Kaneko I, Morimoto K, Kubo T
Neuroscience and Immunology Research Laboratories, Sankyo Co., Ltd., 1-2-58, Hiromachi, Shinagawa-ku, Tokyo 140-8710, Japan.
Neuroscience. 2001;104(4):1003-11. doi: 10.1016/s0306-4522(01)00155-5.
It is unclear how and when insoluble beta-amyloid in senile plaques exerts degenerative effects on distant hippocampal neurons in Alzheimer's disease. Racemization of Ser and Asp residues of insoluble beta-amyloid is a typical age-dependent process. In this study, we investigated the fibril formation activity and cytotoxic activity of beta-amyloid 1-40 racemized at the Asp or Ser residue. In contrast to beta-amyloid 1-40 and its derivative substituted with the D-Asp(1, 7 or 23) or D-Ser(8) residue, [D-Ser(26)]beta-amyloid 1-40 was non-toxic to PC12 cells, and did not exhibit significant fibril formation activity making it soluble. However, [D-Ser(26)]beta-amyloid 1-40, but not beta-amyloid 1-40, was converted in vitro to a potent neurotoxic and truncated peptide, [D-Ser(26)]beta-amyloid 25-35 or [D-Ser(26)]beta-amyloid 25-40, by chymotrypsin-like enzymes and aminopeptidase M. Soluble [D-Ser(26)]beta-amyloid 1-40 was injected into rat hippocampus with a non-toxic dose of ibotenic acid, an excitatory amino acid. Nissl staining and microtubule-associated protein-2 immunostaining revealed that [D-Ser(26)]beta-amyloid 1-40, as well as [D-Ser(26)]beta-amyloid 25-35, produced a drastic degeneration of the CA1 neurons with ibotenic acid although [D-Ser(26)]beta-amyloid 1-40 alone or ibotenic acid alone did not exert neuronal damage. This suggests the in vivo conversion of non-toxic [D-Ser(26)]beta-amyloid 1-40 to the toxic and truncated peptides which enhance the susceptibility of neurons to the excitatory amino acid.These results and the presence of [D-Ser(26)]beta-amyloid 25-35-like antigens in Alzheimer's disease brains suggest that soluble [D-Ser(26)]beta-amyloid 1-40, possibly formed during the aging process, is released from senile plaques, and converted by brain proteinases to truncated [D-Ser(26)]beta-amyloid 25-35(40)-like peptides, which degenerate hippocampal neurons by enhancing the susceptibility to excitatory amino acids in Alzheimer's disease brains. These findings may provide the basis for a new therapeutic approach to prevent the neurodegeneration in Alzheimer's disease.
目前尚不清楚老年斑中不溶性β-淀粉样蛋白如何以及何时对阿尔茨海默病中远处的海马神经元产生退行性影响。不溶性β-淀粉样蛋白的丝氨酸（Ser）和天冬氨酸（Asp）残基的消旋化是一个典型的年龄依赖性过程。在本研究中，我们研究了在Asp或Ser残基处消旋的β-淀粉样蛋白1-40的纤维形成活性和细胞毒性活性。与β-淀粉样蛋白1-40及其被D-Asp（1、7或23）或D-Ser（8）残基取代的衍生物不同，[D-Ser（26）]β-淀粉样蛋白1-40对PC12细胞无毒，并且没有表现出显著的纤维形成活性，使其可溶。然而，[D-Ser（26）]β-淀粉样蛋白1-40而非β-淀粉样蛋白1-40在体外被类胰凝乳蛋白酶和氨肽酶M转化为一种强效神经毒性和截短肽，[D-Ser（26）]β-淀粉样蛋白25-35或[D-Ser（26）]β-淀粉样蛋白25-40。将可溶性[D-Ser（26）]β-淀粉样蛋白1-40与无毒剂量的兴奋性氨基酸鹅膏蕈氨酸一起注射到大鼠海马中。尼氏染色和微管相关蛋白-2免疫染色显示，[D-Ser（26）]β-淀粉样蛋白1-40以及[D-Ser（26）]β-淀粉样蛋白25-35与鹅膏蕈氨酸一起导致CA1神经元严重退变，尽管单独的[D-Ser（26）]β-淀粉样蛋白1-40或单独的鹅膏蕈氨酸不会造成神经元损伤。这表明无毒的[D-Ser（26）]β-淀粉样蛋白1-40在体内转化为有毒的截短肽，这增强了神经元对兴奋性氨基酸的易感性。这些结果以及阿尔茨海默病大脑中存在[D-Ser（26）]β-淀粉样蛋白25-35样抗原表明，可溶性[D-Ser（26）]β-淀粉样蛋白1-40可能在衰老过程中形成，从老年斑中释放出来，并被脑蛋白酶转化为截短的[D-Ser（26）]β-淀粉样蛋白25-35（40）样肽，这些肽通过增强对阿尔茨海默病大脑中兴奋性氨基酸的易感性而使海马神经元退变。这些发现可能为预防阿尔茨海默病神经退行性变的新治疗方法提供基础。
