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 10 μmol/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 10 μmol/L Ex9-39 for 2 h, then 10 μmol/L DPP-4I for 2 h followed by 0.03 μmol/L wortmannin for 12 h), and Ex9-39 intervention group (Ex9-39 group, treated with 10 μmol/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-3β insulin signaling pathway to improve the hyperphosphorylated tau and NFs induced by wortmannin, and to protect AD- like neurodegeneration.

Key words: dipeptidyl- peptidase Ⅳ inhibitors, Alzheimer’ s disease, glucagon- like peptides, tau proteins, protein kinases, neurofilaments, insulin signaling pathway