TNFα- and NF-κB-dependent induction of the chemokine CCL1 in human macrophages exposed to the atherogenic lipoprotein(a)

Abstract

Aims CCL1 is a chemokine thought to contribute to cardiovascular diseases and recently reported to be regulated by the pro-atherogenic lipoprotein(a) (Lp(a)) and the ligand-activated aryl hydrocarbon receptor (AhR). The present study was designed to investigate molecular regulatory pathways involved in Lp(a)-mediated induction of CCL1. Main methods CCL1 regulation was studied in Lp(a)-exposed human primary macrophages using mainly quantitative reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay and electrophoretic mobility shift assay (EMSA). Key findings Using the AhR antagonist α-napthtoflavone, the translational inhibitor cycloheximide and anti-tumor necrosis factor α (TNFα) neutralizing antibodies, we demonstrated that Lp(a)-mediated mRNA induction of CCL1 occurs in an AhR-independent manner and requires de novo protein synthesis of TNFα. Involvement of this cytokine was further underlined by the fact that it increased expression and secretion of CCL1 by itself in macrophages. DNA binding activity of NF-κB, a well-known molecular effector of TNFα, was moreover activated by Lp(a) in a TNFα-dependent manner and the use of the NF-κB inhibitor Bay 11-7082 blocked Lp(a)-triggered CCL1 induction. In addition, Lp(a) induced binding of NF-κB to a NF-κB consensus element on CCL1 promoter as assessed by EMSA. Co-exposure to Lp(a) and the AhR ligand benzo(a)pyrene was finally shown to superinduce CCL1 expression in human macrophages, supporting the conclusion that Lp(a) and AhR ligands act on CCL1 through independent ways. Significance These data suggest that Lp(a)-triggered induction of CCL1 expression is mediated by TNFα and subsequent activation of NF-κB, without AhR involvement.