Instruct: Given a scientific claim, retrieve documents that support or refute the claim.
Query: Increased LDL receptors plays a role in the reduction of plasma Lp(a).
BACKGROUND Alirocumab, a monoclonal antibody to proprotein convertase subtilisin/kexin type 9 (PCSK9), lowers plasma low-density lipoprotein (LDL) cholesterol and apolipoprotein B100 (apoB). Although studies in mice and cells have identified increased hepatic LDL receptors as the basis for LDL lowering by PCSK9 inhibitors, there have been no human studies characterizing the effects of PCSK9 inhibitors on lipoprotein metabolism. In particular, it is not known whether inhibition of PCSK9 has any effects on very low-density lipoprotein or intermediate-density lipoprotein (IDL) metabolism. Inhibition of PCSK9 also results in reductions of plasma lipoprotein (a) levels. The regulation of plasma Lp(a) levels, including the role of LDL receptors in the clearance of Lp(a), is poorly defined, and no mechanistic studies of the Lp(a) lowering by alirocumab in humans have been published to date. METHODS Eighteen (10 F, 8 mol/L) participants completed a placebo-controlled, 2-period study. They received 2 doses of placebo, 2 weeks apart, followed by 5 doses of 150 mg of alirocumab, 2 weeks apart. At the end of each period, fractional clearance rates (FCRs) and production rates (PRs) of apoB and apo(a) were determined. In 10 participants, postprandial triglycerides and apoB48 levels were measured. RESULTS Alirocumab reduced ultracentrifugally isolated LDL-C by 55.1%, LDL-apoB by 56.3%, and plasma Lp(a) by 18.7%. The fall in LDL-apoB was caused by an 80.4% increase in LDL-apoB FCR and a 23.9% reduction in LDL-apoB PR. The latter was due to a 46.1% increase in IDL-apoB FCR coupled with a 27.2% decrease in conversion of IDL to LDL. The FCR of apo(a) tended to increase (24.6%) without any change in apo(a) PR. Alirocumab had no effects on FCRs or PRs of very low-density lipoproteins-apoB and very low-density lipoproteins triglycerides or on postprandial plasma triglycerides or apoB48 concentrations. CONCLUSIONS Alirocumab decreased LDL-C and LDL-apoB by increasing IDL- and LDL-apoB FCRs and decreasing LDL-apoB PR. These results are consistent with increases in LDL receptors available to clear IDL and LDL from blood during PCSK9 inhibition. The increase in apo(a) FCR during alirocumab treatment suggests that increased LDL receptors may also play a role in the reduction of plasma Lp(a). CLINICAL TRIAL REGISTRATION URL: http://www.clinicaltrials.gov. Unique identifier: NCT01959971.
Background: The relationship of LPA single nucleotide polymorphisms (SNPs), apolipoprotein(a) isoforms, and lipoprotein(a) [Lp(a)] levels with major adverse cardiovascular events (MACE) in different ethnic groups is not well known. Methods: LPA SNPs, apolipoprotein(a) isoforms, Lp(a), and oxidized phospholipids on apolipoprotein B-100 (OxPL-apoB) levels were measured in 1792 black, 1030 white, and 597 Hispanic subjects enrolled in the Dallas Heart Study. Their interdependent relationships and prospective association with MACE after median 9.5-year follow-up were determined. Results: LPA SNP rs3798220 was most prevalent in Hispanics (42.38%), rs10455872 in whites (14.27%), and rs9457951 in blacks (32.92%). The correlation of each of these SNPs with the major apolipoprotein(a) isoform size was highly variable and in different directions among ethnic groups. In the entire cohort, Cox regression analysis with multivariable adjustment revealed that quartiles 4 of Lp(a) and OxPL-apoB were associated with hazard ratios (95% confidence interval) for time to MACE of 2.35 (1.50–3.69, P<0.001) and 1.89 (1.26–2.84, P=0.003), respectively, versus quartile 1. Addition of the major apolipoprotein(a) isoform and the 3 LPA SNPs to these models attenuated the risk, but significance was maintained for both Lp(a) and OxPL-apoB. Evaluating time to MACE in specific ethnic groups, Lp(a) was a positive predictor and the size of the major apolipoprotein(a) isoform was an inverse predictor in blacks, the size of the major apolipoprotein(a) isoform was an inverse predictor in whites, and OxPL-apoB was a positive predictor in Hispanics. Conclusions: The prevalence and association of LPA SNPs with size of apolipoprotein(a) isoforms, Lp(a), and OxPL-apoB levels are highly variable and ethnicity-specific. The relationship to MACE is best explained by elevated plasma Lp(a) or OxPL-apoB levels, despite significant ethnic differences in LPA genetic markers.
Molecular mechanisms underlying the cold-associated high cardiovascular risk remain unknown. Here, we show that the cold-triggered food-intake-independent lipolysis significantly increased plasma levels of small low-density lipoprotein (LDL) remnants, leading to accelerated development of atherosclerotic lesions in mice. In two genetic mouse knockout models (apolipoprotein E(-/-) [ApoE(-/-)] and LDL receptor(-/-) [Ldlr(-/-)] mice), persistent cold exposure stimulated atherosclerotic plaque growth by increasing lipid deposition. Furthermore, marked increase of inflammatory cells and plaque-associated microvessels were detected in the cold-acclimated ApoE(-/-) and Ldlr(-/-) mice, leading to plaque instability. Deletion of uncoupling protein 1 (UCP1), a key mitochondrial protein involved in thermogenesis in brown adipose tissue (BAT), in the ApoE(-/-) strain completely protected mice from the cold-induced atherosclerotic lesions. Cold acclimation markedly reduced plasma levels of adiponectin, and systemic delivery of adiponectin protected ApoE(-/-) mice from plaque development. These findings provide mechanistic insights on low-temperature-associated cardiovascular risks.
BACKGROUND LDL cholesterol has a causal role in the development of cardiovascular disease. Improved understanding of the biological mechanisms that underlie the metabolism and regulation of LDL cholesterol might help to identify novel therapeutic targets. We therefore did a genome-wide association study of LDL-cholesterol concentrations. METHODS We used genome-wide association data from up to 11,685 participants with measures of circulating LDL-cholesterol concentrations across five studies, including data for 293 461 autosomal single nucleotide polymorphisms (SNPs) with a minor allele frequency of 5% or more that passed our quality control criteria. We also used data from a second genome-wide array in up to 4337 participants from three of these five studies, with data for 290,140 SNPs. We did replication studies in two independent populations consisting of up to 4979 participants. Statistical approaches, including meta-analysis and linkage disequilibrium plots, were used to refine association signals; we analysed pooled data from all seven populations to determine the effect of each SNP on variations in circulating LDL-cholesterol concentrations. FINDINGS In our initial scan, we found two SNPs (rs599839 [p=1.7x10(-15)] and rs4970834 [p=3.0x10(-11)]) that showed genome-wide statistical association with LDL cholesterol at chromosomal locus 1p13.3. The second genome screen found a third statistically associated SNP at the same locus (rs646776 [p=4.3x10(-9)]). Meta-analysis of data from all studies showed an association of SNPs rs599839 (combined p=1.2x10(-33)) and rs646776 (p=4.8x10(-20)) with LDL-cholesterol concentrations. SNPs rs599839 and rs646776 both explained around 1% of the variation in circulating LDL-cholesterol concentrations and were associated with about 15% of an SD change in LDL cholesterol per allele, assuming an SD of 1 mmol/L.   INTERPRETATION We found evidence for a novel locus for LDL cholesterol on chromosome 1p13.3. These results potentially provide insight into the biological mechanisms that underlie the regulation of LDL cholesterol and might help in the discovery of novel therapeutic targets for cardiovascular disease.
In humans, apolipoprotein E (apoE) is a polymorphic multifunctional protein.1 It is coded by three alleles (e2, e3, e4) of a modulator gene (level, variability, and susceptibility gene) at the apoE locus on chromosome 19, determining six apoE genotypes and plasma phenotypes. Its pleiotropic effects are exerted on plasma lipoprotein metabolism, coagulation, oxidative processes, macrophage, glial cell and neuronal cell homeostasis, adrenal function, central nervous system physiology, inflammation, and cell proliferation.2,3 ApoE polymorphism modulates susceptibility to many diseases. It is, however, particularly notorious for its role in neurodegenerative disorders4 and atherosclerotic arterial disease.5,6 The e4 allele (phenotypes E4/4 and E4/3) that is associated with higher low density lipoprotein cholesterol (LDL-C) is considered proatherogenic, whereas the presence of the e2 allele (E3/2, E2/2), being associated with lower LDL-C levels, is deemed to have the opposite effect (although it may be associated with increased plasma triglycerides and lipoprotein remnants). This simple equation, however, is an oversimplification because these properties are subject to many environmental and genetic influences. ApoE has allele- and gender-dependent effects on reverse cholesterol transport, platelet aggregation, and oxidative processes that are likely to affect the overall atherogenic potential ascribed to modulation of lipoprotein metabolism.2,3,6 Notwithstanding the context dependency, a recent meta-analysis fully supports the presence of the e4 allele as a significant risk factor for coronary artery disease.7 Several mechanisms have been evoked to link apoE with atherosclerosis, but the relationship is not fully unraveled in humans. Nevertheless, some apoE mimetic peptides that promote LDL clearance are currently tested in animals for potential clinical applications.8,9  See page 436   The situation is relatively simpler in animals. The mouse model has been prominently useful to test mechanisms …
Inflammation and macrophage foam cells are characteristic features of atherosclerotic lesions, but the mechanisms linking cholesterol accumulation to inflammation and LXR-dependent response pathways are poorly understood. To investigate this relationship, we utilized lipidomic and transcriptomic methods to evaluate the effect of diet and LDL receptor genotype on macrophage foam cell formation within the peritoneal cavities of mice. Foam cell formation was associated with significant changes in hundreds of lipid species and unexpected suppression, rather than activation, of inflammatory gene expression. We provide evidence that regulated accumulation of desmosterol underlies many of the homeostatic responses, including activation of LXR target genes, inhibition of SREBP target genes, selective reprogramming of fatty acid metabolism, and suppression of inflammatory-response genes, observed in macrophage foam cells. These observations suggest that macrophage activation in atherosclerotic lesions results from extrinsic, proinflammatory signals generated within the artery wall that suppress homeostatic and anti-inflammatory functions of desmosterol.
Background: Atherosclerosis is characterized by infiltration of inflammatory cells from circulating blood. Blood cell activation could play an important role in plaque formation. Methods: We analyzed the relationship between blood cellular markers and quantitative measures of carotid wall components in 1,546 participants from the ARIC (Atherosclerosis Risk in Communities) Carotid MRI Study. Carotid imaging was performed using a gadolinium contrast-enhanced MRI and cellular phenotyping by flow cytometry. Results: Monocyte Toll-like receptor (TLR)-2 is associated with larger plaques, while CD14, myeloperoxidase, and TLR-4 associate with smaller. Platelet CD40L is associated with smaller plaques and thinner caps, while P-selectin is associated with smaller core size. Conclusions: Blood cell activation is significantly associated with atherosclerotic changes of the carotid wall.
OBJECTIVE T cell immunoglobulin and mucin domain (Tim) proteins are expressed by numerous immune cells, recognize phosphatidylserine on apoptotic cells, and function as costimulators or coinhibitors. Tim-1 is expressed by activated T cells but is also found on dendritic cells and B cells. Tim-4, present on macrophages and dendritic cells, plays a critical role in apoptotic cell clearance, regulates the number of phosphatidylserine-expressing activated T cells, and is genetically associated with low low-density lipoprotein and triglyceride levels. Because these functions of Tim-1 and Tim-4 could affect atherosclerosis, their modulation has potential therapeutic value in cardiovascular disease. APPROACH AND RESULTS ldlr(-/-) mice were fed a high-fat diet for 4 weeks while being treated with control (rat immunoglobulin G1) or anti-Tim-1 (3D10) or -Tim-4 (21H12) monoclonal antibodies that block phosphatidylserine recognition and phagocytosis. Both anti-Tim-1 and anti-Tim-4 treatments enhanced atherosclerosis by 45% compared with controls by impairment of efferocytosis and increasing aortic CD4(+)T cells. Consistently, anti-Tim-4-treated mice showed increased percentages of activated T cells and late apoptotic cells in the circulation. Moreover, in vitro blockade of Tim-4 inhibited efferocytosis of oxidized low-density lipoprotein-induced apoptotic macrophages. Although anti-Tim-4 treatment increased T helper cell (Th)1 and Th2 responses, anti-Tim-1 induced Th2 responses but dramatically reduced the percentage of regulatory T cells. Finally, combined blockade of Tim-1 and Tim-4 increased atherosclerotic lesion size by 59%. CONCLUSIONS Blockade of Tim-4 aggravates atherosclerosis likely by prevention of phagocytosis of phosphatidylserine-expressing apoptotic cells and activated T cells by Tim-4-expressing cells, whereas Tim-1-associated effects on atherosclerosis are related to changes in Th1/Th2 balance and reduced circulating regulatory T cells.
Lowering low-density lipoprotein-cholesterol (LDL-C) is the primary target in the management of dyslipidemia in patients at high risk of cardiovascular disease. However, patients who have achieved LDL-C levels below the currently recommended targets may still experience cardiovascular events. This may result, in part, from elevated triglyceride (TG) levels and low levels of high-density lipoprotein-cholesterol (HDL-C). Low HDL-C and high TG levels are common and are recognized as independent risk factors for cardiovascular morbidity and mortality. Furthermore, atherogenic dyslipidemia, characterized by low levels of HDL-C, high TG, and small, dense LDL particles, is a typical phenotype of dyslipidemia in subjects with insulin resistance and metabolic syndrome. Therefore, to reduce further the risk of coronary heart disease (CHD), raising HDL-C and lowering TG may be the secondary therapeutic target for patients who achieve LDL-C levels below the currently recommended targets but are still at risk of CHD. However, whether increasing HDL-C levels alone reduces CHD has not yet been confirmed in large randomized clinical trials, and whether functional HDL is more important than HDL-C in reducing CHD remains controversial. Large CHD endpoint trials that include many patients with diabetes are underway to compare combination treatments with statin and niacin, fibrates, or cholesteryl ester transfer protein inhibitors with statin alone treatments. In this review, we discuss the rationale and importance of increasing HDL-C levels with and without lowering TG levels in the treatment and prevention of cardiovascular events.
The physiological role of autophagic flux within the vascular endothelial layer remains poorly understood. Here, we show that in primary endothelial cells, oxidized and native LDL stimulates autophagosome formation. Moreover, by both confocal and electron microscopy, excess native or modified LDL appears to be engulfed within autophagic structures. Transient knockdown of the essential autophagy gene ATG7 resulted in higher levels of intracellular (125) I-LDL and oxidized LDL (OxLDL) accumulation, suggesting that in endothelial cells, autophagy may represent an important mechanism to regulate excess, exogenous lipids. The physiological importance of these observations was assessed using mice containing a conditional deletion of ATG7 within the endothelium. Following acute intravenous infusion of fluorescently labeled OxLDL, mice lacking endothelial expression of ATG7 demonstrated prolonged retention of OxLDL within the retinal pigment epithelium (RPE) and choroidal endothelium of the eye. In a chronic model of lipid excess, we analyzed atherosclerotic burden in ApoE(-/-) mice with or without endothelial autophagic flux. The absence of endothelial autophagy markedly increased atherosclerotic burden. Thus, in both an acute and chronic in vivo model, endothelial autophagy appears critically important in limiting lipid accumulation within the vessel wall. As such, strategies that stimulate autophagy, or prevent the age-dependent decline in autophagic flux, might be particularly beneficial in treating atherosclerotic vascular disease.
The Apolipoprotein (Apo) family is implicated in lipid metabolism. There are five types of Apo: Apoa, Apob, Apoc, Apod, and Apoe. Apoe has been demonstrated to play a central role in lipoprotein metabolism and to be essential for efficient receptor-mediated plasma clearance of chylomicron remnants and VLDL remnant particles by the liver. Apoe-deficient (Apoe(-/-)) mice develop atherosclerotic plaques spontaneously, followed by obesity. In this study, we investigated whether lipid deposition caused by Apoe knockout affects reproduction in female mice. The results demonstrated that Apoe(-/-) mice were severely hypercholesterolemic, with their cholesterol metabolism disordered, and lipid accumulating in the ovaries causing the ovaries to be heavier compared with the WT counterparts. In addition, estrogen and progesterone decreased significantly at D 100. Quantitative PCR analysis demonstrated that at D 100 the expression of cytochromeP450 aromatase (Cyp19a1), 3β-hydroxysteroid dehydrogenase (Hsd3b), mechanistic target of rapamycin (Mtor), and nuclear factor-κB (Nfkb) decreased significantly, while that of BCL2-associated agonist of cell death (Bad) and tuberous sclerosis complex 2 (Tsc2) increased significantly in the Apoe(-/-) mice. However, there was no difference in the fertility rates of the Apoe(-/-) and WT mice; that is, obesity induced by Apoe knockout has no significant effect on reproduction. However, the deletion of Apoe increased the number of ovarian follicles and the ratio of ovarian follicle atresia and apoptosis. We believe that this work will augment our understanding of the role of Apoe in reproduction.
Macrophage-derived foam cells play important roles in the progression of atherosclerosis. We reported previously that ERK1/2-dependent granulocyte/macrophage colony-stimulating factor (GM-CSF) expression, leading to p38 MAPK/ Akt signaling, is important for oxidized low density lipoprotein (Ox-LDL)-induced macrophage proliferation. Here, we investigated whether activation of AMP-activated protein kinase (AMPK) could suppress macrophage proliferation. Ox-LDL-induced proliferation of mouse peritoneal macrophages was assessed by [(3)H]thymidine incorporation and cell counting assays. The proliferation was significantly inhibited by the AMPK activator 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) and restored by dominant-negative AMPKalpha1, suggesting that AMPK activation suppressed macrophage proliferation. AICAR partially suppressed Ox-LDL-induced ERK1/2 phosphorylation and GM-CSF expression, suggesting that another mechanism is also involved in the AICAR-mediated suppression of macrophage proliferation. AICAR suppressed GM-CSF-induced macrophage proliferation without suppressing p38 MAPK/Akt signaling. GM-CSF suppressed p53 phosphorylation and expression and induced Rb phosphorylation. Overexpression of p53 or p27(kip) suppressed GM-CSF-induced macrophage proliferation. AICAR induced cell cycle arrest, increased p53 phosphorylation and expression, and suppressed GM-CSF-induced Rb phosphorylation via AMPK activation. Moreover, AICAR induced p21(cip) and p27(kip) expression via AMPK activation, and small interfering RNA (siRNA) of p21(cip) and p27(kip) restored AICAR-mediated suppression of macrophage proliferation. In conclusion, AMPK activation suppressed Ox-LDL-induced macrophage proliferation by suppressing GM-CSF expression and inducing cell cycle arrest. These effects of AMPK activation may represent therapeutic targets for atherosclerosis.
LXR alpha is a nuclear receptor that has previously been shown to regulate the metabolic conversion of cholesterol to bile acids. Here we define a role for this transcription factor in the control of cellular cholesterol efflux. We demonstrate that retroviral expression of LXR alpha in NIH 3T3 fibroblasts or RAW264.7 macrophages and/or treatment of these cells with oxysterol ligands of LXR results in 7- to 30-fold induction of the mRNA encoding the putative cholesterol/phospholipid transporter ATP-binding cassette (ABC)A1. In contrast, induction of ABCA1 mRNA in response to oxysterols is attenuated in cells that constitutively express dominant-negative forms of LXR alpha or LXR beta that lack the AF2 transcriptional activation domain. We further demonstrate that expression of LXR alpha in NIH 3T3 fibroblasts and/or treatment of these cells with oxysterols is sufficient to stimulate cholesterol efflux to extracellular apolipoprotein AI. The ability of oxysterol ligands of LXR to stimulate efflux is dramatically reduced in Tangier fibroblasts, which carry a loss of function mutation in the ABCA1 gene. Taken together, these results indicate that cellular cholesterol efflux is controlled, at least in part, at the level of transcription by a nuclear receptor-signaling pathway. They suggest a model in which activation of LXRs by oxysterols in response to cellular sterol loading leads to induction of the ABCA1 transporter and the stimulation of lipid efflux to extracellular acceptors. These findings have important implications for our understanding of mammalian cholesterol homeostasis and suggest new opportunities for pharmacological regulation of cellular lipid metabolism.
Liver X receptors (LXRs) and farnesoid X receptor (FXR) are nuclear receptors that function as intracellular sensors for sterols and bile acids, respectively. In response to their ligands, these receptors induce transcriptional responses that maintain a balanced, finely tuned regulation of cholesterol and bile acid metabolism. LXRs also permit the efficient storage of carbohydrate- and fat-derived energy, whereas FXR activation results in an overall decrease in triglyceride levels and modulation of glucose metabolism. The elegant, dual interplay between these two receptor systems suggests that they coevolved to constitute a highly sensitive and efficient system for the maintenance of total body fat and cholesterol homeostasis. Emerging evidence suggests that the tissue-specific action of these receptors is also crucial for the proper function of the cardiovascular, immune, reproductive, endocrine pancreas, renal, and central nervous systems. Together, LXRs and FXR represent potential therapeutic targets for the treatment and prevention of numerous metabolic and lipid-related diseases.
RATIONALE Hemizygous deficiency of the transcription factor Krüppel-like factor 2 (KLF2) has been shown previously to augment atherosclerosis in hypercholesterolemic mice. However, the cell type responsible for the increased atherosclerosis due to KLF2 deficiency has not been identified. This study examined the consequence of myeloid cell-specific KLF2 inactivation in atherosclerosis. METHODS AND RESULTS Cell-specific knockout mice were generated by Cre/loxP recombination. Macrophages isolated from myeloid-specific Klf2 knockout (myeKlf2(-/-)) mice were similar to myeKlf2(+/+) macrophages in response to activation, polarization, and lipid accumulation. However, in comparison to myeKlf2(+/+) macrophages, myeKlf2(-/-) macrophages adhered more robustly to endothelial cells. Neutrophils from myeKlf2(-/-) mice also adhered more robustly to endothelial cells, and fewer myeKlf2(-/-) neutrophils survived in culture over a 24-hour period in comparison with myeKlf2(+/+) neutrophils. When myeKlf2(-/-) mice were mated to Ldlr(-/-) mice and then fed a high fat and high cholesterol diet, significant increase in atherosclerosis was observed in the myeKlf2(-/-)Ldlr(-/-) mice compared with myeKlf2(+/+)Ldlr(-/-) littermates. The increased atherosclerosis in myeKlf2(-/-)Ldlr(-/-) mice was associated with elevated presence of neutrophils and macrophages, with corresponding increase of myeloperoxidase as well as chlorinated and nitrosylated tyrosine epitopes in their lesion areas compared with myeKlf2(+/+)Ldlr(-/-) mice. CONCLUSIONS This study documents a role for myeloid KLF2 expression in modulating atherosclerosis. The increased neutrophil accumulation and atherosclerosis progression with myeloid-specific KLF2 deficiency also underscores the importance of neutrophils in promoting vascular oxidative stress and atherosclerosis. Collectively, these results suggest that elevating KLF2 expression may be a novel strategy for prevention and treatment of atherosclerosis.
Chronic, nonresolving inflammation is a critical factor in the clinical progression of advanced atherosclerotic lesions. In the normal inflammatory response, resolution is mediated by several agonists, among which is the glucocorticoid-regulated protein called annexin A1. The proresolving actions of annexin A1, which are mediated through its receptor N-formyl peptide receptor 2 (FPR2/ALX), can be mimicked by an amino-terminal peptide encompassing amino acids 2–26 (Ac2-26). Collagen IV (Col IV)–targeted nanoparticles (NPs) containing Ac2-26 were evaluated for their therapeutic effect on chronic, advanced atherosclerosis in fat-fed Ldlr−/− mice. When administered to mice with preexisting lesions, Col IV–Ac2-26 NPs were targeted to lesions and led to a marked improvement in key advanced plaque properties, including an increase in the protective collagen layer overlying lesions (which was associated with a decrease in lesional collagenase activity), suppression of oxidative stress, and a decrease in plaque necrosis. In mice lacking FPR2/ALX in myeloid cells, these improvements were not seen. Thus, administration of a resolution-mediating peptide in a targeted NP activates its receptor on myeloid cells to stabilize advanced atherosclerotic lesions. These findings support the concept that defective inflammation resolution plays a role in advanced atherosclerosis, and suggest a new form of therapy.
Membrane cholesterol modulates a variety of cell signaling pathways and functions. While cholesterol depletion by high-density lipoproteins (HDLs) has potent anti-inflammatory effects in various cell types, its effects on inflammatory responses in macrophages remain elusive. Here we show overt pro-inflammatory effects of HDL-mediated passive cholesterol depletion and lipid raft disruption in murine and human primary macrophages in vitro. These pro-inflammatory effects were confirmed in vivo in peritoneal macrophages from apoA-I transgenic mice, which have elevated HDL levels. In line with these findings, the innate immune responses required for clearance of P. aeruginosa bacterial infection in lung were compromised in mice with low HDL levels. Expression analysis, ChIP-PCR, and combinatorial pharmacological and genetic intervention studies unveiled that both native and reconstituted HDL enhance Toll-like-receptor-induced signaling by activating a PKC-NF-κB/STAT1-IRF1 axis, leading to increased inflammatory cytokine expression. HDL's pro-inflammatory activity supports proper functioning of macrophage immune responses.
Interleukin-18 (IL18) participates in atherogenesis through several putative mechanisms. Interruption of IL18 action reduces atherosclerosis in mice. Here, we show that absence of the IL18 receptor (IL18r) does not affect atherosclerosis in apolipoprotein E–deficient (Apoe−/−) mice, nor does it affect IL18 cell surface binding to or signaling in endothelial cells. As identified initially by co-immunoprecipitation with IL18, we found that IL18 interacts with the Na-Cl co-transporter (NCC; also known as SLC12A3), a 12-transmembrane-domain ion transporter protein preferentially expressed in the kidney. NCC is expressed in atherosclerotic lesions, where it colocalizes with IL18r. In Apoe−/− mice, combined deficiency of IL18r and NCC, but not single deficiency of either protein, protects mice from atherosclerosis. Peritoneal macrophages from Apoe−/− mice or from Apoe−/− mice lacking IL18r or NCC show IL18 binding and induction of cell signaling and cytokine and chemokine expression, but macrophages from Apoe−/− mice with combined deficiency of IL18r and NCC have a blunted response. An interaction between NCC and IL18r on macrophages was detected by co-immunoprecipitation. IL18 binds to the cell surface of NCC-transfected COS-7 cells, which do not express IL18r, and induces cell signaling and cytokine expression. This study identifies NCC as an IL18-binding protein that collaborates with IL18r in cell signaling, inflammatory molecule expression, and experimental atherogenesis.
Atherosclerosis is often associated with chronic vascular inflammation. High-mobility group box 1 protein (HMGB1) plays various roles, not only as a transcriptional regulatory factor in the nucleus, but also as an inflammatory mediator. A previous study suggested that fibrinogen is an important factor associated with atherosclerosis progression. The present study was performed to examine the levels of plasma HMGB1 protein in atherosclerosis patients. We studied 24 patients with peripheral artery disease (PAD) with atherosclerosis, and 10 healthy controls. We found that the concentrations of HMGB1 were increased in the plasma of the patients with atherosclerosis, and there were significant correlations between the plasma HMGB1 and fibrinogen levels. Plasma HMGB1 may play a key role in the pathogenesis of clinical and experimental atherosclerosis.
Inflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha) have been implicated in atherogenesis. However, the precise role of TNF-alpha in atherogenesis is still unclear. To examine the effect of TNF-alpha on atherogenesis, we generated compound-deficient mice in apolipoprotein E (apoE) and TNF-alpha (apoE-/-/TNF-alpha-/-) and compared them with apoE-/- mice. Although serum total cholesterol levels were markedly elevated in both apoE-/-/TNF-alpha-/- and apoE-/- mice compared to wild-type mice, no differences were observed between apoE-/-/TNF-alpha-/- and apoE-/- mice. The atherosclerotic plaque area in the aortic luminal surface of apoE-/-/TNF-alpha-/- mice (n=8, 3.1+/-0.4%) was significantly smaller than that of apoE-/- mice (n=7, 4.7+/-0.4%, p<0.001) despite the lack of difference in serum cholesterol levels. The atherosclerotic lesion size in the aortic sinus of apoE-/-/TNF-alpha-/- mice (n=10, 5.1+/-0.3 x 10(5)microm(2)) was also significantly smaller than that of apoE-/- mice (n=11, 7.0+/-0.3 x 10(5)microm(2), p<0.0001). RT-PCR analysis indicated that the expression levels of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein-1 (MCP-1) were significantly higher in apoE-/- than apoE-/-/TNF-alpha-/- mice. Macrophages from apoE(-/-) mice showed higher uptake level of oxidized LDL and increased expression level of scavenger receptor class A (SRA) compared to those from apoE-/-/TNF-alpha-/- mice. These results indicate that TNF-alpha plays an atherogenic role by upregulating the expressions of ICAM-1, VCAM-1 and MCP-1 in the vascular wall, and by inducing SRA expression and oxidized LDL uptake in macrophages.
ContextSeveral novel risk factors for atherosclerosis have recently been proposed, but few comparative data exist to guide clinical use of these emerging biomarkers. ObjectiveTo compare the predictive value of 11 lipid and nonlipid biomarkers as risk factors for development of symptomatic peripheral arterial disease (PAD).Design, Setting, and ParticipantsNested case-control study using plasma samples collected at baseline from a prospective cohort of 14 916 initially healthy US male physicians aged 40 to 84 years, of whom 140 subsequently developed symptomatic PAD (cases); 140 age- and smoking status–matched men who remained free of vascular disease during an average 9-year follow-up period were randomly selected as controls. Main Outcome MeasureIncident PAD, as determined by baseline total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total cholesterol–HDL-C ratio, triglycerides, homocysteine, C-reactive protein (CRP), lipoprotein(a), fibrinogen, and apolipoproteins (apo) A-I and B-100.ResultsIn univariate analyses, plasma levels of total cholesterol (P<.001), LDL-C (P = .001), triglycerides (P = .001), apo B-100 (P = .001), fibrinogen (P = .02), CRP (P = .006), and the total cholesterol–HDL-C ratio (P<.001) were all significantly higher at baseline among men who subsequently developed PAD compared with those who did not, while levels of HDL-C (P = .009) and apo A-I (P = .05) were lower. Nonsignificant baseline elevations of lipoprotein(a) (P = .40) and homocysteine (P = .90) were observed. In multivariable analyses, the total cholesterol–HDL-C ratio was the strongest lipid predictor of risk (relative risk [RR] for those in the highest vs lowest quartile, 3.9; 95% confidence interval [CI], 1.7-8.6), while CRP was the strongest nonlipid predictor (RR for the highest vs lowest quartile, 2.8; 95% CI, 1.3-5.9). In assessing joint effects, addition of CRP to standard lipid screening significantly improved risk prediction models based on lipid screening alone (P<.001).ConclusionsOf 11 atherothrombotic biomarkers assessed at baseline, the total cholesterol–HDL-C ratio and CRP were the strongest independent predictors of development of peripheral arterial disease. C-reactive protein provided additive prognostic information over standard lipid measures.
Although the entire coronary tree is exposed to the atherogenic effect of the systemic risk factors, atherosclerotic lesions form at specific arterial regions, where low and oscillatory endothelial shear stress (ESS) occur. Low ESS modulates endothelial gene expression through complex mechanoreception and mechanotransduction processes, inducing an atherogenic endothelial phenotype and formation of an early atherosclerotic plaque. Each early plaque exhibits an individual natural history of progression, regression, or stabilization, which is dependent not only on the formation and progression of atherosclerosis but also on the vascular remodeling response. Although the pathophysiologic mechanisms involved in the remodeling of the atherosclerotic wall are incompletely understood, the dynamic interplay between local hemodynamic milieu, low ESS in particular, and the biology of the wall is likely to be important. In this review, we explore the molecular, cellular, and vascular processes supporting the role of low ESS in the natural history of coronary atherosclerosis and vascular remodeling and indicate likely mechanisms concerning the different natural history trajectories of individual coronary lesions. Atherosclerotic plaques associated with excessive expansive remodeling evolve to high-risk plaques, because low ESS conditions persist, thereby promoting continued local lipid accumulation, inflammation, oxidative stress, matrix breakdown, and eventually further plaque progression and excessive expansive remodeling. An enhanced understanding of the pathobiologic processes responsible for atherosclerosis and vascular remodeling might allow for early identification of a high-risk coronary plaque and thereby provide a rationale for innovative diagnostic and/or therapeutic strategies for the management of coronary patients and prevention of acute coronary syndromes.
OBJECTIVE C-Reactive protein (CRP), a cardiovascular risk marker, could also participate in atherosclerosis. Atherosclerotic plaques express CRP and interleukin (IL)-10, a major antiinflammatory cytokine. IL-10 deficiency results in increased lesion formation, whereas IL-10 delivery attenuates lesions. We tested the effect of CRP on lipopolysaccharide (LPS)-induced IL-10 secretion in human monocyte-derived macrophages (HMDMs). METHODS AND RESULTS Incubation of HMDMs with CRP significantly decreased LPS-induced IL-10 mRNA and intracellular and secreted IL-10 protein and destabilized IL-10 mRNA. Also, CRP alone increased secretion of IL-8, IL-6, and tumor necrosis factor from HMDMs and did not inhibit LPS-induced secretion of these cytokines. Fc gamma receptor I antibodies significantly reversed CRP-mediated IL-10 inhibition. CRP significantly decreased intracellular cAMP, phospho-cAMP response element binding protein (pCREB), and adenyl cyclase activity. cAMP agonists reversed CRP-mediated IL-10 inhibition. Overexpression of wild-type and constitutively active CREB in THP-1 cells revealed attenuation of the inhibitory effect of CRP on LPS-induced IL-10 levels. CRP also inhibited hemoglobin:haptoglobin-induced IL-10 and heme oxygenase-1. Furthermore, administration of human CRP to rats significantly decreased IL-10 levels. CONCLUSIONS This study provides novel evidence that CRP, by decreasing IL-10 alters the antiinflammatory/proinflammatory balance, accentuating inflammation, which is pivotal in atherothrombosis.
BACKGROUND Although Toll-like receptor 4 (TLR-4) is involved in monocyte activation in patients with accelerated forms of atherosclerosis, the relationship between the expression of TLR-4 on circulating monocytes and coronary plaque vulnerability has not previously been evaluated. We investigated this relationship using 64-slice multidetector computed tomography (MDCT) in patients with stable angina pectoris (SAP).Methods and Results:We enrolled 65 patients with SAP who underwent MDCT. Three monocyte subsets (CD14++CD16-, CD14++CD16+, and CD14+CD16+) and expression of TLR-4 were measured by flow cytometry. Intracoronary plaques were assessed by 64-slice MDCT. We defined vulnerability of intracoronary plaques according to the presence of positive remodeling (remodeling index >1.05) and/or low CT attenuation (<35 HU). The circulating CD14++CD16+monocytes more frequently expressed TLR-4 than CD14++CD16-and CD14+CD16+monocytes (P<0.001). The relative proportion of the expression of TLR-4 on CD14++CD16+monocytes was significantly greater in patients with vulnerable plaque compared with those without (10.4 [4.1-14.5] % vs. 4.5 [2.8-7.8] %, P=0.012). In addition, the relative proportion of TLR-4 expression on CD14++CD16+monocytes positively correlated with the remodeling index (r=0.28, P=0.025) and negatively correlated with CT attenuation value (r=-0.31, P=0.013). CONCLUSIONS Upregulation of TLR-4 on CD14++CD16+monocytes might be associated with coronary plaque vulnerability in patients with SAP.
BACKGROUND Fibroblast growth factor 21 (FGF21) is a metabolic hormone with pleiotropic effects on glucose and lipid metabolism and insulin sensitivity. It acts as a key downstream target of both peroxisome proliferator-activated receptor α and γ, the agonists of which have been used for lipid lowering and insulin sensitization, respectively. However, the role of FGF21 in the cardiovascular system remains elusive. METHODS AND RESULTS The roles of FGF21 in atherosclerosis were investigated by evaluating the impact of FGF21 deficiency and replenishment with recombinant FGF21 in apolipoprotein E(-/-) mice. FGF21 deficiency causes a marked exacerbation of atherosclerotic plaque formation and premature death in apolipoprotein E(-/-) mice, which is accompanied by hypoadiponectinemia and severe hypercholesterolemia. Replenishment of FGF21 protects against atherosclerosis in apolipoprotein E(-/-)mice via 2 independent mechanisms, inducing the adipocyte production of adiponectin, which in turn acts on the blood vessels to inhibit neointima formation and macrophage inflammation, and suppressing the hepatic expression of the transcription factor sterol regulatory element-binding protein-2, thereby leading to reduced cholesterol synthesis and attenuation of hypercholesterolemia. Chronic treatment with adiponectin partially reverses atherosclerosis without obvious effects on hypercholesterolemia in FGF21-deficient apolipoprotein E(-/-) mice. By contrast, the cholesterol-lowering effects of FGF21 are abrogated by hepatic expression of sterol regulatory element-binding protein-2. CONCLUSIONS FGF21 protects against atherosclerosis via fine tuning the multiorgan crosstalk among liver, adipose tissue, and blood vessels.