Effect Of Circadian Rhythm On Sepsis In Mice Induced By High-dose LPS

The circadian rhythm is an approximately 24-hour periodical oscillation that organisms have evolved to adapt to changes in the earth's environment.It is driven by an autonomous biological clock in the organism.The circadian clock is regulated by a transcription-translation negative feedback loop composed of transcriptional regulatory elements.Its core is the transcriptional activation complex CLOCK-BMAL1 and transcriptional repressors PER and CRY.The biological clock system in mammals can regulate and influence most of the processes of physiological reactions in the body,including immune responses.The SCN of the mammalian hypothalamus is called the “master circadian pacemaker”,which acts as a central rhythm oscillator to synchronize and regulate other peripheral rhythm oscillators in the body.The circadian rhythm is found in a variety of immune cells and affects the immune response by regulating the secretion of cytokines.In addition,the inflammatory response can interfere with the operation of the internal biological clock.When the cell is stimulated by LPS,the protein levels of CLOCK,REV-ERB? and BMAL1 in the cell will drop rapidly,which indicates the disturbance of the biological clock.In addition,some scholars pointed out that the circadian rhythm itself is an innate immune sensor,when the body is infected,it will automatically transform the cells into a pro-inflammatory state.Sepsis is a systemic inflammatory response syndrome,which can cause a series of damage to the body,and death will occur in severe cases.In recent decades,the incidence of sepsis has been increasing,and its death toll has been increasing.The basis of sepsis is inflammation imbalance.After pathogens invade the body,macrophages will engulf the pathogens and produce a series of pro-inflammatory factors,which will trigger a cytokine storm and activate the innate immune system.LPS is the strongest symptom among the many conditions in which the organism is induced to sepsis.After the LPS molecule enters the body,it will be delivered to the TLR4 receptor,which then recruits a series of kinases,and finally activates the expression of pro-inflammatory cytokines.In recent years,studies have found that injecting LPS into mice at different times of the day to induce sepsis will lead to different mortality in mice.Among them,the circadian rhythm of immune cells will affect the diurnal changes of the severity of sepsis in mice.However,the previous studies only simply and partially demonstrated the differences in inflammation in mice at different time points,lacked specific and comprehensive exploration of the physiological and biochemical changes in mice,and failed to find the decisive factors and internal mechanisms of circadian rhythms affecting the severity of sepsis.This subject induces sepsis through intraperitoneal injection of LPS to mice at different time points of the day,and uses metabolic cages to detect the mortality,metabolism,body temperature changes,food and water intake and exercise behavior of mice 5 days after injection.Techniques such as paraffin section and q PCR were used to detect liver tissue damage,pro-inflammatory cytokines,Toll-like receptors,and circadian gene expression in mice.In addition,we also stimulated macrophage RAW cells with LPS at different time points to observe the difference in inflammatory response of RAW cells.We found that mice injected with LPS during the day(ZT6)had a higher mortality rate,lower metabolic and body temperature levels,more severe liver tissue damage,more disordered circadian rhythms,and lower cytokine expression than night(ZT18)injections.In addition,compared with the ZT6 experimental group,the ZT18 experimental group has a lower degree of body temperature decrease and lasts longer in the hypothermic state.We guess that the body temperature level has a more direct effect on the survival rate of mice than the cytokine expression level.On macrophages,RAW cells will show significantly different inflammatory manifestations after being stimulated by LPS at different times.Compared to the lowest point,more severe inflammation occurs at the highest point of the rhythm shock,and RAW cells are phagocytosed or combined with LPS.The number of molecules does not directly affect the severity of cell inflammation.