Study of generation of Alzheimer's amyloid β peptide

淀粉样前体蛋白（APP）的加工包括α和β裂解途径。APP的蛋白水解产物Aβ通过初始β裂解和随后的γ裂解途径产生。Aβ被认为是阿尔茨海默病发病机制的核心，因此阐明APP加工是一个重要问题。在我们2001年进行的先前研究中，我们证明APP在α/β裂解之前经历由γ裂解组成的加工的可能性非常低。即APP独特地经历由初始α/β裂解和随后的γ裂解途径组成的加工。基于这些结果，我们研究了α和β裂解的亚细胞区室。第一个APP分子通过添加重靶向基序进行修饰，其限制分子在ER中表达而不分选到随后的隔室。发现该突变APP产生α和β裂解。第二个APP在ER中的加工重建使用布雷菲德菌素A，破坏高尔基体，从而抑制分选出表达的蛋白质的ER的代理。在此条件下，APP显示α切割而非β切割。因此，在ER中限制性表达的APP显示切割。细胞表面已被确定为α裂解发生的亚细胞位点。ER是α裂解的另一个亚细胞位点。

Processing of the amyloid precursor protein (APP) includes αand βcleavage pathways. The proteolytic product of the APP, Aβ is generated through initial β cleavage and subsequent γ cleavage pathway. Aβ is considered central in the pathogenesis of Alzheimer's disease, and therefore clarification of the APP processing is an important issue. In our previous study performed in 2001, we demonstrated that the possibility is quite low that APP undergoes processing consisting of γ cleavage prior to α/β cleavage. Namely APP is subject uniquely to the processing consisting of initial α/β cleavage and subsequent γ cleavage pathway. Based on these results, we studied the eubcellular compartments for α and β cleavages. First APP molecule was modified by addition of the Retargeting motif, which restricts the molecule to be expressed in ER without sorting to afterward compartments. This mutant APP was found to give α and β cleavages. Second APP processing in ER was reconstructed using brefeldin A, an agent that destructs Golgi apparatus and thereby inhibits sorting out from ER of expressed proteins. Under this condition APP was found to show α but not β cleavage. Thus APP expressed restrictedly in ER shows a cleavage. The cell surface has been identified as the subcellular site for α cleavage to occur. Here ER was identified another subcellular site for α cleavage.