Nicastrin: Physiological Role and Therapeutic Target Validation

尼古丁(NCT)是一种I型跨膜糖蛋白，与早老素(PS)形成高分子量复合体，是伽玛分泌酶活性和APP转运所必需的多聚体复合体的重要组成部分。我们最近的研究表明，NCT具有较大的胞外结构域，可能是AD的潜在治疗靶点。因为PS/伽马分泌酶活性是各种基本信号通路所必需的，再加上我们最近发现BACE1基因缺失的小鼠存在认知缺陷，完整的 抑制任何一种分泌酶活性可能不是完全没有基于机制的毒性。为了将潜在的毒性降到最低，调节β-和γ-分泌酶的活性可能是有益的，这样就可以在不影响其他关键信号通路的情况下显著改善Abeta的沉积。由于我们最近的研究表明Abeta沉积对NCT和BACE1的剂量都很敏感，我们假设Abeta沉积可以通过降低NCT和BACE1的水平来改善。作为原理的证明，我们将在目标1中检查NCT的部分减少或NCT和BACE1的共同减少是否会减少突变的APP；PS1小鼠大脑中的Aβ负担。根据我们最近的发现，我们假设NCT和APH-1需要相互调节彼此的稳定性，以形成稳定的PS和Pen-2组装前复合体。由于我们最近的研究表明，与PS1-/-；NCT+/-胚胎相比，PS1-/-；NCT+/-胚胎表现出更严重的表型，我们推测这是由于依赖PS2的伽马分泌酶复合体水平降低所致。 在PST-/-；NCT+/-胚胎中。在目标2中，我们将测试在没有PS1的情况下，依赖PS2的伽马分泌酶活性是否对NCT的剂量敏感。此外，我们计划测试NCT和PS1的部分减少是否可以在不改变Notch信号的情况下进一步降低Abeta的水平。这些研究的积极结果支持了这样的观点，即NCT和PS特异性抑制剂的组合可能是一种有用的治疗策略。在目标3中，我们将通过在神经元特异性Thy1启动子的控制下产生表达NCT的转基因小鼠来检验成年外周组织中NCT缺失的影响。 从基因上补充NCT-/-小鼠的胚胎致死性。这些研究的结果将对理解NCT的生物学和开发AD的抗Aβ治疗策略具有重要意义。

Nicastrin (NCT), a type I transmembrane glycoprotein which forms high molecular weight complexes with presenilins (PS), is an essential component of the multimeric gamma-secretase complex required for both gamma-secretase activity and APP trafficking. Our recent studies suggest that NCT, with its large ectodomain, may be a potential therapeutic target for AD. Because PS/gamma-secretase activity is required for a variety of essential signaling pathways coupled with our recent finding that cognitive deficits occur in BACE1 null mice, complete inhibition of either secretase activity may not be completely free of mechanism-based toxicity. To minimize any potential toxicity, it may be beneficial to modulate both beta- and gamma-secretase activity such that a significant amelioration of Abeta deposition occurs without affecting other critical signaling pathways. Since our recent studies showed that Abeta deposits are sensitive to the dosage of both NCT and BACE1, we hypothesize that Abeta deposits could be ameliorated by decreasing levels of NCT and BACE1. As proof of principal, we will examine in Aim 1 whether partial reductions of NCT or both NCT and BACE1 will reduce Abeta burden in brains of mutant APP;PS1 mice. Based on our recent findings, we hypothesize that NCT and Aph-1 are required to regulate the stability of each other to form a stable pre-complex for assembly of PS and Pen-2. Since our recent studies indicated that PS1-/-;NCT+/- embryos exhibited a more severe phenotype as compared to PS1-/-;NCT+/- embryos, we hypothesize that this is due to reduced level of PS2-depenedant gamma-secretase complex in PST-/-;NCT+/- embryos. In Aim 2 we will to test whether PS2-dependent gamma-secretase activity is sensitive to the dosage of NCT in the absence of PS1. In addition, we plan to test whether partial reduction of both NCT and PS1 can further reduce the level of Abeta without altering Notch signaling. Positive outcomes from these studies provide support for the view that a combination of NCT- and PS-specific inhibitors may be a useful therapeutic strategy. In Aim 3, we will examine the impact of the absence of NCT in adult peripheral tissues by generation of transgenic mice expressing NCT under the control of the neuronal-specific Thy1 promoter to genetically complement the embryonic lethality of NCT-/- mice. Results from these studies will have important implications for understanding the biology of NCT and development of anti-Abeta therapeutic strategies in AD.