| Background:Parkinson’s disease(PD)is characterized by progressive degeneration of dopaminergic neurons within the substantia nigra compacta(SNpc)of the midbrain,accompanied by the abnormal aggregation of α-synuclein.Currently,levodopa replacement therapy is the common treatment of PD,which can alleviate symptoms.But it may produce many adverse reactions and can’t prevent or delay the development of PD.Therefore,it’s necessary for us to explore a drug that protects dopaminergic neurons.The etiology and pathogenesis of PD are complicated.And it has been reported that endoplasmic reticulum stress(ERS),autophagy and dysfunction of mitochondrial are involved in the pathogenesis of PD.Mounting evidence indicated that there are dysfunction of autophagy,activation of ERS and the abnormal aggregation of α-synuclein even post-translationally modification in the PD model in vitro and in vivo,which accelerates the apoptosis of dopaminergic neurons.Apelin is a kind of neuroendocrine peptide,and APJ(putative receptor protein related to the angiotensin receptor AT1)is proved to be the receptor of Apelin.Apelin/APJ system exists throughout the brain,including cerebral cortex,hippocampus,hypothalamus,SNpc and striatum(STR),and it plays an important role in many central nervous system diseases.In the present study,1-methy1-4-phenyl-1,2,3,6-tetrahydropyridin(MPTP)was used to construct PD animal model.The neuroprotective effect of Apelin-36 in PD model and possible mechanisms are explored in our work,and for the development of new drugs of PD,a theoretical basis may be provided.Objective:To investigate the neuroprotective effect of Apelin-36 in MPTP-induced PD mice model from the aspects of autophagy and ERS.Methods:Male C57BL/6 mice aged 9-11 weeks(weighting 23-27 g)were accommodated for 1 week.All the mice were randomly divided into control group(intraperitoneal saline injection for 5 days,intranigral saline injection by Alzet osmotic mini-pumps for 7 days),Apelin-36 group(intraperitoneal saline injection for 5 days,intranigral Apelin-36 injection by Alzet osmotic mini-pumps for 7 days),MPTP group(intraperitoneal MPTP injection for 5 days,intranigral saline injection by Alzet osmotic mini-pumps for 7 days)and Apelin-36+MPTP group(intraperitoneal MPTP injection for 5 days,intranigral Apelin-36 injection by Alzet osmotic mini-pumps for 7 days).The dose of MPTP was 25mg/kg/day and the dose of Apelin-36 was 0.5 μg/mice/day.The motor ability of mice was measured by rota-rod test.TH+neurons in the SNpc were measured by immunohistochemistry.The expression of TH,APJ,autophagy associated proteins(LC3B and p62),α-synuclein and ERS associated proteins(GRP78,CHOP,p-IRE1α,p-ASK1 and p-JNK)in the SNpc were determined by western blot assay.The expression of ERS marker proteins(GRP78 and CHOP)in the dopaminergic neurons were determined by double fluorescence immunostaining.Results:1.The time of latency to fall on the rod was significantly decreased in MPTP group compared with control group.However,the intranigral injection of Apelin-36 significantly increased the time of latency to fall on the rod in Apelin-36+MPTP group compared with MPTP group.2.The expression of APJ in the SNpc of MPTP-treated mice was significantly decreased compared with control group,and Apelin-36 markedly improved the APJ expression in the SNpc of MPTP-treated mice.3.Immunohistochemical assay showed that TH+neurons in the SNpc were significantly decreased in MPTP-treated mice.And western blot assay showed that the expression of TH was significantly decreased in the SNpc of MPTP-lesioned mice.The treatment of Apelin-36 significantly prevented the loss of TH+neurons in the SNpc,and reversed the TH expression in the SNpc of MPTP-lesioned mice.4.The expression of LC3B-Ⅱ was significantly decreased in the SNpc of mice in MPTP group compared with control group,as well as the increased p62 expression.Apelin-36 significantly increased the expression of LC3B-Ⅱ in the SNpc of mice treated with MPTP,and decreased the expression of p62.5.The expression of α-synuclein in the SNpc of MPTP-treated mice was significantly increased compared with control group.Apelin-36 markedly decreased the α-synuclein expression in the SNpc of MPTP-treated mice.6.The expression of GRP78,CHOP,p-IRE1α,p-ASK1and p-JNK were significantly increased in the SNpc of mice in MPTP group compared with control group.Furthermore,we found the increased GRP78 and CHOP in the dopaminergic neurons by co-localization of the above two proteins and TH in MPTP group compared with control group.Apelin-36 significantly decreased the expression of GRP78,CHOP,p-IRE1α,p-ASK1 and p-JNK in the SNpc of mice treated with MPTP.Similarly,Apelin-36 significantly decreased the GRP78 and CHOP expressions in the dopaminergic neurons of MPTP-lesioned mice by co-localization of the above two proteins and TH.Conclusion:Autophagy and ERS are involved in the neuroprotective effect Apelin-36 in MPTP-induced Parkinson’s Disease model mice. |
