Changes in calcium dynamics following the reversal of the sodium-calcium exchanger have a key role in AMPA receptor-mediated neurodegeneration via calpain activation in hippocampal neurons
Changes in calcium dynamics following the reversal of the sodium-calcium exchanger have a key role in AMPA receptor-mediated neurodegeneration via calpain activation in hippocampal neurons
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DOI：
10.1038/sj.cdd.4402171
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发表时间：
2007-09-01
影响因子：
12.4
通讯作者：
Carvalho, C. M.
中科院分区：
文献类型：
--
作者：
Araujo, I. M.;Carreira, B. P.;Carvalho, C. M.
钙蛋白酶对Na+/Ca 2+交换器（NCX）的蛋白水解裂解损害钙稳态，导致延迟的钙超载和兴奋性毒性细胞死亡。然而，目前尚不清楚交换器的逆转是否有助于激活钙蛋白酶并触发神经元死亡。我们研究了在α-氨基-3-羟基-5-甲基异恶唑-4-丙酸酯（AMPA）受体刺激的海马神经元中，NCX逆转在Ca 2+动力学、钙蛋白酶激活和细胞活力中的作用。AMPA受体的选择性过度激活引起NCX的逆转，其占细胞内游离钙浓度（[Ca 2 +]（i））升高的约30%。NCX反向模式抑制剂2-[2-[4-（4-硝基苄氧基）苯基]乙基]异噻唑烷（KB-R7943）部分抑制[Ca 2 +]（i）的初始增加，并阻止[Ca 2 +]（i）的延迟增加。同时，AMPA受体的过度激活强烈激活钙蛋白酶，并导致NCX 3的蛋白水解。KB-R7943阻止钙蛋白酶活化、NCX 3的切割，并且具有神经保护作用。NCX 3的沉默减少了Ca 2+摄取，钙蛋白酶激活，并具有神经保护作用。我们的数据首次表明，NCX逆转是AMPA受体刺激后的早期事件，并与钙蛋白酶的激活有关。由于钙蛋白酶激活随后使NCX失活，导致二次Ca 2+进入，NCX可被视为一种新的自杀底物，在一个Ca 2+依赖性环中操作，触发细胞死亡，并作为神经保护的靶点。
Proteolytic cleavage of the Na+/Ca2+ exchanger (NCX) by calpains impairs calcium homeostasis, leading to a delayed calcium overload and excitotoxic cell death. However, it is not known whether reversal of the exchanger contributes to activate calpains and trigger neuronal death. We investigated the role of the reversal of the NCX in Ca2+ dynamics, calpain activation and cell viability, in alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-stimulated hippocampal neurons. Selective overactivation of AMPA receptors caused the reversal of the NCX, which accounted for approximately 30% of the rise in intracellular free calcium concentration ([Ca2+](i)). The NCX reverse-mode inhibitor, 2-[2-[4-(4-nitrobenzyloxy) phenyl]ethyl] isothiourea (KB-R7943), partially inhibited the initial increase in [Ca2+](i), and prevented a delayed increase in [Ca2+](i). In parallel, overactivation of AMPA receptors strongly activated calpains and led to the proteolysis of NCX3. KB-R7943 prevented calpain activation, cleavage of NCX3 and was neuroprotective. Silencing of NCX3 reduced Ca2+ uptake, calpain activation and was neuroprotective. Our data show for the first time that NCX reversal is an early event following AMPA receptor stimulation and is linked to the activation of calpains. Since calpain activation subsequently inactivates NCX, causing a secondary Ca2+ entry, NCX may be viewed as a new suicide substrate operating in a Ca2+-dependent loop that triggers cell death and as a target for neuroprotection.