IFN-γ Down-regulates ABCA1 Expression And Cholesterol Efflux In A JAK-STAT1 Signaling Pathway-Dependent Manner

OBJECTIVE: Interferon gamma (IFN-γ) is an immunomodulatory and anti-microbial cytokine, and has a variety of proatherogenic effects. It has been reported that IFN-γdown-regulated ATP-binding cassette transporter A1 (ABCA1) expression. However, its mechanism is elusive. With an attempt to demonstrate the possible mechanism, we conducted our experiments using THP-1 macrophage-derived foam cells with a series of methods.MEHTODS: In the present study, Real-time quantitative PCR (RT-PCR) and western blot were conducted to determine the effects of IFN-γon the expression of ABCA1 and Liver X receptorα(LXRα). Liquid scintillation counting and high performance liquid chromatography assays were used to test cellular cholesterol efflux and cholesterol content. And western blot was conducted to investigate the phosphorylation of STAT1 and the level of STAT1 in nucleus.RESULTS: It turned out that the expression of ABCA1 and LXRαwere both down-regulated by IFN-γat both transcriptional and translational levels in a dose-dependent manner. Cellular cholesterol content was increased while cholesterol efflux was decreased by IFN-γtreatment. Specific agonist and inhibitor for LXRαnamed 22(R)-Hch and DIDS were then used to treat cells and RT-PCR was conducted to test the expression of ABCA1. Results showed that 22(R)-Hch almost compensated the down-regulation of ABCA1 expression by IFN-γ, while DIDS made the down-regulation of ABCA1 expression more significantly than IFN-γ. Then we tested the effects of IFN-γon the phosphorylation of STAT1 and expression of STAT1αin the nucleus. It turned out that IFN-γinduced phosphorylation of STAT1 and expression of STAT1αin the nucleus, which was inhibited by a Janus kinase (JAK) inhibitor AG-490. And then we investigated the effect of IFN-γon LXRαmRNA expression in THP-1 macrophage-derived foam cells. We found that IFN-γdecreased LXRαexpression in a concentrate-dependent manner. We further demonstrated that AG-490 could compensate the effects of IFN-γon the expression of ABCA1 and cellular efflux.CONCLUSION: IFN-γmay first down-regulate expression of LXRαthrough the JAK/STAT1 signaling pathway and then decrease the expression of ABCA1 and cholesterol efflux in THP-1 macrophage-derived foam cells. Therefore, our study may be useful in understanding the critical effect of IFN-γin pathogenesis of atherosclerosis.