APOLIPOPROTEINS AND A-BETA CATABOLISM

人们对可溶性、低聚和纤维状Abeta的分解代谢知之甚少。有限的已发表的工作和我们自己在实验动物中的初步数据表明，当系统地将Abeta肽注射到小鼠体内时，Aβ肽在循环中的半衰期很短，肝脏是主要的分解代谢器官，肝细胞是参与摄取和降解的细胞。与细胞表面的结合和剂量依赖的内化暗示了受体介导的机制。此外，在载脂蛋白E转基因动物中，Aβ分解代谢似乎受到转基因表达的载脂蛋白E亚型的不同影响。 无论脑细胞中是否发生了类似的机制，这些发现都引发了各种机制问题，这些问题是这项提议的焦点。大脑中是否存在受体介导的Abeta摄取？它依赖于多肽的结构吗？它是否仅限于特定的细胞类型？这种机制与年龄有关吗？载脂蛋白在Abeta的清除和分解代谢中起什么作用？我们假设，Abeta(单体-寡聚-纤维)的构象转变极大地影响了它们在脑细胞内的分解代谢，导致Abeta的积累和伴随而来的淀粉样蛋白沉积在AD中的形成。我们建议(目标1)研究野生型小鼠脑内的Abeta分解代谢，人apoES和apoE4的转基因，apoE和apoJ的KOS，LRP-1的诱导KO，以及 (目标2)利用组织培养技术分析脑细胞中Abeta单体/二聚体、寡聚体和纤维样蛋白的分解代谢机制，以评估Abeta的表面结合、摄取和降解模式以及参与Abeta与细胞相互作用的可能受体(S)的身份。

Very little is known about the catabolism of Abeta in its soluble, oligomeric and fibrillar forms. Limited published work and our own preliminary data in laboratory animals indicate that Abeta peptides, when systemically injected in mice, have a short half-life in the circulation, being the liver the main catabolic organ and the hepatocytes the cells involved in the uptake and degradation. Binding on the cell surface and dose-dependent internalization suggest a receptor-mediated mechanism. In addition, in apoE transgenic animals, Abeta catabolism seems to be differentially influenced by the apoE isoform expressed by the transgenesis. Whether or not similar mechanisms take place in brain cells, these findings prompted various mechanistic questions that are the focus in this proposal. Is there a receptor-mediated Abeta uptake in the brain? Is it dependent on the peptide's structure? Is it restricted to a particular cell type? Is this mechanism age-related? Which is the role of apolipoproteins in the clearance and catabolism of Abeta? We hypothesize that conformational transitions of Abeta (monomeric-oligomeric-fibrillar) greatly affect their catabolism within brain cells, resulting in Abeta accumulation and the concomitant formation of the amyloid deposits seen in AD. We propose to (aim 1) study Abeta catabolism in vivo in the brain of wild-type mice, transgenics for human apoES and apoE4, KOs for apoE and apoJ, inducible KOs for LRP-1, as well as in transgenic animals with well established amyloid lesions (i.e. APPsw) using monomeric/dimeric, oligomeric and fibrillar Abeta species in conjunction with the tyramine-cellobiose cellular trapping technique; and (aim 2) dissect the catabolic mechanism of Abeta monomers/dimers, oligomers and fibrils in brain cells using tissue culture techniques to assess the mode of Abeta surface binding, uptake, and degradation as well as the identity of the putative receptor(s) involved in the Abeta - cell interaction.