title: IRAK1 mediates TLR4-induced ABCA1 downregulation and lipid accumulation in VSMCs.
abstract: The activation of Toll-like receptor 4 (TLR4) signaling has an important role in promoting lipid accumulation and pro-inflammatory effects in vascular smooth muscle cells (VSMCs), which facilitate atherosclerosis development and progression. Previous studies have demonstrated that excess lipid accumulation in VSMCs is due to an inhibition of the expression of ATP-binding cassette transporter A1 (ABCA1), an important molecular mediator of lipid efflux from VSMCs. However, the underlying molecular mechanisms of this process are unclear. The purpose of this study was to disclose the underlying molecular mechanisms of TLR4 signaling in regulating ABCA1 expression. Primary cultured VSMCs were stimulated with 50 μg/ml oxidized low-density lipoprotein (oxLDL). We determined that enhancing TLR4 signaling using oxLDL significantly downregulated ABCA1 expression and induced lipid accumulation in VSMCs. However, TLR4 knockout significantly rescued oxLDL-induced ABCA1 downregulation and lipid accumulation. In addition, IL-1R-associated kinase 1 (IRAK1) was involved in the effects of TLR4 signaling on ABCA1 expression and lipid accumulation. Silencing IRAK1 expression using a specific siRNA reversed TLR4-induced ABCA1 downregulation and lipid accumulation in vitro. These results were further confirmed by our in vivo experiments. We determined that enhancing TLR4 signaling by administering a 12-week-long high-fat diet (HFD) to mice significantly increased IRAK1 expression, which downregulated ABCA1 expression and induced lipid accumulation. In addition, TLR4 knockout in vivo reversed the effects of the HFD on IRAK1 and ABCA1 expression, as well as on lipid accumulation. In conclusion, IRAK1 is involved in TLR4-mediated downregulation of ABCA1 expression and lipid accumulation in VSMCs.
authors.affiliation: Department of Neurology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: L
authors.initials: L
authors.lastname: Guo
authors.affiliation: Department of Occupational Health, Faculty of Preventive Medicine, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: C-H
authors.initials: CH
authors.lastname: Chen
authors.affiliation: Department of Neurology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: L-L
authors.initials: LL
authors.lastname: Zhang
authors.affiliation: Department of Neurology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: X-J
authors.initials: XJ
authors.lastname: Cao
authors.affiliation: Department of Occupational Health, Faculty of Preventive Medicine, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: Q-L
authors.initials: QL
authors.lastname: Ma
authors.affiliation: Department of Occupational Health, Faculty of Preventive Medicine, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: P
authors.initials: P
authors.lastname: Deng
authors.affiliation: Department of Occupational Health, Faculty of Preventive Medicine, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: G
authors.initials: G
authors.lastname: Zhu
authors.affiliation: Department of Neurology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: C-Y
authors.initials: CY
authors.lastname: Gao
authors.affiliation: Department of Neurology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: B-H
authors.initials: BH
authors.lastname: Li
authors.affiliation: Department of Neurology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: Y
authors.initials: Y
authors.lastname: Pi
authors.affiliation: Department of Neurology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Neurology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: Z-C
authors.initials: ZC
authors.lastname: Hu
authors.affiliation: Department of Occupational Health, Faculty of Preventive Medicine, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: L
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Department of Occupational Health, Faculty of Preventive Medicine, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: Z-P
authors.initials: ZP
authors.lastname: Yu
authors.affiliation: Department of Occupational Health, Faculty of Preventive Medicine, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: Z
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: Department of Neurology, Institute of Surgery Research, Daping Hospital, Third Military Medical University, Chongqing, People's Republic of China.
authors.forename: J-C
authors.initials: JC
authors.lastname: Li
mesh_terms: D064286:ATP Binding Cassette Transporter 1 / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D015536:Down-Regulation; D017353:Gene Deletion; D053592:Interleukin-1 Receptor-Associated Kinases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D050356:Lipid Metabolism; D051379:Mice; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D064286:ATP Binding Cassette Transporter 1; D053592:Interleukin-1 Receptor-Associated Kinases; D051197:Toll-Like Receptor 4; C577833:Abca1 protein, mouse; C493487:Tlr4 protein, mouse; C507769:Irak1 protein, mouse