MOLECULAR PATHOLOGICAL STUDIE OF ALZHEIMER'S DISEASE : ROLE OF β-AMYLOID AND PRESENILINS

淀粉样β肽（Aβ）作为老年斑（SP）沉积是阿尔茨海默病（AD）大脑的不变特征。a β是一种40-42个氨基酸的肽，由β-和γ-分泌酶通过序列裂解从β app蛋白水解产生。早老素（PS）作为γ-分泌酶的催化亚基的作用最近得到了强调。我们和其他人已经证明，与家族性AD （FAD）相关的PS（即PS1和PS2）基因突变增加了a - β42的产生和分泌，a - β42最初主要沉积在所有类型AD患者的大脑中。在本研究中，我们发现在FAD突变体的基础上，PS C端的修饰使PS片段稳定化和Aβ42的过量产生，这表明稳定片段形式的PS是病理上活跃的物种。我们进一步搜索了对其稳定性和功能至关重要的PS子域，并确定了另一个基序，我们将其命名为“PALP”。PALP基序位于PS的C端近端（与人类PS2的残基414-417相对应），高度保守，果蝇PS和线虫spe-4中的突变将PALP的第1 Pro替换为Leu，导致PS功能丧失导致Notch表型，尽管这些突变使PS功能恶化的机制尚不清楚。我们发现，在PALP的第一个残基上含有Pro to Leu突变的人类PS在FAD突变的基础上不能促进Aβ42的过量产生和Notch加工，通过在PS C端修饰的PS的稳定和高分子量复合物的形成失败。因此，寻找作为PS/γ-分泌酶稳定或调节亚基的辅助因子，以及了解γ-裂解的机制，应该是PS研究的下一个目标。

Deposition of amyloid β peptides (Aβ) as senile plaques (SP) is an invariant feature of Alzheimer's disease (AD) brains. Aβ is a 40-42 amino acid peptide that is proteolytically produced from βAPP through sequential cleavages by β- and γ-secretases. The role of presenilin (PS) as a catalytic subunit of γ-secretase is recently highlighted. We and others have shown that mutations in PS (i.e., PS1 and PS2) genes linked to familial AD (FAD) increase production and secretion of Aβ42, that initially and predominantly deposits in the brains of patients with all types of AD.In the present study, we showed that modifications at the C terminus of PS abolish stabilization of PS fragments as well as overproduction of Aβ42 on FAD mutant basis, suggesting that stable fragment forms of PS is the pathologically active species. We further searched for PS subdomains that is critical to its stabilization and function, and identified another motif which we designated "PALP". PALP motif is located at the proximal site of the C terminus of PS (corresponding to residues 414-417 based on human PS2) and is highly conserved, and mutations in drosophila PS and spe-4 in C.elegans that replace the 1st Pro of PALP with Leu lead to Notch phenotype caused by loss-of-function of PS, although the mechanism whereby these mutations deteriorate PS function remained unknown. We found that human PS harboring Pro to Leu mutation at the 1st residue of PALP fails to promote Aβ42 overproduction on FAD mutant basis as well as Notch processing through failure in stabilization and high-molecular-weight complex formation of PS, as observed with modifications at PS C terminus. Hence, search for cofactors that serve as stabilizing or regulatory subunit (s) of PS/γ-secretase, as well as understanding of the mechanism of γ-cleavage, should be the next goal in PS research.