Mandrekar Shweta, Jiang Qingguang, Lee C Y Daniel, Koenigsknecht-Talboo Jessica, Holtzman David M, Landreth Gary E
Alzheimer Research Laboratory, Department of Neurosciences, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA.
J Neurosci. 2009 Apr 1;29(13):4252-62. doi: 10.1523/JNEUROSCI.5572-08.2009.
Alzheimer's disease is characterized by the progressive deposition of beta-amyloid (Abeta) within the brain parenchyma and its subsequent accumulation into senile plaques. Pathogenesis of the disease is associated with perturbations in Abeta homeostasis and the inefficient clearance of these soluble and insoluble peptides from the brain. Microglia have been reported to mediate the clearance of fibrillar Abeta (fAbeta) through receptor-mediated phagocytosis; however, their participation in clearance of soluble Abeta peptides (sAbeta) is largely unknown. We report that microglia internalize sAbeta from the extracellular milieu through a nonsaturable, fluid phase macropinocytic mechanism that is distinct from phagocytosis and receptor-mediated endocytosis both in vitro and in vivo. The uptake of sAbeta is dependent on both actin and tubulin dynamics and does not involve clathrin assembly, coated vesicles or membrane cholesterol. Upon internalization, fluorescently labeled sAbeta colocalizes to pinocytic vesicles. Microglia rapidly traffic these soluble peptides into late endolysosomal compartments where they are subject to degradation. Additionally, we demonstrate that the uptake of sAbeta and fAbeta occurs largely through distinct mechanisms and upon internalization are segregated into separate subcellular vesicular compartments. Significantly, we found that upon proteolytic degradation of fluorescently labeled sAbeta, the fluorescent chromophore is retained by the microglial cell. These studies identify an important mechanism through which microglial cells participate in the maintenance of Abeta homeostasis, through their capacity to constitutively clear sAbeta peptides from the brain.
阿尔茨海默病的特征是β-淀粉样蛋白（Aβ）在脑实质内进行性沉积，并随后聚积形成老年斑。该疾病的发病机制与Aβ稳态的紊乱以及这些可溶性和不溶性肽从脑中的清除效率低下有关。据报道，小胶质细胞通过受体介导的吞噬作用介导纤维状Aβ（fAβ）的清除；然而，它们在可溶性Aβ肽（sAβ）清除中的参与情况在很大程度上尚不清楚。我们报告，小胶质细胞通过一种非饱和的液相巨胞饮机制从细胞外环境中摄取sAβ，该机制在体外和体内均不同于吞噬作用和受体介导的内吞作用。sAβ的摄取依赖于肌动蛋白和微管蛋白的动力学，并且不涉及网格蛋白组装、被膜小泡或膜胆固醇。内化后，荧光标记的sAβ与胞饮小泡共定位。小胶质细胞迅速将这些可溶性肽转运到晚期内溶酶体区室，在那里它们会被降解。此外，我们证明sAβ和fAβ的摄取主要通过不同的机制发生，并且内化后被分隔到不同的亚细胞小泡区室中。重要的是，我们发现荧光标记的sAβ经蛋白水解降解后，荧光发色团被小胶质细胞保留。这些研究确定了一种重要机制，通过该机制小胶质细胞通过其从脑中组成性清除sAβ肽的能力参与维持Aβ稳态。
