Hypoxia induces an autocrine-paracrine survival pathway via platelet-derived growth factor (PDGF)-B/PDGF-β receptor/phosphatidylinositol 3-kinase/Akt signaling in RN46A neuronal cells

In neurons, hypoxia activates intracellular death-related pathways, yet the antiapoptotic mechanisms triggered by hypoxiaremainunclear.InRN46Aneuronalcells,minimum media growth conditions induced cell death as early as 12 h after the cells were placed in these conditions(i.e.,after removal of B-27 supplement). However, apoptosis occurred in hypoxia(1% O-2) only after 48 h,and in fact hypoxia reduced the apoptosis associated with trophic factor withdrawal. Furthermore, hypoxia induced time-dependent increases in expression of platelet-derived growth factor(PDGF) B mRNA and protein, as well as PDGF-beta receptor phosphorylation. Although exogenous PDGF-BB-induced only transient Akt activation,hypoxia triggered persistent activation of Akt for up to 2 4 h. Inhibition of phosphatidylinositol 3-kinase(PI3K)or of PDGF-beta receptor phosphorylation abrogated both hypoxia-induced and exogenous PDGF-BB-induced Akt phosphorylation, and it completely abolished hypoxia-induced protection from media supplement deprivation, which suggests that the long-lasting activation of Akt during hypoxia and the prosurvival induction were due to endogenously generated PDGF-BB. Furthermore,these inhibitors decreased hypoxia-inducible factor 1alpha(HIF-1alpha) DNA binding, which suggests that the PDGF/PDGF-beta receptor/Akt pathway induces downstream HIF-1alpha gene transcription. We conclude that in RN46A neuronal cells, hypoxia activates an autocrine-paracrine antiapoptotic mechanism that involves up-regulation of PDGF-B and PDGF-beta receptor-dependent activation of the PI3K/Akt signaling pathway to induce downstream transcription of survival genes.