Oxidized low density lipoprotein blocks lipopolysaccharide-induced interferon beta synthesis in human macrophages by interfering with IRF3 activation.

In response to lipopolysaccharide (LPS) exposure, macrophages activate the transcription of a large number of pro-inflammatory genes by way of signaling pathways downstream of the LPS receptor, Toll-Like Receptor 4. Many of these genes are expressed sequentially in time, with early synthesis events resulting in the secretion of soluble factors that drive the transcription of genes expressed later in the activation cycle. In this study we show that human blood-derived macrophages pretreated with oxidized low density lipoprotein (OxLDL) fail to transcribe and secrete interferon beta (IFNbeta) immediately following LPS stimulation. As such, the normal downstream activation of Stat1 is blocked, and numerous IFNbeta/Stat1-activated genes, including the chemokines IP10 and ITAC, are weakly expressed or not expressed at all in these cells. Inspection of the LPS-induced activation state of several transcription factors known to play a prominent role in IFNbeta transcription reveals that, although NFkappaB, c-Jun, and ATF-2 activation appears normal, the LPS-induced activation of IFNbeta regulatory factor 3 (IRF3), as measured by DNA-binding activity and association with the coactivator CBP, is inhibited in the OxLDL pre-treated cells. These IRF3 activities have been shown to be essential for the initiation of transcription of the IFNbeta gene, and the loss of these activities presumably accounts for the lack of LPS-induced IFN beta transcription seen in the OxLDL pre-treated cells.