MicroRNA-155 deficiency results in decreased macrophage inflammation and attenuated atherogenesis in apolipoprotein E-deficient mice

Objective-microRNA-155 (miR155) plays a critical role in immunity and macrophage inflammation. We aim to investigate the role of miR155 in atherogenesis. Approach and results-Quantitative real-time polymerase chain reaction showed that miR155 was expressed in mouse and human atherosclerotic lesions. miR155 expression in macrophages was correlated positively with proinflammatory cytokine expression. Lentivirus-mediated overexpression of miR155 in macrophages enhanced their inflammatory response to lipopolysaccharide through targeting suppressor of cytokine signaling-1 and impaired cholesterol efflux from acetylated low-density lipoprotein-loaded macrophages, whereas deficiency of miR155 blunted macrophage inflammatory responses and enhanced cholesterol efflux possibly via enhancing lipid loading-induced macrophage autophagy. We next examined the atherogenesis in apolipoprotein E-deficient (apoE^-/-) and miR155^-/-/apoE^-/- (double knockout) mice fed a Western diet. Compared with apoE^-/- mice, the double knockout mice developed less atherosclerosis lesion in aortic root, with reduced neutral lipid content and macrophages. Flow cytometric analysis showed that there were increased number of regulatory T cells and reduced numbers of Th17 cells and CD11b+/Ly6C^high cells in the spleen of double knockout mice. Peritoneal macrophages from the double knockout mice had significantly reduced proinflammatory cytokine expression and secretion both in the absence and presence of lipopolysaccharide stimulation. To determine whether miR155 in leukocytes contributes to atherosclerosis, we performed a bone marrow transplantation study. Deficiency of miR155 in bone marrow-derived cells suppressed atherogenesis in apoE^-/- mice, demonstrating that hematopoietic cell-derived miR155 plays a critical role. Conclusions-miR155 deficiency attenuates atherogenesis in apoE^-/- mice by reducing inflammatory responses of macrophages, enhancing macrophage cholesterol efflux and resulting in an antiatherogenic leukocyte profile. Targeting miR155 may be a promising strategy to halt atherogenesis.