Evidence for multipotent endodermal stem/progenitor cell populations in human gallbladder

Biliary stem cells in health and cholangiopathies and cholangiocarcinoma

PURPOSE OF REVIEW

This review discusses evidence regarding progenitor populations of the biliary tree in the tissue regeneration and homeostasis, and the pathobiology of cholangiopathies and malignancies.

RECENT FINDINGS

In embryogenesis biliary multipotent progenitor subpopulation contributes cells not only to the pancreas and gall bladder but also to the liver. Cells equipped with a constellation of markers suggestive of the primitive endodermal phenotype exist in the peribiliary glands, the bile duct glands, of the intra- and extrahepatic bile ducts. These cells are able to be isolated and cultured easily, which demonstrates the persistence of a stable phenotype during in vitro expansion, the ability to self-renew in vitro, and the ability to differentiate between hepatocyte and biliary and pancreatic islet fates.

SUMMARY

In normal human livers, stem/progenitors cells are mostly restricted in two distinct niches, which are the bile ductules/canals of Hering and the peribiliary glands (PBGs) present inside the wall of large intrahepatic bile ducts. The existence of a network of stem/progenitor cell niches within the liver and along the entire biliary tree inform a patho-biological-based translational approach to biliary diseases and cholangiocarcinoma since it poses the basis to understand biliary regeneration after extensive or chronic injuries and progression to fibrosis and cancer.

Fibrolamellar carcinomas-growth arrested by paracrine signals complexed with synthesized 3-O sulfated heparan sulfate oligosaccharides

Fibrolamellar carcinomas (FLCs), lethal tumors occurring in children to young adults, have genetic signatures implicating derivation from biliary tree stem cell (BTSC) subpopulations, co-hepato/pancreatic stem cells, involved in hepatic and pancreatic regeneration. FLCs and BTSCs express pluripotency genes, endodermal transcription factors, and stem cell surface, cytoplasmic and proliferation biomarkers. The FLC-PDX model, FLC-TD-2010, is driven ex vivo to express pancreatic acinar traits, hypothesized responsible for this model's propensity for enzymatic degradation of cultures. A stable ex vivo model of FLC-TD-2010 was achieved using organoids in serum-free Kubota's Medium (KM) supplemented with 0.1% hyaluronans (KM/HA). Heparins (10 ng/ml) caused slow expansion of organoids with doubling times of ∼7-9 days. Spheroids, organoids depleted of mesenchymal cells, survived indefinitely in KM/HA in a state of growth arrest for more than 2 months. Expansion was restored with FLCs co-cultured with mesenchymal cell precursors in a ratio of 3:7, implicating paracrine signaling. Signals identified included FGFs, VEGFs, EGFs, Wnts, and others, produced by associated stellate and endothelial cell precursors. Fifty-three, unique heparan sulfate (HS) oligosaccharides were synthesized, assessed for formation of high affinity complexes with paracrine signals, and each complex screened for biological activity(ies) on organoids. Ten distinct HS-oligosaccharides, all 10-12 mers or larger, and in specific paracrine signal complexes elicited particular biological responses. Of note, complexes of paracrine signals and 3-O sulfated HS-oligosaccharides elicited slowed growth, and with Wnt3a, elicited growth arrest of organoids for months. If future efforts are used to prepare HS-oligosaccharides resistant to breakdown in vivo, then [paracrine signal-HS-oligosaccharide] complexes are potential therapeutic agents for clinical treatments of FLCs, an exciting prospect for a deadly disease.

A postnatal network of co-hepato/pancreatic stem/progenitors in the biliary trees of pigs and humans

A network of co-hepato/pancreatic stem/progenitors exists in pigs and humans in Brunner's Glands in the submucosa of the duodenum, in peribiliary glands (PBGs) of intrahepatic and extrahepatic biliary trees, and in pancreatic duct glands (PDGs) of intrapancreatic biliary trees, collectively supporting hepatic and pancreatic regeneration postnatally. The network is found in humans postnatally throughout life and, so far, has been demonstrated in pigs postnatally at least through to young adulthood. These stem/progenitors in vivo in pigs are in highest numbers in Brunner's Glands and in PDGs nearest the duodenum, and in humans are in Brunner's Glands and in PBGs in the hepato/pancreatic common duct, a duct missing postnatally in pigs. Elsewhere in PDGs in pigs and in all PDGs in humans are only committed unipotent or bipotent progenitors. Stem/progenitors have genetic signatures in liver/pancreas-related RNA-seq data based on correlation, hierarchical clustering, differential gene expression and principal component analyses (PCA). Gene expression includes representative traits of pluripotency genes (SOX2, OCT4), endodermal transcription factors (e.g. SOX9, SOX17, PDX1), other stem cell traits (e.g. NCAM, CD44, sodium iodide symporter or NIS), and proliferation biomarkers (Ki67). Hepato/pancreatic multipotentiality was demonstrated by the stem/progenitors' responses under distinct ex vivo conditions or in vivo when patch grafted as organoids onto the liver versus the pancreas. Therefore, pigs are logical hosts for translational/preclinical studies for cell therapies with these stem/progenitors for hepatic and pancreatic dysfunctions.

Gallstone and Gallbladder Disease: Biliary Tract and Cholangiopathies

Cholestatic liver diseases are named primarily due to the blockage of bile flow and buildup of bile acids in the liver. Cholestasis can occur in cholangiopathies, fatty liver diseases, and during COVID-19 infection. Most literature evaluates damage occurring to the intrahepatic biliary tree during cholestasis; however, there may be associations between liver damage and gallbladder damage. Gallbladder damage can manifest as acute or chronic inflammation, perforation, polyps, cancer, and most commonly gallstones. Considering the gallbladder is an extension of the intrahepatic biliary network, and both tissues are lined by biliary epithelial cells that share common mechanisms and properties, it is worth further evaluation to understand the association between bile duct and gallbladder damage. In this comprehensive article, we discuss background information of the biliary tree and gallbladder, from function, damage, and therapeutic approaches. We then discuss published findings that identify gallbladder disorders in various liver diseases. Lastly, we provide the clinical aspect of gallbladder disorders in liver diseases and ways to enhance diagnostic and therapeutic approaches for congruent diagnosis. © 2023 American Physiological Society. Compr Physiol 13:4909-4943, 2023.

Liver cell therapies: cellular sources and grafting strategies

The liver has a complex cellular composition and a remarkable regenerative capacity. The primary cell types in the liver are two parenchymal cell populations, hepatocytes and cholangiocytes, that perform most of the functions of the liver and that are helped through interactions with non-parenchymal cell types comprising stellate cells, endothelia and various hemopoietic cell populations. The regulation of the cells in the liver is mediated by an insoluble complex of proteins and carbohydrates, the extracellular matrix, working synergistically with soluble paracrine and systemic signals. In recent years, with the rapid development of genetic sequencing technologies, research on the liver's cellular composition and its regulatory mechanisms during various conditions has been extensively explored. Meanwhile breakthroughs in strategies for cell transplantation are enabling a future in which there can be a rescue of patients with end-stage liver diseases, offering potential solutions to the chronic shortage of livers and alternatives to liver transplantation. This review will focus on the cellular mechanisms of liver homeostasis and how to select ideal sources of cells to be transplanted to achieve liver regeneration and repair. Recent advances are summarized for promoting the treatment of end-stage liver diseases by forms of cell transplantation that now include grafting strategies.

Human duodenal submucosal glands contain a defined stem/progenitor subpopulation with liver-specific regenerative potential

BACKGROUND & AIMS

Common precursors for the liver, biliary tree, and pancreas exist at an early stage of development in the definitive endoderm forming the foregut. We have identified and characterised endodermal stem/progenitor cells with regenerative potential persisting in the adult human duodenum.

METHODS

Human duodena were obtained from organ donors, and duodenal submucosal gland cells were isolated after removal of the mucosa layer. Cells were cultured on plastic or as organoids and were transplanted into severe combined immunodeficient (SCID) mouse livers.

RESULTS

In situ studies of submucosal glands in the human duodenum revealed cells expressing stem/progenitor cell markers that had unique phenotypic traits distinguishable from intestinal crypt cells. Genetic signature studies indicated that the cells are closer to biliary tree stem cells and to definitive endodermal cells than to adult hepatocytes, supporting the interpretation that they are endodermal stem/progenitor cells. In vitro, human duodenal submucosal gland cells demonstrated clonal growth, capability to form organoids, and ability to acquire functional hepatocyte traits. In vivo, transplanted cells engrafted into the livers of immunocompromised mice and differentiated to mature liver cells. In an experimental model of fatty liver, human duodenal submucosal gland cells were able to rescue hosts from liver damage by supporting repopulation and regeneration of the liver.

CONCLUSIONS

A cell population with clonal growth and organoid formation capability, which has liver differentiation potency in vitro and in vivo in murine experimental models, is present within adult duodenal submucosal glands. These cells can be isolated, do not require reprogramming, and thus could potentially represent a novel cell source for regenerative medicine of the liver.

IMPACT AND IMPLICATIONS

Cell therapies for liver disease could represent an option to support liver function, but the identification of sustainable and viable cell sources is critical. Here, we describe a cell population with organoid formation capability and liver-specific regenerative potential in submucosal glands of the human duodenum. Duodenal submucosal gland cells are isolated from adult organs, do not require reprogramming, and could rescue hepatocellular damage in preclinical models of chronic, but not acute, liver injury. Duodenal submucosal gland cells could represent a potential candidate cell source for regenerative medicine of the liver, but the determination of cell dose and toxicity is needed before clinical testing in humans.

Single-cell dissection of remodeled inflammatory ecosystem in primary and metastatic gallbladder carcinoma

Gallbladder carcinoma (GBC) is the most common biliary tract malignancy with the lowest survival rate, primarily arising from chronic inflammation. To better characterize the progression from inflammation to cancer to metastasis, we performed single-cell RNA sequencing across samples of 6 chronic cholecystitis, 12 treatment-naive GBCs, and 6 matched metastases. Benign epithelial cells from inflamed gallbladders displayed resting, immune-regulating, and gastrointestinal metaplastic phenotypes. A small amount of PLA2G2A⁺ epithelial cells with copy number variation were identified from a histologically benign sample. We validated significant overexpression of PLA2G2A across in situ GBCs, together with increased proliferation and cancer stemness in PLA2G2A-overexpressing GBC cells, indicating an important role for PLA2G2A during early carcinogenesis. Malignant epithelial cells displayed pervasive cancer hallmarks and cellular plasticity, differentiating into metaplastic, inflammatory, and mesenchymal subtypes with distinct transcriptomic, genomic, and prognostic patterns. Chronic cholecystitis led to an adapted microenvironment characterized by MDSC-like macrophages, CD8⁺ T_RM cells, and CCL2⁺ immunity-regulating fibroblasts. By contrast, GBC instigated an aggressive and immunosuppressive microenvironment, featured by tumor-associated macrophages, Treg cells, CD8⁺ T_EX cells, and STMN1⁺ tumor-promoting fibroblasts. Single-cell and bulk RNA-seq profiles consistently showed a more suppressive immune milieu for GBCs with inflammatory epithelial signatures, coupled with strengthened epithelial-immune crosstalk. We further pinpointed a subset of senescence-like fibroblasts (FN1⁺TGM2⁺) preferentially enriched in metastatic lesions, which promoted GBC migration and invasion via their secretory phenotype. Collectively, this study provides comprehensive insights into epithelial and microenvironmental reprogramming throughout cholecystitis-propelled carcinogenesis and metastasis, laying a new foundation for the precision therapy of GBC.

Persistent biliary hypoxia and lack of regeneration are key mechanisms in the pathogenesis of posttransplant nonanastomotic strictures

BACKGROUND AND AIMS

Nonanastomotic biliary strictures (NAS) are a major cause of morbidity after orthotopic liver transplantation (OLT). Although ischemic injury of peribiliary glands (PBGs) and peribiliary vascular plexus during OLT has been associated with the later development of NAS, the exact underlying mechanisms remain unclear. We hypothesized that bile ducts of patients with NAS suffer from ongoing biliary hypoxia and lack of regeneration from PBG stem/progenitor cells.

APPROACH AND RESULTS

Forty-two patients, requiring retransplantation for either NAS (n = 18), hepatic artery thrombosis (HAT; n = 13), or nonbiliary graft failure (controls; n = 11), were included in this study. Histomorphological analysis of perihilar bile ducts was performed to assess differences in markers of cell proliferation and differentiation in PBGs, microvascular density (MVD), and hypoxia. In addition, isolated human biliary tree stem cells (hBTSCs) were used to examine exo-metabolomics during in vitro differentiation toward mature cholangiocytes. Bile ducts of patients with NAS or HAT had significantly reduced indices of PBG mass, cellular proliferation and differentiation (mucus production, secretin receptor expression, and primary cilia), reduced MVD, and increased PBG apoptosis and hypoxia marker expression, compared to controls. Metabolomics of hBTSCs during in vitro differentiation toward cholangiocytes revealed a switch from a glycolytic to oxidative metabolism, indicating the need for oxygen.

CONCLUSIONS

NAS are characterized by a microscopic phenotype of chronic biliary hypoxia attributed to loss of microvasculature, resulting in reduced proliferation and differentiation of PBG stem/progenitor cells into mature cholangiocytes. These findings suggest that persistent biliary hypoxia is a key mechanism underlying the development of NAS after OLT.

Islet Regeneration and Pancreatic Duct Glands in Human and Experimental Diabetes

Contrasting evidence is present regarding the contribution of stem/progenitor cell populations to pancreatic regeneration in diabetes. Interestingly, a cell compartment with stem/progenitor cell features has been identified in the pancreatic duct glands (PDGs). The aims of the present study were to evaluate pancreatic islet injury and regeneration, and the participation of the PDG compartment in type 2 diabetic mellitus (T2DM) and in an experimental model of diabetes. Human pancreata were obtained from normal (N = 5) or T2DM (N = 10) cadaveric organ donors. Experimental diabetes was generated in mice by intraperitoneal injection of 150 mg/kg of streptozotocin (STZ, N = 10); N = 10 STZ mice also received daily intraperitoneal injections of 100 µg of human recombinant PDX1 peptide (STZ + PDX1). Samples were examined by immunohistochemistry/immunofluorescence or RT-qPCR. Serum glucose and c-peptide levels were measured in mice. Islets in T2DM patients showed β-cell loss, signs of injury and proliferation, and a higher proportion of central islets. PDGs in T2DM patients had a higher percentage of proliferating and insulin⁺ or glucagon⁺ cells compared to controls; pancreatic islets could be observed within pancreatic duct walls of T2DM patients. STZ mice were characterized by reduced islet area compared to controls. PDX1 treatment increased islet area and the percentage of central islets compared to untreated STZ mice but did not revert diabetes. In conclusion, T2DM patients show signs of pancreatic islet regeneration and involvement of the PDG niche. PDX1 administration could support increased endocrine pancreatic regeneration in STZ. These findings contribute to defining the role and participation of stem/progenitor cell compartments within the pancreas.

Induction and Maturation of Hepatocyte-Like Cells In Vitro: Focus on Technological Advances and Challenges

Limited by the poor proliferation and restricted sources of adult hepatocytes, there is an urgent need to find substitutes for proliferation and cultivation of mature hepatocytes in vitro for use in disease treatment, drug approval, and toxicity testing. Hepatocyte-like cells (HLCs), which originate from undifferentiated stem cells or modified adult cells, are considered good candidates because of their advantages in terms of cell source and in vitro expansion ability. However, the majority of induced HLCs are in an immature state, and their degree of differentiation is heterogeneous, diminishing their usability in basic research and limiting their clinical application. Therefore, various methods have been developed to promote the maturation of HLCs, including chemical approaches, alteration of cell culture systems, and genetic manipulation, to meet the needs of in vivo transplantation and in vitro model establishment. This review proposes different cell types for the induction of HLCs, and provide a comprehensive overview of various techniques to promote the generation and maturation of HLCs in vitro.

Cancer stem cells: advances in biology and clinical translation-a Keystone Symposia report

The test for the cancer stem cell (CSC) hypothesis is to find a target expressed on all, and only CSCs in a patient tumor, then eliminate all cells with that target that eliminates the cancer. That test has not yet been achieved, but CSC diagnostics and targets found on CSCs and some other cells have resulted in a few clinically relevant therapies. However, it has become apparent that eliminating the subset of tumor cells characterized by self-renewal properties is essential for long-term tumor control. CSCs are able to regenerate and initiate tumor growth, recapitulating the heterogeneity present in the tumor before treatment. As great progress has been made in identifying and elucidating the biology of CSCs as well as their interactions with the tumor microenvironment, the time seems ripe for novel therapeutic strategies that target CSCs to find clinical applicability. On May 19-21, 2021, researchers in cancer stem cells met virtually for the Keystone eSymposium "Cancer Stem Cells: Advances in Biology and Clinical Translation" to discuss recent advances in the understanding of CSCs as well as clinical efforts to target these populations.

Patch grafting, strategies for transplantation of organoids into solid organs such as liver

Epithelial cell therapies have been at an impasse because of inefficient methods of transplantation to solid organs. Patch grafting strategies were established enabling transplantation of ≥10^7th organoids/patch of porcine GFP+ biliary tree stem/progenitors into livers of wild type hosts. Grafts consisted of organoids embedded in soft (~100 Pa) hyaluronan hydrogels, both prepared in serum-free Kubota's Medium; placed against target sites; covered with a silk backing impregnated with more rigid hyaluronan hydrogels (~700 Pa); and use of the backing to tether grafts with sutures or glue to target sites. Hyaluronan coatings (~200-300 Pa) onto the serosal surface of the graft served to minimize adhesions with neighboring organs. The organ's clearance of hyaluronans enabled restoration of tissue-specific paracrine and systemic signaling, resulting in return of normal hepatic histology, with donor parenchymal cells uniformly integrated amidst host cells and that had differentiated to mature hepatocytes and cholangiocytes. Grafts containing donor mature hepatocytes, partnered with endothelia, and in the same graft biomaterials as for stem/progenitor organoids, did not engraft. Engraftment occurred if porcine liver-derived mesenchymal stem cells (MSCs) were co-transplanted with donor mature cells. RNA-seq analyses revealed that engraftment correlated with expression of matrix-metalloproteinases (MMPs), especially secreted isoforms that were found expressed strongly by organoids, less so by MSCs, and minimally, if at all, by adult cells. Engraftment with patch grafting strategies occurred without evidence of emboli or ectopic cell distribution. It was successful with stem/progenitor organoids or with cells with a source(s) of secreted MMP isoforms and offers significant potential for enabling cell therapies for solid organs.

Cell Therapy and Bioengineering in Experimental Liver Regenerative Medicine: In Vivo Injury Models and Grafting Strategies

Purpose of Review

To describe experimental liver injury models used in regenerative medicine, cell therapy strategies to repopulate damaged livers and the efficacy of liver bioengineering.

Recent Findings

Several animal models have been developed to study different liver conditions. Multiple strategies and modified protocols of cell delivery have been also reported. Furthermore, using bioengineered liver scaffolds has shown promising results that could help in generating a highly functional cell delivery system and/or a whole transplantable liver.

Summary

To optimize the most effective strategies for liver cell therapy, further studies are required to compare among the performed strategies in the literature and/or innovate a novel modifying technique to overcome the potential limitations. Coating of cells with polymers, decellularized scaffolds, or microbeads could be the most appropriate solution to improve cellular efficacy. Besides, overcoming the problems of liver bioengineering may offer a radical treatment for end-stage liver diseases.

Cell of origin in biliary tract cancers and clinical implications

Biliary tract cancers (BTCs) are aggressive epithelial malignancies that can arise at any point of the biliary tree. Albeit rare, their incidence and mortality rates have been rising steadily over the past 40 years, highlighting the need to improve current diagnostic and therapeutic strategies. BTCs show high inter- and intra-tumour heterogeneity both at the morphological and molecular level. Such complex heterogeneity poses a substantial obstacle to effective interventions. It is widely accepted that the observed heterogeneity may be the result of a complex interplay of different elements, including risk factors, distinct molecular alterations and multiple potential cells of origin. The use of genetic lineage tracing systems in experimental models has identified cholangiocytes, hepatocytes and/or progenitor-like cells as the cells of origin of BTCs. Genomic evidence in support of the distinct cell of origin hypotheses is growing. In this review, we focus on recent advances in the histopathological subtyping of BTCs, discuss current genomic evidence and outline lineage tracing studies that have contributed to the current knowledge surrounding the cell of origin of these tumours.

Regional Differences in Human Biliary Tissues and Corresponding In Vitro-Derived Organoids

BACKGROUND AND AIMS

Organoids provide a powerful system to study epithelia in vitro. Recently, this approach was applied successfully to the biliary tree, a series of ductular tissues responsible for the drainage of bile and pancreatic secretions. More precisely, organoids have been derived from ductal tissue located outside (extrahepatic bile ducts; EHBDs) or inside the liver (intrahepatic bile ducts; IHBDs). These organoids share many characteristics, including expression of cholangiocyte markers such as keratin (KRT) 19. However, the relationship between these organoids and their tissues of origin, and to each other, is largely unknown.

APPROACH AND RESULTS

Organoids were derived from human gallbladder, common bile duct, pancreatic duct, and IHBDs using culture conditions promoting WNT signaling. The resulting IHBD and EHBD organoids expressed stem/progenitor markers leucine-rich repeat-containing G-protein-coupled receptor 5/prominin 1 and ductal markers KRT19/KRT7. However, RNA sequencing revealed that organoids conserve only a limited number of regional-specific markers corresponding to their location of origin. Of particular interest, down-regulation of biliary markers and up-regulation of cell-cycle genes were observed in organoids. IHBD and EHBD organoids diverged in their response to WNT signaling, and only IHBDs were able to express a low level of hepatocyte markers under differentiation conditions.

CONCLUSIONS

Taken together, our results demonstrate that differences exist not only between extrahepatic biliary organoids and their tissue of origin, but also between IHBD and EHBD organoids. This information may help to understand the tissue specificity of cholangiopathies and also to identify targets for therapeutic development.

Genotoxic Effect of Salmonella Paratyphi A Infection on Human Primary Gallbladder Cells

Bacterial infections are increasingly being recognized as risk factors for the development of adenocarcinomas. The strong epidemiological evidence linking Helicobacter pylori infection to stomach cancer has paved the way to the demonstration that bacterial infections cause DNA damage in the host cells, initiating transformation. In this regard, the role of bacterial genotoxins has become more relevant. Salmonella enterica serovars Typhi and Paratyphi A have been clinically associated with gallbladder cancer. By harnessing the stem cell potential of cells from healthy human gallbladder explant, we regenerated and propagated the epithelium of this organ in vitro and used these cultures to model S. Paratyphi A infection. This study demonstrates the importance of the typhoid toxin, encoded only by these specific serovars, in causing genomic instability in healthy gallbladder cells, posing intoxicated cells at risk of malignant transformation.

Carcinoma of the gallbladder (GBC) is the most frequent tumor of the biliary tract. Despite epidemiological studies showing a correlation between chronic infection with Salmonella enterica Typhi/Paratyphi A and GBC, the underlying molecular mechanisms of this fatal connection are still uncertain. The murine serovar Salmonella Typhimurium has been shown to promote transformation of genetically predisposed cells by driving mitogenic signaling. However, insights from this strain remain limited as it lacks the typhoid toxin produced by the human serovars Typhi and Paratyphi A. In particular, the CdtB subunit of the typhoid toxin directly induces DNA breaks in host cells, likely promoting transformation. To assess the underlying principles of transformation, we used gallbladder organoids as an infection model for Salmonella Paratyphi A. In this model, bacteria can invade epithelial cells, and we observed host cell DNA damage. The induction of DNA double-strand breaks after infection depended on the typhoid toxin CdtB subunit and extended to neighboring, non-infected cells. By cultivating the organoid derived cells into polarized monolayers in air-liquid interphase, we could extend the duration of the infection, and we observed an initial arrest of the cell cycle that does not depend on the typhoid toxin. Non-infected intoxicated cells instead continued to proliferate despite the DNA damage. Our study highlights the importance of the typhoid toxin in causing genomic instability and corroborates the epidemiological link between Salmonella infection and GBC.

Distinct EpCAM-Positive Stem Cell Niches Are Engaged in Chronic and Neoplastic Liver Diseases

In normal human livers, EpCAM^pos cells are mostly restricted in two distinct niches, which are (i) the bile ductules and (ii) the mucous glands present inside the wall of large intrahepatic bile ducts (the so-called peribiliary glands). These EpCAM^pos cell niches have been proven to harbor stem/progenitor cells with great importance in liver and biliary tree regeneration and in the pathophysiology of human diseases. The EpCAM^pos progenitor cells within bile ductules are engaged in driving regenerative processes in chronic diseases affecting hepatocytes or interlobular bile ducts. The EpCAM^pos population within peribiliary glands is activated when regenerative needs are finalized to repair large intra- or extra-hepatic bile ducts affected by chronic pathologies, including primary sclerosing cholangitis and ischemia-induced cholangiopathies after orthotopic liver transplantation. Finally, the presence of distinct EpCAM^pos cell populations may explain the histological and molecular heterogeneity characterizing cholangiocarcinoma, based on the concept of multiple candidate cells of origin. This review aimed to describe the precise anatomical distribution of EpCAM^pos populations within the liver and the biliary tree and to discuss their contribution in the pathophysiology of human liver diseases, as well as their potential role in regenerative medicine of the liver.

Peribiliary Gland Niche Participates in Biliary Tree Regeneration in Mouse and in Human Primary Sclerosing Cholangitis

BACKGROUND AND AIMS

Mechanisms underlying the repair of extrahepatic biliary tree (EHBT) after injury have been scarcely explored. The aims of this study were to evaluate, by using a lineage tracing approach, the contribution of peribiliary gland (PBG) niche in the regeneration of EHBT after damage and to evaluate, in vivo and in vitro, the signaling pathways involved.

APPROACH AND RESULTS

Bile duct injury was induced by the administration of 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet for 14 days to Krt19^Cre TdTomato^LSL mice. Human biliary tree stem/progenitor cells (BTSC) within PBGs were isolated from EHBT obtained from liver donors. Hepatic duct samples (n = 10) were obtained from patients affected by primary sclerosing cholangitis (PSC). Samples were analyzed by histology, immunohistochemistry, western blotting, and polymerase chain reaction. DDC administration causes hyperplasia of PBGs and periductal fibrosis in EHBT. A PBG cell population (Cytokeratin19^- /SOX9⁺ ) is involved in the renewal of surface epithelium in injured EHBT. The Wnt signaling pathway triggers human BTSC proliferation in vitro and influences PBG hyperplasia in vivo in the DDC-mediated mouse biliary injury model. The Notch signaling pathway activation induces BTSC differentiation in vitro toward mature cholangiocytes and is associated with PBG activation in the DDC model. In human PSC, inflammatory and stromal cells trigger PBG activation through the up-regulation of the Wnt and Notch signaling pathways.

CONCLUSIONS

We demonstrated the involvement of PBG cells in regenerating the injured biliary epithelium and identified the signaling pathways driving BTSC activation. These results could have relevant implications on the pathophysiology and treatment of cholangiopathies.

Cholest-4,6-Dien-3-One Promote Epithelial-To-Mesenchymal Transition (EMT) in Biliary Tree Stem/Progenitor Cell Cultures In Vitro

Human biliary tree stem/progenitor cells (hBTSCs), reside in peribiliary glands, are mainly stimulated by primary sclerosing cholangitis (PSC) and cholangiocarcinoma. In these pathologies, hBTSCs displayed epithelial-to-mesenchymal transition (EMT), senescence characteristics, and impaired differentiation. Here, we investigated the effects of cholest-4,6-dien-3-one, an oxysterol involved in cholangiopathies, on hBTSCs biology. hBTSCs were isolated from donor organs, cultured in self-renewal control conditions, differentiated in mature cholangiocytes by specifically tailored medium, or exposed for 10 days to concentration of cholest-4,6-dien-3-one (0.14 mM). Viability, proliferation, senescence, EMT genes expression, telomerase activity, interleukin 6 (IL6) secretion, differentiation capacity, and HDAC6 gene expression were analyzed. Although the effect of cholest-4,6-dien-3-one was not detected on hBTSCs viability, we found a significant increase in cell proliferation, senescence, and IL6 secretion. Interestingly, cholest-4.6-dien-3-one impaired differentiation in mature cholangiocytes and, simultaneously, induced the EMT markers, significantly reduced the telomerase activity, and induced HDAC6 gene expression. Moreover, cholest-4,6-dien-3-one enhanced bone morphogenic protein 4 (Bmp-4) and sonic hedgehog (Shh) pathways in hBTSCs. The same pathways activated by human recombinant proteins induced the expression of EMT markers in hBTSCs. In conclusion, we demonstrated that chronic exposition of cholest-4,6-dien-3-one induced cell proliferation, EMT markers, and senescence in hBTSC, and also impaired the differentiation in mature cholangiocytes.

Generation of insulin-secreting cells from mouse gallbladder stem cells by small molecules in vitro

Background

Stem cell-derived pancreatic β-like cells hold great promise for treating diabetes. Gallbladder belongs to the extrahepatic bile duct system and possesses stem-like cells. These stem cells could be expanded in vitro and have the potential of differentiating into hepatocytes, cholangiocytes, or pancreatic cells. As the gallbladder is highly available, gallbladder stem cells provide a new cell source of pancreatic β-like cells. In this study, we aimed to investigate an approach for the generation of pancreatic β-like cells from gallbladder stem cells (GSCs) without genetic modification.

Methods

A CK19Cre^ERT;Rosa26R-GFP mouse was used to isolate CK19⁺ cells, which represented EpCAM⁺ stem cells in the gallbladder. They were cultured in the modified Kubota’s medium for expansion and further analyzed. Then, we developed a strategy to screen a combination of small molecules that can generate insulin-secreting cells from gallbladder stem cells. These cells were identified with markers of pancreatic cells. Finally, they were seeded into the cellulosic sponge and transplanted to the diabetic mice for functional examination in vivo.

Results

Gallbladder stem cells could be expanded for more than 15 passages. They expressed typical hepatic stem cell markers including CK19, EpCAM, Sox9, and albumin. By screening method, we found that adding Noggin, FR180204, and cyclopamine could efficiently induce gallbladder stem cells differentiating into insulin-secreting cells. These cells expressed Pdx1, Nkx6.1, and insulin but were negative for Gcg. After transplantation with the cellulosic sponge, they could ameliorate hyperglycemia in the diabetic mice.

Conclusion

This study provides a new approach which can generate insulin-secreting cells from the gallbladder without genetic modification. This offers an option for β cell therapy in treating type 1 diabetes.

Functions and the Emerging Role of the Foetal Liver into Regenerative Medicine

During foetal life, the liver plays the important roles of connection and transient hematopoietic function. Foetal liver cells develop in an environment called a hematopoietic stem cell niche composed of several cell types, where stem cells can proliferate and give rise to mature blood cells. Embryologically, at about the third week of gestation, the liver appears, and it grows rapidly from the fifth to 10th week under WNT/β-Catenin signaling pathway stimulation, which induces hepatic progenitor cells proliferation and differentiation into hepatocytes. Development of new strategies and identification of new cell sources should represent the main aim in liver regenerative medicine and cell therapy. Cells isolated from organs with endodermal origin, like the liver, bile ducts, and pancreas, could be preferable cell sources. Furthermore, stem cells isolated from these organs could be more susceptible to differentiate into mature liver cells after transplantation with respect to stem cells isolated from organs or tissues with a different embryological origin. The foetal liver possesses unique features given the co-existence of cells having endodermal and mesenchymal origin, and it could be highly available source candidate for regenerative medicine in both the liver and pancreas. Taking into account these advantages, the foetal liver can be the highest potential and available cell source for cell therapy regarding liver diseases and diabetes.

Hyaluronan-Based Grafting Strategies for Liver Stem Cell Therapy and Tracking Methods

Cell adhesion is essential for survival, it plays important roles in physiological cell functions, and it is an innovative target in regenerative medicine. Among the molecular interactions and the pathways triggered during cell adhesion, the binding of cluster of differentiation 44 (CD44), a cell-surface glycoprotein involved in cell-cell interactions, to hyaluronic acid (HA), a major component of the extracellular matrix, is a crucial step. Cell therapy has emerged as a promising treatment for advanced liver diseases; however, so far, it has led to low cell engraftment and limited cell repopulation of the target tissue. Currently, different strategies are under investigation to improve cell grafting in the liver, including the use of organic and inorganic biomatrices that mimic the microenvironment of the extracellular matrix. Hyaluronans, major components of stem cell niches, are attractive candidates for coating stem cells since they improve viability, proliferation, and engraftment in damaged livers. In this review, we will discuss the new strategies that have been adopted to improve cell grafting and track cells after transplantation.

Simulated microgravity promotes the formation of tridimensional cultures and stimulates pluripotency and a glycolytic metabolism in human hepatic and biliary tree stem/progenitor cells

Many pivotal biological cell processes are affected by gravity. The aim of our study was to evaluate biological and functional effects, differentiation potential and exo-metabolome profile of simulated microgravity (SMG) on human hepatic cell line (HepG2) and human biliary tree stem/progenitor cells (hBTSCs). Both hBTSCs and HepG2 were cultured in a weightless and protected environment SGM produced by the Rotary Cell Culture System (Synthecon) and control condition in normal gravity (NG). Self-replication and differentiation toward mature cells were determined by culturing hBTSCs in Kubota’s Medium (KM) and in hormonally defined medium (HDM) tailored for hepatocyte differentiation. The effects on the expression and cell exo-metabolome profiles of SMG versus NG cultures were analyzed. SMG promotes tridimensional (3D) cultures of hBTSCs and HepG2. Significative increase of stemness gene expression (p < 0.05) has been observed in hBTSCs cultured in SMG when compared to NG condition. At the same time, the expression of hepatocyte lineage markers in hBTSCs differentiated by HDM was significantly lower (p < 0.05) in SMG compared to NG, demonstrating an impaired capability of hBTSCs to differentiate in vitro toward mature hepatocytes when cultured in SMG condition. Furthermore, in HepG2 cells the SMG caused a lower (p < 0.05 vs controls) transcription of CYP3A4, a marker of late-stage (i.e. Zone 3) hepatocytes. Exo-metabolome NMR-analysis showed that both cell cultures consumed a higher amount of glucose and lower glutamate in SMG respect to NG (p < 0.05). Moreover, hBTSCs media cultures resulted richer of released fermentation (lactate, acetate) and ketogenesis products (B-hydroxybutyrate) in SGM (p < 0.05) than NG. While, HepG2 cells showed higher consumption of amino acids and release of ketoacids (3-Methyl-2-oxovalerate, 2-oxo-4-methyl-valerate) and formiate with respect to normogravity condition (p < 0.05). Based on our results, SMG could be helpful for developing hBTSCs-derived liver devices. In conclusion, SMG favored the formation of hBTSCs and HepG2 3D cultures and the maintenance of stemness contrasting cell differentiation; these effects being associated with stimulation of glycolytic metabolism. Interestingly, the impact of SMG on stem cell biology should be taken into consideration for workers involved in space medicine programs.

Neoplastic Transformation of the Peribiliary Stem Cell Niche in Cholangiocarcinoma Arisen in Primary Sclerosing Cholangitis

Primary sclerosing cholangitis (PSC) is a chronic inflammatory cholangiopathy frequently complicated by cholangiocarcinoma (CCA). Massive proliferation of biliary tree stem/progenitor cells (BTSCs), expansion of peribiliary glands (PBGs), and dysplasia were observed in PSC. The aims of the present study were to evaluate the involvement of PBGs and BTSCs in CCA which emerged in PSC patients. Specimens from normal liver (n = 5), PSC (n = 20), and PSC-associated CCA (n = 20) were included. Samples were processed for histology, immunohistochemistry, and immunofluorescence. In vitro experiments were performed on human BTSCs, human mucinous primary CCA cell cultures, and human cholangiocyte cell lines (H69). Our results indicated that all CCAs emerging in PSC patients were mucin-producing tumors characterized by PBG involvement and a high expression of stem/progenitor cell markers. Ducts with neoplastic lesions showed higher inflammation, wall thickness, and PBG activation compared to nonneoplastic PSC-affected ducts. CCA showed higher microvascular density and higher expression of nuclear factor kappa B, interleukin-6, interleukin-8, transforming growth factor β, and vascular endothelial growth factor-1 compared to nonneoplastic ducts. CCA cells were characterized by a higher expression of epithelial-to-mesenchymal transition (EMT) traits and by the absence of primary cilia compared to bile ducts and PBG cells in controls and patients with PSC. Our in vitro study demonstrated that lipopolysaccharide and oxysterols (PSC-related stressors) induced the expression of EMT traits, the nuclear factor kappa B pathway, autophagy, and the loss of primary cilia in human BTSCs. Conclusion: CCA arising in patients with PSC is characterized by extensive PBG involvement and by activation of the BTSC niche in these patients, the presence of duct lesions at different stages suggests a progressive tumorigenesis.

The FXR agonist obeticholic acid inhibits the cancerogenic potential of human cholangiocarcinoma

Cholangiocarcinoma (CCA) is an aggressive cancer with high resistance to chemotherapeutics. CCA is enriched in cancer stem cells, which correlate with aggressiveness and prognosis. FXR, a member of the metabolic nuclear receptor family, is markedly down-regulated in human CCA. Our aim was to evaluate, in primary cultures of human intrahepatic CCA (iCCA), the effects of the FXR agonist obeticholic acid (OCA), a semisynthetic bile acid derivative, on their cancerogenic potential. Primary human iCCA cell cultures were prepared from surgical specimens of mucinous or mixed iCCA subtypes. Increasing concentrations (0-2.5 μM) of OCA were added to culture media and, after 3-10 days, effects on proliferation (MTS assay, cell population doubling time), apoptosis (annexin V-FITC/propidium iodide), cell migration and invasion (wound healing response and Matrigel invasion assay), and cancerogenic potential (spheroid formation, clonogenic assay, colony formation capacity) were evaluated. Results: FXR gene expression was downregulated (RT-qPCR) in iCCA cells vs normal human biliary tree stem cells (p < 0.05) and in mucinous iCCA vs mixed iCCA cells (p < 0.05) but was upregulated by addition of OCA. OCA significantly (p < 0.05) inhibited proliferation of both mucinous and mixed iCCA cells, starting at a concentration as low as 0.05 μM. Also, CDCA (but not UDCA) inhibited cell proliferation, although to a much lower extent than OCA, consistent with its different affinity for FXR. OCA significantly induced apoptosis of both iCCA subtypes and decreased their in vitro cancerogenic potential, as evaluated by impairment of colony and spheroid formation capacity and delayed wound healing and Matrigel invasion. In general, these effects were more evident in mixed than mucinous iCCA cells. When tested together with Gemcitabine and Cisplatin, OCA potentiated the anti-proliferative and pro-apoptotic effects of these chemotherapeutics, but mainly in mixed iCCA cells. OCA abolished the capacity of both mucinous and mixed iCCA cells to form colonies when administered together with Gemcitabine and Cisplatin. In subcutaneous xenografts of mixed iCCA cells, OCA alone or combined with Gemcitabine or Cisplatin markedly reduced the tumor size after 5 weeks of treatment by inducing necrosis of tumor mass and inhibiting cell proliferation. In conclusion, FXR is down-regulated in iCCA cells, and its activation by OCA results in anti-cancerogenic effects against mucinous and mixed iCCA cells, both in vitro and in vivo. The effects of OCA predominated in mixed iCCA cells, consistent with the lower aggressiveness and the higher FXR expression in this CCA subtype. These results, showing the FXR-mediated capacity of OCA to inhibit cholangiocarcinogenesis, represent the basis for testing OCA in clinical trials of CCA patients.

Contribution of Resident Stem Cells to Liver and Biliary Tree Regeneration in Human Diseases

Two distinct stem/progenitor cell populations of biliary origin have been identified in the adult liver and biliary tree. Hepatic Stem/progenitor Cells (HpSCs) are bipotent progenitor cells located within the canals of Hering and can be differentiated into mature hepatocytes and cholangiocytes; Biliary Tree Stem/progenitor Cells (BTSCs) are multipotent stem cells located within the peribiliary glands of large intrahepatic and extrahepatic bile ducts and able to differentiate into hepatic and pancreatic lineages. HpSCs and BTSCs are endowed in a specialized niche constituted by supporting cells and extracellular matrix compounds. The actual contribution of these stem cell niches to liver and biliary tree homeostatic regeneration is marginal; this is due to the high replicative capabilities and plasticity of mature parenchymal cells (i.e., hepatocytes and cholangiocytes). However, the study of human liver and biliary diseases disclosed how these stem cell niches are involved in the regenerative response after extensive and/or chronic injuries, with the activation of specific signaling pathways. The present review summarizes the contribution of stem/progenitor cell niches in human liver diseases, underlining mechanisms of activation and clinical implications, including fibrogenesis and disease progression.

Hepatic Stem/Progenitor Cell Activation Differs between Primary Sclerosing and Primary Biliary Cholangitis

Primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC) are human primary cholangiopathies characterized by the damage of mature cholangiocytes and by the appearance of ductular reaction (DR) as the results of hepatic progenitor cell activation. This study evaluated the differences in progenitor cell niche activation between these two cholangiopathies. Liver tissue was obtained from healthy liver donors (n = 5) and from patients with PSC (n = 20) or PBC (n = 20). DR, progenitor cell phenotype, and signaling pathways were investigated by IHC analysis and immunofluorescence. Our results indicated that DR was more extended, appeared earlier, and had a higher proliferation index in PBC compared with PSC. In PBC, DR was strongly correlated with clinical prognostic scores. A higher percentage of sex determining region Y-box (SOX)9⁺ and cytokeratin 19⁺ cells but fewer features of hepatocyte fate characterized progenitor cell activation in PBC versus PSC. Lower levels of laminin and neurogenic locus notch homolog protein 1 but higher expression of wingless-related integration site (WNT) family pathway components characterize progenitor cell niche in PSC compared with PBC. In conclusion, progenitor cell activation differs between PSC and PBC and is characterized by a divergent fate commitment and different signaling pathway predominance. In PBC, DR represents a relevant histologic prognostic marker.

PNPLA3 variant and portal/periportal histological pattern in patients with biopsy-proven non-alcoholic fatty liver disease: a possible role for oxidative stress

Pathogenesis of non-alcoholic fatty liver disease (NAFLD) is influenced by predisposing genetic variations, dysmetabolism, systemic oxidative stress, and local cellular and molecular cross-talks. Patatin-like phospholipase domain containing 3 (PNPLA3) gene I148M variant is a known determinant of NAFLD. Aims were to evaluate whether PNPLA3 I148M variant was associated with a specific histological pattern, hepatic stem/progenitor cell (HpSC) niche activation and serum oxidative stress markers. Liver biopsies were obtained from 54 NAFLD patients. The activation of HpSC compartment was evaluated by the extension of ductular reaction (DR); hepatic stellate cells, myofibroblasts (MFs), and macrophages were evaluated by immunohistochemistry. Systemic oxidative stress was assessed measuring serum levels of soluble NOX2-derived peptide (sNOX2-dp) and 8-isoprostaglandin F_2α (8-iso-PGF_2α). PNPLA3 carriers showed higher steatosis, portal inflammation and HpSC niche activation compared to wild-type patients. DR was correlated with NAFLD activity score (NAS) and fibrosis score. Serum 8-iso-PGF_2α were significantly higher in I148M carriers compared to non-carriers and were correlated with DR and portal inflammation. sNox2-dp was correlated with NAS and with HpSC niche activation. In conclusion, NAFLD patients carrying PNPLA3 I148M are characterized by a prominent activation of HpSC niche which is associated with a more aggressive histological pattern (portal fibrogenesis) and increased oxidative stress.

Cryopreservation protocol for human biliary tree stem/progenitors, hepatic and pancreatic precursors

Human biliary tree stem/progenitor cells (hBTSCs) are being used for cell therapies of patients with liver cirrhosis. A cryopreservation method was established to optimize sourcing of hBTSCs for these clinical programs and that comprises serum-free Kubota’s Medium (KM) supplemented with 10% dimethyl sulfoxide (DMSO), 15% human serum albumin (HSA) and 0.1% hyaluronans. Cryopreserved versus freshly isolated hBTSCs were similar in vitro with respect to self-replication, stemness traits, and multipotency. They were able to differentiate to functional hepatocytes,cholangiocytes or pancreatic islets, yielding similar levels of secretion of albumin or of glucose-inducible levels of insulin. Cryopreserved versus freshly isolated hBTSCs were equally able to engraft into immunocompromised mice yielding cells with human-specific gene expression and human albumin levels in murine serum that were higher for cryopreserved than for freshly isolated hBTSCs. The successful cryopreservation of hBTSCs facilitates establishment of hBTSCs cell banking offering logistical advantages for clinical programs for treatment of liver diseases.

Cholangiocytes: Cell transplantation

BACKGROUND

Due to significant limitations to the access to orthotropic liver transplantation, cell therapies for liver diseases have gained large interest worldwide.

SCOPE OF REVIEW

To revise current literature dealing with cell therapy for liver diseases. We discussed the advantages and pitfalls of the different cell sources tested so far in clinical trials and the rationale underlying the potential benefits of transplantation of human biliary tree stem cells (hBTSCs).

MAJOR CONCLUSIONS

Transplantation of adult hepatocytes showed transient benefits but requires immune-suppression that is a major pitfall in patients with advanced liver diseases. Mesenchymal stem cells and hematopoietic stem cells transplanted into patients with liver diseases are not able to replace resident hepatocytes but rather they target autoimmune or inflammatory processes into the liver. Stem cells isolated from fetal or adult liver have been recently proposed as alternative cell sources for advanced liver cirrhosis and metabolic liver disease. We demonstrated the presence of multipotent cells expressing a variety of endodermal stem cell markers in (peri)-biliary glands of bile ducts in fetal or adult human tissues, and in crypts of gallbladder epithelium. In the first cirrhotic patients treated in our center with biliary tree stem cell therapy, we registered no adverse event but significant benefits.

GENERAL SIGNIFICANCE

The biliary tree stem cell could represent the ideal cell source for the cell therapy of liver diseases. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

PD-L1 and epithelial-mesenchymal transition in circulating tumor cells from non-small cell lung cancer patients: A molecular shield to evade immune system

The programmed cell death 1 (PD-1)/PD-1 ligand 1 (PD-L1) pathway has emerged as a critical inhibitory pathway regulating T-cell response in non-small-cell lung cancer (NSCLC), and the development of PD-1/PD-L1 inhibitors has changed the landscape of NSCLC therapy. Nevertheless, the high degree of non-responders demonstrates that we are still far from completely understanding the events underlying tumor immune resistance. Although the expression of PD-L1 in tumor tissue has been correlated with clinical response to anti PD-1 inhibitors, the ability of this marker to discriminate the subgroup of patients who derive benefit from immunotherapy is suboptimal. Circulating tumor cells (CTCs), as an accessible source of tumor for biologic characterization that can be serially obtained with minimally invasive procedure, hold significant promise to facilitate treatment-specific biomarkers discovery. We recently demonstrated that the presence of PD-L1 on CTCs apparently predicts resistance to the anti-PD-1 Nivolumab in metastatic NSCLC patients and that PD-L1 positive CTCs usually have an elongated morphology that can be ascribed to epithelial-mesenchymal transition (EMT). We here demonstrate for the first time that PD-L1 positive CTCs isolated from NSCLC patients are characterized by partial EMT phenotype, and hypothesize that the co-expression of PD-L1 and EMT markers might represent for these cells a possible molecular background for immune escape.

Human biliary tree stem/progenitor cells immunomodulation: Role of hepatocyte growth factor

AIM

Human biliary tree stem/progenitor cells (hBTSC) are multipotent epithelial stem cells with the potential for allogenic transplant in liver, biliary tree, and pancreatic diseases. Human mesenchymal stem cells, but also epithelial stem cells, are able to modulate immune responses with different types of secretion molecules.

METHODS

The initial aim of the present study was to develop for the first time a culture protocol in order to expand hBTSC in vitro through passages, allowing to maintain a similar stem cell and secretome profile. Furthermore, we investigated the secretome profile of the hBTSC to assess the production of molecules capable of affecting immune feedback.

RESULTS

We found that hepatocyte growth factor produced by hBTSC exerts its cytoprotective role inducing apoptosis in human immune cells, such as lymphocytes.

CONCLUSIONS

The present study, therefore, supports the hypothesis that hBTSC can be useful for the purpose of regenerative medicine, as they can be banked and expanded, and they can secrete immunoregulatory factors.

miR-18a counteracts AKT and ERK activation to inhibit the proliferation of pancreatic progenitor cells

Activation of endogenous stem/progenitor cells to repair injured tissues is an ideal option for disease treatment. However, adult pancreatic progenitor cells remain in a quiescent state in vivo. Thus, it is difficult to stimulate proliferation and differentiation in these progenitor cells, and the cause remains elusive. miR-17-92 cluster miRNAs are highly conserved in mammals and are expressed in multiple tissue stem/progenitor cells, but their role in pancreatic progenitor cells are less well known. In the present study, we demonstrate that miR-18a, but not the other members of the miR-17-92 gene cluster, inhibits the proliferation of pancreatic progenitor cells in vitro and ex vivo. miR-18a inhibits proliferation of adult pancreatic progenitor cells through arresting the cell cycle at G1 stage, indicating that miR-18a plays a role in keeping the adult pancreatic progenitor cells in quiescence. miR-18a inhibits pancreatic progenitor proliferation by targeting the gene expressions of connective tissue growth factor (CTGF), neural precursor cell expressed, developmentally down-regulated 9 (Nedd9), and cyclin dependent kinase 19 (CDK19), as well as by suppressing activation of the proliferation-related signaling pathways phosphatidylinositol 3-kinase–protein kinase B (PI3K/AKT) and extracellular signal-regulated kinase (ERK).

Hyaluronan coating improves liver engraftment of transplanted human biliary tree stem/progenitor cells

BACKGROUND

Cell therapy of liver diseases with human biliary tree stem cells (hBTSCs) is biased by low engraftment efficiency. Coating the hBTSCs with hyaluronans (HAs), the primary constituents of all stem cell niches, could facilitate cell survival, proliferation, and, specifically, liver engraftment given that HAs are cleared selectively by the liver.

METHODS

We developed a fast and easy method to coat hBTSCs with HA and assessed the effects of HA-coating on cell properties in vitro and in vivo.

RESULTS

The HA coating markedly improved the viability, colony formation, and population doubling of hBTSCs in primary cultures, and resulted in a higher expression of integrins that mediate cell attachment to matrix components. When HA-coated hBTSCs were transplanted via the spleen into the liver of immunocompromised mice, the engraftment efficiency increased to 11% with respect to 3% of uncoated cells. Notably, HA-coated hBTSC transplantation in mice resulted in a 10-fold increase of human albumin gene expression in the liver and in a 2-fold increase of human albumin serum levels with respect to uncoated cells. Studies in distant organs showed minimal ectopic cell distribution without differences between HA-coated and uncoated hBTSCs and, specifically, cell seeding in the kidney was excluded.

CONCLUSIONS

A ready and economical procedure of HA cell coating greatly enhanced the liver engraftment of transplanted hBTSCs and improved their differentiation toward mature hepatocytes. HA coating could improve outcomes of stem cell therapies of liver diseases and could be immediately translated into the clinic given that GMP-grade HAs are already available for clinical use.

Peribiliary Gland Dilatation in Cirrhosis: Relationship with Liver Failure and Stem Cell/Proliferation Markers

BACKGROUND AND AIMS

Dilated peribiliary glands (PBG) in patients with cirrhosis are often an incidental finding although their significance and physiopathology remain unclear. We aimed to identify clinical factors associated with dilated PBG and to perform a detailed morphometric assessment of dilated PBG in cirrhotic patients undergoing liver transplantation (LT).

METHODS

All consecutive cirrhotic patients undergoing LT at our institution between October 2006 and October 2011 were assessed for inclusion. Ten non-cirrhotic patients were included as controls. We performed morphometrical assessment of PBG, assessed baseline clinical factors associated with dilated PBG, immunohistochemistry staining with CK-19, MiB-1 and EpCAM, and radiological assessment of all available cases.

RESULTS

Seventy-one patients met the inclusion criteria, 24% had PBG dilatation of >1000 µm. On multivariable analysis, MELD (OR 1.11 per unit increase in MELD, p = 0.004) was the only significant factor associated with dilated PBG. Compared to PBG < 1000 µm, large PBG had a higher proportion of EpCAM-positive (69 vs. 28%, p < 0.001) and MiB-1-positive lining cells (2.8 vs. 0.55%, p = 0.036). Computed tomography and magnetic resonance imaging had high specificity but low sensitivity for the diagnosis of dilated PBG > 1000 µm (specificity 90-100%, sensitivity 25-29%).

CONCLUSIONS

Dilated PBGs are a common finding in explants of cirrhotic subjects undergoing LT and are associated with liver failure although diagnostic performance of cross-sectional imaging is inconstant. The high number of proliferative and EpCAM-positive cells lining the PBG may suggest a role of PBG in organ repair during liver failure.

On the development of the hepatopancreatic ductal system

The hepatopancreatic ductal system is the collection of ducts that connect the liver and pancreas to the digestive tract. The formation of this system is necessary for the transport of exocrine secretions, for the correct assembly of the pancreatobiliary ductal system, and for the overall function of the digestive system. Studies on endoderm organ formation have significantly advanced our understanding of the molecular mechanisms that govern organ induction, organ specification and morphogenesis of the major foregut-derived organs. However, little is known about the mechanisms that control the development of the hepatopancreatic ductal system. Here, we provide a description of the different components of the system, summarize its development from the endoderm to a complex system of tubes, list the pathologies produced by anomalies in its development, as well as the molecules and signaling pathways that are known to be involved in its formation. Finally, we discuss its proposed potential as a multipotent cell reservoir and the unresolved questions in the field.

Docosahexanoic Acid Plus Vitamin D Treatment Improves Features of NAFLD in Children with Serum Vitamin D Deficiency: Results from a Single Centre Trial

BACKGROUND

There are no licensed treatments for non alcoholic fatty liver disease (NAFLD) in adults or children. In NAFLD, several studies have shown a benefit of omega-3 fatty acid treatment on lipid profile, insulin-sensitivity and hepatic steatosis and it has also been suggested that Vitamin D treatment has potential antifibrotic properties in liver disease.

TRIAL DESIGN

To date, however, there are no studies that have tested the combination of Docosahexanoic acid (DHA) and vitamin D treatment which may benefit the whole spectrum of disease in NAFLD. Our aim therefore, was to test the effect of daily DHA (500 mg) plus vitamin D (800 IU) treatment, in obese children with biopsy-proven NAFLD and vitamin D deficiency, in a randomized, double-blind placebo-controlled trial.

METHODS

The 41/43 patients completed the study (18-treatment, 23-placebo). At 12 months: i) the main outcome was liver histology improvement, defined by NAS; ii) the secondary outcome was amelioration of metabolic parameters.

RESULTS

DHA plus vitamin D treatment reduced the NAFLD Activity Score (NAS), in the treatment group (5.4 v1.92; p<0.001 for baseline versus end of study). There was no change in fibrosis score, but a reduction of the activation of hepatic stellate cells (HSC) and fibrillar collagen content was noted (3.51±1.66 v. 1.59±1.37; p = 0.003) in treatment group. Moreover, the triglycerides (174.5 vs. 102.15 mg/dl), ALT (40.25 vs. 24.5 UI/l) and HOMA-IR (4.59 vs. 3.42) were all decreased with treatment.

CONCLUSION

DHA plus vitamin D treatment improved insulin-resistance, lipid profile, ALT and NAS. There was also decreased HSC activation and collagen content with treatment.

The hepatic, biliary, and pancreatic network of stem/progenitor cell niches in humans: A new reference frame for disease and regeneration

Stem/progenitors for liver, biliary tree, and pancreas exist at early stages of development in the definitive ventral endoderm forming the foregut. In humans, they persist postnatally as part of a network, with evidence supporting their contributions to hepatic and pancreatic organogenesis throughout life. Multiple stem cell niches persist in specific anatomical locations within the human biliary tree and pancreatic ducts. In liver and pancreas, replication of mature parenchymal cells ensures the physiological turnover and the restoration of parenchyma after minor injuries. Although actively debated, multiple observations indicate that stem/progenitor cells contribute to repair pervasive, chronic injuries. The most primitive of the stem/progenitor cells, biliary tree stem cells, are found in peribiliary glands within extrahepatic and large intrahepatic bile ducts. Biliary tree stem cells are comprised of multiple subpopulations with traits suggestive of maturational lineage stages and yet capable of self-replication and multipotent differentiation, being able to differentiate to mature liver cells (hepatocytes, cholangiocytes) and mature pancreatic cells (including functional islet endocrine cells). Hepatic stem cells are located within canals of Hering and bile ductules and are capable of differentiating to hepatocyte and cholangiocyte lineages. The existence, phenotype, and anatomical location of stem/progenitors in the adult pancreas are actively debated. Ongoing studies suggest that pancreatic stem cells reside within the biliary tree, primarily the hepatopancreatic common duct, and are rare in the pancreas proper. Pancreatic ducts and pancreatic duct glands harbor committed pancreatic progenitors.

CONCLUSION

The hepatic, biliary, and pancreatic network of stem/progenitor cell niches should be considered as a framework for understanding liver and pancreatic regeneration after extensive or chronic injuries and for the study of human chronic diseases affecting these organs. (Hepatology 2016;64:277-286).

The potential of induced pluripotent stem cell derived hepatocytes

Orthotopic liver transplantation remains the only curative treatment for liver disease. However, the number of patients who die while on the waiting list (15%) has increased in recent years as a result of severe organ shortages; furthermore the incidence of liver disease is increasing worldwide. Clinical trials involving hepatocyte transplantation have provided encouraging results. However, transplanted cell function appears to often decline after several months, necessitating liver transplantation. The precise aetiology of the loss of cell function is not clear, but poor engraftment and immune-mediated loss appear to be important factors. Also, primary human hepatocytes (PHH) are not readily available, de-differentiate, and die rapidly in culture. Hepatocytes are available from other sources, such as tumour-derived human hepatocyte cell lines and immortalised human hepatocyte cell lines or porcine hepatocytes. However, all these cells suffer from various limitations such as reduced or differences in functions or risk of zoonotic infections. Due to their significant potential, one possible inexhaustible source of hepatocytes is through the directed differentiation of human induced pluripotent stem cells (hiPSCs). This review will discuss the potential applications and existing limitations of hiPSC-derived hepatocytes in regenerative medicine, drug screening, in vitro disease modelling and bioartificial livers.

Macrophage Activation in Pediatric Nonalcoholic Fatty Liver Disease (NAFLD) Correlates with Hepatic Progenitor Cell Response via Wnt3a Pathway

Non-alcoholic fatty liver disease is one of the most important causes of liver-related morbidity in children. In non-alcoholic fatty liver disease, the activation of liver resident macrophage pool is a central event in the progression of liver injury. The aims of the present study were to evaluate the polarization of liver macrophages and the possible role of Wnt3a production by macrophages in hepatic progenitor cell response in the progression of pediatric non-alcoholic fatty liver disease. 32 children with biopsy-proven non-alcoholic fatty liver disease were included. 20 out of 32 patients were treated with docosahexaenoic acid for 18 months and biopsies at the baseline and after 18 months were included. Hepatic progenitor cell activation, macrophage subsets and Wnt/β-catenin pathway were evaluated by immunohistochemistry and immunofluorescence. Our results indicated that in pediatric non-alcoholic fatty liver disease, pro-inflammatory macrophages were the predominant subset. Macrophage polarization was correlated with Non-alcoholic fatty liver disease Activity Score, ductular reaction, and portal fibrosis; docosahexaenoic acid treatment determined a macrophage polarization towards an anti-inflammatory phenotype in correlation with the reduction of serum inflammatory cytokines, with increased macrophage apoptosis, and with the up-regulation of macrophage Wnt3a expression; macrophage Wnt3a expression was correlated with β-catenin phosphorylation in hepatic progenitor cells and signs of commitment towards hepatocyte fate. In conclusion, macrophage polarization seems to have a key role in the progression of pediatric non-alcoholic fatty liver disease; the modulation of macrophage polarization could drive hepatic progenitor cell response by Wnt3a production.

R-spondin 1 and noggin facilitate expansion of resident stem cells from non-damaged gallbladders

Pioneering studies within the last few years have allowed the in vitro expansion of tissue‐specific adult stem cells from a variety of endoderm‐derived organs, including the stomach, small intestine, and colon. Expansion of these cells requires activation of the receptor Lgr5 by its ligand R‐spondin 1 and is likely facilitated by the fact that in healthy adults the stem cells in these organs are highly proliferative. In many other adult organs, such as the liver, proliferating cells are normally not abundant in adulthood. However, upon injury, the liver has a strong regenerative potential that is accompanied by the emergence of Lgr5‐positive stem cells; these cells can be isolated and expanded in vitro as organoids. In an effort to isolate stem cells from non‐regenerating mouse livers, we discovered that healthy gallbladders are a rich source of stem/progenitor cells that can be propagated in culture as organoids for more than a year. Growth of these organoids was stimulated by R‐spondin 1 and noggin, whereas in the absence of these growth factors, the organoids differentiated partially toward the hepatocyte fate. When transplanted under the liver capsule, gallbladder‐derived organoids maintained their architecture for 2 weeks. Furthermore, single cells prepared from dissociated organoids and injected into the mesenteric vein populated the liver parenchyma of carbon tetrachloride‐treated mice. Human gallbladders were also a source of organoid‐forming stem cells. Thus, under specific growth conditions, stem cells can be isolated from healthy gallbladders, expanded almost indefinitely in vitro, and induced to differentiate toward the hepatocyte lineage.

Peribiliary Glands as a Niche of Extrapancreatic Precursors Yielding Insulin-Producing Cells in Experimental and Human Diabetes

Peribiliary glands (PBGs) are niches in the biliary tree and containing heterogeneous endodermal stem/progenitors cells that can differentiate, in vitro and in vivo, toward pancreatic islets. The aim of this study was to evaluate, in experimental and human diabetes, proliferation of cells in PBGs and differentiation of the biliary tree stem/progenitor cells (BTSCs) toward insulin-producing cells. Diabetes was generated in mice by intraperitoneal injection of a single dose of 200 mg/kg (N = 12) or 120 mg/kg (N = 12) of streptozotocin. Liver, pancreas, and extrahepatic biliary trees were en bloc dissected and examined. Cells in PBGs proliferated in experimental diabetes, and their proliferation was greatest in the PBGs of the hepatopancreatic ampulla, and inversely correlated with the pancreatic islet area. In rodents, the cell proliferation in PBGs was characterized by the expansion of Sox9-positive stem/progenitor cells that gave rise to insulin-producing cells. Insulin-producing cells were located mostly in PBGs in the portion of the biliary tree closest to the duodenum, and their appearance was associated with upregulation of MafA and Gli1 gene expression. In patients with type 2 diabetes, PBGs at the level of the hepatopancreatic ampulla contained cells showing signs of proliferation and pancreatic fate commitment. In vitro, high glucose concentrations induced the differentiation of human BTSCs cultures toward pancreatic beta cell fates. The cells in PBGs respond to diabetes with proliferation and differentiation towards insulin-producing cells indicating that PBG niches may rescue pancreatic islet impairment in diabetes. These findings offer important implications for the pathophysiology and complications of this disease. Stem Cells 2016;34:1332-1342.

Stem/Progenitor Cell Niches Involved in Hepatic and Biliary Regeneration

Niches containing stem/progenitor cells are present in different anatomical locations along the human biliary tree and within liver acini. The most primitive stem/progenitors, biliary tree stem/progenitor cells (BTSCs), reside within peribiliary glands located throughout large extrahepatic and intrahepatic bile ducts. BTSCs are multipotent and can differentiate towards hepatic and pancreatic cell fates. These niches' matrix chemistry and other characteristics are undefined. Canals of Hering (bile ductules) are found periportally and contain hepatic stem/progenitor cells (HpSCs), participating in the renewal of small intrahepatic bile ducts and being precursors to hepatocytes and cholangiocytes. The niches also contain precursors to hepatic stellate cells and endothelia, macrophages, and have a matrix chemistry rich in hyaluronans, minimally sulfated proteoglycans, fetal collagens, and laminin. The microenvironment furnishes key signals driving HpSC activation and differentiation. Newly discovered third niches are pericentral within hepatic acini, contain Axin2+ unipotent hepatocytic progenitors linked on their lateral borders to endothelia forming the central vein, and contribute to normal turnover of mature hepatocytes. Their relationship to the other stem/progenitors is undefined. Stem/progenitor niches have important implications in regenerative medicine for the liver and biliary tree and in pathogenic processes leading to diseases of these tissues.

Progenitor cell niches in the human pancreatic duct system and associated pancreatic duct glands: an anatomical and immunophenotyping study

Pancreatic duct glands (PDGs) are tubule-alveolar glands associated with the pancreatic duct system and can be considered the anatomical counterpart of peribiliary glands (PBGs) found within the biliary tree. Recently, we demonstrated that endodermal precursor niches exist fetally and postnatally and are composed functionally of stem cells and progenitors within PBGs and of committed progenitors within PDGs. Here we have characterized more extensively the anatomy of human PDGs as novel niches containing cells with multiple phenotypes of committed progenitors. Human pancreata (n = 15) were obtained from cadaveric adult donors. Specimens were processed for histology, immunohistochemistry and immunofluorescence. PDGs were found in the walls of larger pancreatic ducts (diameters > 300 μm) and constituted nearly 4% of the duct wall area. All of the cells identified were negative for nuclear expression of Oct4, a pluripotency gene, and so are presumably committed progenitors and not stem cells. In the main pancreatic duct and in large interlobular ducts, Sox9(+) cells represented 5-30% of the cells within PDGs and were located primarily at the bottom of PDGs, whereas rare and scattered Sox9(+) cells were present within the surface epithelium. The expression of PCNA, a marker of cell proliferation, paralleled the distribution of Sox9 expression. Sox9(+) PDG cells proved to be Pdx1(+) /Ngn3(+/-) /Oct4A(-) . Nearly 10% of PDG cells were positive for insulin or glucagon. Intercalated ducts contained Sox9(+) /Pdx1(+) /Ngn3(+) cells, a phenotype that is presumptive of committed endocrine progenitors. Some intercalated ducts appeared in continuity with clusters of insulin-positive cells organized in small pancreatic islet-like structures. In summary, PDGs represent niches of a population of Sox9(+) cells exhibiting a pattern of phenotypic traits implicating a radial axis of maturation from the bottoms of the PDGs to the surface of pancreatic ducts. Our results complete the anatomical background that links biliary and pancreatic tracts and could have important implications for the common patho-physiology of biliary tract and pancreas.

Development and functional characterization of extrahepatic cholangiocyte lines from normal rats

BACKGROUND

Since limited in vitro tools exist for evaluating the pathophysiology of extrahepatic bile ducts, we aim to develop an extrahepatic cholangiocyte culture system from normal rats.

METHODS

Extrahepatic ducts were dissected from rats, cut in half length-wise and cultured on collagen-I coated plates. Transepithelial electrical resistance was measured. At ∼85% confluence, in extrahepatic cholangiocytes we measured: (i) cell size and distribution, and expression for cytokeratin-19, secretin, secretin receptor and somatostatin receptor type II (SSTR2), cystic fibrosis transmembrane conductance regulator (CFTR), chloride bicarbonate anion exchanger 2 (AE2), vascular endothelial growth factor-A (VEGF-A) and nerve growth factor (NGF); and (ii) the effect of secretin and/or somatostatin on 3'-5'-cyclic adenosine monophosphate (cAMP) levels and proliferation.

RESULTS

Cytokeratin-positive extrahepatic cholangiocytes were cultured for 6 passages to form a cell monolayer. Cholangiocytes proliferated to confluence over a 2-week period. The size of extrahepatic cholangiocytes averaged ∼16 μm. Extrahepatic ducts and cholangiocytes were positive for secretin, secretin receptor and SSTR2, CFTR, AE2, VEGF-A and NGF. In extrahepatic cholangiocyte cultures, secretin increased cAMP (prevented by somatostatin), chloride efflux and proliferation.

CONCLUSIONS

Extrahepatic cholangiocyte cultures may be important for studying diseases targeting extrahepatic cholangiocytes such as biliary atresia.

Activation of biliary tree stem cells within peribiliary glands in primary sclerosing cholangitis

BACKGROUND & AIMS

Primary sclerosing cholangitis (PSC) is characterised by fibro-stenosing strictures involving extrahepatic and/or large intrahepatic bile ducts. Mechanisms leading to bile duct injury are poorly understood. We aimed to study the biliary tree stem cell compartment located in peribiliary glands of extrahepatic and large intrahepatic bile ducts and its role in the pathogenesis of biliary fibrosis in PSC.

METHODS

Specimens containing extrahepatic or large intrahepatic bile ducts were obtained from normal liver (n=6), liver explants from patients with PSC (n=11), and primary biliary cirrhosis (n=6). Specimens were processed for histology, immunohistochemistry and immunofluorescence.

RESULTS

In PSC samples, progressive hyperplasia and mucinous metaplasia of peribiliary glands were observed in large ducts with fibrosis, but not in inflamed ducts without fibrosis. Peribiliary gland hyperplasia was associated with progressive biliary fibrosis and the occurrence of dysplastic lesions. Hyperplasia of peribiliary glands was determined by the expansion of biliary tree stem cells, which sprouted towards the surface epithelium. In PSC, peribiliary glands and myofibroblasts displayed enhanced expression of Hedgehog pathway components. Peribiliary glands in ducts with onion skin-like fibrosis expressed epithelial-to-mesenchymal transition traits associated with components of Hedgehog pathway, markers of senescence and autophagy.

CONCLUSIONS

The biliary tree stem cell compartment is activated in PSC, its activation contributes to biliary fibrosis, and is sustained by the Hedgehog pathway. Our findings suggest a key role for peribiliary glands in the progression of bile duct lesions in PSC and could explain the associated high risk of cholangiocarcinoma.