Shuichi Horie

Genome-wide Expression Analysis of Mouse Liver Reveals CLOCK-regulated Circadian Output Genes

CLOCK is a positive component of a transcription/translation-based negative feedback loop of the central circadian oscillator in the suprachiasmatic nucleus in mammals. To examine CLOCK-regulated circadian transcription in peripheral tissues, we performed microarray analyses using liver RNA isolated from Clock mutant mice. We also compared expression profiles with those of Cryptochromes (Cry1 and Cry2) double knockout mice. We identified more than 100 genes that fluctuated from day to night and of which expression levels were decreased in Clock mutant mice. In Cry-deficient mice, the expression levels of most CLOCK-regulated genes were elevated to the upper range of normal oscillation. Most of the screened genes had a CLOCK/BMAL1 binding site (E box) in the 5′-flanking region. We found that CLOCK was absolutely concerned with the circadian transcription of one type of liver genes (such as DBP, TEF, and Usp2) and partially with another (such as mPer1, mPer2, mDec1, Nocturnin, P450 oxidoreductase, and FKBP51) because the latter were damped but remained rhythmic in the mutant mice. Our results showed that CLOCK and CRY proteins are involved in the transcriptional regulation of many circadian output genes in the mouse liver. In addition to being a core component of the negative feedback loop that drives the circadian oscillator, CLOCK also appears to be involved in various physiological functions such as cell cycle, lipid metabolism, immune functions, and proteolysis in peripheral tissues.

Effects of fat content in the diet on hepatic peroxisomes of the rat.

Effects of fat content in the diet on rat liver peroxisomes was examined. In the livers of rats fed for one week on the high-fat diet containing 30% fat, the cyanide-insensitive palmitoyl-CoA oxidation was accelerated to eight times that of control and the enzymic activities of catalase, carnitine acetyltransferase and carnitine palmitoyltransferase were elevated by the factors of 1.3, 5 and 2, respectively. In contrast, the activities of D-amino acid oxidase in addition to the three enzymes mentioned above were all lowered by 20% when the animals were maintained on a fat-free diet for the same period of time. It appears that the high-fat diet-induced increase in the activity of carnitine palmitoyltransferase is a result of the raised activity of this enzyme in mitochondria only while the apparent high activity reflects stimulation of carnitine acetyltransferase in all the subcellular fractions. Another notable effect of the high-fat diet was a remarkable increase in the quantity of a peroxisome-associated polypeptide which was separable by sodium dodecyl sulfate polyacrylamide gel electrophoresis. It is noteworthy that this effect of the high-fat diet resemble that of clofibrate. If the diet was deprived of fat, however, this polypeptide species, with an estimated molecular weight of 80 000, decreased to a level slightly lower than normal. On the basis of the electron micrographic criteria, the high-fat diet provoked a marked proliferation of hepatic peroxisomes.

Pitavastatin-Induced Thrombomodulin Expression by Endothelial Cells Acts Via Inhibition of Small G Proteins of the Rho Family

Objective—3-Hydroxyl-3-methyl coenzyme A reductase inhibitors (statins) can function to protect the vasculature in a manner that is independent of their lipid-lowering activity. The main feature of the antithrombotic properties of endothelial cells is an increase in the expression of thrombomodulin (TM) without induction of tissue factor (TF) expression. We investigated the effect of statins on the expression of TM and TF by endothelial cells. Methods and Results—The incubation of endothelial cells with pitavastatin led to a concentration- and time-dependent increase in cellular TM antigen and mRNA levels. In contrast, the expression of TF mRNA was not induced under the same conditions. A nuclear run-on study revealed that pitavastatin accelerates TM transcription rate. The stimulation of TM expression by pitavastatin was prevented by either mevalonate or geranylgeranylpyrophosphate. Specific inhibition of geranylgeranyltransferase-I and Rac/Cdc42 by GGTI-286 and Clostridium sordellii lethal toxin, respectively, enhanced TM expression, whereas inactivation of Rho by Clostridium botulinum C3 exoenzyme was ineffective. Conclusions—Statins regulate TM expression via inhibition of small G proteins of the Rho family; Rac/Cdc42. A statin-mediated increase in TM expression by endothelial cells may contribute to the beneficial effects of statins on endothelial function.

Heparin-like glycosaminoglycan is a receptor for Antithrombin III-dependent but not for thrombin-dependent prostacyclin production in human endothelial cells

Antithrombin III (ATIII) induced a marked increase in prostacyclin (PGI2) release from cultured human umbilical vein endothelial cells (HUVEC) after incubation for more than 2 hr and the induction continued for 8 hr, while thrombin induced the increase within 10 min. ATIII-dependent production of PGI2 was abolished by addition of heparin, but pretreatment of HUVEC with polyclonal antibody against thrombomodulin could not prevent the PGI2 productions by ATIII and thrombin. ATIII-dependent PGI2 production was significantly inhibited by pretreatment of HUVEC with beta-D-xylosides or heparitinase, though neither pretreatment affected thrombin-induced PGI2 production. After treatment of HUVEC with 1 micrograms/ml cycloheximide. ATIII-dependent PGI2 production was completely abolished. These results indicate that the mechanism of the induction of PGI2 production by ATIII involves heparin-like glycosaminoglycans on HUVEC and the stimulation of synthesis of a protein related to PGI2 production. The ATIII-induced PGI2 production is very different from that induced by thrombin.

Thrombomodulin Is a Clock-controlled Gene in Vascular Endothelial Cells

Cardiovascular diseases are closely related to circadian rhythm, which is under the control of an internal biological clock mechanism. Although a biological clock exists not only in the hypothalamus but also in each peripheral tissue, the biological relevance of the peripheral clock remains to be elucidated. In this study we searched for clock-controlled genes in vascular endothelial cells using microarray technology. The expression of a total of 229 genes was up-regulated by CLOCK/BMAL2. Among the genes that we identified, we examined the thrombomodulin (TM) gene further, because TM is an integral membrane glycoprotein that is expressed primarily in vascular endothelial cells and plays a major role in the regulation of intravascular coagulation. TM mRNA and protein expression showed a clear circadian oscillation in the mouse lung and heart. Reporter analyses, gel shift assays, and chromatin immunoprecipitation analyses using the TM promoter revealed that a heterodimer of CLOCK and BMAL2 binds directly to the E-box of the TM promoter, resulting in TM promoter transactivation. Indeed, the oscillation of TM gene expression was abolished in clock mutant mice, suggesting that TM expression is regulated by the clock gene in vivo. Finally, the phase of circadian oscillation of TM mRNA expression was altered by temporal feeding restriction, suggesting TM gene expression is regulated by the peripheral clock system. In conclusion, these data suggest that the peripheral clock in vascular endothelial cells regulates TM gene expression and that the oscillation of TM expression may contribute to the circadian variation of cardiovascular events.

Enhancement of peroxisomal β-oxidation in the liver of rats and mice treated with valproic acid

The effects of valproic acid on peroxisomal beta-oxidation and on lipid levels of liver and serum in the rat and mouse were studied. When the animals were fed diet containing 1% valproic acid for 2 weeks, the activity of peroxisomal beta-oxidation increased 4-fold in the rat liver and 2-fold in the mouse liver. Other peroxisomal enzymes such as catalase and urate oxidase also increased by the treatment though to a lesser extent than beta-oxidation. The contents of triglyceride and cholesterol in the serum decreased significantly in the rat but not in the mouse. The time course curves of the activities of cyanide-insensitive palmitoyl-CoA oxidation and carnitine-dependent palmitoyltransferase indicated that peroxisomal beta-oxidation was enhanced more rapidly than that of mitochondrial. The distributions of these enzymes were not changed by the treatment with valproic acid, though increases in liver weight and protein content were observed. These results indicate that the action of valproic acid in enhancing hepatic beta-oxidation is similar to that of clofibrate and other hypolipidemic drugs.

Clock mutation affects circadian regulation of circulating blood cells

Background Although the number of circulating immune cells is subject to high-amplitude circadian rhythms, the underlying mechanisms are not fully understood. Methods To determine whether intact CLOCK protein is required for the circadian changes in peripheral blood cells, we examined circulating white (WBC) and red (RBC) blood cells in homozygous Clock mutant mice. Results Daytime increases in total WBC and lymphocytes were suppressed and slightly phase-delayed along with plasma corticosterone levels in Clock mutant mice. The peak RBC rhythm was significantly reduced and phase-advanced in the Clock mutants. Anatomical examination revealed hemoglobin-rich, swollen red spleens in Clock mutant mice, suggesting RBC accumulation. Conclusion Our results suggest that endogenous clock-regulated circadian corticosterone secretion from the adrenal gland is involved in the effect of a Clock mutation on daily profiles of circulating WBC. However, intact CLOCK seems unnecessary for generating the rhythm of corticosterone secretion in mice. Our results also suggest that CLOCK is involved in discharge of RBC from the spleen.

Circadian clock molecules CLOCK and CRYs modulate fibrinolytic activity by regulating the PAI-1 gene expression

Summary.  Disruptions of circadian rhythms are associated with the development of many disorders. However, whether a disruption of the circadian clock can cause anomalies of the hemostatic balance remains unknown. The present study examines coagulation and fibrinolytic activities in circadian clock mutants, a homozygous Clock mutant and Cry1/Cry2 double knockout (Cry1/2‐deficient) mice. The euglobulin clot lysis time (ELT) showed circadian variations that peaked at 21:00 (early night) in wild‐type mice, suggesting that fibrinolytic activity is lowest at this time. The ELT was continuously reduced in Clock mutants, while the ELT was significantly increased and did not differ between day and night (9:00 and 21:00) in Cry1/2‐deficient mice. The prothrombin time (PT) and activated partial prothrombin time (APTT) were constant in all genotypes. To identify which factors cause the loss of ELT rhythm, we measured fibrinolytic parameters in Clock mutant and Cry1/2‐deficient mice. The robust circadian fluctuation of plasma plasminogen activator inhibitor 1 (PAI‐1) that peaked at early night was damped to trough levels in Clock mutant mice. On the other hand, PAI‐1 levels in Cry1/2‐deficient mice remained equivalent to the peak levels of those in wild‐type mice at both 9:00 and 21:00. Circadian changes in plasma PAI‐1 levels seemed to be regulated at the level of gene expression, because the plasma PAI‐1 levels in Clock mutant and Cry1/2‐deficient mice were closely correlated with the level of PAI‐1 mRNA transcript in these mice. Plasma plasminogen and hepatic mRNA levels were not rhythmic in wild‐type mice, and continuously higher in Clock mutant than in wild‐type or Cry1/2‐deficient mice. In contrast, the activity and mRNA levels of tissue type plasminogen activator (t‐PA), plasma levels and mRNA levels of plasminogen, and plasma levels of α2 plasmin inhibitor (α2PI) in all genotypes were constant throughout the day. Coagulation parameters such as factor VII, factor X, prothrombin and fibrinogen remained constant throughout the day, and were not affected by clock gene mutations. These results suggest that circadian clock molecules play an important role in hemostatic balance by regulating the fibrinolytic systems.

Ketogenic Diet Disrupts the Circadian Clock and Increases Hypofibrinolytic Risk by Inducing Expression of Plasminogen Activator Inhibitor-1

Objectives—Metabolic disorders such as diabetes and obesity are considered risk factors for cardiovascular diseases by increasing levels of blood plasminogen activator inhibitor-1 (PAI-1). Ketogenic diets (KDs) have been used as an approach to weight loss in both obese and nonobese individuals. We examined circadian changes in plasma PAI-1 and its mRNA expression levels in tissues from mice fed with a KD (KD mice), to evaluate its effects on fibrinolytic functions. Methods and Results—Two weeks on the kDa increased plasma levels of free fatty acids and ketones accompanied by hypoglycemia in mice. Plasma PAI-1 concentrations were extremely elevated in accordance with mRNA expression levels in the heart and liver, but not in the kidneys of KD mice. Circadian expression of PAI-1 mRNA was phase-advanced for 4.7, 7.9, and 7.8 hours in the heart, kidney, and adipose tissues, respectively, as well as that of circadian genes mPer2 and DBP in KD mice, suggesting that peripheral clocks were phase-advanced by ketosis despite feeding ad libitum under a periodic light-dark cycle. The circadian clock that regulates behavioral activity rhythms was also phase-advanced, and its free-running period was significantly shortened in KD mice. Conclusions—Our findings suggest that ketogenic status increases hypofibrinolytic risk by inducing abnormal circadian expression of PAI-1.

Cyclic AMP increases thrombomodulin expression on membrane surface of cultured human umbilical vein endothelial cells

Dibutyryl-cyclic AMP (Bt2cAMP; final concentration 1-5 mM) or beraprost sodium (synthetic prostacyclin, 100 nM) enhanced the expression of thrombomodulin (TM; an anticoagulant factor of endothelial cells) on the membrane surface of cultured human umbilical vein endothelial cells up to 1.4 times over the control within 9 hrs after the treatment, while the expression fell below the control level at 12 hrs and thereafter. 8-Bromo-cAMP (final concentration 1-5 mM) or 3-isobutyl-1-methylxanthine (IBMX; an inhibitor of phosphodiesterase; final concentration 10-1000 microM) enhanced the expression of TM on the cell surface at 12 hrs after the treatment. The enhancement of TM expression caused by Bt2cAMP was inhibited by incubation with phorbol 12-myristate 13-acetate. These results suggest that cAMP stimulates expression of TM in the endothelial cells.