Long term organ culture of rat liver rudiment in a synthetic medium: morphological and biochemical development

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.

Functional analysis of developmentally regulated chromatin-hypersensitive domains carrying the alpha 1-fetoprotein gene promoter and the albumin/alpha 1-fetoprotein intergenic enhancer

During liver development, the tandem alpha 1-fetoprotein (AFP)/albumin locus is triggered at the AFP end and then asymmetrically enhanced; this is followed by autonomous repression of the AFP-encoding gene. To understand this regulation better, we characterized the two early developmental stage-specific DNase I-hypersensitive (DH) sites so far identified in rat liver AFP/albumin chromatin: an intergenic DH-enhancer site and the AFP DH-promoter site. Mutation-transfection analyses circumscribed the DH-enhancer domain to a 200-bp DNA segment stringently conserved among species. Targeted mutations, DNA-protein-binding assays, and coexpression experiments pinpointed C/EBP as the major activatory component of the intergenic enhancer. Structure-function relationships at the AFP DH-promoter site defined a discrete glucocorticoid-regulated domain activated cooperatively by HNF1 and a highly specific AFP transcription factor, FTF, which binds to a steroid receptor recognition motif. The HNF1/FTF/DNA complex is deactivated by glucocorticoid receptors or by the ubiquitous factor NF1, which eliminates HNF1 by competition at an overlapping, high-affinity binding site. We propose that the HNF1-NF1 site might serve as a developmental switch to direct autonomous AFP gene repression in late liver development. We also conclude that the intergenic enhancer is driven by C/EBP alpha primarily to fulfill albumin gene activation functions at early developmental stages. Factor FTF seems to be the key regulator of AFP gene-specific functions in carcinoembryonic states.

Functional analysis of developmentally regulated chromatin-hypersensitive domains carrying the alpha 1-fetoprotein gene promoter and the albumin/alpha 1-fetoprotein intergenic enhancer

During liver development, the tandem alpha 1-fetoprotein (AFP)/albumin locus is triggered at the AFP end and then asymmetrically enhanced; this is followed by autonomous repression of the AFP-encoding gene. To understand this regulation better, we characterized the two early developmental stage-specific DNase I-hypersensitive (DH) sites so far identified in rat liver AFP/albumin chromatin: an intergenic DH-enhancer site and the AFP DH-promoter site. Mutation-transfection analyses circumscribed the DH-enhancer domain to a 200-bp DNA segment stringently conserved among species. Targeted mutations, DNA-protein-binding assays, and coexpression experiments pinpointed C/EBP as the major activatory component of the intergenic enhancer. Structure-function relationships at the AFP DH-promoter site defined a discrete glucocorticoid-regulated domain activated cooperatively by HNF1 and a highly specific AFP transcription factor, FTF, which binds to a steroid receptor recognition motif. The HNF1/FTF/DNA complex is deactivated by glucocorticoid receptors or by the ubiquitous factor NF1, which eliminates HNF1 by competition at an overlapping, high-affinity binding site. We propose that the HNF1-NF1 site might serve as a developmental switch to direct autonomous AFP gene repression in late liver development. We also conclude that the intergenic enhancer is driven by C/EBP alpha primarily to fulfill albumin gene activation functions at early developmental stages. Factor FTF seems to be the key regulator of AFP gene-specific functions in carcinoembryonic states.

Regulation of rat liver maturation in vitro by glucocorticoids

The biochemistry of liver maturation was studied by using the RLA209-15 fetal rat hepatocyte line that is temperature sensitive for maintenance of the differentiated fetal liver phenotype. At 33 degrees C these cells were dedifferentiated; but at 40 degrees C they were phenotypically differentiated and, like normal fetal hepatocytes, synthesized moderate levels of albumin and transferrin, high levels of authentic (69,000 and 73,000 molecular weight) rat fetal alpha-fetoprotein (AFP), and low levels of a 65,000-molecular-weight variant AFP. Our results indicated that administration of glucocorticoid hormones to RLA209-15 cells at 40 degrees C induced a series of events associated with normal hepatocyte maturation; synthesis of fetal AFP was inhibited, whereas the synthesis of variant AFP, albumin, transferrin, tyrosine aminotransferase, and alpha 1-acid glycoprotein was induced. The variant AFP was produced by RLA209-15 cells at both temperatures and was encoded by an mRNA of 1.7 kilobases (kb). The fetal AFP was encoded by an mRNA of 2.2 kb. Normal adult rat liver contained three AFP mRNAs of 2.2 (minor), 1.7, and 1.5 kb. The 1.7-kb adult liver AFP mRNA comigrated with the RNA found in RLA209-15 cells, and both directed the synthesis of a 50,000-molecular-weight precursor polypeptide of the variant AFP. Administration of glucocorticoids to RLA209-15 cells grown at 33 degrees C stimulated synthesis of both the fetal and variant AFPs, but the levels of the 2.2-kb AFP mRNA were preferentially increased. RLA209-15 cells contained two glucocorticoid receptor mRNAs of 6.8 and 4.5 kb. The glucocorticoid-mediated maturation described above was blocked by the antiglucocorticoid RU486.

Regulation of rat liver maturation in vitro by glucocorticoids

The biochemistry of liver maturation was studied by using the RLA209-15 fetal rat hepatocyte line that is temperature sensitive for maintenance of the differentiated fetal liver phenotype. At 33 degrees C these cells were dedifferentiated; but at 40 degrees C they were phenotypically differentiated and, like normal fetal hepatocytes, synthesized moderate levels of albumin and transferrin, high levels of authentic (69,000 and 73,000 molecular weight) rat fetal alpha-fetoprotein (AFP), and low levels of a 65,000-molecular-weight variant AFP. Our results indicated that administration of glucocorticoid hormones to RLA209-15 cells at 40 degrees C induced a series of events associated with normal hepatocyte maturation; synthesis of fetal AFP was inhibited, whereas the synthesis of variant AFP, albumin, transferrin, tyrosine aminotransferase, and alpha 1-acid glycoprotein was induced. The variant AFP was produced by RLA209-15 cells at both temperatures and was encoded by an mRNA of 1.7 kilobases (kb). The fetal AFP was encoded by an mRNA of 2.2 kb. Normal adult rat liver contained three AFP mRNAs of 2.2 (minor), 1.7, and 1.5 kb. The 1.7-kb adult liver AFP mRNA comigrated with the RNA found in RLA209-15 cells, and both directed the synthesis of a 50,000-molecular-weight precursor polypeptide of the variant AFP. Administration of glucocorticoids to RLA209-15 cells grown at 33 degrees C stimulated synthesis of both the fetal and variant AFPs, but the levels of the 2.2-kb AFP mRNA were preferentially increased. RLA209-15 cells contained two glucocorticoid receptor mRNAs of 6.8 and 4.5 kb. The glucocorticoid-mediated maturation described above was blocked by the antiglucocorticoid RU486.

Comparative effects of insulin and hydrocortisone on glycogen content of fetal and newborn rat liver cultures

Organ cultures prepared from 18- to 19-day fetal and 3- to 6-day-old newborn rat liver were maintained for 2 days in Trowell's T8 medium without insulin and supplemented with 0.1% albumin and 300 mg% glucose. The atmosphere for culture was 95% O2 and 5% CO2. Medium alone was used for control cultures, whereas insulin, hydrocortisone, or insulin plus hydrocortisone were used in experimental groups. Explant glycogen stores were maintained better in cultures grown in hormone-supplemented media than in control cultures. Fetal explants were found to have higher levels of glycogen than controls in the insulin or insulin plus hydrocortisone groups. Postnatal explants did not have higher levels of glycogen in the hormone-treated groups. Gestational age appeared to determine whether the liver explants reacted to hydrocortisone or insulin to maintain glycogen stores. Enzymatic assays, in vitro of glycogen synthetase and phosphorylase, indicated that the fetal liver response to insulin plus hydrocortisone by increasing the total and independent form of glycogen synthetase; but similar enzyme studies on postnatal rat liver did not show convincing differences as to an effect on synthetase. No definite in vitro temporal relationships could be identified. Late in gestation, the effect of hydrocortisone on glycogen synthesis is apparently dependent on the presence of insulin. Insulin appears to be required for glycogen storage in vitro in the cultures of postnatal rat liver.

Differentiation of fetal liver cells in vitro

Fetal mouse liver hepatocytes proliferate on a substrate of irradiated pigskin epidermis scored with scalpel blade slits to permit cell access to the basement membrane. At the time the cells are explanted, fetal genes, such as those responsible for production of alpha-fetoprotein (AFP) and gamma-glutamyltransferase (GGTase), are strongly expressed. The levels of GGTase decrease rapidly and become undetectable within 2 weeks. The levels of AFP decrease more gradually but become undetectable after 3-5 weeks in culture. As the AFP levels decrease, there is a concomitant increase in albumin production. Hydrocortisone prolongs production of AFP (for up to 8 weeks) but not of GGTase, and it decreases albumin production for up to 8 weeks. Once cells lose AFP expression, addition of hydrocortisone does not restart it. Based on these data, fetal mouse liver hepatocytes, cultured on pigskin, seem to be an excellent in vitro model for liver cell maturation.

Evidence for fibrinogen synthesis and secretion by rat foetal hepatocytes

Fibrinogen concentration in rat foetal plasma is very low at 18 days of gestation but increases rapidly thereafter. The present study provides evidence that this increase is due to synthesis by the foetus itself. (1) 125I-labelled human fibrinogen, injected intravenously into the pregnant adult, did not reach the foetal circulation; (2) turpentine administration to the adult induced an increased maternal plasma fibrinogen concentration without affecting the foetal one; (3) conversely, in utero administration of turpentine to foetuses increased their plasmas fibrinogen concentration without affecting the maternal one; (4) using sheep anti-rat fibrinogen antibodies labelled with peroxidase, in electron microscopy, fibrinogen was located in foetal hepatocytes within the organelles known to be responsible for the synthesis and the ultimate secretion of the protein.

Synthesis and secretion of albumin and transferrin by foetal rat hepatocyte cultures

Hepatocytes derived from foetal rat liver synthesize and secrete albumin and transferrin when maintained in primary culture. These proteins are produced for at least seven days under the conditions of culture. Studies on hepatocyte cultures derived from 12, 13, 14, 15 and 19-day foetal rats show that the maximal cellular rate of secretion of both proteins increases about 50-fold over this period. The maximal rate of albumin secretion in all cultures is achieved after one day in culture and decreases in hepatocytes from early foetuses after the fourth to sixth day in culture. Transferrin secretion by hepatocytes from 12 to 15 day foetuses increases markedly during the second day of culture and is relatively constant thereafter. In contrast, secretion of transferrin by hepatocytes from 19-day foetuses is constant from the first day of culture. The results show that both albumin and transferrin are synthesized and secreted by the foetal liver as early as the twelfth day of gestation. The increase in the rate of transferrin secretion that occurs during culture of hepatocytes from 12 to 15 day foetuses may reflect the development of a secretory mechanism that is different from that for albumin.

Conditions affecting primary cell cultures of functional adult rat hepatocytes. II. Dexamethasone enhanced longevity and maintenance of morphology

Primary monolayer cell cultures of adult rat hepatocytes underwent change in morphology and substantial cell loss between 1 and 3 days postinoculation. Dexamethasone-supplementation (1 micronM) of the culture medium maintained the polygonal epithelial morphology of the hepatocytes and increased longevity such that over 80% of the cells survived for 3 days and at least 30% for 8 or 9 days. This enhancement of survival was obtained up to 48 hr postinoculation, but the earlier the time of dexamethason supplementation the greater the effect. Removal of dexamethasone resulted in a decrease in longevity. The positive effect of dexamethasone on longevity was observed following dexamethasone replacement of insulin in supplemented cultures, but the combination of insulin and dexamethasone resulted in poorer survival than with dexamethasone alone. The results are interpreted to indicate that dexamethasone provided a requirement of the in vitro environment for survival and suggest that elaboration of a complex medium is required to maintain hepatocytes in culture.

Culture of fetal mouse liver in plastic chambers: a new technique for organ culture

A new technique for organ culture which uses plastic culture chambers and the advantages of the cellophane-sheet technique is described with the results of a study of cultivations of fetal mouse liver. Two chambers, each containing cells, were placed in gas permeable roller tubes and rotated at 0.1 rpm in a CO2-air gassed incubator. The fetal mouse liver cells developed electron microscopic features similar to those of the in vivo adult liver by 9 days of cultivation. The albumin content and tyrosine aminotransferase (TAT) activity were detected in the cultivated liver. TAT activity was further induced by prednisolone. These results indicate that potential of this culture method for the study of physiological and pathological processes.