The daily rhythms of mitochondrial gene expression and oxidative stress regulation are altered by aging in the mouse liver

The circadian clock regulates many cellular processes, notably including the cell cycle, metabolism and aging. Mitochondria play essential roles in metabolism and are the major sites of reactive oxygen species (ROS) production in the cell. The clock regulates mitochondrial functions by driving daily changes in NAD⁺ levels and Sirt3 activity. In addition to this central route, in the present study, we find that the expression of some mitochondrial genes is also rhythmic in the liver, and that there rhythms are disrupted by the Clock^Δ19 mutation in young mice, suggesting that they are regulated by the core circadian oscillator. Related to this observation, we also find that the regulation of oxidative stress is rhythmic in the liver. Since mitochondria and ROS play important roles in aging, and mitochondrial functions are also disturbed by aging, these related observations prompt the compelling hypothesis that circadian oscillators influence aging by regulating ROS in mitochondria. During aging, the expression rhythms of some mitochondrial genes were altered in the liver and the temporal regulation over the dynamics of mitochondrial oxidative stress was disrupted. However, the expression of clock genes was not affected. Our results suggested that mitochondrial functions are combinatorially regulated by the clock and other age-dependent mechanism(s), and that aging disrupts mitochondrial rhythms through mechanisms downstream of the clock.     

Systemic oscillator-driven and nutrient-responsive hormonal regulation of daily expression rhythms for gluconeogenic enzyme genes in the mouse liver

Gluconeogenesis is de novo glucose synthesis from substrates such as amino acids and is vital when glucose is lacking in the diurnal nutritional fluctuation. Accordingly, genes for hepatic gluconeogenic enzymes exhibit daily expression rhythms, whose detailed regulations under nutritional variations remain elusive. As a first step, we performed general systematic characterization of daily expression profiles of gluconeogenic enzyme genes for phosphoenolpyruvate carboxykinase (PEPCK), cytosolic form (Pck1), glucose-6-phosphatase (G6Pase), catalytic subunit (G6pc), and tyrosine aminotransferase (TAT) (Tat) in the mouse liver. On a standard diet fed ad libitum, mRNA levels of these genes showed robust daily rhythms with a peak or an elevation phase during the late sleep-fasting period in the diurnal feeding/fasting (wake/sleep) cycle. The rhythmicity was preserved in constant darkness, modulated with prolonged fasting, attenuated by Clock mutation, and entrained to varied photoperiods and time-restricted feedings. These results are concordant with the notion that gluconeogenic enzyme genes are under the control of the intrinsic circadian oscillator, which is entrained by the light/dark cycle, and which in turn entrains the feeding/fasting cycle and also drives systemic signaling pathways such as the hypothalamic-pituitary-adrenal axis. On the other hand, time-restricted feedings also showed that the ingestion schedule, when separated from the light/dark cycle, can serve as an independent entrainer to daily expression rhythms of gluconeogenic enzyme genes. Moreover, nutritional changes dramatically modified expression profiles of the genes. In addition to prolonged fasting, a high-fat diet and a high-carbohydrate (no-protein) diet caused modification of daily expression rhythms of the genes, with characteristic changes in profiles of glucoregulatory hormones such as corticosterone, glucagon, and insulin, as well as their modulators including ghrelin, leptin, resistin, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1). Remarkably, high-protein (60% casein or soy-protein) diets activated the gluconeogenic enzyme genes atypically during the wake-feeding period, with paradoxical up-regulation of glucagon, which frequently formed correlation networks with other humoral factors. Based on these results, we propose that daily expression rhythms of gluconeogenic enzyme genes are under the control of systemic oscillator-driven and nutrient-responsive hormones.     

鸡、鸭甲状腺激素应答基因(THRSP)的研究进展

甲状腺激素应答Spot 14(Thyroid hormone responsive spot 14, THRSP)是一个参与多种脂肪合成限速酶基因表达的转录调控因子, 在动物肝脏、乳腺和脂肪组织中高度表达。家禽中鸡和鸭THRSP基因在cDNA水平均发现THRSPα和THRSPβ两种同工型, 其中鸡THRSPα基因编码区碱基的插入/缺失影响鸡体重和腹脂性状, 与鸡的生长发育和脂肪代谢有关。文章综述了鸡THRSP基因与鸭同源基因结构特性和表达差异, 以及鸡、鸭THRSP基因多态性及其遗传效应。     

Examination of ethanol responsive liver and brain specific gene expression,in the mouse strains with variable ethanol preferences,using cDNA expression arrays

Strains of mice that differ in voluntary alcohol consumption (VAC) are valuable models for the identification of genes involved in the complex etiology of alcohol effects and alcoholism. These mice offer a novel approach to the identification of strain-specific ethanol responsive (SSER) genes in tissues directly involved in alcohol metabolism and preference. We assessed mRNA from the liver and brain from male mice representing C57BL/6J, BALB/c, A/J, and DBA/2J strains following ethanol treatment (chronic ethanol fed liquid diet for 14 days or acute i.p. injection at two doses; 4 g/kg or 8 g/kg), using an expression array containing 588 genes (Clontech #7741-1). The results have identified NADPH cytochrome P450 oxidoreductase, insulin-like growth factor binding protein-1, glutathione S-transferase Mu 1, and cathepsin L as ethanol responsive genes in the liver. Further, we have established that IkB-alpha and clusterin genes in the brain are ethanol responsive, but only at the lower dose of the ethanol challenge. Although a number of other genes showing subtle (<2X) differences across strains and treatment combinations were reproducible in repeated blots, they were not confirmed by still evolving independent technologies of gene specific mRNA quantitation. The results demonstrate that comparative expression studies are an efficient approach to discover interacting gene networks that underlie the etiology of complex phenotypes including response to alcohols.     

Cellular density regulation of plasminogen gene expression in mouse hepatocytes

The liver produces a variety of proteins including plasminogen. Plasminogen is pro-enzyme that is converted into plasmin by plasminogen activator. Plasmin has a broad substrate spectrum and participates in several biological processes, such as fibrinolysis, tissue remodeling, cell migration, angiogenesis and embryogenesis. In the present study, the regulation of plasminogen expression in mouse hepatocytes was investigated in the primary culture system. Expression level of plasminogen mRNA in the culture at the low cell density condition (0.2 x 10(5) cells / cm(2)) was compared with that at the high cell density condition (1.0 x 10 (5) cells / cm(2)). In the low cell density culture, the expression level of plasminogen mRNA decreased by a time-dependent manner. However, mRNAs for albumin and alpha(2)-antiplasmin were not influenced by the low cell density culture. On the other hand, in the high cell density culture, plasminongen mRNA expressed constantly as well as albumin and alpha(2)-antiplasmin mRNAs. Thus, the decrease in plasminogen mRNA expression could specifically occur when the density of hepatocytes was low. The down-regulation of plasminogen mRNA in the low cell density culture is not observed in the presence of cycloheximide, suggesting that the de novo protein synthesis is required for the regulatory mechanism. These findings indicate that the expression of plasminogen mRNA from hepatocyte is dependent on the cell density and the stimulation by cell-cell contact may be an important factor for the constitutive expression of plasminogen gene in hepatocytes.