3β,23,28-Trihydroxy-12-oleanene 3β-Caffeate from Desmodium sambuense-Induced Neurogenesis in PC12 Cells Mediated by ER Stress and BDNF-TrkB Signaling Pathways.

3β,23,28-Trihydroxy-12-oleanene 3β-caffeate (compound 1) is a neuritogenic pentacyclic triterpenoid, which was isolated from Desmodium sambuense based on a PC12 cell bioassay system. Compound 1 induced neurite outgrowth dose-dependently in PC12 cells and primary cortical neurons at doses of 0.1, 0.3, and 1 μM. The potential target of compound 1 was predicted by ChemProteoBase profiling, and the mechanism of action was investigated using specific inhibitors, Western blot analysis, and PC12 [rasN17] and PC12 [mtGAP] mutants. Compound 1 activates endoplasmic reticulum (ER) as an ER stress inducer, and the maker of ER stress GRP78 protein significantly increased after treatment with compound 1. The inhibitors of tyrosine kinase B (TrkB), insulin-like growth factor 1 receptor (IGF-1R), mitogen-activated protein kinase (MEK), and phosphatidylinositol 3 kinase (PI3K) significantly decreased the neurite outgrowth induced by compound 1. Furthermore, the increases of phosphorylation of TrkB, IGF-1R, extracellular signal-regulated kinase (ERK), and protein kinase B (AKT) were observed in the compound 1-treated group, and the phosphorylation of these proteins was diminished by corresponding inhibitors. Thus, the compound-1-induced neuritogenic activity depended on the activation of slight ER stress and associated BDNF-TrkB/Ras/Raf/ERK and IGF-1R/PI3K/AKT signaling pathways in PC12 cells.