Sweeney David, Martins Ralph, LeVine Harry, Smith Jonathan D, Gandy Sam
Farber Institute for Neurosciences Thomas Jefferson University 900 Walnut Street, JHN 467 Philadelphia, PA 19107-5587 USA.
J Neuroinflammation. 2004 Aug 16;1(1):15. doi: 10.1186/1742-2094-1-15.
The apolipoprotein E epsilon4 allele contributes to the genetic susceptibility underlying a large proportion (~40-60%) of typical, sporadic Alzheimer disease. Apolipoprotein E deficient mice made transgenic for human apolipoprotein E epsilon4 accumulate excess cerebral amyloid when compared to similarly prepared mice expressing human apolipoprotein E epsilon3. Therefore, it is important to search for relevant interactions(s) between apolipoprotein E epsilon4 and Abeta in order to clarify the biological role for apolipoprotein E epsilon4 in Alzheimer disease. Using a thioflavine T (ThT)-based assay, we have investigated the effects of native human apolipoprotein E isoforms on the kinetics of Abeta fibrillogenesis. No obvious profibrillogenic activity was detected in Abeta1-40-based assays of any native apolipoprotein E isoform. However, when ThT assays were repeated using Abeta1-42, modest, but statistically significant, profibrillogenic activity was detected in both apolipoprotein E epsilon3- and apolipoprotein E epsilon4-containing media and was similar in magnitude for the two isoforms. These data demonstrate that native apolipoprotein E possesses "pathological chaperone"-type activity for Abeta: in other words, the data indicate that a chaperone-like misfolding reaction can occur between native apolipoprotein E and Abeta. However, the equipotent activities of the apolipoprotein E epsilon3 and epsilon4 isoforms suggests the possibility that either extended co-incubation of apolipoprotein E and Abeta, or, perhaps, the inclusion in the reaction of other fibrillogenesis-modulation co-factors (such as metal ions, or inflammatory mediators such as reactive oxygen species, alpha2-macroglobulin, apolipoprotein J, etc.) may be required for modeling in vitro the apolipoprotein E-isoform-specific-regulation of extracellular Abeta accumulation that occurs in vivo. Alternatively, other events, such as differential apolipoprotein E-isoform-mediated clearance of Abeta or of apolipoprotein E/Abeta complexes may underlie apolipoprotein E-isoform-dependent Abeta accumulation.
载脂蛋白Eε4等位基因导致了大部分（约40%-60%）典型散发性阿尔茨海默病的遗传易感性。与表达人载脂蛋白Eε3的类似制备小鼠相比，转染人载脂蛋白Eε4的载脂蛋白E缺陷小鼠会积累过量的脑淀粉样蛋白。因此，寻找载脂蛋白Eε4与β-淀粉样蛋白（Aβ）之间的相关相互作用，对于阐明载脂蛋白Eε4在阿尔茨海默病中的生物学作用非常重要。我们使用基于硫黄素T（ThT）的检测方法，研究了天然人载脂蛋白E异构体对Aβ纤维形成动力学的影响。在基于Aβ1-40的检测中，未检测到任何天然载脂蛋白E异构体具有明显的促纤维形成活性。然而，当使用Aβ1-42重复进行ThT检测时，在含有载脂蛋白Eε3和载脂蛋白Eε4的培养基中均检测到适度但具有统计学意义的促纤维形成活性，且两种异构体的活性强度相似。这些数据表明，天然载脂蛋白E对Aβ具有“病理性伴侣”样活性：换句话说，数据表明天然载脂蛋白E与Aβ之间可能发生类似伴侣的错误折叠反应。然而，载脂蛋白Eε3和ε4异构体的等效活性表明，可能需要延长载脂蛋白E与Aβ的共孵育时间，或者在反应中加入其他纤维形成调节辅助因子（如金属离子，或炎症介质如活性氧、α2-巨球蛋白、载脂蛋白J等），才能在体外模拟体内发生的载脂蛋白E异构体特异性调节细胞外Aβ积累。或者，其他事件，如载脂蛋白E异构体介导的Aβ或载脂蛋白E/Aβ复合物清除差异，可能是载脂蛋白E异构体依赖性Aβ积累的基础。
