ABSTRACT
Knockout of C/EBPalpha causes a severe loss of liver function and, subsequently, neonatal lethality in mice. By using a gene replacement approach, we generated a new C/EBPalpha-null mouse strain in which C/EBPbeta, in addition to its own expression, substituted for C/EBPalpha expression in tissues. The homozygous mutant mice C/ebpalpha(beta/beta) are viable and fertile and show none of the overt liver abnormalities found in the previous C/EBPalpha-null mouse line. Levels of hepatic PEPCK mRNA are not different between C/ebpalpha(beta/beta) and wild-type mice. However, despite their normal growth rate, C/ebpalpha(beta/beta) mice have markedly reduced fat storage in their white adipose tissue (WAT). Expression of two adipocyte-specific factors, adipsin and leptin, is significantly reduced in the WAT of C/ebpalpha(beta/beta) mice. In addition, expression of the non-adipocyte-specific genes for transferrin and cysteine dioxygenase is reduced in WAT but not in liver. Our study demonstrates that when expressed from the C/ebpalpha gene locus, C/EBPbeta can act for C/EBPalpha to maintain liver functions during development. Moreover, our studies with the C/ebpalpha(beta/beta) mice provide new insights into the nonredundant functions of C/EBPalpha and C/EBPbeta on gene regulation in WAT.
Subject(s)
Adipose Tissue/metabolism , DNA-Binding Proteins/genetics , DNA-Binding Proteins/physiology , Dioxygenases , Gene Expression Regulation , Liver Failure/genetics , Liver/metabolism , Nuclear Proteins/genetics , Nuclear Proteins/physiology , Promoter Regions, Genetic , Animals , Blood Glucose/metabolism , CCAAT-Enhancer-Binding Proteins , Chimera , Complement Factor D , Crosses, Genetic , Cysteine Dioxygenase , DNA-Binding Proteins/biosynthesis , DNA-Binding Proteins/deficiency , Female , Fertility , Genotype , Leptin/biosynthesis , Leptin/genetics , Lipid Metabolism , Liver Failure/metabolism , Liver Failure/prevention & control , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Nuclear Proteins/biosynthesis , Nuclear Proteins/deficiency , Organ Specificity , Oxygenases/biosynthesis , Oxygenases/genetics , RNA, Messenger/biosynthesis , RNA, Messenger/genetics , Recombinant Fusion Proteins/biosynthesis , Recombinant Fusion Proteins/physiology , Serine Endopeptidases/biosynthesis , Serine Endopeptidases/genetics , Transferrin/biosynthesis , Transferrin/geneticsABSTRACT
Mice deficient in hepatocyte nuclear factor 1alpha (HNF-1alpha) develop Laron dwarfism and non-insulin-dependent diabetes mellitus (Lee et al., 1998). Oxidative stress was present in the diabetic HNF-1alpha-null mice. To understand the mechanism underlying the oxidative stress in HNF-1alpha-null mice, we examined whether HNF-1alpha deficiency affects the integrity of the cellular defense system against oxidative stress. The glutathione level and activities of superoxide dismutase and glutathione reductase in liver and other tissues examined were not affected by HNF-1alpha deficiency. However, activities of cytosolic glutathione peroxidase and catalase, two enzymes responsible for detoxification of hydrogen peroxide within cells, were reduced specifically in liver of HNF-1alpha-null mice. The mRNA and protein levels of hepatic catalase in HNF-1alpha-null mice did not differ from those in normal mice. The loss of hepatic catalase activity in HNF-1alpha-null mice is probably caused by an insufficient heme pool in liver cells, because the mRNA level of ferrochelatase, the enzyme that catalyzes the last step of heme biosynthesis, was significantly reduced in liver, and the daily hemin treatment restored partial catalase activity in liver of HNF-1alpha-null mice. Furthermore, our results of cell transfection and luciferase reporter assay indicated that the mouse ferrochelatase promoter could be trans-activated directly by HNF-1alpha.
