An increasing number of studies have demonstrated that insulin-degrading enzyme (IDE)
plays an essential role in both the degradation and its activity of β-amyloid (Aβ). Therefore, the
regulation of IDE expression and/or modification of IDE-dependent actions are two emerging strategies
for the treatment of Alzheimer’s disease (AD). We previously observed that geniposide, a novel agonist
of glucagon-like peptide 1 receptor (GLP-1R), could attenuate Aβ-induced neurotoxicity by regulating the expression of
IDE in primary cortical neurons. However, the signal transduction mechanisms underlying this effect were not elucidated.
The present study, therefore examined and explored the cell signaling transduction and molecular mechanisms by which
geniposide induces the expression of IDE in primary cortical neurons. The current study revealed that LY294002 (an
inhibitor for phosphatidyl inositol 3-kinase, PI3K), PP1 (inhibitor for c-Src), GW9662 (antagonist for peroxisome
proliferator-activated receptor γ, PPARγ), H89 (an inhibitor for protein kinase A, PKA) and AG1478 (an antagonist for
epidermal growth factor receptor, EGFR) prohibited the up-regulation of IDE induced by geniposide in primary cortical
neurons. Further, geniposide also enhanced the phosphorylation of PPARγ and accelerated the release of phosphorylated
FoxO1 (forkhead box O1) from nuclear fraction to the cytosol. Moreover, geniposide directly activated the activity of IDE
promoter in PC12 cells, which confirmed the presence of the GLP-1 receptor. Taken together, our findings reveal for the
first time the cell signaling transduction pathway of geniposide regulating the expression of IDE in neurons.