Skovronsky D M, Pijak D S, Doms R W, Lee V M
Center for Neurodegenerative Disease Research, Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Biochemistry. 2000 Feb 1;39(4):810-7. doi: 10.1021/bi991728z.
The deposition of amyloid-beta peptides (Abeta) in senile plaques (SPs) is a central pathological feature of Alzheimer's disease (AD). Since SPs are composed predominantly of Abeta1-42, which is more amyloidogenic in vitro, the enzymes involved in generating Abeta1-42 may be particularly important to the pathogenesis of AD. In contrast to Abeta1-40, which is generated in the trans-Golgi network and other cytoplasmic organelles, intracellular Abeta1-42 is produced in the endoplasmic reticulum/intermediate compartment (ER/IC), where it accumulates in a stable insoluble pool. Since this pool of insoluble Abeta1-42 may play a critical role in AD amyloidogenesis, we sought to determine how the production of intracellular Abeta is regulated. Surprisingly, the production of insoluble intracellular Abeta1-42 was increased by a putative gamma-secretase inhibitor as well as by an inhibitor of the proteasome. We further demonstrate that this increased generation of Abeta1-42 in the ER/IC is due to a reduction in the turnover of Abeta-containing APP C-terminal fragments. We conclude that the proteasome is a novel site for degradation of ER/IC-generated APP fragments. Proteasome inhibitors may augment the availability of APP C-terminal fragments for gamma-secretase cleavage and thereby increase production of Abeta1-42 in the ER/IC. Based on the organelle-specific differences in the generation of Abeta by gamma-secretase, we conclude that intracellular ER/IC-generated Abeta1-42 and secreted Abeta1-40 are produced by different gamma-secretases. Further, the fact that a putative gamma-secretase inhibitor had opposite effects on the production of secreted and intracellular Abeta may have important implications for AD drug design.
β-淀粉样肽（Aβ）在老年斑（SPs）中的沉积是阿尔茨海默病（AD）的核心病理特征。由于SPs主要由体外淀粉样生成性更强的Aβ1-42组成，参与生成Aβ1-42的酶可能对AD的发病机制尤为重要。与在反式高尔基体网络和其他细胞质细胞器中生成的Aβ1-40不同，细胞内Aβ1-42在内质网/中间区室（ER/IC）中产生，并在那里积累形成稳定的不溶性池。由于这一不溶性Aβ1-42池可能在AD淀粉样蛋白生成中起关键作用，我们试图确定细胞内Aβ的产生是如何被调控的。令人惊讶的是，一种假定的γ-分泌酶抑制剂以及蛋白酶体抑制剂均可增加不溶性细胞内Aβ1-42的产生。我们进一步证明，ER/IC中Aβ1-42生成的增加是由于含Aβ的APP C末端片段的周转减少所致。我们得出结论，蛋白酶体是ER/IC生成的APP片段降解的新位点。蛋白酶体抑制剂可能会增加APP C末端片段用于γ-分泌酶切割的可用性，从而增加ER/IC中Aβ1-42的产生。基于γ-分泌酶在Aβ生成中的细胞器特异性差异，我们得出结论，细胞内ER/IC生成的Aβ1-42和分泌的Aβ1-40由不同的γ-分泌酶产生。此外，一种假定的γ-分泌酶抑制剂对分泌型和细胞内Aβ的产生具有相反作用这一事实，可能对AD药物设计具有重要意义。
