BRIEF COMMUNICATIONCLOCK regulates circadian platelet activity
Introduction
Circadian rhythms have been implicated in the genesis of cardiovascular and cerebral diseases. In fact, myocardial infarction, cardiac arrhythmias, sudden cardiac death and stroke have peak incidences in the morning hours and lower incidences at night [1]. Platelet hyperaggregability coupled with hypofibrinolysis of blood is associated with the increased risks of cardiovascular events in the morning [2].
Clock was the first clock gene to be identified in vertebrates by forward mutagenesis using N-ethyl-N-nitrosourea in a behavioral screening [3]. When transferred from a light-dark cycle to constant darkness, the behavioral periodicity of homozygous Clock mutants becomes unusually long [4]. Clock encodes a basic helix-loop-helix (bHLH)-PAS transcription factor that is a positive regulator of an autoregulatory transcription-translation feedback loop [5]. CLOCK forms heterodimers with BMAL1 (a bHLH-PAS transcription factor) and transactivates other clock genes and a lot of clock-controlled genes that are involved in various physiological functions such as lipid metabolism [6], obesity [7], [8], cell cycle [9] and the generation of cancer [10]. Studies from rodents have shown that Clock mutation involved in many physiological functions. We have already reported that circadian clock proteins, such as CLOCK and CRYs, regulate the circadian expression of plasminogen activator inhibitor-1 (PAI-1), which is the principal determinant of the fibrinolytic activity [11]. Recently, we showed that thrombomodulin, an endothelial anticoagulant molecule, expresses in a circadian manner in both mRNA and protein levels [12]. Furthermore, the circadian expression of thrombomodulin mRNA was directly transactivated by CLOCK protein [12]. These observations suggest that circadian changes in blood coagulation and fibrinolytic activities are regulated by molecular clock.
Although the circadian rhythm of platelet activity is a highly regular and reproducible phenomenon in humans, as is the case for many physiological rhythms, it may result from the interactions among various endogenous rhythms with environmental influences [2]. To elucidate the circadian regulation of platelet functions and its involvement in hemostatic activity, we examined platelet aggregation in the circadian clock-disrupted Clock mutant mice [4], [13].
Section snippets
Materials
Adenosine 5′-diphosphate (ADP) and collagen were purchased from Sigma (St. Louis, MO) and Nycomed Arzneimittel GmbH. (München, Germany), respectively.
Animals
The mouse model used this study was described in a previous report [13]. Male mice were housed under a 12 h light–12 h dark cycle [LD 12:12; lights on at 07:00] and given food and water ad libitum. A white fluorescent lamp was the source of light during the day (150–200 lux at the level of the cages).
Tail bleeding
Mice were anesthetized and placed in a
Results
Circadian fluctuation in tail bleeding, which peaked at midnight and decreased during the day, was observed in wild-type (WT) mice (P = 0.0041) (Fig. 1A). Circadian rhythm of tail bleeding was remarkably weaker in Clock mutant mice (P > 0.05), and the bleeding was continuously low at almost the trough levels of WT mice.
The number of circulating platelets fluctuated slightly but significantly (P = 0.0361) with a peak in the afternoon in WT mice (Fig. 1B). The platelet number was significantly reduced
Discussion
We have demonstrated circadian fluctuation in hemostatic activity, which peaked in the morning, in WT mice. This fluctuation seemed to result from platelet aggregability, which was also increased in the morning. These circadian changes were completely abolished in Clock mutant mice, suggesting that these time-of-day differences in hemostatic activity were governed by the endogenous circadian clock. Furthermore, hemostatic activity was continuously increased by the Clock mutation, although the
Summary
In this study, to elucidate the circadian regulation of platelet functions and its involvement in hemostatic activity, we examined platelet aggregation in the Clock mutant mice. Circadian fluctuation in tail bleeding observed in WT was remarkably weaker in Clock mutant mice, and the bleeding was continuously low at almost the trough levels of WT mice. Day/night fluctuations in the maximum aggregation rates of platelet induced by ADP and collagen observed in WT mice were not rhythmic and
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Cited by (27)
Impact of the circadian clock on fibrinolysis and coagulation in healthy individuals and cardiovascular patients – A systematic review
2021, Thrombosis ResearchCitation Excerpt :A recent study by Hemmeryckx et al. [48] showed that the clock gene Bmal1 has significantly influence on the circadian regulation of coagulation by showing that Bmal1 deficiency in mice shows an early prothrombotic risk characterized by elevated plasma FVII, FVIII and fibrinogen levels in combination with endothelial dysfunction. This study by Hemmeryckx et al. together with previous studies showing hyperaggregability of platelets and PAI-1 level disturbances in CLOCK deficiency [49], determines the link between circadian disturbances and disturbances of hemostasis which supports the clot risk in circadian disruption. However, the understanding of the pathways between the clock genes and parameters of coagulation and fibrinolysis is still unknown.
Circadian Rhythm of Infarct Size and Left Ventricular Function Evaluated with Tissue Doppler Echocardiography in ST Elevation Myocardial Infarction
2016, Heart Lung and CirculationCitation Excerpt :It is well-established that sympathetic tone [28], coagulation factors [29], vascular tone of the coronary artery [30] and hormones such as aldosterone and cortisol [2] have a time-dependent pattern. Previous studies have shown that clock genes regulate related hormones; therefore, adverse cardiovascular events tend to occur in the early morning [31,32]. A recent study showed a relationship between the cardiomyocyte circadian clock and myocardial reperfusion injury tolerance [7].
Lesion size and behavioral deficits after endothelin-1-induced ischemia are not dependent on time of day
2013, Journal of Stroke and Cerebrovascular DiseasesCitation Excerpt :In addition, many factors that influence the prevalence of stroke in humans peak after waking, and we expected that this phase would be most sensitive to stroke. The species used in the present study exhibits similar circadian variation, although in antiphase to humans given that rats are nocturnal.33-37 The combined effect of high GABAergic tone during the early part of the sleep phase and the trough in many factors that influence stroke prevalence (eg, blood pressure, heart rate, and catecholamine levels) was predicted to decrease the severity of the stroke at this phase.
The clock gene Per2 is required for normal platelet formation and function
2011, Thrombosis ResearchCitation Excerpt :Loss of Per2 function resulted in enhanced Clock expression [13]. In Per2-null mice the number of circulating platelets decreased by half, suggesting clock level was not directed related to platelets formation [27]. Potentially, loss of Clock function caused to impaired Per2 expression, influencing normal platelet formation and function.
Carotid endarterectomy performed in the morning is associated with increased cerebral microembolization
2009, Journal of Vascular SurgeryCitation Excerpt :In addition, circadian variations in epinephrine levels and in platelet activity are not purely posture related; catecholamine levels vary depending on the time of day as well being influenced by stressful events such as surgery.44 Recent studies have also suggested regulation of diurnal platelet function at a molecular level, with genes such as circadian locomotors output cycles kaput protein (CLOCK) that are normally involved in the regulation of mammalian circadian rhythms influencing platelet activity directly.45 It should also be recognized that additional hemostatic factors showing diurnal variation in activity are likely to be of some importance in the observed morning peak of microemboli.
- [1]
N.O. K.O. and T.S. contributed equally to this study.