Dendritic ion channel trafficking in plasticity

描述(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。突触电导变化的本质和机制已被广泛研究。然而，与突触可塑性相关的兴奋性和EPSP-棘波耦合经常发生变化。神经可塑性的另一个组成部分--内在可塑性的机制尚不清楚。 膜兴奋性的可塑性改变的一个机制是通过依赖于激酶的离子通道表面表达或运输的调节。Kv4.2亚基介导的A-型钾电流(IA)是控制信号传递和膜兴奋性的关键因素。我们最近有一个意想不到的发现，CaMKII活性增加了COS细胞表面Kv4.2的表达。此外，我们证明了Kv4.2是CaMKII的底物，确定了准确的磷酸化位点，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，即突触活性和/或CaMKII磷酸化促使新的K通道进入神经元的质膜，从而调节和建立A型K通道的树突分布。在突触电导增强的同时，K通道表面表达的促进可能通过降低神经元的整体兴奋性来提供一种动态平衡机制。对于这项提议，我将对上述假设进行实验测试，并将我们的研究扩展到Angelman综合征(AS)的小鼠模型。这些研究的意义更广泛，因为它们可以作为一个分子模型，在神经元可塑性过程中通过蛋白激酶运输和调节其他离子通道。此外，上面提出的研究代表了我们在人类神经疾病动物模型中所涉及的精确树突状细胞机制的努力。

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.