Role of BACE stabilization in Alzheimer's disease

描述（由申请人提供）：阿尔茨海默病（AD）是影响530万美国人的最常见的痴呆症形式。在一小部分（>1%）病例中，AD是作为常染色体显性遗传性状（家族性AD）遗传的，但大多数病例是散发性的。AD中的一个关键神经病理事件是A？的脑内蓄积，A？是一种约4kDa的肽，由淀粉样前体蛋白（APP）通过？和？分泌酶β-位点APP裂解酶（BACE 1）是一种被鉴定为β-分泌酶的β-酰基蛋白酶的膜系成员。一些研究表明，BACE 1蛋白水平和β-分泌酶活性在AD大脑中增加。因此，BACE 1升高可能是增加A？和触发AD病理的第一步，至少在散发病例中是这样。我们的研究阐明了一种新的由BACE 1相互作用分子GGA 3（Golgi定位？含耳ARF结合蛋白3）。我们已经确定，GGA 3消耗稳定BACE 1和增加β-分泌酶活性。我们还发现，GGA 3水平在死后AD脑中降低，并且与BACE 1水平呈负相关。我们已经证明BACE 1通过溶酶体途径降解，并证明GGA 3调节BACE 1向溶酶体的递送。BACE 1-C-末端片段（CTF）含有特异性双亮氨酸（DXXLL）分选信号，已显示其结合GGA蛋白家族的三个成员GGA 1、2和3的VHS结构域。我们意外地发现，GGA 3 VHS结构域与BACE 1双亮氨酸基序的直接结合对于这种调节不是必需的。相反，GGA 3与泛素的相互作用对于调节BACE 1水平至关重要。因此，我们发现BACE 1主要是单-和K63-连接的多泛素化的赖氨酸501。这一提议的中心假设是，BACE 1降解受损是受AD影响的受试者大脑中BACE 1升高的潜在机制。本提案的总体目标是确定GGA和泛素介导的BACE 1调节在多大程度上代表了治疗AD的潜在靶点。因此，我们提出具体解决以下目标：1）确定BACE 1泛素化通过蛋白酶体或溶酶体途径调节BACE 1运输、活性和降解的程度; 2）确定GGA 3的过表达在体内以泛素依赖性方式降低BACE 1和A2水平的程度; 3）确定GGA 1（GGA蛋白家族的另一成员）在体外和体内独立调节BACE 1和A？水平以及与GGA 3相关的程度。

DESCRIPTION (provided by applicant): Alzheimer's Disease (AD) is the most common form of dementia that affects 5.3 million Americans. In a small percentage (>1%) of cases AD is inherited as an autosomal dominant trait (Familial AD), however the majority of cases are sporadic. A key neuropathological event in AD is the cerebral accumulation of A¿, a ~4kDa peptide derived by serial proteolysis of the amyloid precursor protein (APP) by ¿- and ?-secretase. Beta-site APP-cleaving enzyme (BACE1) is a membrane-tethered member of the aspartyl proteases that has been identified as ¿-secretase. Several studies have shown that BACE1 protein levels and ¿-secretase activity are increased in AD brains. Thus, BACE1 elevation may be the first step in increasing A¿ and triggering AD pathology, at least in the sporadic cases. Our studies have elucidated a novel post-translational mechanism of regulation of BACE1 mediated by the BACE1-interacting molecule, GGA3 (Golgi-localized ?-ear-containing ARF binding protein 3). We have determined that GGA3 depletion stabilizes BACE1 and increases ¿-secretase activity. We also found that levels of GGA3 are decreased in post-mortem AD brains and are inversely correlated with BACE1 levels. We have shown that BACE1 is degraded via the lysosomal pathway and demonstrated that GGA3 regulates the delivery of BACE1 to the lysosomes. The BACE1-C-terminal fragment (CTF) contains a specific di-leucine (DXXLL) sorting signal that has been shown to bind the VHS domain of the three members of the GGA family of proteins, GGA1, 2, and 3. We have found that, unexpectedly, direct binding of GGA3 VHS domain to the BACE1 di-leucine motif is not necessary for this regulation. Instead, GGA3 interaction with ubiquitin is essential for regulating BACE1 levels. Accordingly, we have found that BACE1 is mainly mono- and K63-linked polyubiquitinated at lysine 501. The central hypothesis of this proposal is that the impairment of BACE1 degradation is the underlying mechanism of BACE1 elevation in the brains of subjects affected by AD. The overarching goal of this proposal is to determine the extent to which GGA- and ubiquitin-mediated regulation of BACE1 represent a potential target for the treatment of AD. Thus, we propose to specifically address the following aims: 1) To determine the extent to which BACE1 ubiquitination regulates BACE1 trafficking, activity and degradation via the proteasomal or lysosomal pathway; 2) To determine the extent to which over-expression of GGA3 reduces levels of BACE1 and A2 in a ubiquitin-dependent fashion in vivo; 3) To determine the extent to which GGA1, another member of the GGA family of proteins, regulates levels of BACE1 and A¿ independently and in association with GGA3 in vitro and in vivo.