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 alpha2
plasmin inhibitor (alpha2PI) 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.
