Ring Sabine, Weyer Sascha W, Kilian Susanne B, Waldron Elaine, Pietrzik Claus U, Filippov Mikhail A, Herms Jochen, Buchholz Christian, Eckman Christopher B, Korte Martin, Wolfer David P, Müller Ulrike C
Department of Bioinformatics and Functional Genomics, Institute for Pharmacy and Molecular Biotechnology, University of Heidelberg, D-69120 Heidelberg, Germany.
J Neurosci. 2007 Jul 18;27(29):7817-26. doi: 10.1523/JNEUROSCI.1026-07.2007.
It is well established that the proteolytic processing of the beta-amyloid precursor protein (APP) generates beta-amyloid (Abeta), which plays a central role in the pathogenesis of Alzheimer's disease (AD). In contrast, the physiological role of APP and of its numerous proteolytic fragments and the question of whether a loss of these functions contributes to AD are still unknown. To address this question, we replaced the endogenous APP locus by gene-targeted alleles and generated two lines of knock-in mice that exclusively express APP deletion variants corresponding either to the secreted APP ectodomain (APPs alpha) or to a C-terminal (CT) truncation lacking the YENPTY interaction motif (APPdeltaCT15). Interestingly, the deltaCT15 deletion resulted in reduced turnover of holoAPP, increased cell surface expression, and strongly reduced Abeta levels in brain, likely because of reduced processing in the endocytic pathway. Most importantly, we demonstrate that in both APP knock-in lines the expression of APP N-terminal domains either grossly attenuated or completely rescued the prominent deficits of APP knock-out mice, such as reductions in brain and body weight, grip strength deficits, alterations in circadian locomotor activity, exploratory activity, and the impairment in spatial learning and long-term potentiation. Together, our data suggest that the APP C terminus is dispensable and that APPs alpha is sufficient to mediate the physiological functions of APP assessed by these tests.
β-淀粉样前体蛋白（APP）的蛋白水解加工会产生β-淀粉样蛋白（Aβ），这在阿尔茨海默病（AD）的发病机制中起着核心作用，这一点已得到充分证实。相比之下，APP及其众多蛋白水解片段的生理作用，以及这些功能的丧失是否导致AD这一问题，仍然未知。为了解决这个问题，我们通过基因靶向等位基因取代了内源性APP基因座，并生成了两系敲入小鼠，它们只表达与分泌型APP胞外结构域（APPsα）或缺乏YENPTY相互作用基序的C末端（CT）截短体（APPdeltaCT15）相对应的APP缺失变体。有趣的是，deltaCT15缺失导致全长APP的周转减少、细胞表面表达增加，以及大脑中Aβ水平大幅降低，这可能是由于内吞途径中的加工减少所致。最重要的是，我们证明，在两个APP敲入系中，APP N末端结构域的表达要么显著减轻，要么完全挽救了APP敲除小鼠的显著缺陷，如脑重和体重减轻、握力缺陷、昼夜运动活动改变、探索活动以及空间学习和长时程增强受损。总之，我们的数据表明APP的C末端是可有可无的，并且APPsα足以介导通过这些测试评估的APP的生理功能。
