Liu Baosong, Liao Mingxia, Mielke John G, Ning Ke, Chen Yonghong, Li Lei, El-Hayek Youssef H, Gomez Everlyne, Zukin R Suzanne, Fehlings Michael G, Wan Qi
Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, M5T 2S8, Canada.
J Neurosci. 2006 May 17;26(20):5309-19. doi: 10.1523/JNEUROSCI.0567-06.2006.
Regulated AMPA receptor (AMPAR) trafficking at excitatory synapses is a mechanism critical to activity-dependent alterations in synaptic efficacy. The role of regulated AMPAR trafficking in insult-induced synaptic remodeling and/or cell death is, however, as yet unclear. Here we show that brief oxygen-glucose deprivation (OGD), an in vitro model of brain ischemia, promotes redistribution of AMPARs at synapses of hippocampal neurons, leading to a switch in AMPAR subunit composition. Ischemic insults promote internalization of glutamate receptor subunit 2 (GluR2)-containing AMPARs from synaptic sites via clathrin-dependent endocytosis and facilitate delivery of GluR2-lacking AMPARs to synaptic sites via soluble N-ethylmaleimide-sensitive factor attachment protein receptor-dependent exocytosis, evident at early times after insult. The OGD-induced switch in receptor subunit composition requires PKC activation, dissociation of GluR2 from AMPA receptor-binding protein, and association with protein interacting with C kinase-1. We further show that AMPARs at synapses of insulted neurons exhibit functional properties of GluR2-lacking AMPARs. AMPAR-mediated miniature EPSCs exhibit increased amplitudes and enhanced sensitivity to subunit-specific blockers of GluR2-lacking AMPARs, evident at 24 h after ischemia. The OGD-induced alterations in synaptic AMPA currents require clathrin-mediated receptor endocytosis and PKC activation. Thus, ischemic insults promote targeting of GluR2-lacking AMPARs to synapses of hippocampal neurons, mechanisms that may be relevant to ischemia-induced synaptic remodeling and/or neuronal death.
在兴奋性突触处，受调控的α-氨基-3-羟基-5-甲基-4-异恶唑丙酸受体（AMPAR）转运是对突触效能中活动依赖性改变至关重要的一种机制。然而，受调控的AMPAR转运在损伤诱导的突触重塑和/或细胞死亡中的作用尚不清楚。在此我们表明，短暂氧糖剥夺（OGD），一种脑缺血的体外模型，促进海马神经元突触处AMPAR的重新分布，导致AMPAR亚基组成的转变。缺血性损伤通过网格蛋白依赖性内吞作用促进含谷氨酸受体亚基2（GluR2）的AMPAR从突触位点内化，并通过可溶性N-乙基马来酰亚胺敏感因子附着蛋白受体依赖性胞吐作用促进缺乏GluR2的AMPAR向突触位点的递送，在损伤后的早期即可明显观察到。OGD诱导的受体亚基组成转变需要蛋白激酶C（PKC）激活、GluR2从AMPA受体结合蛋白解离以及与蛋白激酶C相互作用蛋白1结合。我们进一步表明，受损伤神经元突触处的AMPAR表现出缺乏GluR2的AMPAR的功能特性。AMPAR介导的微小兴奋性突触后电流（mEPSC）幅度增加，并且对缺乏GluR2的AMPAR的亚基特异性阻断剂的敏感性增强，在缺血后24小时即可明显观察到。OGD诱导的突触AMPA电流改变需要网格蛋白介导的受体内吞作用和PKC激活。因此，缺血性损伤促进缺乏GluR2的AMPAR靶向海马神经元的突触，这些机制可能与缺血诱导的突触重塑和/或神经元死亡有关。
