ABSTRACT
Inflammatory responses and cholesterol homeostasis are interconnected in atherogenesis. Interleukin (IL)-10 is an important anti-inflammatory cytokine, known to suppress atherosclerosis development. However, the specific cell types responsible for the atheroprotective effects of IL-10 remain to be defined and knowledge on the actions of IL-10 in cholesterol homeostasis is scarce. Here we investigated the functional involvement of myeloid IL-10-mediated atheroprotection. To do so, bone marrow from IL-10 receptor 1 (IL-10R1) wild-type and myeloid IL-10R1-deficient mice was transplanted to lethally irradiated female LDLR-/- mice. Hereafter, mice were given a high cholesterol diet for 10 weeks after which atherosclerosis development and cholesterol metabolism were investigated. In vitro, myeloid IL-10R1 deficiency resulted in a pro-inflammatory macrophage phenotype. However, in vivo significantly reduced lesion size and severity was observed. This phenotype was associated with lower myeloid cell accumulation and more apoptosis in the lesions. Additionally, a profound reduction in plasma and liver cholesterol was observed upon myeloid IL-10R1 deficiency, which was reflected in plaque lipid content. This decreased hypercholesterolaemia was associated with lowered very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) levels, likely as a response to decreased intestinal cholesterol absorption. In addition, IL-10R1 deficient mice demonstrated substantially higher faecal sterol loss caused by increased non-biliary cholesterol efflux. The induction of this process was linked to impaired ACAT2-mediated esterification of liver and plasma cholesterol. Overall, myeloid cells do not contribute to IL-10-mediated atheroprotection. In addition, this study demonstrates a novel connection between IL-10-mediated inflammation and cholesterol homeostasis in atherosclerosis. These findings make us reconsider IL-10 as a beneficial influence on atherosclerosis.
Subject(s)
Atherosclerosis/metabolism , Cholesterol/metabolism , Receptors, Interleukin-10/deficiency , Receptors, LDL/deficiency , Animals , Apoptosis , Atherosclerosis/etiology , Atherosclerosis/prevention & control , Biological Transport, Active , Cholesterol, Dietary/administration & dosage , Disease Models, Animal , Female , Hypercholesterolemia/prevention & control , Inflammation/etiology , Inflammation/metabolism , Inflammation/pathology , Intestinal Mucosa/metabolism , Macrophages/metabolism , Macrophages/pathology , Mice , Mice, Knockout , Myeloid Cells/metabolism , Myeloid Cells/pathology , Plaque, Atherosclerotic/etiology , Plaque, Atherosclerotic/metabolism , Plaque, Atherosclerotic/pathology , Receptors, Interleukin-10/genetics , Receptors, LDL/genetics , Signal Transduction , Sterol O-Acyltransferase/metabolism , Sterol O-Acyltransferase 2ABSTRACT
microRNA-155 (miR155) is a central regulator of immune responses that is induced by inflammatory mediators. Although miR155 is considered to be a pro-inflammatory microRNA, in vitro reports show anti-inflammatory effects in lipid-loaded cells. In this study we examined the role of miR155 in atherosclerosis in vivo using bone marrow transplantation from miR155 deficient or wildtype mice to hyperlipidemic mice. Hematopoietic deficiency of miR155 enhanced atherosclerotic plaque development and decreased plaque stability, as evidenced by increased myeloid inflammatory cell recruitment to the plaque. The increased inflammatory state was mirrored by a decrease in circulating CD4(+)CD25(+)FoxP3(+) regulatory T cells, and an increase in granulocytes (CD11b(+)Ly6G(+)) in blood of miR155(-/-) transplanted mice. Moreover, we show for the first time a crucial role of miR155 in monocyte subset differentiation, since hematopoietic deficiency of miR155 increases the 'inflammatory' monocyte subset (CD11b(+)Ly6G(-)Ly6C(hi)) and reduces 'resident' monocytes (CD11b(+)Ly6G(-)Ly6C(low)) in the circulation. Furthermore, cytokine production by resident peritoneal macrophages of miR155(-/-) transplanted hyperlipidemic mice was skewed towards a more pro-inflammatory state since anti-inflammatory IL-10 production was reduced. In conclusion, in this hyperlipidemic mouse model miR155 acts as an anti-inflammatory, atheroprotective microRNA. Additionally, besides a known role in lymphoid cell development, we show a crucial role of miR155 in myeloid lineage differentiation.
