ABSTRACT
Obesity is associated with infiltration of macrophages into adipose tissue (AT), contributing to insulin resistance and diabetes. However, relatively little is known regarding the origin of AT macrophages (ATMs). We discovered that murine models of obesity have prominent monocytosis and neutrophilia, associated with proliferation and expansion of bone marrow (BM) myeloid progenitors. AT transplantation conferred myeloid progenitor proliferation in lean recipients, while weight loss in both mice and humans (via gastric bypass) was associated with a reversal of monocytosis and neutrophilia. Adipose S100A8/A9 induced ATM TLR4/MyD88 and NLRP3 inflammasome-dependent IL-1ß production. IL-1ß interacted with the IL-1 receptor on BM myeloid progenitors to stimulate the production of monocytes and neutrophils. These studies uncover a positive feedback loop between ATMs and BM myeloid progenitors and suggest that inhibition of TLR4 ligands or the NLRP3-IL-1ß signaling axis could reduce AT inflammation and insulin resistance in obesity.
Subject(s)
Adipose Tissue/metabolism , Macrophages/metabolism , Monocytes/metabolism , Myelopoiesis/physiology , Obesity/metabolism , Animals , Bone Marrow/metabolism , Carrier Proteins/metabolism , Cell Proliferation/physiology , Humans , Inflammasomes/metabolism , Interleukin-1beta/metabolism , Male , Mice , Mice, Inbred C57BL , Myeloid Differentiation Factor 88/metabolism , NLR Family, Pyrin Domain-Containing 3 Protein , Neutrophils/metabolism , Receptors, Interleukin-1/metabolism , Toll-Like Receptor 4/metabolismABSTRACT
RATIONALE: Plasma high-density lipoprotein levels are inversely correlated with atherosclerosis. Although it is widely assumed that this is attributable to the ability of high-density lipoprotein to promote cholesterol efflux from macrophage foam cells, direct experimental support for this hypothesis is lacking. OBJECTIVE: To assess the role of macrophage cholesterol efflux pathways in atherogenesis. METHODS AND RESULTS: We developed mice with efficient deletion of the ATP-binding cassette transporters A1 and G1 (ABCA1 and ABCG1) in macrophages (MAC-ABC(DKO) mice) but not in hematopoietic stem or progenitor populations. MAC-ABC(DKO) bone marrow (BM) was transplanted into Ldlr(-/-) recipients. On the chow diet, these mice had similar plasma cholesterol and blood monocyte levels but increased atherosclerosis compared with controls. On the Western-type diet, MAC-ABC(DKO) BM-transplanted Ldlr(-/-) mice had disproportionate atherosclerosis, considering they also had lower very low-density lipoprotein/low-density lipoprotein cholesterol levels than controls. ABCA1/G1-deficient macrophages in lesions showed increased inflammatory gene expression. Unexpectedly, Western-type diet-fed MAC-ABC(DKO) BM-transplanted Ldlr(-/-) mice displayed monocytosis and neutrophilia in the absence of hematopoietic stem and multipotential progenitor cells proliferation. Mechanistic studies revealed increased expressions of machrophage colony stimulating factor and granulocyte colony stimulating factor in splenic macrophage foam cells, driving BM monocyte and neutrophil production. CONCLUSIONS: These studies show that macrophage deficiency of ABCA1/G1 is proatherogenic likely by promoting plaque inflammation and uncover a novel positive feedback loop in which cholesterol-laden splenic macrophages signal BM progenitors to produce monocytes, with suppression by macrophage cholesterol efflux pathways.
