Curcumin Improves Cognitive Of 5XFAD Transgenic Mice Via Inhibiting BACE1 Expression And The Apoptosis Pathway Induced By Aβ/Appoptosin

Objective: Recently SLC25A38 was identified as a new pro-apoptotic protein and designated as Appoptosin. Appoptosin is upregulated in neurons treated with β-amyloid(Aβ) as well as in brain of Alzheimer disease(AD) patients. Appoptosin can initiate cellular apoptosis mediated by the intrinsic caspase-dependent pathway. Because Aβ can intimate cellular pathological lesion through Appoptosin-regulated apoptosis in AD, preveting Appoptosin-inducing apoptosis might be a possible new therapeutic target for AD treatment. Our object is to reveal whether curcumin can prevent the development of AD by blocking Aβ/Appoptosin-inducing apoptosis and elucidate the underlying mechanism.Methods:1. In vivo study, 4-month-old male 5XFAD transgenic mice were randomly assigned to three groups as: the vehicle group treated with 0.9%Na Cl, the 150mg/kg/d curcumin-treated group and the 300mg/kg/d curcumin-treated group. Littermate wild type(WT) C57BL/6J mice treated with 0.9%Na Cl was used as control. All mice were intragastrically administered for 60 days. Then their spatial learning and memory were evaluated by Y maze and Morris water maze tests. Synaptic ultrastructure of the brain was observed by electron microscopy. Synaptophsin, one protein relating to Synapse plasticity was detected by Western blot. The expression of Appoptosin was tested by immunohistochemistry and Western blot. The level of Aβ was detected by immunohistochemistry staining and ELISA. The main APP-cleaving enzymes(including BACE1 and ADAM17) and Aβ-degrading enzymes(including NEP and IDE) were detected by Western blot.Full length APP(APP-FL) and APP CTF-β fragments were also detected by Western blot.2. In vitro study, Untreated SHSY5 Y cells and cells transfected with control or Appoptosin vectors were treated with various concentrations of curcumin or vehicle for 24 hours. Cellular apoptosis and intracellular ROS were detected by flow cytometry analysis. The expression of cleaved-caspase3 and HO-1 were tested by Western blot. Mitochondrial membrane potential ΔΨm was analyzed through fluorescence microscope and fluorescence ratio detection with JC-1 staining. Intracelluar heme level was measured with Hemin Assay Kit.Results:1. In vivo study, Compared with those of wild type mice, the spatial learning and memory of 5XFAD transgenic mice were impaired. Aβ levels are dramatically high and Ab deposits are abundant in the brain of 5XFAD transgenic mice. In addition, the synaptic ultrastructure was compromised. The level of synaptophsin was downregulated while levels of Appoptosin, BACE1 and CTF-β were upregulated. We also found that curcumin treatments improved the spatial learning and memory of 5XFAD transgenic mice, prevented the synaptic ultrastructure damage, upregulated Synaptophsin while downregulated Appoptosin, BACE1 and CTF-β, and reduced Aβ accumulation and deposition in brain of 5XFAD transgenic mice. The expressions of APP, ADAM17, NEP, IDE in brain of 5XFAD transgenic mice were not affected by curcumin treatments.2. In vitro study, Overexpression of Appoptosin in SHSY5 Y cells dramatically increased levels of cleaved caspase 3, intracelluar ROS and heme, and decreased HO-1 level. ΔΨm was also impaired upon Appoptosin overexpression. All these changes can be alleviated by curcumin treatments.Conclusion: Curcumin can inhibit the expression of BACE1, reduce the production and accumulation of Aβ, downregulate Appoptoin, attenuate synapse lesion in brain of AD. In addition, curcumin can prevend Appoptosin-induced apoptosis by upregulating HO-1, reducing intracellular heme and ROS, then attenuating oxidative pressure and ΔΨm damage. So we come to a conclusion that curcumin can improve cognition of 5XFAD transgenic mice via inhibiting BACE1 expression and the apoptosis pathway induced by Aβ/Appoptosin.