Lipid loading in macrophages is regulated by Nur77 nuclear import and its DNA binding activity

AIM:To investigate the role of Nur77 and its transcriptional function in lipid loading in macrophages. METHODS: We established four stable RAW264.7 strains expressing GFP, GFP-Nur77, GFP-Nur77/ΔDBD and GFP-Nur77/ΔTAD, respectively, by transfecting with corresponding plasmids. After 24 h stimulation by ox-LDL, intracellular lipid loading of each strain was observed by Oil red O dye. The intracellular cholesterol level was measured by liquid chromatographic-mass spectrometry (LC-MS). Transcriptional changes of CD36 and ABCA1 were monitored by real-time quantitative-PCR, and the expressions of these two proteins were assayed by flow cytometry and Western blot, respectively. RESULTS: Compared with GFP RAW264.7 cells, the high expression of Nur77 lowered the intracellular lipid loading in macrophages induced by ox-LDL, and downregulated CD36 and upregulated ABCA1 mRNA transcription and protein expression. However, the intracellular lipid loading in GFP-Nur77/ΔDBD and GFP-Nur77/ΔTAD RAW264.7 cells increased significantly with the increasing of CD36 mRNA and protein and the decreasing of ABCA1 mRNA and protein. CONCLUSION: Orphan nuclear receptor Nur77 reduces intracellular lipid loading in macrophages through decreasing cholesterol influx and increasing cholesterol efflux. The anti-atherosclerotic effect of Nur77 may be associated with its nuclear import and its DNA binding activity.