ABSTRACT
Objective To explore the protective effects of dipeptidyl peptidase-4 inhibitor (DPP-4I) on AD-like neurodegenerative changes and its mechanism. Methods The human neuroblastoma cell line SH-SY5Y on the logarithmic phase was divided into six groups:control group (CON group, treated with PBS contained 1‰DMSO for 12 h), wortmannin intervention group (W group, treated with 0.03 μmol/L wortmannin for 12 h), DPP-4I intervention group (DPP-4I group, treated with 10μmol/L DPP-4I for 12 h), both DPP-4I and wortmannin intervention group (DPP-4I+W group, pre-treated with 10 μmol/L DPP-4I for 2 h, then 0.03 μmol/L wortmannin for 12 h), DPP-4I, wortmannin and Ex9-39 intervention group (DPP-4I+W+Ex9-39 group, pre-treated with 10μmol/L Ex9-39 for 2 h, then 10μmol/L DPP-4I for 2 h followed by 0.03μmol/L wortmannin for 12 h), and Ex9-39 intervention group (Ex9-39 group, treated with 10μmol/L Ex9-39 for 12 h). MTT assay was used to detect the cell vitality. Western blot assay was used to detect the level of total tau protein (tau-5) and phosphorylated tau at different sites (pSpS199/202, pT231 and pS396), the level of phosphorylated neurofilaments (NF-H, NF-M) and phosphorylation of critical enzyme in PI3K/Akt/GSK-3β signaling pathway. Results (1) The cell vitality decreased, the levels of pSpS199/202, pT231, pS396 and NF-H/M increased significantly in W group than those in CON group. However, comparing with CON group, the above mentioned parameters reversed in DPP-4I group. Comparing with W group, the cell vitality increased and phosphorylated levels of above mentioned indices were decreased in DPP-4I+W group. (2) The cell vitality showed a decline trend while the levels of phosphorylation tau at three different sites and NF-H/M were higher in Ex9-39 group than those in CON group. Comparing with DPP-4I+W group, the results of the phosphorylated levels showed the same changes in DPP-4I+W+Ex9-39 group. (3) Comparing with CON group, the expression levels of phosphorylated PI3K, Akt and GSK3β increased significantly in DPP-4I group, while those decreased in W group. Additionally, the expression levels of phosphorylated PI3K, Akt and GSK3β were significantly increased in DPP-4I+W group than those in W group. Conclusion DPP-4I can enhance the level of GLP-1 and activate PI3K/Akt/GSK-3βinsulin signaling pathway to improve the hyperphosphorylated tau and NFs induced by wortmannin, and to protect AD-like neurodegeneration.
ABSTRACT
Objective To investigate the effects of type 2 diabetes on learning and memory of APP/PS1/Tau triple transgenic (3 × Tg) mice of Alzheimer’s disease, and the protective mechanism of liraglutide (LIR) thereof. Methods One month old C57BL/6 mice were set to be control group (WT). One month old 3×Tg mice were divided into control group (Tg), liraglutide group (Tg+LIR), type 2 diabetes group (Tg+T2DM) and liraglutide treatment group (Tg+T2DM+LIR). The model of T2DM was established by feeding the high fat and sugar fodder, and then injecting streptozotocin (STZ) in mice, making sure the fasting blood glucose was more than 7 mmol/L. Then the subcutaneous injection of LIR was administered for 2 months. The values of body weight and fasting blood glucose were detected at age of 5-month. Morris water maze was applied to evaluate the spatial learning and memory ability. Western blotting assay was used to measure the levels of phosphorylated Tau, neurofilament (NFs) and insulin receptor substrates. ELISA was used to detect the human Aβ42 to evaluate the effect of LIR on-amyloid. Results LIR can reduce body weight and blood glucose, can alleviate spatial learning and memory damaging caused by T2DM, and also can improve phosphorylated Tau levels, NFs and insulin receptor substrates caused by T2DM, and finally can reduce the deposition ofβ-amyloid of 3 × Tg mice. Conclusion T2DM can aggravate symptoms of AD in 3×Tg mice, and LIR has a protective effect on it.