Zinc-induced inhibition of protein synthesis and reduction of connexin-43 expression and intercellular communication in mouse cortical astrocytes Mehrdad Alirezaei, 1 Elodie Mordelet, 2 Nathalie Rouach 1 , Angus C. Nairn, 3 Jacques Glowinski 1 and Joe Èl Pre  mont 1 1 INSERM U114, Colle Á ge de France, 11, Place Marcelin Berthelot, 75231 Paris Cedex 05, France 2 Unite  de ge Âne  tique mole  culaire des virus respiratoires Institut Pasteur 25±28 rue du Dr Roux, 75274 Paris Cedex 15 Paris, France 3 Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York 10021, USA Keywords: astrocytes, cerebral cortex, connexin, mouse, protein synthesis, zinc Abstract Zinc released from a subpopulation of glutamatergic synapses, mainly localized in the cerebral cortex and the hippocampus, facilitates or reduces glutamatergic transmission by acting on neuronal AMPA and NMDA receptors, respectively. However, neurons are not the only targets of zinc. In the present study, we provide evidence that zinc inhibits protein synthesis in cultured astrocytes from the cerebral cortex of embryonic mice. This inhibition, which reached 85% in the presence of 100 mM zinc, was partially and slowly reversible and resulted from the successive inhibition of the elongation and the initiation steps of the protein translation process. This was assessed by measuring the phosphorylation level of the elongation factor eEF-2 and of the a subunit of the initiation factor eIF-2. Due to the rapid turnover of connexin-43 that forms junction channels in cultured astrocytes, the zinc-induced decrease of protein synthesis led to a partial disappearance of connexin-43, which was associated with an inhibition of the cellular coupling in the astrocytic syncitium. In conclusion, zinc not only inhibits protein synthesis in neurons, as previously demonstrated, but also in astrocytes. The resulting decrease in the intercellular communication between astrocytes should alter the function of surrounding neurons as well as their survival. Introduction Zinc is non-uniformly distributed in the brain, the highest concen- tration being found in the cerebral cortex, the hippocampus and the amygdala (Assaf & Chung, 1984; Howell et al., 1984; Frederickson & Danscher, 1990). Zinc is released from nerve terminals under neuronal stimulation and its extracellular concentration can reach a local concentration estimated to be in the 100- to 300-mM range (Howell et al., 1984). Zinc is co-located and co-released with glutamate from some excitatory synapses (Choi et al., 1989; Choi & Koh, 1998). Glutamate responses mediated by either AMPA or NMDA receptors can be, respectively, ampli®ed or reduced by zinc (Peters et al., 1987) (Rassendren et al., 1990). Zinc is strongly neurotoxic for cultured neurons and there is strong evidence favouring a prominent role of zinc in neuronal death occurring in the hippocampus after transient global ischemia. Indeed, a close correspondence has been shown between the localization of neurons that accumulate zinc and those that degenerate in this pathological situation (Koh et al., 1996). Accumulating observations indicate that astrocyto±neuronal inter- actions contribute in several ways to synaptic transmission, in addition to the well-documented glutamatergic transmission. Indeed, astrocytes have been shown to take up glutamate released from neurons through a regulated process involving speci®c transporters and reciprocally, glutamate can be released from astrocytes through a calcium-dependent process (Araque et al., 1998; Araque et al., 1999a; Araque et al., 1999b). Zinc can also accumulate into astrocytes and promote the expression of metallothioneins, which exert a protecting effect against ischemia- or epilepsy-induced neurodegeneration (Aschner, 1997a; Aschner et al., 1998). We have recently demonstrated that zinc strongly depresses protein synthesis in mouse cortical neurons through a process involving blockade of the initiation step of protein translation (Alirezaei et al., 1999). Such an effect may contribute to the neurotoxic effect of Zn 2+ . This study was undertaken to determine whether Zn 2+ could also inhibit the rate of protein synthesis in cortical astrocytes from mouse and whether such an effect could have critical physiological consequences. Astrocyte coupling through gap junctions, which intervenes in astrocyto±neuronal interactions (Tabernero et al., 2001), was also investigated. Gap junctions are composed of integral membrane proteins called connexins, and connexin-43 (Cx43) is the main constituent of astrocytic gap junctions (Falk et al., 1997; Ahmad et al., 1998). One of the most unusual properties of connexins is their high turnover rate (half-life between 1.5 and 5 h) even after their incorporation into gap junction plaques (Laird et al., 1991; Laird et al., 1995). Therefore, attempts were made to determine whether the effect of Zn 2+ on the rate of protein synthesis in astrocytes might in¯uence the amount of Cx43 and thus modulate intercellular coupling. Correspondence: Dr J. Pre Âmont, as above. E-mail: joel.premont@college-de-france.fr Received 22 February 2002, revised 4 June 2002, accepted 11 July 2002 doi:10.1046/j.1460-9568.2002.02180.x European Journal of Neuroscience, Vol. 16, pp. 1037±1044, 2002 ã Federation of European Neuroscience Societies