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Objective: Tissue macrophages induce and perpetuate proinflammatory responses, thereby promoting metabolic and cardiovascular disease. Lipoprotein lipase (LpL), the rate-limiting enzyme in blood triglyceride catabolism, is expressed by macrophages in atherosclerotic plaques. We questioned whether LpL, which is also expressed in the bone marrow (BM), affects circulating white blood cells and BM proliferation and modulates macrophage retention within the artery. Approach and Results: We characterized blood and tissue leukocytes and inflammatory molecules in transgenic LpL knockout mice rescued from lethal hypertriglyceridemia within 18 hours of life by muscle-specific LpL expression (MCKL0 mice). LpL-deficient mice had ≈40% reduction in blood white blood cell, neutrophils, and total and inflammatory monocytes (Ly6C/Ghi). LpL deficiency also significantly decreased expression of BM macrophage-associated markers (F4/80 and TNF-α [tumor necrosis factor α]), master transcription factors (PU.1 and C/EBPα), and colony-stimulating factors (CSFs) and their receptors, which are required for monocyte and monocyte precursor proliferation and differentiation. As a result, differentiation of macrophages from BM-derived monocyte progenitors and monocytes was decreased in MCKL0 mice. Furthermore, although LpL deficiency was associated with reduced BM uptake and accumulation of triglyceride-rich particles and macrophage CSF–macrophage CSF receptor binding, triglyceride lipolysis products (eg, linoleic acid) stimulated expression of macrophage CSF and macrophage CSF receptor in BM-derived macrophage precursor cells. Arterial macrophage numbers decreased after heparin-mediated LpL cell dissociation and by genetic knockout of arterial LpL. Reconstitution of LpL-expressing BM replenished aortic macrophage density. Conclusions: LpL regulates peripheral leukocyte levels and affects BM monocyte progenitor differentiation and aortic macrophage accumulation.

In the past few years, inflammation has emerged as a major driving force of atherosclerotic lesion development. It is now well-established that from early lesion to vulnerable plaque formation, numerous cellular and molecular inflammatory components participate in the disease process. The most prominent cells that invade in evolving lesions are monocyte-derived macrophages and T-lymphocytes. Both cell types produce a wide array of soluble inflammatory mediators (cytokines, chemokines) which are critically important in the initiation and perpetuation of the disease. This review summarizes the currently available information from mouse studies on the contribution of a specified group of cytokines expressed in atherosclerotic lesions, viz. interleukins (IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-10, IL-12, IL-18, IL-20) and macrophage-associated cytokines [tumour necrosis factor-α (TNF-α); macrophage migration inhibitory factor (MIF); interferon-γ (IFN-γ); colony stimulating factors G-CSF,-M-CSF,-GM-CSF) to atherogenesis. Emphasis is put on the consistency of the effects of these cytokines, i.e. inasmuch an effect depends on the experimental approach applied (overexpression/deletion, strain, gender, dietary conditions, and disease stage). An important outcome of this survey is (i) that only for a few cytokines there is sufficient consistent data allowing classifying them as typically proatherogenic (IL-1, IL-12, IL-18, MIF, IFN-γ, TNF-α, and M-CSF) or antiatherogenic (IL-10) and (ii) that some cytokines (IL-4, IL-6 and GM-CSF) can exert pro- or anti-atherogenic effects depending on the experimental conditions. This knowledge can be used for improved early detection, prevention and treatment of atherosclerosis. © The Author 2008. Chemicals / CAS: colony stimulating factor 1, 81627-83-0; gamma interferon, 82115-62-6; interleukin 12, 138415-13-1; interleukin 18, 189304-55-0; interleukin 2, 85898-30-2; Colony-Stimulating Factors; Cytokines; Interferon-gamma, 82115-62-6; Interl

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-dependent transcription factor that has been demonstrated to regulate fat cell development and glucose homeostasis. PPARgamma is also expressed in a subset of macrophages and negatively regulates the expression of several proinflammatory genes in response to natural and synthetic ligands. We here demonstrate that PPARgamma is expressed in macrophage foam cells of human atherosclerotic lesions, in a pattern that is highly correlated with that of oxidation-specific epitopes. Oxidized low density lipoprotein (oxLDL) and macrophage colony-stimulating factor, which are known to be present in atherosclerotic lesions, stimulated PPARgamma expression in primary macrophages and monocytic cell lines. PPARgamma mRNA expression was also induced in primary macrophages and THP-1 monocytic leukemia cells by the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). Inhibition of protein kinase C blocked the induction of PPARgamma expression by TPA, but not by oxLDL, suggesting that more than one signaling pathway regulates PPARgamma expression in macrophages. TPA induced the expression of PPARgamma in RAW 264.7 macrophages by increasing transcription from the PPARgamma1 and PPARgamma3 promoters. In concert, these observations provide insights into the regulation of PPARgamma expression in activated macrophages and raise the possibility that PPARgamma ligands may influence the progression of atherosclerosis.

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-dependent transcription factor that has been demonstrated to regulate fat cell development and glucose homeostasis. PPARgamma is also expressed in a subset of macrophages and negatively regulates the expression of several proinflammatory genes in response to natural and synthetic ligands. We here demonstrate that PPARgamma is expressed in macrophage foam cells of human atherosclerotic lesions, in a pattern that is highly correlated with that of oxidation-specific epitopes. Oxidized low density lipoprotein (oxLDL) and macrophage colony-stimulating factor, which are known to be present in atherosclerotic lesions, stimulated PPARgamma expression in primary macrophages and monocytic cell lines. PPARgamma mRNA expression was also induced in primary macrophages and THP-1 monocytic leukemia cells by the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). Inhibition of protein kinase C blocked the induction of PPARgamma expression by TPA, but not by oxLDL, suggesting that more than one signaling pathway regulates PPARgamma expression in macrophages. TPA induced the expression of PPARgamma in RAW 264.7 macrophages by increasing transcription from the PPARgamma1 and PPARgamma3 promoters. In concert, these observations provide insights into the regulation of PPARgamma expression in activated macrophages and raise the possibility that PPARgamma ligands may influence the progression of atherosclerosis.

A number of macrophage functions were sequentially expressed when the bone marrow precursors of mononuclear phagocytes differentiated in culture in the presence of a specific growth factor, colony-stimulating factor-1. We have defined the expression of apoprotein E (ApoE), a major secreted protein of resident peritoneal macrophages, during maturation of adherent bone marrow-derived mononuclear phagocytes into macrophages. By 5 d the bone marrow macrophages were active secretory cells, but few cells contained intracellular immunoreactive ApoE, and little, if any, ApoE was secreted. ApoE secretion was initiated at 9 d, and this correlated with an increase in the percentage of macrophages containing intracellular ApoE. The onset of ApoE secretion was selective, and little change occurred in the other major secreted proteins detected by [35S]methionine incorporation. In parallel, the high rate of plasminogen activator secretion, which peaked at 7 d, decreased markedly. ApoE secretion was not associated with altered expression of the macrophage surface antigen, Ia, or with secretion of fibronectin. Virtually all cells in independent colonies of bone marrow-derived macrophages eventually expressed ApoE. The proliferating monocyte/macrophage-like cell lines P388D1, J774.2, WEHI-3, RAW 264.1, and MGI.D+ secreted little or no ApoE. These data establish that ApoE secretion is developmentally regulated.

Lactoferrin (LF) has been recently proposed as a physiologic regulator of the granulocyte monocyte progenitor (CFU-GM). This glycoprotein, when saturated with iron, has been said to limit CFU-GM growth by decreasing production and release of colony stimulating activity (CSA) by monocytes and macrophages. Human milk LF saturated with iron, at concentrations ranging from 10(-18) to 10(-8) M was added either to endogenously stimulated bone marrow cells or to mononucleated cells used as feeder layers for adherent cell-depleted marrow. Irrespective of the concentration of LF within the culture system used, no significant inhibition of CFU-GM growth was observed. Moreover, the CFU-GM stimulating activity of medium conditioned by a 4-day incubation of 1 X 10(6) mononucleated blood cells in the presence or in the absence of LF was the same. Various possible explanations for not confirming the reported inhibiting activity of iron saturated LF were explored: 1) masking inhibition of the system by prostaglandin E2 (PGE2), 2) masking inhibition of the system by bovine LF still detectable in the fetal calf serum after heating, 3) preinhibition of the system by leukemic-associated inhibitory activity (LIA) possibly present in the culture system, 4) the iron and calcium content of the culture medium used, 5) the fixation of LF to plastic compounds, 6) the source of the human LF used, 7) the marrow cell separation methods used. None of these factors was shown to play a role in vitro in the activity of LF and thus no evidence was found for a significant role of LF in the regulation of CSA production by monocytes. Peripheral blood human monocytes isolated by elutriation and incubated in albumin free medium in the presence of either 125I-LF or colloidal gold-labeled LF showed no LF binding., Comparative Study, Journal Article, Research Support, Non-U.S. Gov't, info:eu-repo/semantics/published

A number of macrophage functions were sequentially expressed when the bone marrow precursors of mononuclear phagocytes differentiated in culture in the presence of a specific growth factor, colony-stimulating factor-1. We have defined the expression of apoprotein E (ApoE), a major secreted protein of resident peritoneal macrophages, during maturation of adherent bone marrow-derived mononuclear phagocytes into macrophages. By 5 d the bone marrow macrophages were active secretory cells, but few cells contained intracellular immunoreactive ApoE, and little, if any, ApoE was secreted. ApoE secretion was initiated at 9 d, and this correlated with an increase in the percentage of macrophages containing intracellular ApoE. The onset of ApoE secretion was selective, and little change occurred in the other major secreted proteins detected by [35S]methionine incorporation. In parallel, the high rate of plasminogen activator secretion, which peaked at 7 d, decreased markedly. ApoE secretion was not associated with altered expression of the macrophage surface antigen, Ia, or with secretion of fibronectin. Virtually all cells in independent colonies of bone marrow-derived macrophages eventually expressed ApoE. The proliferating monocyte/macrophage-like cell lines P388D1, J774.2, WEHI-3, RAW 264.1, and MGI.D+ secreted little or no ApoE. These data establish that ApoE secretion is developmentally regulated.

Lactoferrin (LF) has been recently proposed as a physiologic regulator of the granulocyte monocyte progenitor (CFU-GM). This glycoprotein, when saturated with iron, has been said to limit CFU-GM growth by decreasing production and release of colony stimulating activity (CSA) by monocytes and macrophages. Human milk LF saturated with iron, at concentrations ranging from 10(-18) to 10(-8) M was added either to endogenously stimulated bone marrow cells or to mononucleated cells used as feeder layers for adherent cell-depleted marrow. Irrespective of the concentration of LF within the culture system used, no significant inhibition of CFU-GM growth was observed. Moreover, the CFU-GM stimulating activity of medium conditioned by a 4-day incubation of 1 X 10(6) mononucleated blood cells in the presence or in the absence of LF was the same. Various possible explanations for not confirming the reported inhibiting activity of iron saturated LF were explored: 1) masking inhibition of the system by prostaglandin E2 (PGE2), 2) masking inhibition of the system by bovine LF still detectable in the fetal calf serum after heating, 3) preinhibition of the system by leukemic-associated inhibitory activity (LIA) possibly present in the culture system, 4) the iron and calcium content of the culture medium used, 5) the fixation of LF to plastic compounds, 6) the source of the human LF used, 7) the marrow cell separation methods used. None of these factors was shown to play a role in vitro in the activity of LF and thus no evidence was found for a significant role of LF in the regulation of CSA production by monocytes. Peripheral blood human monocytes isolated by elutriation and incubated in albumin free medium in the presence of either 125I-LF or colloidal gold-labeled LF showed no LF binding., Comparative Study, Journal Article, Research Support, Non-U.S. Gov't, info:eu-repo/semantics/published