Yamada Kaoru, Hashimoto Tadafumi, Yabuki Chiori, Nagae Yusuke, Tachikawa Masanori, Strickland Dudley K, Liu Qiang, Bu Guojun, Basak Jacob M, Holtzman David M, Ohtsuki Sumio, Terasaki Tetsuya, Iwatsubo Takeshi
Department of Neuropathology and Neuroscience, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo 113-0033, Japan.
J Biol Chem. 2008 Dec 12;283(50):34554-62. doi: 10.1074/jbc.M801487200. Epub 2008 Oct 21.
The metabolism of amyloid beta peptide (A beta) in the brain is crucial to the pathogenesis of Alzheimer disease. A body of evidence suggests that A beta is actively transported from brain parenchyma to blood across the blood-brain barrier (BBB), although the precise mechanism remains unclear. To unravel the cellular and molecular mechanism of A beta transport across the BBB, we established a new in vitro model of the initial internalization step of A beta transport using TR-BBB cells, a conditionally immortalized endothelial cell line from rat brain. We show that TR-BBB cells rapidly internalize A beta through a receptor-mediated mechanism. We also provide evidence that A beta internalization is mediated by LRP1 (low density lipoprotein receptor-related protein 1), since administration of LRP1 antagonist, receptor-associated protein, neutralizing antibody, or small interference RNAs all reduced A beta uptake. Despite the requirement of LRP1-dependent internalization, A beta does not directly bind to LRP1 in an in vitro binding assay. Unlike TR-BBB cells, mouse embryonic fibroblasts endogenously expressing functional LRP1 and exhibiting the authentic LRP1-mediated endocytosis (e.g. of tissue plasminogen activator) did not show rapid A beta uptake. Based on these data, we propose that the rapid LRP1-dependent internalization of A beta occurs under the BBB-specific cellular context and that TR-BBB is a useful tool for analyzing the molecular mechanism of the rapid transport of A beta across BBB.
大脑中β淀粉样肽（Aβ）的代谢对阿尔茨海默病的发病机制至关重要。大量证据表明，Aβ可通过血脑屏障（BBB）从脑实质主动转运至血液，尽管确切机制尚不清楚。为了阐明Aβ跨血脑屏障转运的细胞和分子机制，我们利用TR-BBB细胞建立了一种新的体外Aβ转运初始内化步骤模型，TR-BBB细胞是一种源自大鼠脑的条件永生化内皮细胞系。我们发现TR-BBB细胞通过受体介导的机制快速内化Aβ。我们还提供证据表明，Aβ内化是由低密度脂蛋白受体相关蛋白1（LRP1）介导的，因为给予LRP1拮抗剂、受体相关蛋白、中和抗体或小干扰RNA均能降低Aβ摄取。尽管需要LRP1依赖性内化，但在体外结合试验中Aβ并不直接与LRP1结合。与TR-BBB细胞不同，内源性表达功能性LRP1并表现出真正的LRP1介导的内吞作用（如组织纤溶酶原激活物的内吞作用）的小鼠胚胎成纤维细胞并未显示出快速的Aβ摄取。基于这些数据，我们提出，Aβ的快速LRP1依赖性内化发生在血脑屏障特异性细胞环境下，并且TR-BBB是分析Aβ跨血脑屏障快速转运分子机制的有用工具。
