Neuroprotective Effects And Underlying Mechanisms Of Ginsenoside Rb1 In Parkinson's Disease

Parkinson's disease(PD)is a common neurodegenerative disease that mainly affects the human body's motor system.In the early stage,its main symptoms are motor symptoms such as resting tremor,muscle rigidity and bradykinesia.In the late stage,patients will develop nonmotor symptoms such as dementia,anxiety,sleep disturbance,and impaired cognitive functions.Due to the impaired motor functions,PD patients cannot take care of themselves,which places a heavy burden on the patients,their families and even the whole society.The popular medications for PD treatment include levodopa,dopamine receptor agonists,and monoamine oxidase B inhibitors,etc.However,these medications cannot prevent the development of PD,and long-term use causes side effects such as nephrotoxicity,edema,and gastrointestinal reactions,etc.So it is urgent to find the effective medicines.Traditional Chinese medicine has played an irreplaceable role in people's health for thousands of years,after Tu Yoyo won the Nobel Prize in Physiology and Medicine for discovering artemisinin in 2015,a new round of researches in Chinese medicine is popular both in China and abroad.Then we searched the library of traditional Chinese medicine,tried to find a drug which can potentially improve or cure PD.After reading a lot of papers and performing pre-experiments,we chose Ginsenoside Rbl,an active ingredient of Ginseng,to study its role in PD.Ginseng(Panax ginseng C.A.Mey.)is a perennial herbaceous plant of the genus Panax Ginseng.The main active ingredients of Ginseng include ginsenosides,alkaloids,polysaccharides,glucosides,and phenolic acids,etc.According to the different glycosides,more than 80 kinds of ginsenosides have been isolated from Ginseng,including Rbl,Rb2,Rc,Rd,Rg1,Rg2 and Re,etc.And Ginsenoside Rbl is dammarane-type triterpenoid saponin.Studies have shown that Rb1 has some neuropsychiatric effects such as central inhibition and stability,improving learning and memory and resisting cerebral ischemic injury.In this thesis,we focused on the role of Rb1 in PD.We used the neurotoxin 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP)to establish PD model mice,and we found that Rb1 can significantly improve the dyskinesia in PD mice.Also,the imbalance of the neural circuits is one of the main pathogenesis factors in PD,and there are two main pathways,the inhibitory pathway which is mediated by ?aminobutyric acid(GABA)and the excitatory pathway which is mediated by glutamic acid.Some papers have proved that the inhibitory neural pathways were significantly downregulated during the development of PD.Then we further investigated the effect of Rb1 on GABAergic synaptic transmission in the prefrontal cortex in PD mice.The data showed that Rbl can significantly increase the level of the inhibitory neurotransmitter GABA and regulate both GABAA and GABAB receptors.Rb1 can bind to the active site of GABAB receptor antagonist,inhibit the expression of presynaptic GABAB receptors,and promote the release of neurotransmitter GABA.At the same time,Rb1 can also interact with the transmembrane domain(TMD)of GABAA receptors,and promote the expression and function of postsynaptic GABAA receptors.In addition,Rbl can significantly up-regulate the expression of Gephyrin,the GABAA receptor anchoring protein,to further enhance GABAergic synaptic transmission in the prefrontal cortex.Rbl not only has effects on inhibitory synaptic transmission,but also plays a role in excitatory neural circuits.It is well known that apoptosis of dopamine neurons in the substantia nigra is the main mechanism of PD.The glutamate excitotoxicity is one of the important reasons for the apoptosis of dopamine neurons.The glutamate transporter-1(GLT-1)is expressed on astrocytes,and its main function is to eliminate excessive glutamate in the synaptic cleft to reduce glutamate excitotoxicity.We used AAV-GLT-1 shRNA virus to knock down GLT-1 on astrocytes in substantia nigra,and we found it can induce Parkinsonism phenotypes after knocking down GLT-1,such as imbalance in muscle strength and motor coordination functions,dopamine neurons injury,abnormal expression of related excitatory synaptic proteins,astrocytosis and microgliosis.Also,according to RNA sequencing analysis,we obtained more than two thousand potential differentially expressed genes(DEGs)with GLT-1 knockdown.The most obvious differences were calcium signaling pathway,ErbB signaling pathway,and MAPK signaling pathway,which provided us more references to study the relationship between PD and GLT-1.At the same time,using GLT-1 as the target,we found Rbl can significantly increase the expression of GLT-1 in PD mice brain,and promote the glutamate reuptake capacity in astrocytes,and significantly improve the dyskinesia in PD mice.Although the large accumulation of ?-synuclein is another typical pathogenesis of PD,in the normal circumstances,?-synuclein is a presynaptic protein,which plays an important role in neurotransmitter release and maintenance of learning and memory.Cognitive dysfunction is one of the non-motor symptoms of PD,in this thesis,we also studied the effect of Rb1 on the learning and memory function by regulating ?-synuclein in PD mice.First,we examined the effect of Rb1 on learning and memory in PD mice,the results showed that Rb1 can significantly improve the learning and memory in PD mice.In addition,Rb1 can significantly up-regulate the expression of ?-synuclein in the hippocampus,then influence the excitatory glutamatergic synaptic transmission which is mediated by AMPA receptors,including promoting the release of glutamate in presynapse,and up-regulating the expression and function of related excitatory synaptic proteins such as AMAP receptors,NMDA receptors and PSD-95,and PSD-95 was the most significant one.When knocking down the expression of ?-synuclein in the hippocampus,the expression of postsynaptic PSD-95 was also decreased,and ?-synuclein knockdown significantly inhibited the effect of Rb1 on increasing PSD-95 expression,enhancing hippocampal synaptic plasticity,and improving learning and memory in PD mice.It is suggested that the effect of Rb1 on ?-synuclein plays an important role in improving cognitive function in PD mice.In summary,Ginsenoside Rb1 can improve dyskinesia and cognitive dysfunction in PD mice,the potential mechanisms may include regulating GABAergic signaling pathway,GLT-1 expression and ?-synuclein/PSD-95 pathway.It is suggested that Rbl can be used as a potential drug to cure PD for indepth research and development.