Comparative Mechanism Of Astrocytic Uptake, Trafficking And Clearance Of Soluble Monomer Versus Oligomer β-amyloid Proteins

Alzheimer’s disease （AD） is a common neurodegenerative disease, which has thecharacteristics of high disease incidence, prevalence and morbidity. Many studies haveproved that β-amyloid oligomers （oAβ） can induce neuron death because of their greattoxicity, which lead to AD happens. Astrocytes are capable of oAβ clearance, but themechanism remains unclear. Hence, we took gliocytoma U87cell line as experimentalobject and used confocal microscopy to study the mechanisms difference of astrocyticuptake, trafficking and degradation of souble monomer and oligomer Aβ₄₂, which wereprepared in vitro and characterized by thioflavin T （ThT） staining and transmissionelectron microscopy. Internalization assays show astrocytes uptake both soluble Aβ₄₂(sAβ₄₂) and oAβ₄₂through macropinocytosis and require cholesterol, but, the statisticanalysis indicates the degree of their macropinocytosis dependence is different.Simultaneously, the classic clathrin-mediated endocytosis isn’t involved in the uptake ofAβ₄₂, and the clipping function of dynamin2, not dynamin1, is essential for the process.Besides, lipoprotein receptor-related protein1（LRP1） knockdown using RNA interferencetechnology inhibits sAβ₄₂internalization but not oAβ₄₂. The above conclusions suggestthat the mechanism of astrcytic sAβ₄₂and oAβ₄₂uptake is distinct and the astrocytesprefer to taking up oAβ₄₂. Co-localization assays show the internalized sAβ₄₂and oAβ₄₂are trafficked into early endosome at the early stage of cellular trafficking andaccumulated in lysosomes finally. Influence of Aβ₄₂on MTS reduction and intracellularAβ₄₂degradation experiments provide evidence for that astrocytes have the ability ofclearing sAβ₄₂and oAβ₄₂, so as to avoiding cell toxicity of oAβ₄₂timely, however, sAβ₄₂is more easier than oAβ₄₂to be degraded. So, we are the first to study the comparativemechanism of astrocytic uptake, trafficking and clearance of sAβ₄₂versus oAβ₄₂, whichmay provide new targets for AD prevention and therapy.