The Expression Of Astrocytes Amyloid Precursor Protein, Presenilin-1 And The Protection Of Ginkgo Biloba Extract Against Glutamate Induced-excitotoxicity

objective : Glutamate is the most abundant excitatory neuro- transmitter in the brain.Increased level of extracellular glutamate causes over-stimulation of glutamate receptors that may result in secondary events, leading to neuronal cell death. Astrocytes are responsible for most glutamate uptake in synaptic and non-synaptic areas and consequently are the major regulators of glutamate homeostasis. Amyloid precursor protein (APP) is an integral membrane protein. APP is cleavage byα-Secretaseβ-Secretase andγ-Secretase(Presenilin-1,Presenilin-2,Nicastrin,Aph-1 and Pen-2 complexes).Cleavage of APP releases secreted APP (sAPPα, sAPPβ) and amyloidβ-protein(Aβ) and other metabolic products. We have observed the expression of APP and PS1 of hippocampal astrocytes in the glutamate induced- excitotoxicity.Ginkgo biloba extract (GBE) contains multiple compounds such as flavonoids and terpenoids, it has many neuroprotective effects such as removing free radicle, protecting neurons against apoptosis induced by ischemia injury, and influencing the transport of neurotransmitters. GBE has been therapeutically used for several decades to increase peripheral and cerebral blood flow as well as for the treatment of cognitive speed, dementia, and aging damages. The objective of this study is to observe the relationship between excitotoxicity in rat hippocampal astrocytes and expression of APP and Presenilin-1(PS1), and to explore the effect of GBE on damages and reparation of excitotoxicity.Methods : Acoording to the report of Juurlink and Hertz,the hippocampal astrocytes from neonatal SD rat(24h), after two or more consecutive passages, astrocytes were treated with 50/100μM glutamate and10μM glycine at 12 day in vitro. Trypan blue staining were used to study the glutamate-induced injury in astrocytes, And double immunofluorescent staining was used to observe the glutamate-induced expression and distribution changes of APP and PS1, and the effects of GBE on this process.Results:1. 15min after 100μM glutamate exposure, marked damage could be induced in hippocampal astrocytes. Survival rate demonstrated by trypan blue staining of GBE pretreatment group and GBE posttreatment group is 60.8±2.7% and 51.1±2.8% respectively, show that GBE pre- treatment has protective effect on the glutamate induced damage on morphous. 2. Expressive location of APP and PS1 is uniform not very well, both of them are expressed on nuclei, soma and processes of astrocytes . PS1 is more diffused distribution in soma around nuclei, while APP is more in processes of astrocytes than in nuclei, soma. And the level of APP is 233.33% times compared with normal group, the level of PS1 is161.90% times compared with normal group.3. GBE pretreatment could inhibit expressive changes of APP and PS1 induced by glutamate.Conclusions: 1.100μM glutamate added induces astrocytes excito- toxicity.2.In protein levels, the expression of APP and PS1 was changed in glutamate-induced exicitotoxicty. It proves that the excitotoxicity induced by glutamate is related to APP and PS1 closely.3.GBE pretreatment can protect astrocytes against glutamate- induced excitotoxicity,...