The amyloid β-protein precursor of Alzheimer's disease is degraded extracellularly by a Kunitz protease inhibitor domain-sensitive trypsin-like serine protease in cultures of chick sympathetic neurons
The amyloid β-protein precursor of Alzheimer's disease is degraded extracellularly by a Kunitz protease inhibitor domain-sensitive trypsin-like serine protease in cultures of chick sympathetic neurons
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DOI：
10.1046/j.1432-1327.1999.00886.x
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发表时间：
1999-12-01
期刊：
影响因子：
--
通讯作者：
Small, DH
中科院分区：
文献类型：
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作者：
Caswell, MD;San Mok, S;Small, DH
阿尔茨海默病(AD)的淀粉样蛋白前体(APP)被α-分泌酶切割，产生N端分泌片段，或者被β-和伽马分泌酶切割，产生β-淀粉样蛋白(Aβ)。Aβ在脑内的蓄积是AD发病机制中的重要一步。选择性的信使核糖核酸剪接可以产生APP的亚型，它含有一个库尼茨蛋白酶抑制因子(KPI)结构域。然而，人们对该结构域的生理功能知之甚少。在本研究中，我们观察了APP在培养的鸡交感神经细胞中的代谢变化。将神经元与[S-35]蛋氨酸和[35S]半胱氨酸孵育5h，标记APP。细胞内标记的APP以双相模式衰退，表明转运通过两个代谢区段发生。APP在各隔室的半衰期分别为1.5h和5.7h。一小部分APP(10%)被分泌到培养基中，在那里被降解，半衰期为9h。使用特定的蛋白酶抑制剂的研究表明，这种胞外分解是由于分泌到培养液中的一种类胰酶丝氨酸蛋白酶的裂解。值得注意的是，该酶被APP的一个重组异构体(SAPP(751))所抑制，该APP含有一个与kunitz蛋白酶抑制因子(KPI)结构域同源的区域。这些结果表明，KPI形式的APP通过抑制分泌的APP降解酶的活性来调节分泌的APP的胞外切割。
The amyloid P-protein precursor (APP) of Alzheimer's disease (AD) is cleaved either by alpha-secretase to generate an N-terminally secreted fragment, or by beta- and gamma-secretases to generate the beta-amyloid protein (A beta). The accumulation of A beta in the brain is an important step in the pathogenesis of AD. Alternative mRNA splicing can generate isoforms of APP which contain a Kunitz protease inhibitor (KPI) domain. However, little is known about the physiological function of this domain. In the present study, the metabolic turnover of APP was examined in cultured chick sympathetic neurons. APP was labelled by incubating neurons for 5 h with [S-35]methionine and [35S]cysteine. Intracellular labelled APP decayed in a biphasic pattern suggesting that trafficking occurs through two metabolic compartments. The half-lives for APP in each compartment were 1.5 and 5.7 h, respectively. A small fraction (10%) of the total APP was secreted into the culture medium where it was degraded with a half-life of 9h. Studies using specific protease inhibitors demonstrated that this extracellular breakdown was due to cleavage by a trypsin-like serine protease that was secreted into the culture medium. Significantly, this protease was inhibited by a recombinant isoform of APP (sAPP(751)), which contains a region homologous to the Kunitz protease,inhibitor (KPI) domain. These results suggest that KPI forms of APP regulate extracellular cleavage of secreted APP by inhibiting the activity of a secreted APP-degrading protease.