A Novel Ionic Mechanism of Ischemic Neuronal Injury

描述（由申请人提供）：脑缺血导致神经元死亡的潜在机制尚不清楚，这在很大程度上限制了中风的有效治疗。本研究将探讨缺血性神经元损伤的离子机制。短暂性脑缺血导致某些脑区域选择性神经元死亡，包括新纹状体，这是感觉运动学习，运动控制和认知功能的基础。保护纹状体神经元免受缺血将促进脑卒中后纹状体介导功能的恢复。研究表明，神经元兴奋性的增加和细胞内离子稳态的破坏是缺血后神经元损伤的关键。超极化激活的阳离子电流（Ih）介导Na+和K+的内流，在控制神经元兴奋性中起关键作用。以往的研究大多集中在兴奋毒性和去极化激活的离子通道上，并指出缺血后去极化可能导致细胞死亡，超极化可能参与神经保护。然而，纹状体神经元超极化期间的Ih活性可能与缺血性神经元损伤有关。事实上，我们已经发现短暂的前脑缺血诱导了新纹状体中缺血易感的棘神经元中功能性Ih的表达，而这在对照条件下是不存在的。同时，缺血后抗缺血纹状体胆碱能中间神经元中的Ih受到抑制。最重要的是，我们的初步数据表明，阻断Ih可以保护纹状体神经元免受缺血。我们假设功能性Ih的上调有助于新纹状体缺血性神经元死亡。本课题通过实验研究纹状体神经元缺血后Ih的变化及其机制，以及Ih变化与缺血性神经元死亡的关系。前脑短暂性缺血后纹状体神经元Ih的时间变化将采用电生理记录的方法进行表征。为了研究Ih变化的潜在机制，我们将比较缺血前后环AMP和膜磷脂（PIP2）对Ih的调节。此外，还将研究Ih通道相互作用蛋白（TRIP8b）的改变，该蛋白对Ih功能有深远的调节作用。最后，将在体内缺血模型中确定特定Ih通道亚基的参与。该项目可能为保护神经元免受缺血性损伤提供新的策略。

DESCRIPTION (provided by applicant): Effective treatment for stroke is limited largely by the fact that the underlying mechanisms of neuronal death caused by cerebral ischemia are still unclear. This proposal will investigate the ionic mechanisms of ischemic neuronal injury. Transient cerebral ischemia causes selective neuronal death in certain brain regions, including the neostriatum, which is fundamental to sensorimotor learning, movement control and cognitive functions. Protecting striatal neurons against ischemia will improve the recovery of striatum-mediated functions after stroke. Studies have shown that increase of neuronal excitability and disruption of intracellular ion homeostasis are critical for neuronal injury after ischemia. Hyperpolarization-activated cation current (Ih) mediates influx of Na+ and K+, and plays critical roles in controlling neuronal excitability. Most of previous studies have focused on the excitotoxicity and depolarization-activated ion channels, and indicate that post-ischemic depolarization may contribute to cell death, and that hyperpolarization may be involved in neuroprotection. However, active Ih during hyperpolarization in striatal neurons may be associated with ischemic neuronal injury. Indeed, we have found that transient forebrain ischemia induces an expression of functional Ih in ischemia-vulnerable spiny neurons in the neostriatum, which is absent under control conditions. Meanwhile, Ih in ischemia-resistant striatal cholinergic interneurons is inhibited after ischemia. Most importantly, our preliminary data have shown that blocking Ih protects striatal neurons against ischemia. We hypothesize that upregulation of functional Ih contributes to ischemic neuronal death in the neostriatum. In this project, experiments are designed to investigate how Ih in striatal neurons is altered after ischemia, what are the underlying mechanisms, and what are the relations of Ih change with ischemic neuronal death. The temporal changes of Ih in striatal neurons following transient forebrain ischemia will be characterized using electrophysiological recording. To investigate the underlying mechanisms of Ih changes, the modulation of Ih by cyclic AMP and membrane phospholipids (PIP2) will be compared before and after ischemia. In addition, alterations of Ih channel interacting proteins (TRIP8b), which profoundly regulate Ih function, will be examined. Finally, the involvement of specific Ih channel subunits will be identified in ischemia in vivo models. This project may provide novel strategies to protect neurons against ischemic insults. PUBLIC HEALTH RELEVANCE: This proposal will identify the cellular mechanisms underlying the post-ischemic changes of Ih in striatal neurons, and the functional significance of Ih in ischemic cell death. An understanding of the cellular mechanisms of neuronal injury has great potential in developing novel therapeutic strategies for stroke patients.