Calcium Permeable AMPA Receptors: Signaling, Toxicity and Control

Ca2 渗透性 AMPA 受体在比 NMDA 受体限制更少的条件下被激活，存在于多种神经元类型中，并且可以调节通常由 NMDAR Ca2 电流控制的通路。我们已经证明，Ca2 渗透性 AMPAR 与 NMDAR 一样，可以激活神经元一氧化氮合酶 (nNOS)。在我们的第一个目标中，我们将确定 Ca2 渗透性 AMPA 受体是否可以通过 Akt 和 CaMKII 激活 nNOS 的连续调节磷酸化，我们之前（Rameau 等人，2007）表明这是由 NMDAR 诱导的。我们将研究有助于 Ca2 渗透性 AMPAR 控制 nNOS 的脚手架结构和生化途径 Akt 和 CaMKII。当通过 RNA 编辑修饰时，GluR2 主要阻断 AMPAR 通道的 Ca2 电导。相比之下，未经编辑的 GluR2 通过其 Ca2 渗透性和组成型运输而具有剧毒（Mahajan 和 Ziff，2007）。最近我们发现NMDAR活性可以降解GluR2前mRNA编辑酶ADAR2。我们的第二个目标是分析 ADAR2 的病理性 NMDAR 依赖性蛋白水解裂解、RNA 编辑活性下降时未编辑的 GluR2 的产生，以及 Ca2 渗透性 AMPAR（包括未编辑的 GluR2）杀死神经元的机制。为了限制Ca2+毒性，细胞进化出了限制突触AMPARCa2+电流的机制，其中Ca2+不可渗透的AMPA受体取代了突触处Ca2+不可渗透的受体。在初步研究中，我们发现 ER 库中 Ca2 的释放与 CaMKII 协同刺激 GluR2 从内质网到质膜的运输。在我们的第三个目标中，我们将研究 GluR2 从 ER 中的 Ca2 依赖性运输，并区分其控制是否依赖于 GluR2 组装成四聚体或 GluR2 从 ER 保留中释放。我们将确定响应 Ca2 的 GluR2 结构域以及细胞内 Ca2 水平、CaMKII、PICK1 在输出机制中的作用，包括 PICK1-CaMKII 复合物的作用。这些研究将对 Ca2 渗透性 AMPAR 控制的生理和病理途径以及调节 Ca2 渗透性 AMPAR 功能的机制进行全面分析。

Ca2+-permeable AMPA receptors are activated under less restrictive conditions than the NMDA receptor, are found in numerous neuron types, and may regulate pathways that are more generally controlled by NMDAR Ca2+ currents. We have shown that Ca2+-permeable AMPARs, like the NMDAR, can activate neuronal nitric oxide synthase (nNOS). In our first Aim we will determine if Ca2+-permeable AMPA receptors can activate successive regulatory phosphorylations of nNOS by Akt and CaMKII, previously shown by us (Rameau et al., 2007) to be induced by the NMDAR. We will study scaffolding structures and biochemical pathways Akt and CaMKII that contribute to nNOS control by Ca2+-permeable AMPARs. GluR2 when modified by RNA editing dominantly blocks the Ca2+ conductance of AMPAR channels. In contrast, unedited GluR2 is highly toxic through its Ca2+ permeability and constitutive trafficking (Mahajan and Ziff, 2007). Recently we have found that NMDAR activity can degrade the GluR2 pre mRNA editing enzyme, ADAR2. Our second Aim is to analyze the pathological, NMDAR-dependent proteolytic cleavage of ADAR2, the production of unedited GluR2 as RNA editing activity declines, and the mechanisms by which Ca2+-permeable AMPARs including the unedited GluR2 can kill neurons. To limit Ca2+-toxicity, cells have evolved mechanisms for restricting synaptic AMPAR Ca2+ currents in which Ca2+-impermeable AMPA receptors replace Ca2+-impermeable ones at the synapse. In preliminary studies, we have found that release of Ca2+ from ER stores cooperates with CaMKII to stimulate trafficking of GluR2 from the endoplasmic reticulum to the plasma membrane. In our third Aim, we will study the Ca2+-dependent trafficking of GluR2 from the ER, and distinguish if its control relies on the assembly of GluR2 into tetramers or release of GluR2 from ER retention. We will determine the domains of GluR2 that respond to Ca2+ and the roles of intracellular Ca2+ levels, CaMKII, PICK1 in the export mechanism, including the roles of PICK1-CaMKII complexes. These studies will provide a comprehensive analysis of physiologic and pathologic pathways controlled by Ca2+-permeable AMPARs and mechanisms for regulating Ca2+-permeable AMPAR function.