STATIN, A MARKER OF CELL-CYCLE ARREST, IS OVEREXPRESSED DURING THE EARLY PHASE OF DELAYED NMDA TOXICITY IN HIPPOCAMPAL CELL-CULTURES

Statin is a 57-kDa protein exclusively expressed in nuclei of nonproli ferating mammalian cells. Recent studies have suggested that statin ma y play a role in the maintenance of growth arrest. Several lines of ev idence also support the notion that a variety of genes and gene produc ts are modulated during cell proliferation and cell death. The present study examined the possibility that statin expression could be modula ted during neuronal injury using N-methyl-Daspartate (NMDA)-induced to xicity to rat embryonic hippocampal cultures as a model. Immunocytoche mical studies using a monoclonal antibody to statin revealed a promine nt nuclear localization of statin in cultured hippocampal cells. Weste rn blot analysis showed that this antibody recognizes a 57-kDa protein band, indicative of the presence of statin in this preparation. Brief exposure of hippocampal neurons to NMDA (500 mu M) produced severe ne uronal degeneration over the subsequent hours. NMDA-treated neurons ma rkedly overexpressed statin. Both NMDA-induced neuronal toxicity and s tatin overexpression were prevented by the NMDA receptor antagonist ()-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohept-5,10-imine hydroge n maleate (MK-801). Interestingly, time course studies indicate that t he increased expression of statin observed following NMDA exposure cle arly preceded the appearance of the first signs of neuronal death as d etermined by vital staining. In addition, exposure of hippocampal neur ons to the Ca2+ ionophore, A23187, produced a marked increase in stati n immunodetection, indicating that statin expression is likely regulat ed in a Ca2+-dependent manner. Thus, these results show that statin, w hich is expressed at low levels in embryonic rat cultured hippocampal neurons, is rapidly overexpressed following a toxic insult produced by the activation of the NMDA receptor. The observation that statin over expression occurs prior to neuronal death raises the possibility that the up-regulation of statin could be used as an early index Of neurona l injury. (C) 1994 Academic Press, Inc.