Proatherogenic role for NK cells revealed.
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Animals↗
Biomedical subjects
MacRae F Linton
Publications and source records attributed to MacRae F Linton.
Unique pathway for cholesterol uptake in fat cells.
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Adipocytes↗
Premature coronary-artery atherosclerosis in systemic lupus erythematosus.
BACKGROUND: Premature coronary artery disease is a major cause of illness and death in patients with systemic lupus erythematosus, but little is known about the prevalence, extent, and causes of coronary-artery atherosclerosis. METHODS: We used electron-beam computed tomography to screen for the presence of coronary-artery calcification in 65 patients with systemic lupus erythematosus (mean [+/-SD] age, 40.3+/-11.6 years) and 69 control subjects (mean age, 42.7+/-12.6 years) with no history of coronary artery disease. When calcification was detected, the extent was measured by means of the Agatston score. The frequency of risk factors for coronary artery disease was compared in patients and controls, and the relation between the patients' clinical characteristics and the presence or absence of coronary-artery calcification was examined. RESULTS: The two groups were similar with respect to age, race, and sex. Coronary-artery calcification was more frequent in patients with lupus (20 of 65 patients) than in control subjects (6 of 69 subjects) (P=0.002). The mean calcification score was 68.9+/-244.2 in the patients and 8.8+/-41.8 (P<0.001) in controls. Levels of total, high-density lipoprotein, and low-density lipoprotein cholesterol were not elevated in patients with lupus, but levels of triglycerides (P=0.02) and homocysteine (P<0.001) were. Among patients with lupus, measures of disease activity were similar in those with and those without coronary-artery calcification, but those with calcification were more likely to be older (P<0.001) and male (P=0.008). CONCLUSIONS: In patients with systemic lupus erythematosus, the prevalence of coronary-artery atherosclerosis is elevated and the age at onset is reduced. Early detection of atherosclerosis may provide an opportunity for therapeutic intervention.
Adult↗
Inactivation of macrophage scavenger receptor class B type I promotes atherosclerotic lesion development in apolipoprotein E-deficient mice.
BACKGROUND: Scavenger receptor class B type I (SR-BI) is expressed in macrophages, where it has been proposed to facilitate cholesterol efflux. However, direct evidence that the expression of macrophage SR-BI is protective against atherosclerosis is lacking. In this study, we examined the in vivo role of macrophage SR-BI in atherosclerotic lesion development in the apolipoprotein (apo) E-deficient mouse model. METHODS AND RESULTS: ApoE-deficient mice with (n=16) or without (n=15) expression of macrophage SR-BI were created by transplanting lethally irradiated apoE-deficient mice with bone marrow cells collected from SR-BI-/- apoE-/- mice or SR-BI+/+ apoE-/- mice. The recipient mice were fed a chow diet for 12 weeks after transplantation for analysis of atherosclerosis. Quantification of macrophage SR-BI mRNA by real-time reverse transcription-polymerase chain reaction indicated successful engraftment of donor bone marrow and inactivation of macrophage SR-BI in recipient mice reconstituted with SR-BI-/- apoE-/- bone marrow. There were no significant differences in plasma lipid levels, lipoprotein distributions, and HDL subpopulations between the 2 groups. Analysis of the proximal aorta demonstrated an 86% increase in mean atherosclerotic lesion area in SR-BI-/- apoE-/- --> apoE-/- mice compared with SR-BI+/+ apoE-/- --> apoE-/- mice (109.50+/-18.08 versus 58.75+/-9.58x10(3) microm2; mean+/-SEM, P=0.017). No difference in cholesterol efflux from SR-BI+/+ apoE-/- or SR-BI-/- apoE-/- macrophages to HDL or apoA-I discs was detected. CONCLUSIONS: Expression of macrophage SR-BI protects mice against atherosclerotic lesion development in apoE-deficient mice in vivo without influencing plasma lipids, HDL subpopulations, or cholesterol efflux. Thus, macrophage SR-BI plays an antiatherogenic role in vivo, providing a new therapeutic target for the design of strategies to prevent and treat atherosclerosis.
ATP Binding Cassette Transporter 1↗
A practical approach to risk assessment to prevent coronary artery disease and its complications.
The recent focus on emerging cardiovascular risk factors, such as C-reactive protein, homocysteine, and small, dense low-density lipoprotein (LDL), may give the false impression that the current approach to the assessment of cardiovascular disease risk fails to identify a large section of the high-risk population. On the contrary, the new guidelines of the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) propose classifying an enormous number of individuals, including people with any form of atherosclerotic disease, diabetes, and a combination of major risk factors, into the category of high risk (>20% likelihood of a major coronary event or stroke in 10 years). Considering the widespread prevalence of the metabolic syndrome-a high-risk condition characterized by mild hypertension, mild dyslipidemia, hyperglycemia, and visceral obesity-we may be faced with the challenge of implementing aggressive risk reduction therapies in as much as 30% of the adult US population. From the point of view of risk assessment, a practical approach is to follow the NCEP guidelines (ie, place patients with diabetes and those with atherosclerotic complications in the highest risk category), apply the Framingham calculation to determine risk in people with common risk factors, and initiate early intervention in people who have familial hypercholesterolemia (LDL cholesterol >200 mg/dL) or a family history of early cardiovascular disease. The emerging risk factors may be useful for further stratifying risk in individuals with intermediate risk and the presence of risk factors not included in the Framingham calculation.
Cholesterol, LDL↗
Hepatocyte-derived ApoE is more effective than non-hepatocyte-derived ApoE in remnant lipoprotein clearance.
The importance of hepatocyte-derived apolipoprotein (apo) E in the clearance of remnant lipoproteins in the liver is controversial. To address this controversy, we compared remnant clearance in two mouse models in which apoE is primarily derived either from hepatocytes or from an extrahepatic source. Hypomorphic apoE mice universally express reduced levels of apoE in all tissues, with the liver remaining the primary source of apoE. This mouse model of hepatocyte-derived apoE was compared with Apoe(-/-) mice transplanted with mouse bone marrow as a model of primarily non-hepatocyte-derived apoE. Immunohistochemical analysis of liver sections revealed that only the hepatocyte-derived apoE model had detectable levels of apoE on hepatic sinusoidal surfaces. The non-hepatocyte-derived apoE model with plasma apoE levels similar to those in the hepatocyte-derived model had 2-fold more total plasma cholesterol, 4-fold more total plasma triglycerides, and 8-fold higher levels of apoB48, similar to Apoe(-/-) mice. Both the hepatocyte-derived and the non-hepatocyte-derived apoE models had delayed clearance of an infused bolus of (125)I-labeled remnants compared with wild-type mice. However, after 3 h, plasma remnants reached wild-type levels only in the hepatocyte-derived apoE model, which had accumulated 70 +/- 5% of wild-type levels of remnants in the liver while the non-hepatocyte-derived apoE model had accumulated only 38 +/- 4%. These results demonstrate the existence of a role for both hepatically derived and localized apoE in remnant clearance. This role likely represents the enrichment of remnants sequestered on hepatocyte, with hepatocyte-derived apoE, facilitating their receptor-mediated internalization.
Animals↗
The recycling of apolipoprotein E in primary cultures of mouse hepatocytes. Evidence for a physiologic connection to high density lipoprotein metabolism.
Internalization of apoE-containing very low density protein (VLDL) by hepatocytes in vivo and in vitro leads to apoE recycling and resecretion. Because of the role of apoE in VLDL metabolism, apoE recycling may influence lipoprotein assembly or remnant uptake. However, apoE is also a HDL protein, and apoE recycling may be related to reverse cholesterol transport. To investigate apoE recycling, apoE(-/-) mouse hepatocytes were incubated (pulsed) with wild-type mouse lipoproteins, and cells and media were collected at chase periods up to 24 h. When cells were pulsed with VLDL, apoE was resecreted within 30 min. Although the mass of apoE in the media decreased with time, it could be detected up to 24 h after the pulse. Intact intracellular apoE was also detectable 24 h after the pulse. ApoE was also resecreted when cells were pulsed with HDL. When apoA-I was included in the chase media after a pulse with VLDL, apoE resecretion increased 4-fold. Furthermore, human apoE was resecreted from wild-type mouse hepatocytes after a pulse with human VLDL. Finally, apoE was resecreted from mouse peritoneal macrophages after pulsing with VLDL. We conclude that 1) HDL apoE recycles in a quantitatively comparable fashion to VLDL apoE; 2) apoE recycling can be modulated by extracellular apoA-I but is not affected by endogenous apoE; and 3) recycling occurs in macrophages as well as in hepatocytes, suggesting that the process is not cell-specific.
Animals↗
Macrophage apolipoprotein A-I expression protects against atherosclerosis in ApoE-deficient mice and up-regulates ABC transporters.
The antiatherogenic effect of high-density lipoprotein (HDL) and its major protein component apolipoprotein A-I (apoA-I) has been largely attributed to their key roles in reverse cholesterol transport (RCT) and cellular cholesterol efflux. Substantial evidence shows that overexpression of human apoA-I reduces atherosclerosis in animal models. However, it is uncertain whether this protection is due to an increase in plasma HDL level or to a local effect in the artery wall. To test the hypothesis that expression of human apoA-I in macrophages can promote RCT in the artery wall, we used a retroviral construct expressing human apoA-I cDNA (MFG-HAI) to transduce ApoE(-/-) bone marrow cells and then transplanted these cells into ApoE(-/-) mice with preexisting atherosclerosis. ApoE(-/-) mice reconstituted with MFG-HAI marrow had a significant reduction (30%) in atherosclerotic lesions in the proximal aorta compared to control mice that received marrow expressing MFG parental virus. Peritoneal macrophages isolated from MFG-HAI mice showed a four- to fivefold increase in mRNA expression levels of both ATP-binding cassette (ABC) A1 and ABCG1 compared to controls. Our data demonstrate that gene transfer-mediated expression of human apoA-I in macrophages can compensate in part for apoE deficiency and delay the progression of atherosclerotic lesions by stimulating ABC-dependent cholesterol efflux and RCT.
ATP-Binding Cassette Transporters↗
Macrophages, inflammation, and atherosclerosis.
The macrophage plays a diverse array of roles in atherogenesis and lipoprotein metabolism. The macrophage functions as a scavenger cell, an immune mediator cell, and as a source of chemotactic molecules and cytokines. Chemokines have been implicated in promoting migration of monocytes into the arterial intima. Monocyte chemoattractant protein-1 (MCP-1) attracts monocytes bearing the chemokine receptor CCR-2. Macrophage expression of cyclooxygenase-2, a key enzyme in inflammation, promotes atherosclerotic lesion formation in low-density lipoprotein receptor (LDLR)-deficient mice. In the arterial intima, monocytes differentiate into macrophages, which accumulate cholesterol esters to form lipid-laden foam cells. Foam cell formation can be viewed as an imbalance in cholesterol homeostasis. The uptake of atherogenic lipoproteins is mediated by scavenger receptors, including SR-A and CD36. In the macrophage, ACAT-1 is responsible for esterifying free cholesterol with fatty acids to form cholesterol esters. Surprisingly, deficiency of macrophage ACAT-1 promotes atherosclerosis in LDLR-deficient mice. A number of proteins have been implicated in the process of promoting the efflux of free cholesterol from the macrophage, including apoE, ABCA1, and SRB-1. Macrophage-derived foam cells express the adipocyte fatty acid-binding protein (FABP), aP2, a cytoplasmic FABP that plays an important role in regulating systemic insulin resistance in the setting of obesity. ApoE-deficient mice null for macrophage aP2 expression develop significantly less atherosclerosis than controls wild type for macrophage aP2 expression. These results demonstrate a significant role for macrophage aP2 in the formation of atherosclerotic lesions independent of its role in systemic glucose and lipid metabolism. Furthermore, macrophages deficient in aP2 display alterations in inflammatory cytokine production. Through its distinct actions in adipocytes and macrophages, aP2 links features of the metabolic syndrome including insulin resistance, obesity, inflammation, and atherosclerosis.
Animals↗
Apolipoprotein AI as therapy for atherosclerosis: does the future of preventive cardiology include weekly injections of the HDL protein?
Conventional wisdom suggests that halting or reversing long-term atherosclerosis requires increasing the amount of circulating high-density lipoprotein (HDL) coursing through the vasculature. However, recent evidence seems to indicate that reducing the size of cholesterol-containing lipid plaques might be accomplished by methods that either do not raise or, in fact, lower the amount of circulating HDL. Carriers of apoAI(Milano), a variant of apoprotein AI (a component of HDL), have reduced levels of circulating low-density lipoprotein (LDL). Intriguingly, these individuals have reduced amounts of circulating HDL and total apoAI. Infusions of the ApoAI(Milano) variant given to patients with coronary atherosclerosis appear to lead to disease regression and reduced plaque size. However, larger studies are required to provide definitive proof of apoAI(Milano)'s benefits. What is certain is that attention should be focused on the removal of cholesterol from plaques rather than simply desiring to raise HDL concentrations in patients.
Apolipoprotein A-I↗
B-lymphocyte deficiency increases atherosclerosis in LDL receptor-null mice.
OBJECTIVE: Atherosclerosis is an inflammatory disease characterized by innate and adaptive immune responses. We investigated the role of B cells and antibodies in the development of atherosclerosis in low density lipoprotein (LDL) receptor-deficient (LDLR(-/-)) mice. METHODS AND RESULTS: Using wild-type and B cell-deficient mice as bone marrow donors, we were able to generate LDLR(-/-) mice that possessed <1.0% of their normal B cell population. B cell-deficient LDLR(-/-) mice on a Western diet showed marked decreases in total serum antibody and anti-oxidized LDL antibody. B cell deficiency was associated with a 30% to 40% increase in the lesion area in the proximal and distal aortas. Real-time reverse transcription-polymerase chain reaction and enzyme-linked immunospot analyses showed a decrease in proatherogenic (interferon-gamma) and antiatherogenic (interleukin-10 and transforming growth factor-beta) cytokine mRNA and a decrease in interleukin-4- and interferon-gamma-producing cells. Additionally, we observed a decrease in splenocyte proliferation to oxidized LDL in the B cell-deficient LDLR(-/-) mice, suggesting that B lymphocytes may play a role in the presentation of lipid antigen. CONCLUSIONS: Collectively, these data demonstrate that B cells and/or antibodies are protective against atherosclerosis and that this protection may be conferred by B cell-mediated immune regulation.
Animals↗
Adipocyte fatty acid-binding protein, aP2, alters late atherosclerotic lesion formation in severe hypercholesterolemia.
OBJECTIVE: The adipocyte fatty acid-binding protein, aP2, has important effects on insulin resistance, lipid metabolism, and atherosclerosis. Its expression in macrophages enhances early foam cell formation and atherosclerosis in vivo. This study was designed to determine whether aP2 deficiency has a similar effect in the setting of advanced atherosclerosis and severe hypercholesterolemia. METHODS AND RESULTS: Mice deficient in aP2 and apolipoprotein E (aP2(-/-)apoE(-/-) mice) and apolipoprotein E-deficient control mice (apoE(-/-) mice) were fed a Western diet for 14 weeks. No significant differences in fasting serum levels of cholesterol, triglycerides, or free fatty acids were found between groups for each sex. Compared with apoE(-/-) control mice, male and female aP2(-/-)apoE(-/-) mice had significant reductions in mean atherosclerotic lesion size in the proximal aorta, en face aorta, and innominate/right carotid artery. Feeding the Western diet in the apoE-deficient background did not cause a significant reduction in insulin sensitivity in vivo, as determined by steady-state serum glucose levels and insulin tolerance testing. CONCLUSIONS: These data demonstrate an important role for aP2 expression in the advanced stages of atherosclerotic lesion formation. Thus, aP2 provides an important physiological link between different features of the metabolic syndrome and is a potential target for therapy of atherosclerosis.
Animals↗
Cyclooxygenase-2 promotes early atherosclerotic lesion formation in LDL receptor-deficient mice.
BACKGROUND: Atherosclerosis has features of an inflammatory disease. Because cyclooxygenase (COX)-2 is expressed in atherosclerotic lesions and promotes inflammation, we tested the hypotheses that selective COX-2 inhibition would reduce early lesion formation in LDL receptor-deficient (LDLR-/-) mice and that macrophage COX-2 expression contributes to atherogenesis in LDLR-/- mice. METHODS AND RESULTS: Treatment of male LDLR-/- mice fed the Western diet with rofecoxib or indomethacin for 6 weeks resulted in significant reductions in atherosclerosis in the proximal aorta (25% and 37%) and in the aorta en face (58% and 57%), respectively. Rofecoxib treatment did not inhibit platelet thromboxane production, a COX-1-mediated process, but it significantly reduced the urinary prostacyclin metabolite 2,3-dinor-6-keto-PGF1alpha. Fetal liver cell transplantation was used to generate LDLR-/- mice null for expression of the COX-2 gene by macrophages. After 8 weeks on the Western diet, COX-2-/- --> LDLR-/- mice developed significantly less (33% to 39%) atherosclerosis than control COX-2+/+ --> LDLR-/- mice. In both the inhibitor studies and the transplant studies, serum lipids did not differ significantly between groups. CONCLUSIONS: The present studies provide strong pharmacological and genetic evidence that COX-2 promotes early atherosclerotic lesion formation in LDLR-/- mice in vivo. These results support the potential of anti-inflammatory approaches to the prevention of atherosclerosis.
Animals↗
Retroviral mediated expression of the human myeloid nuclear antigen in a null cell line upregulates Dlk1 expression.
The human myeloid nuclear differentiation antigen (MNDA) is a hematopoietic cell specific nuclear protein. MNDA and other related gene products interact with and alter the activity of a large number of proteins involved in regulating specific gene transcription. MNDA and related genes exhibit expression characteristics, which suggest functions unique to specific lineages of cells, in addition to mediating the effects of interferons. Cells of the human K562 myeloid line do not express MNDA and are relatively immature compared to lines that express MNDA (HL-60, U937, and THP1). The hypothesis that MNDA influences the expression of specific genes was tested by creating MNDA expressing K562 cells using stable retroviral mediated gene transfer followed by evaluation of transcription profiles. Two macroarrays containing a total of 2,350 cDNAs of known genes showed a specific up-regulation of Dlk1 expression in MNDA expressing K562 cell clones. Real time quantitative RT-PCR analysis confirmed an average of over 3- and 7-fold upregulation of Dlk1 in two clones of MNDA expressing K562 cells. The effects on Dlk1 were also confirmed by Northern blotting. Dlk1 is essential for normal hematopoiesis and abnormal expression is a proposed marker of myelodysplastic syndrome. Additional screening of transcription profiles after induced erythroid and megakaryoblastic differentiation showed no additional gene transcripts altered by the presence of MNDA. These results indicate that MNDA alters expression of a gene essential for normal hematopoiesis.
Animals↗
Cytoplasmic fatty acid-binding proteins: emerging roles in metabolism and atherosclerosis.
Cytoplasmic fatty acid-binding proteins (FABPs) are a family of proteins, expressed in a tissue-specific manner, that bind fatty acid ligands and are involved in shuttling fatty acids to cellular compartments, modulating intracellular lipid metabolism, and regulating gene expression. Several members of the FABP family have been shown to have important roles in regulating metabolism and have links to the development of insulin resistance and the metabolic syndrome. Recent studies demonstrate a role for intestinal FABP in the control of dietary fatty acid absorption and chylomicron secretion. Heart FABP is essential for normal myocardial fatty acid oxidation and modulates fatty acid uptake in skeletal muscle. Liver FABP is directly involved in fatty acid ligand signaling to the nucleus and interacts with peroxisome proliferator-activated receptors in hepatocytes. The adipocyte FABP (aP2) has been shown to affect insulin sensitivity, lipid metabolism and lipolysis, and has recently been shown to play an important role in atherosclerosis. Interestingly, expression of aP2 by the macrophage promotes atherogenesis, thus providing a link between insulin resistance, intracellular fatty acid disposition, and foam cell formation. The FABPs are promising targets for the treatment of dyslipidemia, insulin resistance, and atherosclerosis in humans.
Animals↗
Cyclooxygenase-2 and atherosclerosis.
Cyclooxygenase regulates the production of eicosanoids, which modulate physiologic processes in the vessel wall contributing to atherosclerosis and thrombosis, including platelet aggregation, control of vascular tone, and the local inflammatory response. Cyclooxygenase-1 mediates production of platelet thromboxane A(2), a potent vasoconstrictor and platelet agonist, whereas both cyclooxygenase 1 and 2 contribute to production of endothelial prostacyclin, a vasodilator that inhibits platelet activation. Concerns have been raised that cyclooxygenase-2 inhibitors may increase thrombotic cardiovascular events by disturbing the balance between platelet thromboxane A(2) and endothelial prostacyclin, but this controversial issue will only be resolved by prospective clinical trials. Because cyclooxygenase-2 is upregulated in activated monocyte/macrophages, which play a key role in the pathogenesis of atherosclerosis, we have recently tested the hypothesis that pharmacological inhibition of cyclooxygenase-2 in LDL-receptor deficient mice would reduce early atherosclerosis. After 6 weeks on a Western-type diet, male LDL-receptor deficient mice treated with either rofecoxib (a selective cyclooxygenase-2 inhibitor) or indomethacin (a non-selective cyclooxygenase inhibitor) had significant reductions in atherosclerosis when compared with control mice. Also, LDL-receptor deficient mice null for macrophage cyclooxygenase-2 were generated by fetal liver cell transplantation and developed significantly less atherosclerosis than control LDL-receptor deficient mice transplanted with fetal liver cells wildtype for cyclooxygenase-2, providing genetic evidence in support of a proatherogenic role for macrophage cyclooxygenase-2 expression. These results support the potential of antiinflammatory approaches for the prevention of atherosclerosis and identify cyclooxygenase-2 as a target for intervention.
Animals↗
Absence of angiotensin II type 1 receptor in bone marrow-derived cells is detrimental in the evolution of renal fibrosis.
We examined the in vivo function of the angiotensin II type 1 receptor (Agtr1) on macrophages in renal fibrosis. Fourteen days after the induction of unilateral ureteral obstruction (UUO), wild-type mice reconstituted with marrow lacking the Agtr1 gene (Agtr1(-/-)) developed more severe interstitial fibrosis with fewer interstitial macrophages than those in mice reconstituted with Agtr1(+/+) marrow. These differences were not observed at day 5 of UUO. The expression of profibrotic genes - including TGF-beta1, alpha1(I) collagen, and alpha1(III) collagen - was substantially higher in the obstructed kidneys of mice with Agtr1(-/-) marrow than in those with Agtr1(+/+) marrow at day 14 but not at day 5 of UUO. Mice with Agtr1(-/-) marrow were characterized by reduced numbers of peripheral-blood monocytes and macrophage progenitors in bone marrow. In vivo assays revealed a significantly impaired phagocytic capability in Agtr1(-/-) macrophages. In vivo treatment of Agtr1(+/+) mice with losartan reduced phagocytic capability of Agtr1(+/+) macrophages to a level comparable to that of Agtr1(-/-) macrophages. Thus, during urinary tract obstruction, the Agtr1 on bone marrow-derived macrophages functions to preserve the renal parenchymal architecture, and this function depends in part on its modulatory effect on phagocytosis.
Animals↗
Rapid quantification of murine ABC mRNAs by real time reverse transcriptase-polymerase chain reaction.
Several ATP-binding cassette (ABC) transporters are critically involved in cholesterol and phospholipid efflux, reverse cholesterol transport, and play an important role in the development of atherosclerosis. Quantification of ABC mRNA is important in studying the regulation of cellular cholesterol homeostasis and mechanisms related to the pathogenesis of atherosclerosis. We have developed a one-step real time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method for measuring mRNA levels of ABCA1, ABCG1, and ABCA2 in murine tissues using the TaqMan(TM) technology. It has significant methodological benefits when compared to classic Northern blotting or semi-quantitative RT-PCR analysis. Using this method, we found high expression levels of ABCA1 in liver and macrophages, and of ABCG1 in the brain and macrophages. The expression of ABCA1 and ABCG1 were further induced in macrophages loaded with acLDL. In contrast, ABCA2 was expressed exclusively in the brain with low expression levels in the macrophages. This method provides a rapid, highly sensitive, specific, and reproducible quantification of ABC mRNA, and can be performed with nanograms of total RNA sample, thus making it a superior method for studying the regulation of ABC transporters in cholesterol efflux and its role in the pathogenesis of atherosclerosis in murine models.
ATP-Binding Cassette Transporters↗