Identification and propagation of liver stem cells

Immunomodulatory effects of umbilical cord-derived mesenchymal stem cells

Umbilical cord blood (UCB) is of great interest as a source of stem cells for use in cellular therapies. The immunomodulatory effect of mesenchymal stem cells (MSCs) originating from bone marrow, adipose tissue and amniotic membrane has previously been reported. In this study, MSCs were isolated from UCB with the aim of evaluating their immunomodulatory effects on proliferation of PB lymphocytes by two different techniques; namely, 5-bromo-2-deoxyuridine ELISA and a carboxy fluorescein diacetate succinimidyl ester flow cytometric technique. MSCs were isolated from UCB, propagated until Passage four, and then characterized for cell surface markers by flow cytometry and ability to differentiate towards osteocytes and adipocytes. Immunosuppressive effects on PB lymphocytes were examined by co-culturing mitomycin C-treated UCB MSCs with mitogen-stimulated lymphocytes for 72 hr. Thereafter, proliferation of lymphocytes was detected by CFSE flow cytometry and colorimetric ELISA. The titers of cytokines in cell culture supernatant were also assayed to clarify possible mechanisms of immunomodulation. UCB MSCs suppressed mitogen-stimulated lymphocyte proliferation, which occurs via both cell-cell contact and cytokine secretion. Titers of transforming growth factor beta and IL 10 increased, whereas that of IFN-γ decreased in the supernatants of co-cultures. Thus, UCB MSCs suppress the proliferation of mitogen-stimulated lymphocytes. However further in vivo studies are required to fully evaluate the immunomodulatory effects of UCB MSCs.

Convenient and efficient enrichment of the CD133+ liver cells from rat fetal liver cells as a source of liver stem/progenitor cells

Although the stem cells are commonly isolated by FACS or MACS, they are very expensive and these is no specific marker for liver stem/progentior cells (LSPCs). This paper applied a convenient and efficient method to enrich LSPCs. The fetal liver cells (FLCs) were firstly enriched by Percoll discontinuous gradient centrifugation (PDGC) from the rat fetal liver. Then the FLCs in culture were purified to be homogeneous in size by differential trypsinization and differential adherence (DTDA). Flow cytometric analysis revealed more than half of the purified FLCs expressed alternative markers of LSPCs (CD117, c-Met, Sca-1, CD90, CD49f and CD133). In other words, the purified FLCs were heterogeneous. Therefore, they were sequentially layered into six fractions by Percoll continuous gradient centrifugation (PCGC). Both CD133 and CD49f expressed decreasingly from fraction 1 to 6. In fraction 1 and 2, about 85% FLCs expressed CD133, which were revealed to be LSPCs by high expressions of AFP and CK-19, low expressions of G-6-P and ALB. To conclude, the purity of CD133(+) LSPCs enriched by combination of PDGC, DTDA and PCGC is close to that obtained by MACS. This study will greatly contribute to two important biological aspects: liver stem cells isolation and liver cell therapy.

The existence of multipotent stem cells with epithelial-mesenchymal transition features in the human liver bud

During early stage of embryonic development, the liver bud, arising from the foregut endoderm, is the beginning for the formation of future liver three-dimensional structure. While the gene expression profiles associated with this developmental stage have been well explored, the detailed cellular events are not as clear. Epithelial-mesenchymal transition (EMT) was thought to be essential for cell migration in the early vertebrate embryo but seldom demonstrated in human liver development. In this study, we tried to identify the cell populations with both stem cell and EMT features in the human liver bud. Our in situ studies show that the phenotype of EMT occurs at initiation of human liver development, accompanied by up-regulation of EMT associated genes. A human liver bud derived stem cell line (hLBSC) was established, which expressed not only genes specific to both mesenchymal cells and hepatic cells, but also octamer-binding protein 4 (OCT4) and nanog. Placed in appropriate media, hLBSC differentiated into hepatocytes, adipocytes, osteoblast-like cells and neuron-like cells in vitro. When transplanted into severe combined immunodeficiency mice pre-treated by carbon tetrachloride, hLBSC engrafted into the liver parenchyma and proliferated. These data suggests that there are cell populations with stem cell and EMT-like properties in the human liver bud, which may play an important role in the beginning of the spatial structure construction of the liver.

Fetal liver very small embryonic/epiblast like stem cells follow developmental migratory pathway of hematopoietic stem cells

Fetal liver (FL) has been described as a source of both hematopoietic and nonhematopoietic stem cells. Recently we have purified from murine adult bone marrow (BM) a population of CXCR4(+)Oct-4(+)SSEA-1(+)Sca-1(+)Lin(-)CD45(-) very small embryonic/epiblast-like stem cells (VSELs). By employing several complementary imaging and molecular strategies, we report in this study that VSELs, like hematopoietic stem cells (HSCs), are highly enriched in murine FL during the second trimester of gestation. Subsequently, at the beginning of the third trimester of gestation their number decreases, which corresponds to the time when HSCs egress FL and follow the stromal derived factor-1 (SDF-1) gradient in order to colonize developing BM. Thus, our data support the hypothesis that VSELs are a mobile pool of primitive stem cells that respond to similar chemotactic gradients as HSCs and follow their developmental migratory route.

Epigenetic gene regulation in stem cells and correlation to cancer

Through the classic study of genetics, much has been learned about the regulation and progression of human disease. Specifically, cancer has been defined as a disease driven by genetic alterations, including mutations in tumor-suppressor genes and oncogenes, as well as chromosomal abnormalities. However, the study of normal human development has identified that in addition to classical genetics, regulation of gene expression is also modified by 'epigenetic' alterations including chromatin remodeling and histone variants, DNA methylation, the regulation of polycomb group proteins, and the epigenetic function of non-coding RNA. These changes are modifications inherited during both meiosis and mitosis, yet they do not result in alterations of the actual DNA sequence. A number of biological questions are directly influenced by epigenetics, such as how does a cell know when to divide, differentiate or remain quiescent, and more importantly, what happens when these pathways become altered? Do these alterations lead to the development and/or progression of cancer? This review will focus on summarizing the limited current literature involving epigenetic alterations in the context of human cancer stems cells (CSCs). The extent to which epigenetic changes define cell fate, identity, and phenotype are still under intense investigation, and many questions remain largely unanswered. Before discussing epigenetic gene silencing in CSCs, the different classifications of stem cells and their properties will be introduced. This will be followed by an introduction to the different epigenetic mechanisms. Finally, there will be a discussion of the current knowledge of epigenetic modifications in stem cells, specifically what is known from rodent systems and established cancer cell lines, and how they are leading us to understand human stem cells.

Therapeutic potential of adult bone marrow stem cells in liver disease and delivery approaches

Hematopoietic stem cells (HSCs) and mesenchymal stem cell (MSCs) are two main subtypes of bone marrow stem cells. Extensive studies have been carried out to investigate the therapeutic potential of BMSCs in liver disease. A number of animal and human studies demonstrated that either HSCs or MSCs could be applied to therapeutic purposes in certain liver diseases. The diseased liver may recruit migratory stem cells, particularly from the bone marrow, to generate hepatocyte-like cells either by transdifferentiation or cell fusion. Transplantation of BMSCs has therapeutic effects of restoration of liver mass and function, alleviation of fibrosis and correction of inherited liver diseases. There are still controversial results over the potential effects of BMSCs on liver diseases, and some of the discrepancies are thought to be lied in the differences of experimental protocols, differences in individual research laboratory, and the uncertainties of the techniques employed. Several potential approaches for BMSCs delivery in liver diseases have been proposed in animal studies and human trials. BMSCs can be delivered via intraportal vein, systemic infusion, intraperitoneal, intrahepatic, intrasplenic. The optimal stem cells delivery should be easy to perform, less invasive and traumatic, minimum side effects, and with high cells survival rate. In this review, we focus on the up-to-date evidence of therapeutic effects of BMSCs on liver disease, the characteristics of various delivery approaches, and the considerations for future studies.

Fluorescence-activated cell sorting purification of pancreatic progenitor cells

Here we review progress on isolation and characterization of progenitor cells in the pancreas. We discuss advantages and current limitations of experiments with purified pancreatic cells, and areas where future growth in our understanding is needed to advance experiments in pancreas biology based on cell purification.

In vitro hepatic differentiation of human umbilical cord blood and bone marrow cells

The purpose of the present study was to investigate whether human umbilical cord blood (UCB) as well as bone marrow (BM) can generate hepatocyte lineage cells in a simple culture condition. Mononuclear cells (MNCs) separated from UCB and BM were cultured in the presence of fibroblast growth factor (FGF)-1, FGF-2, stem cell factor (SCF), and hepatocyte growth factor (HGF). The cultured cells were analyzed for morphology and for the expression of mRNAs and/or proteins of hepatocyte lineage markers. Both the UCB and BM MNCs grown in the given culture condition yielded large, round cells that were adherent to the culture dishes. RT-PCR analysis showed that mRNAs of albumin (ALB), cytokeratin (CK)-18, and alpha-fetoprotein were expressed from day 7 in both the UCB- and BM-derived cells. Immunofluorescent staining showed that the large, round cells expressed not only ALB and CK-19 but also proliferating cell nuclear antigen, implying the proliferative potential of hepatocyte lineage cells. Therefore, UCB as well as BM can give rise to hepatocyte lineage cells in the simple culture condition with HGF, SCF, FGF-1, and FGF-2. These cells may be one of the potential candidates of cell sources for the cytotherapy of hepatic disease, although it remains to be determined if the hepatocyte lineage cells are derived from plastic hematopoietic stem cells or from liver stem cells that reside in UCB or BM.

The MRL mouse repairs both cryogenic and ischemic myocardial infarcts with scar

OBJECTIVE

The MRL mouse strain shows extraordinary wound healing capacities. Some years ago, Leferovich et al. (Proc Natl Acad Sci U S A 2001;98:9830-35) have reported the absence of scar formation after cryogenically-induced right ventricular myocardial infarcts in adult MRL mice. An independent group (Oh et al., Cardiovasc Pathol 2004;13:203-6) found that MRL mice repair left ventricular ischemic infarcts after coronary artery ligation with regular scar formation. Given the divergent outcomes in infarct healing in MRL mice reported by those two studies, we have investigated whether MRL mice heal myocardial infarcts without scar both in the cryoinjury and in the coronary ligation model.

METHODS AND RESULTS

Four different protocols of cryogenically induced right and left ventricular injury, as well as permanent ligation of the left anterior descending coronary artery, were tested in adult MRL and control C57Bl/6 mice. At 60 days after experimental infarction, MRL mice showed pronounced scarring of the affected right and left ventricular areas, with no significant differences in infarct size and thickness between MRL and C57Bl/6 mice using any of the five experimental protocols. Analysis of cell proliferation by 5-bromo-2'-deoxyuridine (BrdU) incorporation into the DNA did not show any difference between the two strains of mice after infarction. Histological analysis of infarct areas using picrosirius red staining did not show differences in extent of collagen and distribution between the two mouse strains.

CONCLUSIONS

MRL mice heal myocardial infarcts with scar formation in response to ischemic as well as to cryogenic injuries.

Differentiation of a hepatic phenotype after heterotropic transplantation of heart, kidney, brain, and skin tissues into liver in F344 rats

While organ-specific stem cells with roles in tissue injury repair have been documented, their pathogenic significance in diseases and the factors potentially responsible for their activation remain largely unclear. In the present study, heart, kidney, brain, and skin samples from F344 transgenic rats carrying the GFP gene were transplanted into normal F344 rat liver one day after an intraperitoneal injection (i.p.) of carbon tetrachloride (CCl(4)) to test their differentiation capacity. The transplantation was carried out by female donors to male recipients, and vice versa. One week after transplantation, GFP antigen-positive cells with phenotypic characteristics of hepatocytes were noted. After two weeks, their extent increased, and at 4 weeks, large areas of strongly GFP-stained cells developed. All recipient livers had GFP antigen-positive hepatocyte cells. PCR analysis coupled with laser capture micro-dissection (LCM) revealed those cells to contain GFP DNA. Thus, our results indicate that tissue stem cells have multipotential ability, differentiating into hepatocytes when transplanted into an injured liver.

Side population cells derived from adult human liver generate hepatocyte-like cells in vitro

We sought to determine whether hepatic side population (SP) cells derived from adult human liver possess the potential of a novel candidate hepatic stem cell. Human cadaveric donor liver was subjected to collagenase perfusion and hepatocytes were separated from nonparenchymal cells by differential centrifugation. SP cells were isolated from the nonparenchymal portion after Hoechst 33342 staining. Since CD45 is a panleukocyte antigen, CD45-negative SP cells were separated from the vast majority of CD45-positive SP cells (90%), and hepatic growth medium was used to culture both groups. Both CD45-negative and CD45-positive hepatic SP cells generated colonies in the hepatic growth medium in 2-3 weeks. The colonies yielded large cells morphologically consistent with human hepatocytes, demonstrating granule-rich cytoplasm, dense, often double nuclei, and intracellular lipofuscin pigment. The cultured cells from both sources were positive for markers of human hepatocytes: HepPar, cytokeratin 8 (CK8), and human albumin. Reverse transcriptase-polymerase chain reaction (RT-PCR) performed on both groups demonstrated positivity for additional liver markers including human albumin, CK18, alpha-1 anti-trypsin, and the human cytochrome P450 enzyme CYP2B6. Double immunostaining (CD45 and HepPar) and RT-PCR confirmed that the hepatocyte-like cells derived from the CD45-negative SP cells acquired HepPar positivity but had no detectable CD45 antigen expression. In contrast, the cultured cells derived from the CD45-positive SP cells also acquired HepPar positivity, but only a minimal fraction expressed the CD45 antigen. We conclude that hepatic SP cells derived from the nonparenchymal portion of human liver are a potential source of human hepatocytes irrespective of their CD45 status, and further animal studies will be required to assess their regenerative potential.

Regeneration in the ears of immunodeficient mice: identification and lineage analysis of mesenchymal stem cells

Wound healing in the ears of Athymic Nude-nu mice resembles regeneration. Histological analysis of the ear-punched tissues revealed the initial formation of a blastema-like structure followed by dermal, vascular, cartilage, and muscle regrowth exclusively in Athymic Nude-nu mice but not in wild-type controls (C57BL/6J). A subset of stem cells referred to here as ear mesenchymal stem cells (EMSCs) has been isolated from the external ears of regenerative (Athymic Nude-nu) and nonregenerative strains of mice. Morphological, histochemical, and molecular analysis after the induction of EMSC differentiation revealed multiple mesenchymal cell lineages (adipocytes, chondrocytes, and osteocytes) in all murine strains independent of their ability for regeneration. Thus, the absence of regeneration in wounded ears of C57BL/6J wild-type mice is not related to the absence of mesenchymal stem cell differentiation in tissue culture. Because nude mice lack T lymphocytes, it appears that in this model the absence of T lymphocytes in the wounded ears provides a microenvironment conducive to regeneration of mesenchymal tissues. These findings provide a new model to study the influence of the immune system on tissue regeneration.

Molecular therapeutics: promise and challenges

The ability to analyze the genetic and epigenetic aberrations present in a particular patient's tumor on a global basis is rapidly maturing. The emerging fields of functional genomics and functional proteomics offer the opportunity to translate these advances into a full comprehension of the pathophysiology of cancer. Linking these approaches to chemical genomics and molecular therapeutics should provide an expanding repertoire of targeted therapeutics for clinical evaluation. Novel clinical trial designs that can determine the efficacy of targeted therapeutics in patients selected for aberrations in the target are needed to evaluate the wealth of new drugs becoming available. The promise of these technologies and advances in our understanding of cancer is immense, making it our responsibility to see them to fruition. These technologies should lead to a new era of individualized molecular medicine, wherein we will treat each patient with a "prescription" based on the genetic changes in each patient's tumor and their own genetic make-up, resulting in more effective and less toxic therapy.