Gli1 deletion prevents Helicobacter-induced gastric metaplasia and expansion of myeloid cell subsets

Hedgehog signaling pathway regulates Th17 cell differentiation in asthma via IL-6/STAT3 signaling

Asthma is the most prevalent chronic inflammatory disease of the airways in children. The most prevalent phenotype of asthma is eosinophilic asthma, which is driven by a Th2 immune response and can be effectively managed by inhaled corticosteroid therapy. However, there are phenotypes of asthma with Th17 immune response that are insensitive to corticosteroid therapy and manifest a more severe phenotype. The treatment of this corticosteroid-insensitive asthma is currently immature and requires further attention. The objective of this study is to elucidate the regulation of the Hedgehog signaling pathway in Th17 cell differentiation in asthma. The study demonstrated that both Smo and Gli3, key components of the Hedgehog signaling pathway, were upregulated in Th17 polarization in vitro and in a Th17-dominant asthma model in vivo. Inhibiting Smo with a small molecule inhibitor or genetically knocking down Gli3 was found to suppress Th17 polarization. Smo was found to increase in Th1, Th2, Th17 and Treg polarization, while Gli3 specifically increased in Th17 polarization. ChIP-qPCR analyses indicated that Gli3 can directly interact with IL-6 in T cells, inducing STAT3 phosphorylation and promoting Th17 cell differentiation. Furthermore, the study demonstrated a correlation between elevated Gli3 expression and IL-17A and IL-6 expression in children with asthma. In conclusion, the study demonstrated that the Hedgehog signaling pathway plays an important role in the pathogenesis of asthma, as it regulates the differentiation of Th17 cells through the IL-6/STAT3 signaling. This may provide a potential therapeutic target for corticosteroid-insensitive asthma driven by Th17 cells.

Positive GLI1/INHBA feedback loop drives tumor progression in gastric cancer

GLI1, a key transcription factor of the Hedgehog (Hh) signaling pathway, plays an important role in the development of cancer. However, the function and mechanisms by which GLI1 regulates gene transcription are not fully understood in gastric cancer (GC). Here, we found that GLI1 induced the proliferation and metastasis of GC cells, accompanied by transcriptional upregulation of INHBA. This increased INHBA expression exerted a promoting activity on Smads signaling and then transcriptionally activated GLI1 expression. Notably, our results demonstrate that disrupting the interaction between GLI1 and INHBA could inhibit GC tumorigenesis in vivo. More intriguingly, we confirmed the N6-methyladenosine (m6A) activation mechanism of the Helicobacter pylori/FTO/YTHDF2/GLI1 pathway in GC cells. In conclusion, our study confirmed that the GLI1/INHBA positive feedback loop influences GC progression and revealed the mechanism by which H. pylori upregulates GLI1 expression through m6A modification. This positive GLI1/INHBA feedback loop suggests a novel noncanonical mechanism of GLI1 activity in GC and provides potential therapeutic targets for GC treatment.

The Cxcr2+ subset of the S100a8+ gastric granylocytic myeloid-derived suppressor cell population (G-MDSC) regulates gastric pathology

Introduction

Gastric myeloid-derived suppressor cells (MDSCs) are a prominent population that expands during gastric pre-neoplastic and neoplastic development in humans and mice. However, the heterogeneity of this population has circumvented the ability to study these cells or understand their functions. Aside from Schlafen-4+ (Slfn-4+) MDSCs in mouse studies, which constitute a subset of this population, limitations exist in characterizing the heterogeneity of the gastric CD11b+Ly6G+ population and targeting its different subsets. Here we identify S100a8 as a pan-specific marker for this population and utilize it to study the role of the S100a8+Cxcr2+ subset.

Methods

We profiled gastric CD11b+Ly6G+ versus CD11b+Ly6G- myeloid cells by transcriptomic and single-cell RNA sequencing. We identified S100a8 as a pan-specific marker of the gastric granulocytic MDSC (G-MDSC) population, and generated S100a8CreCxcr2flox/flox to study the effects of Cxcr2 knockdown.

Results

Following 6-months of Helicobacter felis infection, gastric CD11b+Ly6G+ G-MDSCs were highly enriched for the expression of S100a8, S100a9, Slfn4, Cxcr2, Irg1, Il1f9, Hcar2, Retnlg, Wfdc21, Trem1, Csf3R, Nlrp3, and Il1b. The expression of these distinct genes following 6mo H. felis infection marked heterogeneous subpopulations, but they all represented a subset of S100a8+ cells. S100a8 was identified as a pan-marker for CD11b+Ly6G+ cells arising in chronic inflammation, but not neutrophils recruited during acute gut infection. 6mo Helicobacter felis-infected S100a8CreCxcr2flox/flox mice exhibited worsened gastric metaplastic pathology than Cxcr2flox/flox mice, which was associated with dysregulated lipid metabolism and peroxidation.

Conclusion

S100a8 is a pan-specific marker that can be used to target gastric G-MDSC subpopulations, of which the Cxcr2+ subset regulates gastric immunopathology and associates with the regulation of lipid peroxidation.

Schlafen4+-MDSC in Helicobacter-induced gastric metaplasia reveals role for GTPases

Introduction

MDSCs express SCHLAFEN 4 (SLFN4) in Helicobacter-infected stomachs coincident with spasmolytic polypeptide-expressing metaplasia (SPEM), a precursor of gastric cancer. We aimed to characterize SLFN4+ cell identity and the role of Slfn4 in these cells.

Methods

Single-cell RNA sequencing was performed on immune cells sorted from PBMCs and stomachs prepared from uninfected and 6-month H. felis-infected mice. Knockdown of Slfn4 by siRNA or PDE5/6 inhibition by sildenafil were performed in vitro. Intracellular ATP/GTP levels and GTPase activity of immunoprecipitated Slfn4 complexes were measured using the GTPase-Glo assay kit. The intracellular level of ROS was quantified by the DCF-DA fluorescent staining, and apoptosis was determined by cleaved Caspase-3 and Annexin V expression. Gli1CreERT2 x Slfn4 fl/fl mice were generated and infected with H. felis. Sildenafil was administered twice over 2 weeks by gavaging H. felis infected mice ~4 months after inoculation once SPEM had developed.

Results

Slfn4 was highly induced in both monocytic and granulocytic MDSCs from infected stomachs. Both Slfn4 +-MDSC populations exhibited strong transcriptional signatures for type-I interferon responsive GTPases and exhibited T cell suppressor function. SLFN4-containing protein complexes immunoprecipitated from myeloid cell cultures treated with IFNa exhibited GTPase activity. Knocking down Slfn4 or PDE5/6 inhibition with sildenafil blocked IFNa induction of GTP, SLFN4 and NOS2. Moreover, IFNa induction of Slfn +-MDSC function was inhibited by inducing their reactive oxygen species (ROS) production and apoptosis through protein kinase G activation. Accordingly, in vivo disruption of Slfn4 in Gli1CreERT2 x Slfn4 fl/fl mice or pharmacologic inhibition by sildenafil after Helicobacter infection also suppressed SLFN4 and NOS2, reversed T cell suppression and mitigated SPEM development.

Conclusion

Taken together, SLFN4 regulates the activity of the GTPase pathway in MDSCs and precludes these cells from succumbing to the massive ROS generation when they acquire MDSC function.

Hedgehog/GLI and gastric cancer: Research progress and current status

Hedgehog/GLI (Hh/GLI) is an important signaling pathway. It has been confirmed in various cancer studies that mutated or dysregulated Hh signals may be the behavioral phenotype of tumors, leading to the occurrence of various cancers. The abnormally activated Hh pathway endows tumor cells with a tendency to occur, proliferate, and migrate. In recent years, studies have found that the Hh signaling pathway induces gastric cancer (GC) invasion and epithelial mesenchymal transition. This article reviews the research progress and current status of Hh/GLI related to GC. Unveiling the new veil of GC occurrence will open a new approach for targeted therapy of this malignancy.

C-X-C motif chemokine ligand 1 induced by Hedgehog signaling promotes mouse extrahepatic bile duct repair after acute injury

BACKGROUND AND AIMS

In extrahepatic bile duct (EHBD) cholangiopathies, including primary sclerosing cholangitis, a reactive cholangiocyte phenotype is associated with inflammation and epithelial hyperproliferation. The signaling pathways involved in EHBD injury response are poorly understood. In this study, we investigated the role of Hedgehog (HH) signaling and its downstream effectors in controlling biliary proliferation and inflammation after EHBD injury.

APPROACH AND RESULTS

Using mouse bile duct ligation as an acute EHBD injury model, we used inhibitory paradigms to uncover mechanisms promoting the proliferative response. HH signaling was inhibited genetically in Gli1^-/- mice or by treating wild-type mice with LDE225. The role of neutrophils was tested using chemical (SB225002) and biological (lymphocyte antigen 6 complex locus G6D [Ly6G] antibodies) inhibitors of neutrophil recruitment. The cellular response was defined through morphometric quantification of proliferating cells and CD45+ and Ly6G+ immune cell populations. Key signaling component expression was measured and localized to specific EHBD cellular compartments by in situ hybridization, reporter strain analysis, and immunohistochemistry. Epithelial cell proliferation peaked 24 h after EHBD injury, preceded stromal cell proliferation, and was associated with neutrophil influx. Indian HH ligand expression in the biliary epithelium rapidly increased after injury. HH-responding cells and neutrophil chemoattractant C-X-C motif chemokine ligand 1 (CXCL1) expression mapped to EHBD stromal cells. Inhibition of HH signaling blocked CXCL1 induction, diminishing neutrophil recruitment and the biliary proliferative response to injury. Directly targeting neutrophils by inhibition of the CXCL1/C-X-C motif chemokine receptor 2/Ly6G signaling axis also decreased biliary proliferation.

CONCLUSIONS

HH-regulated CXCL1 orchestrates the early inflammatory response and biliary proliferation after EHBD injury through complex cellular crosstalk.

Schlafen family is a prognostic biomarker and corresponds with immune infiltration in gastric cancer

The Schlafen (SLFN) gene family plays an important role in immune cell differentiation and immune regulation. Previous studies have found that the increased SLFN5 expression in patients with intestinal metaplasia correlates with gastric cancer (GC) progression. However, no investigation has been conducted on the SLFN family in GC. Therefore, we systematically explore the expression and prognostic value of SLFN family members in patients with GC, elucidating their possible biological function and its correlation with tumor immune cells infiltration. TCGA database results indicated that the SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN13 expression was significantly higher in GC. The UALCAN and KM plotter databases indicated that enhanced the SLFN family expression was associated with lymph node metastasis, tumor stage, and tumor grade and predicted an adverse prognosis. cBioportal database revealed that the SLFN family had a high frequency of genetic alterations in GC (about 12%), including mutations and amplification. The GeneMANIA and STRING databases identified 20 interacting genes and 16 interacting proteins that act as potential targets of the SLFN family. SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN14 may be implicated in the immunological response, according to Gene Set Enrichment Analysis (GSEA) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Additionally, Timer and TISIDB databases indicate that SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN14 are involved in the immune response. Furthermore, Timer, TCGA, and TISIDB databases suggested that the SLFN5, SLFN11, SLFN12, SLFN12L, and SLFN14 expression in GC is highly linked with immune cell infiltration levels, immune checkpoint, and the many immune cell marker sets expression. We isolated three samples of peripheral blood mononuclear cell (PBMC) and activated T cells; the results showed the expression of SLFN family members decreased significantly when T cell active. In conclusion, the SLFN family of proteins may act as a prognostic indicator of GC and is associated with immune cell infiltration and immune checkpoint expression in GC. Additionally, it may be involved in tumor immune evasion by regulating T cell activation.

Effects of helicobacter pylori on tumor microenvironment and immunotherapy responses

Helicobacter pylori is closely associated with gastric cancer. During persistent infection, Helicobacter pylori can form a microenvironment in gastric mucosa which facilitates the survival and colony formation of Helicobacter pylori. Tumor stromal cells are involved in this process, including tumor-associated macrophages, mesenchymal stem cells, cancer-associated fibroblasts, and myeloid-derived suppressor cells, and so on. The immune checkpoints are also regulated by Helicobacter pylori infection. Helicobacter pylori virulence factors can also act as immunogens or adjuvants to elicit or enhance immune responses, indicating their potential applications in vaccine development and tumor immunotherapy. This review highlights the effects of Helicobacter pylori on the immune microenvironment and its potential roles in tumor immunotherapy responses.

The immune microenvironment in gastric adenocarcinoma

Like most solid tumours, the microenvironment of epithelial-derived gastric adenocarcinoma (GAC) consists of a variety of stromal cell types, including fibroblasts, and neuronal, endothelial and immune cells. In this article, we review the role of the immune microenvironment in the progression of chronic inflammation to GAC, primarily the immune microenvironment driven by the gram-negative bacterial species Helicobacter pylori. The infection-driven nature of most GACs has renewed awareness of the immune microenvironment and its effect on tumour development and progression. About 75-90% of GACs are associated with prior H. pylori infection and 5-10% with Epstein-Barr virus infection. Although 50% of the world's population is infected with H. pylori, only 1-3% will progress to GAC, with progression the result of a combination of the H. pylori strain, host susceptibility and composition of the chronic inflammatory response. Other environmental risk factors include exposure to a high-salt diet and nitrates. Genetically, chromosome instability occurs in ~50% of GACs and 21% of GACs are microsatellite instability-high tumours. Here, we review the timeline and pathogenesis of the events triggered by H. pylori that can create an immunosuppressive microenvironment by modulating the host's innate and adaptive immune responses, and subsequently favour GAC development.

Helicobacter pylori infection induces stem cell-like properties in Correa cascade of gastric cancer

Gastric cancer (GC) is the fourth leading cause of cancer-related death. Its poor prognosis is attributed to unclear pathogenesis. Currently, the most widely accepted model for elucidating the mechanism of GC is the Correa cascade, which covers several histological lesions of the gastric mucosa. GC stem cells (CSCs) are crucial for oncogenesis in the Correa cascade and GC progression. As Helicobacter pylori (H. pylori) is the etiological factor in the Correa cascade, growing evidence suggests that enhancement of gastric stem cell-like properties and increase in CSCs correlate with H. pylori infection. In this paper, we review recent studies that present pathogenic mechanisms by which H. pylori induces gastric stem cell-like properties and CSCs, which may supplement the existing Correa model of GC. First, the dysfunction of developmental signaling pathways associated with H. pylori infection leads to the enhancement of gastric stemness. Second, H. pylori infection promotes alteration of the gastric mucosal microenvironment. In addition, epithelial-mesenchymal transition (EMT) may contribute to H. pylori-induced gastric stemness. Taken together, understanding these pathogeneses will provide potential therapeutic targets for the treatment of CSCs and malignant GC in H. pylori induced-Correa cascade of GC.

GM-CSF is key in the efficacy of vaccine-induced reduction of Helicobacter pylori infection

BACKGROUND

Helicobacter pylori (H. pylori) colonizes the human gastric mucosa with a high worldwide prevalence. Currently, H. pylori is eradicated by the use of antibiotics. However, elevated antibiotic resistance suggests new therapeutic strategies need to be envisioned: one approach being prophylactic vaccination. Pre-clinical and clinical data show that a urease-based vaccine is efficient in decreasing H. pylori infection through the mobilization of T helper (Th) cells, especially Th17 cells. Th17 cells produce interleukins such as IL-22 and IL-17, among others, and are key players in vaccine efficacy. Recently, granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing Th17 cells have been identified.

AIM

This study explores the possibility that GM-CSF plays a role in the reduction of H. pylori infection following vaccination.

RESULTS

We demonstrate that GM-CSF⁺ IL-17⁺ Th17 cells accumulate in the stomach mucosa of H. pylori infected mice during the vaccine-induced reduction of H. pylori infection. Secondly, we provide evidence that vaccinated GM-CSF deficient mice only modestly reduce H. pylori infection. Conversely, we observe that an increase in GM-CSF availability reduces H. pylori burden in chronically infected mice. Thirdly, we show that GM-CSF, by acting on gastric epithelial cells, promotes the production of βdefensin3, which exhibits H. pylori bactericidal activities.

CONCLUSION

Taken together, we demonstrate a key role of GM-CSF, most probably originating from Th17 cells, in the vaccine-induced reduction of H. pylori infection.

Schlafens Can Put Viruses to Sleep

The Schlafen gene family encodes for proteins involved in various biological tasks, including cell proliferation, differentiation, and T cell development. Schlafens were initially discovered in mice, and have been studied in the context of cancer biology, as well as their role in protecting cells during viral infection. This protein family provides antiviral barriers via direct and indirect effects on virus infection. Schlafens can inhibit the replication of viruses with both RNA and DNA genomes. In this review, we summarize the cellular functions and the emerging relationship between Schlafens and innate immunity. We also discuss the functions and distinctions of this emerging family of proteins as host restriction factors against viral infection. Further research into Schlafen protein function will provide insight into their mechanisms that contribute to intrinsic and innate host immunity.

Slfn4 deficiency improves MAPK-mediated inflammation, oxidative stress, apoptosis and abates atherosclerosis progression in apolipoprotein E-deficient mice

BACKGROUND AND AIMS

Atherosclerosis, a progressive inflammatory disease characterized by elevated inflammation and lipid accumulation in the aortic endothelium, arises in part from the infiltration of inflammatory cells into the vascular wall. However, it is not fully defined how inflammatory cells, especially macrophages, affect the pathogenesis of atherosclerosis. Schlafen4 (Slfn4) mRNA is remarkably upregulated upon ox-LDL stimulation in macrophages. Nonetheless, the role of Slfn4 in foam cell formation remains unclear.

METHODS

To determine whether and how Slfn4 regulates lesion macrophage function during atherosclerosis，we engineered ApoE-/-Slfn4-/- double-deficient mice on an ApoE-/- background and evaluated the deficiency of Slfn4 expression in atherosclerotic lesion formation in vivo.

RESULTS

Our results demonstrate that total absence of SLFN4 and the bone marrow-restricted deletion of Slfn4 in ApoE-/- mice remarkably diminish inflammatory cell numbers within arterial plaques as well as limit development of atherosclerosis in moderate hypercholesterolemia condition. This is linked to a marked reduction in the expression of proinflammatory cytokines, the generation of the reactive oxygen species (ROS) and the apoptosis of cells. Furthermore, the activation of MAPKs and apoptosis signaling pathways is compromised in the absence of Slfn4.

CONCLUSIONS

These findings demonstrate a novel role of Slfn4 in modulating vascular inflammation and atherosclerosis, highlighting a new target for the related diseases.

The TLR4-TRIF-type 1 IFN-IFN-γ pathway is crucial for gastric MALT lymphoma formation after Helicobacter suis infection

Helicobacter suis, a zoonotic infection-related bacterium, can induce gastric mucosa-associated lymphoid tissue (MALT) lymphoma in humans and animals. Recently, we reported that the formation of gastric MALT lymphoma after H. suis infection is induced by interferon (IFN)-γ activation. Here, we revealed that activation of the Toll-like receptor (TLR) 4–Toll/IL-1 receptor domain-containing adapter-inducing interferon-β (TRIF) pathway after H. suis infection is associated with the production of type 1 IFNs (IFN-α, IFN-β) by gastric epithelial cells. Additionally, these type 1 IFNs interact with type 1 IFN receptors on gastric B cells, facilitating the secretion of IFN-γ and the activation of which is enhanced by positive feedback regulation in B cells. These results suggest that the TLR4–TRIF-type 1 IFN–IFN-γ pathway is crucial in the development of gastric MALT lymphoma after H. suis infection and may, therefore, represent a therapeutic target for the prevention of this condition.

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H. suis MPLA causes type 1 IFN production in the stomach via TLR4–TRIF signaling

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The interaction between type 1 IFNs and IFNAR on B cells causes IFN-γ production

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Interaction of IFN-γ and IFNGR on B cells causes IFN-γ positive feedback regulation

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IFN-γ from gastric B cells induces gastric lymphoid follicles after H. suis infection

Schlafens: Emerging Proteins in Cancer Cell Biology

Schlafens (SLFN) are a family of genes widely expressed in mammals, including humans and rodents. These intriguing proteins play different roles in regulating cell proliferation, cell differentiation, immune cell growth and maturation, and inhibiting viral replication. The emerging evidence is implicating Schlafens in cancer biology and chemosensitivity. Although Schlafens share common domains and a high degree of homology, different Schlafens act differently. In particular, they show specific and occasionally opposing effects in some cancer types. This review will briefly summarize the history, structure, and non-malignant biological functions of Schlafens. The roles of human and mouse Schlafens in different cancer types will then be outlined. Finally, we will discuss the implication of Schlafens in the anti-tumor effect of interferons and the use of Schlafens as predictors of chemosensitivity.

Plasmacytoid dendritic cells-derived IFN-α is involved in Helicobacter pylori infection-induced differentiation of Schlafen 4-expressing myeloid-derived suppressor cells

During chronic infection with Helicobacter pylori, Schlafen 4-expressing myeloid-derived suppressor cells (SLFN4⁺ MDSCs) create a microenvironment favoring intestinal metaplasia and neoplastic transformation. SLFN4 can be induced by IFN-α, which is mainly secreted from plasmacytoid dendritic cells (pDCs). This study tested the hypothesis that Helicobacter pylori infection promotes SLFN4⁺ MDSC differentiation by inducing pDCs to secrete IFN-α. C57BL/6 mice were gavaged with H. pylori and infection lasted 2, 4, or 6 months. The mouse pDCs were isolated from the bone marrow from wild type C57BL/6J mice. The results showed that H. pylori infection increased the number of SLFN4⁺ MDSCs by inducing IFN-α expression in mice. Further mechanistic experiments unraveled that IFN-α induced SLFN4 transcription by binding to the SLFN4 promoter. Furthermore, H. pylori infection stimulated pDCs to secrete IFN-α by activating the TLR9-MyD88-IRF7 pathway. Collectively, Helicobacter pylori infection promotes SLFN4⁺ MDSC differentiation by inducing secretion of IFN-α from pDCs.

Stomach-specific c-Myc overexpression drives gastric adenoma in mice through AKT/mammalian target of rapamycin signaling

Gastric cancer (GC) is one of the most common malignant cancers in the world. c-Myc, a well-known oncogene, is commonly amplified in many cancers, including gastric cancer. However, it is still not completely understood how c-Myc functions in GC. Here, we generated a stomach-specific c-Myc transgenic mouse model to investigate its role in GC. We found that overexpression of c-Myc in Atp4b+ gastric parietal cells could induce gastric adenoma in mice. Mechanistically, c-Myc promoted tumorigenesis via the AKT/mTOR pathway. Furthermore, AKT inhibitor (MK-2206) or mTOR inhibitor (Rapamycin) inhibited the proliferation of c-Myc overexpressing gastric cancer cell lines. Thus, our findings highlight that gastric tumorigenesis can be induced by c-Myc overexpression through activation of the AKT/mTOR pathway.

Hedgehog signaling modulates cigarette-induced COPD development

Hedgehog (Hh) signaling is involved in early embryogenesis and maintains quiescence in the adult lungs. The interruption of Hh signaling may lead to the development of chronic obstructive pulmonary disease (COPD). The current study aimed to assess whether the Hh pathway affects cigarette-induced emphysema and airway inflammation by regulating inflammatory cytokines. C57BL/6J mice were randomized into control, cigarette smoke (CS) or CS + cyclopamine (CSC) groups. Control mice were exposed to normal room air, CS mice were exposed to tobacco smoke and CSC mice were exposed to CS and received cyclopamine treatment. Histopathological examination of lung tissues was performed, and the expression of sonic hedgehog (HH), glioma-associated oncogene homolog 1 (Gli1), hedgehog-interacting protein (HIP) and several inflammatory mediators (intracellular adhesion molecule-1, IL-6, IL-8 and TNF-α) were compared using reverse transcription-quantitative PCR and western blotting. The emphysema of lung tissues by histopathological examination demonstrated partial amelioration in the CSC group compared with that in the CS group. Additionally, expression levels of SHH, Gli1 and inflammatory mediators were significantly higher in the CS group compared with the control group but were significantly decreased in the CSC group. The expression of HIP was decreased in the CS group, but significantly increased in the CSC group. Hh signaling may serve an important role in cigarette-induced emphysema and airway inflammation by regulating inflammatory cytokines in animal models. Therefore, diminishing the activation of the Hh signal may serve as a novel therapeutic strategy for patients suffering from smoking-related COPD.

Programmed Death Ligand 1-Expressing Classical Dendritic Cells MitigateHelicobacter-Induced Gastritis

BACKGROUND & AIMS

Helicobacter pylori has been reported to modulate local immune responses to colonize persistently in gastric mucosa. Although the induced expression of programmed cell death ligand 1 (PD-L1) has been suggested as an immune modulatory mechanism for persistent infection of H pylori, the main immune cells expressing PD-L1 and their functions in Helicobacter-induced gastritis still remain to be elucidated.

METHODS

The blockades of PD-L1 with antibody or PD-L1-deficient bone marrow transplantation were performed in Helicobacter-infected mice. The main immune cells expressing PD-L1 in Helicobacter-infected stomach were determined by flow cytometry and immunofluorescence staining. Helicobacter felis or H pylori-infected dendritic cell (DC)-deficient mouse models including Flt3-/-, Zbtb46-diphtheria toxin receptor, and BDCA2-diphtheria toxin receptor mice were analyzed for pathologic changes and colonization levels. Finally, the location of PD-L1-expressing DCs and the correlation with H pylori infection were analyzed in human gastric tissues using multiplexed immunohistochemistry.

RESULTS

Genetic or antibody-mediated blockade of PD-L1 aggravated Helicobacter-induced gastritis with mucosal metaplasia. Gastric classical DCs expressed considerably higher levels of PD-L1 than other immune cells and co-localized with T cells in gastritis lesions from Helicobacter-infected mice and human beings. H felis- or H pylori-infected Flt3-/- or classical DC-depleted mice showed aggravated gastritis with severe T-cell and neutrophil accumulation with low bacterial loads compared with that in control mice. Finally, PD-L1-expressing DCs were co-localized with T cells and showed a positive correlation with H pylori infection in human subjects.

CONCLUSIONS

The PD-1/PD-L1 pathway may be responsible for the immune modulatory function of gastric DCs that protects the gastric mucosa from Helicobacter-induced inflammation, but allows persistent Helicobacter colonization.

Cellular plasticity at the nexus of development and disease

In October 2020, the Keystone Symposia Global Health Series hosted a Keystone eSymposia entitled 'Tissue Plasticity: Preservation and Alteration of Cellular Identity'. The event synthesized groundbreaking research from unusually diverse fields of study, presented in various formats, including live and virtual talks, panel discussions and interactive e-poster sessions. The meeting focused on cell identity changes and plasticity in multiple tissues, species and developmental contexts, both in homeostasis and during injury. Here, we review the key themes of the meeting: (1) cell-extrinsic drivers of plasticity; (2) epigenomic regulation of cell plasticity; and (3) conserved mechanisms governing plasticity. A salient take-home conclusion was that there may be conserved mechanisms used by cells to execute plasticity, with autodegradative activity (autophagy and lysosomes) playing a crucial initial step in diverse organs and organisms.

Hedgehog Signaling: Implications in Cancers and Viral Infections

The hedgehog (SHH) signaling pathway is primarily involved in embryonic gut development, smooth muscle differentiation, cell proliferation, adult tissue homeostasis, tissue repair following injury, and tissue polarity during the development of vertebrate and invertebrate organisms. GLIoma-associated oncogene homolog (GLI) family of zinc-finger transcription factors and smoothened (SMO) are the signal transducers of the SHH pathway. Both SHH ligand-dependent and independent mechanisms activate GLI proteins. Various transcriptional mechanisms, posttranslational modifications (phosphorylation, ubiquitination, proteolytic processing, SUMOylation, and acetylation), and nuclear-cytoplasmic shuttling control the activity of SHH signaling pathway proteins. The dysregulated SHH pathway is associated with bone and soft tissue sarcomas, GLIomas, medulloblastomas, leukemias, and tumors of breast, lung, skin, prostate, brain, gastric, and pancreas. While extensively studied in development and sarcomas, GLI family proteins play an essential role in many host-pathogen interactions, including bacterial and viral infections and their associated cancers. Viruses hijack host GLI family transcription factors and their downstream signaling cascades to enhance the viral gene transcription required for replication and pathogenesis. In this review, we discuss a distinct role(s) of GLI proteins in the process of tumorigenesis and host-pathogen interactions in the context of viral infection-associated malignancies and cancers due to other causes. Here, we emphasize the potential of the Hedgehog (HH) pathway targeting as a potential anti-cancer therapeutic approach, which in the future could also be tested in infection-associated fatalities.

Interleukin-1β Suppresses Gastrin via Primary Cilia and Induces Antral Hyperplasia

BACKGROUND & AIMS

Helicobacter pylori infection in humans typically begins with colonization of the gastric antrum. The initial Th1 response occasionally coincides with an increase in gastrin secretion. Subsequently, the gastritis segues to chronic atrophic gastritis, metaplasia, dysplasia and distal gastric cancer. Despite these well characterized clinical events, the link between inflammatory cytokines and non-cardia gastric cancer remains difficult to study in mouse models. Prior studies have demonstrated that overexpression of the Hedgehog (HH) effector GLI2 induces loss of gastrin (atrophy) and antral hyperplasia. To determine the link between specific cytokines, HH signaling and pre-neoplastic changes in the gastric antrum.

METHODS

Mouse lines were created to conditionally direct IL1β or IFN-γ to the antrum using the Gastrin-CreERT2 and Tet activator. Primary cilia, which transduces HH signaling, on G cells were disrupted by deleting the ciliary motor protein KIF3a. Phenotypic changes were assessed by histology and western blots. A subclone of GLUTag enteroendocrine cells selected for gastrin expression and the presence of primary cilia was treated with recombinant SHH, IL1β or IFN-γ with or without kif3a siRNA.

RESULTS

IFN-γ increased gastrin and induced antral hyperplasia. However, antral expression of IL1β suppressed tissue and serum gastrin, while also inducing antral hyperplasia. IFN-γ treatment of GLUTAg cells suppressed GLI2 and induced gastrin, without affecting cilia length. By contrast, IL1β treatment doubled primary cilia length, induced GLI2 and suppressed gastrin gene expression. Knocking down kif3a in GLUTAg cells mitigated SHH or IL1β suppression of gastrin.

CONCLUSIONS

Overexpression of IL1β in the antrum was sufficient to induce antral hyperplasia coincident with suppression of gastrin via primary cilia. ORCID: #0000-0002-6559-8184.

MiR130b from Schlafen4+ MDSCs stimulates epithelial proliferation and correlates with preneoplastic changes prior to gastric cancer

The myeloid differentiation factor Schlafen4 (Slfn4) marks a subset of myeloid-derived suppressor cells (MDSCs) in the stomach during Helicobacter-induced spasmolytic polypeptide-expressing metaplasia (SPEM).

OBJECTIVE

To identify the gene products expressed by Slfn4⁺-MDSCs and to determine how they promote SPEM.

DESIGN

We performed transcriptome analyses for both coding genes (mRNA by RNA-Seq) and non-coding genes (microRNAs using NanoString nCounter) using flow-sorted SLFN4⁺ and SLFN4^- cells from Helicobacter-infected mice exhibiting metaplasia at 6 months postinfection. Thioglycollate-elicited myeloid cells from the peritoneum were cultured and treated with IFNα to induce the T cell suppressor phenotype, expression of MIR130b and SLFN4. MIR130b expression in human gastric tissue including gastric cancer and patient sera was determined by qPCR and in situ hybridisation. Knockdown of MiR130b in vivo in Helicobacter-infected mice was performed using Invivofectamine. Organoids from primary gastric cancers were used to generate xenografts. ChIP assay and Western blots were performed to demonstrate NFκb p65 activation by MIR130b.

RESULTS

MicroRNA analysis identified an increase in MiR130b in gastric SLFN4⁺ cells. Moreover, MIR130b colocalised with SLFN12L, a human homologue of SLFN4, in gastric cancers. MiR130b was required for the T-cell suppressor phenotype exhibited by the SLFN4⁺ cells and promoted Helicobacter-induced metaplasia. Treating gastric organoids with the MIR130b mimic induced epithelial cell proliferation and promoted xenograft tumour growth.

CONCLUSION

Taken together, MiR130b plays an essential role in MDSC function and supports metaplastic transformation.

Resveratrol Inhibition of Renal Cancer Stem Cell Characteristics and Modulation of the Sonic Hedgehog Pathway

AIMS

Renal cell cancers typically exhibit high metastasis and recurrence, and this is thought to be due to renal cancer stem cells (CSCs). Meanwhile, aberrant activation of Sonic hedgehog (Shh) signaling is linked with CSCs. Resveratrol has direct or indirect impacts on the pathological activities of CSCs. However, the effects of resveratrol on renal CSCs remain to be elucidated.

METHODS

We cultured renal CSCs in serum-free medium. Western blotting was used to analyze the expression levels of related proteins. The mRNA changes were detected by qRT-PCR after resveratrol treatment. The CD133⁺ cells were quantified by flow cytometry analysis. Immunofluorescence staining images showed the changes in CD44 and Smoothened expression in the cell spheres.

RESULTS

Renal CSCs were enriched by tumorsphere formation assays of ACHN and 786-O cells. Resveratrol treatments markedly decreased the size and number of cell spheres and downregulated the expression of the Shh pathway-related proteins and CSCs markers. Moreover, we observed that resveratrol inhibited cell proliferation and induced cell apoptosis, while purmorphamine upregulated the Shh pathway and weakened the effects of resveratrol on renal CSCs.

CONCLUSIONS

These results suggested that resveratrol is a potential novel therapeutic agent that targets inactivation of renal CSCs by affecting the function of the Shh pathway.

Aim2-mediated/IFN-β-independent regulation of gastric metaplastic lesions via CD8+ T cells

Development of gastric cancer is often preceded by chronic inflammation, but the immune cellular mechanisms underlying this process are unclear. Here we demonstrated that an inflammasome molecule, absent in melanoma 2 (Aim2), was upregulated in patients with gastric cancer and in spasmolytic polypeptide-expressing metaplasia of chronically Helicobacter felis-infected stomachs in mice. However, we found that Aim2 was not necessary for inflammasome function during gastritis. In contrast, Aim2 deficiency led to an increase in gastric CD8+ T cell frequency, which exacerbated metaplasia. These gastric CD8+ T cells from Aim2-/- mice were found to have lost their homing receptor expression (sphingosine-1-phosphate receptor 1 [S1PR1] and CD62L), a feature of tissue-resident memory T cells. The process was not mediated by Aim2-dependent regulation of IFN-β or by dendritic cell-intrinsic Aim2. Rather, Aim2 deficiency contributed to an increased production of CXCL16 by B cells, which could suppress S1PR1 and CD62L in CD8+ T cells. This study describes a potentially novel function of Aim2 that regulates CD8+ T cell infiltration and retention within chronically inflamed solid organ tissue. This function operates independent of the inflammasome, IFN-β, or dendritic cells. We provide evidence that B cells can contribute to this mechanism via CXCL16.

The extracellular sulfatase SULF2 promotes liver tumorigenesis by stimulating assembly of a promoter-looping GLI1-STAT3 transcriptional complex

The expression of the extracellular sulfatase SULF2 has been associated with increased hepatocellular carcinoma (HCC) growth and poor patient survival. However, the molecular mechanisms underlying SULF2-associated tumor growth remain unclear. To address this gap, here we developed a transgenic mouse overexpressing Sulf2 in hepatocytes under the control of the transthyretin promoter. In this model, Sulf2 overexpression potentiated diethylnitrosamine-induced HCC. Further analysis indicated that the transcription factor GLI family zinc finger 1 (GLI1) mediates Sulf2 expression during HCC development. A cross of the Sulf2-overexpressing with Gli1-knockout mice revealed that Gli1 inactivation impairs SULF2-induced HCC. Transcriptomic analysis revealed that Sulf2 overexpression is associated with signal transducer and activator of transcription 3 (STAT3)-specific gene signatures. Interestingly, the Gli1 knockout abrogated SULF2-mediated induction of several STAT3 target genes, including suppressor of cytokine signaling 2/3 (Socs2/3); Pim-1 proto-oncogene, Ser/Thr kinase (Pim1); and Fms-related tyrosine kinase 4 (Flt4). Human orthologs were similarly regulated by SULF2, dependent on intact GLI1 and STAT3 functions in HCC cells. SULF2 overexpression promoted a GLI1-STAT3 interaction and increased GLI1 and STAT3 enrichment at the promoters of their target genes. Interestingly, the SULF2 overexpression resulted in GLI1 enrichment at select STAT3 consensus sites, and vice versa. siRNA-mediated STAT3 or GLI1 knockdown reduced promoter binding of GLI1 and STAT3, respectively. Finally, chromatin-capture PCR confirmed long-range co-regulation of SOCS2 and FLT3 through changes in promoter conformation. These findings define a mechanism whereby SULF2 drives HCC by stimulating formation of a GLI1-STAT3 transcriptional complex.

Hedgehog/GLI signaling in tumor immunity - new therapeutic opportunities and clinical implications

Uncontrolled activation of the Hedgehog/Glioma-associated oncogene (HH/GLI) pathway is a potent oncogenic driver signal promoting numerous cancer hallmarks such as proliferation, survival, angiogenesis, metastasis and metabolic rewiring. Several HH pathway inhibitors have already been approved for medical therapy of advanced and metastatic basal cell carcinoma and acute myeloid leukemia with partially impressive therapeutic activity. However, de novo and acquired resistance as well as severe side effects and unexplained lack of therapeutic efficacy are major challenges that urgently call for improved treatment options with more durable responses. The recent breakthroughs in cancer immunotherapy have changed our current understanding of targeted therapy and opened up promising therapeutic opportunities including combinations of selective cancer pathway and immune checkpoint inhibitors. Although HH/GLI signaling has been intensely studied with respect to the classical hallmarks of cancer, its role in the modulation of the anti-tumoral immune response has only become evident in recent studies. These have uncovered HH/GLI regulated immunosuppressive mechanisms such as enhanced regulatory T-cell formation and production of immunosuppressive cytokines. In light of these exciting novel data on oncogenic HH/GLI signaling in immune cross-talk and modulation, we summarize and connect in this review the existing knowledge from different HH-related cancers and chronic inflammatory diseases. This is to provide a basis for the investigation and evaluation of novel treatments combining immunotherapeutic strategies with approved as well as next-generation HH/GLI inhibitors. Further, we also critically discuss recent studies demonstrating a possible negative impact of current HH/GLI pathway inhibitors on the anti-tumoral immune response, which may explain some of the disappointing results of several oncological trials with anti-HH drugs.

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Hedgehog Signaling Modulates Interleukin-33-Dependent Extrahepatic Bile Duct Cell Proliferation in Mice

Hedgehog (HH) signaling participates in hepatobiliary repair after injury and is activated in patients with cholangiopathies. Cholangiopathies are associated with bile duct (BD) hyperplasia, including expansion of peribiliary glands, the niche for biliary progenitor cells. The inflammation-associated cytokine interleukin (IL)-33 is also up-regulated in cholangiopathies, including cholangiocarcinoma. We hypothesized that HH signaling synergizes with IL-33 in acute inflammation-induced BD hyperplasia. We measured extrahepatic BD (EHBD) thickness and cell proliferation with and without an IL-33 challenge in wild-type mice, mice overexpressing Sonic HH (pCMV-Shh), and mice with loss of the HH pathway effector glioma-associated oncogene 1 (Gli1lacZ/lacZ ). LacZ reporter mice were used to map the expression of HH effector genes in mouse EHBDs. An EHBD organoid (BDO) system was developed to study biliary progenitor cells in vitro. EHBDs from the HH overexpressing pCMV-Shh mice showed increased epithelial cell proliferation and hyperplasia when challenged with IL-33. In Gli1lacZ/lacZ mice, we observed a decreased proliferative response to IL-33 and decreased expression of Il6. The HH ligands Shh and Indian HH (Ihh) were expressed in epithelial cells, whereas the transcriptional effectors Gli1, Gli2, and Gli3 and the HH receptor Patched1 (Ptch1) were expressed in stromal cells, as assessed by in situ hybridization and lacZ reporter mice. Although BDO cells lacked canonical HH signaling, they expressed the IL-33 receptor suppression of tumorigenicity 2. Accordingly, IL-33 treatment directly induced BDO cell proliferation in a nuclear factor κB-dependent manner. Conclusion: HH ligand overexpression enhances EHBD epithelial cell proliferation induced by IL-33. This proproliferative synergism of HH and IL-33 involves crosstalk between HH ligand-producing epithelial cells and HH-responding stromal cells.

Pseudopod-associated protein KIF20B promotes Gli1-induced epithelial-mesenchymal transition modulated by pseudopodial actin dynamic in human colorectal cancer

Kinesin family member 20B (KIF20B) has been reported to have an oncogenic role in bladder and hepatocellular cancer cells, but its role in colorectal cancer (CRC) progression remains unclear. In this study, we assessed the mRNA and protein levels of KIF20B in CRC tissues using qRT-PCR and immunohistochemistry, respectively. KIF20B was overexpressed in CRC tissues and was associated with cancer invasion and metastasis. Mechanistically, KIF20B overexpression promoted the epithelial-mesenchymal transition (EMT) process mediated by glioma-associated oncogene 1 (Gli1) as well as CRC cell migration and invasion. Interestingly, KIF20B was localized in pseudopod protrusions of CRC cells and influenced the formation of cell protrusions, especially the EMT-related invadopodia. Moreover, intracellular actin dynamic participated in the modulation of the Gli1-mediated EMT and EMT-related cell pseudopod protrusion formation induced by KIF20B. We identified a role for KIF20B in CRC progression and revealed a correlation between KIF20B expression in CRC tissues and patient prognosis. The underlying mechanism was associated with the Gli1-mediated EMT and EMT-related cell protrusion formation modulated by intracellular actin dynamic. Thus, KIF20B may be a potential biomarker and promising treatment target for CRC.

Gastric cancer and Hedgehog signaling pathway: emerging new paradigms

Ever since its initial discovery in Drosophila, hedgehog signaling has been linked to foregut development, The mammalian genome expresses three Hedgehog paralogues, sonic hedgehog (Shh), Indian Hedgehog, and desert hedgehog. In the mucosa of the embryonic and adult foregut, Shh expression is the highest. It has now become clear that hedgehog signaling is of pivotal importance in gastric homeostasis. Aberrant activation of hedgehog signaling is associated with a range of pathological consequences including various cancers. Also in gastric cancer, clinical and preclinical data support a role of Hedgehog signaling in neoplastic transformation, and gastrointestinal cancer development, also through cancer stroma interaction. Technological advance are facilitating monitoring Hedgehog signaling broadening options for the more efficient screening of individuals predisposed to eventually developing gastric cancer and targeting Hedgehog signaling may provide opportunities for prophylactic therapy once atrophic gastritis develops. Nevertheless, convincing evidence that Hedgehog antagonists are of clinically useful in the context of gastric cancer is still conspicuously lacking. Here we analyze review the role of Hedgehog in gastric physiology and the potential usefulness of targeting Hedgehog signaling in gastric cancer.

Molecular Characterization of Gastric Epithelial Cells Using Flow Cytometry

The ability to analyze individual epithelial cells in the gastric mucosa would provide important insight into gastric disease, including chronic gastritis and progression to gastric cancer. However, the successful isolation of viable gastric epithelial cells (parietal cells, neck cells, chief cells, and foveolar cells) from gastric glands has been limited due to difficulties in tissue processing. Furthermore, analysis and interpretation of gastric epithelial cell flow cytometry data has been difficult due to the varying sizes and light scatter properties of the different epithelial cells, high levels of autofluorescence, and poor cell viability. These studies were designed to develop a reliable method for isolating viable single cells from the corpus of stomachs and to optimize analyses examining epithelial cells from healthy and diseased stomach tissue by flow cytometry. We performed a two stage enzymatic digestion in which collagenase released individual gastric glands from the stromal tissue of the corpus, followed by a Dispase II digestion that dispersed these glands into greater than 1 × 10⁶ viable single cells per gastric corpus. Single cell suspensions were comprised of all major cell lineages found in the normal gastric glands. A method describing light scatter, size exclusion, doublet discrimination, viability staining, and fluorescently-conjugated antibodies and lectins was used to analyze individual epithelial cells and immune cells. This technique was capable of identifying parietal cells and revealed that gastric epithelial cells in the chronically inflamed mucosa significantly upregulated major histocompatibility complexes (MHC) I and II but not CD80 or CD86, which are costimulatory molecules involved in T cell activation. These studies describe a method for isolating viable single cells and a detailed description of flow cytometric analysis of cells from healthy and diseased stomachs. These studies begin to identify effects of chronic inflammation on individual gastric epithelial cells, a critical consideration for the study of gastric cancer.

Indoleamine 2,3-Dioxygenase 1, Increased in Human Gastric Pre-Neoplasia, Promotes Inflammation and Metaplasia in Mice and Is Associated With Type II Hypersensitivity/Autoimmunity

BACKGROUND & AIMS

Chronic gastrointestinal inflammation increases the risk of cancer by mechanisms that are not well understood. Indoleamine-2,3-dioxygenase 1 (IDO1) is a heme-binding enzyme that regulates the immune response via catabolization and regulation of tryptophan availability for immune cell uptake. IDO1 expression is increased during the transition from chronic inflammation to gastric metaplasia. We investigated whether IDO1 contributes to the inflammatory response that mediates loss of parietal cells leading to metaplasia.

METHODS

Chronic gastric inflammation was induced in Ido1^-/- and CB57BL/6 (control) mice by gavage with Helicobacter felis or overexpression of interferon gamma in gastric parietal cells. We also performed studies in Jh^-/- mice, which are devoid of B cells. Gastric tissues were collected and analyzed by flow cytometry, immunostaining, and real-time quantitative polymerase chain reaction. Plasma samples were analyzed by enzyme-linked immunosorbent assay. Gastric tissues were obtained from 20 patients with gastric metaplasia and 20 patients without gastric metaplasia (controls) and analyzed by real-time quantitative polymerase chain reaction; gastric tissue arrays were analyzed by immunohistochemistry. We collected genetic information on gastric cancers from The Cancer Genome Atlas database.

RESULTS

H felis gavage induced significantly lower levels of pseudopyloric metaplasia in Ido1^-/- mice, which had lower frequencies of gastric B cells, than in control mice. Blood plasma from H felis-infected control mice had increased levels of autoantibodies against parietal cells, compared to uninfected control mice, but this increase was lower in Ido1^-/- mice. Chronically inflamed stomachs of Ido1^-/- mice had significantly lower frequencies of natural killer cells in contact with parietal cells, compared with stomachs of control mice. Jh^-/- mice had lower levels of pseudopyloric metaplasia than control mice in response to H felis infection. Human gastric pre-neoplasia and carcinoma specimens had increased levels of IDO1 messenger RNA compared with control gastric tissues, and IDO1 protein colocalized with B cells. Co-clustering of IDO1 messenger RNA with B-cell markers was corroborated by The Cancer Genome Atlas database.

CONCLUSIONS

IDO1 mediates gastric metaplasia by regulating the B-cell compartment. This process appears to be associated with type II hypersensitivity/autoimmunity. The role of autoimmunity in the progression of pseudopyloric metaplasia warrants further investigation.

Regulation of Hedgehog Signaling in Cancer by Natural and Dietary Compounds

The aberrant Hedgehog (Hh) signaling induced by mutations or overexpression of the signaling mediators has been implicated in cancer, associated with processes including inflammation, tumor cell growth, invasion, and metastasis, as well as cancer stemness. Small molecules targeting the regulatory components of the Hh signaling pathway, especially Smoothened (Smo), have been developed for the treatment of cancer. However, acquired resistance to a Smo inhibitor vismodegib observed in clinical trials suggests that other Hh signaling components need to be explored as potential anticancer targets. Natural and dietary compounds provide a resource for the development of potent agents affecting intracellular signaling cascades, and numerous studies have been conducted to evaluate the efficacy of natural products in targeting the Hh signaling pathway. In this review, we summarize the role of Hh signaling in tumorigenesis, discuss results from recent studies investigating the effect of natural products and dietary components on Hh signaling in cancer, and provide insight on novel small molecules as potential Hh signaling inhibitors.

The Hedgehog Signaling Pathway Emerges as a Pathogenic Target

The Hedgehog (Hh) signaling pathway plays an essential role in the growth, development, and homeostatis of many tissues in vertebrates and invertebrates. Much of what is known about Hh signaling is in the context of embryonic development and tumor formation. However, a growing body of evidence is emerging indicating that Hh signaling is also involved in postnatal processes such as tissue repair and adult immune responses. To that extent, Hh signaling has also been shown to be a target for some pathogens that presumably utilize the pathway to control the local infected environment. In this review, we discuss what is currently known regarding pathogenic interactions with Hh signaling and speculate on the reasons for this pathway being a target. We also hope to shed light on the possibility of using small molecule modulators of Hh signaling as effective therapies for a wider range of human diseases beyond their current use in a limited number of cancers.

From inflammation to gastric cancer - the importance of Hedgehog/GLI signaling in Helicobacter pylori-induced chronic inflammatory and neoplastic diseases

Infections with the human pathogen Helicobacter pylori (H. pylori) are closely associated with the development of inflammatory disorders and neoplastic transformation of the gastric epithelium. Drastic changes in the micromilieu involve a complex network of H. pylori-regulated signal transduction pathways leading to the release of proinflammatory cytokines, gut hormones and a wide range of signaling molecules. Besides controlling embryonic development, the Hedgehog/GLI signaling pathway also plays important roles in epithelial proliferation, differentiation, and regeneration of the gastric physiology, but also in the induction and progression of inflammation and neoplastic transformation in H. pylori infections. Here, we summarize recent findings of H. pylori-associated Hedgehog/GLI signaling in gastric homeostasis, malignant development and the modulation of the gastric tumor microenvironment.

Initiation and Maintenance of Gastric Cancer: A Focus on CD44 Variant Isoforms and Cancer Stem Cells

Gastric cancer is the third most common cause of cancer-related death. Although the incidence of gastric cancer in the United States is relatively low, it remains significantly higher in some countries, including Japan and Korea. Interactions between cancer stem cells and the tumor microenvironment can have a substantial impact on tumor characteristics and contribute to heterogeneity. The mechanisms responsible for maintaining malignant cancer stem cells within the tumor microenvironment in human gastric cancer are largely unknown. Tumor cell and genetic heterogeneity contribute to either de novo intrinsic or the therapy-induced emergence of drug-resistant clones and eventual tumor recurrence. Although chemotherapy often is capable of inducing cell death in tumors, many cancer patients experience recurrence because of failure to effectively target the cancer stem cells, which are believed to be key tumor-initiating cells. Among the population of stem cells within the stomach that may be targeted during chronic Helicobacter pylori infection and altered into tumor-initiating cells are those cells marked by the cluster-of-differentiation (CD)44 cell surface receptor. CD44 variable isoforms (CD44v) have been implicated as key players in malignant transformation whereby their expression is highly restricted and specific, unlike the canonical CD44 standard isoform. Overall, CD44v, in particular CD44v9, are believed to mark the gastric cancer cells that contribute to increased resistance for chemotherapy- or radiation-induced cell death. This review focuses on the following: the alteration of the gastric stem cell during bacterial infection, and the role of CD44v in the initiation, maintenance, and growth of tumors associated with gastric cancer.

Role of Dietary Metabolites in Regulating the Host Immune Response in Gastrointestinal Disease

The host immune response to gastrointestinal (GI) infections, hypersensitivity reactions, or GI cancers comprises numerous pathways that elicit responses on different host cells. Some of these include (1) the stimulation of mast cells via their IgE receptor, (2) the production of antibodies leading to antibody-mediated cytotoxic T/natural killer cell killing, (3) the activation of the complement pathway, and (4) the activation of the adaptive immune response via antigen-presenting cell, T cell, and B cell interactions. Within the plethora of these different responses, several host immune cells represent major key players such as those of myeloid lineage (including neutrophils, macrophages, myeloid-derived suppressor cells) or lymphoid lineage (including T and B cells). In this review, we focus on newly identified metabolites and metabolite receptors that are expressed by either myeloid or lymphoid lineages. Irrespective of their source, these metabolites can in certain instances elicit responses on a wide range of cell types. The myeloid-expressed metabolic enzymes and receptors which we will discuss in this review include arginase 2 (Arg2), indoleamine-2,3-dioxygenase 1 (IDO1), hydroxycarboxylic acid receptor 2 (Hcar2; also called GPR109A), and immunoresponsive gene 1 (Irg1). We will also review the role of the lymphoid-expressed metabolite receptor that binds to the sphingosine-1-phosphate (S1P) sphingolipid. Moreover, we will describe the synthesis and metabolism of retinoic acid, and its effect on T cell activation. The review will then discuss the function of these metabolites in the context of GI disease. The review provides evidence that metabolic pathways operate in a disease- and context-dependent manner-either independently or concomitantly-in the GI tract. Therefore, an integrated approach and combinatorial analyses are necessary to devise new therapeutic strategies that can synergistically improve prognoses.

Hedgehog Signaling Links Chronic Inflammation to Gastric Cancer Precursor Lesions

Since its initial discovery in Drosophila, Hedgehog (HH) signaling has long been associated with foregut development. The mammalian genome expresses 3 HH ligands, with sonic hedgehog (SHH) levels highest in the mucosa of the embryonic foregut. More recently, interest in the pathway has shifted to improving our understanding of its role in gastrointestinal cancers. The use of reporter mice proved instrumental in our ability to probe the expression pattern of SHH ligand and the cell types responding to canonical HH signaling during homeostasis, inflammation, and neoplastic transformation. SHH is highly expressed in parietal cells and is required for these cells to produce gastric acid. Furthermore, myofibroblasts are the predominant cell type responding to HH ligand in the uninfected stomach. Chronic infection caused by Helicobacter pylori and associated inflammation induces parietal cell atrophy and the expansion of metaplastic cell types, a precursor to gastric cancer in human subjects. During Helicobacter infection in mice, canonical HH signaling is required for inflammatory cells to be recruited from the bone marrow to the stomach and for metaplastic development. Specifically, polarization of the invading myeloid cells to myeloid-derived suppressor cells requires the HH-regulated transcription factor GLI1, thereby creating a microenvironment favoring wound healing and neoplastic transformation. In mice, GLI1 mediates the phenotypic shift to gastric myeloid-derived suppressor cells by directly inducing Schlafen 4 (slfn4). However, the human homologs of SLFN4, designated SLFN5 and SLFN12L, also correlate with intestinal metaplasia and could be used as biomarkers to predict the subset of individuals who might progress to gastric cancer and benefit from treatment with HH antagonists.

Adult gastric stem cells and their niches

Adult gastric stem cells replenish the gastric epithelium throughout life. Recent studies have identified diverse populations of stem cells, progenitor cells, and even differentiated cells that can regain stem cell capacity, so highlighting an unexpected plasticity within the gastric epithelium, both in the corpus and antrum. Two niches seem to co-exist in the gastric unit: one in the isthmus region and the other at the base of the gland, although the precise features of the cell populations and the two niches are currently under debate. A variety of gastric organoid models have been established, providing new insights into niche factors required by the gastric stem cell populations. Here we review our current knowledge of gastric stem cell populations, their markers and interactions, important niche factors, and different gastric organoid systems. WIREs Dev Biol 2017, 6:e261. doi: 10.1002/wdev.261 For further resources related to this article, please visit the WIREs website.

SCHLAFEN 5 expression correlates with intestinal metaplasia that progresses to gastric cancer

BACKGROUND

Intestinal metaplasia (IM) is a gastric cancer precursor lesion (GCPL) and an extremely high risk factor for progression to gastric cancer (GC). Clinical guidelines recommend that patients with extensive IM undergo a gastroscopy every 3 years. However, protein biomarkers that indicate a transition from IM to GC are lacking. Our group recently identified an interferon-alpha (IFNα)-responsive gene, Schlafen 4 (Slfn4), in immune cells that correlates with metaplastic changes in Helicobacter-infected mice. We therefore tested the hypothesis that a human homolog of Slfn4, namely, Schlafen 5 (SLFN5), correlates with progression of GCPL to GC.

METHODS

Jurkat T-lymphoid and HL-60 myeloid cell lines were treated with IFNα, and SLFN5 mRNA was quantified by quantitative PCR. SLFN5 protein expression in the inflamed gastric mucosa was co-localized to specific immune cell types by immunohistochemistry using CD20, CD2, and MAC2 antibodies. SLFN5 expression was also determined by immunohistochemistry in formalin-fixed paraffin-embedded samples from individuals with non-atrophic gastritis, atrophic gastritis, complete IM, incomplete IM, and GC, respectively.

RESULTS

The IFNα treatment of Jurkat and HL-60 cells induced SLFN5 mRNA. SLFN5 protein was expressed mainly by T lymphocytes in inflamed gastric mucosa. The highest level of SLFN5 expression was observed in patients with IM that progressed to GC. Receiver operating characteristic curves demonstrated that correlating SLFN5 expression with the histologic diagnosis of IM significantly increased the probability of identifying patients who may progress to GC.

CONCLUSION

In this study population, elevated SLFN5 protein expression in patients with IM correlated with progression to GC.

Disruption of the Hedgehog signaling pathway in inflammatory bowel disease fosters chronic intestinal inflammation

Hedgehog (Hh) signaling is essential for intestinal homeostasis and has been associated with inflammation and tissue repair. We hypothesized that Hh signaling could affect the inflammatory process in inflammatory bowel disease (IBD). For this purpose, colon specimens from the inflamed and non-inflamed mucosa of 15 patients with Crohn's disease (CD), 15 with ulcerative colitis, and 15 controls were analyzed by immunohistochemistry and real-time PCR. The production and modulation of cytokines were measured by ELISA from culture explants. Apoptosis was assessed by TUNEL and caspase-3 activity assays. Chemotaxis was evaluated using a transwell system. Primary human intestinal and skin fibroblasts were used for analyzing migration and BrdU incorporation. Hh proteins were generally expressed at the superficial epithelium, and a marked reduction was observed in CD. In the lamina propria, Gli-1 predominantly co-localized with vimentin- and alpha-smooth muscle actin-positive cells, with lower levels observed in CD. In colon explants, Hh stimulation resulted in reduction, while blockade increased, TNF α, IL-17, and TGF β levels. Apoptotic rates were higher in inflamed samples, and they increased after Hh blockade. Levels of Gli-1 mRNA were negatively correlated with caspase-3 activity. Hh blockade increased chemoattraction of monocytes. Primary fibroblasts incorporated more BrdU, but migrated less after Hh blockade. These results suggest that Hh signaling provides a negative feedback to the lamina propria, down-regulating inflammatory cytokines, and inhibiting leukocyte migration and fibroblast proliferation, while favoring fibroblast migration. Therefore, Hh signaling is strongly implicated in the pathogenesis of intestinal inflammation, and it may represent a novel therapeutic target for IBD.

Schlafen 4-expressing myeloid-derived suppressor cells are induced during murine gastric metaplasia

Chronic Helicobacter pylori infection triggers neoplastic transformation of the gastric mucosa in a small subset of patients, but the risk factors that induce progression to gastric metaplasia have not been identified. Prior to cancer development, the oxyntic gastric glands atrophy and are replaced by metaplastic cells in response to chronic gastritis. Previously, we identified schlafen 4 (Slfn4) as a GLI1 target gene and myeloid differentiation factor that correlates with spasmolytic polypeptide-expressing metaplasia (SPEM) in mice. Here, we tested the hypothesis that migration of SLFN4-expressing cells from the bone marrow to peripheral organs predicts preneoplastic changes in the gastric microenvironment. Lineage tracing in Helicobacter-infected Slfn4 reporter mice revealed that SLFN4+ cells migrated to the stomach, where they exhibited myeloid-derived suppressor cell (MDSC) markers and acquired the ability to inhibit T cell proliferation. SLFN4+ MDSCs were not observed in infected GLI1-deficient mice. Overexpression of sonic hedgehog ligand (SHH) in infected WT mice accelerated the appearance of SLFN4+ MDSCs in the gastric corpus. Similarly, in the stomachs of H. pylori-infected patients, the human SLFN4 ortholog SLFN12L colocalized to cells that expressed MDSC surface markers CD15+CD33+HLA-DRlo. Together, these results indicate that SLFN4 marks a GLI1-dependent population of MDSCs that predict a shift in the gastric mucosa to a metaplastic phenotype.

Hedgehog signaling: modulation of cancer properies and tumor mircroenvironment

Cancer poses a serious health problem in society and is increasingly surpassing cardiovascular disease as the leading cause of mortality in the United States. Current therapeutic strategies for cancer are extreme and harsh to patients and often have limited success; the danger of cancer is intensified as it metastasizes to secondary locations such as lung, bone, and liver, posing a dire threat to patient treatment and survival. Hedgehog signaling is an important pathway for normal development. Initially identified in Drosophila, the vertebrate and mammalian equivalent of the pathway has been studied extensively for its role in cancer development and progression. As this pathway regulates key target genes involved in development, its action also allows for the modulation of the microenvironment to prepare a tumor-suitable niche by manipulating tumor cell growth, differentiation, and immune regulation, thus creating an enabling environment for progression and metastasis. In this review, we will summarize recent scientific discoveries reporting the impact of the Hedgehog signaling pathway on the tumor initiation process and metastatic cascade, shedding light on the ability of the tumor to take over a mechanism crucially intended for development and normal function.

Hedgehog signaling: modulation of cancer properies and tumor mircroenvironment

Cancer poses a serious health problem in society and is increasingly surpassing cardiovascular disease as the leading cause of mortality in the United States. Current therapeutic strategies for cancer are extreme and harsh to patients and often have limited success; the danger of cancer is intensified as it metastasizes to secondary locations such as lung, bone, and liver, posing a dire threat to patient treatment and survival. Hedgehog signaling is an important pathway for normal development. Initially identified in Drosophila, the vertebrate and mammalian equivalent of the pathway has been studied extensively for its role in cancer development and progression. As this pathway regulates key target genes involved in development, its action also allows for the modulation of the microenvironment to prepare a tumor-suitable niche by manipulating tumor cell growth, differentiation, and immune regulation, thus creating an enabling environment for progression and metastasis. In this review, we will summarize recent scientific discoveries reporting the impact of the Hedgehog signaling pathway on the tumor initiation process and metastatic cascade, shedding light on the ability of the tumor to take over a mechanism crucially intended for development and normal function.

CtBP2 is an independent prognostic marker that promotes GLI1 induced epithelial-mesenchymal transition in hepatocellular carcinoma

C-terminal binding protein 2 (CtBP2) is a transcriptional co-repressor that promotes cancer cell migration and invasion by inhibiting multiple tumor suppressor genes that contribute to cell mobility and adhesion. In this investigation, we showed thatCtBP2 expression was increased significantly in HCC tissues when compared to matched normal adjacent liver tissues. We also showed that CtBP2 expression is associated with worse HCC patient prognosis after liver resection. CtBP2 over-expression induced epithelial-mesenchymal transition (EMT) in Huh7 cells and, correspondingly, silencing CtBP2 suppressed EMT in MHCC97H cells. ChIP assays revealed that GLI1 increased CtBP2 transcription by directly binding its promoter. Furthermore, interaction of CtBP2 and Snail Family Zinc Finger 1 (SNAI1), both of which were found to be positively regulated by GLI1, was confirmed by Co-IP assay. SNAI1 knockdown revealed that SNAI1 was essential for CtBP2 induction of the EMT phenotype of HCC cells, and CtBP2 knockdown reversed GLI1-SNAI1 driven EMT in Huh7 cells. Finally, in vivo experiments demonstrated that enhanced CtBP2expression promoted HCC xenograft growth and induced EMT. In conclusion, CtBP2 may serve as a prognostic marker for post liver resection HCC and may play a role during GLI1-driven EMT as a transcriptional co-repressor of SNAI1.

Recapitulating Human Gastric Cancer Pathogenesis: Experimental Models of Gastric Cancer

This review focuses on the various experimental models to study gastric cancer pathogenesis, with the role of genetically engineered mouse models (GEMMs) used as the major examples. We review differences in human stomach anatomy compared to the stomachs of the experimental models, including the mouse and invertebrate models such as Drosophila and C. elegans. The contribution of major signaling pathways, e.g., Notch, Hedgehog, AKT/PI3K is discussed in the context of their potential contribution to foregut tumorigenesis. We critically examine the rationale behind specific GEMMs, chemical carcinogens, dietary promoters, Helicobacter infection, and direct mutagenesis of relevant oncogenes and tumor suppressor that have been developed to study gastric cancer pathogenesis. Despite species differences, more efficient and effective models to test specific genes and pathways disrupted in human gastric carcinogenesis have yet to emerge. As we better understand these species differences, "humanized" versions of mouse models will more closely approximate human gastric cancer pathogenesis. Towards that end, epigenetic marks on chromatin, the gut microbiota, and ways of manipulating the immune system will likely move center stage, permitting greater overlap between rodent and human cancer phenotypes thus providing a unified progression model.

Reserve stem cells: Differentiated cells reprogram to fuel repair, metaplasia, and neoplasia in the adult gastrointestinal tract

It has long been known that differentiated cells can switch fates, especially in vitro, but only recently has there been a critical mass of publications describing the mechanisms adult, postmitotic cells use in vivo to reverse their differentiation state. We propose that this sort of cellular reprogramming is a fundamental cellular process akin to apoptosis or mitosis. Because reprogramming can invoke regenerative cells from mature cells, it is critical to the long-term maintenance of tissues like the pancreas, which encounter large insults during adulthood but lack constitutively active adult stem cells to repair the damage. However, even in tissues with adult stem cells, like the stomach and intestine, reprogramming may allow mature cells to serve as reserve ("quiescent") stem cells when normal stem cells are compromised. We propose that the potential downside to reprogramming is that it increases risk for cancers that occur late in adulthood. Mature, long-lived cells may have years of exposure to mutagens. Mutations that affect the physiological function of differentiated, postmitotic cells may lead to apoptosis, but mutations in genes that govern proliferation might not be selected against. Hence, reprogramming with reentry into the cell cycle might unmask those mutations, causing an irreversible progenitor-like, proliferative state. We review recent evidence showing that reprogramming fuels irreversible metaplastic and precancerous proliferation in the stomach and pancreas. Finally, we illustrate how we think reprogrammed differentiated cells are likely candidates as cells of origin for cancers of the intestine.