Expansion conditions for early hepatic progenitor cells from embryonal and neonatal rat livers

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.

Prenatal glucocorticoid administration enhances bilirubin metabolic capacity and increases Ugt1a and Abcc2 gene expression via glucocorticoid receptor and PXR in rat fetal liver

AIM

Jaundice is especially common in premature infant born before 35 weeks. Because the premature infant liver is not fully developed at birth it may be incomplete the bilirubin metabolism. The purpose was to evaluate the metabolism and the excretion of bilirubin in the premature infant rat liver following prenatal glucocorticoid (GC) administration.

METHODS

Dexamethasone (DEX) was administered subcutaneously to pregnant Wistar rats for two consecutive days on gestational days 17 and 19. The fetus were delivered by cesarean section in gestational days 19 and 21. The mRNA levels and protein levels of bilirubin-metabolic enzymes and transporters in the fetal liver tissues were analyzed using RT-PCR immunohistochemistry staining and ELISA, respectively. We evaluated that the effect of bilirubin-metabolic enzymes in the primary fetal rat hepatocytes treated with DEX after pretreated with glucocorticoid receptor (GR, Nr3c1) and Pxr (Nr1i2) siRNA.

RESULTS

Ugt1a1 and Bsep (Abcb11) mRNA levels were significantly increased in the fetuses by prenatal GC administration. The mRNA levels of nuclear transcription factors Nr1i2, Car (Nr1i3), and Rxrα (Nr2b1) were also significantly increased in the fetuses by prenatal GC administration. In addition, DEX increased Nr1i2, Ugt1a1, and Abcc2 (Mrp2) mRNA levels in the primary fetal hepatocytes. The Nr3c1 or Nr1i2 siRNA-mediated knockdown suppressed the increases of Ugt1a1, and Abcc2 mRNA levels induced by DEX, indicating that DEX are mediated by GC receptor and PXR in primary fetal hepatocytes.

CONCLUSIONS

These results suggest that prenatal GC administration increases bilirubin-metabolic ability, in the premature liver, which may prevent jaundice in neonates.

Culture of newborn monkey liver epithelial progenitor cells in chemical defined serum-free medium

Studies with hepatic progenitor cells from non-human primates would allow better understanding of their human counterparts. In this study, rhesus monkey liver epithelial progenitor cells (mLEPCs) were derived from a small piece of newborn livers in chemical defined serum-free medium. Digested hepatic cells were treated in Ca(2+)-containing medium to form cell aggregates. Two types of cell aggregates were generated: elongated spindle cells and polygonal epithelial cells. Elongated spindle cells were expressed as vimentin and brachyury, and they were disappeared within 5 d in our cultures. The remaining type consisted of small polygonal epithelial cells that expressed cytokeratin 7 (CK7), CK8, CK18, nestin, CD49f, and E-cad, the markers of hepatic stem cells, but were negative for alpha-fetoprotein, albumin, and CK19. They can proliferate and be passaged, if on laminin or rat tail collagen gel, to initiate colonies. When cultured with dexamethasone and oncostatin M, the expression of mature hepatocyte markers, such as alpha-1-antitrypsin, intracytoplasmic glycogen storage, indocyanine green uptake, and lipid droplet generation, were induced in differentiated cells. If transferred onto mouse embryonic fibroblasts feeders, they gave rise to CK19-positive cholangiocytes with formation of doughnut-like structure. Thus, mLEPCs with bipotency were derived from newborn monkey liver and may serve as a preclinical model for assessment of cell therapy in humans.

Induced differentiation and maturation of newborn liver cells into functional hepatic tissue in macroporous alginate scaffolds

The present work explores cell cultivation in macroporous alginate scaffolds as a means to reproduce hepatocyte terminal differentiation in vitro. Newborn rat liver cell isolates, consisting of proliferating hepatocytes and progenitors, were seeded at high cell density of 125 x 10(6)/cm(3) within the scaffold and then cultivated for 6 wk in chemically defined medium. Within 3 days, the alginate-seeded cells expressed genes for mature liver enzymes, such as tryptophan oxygenase, secreted a high level of albumin, and performed phase I drug metabolism. The cells formed compacted spheroids, establishing homotypic and heterotypic cell-to-cell interactions. By 6 wk, the spheroids developed into organoids, with an external mature hepatocyte layer covered by a laminin layer encasing inner vimentin-positive cells within a laminin-rich matrix also containing collagen. The hepatocytes presented a distinct apical surface between adjacent cells and a basolateral surface with microvilli facing extracellular matrix deposits. By contrast, viable adherent cells within collagen scaffolds presenting the identical porous structure did not express adult liver enzymes or secrete albumin after 6 wk. This study thus illustrates the benefits of cell cultivation in macroporous alginate scaffolds as an effective promoter for the maturation of newborn liver cells into functional hepatic tissue, capable of maintaining prolonged hepatocellular functions.

Stem cells derived from goiters in adults form spheres in response to intense growth stimulation and require thyrotropin for differentiation into thyrocytes

OBJECTIVE

This study aimed to analyze under which conditions quiescent stem cells derived from human goiters can be propagated to outgrow and whether these cells have retained the capacity to differentiate into thyroid cells.

DESIGN

Stem cells were isolated by fluorescence-activated cell sorting as a side population by the Hoechst 33342 efflux technique. Growth pattern of stem cells and cocultures of stem cells with thyrocytes grown as monolayer and in Matrigel was investigated. Expression of stem cell markers, endodermal markers, and thyroid-specific markers was analyzed by RT-PCR. In stem cell-derived thyrocytes, embedded in collagen to form follicles, TSH-dependent (125)iodide uptake was measured.

RESULTS

Stem cells were isolated as a side population from a non-side population fraction that consisted of endodermal marker-positive cells and thyroid cells. Intense growth stimulation of stem cells in coculture with thyrocytes resulted in formation of nonadherent, three-dimensional spheres that consisted of highly proliferating stem cells with their characteristic expression profiles. In response to TSH and serum, sphere-derived progenitor cells differentiated into thyrocytes that expressed paired box gene 8, thyroglobulin, sodium iodide symporter, thyroid-stimulating hormone receptor, and thyroperoxidase mRNA and showed TSH-dependent (125)iodide uptake.

CONCLUSION

Quiescent stem cells derived from goiters can be propagated to form spheres that consist of highly proliferating stem cells that are able to differentiate TSH dependently into thyroid cells. Compared with thyrocytes, stem cells display a much higher proliferation rate on acute growth stimulation, which may suggest a putative role of the offspring of stem cells in the chronic growth factor-stimulated nodular transformation of the thyroid.

In vitro differentiation of hepatic progenitor cells from mouse embryonic stem cells induced by sodium butyrate

Recently it was shown that embryonic stem (ES) cells could differentiate into hepatocytes both in vitro and in vivo, however, prospective hepatic progenitor cells have not yet been isolated and characterized from ES cells. Here we presented a novel 4-step procedure for the differentiation of mouse ES cells into hepatic progenitor cells and then hepatocytes. The differentiated hepatocytes were identified by morphological, biochemical, and functional analyses. The hepatic progenitor cells were isolated from the cultures after the withdrawal of sodium butyrate, which was characterized by scant cytoplasm, ovoid nuclei, the ability of rapid proliferation, expression of a series of hepatic progenitor cell markers, and the potential of differentiation into hepatocytes and bile duct-like cells under the proper conditions that favor hepatocyte and bile epithelial differentiation. The differentiation of hepatocytes from hepatic progenitor cells was characterized by a number of hepatic cell markers including albumin secretion, upregulated transcription of glucose-6-phosphatase and tyrosine aminotransferase, and functional phenotypes such as glycogen storage. The results from our experiments demonstrated that ES cells could differentiate into a novel bipotential hepatic progenitor cell and mature into hepatocytes with typical morphological, phenotypic and functional characteristics, which provides an useful model for the studies of key events during early liver development and a potential source of transplantable cells for cell-replacement therapies.

Functional analysis of encapsulated hepatic progenitor cells

A major challenge in developing therapies based on progenitor or stem cell populations (from sources other than bone marrow) involves developing a mode to deliver these cells in a manner that optimizes their viability, engraftment, proliferation, and differentiation. We have previously isolated a hepatic progenitor cell (HPC) population from adult liver tissue that differentiates into hepatic and biliary cell subtypes. We postulated that, using electrostatic encapsulation, we could reproducibly generate an ex vivo environment for the HPCs. We also theorized that this approach would foster cellular viability and function of the progenitor cell population. Using this encapsulation process, we consistently produced beads with uniform diameters between 200 and 700 microm. In vitro analysis of the encapsulated beads demonstrated extended periods of viability and function based on albumin production, urea metabolism, and glycogen storage. In conclusion, HPC encapsulation fosters the subsequent differentiation of HPCs into functional cells while maintaining their viability in long-term culture. These results demonstrate the efficacy of this method using somatic-derived progenitor cell populations and pave the way for clinical therapies.

Isolation, characterization and culture of Thy1-positive cells from fetal rat livers

AIM: To investigate whether Thy1 recognizes oval cells in the fetal liver and to characterize the cultured Thy1- selected cells from E14 rat livers.

METHODS: Thy1 populations were analyzed by fluorescence activated cell sorter analysis. Thy1 positive cells were isolated using magnetic beads. Hepatic markers were detected by Western blotting, immunocytochemistry and RT-PCR.

RESULTS: The percentage of Thy1-positive cells decreased during early development of fetal rat liver (E13-E16). E14 fetal livers contained 7.8% Thy1 positive cells, of which 61% were positive for α-fetoprotein (AFP) and 25% expressed albumin. The Thy1+ population expressed oval cell markers c-Kit and CXCR4, liver enriched-transcription factors HNF1α and HNF6, hepatocytic markers albumin, AFP and cytokeratin 18, and biliary marker cytokeratin 19. Thy1- selected cells formed only mesenchymal colonies when plated on collagen and in serum-containing media. Thy1 selected cells were able to form hepatic colonies positive for HNF1α, HNF6, albumin, AFP, cytokeratin 18, cytokeratin 19 and glycogen, when grown on STO feeder layers in serum free-media.

CONCLUSION: Oval cells positive for Thy1 are present in early liver embryonic stages.

Chimeric molecule IL-6/soluble IL-6 receptor is a potent mitogen for fetal hepatocytes

A novel recombinant molecule, termed IL-6c and consisting of a chimera of interleukin 6 (IL-6) and its soluble receptor is extremely potent in stimulating proliferation of hematopoietic progenitors. We investigated the effect of the IL-6c on the proliferation and differentiation of E14 fetal hepatocytes. IL-6c, in a dose-dependent manner, stimulated proliferation of E14 fetal rat hepatocytes. Adult hepatocyte mitogens together with IL-6c showed no further effect on proliferation. Hematopoietic stem cells mitogens SCF and flt3 ligand (FL) were also mitogenic for fetal hepatocytes, but did not further enhance the effect of IL-6c on cell proliferation. IL-6c decreased expression of fetal markers alpha-fetoprotein (AFP) and gamma-glutamyltranspeptidase, and induced expression of adult enzyme glucose-6-phosphatase (Gluc-6-P) in E14 hepatocytes. On the other hand, IL-6c strongly reduced, in a dose-dependant manner, expression of albumin and tyrosine aminotransferase (TAT). However, when the cells were grown for 3 days with IL-6c, and IL-6c was removed for the next 5 days, expression of albumin and TAT returned to levels found in control cultures. In conclusion, IL-6c stimulated proliferation and affected gene expression in fetal hepatocytes in culture.

Liver stem cells: prospects for treatment of inherited and acquired liver diseases

It is now understood that there are three cell compartments which physiologically contribute to vertebrate liver parenchymal maintenance and regeneration after injury: mature liver cells (hepatocytes, cholangiocytes), intraorgan stem/progenitor cells (cells of the proximal biliary tree, periductal cells) and extraorgan stem cells (from the circulation and the bone marrow). All of these cell populations, as well as other, non-physiologic stem cells (e.g., mesenchymal stromal cells from the bone marrow, fetal hepatoblasts, embryonic stem [ES] cells), may be used therapeutically for treatment of inherited and acquired liver diseases. This article will summarise our current understanding of these various cell populations, and review possible approaches to their therapeutic use, including cell transplantation, bioartificial liver devices (BLDs), gene therapy and administration of exogenous factors to stimulate normal physiological responses to repair.

Biologic liver support: optimal cell source and mass

Hepatic support is indicated in acute liver failure (ALF) patients to foster liver regeneration, or until a liver becomes available for orthotopic liver transplantation (OLT), in primary non function of the transplanted liver, and hopefully in chronic liver disease patients affected by ALF episodes, in whom OLT is not a therapeutic option. The concept of bioartificial liver (BAL) is based on the assumption that only the hepatocytes can perform the whole spectrum of biotransformation functions, which are needed to prevent hepatic encephalopathy, coma and cerebral edema. Among others, two important issues are related to BAL development: 1) the choice of the cellular component; 2) the cell mass needed to perform an adequate BAL treatment. Primary hepatocytes, of human or animal origin, should be considered the first choice because they express highly differentiated functions. Accordingly, a minimal cell mass corresponding to 10% of a human adult liver, i.e. 150 grams of freshly isolated, > or = 90% viable hepatocytes should be used. When 4 degrees C cold-stored or cryopreserved hepatocytes are used, the cellular mass should be increased because of a drop in cell viability and function. In case of hepatoma-derived cells, cultured cell lines or engineered cells, an adequate functional cell mass should be used, expressing metabolic and biotransformation activities comparable to those of primary hepatocytes. Finally, the use of porcine hepatocytes or other animal cells in BAL devices should be presently directed only to ALF patients as a bridge treatment to OLT, because of potential transmission of animal retrovirus and prions which may potentially cause major pandemics.

Engineering liver therapies for the future

Treatment of liver disease has been greatly improved by the advent and evolution of liver transplantation. However, as demand for donor organs continues to increase beyond their availability, the need for alternative liver therapies is clear. Several approaches including extracorporeal devices, cell transplantation, and tissue-engineered constructs have been proposed as potential adjuncts or even replacements for transplantation. Simultaneously, experience from the liver biology community have provided valuable insight into tissue morphogenesis and in vitro stabilization of the hepatocyte phenotype. The next generation of cellular therapies must therefore consider incorporating cell sources and cellular microenvironments that provide both a large population of cells and strategies to maintain liver-specific functions over extended time frames. As cell-based therapies evolve, their success will require contribution from many diverse disciplines including regenerative medicine, developmental biology, and transplant medicine.

Derivation, characterization, and phenotypic variation of hepatic progenitor cell lines isolated from adult rats

Liver progenitor cells (LPCs) cloned from adult rat livers following allyl alcohol injury express hematopoietic stem cell and early hepatic lineage markers when cultured on feeder layers; under these conditions, neither mature hepatocyte nor bile duct, Ito, stellate, Kupffer cell, or macrophage markers are detected. These phenotypes have remained stable without aneuploidy or morphological transformation after more than 100 population doublings. When cultured without feeder layers, the early lineage markers disappear, and mature hepatocyte markers are expressed; mature hepatocytic differentiation and cell size are also augmented by polypeptide and steroidal growth factors. In contrast to hepatocytic potential, duct-like structures and biliary epithelial markers are expressed on Matrigel. Because they were derived without carcinogens or mutagens, these bipotential LPC lines provide novel tools for models of cellular plasticity and hepatocarcinogenesis, as well as lines for use in cellular transplantation, gene therapy, and bioreactor construction.

Hepatic progenitors and strategies for liver cell therapies

Liver cell therapies, including liver cell transplantation and bioartificial livers, are being developed as alternatives to whole liver transplantation for some patients with severe liver dysfunction. Hepatic progenitors are proposed as ideal cells for use in these liver cell therapies given their ability to expand extensively, differentiate into all mature liver cells, have minimal immunogenicity, be cryopreservable, and reconstitute liver tissue when transplanted. We summarize our ongoing efforts to develop clinical programs of hepatic progenitor cell therapies with a focus on hepatic stem cell biology and strategies that have emerged in analyzing that biology.

Applications of developmental biology to medicine and animal agriculture

With the complete sequence of the human genome expected by winter 2001, genomic-based drug discovery efforts of the pharmaceutical industry are focusing on finding the relatively few therapeutically useful genes from among the total gene set. Methods to rapidly elucidate gene function will have increasing value in these investigations. The use of model organisms in functional genomics has begun to be recognized and exploited and is one example of the emerging use of the tools of developmental biology in recent drug discovery efforts. The use of protein products expressed during embryo-genesis and the use of certain pluripotent cell populations (stem cells) as candidate therapeutics are other applications of developmental biology to the treatment of human diseases. These agents may be used to repair damaged or diseased tissues by inducing or directing developmental programs that recapitulate embryonic processes to replace specialized cells. The activation or silencing of embryonic genes in the disease state, particularly those encoding transcription factors, is another avenue of exploitation. Finally, the direct drug-induced manipulation of embryonic development is a unique application of developmental biology in animal agriculture.

Cells for tissue engineering

Recent advances in stem-cell technology have improved the prognosis for tissue engineering. The use of cultured stem and/or progenitor cells has the potential to improve the extent of regeneration, and also increases the likelihood that the transplanted tissue will integrate with the surrounding tissue. It could eventually even reduce or eliminate the need for immunosuppressive drugs.