Soluble Aβ_1-42 suppresses TNF-α and activates NLRP3 inflammasome in THP-1 macrophages

Deposition of amyloid-β in Alzheimer's disease is accompanied by chronic inflammation, which involves raised levels of pro-inflammatory cytokines TNF-α, IL-6 and IL-1β. However, the role of Aβ₁-₄₂ in the inflammatory process, before it gets deposited into aggregates has not been investigated thoroughly. Through this study, we are illustrating the dual role of soluble Aβ₁-₄₂ (sAβ_1-42) in activating the NLRP3 inflammasome and simultaneously inhibiting TNF-α secretion. Our data suggested that the treatment of chronically induced THP-1 macrophages and N9 microglial cells with sAβ₁-₄₂ can suppress the major inflammatory cytokine TNF-α without affecting the level of IL-6. However, the activation of NLRP3 inflammasome was well evidenced by secretion of IL-1β, increased expression of NLRP3 and caspase-1, implicating sAβ₁-₄₂ in enhancing and suppressing one or other type of inflammation. Further investigation revealed that sAβ₁-₄₂ was able to severely abrogate the expression of NF-κB, p50 and restricting the translocation of NF-κB, p65 to nucleus by inhibiting phosphorylation of IκB-α in THP-1 macrophages. These data indicate that the sAβ₁-₄₂ may play a dual role during inflammatory process, wherein, it may be involved in protecting the cells from inflammatory damage due to TNF-α. This ability of sAβ₁-₄₂ might be playing some role in protecting the brain cells during the process of aging and Alzheimer's disease, where, chronic inflammatory environment plays a vital role.