Study of generation of Alzheimer's amyloid β peptide

淀粉样蛋白前体蛋白（APP）的加工包括α和β裂解途径。APP的蛋白水解产物Aβ是通过最初的β裂解和随后的γ裂解途径产生的。Aβ被认为是阿尔茨海默病发病机制的核心，因此阐明APP的加工过程是一个重要的问题。在我们2001年的研究中，我们证明了APP在α/β裂解之前经历γ裂解的可能性很低。也就是说，APP独特地受到由初始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裂解的准细胞区室。第一个APP分子通过添加Retargeting基序进行修饰，这限制了分子在内质网中表达而不被分选到后区室。发现该突变体APP具有α和β裂解。利用brefeldin A重建内质网中的第二个APP加工，brefeldin A是一种破坏高尔基体从而抑制从内质网中分选表达蛋白的物质。在此条件下，APP呈现α裂解而非β裂解。因此，APP在内质网中的限制性表达呈现出一种卵裂。细胞表面已被确定为发生α裂解的亚细胞位点。在这里，ER被确定为α切割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.