Activation of microglia, the resident macrophages of the brain, around the amyloid plaques is a key hallmark of Alzheimer’s disease (AD). Recent evidence in mouse models indicates that microglia are required for the neurodegenerative process of AD. Amyloid-β (Aβ) peptides, the core components of the amyloid plaques, can trigger microglial activation by interacting with several Toll-like receptors (TLRs), including TLR4. Here, we show that resveratrol, a natural polyphenol associated with anti-inflammatory effects and currently in clinical trials for AD, prevented the activation of murine RAW 264.7 macrophages and microglial BV-2 cells treated with the TLR4 ligand, lipopolysaccharide (LPS). Resveratrol preferentially inhibited NF-κB activation upon LPS stimulation by interfering with IKK and IκB phosphorylation, an effect that potently reduced the transcriptional stimulation of several NF-κB target genes, including TNF-α and IL-6. Consequently, downstream phosphorylation of STAT1 and STAT3 upon LPS stimulation was also inhibited by resveratrol. We found that resveratrol acted upstream in the activation cascade by interfering with TLR4 oligomerization upon receptor stimulation. Resveratrol treatment also prevented the pro-inflammatory effect of fibrillar Aβ on macrophages by potently inhibiting the effect of Aβ on IκB phosphorylation, activation of STAT1 and STAT3, and on TNF-α and IL-6 secretion. Importantly, orally administered resveratrol in a mouse model of cerebral amyloid deposition lowered microglial activation associated with cortical amyloid plaque formation. Together this work provides strong evidence that resveratrol has in vitro and in vivo anti-inflammatory effects against Aβ-triggered microglial activation. Further studies in cell culture systems showed that resveratrol acted via a mechanism involving the TLR4/NF-κB/STAT signaling cascade.
Signal transducer and activator of transcription 3 (STAT3) is a key mediator of the inflammatory response by macrophages and other immune cell types. The naturally occurring polyphenol resveratrol is associated with anti-proliferative and anti-inflammatory properties via mechanisms implicating inhibition of STAT3 signaling. Here, we report that the small-molecule analogs of resveratrol, RSVA314 and RSVA405, are potent inhibitors of STAT3. RSVA314 and RSVA405 inhibited both constitutive and stimulated STAT3 in HEK293 cells and lipopolysaccharide (LPS)-activated RAW 264.7 macrophages, respectively. The small-molecule analogs inhibited STAT3 nearly 50 times more potently than did resveratrol (apparent IC50 ~ 0.5 μM). We further show that RSVA405 interfered with the inflammatory response by RAW 264.7 cells upon LPS stimulation by inhibiting IKK and IκBα phosphorylation and by decreasing the expression of several cytokines, including the NF-κB target genes, tumor necrosis factor-α and interleukin-6. Downstream activation of STAT1 upon LPS stimulation was also inhibited by RSVA405. Consequently, RSVA405 significantly interfered with the phagocytotic activity and proliferation of LPS-activated RAW 264.7 macrophages. Finally, we found that the effect of the two small-molecule analogs on STAT3 phosphorylation could be prevented by inhibitors of protein tyrosine phosphatases (PTPs), indicating that the small-molecules acted by promoting the dephosphorylation of STAT3 by PTPs.
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