Effects of long-term dietary intake of magnesium on rat liver transcriptome.

In the present study we investigated the effect of a two-year treatment period with a diet containing 3.2g, 0.8 g and 0.15 g Mg/kg, on the rat liver transcriptome. At the end of the study, a treatment-dependent decrease in plasmatic Mg concentration was found (0.86 +/- 0.02 mmol/L, 0.70 +/- 0.02 mmol/L and 0.52 +/- 0.03 mmol/L for groups receiving 3.2g, 0.8 g and 0.15 g Mg/kg diet, respectively). No significant treatment-related effect on body and liver weights was observed, however a dietary Mg intake-dependent increase in mortality rate occurred in animals (11%, 25% and 38% death of animals). Mg content in the diet affected gene expression in rat livers, as assessed by rat specific DNA microarrays. We identified 11 genes up-regulated and 39 genes down-regulated by at least two-fold by a decrease in Mg content and grouped them within five functional pathways: metabolism 20%, cytoarchitecture (connective tissue/cell adhesion/cytoskeleton) 12%, channels/ transporters 20%, turn-over (nucleic acid and protein) 16%, and homeostasis (stress/DNA damage/apoptosis/ageing) 32%. The results of the present study confirm the pleiotropic effects of Mg and provide further evidence that a Mg decrease in the diet may be considered as a promoting factor for pathologies, especially in the liver, during ageing.

Effects of clofibric acid on mRNA expression profiles in primary cultures of rat, mouse and human hepatocytes.

The mRNA expression profile in control and clofibric acid (CLO)-treated mouse, rat, and human hepatocytes was analyzed using species-specific oligonucleotide DNA microarrays (Affymetrix). A statistical empirical Bayes procedure was applied in order to select the significantly differentially expressed genes. Treatment with the peroxisome proliferator CLO induced up-regulation of genes involved in peroxisome proliferation and in cell proliferation as well as down-regulation of genes involved in apoptosis in hepatocytes of rodent but not of human origin. CLO treatment induced up-regulation of microsomal cytochrome P450 4a genes in rodent hepatocytes and in two of six human hepatocyte cultures. In addition, genes encoding phenobarbital-inducible cytochrome P450s were also up-regulated by CLO in rodent and human hepatocyte cultures. Up-regulation of phenobarbital-inducible UDP-glucuronosyl-transferase genes by CLO was observed in both rat and human but not in mouse hepatocytes. CLO treatment induced up-regulation of L-fatty acid binding protein (L-FABP) gene in hepatocytes of both rodent and human origin. However, while genes of the cytosolic, microsomal, and mitochondrial pathways involved in fatty acid transport and metabolism were up-regulated by CLO in both rodent and human hepatocyte cultures, genes of the peroxisomal pathway of lipid metabolism were up-regulated in rodents only. An up-regulation of hepatocyte nuclear factor 1alpha (HNF1alpha) by CLO was observed only in human hepatocyte cultures, suggesting that this trans-activating factor may play a key role in the regulation of fatty acid metabolism in human liver as well as in the nonresponsiveness of human liver to CLO-induced regulation of cell proliferation and apoptosis.

Overexpression of the mouse Fas gene in human Hep3B hepatoma cells overcomes their resistance to Fas-mediated apoptosis.

BACKGROUND/AIMS: Fas-induced apoptosis is one of the main forms of apoptosis occurring in hepatocytes. We have previously demonstrated that the human hepatoma cell line Hep3B is resistant to Fas-mediated apoptosis. In this study, we investigated whether the human Fas receptor itself, or the Fas transduction pathway was responsible for the resistant phenotype. METHODS: Clones of Hep3B cells overexpressing the mouse Fas gene (Hep3B(mfas)) were generated by transfection, and apoptosis was studied by (i) chromatin condensation and nuclear fragmentation, (ii) flow cytometry, (iii) DNA fragmentation and (iv) poly (ADP-ribose) polymerase cleavage. RESULTS: Use of the species-specific and agonistic anti-mFas monoclonal antibody (JO2), showed that the mFas receptor was correctly routed to the plasma membrane of Hep3B(mfas) cells. Using the four above-mentioned criteria, we demonstrated that JO2 triggered mFas-mediated apoptosis of Hep3B(mfas), but not of Hep3B(pCi) cells (transfected with an empty vector). CONCLUSIONS: Our data show (i) that the Fas signaling pathway can be completed when a functional mFas receptor is expressed in Hep3B cells, and thus, (ii) that the death-inducing signaling complex components and the effector caspases are functional in Hep3B cells. Moreover, they suggest that the Fas subunits are not pre-assembled at the cell membrane before receptor-ligand interaction.