Qiu W Q, Ye Z, Kholodenko D, Seubert P, Selkoe D J
Center for Neurologic Diseases, Harvard Medical School, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
J Biol Chem. 1997 Mar 7;272(10):6641-6. doi: 10.1074/jbc.272.10.6641.
Amyloid beta-protein (Abeta) is the major component of neuritic (amyloid) plaques in Alzheimer's disease, and its deposition is an early and constant event in the complex pathogenetic cascade of the disease. Although many studies have focused on the biosynthetic processing of the beta-amyloid precursor protein and on the production and polymerization of Abeta, understanding the degradation and clearance of Abeta has received very little attention. By incubating the conditioned medium of metabolically labeled Abeta-secreting cells with media of various cultured cell lines, we observed a time-dependent decrease in the amount of Abeta in the mixed media. The factor principally responsible for this decrease was a secreted metalloprotease released by both neural and non-neural cells. Among the cells examined, the microglial cell line, BV-2, produced the most Abeta-degrading activity. The protease was completely blocked by the metalloprotease inhibitor, 1,10-phenanthroline, and partially inhibited by EDTA, whereas inhibitors of other protease classes produced little or no inhibition. Substrate analysis suggests that the enzyme was a non-matrix metalloprotease. The protease cleaved both Abeta1-40 and Abeta1-42 peptides secreted by beta-amyloid precursor protein-transfected cells but failed to degrade low molecular weight oligomers of Abeta that form in the culture medium. Lipopolysaccharide, a stimulator of macrophages/microglia, activated BV-2 cells to increase their Abeta-degrading metalloprotease activity. We conclude that secreted Abeta1-40 and Abeta1-42 peptides are constitutively degraded by a metalloprotease released by microglia and other neural cells, providing a potential mechanism for the clearance of Abeta in brain tissue.
β-淀粉样蛋白（Aβ）是阿尔茨海默病中神经炎性（淀粉样）斑块的主要成分，其沉积是该疾病复杂发病机制级联反应中的早期且持续存在的事件。尽管许多研究聚焦于β-淀粉样前体蛋白的生物合成过程以及Aβ的产生和聚合，但对Aβ的降解和清除的了解却非常少。通过将代谢标记的分泌Aβ细胞的条件培养基与各种培养细胞系的培养基一起孵育，我们观察到混合培养基中Aβ的量随时间减少。导致这种减少的主要因素是神经细胞和非神经细胞分泌的一种金属蛋白酶。在所检测的细胞中，小胶质细胞系BV-2产生的Aβ降解活性最高。该蛋白酶被金属蛋白酶抑制剂1,10-菲咯啉完全阻断，被乙二胺四乙酸部分抑制，而其他蛋白酶类别的抑制剂几乎没有抑制作用或完全没有抑制作用。底物分析表明该酶是一种非基质金属蛋白酶。该蛋白酶可切割由β-淀粉样前体蛋白转染细胞分泌的Aβ1-40和Aβ1-42肽段，但无法降解在培养基中形成的低分子量Aβ寡聚体。脂多糖是巨噬细胞/小胶质细胞的刺激剂，可激活BV-2细胞以增加其Aβ降解金属蛋白酶活性。我们得出结论，分泌的Aβ1-40和Aβ1-42肽段可被小胶质细胞和其他神经细胞释放的金属蛋白酶持续降解，这为脑组织中Aβ的清除提供了一种潜在机制。
