Tissue-specific gene expression in mouse hepatocytes cultured in growth-restricting medium

In Contrast to Dietary Restriction, Application of Resveratrol in Mice Does not Alter Mouse Major Urinary Protein Expression

Resveratrol (RSV) supplementation in mice has been discussed as partly mimicking the beneficial effects of dietary restriction (DR). However, data on putative benefits from resveratrol application in mice and other model organisms including humans is contradictory. Mouse major urinary proteins (MUPs) are a family of proteins that are expressed in rodent liver and secreted via urine. Impacting (mating) behavior and pheromone communication, they are severely down-regulated upon DR. We carried out two studies in C57BL/6Rj mice where RSV was either supplemented via diet or injected intraperitoneally for 8 weeks. Contrary to −40% DR, RSV did not decrease total MUP protein expression or Mup (amongst others Mup3, Mup5, Mup6, Mup15, and Mup20) mRNA levels in mouse liver when compared to ad-libitum (AL)-fed controls. Since inhibitory glucocorticoid response elements can be found in Mup promoters, we also measured glucocorticoid receptor (GR) levels in nuclear hepatic extracts. Consistent with differential MUP expression, we observed more nuclear GR in DR mice than in RSV-supplemented and AL control mice with no difference between RSV and AL. These findings point to the notion that, in mice, RSV does not mimic DR in terms of differential MUP expression.

Evaluation of a hepatocyte-entrapment hollow fiber bioreactor: a potential bioartificial liver

We have developed a hepatocyte entrapment hollow fiber bioreactor for potential use as a bioartificial liver. Hepatocytes were entrapped in collagen gel inside the lumen of the hollow fibers. Medium was perfused through the intraluminal region after contraction of the hepatocyte-entrapment gel. Another medium stream, comparable to the patient's blood during clinical application, passed through the extracapillary space. Viability of hepatocytes remained high after 5 days as judged by the rate of oxygen uptake and viability staining. Urea and albumin synthetic activities were also sustained. Transmission electron microscopic examination demonstrated normal ultrastructural integrity of hepatocytes in such a bioreactor. With its sort-term, extracorporeal support of acute liver failure, the current bioreactor warrants further investigation.

Short-term arginine deprivation results in large-scale modulation of hepatic gene expression in both normal and tumor cells: microarray bioinformatic analysis

Background

We have reported arginine-sensitive regulation of LAT1 amino acid transporter (SLC 7A5) in normal rodent hepatic cells with loss of arginine sensitivity and high level constitutive expression in tumor cells. We hypothesized that liver cell gene expression is highly sensitive to alterations in the amino acid microenvironment and that tumor cells may differ substantially in gene sets sensitive to amino acid availability. To assess the potential number and classes of hepatic genes sensitive to arginine availability at the RNA level and compare these between normal and tumor cells, we used an Affymetrix microarray approach, a paired in vitro model of normal rat hepatic cells and a tumorigenic derivative with triplicate independent replicates. Cells were exposed to arginine-deficient or control conditions for 18 hours in medium formulated to maintain differentiated function.

Results

Initial two-way analysis with a p-value of 0.05 identified 1419 genes in normal cells versus 2175 in tumor cells whose expression was altered in arginine-deficient conditions relative to controls, representing 9–14% of the rat genome. More stringent bioinformatic analysis with 9-way comparisons and a minimum of 2-fold variation narrowed this set to 56 arginine-responsive genes in normal liver cells and 162 in tumor cells. Approximately half the arginine-responsive genes in normal cells overlap with those in tumor cells. Of these, the majority was increased in expression and included multiple growth, survival, and stress-related genes. GADD45, TA1/LAT1, and caspases 11 and 12 were among this group. Previously known amino acid regulated genes were among the pool in both cell types. Available cDNA probes allowed independent validation of microarray data for multiple genes. Among genes downregulated under arginine-deficient conditions were multiple genes involved in cholesterol and fatty acid metabolism. Expression of low-density lipoprotein receptor was decreased in both normal and tumor cells.

Conclusion

Arginine-sensitive regulation appears to be an important homeostatic mechanism to coordinate cell response and nutrient availability in hepatic cells. Genes predicted as arginine-responsive in stringent microarray data analysis were confirmed by Northern blot and RT-PCR. Although the profile of arginine-responsive genes is altered and increased, a considerable portion of the "arginome" is maintained upon neoplastic transformation.

Major urinary proteins, alpha(2U)-globulins and aphrodisin

The major urinary proteins (MUPs) are proteins secreted by the liver and filtered by the kidneys into the urine of adult male mice and rats, the MUPs of rats being also referred to as alpha(2U)-globulins. The MUP family also comprises closely related proteins excreted by exocrine glands of rodents, independently of their sex. The MUP family is an expression of a multi-gene family. There is complex hormonal and tissue-specific regulation of MUP gene expression. The multi-gene family and its outflow are characterized by a polymorphism which extends over species, strains, sexes, and individuals. There is evidence of evolutionary conservation of the genes and their outflow within the species and evidence of change between species. MUPs share the eight-stranded beta-barrel structure lining a hydrophobic pocket, common to lipocalins. There is also a high degree of structural conservation between mouse and rat MUPs. MUPs bind small natural odorant molecules in the hydrophobic pocket with medium affinity in the 10(4)-10(5) M(-1) range, and are excreted in the field, with bound odorants. The odorants are then released slowly in air giving a long lasting olfactory trace to the spot. MUPs seem to play complex roles in chemosensory signalling among rodents, functioning as odorant carriers as well as proteins that prime endocrine reactions in female conspecifics. Aphrodisin is a lipocalin, found in hamster vaginal discharge, which stimulates male copulatory behaviour. Aphrodisin does not seem to bind odorants and no polymorphism has been shown. Both MUPs and aphrodisin stimulate the vomeronasal organ of conspecifics.

Transferrin and its receptor in the development of genetically determined neural tube defects in the mouse embryo

The iron-binding growth factor transferrin is taken up and localised in the hindgut of midgestation mouse embryos. We investigated whether the distribution of transferrin may be disturbed in mutant curly tail embryos, a proportion of which exhibit a cell proliferation defect affecting the hindgut endoderm, as part of the pathogenetic sequence leading to development of neural tube defects. Immunostaining revealed a reduction in the binding and/or uptake of transferrin by hindgut epithelial cells in affected curly tail embryos compared with their unaffected littermates. There was no apparent difference between the two embryo types, however, in the distribution or level of expression of the transferrin receptor. The receptor is expressed specifically in the hindgut endoderm of the 10.5-day embryo, although its mRNA is present in all tissues of the posterior neuropore region, suggesting posttranscriptional control of gene expression. These findings may indicate a role for transferrin binding and/or uptake in the regulation of cell proliferation in the hindgut endoderm, with a defect in this process in the curly tail mutant. However, an alternative explanation is suggested by our finding that transferrin immunostaining is more intense in the hindgut of unaffected curly tail embryos than in nonmutant CBA/Ca and CD-1 embryos. Thus, mutant embryos may increase their uptake of transferrin in an attempt to compensate for defective cell proliferation in the hindgut resulting from a defect in another pathway. Only a proportion of embryos are able to mount this compensatory response leading to the observed partial penetrance of developmental defects in the curly tail mutant mouse.

Transcriptional induction of rat liver apolipoprotein A-I gene expression by glucocorticoids requires the glucocorticoid receptor and a labile cell-specific protein

Treatment with glucocorticoids increases the concentration of plasma high-density lipoprotein (HDL), which is inversely correlated to the development of atherosclerosis. Previously, we demonstrated that repeated administration of glucocorticoids increases apolipoprotein (apo) A-I gene expression and decreases apoA-II gene expression in rat liver. In the present study, the mechanism of glucocorticoid action on hepatic apoA-I and apoA-II expression was studied. A single injection of rats with dexamethasone increased hepatic apoA-I mRNA levels within 6 h and further increases were observed after 12 h and 24 h. In contrast, liver apoA-II mRNA levels gradually decreased after dexamethasone treatment to less than 25% control levels after 24 h. In rat primary hepatocytes and McARH8994 hepatoma cells, addition of dexamethasone increased apoA-I mRNA levels in a time-dependent and dose-dependent manner, whereas apoA-II mRNA levels were unchanged. Simultaneous addition of the glucocorticoid antagonist RU486 prevented the increase in apoA-I mRNA levels after dexamethasone treatment, which suggests that the effects of dexamethasone are mediated through the glucocorticoid receptor. Inhibition of transcription by actinomycin D and nuclear-run-on experiments in McARH8994 cells and primary hepatocytes showed that dexamethasone induced apoA-I, but not apoA-II, gene transcription. Transient-transfection assays in McARH8994 cells with a chloramphenicol acetyl transferase vector driven by the rat-apoA-I-gene promoter demonstrated that the proximal apoA-I promoter could be induced by dexamethasone, and this effect could be abolished by simultaneous treatment with RU486. However, in COS-1 cells, apoA-I promoter transcription was not induced by dexamethasone or cotransfected glucocorticoid receptor. In addition, the induction of apoA-I gene transcription by dexamethasone was blocked by the protein-synthesis inhibitor cycloheximide, which suggests the presence of a labile protein involved in apoA-I gene activation by dexamethasone. In conclusion, our results demonstrate that dexamethasone regulates rat apoA-I, but not apoA-II, gene expression through direct action on the hepatocyte. The induction of apoA-I gene transcription by dexamethasone requires the glucocorticoid receptor and a labile cell-specific protein.

Gene expression in astrocytes is affected by subculture

We have investigated the effects of cell passaging and time in culture on astrocyte morphology, transferrin expression and the expression of two main astrocyte markers, glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS: EC 6.3.1.2). When primary astrocytes were subcultured, giving rise to secondary and tertiary cultures, their morphology changed, regardless of the split ratio used to passage the cells. Correlating with this morphological change, a dramatic increase in the accumulation of GFAP and GS mRNAs was observed after cells had been passaged. This effect was in marked contrast to the moderate increase in the levels of GFAP and GS mRNAs observed over several weeks in primary culture. Hydrocortisone induction of GS gene expression was not affected by cell passage. Transferrin mRNA, which is not normally found in astrocytes in vivo, was expressed at a high level in primary cultures of astrocytes. However, transferring mRNA almost completely disappeared after the second passage. Astrocyte-conditioned media, or co-cultures with oligodendrocytes, modified transferrin gene expression. Taken together, these results show that subculturing of primary rat astrocytes leads to a dramatic change in the genetic expression of several proteins and provides a new approach to modify astrocyte differentiation in vitro.

Isolation and long-term maintenance of differentiated adult chicken hepatocytes in primary culture

Adult chicken hepatocytes were obtained by an adaptation of the two step in situ collagenase perfusion. Usually 0.5 to 1 x 10(9) cells were obtained, with 75 to 95% viability. Hepatocytes attached within 2 h when plated on plastic cell culture dishes and spread in 4 h, surviving for several months in a specific serum-free medium. These cells retained a typical parenchymal cell morphology and the ability to produce a specific protein (albumin) throughout the culture period. We hereby provide a suitable model for studying hepatic metabolism in birds.

Heterologous protein expression by transimmortalized differentiated liver cell lines derived from transgenic mice (hepatomas/alpha 1 antitrypsin/ONC mouse)

A number of therapeutic plasma proteins are synthesized by human hepatocytes. Since many of these proteins undergo liver-specific post-translational modifications which are required for full biological activity, it may therefore be necessary to develop hepatocyte-based expression systems for their production. Using transgenic mice we have developed a transimmortalisation technique for the isolation of differentiated hepatic cell lines, already engineered to secrete human alpha 1 antitrypsin (alpha 1 AT), a plasma protein which is produced mainly in liver cells. This was achieved by co-expression of the mouse c-myc proto-oncogene and a genomic copy of the human alpha 1 AT gene, both under the control of the human alpha 1 AT promoter. Transgenic mice carrying this construct developed hepatomas producing human alpha 1 AT. Under defined culture conditions, cell lines secreting active alpha 1 AT were derived from these tumours. These cells maintain a differentiated hepatic phenotype and continue to secrete human alpha 1 AT for at least 40 generations.