Presenilins, Gamma-Secretase and Notch in Neuronal Death

描述（由申请人提供）：通过对一系列早老素（PS）突变小鼠的开发和多学科分析，我们先前已经确定了早老素（PS）在中枢神经系统中的生理功能。在皮质发育过程中，早老素调节神经发生和神经元迁移，主要通过3-分泌酶依赖性激活Notch信号通路。在成人大脑皮层中，早老素在记忆、突触可塑性和神经元存活中起着重要作用。然而，目前尚不清楚Notch受体是否是成年大脑皮层PS功能的关键介质，以及早老素是否以γ-分泌酶依赖性或γ-非依赖性方式执行这些基本功能。与PS一样，Nicastrin（NCT）是γ-分泌酶复合物的重要组分，小鼠胚胎成纤维细胞中的NCT缺乏会消除γ-分泌酶依赖性活性。然而，PS似乎也具有γ-分泌酶独立的功能。在这一竞争性续期申请中，我们提出了以下两个具体目标来解决这些悬而未决的问题。首先，我们将产生和分析缺乏Notch 1和/或2的条件性敲除小鼠，以确定成年大脑皮层中Notch受体的失活是否会导致记忆和突触可塑性损伤以及神经退行性变，这些损伤与之前在PS条件性双敲除（PS cDKO）小鼠中观察到的相似。第二，我们将测试NCT在成年皮质表型中的条件失活是否模仿PS cDKO小鼠，然后检查先前发现在PS cDKO小鼠中受损的信号传导机制。指导我们的建议的中心假设是，在我们以前的工作中确定的突触可塑性，记忆和神经元存活的PS的重要作用是通过NCT依赖的γ-分泌酶活性介导的，可能通过γ-分泌酶依赖的激活Notch信号。两个目标中的拟议研究将检验这一中心假设，并确定PS的γ分泌酶非依赖性活性是否对其在成人大脑中的基本功能有显著贡献。我们提出的研究的意义在于，我们将揭示Notch和NCT在成人大脑皮层中的生理作用，这是目前未知的，并确定PS在成人脑功能中的重要作用是否完全依赖于γ-分泌酶活性，特别是γ-分泌酶依赖的Notch信号激活。我们的长期目标是了解早老素及其下游效应物在成人大脑中的正常功能。对正常PS功能的深入了解可能反过来揭示阿尔茨海默病和额颞叶痴呆的痴呆和神经变性的致病机制。公共卫生相关性：早老素基因的突变与阿尔茨海默病和额颞叶痴呆有关。在当前的应用中，我们建议调查早老素是如何参与记忆维持和神经元存活。更好地了解早老素调节认知和神经元完整性的分子途径将为这些疾病的发病机制提供重要的见解，并可能提供新的治疗靶点。

DESCRIPTION (provided by applicant): Through the development and multidisciplinary analysis of a series of presenilin (PS) mutant mice, we have previously established the physiological functions of the presenilins (PSs) in the central nervous system. During cortical development, presenilins regulate neurogenesis and neuronal migration, primarily through 3- secretase-dependent activation of the Notch signaling pathway. In the adult cerebral cortex, presenilins play a central role in memory, synaptic plasticity and neuronal survival. However, it is unclear if Notch receptors are key mediators of PS functions in the adult cerebral cortex, and whether presenilins carry out these essential functions in a gamma-secretase-dependent or gamma-independent manner. Like PS, Nicastrin (NCT) is an essential component of the gamma-secretase complex, and NCT deficiency in mouse embryonic fibroblasts abolishes gamma- secretase-dependent activities. However, PSs also appear to possess gamma-secretase-independent functions. In this competing renewal application, we propose the following two Specific Aims to address these unanswered questions. First, we will generate and analyze conditional knockout mice lacking Notch1 and/or 2 to determine if inactivation of Notch receptors in the adult cerebral cortex causes memory and synaptic plasticity impairments and neurodegeneration similar to those previously observed in PS conditional double knockout (PS cDKO) mice. Second, we will test if conditional inactivation of NCT in the adult cortex phenocopies PS cDKO mice, and then examine signaling mechanisms previously found to be impaired in PS cDKO mice. The central hypothesis guiding our proposal is that the essential roles of PS in synaptic plasticity, memory and neuronal survival identified in our prior work are mediated via NCT-dependent gamma-secretase activity, possibly through gamma-secretase-dependent activation of Notch signaling. The proposed studies in both Aims will test this central hypothesis and determine if gamma-secretase-independent activity of PS contributes significantly towards its essential functions in the adult brain. The significance of our proposed study is that we will uncover the physiological roles of Notch and NCT in the adult cerebral cortex, which are presently unknown, and determine whether the essential roles of PS in adult brain function depend exclusively on gamma-secretase activity, especially gamma-secretase-dependent activation of Notch signaling. Our long-term goal is to understand the normal functions of presenilins and their downstream effectors in the adult brain. Insight into normal PS function may in turn shed light on the pathogenic mechanisms underlying dementia and neurodegeneration in Alzheimer's disease and frontotemporal dementia. PUBLIC HEALTH RELEVANCE: Mutations in the presenilin genes have been linked to Alzheimer's disease and frontotemporal dementia. In the current application, we propose to investigate how presenilins are involved in memory maintenance and neuronal survival. Better understanding of the molecular pathways by which presenilins regulate cognitive and neuronal integrity will provide important insights into the pathogenesis of these disorders and may provide novel therapeutic targets.