Effects Of(Val8)GLP-1-Glu-PAL On Behavioral Impairment,Pathological Changes, Apoptin In MPTP-induced Parkinson’s Disease Mice Model

Background:Parkinson’s disease(PD) is one of the common progressive neurological diseases in elderly population. Although the pathogenesis and relative mechanism of this disease has not been fully elucidated, the main pathological characteristics is that progressive loss of dopaminergic neurons, mainly in the substantia nigra pars compacta(SNpc). It causes the substantia nigra-striatum pathways degeneration and disorder, and declines the dopaminergic neurotransmitter, and further damaged the function of extrapyramidal motor and regulation. It causes many clinical characteristics such as dyskinesia, resting tremors. Several hypotheses related to the possible causes for neuronal degeneration in patients with PD have been postulated. These include aging, oxidative stress,environmental toxins, genetic factors, mitochondrial dysfunction, etc. It also may be associated with the obstacles of insulin signaling pathways[1]. And recent some papers pointed out [2-4] that diabetes is an independent risk factor for Parkinson’s disease. A lots of studies showed that Glucagon-like peptide-1(GLP-1), a new novel to treat diabetes,provide a possibility to treat and prevent PD. GLP-1 can regulate insulin signaling pathway via Glucagon-like peptide-1 receptor(GLP-1R). Insulin signaling pathway involved in various physiological processes in the brain, not only can promote the growth and development of neurons, but also participate in the neurotransmitter release and regulation [24]. Therefore, we hypothsis that the protective effects of new GLP-1analogue(Val8)GLP-1-Glu-PAL for dopaninergic neurons on PD mice.Objective:To investigate(Val8)GLP-1-Glu-PAL reverse the behavioral impairment,pathological changes of dopaninergic neurons and expression of apoptin in MPTP-induced Parkinson’s disease mice model.Methods:56 male C57BL/6 mice, 10-12 weeks, were randomly divided into control, MPTP,Val8 and MPTP+Val8 groups by random number table method. Mice in MPTP group were received MPTP(30 mg/kg·d) IP. The control group were treated with 0.9% saline with the same volume, Val8 group were injected with(Val8)GLP-1-Glu-PAL(25nmol/kg), and MPTP+Val8 group were received(Val8)GLP-1-Glu-PAL 1h after treatment of MPTP. All the groups were treated for 8 consecutive days. Behavior test were processed 2h after drug IP injection, including swimming test and rotarod test. Mice were sacrificed immediately 1h after the final trail of behavior test in 8thday and brains were withdraw for IHC assay which tested the number TH positive neurons and TUNEL assay which tested the positive cell in SNpc area. Using the western blot assay expression protein of TH, Bcl-2, Bax, Pro-caspase3, Cleaved-caspase3 were measured.Results:(1) With the accumulation of MPTP, the activity of MPTP group mice gradually was decreased.(2) Balance coordination capacity is bad after treating by MPTP as compared with the control group(P<0.05). But after injecting(Val8)GLP-1-Glu-PAL, their exercise capacity was increased(P<0.05).(3) The immunohistochemical assay showed that TH positive neurons of the midbrain nigra area decreased significantly(P<0.05) in MPTP group as compared with the control group, TH positive neurons in midbrain nigra area of MPTP+Val8 group were relatively elevated(P<0.05).(4) The TUNEL assay showed that the positive apoptosis cells of the model groupwere significantly more than the control group in the midbrain nigra area(P<0.05), the MPTP+Val8 group was relatively less than the MPTP group(P<0.05).(5) The Western blot assay showed that MPTP could decrease expression of TH,Bcl-2 and Pro-caspase-3 protein(P<0.05), and increase expression of Bax and Cleaved-caspase3 protein(P<0.05). All damages induced by MPTP were reversed by(Val8)GLP-1-Glu-PAL.Conclusion:(1) The classical PD behavior damages were induced by MPTP and(Val8)GLP-1-Glu-PAL reversed the damages in PD mice.(2)(Val8)GLP-1-Glu-PAL can prevent apoptosis of the dopaminergic neurons in the substantia nigra area and provide protective effects on PD mice induced by MPTP.(3)(Val8)GLP-1-Glu-PAL can reverse expression of Bcl-2, Bax, Pro-caspase3 and Cleaved-caspase3 in PD mice, and have the effect of inhibiting neuronal apoptosis.(4) Our research showed that(Val8)GLP-1-Glu-PAL could be an effective medication to prevent PD.