Calcium Permeable AMPA Receptors: Signaling, Toxicity and Control

Ca 2+渗透性AMPA受体在比NMDA受体限制性更低的条件下被激活，在许多神经元类型中发现，并且可以调节更通常由NMDAR Ca 2+电流控制的途径。我们已经表明，钙渗透AMPAR，像NMDAR，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Ca 2+渗透性AMPA受体是否可以通过Akt和CaMK II激活nNOS的连续调节磷酸化，这是我们先前所示的（Rameau et al.，2007年，由NMDAR诱导。我们将研究支架结构和生化途径Akt和CaMKII，有助于通过Ca 2+渗透性AMPAR控制nNOS。当通过RNA编辑修饰时，GluR 2主要阻断AMPAR通道的Ca 2+传导。相比之下，未经编辑的GluR 2通过其Ca 2+渗透性和组成性运输而具有高度毒性（Mahajan和Ziff，2007）。最近，我们发现NMDAR活性可以降解GluR 2前mRNA编辑酶ADAR 2。我们的第二个目的是分析ADAR 2的病理性NMDAR依赖性蛋白水解裂解，随着RNA编辑活性下降而产生的未编辑GluR 2，以及包括未编辑GluR 2在内的Ca 2+渗透性AMPAR可以杀死神经元的机制。为了限制Ca 2+毒性，细胞已经进化出限制突触AMPAR Ca 2+电流的机制，其中Ca 2+不可渗透的AMPA受体取代突触处的Ca 2+不可渗透的受体。在初步的研究中，我们已经发现，释放的Ca 2+从ER商店与CaMKII合作，刺激运输的GluR 2从内质网到质膜。在我们的第三个目标，我们将研究钙离子依赖的运输GluR 2从ER，并区分其控制依赖于组装成四聚体的GluR 2或释放GluR 2从ER保留。我们将确定响应于Ca 2+的GluR 2的结构域以及胞内Ca 2+水平、CaMKII、PICK 1在输出机制中的作用，包括PICK 1-CaMKII复合物的作用。这些研究将提供一个全面的分析的生理和病理途径控制的Ca 2+渗透AMPAR和调节Ca 2+渗透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.