Ahn Y H, Kim Y H, Hong S H, Koh J Y
Department of Molecular Biology, Seoul National University, Korea.
Exp Neurol. 1998 Nov;154(1):47-56. doi: 10.1006/exnr.1998.6931.
The central nervous system (CNS) contains a large amount of zinc; a substantial fraction of it is located inside synaptic vesicles of glutamatergic terminals in chelatable forms and released in a calcium-dependent manner with intense neuronal activity. Recently, it has been shown that excessive zinc influx can kill neurons in rats subjected to transient forebrain ischemia. On the other hand, severe depletion of zinc has been also reported to induced cell death in certain nonneuronal cells. Since decreases in tissue zinc have been associated with Alzheimer's disease (AD) and senile macular degeneration, we examined whether depletion of intracellular zinc with a zinc chelator can directly induce neuronal death in mouse cortical cultures. Exposure of cortical cultures to a cell-permeant zinc-chelator, N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN, 0.5-3.0 microM) induced gradually developing neuronal degeneration accompanied by various features of apoptosis: cell body shrinkage, nuclear condensation and fragmentation, and internucleosomal DNA breakage. At higher concentrations, TPEN induced additional glial cell death. TPEN-induced cell death was completely blocked by coaddition of zinc. Addition of a protein synthesis inhibitor cycloheximide as well as a caspase inhibitor carbobenzoxy-valyl-alanyl-aspartyl-fluoromethyl ketone (zVAD-fmk) markedly attenuated TPEN-induced neuronal death. On the other hand, brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), phorbol 12-myristate 13-acetate (PMA), high K+, or an antioxidant, trolox, did not show any protective effect. The present results demonstrated that depletion of intracellular zinc induces protein synthesis-dependent neuronal apoptosis in cortical culture. Combined with the findings that extracellular zinc may promote extracellular beta-amyloid (A beta) aggregation and that total tissue zinc is reduced in AD, present results suggest a possibility that redistribution of zinc from intracellular to extracellular space may synergistically contribute to neuronal apoptosis in AD.
中枢神经系统（CNS）含有大量锌；其中很大一部分以可螯合的形式存在于谷氨酸能终末的突触小泡内，并在强烈的神经元活动时以钙依赖的方式释放。最近，研究表明过量的锌流入会导致短暂性前脑缺血大鼠的神经元死亡。另一方面，也有报道称锌的严重缺乏会诱导某些非神经元细胞死亡。由于组织锌含量的降低与阿尔茨海默病（AD）和老年性黄斑变性有关，我们研究了用锌螯合剂耗尽细胞内锌是否能直接诱导小鼠皮质培养物中的神经元死亡。将皮质培养物暴露于细胞可渗透的锌螯合剂N，N，N'，N'-四（2-吡啶甲基）乙二胺（TPEN，0.5 - 3.0 microM）会诱导逐渐发展的神经元变性，并伴有凋亡的各种特征：细胞体收缩、核浓缩和碎片化以及核小体间DNA断裂。在较高浓度下，TPEN会诱导额外的胶质细胞死亡。锌的共同添加完全阻断了TPEN诱导的细胞死亡。添加蛋白质合成抑制剂环己酰亚胺以及半胱天冬酶抑制剂苄氧羰基 - 缬氨酰 - 丙氨酰 - 天冬氨酰 - 氟甲基酮（zVAD - fmk）可显著减轻TPEN诱导的神经元死亡。另一方面，脑源性神经营养因子（BDNF）、胰岛素样生长因子 - 1（IGF - 1）、佛波酯12 - 肉豆蔻酸酯13 - 乙酸酯（PMA）、高钾或抗氧化剂生育三烯酚均未显示出任何保护作用。目前的结果表明，细胞内锌的耗尽会在皮质培养物中诱导蛋白质合成依赖性的神经元凋亡。结合细胞外锌可能促进细胞外β淀粉样蛋白（Aβ）聚集以及AD中总组织锌减少的发现，目前的结果表明锌从细胞内空间重新分布到细胞外空间可能协同导致AD中的神经元凋亡。
