Amyloid-β Secretion, Generation, and Lysosomal Sequestration in Response to Proteasome Inhibition: Involvement of Autophagy
Amyloid-β Secretion, Generation, and Lysosomal Sequestration in Response to Proteasome Inhibition: Involvement of Autophagy
复制标题
DOI：
10.3233/jad-2012-120001
复制
发表时间：
2012-01-01
影响因子：
4
通讯作者：
Kagedal, Katarina
中科院分区：
文献类型：
--
作者：
Agholme, Lotta;Hallbeck, Martin;Kagedal, Katarina
蛋白酶体对于磨损和错误折叠的蛋白质的降解是重要的。蛋白酶体活性降低与阿尔茨海默病（AD）有关。蛋白酶体抑制诱导自噬，但自噬对AD神经元是有益的还是有害的仍然是未知的，因为自噬体已被认为是淀粉样蛋白β（A β）产生的位点。在这项研究中，我们研究了蛋白酶体抑制对A β积累和分泌的影响，以及A β PPSwe转染的SH-SY 5 Y神经母细胞瘤细胞中淀粉样β蛋白前体（A β PP）的加工。我们发现，蛋白酶体抑制导致A β在溶酶体中的自噬依赖性积累，并增加细胞内和分泌A β的水平。A β水平的增加不能用A β PP的增加来解释。相反，蛋白酶体对A β PP（C99）C-末端片段的降解减少，使C99可用于γ-分泌酶切割，导致A β生成。在蛋白酶体抑制后抑制自噬导致细胞内A β水平降低，但不分泌A β，并且倾向于进一步增加C99与A β PP的比率，支持自噬体参与A β生成。此外，蛋白酶体抑制引起细胞活力降低，这是通过抑制自噬恢复。蛋白酶体的功能障碍可导致A β的溶酶体蓄积，以及A β的产生和分泌增加，这部分是由自噬促进的。由于还检测到细胞活力的降低，因此自噬的上调可能是不成功的拯救机制，其不是保护性的，而是有助于AD发病机制。
The proteasome is important for degradation of worn out and misfolded proteins. Decreased proteasome activity has been implicated in Alzheimer's disease (AD). Proteasome inhibition induces autophagy, but it is still unknown whether autophagy is beneficial or deleterious to AD neurons, as the autophagosome has been suggested as a site of amyloid-beta (A beta) generation. In this study, we investigated the effect of proteasome inhibition on A beta accumulation and secretion, as well as the processing of amyloid-beta protein precursor (A beta PP) in A beta PPSwe transfected SH-SY5Y neuroblastoma cells. We show that proteasome inhibition resulted in autophagy-dependent accumulation of A beta in lysosomes, and increased levels of intracellular and secreted A beta. The enhanced levels of A beta could not be explained by increased amounts of A beta PP. Instead, reduced degradation of the C-terminal fragment of A beta PP (C99) by the proteasome makes C99 available for gamma-secretase cleavage, leading to A beta generation. Inhibition of autophagy after proteasome inhibition led to reduced levels of intracellular, but not secreted A beta, and tended to further increase the C99 to A beta PP ratio, supporting involvement of the autophagosome in A beta generation. Furthermore, proteasome inhibition caused a reduction in cellular viability, which was reverted by inhibition of autophagy. Dysfunction of the proteasome could cause lysosomal accumulation of A beta, as well as increased generation and secretion of A beta, which is partly facilitated by autophagy. As a decrease in cellular viability was also detected, it is possible that upregulation of autophagy is an unsuccessful rescue mechanism, which instead of being protective, contributes to AD pathogenesis.