Gamma Tocotrienol Suppresses NLRP3 Inflammasome by Dual Mechanism of A20‐ mediated Priming Inhibition and AMPK/autophagy Axis Activation

Abstract

Nod‐like receptor 3 (NLRP3) inflammasome is the intracellular innate immunity sensor that processes and releases IL‐1β in response to microbial invasion or metabolic danger signals such as saturated fatty acids and free cholesterol. Aberrant activation of NLRP3 is intimately associated with numerous chronic inflammatory diseases. However, little information is available as to whether NLRP3 inflammasome is regulated by dietary factors. The aim of this study is to investigate whether gamma‐tocotrienol (γT3), an unsaturated form of vitamin E, downregulates NLRP3 inflammasome activation, and to determine the molecular mechanisms. Pretreatment of γT3 (0.5–10 mM) significantly suppressed activation of NLRP3 inflammasome reporter, caspase‐1 cleavage, and IL‐1β and IL‐18 secretion in J774 macrophages as well as bone marrow‐derived murine macrophages (BMDM). To further determine the mechanisms, we investigate the role of γT3 on NFκB activation and AMPK/autophagy axis activation. γT3 significantly attenuated proinflammatory gene expressions of IL‐1β, IL‐18 and NLRP3, and induced A20 expression, an ubiquitin‐editing enzyme to interrupt NFκB signaling. Induction of A20 concurred with 1) the decrease of p‐IKKα/β, p‐ERK, and p‐IκBα; 2) the reappearance of IκBα, and 3) the disappearance of TRAF6, suggesting a negative feedback of A20 on TRAF6/IKK/NF‐κB signaling. Moreover, silencing of A20 markedly dampened the inflammasome inhibitory effects of γT3. Intriguingly, γT3 treatment was also associated with AMPK/autophagy axis activation shown through LC3II accumulation and increased levels of AMPK phosphorylation. The inhibition of AMPK with Compound C completely reversed γT3's inhibitory role on NLRP3 inflammasome and caspase‐1 cleavage. Taken together, we demonstrated that γT3 suppresses NLRP3 inflammasome by two mechanisms, 1) inhibition of TRAF6/NFκB axis activation through induction of A20, and 2) activation of AMP kinase/autophagy thereby inhibiting inflammasome assembly.Support or Funding InformationAmerican Heart Association