ProNGF Induces PTEN via p75 NTR to Suppress Trk-Mediated Survival Signaling in Brain Neurons

Proneurotrophins and mature neurotrophins activate different signaling pathways with distinct effects on their target cells: proneurotrophins can induce apoptotic signaling via p75 NTR , whereas mature neurotrophins activate Trk receptors to influence survival and differentiation. Here, we demonstrate that the PTEN (phosphatase and tensin homolog deleted on chromosome 10) phosphatase represents a novel switch between the survival and apoptotic signaling pathways in rat CNS neurons. Simultaneous activation of p75 NTR by proNGF and TrkB signaling by BDNF elicited apoptosis despite TrkB phosphorylation. Apoptosis induced by p75 NTR required suppression of TrkB-induced phosphoinositide-3 kinase signaling, mediated by induction of PTEN, for apoptosis to proceed. Inhibition of PTEN restored the ability of BDNF to phosphorylate Akt and protect cultured basal forebrain neurons from proNGF-induced death. In vivo , inhibition or knockdown of PTEN after pilocarpine-induced seizures protected CNS neurons from p75 NTR -mediated death, demonstrating that PTEN is a crucial factor mediating the balance between p75 NTR -induced apoptotic signaling and Trk-mediated survival signaling in brain neurons.