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

淀粉样蛋白β多肽(Aβ)沉积为老年斑(SP)是阿尔茨海默病(AD)脑的一个不变特征。β是一种40-42个氨基酸的多肽，由βAPP通过β-和γ-分泌酶的顺序切割而产生。早老素(PS)作为γ-分泌酶的催化亚单位的作用最近受到重视。我们和其他人已经证明了与家族性AD(FAD)相关的PS(即PS1和PS2)基因的突变增加了Aβ42的产生和分泌，Aβ42最初主要沉积在所有类型的AD患者的大脑中。在本研究中，我们证明了PS C末端的修饰在FAD突变的基础上取消了PS片段的稳定以及A DNA 42的过度生产，表明PS的稳定片段形式是病理活性物种。我们进一步寻找对其稳定性和功能至关重要的PS亚域，并确定了另一个基序，我们将其命名为“PALP”。PALP基序位于PS C末端的近端(对应于人类PS2的414-417残基)，是高度保守的，而果蝇PS和线虫中Spe-4的突变用Leu取代PALP的第一个Pro会导致PS功能丧失而导致Notch表型，尽管这些突变恶化PS功能的机制尚不清楚。我们发现，在PALP的第一个残基上含有Pro到Leu突变的人PS未能促进Aβ42在FAD突变基础上的过量生产，以及通过PS C末端的修饰未能稳定和形成PS的高分子量复合体而导致的Notch加工。因此，寻找PS/γ-分泌酶的稳定或调节亚基(S)的辅因子，以及对γ-裂解机制的了解，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.