was characteristic of PMφ but not BMMφ. To further investigate this result, we selected the small molecule compound R243 from a library of compounds with CCR8-antagonistic effects on CCL1-induced Ca2+ flux and CCL1-driven PMφ aggregation. Similar to CCR8-/- PMφ, R243 attenuated secretion of TNF-α, IL-6, and most strikingly IL-10 from WT PMφ, but not BMMφ. CCR8-/- PMφ and R243-treated WT PMφ both showed suppressed c-jun N-terminal kinase activity and nuclear factor-κB signaling after LPS treatment when compared with WT PMφ. A c-Jun signaling pathway inhibitor also produced an inhibitory effect on LPS-induced cytokine secretion that was similar to that of CCR8 deficiency or R243 treatment. As seen in CCR8-/- mice, administration of R243 attenuated peritoneal adhesions in vivo. R243 also prevented hapten-induced colitis. These results are indicative of cross talk between signaling pathways downstream of CCR8 and TLR-4 that induces cytokine production by PMφ. Through use of CCR8-/- mice and the new CCR8 inhibitor, R243, we identified a novel macrophage innate immune response pathway that involves a chemokine receptor.

SOCS, inflammation, and cancer.

Signal transduction pathways elicited by cytokines and hormones have been shown to regulate distinct stages of development. Suppressor of cytokine signaling (SOCS) proteins are negative feedback regulators of cytokine signaling mediated by the JAK-STAT signaling pathway. In particular, SOCS1 and SOCS3 are potent inhibitors of JAKs and can play pivotal roles in inflammation, as well as in the development and progression of cancers. Abnormal expression of SOCS1 and SOCS3 in cancer cells has been reported in human carcinoma associated with dysregulation of signals from cytokine receptors, Toll-like receptors (TLRs), and hormone receptors, resulting in malignancies. In this review, we focus on the role of SOCS1 and SOCS3 in cancer development. In addition, the potential of SOCS as a therapeutic target and diagnostic aid will be discussed.

Adrenomedullin as a potential therapeutic agent for inflammatory bowel disease.

Adrenomedullin (AM) was originally isolated from human pheochromocytoma as a biologically active peptide with potent vasodilating action but is now known to exert a wide range of physiological effects, including cardiovascular protection, neovascularization, and apoptosis suppression. A variety of tissues, including the gastrointestinal tract, have been shown to constitutively produce AM. Pro-inflammatory cytokines, such as tumor necrosis factor-α and interleukin-1, and lipopolysaccharides, induce the production and secretion of AM. Conversely, AM induces the downregulation of inflammatory cytokines in cultured cells. Furthermore, AM downregulates inflammatory processes in a variety of different colitis models, including acetic acid-induced colitis and dextran sulfate sodium-induced colitis. AM exerts antiinflammatory and antibacterial effects and stimulates mucosal regeneration for the maintenance of the colonic epithelial barrier. Here, we describe the first use of AM to treat patients with refractory ulcerative colitis. The results strongly suggest that AM has potential as a new therapeutic agent for the treatment of refractory ulcerative colitis.

Microbiota-derived lactate accelerates colon epithelial cell turnover in starvation-refed mice.

Oral food intake influences the morphology and function of intestinal epithelial cells and maintains gastrointestinal cell turnover. However, how exactly these processes are regulated, particularly in the large intestine, remains unclear. Here we identify microbiota-derived lactate as a major factor inducing enterocyte hyperproliferation in starvation-refed mice. Using bromodeoxyuridine staining, we show that colonic epithelial cell turnover arrests during a 12- to 36-h period of starvation and increases 12-24 h after refeeding. Enhanced epithelial cell proliferation depends on the increase in live Lactobacillus murinus, lactate production and dietary fibre content. In the model of colon tumorigenesis, mice exposed to a carcinogen during refeeding develop more aberrant crypt foci than mice fed ad libitum. Furthermore, starvation after carcinogen exposure greatly reduced the incidence of aberrant crypt foci. Our results indicate that the content of food used for refeeding as well as the timing of carcinogen exposure influence the incidence of colon tumorigenesis in mice.

Interleukin-17A is involved in enhancement of tumor progression in murine intestine.

Interleukin (IL)-17A is a cytokine involved in neutrophilic inflammation but the role of IL-17A in anti-tumor immunity is controversial because both pro- and anti-tumor activities of IL-17A have been reported. We hypothesized that constitutive expression of IL-17A in intestinal environment modifies tumor growth. To address the issue, mice were inoculated into subserosa of cecum (i.c.) with murine EL4 lymphoma expressing a model tumor antigen, and tumor growth was monitored. IL-17A-producing cells were detected both in tumor mass and in normal intestinal tissue of i.c. tumor-bearing wild type mice. Tumor size in the wild-type mice was significantly higher than that in the cecum of IL-17A gene-knockout mice. Furthermore, anti-IL-17A monoclonal antibody treatment of wild-type mice resulted in decreased tumor size in the cecum. Model tumor-antigen-specific interferon-γ production was not modified in draining mesenteric lymph node cells in the absence or after neutralization of IL-17A. All the results suggest that constitutive expression of IL-17A in intestine enhances tumor growth, and anti-IL-17A antibody treatment is a candidate of a new anti-tumor immunotherapy against intestinal tumors.