The Study On Tree Shrew Model Of Parkinson’s Disease Induced By Overexpressed A-synuclein A53T

Parkinson’s disease(PD)is a chronic,progressive,disabling neurodegenerative disease that results from selective degeneration of dopaminergic neurons in the substantia nigra(SN).It is a serious health risk for middle-aged and elderly people and is growing at the highest rate among neurological diseases.The pathological characteristics and clinical manifestations of PD are relatively clear at present,but its pathogenesis is not yet fully understood.There is no treatment available to improve the disease.To establish suitable animal models for PD is of great research value to promote the study of the pathogenesis of PD and drug development.Toxin-induced models cannot mimic the molecular pathology of PD.Most transgenic mouse models do not reproduce the typical features of PD.α-synuclein(α-syn)is a major component of the main pathology of PD-Lewy bodies(LBs),whose aggregation is critical for disease progression and plays an important role in both familial and sporadic PD.The establishment of animal models of PD based on α-syn is not only helpful for drug development and treatment,but also can mimic the disease changes of human PD.Studies on non-human primates(NHPs)in Parkinson’s disease are often used for preclinical evaluation of therapies due to high costs and ethical concerns.The physiological neurodevelopment of rodents is so different from that of humans that it is difficult to simulate human pathophysiological processes.The tree shrew which is a small animal closely related to primates,has the largest brain-to-body weight ratio of mammals.It is an ideal model for studying brain function and neurodegenerative diseases.Besides,the α-syn cDNA sequences of tree shrews and humans are strongly conserved.The secondary protein structure of α-syn is identical to that of humans and is consistent with the spatial similarity predicted for humans.Tree shrews may be a potential new animal model for studying the pathogenesis ofα-synopathy.In this study,an animal model of PD was established by injecting AAV2/9-EGFP-A53T-α-syn viral vector into the left brain SN of tree shrews using stereotaxic technique.There are 6 animals in each of the experimental and control groups.Open field test were performed on 12 tree shrews at 3 months.Serum was then collected from all these animals.Three animals were taken from both experimental and control groups for western blot assay.Three animals in the experimental group and two animals in the control group were used for pathological testing.Motor features(open field test),non-motor features(anxiety,depression and cognitive ability changes)and pathological changes(reduced number of SN dopaminergic neurons,LBs)emerged after modeling.These results demonstrate the feasibility of using the tree shrew which is a new experimental animal in establishing a animal model of PD.Results;1.The results of the open field test showed that the total distance decreased(P<0.01),the average speed decreased(P<0.01),and the total resting time decreased(P<0.001).It indicated that α-syn overexpression led to a decrease of the voluntary motor ability of animals,which developed anxiety and depression at the same time.2.SOD activity decreased(P<0.05)and MDA levels increased(P<0.05)in serum,indicating that α-syn overexpression led to elevated levels of oxidative stress.3.Western blot results showed increased expression of α-syn protein in SN and striatum(Str)(P<0.05).It indicates the effective expression of exogenous gene A53T-α-syn.BDNF protein expression reduced in the hippocampus(P<0.05),which suggests a decline in cognitive ability.MEF2D protein expression reduced in Str(P<0.05).Impaired autophagy occurred in the brain due to α-syn overexpression.Caspase-3 protein expression increased in SN and Str(P<0.01),which indicates enhanced apoptosis.4.Immunofluorescence results showed that EGFP and α-syn were expressed in SN and Str.This demonstrates that the viral vector has been injected into the SN and expressed along the nigrostriatal pathway.Immunohistochemical results showed an increase in the number of activated microglia(P<0.05)and astrocytes(P<0.01)at both SN and Str,which suggests an inflammatory response in the brain.The number of dopaminergic neurons in the SN of the left brain was significantly reduced(P<0.05),and LBs appeared with nerve fiber degeneration of Str.In conclusion,we successfully established the tree shrew Parkinson’s disease model by overexpressed α-synuclein A53T.Our results provide a novel animal model for the study of pathological mechanism,drug development and treatment of PD.