Chandra T, Maier W, König H-G, Hirzel K, Kögel D, Schüler T, Chandra A, Demirhan I, Laube B
Abteilung Neurochemie, Max-Planck-Institut für Hirnforschung, Deutschordenstr. 46, 60528 Frankfurt, Germany.
Neuroscience. 2005;134(1):145-53. doi: 10.1016/j.neuroscience.2005.02.049.
We investigated the effect of type 1 human immunodeficiency virus (HIV-1) regulatory protein Tat on N-methyl-d-aspartate (NMDA) receptors expressed in Xenopus oocytes by voltage-clamp recording and its role in NMDA-mediated neurotoxicity using cultured rat hippocampal neurons. Tat (0.01-1muM) potentiated NMDA-induced currents of recombinant NMDA receptors. However, in the presence of Zn(2+), the potentiating effect of Tat was much more pronounced, indicating an additional Zn(2+)-related effect on NMDA receptors. Consistently, Tat potentiated currents of the particularly Zn(2+)-sensitive NR1/NR2A NMDA receptor with a higher efficacy, whereas currents from a Zn(2+)-insensitive mutant were only marginally augmented. In addition, chemical-modified Tat, deficient for metal binding, did not reverse Zn(2+)-mediated inhibition of NMDA responses, demonstrating that Tat disinhibits NMDA receptors from Zn(2+)-mediated antagonism by complexing the cation. We therefore investigated the interplay of Tat and Zn(2+) in NMDA-mediated neurotoxicity using cultures of rat hippocampal neurons. Zn(2+) exhibited a prominent rescuing effect when added together with the excitotoxicant NMDA, which could be reverted by the Zn(2+)-chelator tricine. Similar to tricine, Tat enhanced NMDA-mediated neurotoxicity in the presence of neuroprotective Zn(2+) concentrations. Double-staining with antibodies against Tat and the NR1 subunit of the NMDA receptor revealed partial colocalization of the immunoreactivities in membrane patches of hippocampal neurons, supporting the idea of a direct interplay between Tat and glutamatergic transmission. We therefore propose that release of Zn(2+)-mediated inhibition of NMDA receptors by HIV-1 Tat contributes to the neurotoxic effect of glutamate and may participate in the pathogenesis of AIDS-associated dementia.
我们通过电压钳记录研究了1型人类免疫缺陷病毒（HIV-1）调节蛋白Tat对非洲爪蟾卵母细胞中表达的N-甲基-D-天冬氨酸（NMDA）受体的影响，并利用培养的大鼠海马神经元研究了其在NMDA介导的神经毒性中的作用。Tat（0.01-1μM）增强了重组NMDA受体的NMDA诱导电流。然而，在锌离子（Zn²⁺）存在的情况下，Tat的增强作用更为明显，表明对NMDA受体存在额外的与锌离子相关的影响。一致地，Tat对特别锌离子敏感的NR1/NR2A NMDA受体电流的增强效果更高，而来自锌离子不敏感突变体的电流仅略有增加。此外，缺乏金属结合能力的化学修饰Tat并不能逆转锌离子介导的对NMDA反应的抑制作用，表明Tat通过与阳离子络合解除了锌离子对NMDA受体的拮抗作用。因此，我们利用大鼠海马神经元培养物研究了Tat和锌离子在NMDA介导的神经毒性中的相互作用。当与兴奋性毒性剂NMDA一起添加时，锌离子表现出显著的挽救作用，而锌离子螯合剂曲昔派特可以逆转这种作用。与曲昔派特类似，在具有神经保护作用的锌离子浓度存在的情况下，Tat增强了NMDA介导的神经毒性。用抗Tat抗体和NMDA受体的NR1亚基进行双重染色显示，免疫反应性在海马神经元的膜片中部分共定位，支持了Tat与谷氨酸能传递之间直接相互作用的观点。因此，我们提出HIV-1 Tat解除锌离子介导的对NMDA受体的抑制作用有助于谷氨酸的神经毒性作用，并可能参与艾滋病相关痴呆的发病机制。
