Inhibition of seizures and neuron excitability by acid-sensing ion channels

描述（由申请人提供）：癫痫发作性疾病引起显著的发病率和死亡率，许多病例对当前的医疗管理是难治性的。因此，需要改进治疗方法。更好地了解脑酸中毒的抗癫痫机制可能会促进治疗进展。人们早就知道，低pH能有效地抑制癫痫发作，降低神经元的兴奋性，但这些作用背后的分子机制尚不清楚。最近在大脑中发现的质子受体可能提供了大脑pH值和癫痫发作之间的分子联系。最近发现其中一种受体，酸感应离子通道ASIC1a是中枢神经元酸诱发电流所必需的。与对癫痫发作的抑制作用一致，初步数据表明，在小鼠中过表达ASIC1a可以减轻癫痫发作。相反，干扰ASIC1a会使癫痫发作加重。总之，这些观察结果表明ASIC1a介导中枢酸中毒的抗癫痫作用并降低神经元兴奋性的假设。为了验证这一假设，计划了三个目标。第一个目的是测试ASIC1a是否介导二氧化碳的抗癫痫作用，二氧化碳可以迅速穿过血脑屏障并降低中枢ph值。将给野生型小鼠、ASIC1a缺失小鼠和ASIC1a过表达转基因小鼠注射化学惊厥药，并比较不同基因型之间二氧化碳相对于空气的抗癫痫作用。该结果将为ASIC1a和CO2的抗癫痫特性是否相关提供指示。第二个目标是测试ASIC1a是否介导酸在pH值可以更好控制的脑切片中的抗癫痫作用。第三个目的是测试ASIC1a对培养海马神经元动作电位的酸抑制作用。初步数据表明ASIC1a可能抑制动作电位，这可能有助于解释ASIC1a如何在体内抑制癫痫发作。总之，这些实验将为历史上公认的酸的抗癫痫作用提供重要的见解。它们还将导致更多的机制研究，以更深入地阐明ASIC1a如何发挥其抗癫痫作用。重要的是，这些研究也可能提示ASIC1a作为抑制患者癫痫发作的新治疗靶点。发现新的和广泛的抗癫痫机制可能对难治性疾病的患者特别有益。癫痫发作性疾病引起显著的发病率和死亡率，往往难以医疗管理。研究癫痫发作抑制的新特征可能会导致具有替代作用机制的治疗。在这个应用中，我们探索了一个鲜为人知的基因，酸感应离子通道1a的癫痫抑制作用，我们测试了ASIC1a是否有助于建立但知之甚少的脑酸中毒抗癫痫作用。这些研究有可能促进Asic1a拮抗剂作为癫痫发作的新治疗方法的发展。

DESCRIPTION (provided by applicant): Seizure disorders cause significant morbidity and mortality, and many cases are refractory to current medical management. Thus, improved treatments are needed. Therapeutic advances might be developed from a better understanding of the antiepileptic mechanisms of brain acidosis. It has long been known that low pH effectively inhibits seizures and reduces neuron excitability, but the molecular mechanisms underlying these effects are poorly understood. The recent identification of proton receptors in the brain may provide a molecular link between brain pH and seizures. It was recently found that one of these receptors, the acid sensing ion channel ASIC1a is required for acid-evoked currents in central neurons. And consistent with an inhibitory effect on seizures, preliminary data indicate overexpressing ASIC1a in mice attenuates seizures. In contrast, disrupting ASIC1a makes seizures worse. Together, these observations suggest the hypothesis that ASIC1a mediates the antiepileptic effects of central acidosis and reduces neuron excitability. To test this hypothesis three aims are planned. The first aim will test whether ASIC1a mediates antiepileptic effects of CO2, which rapidly crosses the blood-brain barrier and lowers central pH. Wild-type mice, ASIC1a null mice, and ASIC1a overexpressing transgenic mice will be injected with a chemoconvulsant and the anti-epileptic effects of CO2 relative to air will be compared between genotypes. The results will provide an indication of whether the anti-epileptic properties of ASIC1a and CO2 are related. The second aim will test whether ASIC1a mediates the antiepileptic effects of acid in brain slices where pH can be better controlled. The third aim will test the effects of ASIC1a on acid inhibition of action potentials in cultured hippocampal neurons. Preliminary data suggest ASIC1a may inhibit action potentials, which may help explain how ASIC1a inhibits seizures in vivo. Together these experiments will provide important insight into the historically well established but poorly understood antiepileptic effects of acid. They will also lead to additional mechanistic studies to clarify in more depth how ASIC1a exerts its antiepileptic effects. Importantly, these studies may also suggest ASIC1a as a novel therapeutic target for inhibiting seizures in patients. Identifying novel and broad antiepileptic mechanisms may be especially beneficial to patients with refractory disease. Seizures disorders cause significant morbidity and mortality and are often refractory to medical management. Studying novel features of seizure inhibition may lead to treatments with alternative mechanisms of action. In this application we explore the seizure inhibiting effects of a poorly understood gene, acid-sensing ion channel 1a, and we test whether ASIC1a contributes to the well-established but poorly understood antiepileptic effects of brain acidosis. These studies have the potential to foster the development of Asic1a antagonists as a novel therapeutic approach to seizures.