Effect of macrophage differentiation and exposure to mildly oxidized LDL on the proteolytic repertoire of THP-1 monocytes

Vascular extracellular matrix in atherosclerosis

The extracellular matrix (ECM) is an essential component of the human body that is responsible for the proper function of various organs. Changes in the ECM have been implicated in the pathogenesis of several cardiovascular conditions including atherosclerosis, restenosis, and heart failure. Matrix components, such as collagens and noncollagenous proteins, influence the function and activity of vascular cells, particularly vascular smooth muscle cells and macrophages. Matrix proteins have been shown to be implicated in the development of atherosclerotic complications, such as plaque rupture, aneurysm formation, and calcification. ECM proteins control ECM remodeling through feedback signaling to matrix metalloproteinases (MMPs), which are the key players of ECM remodeling in both normal and pathological conditions. The production of MMPs is closely related to the development of an inflammatory response and is subjected to significant changes at different stages of atherosclerosis. Indeed, blood levels of circulating MMPs may be useful for the assessment of the inflammatory activity in atherosclerosis and the prediction of cardiovascular risk. The availability of a wide variety of low-molecular MMP inhibitors that can be conjugated with various labels provides a good perspective for specific targeting of MMPs and implementation of imaging techniques to visualize MMP activity in atherosclerotic plaques and, most interestingly, to monitor responses to antiatheroslerosis therapies. Finally, because of the crucial role of ECM in cardiovascular repair, the regenerative potential of ECM could be successfully used in constructing engineered scaffolds and vessels that mimic properties of the natural ECM and consist of the native ECM components or composite biomaterials. These scaffolds possess a great promise in vascular tissue engineering.

Oxidized low-density lipoprotein suppresses expression of prostaglandin E receptor subtype EP3 in human THP-1 macrophages

EP3, one of four prostaglandin E2 (PGE2) receptors, is significantly lower in atherosclerotic plaques than in normal arteries and is localized predominantly in macrophages of the plaque shoulder region. However, mechanisms behind this EP3 expression pattern are still unknown. We investigated the underlying mechanism of EP3 expression in phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1 macrophages with oxidized low-density lipoprotein (oxLDL) treatment. We found that oxLDL decreased EP3 expression, in a dose-dependent manner, at both the mRNA and protein levels. Moreover, oxLDL inhibited nuclear factor-κB (NF-κB)-dependent transcription of the EP3 gene by the activation of peroxisome proliferator-activated receptor-γ (PPAR-γ). Finally, chromatin immunoprecipitation revealed decreased binding of NF-κB to the EP3 promoter with oxLDL and PPAR-γ agonist treatment. Our results show that oxLDL suppresses EP3 expression by activation of PPAR-γ and subsequent inhibition of NF-κB in macrophages. These results suggest that down-regulation of EP3 expression by oxLDL is associated with impairment of EP3-mediated anti-inflammatory effects, and that EP3 receptor activity may exert a beneficial effect on atherosclerosis.

Role of renin-angiotensin system in activation of macrophages by modified lipoproteins

Angiotensin II favors the development of atherosclerosis. Our goal was to determine if foam cell formation increases angiotensin II generation by the endogenous renin-angiotensin system (RAS) and if endogenously produced angiotensin II promotes lipid accumulation in macrophages. Differentiated THP-1 cells were treated with acetylated low-density lipoproteins (ac-LDL), native LDL (n-LDL), or no LDL. Expression of RAS genes was assessed and angiotensin I/II levels were quantified in media and cell lysate. Ac-LDL increased angiotensin I/II levels and the angiotensin II/I ratio in cells and media after foam cell formation. Renin mRNA or activity did not change, but renin blockade completely inhibited the increase in angiotensin II. Angiotensinogen mRNA but not protein level was increased. Angiotensin-converting enzyme (ACE) and cathepsin G mRNA and activities were enhanced by ac-LDL. Inhibition of renin, ACE, or the angiotensin II receptor 1 (AT1-receptor) largely abolished cholesteryl ester formation in cells exposed to ac-LDL and decreased scavenger receptor A (SR-A) and acyl-coenzyme A:cholesterol acyltransferase 1 (ACAT-1) protein levels. Inhibition of renin or the AT1-receptor in cells treated with oxidized LDL also decreased SR-A and ACAT-1 protein and foam cell formation. ac-LDL also increased angiotensin II by human peripheral blood monocyte-derived macrophages, whereas blockade of renin decreased cholesterol ester formation in these macrophages. These findings indicate that, during foam cell formation, angiotensin II generation by the endogenous RAS is stimulated and that endogenously generated angiotensin II is crucial for cholesterol ester accumulation in macrophages exposed to modified LDL.

Combined chromatin and expression analysis reveals specific regulatory mechanisms within cytokine genes in the macrophage early immune response

Macrophages play a critical role in innate immunity, and the expression of early response genes orchestrate much of the initial response of the immune system. Macrophages undergo extensive transcriptional reprogramming in response to inflammatory stimuli such as Lipopolysaccharide (LPS).To identify gene transcription regulation patterns involved in early innate immune responses, we used two genome-wide approaches--gene expression profiling and chromatin immunoprecipitation-sequencing (ChIP-seq) analysis. We examined the effect of 2 hrs LPS stimulation on early gene expression and its relation to chromatin remodeling (H3 acetylation; H3Ac) and promoter binding of Sp1 and RNA polymerase II phosphorylated at serine 5 (S5P RNAPII), which is a marker for transcriptional initiation. Our results indicate novel and alternative gene regulatory mechanisms for certain proinflammatory genes. We identified two groups of up-regulated inflammatory genes with respect to chromatin modification and promoter features. One group, including highly up-regulated genes such as tumor necrosis factor (TNF), was characterized by H3Ac, high CpG content and lack of TATA boxes. The second group, containing inflammatory mediators (interleukins and CCL chemokines), was up-regulated upon LPS stimulation despite lacking H3Ac in their annotated promoters, which were low in CpG content but did contain TATA boxes. Genome-wide analysis showed that few H3Ac peaks were unique to either +/-LPS condition. However, within these, an unpacking/expansion of already existing H3Ac peaks was observed upon LPS stimulation. In contrast, a significant proportion of S5P RNAPII peaks (approx 40%) was unique to either condition. Furthermore, data indicated a large portion of previously unannotated TSSs, particularly in LPS-stimulated macrophages, where only 28% of unique S5P RNAPII peaks overlap annotated promoters. The regulation of the inflammatory response appears to occur in a very specific manner at the chromatin level for specific genes and this study highlights the level of fine-tuning that occurs in the immune response.

The use of THP-1 cells as a model for mimicking the function and regulation of monocytes and macrophages in the vasculature

Since their establishment thirty years ago, THP-1 cells have become one of most widely used cell lines to investigate the function and regulation of monocytes and macrophages in the cardiovascular system. However, because this cell line was derived from the blood of a patient with acute monocytic leukemia, the extent to which THP-1 cells mimic monocytes and macrophages in the vasculature is not entirely known. This article serves as a meaningful attempt to address this question by reviewing the recent publications. The interactions between THP-1 cells and various vascular cells (such as endothelial cells, smooth muscle cells, adipocytes, and T cells) provide insight into the roles of the interconnection of monocytes-macrophages with other vascular cells during vascular inflammation, particularly atherogenesis and obesity. Transcriptome, microRNA profile, and histone modifications of THP-1 cells shed new light on the regulatory mechanism of the monocytes-macrophages in response to various inflammatory mediators, such as oxidized low density lipoprotein, lipopolysaccharide, and glucose. These studies hint that under certain defined conditions, THP-1 cells not only resemble primary monocytes-macrophages isolated from healthy donors or donors with disease, such as diabetes mellitus, but also mimic the in situ alteration of macrophages in the adipose tissue of obese subjects and in atherosclerotic lesions. A potential trajectory is to use this cell line to study the novel molecular mechanisms in monocytes and macrophages in relation to the physiology and pathophysiology of the cardiovascular system, however, the conclusion of studies employing THP-1 cells requires further verification using primary cells and/or in vivo models to be generalized to monocytes and macrophages.

A common polymorphism in the promoter region of the TNFSF4 gene is associated with lower allele-specific expression and risk of myocardial infarction

Background

The TNFSF4/TNFRSF4 system, along with several other receptor-ligand pairs, is involved in the recruitment and activation of T-cells and is therefore tentatively implicated in atherosclerosis and acute coronary syndromes. We have previously shown that genetic variants in TNFSF4 are associated with myocardial infarction (MI) in women. This prompted functional studies of TNFSF4 expression.

Methods and Results

Based on a screening of the TNFSF4 genomic region, a promoter polymorphism (rs45454293) and a haplotype were identified, conceivably involved in gene regulation. The rs45454293T-allele, in agreement with the linked rs3850641G-allele, proved to be associated with increased risk of MI in women. Haplotype-specific chromatin immunoprecipitation of activated polymerase II, as a measure of transcriptional activity in vivo, suggested that the haplotype including the rs45454293 and rs3850641 polymorphisms is functionally important, the rs45454293T- and rs3850641G-alleles being associated with lower transcriptional activity in cells heterozygous for both polymorphisms. The functional role of rs45454293 on transcriptional levels of TNFSF4 was clarified by luciferase reporter assays, where the rs45454293T-allele decreased gene expression when compared with the rs45454293C-allele, while the rs3850641 SNP did not have any effect on TNFSF4 promoter activity. Electromobility shift assay showed that the rs45454293 polymorphism, but not rs3850641, affects the binding of nuclear factors, thus suggesting that the lower transcriptional activity is attributed to binding of one or more transcriptional repressor(s) to the T-allele.

Conclusions

Our data indicate that the TNFSF4 rs45454293T-allele is associated with lower TNFSF4 expression and increased risk of MI.

Emerging diagnostic and therapeutic molecular imaging applications in vascular disease

Assessment of vascular disease has evolved from mere indirect and direct measurements of luminal stenosis to sophisticated imaging methods to depict millimeter structural changes of the vasculature. In the near future, the emergence of multimodal molecular imaging strategies may enable robust therapeutic and diagnostic ('theragnostic') approaches to vascular diseases that comprehensively consider structural, functional, biological and genomic characteristics of the disease in individualized risk assessment, early diagnosis and delivery of targeted interventions.This review presents a summary of recent preclinical and clinical developments in molecular imaging and theragnostic applications covering diverse atherosclerosis events such as endothelial activation, macrophage inflammatory activity, plaque neovascularization and arterial thrombosis. The main focus is on molecular targets designed for imaging platforms commonly used in clinical medicine including magnetic resonance, computed tomography and positron emission tomography. A special emphasis is given to vascular ultrasound applications, considering the important role this imaging platform plays in the clinical and research practice of the vascular medicine specialty.

MicroRNA-29a regulates pro-inflammatory cytokine secretion and scavenger receptor expression by targeting LPL in oxLDL-stimulated dendritic cells

There is increasing evidence that microRNAs (miRNAs) play important roles in cell proliferation, apoptosis and differentiation that accompany inflammatory responses. However, whether microRNAs are associated with DC immuno-inflammatory responses with oxidized low density lipoprotein (oxLDL) stimulation is not yet known. Our study aims to explore the link of miRNAs with lipid-overload and immuno-inflammatory mechanism for atherosclerosis. In DCs transfected with microRNA-29a mimics or inhibitors, we showed that microRNA-29a plays an important role in proinflammatory cytokine secretion and scavenger receptor expression upon oxLDL-treatment. Furthermore, we suggest an additional explanation for the mechanism of microRNA-29a regulation of its functional target, lipoprotein lipase. We conclude that microRNA-29a could regulate pro-inflammatory cytokine secretion and scavenger receptor expression by targeting lipoprotein lipase in oxLDL-stimulated dendritic cells.

Human T cell microparticles circulate in blood of hepatitis patients and induce fibrolytic activation of hepatic stellate cells

Microparticles (MPs) are small cell membrane vesicles that are released from cells during apoptosis or activation. Although circulating platelet MPs have been studied in some detail, the existence and functional role of T cell MPs remain elusive. We show that blood from patients with active hepatitis C (alanine aminotransferase [ALT] level >100 IU/mL) contains elevated numbers of T cell MPs compared with patients with mild hepatitis C (ALT <40 IU/mL) and healthy controls. T cell MPs fuse with cell membranes of hepatic stellate cells (HSCs), the major effector cells for excess matrix deposition in liver fibrosis and cirrhosis. MP uptake is partly intercellular adhesion molecule 1-dependent and leads to activation of nuclear factor kappa B and extracellular signal-regulated kinases 1 and 2 and subsequent up-regulation of fibrolytic genes in HSCs, down-regulation of procollagen α1(I) messenger RNA, and blunting of profibrogenic activities of transforming growth factor β1. Ex vivo, the induced fibrolytic activity is evident in MPs derived from activated CD4+ T cells and is highest in MPs derived from activated and apoptotic CD8+ T cells. Mass spectrometry, fluorescence-activated cell sorting analysis, and function blocking antibodies revealed CD147/Emmprin as a candidate transmembrane molecule in HSC fibrolytic activation by CD8+ T cell MPs.

CONCLUSION

Circulating T cell MPs are a novel diagnostic marker for inflammatory liver diseases, and in vivo induction of T cell MPs may be a novel strategy to induce regression of liver fibrosis.

ADAMTS proteases: key roles in atherosclerosis?

The ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) proteases are secreted enzymes that regulate extracellular matrix turnover by degrading specific matrix components. Roles for the proteases in inflammation and atherosclerosis have been suggested by a number of recent studies, and the role of ADAMTS-4 and -5 in the breakdown of aggrecan and subsequent degradation of cartilage during osteoarthritis has also been established. The ability of the ADAMTS proteases to degrade versican, the primary proteoglycan in the vasculature, is thought to be central to any hypothesized role for the proteases in atherosclerosis. In this review, we introduce the structure and function of the ADAMTS family of proteases and review the literature that links them with inflammation and atherosclerosis.

Elevated level of ADAMTS4 in plasma and peripheral monocytes from patients with acute coronary syndrome

OBJECTIVES

A recent study shows that ADAMTS4 is expressed in macrophage-rich areas of human atherosclerotic carotid plaques and coronary unstable plaques, suggesting a pathogenic role of ADAMTS4 in the development of acute coronary syndrome (ACS). We investigated (a) whether the expression level of ADAMTS4 in plasma and peripheral blood mononuclear cells was affected; and (b) whether there was a relationship with hs-CRP level and the stability of coronary atherosclerotic plaque in patients with ACS.

METHODS

Our study included 30 normal controls and 120 patients including 40 with stable angina (SA), 50 with unstable angina (UA), and 30 with acute myocardial infarction (AMI). The expression of ADAMTS4 in monocytes was analyzed by RT-PCR and plasma ADAMTS4 level was determined by ELISA. All coronary stenosis with >30% diameter reduction was assessed by angiographic coronary stenosis morphology.

RESULTS

Patients with ACS showed a significant increase of ADAMTS4 (2.7 ± 0.4) expression in monocytes compared with controls (1.1 ± 0.2) and the SA group (1.3 ± 0.2) (P < 0.001). Plasma ADAMTS4 also showed a higher level in ACS patients (100.2 ± 31.6 ng/ml) than in control (47.5 ± 9.0 ng/ml, P < 0.001) and the SA group (54.3 ± 13.2 ng/ml, P < 0.001). Moreover, we found a positive correlation between hs-CRP and ADAMTS4 expression in monocytes as well as in plasma. There was also a positive correlation of ADAMTS4 expression in monocytes and plasma with complex coronary stenosis (r (1) = 0.61, r (2) = 0.57, P < 0.001).

CONCLUSIONS

Patients with ACS showed increased ADAMTS4 expression, which may aggravate the development of atherosclerosis and instability of atherosclerotic plaques. Therefore, the ADAMTS4 expression may be a valuable marker for predicting the severity of ACS.

Allele-specific regulation of MTTP expression influences the risk of ischemic heart disease

Promoter polymorphisms in microsomal triglyceride transfer protein (MTTP) have been associated with decreased plasma lipids but an increased risk for ischemic heart disease (IHD), indicating that MTTP influences the susceptibility for IHD independent of plasma lipids. The objective of this study was to characterize the functional promoter polymorphism in MTTP predisposing to IHD and its underlying mechanism. Use of pyrosequencing technology revealed that presence of the minor alleles of the promoter polymorphisms -493G>T and -164T>C result in lower transcription of MTTP in vivo in the heart, liver, and macrophages. In vitro experiments indicated that the minor -164C allele mediates the lower gene expression and that C/EBP binds to the polymorphic region in an allele-specific manner. Furthermore, homozygous carriers of the -164C were found to have increased risk for IHD as shown in a case-control study including a total of 544 IHD patients and 544 healthy control subjects. We concluded that carriers of the minor -164C allele have lower expression of MTTP in the heart, mediated at least partly by the transcription factor CCAAT/enhancer binding protein, and that reduced concentration of MTTP in the myocardium may contribute to IHD upon ischemic damage.

Commandeering a biological pathway using aptamer-derived molecular adaptors

Induction of molecular proximity can mediate a discrete functional response in biological systems. Therefore, creating new and specific connectivity between non-interacting proteins is a means of imposing rational control over biological processes. According to this principle, here we use composite RNA aptamers to generate molecular adaptors that link various ‘target’ molecules to a common ‘utility’ molecule, with the utility molecule being an entry point to a pathway conscripted to process the target molecule. In particular, we created a bi-functional aptamer that simultaneously binds to the green fluorescent protein (serving as a surrogate extracellular target) and the opsonin C3b/iC3b (serving as the utility molecule). This bi-functional aptamer enabled us to commandeer the C3-based opsonization-phagocytosis pathway to selectively transport an extracellular target into the lysosome for degradation. This novel strategy has the potential for powerful therapeutic applications with extracellular proteins involved in tumor development or surface markers on cancer cells as the target molecules.

MicroRNA-125a-5p partly regulates the inflammatory response, lipid uptake, and ORP9 expression in oxLDL-stimulated monocyte/macrophages

AIMS

The inflammatory responses of monocytes/macrophages and the stimulation of lipid uptake into these cells by oxidized low density lipoprotein (oxLDL) are critical to the initiation and development of atherosclerosis. Increasing evidence has demonstrated that many microRNAs play important roles in the cell proliferation, apoptosis, and differentiation that accompany inflammatory responses. However, whether microRNAs are associated with monocyte/macrophage inflammatory responses or oxLDL stimulation is not yet known. The aim of the present study is to investigate microRNAs in monocytes/macrophages and their potential role in oxLDL-stimulation of lipid uptake and other atherosclerotic responses.

METHODS AND RESULTS

Microarrays were used to analyse the global expression of microRNAs in oxLDL-stimulated human primary peripheral blood monocytes. Expression profiles of the microRNAs were verified using TaqMan real-time PCR. Five microRNAs (microRNA-125a-5p, microRNA-9, microRNA-146a, microRNA-146b-5p, and microRNA-155) were aberrantly expressed after oxLDL treatment of human primary monocytes. Bioinformatics analysis suggested that microRNA-125a-5p is related to a protein similar to ORP9 (oxysterol binding protein-like 9) and this was confirmed by a luciferase reporter assay. MicroRNA-125a-5p was found to mediate lipid uptake and to decrease the secretion of some inflammatory cytokines (interleukin-2, interleukin-6, tumour necrosis factor-alpha, transforming growth factor-beta) in oxLDL-stimulated monocyte-derived macrophages.

CONCLUSION

MicroRNA-125a-5p may partly provide post-transcriptional regulation of the proinflammatory response, lipid uptake, and expression of ORP9 in oxLDL-stimulated monocyte/macrophages.

Monocyte chemotactic protein-1 regulates voltage-gated K+ channels and macrophage transmigration

Progressive human immunodeficiency virus (HIV)-1 infection and virus-induced neuroinflammatory responses effectuate monocyte-macrophage transmigration across the blood-brain barrier (BBB). A key factor in mediating these events is monocyte chemotactic protein-1 (MCP-1). Upregulated glial-derived MCP-1 in HIV-1-infected brain tissues generates a gradient for monocyte recruitment into the nervous system. We posit that the inter-relationships between MCP-1, voltage-gated ion channels, cell shape and volume, and cell mobility underlie monocyte transmigration across the BBB. In this regard, MCP-1 serves both as a chemoattractant and an inducer of monocyte-macrophage ion flux affecting cell shape and mobility. To address this hypothesis, MCP-1-treated bone marrow-derived macrophages (BMM) were analyzed for gene and protein expression, electrophysiology, and capacity to migrate across a laboratory constructed BBB. MCP-1 enhanced K+ channel gene (KCNA3) and channel protein expression. Electrophysiological studies revealed that MCP-1 increased outward K+ currents in a dose-dependent manner. In vitro studies demonstrated that MCP-1 increased BMM migration across an artificial BBB, and the MCP-1-induced BMM migration was blocked by tetraethylammonium, a voltage-gated K+ channel blocker. Together these data demonstrated that MCP-1 affects macrophage migratory movement through regulation of voltage-gated K+ channels and, as such, provides a novel therapeutic strategy for neuroAIDS.

Infection with human cytomegalovirus alters the MMP-9/TIMP-1 balance in human macrophages

Human cytomegalovirus (HCMV) has been suggested to contribute to the development of vascular diseases. Since matrix metalloproteinases (MMPs) have been implicated in atherosclerosis and plaque rupture, we investigated the effect of HCMV infection on MMP expression in human macrophages. We used quantitative real-time PCR, Western blotting, and gelatin zymography to study the expression and activity of MMP-2, -3, -7, -9, -12, -13, and -14 and of tissue inhibitor of metalloproteinase 1 (TIMP-1), -2, -3, and -4. HCMV infection reduced MMP-9 mRNA, protein, and activity levels but increased TIMP-1 mRNA and protein levels. Furthermore, a decrease in MMP-12, MMP-14, TIMP-2, and TIMP-3 mRNA levels could be detected. The MMP-9 and TIMP-1 mRNA alterations required viral replication. MMP-9 mRNA expression was affected by an immediate-early or early viral gene product, whereas TIMP-1 mRNA expression was affected by late viral gene products. We conclude that HCMV infection specifically alters the MMP-9/TIMP-1 balance in human macrophages, which in turn reduces MMP-9 activity in infected cells. Since MMP-9 prevents atherosclerotic plaque development in mice, these results suggest that HCMV may contribute to atherogenesis through specific effects on MMP-9 activity.

Extracellular catalase activity protects cysteine cathepsins from inactivation by hydrogen peroxide

The resistance of secreted cysteine cathepsins to peroxide inactivation was evaluated using as model THP-1 cells. Differentiated cells released mostly cathepsin B, but also cathepsins H, K, and L, with a maximum of endopeptidase activity at day 6. Addition of non-cytotoxic concentrations of H(2)O(2) did not affect mRNA expression levels and activity of cathepsins, while the catalase activity remained also unchanged, consistently with RT-PCR analysis. Conversely inhibition of extracellular catalase led to a striking inactivation of secreted cysteine cathepsins by H(2)O(2). This report suggests that catalase may participate in the protection of extracellular cysteine proteases against peroxidation.

ADAMTS-4 and -8 are inflammatory regulated enzymes expressed in macrophage-rich areas of human atherosclerotic plaques

OBJECTIVES

Remodeling of extracellular matrix (ECM) plays an important role in inflammatory disorders such as atherosclerosis. ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) is a recently described family of proteinases that is able to degrade the ECM proteins aggrecan and versican expressed in blood vessels. The purpose of the present study was to analyze the expression and regulation of several ADAMTSs before and after macrophage differentiation and after stimulation with IFN-gamma, IL-1beta and TNF-alpha. ADAMTS expression was also examined during atherosclerosis development in mice and in human atherosclerotic plaques.

METHODS AND RESULTS

Real time RTPCR showed that, of the nine different ADAMTS members examined, only ADAMTS-4 and -8 were induced during monocyte to macrophage differentiation, which was also seen at protein level. Macrophage expression of ADAMTS-4, -7, -8 and -9 mRNA were enhanced upon stimulation with IFN-gamma or TNF-alpha. Furthermore, immunohistochemical analyses revealed that ADAMTS-4 and -8 were expressed in macrophage rich areas of human atherosclerotic carotid plaques and coronary unstable plaques. In addition, ADAMTS-4 expression was upregulated during the development of atherosclerosis in LDLR(-/-)ApoB(100/100) mice. Whereas ADAMTS-4 expression was low in non-atherosclerotic aortas, it was significantly higher in aortas from 30-40-week old atherosclerotic animals.

CONCLUSION

The present study suggests that ADAMTS-4 and -8 are inflammatory regulated enzymes expressed in macrophage-rich areas of atherosclerotic plaques. This is the first study associating ADAMTS-4 and -8 expression with atherosclerosis. However, further experiments are required to understand the physiological and pathological functions of ADAMTS in the vascular wall, and tools to measure ADAMTS activity need to be developed.

Genomics of Foam Cells and Nonfoamy Macrophages From Rabbits Identifies Arginase-I as a Differential Regulator of Nitric Oxide Production

Objective— Conversion of macrophages to foam cells is a critical step in the initiation and progression of atherosclerosis. We sought to identify genes differentially regulated in foam cells, since these are likely to include new targets for intervention.

Methods and Results— We used suppression subtraction hybridization to compare foam cells and nonfoamy macrophages isolated from subcutaneous granulomas of rabbits fed a cholesterol-rich or normal chow diet and confirmed upregulation of 3 genes, including matrix metalloproteinase-12 (mRNA 2.0-fold, P <0.005; protein 3.9-fold, P <0.03). Arginase-I mRNA showed the biggest decrease among 11 downregulated genes in foam cells (2.7-fold, P <0.001) and was accompanied by significantly reduced arginase enzymatic activity (60-fold, P <0.01). Arginase-I competes for substrate L-arginine with nitric oxide synthase and consequently nitric oxide production was significantly increased (3-fold, P <0.02) in foam cells compared with nonfoamy macrophages despite no difference in nitric oxide synthase isoenzyme expression. We validated upregulation of matrix metalloproteinase-12 and downregulation of arginase-1 in foam cells of rabbit and human atherosclerotic plaques.

Conclusions— Our study identified several differentially expressed genes in foam cells and nonfoamy macrophages derived from live rabbits. The altered pattern of gene expression in foam cells is likely to influence atherosclerosis formation and stability.

Allele-specific MMP-3 transcription under in vivo conditions

A common matrix metalloproteinases-3 (MMP-3) -1612 5A/6A promoter polymorphism is associated with risk for cardiovascular disease, rheumatoid arthritis, and other diseases. Here we used the haplotype chromatin immunoprecipitation method to study allele-specific MMP-3 expression under in vivo conditions in heterozygous THP-1 cells. Pyrosequencing was used to analyse the ratio of 5A-allele to 6A-allele after chromatin immunoprecipitation using an antibody against phosphorylated active RNA polymerase II. There was no allele-specific difference in transcriptional activity during basal conditions, i.e., in unstimulated monocytic THP-1 cells. However, after stimulation of MMP-3 expression by monocyte differentiation or incubation with IL-1beta, the haplotype containing the 5A-allele was associated with higher transcriptional activity compared with the 6A-containing haplotype. Electromobility shift assay demonstrated increased binding of nuclear proteins to the 5A-allele after monocyte differentiation. In conclusion, the common MMP-3 5A/6A promoter polymorphism appears to be functional only during specific environmental conditions involving inflammation.

Alternative promoter usage of the membrane glycoprotein CD36

BACKGROUND

CD36 is a membrane glycoprotein involved in a variety of cellular processes such as lipid transport, immune regulation, hemostasis, adhesion, angiogenesis and atherosclerosis. It is expressed in many tissues and cell types, with a tissue specific expression pattern that is a result of a complex regulation for which the molecular mechanisms are not yet fully understood. There are several alternative mRNA isoforms described for the gene. We have investigated the expression patterns of five alternative first exons of the CD36 gene in several human tissues and cell types, to better understand the molecular details behind its regulation.

RESULTS

We have identified one novel alternative first exon of the CD36 gene, and confirmed the expression of four previously known alternative first exons of the gene. The alternative transcripts are all expressed in more than one human tissue and their expression patterns vary highly in skeletal muscle, heart, liver, adipose tissue, placenta, spinal cord, cerebrum and monocytes. All alternative first exons are upregulated in THP-1 macrophages in response to oxidized low density lipoproteins. The alternative promoters lack TATA-boxes and CpG islands. The upstream region of exon 1b contains several features common for house keeping gene and monocyte specific gene promoters.

CONCLUSION

Tissue-specific expression patterns of the alternative first exons of CD36 suggest that the alternative first exons of the gene are regulated individually and tissue specifically. At the same time, the fact that all first exons are upregulated in THP-1 macrophages in response to oxidized low density lipoproteins may suggest that the alternative first exons are coregulated in this cell type and environmental condition. The molecular mechanisms regulating CD36 thus appear to be unusually complex, which might reflect the multifunctional role of the gene in different tissues and cellular conditions.

Difference in Matrix-Degrading Protease Expression and Activity Between Thrombus-Free and Thrombus-Covered Wall of Abdominal Aortic Aneurysm

OBJECTIVE

It has been suggested that the intraluminal thrombus of abdominal aortic aneurysms (AAAs) predisposes for AAA rupture. Here, we examined the possibility that the intraluminal thrombus influences expression and activity of matrix-degrading proteases in the AAA wall.

METHODS AND RESULTS

Twenty patients undergoing elective repair of AAAs were included. From each patient, specimens from both thrombus-covered and thrombus-free wall were taken for analysis. Gene arrays and quantitative real-time polymerase chain reaction showed that matrix metalloproteinase (MMP)-1, -7, -9, and -12 expressions were upregulated in the thrombus-free wall compared with the thrombus-covered wall. Immunohistochemistry confirmed the differential expression of MMP-9 but also localized MMP-9 to the interface between the thrombus and the underlying vessel wall. MMP-9 expression was colocalized with the presence of macrophages. Similar expression patterns were observed for urokinase plasminogen activator (uPA), uPA receptor, and plasminogen activator inhibitor-1. Gelatinase activity was detected in the same regions as MMP-9 protein expression, ie, within the thrombus-free wall and in the interface between the thrombus and the underlying wall.

CONCLUSIONS

The present work demonstrates that protease expression and activity differs within the aneurysm wall. The source and activity of the proteases responsible for the degradation of the thrombus-covered wall need to be further determined.