Differentiation of functional hepatocytes and biliary epithelial cells from immature hepatocytes of the fetal mouse in vitro

Inversin-deficient (inv) mice do not establish a polarized duct system in the liver and pancreas

Inversin-deficient (inv) mice have anomalies in liver and pancreatic development in addition to an inverted left-right axis of the body. The present study was undertaken to unveil mechanisms of bile and pancreatic duct development from immunohistochemical analyses of anomalies in inv mice. Intrahepatic bile ducts having proximodistal polarity in size and the height of their epithelia, and ductules were formed in livers of wild-type neonates. By contrast, in inv mice, ductal plates, precursor structures of intrahepatic bile ducts and ductules, persisted without the proximodistal polarity. Their epithelial cells did not acquire planar cell polarity (PCP) in terms of expression of tight junction proteins although they expressed bile duct markers, HNF1β and SOX9. They had an apicobasal polarity from expression of basal laminar components. Enlargement of the hepatic artery and poor connective tissue development, including the abnormal deposition of the extracellular matrices, were also noted in inv mice, suggesting that bile duct development was coupled to that of the hepatic artery and portal vein. In pancreata of inv neonates, neither the main pancreatic duct was formed, nor dilated duct-like structures had the morphological polarity from the connecting point with the common bile duct. Lumina of acini was dilated, and centroacinar cells changed their position in the acini to their neck region. Immunohistochemical analyses of tight junction proteins suggested that epithelial cells of the duct-like structures did not have a PCP. Thus, Invs may be required for the establishment of the PCP of the whole duct system in the liver and pancreas.

Current Perspectives Regarding Stem Cell-Based Therapy for Liver Cirrhosis

Liver cirrhosis is a major cause of mortality and a common end of various progressive liver diseases. Since the effective treatment is currently limited to liver transplantation, stem cell-based therapy as an alternative has attracted interest due to promising results from preclinical and clinical studies. However, there is still much to be understood regarding the precise mechanisms of action. A number of stem cells from different origins have been employed for hepatic regeneration with different degrees of success. The present review presents a synopsis of stem cell research for the treatment of patients with liver cirrhosis according to the stem cell type. Clinical trials to date are summarized briefly. Finally, issues to be resolved and future perspectives are discussed with regard to clinical applications.

A case of an infant with congenital combined pituitary hormone deficiency and normalized liver histology of infantile cholestasis after hormone replacement therapy

Congenital combined pituitary hormone deficiency (CPHD) may present with cholestasis in the neonate or during early infancy. However, its precise mechanism is unknown. A 3-mo-old boy presented with cryptorchidism and hypoplastic scrotum after birth. Neonatal jaundice was noted but temporarily improved with phototherapy. Jaundice recurred at 2 mo of age. Elevated direct bilirubin (D-Bil) and liver dysfunction were found but cholangiography showed no signs of biliary atresia (BA). Liver biopsy findings showed giant cell formation of hepatocytes with hypoplastic bile ducts. Subsequent magnetic resonance imaging (MRI) of the head revealed a hypoplastic pituitary gland with an ectopic posterior lobe, and the patient was diagnosed with congenital CPHD based on decreased secretion of cortisol and GH by the pituitary anterior lobe load test. D-Bil levels promptly improved after hydrocortisone (HDC) replacement. We subsequently began replacement with levothyroxine (L-T₄) and GH, and liver histology showed normal interlobular bile ducts at 8 mo old. This is the first case report of proven histological improvement after hormone replacement therapy. This suggested that pituitary-mediated hormones, especially cortisol, might be involved in the development of the bile ducts.

Circadian system from conception till adulthood

In mammals, the circadian system is composed of the central clock in the hypothalamic suprachiasmatic nuclei and of peripheral clocks that are located in other neural structures and in cells of the peripheral tissues and organs. In adults, the system is hierarchically organized so that the central clock provides the other clocks in the body with information about the time of day. This information is needed for the adaptation of their functions to cyclically changing external conditions. During ontogenesis, the system undergoes substantial development and its sensitivity to external signals changes. Perinatally, maternal cues are responsible for setting the phase of the developing clock, while later postnatally, the LD cycle is dominant. The central clock attains its functional properties during a gradual and programmed process. Peripheral clocks begin to exhibit rhythmicity independent of each other at various developmental stages. During the early developmental stages, the peripheral clocks are set or driven by maternal feeding, but later the central clock becomes fully functional and begins to entrain the periphery. During the perinatal period, the central and peripheral clocks seem to be vulnerable to disturbances in external conditions. Further studies are needed to understand the processes of how the circadian system develops and what degree of plasticity and resilience it possesses during ontogenesis. These data may lead to an assessment of the contribution of disturbances of the circadian system during early ontogenesis to the occurrence of circadian diseases in adulthood.

Culture of porcine hepatocytes or bile duct epithelial cells by inductive serum-free media

A serum-free, feeder cell-dependent, selective culture system for the long-term culture of porcine hepatocytes or cholangiocytes was developed. Liver cells were isolated from 1-wk-old pigs or young adult pigs (25 and 63 kg live weight) and were placed in primary culture on feeder cell layers of mitotically blocked mouse fibroblasts. In serum-free medium containing 1% DMSO and 1 μM dexamethasone, confluent monolayers of hepatocytes formed and could be maintained for several wk. Light and electron microscopic analysis showed hepatocytes with in vivo-like morphology, and many hepatocytes were sandwiched between the feeder cells. When isolated liver cells were cultured in medium without dexamethasone but with 0.5% DMSO, monolayers of cholangioctyes formed that subsequently self-organized into networks of multicellular ductal structures, and whose cells had monocilia projecting into the lumen of the duct. Gamma-glutamyl transpeptidase (GGT) was expressed by the cholangiocytes at their apical membranes, i.e., at the inner surface of the ducts. Cellular GGT activity increased concomitantly with the development of ductal structures. Cytochrome P-450 was determined in microsomes following addition of metyrapone to the cultures. In vivo-like levels of P-450s were found in hepatocyte monolayers while levels of P-450 were markedly reduced in cholangiocyte monolayers. Serum protein secretion in conditioned media was analyzed by Western blot and indicated that albumin, transferrin, and haptoglobin levels were maintained in hepatocytes while albumin and haptoglobin declined over time in cholangiocytes. Quantitative RT-PCR analysis showed that serum protein mRNA levels were significantly elevated in the hepatocytes monolayers in comparison to the bile ductule-containing monolayers. Further, mRNAs specific to cholangiocyte differentiation and function were significantly elevated in bile ductule monolayers in comparison to hepatocyte monolayers. The results demonstrate an in vitro model for the study of either porcine hepatocytes or cholangiocytes with in vivo-like morphology and function.

Three patterns of cytochrome P450 gene expression during liver maturation in mice

The neonatal period of liver development is an often overlooked phase of development. For instance, ontogeny of xenobiotic-metabolizing enzymes can markedly affect biotransformation as the liver matures. To systematically examine the ontogenic gene expression patterns of cytochrome P450 genes (P450) in mice, the gene expression profiles of 19 xenobiotic-metabolizing P450 in Cyp1 to 4 families were determined. The mRNA levels in C57BL/6 mouse livers were quantified using branched DNA technology at the following ages: gestational day 17 (2 days before birth) and postnatal days 0, 1, 3, 5, 10, 15, 20, 30, and 45. Among the 13 P450 genes expressed in mouse livers, three distinct ontogenic expression patterns were identified by cluster analysis. Genes in group 1 (Cyp3a16 as well as 3a41b in male) were expressed in the perinatal period, but they were essentially nondetectable by 30 days of age. Genes in group 2 (Cyp2e1, 3a11, and 4a10 as well as 3a41b in female) quickly increased after birth and reached maximal expression levels by day 5. Genes in group 3 (Cyp1a2, 2a4, 2b10, 2c29, 2d22, 2f2, 3a13, and 3a25) were expressed at low levels until days 10 to 15, but they markedly increased at day 20 to a high and stable level. In conclusion, the developmental expression of P450 in mouse liver can be divided into three patterns, suggesting that different mechanisms are responsible for the expression of P450 during liver maturation.

Adult rat hepatic bipotent progenitor cells remain dormant even after extensive hepatectomy

S It remains unknown whether the normal adult liver contains bipotent stem/progenitor cells, and if it does, then what are the circumstances under which they proliferate. The aim of this study was to clarify whether the normal adult liver contains hepatic stem/progenitor cells, and if it does, will they be activated by extensive hepatectomy? Adult rat liver cells were isolated and cultured at a low-density, and the colony-forming assay was performed to evaluate the cell proliferative capacity. Immunocytochemistry and reverse transcription-polymerase chain reaction were used to investigate the multilineage differentiation capability. The rate of colony formation by cells from the normal liver and those from the regenerating liver after partial hepatectomy (PH) were compared to determine whether progenitor cell proliferation might be activated by PH. Only a few epithelial colonies (0.043+/-0.009% of nonparenchymal cells) continued to proliferate for more than 1 month. Reverse transcription-polymerase chain reaction and immnocytochemistry showed that these progenitor colonies expressed both hepatocyte and cholangiocyte markers. The proportion of progenitor cells that formed bipotential colonies did not differ significantly between the cells obtained from the normal and PH livers. Adult normal liver contains bipotent hepatic progenitor cells, but they are scarcely activated even after extensive hepatectomy.

Neuroregulation of the neuroendocrine compartment of the liver

Liver progenitor cells as well as hepatic stellate cells have neuroendocrine features. Progenitor cells express chromogranin-A and neural cell adhesion molecule, parathyroid hormone-related peptide, S-100 protein, neurotrophins, and neurotrophin receptors, while hepatic stellate cells express synaptophysin, glial fibrillary acidic protein, neural cell adhesion molecule, nestin, neurotrophins, and their receptors. This phenotype suggests that these cell types form a neuroendocrine compartment of the liver, which could be under the control of the central nervous system. We recently showed that the parasympathetic nervous system promotes progenitor cell expansion after liver injury, since selective vagotomy reduces the number of progenitor cells after chemical injury in the rat. Similarly, after transplantation, which surgically denervates the liver, human livers that develop hepatitis have fewer progenitor cells than native, fully innervated livers with similar degrees of liver injury. There is also accumulating experimental evidence linking the autonomic system, in particular the sympathetic nervous system (SNS), with the pathogenesis of cirrhosis and its complications. Recently, it has been shown that hepatic stellate cells themselves respond to neurotransmitters. Moreover, inhibition of the SNS reduced fibrosis in carbon tetrachloride-induced liver injury. In view of the denervated state of transplanted livers, it is very important to unravel the neural control mechanisms of regeneration and fibrogenesis. Moreover, since there is a shortage of donor organs, a better understanding of the mechanisms of regeneration could have therapeutic possibilities, which could even obviate the need for orthotopic liver transplantation.

A population of c-Kit(low)(CD45/TER119)- hepatic cell progenitors of 11-day postcoitus mouse embryo liver reconstitutes cell-depleted liver organoids

Embryo liver morphogenesis takes place after gastrulation and starts with a ventral foregut evagination that reacts to factor signaling from both cardiac mesoderm and septum transversum mesenchyme. Current knowledge of the progenitor stem cell populations involved in this early embryo liver development is scarce. We describe here a population of 11-day postcoitus c-Kit(low)(CD45/TER119)- liver progenitors that selectively expressed hepatospecific genes and proteins in vivo, was self-maintained in vitro by long-term proliferation, and simultaneously differentiated into functional hepatocytes and bile duct cells. Purified c-Kit(low)(CD45/TER119)- liver cells cocultured with cell-depleted fetal liver fragments engrafted and repopulated the hepatic cell compartments of the latter organoids, suggesting that they may include the embryonic stem cells responsible for liver development.

Multi-stage analysis of differential gene expression in BALB/C mouse liver development by high-density microarrays

The development of a complex organ such as the liver relies on precise temporal and spatial gene expression patterns during ontogenesis. The unique adult phenotype is a result of a cascade of transcriptional events that finally trigger gene expression in a liver-specific fashion. Development in mice starts at embryonic stage E8.5-9.5 with the expression of several genes typically associated with liver tissue. While the role of some genes and their expression is well studied, little is known about the complex expression pattern changes during embryonic and fetal liver development. High-density oligonucleotide microarrays, which allow simultaneous expression analysis of 12,488 mouse mRNA transcripts and EST sequences, were used to study the gene expression profiles in day 7.5 embryonic tissue, in micro-dissected fetal liver tissue from day 11.5 and day 13.5 embryos, and in adult liver. In pairwise comparisons of all stages, a total of 4242 distinct genes or ESTs were found to be differentially regulated. Cross-comparisons of data from all stages detected the highest number of differentially regulated genes in E11.5 fetal liver tissue versus adult liver (3063 genes) and the lowest number in E11.5 versus E13.5 fetal liver tissue (517 genes). Using adult liver as reference tissue, 212 genes were regulated exclusively in E7.5 embryonic tissue, 303 genes in E11.5 and 198 in E13.5 fetal liver tissue. Expression profiles of the 31 genes with significant regulation at all stages as well as of a number of known developmentally regulated genes were compared with published results and interpreted. The gene expression profiles detected by microarray hybridization were independently confirmed for selected genes by quantitative RT-PCR. Our data presented here suggest that a relatively small number of stage-specific genes exist, which may be of particular importance for liver development, growth and differentiation. Furthermore, the microarray approach led to the identification of a number of genes, which have not yet been associated with liver organogenesis and maturation.

Effects of endogenous and exogenous glucocorticoids on liver differentiation

The effects of maternal bilateral adrenalectomy on day 1 of gestation and betamethasone treatment on fetal liver development were compared, in terms of biochemical and morphological parameters. For fetuses 20 days old (E20), absence of maternal glucocorticoids during gestation caused an increase in the number of nuclei in whole livers, and a significantly decrease of both body weight and protein content per nucleus, in comparison with the control group (C). Betamethasone injection on days 15, 16 and 17 of gestation into adrenalectomized pregnant rats (ADX + BET) did not completely prevent these effects. The electron microscopic analysis of the ADX fetal liver (E20) showed some hepatocyte lesions such as loss of cytoplasmic organelles, increase in hematopoietic cell number as well as a lower cellular maturation in comparison with the control group. The fetal liver from ADX + BET mothers 20 days after gestation displayed a noticeable involution of the hematopoietic component in spite of its relatively immature stage. However, there was no significant change in the degree of fetal hepatocyte lesions. Therefore, supply of maternal glucocorticoids from the beginning of gestation is essential for maintenance of the integral structure of the rat fetal hepatic parenchyma, for the correct maturation of the blood strains and for the beginning of involution of the hematopoietic tissue at the end of gestation.

Identification of differentially expressed genes in epithelial stem/progenitor cells of fetal rat liver

Differentially expressed cDNA clones from fetal rat liver were isolated using suppression subtractive hybridization, combined with an efficient screening strategy. Approximately 30,000 clones were screened, yielding 643 genes whose expression was induced, of which 201 clones were distinct and 68 represented ESTs or newly discovered genes of unknown function. Based on their expression patterns in different organs, fetal liver, liver regeneration models, and gut epithelial progenitor cell lines, the subtracted clones presented in this work were placed into four categories: (1) hepatoblast-specific genes; (2) hematopoietic cell-specific genes; (3) genes expressed in hepatoblasts, in hematopoietic cells, and at varying levels in other tissues; and (4) genes overexpressed in fetal liver, in models of activation of liver progenitor cells, and in epithelial progenitor cell lines. Hepatoblast-specific clones and those representing genes induced during liver regeneration are under further study to define their specific function(s) in liver cell growth control and/or differentiation.

Proliferation and differentiation of fetal liver epithelial progenitor cells after transplantation into adult rat liver

To identify cells that have the ability to proliferate and differentiate into all epithelial components of the liver lobule, we isolated fetal liver epithelial cells (FLEC) from ED 14 Fischer (F) 344 rats and transplanted these cells in conjunction with two-thirds partial hepatectomy into the liver of normal and retrorsine (Rs) treated syngeneic dipeptidyl peptidase IV mutant (DPPIV(-)) F344 rats. Using dual label immunohistochemistry/in situ hybridization, three subpopulations of FLEC were identified: cells expressing both alpha-fetoprotein (AFP) and albumin, but not CK-19; cells expressing CK-19, but not AFP or albumin, and cells expressing AFP, albumin, and cytokeratins-19 (CK-19). Proliferation, differentiation, and expansion of transplanted FLEC differed significantly in the two models. In normal liver, 1 to 2 weeks after transplantation, mainly cells with a single phenotype, hepatocytic (expressing AFP and albumin) or bile ductular (expressing only CK-19), had proliferated. In Rs-treated rats, in which the proliferative capacity of endogenous hepatocytes is impaired, transplanted cells showed mainly a dual phenotype (expressing both AFP/albumin and CK-19). One month after transplantation, DPPIV(+) FLEC engrafted into the parenchyma exhibited an hepatocytic phenotype and generated new hepatic cord structures. FLEC, localized in the vicinity of bile ducts, exhibited a biliary epithelial phenotype and formed new bile duct structures or were incorporated into pre-existing bile ducts. In the absence of a proliferative stimulus, ED 14 FLEC did not proliferate or differentiate. Our results demonstrate that 14-day fetal liver contains lineage committed (unipotential) and uncommitted (bipotential) progenitor cells exerting different repopulating capacities, which are affected by the proliferative status of the recipient liver and the host site within the liver where the transplanted cells become engrafted. These findings have important implications in future studies directed toward liver repopulation and ex vivo gene therapy.

Alpha3beta1-integrin as a critical mediator of the hepatic differentiation response to the extracellular matrix

The extracellular matrix (ECM) promotes the differentiation of many cell types, and ECM remodeling in the liver has been implicated in embryonic development, tissue injury, and oncogenesis. Integrins are heterodimeric ECM receptors that play critical roles in transducing the composition of the ECM in the cell environment. We previously showed that mouse H2.35 cells, a conditionally transformed, liver-derived cell line, assume a more differentiated hepatocyte morphology and enhanced liver-specific gene expression when the cells are cultured on gelatinous ECM substrata. Here we show that H2. 35 cells express relatively high levels of alpha3beta1-integrins, similar to that previously shown for immature hepatocytes, transformed hepatocytes, and biliary cells. However, the cell morphological responses that depend on alpha3beta1-integrin have not been defined. We found that transfecting H2.35 cells with antisense RNA construct directed to alpha3-subunit messenger RNA perturbs the initial cell attachment to laminin and collagen, and strongly inhibits cell morphological, proliferative, and gene expression responses to a collagen gel substratum. In situ hybridization to mouse embryo tissues demonstrates the presence of alpha3-subunit messenger RNAs in newly formed hepatocytes. We suggest that alpha3beta1-integrins are important for immature and transformed hepatocytes to respond morphologically to the extracellular matrix.

Maturation-dependent gene expression in a conditionally transformed liver progenitor cell line

We have isolated a conditionally transformed liver progenitor cell line with phenotypic similarities to both hepatoblasts (bipotent embryonic liver cells that give rise to hepatocytes and intrahepatic biliary epithelial cells) and liver epithelial cells (primitive hepatic cells isolated from adult livers capable of generating both hepatocytic and biliary lineages). Cell line L2039 was derived from E14 fetal mouse liver after transformation with temperature-sensitive SV-40 large T antigen. At 33 degrees C, these cells have an epithelial morphology with a high nucleocytoplasmic ratio and express both hepatocytic and biliary genes, including albumin, alpha-fetoprotein, glutamine synthetase, insulinlike growth factor II receptor, fibronectin and laminin, and cytokeratins 8 and 19, a set of markers characteristic for hepatoblasts. The presence of cytokeratin 14, vimentin, and several oval-cell antigens link cell line L2039 to nonparenchymal liver epithelial cell populations thought to contain progenitor cells. Serum-free, hormonally defined media conditions and extracellular matrix requirements were determined for growth and differentiation of this cell line. During culture on type IV collagen at 39 degrees C, L2039 cells cease dividing and demonstrate hepatocytic differentiation with the assumption of a hepatocytelike morphology and glucocorticoid-dependent regulation of liver-specific genes, including albumin, alpha-fetoprotein, phosphoenolpyruvate carboxykinase, and liver-enriched transcription factors. The number of albumin-positive cells increases during culture at 39 degrees C, indicating that L2039 cells convert from a prehepatocytic to a hepatocytic phenotype. Under conditions specific for hepatocytic differentiation, C/EBPs were expressed and differentially regulated, with C/EBPbeta and C/EBPdelta upregulated early and C/EBPalpha only slightly expressed after 7 d, indicating that C/EBPalpha may not be a crucial factor in commitment to the hepatocytic phenotype.

Spatial distribution of cytoskeleton intermediate filaments during fetal rat hepatocyte differentiation

The construction of the liver parenchyma throughout fetal development depends on the elaboration of intercellular contacts between epithelial cells and between epithelial and mesenchymal cells. During this time, the spatial distribution of cytokeratins in hepatocytes shows a striking evolution as demonstrated by confocal microscopy and image analysis. In the early stages of fetal rat development, the liver is mainly a hematopoietic organ and hepatocytes represent fewer than 40% of all liver cells. At this time, cytokeratin filaments are scarce and are randomly distributed inside the cytoplasm. A coexpression of desmin and cytokeratin is found in some cells. Intercellular contacts between epithelial and mesenchymal cells are more numerous than between epithelial cells. Later in development, hepatocytes are arranged in a "muralium duplex" architecture (two-cell-thick sheets). Contacts between hepatocytes become more numerous and bile canaliculi become well developed. The density of cytokeratin filaments increases and appears to be very high near the bile canaliculi. In adult liver, hepatocytes are arranged in a "muralium simplex" architecture. Cytokeratin filaments show a symmetrical distribution in relation to the nuclear region. The highest density of filaments is found near the cytoplasmic membrane. Variations of the spatial distribution of intermediate filaments throughout hepatocyte differentiation were investigated in a pilot study using computerized image analysis. We found significant differences between the filament networks in fetal and adult hepatocytes.

Development and differentiation of bile ducts in the mammalian liver

The development and differentiation of bile ducts in the human and rodent liver are reviewed. The liver primordium develops as a ventral diverticulum in the anterior intestinal portal region, which consists of endodermal and mesodermal components. The endodermal cells differentiate into hepatocytes and all epithelial cells of the bile ducts in the adult liver. The gallbladder and extrahepatic bile ducts also start to develop from hepatic endodermal cells and hepatoblasts just after liver primordium formation. The gallbladder and cystic duct do not develop through hepatic development in the rat. Intrahepatic bile ducts are formed from periportal hepatoblasts forming the "ductal plate" and expressing alpha-fetoprotein, and albumin and bile duct-specific cytokeratin and develop independently of extrahepatic bile duct formation. The first sign of intrahepatic bile duct differentiation is the increased expression of bile duct-specific cytokeratin and large lumina formation in periportal hepatoblasts, and then deposition of basal laminar components occurs on the basal side. Their development takes place discontinuously along portal veins at the early stage of development, and they then become confluent through development. Periportal connective tissue, glucocorticoid hormones, and basal laminar components may play important roles in the differentiation of bile ducts.

Differentiation of the mouse hepatic primordium cultured in vitro

The differentiation of hepatic endodermal cells is affected by endodermal-mesodermal interactions. To examine the control mechanisms of this differentiation, we cultured mouse liver primordium and tissue recombinants of the hepatic endoderm with homo- or heterologous mesenchyme in vitro. When the hepatic primordia at somite stages 15-23 were cultured in vitro for 5-10 days, the endodermal cells differentiated into large hepatocytes expressing alpha-fetoprotein (AFP), albumin and carbamoylphosphate synthetase I (CPSI) and storing glycogen. AFP continued to be expressed in hepatocytes through culture for 10 days. Albumin and CPSI expression started in hepatocytes at 1 and 2 days after culture, respectively. Dexamethasone stimulated hepatocyte differentiation (expression of CPSI and glycogen accumulation) and large lumen formation of hepatocytes, but it did not change the commencement of differentiation. When the hepatic endoderm was recombined with hepatic mesenchyme or 4-day embryonic chick lung mesenchyme, clotted in Matrigel, which is a basement-membrane-like substratum, and cultured for 5 days in vitro, it differentiated into large hepatocytes expressing albumin and CPSI and accumulating glycogen. Lung mesenchyme promoted duct formation more efficiently than the hepatic mesenchyme did. However, the hepatic endodermal cells failed to differentiate into large hepatocytes when cultured with 6-day embryonic chick metanephric mesenchyme or with 2.5-day chick somitic mesenchyme, or cultured alone in Matrigel, suggesting that the endodermal cells require the presence of splanchnic mesoderm for their differentiation in vitro. Addition of HGF (hepatocyte growth factor), aFGF (acidic fibroblast growth factor), or bFGF (basic fibroblast growth factor) also did not support the survival of hepatic endodermal cells or hepatocyte differentiation in culture without mesenchyme. Matrigel and those growth factors might not be a suitable substitute for the mesenchyme.