Molecular mechanisms of zinc toxicity in primary cultured cortical neurons and glial cells

Abstract

Zinc is released from synaptic terminals and mediates synaptic plasticity in various physiological conditions. In pathological conditions, high concentration of zinc released from synaptic terminals and translocated to postsynaptic neurons could induce neuronal cell death. In this study, the molecular mechanisms underlying zinc toxicity in primary cultured cortical neurons and in glial cells were explored. The mechanism by which neurotrophic factors potentiate zinc toxicity was investigated using primary cultured cortical neurons, While a brief treatment of low concentration of zinc [eg. 80 uM, 30 min] produced a low level [eg. 25%] of cell death, such zinc toxicity was strongly potentiated by pretreatment of various neurotrophic factors including BDNF, NT-3, NT-4, insulin and IGF-I, indicating that these neurotrophic factors would act as cytotoxic factors in certain conditions. In the current study, IGF-I was used in studying the mechanism underlying the zinc-toxicity potentiation by IGF-L Administration of cycloheximide and anisomycin during IGF-1 pretreatment inhibited the potentiation of zinc toxicity, indicating that new protein synthesis was essential in the process of potentiated cell death by IGF-I. The potentiation of zinc toxicity was completely or partly inhibited by GF109203X (a general inhibitor of PKC), LY294002 (a specific inhibitor of PI-3K), or rapamycin (a specific inhibitor of p70s6K), suggesting that PKC, PI-3K, and p70s6K signaling pathways were involved in the IGF-I mediated zinc-toxicity potentiation. In addition, the zinc-toxicity potentiation was suppressed by deferoxamine, an inhibitor of G1 to S cell cycle progression, and olomoucine, a specific inhibitor of cdk4, 6, indicating that the cell cycle regulators, cdk4 and cdk6, could be involved in the zinc-toxicity potentiation. Consistently, it was observed that the cyclin D1 expression was increased during IGF-I treatment. These results suggest that cyclin Dl may act as an endogenous f...