ApoA-I Inhitits LPS-induced Inflammatory Cytokines Expression In Macrophage-derived Foam Cells Via Regulating Tristetraprolin Dephosphorylation

Objective: To observe the effect of apolipoprotein A1(apoA-I) on the expression ofinflammatory cytokines and explore the role of TTP-translational modification in theanti-inflammatory effect of apoA-I in macrophage-derived foam cells.Methods: Human THP-1monocytes were treated in vitro with phorbol12-myristate13-acetate (PMA)(100μmol/L) for24h, and then the medium was replaced byserum-free medium containing oxLDL (50μg/ml) to become fully differentiatedmacrophage foam cells before their use in experiments. Cells were cultured andtreated with apoA-I and (or) LPS. Protein was extracted and subjected to ELISAanalysis for interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), IL-6and IL-8.Total protein extracts from cells were subjected to Western-Blot analyses fortristetraprolin (TTP), phospho-TTP, calmodulin (CaM), Calcineurin (CaN). The Act Dwas added to stop the transcription, RNA were extracted and subjected to RT-PCRanalysis for inflammatory cytokines mRNA analysis. Cells were treated with CaMantagonist W7, CaN antagonist FK506and siRNA of TTP. Protein and RNA wereextracted and subjected to ELISA or RT-PCR analysis for inflammatory cytokines.Protein was extracted and subjected to chromogenic substrate analysis for CaM andCaN activity.Results: Human THP-1macrophage-derived foam cells were pretreated by apoA-I for2h, LPS-induced up-regulation of IL-1β, TNF-α, IL-6and IL-8were significantlysuppressed relative to LPS alone group. The results of RT-PCR indicated that apoA-Ireduced the mRNA levels of IL-1β after treatment of act D. ApoA-I treatmentsignificantly decreased the levels of tristetraprolin phosphorylation, had no effect onexpression, but enhanced the activity of CaM and CaN in LPS-stimulated THP-1macrophage-derived foam cells. Treatment with siRNA for TTP significantlydown-regulated apoA-I-induced IL-1β mRNA decay in LPS-treated THP-1cells. W7,a CaM inhibitor, and FK506for CaN inhibitor significantly inhibited activity of CaMand CaN, which further abolished the inhibition effect of apoA-I on phospho-TTPexpression in LPS-treated THP-1cells as well as IL-1β mRNA decay.Conclusions: ApoA-I enhanced the interaction of CaN and TTP through a CaM/CaNsignaling pathway-dependent manner in LPS-stimulated human THP-1macrophage-derived foam cells, and apoA-I increased some inflammatory cytokinesmRNA decay via promoting the function and dephosphorylation of TTP, which canbind and target ARE-containing mRNAs for rapid degradation.