Gx-50 reduces β-amyloid-induced TNF-α, IL-1β, NO, and PGE2 expression and inhibits NF-κB signaling in a mouse model of Alzheimer's disease

Chronic inflammation, which is regulated by overactivated microglia in the brain, accelerates the occurrence and development of Alzheimer's disease (AD). Gx-50 has been investigated as a novel drug for the treatment of AD in our previous studies. Here, we investigated whether gx-50 possesses anti-inflammatory effects in primary rat microglia and a mouse model of AD, amyloid precursor protein (APP) Tg mice. The expression of TNF-alpha, IL-1 beta, NO, prostaglandin E2, and the expression of iNOS and COX2 were inhibited by gx-50 in amyloid beta (A beta) treated rat microglia; additionally, microglial activation and the expression of IL-1 beta, iNOS, and COX2 were also significantly suppressed by gx-50 in APP(+) transgenic mice. Furthermore, gx-50 inhibited the activation of NF-kappa B and MAPK cascades in vitro and in vivo in APP-Tg mice. Moreover, the expression of TLR4 and its downstream signaling proteins MyD88 and tumor necrosis factor receptor associated factor 6 (TRAF6) was reduced by gx-50 in vitro and in vivo. Interestingly, silencing of TLR4 reduced A beta-induced upregulation of IL-1 beta and TRAF6 to levels similar to gx-50 inhibition; moreover, overexpression of TLR4 increased the expression of MyD88 and TRAF6, which was significantly reduced by gx-50. These findings provide strong evidence that gx-50 has anti-inflammatory effects against A beta-triggered microglial overactivation via a mechanism that involves the TLR4-mediated NF-kappa BB/MAPK signaling cascade.