Neuroprotective Effects And Mechanism Of Furin And NPAS4 On Alzhermer’s Disease

Background: Alzheimer’s disease(AD) is a progressive neurodegenerative disorder, which is characterized by senile plagues and intracellular neurofibrillary tangles(NTFs). AD etiology and pathogenesis are still not completely clarified, but so far Aβ deposition has identified as the main component of senile plaques and the hyperphosphorylation-tau proteins cause NTFs.Nerve growth factor(NGF) had been used to treat AD and had entered phase II clinical trials. Furin promotes NGF precursor into mature NGF, is reduced in AD brain. Furin is a member of proprotein convertases(PC)family, and it can efficiently cleave brain derived neurotrophic factor(BDNF) precursor and matrix metalloproteinase(MMP) into their biologically active products. This suggests that Furin may play much more important roles than NGF in AD pathogenesis.Objectives:(1) To analyse Furin and autophagy, apoptosis, the endoplasmic reticulum stress and Abeta metabolic through stable expression Furin neuron cell line;(2) Neurons were transfected with eukaryotic expression plasmid NPAS4, analysing the relationship ofNPAS4 and tau protein. In order to interpret Furin and/or NPAS4 in AD pathology, lay a foundation for screening of molecular targets for the treatment of AD.Methods: The neuron cell line SH-SY5 Y were transfected with Furin plasmid, and after G418 screening to establish stable expression cell lines,then using Western blot method to detect autophagy, apoptosis,endoplasmic reticulum stress and the Abeta metabolism. Neurons were transfected with eukaryotic expression plasmid NPAS4, we analyze autophagy related molecular and tau protein expression using immunofluorescence and Western blot.Results:(1) Furin overexpression can induce autophagy, inhibit apoptosis induced by oxidative stress and endoplasmic reticulum stress. We also found that hosphorylation of IRE1 alpha increased significantly in Furin cells. We speculate that Furin activated selectively IRE1 alpha, but further validation in animal is need.(2) JNK and ERK are downstream molecules of IRE1 alpha pathway. The results showed that IRE1 alpha may regulate autophagy through the JNK/ERK pathway.(3) Furin can affect APP metabolic enzymes and reduce Abeta production.(4) NPAS4 overexpression induced autophagy and autophagic flux in neurons.(5) The activation of autophagy by serum depletion significantly decreased endogenous total and phosphorylated tau levels. Autophagy inhibitors, such as 3-methyladenine(3-MA) and chloroquine(CQ), induced tau aggregation.However, NPAS4 over-expression reversed the aggregation of tau that was induced by the inhibition of autophagy.(6) The proteasome inhibition by MG132, had no effect on autophagy, but did reduce tau levels, indicating that NPAS4 may also degrade tau proteins through an unknown proteasome-mediated mechanism.(7) NPAS4 did not alter the activity of two major tau kinases, glycogen synthase kinase 3β(GSK3β) and cyclin-dependent kinase 5(CDK5).Conclusion: On the one hand, Furin promotes learning and memory,and against oxidative stress injury and apoptosisthrough BDNF neuron dendritic growth; on the other hand, Furin eventually relieves Abeta deposition and improves the cognitive impairment of AD by IRE1alpha-autophagy and ADAM10/PS1 pathway. NPAS4 overexpression can induce autophagy and reduce the expression of endogenous tau, and the mechanism is mediated by autophagy. It is significance to remove tau protein(phosphor-tau) for treating AD and Tau disease. Therefore the present study may provide a new strategy for the treatment of neurodegenerative diseases.