Altered sodium channel metabolism in Alzheimer's disease

简介(申请人提供)：阿尔茨海默病(AD)是痴呆症最常见的原因，其特征是记忆和认知功能进行性下降。此外，AD患者经常表现出严重的人格变化和各种精神症状，以及癫痫和肌阵挛发作。其中一些功能障碍可能反映了AD患者神经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，电压门控钠通道(NAV1)22亚基(22)经历了由BACE1、ADAM10和伽马分泌酶介导的蛋白质降解过程，类似于AD淀粉样前体蛋白(APP)的加工过程。22对于维持NAV11-亚基的表达、运输和细胞表面定位是必不可少的，NAV11-亚基是调节神经细胞膜兴奋性的主要通道形成亚基。我们的初步数据表明，在细胞和动物模型系统中，BACE1活性的提高通过增强22的处理减少了细胞表面NAV1亚基的表达，从而显著降低了钠电流密度。有趣的是，我们还发现在BACE1活性升高的AD患者的大脑中，22处理水平高度升高，NAV1 1亚单位水平发生变化。NAV1活性障碍会导致精神症状和癫痫发作。由于AD患者大脑中BACE1活性显著增加，22加工增强和随之而来的NAV1功能障碍可能导致或促成在疾病过程中频繁发生的精神症状和癫痫发作。基于这一推论，我们建议检验这样一种假设，即BACE1和早老素/γ-分泌酶上调22处理会损害AD患者脑内正常NAV1代谢，包括NAV1亚基的运输和表面表达，从而参与AD病理。为了验证这一假设，我们提出了以下目标：在AIM中。1，我们将利用BACE1转基因小鼠(一种模拟AD患者BACE1活性升高的动物模型)来表征BACE1活性升高引起的NAV1代谢变化及其对神经细胞的生理影响。为了探索我们的发现的治疗应用，我们将测试BACE1和/或伽马分泌酶抑制剂是否可以恢复BACE1转基因小鼠改变的NAV1代谢。此外，我们还将测试这些抑制剂是否会影响野生型小鼠的正常NAV1代谢。瞄准了。2、用免疫组织化学和生化方法研究AD患者脑内NAV1代谢的改变。这项建议的目标是确定改变的22处理和NAV1代谢如何影响AD神经元的生理，导致疾病过程中观察到的功能障碍和选择性退化。我们的研究还将提示BACE1抑制剂和钠通道调节药物在治疗AD患者异常神经元活动方面的潜在治疗应用。公共卫生相关性：在这项提案中，我们试图阐明电压门控钠通道水平和活性改变对阿尔茨海默病的致病作用。我们的研究还将提示BACE1抑制剂和钠通道调节药物在治疗AD患者异常神经元活动方面的潜在治疗应用。

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.