Downregulation of Clock in circulatory system leads to an enhancement of fibrinolysis in mice.

As a main component of circadian genes, clock plays not only an important role in circadian rhythm but also in the regulation of many physiological systems. The dysfunction of clock genes is associated with the development of various disorders. Many studies have investigated the association between clock genes and blood coagulation and the fibrinolytic system. The present study was designed to investigate the effect of downregulation of circulatory Clock on blood coagulation and fibrinolysis at the initial stage of active phase in male mice. Downregulation of the expression of the Clock gene by siRNA and, subsequently, its effect on the thrombotic potential and the expression of relative coagulative and/or fibrinolytic factors were investigated. It was found that the Clock interfered mice were less liable to thrombosis and showed prolonged prothrombin time (PT) and activated partial thromboplastin time (APTT) at Zeitgeber time (ZT) 15. Meanwhile, these mice also showed an increase in factor VII (FVII) and a decrease in thrombomodulin (TM) and plasminogen activator inhibitor 1 (PAI-1) at ZT 15 at both transcriptional and translational levels. PT, APTT and mRNA expressions of fvii, tm and pai-1 were analyzed with the least-squares fit of a 24-h cosine function by single cosinor method; no circadian rhythm was determined in PT and APTT, and a higher amplitude of fvii in the Clock RNAi group was found with a circadian phase shift, while lower amplitudes of tm and pai-1 were found in the Clock RNAi group with nearly no phase shift. All these results suggest that downregulation of the Clock gene in circulatory system has an effect on factors involved in both blood coagulation and fibrinolysis resulting in an enhancement in mice. This may be considered as an indication that Clock regulates thrombotic homeostasis through the fibrinolytic system.