Signaling pathways mediating anti-apoptotic action of neurotrophins

Neurotrophins promote survival and suppress apoptosis in many populations of neurons. Currently, phosphatidylinositol-3 kinase (PI-3K) is recognized as the main mediator of this protective effect. However, most of the data collected so far on the anti-apoptotic signaling of neurotrophins were obtained using trophic withdrawal paradigms. Recent data from our and other groups indicate that extracellular-signal-regulated kinase 1/2 (Erk1/2) may play a critical role in suppressing neuronal apoptosis triggered by cellular damage. Thus, it appears that either Erk1/2 or PI-3K, depending on the nature of the death-inducing stimulus, can mediate anti-apoptotic signaling of neurotrophins. In this review, we discuss the contribution of Erk1/2 and PI-3K to neuroprotection by neurotrophins. We also present data suggesting possible mechanisms by which these pathways might suppress neuronal death.