Dendritic ion channel trafficking in plasticity

描述（由申请人提供）：突触反应和膜兴奋性的长期变化是神经元可塑性的不同形式，被认为是记忆的基础。突触传导变化的本质和机制已被广泛研究。然而，突触可塑性的变化往往与兴奋性和EPSP-锋电位耦合有关。神经可塑性的另一个组成部分，内在可塑性的机制仍然未知。 可以实现膜兴奋性的可塑性变化的一种机制是通过离子通道表面表达或运输的激酶依赖性调节。Kv4.2亚基介导的A型K电流（IA）成为控制信号传播和膜兴奋性的关键参与者。我们最近有一个意想不到的发现，CaMK II活性增加COS细胞中Kv4.2的细胞表面表达。此外，我们证明了Kv4.2是CaMKII的底物，确定了磷酸化的确切位点，并表明这些位点的直接磷酸化是CaMKII介导的K通道表达上调所必需的。 这些结果导致了一个有趣的想法，即突触活动和/或CaMKII磷酸化驱动新的K通道进入神经元的质膜，从而调节和建立A型K通道的树突状分布。与突触电导的增强一致，K通道表面表达的促进可以通过降低神经元的总体兴奋性来提供稳态机制。对于这个建议，我将实验测试上述假设，并扩展我们的研究，以小鼠模型Angelman综合征（AS）。这些研究的意义是更普遍的，因为它们可以作为一个分子模型，在神经元可塑性的蛋白激酶的其他离子通道的运输和调节。此外，上述研究代表了我们在人类神经系统疾病动物模型中定义精确树突机制的努力。

DESCRIPTION (provided by applicant): Long-term changes in synaptic responses and membrane excitability are different forms of neuronal plasticity thought to underlie memory. The nature of and mechanisms underlying the synaptic conductance changes have been extensively investigated. However, there are often changes in excitability and EPSP-spike coupling associated with synaptic plasticity. The mechanisms involved in intrinsic plasticity, the other component of neural plasticity, remain unknown. One mechanism through which plastic changes in membrane excitability can be achieved is via kinase dependent regulation of ion channel surface expression or trafficking. Kv4.2 subunits-mediated A-type K currents (IA) emerged as a key player controlling signal propagation and membrane excitability. We have recently made an unexpected finding that CaMKII activity increases the cell surface expression of Kv4.2 in COS cells. Furthermore, we demonstrated that Kv4.2 is a substrate for CaMKII, identified the exact sites of phosphorylation, and showed that direct phosphorylation of these sites is necessary for CaMKII-mediated upregulation of K channel expression. These results lead to the intriguing idea that synaptic activity and/or CaMKII phosphorylation drives new K channels into the plasma membrane of neurons, consequently regulating and establishing the dendritic distribution of A-type K channels. In concert with the potentiation of synaptic conductances, promotion of K channel surface expression may provide a homeostatic mechanism by reducing overall excitability of a neuron. For this proposal I will test experimentally the above hypotheses, and extend our studies to a mouse model for Angelman syndrome (AS). The implications of these studies are more general in that they can be applied as a molecular model for the trafficking and regulation of other ion channels by protein kinases during neuronal plasticity. Moreover, the studies proposed above represent our efforts to define the precise dendritic mechanisms involved in an animal model for human neurological diseases.