Activated Scavenger Receptor A Promotes Glial Internalization of Aβ

Beta-amyloid (Ab) aggregates have a pivotal role in pathological processing of Alzheimer's disease (AD). The clearance of Ab monomer or aggregates is a causal strategy for AD treatment. Microglia and astrocytes are the main macrophages that exert critical neuroprotective roles in the brain. They may effectively clear the toxic accumulation of Ab at the initial stage of AD, however, their functions are attenuated because of glial overactivation. In this study, we first showed that heptapeptide XD4 activates the class A scavenger receptor (SR-A) on the glia by increasing the binding of Ab to SR-A, thereby promoting glial phagocytosis of Ab oligomer in microglia and astrocytes and triggering intracellular mitogen-activated protein kinase (MAPK) signaling cascades. Moreover, XD4 enhances the internalization of A beta monomers to microglia and astrocytes through macropinocytosis or SR-A-mediated phagocytosis. Furthermore, XD4 significantly inhibits A beta oligomer-induced cytotoxicity to glial cells and decreases the production of proinflammatory cytokines, such as TNF-alpha and IL-1 beta, in vitro and in vivo. Our findings may provide a novel strategy for AD treatment by activating SR-A.