Identification of a stable fragment of the Alzheimer amyloid precursor containing the beta-protein in brain microvessels.

Altered proteolysis of the beta-amyloid precursor protein (beta APP) resulting in release of the approximately 40-residue amyloid beta-protein (A beta P) may be a seminal pathogenetic event in Alzheimer disease. Using region-specific beta APP antibodies, we searched for stable proteolytic intermediates containing the intact A beta P region in brain tissue. A 22-kDa beta APP fragment was selectively detected in microvessels purified from cerebral cortex and other brain regions. On immunoblots, the 22-kDa band is labeled by five distinct antisera to beta APP carboxyl-terminal peptides and by affinity-purified antibodies to the recombinant proteins beta APP444-592 and beta APP592-695, which flank the A beta P region. The protein is virtually undetectable in whole-brain homogenates or microvessel-free fractions of brain. The protein is extractable from microvessels in Triton X-100 and other detergents, indicating its membrane association. In comparison with cortical microvessels, microvessels purified from white matter, cerebellum, and nonneural tissues contain lower amounts of the 22-kDa protein. The protein is found in microvessels of both normal and Alzheimer disease brains and occurs in low amounts in microvessels from fresh bovine brain. The size and specific immunoreactivity of the 22-kDa protein indicate that it is a stable fragment of beta APP containing the intact A beta P. The occurrence of this potentially amyloidogenic intermediate in microvessels is consistent with a vascular or hematogenous origin for some A beta P deposits in Alzheimer disease. IMAGES:

β淀粉样前体蛋白（beta APP）的蛋白水解过程异常，导致约40个氨基酸残基的β淀粉样蛋白（AβP）释放，这可能是阿尔茨海默病（Alzheimer disease）的关键致病事件。本研究使用区域特异性beta APP抗体，在脑组织中搜寻包含完整AβP区域的稳定蛋白水解中间体。研究人员在从大脑皮层及其他脑区纯化的微血管中，特异性检测到一条22 kDa的beta APP片段。免疫印迹实验显示，该22 kDa条带可被五种针对beta APP羧基末端肽的不同抗血清，以及针对侧翼覆盖AβP区域的重组蛋白beta APP444-592和beta APP592-695的亲和纯化抗体所标记。在全脑匀浆或无微血管的脑组织组分中，几乎无法检测到该蛋白。该蛋白可通过曲拉通X-100（Triton X-100）及其他去污剂从微血管中提取，表明其具有膜结合特性。与皮层微血管相比，从白质、小脑及非神经组织纯化的微血管中，该22 kDa蛋白的含量更低。该蛋白在正常及阿尔茨海默病患者脑组织的微血管中均有存在，且在新鲜牛脑微血管中含量较低。该22 kDa蛋白的分子量及特异性免疫反应性表明，其是包含完整AβP区域的稳定beta APP片段。这种潜在淀粉样生成中间体在微血管中的存在，支持了阿尔茨海默病中部分AβP沉积源于血管或血源性的假说。图像：