Neuronal pentraxin 1 induction in hypoxic-ischemic neuronal death is regulated via a glycogen synthase kinase-3α/β dependent mechanism

Intracellular signaling pathways that regulate the production of lethal proteins in central neurons are not fully characterized. Previously, we reported induction of a novel neuronal protein neuronal pentraxin 1 (NP1) in neonatal brain injury following hypoxia-ischemia (HI); however, how NP1 is induced in hypoxic-ischemic neuronal death remains elusive. Here, we have elucidated the intracellular signaling regulation of NP1 induction in neuronal death. Primary cortical neurons showed a hypoxic-ischemia time-dependent increase in cell death and that NP1 induction preceded the actual neuronal death. NP1 gene silencing by NP1-specific siRNA significantly reduced neuronal death. The specificity of NP1 induction in neuronal death was further confirmed by using NP1 (-/-) null primary cortical neurons. Declines in phospho-Akt (i.e. deactivation) were observed concurrent with decreased phosphorylation of its downstream substrate GSK-3 alpha/beta (at Ser21/Ser9) (i.e. activation) and increased GSK-3 alpha and GSK-3 beta kinase activities, which occurred prior to NP1 induction. Expression of a dominant-negative inhibitor of Akt (Akt-kd) blocked phosphorylation of GSK-3 alpha/beta and subsequently enhanced NP1 induction. Whereas, overexpression of constitutively activated Akt (Akt-myr) or wild-type Akt (wtAkt) increased GSK-alpha/beta phosphorylation and attenuated NP1 induction. Transfection of neurons with GSK-3 alpha siRNA completely blocked NP1 induction and cell death. Similarly, overexpression of the GSK-3 beta inhibitor Frat1 or the kinase mutant GSK-3 beta KM, but not the wildtype GSK-3 beta WT, blocked NP1 induction and rescued neurons from death. Our findings clearly implicate both GSK-3 alpha- and GSK-3 beta-dependent mechanism of NP1 induction and point to a novel mechanism in the regulation of hypoxic-ischemic neuronal death. (C) 2010 Elsevier Inc. All rights reserved.