Calcium Permeable AMPA Receptors: Signaling, Toxicity and Control

与NMDA受体相比，钙通透性AMPA受体在限制性较低的条件下被激活，存在于多种神经元类型中，并可能调节更普遍地由NMDAR钙电流控制的通路。我们已经证明，与NMDAR一样，钙离子通透性AMPAR可以激活神经元型一氧化氮合酶(NNOS)。在我们的第一个目标中，我们将确定可渗透钙的AMPA受体是否能激活Akt和CaMKII对nNOS的连续调节磷酸化，这是我们以前(Rameau等人，2007)所证明的由NMDAR诱导的。我们将研究支架结构和生物化学途径Akt和CaMKII，它们有助于钙通透性AMPAR对nNOS的控制。当GluR2被RNA编辑修饰时，主要阻断AMPAR通道的钙电导。相比之下，未经编辑的GluR2由于其钙渗透性和结构性贩运而具有高度毒性(Mahajan和Ziff，2007)。最近我们发现，NMDAR活性可以降解GluR2 Pre mRNA编辑酶ADAR2。我们的第二个目标是分析ADAR2依赖于NMDAR的病理性蛋白分解，随着RNA编辑活性的下降而产生未编辑的GluR2，以及包括未编辑的GluR2在内的钙通透性AMPAR可以杀死神经元的机制。为了限制钙毒性，细胞已经进化出限制突触AMPAR钙电流的机制，在突触上，不透钙的AMPA受体取代不透钙的受体。在初步研究中，我们发现内质网钙的释放与CaMKII协同作用，刺激GluR2从内质网到质膜的运输。在我们的第三个目标中，我们将研究内质网对GluR2的依赖运输，并区分其控制是否依赖于GluR2组装成四聚体或从内质网滞留中释放GluR2。我们将确定GluR2响应钙的结构域以及细胞内钙水平、CaMKII、PICK1在输出机制中的作用，包括PICK1-CaMKII复合体的作用。这些研究将全面分析钙通透性AMPAR控制的生理和病理途径，以及调节钙通透性AMPAR功能的机制。

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.