Involvement of phosphatidylinositol 3-kinase and insulin-like growth factor-I in YXLST-mediated neuroprotection

Abstract In the present study, we examine the neuroprotective role of the external Qi of YXLST in cultured retinal neurons. Primary retinal neuronal cultures were grown from retinas of 0–2-day-old Sprague–Dawley rats. Cultures were treated directly with external Qi of YXLST 30 min prior to H 2 O 2 exposure in most experiments. Cell viability was measured by 3,(4,5-dimethylthiazol-2-yl)2,5-diphenyl-tetrazolium bromide (MTT) assay. Apoptotic cell death was evaluated by the TdT-mediated digoxigenin-dUTP nick-end labeling TUNEL assay, and by DNA laddering analysis. Northern blot analysis was performed to examine the level of insulin-like growth factor-I (IGF-I) gene expression. Phosphatidylinositol 3-kinase (PI3K) assay was performed to study the PI3K activity. The results showed that treatment of external Qi of YXLST significantly attenuated neuronal death that was induced by 24-h exposure to hydrogen peroxide, and greatly inhibited hydrogen peroxide-induced apoptosis. External Qi of YXLST also upregulated IGF-I gene expression and increased PI3K activity. These observations indicate that external Qi-mediated IGF-I expression and PI3K signaling could be one of the mechanisms in neuroprotection by YXLST.