Amyloid ß oligomers induce interleukin-1ß production in primary microglia in a cathepsin B- and reactive oxygen species-dependent manner.

Amyloid ß (Aß) peptide, a causative agent of Alzheimer's disease, forms two types of aggregates: oligomers and fibrils. These aggregates induce inflammatory responses, such as interleukin-1ß (IL-1ß) production by microglia, which are macrophage-like cells located in the brain. In this study, we examined the effect of the two forms of Aß aggregates on IL-1ß production in mouse primary microglia. We prepared Aß oligomer and fibril from Aß (1-42) peptide in vitro. We analyzed the characteristics of these oligomers and fibrils by electrophoresis and atomic force microscopy. Interestingly, Aß oligomers but not Aß monomers or fibrils induced robust IL-1ß production in the presence of lipopolysaccharide. Moreover, Aß oligomers induced endo/phagolysosome rupture, which released cathepsin B into the cytoplasm. Aß oligomer-induced IL-1ß production was inhibited not only by the cathepsin B inhibitor CA-074-Me but also by the reactive oxygen species (ROS) inhibitor N-acetylcysteine. Random chemical crosslinking abolished the ability of the oligomers to induce IL-1ß. Thus, multimerization and fibrillization causes Aß oligomers to lose the ability to induce IL-1ß. These results indicate that Aß oligomers, but not fibrils, induce IL-1ß production in primary microglia in a cathepsin B- and ROS-dependent manner.

Particle size of latex beads dictates IL-1ß production mechanism.

Macrophages (Mϕ) are well documented to produce IL-1ß through various signaling pathways in response to small particles such as silica, asbestos and urea crystals, in the presence of lipopolysaccharide (LPS). However, it has not been clear to what extent particle size affects the response. To investigate this point, we stimulated bone marrow-derived macrophages (BMDM) with size-defined latex beads (LxB). Although both nano-sized (20 nm) and micro-sized (1,000 nm) LxB induced IL-1ß production, only the nano-sized particles formed large intracellular vacuoles. In contrast, 100 nm LxB did not induce either of the responses. The same cellular responses were also observed in primary microglia cells. Although K(+) efflux and NLRP3 activation in BMDM were crucial in response to both 20 and 1,000 nm LxB, only IL-1ß production by 20 nm LxB was sensitive to cathepsin B and P2X7, a receptor for ATP. The response by 1,000 nm LxB relied on a robust production of reactive oxygen species (ROS), since IL-1ß production was remarkably reduced by ROS inhibitors such as diphenylene iodonium (DPI) and N-acetylcysteine (NAC). In contrast, IL-1ß production by 20 nm LxB was augmented by NAC and in BMDM deficient in thioredoxin-binding protein-2 (TBP-2), a negative regulator of the ROS scavenger thioredoxin. These results suggest that the cells responded differently in their secretion of IL-1ß depending on particle size, and that there is a range within which neither pathway works.