The Roles of NR2A and NR2B in Excitotoxicity

描述（由申请人提供）：众所周知，缺血性损伤后的兴奋性毒性损伤是卒中后细胞死亡的主要原因之一。尽管有大量证据表明NMDA受体与兴奋性毒性有关，但NMDA受体（NMDAR）拮抗剂在治疗中风方面尚未证明具有临床益处。这可能是因为过多的NMDAR信号是有害的，但一些信号是必要的和神经保护的。因此，重要的是剖析NMDAR激活的下游途径，以便可以靶向特定的促死亡途径。 一种方法是鉴定和研究与NMDAR的C末端尾部直接相关的蛋白质。事实上，通过NMDAR的Ca 2+内流比通过其他Ca 2+可渗透通道更有效地促进细胞死亡，表明参与兴奋性毒性细胞死亡的蛋白质与NMDAR直接相关。最初的药理学数据表明，特定的NMDAR亚基，特别是NR 2A和NR 2B，可能在兴奋性毒性中发挥不同的作用。然而，迄今为止的结果令人困惑和矛盾。这可能是由于药理学拮抗剂的局限性，其没有解决单个亚基特异性募集到突触并随后激活哪些蛋白质的问题。我们建议专门研究与NR 2A和NR 2B的尾部相关的蛋白质，并使用分子遗传学工具来剖析NR 2A和NR 2B在兴奋性毒性中的作用。我们相信这些研究将阐明NMDAR激活下游的关键途径，这些途径可能是治疗靶点。 具体而言，我们将：1）确定NR 2A和NR 2B NMDA亚基在一般兴奋性毒性中的作用，以及它们在中间神经元亚型对兴奋性毒性的不同敏感性中发挥的作用。大量的数据表明NR 2A和NR 2B在可塑性和可能的兴奋毒性中起不同的作用。然而，已经使用的药理学工具提供了相互矛盾的结果。我们将使用分子工具来进一步表征这些亚基的作用。2)筛选与NR 2A的C-末端尾部相互作用的LTP负调节因子。我们的初步数据表明，LTP的负调节剂特异性结合到NR 2A的尾部，而不是NR 2B。被鉴定为在LTP中起作用的分子也可能参与缺氧LTP，这是一种由兴奋性毒性机制引起的病理性和有害形式的可塑性。 公共卫生相关性：尽管有大量证据表明NMDA受体与兴奋性毒性有关，但NMDA受体（NMDAR）拮抗剂在治疗中风方面尚未证明具有临床益处。这可能是因为过多的NMDAR信号是有害的，但一些信号是必要的和神经保护的。通过鉴定和剖析NMDAR激活下游的各个途径，可以阻断特定的促死亡途径，从而减轻兴奋性毒性损伤而不干扰神经保护性NMDAR信号传导。

DESCRIPTION (provided by applicant): Excitotoxic damage following ischemic insult is well known to be one of the major causes of cell death following stroke. In spite of the large amount of evidence implicating NMDA receptors in excitotoxicity, NMDA receptor (NMDAR) antagonists have not proven clinically beneficial in the treatment of stroke. This could be due to the fact that too much NMDAR signaling is harmful, but some signaling is necessary and neuroprotective. Thus it is important to dissect the pathways downstream of NMDAR activation so that specific pro-death pathways may be targeted. One way to do this is to identify and investigate proteins that are directly associated with the C-terminal tails of the NMDARs. Indeed, Ca2+ influx through NMDARs promotes cell death more efficiently than through other Ca2+ permeable channels, suggesting that proteins involved in excitotoxic cell death are directly associated with NMDARs. Initial pharmacological data indicate that specific NMDAR subunits, specifically NR2A and NR2B, may play different roles in excitotoxicity. However, the results thus far are confusing and contradictory. This may be due to limitations of pharmacological antagonists which do not address the question of which proteins the individual subunits are specifically recruiting to the synapses and subsequently activating. We propose to specifically investigate the proteins associated with the tails of NR2A and NR2B and to use molecular genetic tools to dissect the roles of NR2A and NR2B in excitotoxicity. We believe these studies will elucidate critical pathways downstream of NMDAR activation that may be targeted therapeutically. Specifically, we will: 1) Determine the roles of the NR2A and NR2B NMDA subunits in excitotoxicity in general, as well as what role they play in the differential sensitivity of subtypes of interneurons to excitotoxicity. Considerable data indicates NR2A and NR2B play differential roles in plasticity and perhaps also excitotoxicity. However, the pharmacological tools that have been used have provided conflicting results. We will use molecular tools to further characterize the roles of these subunits. 2) Screen for a negative regulator of LTP that interacts with the C-terminal tail of NR2A. Our preliminary data indicate a negative regulator of LTP binds specifically to the tail of NR2A and not NR2B. Molecules identified as having a role in LTP may also participate in anoxic LTP, a pathological and harmful form of plasticity resulting from excitotoxic mechanisms. PUBLIC HEALTH RELEVANCE: In spite of the large amount of evidence implicating NMDA receptors in excitotoxicity, NMDA receptor (NMDAR) antagonists have not proven clinically beneficial in the treatment of stroke. This could be due to the fact that too much NMDAR signaling is harmful, but some signaling is necessary and neuroprotective. By identifying and dissecting the individual pathways downstream of NMDAR activation, specific pro-death pathways may be blocked, thus mitigating excitotoxic damage without interfering with neuroprotective NMDAR signaling.