Apolipoprotein CI enhances the biological response to LPS via the CD14/TLR4 pathway by LPS-binding elements in both its N- and C-terminal helix

• Published in: Journal of lipid research 2010-07, Vol.51 (7), p.1943-1952
• Main Authors: Berbée, Jimmy F.P., Coomans, Claudia P., Westerterp, Marit, Romijn, Johannes A., Havekes, Louis M., Rensen, Patrick C.N.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Apolipoprotein C-I - chemistry; Apolipoprotein C-I - genetics; Apolipoprotein C-I - immunology; Cell Line; endotoxins; inflammation; Lipopolysaccharide Receptors - immunology; Lipopolysaccharides - immunology; Lipopolysaccharides - pharmacology; Macrophages - cytology; Macrophages - drug effects; Macrophages - immunology; Mice; Mice, Inbred C57BL; Models, Molecular; Molecular Sequence Data; peptide; Peptides - chemistry; Peptides - genetics; Peptides - immunology; Protein Binding; Protein Structure, Secondary; Sequence Alignment; Signal Transduction - immunology; TNFα; Toll-Like Receptor 4 - immunology; Tumor Necrosis Factor-alpha - immunology
• ISSN: 0022-2275; 1539-7262
• DOI: 10.1194/jlr.M006809

Timely sensing of lipopolysaccharide (LPS) is critical for the host to fight invading Gram-negative bacteria. We recently showed that apolipoprotein CI (apoCI) (apoCI1–57) avidly binds to LPS, involving an LPS-binding motif (apoCI48–54), and thereby enhances the LPS-induced inflammatory response. Our current aim was to further elucidate the structure and function relationship of apoCI with respect to its LPS-modulating characteristics and to unravel the mechanism by which apoCI enhances the biological activity of LPS. We designed and generated N- and C-terminal apoCI-derived peptides containing varying numbers of alternating cationic/hydrophobic motifs. ApoCI1–38, apoCI1–30, and apoCI35–57 were able to bind LPS, whereas apoCI1–23 and apoCI46–57 did not bind LPS. In line with their LPS-binding characteristics, apoCI1–38, apoCI1–30, and apoCI35–57 prolonged the serum residence of 125I-LPS by reducing its association with the liver. Accordingly, both apoCI1–30 and apoCI35–57 enhanced the LPS-induced TNFα response in vitro (RAW 264.7 macrophages) and in vivo (C57Bl/6 mice). Additional in vitro studies showed that the stimulating effect of apoCI on the LPS response resembles that of LPS-binding protein (LBP) and depends on CD14/ Toll-like receptor 4 signaling. We conclude that apoCI contains structural elements in both its N-terminal and C-terminal helix to bind LPS and to enhance the proinflammatory response toward LPS via a mechanism similar to LBP.