Altered sodium channel metabolism in Alzheimer's disease

描述（由申请人提供）：摘要阿尔茨海默病（AD）是痴呆的最常见原因，其特征在于记忆和认知功能的进行性下降。此外，AD患者经常表现出严重的人格改变和各种精神症状，以及癫痫和肌阵挛发作。这些功能障碍中的一些可能反映了AD患者神经元细胞膜兴奋性的改变。然而，其潜在的分子机制尚不清楚。最近，我们和其他人报道了电压门控钠通道（Nav 1）22-亚基（22）经历由BACE 1、ADAM 10和γ-分泌酶介导的蛋白水解加工，类似于AD淀粉样前体蛋白（APP）的加工。22对于维持Navl 1-亚基的表达、运输和细胞表面定位是必需的，Navl 1-亚基是调节神经元细胞中膜兴奋性的主要通道形成亚基。我们的初步数据表明，升高的BACE 1活性通过在基于细胞的系统和动物模型系统中增强22的加工来降低Nav 1 1-亚基的细胞表面表达，从而显著降低钠电流密度。有趣的是，我们还发现在具有升高的BACE 1活性的AD患者的脑中高度升高的22加工和改变的Nav 11-亚基水平。Nav 1活性的功能障碍导致精神症状和癫痫发作。由于BACE 1活性在AD患者的大脑中显著增加，因此增强的22处理和随后的Nav 1功能障碍可能导致或促成在疾病过程中经常发生的精神症状和癫痫发作。基于这一推理，我们提出测试的假设，即升高的BACE 1和早老素/γ-分泌酶的加工损害了正常的Nav 1代谢，包括运输和表面表达的Nav 1 1 1-亚基在AD患者的大脑，有助于AD病理。为了验证这一假设，我们提出了以下目标：在目标。1，我们将通过使用BACE 1转基因小鼠（一种模拟AD患者中BACE 1活性升高的动物模型）来表征BACE 1活性升高引起的Nav 1代谢改变及其对神经元细胞的生理作用。为了探索我们的研究结果的治疗应用，我们将测试BACE 1和/或γ-分泌酶抑制剂是否可以恢复BACE 1转基因小鼠中改变的Nav 1代谢。此外，我们将测试这些抑制剂是否也会影响野生型小鼠的正常Nav 1代谢。在Aim。2、应用免疫组化和生化方法研究AD患者脑内Nav 1代谢的改变。该提案的目标是确定改变的22处理和Nav 1代谢如何影响AD中神经元的生理学，导致在疾病过程中观察到的功能障碍和选择性变性。我们的研究还将提示BACE 1抑制剂和钠通道调节药物在治疗AD患者异常神经元活动中的潜在治疗应用。公共卫生相关性：在这个提议中，我们试图阐明改变电压门控钠通道水平和活性对阿尔茨海默病的致病作用。我们的研究还将提示BACE 1抑制剂和钠通道调节药物在治疗AD患者异常神经元活动中的潜在治疗应用。

DESCRIPTION (provided by applicant): Abstract Alzheimer's disease (AD) is the most common cause of dementia, and is characterized by progressive decline in memory and cognitive functions. In addition, AD patients frequently show severe personality changes and various psychiatric symptoms, as well as epileptic and myoclonic seizures. Some of these functional disturbances may reflect altered membrane excitability of neuronal cells in AD patients. However, the underlying molecular mechanism is not known. Recently we and others reported that the voltage-gated sodium channel (Nav1) 22-subunit (22) undergoes proteolytic processing mediated by BACE1, ADAM10, and gamma- secretase, similar to the processing of the AD amyloid precursor protein (APP). 22 is essential for maintaining expression, trafficking, and cell surface localization of the Nav1 1-subunits, the major channel-forming subunits regulating membrane excitability in neuronal cells. Our preliminary data indicate that elevated BACE1 activity dramatically decreases sodium current densities by reducing cell surface expression of Nav1 1-subunits through the enhanced processing of 22 in both cell-based and animal model systems. Interestingly, we also found highly elevated 22 processing and altered Nav1 1-subunit levels in brains of AD patients with elevated BACE1 activity. Dysfunctions in Nav1 activity lead to psychiatric symptoms and epileptic seizures. Since BACE1 activities significantly increased in brains of AD patients, enhanced 22 processing and consequent Nav1 dysfunction may lead or contribute to psychiatric symptoms and epileptic seizures that frequently occur in the course of the disease. Based on this reasoning, we propose to test the hypothesis that elevated 22 processing by BACE1 and presenilin/gamma-secretase impairs the normal Nav1 metabolism including trafficking and surface expression of Nav1 1-subunits in brains of AD patients, contributing to AD pathology. To test this hypothesis, we propose the following Aims: In Aim. 1, we will characterize the altered Nav1 metabolism by elevated BACE1 activity and its physiological effects on neuronal cells by using BACE1- transgenic mice, an animal model mimicking the elevated BACE1 activity in AD patients. In an attempt to explore the therapeutic application of our findings, we will test whether BACE1 and/or gamma-secretase inhibitors can restore altered Nav1 metabolism in BACE1-trangenic mice. In addition, we will test whether these inhibitors can affect normal Nav1 metabolism in wild-type mice as well. In Aim. 2, we will study altered Nav1 metabolism in brains of AD patients by using immunohistochemical and biochemical methods. The goal of this proposal is to determine how altered 22 processing and Nav1 metabolism affect the physiology of neurons in AD, leading to dysfunction and selective degeneration observed in the course of the disease. Our study will also suggest potential therapeutic applications of BACE1 inhibitors and sodium channel modulating drugs in treating abnormal neuronal activities in AD patients. PUBLIC HEALTH RELEVANCE: In this proposal, we seek to elucidate the pathogenic contribution of altered voltage-gated sodium channel levels and activity to Alzheimer's disease. Our study will also suggest potential therapeutic applications of BACE1 inhibitors and sodium channel modulating drugs in treating abnormal neuronal activities in AD patients.