Bone marrow fails to differentiate into liver epithelium during murine development and regeneration

Transplantation of Adipose-Derived Mesenchymal Stem Cells Efficiently Rescues Thioacetamide-Induced Acute Liver Failure in Mice

BACKGROUND

We aimed to investigate the efficacy of adipose-derived mesenchymal stem cell (ADMSC) transplantation in acute liver failure caused by thioacetamide in mice as well as its underlying mechanism by comparing transplantation routes.

METHODS

ADMSCs were isolated from inguinal fat pads of enhanced green fluorescent protein (EGFP) transgenic mice and analyzed regarding their surface markers and differentiation potential. Acute liver failure models were established by infusion of thioacetamide, and then we injected EGFP-ADMSCs or phosphate-buffered saline solution by intrasplenic or intravenous route. The restoration of biologic functions of the livers receiving transplantation was assessed by means of a variety of approaches, such as survival rates, live function parameters, histology, localization of EGFP-ADMSCs, and immunofluorescence analysis.

RESULTS

ADMSCs were positive for CD90 and CD44 and negative for CD34 and had adipogenic and osteogenic differentiation potential. And they prevented the release of liver injury biomarkers. Transplantation via tail vein provided a significant survival benefit, but no significant differences were observed in the intrasplenic pathway and between the 2 pathways in our animal experiments. Furthermore, the transplanted cells were well integrated into injured livers and produced albumin and cytokeratin-8.

CONCLUSIONS

Direct transplantation of ADMSCs is an effective treatment for acute liver failure rather than intrasplenic transplantation. The transplanted ADMSCs exhibit the potential to differentiate into hepatocyte-like cells in the injured livers. Thus, ADCMSCs would be a potential option for treatment of acute liver failure.

Adipose derived mesenchymal stem cells efficiently rescue carbon tetrachloride-induced acute liver failure in mouse

Background and Aim. Adipose derived mesenchymal stem cells (ADMSCs) may be an attractive source for acute and chronic liver injury because they are abundant and easy to obtain. We aim to investigate the efficacy of ADMSCs transplantation in the acute liver failure (ALF) caused by carbon tetrachloride (CCl₄) in mice. Methods. ADMSCs were isolated from inguinal fat pads of enhanced green fluorescent protein (EGFP) transgenic mice and their surface markers and differentiation potential were analyzed. ALF models were established by infusion of CCl₄ and divided into two groups: control group; EGFP-ADMSCs transplantation group. The restoration of biological functions of the livers receiving transplantation was assessed via a variety of approaches such as survival rates, live function parameters, histological localization of EGFP-ADMSCs, and Immunofluorescence analysis. Results. ADMSCs were positive for CD105, CD44 but negative for CD45, CD34 and had adipogenic, osteogenic differentiation potential. The survival rate of transplantation group significantly increased compared to PBS group. Furthermore, the transplanted cells were well integrated into injured livers and produced albumin, cytokeratin-18. Conclusion. Direct transplantation of ADMSCs is an effective treatment for ALF. The transplanted ADMSCs exhibit the potential to differentiate into hepatocyte-like cells in the injured livers.

The origin, biology, and therapeutic potential of facultative adult hepatic progenitor cells

The liver plays an essential role in glucose and lipid metabolism, synthesis of plasma proteins, and detoxification of xenobiotics and other toxins. Chronic disease of this important organ is one of the leading causes of death in the United States. Following loss of tissue, liver mass can be restored by two mechanisms. Under normal conditions, or after massive loss of parenchyma by surgical resection, liver mass is maintained by division of hepatocytes. After chronic injury, or when proliferation of hepatocytes is impaired, facultative adult hepatic progenitor cells (HPCs) proliferate and differentiate into hepatocytes and cholangiocytes (biliary epithelial cells). HPCs are attractive candidates for cell transplantation because of their potential contribution to liver regeneration. However, until recently, the lack of highly specific markers has hampered efforts to better understand the origin and physiology of HPCs. Recent advances in cell isolation methods and genetic lineage tracing have enabled investigators to explore multiple aspects of HPC biology. In this review, we describe the potential origins of HPCs, the markers used to detect them, the contribution of HPCs to recovery, and the signaling pathways that regulate their biology. We end with an examination of the therapeutic potential of HPCs and their derivatives.

Promotion of hepatic differentiation of bone marrow mesenchymal stem cells on decellularized cell-deposited extracellular matrix

Interactions between stem cells and extracellular matrix (ECM) are requisite for inducing lineage-specific differentiation and maintaining biological functions of mesenchymal stem cells by providing a composite set of chemical and structural signals. Here we investigated if cell-deposited ECM mimicked in vivo liver's stem cell microenvironment and facilitated hepatogenic maturation. Decellularization process preserved the fibrillar microstructure and a mix of matrix proteins in cell-deposited ECM, such as type I collagen, type III collagen, fibronectin, and laminin that were identical to those found in native liver. Compared with the cells on tissue culture polystyrene (TCPS), bone marrow mesenchymal stem cells (BM-MSCs) cultured on cell-deposited ECM showed a spindle-like shape, a robust proliferative capacity, and a suppressed level of intracellular reactive oxygen species, accompanied with upregulation of two superoxide dismutases. Hepatocyte-like cells differentiated from BM-MSCs on ECM were determined with a more intensive staining of glycogen storage, an elevated level of urea biosynthesis, and higher expressions of hepatocyte-specific genes in contrast to those on TCPS. These results demonstrate that cell-deposited ECM can be an effective method to facilitate hepatic maturation of BM-MSCs and promote stem-cell-based liver regenerative medicine.

Immediate intraportal transplantation of human bone marrow mesenchymal stem cells prevents death from fulminant hepatic failure in pigs

The effectiveness of human bone marrow mesenchymal stem cell (hBMSC) transplantation to treat acute and chronic liver injury has been demonstrated in animal models and in a few nonrandomized clinical trials. However, no studies have investigated hBMSC transplantation in the treatment of fulminant hepatic failure (FHF), especially in large animal (pig) models. The aim of this study was to demonstrate the safety, effectiveness, and underlying mechanism of hBMSC transplantation for treating FHF in pigs through the intraportal route. Human BMSCs (3 × 10(7) ) were transplanted into pigs with FHF via the intraportal route or peripheral vein immediately after D-galactosamine injection, and a sham group underwent intraportal transplantation (IPT) without cells (IPT, peripheral vein transplantation [PVT], and control groups, respectively, n = 15 per group). All of the animals in the PVT and control groups died of FHF within 96 hours. In contrast, 13 of 15 animals in the IPT group achieved long-term survival (>6 months). Immunohistochemistry demonstrated that transplanted hBMSC-derived hepatocytes in surviving animals were widely distributed in the hepatic lobules and the liver parenchyma from weeks 2 to 10. Thirty percent of the hepatocytes were hBMSC-derived. However, the number of transplanted cells decreased significantly at week 15. Only a few single cells were scattered in the regenerated liver lobules at week 20, and the liver tissues exhibited a nearly normal structure.

CONCLUSION

Immediate IPT of hBMSCs is a safe and effective treatment for FHF. The transplanted hBMSCs may quickly participate in liver regeneration via proliferation and transdifferentiation into hepatocytes during the initial stage of FHF. This method can possibly be used in future clinical therapy.

Isolation of CD133+ liver stem cells for clonal expansion

Liver stem cell, or oval cells, proliferate during chronic liver injury, and are proposed to differentiate into both hepatocytes and cholangiocytes. In addition, liver stem cells are hypothesized to be the precursors for a subset of liver cancer, Hepatocellular carcinoma. One of the primary challenges to stem cell work in any solid organ like the liver is the isolation of a rare population of cells for detailed analysis. For example, the vast majority of cells in the liver are hepatocytes (parenchymal fraction), which are significantly larger than non-parenchymal cells. By enriching the specific cellular compartments of the liver (i.e. parenchymal and non-parenchymal fractions), and selecting for CD45 negative cells, we are able to enrich the starting population of stem cells by over 600-fold.The proceduresdetailed in this report allow for a relatively rare population of cells from a solid organ to be sorted efficiently. This process can be utilized to isolateliver stem cells from normal murine liver as well as chronic liver injury models, which demonstrate increased liver stem cell proliferation. This method has clear advantages over standard immunohistochemistry of frozen or formalin fixed liver as functional studies using live cells can be performed after initial co-localization experiments. To accomplish the procedure outlined in this report, a working relationship with a research based flow-cytometry core is strongly encouraged as the details of FACS isolation are highly dependent on specialized instrumentation and a strong working knowledge of basic flow-cytometry procedures. The specific goal of this process is to isolate a population of liver stem cells that can be clonally expanded in vitro.

3D PLGA scaffolds improve differentiation and function of bone marrow mesenchymal stem cell-derived hepatocytes

Liver tissue engineering with hepatic stem cells provides a promising alternative to liver transplantation in patients with acute and chronic hepatic failure. In this study, a three-dimensional (3D) bioscaffold was introduced for differentiation of rat bone marrow mesenchymal stem cells (BMSCs) into hepatocytes. For hepatocyte differentiation, third passage BMSCs isolated from normal adult F344 rats were seeded into collagen-coated poly(lactic-co-glycolic acid) (C-PLGA) 3D scaffolds with hepatocyte differentiation medium for 3 weeks. Hepatogenesis in scaffolds was characterized by reverse transcript PCR, western blot, confocal laser scanning microscopy (CLSM), periodic acid-Schiff staining, histochemistry, and biochemical assays with hepatic-specific genes and markers. A monolayer culture system was used as a control differentiation group. The results showed that isolated cells possessed the basic features of BMSCs. Differentiated hepatocyte-like cells in C-PLGA scaffolds expressed hepatocyte-specific markers [eg, albumin (ALB), alpha-fetoprotein, cytokeratin 18, hepatocyte nuclear factor 4alpha, and cytochrome P450] at mRNA and protein levels. Most markers were expressed in C-PLGA group 1 week earlier than in the control group. Results of biocompatibility indicated that the differentiated hepatocyte-like cells grew more stably in C-PLGA scaffolds than that in controls during a 3-week differentiation period. The significantly higher metabolic functions in hepatocyte-like cells in the C-PLGA scaffold group further demonstrated the important role of the scaffold.

CONCLUSION

As the phenomenon of transdifferentiation is uncommon, our successful transdifferentiation rates of BMSCs to mature hepatocytes prove the superiority of the C-PLGA scaffold in providing a suitable environment for such a differentiation. This material can possibly be used as a bioscaffold for liver tissue engineering in future clinical therapeutic applications.

Portal venous endothelium in developing human liver contains haematopoietic and epithelial progenitor cells

Future treatments for chronic liver disease are likely to involve manipulation of liver progenitor cells (LPCs). In the human, data characterising the regenerative response is limited and the origin of adult LPCs is unknown. However, these remain critical factors in the design of cell-based liver therapies. The developing human liver provides an ideal model to study cell lineage derivation from progenitors and to understand how foetal haematopoiesis and liver development might explain the nature of the adult LPC population. In 1st trimester human liver, portal venous endothelium (PVE) expressed adult LPC markers and markers of haematopoietic progenitor cells (HPCs) shared with haemogenic endothelium found in the embryonic dorsal aorta. Sorted PVE cells were able to generate hepatoblast-like cells co-expressing CK18 and CK19 in addition to Dlk/pref-1, E-cadherin, albumin and fibrinogen in vitro. Furthermore, PVE cells could initiate haematopoiesis. These data suggest that PVE shares phenotypical and functional similarities both with adult LPCs and embryonic haemogenic endothelium. This indicates that a temporal relationship might exist between progenitor cells in foetal liver development and adult liver regeneration, which may involve progeny of PVE.

Transcriptional profiling and hepatogenic potential of acute hepatic failure-derived bone marrow mesenchymal stem cells

Liver stem cell (LSC) transplantation is a promising alternate approach to liver transplantation for patients with end-stage liver disease. However, the precise origin of LSCs remains unclear. Herein we determine if bone marrow mesenchymal stem cells (BMSCs) isolated from rats in acute hepatic failure (AHF) possess hepatic characteristics and have differentiation potential. BMSCs were isolated from AHF and sham-operated rats, and primary hepatocytes were isolated from normal rats for comparison. The transcriptomic profile of BMSCs and primary hepatocytes was analyzed using the Affymetrix GeneChip Rat Genome 230 2.0 Array. BMSCs isolated from AHF and normal rats were induced to differentiate into hepatocytes in vitro and the degree of hepatic differentiation was assessed using quantitative real time RT-PCR, immunohistochemistry, and biochemical assays. AHF-derived BMSCs had a significantly different gene expression profile compared to control BMSCs. Thirty-four gene/probe sets were expressed in both AHF-derived BMSCs and primary hepatocytes, but were absent in control-derived BMSCs, including 3 hepatocyte-specific genes. Forty-four genes were up-regulated more than 2-fold in AHF-derived BMSCs compared to controls, including 3 genes involved in hepatocyte metabolism and development. Furthermore, AHF-derived BMSCs expressed more hepatocyte related genes than control BMSCs. Additional experiments to validate the differentiation of AHF-derived BMSCs, compared to control-derived BMSCs, showed that several hepatocyte-specific genes and proteins [such as albumin (ALB) and alpha fetoprotein (AFP)] were expressed earlier, and at higher levels, after 1 week of differentiation. Hepatocyte-specific metabolic functions were also significantly higher in the AHF group compared to control cells.

CONCLUSION

AHF-derived BMSCs had a hepatic transcriptional profile and expressed hepatocyte specific genes early during differentiation, and possessed greater hepatogenic potency in vitro compared to cells isolated from control animals, further confirming their potential as a stem cell-based therapy for end-stage liver disease.

Expansion of CD133-expressing liver cancer stem cells in liver-specific phosphatase and tensin homolog deleted on chromosome 10-deleted mice

PTEN (phosphatase and tensin homolog deleted on chromosome 10) is a lipid phosphatase that regulates mitogenic signaling pathways, and deficiency of PTEN results in cell proliferation, survival, and malignancy. Murine liver-specific Pten deletion models develop liver malignancy by 12 months of age. Using this model, we describe a population of CD133+ liver cancer stem cells isolated during the chronic injury phase of disease progression and before primary carcinoma formation. We performed immunohistochemistry and flow cytometry isolation using livers from 3- and 6-month-old Pten(loxP/loxP); Alb-Cre+ mice (mutants) and controls. CD133+CD45- nonparenchymal (NP) cells were analyzed for gene expression profile and protein levels. Single CD133+CD45- oval cells were isolated for clonal expansion and tumor analysis. Cultured and freshly isolated liver CD133+CD45- and CD133-CD45- NP cells were injected into immune-deficient and immune-competent mice. In mutant mice, the NP fraction increased in CD133+CD45- cells in 3- and 6-month-old Pten-deleted animals compared with controls. Clone lines expanded from single CD133+CD45- cells demonstrated consistent liver progenitor cell phenotype, with bilineage gene expression of hepatocyte and cholangiocyte markers. CD133+ cells from expanded clone lines formed robust tumors in immune-deficient and immune-competent mice. Furthermore, freshly isolated CD133+CD45- NP liver cells from 6-month-old mutants formed tumors in vivo, and CD133-CD45- NP cells did not. Consistent with a cancer stem cell phenotype, CD133+ cells demonstrate resistance to chemotherapy agents compared with CD133- cells. CD133+CD45- nonparenchymal cells from chronic injury Pten(loxP/loxP); Alb-Cre+ mice represent a bipotent liver progenitor cell population with cancer stem cell phenotype.

Stem cells in liver regeneration, fibrosis and cancer: the good, the bad and the ugly

The worldwide shortage of donor livers to transplant end stage liver disease patients has prompted the search for alternative cell therapies for intractable liver diseases, such as acute liver failure, cirrhosis and hepatocellular carcinoma (HCC). Under normal circumstances the liver undergoes a low rate of hepatocyte 'wear and tear' renewal, but can mount a brisk regenerative response to the acute loss of two-thirds or more of the parenchymal mass. A body of evidence favours placement of a stem cell niche in the periportal regions, although the identity of such stem cells in rodents and man is far from clear. In animal models of liver disease, adopting strategies to provide a selective advantage for transplanted hepatocytes has proved highly effective in repopulating recipient livers, but the poor success of today's hepatocyte transplants can be attributed to the lack of a clinically applicable procedure to force a similar repopulation of the human liver. The activation of bipotential hepatic progenitor cells (HPCs) is clearly vital for survival in many cases of acute liver failure, and the signals that promote such reactions are being elucidated. Bone marrow cells (BMCs) make, at best, a trivial contribution to hepatocyte replacement after damage, but other BMCs contribute to the hepatic collagen-producing cell population, resulting in fibrotic disease; paradoxically, BMC transplantation may help alleviate established fibrotic disease. HCC may have its origins in either hepatocytes or HPCs, and HCCs, like other solid tumours appear to be sustained by a minority population of cancer stem cells.

Recent progress on tissue-resident adult stem cell biology and their therapeutic implications

Recent progress in the field of the stem cell research has given new hopes to treat and even cure diverse degenerative disorders and incurable diseases in human. Particularly, the identification of a rare population of adult stem cells in the most tissues/organs in human has emerged as an attractive source of multipotent stem/progenitor cells for cell replacement-based therapies and tissue engineering in regenerative medicine. The tissue-resident adult stem/progenitor cells offer the possibility to stimulate their in vivo differentiation or to use their ex vivo expanded progenies for cell replacement-based therapies with multiple applications in human. Among the human diseases that could be treated by the stem cell-based therapies, there are hematopoietic and immune disorders, multiple degenerative disorders, such as Parkinson's and Alzheimer's diseases, type 1 or 2 diabetes mellitus as well as eye, liver, lung, skin and cardiovascular disorders and aggressive and metastatic cancers. In addition, the genetically-modified adult stem/progenitor cells could also be used as delivery system for expressing the therapeutic molecules in specific damaged areas of different tissues. Recent advances in cancer stem/progenitor cell research also offer the possibility to targeting these undifferentiated and malignant cells that provide critical functions in cancer initiation and progression and disease relapse for treating the patients diagnosed with the advanced and metastatic cancers which remain incurable in the clinics with the current therapies.

Alpha-fetoprotein, stem cells and cancer: how study of the production of alpha-fetoprotein during chemical hepatocarcinogenesis led to reaffirmation of the stem cell theory of cancer

Identification of the cells in the liver that produce alpha-fetoprotein during development, in response to liver injury and during the early stages of chemical hepatocarcinogenesis led to the conclusion that maturation arrest of liver-determined tissue stem cells was the cellular process that gives rise to hepatocellular carcinomas. When the cellular changes in these processes were compared to that of the formation of teratocarcinomas, the hypothesis arose that all cancers arise from maturation arrest of tissue-determined stem cells. This was essentially a reinterpretation of the embryonal rest theory of cancer whereby tissue stem cells take the role of embryonal rests. A corollary of the stem cell theory of the origin of cancer is that cancers contain the same functional cell populations as normal tissues: stem cells, transit-amplifying cells and mature cells. Cancer stem cells retain the essential feature of normal stem cells: the ability to self-renew. Growth of cancers is due to continued proliferation of cancer transit-amplifying cells that do not differentiate to mature cells (maturation arrest). On the other hand, cancer stem cells generally divide very rarely and contribute little to tumor growth. However, the presence of cancer stem cells in tumors is believed to be responsible for the properties of immortalization, transplantability and resistance to therapy characteristic of cancers. Current therapies for cancer (chemotherapy, radiotherapy, antiangiogenesis and differentiation therapy) are directed against the cancer transit-amplifying cells. When these therapies are discontinued, the cancer reforms from the cancer stem cells. Therapy directed toward interruption of the cell signaling pathways that maintain cancer stem cells could lead to new modalities to the prevention of regrowth of the cancer.

Hepatocyte nuclear factor-1 as marker of epithelial phenotype reveals marrow-derived hepatocytes, but not duct cells, after liver injury in mice

The potential bone marrow origin of hepatocytes, cholangiocytes, and ductal progenitor cells in the liver was examined in female mice after transplantation of bone marrow cells from male green fluorescent protein (GFP) transgenic donors. Following stable hematopoietic engraftment, the livers of the recipients were injured with carbon tetrachloride (CCl(4), with or without local irradiation of the liver) or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC, with or without local irradiation of the liver). The presence of numerous marrow-derived, GFP-positive inflammatory cells had the potential to lead to erroneous interpretation of marrow-derived hepatocytes, cholangiocytes, and ductal progenitor cells. Identification of marrow-derived ductal progenitor or cholangiocyte phenotype using colocalization of GFP or Y chromosome with pancytokeratin staining also failed to distinguish epithelial cells from closely apposed inflammatory cells. To address this inadequacy, we developed a rigorous new immunofluorescence protocol to identify marrow-derived epithelial cells in the liver using Y chromosome (donor marker) and hepatocyte nuclear factor-1 (HNF1, a nuclear marker of liver epithelial, nonhematopoietic phenotype). Using the Y/HNF1 method, rare (approximately one in 20,000) hepatocytes in female mice transplanted with male bone marrow contained a donor-derived Y chromosome. On the other hand, no Y chromosomes were found in cholangiocytes or ductal progenitor cells in mice with liver injury due to DDC or CCl(4). The use of a nuclear marker of mature hepatocytes or cholangiocytes, such as HNF1, improves discrimination of marrow-derived epithelial cells in tissue sections.

Bone marrow multipotent mesenchymal stromal cells do not reduce fibrosis or improve function in a rat model of severe chronic liver injury

The objective of our study was to evaluate the therapeutic potential of bone marrow mesenchymal stromal cells (MSC) in a rat model of severe chronic liver injury. Fourteen female Wistar rats were fed exclusively an alcoholic liquid diet and received intraperitoneal injections of carbon tetrachloride every other day during 15 weeks. After this period, eight animals (MSC group) had 1 x 10(7) cells injected into the portal vein while six animals (placebo group) received vehicle. Blood analysis was performed to evaluate alanine aminotransferase (ALT), aspartate aminotransferase (AST), and albumin before cell therapy and 1 and 2 months after cell or placebo infusion. Fibrosis was evaluated before and 1 month after cell or placebo injection by liver biopsies. Two months after cell delivery, animals were sacrificed and histological analysis of the livers was performed. Fibrosis was quantified by histomorphometry. Biopsies obtained before cell infusion showed intense collagen deposition and septa interconnecting regenerative nodules. One month after cell injection, this result was unaltered and differences in fibrosis quantification were not found between MSC and placebo groups. ALT and AST returned to normal values 2 weeks after cell or placebo infusion, without significant differences between experimental groups. Two months after cell or placebo injection, albumin had also returned to normal values and histological results were maintained, again without differences between MSC and placebo groups. Therefore, under our experimental conditions, MSC were unable to reduce fibrosis or improve liver function in a rat model of severe chronic liver injury.

Expansion of liver cancer stem cells during aging in methionine adenosyltransferase 1A-deficient mice

Methionine adenosyltransferase (MAT) is an essential enzyme that catalyzes the biosynthesis of S-adenosylmethionine. Hepatic MAT activity falls in chronic liver diseases, and mice lacking Mat1a are predisposed to liver injury and develop hepatocellular carcinoma (HCC) spontaneously by 18 months. The current work examined the hypothesis that liver cancer stem cells contribute to HCC in this model. Livers from 6- and 18-month-old Mat1a-knockout (KO) mice and their wild-type (WT) littermates were fractionated and isolated by flow cytometry. CD45- nonparenchymal (NP) cells were cultured using liver stem cell conditions. Cells were analyzed by real-time PCR and fluorescent immunohistochemistry (FIHC). Tumor formation was assessed by injecting 1 x 10(6) CD133+CD49f+ cells intraperitoneally into immune-deficient mice. The proportion of CD49f+ and CD133+ cells in the CD45-NP fraction increased 4.5- to 5.5-fold from 6 to 18 months in KO mice but not in their WT littermates. Compared to CD49f- cells from old KO mice, CD49f+ cells from the same animals had a markedly increased expression of several oncogenes. CD133+ cells with CD49f coexpression were selected in vitro and exhibited rapid growth, with the expression of biliary cytokeratins, alpha-fetoprotein, and c-Met by FIHC. Clonal expansion of single CD133+CD49f+ cells revealed maintenance of bipotency. After CD133+CD49f+ cells were injected into immune-deficient mice, 3 of the 8 mice developed tumors of liver epithelial cells after 6-8 weeks.

CONCLUSION

Mat1a(-/-) mice have expansion of liver stem cells as they age. These cells have increased expression of several oncogenes and are tumorigenic in vivo. This is the first demonstration of adult liver stem cells possessing tumorigenic potential without the use of a carcinogen or manipulation of tumor-suppressor or oncogene expression.

Application of liver stem cells for cell therapy

The worldwide shortage of donor livers to transplant end stage liver disease patients has prompted the search for alternative cell therapies for intractable liver disease. Embryonic stem cells can be readily differentiated into hepatocytes, and their transplantation into animals has improved liver function in the absence of teratoma formation: their use in bioartificial liver support is an obvious application. In animal models of liver disease, adopting strategies to provide a selective advantage for transplanted foetal or adult hepatocytes have proved highly effective in repopulating recipient livers, but the poor success of today's hepatocyte transplants can be attributed to the lack of a clinically applicable procedure to force a similar repopulation of the human liver. The activation of bipotential hepatic progenitor cells is clearly vital for survival in many cases of acute liver failure, but surprisingly little progress has been made with these cells in terms of transplantation. Finally there is the controversial subject of autologous bone marrow, and while the contribution of these indigenous cells to liver turnover seems at best, trivial, results from a small number of phase 1 studies of transplantation of bone marrow to cirrhotic patients have been moderately encouraging.

Fibroblast growth factor 10 is critical for liver growth during embryogenesis and controls hepatoblast survival via beta-catenin activation

Fibroblast growth factor (FGF) signaling and beta-catenin activation have been shown to be crucial for early embryonic liver development. This study determined the significance of FGF10-mediated signaling in a murine embryonic liver progenitor cell population as well as its relation to beta-catenin activation. We observed that Fgf10(-/-) and Fgfr2b(-/-) mouse embryonic livers are smaller than wild-type livers; Fgf10(-/-) livers exhibit diminished proliferation of hepatoblasts. A comparison of beta-galactosidase activity as a readout of Fgf10 expression in Fgf10(+/LacZ) mice and of beta-catenin activation in TOPGAL mice, demonstrated peak Fgf10 expression from E9 to E13.5 coinciding with peak beta-catenin activation. Flow cytometric isolation and marker gene expression analysis of LacZ(+) cells from E13.5 Fgf10(+/LacZ) and TOPGAL livers, respectively, revealed that Fgf10 expression and beta-catenin signaling occur distinctly in stellate/myofibroblastic cells and hepatoblasts, respectively. Moreover, hepatoblasts express Fgfr2b, which strongly suggests they can respond to recombinant FGF10 produced by stellate cells. Fgfr2b(-/-)/TOPGAL(+/+) embryonic livers displayed less beta-galactosidase activity than livers of Fgfr2b(+/+)/TOPGAL(+/+) littermates. In addition, cultures of whole liver explants in Matrigel or cell in suspension from E12.5 TOPGAL(+/+)mice displayed a marked increase in beta-galactosidase activity and cell survival upon treatment with recombinant FGF10, indicating that FGFR (most likely FGFR2B) activation is upstream of beta-catenin signaling and promote hepatoblast survival.

CONCLUSION

Embryonic stellate/myofibroblastic cells promote beta-catenin activation in and survival of hepatoblasts via FGF10-mediated signaling. We suggest a role for stellate/myofibroblastic FGF10 within the liver stem cell niche in supporting the proliferating hepatoblast.

A CD133-expressing murine liver oval cell population with bilineage potential

Although oval cells are postulated to be adult liver stem cells, a well-defined phenotype of a bipotent liver stem cell remains elusive. The heterogeneity of cells within the oval cell fraction has hindered lineage potential studies. Our goal was to identify an enriched population of bipotent oval cells using a combination of flow cytometry and single cell gene expression in conjunction with lineage-specific liver injury models. Expression of cell surface markers on nonparenchymal, nonhematopoietic (CD45-) cells were characterized. Cell populations were isolated by flow cytometry for gene expression studies. 3,5-Diethoxycarbonyl-1,4-dihydrocollidine toxic injury induced cell cycling and expansion specifically in the subpopulation of oval cells in the periportal zone that express CD133. CD133+CD45- cells expressed hepatoblast and stem cell-associated genes, and single cells coexpressed both hepatocyte and cholangiocyte-associated genes, indicating bilineage potential. CD133+CD45- cells proliferated in response to liver injury. Following toxic hepatocyte damage, CD133+CD45- cells demonstrated upregulated expression of the hepatocyte gene Albumin. In contrast, toxic cholangiocyte injury resulted in upregulation of the cholangiocyte gene Ck19. After 21-28 days in culture, CD133+CD45- cells continued to generate cells of both hepatocyte and cholangiocyte lineages. Thus, CD133 expression identifies a population of oval cells in adult murine liver with the gene expression profile and function of primitive, bipotent liver stem cells. In response to lineage-specific injury, these cells demonstrate a lineage-appropriate genetic response. Disclosure of potential conflicts of interest is found at the end of this article.

Stem cell plasticity: Learning from hepatogenic differentiation strategies

Many studies on stem cell plasticity are challenging the concept that stem cells contain an intrinsically predefined, unidirectional differentiation program. This means that the developmental fate of a stem cell is dependent on the general potential of the cell (pre-determined stem cell fate) as well as on microenvironmental cues, such as stimuli from growth factors (stem cell niche). Here, we reviewed reports that examined the hepatocyte differentiation ability of stem cells from two different sources: embryonic stem cells and adult stem cells. All of those stem cells revealed the ability to give rise to hepatocyte-like cells using different induction strategies. However, it is still not clear which of those stem cells would be the best source for hepatocyte replacement or which would be the best protocol. We herein present the current knowledge regarding available protocols and factors used in order to obtain functional hepatocytes from stem cells.

FDG PET can replace bone scintigraphy in primary staging of malignant lymphoma

Recent studies indicated that 18F-fluorodeoxyglucose (FDG) PET may be more accurate than CT in staging nodal and extranodal malignant lymphoma. The objective of this study was to compare conventional bone scintigraphy as an established skeletal staging procedure with PET using FDG in the detection of osseous involvement in malignant lymphoma.

METHODS

Whole-body PET-based staging studies of 56 consecutive patients with proven Hodgkin's disease (n = 34) or non-Hodgkin's lymphoma (n = 22) were compared with the results of bone scintigraphy. Positive PET or bone scintigraphic findings were confirmed, if possible, by biopsy, MRI, CT or radiographic investigations.

RESULTS

Of the 56 patients studied, 12 were found to have skeletal involvement on both studies (PET, 30 regions; bone scintigraphy, 20 regions). Findings were confirmed in all 12 patients. FDG PET detected an additional 12 involved regions in 5 patients. This was subsequently verified in 3 patients, although the other 2 cases remained unresolved. Conversely, bone scintigraphy revealed five abnormalities compatible with lymphoma in 5 patients. Three of these lesions were found to be erroneous; final evaluation of the remaining two findings was not possible.

CONCLUSION

FDG PET is suitable for identifying osseous involvement in malignant lymphoma with a high positive predictive value and is thereby more sensitive and specific than bone scintigraphy.