Elucidation of aggregation mechanism of Alzheimer's β-peptides and development of their aggregation inhibitors

阿尔茨海默病的神经病理学特征是在辫子实质和皮质血管中进行性沉积淀粉样蛋白。这种沉积主要由40和42聚体的β-淀粉样多肽(Aβ40，Aβ42)组成，具有神经毒性和聚集能力。家族性阿尔茨海默病中的脑淀粉样血管病与这些Aβ多肽编码区内的错义突变有关。为了阐明Aβ多肽的聚集机制，以高纯度的形式合成了Aβ40和Aβ42的突变体，并检测了其对PC12细胞的神经毒性和聚集能力，所有位于22和23位的Aβ40突变体具有比野生型Aβ40更强的神经毒性。位于22和23位的Aβ42突变体的神经毒性比相应的Aβ40突变体强50~200倍，提示Aβ42突变体主要参与慢性再生障碍性贫血的发病机制。尤其是E…更多的22Q-Aβ42(荷兰)和E22K-Aβ42(意大利)广泛聚集，支持荷兰和意大利患者被诊断为遗传性脑出血伴淀粉样变性的临床证据。相反，21 G(佛兰德)突变需要另一种解释，除了Aβ突变体的物理化学性质。红外光谱分析表明，聚集增加了A-β-β多肽的DNA-Sheet含量。然而，TURN也是聚集的关键二级结构，因为22和23位残基优先形成两个残基β-TURN显著提高聚集能力。为了鉴定对β-SHAP形成重要的氨基酸残基，合成了一系列Aβ42的Pro取代突变体，并研究了它们的聚集能力和神经毒性。只有E22P-Aβ42广泛聚集，具有比野生型Aβ42更强的神经毒性，这表明15~21和24~32位残基参与了分子间β-SHAP的形成，而22和23位的转弯形成在Aβ多肽的聚集和神经毒性中起着关键作用。这些发现为设计新的Aβ多肽聚集抑制剂奠定了基础。较少

Alzheimer's disease is neuropathologically characterized by the progressive deposition of amyloid in the braid parenchyma and cortical blood vessels. This deposition mainly consists of 40-and 42-mer β-amyloid peptides (Aβ40, Aβ42) which show neurotoxicity and aggregative ability. Cerebral amyloid angiopathy (CAA) in familial Alzheimer's disease is related to missense mutations inside the coding region of these Aβpeptides. In order to clarify the aggregation mechanism of Aβpeptides, all of the variants of Aβ40 and Aβ42 found in CAA were synthesized in a highly pure form and examined for neurotoxicity in PC12 cells and aggregative ability.All of the Aβ40 mutants at positions 22 and 23 showed stronger neurotoxicity than wild-type Aβ40. Similar tendency was observed for Aβ42 mutants at positions 22 and 23 whose neurotoxicity was 50〜200 times stronger than that of the corresponding Aβ40 mutants, indicating that these Aβ42 mutants are mainly involved in the pathogenesis of CAA. Especially, E … More 22Q-Aβ42 (Dutch) and E22K-Aβ42 (Italian) aggregated extensively, supporting the clinical evidence that Dutch and Italian patients are diagnosed as hereditary cerebral hemorrhage with amyloidosis. In contrast, A21 G (Flemish) mutation needs alternative explanation with the exception of physicochemical properties of Aβmutants. The FI-IR spectra suggested that aggregation increases theβ-sheet contents of the Aβpeptides. However, turn was also a critical secondary structure for aggregation since residues at positions 22 and 23 that preferably form two-residue β-turn significantly enhanced the aggregative ability.To identify amino acid residues that are important for the β-sheet formation, a series of proline-substituted mutants of Aβ42 was synthesized and their aggregative ability and neurotoxicity were investigated. Only E22P-Aβ42 extensively aggregated with stronger neurotoxicity than wild-type Aβ42, suggesting that the residues at positions 15〜21 and 24〜32 are involved in the intermolecular β-sheet formation, and that turn formation at positions 22 and 23 plays a crucial role in the aggregation and neurotoxicity of Aβpeptides. These findings become a basis for designing new aggregation inhibitors of Aβpeptides. Less