Tripchlorolide Ameliorates Cognitive Impairment Of5XFAD Transgenic Mice Via Improving Synaptic Plasticity, Modifying AβMetabolism And Inhibiting Neuroinflammatory Response

Object Abnormal metabolism of β-amyloid （Aβ） is central to the pathogenesis ofAlzheimer’s disease （AD）. An imbalance between Aβ production and clearance resultsin Aβ aggregation and deposition, which triggers the pathophysiological cascadereaction, including synaptic dysfunction and neuroinflammatory induced by activatedglial cell, eventually leads to neuronal damage and cognitive impairment. In thisstudy we aimed to test the effects of T₄on cognitive function of5XFAD transgenicmice and explore the potential mechanisms in synaptic plasticity, Aβ metabolism andneuroinflammation.Methods5-month-old male5XFAD transgenic mice and littermate wild typemice were randomly assigned to a vehicle control group （0.9%NaCl） and T₄treatment groups which intraperitoneally injected with5，25μg/kg T₄every other dayfor60days, respectively.1. Spatial learning and memory performance was tested with Y maze and Morriswater maze.2. Synaptic ultrastructure in the hippocampal CA1region was observed byelectron microscopy. Synapse plasticity related proteins, including synaptophsin,PSD-95, p-NMDAR1/NMDAR1, p-CaMKIIα/CaMKIIα and p-CREB/CREB, and proteinsparticipating in the PI3K-Akt-mTOR signaling pathway were tested by Western blot.3. The level of Aβ, the major APP-cleaving enzymes and Aβ-degrading enzymesincluding β-secretase, α-secretase, NEP and IDE, were detected byimmunohistochemistry staining, ELISA and Western blot.4. Microglial and astrocytic activation was evaluated with immuno-histochemistry staining. The expression of GFAP was detected by Western blot. The mRNA levels of inflammatory mediators in hippocampus were quantified by real-timePCR。Results1. T₄treatment improved learning and memory in5XFAD transgenic mice.2. T₄treatment alleviated degradation of synaptic ultrastructure. T₄treatmentnot only up-regulated the expression of synapse plasticity related proteins, includingsynaptophsin, PSD-95, p-NMDAR1/NMDAR1, p-CaMKIIα/CaMKIIα and p-CREB/CREB,but also increased the expression of pAkt/Akt、pmTOR/mTOR.3. T₄treatment reduced the level of Aβ deposition, BACE1, sAPP-β and CTF-β,increased the expression of NEP. While there were no significantly change in APP,ADAM10, ADAM17and IDE after T₄treatment.4. T₄treatment suppressed microglia activation and mRNA levels ofinflammatory mediators, including IL-1β, TNF-α, IL-6, TGF-β, CCL2and NOS2. But T₄treatment did not affect astrocyte activation.Conclusion5XFAD transgenic mice display spatial learning and memoryimpairment, synapse dysfunction, Aβ deposition and neuroinflammation. T₄improves the cognitive dysfunction in the transgenic mice. T₄might promoteactivation of the PI3K-Akt-mTOR signaling pathway to increase the synthesis ofsynapse plasticity related proteins, reduce BACE1activity and increase NEPexpression to decrease Aβ production and promote its degradation, suppressneuroinflammation by inbibitting microglial activation. Therefore, T₄is expected tobecome a promising drug candidates for the treatment of AD.