Stem cells in gastroenterology and hepatology

ID1 is a functional marker for intestinal stem and progenitor cells required for normal response to injury

LGR5 and BMI1 mark intestinal stem cells in crypt base columnar cells and +4 position cells, respectively, but characterization of functional markers in these cell populations is limited. ID1 maintains the stem cell potential of embryonic, neural, and long-term repopulating hematopoietic stem cells. Here, we show in both human and mouse intestine that ID1 is expressed in cycling columnar cells, +4 position cells, and transit-amplifying cells in the crypt. Lineage tracing revealed ID1+ cells to be self-renewing, multipotent stem/progenitor cells that are responsible for the long-term renewal of the intestinal epithelium. Single ID1+ cells can generate long-lived organoids resembling mature intestinal epithelium. Complete knockout of Id1 or selective deletion of Id1 in intestinal epithelium or in LGR5+ stem cells sensitizes mice to chemical-induced colon injury. These experiments identify ID1 as a marker for intestinal stem/progenitor cells and demonstrate a role for ID1 in maintaining the potential for repair in response to colonic injury.

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ID1 is expressed in mouse and human intestinal and colonic stem and progenitor cells

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ID1+ cells are long-lived and multipotent

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Deletion of Id1 in stem and progenitor cells sensitizes mice to colon injury

Increased expression of chemerin in squamous esophageal cancer myofibroblasts and role in recruitment of mesenchymal stromal cells

Stromal cells such as myofibroblasts influence tumor progression. The mechanisms are unclear but may involve effects on both tumor cells and recruitment of bone marrow-derived mesenchymal stromal cells (MSCs) which then colonize tumors. Using iTRAQ and LC-MS/MS we identified the adipokine, chemerin, as overexpressed in esophageal squamous cancer associated myofibroblasts (CAMs) compared with adjacent tissue myofibroblasts (ATMs). The chemerin receptor, ChemR23, is expressed by MSCs. Conditioned media (CM) from CAMs significantly increased MSC cell migration compared to ATM-CM; the action of CAM-CM was significantly reduced by chemerin-neutralising antibody, pretreatment of CAMs with chemerin siRNA, pretreatment of MSCs with ChemR23 siRNA, and by a ChemR23 receptor antagonist, CCX832. Stimulation of MSCs by chemerin increased phosphorylation of p42/44, p38 and JNK-II kinases and inhibitors of these kinases and PKC reversed chemerin-stimulated MSC migration. Chemerin stimulation of MSCs also induced expression and secretion of macrophage inhibitory factor (MIF) that tended to restrict migratory responses to low concentrations of chemerin but not higher concentrations. In a xenograft model consisting of OE21 esophageal cancer cells and CAMs, homing of MSCs administered i.v. was inhibited by CCX832. Thus, chemerin secreted from esophageal cancer myofibroblasts is a potential chemoattractant for MSCs and its inhibition may delay tumor progression.

Intestinal stem cells and celiac disease

Stem cells (SCs) are the key to tissue genesis and regeneration. Given their central role in homeostasis, dysfunctions of the SC compartment play a pivotal role in the development of cancers, degenerative disorders, chronic inflammatory pathologies and organ failure. The gastrointestinal tract is constantly exposed to harsh mechanical and chemical conditions and most of the epithelial cells are replaced every 3 to 5 d. According to the so-called Unitarian hypothesis, this renewal is driven by a common intestinal stem cell (ISC) residing within the crypt base at the origin of the crypt-to-villus hierarchical migratory pattern. Celiac disease (CD) can be defined as a chronic immune-mediated disease that is triggered and maintained by dietary proteins (gluten) in genetically predisposed individuals. Many advances have been achieved over the last years in understanding of the pathogenic interactions among genetic, immunological and environmental factors in CD, with a particular emphasis on intestinal barrier and gut microbiota. Conversely, little is known about ISC modulation and deregulation in active celiac disease and upon a gluten-free diet. Nonetheless, bone marrow-derived SC transplantation has become an option for celiac patients with complicated or refractory disease. This manuscript summarizes the “state of the art” regarding CD and ISCs, their niche and potential role in the development and treatment of the disease.

Liver support strategies: cutting-edge technologies

The treatment of end-stage liver disease and acute liver failure remains a clinically relevant issue. Although orthotopic liver transplantation is a well-established procedure, whole-organ transplantation is invasive and increasingly limited by the unavailability of suitable donor organs. Artificial and bioartificial liver support systems have been developed to provide an alternative to whole organ transplantation, but despite three decades of scientific efforts, the results are still not convincing with respect to clinical outcome. In this Review, conceptual limitations of clinically available liver support therapy systems are discussed. Furthermore, alternative concepts, such as hepatocyte transplantation, and cutting-edge developments in the field of liver support strategies, including the repopulation of decellularized organs and the biofabrication of entirely new organs by printing techniques or induced organogenesis are analysed with respect to clinical relevance. Whereas hepatocyte transplantation shows promising clinical results, at least for the temporary treatment of inborn metabolic diseases, so far data regarding implantation of engineered hepatic tissue have only emerged from preclinical experiments. However, the evolving techniques presented here raise hope for bioengineered liver support therapies in the future.

Pancreatic cancer diagnosis by free and exosomal miRNA

Patients with pancreatic adenocarcinoma (PaCa) have a dismal prognosis. This is in part due to late diagnosis prohibiting surgical intervention, which provides the only curative option as PaCa are mostly chemo- and radiation resistance. Hope is raised on a reliable non-invasive/minimally invasive diagnosis that is still missing. Recently two diagnostic options are discussed, serum MicroRNA (miRNA) and serum exosomes. Serum miRNA can be free or vesicle-, particularly, exosomes-enclosed. This review will provide an overview on the current state of the diagnostic trials on free serum miRNA and proceed with an introduction of exosomes that use as a diagnostic tool in serum and other body fluids has not received sufficient attention, although serum exosome miRNA in combination with protein marker expression likely will increase the diagnostic and prognostic power. By their crosstalk with host cells, which includes binding-initiated signal transduction, as well as reprogramming target cells via the transfer of proteins, mRNA and miRNA exosomes are suggested to become a most powerful therapeutics. I will discuss which hurdles have still to be taken as well as the different modalities, which can be envisaged to make therapeutic use of exosomes. PaCa are known to most intensely crosstalk with the host as apparent by desmoplasia and frequent paraneoplastic syndromes. Thus, there is hope that the therapeutic application of exosomes brings about a major breakthrough.

The gastrointestinal tumor microenvironment

Over the past decade, the microenvironment of gastrointestinal tumors has gained increasing attention because it is required for tumor initiation, progression, and metastasis. The tumor microenvironment has many components and has been recognized as one of the major hallmarks of epithelial cancers. Although therapeutic strategies for gastrointestinal cancer have previously focused on the epithelial cell compartment, there is increasing interest in reagents that alter the microenvironment, based on reported interactions among gastrointestinal epithelial, stromal, and immune cells during gastrointestinal carcinogenesis. We review the different cellular components of the gastrointestinal tumor microenvironment and their functions in carcinogenesis and discuss how improving our understanding of the complex stromal network could lead to new therapeutic strategies.

Obesity, cancer, and acetyl-CoA metabolism

As rates of obesity soar in the Unites States and around the world, cancer attributed to obesity has emerged as major threat to public health. The link between obesity and cancer can be attributed in part to the state of chronic inflammation that develops in obesity. Acetyl-CoA production and protein acetylation patterns are highly sensitive to metabolic state and are significantly altered in obesity. In this article, we explore the potential role of nutrient-sensitive lysine acetylation in regulating inflammatory processes in obesity-linked cancer.

Characteristics of hepatic stem/progenitor cells in the fetal and adult liver

BACKGROUND

The liver is an essential organ that maintains vital activity through its numerous important functions. It has a unique capability of fully regenerating after injury. Regulating a balance between self-renewal and differentiation of hepatic stem cells that are resources for functional mature liver cells is required for maintenance of tissue homeostasis.

METHODS

This review describes the characteristics of hepatic stem/progenitor cells and the regulatory mechanism of their self-renewal and differentiation capacity.

RESULTS

In liver organogenesis, undifferentiated hepatic stem/progenitor cells expand their pool by repeated self-renewal in the early stage of liver development and then differentiate into two different types of cell lineage, namely hepatocytes and cholangiocytes. Liver development is regulated by expression of stem cell transcription factors in a complex multistep process. Recent studies suggest that stem cells are maintained by integrative regulation of gene expression patterns related to self-renewal and differentiation by epigenetic mechanisms such as histone modification and DNA methylation.

CONCLUSIONS

Analysis of the proper regulatory mechanism of hepatic stem/progenitor cells is important for regenerative medicine that utilizes hepatic stem cells and for preventing liver cancer through clarification of the carcinogenetic mechanism involved in stem cell system failure.

Identification of lineage-uncommitted, long-lived, label-retaining cells in healthy human esophagus and stomach, and in metaplastic esophagus

BACKGROUND & AIMS

The existence of slowly cycling, adult stem cells has been challenged by the identification of actively cycling cells. We investigated the existence of uncommitted, slowly cycling cells by tracking 5-iodo-2'-deoxyuridine (IdU) label-retaining cells (LRCs) in normal esophagus, Barrett's esophagus (BE), esophageal dysplasia, adenocarcinoma, and healthy stomach tissues from patients.

METHODS

Four patients (3 undergoing esophagectomy, 1 undergoing esophageal endoscopic mucosal resection for dysplasia and an esophagectomy for esophageal adenocarcinoma) received intravenous infusion of IdU (200 mg/m(2) body surface area; maximum dose, 400 mg) over a 30-minute period; the IdU had a circulation half-life of 8 hours. Tissues were collected at 7, 11, 29, and 67 days after infusion, from regions of healthy esophagus, BE, dysplasia, adenocarcinoma, and healthy stomach; they were analyzed by in situ hybridization, flow cytometry, and immunohistochemical analyses.

RESULTS

No LRCs were found in dysplasias or adenocarcinomas, but there were significant numbers of LRCs in the base of glands from BE tissue, in the papillae of the basal layer of the esophageal squamous epithelium, and in the neck/isthmus region of healthy stomach. These cells cycled slowly because IdU was retained for at least 67 days and co-labeling with Ki-67 was infrequent. In glands from BE tissues, most cells did not express defensin-5, Muc-2, or chromogranin A, indicating that they were not lineage committed. Some cells labeled for endocrine markers and IdU at 67 days; these cells represented a small population (<0.1%) of epithelial cells at this time point. The epithelial turnover time of the healthy esophageal mucosa was approximately 11 days (twice that of the intestine).

CONCLUSIONS

LRCs of human esophagus and stomach have many features of stem cells (long lived, slow cycling, uncommitted, and multipotent), and can be found in a recognized stem cell niche. Further analyses of these cells, in healthy and metaplastic epithelia, is required.

Recent achievements in stem cell therapy for pediatric gastrointestinal tract disease

The field of stem cell research has been rapidly expanding. Although the clinical usefulness of research remains to be ascertained through human trials, the use of stem cells as a therapeutic option for currently disabling diseases holds fascinating potential. Many pediatric gastrointestinal tract diseases have defect in enterocytes, enteric nervous system cells, smooth muscles, and interstitial cells of Cajal. Various kinds of therapeutic trials using stem cells could be applied to these diseases. This review article focuses on the recent achievements in stem cell applications for pediatric gastrointestinal tract diseases.

Tspan8, CD44v6 and alpha6beta4 are biomarkers of migrating pancreatic cancer-initiating cells

Pancreatic adenocarcinoma (PaCa) being the deadliest cancer is partly due to early metastatic spread. Thus, we searched for PaCa-initiating cell (PaCIC) markers with emphasis on markers contributing to metastatic progression. PaCIC were enriched from long-term and freshly established lines by repeated selection for spheroid or holoclone growth in advance of evaluating PaCIC markers. Sphere and holoclone formation steeply increased by recloning and remained stable thereafter. Cells not forming spheres or holoclones died on recloning. PaCIC enrichment in spheres and holoclones was accompanied by increased motility, anchorage independence and upregulated CXCR4 expression. After subcutaneous injection in NOD/SCID mice tumorigenicity and, impressively, recovery of metastasizing tumor cells in peripheral blood, spleen, bone marrow, lung and pancreas was strongly increased in spheres and holoclones. PaCIC enrichment in spheres and holoclones was accompanied, besides CXCR4, by upregulated CD44v6, alpha6beta4, weakly CD133 and tetraspanin Tspan8 expression. Notably, CD44v6, alpha6beta4, CXCR4 and Tspan8 expressing PaCa cells had a growth advantage in vivo and became dominating in migrating and in distant organs settled tumor cells. This is the first report showing that CD44v6, alpha6beta4, Tspan8 and CXCR4 are biomarkers in PaCIC allowing for long-term survival, expansion and migration in immunocompromised mice. The stability of the percentage of PaCIC in long-term and freshly established lines after a roughly 8-fold enrichment by cloning indicates PaCIC, though required for long-term survival, concomitantly depending on support by non-CIC.

Pancreatic cancer cells surviving gemcitabine treatment express markers of stem cell differentiation and epithelial-mesenchymal transition

Objective response rates to standard chemotherapeutic regimens remain low in pancreatic cancer. Subpopulations of cells have been identified in various solid tumors which express stem cell-associated markers and are associated with increased resistance against radiochemotherapy. We investigated the expression of stem cell genes and markers of epithelial-mesenchymal transition in pancreatic cancer cells that survived high concentrations of gemcitabine treatment. Capan-1 and Panc-1 cells were continuously incubated with 1 and 10 µM gemcitabine. Surviving cells were collected after 1, 3 and 6 days. Expression of PDX-1, SHH, CD24, CD44, CD133, EpCAM, CBX7, OCT4, SNAIL, SLUG, TWIST, Ki-67, E-cadherin, β-catenin and vimentin were quantified by qPCR or immunocytochemistry. Migration was assessed by wound‑healing assay. SHH was knocked down using RNA interference. Five primary pancreatic cancer cell lines were used to validate the qPCR results. All investigated genes were upregulated after 6 days of gemcitabine incubation. Highest relative expression levels were observed for OCT4 (13.4-fold), CD24 (47.3-fold) and EpCAM (15.9-fold) in Capan-1 and PDX-1 (13.3‑fold), SHH (24.1-fold), CD44 (17.4-fold), CD133 (20.2-fold) and SLUG (15.2-fold) in Panc-1 cells. Distinct upregulation patterns were observed in the primary cells. Migration was increased in Panc-1 cells and changes in the expression of E-cadherin and β-catenin were typical of epithelial-mesenchymal transition in both cell lines. SHH knockdown reduced IC(50) from 30.1 to 27.6 nM in Capan-1 while it strongly inhibited proli-feration in Panc-1 cells. Cells surviving high-dose gemcitabine treatment express increased levels of stem cell genes, show characteristics associated with epithelial-mesenchymal transition and retain their proliferative capacity.

Conditional disruption of Axin1 leads to development of liver tumors in mice

BACKGROUND & AIMS

Mutations in components of the Wnt signaling pathway, including β-catenin and AXIN1, are found in more than 50% of human hepatocellular carcinomas (HCCs). Disruption of Axin1 causes embryonic lethality in mice. We generated mice with conditional disruption of Axin1 to study its function specifically in adult liver.

METHODS

Mice with a LoxP-flanked allele of Axin1 were generated by homologous recombination. Mice homozygous for the Axin1fl/fl allele were crossed with AhCre mice; in offspring, Axin1 was disrupted in liver following injection of β-naphthoflavone (Axin1fl/fl/Cre mice). Liver tissues were collected and analyzed by quantitative real-time polymerase chain reaction and immunoprecipitation, histology, and immunoblot assays.

RESULTS

Deletion of Axin1 from livers of adult mice resulted in an acute and persistent increase in hepatocyte cell volume, proliferation, and transcription of genes that induce the G(2)/M transition in the cell cycle and cytokinesis. A subset of Wnt target genes was activated, including Axin2, c-Myc, and cyclin D1. However, loss of Axin1 did not increase nuclear levels of β-catenin or cause changes in liver zonation that have been associated with loss of the adenomatous polyposis coli (APC) or constitutive activation of β-catenin. After 1 year, 5 of 9 Axin1fl/fl/Cre mice developed liver tumors with histologic features of HCC.

CONCLUSIONS

Hepatocytes from adult mice with conditional disruption of Axin1 in liver have a transcriptional profile that differs from that associated with loss of APC or constitutive activation of β-catenin. It might be similar to a proliferation profile observed in a subset of human HCCs with mutations in AXIN1. Axin1fl/fl mice could be a useful model of AXIN1-associated tumorigenesis and HCC.

Cells and materials for liver tissue engineering

Liver transplantation is currently the most efficacious treatment for end-stage liver diseases. However, one main problem with liver transplantation is the limited number of donor organs that are available. Therefore, liver tissue engineering based on cell transplantation that combines materials to mimic the liver is under investigation with the goal of restoring normal liver functions. Tissue engineering aims to mimic the interactions among cells with a scaffold. Particular materials or a matrix serve as a scaffold and provide a three-dimensional environment for cell proliferation and interaction. Moreover, the scaffold plays a role in regulating cell maturation and function via these interactions. In cultures of hepatic lineage cells, regulation of cell proliferation and specific function using biocompatible synthetic, biodegradable bioderived matrices, protein-coated materials, surface-modified nanofibers, and decellularized biomatrix has been demonstrated. Furthermore, beneficial effects of addition of growth factor cocktails to a flow bioreactor or coculture system on cell viability and function have been observed. In addition, a system for growing stem cells, liver progenitor cells, and primary hepatocytes for transplantation into animal models was developed, which produces hepatic lineage cells that are functional and that show long-term proliferation following transplantation. The major limitation of cells proliferated with matrix-based transplantation systems is the high initial cell loss and dysfunction, which may be due to the absence of blood flow and the changes in nutrients. Thus, the development of vascular-like scaffold structures, the formation of functional bile ducts, and the maintenance of complex metabolic functions remain as major problems in hepatic tissue engineering and will need to be addressed to enable further advances toward clinical applications.

Genetically engineered mouse models of pancreatic cancer

Pancreatic ductal adenocarcinoma is the 10th most common cancer and the fourth leading cause of cancer-related death in the United States. Despite great effort, the prognosis for patients with this disease remains dismal with a 5-year survival rate of just 4% to 6%. Although several important advances have improved our understanding of the underlying biology of pancreatic cancer, this knowledge has not translated into novel therapeutic approaches and effective systemic or targeted therapies. Pancreatic cancer is one of the malignancies most difficult to treat, with remarkable intrinsic resistance to both standard and targeted chemotherapy as well as ionizing radiation. Surgical intervention remains the only potentially curative approach. However, most patients present with inoperable and/or metastatic disease and are therefore excluded from surgery. Accordingly, new therapeutic options are desperately needed. In vivo models to study innovative and alternative treatment approaches are of major importance. A variety of genetically engineered mouse models of pancreatic cancer have been developed over the last decade. However, these models display different characteristics, and not all of them are suited for preclinical studies. In this review, we aim to review the mouse models available, their experimental use, their clinical relevance and limitations, and future directions.

Barrett esophagus: what a mouse model can teach us about human disease

The incidence of esophageal adenocarcinoma (EAC) is rapidly rising in the western world and accounts for 2% of all cancer-related deaths. The precursor lesion for EAC is Barrett esophagus (BE), which is strongly associated with gastresophageal reflux disease. A major limitation to the study of EAC has been the absence of tractable and genetically modifiable preclinical models of BE. A mouse model of BE and EAC that resembles human disease could provide novel insights into the origins and molecular pathogenesis of BE. In addition, validated animal models could help stratify BE patients given the limited predictive power of current standard endoscopic measures and clinical assessment. Here, we review the findings from recently developed mouse models of BE and EAC and their impact on clinical decision making, surveillance programs and therapeutic options. The data, taken together, suggest potential origins of BE from the gastric cardia, a role of bile acid and hypergatrinemia for carcinogenesis, a growing importance for columnar-like epithelium and a critical role for Notch signaling.

Development. Esophageal stem cells, where art thou?

The lumen of the esophagus is lined with a squamous stratified epithelium. In the model of Doupé et al . (based on the mouse esophageal epithelium), a single population of epithelial progenitor cells (yellow) is present above the basal lamina. The epithelium is maintained, under basal conditions, by these cells, which divide and produce both more progenitor cells or differentiate into the layers of the stratified epithelium

CD133 and CD44 cell surface markers do not identify cancer stem cells in primary human gastric tumors

Emerging evidence suggests that tumors contain and are driven by a cellular component that displays stem cell properties, the so-called cancer stem cells (CSCs). CSCs have been identified in several solid human cancers; however, there are no data about CSCs in primary human gastric cancer (GC). By using CD133 and CD44 cell surface markers we investigated whether primary human GCs contain a cell subset expressing stem-like properties and whether this subpopulation has tumor-initiating properties in xenograft transplantation experiments. We examined tissues from 44 patients who underwent gastrectomy for primary GC. The tumorigenicity of the cells separated by flow cytometry using CD133 and CD44 surface markers was tested by subcutaneous or intraperitoneum injection in NOD/SCID and nude mice. GCs included in the study were intestinal in 34 cases and diffuse in 10 cases. All samples contained surface marker-positive cells: CD133(+) mean percentage 10.6% and CD133(+)/CD44(+) mean percentage 27.7%, irrespective of cancer phenotype or grade of differentiation. Purified CD133(+) and CD133(+)/CD44(+) cells, obtained in sufficient number only in 12 intestinal type GC cases, failed to reproduce cancer in two mice models. However, the unseparated cells produced glandular-like structures in 70% of the mice inoculated. In conclusion, although CD133(+) and CD133(+)/CD44(+) were detectable in human primary GCs, they neither expressed stem-like properties nor exhibited tumor-initiating properties in xenograft transplantation experiments.

Adamantyl Retinoid-Related Molecules Induce Apoptosis in Pancreatic Cancer Cells by Inhibiting IGF-1R and Wnt/β-Catenin Pathways

Pancreatic carcinoma has a dismal prognosis as it often presents as locally advanced or metastatic. We have found that exposure to adamantyl-substituted retinoid-related (ARR) compounds 3-Cl-AHPC and AHP3 resulted in growth inhibition and apoptosis induction in PANC-1, Capan-2, and MiaPaCa-2 pancreatic cancer cell lines. In addition, AHP3 and 3-Cl-AHPC inhibited growth and induced apoptosis in spheres derived from the CD44⁺/CD24⁺ (CD133⁺/EpCAM⁺) stem-like cell population isolated from the pancreatic cancer cell lines. 3-Cl-AHPC-induced apoptosis was preceded by decreasing expression of IGF-1R, cyclin D1, β-catenin, and activated Notch-1 in the pancreatic cancer cell lines. Decreased IGF-1R expression inhibited PANC-1 proliferation, enhanced 3-Cl-AHPC-mediated apoptosis, and significantly decreased sphere formation. 3-Cl-AHPC inhibited the Wnt/β-catenin pathway as indicated by decreased β-catenin nuclear localization and inhibited Wnt/β-catenin activation of transcription factor TCF/LEF. Knockdown of β-catenin using sh-RNA also induced apoptosis and inhibited growth in pancreatic cancer cells. Thus, 3-Cl-AHPC and AHP3 induce apoptosis in pancreatic cancer cells and cancer stem-like cells and may serve as an important potential therapeutic agent in the treatment of pancreatic cancer.

Meeting the need for regenerative therapies I: target-based incidence and its relationship to U.S. spending, productivity, and innovation

Regenerative therapies possess high theoretical potential for medical advance yet their success as commercial therapeutics is still open to debate. Appropriate data on target opportunities that provide perspective and enable strategic decision making is necessary for both efficient and effective translation. Up until now, this data have been out of reach to research scientists and many start-up companies-the very groups currently looked to for the critical advance of these therapies. The target-based estimate of opportunity presented in this report demonstrates its importance in evaluating medical need and technology feasibility. In addition, analysis of U.S. research spending, productivity, and innovation reveals that U.S. basic research in this field would benefit from greater interdisciplinarity. Overcoming the barriers that currently prevent translation into high value therapies that are quickly clinically adopted requires simultaneous integration of engineering, science, business, and clinical practice. Achieving this integration is nontrivial.

Polycomb repressive complex 2 impedes intestinal cell terminal differentiation

The crypt-villus axis constitutes the functional unit of the small intestine, where mature absorptive cells are confined to the villi, and stem cells and transit amplifying and differentiating cells are restricted to the crypts. The polycomb group (PcG) proteins repress differentiation and promote self-renewal in embryonic stem cells. PcGs prevent transcriptional activity by catalysing epigenetic modifications, such as the covalent addition of methyl groups on histone tails, through the action of the polycomb repressive complex 2 (PRC2). Although a role for PcGs in the preservation of stemness characteristics is now well established, recent evidence suggests that they may also be involved in the regulation of differentiation. Using intestinal epithelial cell models that recapitulate the enterocytic differentiation programme, we generated a RNAi-mediated stable knockdown of SUZ12, which constitutes a cornerstone for PRC2 assembly and functionality, in order to analyse intestinal cell proliferation and differentiation. Expression of SUZ12 was also investigated in human intestinal tissues, revealing the presence of SUZ12 in most proliferative epithelial cells of the crypt and an increase in its expression in colorectal cancers. Moreover, PRC2 disruption led to a significant precocious expression of a number of terminal differentiation markers in intestinal cell models. Taken together, our data identified a mechanism whereby PcG proteins participate in the repression of the enterocytic differentiation program, and suggest that a similar mechanism exists in situ to slow down terminal differentiation in the transit amplifying cell population.

Colorectal cancer stem cell: a potential therapeutic target

The discovery of cancer stem cells has improved our understanding of tumour occurrence and development. Colorectal cancer stem cells may be derived from mutations in normal intestinal epithelial stem cells. CD133+ and aldehyde dehydrogenase 1 (ALDH1)+ cells have strong tumorigenic capacities and may represent different subpopulations of colorectal cancer stem cells. Multiple signalling pathways, especially the Wnt pathway, are important in colorectal cancer occurrence and development, and maintaining the stemness of colorectal cancer stem cells. Identifying colorectal cancer stem cells and understanding the related signalling pathways are important for developing new targeted interventions for colorectal cancer.

Cancer stem cell hypothesis and gastric carcinogenesis: Experimental evidence and unsolved questions

Traditionally, the clonal evolution model has been used to explain gastric cancer (GC) growth dynamics. According to this model, GC cells result from multiple mutations over time resulting in a population of continually diversifying cells. This heterogeneity enables the survival of different clones under particular conditions allowing growth at metastatic locations or resistance to chemotherapeutics. Cancer stem cell (CSC) theory completely overturns this traditional understanding of cancer suggesting that only CSCs can self-renew and promote tumor growth. CSCs are relatively refractory to conventional therapies, thus explaining why anti-cancer therapies are far from curative and why relapses of cancer are frequent. The identification of the CSC component of a tumor might, thus, open new therapeutic perspective based on the selective targeting of this small population of cells. In this review we examine the current scientific evidence supporting the existence of CSC in gastric tumors and analyze the main unsolved questions of this difficult field of cancer research.

Disruption of Klf4 in villin-positive gastric progenitor cells promotes formation and progression of tumors of the antrum in mice

BACKGROUND & AIMS

Krüppel-like factor 4 (Klf4) is a putative gastric tumor suppressor gene. Rare, villin-positive progenitor cells in the gastric antrum have multilineage potential. We investigated the function of Klf4 in these cells and in gastric carcinogenesis.

METHODS

We created mice with disruption of Klf4 in villin-positive antral mucosa cells (Villin-Cre(+);Klf4(fl/fl) mice). Villin-Cre(+);Klf4(fl/fl) and control mice were given drinking water with or without 240 ppm N-methyl-N-nitrosourea at 5 weeks of age and thereafter on alternating weeks for a total of 10 weeks. Gastric mucosa samples were collected at 35, 50, or 80 weeks of age from mice that were and were not given N-methyl-N-nitrosourea, and analyzed by histopathologic and molecular analyses. Findings were compared with those from human gastric tumor specimens.

RESULTS

Preneoplasia formed progressively in the antrum in 35- to 80-week-old Villin-Cre(+);Klf4(fl/fl) mice. Gastric tumors developed in 29% of 80-week-old Villin-Cre(+);Klf4(fl/fl) mice, which were located exclusively in the lesser curvature of the antrum. N-methyl-N-nitrosourea accelerated tumor formation, and tumors developed significantly more frequently in Villin-Cre(+);Klf4(fl/fl) mice than in control mice, at 35 and 50 weeks of age. Mouse and human gastric tumors had reduced expression of Krüppel-like factor 4 and increased expression of FoxM1 compared with healthy gastric tissue. Expression of Krüppel-like factor 4 suppressed transcription of FoxM1.

CONCLUSIONS

Inactivation of Klf4 in villin-positive gastric progenitor cells induces transformation of the gastric mucosa and tumorigenesis in the antrum in mice. Villin-Cre(+);Klf4(fl/fl) have greater susceptibility to chemical-induced gastric carcinogenesis and increased rates of gastric tumor progression than control mice.

SOX9 is expressed in normal stomach, intestinal metaplasia, and gastric carcinoma in humans

BACKGROUND

SOX9 is a marker for stem cells in the intestine and overexpression of SOX9 is found in some types of cancer. However, the expression of SOX9 in normal stomach, precancerous intestinal metaplasia, and gastric carcinoma has not yet been clarified. This study aimed to investigate SOX9 expression in the corpus and pyloric regions of the normal human stomach, premalignant intestinal metaplasia, and gastric carcinoma by using immunohistochemistry.

METHODS

We evaluated SOX9 expression in 46 clinical samples (early gastric well-differentiated adenocarcinoma including surrounding intestinal metaplasia) resected under esophagogastroduodenoscopy.

RESULTS

A small amount of SOX9 was expressed in the neck/isthmus of the corpus region and SOX9 expression was predominantly restricted to the neck/isthmus of the pyloric region in normal human stomach. In the intestinal metaplastic mucosa, SOX9- and PCNA-positive cells were located at the base of the intestinal metaplastic mucosa. Almost all of the gastric carcinoma cells expressed SOX9.

CONCLUSION

SOX9 is expressed in intestinal metaplasia and gastric carcinoma in humans.

Molecular imaging of cell therapy for gastroenterologic applications

Stem cell therapy has appeared as a possible therapeutic alternative for numerous diseases. Furthermore, cancer stem cells are a focus of significant interest as they may allow for a better understanding of the genesis of different malignancies. The ultimate goal of stem cell therapeutics is to ensure the viability and functionality of the transplanted cells. Similarly, the ultimate goal of understanding cancer stem cells is to understand how they behave in the living subject. Until recently, the efficacy of stem cell therapies has been assessed by overall organ function recovery. Understanding the behavior and biology of stem cells directly in the living subject can also lead to therapy optimization. Thus, there is a critical need for reliable and accurate methods to understand stem cell biology in vivo. Recent advances in both imaging and molecular biology have enabled transplanted stem cells to be successfully monitored in the living subject. The use of molecular imaging modalities has the capability to answer these questions and may one day be translated to patients. In this review, we will discuss the potential imaging strategies and how they can be utilized, depending on the questions that need to be answered.

Cell therapeutic options in liver diseases: cell types, medical devices and regulatory issues

Although significant progress has been made in the field of orthotopic liver transplantation, cell-based therapies seem to be a promising alternative to whole-organ transplantation. The reasons are manifold but organ shortage is the main cause for this approach. However, many problems such as the question which cell type should be used or which application site is best for transplantation have been raised. In addition, some clinicians have had success by cultivating liver cells in bioreactors for temporary life support. Besides answering the question which cell type, which injection site or even which culture form should be used for liver support recent international harmonization of legal requirements is needed to be addressed by clinicians, scientists and companies dealing with cellular therapies. We here briefly summarize the possible cell types used to partially or temporarily correct liver diseases, the most recent development of bioreactor technology and important regulatory issues.

Improved preclinical safety assessment using micro-BAL devices: the potential impact on human discovery and drug attrition

Hepatotoxicity is often unpredictable in the early phase of drug discovery and leads to drug attrition in preclinical and clinical development. Here, we discuss the conventional preclinical liver models that do not mimic in vivo livers. We focus on key components such as new sources of hepatocyte-derived human stem cells, enhanced direct oxygenation, defined biocompatibility nanoscaffolds, organotypical cellular models, dynamic culture, and metabolite status inside and outside the cell for effective configuration for the development of a bioartificial liver (BAL) device to mimic the in vivo liver microenvironment. The potential for development of BAL devices could open up new avenues in: (i) hepatotoxicity assessment for selecting drug candidates during preclinical screening; and (ii) therapeutic approaches for liver cell therapy at the clinical stage.

Gastric epithelial stem cells

Advances in our understanding of stem cells in the gastrointestinal tract include the identification of molecular markers of stem and early progenitor cells in the small intestine. Although gastric epithelial stem cells have been localized, little is known about their molecular biology. Recent reports describe the use of inducible Cre recombinase activity to indelibly label candidate stem cells and their progeny in the distal stomach, (ie, the antrum and pylorus). No such lineage labeling of epithelial stem cells has been reported in the gastric body (corpus). Among stem cells in the alimentary canal, those of the adult corpus are unique in that they lie close to the lumen and increase proliferation following loss of a single mature progeny lineage, the acid-secreting parietal cell. They are also unique in that they neither depend on Wnt signaling nor express the surface marker Lgr5. Because pathogenesis of gastric adenocarcinoma has been associated with abnormal patterns of gastric differentiation and with chronic tissue injury, there has been much research on the response of stomach epithelial stem cells to inflammation. Chronic inflammation, as induced by infection with Helicobacter pylori, affects differentiation and promotes metaplasias. Several studies have identified cellular and molecular mechanisms in spasmolytic polypeptide-expressing (pseudopyloric) metaplasia. Researchers have also begun to identify signaling pathways and events that take place during embryonic development that eventually establish the adult stem cells to maintain the specific features and functions of the stomach mucosa. We review the cytologic, molecular, functional, and developmental properties of gastric epithelial stem cells.

Stem cells and colon cancer: the questionable cancer stem cell hypothesis

The fine-tuning between cell proliferation and differentiation of self-renewing stem cells and pluripotent progenitors in gastric glands and colon epithelial crypts is coordinated by the mechanisms that regulate colon epithelial cell migration and guidance along the crypt axis. This leads to the acquisition of specialized cellular functions and the exfoliation of desquamated senescent and apoptotic epithelial cells at the apical mucosa interface with the gut lumen. Self-renewing stem cells and pluripotent progenitors are involved in the clonal and polyclonal growth of digestive tumors. Several lines of evidence support the existence of a subpopulation of cancer cells with stem cell-like (SCL) phenotypes in solid tumors of breast and digestive system. Consistently, epithelial cancer cell lines in long-term culture are phenotypically and functionally heterogeneous. It is suggested that only a small proportion of transformed cells are clonogenic in vivo and ex vivo to form colonies and to initiate tumor growth in immunodeficient mice. A discrete subpopulation of tumor -initiating SCL cancer cells are highly competent to survive, propagate and spread through the invasive and metastatic cascade. A better understanding of the mechanisms driving the plasticity and pluripotency of stem cells, their derived progenitors and SCL colon cancer initiating cells during tumor progression will open new avenues for the early detection and treatment of local and distant tumors of the digestive tract.

Intestinal stem cells and epithelial-mesenchymal interactions in the crypt and stem cell niche

The intestinal epithelium contains a rapidly proliferating and perpetually differentiating epithelium. The principal functional unit of the small intestine is the crypt-villus axis. Stem cells located in the crypts of Lieberkühn give rise to proliferating progenitor or transit amplifying cells that differentiate into the 4 major epithelial cell types. The study of adult gastrointestinal tract stem cells has progressed rapidly with the recent discovery of several putative stem cell markers. Substantial evidence suggests 2 populations of stem cells: long-term quiescent (reserved) and actively cycling (primed) stem cells. These cells are in adjoining locations and are presumably maintained by the secretion of specific proteins generated in a unique microenvironment or stem cell niche surrounding each population. The relationship between these 2 populations, as well as the cellular sources and composition of the surrounding environment, remains to be defined, and is an active area of research. In this review, we will outline progress in identifying stem cells and in defining epithelial-mesenchymal interactions in the crypt. We will summarize early advances using stem cells for therapy of gastrointestinal disorders.

Cancer stem cells: a novel paradigm for cancer prevention and treatment

Cancer is the second leading cause for mortality in US only after heart disease and lacks a good or effective therapeutic paradigm. Despite the emergence of new, targeted agents and the use of various therapeutic combinations, none of the treatment options available is curative in patients with advanced cancer. A growing body of evidence is supporting the idea that human cancers can be considered as a stem cell disease. Malignancies are believed to originate from a fraction of cancer cells that show self renewal and pluripotency and are capable of initiating and sustaining tumor growth. The cancer-initiating cells or cancer stem cells were originally identified in hematological malignancies but is now being recognized in several solid tumors. The hypothesis of stem cell-driven tumorigenesis raises questions as to whether the current treatments, most of which require rapidly dividing cells are able to efficiently target these slow cycling tumorigenic cells. Recent characterization of cancer stem cells should lead to the identification of key signaling pathways that may make cancer stem cells vulnerable to therapeutic interventions that target drug-effluxing capabilities, anti-apoptotic mechanisms, and induction of differentiation. Dietary phytochemicals possess anti-cancer properties and represent a promising approach for the prevention and treatment of many cancers.

Single-cell cDNA microarray profiling of complex biological processes of differentiation

Gene expression profiling at the single-cell level has been used to identify genes expressed in specific cell populations, in attempts to address various fundamental questions in multicellular organisms. In this article, we review the advance of single-cell cDNA amplification techniques in the last decade, and introduce a recently developed, reliable, quantitative method that is applicable to genome-wide transcriptional analyses with high-density oligonucleotide microarray and massively parallel sequencing. This method has been applied to a variety of biological studies, including developments of blastocyst inner cell mass, neurons, and primordial germ cells, to profile the molecular properties, dynamics during differentiation, and impacts of gene alterations in the individual cells in depth. These studies uncovered complex behaviors of the cells during differentiation in vivo, and identified previously unknown, transient populations that emerged in specific stages of development. These achievements clearly demonstrated that it is now more feasible to analyze gene expression in any cell type of interest in a quantitative, genome-wide manner at the single-cell resolution.

Molecular Genetics of Gastric Adenocarcinoma

Gastric carcinoma is the second leading cause of cancer deaths in the world. Its aetiology is closely linked to the bacterial pathogen Helicobacter pylori which is believed to induce a state of chronic inflammation that predisposes to a cascade of molecular and cellular alterations leading to carcinogenesis. Although the exact process of gastric carcinogenesis has yet to be elucidated fully, the interaction of the genetic factors with environmental factors is likely to be a significant consideration. Numerous genes and molecular pathways have been discovered to be associated with gastric adenocarcinoma and more importantly, it is now becoming possible to use some of these as means of prognostication and targeted therapy. This review will outline our current understanding of the aetiology and molecular genetics of gastric adenocarcinoma and its current clinical applications.