title: The citrus flavonoid naringenin confers protection in a murine endotoxaemia model through AMPK-ATF3-dependent negative regulation of the TLR4 signalling pathway.
abstract: Excessive activation of the TLR4 signalling pathway is critical for inflammation-associated disorders, while negative regulators play key roles in restraining TLR4 from over-activation. Naringenin is a citrus flavonoid with remarkable anti-inflammatory activity, but the mechanisms underlying its inhibition of LPS/TLR4 signalling are less clear. This study investigated the molecular targets and therapeutic effects of naringenin in vitro and in vivo. In LPS-stimulated murine macrophages, naringenin suppressed the expression of TNF-α, IL-6, TLR4, inducible NO synthase (iNOS), cyclo-oxygenase-2 (COX2) and NADPH oxidase-2 (NOX2). Naringenin also inhibited NF-κB and mitogen-activated protein kinase (MAPK) activation. However, it did not affect the IRF3 signalling pathway or interferon production, which upregulate activating transcription factor 3 (ATF3), an inducible negative regulator of TLR4 signalling. Naringenin was demonstrated to directly increase ATF3 expression. Inhibition of AMPK and its upstream calcium-dependent signalling reduced ATF3 expression and dampened the anti-inflammatory activity of naringenin. In murine endotoxaemia models, naringenin ameliorated pro-inflammatory reactions and improved survival. Furthermore, it induced AMPK activation in lung tissues, which was required for ATF3 upregulation and the enhanced anti-inflammatory activity. Overall, this study reveals a novel mechanism of naringenin through AMPK-ATF3-dependent negative regulation of the LPS/TLR4 signalling pathway, which thereby confers protection against murine endotoxaemia.
authors.affiliation: Medical Research Center, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Liu
authors.affiliation: Medical Research Center, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Wang
authors.affiliation: Medical Research Center, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, China.
authors.forename: Shijun
authors.initials: S
authors.lastname: Fan
authors.affiliation: Medical Research Center, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, China.
authors.forename: Xinchuan
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Medical Research Center, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, China.
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Medical Research Center, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, China.
authors.forename: Yuanfeng
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Medical Research Center, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, China.
authors.forename: Yongling
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Medical Research Center, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Chen
authors.affiliation: Department of Pharmacology, College of Pharmacy, the Third Military Medical University, Chongqing 400038, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Medical Research Center, Southwest Hospital, the Third Military Medical University, Chongqing, 400038, China.
authors.forename: Jiang
authors.initials: J
authors.lastname: Zheng
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000276:immunology*; D051700:Activating Transcription Factor 3 / Q000276:immunology*; D000818:Animals; D002957:Citrus / Q000737:chemistry; D004195:Disease Models, Animal; D019446:Endotoxemia / Q000139:chemically induced / Q000188:drug therapy* / Q000276:immunology; D044950:Flavanones / Q000737:chemistry / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000633:toxicity; D020935:MAP Kinase Signaling System / Q000187:drug effects* / Q000276:immunology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D051197:Toll-Like Receptor 4 / Q000276:immunology*
chemical_list: D051700:Activating Transcription Factor 3; C103002:Atf3 protein, mouse; D044950:Flavanones; D008070:Lipopolysaccharides; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D055372:AMP-Activated Protein Kinases; C005273:naringenin