Zhang and Reilly Inflammation and Lipid Metabolism 657 uptake and reduced efflux, total cholesterol mass, including both free and esterified cholesterol, was increased. The authors then revealed that Irf2bp2-deficient macrophages exacerbated atherosclerosis in murine models. 6 Western diet–fed Ldlr−/− recipients of Irf2bp2 KO bone marrow showed increased lesion area, M1 macrophage infiltration, and apoptosis, accompanied by increased CD68+ macrophage infiltration of the myocardium and ventricular hypertrophy, suggesting the profound inflammatory effects of Irf2bp2 deficiency in macrophages. The inflammatory phenotype of BMDM and more extensive atherosclerosis were also observed in Irf2bp2 KO in ApoE−/− background. The translational relevance was illustrated by the finding that a deletion variant that lowers IRF2BP2 expression predisposes to CHD in humans. A 9-nucleotide deletion at the 3′-UTR (untranslated region) of IRF2BP2 was associated with increased CHD risk in a recessive model in a relatively small case–control study of angiographic coronary disease.

Luciferase reporter assay indeed suggested that the deletion mutation leads to reduced luciferase translation. Importantly, carriers for homozygous deletion polymorphism showed reduced IRF2BP2 expression in peripheral blood mononuclear cells. The authors performed mRNA microarray to determine differentially expressed genes between wild-type and KO BMDM. 6 One of the top differentially expressed genes suppressed in KO BMDM is Klf2, an anti-inflammaotry transcription factor. KLF2 inhibits the transcriptional activity of both NF-κB and activator protein 1, in part by means of recruitment of transcriptional coactivator p300/CREB binding protein–associated factor. Klf2 protein levels were barely detectable in atherosclerosis lesion of Irf2bp2 KO Ldlr−/− mice. To establish the functional requirement of KLF2 in IRF2BP2-mediated effects, lentivirus-mediated Klf2 overexpression in Irf2bp2 KO BMDM attenuated inflammation and improved cholesterol handling. Critically, the authors showed that IRF2BP2 is required for myocyte enhancer factor 2–mediated KLF2 transcriptional activation, and that homozygous IRF2BP2 mutation carriers also showed lower KLF2 protein levels in peripheral blood mononuclear cells.