Department of Physiology and Pharmacology, Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada T2N 4N1.
Proc Natl Acad Sci U S A. 2012 Jan 31;109(5):1737-42. doi: 10.1073/pnas.1110789109. Epub 2012 Jan 17.
N-methyl-d-aspartate receptors (NMDARs) mediate critical CNS functions, whereas excessive activity contributes to neuronal damage. At physiological glycine concentrations, NMDAR currents recorded from cultured rodent hippocampal neurons exhibited strong desensitization in the continued presence of NMDA, thus protecting neurons from calcium overload. Reducing copper availability by specific chelators (bathocuproine disulfonate, cuprizone) induced nondesensitizing NMDAR currents even at physiologically low glycine concentrations. This effect was mimicked by, and was not additive with, genetic ablation of cellular prion protein (PrP(C)), a key copper-binding protein in the CNS. Acute ablation of PrP(C) by enzymatically cleaving its cell-surface GPI anchor yielded similar effects. Biochemical studies and electrophysiological measurements revealed that PrP(C) interacts with the NMDAR complex in a copper-dependent manner to allosterically reduce glycine affinity for the receptor. Synthetic human Aβ(1-42) (10 nM-5 μM) produced an identical effect that could be mitigated by addition of excess copper ions or NMDAR blockers. Taken together, Aβ(1-42), copper chelators, or PrP(C) inactivation all enhance the activity of glycine at the NMDAR, giving rise to pathologically large nondesensitizing steady-state NMDAR currents and neurotoxicity. We propose a physiological role for PrP(C), one that limits excessive NMDAR activity that might otherwise promote neuronal damage. In addition, we provide a unifying molecular mechanism whereby toxic species of Aβ(1-42) might mediate neuronal and synaptic injury, at least in part, by disrupting the normal copper-mediated, PrP(C)-dependent inhibition of excessive activity of this highly calcium-permeable glutamate receptor.
N-甲基-D-天冬氨酸受体（NMDAR）介导中枢神经系统的关键功能，而过度的活性则导致神经元损伤。在生理浓度的甘氨酸存在下，从培养的啮齿动物海马神经元记录的 NMDAR 电流在 NMDA 的持续存在下表现出强烈的脱敏，从而保护神经元免受钙超载的影响。通过特异性螯合剂（二亚氨基二硫代苯甲酸，铜锌卟啉）降低铜的可用性，甚至在生理上低的甘氨酸浓度下也会诱导非脱敏的 NMDAR 电流。这种效应被细胞朊蛋白（PrP(C)）的基因缺失所模拟，而不是叠加，PrP(C)是中枢神经系统中关键的铜结合蛋白。通过酶切其细胞表面 GPI 锚定来急性切除 PrP(C)也会产生类似的效果。生化研究和电生理测量表明，PrP(C)以铜依赖性的方式与 NMDAR 复合物相互作用，以变构方式降低受体对甘氨酸的亲和力。合成的人类 Aβ(1-42)（10 nM-5 μM）产生了相同的效果，通过添加过量的铜离子或 NMDAR 阻滞剂可以减轻这种效果。总之，Aβ(1-42)、铜螯合剂或 PrP(C)失活都会增强 NMDAR 上甘氨酸的活性，导致病理性的非脱敏稳态 NMDAR 电流和神经毒性。我们提出了 PrP(C)的生理作用，它限制了过度的 NMDAR 活性，否则可能会促进神经元损伤。此外，我们提供了一个统一的分子机制，即有毒的 Aβ(1-42)物种可能通过干扰正常的铜介导的、PrP(C)依赖的对这种高度钙渗透性谷氨酸受体过度活性的抑制，在一定程度上介导神经元和突触损伤。
