Karolinska Institutet-Alzheimer Disease Research Center, Department of Neurobiology, Care Sciences and Society (NVS), Karolinska Institutet, Novum, SE-141 86 Stockholm, Sweden.
Biochem Biophys Res Commun. 2011 Jan 7;404(1):564-8. doi: 10.1016/j.bbrc.2010.12.029. Epub 2010 Dec 10.
γ-Secretase plays an important function in the development of Alzheimer disease, since it participates in the production of the toxic amyloid β-peptide (Aβ) from the amyloid precursor protein (APP). Besides APP, γ-secretase cleaves many other substrates resulting in adverse side effects when γ-secretase inhibitors are used in clinical trials. γ-Secretase is a membrane bound protein complex consisting of at least four subunits, presenilin (PS), nicastrin, Aph-1 and Pen-2. PS and Aph-1 exist as different homologs (PS1/PS2 and Aph-1a/Aph-1b, respectively), which generates a variation in complex composition. PS1 and PS2 appears to have distinct roles since PS1 is essential during embryonic development whereas PS2 deficient mice are viable with a mild phenotype. The molecular mechanism behind this diversity is, however, largely unknown. In order to investigate whether PS1 and PS2 show different substrate specificity, we used PS1 or PS2 deficient mouse embryonic fibroblasts to study the processing on the γ-secretase substrates APP, Notch, N-cadherin, and ephrinB. We found that whereas depletion of PS1 severely affected the cleavage of all substrates, the effect of PS2 depletion was minor. In addition, less PS2 was found in active γ-secretase complexes. We also studied the effect of PS2 depletion in adult mouse brain and, in concordance with the results from the mouse embryonic fibroblasts, PS2 deficiency did not alter the cleavage of the two most important substrates, APP and Notch. In summary, this study shows that the contribution of PS2 on γ-secretase activity is of less importance, explaining the mild phenotype of PS2-deficient mice.
γ-分泌酶在阿尔茨海默病的发展中起着重要作用，因为它参与了淀粉样前体蛋白（APP）中有毒的淀粉样β肽（Aβ）的产生。除了 APP，γ-分泌酶还切割许多其他底物，当γ-分泌酶抑制剂在临床试验中使用时会产生不良副作用。γ-分泌酶是一种膜结合蛋白复合物，由至少四个亚基组成，即早老素（PS）、尼卡斯特林、Aph-1 和 Pen-2。PS 和 Aph-1 存在不同的同源物（分别为 PS1/PS2 和 Aph-1a/Aph-1b），这导致复合物组成的变化。PS1 和 PS2 似乎具有不同的作用，因为 PS1 在胚胎发育过程中是必不可少的，而 PS2 缺陷小鼠具有轻微表型且存活。然而，这种多样性的分子机制在很大程度上尚不清楚。为了研究 PS1 和 PS2 是否表现出不同的底物特异性，我们使用 PS1 或 PS2 缺陷型小鼠胚胎成纤维细胞来研究 γ-分泌酶底物 APP、Notch、N-钙黏蛋白和 ephrinB 的加工。我们发现，尽管 PS1 的耗竭严重影响了所有底物的切割，但 PS2 的耗竭影响较小。此外，活性 γ-分泌酶复合物中发现的 PS2 较少。我们还研究了 PS2 耗竭对成年小鼠大脑的影响，与小鼠胚胎成纤维细胞的结果一致，PS2 缺陷并不改变两个最重要的底物 APP 和 Notch 的切割。总之，这项研究表明 PS2 对 γ-分泌酶活性的贡献并不重要，这解释了 PS2 缺陷小鼠的轻微表型。
