Effects Of Exercise Under Hindlimb Unloading On Circadian Rhythms In Mice

Background and ObjectiveThe circadian rhythm was biological organisms to resist the natural environment in theevolutionary process and gradually formed the inner body and the natural environmentperiodic change of the circadian rhythm. Circadian rhythms of the central pacemaker pointlocated in the nucleus supraopticus hypothalami, as the supraoptic nuclear received the signalregulating hormones and body fluids, etc., and then the signal transmission to the peripheralorganization of liver, kidney, spleen, etc., so that the peripheral tissue was rhythmic shocks. Inrecent years, studies have shown that circadian rhythms have an important role in theanti-tumor therapy, the regulation of sleep and improve the work performance of theastronauts. In this study, it was assayed that the effects of hindlimb unloading(induced by tailsuspension) on plasma melatonin and corticosterone and liver tissue clock, bmal1, per1, per2,cry1, cry2 mRNA expression rhythmicity in C57 mice in constant darkness(darkness:darkness, DD) conditions.Then circadian rhythm expression under simulatedmicrogravity was investigated.MethodsWith 1 week of normal light/dark schedule (light:darkness=12h:12h) pretreatment, C57mice were tail suspended with -30°head down in DD environment. Plasma and tissues wereobtained at consecutive time points during the 12th, 13th and 14th testing days with equalinterval of 4h. Hormone were used ELISA method to test the Concentration of melatonin andcorticosterone, Total RNA was extracted and reverse transcription real-time polymerase chainreaction (RT-PCR) was used to test the rhythmicity patterns of clock、bmal1、per1、per2、cry1、cry2 mRNA expression. Results(1) In constant darkness conditions, tail suspension group and control group in plasmamelatonin and corticosterone concentrations had no significant difference (P>0.05).(2) Circadian rhythm of clock and bmal1 mRNA expression was found in each testing daywith similar peak phase in both TS and control (Con) mice. Furthermore, compared with Con,the peak phase of clock gene mRNA level in TS advanced approximately 4h, and theamplitude of bmal1 gene mRNA level significantly reduced at ZT2 (zeitgeber time) and ZT6(P<0.05).(3) The maximum and minimum value of mRNA relative expression level of per1 andper2 were both found approximately at the time point ZT14-18 and ZT10 in the liver of tailsuspended group and control.(4) The maximum and minimum value of mRNA relative expression level of cry1 andcry2 were both found approximately at the time point ZT14 and ZT6 in the liver of tailsuspended group and control.ConclusionsIn DD conditions, liver tissue expresses clock and bmal1 mRNA with evident circadianrhythm, and TS treatment (exercise under hindlimb unloading) could lead to the advancementof clock gene’s peak phase and the decrease of bmal1 gene’s amplitude; per1 and per2, cry1and cry2 displayed a synchronous circadian transcription characteristics, separately.