| Objective:To explore the effect and its possible mechanism of circadian rhythm dysfunction on cognitive impairment in MPTP-induced Parkinson’s disease(PD)mouse model,and to clarify the role of circadian rhythm dysfunction in the occurrence and development of cognitive impairment in PD.Methods:C57BL/6 mice were injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridinen(MPTP)as a PD animal model,and intraperitoneally injected with the same amount of saline as control.Then they were randomly divided into 2 groups:4 hours of light/20 hours of darkness biorhythm disruption or 12 hours of light/12 hours of darkness normal biorhythm control for 2 months.The motor ability of the mice was tested by rotarod test,pole test and open field test,and the cognitive function of the mice was tested by novel object recognition test and Morris water maze test.The samples of brain tissue were collected at 6:00,12:00,18:00,24:00(0:00)respectively.Quantitative Real-time PCR(QPCR)was used to examine the mRNA expression levels of clock genes,such as Clock,Bmal1,Per2 and Rora in the Suprachiasmatic nucleus(SCN).Western blotting(WB)was used to measure the expression of Tyrosine hydroxylase(TH)in striatum.WB was used to determine the expression of synapsinl,PSD-95,α-synuclein and Ser129-phosphorylated α-synuclein in hippocampus.QPCR was used to detect the mRNA expression levels of inflammatory factors,such as Tumor necrosis factor-α(TNF-α),Interleukin-1β(IL-1β),Inducible nitric oxide synthase(iNOS)and Cyclooxygenase-2(COX-2)in hippocampus.Immunofluorescence(IF)was used to assess the expression of Ionized calcium binding adapter molecule 1(IBA1)in hippocampus.The phosphorylation of IKK,P65,and IκB of NF-κB signal pathway in hippocampus were estimated by WB.Results:After Chronic circadian rhythm dysfunction,the mRNA level of Bmall decreased in the SCN compared with control group at 6:00 and 12:00(P<0.05),and the mRNA level of Rorα was lower than that of the control group at 12:00(P<0.05).MPTP induced mice had motor deficits in the rotarod test and pole test(P<0.01).Chronic circadian rhythm dysfunction impaired the motor ability of MPTP induced mice in the open field test(P<0.0001).MPTP induced mice had cognitive deficits in the novel object recognition test and Morris water maze test(P<0.01),and MPTP induced mice with circadian rhythm dysfunction had more severe cognitive impairment(P<0.05).MPTP induced mice had a reduction of TH expression in striatum(P<0.0001),and the reduction was more severe in MPTP induced mice with circadian rhythm dysfunction(P<0.05).Compared to MPTP mice,α-synuclein and Ser129-phosphorylated α-synuclein in the hippocampus of MPTP induced mice with circadian rhythm dysfunction increased(P<0.05);the expression of iNOS,COX-2,IL-1β increased(P<0.05)and microglia were activated(P<0.05);the phosphorylation of IKK,P65,and IκB related to the NF-κB signaling pathway increased(P<0.05).Conclusions:Circadian rhythm dysfunction can increase the accumulation ofα-synuclein in the hippocampus of PD mice induced by MPTP,and aggravate the neuroinflammatory response,resulting in further cognitive decline.Therefore,circadian rhythm dysfunction can exacerbate cognitive impairment in PD. |
