Abstract:

Objective Amyloid precursor protein(APP) is one in which neurotrophic and neurotoxic functions occur on the same chain.The APP319-335 segment(APP17 peptide) can enhance neuritic growth.Solube APP17 peptide exerts its effect through binding to specific binding sites on the cell surface.The present work is to investigate the effect of APP17 peptide on the expressions of insulin signaling transduction protein of T2 diabetic KKAy mice hippocampal neurons.Methods KK mice were divided into three groups: a normal control group(C,n=10),a diabetic group(DM,n=10) and an APP17mer peptide-protected diabetic group(DM+APP17P,n=10).Blood glucose in a tail-vein sample was determined by a glucose analyzer.A value>15 mmol/L was accepted as a diabetic model.APP17mer peptide was synthesized by solid phase method and purified by HPLC.Mice in the APP17+DM group were injected peptide subcutaneously at the dose of 8 μg/kg three times a week for 12 weeks.After twelve weeks,all the mice were killed and peripheral blood were obtained to assess the levels of HbA1c,plasma insulin and blood glucose.Homogenates were prepared from mice hippocampal tissue.Immunoprecipitation,Western-blot and immunohistochemistry were used to analyze the proteins related to insulin signaling transduction pathway.Tunnel assay was used to detect the apoptotic cell in hippocampus of KK mice.Immunohistochemical assay was performed with insulin receptor(InsR),insulin receptor substrate-1(IRS-1) and Bcl-2.Results The results of InsR and IRS-1 immunohistochemical staining showed that the hippocampus of C group and DM+APP17P contained darkly stained InsR and IRS-1positive cells.In contrast positive reacting cells in the hippocampus of DM group mice were pale,and were visibly fewer than in those Cgroup and APP17P+DM group mice. The number of positively stained hippocampal cells for Bcl-2 was similar in three groups.The expressions of CREB,phosphorylated CREB(p-CREB) and Bcl-2 showed no significant difference among the three groups.No positive Tunel cell was found in all groups.Conclusion Abnormal signal transduction pathway is present in hippocampal neuron of kk mice.The abnormality may not lead to apoptosis due to auto-regulation of neurons to a certain extent.This abnormal insulin signaling transduction pathway can be improved by APP17 peptide.

Key words: APP17 peptide, KKAy mice, insulin signaling transduction pathway