Myeloid Interferon Regulatory Factor 8 Deficiency Prevents The Development Of Atherosclerosis

Abstract

Background: IRF8 is a haematopoietic transcription factor crucial for the development of myeloid cells and known to mediate their inflammatory responses. Our group has previously shown IRF8 to selectively modulate the expression of macrophage genes involved in atherosclerotic plaque development. Aim: To investigate the role of myeloid-IRF8 in atherosclerosis development.

Methods: We have generated a myeloid-IRF8 deficient mouse model, using the LysM directed Cre recombinase, on the LDLR-deficient background (M-IRF8KOLdlrKO). Mice were challenged with a western diet for 12 weeks after which atherosclerotic lesions were quantified in the aortic root by H&E staining respectively. Results: Plaque coverage in the aortic roots was significantly higher in WTLdlrKO mice compared to M-IRF8KOLdlrKO (20.53 ±0.27% vs 12.83 ±0.27%, P=0.04). Interestingly, M-IRF8KOLdlrKO mice display decreased expression of pro-atherosclerotic genes Cyp27a1, Cxcl16 and iNOS in bone marrow-derived macrophages, via quantitative PCR. Among these, we demonstrated that Cyp27a1, involved in lipid metabolism, inflammation and leukocyte migration, harbours a novel IRF8 binding site by chromatin immunoprecipitation assays and is remarkably reduced in IRF8-deficient macrophages at both mRNA (70% decrease) and protein level, shown via western blots. Furthermore, recent RNA-Seq analysis on the basal bone derived macrophages have highlighted 167 differential upregulated genes and 199 differential downregulated genes. Conclusions: Overall, this suggests myeloid-IRF8 deficiency confers protection against atherosclerosis. Interestingly, myeloid-IRF8 regulates the expression of many genes including those involved in inflammation and lipid homeostasis (catabolism via Cyp27a1 and uptake via Cxcl16). These processes are critical in the development of the atherosclerotic plaque.