Period2 Mediates Light-Dark Cycle To Regulate Behavior And Immune Performance In Mice

Regular environmental light-dark(LD)cycle-regulated period circadian clock 2(Per2)gene expression is essential for circadian oscillation.Mutations in PER2 will disturb sleep rhythm,lead to changes in immune and behavioral rhythms and even cause cancer.However,the specific role and mechanism of Per2 in the regulation of circadian clocks,behavior and immunity is not clear.Herein,we combined environmental LD cycles with PER2 gene knockout to investigate how Per2 mediates light-dark cycle to regulate behavior and immune performance in mice.Experiment 1 Effects of different light-dark cycle on the behavior and immune performance of miceIn this experiment,the changes of immune performance and behavior of mice after different light-dark cycles were studied by measuring the daily behavior of mice,the level of Open Field Test and the level of serum corticosterone,blood routine,blood biochemistry and thymus index,spleen index.Thirty 8-week-old mice were divided into five groups:group A 0h:24h(0h light:24h dark),group B 8h:16h(8h light:16h dark),group C 12h:12h(12h light:12h dark),group D 16h:8h(16h light:8h dark)and group E 24h:0h(24h light:0h dark).Except for light,feeding conditions are all the same.The daily behavior of mice in each group,such as eating,drinking,licking and standing,were observed,then the mice were carried out the Open Field Test.The content of corticosterone,blood routine,blood biochemistry,thymus index and spleen index were further determined.The results showed that:(1)when the lightdark cycle reached 16h:8h,the duration of staying in the central area in the Open Field Test in this group was significantly longer than that in other groups(P<0.05),and the content of corticosterone in this group was significantly different from that in the mice with the lightdark cycle of 12h:12h(P<0.05);(2)when the light-dark cycle reached 24h:0h,the number of standing times of the daily behavior indexes and the number of crossing into the central area times in the Open Field Test in this group were significantly higher than those in other mice.and the levels of corticosterone in this group was significantly higher than that in the mice with the light-dark cycle of 12h:12h or 0h:24h(P<0.05);(3)The number of leukocytes in group A and B was significantly lower than that in group C,D and E(P<0.05),while the percentage of lymphocytes and the content of albumin and globulin in in group A was significantly higher than that in group B,C,D and E(P<0.05);(4)the thymus index and spleen index of group E were significantly higher than those of the other four groups(P<0.05).Overall,this shows that in order to reduce the occurrence of stress reaction in mice,the lightdark cycle of feeding should be controlled to below 16h:8h.The results suggest that different light cycle had a significant impact on the immune performance of mice.The immune data and immune organ index of mice under full dark treatment were lower than those of other groups,and the immune performance was weak,while that of normal light group was stronger.Experiment 2 Effects of Period2 knockout and light-night cycle on the immune performance of miceIn order to explore the effects of rhythm genes and light-dark cycles on the immune performance of mice.Six wild-type(CON)mice and six homozygous(KO)with systemic PER2 gene knockout were selected in this experiment.The animals were reared under a short light(SL)cycle(8h light:16h dark)or normal light-dark(NLD 12h light:12h dark),and the level of blood routine,biochemical Indicators,blood lipids,Toll-like receptors,interleukins,nuclear factor kappa B and myeloid differentiation factor 88 in each group were measured,Thymus index was measured.The results showed that compared with CON mice,the level of neutrophils in PER2 knockout mice was significantly decreased(P<0.05),while the blood glucose was significantly increased(P<0.05).Compared with CON mice,PER2 knockout significantly upregulated expression of toll-like receptor 2,nuclear factor ?B and tumor necrosis factor a in colon epithelial tissue(P<0.05).In terms of cecal epithelial pathwayrelated genes,KO significantly upregulated expression of toll-like receptor 2 and toll-like receptor 4(all P<0.05)but did not impact expression of Myd88 or IL-6(P>0.05)both under NLD and SL.Short light did not alter expression of colonic and cecal epithelial inflammatory pathway-related genes compared with NLD(all P>0.05),except upregulating the expression of TNF-? gene of KO mice in cecal epithelium(P<0.05).In conclusion,PER2 knockout in mice resulted in decreased immune indexes and increased blood glucose and these alterations may potentially lead to inflammation of the large intestine.Short-light treatment had minor impact on intestinal immune function.In conclusion,different light cycles have significant effects on behavior and the immune performance in mice.The immune data and immune organ index of mice under full dark treatment were lower than those of other groups,and the immune performance was weak,while that of normal light group was stronger.When the light-dark cycle reached 16h:8h,the duration of staying in the central area in the Open Field Test in this group was significantly longer than that in other groups,and the content of corticosterone in this group was significantly different from that in the mice with the light-dark cycle of 12h:12h.In addition,the knockout of PER2 gene may affect the glucose metabolism and immune function of mice.KO decreased the level of neutrophils in mice while increased the blood glucose.In terms of inflammatory and barrier functions,KO increased the expression of TLR2?NF-?B and TNFa in the colon while it had no impact on IL-6 or MYD88.Besides,KO increased the expression of TLR2 and TLR4 in the cecum.These alterations may potentially lead to inflammation of the large intestine.Short-light treatment had minor impact on intestinal immune function.