The Effect And Mechanism Of Complement C3a Receptor Antagonist On Tau-Dependent Pathology And Cognitive Functions In P301S Mice

Objective: To investigate the effect and mechanism of complement C3 a receptor antagonists(C3aRA)on tau-dependent pathology and cognitive functions in P301 S mice.Methods: The P301 S transgenic tau mice were used as the animal model,which endogenously expressed human pathological tau protein in the brain.The expression levels of complement C3 aR protein in the P301 S mice brain were detected by western blot and immunofluorescence at the 3th,6th,and 9th months.The P301 S mice were treated with the complement C3 a receptor antagonist SB290157 from the age of 3 months(intraperitoneal injection,1 mg/kg,3 times per week,for 8 weeks).At the same time,WT mice and P301 S mice of the same age were treated with blank solvent.Western blot and immunohistochemistry were used to detect the phosphorylated tau at 6 months and 9 months,respectively.Synapse-associated proteins were detected by western blot;the synaptic number was detected by Golgi staining.Morris water maze was used to detect spatial learning and memory;the emotional memory ability of mice was detected by open field experiment,new object recognition experiment and conditional fear test;synaptic plasticity was detected by long-term potentiation(LTP).In addition,the levels of GSK3?,PP2 A,CDK5,p-GSK3?(Ser9),p-PP2A(Y307),p-CDK5(Tyr15)and activity-regulating subunits p35 and p25 were detected,respectively.Results: 1.The complement C3 aR protein levels in P301 S mice were higher than that in WT mice at 6 months of age and dramatically increased at 9 months of age.2.Behavioral results showed that there was no significant difference in learning and memory ability between P301S-C3 aRA mice and P301S-vehicle mice at 6 months of age;and WT control mice showed a normal learning and memory.At 9 months of age,the P301S-vehicle mice showed an obvious defect in learning and memory compared with WT mice,and C3 aR antagonist attenuated spatial learning and memory in P301 S mice.In the new object recognition experiment,the P301S-C3 aRA mice have a higher ratio to recognize a new object compared with P301S-vehicle mice.No significant difference was detected in the open field test and the conditional fear test among the three groups.3.Compared with WT mice,phosphorylated tau protein was significantly increased in the brain of 6-month-old P301 S mice and was further increased at 9 months of age,the complement C3 a receptor antagonist significantly reduced the expression of hyperphosphorylated tau protein in the P301 S brain.4.The results of synaptic protein assay showed that the expression of synaptic protein markers GluR1,NR2 B and PSD95 in the brain of 6-month-old and 9-month-old P301 S mice was decreased compared with WT mice.The complement C3 a receptor antagonist significantly improved the levels of post-synaptic protein in the brain of P301 S mice.No significant difference in pre-synaptic markers was detected among the 3 groups of mice at 9 months of age.Golgi staining showed that the number of synapses in the brain of P301 S mice at 6 months and 9 months was significantly lower than that in WT mice.Complement C3 a receptor antagonists effectively improved the number of synapses in the brain of P301 S mice.Synaptic long-term potentiation recording was significantly impaired in hippocampal synaptic function in 9-month-old P301 S mice.C3 a receptor antagonists improved hippocampal synaptic function in P301 S mice.5.Compared with WT mice,kinase CDK5 phosphorylation site p-CDK5(Tyr15)and its regulatory subunits p35?p25 were significantly increased in the P301 S mice.Treatment with C3 a receptor antagonist decreased the expression of p-CDK5(Tyr15)and CDK5 activity-regulating subunits p35 and p25 in the brain of P301 S mice.However,there was no statistically difference in levels of GSK3? and PP2 A.Conclusion: The elevated level of complement C3 aR protein is involved in the pathogenesis of tau hyperphosphorylation.C3 aRA reduces hyperphosphorylated tau levels in P301 S mice,protects neuronal synaptic structure and function integrity,and improves P301 S cognitive functions such as learning and memory.The kinase CDK5 signaling pathway is involved in the C3 a receptor antagonist regulating tau phosphorylation in the brain of P301 S mice.These results show the protective effect of C3 aRA on tau disease and suggest that C3 a receptor may serve as a potential therapeutic target for tauopathies.