Apolipoprotein A-I inhibits CD40 proinflammatory signaling via ATP-binding cassette transporter A1-mediated modulation of lipid raft in macrophages.
OBJECTIVE
Apolipoprotein A-I (apoA-I), the major component of high-density lipoprotein (HDL), has been recently found to suppress inflammation. This study was to investigate the effects and potential mechanisms of apoA-I on the CD40/CD40 ligand (CD40L) proinflammatory signaling pathway.


METHODS
Human THP-1 macrophage-derived foam cells were treated with sCD40L alone or in the presence of apoA-I. Secretion of proinflammatory cytokines was performed by enzyme-linked immunosorbent assay(ELISA). The proteins and mRNA expression were examined by western-blot and real-time PCR analysis, respectly. Cholesterol efflux was assessed by liquid scintillation counting. Cholesterol depletion of macrophages was performed with methylated β-cyclodextrin.


RESULTS
ApoA-I inhibits the inflammatory response stimulated by soluble CD40L (sCD40L) in macrophages. In addition, apoA-I inhibited the sCD40L-stimulated activation of nuclear factor-kB (NF-kB). The apoA-I-induced NF-kB deactivation was related to the decreased recruitment of tumor necrosis factor receptor-associated factor 6 (TRAF-6), a crucial adapter protein for CD40 in macrophages, to lipid rafts after being treated by sCD40L. When interfering the expression of ATP-binding cassette transporter A1 (ABCA1), a major cholesterol transporter for apoA-I in macrophages, it could significantly diminish the effect of apoA-I on the sCD40L-stimulated inflammatory response.


CONCLUSIONS
ApoA-I suppresses CD40 proinflammatory signaling in macrophages by preventing TRAF-6 translocation to lipid rafts through ABCA1-dependent regulation of free cholesterol (FC) efflux, which may present a novel mechanism of apoA-I-mediated inflammation inhibition in macrophages.
Institute of Cardiovascular Research, Key Laboratory for Atherosclerology of Hunan Province, Life Science Research Center, University of South China, Hengyang, China.
Kai
K
Yin
Wu-Jun
WJ
Chen
Zhi-Gang
ZG
Zhou
Guo-Jun
GJ
Zhao
Yun-Chen
YC
Lv
Xin-Pin
XP
Ouyang
Xiao-Hua
XH
Yu
Yuchang
Y
Fu
Zhi-Sheng
ZS
Jiang
Chao-Ke
CK
Tang
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D016632:Apolipoprotein A-I / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D019013:CD40 Antigens / Q000235:genetics / Q000378:metabolism*; D023201:CD40 Ligand / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D005487:Foam Cells / Q000378:metabolism*; D006801:Humans; D007124:Immunoenzyme Techniques; D047468:Immunoprecipitation; D018836:Inflammation Mediators / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D021962:Membrane Microdomains / Q000378:metabolism*; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins / Q000235:genetics / Q000378:metabolism
C577836:ABCA1 protein, human; D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D019013:CD40 Antigens; D018836:Inflammation Mediators; D016328:NF-kappa B; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C486460:TRAF7 protein, human; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins; D023201:CD40 Ligand