PI3-K/Akt and ERK pathways activated by VEGF play opposite roles in MPP⁺-induced neuronal apoptosis

Vascular endothelial growth factor (VEGF), a specific pro-angiogenic peptide, has shown neuroprotective effects in the Parkinson's disease (PD) models, but the underlying mechanisms remain elusive. In this study, the neuroprotective properties of VEGF on 1-methyl-4-phenylpyridinium ion (MPP+)-induced neurotoxicity in primary cerebellar granule neurons were investigated. Pretreatment of VEGF prevented MPP+-induced neuronal apoptosis in a concentration- and time-dependent manner. And this prevention was blocked by PTK787/ZK222584, a VEGF receptor-2 specific inhibitor. Both inhibition of the Akt pathway and activation of the extracellular signal-regulated kinase (ERK) pathway contribute to MPP+-induced neuronal apoptosis. VEGF reversed the inhibition of phosphoinositide 3-kinase (PI3-K)/Akt pathway caused by MPP+, but further enhanced the activation of ERK induced by MPP+. Interestingly, VEGF and PD98059 (an ERK kinase inhibitor) play a synergistic role in protecting neurons from MPP+-induced toxicity. Collectively, these findings suggest that the PI3-K/Akt and ERK pathways activated by VEGF play opposite roles in MPP+-induced neuronal apoptosis. This finding offers not only a new and clinically significant modality as to how VEGF exerts its neuroprotective effects but also a novel therapeutic strategy for PD by differentially regulating PD-associated signaling pathways.