Mannose Receptor-positive Macrophages Research Articles

Pro-inflammatory Aorta-Associated Macrophages Are Involved in Embryonic Development of Hematopoietic Stem Cells

SummaryHematopoietic stem cells (HSCs) are generated from specialized endothelial cells of the embryonic aorta. Inflammatory factors are implicated in regulating mouse HSC development, but which cells in the aorta-gonad-mesonephros (AGM) microenvironment produce these factors is unknown. In the adult, macrophages play both pro- and anti-inflammatory roles. We sought to examine whether macrophages or other hematopoietic cells found in the embryo prior to HSC generation were involved in the AGM HSC-generative microenvironment. CyTOF analysis of CD45+ AGM cells revealed predominance of two hematopoietic cell types, mannose-receptor positive macrophages and mannose-receptor negative myeloid cells. We show here that macrophage appearance in the AGM was dependent on the chemokine receptor Cx3cr1. These macrophages expressed a pro-inflammatory signature, localized to the aorta, and dynamically interacted with nascent and emerging intra-aortic hematopoietic cells (IAHCs). Importantly, upon macrophage depletion, no adult-repopulating HSCs were detected, thus implicating a role for pro-inflammatory AGM-associated macrophages in regulating the development of HSCs.

Abstract 17789: Comprehensive Optical Imaging of Macrophages Associated With Intraplaque Hemorrhage Using the Integrated Dual Modal OCT-NIRF Structural-Molecular Imaging

Introduction: Intraplaque hemorrhages (IPHs) are associated with rupture-prone plaques. Within IPHs, macrophages differentiate into a specific phenotype characterized by the expression of mannose receptors. The purpose of this study was to investigate the feasibility of intravascular optical coherence tomography (OCT)-near infrared fluorescence (NIRF) structural-molecular imaging combined with a NIRF probe targeting mannose receptors to estimate IPHs in vivo. Methods and Results: IPH was induced by injecting centrifuged autologous erythrocytes through a micro-infusion catheter into rabbit aortic plaques. Normal chow diet was continued for an additional 6 weeks for macrophage differentiation. 48 hours after intravenous injection of our newly synthesized NIRF labeled nanoprobe (ex/em 750/773 nm) targeting macrophage mannose receptors at a dose of 10 mg/kg, OCT-NIRF imaging demonstrated highly enhanced NIRF signals in IPH lesions characterized by black-dotted neovessels surrounded with heterogenous OCT signals (asterisk), suggesting the association of mannose receptor positive macrophages with intraplaque hemorrhagic transformation (Figure). FM and histologic findings from the corresponding sister sections corroborated the in vivo imagings, which demonstrated the co-localization of NIRF signals with macrophage mannose receptors and hemorrhagic compositions. Conclusions: OCT-NIRF imaging with a NIRF probe targeting mannose receptors could provide a promising novel strategy to estimate IPH-associated macrophages and detect high-risk plaques.

Netrin-1-treated macrophages protect the kidney against ischemia-reperfusion injury and suppress inflammation by inducing M2 polarization

Improper macrophage activation is pathogenically linked to various metabolic, inflammatory, and immune disorders. Therefore, regulatory proteins controlling macrophage activation have emerged as important new therapeutic targets. We recently demonstrated that netrin-1 regulates inflammation and infiltration of monocytes and ameliorates ischemia-reperfusion-induced kidney injury. However, it was not known whether netrin-1 regulates the phenotype of macrophages and the signaling mechanism through which it might do this. In this study, we report novel mechanisms underlying netrin-1's effects on macrophages using in vivo and in vitro studies. Overexpression of netrin-1 in spleen and kidney of transgenic mice increased expression of arginase-1, IL-4, and IL-13 and decreased expression of COX-2, indicating a phenotypic switch in macrophage polarization toward an M2-like phenotype. Moreover, flow cytometry analysis showed a significant increase in mannose receptor-positive macrophages in spleen compared with wild type. In vitro, netrin-1 induced the expression of M2 marker expression in bone marrow-derived macrophages, peritoneal macrophages, and RAW264.7 cells, and suppressed IFNγ-induced M1 polarization and production of inflammatory mediators. Adoptive transfer of netrin-1-treated macrophages suppressed inflammation and kidney injury against ischemia-reperfusion. Netrin-1 activated PPAR pathways and inhibition of PPAR activation abolished netrin-1-induced M2 polarization and suppression of cytokine production. Consistent with in vitro studies, administration of PPAR antagonist to mice abolished the netrin-1 protective effects against ischemia-reperfusion injury of the kidney. These findings illustrate that netrin-1 regulates macrophage polarization through PPAR pathways and confers anti-inflammatory actions in inflammed kidney tissue.

Hemoglobin Directs Macrophage Differentiation and Prevents Foam Cell Formation in Human Atherosclerotic Plaques

The purpose of this study was to examine selective macrophage differentiation occurring in areas of intraplaque hemorrhage in human atherosclerosis. Macrophage subsets are recognized in atherosclerosis, but the stimulus for and importance of differentiation programs remain unknown. We used freshly isolated human monocytes, a rabbit model, and human atherosclerotic plaques to analyze macrophage differentiation in response to hemorrhage. Macrophages characterized by high expression of both mannose and CD163 receptors preferentially exist in atherosclerotic lesions at sites of intraplaque hemorrhage. These hemoglobin (Hb)-stimulated macrophages, M(Hb), are devoid of neutral lipids typical of foam cells. In vivo modeling of hemorrhage in the rabbit model demonstrated that sponges exposed to red cells showed an increase in mannose receptor-positive macrophages only when these cells contained Hb. Cultured human monocytes exposed to Hb:haptoglobin complexes, but not interleukin-4, expressed the M(Hb) phenotype and were characterized by their resistance to cholesterol loading and up-regulation of ATP-binding cassette (ABC) transporters. M(Hb) demonstrated increased ferroportin expression, reduced intracellular iron, and reactive oxygen species (ROS). Degradation of ferroportin using hepcidin increased ROS and inhibited ABCA1 expression and cholesterol efflux to apolipoprotein A-I, suggesting reduced ROS triggers these effects. Knockdown of liver X receptor alpha (LXRα) inhibited ABC transporter expression in M(Hb) and macrophages differentiated in the antioxidant superoxide dismutase. Last, LXRα luciferase reporter activity was increased in M(Hb) and significantly reduced by overnight treatment with hepcidin. Collectively, these data suggest that reduced ROS triggers LXRα activation and macrophage reverse cholesterol transport. Hb is a stimulus for macrophage differentiation in human atherosclerotic plaques. A decrease in macrophage intracellular iron plays an important role in this nonfoam cell phenotype by reducing ROS, which drives transcription of ABC transporters through activation of LXRα. Reduction of macrophage intracellular iron may be a promising avenue to increase macrophage reverse cholesterol transport.

Altered purinergic signaling in CD73‐deficient mice inhibits tumor progression

CD73/ecto-5'-nucleotidase dephosphorylates extracellular AMP into adenosine, and it is a key enzyme in the regulation of adenosinergic signaling. The contribution of host CD73 to tumor growth and anti-tumor immunity has not been studied. Here, we show that under physiological conditions CD73-deficient mice had significantly elevated ATPase and ADPase activities in LN T cells. In a melanoma model, the growth of primary tumors and formation of metastasis were significantly attenuated in mice lacking CD73. Among tumor-infiltrating leukocytes there were fewer Tregs and mannose receptor-positive macrophages, and increased IFN-γ and NOS2 mRNA production in CD73-deficient mice. Treatment of tumor-bearing animals with soluble apyrase, an enzyme hydrolyzing ATP and ADP, significantly inhibited tumor growth and accumulation of intratumoral Tregs and mannose receptor-positive macrophages in the WT C57BL/6 mice but not in the CD73-deficient mice. Pharmacological inhibition of CD73 with α,β-methylene-adenosine-5'-diphosphate in WT mice retarded tumor progression similarly to the genetic deletion of CD73. Together these data show that increased pericellular ATP degradation in the absence of CD73 activity in the host cells is a novel mechanism controlling anti-tumor immunity and tumor progression, and that the purinergic balance can be manipulated therapeutically to inhibit tumor growth.