Yamazaki T, Haass C, Saido T C, Omura S, Ihara Y
Department of Neuropathology, Faculty of Medicine, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan.
Biochemistry. 1997 Jul 8;36(27):8377-83. doi: 10.1021/bi970209y.
Cerebral deposition of amyloid beta-protein (Abeta) as senile plaques is a pathological hallmark of Alzheimer's disease (AD). Abeta falls into two major subspecies defined by their C-termini, Abeta40 and Abeta42, ending in Val-40 and Ala-42, respectively. Although Abeta42 accounts for only approximately 10% of secreted Abeta, Abeta42 is the predominant species accumulated in senile plaques in AD brain and appears to be the initially deposited species. Its secretion level has recently been reported to be increased in the plasma or culture media of fibroblasts from patients affected by any of early-onset familial AD (FAD). Thus, inhibition of Abeta42 production would be one of the therapeutic targets for AD. However, there is little information about the cleavage mechanism via which Abeta40 and Abeta42 are generated and its relationship to intracellular protease activity. Here, we examined by well-characterized enzyme immunoassay the effects of calpain and proteasome inhibitors on the levels of Abeta40 and Abeta42 secretion by cultured cells. A calpastatin peptide homologous to the inhibitory domain of calpastatin, an endogenous calpain specific inhibitor, induced a specific increase in secreted Abeta42 relative to the total secreted Abeta level, a characteristic of the cultured cells transfected with FAD-linked mutated genes, while a proteasome specific inhibitor, lactacystin, showed no such effect. These findings suggest that the Abeta42 secretion ratio is modulated by the calpain-calpastatin system and may point to the possibility of exploring particular compounds that inhibit Abeta42 secretion through this pathway.
淀粉样β蛋白（Aβ）以老年斑形式在大脑中沉积是阿尔茨海默病（AD）的病理标志。Aβ根据其C末端可分为两个主要亚类，即Aβ40和Aβ42，分别以Val-40和Ala-42结尾。尽管Aβ42仅占分泌型Aβ的约10%，但Aβ42是AD大脑老年斑中积累的主要类型，并且似乎是最初沉积的类型。最近有报道称，在任何早发性家族性AD（FAD）患者的成纤维细胞的血浆或培养基中，其分泌水平会升高。因此，抑制Aβ42的产生将是AD的治疗靶点之一。然而，关于Aβ40和Aβ42产生的切割机制及其与细胞内蛋白酶活性的关系，目前知之甚少。在这里，我们通过特征明确的酶免疫测定法，研究了钙蛋白酶和蛋白酶体抑制剂对培养细胞分泌Aβ40和Aβ42水平的影响。一种与内源性钙蛋白酶特异性抑制剂钙蛋白酶抑制蛋白的抑制结构域同源的钙蛋白酶抑制蛋白肽，相对于总分泌Aβ水平，诱导分泌型Aβ42特异性增加，这是转染了与FAD相关突变基因的培养细胞的特征，而蛋白酶体特异性抑制剂乳胞素则没有这种作用。这些发现表明，Aβ42的分泌比例受钙蛋白酶-钙蛋白酶抑制蛋白系统调节，这可能指出了探索通过该途径抑制Aβ42分泌的特定化合物的可能性。
