Acid-sensing channels as novel target for brain ischemia

描述(由申请人提供)：缺血性中风是导致死亡和发病的主要原因，也是导致长期残疾的最常见原因。遗憾的是，对于中风患者，除了使用血栓栓塞剂外，目前还没有有效的治疗方法，因为血栓形成的时间窗口有限，而且可能会出现颅内出血的副作用。几十年来，人们已经认识到细胞内钙离子的积累，特别是通过谷氨酸受体的激活，以及由此产生的钙毒性，在缺血性脑损伤中起着重要的作用。然而，最近使用谷氨酸拮抗剂和最近的自由基清除剂的临床试验，都没有显示出对缺血损伤的保护作用。虽然多种因素可能共同导致了试验的失败，但很可能是谷氨酸非依赖性钙负载途径(S)同样对缺血时的钙毒性起到了作用。事实上，我们最近在神经细胞培养和全动物缺血模型中的研究表明，酸敏感离子通道(ASICs)的激活和随后的钙离子进入是酸中毒介导的谷氨酸受体非依赖性缺血性脑损伤的主要原因。在培养的小鼠皮质神经元中，降低pH可激活对阿米洛利敏感的ASIC电流。在大多数神经元中，ASICs对钙离子具有通透性，这些通道的激活导致细胞内钙离子浓度([Ca2+]i)增加。在电压门控钙通道阻断剂和谷氨酸受体阻断剂存在的情况下，用酸性溶液短暂孵育神经元激活ASICs会导致时间依赖性的细胞损伤。然而，这种酸诱导的谷氨酸非依赖性神经元损伤可以通过阻断ASICs、减少细胞外[Ca~(2+)]或ASIC1基因敲除来抑制。在体内的小鼠缺血模型中，ASIC1阻断或ASIC1基因敲除可显著减少脑梗塞体积。这些发现有力地表明ASICs可能是人类卒中的新治疗靶点。我们的目标是将我们在动物细胞中令人兴奋的发现扩展到人脑神经元，以探索ASICs在酸中毒介导的人脑神经元缺血性损伤中的作用。我们的中心假设是人脑神经元表达ASICs。ASICs的激活诱导细胞内钙离子积聚，参与酸中毒介导的谷氨酸非依赖性神经元损伤。这些研究的成功是将ASICs作为人类中风治疗的新靶点的重要一步。公共卫生相关性：我们计划研究预防中风后细胞丢失的新机制和策略。我们以前的发现有力地表明ASICs可能是人类中风的新的治疗靶点。这些研究的成功是将ASICs作为人类中风治疗的新靶点的重要一步。

DESCRIPTION (provided by applicant): Ischemic stroke is a leading course of mortality and morbidity, and the most common reason for long-term disabilities. Unfortunately there is still no effective treatment for stroke patients other than the use of thrombolitics which have limited time window and potential side effect of intracranial hemorrhage. It has been well-recognized for several decades that that intracellular Ca2+ accumulation, particularly through glutamate receptor activation, and the resultant Ca2+ toxicity, play an important role in ischemic brain injury. However, the recent clinical trials using glutamate antagonists and most recently free radical scavengers, have failed to show protection against ischemic injury. Although multiple factors may have contributed together to the failure of the trials, it is likely that glutamate-independent Ca2+ loading pathway(s) equally contribute to the Ca2+ toxicity in ischemia. Indeed, our recent studies in neuronal cell culture and in whole animal models of ischemia have demonstrated that activation of acid-sensing ion channels (ASICs), and subsequent Ca2+ entry are largely responsible for acidosis- mediated, glutamate receptor-independent ischemic brain injury. In cultured mouse cortical neurons, lowering pH activates amiloride-sensitive ASIC currents. In the majority of these neurons, ASICs are permeable to Ca2+, and activation of these channels induces increased concentration of intracellular Ca2+ ([Ca2+]i). Activation of ASICs by brief incubation of neurons with acidic solutions induces time-dependent cell injury in the presence of blockers for voltage-gated Ca2+ channels and the glutamate receptors. This acid-induced, glutamate-independent neuronal injury is, however, inhibited by blocking the ASICs, by reducing the extracellular [Ca2+], or by ASIC1 gene knockout. In in vivo mouse model of ischemia, ASIC1 blockade or ASIC1 gene knockout dramatically reduced infarct volume. These findings strongly suggest that ASICs may represent novel therapeutic targets for human stroke. Our objective is to extend our exciting findings in animal cells to human brain neurons to explore the role of ASICs in acidosis-mediated ischemic injury of human brain neurons. Our central hypothesis is that human brain neurons express ASICs. Activation of ASICs induces intracellular Ca2+ accumulation, which is involved in acidosis-mediated, glutamate-independent neuronal injury. Success of these studies is an important step for establishing ASICs as novel targets for human stroke therapy. PUBLIC HEALTH RELEVANCE: We plan to investigate novel mechanisms and strategies to prevent cell loss after stroke. Our previous findings strongly suggest that ASICs may represent novel therapeutic targets for human stroke. Success of these studies is an important step for establishing ASICs as novel targets for human stroke therapy.