Calcium Permeable AMPA Receptors: Signaling, Toxicity and Control

Ca2+渗透性AMPA受体比NMDA受体在更少的限制性条件下被激活，在许多神经元类型中发现，并且可能调节更普遍由NMDAR Ca2+电流控制的途径。我们已经证明Ca2+渗透性AMPARs，如NMDAR，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受体是否可以激活Akt和CaMKII对nNOS的连续调节磷酸化，之前我们已经证明（Rameau等人，2007）是由NMDAR诱导的。我们将研究支架结构和生化途径Akt和CaMKII对Ca2+渗透性ampar控制nNOS的贡献。当被RNA编辑修饰时，GluR2主要阻断AMPAR通道的Ca2+传导。相比之下，未经编辑的GluR2通过其Ca2+渗透性和组成运输具有高毒性（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的病理，nmda依赖的蛋白水解裂解，当RNA编辑活性下降时未编辑的GluR2的产生，以及包括未编辑的GluR2在内的Ca2+渗透性ampar杀死神经元的机制。为了限制Ca2+毒性，细胞已经进化出限制突触AMPAR Ca2+电流的机制，其中Ca2+不渗透的AMPA受体在突触上取代Ca2+不渗透的AMPA受体。在初步研究中，我们发现内质网Ca2+的释放与CaMKII合作，刺激GluR2从内质网运输到质膜。在我们的第三个目标中，我们将研究GluR2从内质网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从内质网保留中释放。我们将确定GluR2响应Ca2+的结构域，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。这些研究将全面分析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。

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.