Temporal variations of coagulation factor VII activity in mice are influenced by lighting regime

It was recently reported that the circadian clock machinery controls plasma levels of factor (F) VII, the serine protease triggering blood coagulation. Here, by exploiting the mouse model, this study showed that variations of photoperiod (i.e., winter or summer conditions or simulated chronic jetlag conditions) have a strong impact on plasma FVII activity levels. Under conditions mimicking summer or winter photoperiods, FVII activity showed a clear 24 h rhythmicity. Interestingly, mean daily FVII activity levels were significantly reduced in mice exposed to summer photoperiods. Behavioral activity rhythms under both photoperiods were synchronized to LD cycles, and the amount of activity per 24 h was comparable. The authors also investigated the influence of chronic jetlag (CJL) on the FVII activity rhythms, which can be easily mimicked in mice through continuous abrupt shifts in the lighting schedule. The exposure of mice to simulated CJL of either consecutive westward or consecutive westward and eastward flights for 15 days did not abolish the behavioral activity rhythms but was associated with a period significantly different from 24 h. Intriguingly, both types of CJL exerted a strong influence on FVII activity rhythms, which were virtually suppressed. Moreover, the mean daily FVII activity was significantly lower in the CJL than in the winter photoperiod condition. Taken together, these findings in mice provide novel insights into the modulation of FVII activity levels, which might have implications for human pathophysiology.