Differential display identification of 40 genes with altered expression in activated human smooth muscle cells. Local expression in atherosclerotic lesions of smags, smooth muscle activation-specific genes

LIM-only protein FHL2 attenuates vascular tissue factor activity, inhibits thrombus formation in mice and FHL2 genetic variation associates with human venous thrombosis

Bleeding disorders and thrombotic complications are major causes of morbidity and mortality with many cases being unexplained. Thrombus formation involves aberrant expression and activation of tissue factor (TF) in vascular endothelial and smooth muscle cells. Here, we sought to identify factors that modulate TF gene expression and activity in these vascular cells. The LIM-only protein FHL2 is a scaffolding protein that modulates signal transduction pathways with crucial functions in endothelial and smooth muscle cells. However, the role of FHL2 in TF regulation and thrombosis remains unexplored. Using a murine model of venous thrombosis in mesenteric vessels, we demonstrated that FHL2 deficiency results in exacerbated thrombus formation. Gain- and loss-of-function experiments revealed that FHL2 represses TF expression in endothelial and smooth muscle cells through inhibition of the transcription factors nuclear factor κB and activating protein-1. Furthermore, we observed that FHL2 interacts with the cytoplasmic tail of TF. In line with our in vivo observations, FHL2 decreases TF activity in endothelial and smooth muscle cells whereas FHL2 knockdown or deficiency results in enhanced TF activity. Finally, the FHL2 single nucleotide polymorphism rs4851770 was associated with the risk of venous thrombosis in a large population of venous thrombosis cases and control subjects from 12 studies (INVENT consortium). Altogether, our results highlight functional involvement of FHL2 in TF-mediated coagulation and identify FHL2 as a novel gene associated with venous thrombosis in humans.

Nuclear receptor 4A (NR4A) family - orphans no more

The orphan nuclear receptors NR4A1, NR4A2 and NR4A3 are immediate early genes induced by multiple stressors, and the NR4A receptors play an important role in maintaining cellular homeostasis and disease. There is increasing evidence for the role of these receptors in metabolic, cardiovascular and neurological functions and also in inflammation and inflammatory diseases and in immune functions and cancer. Despite the similarities of NR4A1, NR4A2 and NR4A3 and their interactions with common cis-genomic elements, they exhibit unique activities and cell-/tissue-specific functions. Although endogenous ligands for NR4A receptors have not been identified, there is increasing evidence that structurally-diverse synthetic molecules can directly interact with the ligand binding domain of NR4A1 and act as agonists or antagonists, and ligands for NR4A2 and NR4A3 have also been identified. Since NR4A receptors are key factors in multiple diseases, there are opportunities for the future development of NR4A ligands for clinical applications in treating multiple health problems including metabolic, neurologic and cardiovascular diseases, other inflammatory conditions, and cancer.

The orphan nuclear receptor Nur77 inhibits low shear stress-induced carotid artery remodeling in mice

Shear stress, particularly low and oscillatory shear stress, plays a critical pathophysiological role in vascular remodeling-related cardiovascular diseases. Growing evidence suggests that the orphan nuclear receptor Nur77 [also known as TR3 or nuclear receptor subfamily 4, group A, member 1 (NR4A1)] is expressed in diseased human vascular tissue and plays an important role in vascular physiology and pathology. In the present study, we used a mouse model of flow-dependent remodeling by partial ligation of the left common carotid artery (LCCA) to define the exact role of Nur77 in vascular remodeling induced by low shear stress. Following vascular remodeling, Nur77 was highly expressed in neointimal vascular smooth muscle cells (VSMCs) in the ligated carotid arteries. The reactive oxygen species (ROS) levels were elevated in the remodeled arteries in vivo and in primary rat VSMCs in vitro following stimulation with platelet-derived growth factor (PDGF). Further in vitro experiments revealed that Nur77 expression was rapidly increased in the VSMCs following stimulation with PDGF and H₂O₂, whereas treatment with N-acetyl cysteine (NAC, a ROS scavenger) reversed the increase in the protein level of Nur77 induced by H₂O₂. Moreover, Nur77 overexpression markedly inhibited the proliferation and migration of VSMCs, induced by PDGF. Finally, to determine the in vivo role of Nur77 in low shear stress-induced vascular remodeling, wild-type (WT) and Nur77-deficient mice were subjected to partial ligation of the LCCA. Four weeks following surgery, in the LCCAs of the Nur77-deficient mice, a significant increase in the intima-media area and carotid intima-media thickness was noted, as well as more severe elastin disruption and collagen deposition compared to the WT mice. Immunofluorescence staining revealed an increase in VSMC proliferation [determined by the expression of proliferating cell nuclear antigen (PCNA)] and matrix metalloproteinase 9 (MMP-9) production in the Nur77-deficient mice. There was no difference in the number of intimal apoptotic cells between the groups. Taken together, our results indicate that Nur77 may be a sensor of oxidative stress and an inhibitor of vascular remodeling induced by low shear stress. Nur77, as well as its downstream cell signals, may thus be a potential therapeutic target for the suppression of vascular remodeling.

Nuclear Receptors in atherosclerosis: a superfamily with many 'Goodfellas'

Nuclear Receptors form a superfamily of 48 transcription factors that exhibit a plethora of functions in steroid hormone signaling, regulation of metabolism, circadian rhythm and cellular differentiation. In this review, we describe our current knowledge on the role of Nuclear Receptors in atherosclerosis, which is a multifactorial disease of the vessel wall. Various cell types are involved in this chronic inflammatory pathology in which multiple cellular processes and numerous genes are dysregulated. Systemic risk factors for atherosclerosis are among others adverse blood lipid profiles, enhanced circulating cytokine levels, as well as increased blood pressure. Since many Nuclear Receptors modulate lipid profiles or regulate blood pressure they indirectly affect atherosclerosis. In the present review, we focus on the functional involvement of Nuclear Receptors within the atherosclerotic vessel wall, more specifically on their modulation of cellular functions in endothelial cells, smooth muscle cells and macrophages. Collectively, this overview shows that most of the Nuclear Receptors are athero-protective in atherosclerotic lesions.

Defining molecular and cellular responses after low and high linear energy transfer radiations to develop biomarkers of carcinogenic risk or therapeutic outcome

The variability in radiosensitivity across the human population is governed in part by genetic factors. The ability to predict therapeutic response, identify individuals at greatest risk for adverse clinical responses after therapeutic radiation doses, or identify individuals at high risk for carcinogenesis from environmental or medical radiation exposures has a medical and economic impact on both the individual and society at large. As radiotherapy incorporates particles, particularly particles larger than protons, into therapy, the need for such discriminators, (i.e., biomarkers) will become ever more important. Cellular assays for survival, DNA repair, or chromatid/chromosomal analysis have been used to identify at-risk individuals, but they are not clinically applicable. Newer approaches, such as genome-wide analysis of gene expression or single nucleotide polymorphisms and small copy number variations within chromosomes, are examples of technologies being applied to the discovery process. Gene expression analysis of primary or immortalized human cells suggests that there are distinct gene expression patterns associated with radiation exposure to both low and high linear energy transfer radiations and that those most radiosensitive are discernible by their basal gene expression patterns. However, because the genetic alterations that drive radio response may be subtle and cumulative, the need for large sample sizes of specific cell or tissue types is required. A systems biology approach will ultimately be necessary. Potential biomarkers from cell lines or animal models will require validation in a human setting where possible and before being considered as a credible biomarker some understanding of the molecular mechanism is necessary.

Dual function of Pin1 in NR4A nuclear receptor activation: enhanced activity of NR4As and increased Nur77 protein stability

Nur77, Nurr1 and NOR-1 form the NR4A subfamily of the nuclear receptor superfamily and have been shown to regulate various biological processes among which are cell survival and differentiation, apoptosis, inflammation and metabolism. These nuclear receptors have been proposed to act in a ligand-independent manner and we aim to gain insight in the regulation of NR4A activity. A yeast two-hybrid screen identified the peptidyl-prolyl isomerase Pin1 as a novel binding partner of NR4As, which was confirmed by co-immunoprecipitation. Pin1 enhances the transcriptional activity of all three NR4A nuclear receptors and increases protein stability of Nur77 through inhibition of its ubiquitination. Enhanced transcriptional activity of NR4As requires the WW-domain of Pin1 that interacts with the N-terminal transactivation domain and the DNA-binding domain of Nur77. Most remarkably, this enhanced activity is independent of Pin1 isomerase activity. A systematic mutation analysis of all 17 Ser/Thr-Pro-motifs in Nur77 revealed that Pin1 enhances protein stability of Nur77 in an isomerase-dependent manner by acting on phosphorylated Nur77 involving protein kinase CK2-mediated phosphorylation of the Ser(152)-Pro(153) motif in Nur77. Given the role of Nur77 in vascular disease and metabolism, this novel regulation mechanism provides perspectives to manipulate Nur77 activity to attenuate these processes.

NR4All in the vessel wall

A number of nuclear receptors are involved in maintenance of normal vessel wall physiology as well as in pathophysiological processes such as atherosclerosis, restenosis and remodelling. Recent studies revealed a previously unrecognized function of the NR4A subfamily of nuclear receptors as key regulatory proteins in vascular disease. The NR4A subfamily comprises the members Nur77, Nurr1 and NOR-1 and in the current review a comprehensive overview is given of the data supporting functional involvement of these nuclear receptors in three major cell types in vascular (patho)physiology; endothelial cells, smooth muscle cells and monocytes-macrophages.

The interferon stimulated gene 12 inactivates vasculoprotective functions of NR4A nuclear receptors

RATIONALE

Innate and adaptive immune responses alter numerous homeostatic processes that are controlled by nuclear hormone receptors. NR4A1 is a nuclear receptor that is induced in vascular pathologies, where it mediates protection.

OBJECTIVE

The underlying mechanisms that regulate the activity of NR4A1 during vascular injury are not clear. We therefore searched for modulators of NR4A1 function that are present during vascular inflammation.

METHODS AND RESULTS

We report that the protein encoded by interferon stimulated gene 12 (ISG12), is a novel interaction partner of NR4A1 that inhibits the transcriptional activities of NR4A1 by mediating its Crm1-dependent nuclear export. Using 2 models of vascular injury, we show that ISG12-deficient mice are protected from neointima formation. This effect is dependent on the presence of NR4A1, as mice deficient for both ISG12 and NR4A1 exhibit neointima formation similar to wild-type mice.

CONCLUSIONS

These findings identify a previously unrecognized feedback loop activated by interferons that inhibits the vasculoprotective functions of NR4A nuclear receptors, providing a potential new therapeutic target for interferon-driven pathologies.

FHL2 protein is a novel co-repressor of nuclear receptor Nur77

The three members of the NR4A orphan nuclear receptor subfamily Nur77, Nurr1, and NOR-1, regulate a variety of biological functions including vascular disease and metabolism. In this study, we identified Four and a half LIM domains protein-2 (FHL2) as a novel interacting protein of NR4A nuclear receptors by yeast two-hybrid screen and co-immunoprecipitation studies. Each of the four LIM domains of FHL2 can bind Nur77, and both the amino-terminal domain and the DNA binding domain of Nur77 are involved in the interaction between FHL2 and Nur77. FHL2 represses Nur77 transcriptional activity in a dose-dependent manner, and short hairpin RNA-mediated knockdown of FHL2 results in increased Nur77 transcriptional activity. ChIP experiments on the enolase3 promoter revealed that FHL2 inhibits the association of Nur77 with DNA. FHL2 is highly expressed in human endothelial and smooth muscle cells, but not in monocytes or macrophages. To substantiate functional involvement of FHL2 in smooth muscle cell physiology, we demonstrated that FHL2 overexpression increases the growth of these cells, whereas FHL2 knockdown results in reduced DNA synthesis. Collectively, these studies suggest that association of FHL2 with Nur77 plays a pivotal role in vascular disease.

Differential regulation of Nr4a subfamily nuclear receptors following mast cell activation

The biological function of the Nr4a subfamily of nuclear receptors is only partially understood. Here we show for the fist time that mast cell (MC) activation processes involve the regulation of Nr4a factors. Exposure of murine bone marrow-derived MCs (BMMCs) to live bacteria causes a robust and selective upregulation of all Nr4a members (Nr4a1-Nr4a3). In response to purified LPS, strong upregulation of Nr4a3, but not of Nr4a1 or Nr4a2 was seen. Nr4a3 expression was also induced after the activation of BMMCs by IgE receptor cross-linking. Moreover, Nr4a expression was induced in activated human MCs. As shown by Western blot analysis, Nr4a phosphorylation was induced by IgE receptor cross-linking and calcium ionophore stimulation of BMMCs and LAD2 cells, respectively. By using various inhibitors of signaling pathways, Nr4a3 induction in BMMCs was shown to be strongly dependent on Gö6976-sensitive kinases and partially dependent on the nuclear factor of activated T-cells (NFAT) pathway, while nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) inhibition failed to inhibit Nr4a3 expression in BMMCs. Together, these data reveal selective induction of Nr4a family members in activated MCs and implicate Nr4a family nuclear receptors in the regulation of MC function.

PDGF-induced proliferation of smooth muscular cells is related to the regulation of CREB phosphorylation and Nur77 expression

This study examined the relationship between PDGF-induced proliferation of vascular smooth muscle cells (VSMCs) and Nur77 expression and the effect of atorvastatin on VSMC proliferation and Nur77 in PDGF-treated VSMCs. Rat VSMCs were isolated and cultured. After incubation with atorvastatin or Nur77 siRNA, the cells were stimulated with PDGF and detected for BrdU incorporation to measure the proliferation of the VSMCs. Quantitative PCR and Western blotting were used to determine the Nur77 protein and the CREB phosphorylation level, to observe their relations with PDGF-induced VSMC proliferation. Our results showed that PDGF increased the BrdU incorporation in VSMCs, suggesting that it induced the proliferation of the cells. The VSMC proliferation was associated with increased Nur77 expression and elevated CREB phosphorylation. Atorvastatin inhibited the PDGF-induced VSMC proliferation, suppressed Nur77 expression. After silencing of Nur77 gene, the PDGF-induced VSMC proliferation was decreased. It was concluded that PDGF-induced VSMC proliferation was related to the Nur77 expression and CREB phosphorylation. Atorvastatin reduced the Nur77 expression and, at the same time, inhibited the VSMC proliferation.

Nuclear receptor Nur77 inhibits vascular outward remodelling and reduces macrophage accumulation and matrix metalloproteinase levels

AIMS

Structural adaptation of the vessel wall in response to sustained alterations in haemodynamic forces is known as vascular remodelling. Detailed knowledge on the mechanism underlying this vascular response is limited, and we aimed to study the function of Nur77 in smooth muscle cells (SMCs) in arterial remodelling.

METHODS AND RESULTS

Carotid artery ligation in mice results in flow-induced, outward remodelling of the contralateral carotid artery, and we observed enhanced Nur77 expression during this process. Transgenic mice that express Nur77 or its dominant-negative variant, denoted as 'DeltaTA' in arterial SMCs, were exposed to carotid artery ligation, and after 4 weeks pressure-diameter relationships were measured. Structural outward remodelling is inhibited in Nur77-transgenic mice when compared with wild-type and DeltaTA-transgenic mice. The key determinants of remodelling vascular tone and macrophage accumulation were studied. No difference in contractile and relaxant responses was detected in isolated aorta, carotid, and mesenteric artery segments between transgenic and wild-type mice. SMC-specific overexpression of Nur77 in transgenic mice reduced macrophage accumulation and repressed matrix metalloproteinase (MMP)1 and MMP9 expression at early time points. MMP2 protein expression was reduced in Nur77-transgenic mice, whereas in DeltaTA-transgenic mice MMP2 expression was increased.

CONCLUSION

Nur77 is induced during outward remodelling and inhibits this vascular adaptation in mice. Nur77-mediated inhibition of arterial remodelling involves a reduction in both macrophage accumulation and MMP expression levels.

NR4A Orphan Nuclear Receptors in Cardiovascular Biology

The NR4A orphan nuclear receptor subfamily is comprised of the highly homologous receptors Nur77 (NR4A1), Nurr1 (NR4A2), and NOR1 (NR4A3). These evolutionarily conserved and ancient receptors function as ligand-independent transcription factors that regulate the expression of overlapping target genes. As early response genes, the basal expression level of these receptors is low but rapidly induced as a result of changes in environmental cues. The transcriptional activity of these receptors is primarily regulated by gene induction and posttranslational modifications of the receptor including phosphorylation. NR4A receptors were initially identified in the brain and early functional studies suggested a role for these receptors in signal- and cell-specific stimulation of both apoptosis and proliferation. More recent studies have revealed much broader functions of these orphan receptors including the regulation of genes involved in cancer, metabolism, energy balance, atherosclerosis, and vascular remodeling. In this review, we will discuss our current understanding of the molecular biology of NR4A receptors and summarize recent studies suggesting an important role of these orphan receptors in vascular biology.

Tyk2 mediates effects of urokinase on human vascular smooth muscle cell growth

The urokinase (uPA)/uPA receptor (uPAR) system plays a role in the response of the vessel wall to injury, presumably by modulating vascular smooth muscle cell (VSMC) functional behaviour. The Jak/Stat signaling pathway has been implicated to mediate the uPA/uPAR-directed cell migration and proliferation in VSMC. We have therefore investigated the underlying molecular mechanisms, which remained not completely understood. In particular, we aimed at identification of the kinase involved in the signaling cascade leading to Stat1 phosphorylation by uPA and its impact on VSMC growth. We performed expression in VSMC of kinase-deficient mutant forms of the Janus kinases Jak1 and Tyk2 and used different cell culture models imitating the response to vascular injury. We provide evidence that Tyk2, but not Jak1, mediates uPA-induced Stat1 phosphorylation and VSMC growth inhibition and suggest a novel function for Tyk2 as an important modulator of the uPA-directed VSMC functional behaviour at the place of injury.

Differential display fingerprints: new approach to characterize smooth muscle cells and human coronary atherectomy tissues

AIM OF THE STUDY

Smooth muscle cells build up the normal media and stabilize atherosclerotic lesions whereas an inflammatory component is determinant for unstable angina. Smooth muscle cells, currently identified by alpha-actin, present a phenotypic heterogeneity and alpha-actin can be reduced in pathology. We tried to characterize vascular cell types, particularly smooth muscle cells, and coronary atherosclerotic tissues, by random genes expression fingerprints.

MATERIALS AND METHODS

Expression fingerprints (cDNA electrophoresis) were performed by differential display reverse transcriptase-polymerase chain reaction. Variability of fingerprints was studied for a panel of arterial muscle cell phenotypes and comparisons were made with fingerprints from other cell types (endothelial cells and macrophages). The technique was then applied to human coronary atherectomy samples compared to control human arterial (mammary) smooth muscle.

RESULTS

Arterial smooth muscle cells fingerprints were overall similar whatever the cell phenotype (native contractile, dedifferentiated in culture or epithelioid). Moreover, with two primer pairs, the muscular fingerprints markedly differed from the endothelial and the monocytic fingerprints. Application of differential display to coronary atherectomy samples was feasible. Interestingly, the pathological tissues exhibited either smooth muscle-like or smooth muscle-divergent fingerprints.

CONCLUSIONS

Smooth muscle cells and inflammatory cells exhibited distinct differential display fingerprint patterns. Thus, a simple expression profile of arbitrary genes provides a molecular bar code tool (pattern signature) useful to characterize vascular cell cultures or tissues. The present work proposes a method to analyze coronary atherectomy samples which estimates their whole quality, muscular versus non muscular (inflammatory), this is of interest for clinical research.

NR4A nuclear receptors in atherosclerosis and vein-graft disease

Nur77, Nurr1, and NOR-1 form the NR4A subfamily of the nuclear hormone receptor superfamily of transcription factors and have been described in the regulation of differentiation, proliferation, apoptosis, and survival of many different cell types. The expression of NR4A nuclear receptors in vascular pathologies has only recently been revealed, after which studies on the functional involvement of NR4A receptors in vascular disease were initiated. This review summarizes our current view on involvement of Nur77, Nurr1, and NOR-1 in atherosclerotic vascular disease and discusses NR4A function in vascular response to injury.

Influence of oxidized low density lipoprotein on the proliferation of human artery smooth muscle cells in vitro

The effects of oxidized low density lipoprotein (ox-LDL) on the proliferation of cultured human vascular smooth muscle cells (vSMC) were investigated in vitro. By using NaBr density gradient centrifugation, LDL was isolated and purified from human plasma. Ox-LDL was produced from LDL by being incubated with CuSO(4). ox-LDL was then added to the culture medium at different concentrations (35, 60, 85, 110, 135 and 160 microg/mL) for 7 days. The influence of ox-LDL on vSMC proliferation was observed in growth curve, mitosis index, and in situ determination of apoptosis. The data were analyzed with SPSS 10.0 software. The results showed that the ox-LDL produced in vitro had a good purity and optimal oxidative degree, which was similar to the intrinsic ox-LDL in atherosclerotic plaque. ox-LDL at a concentration of 35 microg/mL demonstrated the strongest proliferation inducement, and at a concentration of 135 microg/mL, ox-LDL could inhibit the growth of vSMC. ox-LDL at concentrations of 35 and 50 microg/mL presented powerful mitotic trigger, and with the increase of ox-LDL concentration, the mitotic index of vSMC was decreased gradually. ox-LDL at higher concentrations promoted more apoptotic vSMCs. ox-LDL at lower concentrations triggered proliferation of vSMCs, and at higher concentrations induced apoptosis in vSMCs. ox-LDL played a promotional role in the pathogenesis and development of atherosclerosis by affecting vSMC proliferation and apoptosis.

Activation of nuclear receptor Nur77 by 6-mercaptopurine protects against neointima formation

BACKGROUND

Restenosis is a common complication after percutaneous coronary interventions and is characterized by excessive proliferation of vascular smooth muscle cells (SMCs). We have shown that the nuclear receptor Nur77 protects against SMC-rich lesion formation, and it has been demonstrated that 6-mercaptopurine (6-MP) enhances Nur77 activity. We hypothesized that 6-MP inhibits neointima formation through activation of Nur77.

METHODS AND RESULTS

It is demonstrated that 6-MP increases Nur77 activity in cultured SMCs, which results in reduced [3H]thymidine incorporation, whereas Nur77 small interfering RNA knockdown partially restores DNA synthesis. Furthermore, we studied the effect of 6-MP in a murine model of cuff-induced neointima formation. Nur77 mRNA is upregulated in cuffed arteries, with optimal expression after 6 hours and elevated expression up to 7 days after vascular injury. Local perivascular delivery of 6-MP with a drug-eluting cuff significantly inhibits neointima formation in wild-type mice. Locally applied 6-MP does not affect inflammatory responses or apoptosis but inhibits expression of proliferating cell nuclear antigen and enhances protein levels of the cell-cycle inhibitor p27(Kip1) in the vessel wall. An even stronger inhibition of neointima formation in response to local 6-MP delivery was observed in transgenic mice that overexpressed Nur77. In contrast, 6-MP does not alter lesion formation in transgenic mice that overexpress a dominant-negative variant of Nur77 in arterial SMCs, which provides evidence for the involvement of Nur77-like factors.

CONCLUSIONS

Enhancement of the activity of Nur77 by 6-MP protects against excessive SMC proliferation and SMC-rich neointima formation. We propose that activation of the nuclear receptor Nur77 is a rational approach to treating in-stent restenosis.

Nuclear receptors Nur77, Nurr1, and NOR-1 expressed in atherosclerotic lesion macrophages reduce lipid loading and inflammatory responses

OBJECTIVE

Atherosclerosis is an inflammatory disease in which macrophage activation and lipid loading play a crucial role. In this study, we investigated expression and function of the NR4A nuclear receptor family, comprising Nur77 (NR4A1, TR3), Nurr1 (NR4A2), and NOR-1 (NR4A3) in human macrophages.

METHODS AND RESULTS

Nur77, Nurr1, and NOR-1 are expressed in early and advanced human atherosclerotic lesion macrophages primarily in areas of plaque activation/progression as detected by in situ-hybridization and immunohistochemistry. Protein expression localizes to the nucleus. Primary and THP-1 macrophages transiently express NR4A-factors in response to lipopolysaccharide and tumor necrosis factor alpha. Lentiviral overexpression of Nur77, Nurr1, or NOR-1 reduces expression and production of interleukin (IL)-1beta and IL-6 proinflammatory cytokines and IL-8, macrophage inflammatory protein-1alpha and -1beta and monocyte chemoattractant protein-1 chemokines. In addition, NR4A-factors reduce oxidized-low-density lipoprotein uptake, consistent with downregulation of scavenger receptor-A, CD36, and CD11b macrophage marker genes. Knockdown of Nur77 or NOR-1 with gene-specific lentiviral short-hairpin RNAs resulted in enhanced cytokine and chemokine synthesis, increased lipid loading, and augmented CD11b expression, demonstrating endogenous NR4A-factors to inhibit macrophage activation, foam-cell formation, and differentiation.

CONCLUSIONS

NR4A-factors are expressed in human atherosclerotic lesion macrophages and reduce human macrophage lipid loading and inflammatory responses, providing further evidence for a protective role of NR4A-factors in atherogenesis.

Changes in aortic endothelial gene expressions and relaxation responses following chronic short-term insulin treatment in diabetic rats

The purpose of the present study was to examine the relationship between the changes in the expressions of several mRNAs and changes in endothelial function in streptozotocin-induced diabetic and chronic short-term insulin-treated rats. Aortas from later-stage (10 week) diabetics, but not those from their insulin-treated counterparts, showed an impaired endothelial function. We found that the mRNA expressions for 30 genes were significantly upregulated, while those for 13 other genes were downregulated in aortic endothelial cells from diabetes. In later-stage diabetes, chronic insulin treatment ameliorated the endothelial dysfunction and normalized the expressions for 20 out of the 43 genes altered in diabetes. Further, 12 of the remaining 23 genes were altered by high-dose insulin treatment in the controls. In early-stage (1 week) diabetic aortas, which did not show impaired endothelial function, expression changes were shown by only 12/30 and 5/13 of the genes up- or downregulated, respectively, in later-stage diabetes. Thus, in the diabetic aortas endothelial gene expressions and function exhibited time-related changes, and several gene expressions and endothelial function were normalized by insulin treatment. The hyperinsulinemia caused by this treatment may oppose the alterations in some gene expressions and the endothelial proliferation (cell growth-related gene expressions) that occur in established diabetes.

Gene Profiling in Atherosclerosis Reveals a Key Role for Small Inducible Cytokines

Background— Pathological aspects of atherosclerosis are well described, but gene profiles during atherosclerotic plaque progression are largely unidentified.

Methods and Results— Microarray analysis was performed on mRNA of aortic arches of ApoE −/− mice fed normal chow (NC group) or Western-type diet (WD group) for 3, 4.5, and 6 months. Of 10 176 reporters, 387 were differentially (>2×) expressed in at least 1 group compared with a common reference (ApoE −/− , 3- month NC group). The number of differentially expressed genes increased during plaque progression. Time-related expression clustering and functional grouping of differentially expressed genes suggested important functions for genes involved in inflammation (especially the small inducible cytokines monocyte chemoattractant protein [MCP]-1, MCP-5, macrophage inflammatory protein [MIP]-1α, MIP-1β, MIP-2, and fractalkine) and matrix degradation (cathepsin-S, matrix metalloproteinase-2/12). Validation experiments focused on the gene cluster of small inducible cytokines. Real-time polymerase chain reaction revealed a plaque progression–dependent increase in mRNA levels of MCP-1, MCP-5, MIP-1α, and MIP-1β. ELISA for MCP-1 and MCP-5 showed similar results. Immunohistochemistry for MCP-1, MCP-5, and MIP-1α located their expression to plaque macrophages. An inhibiting antibody for MCP-1 and MCP-5 (11K2) was designed and administered to ApoE −/− mice for 12 weeks starting at the age of 5 or 17 weeks. 11K2 treatment reduced plaque area and macrophage and CD45 + cell content and increased collagen content, thereby inducing a stable plaque phenotype.

Conclusions— Gene profiling of atherosclerotic plaque progression in ApoE −/− mice revealed upregulation of the gene cluster of small inducible cytokines. Further expression and in vivo validation studies showed that this gene cluster mediates plaque progression and stability.

Activin and TR3 orphan receptor: Two 'atheroprotective' genes as evidenced in dedicated mouse models

1. Atherosclerosis is a multifactorial, inflammatory disease of the arterial vessel wall that is promoted by various well-defined risk factors. Although numerous genes, expressed in different vascular and inflammatory cells, have been implicated in this disease, it is widely appreciated that most of the genes and gene products vital for initiation and progression of atherosclerosis are unknown. 2. We follow two strategies in an attempt to make up for the void of essential knowledge. First, we study candidate genes that have not been implied in human atherosclerosis before, notably the differentiation factor activin A. 3. Second, we performed a genome-wide search by differential display reverse transcription-polymerase chain reaction. This study indicated potential involvement of the TR3 orphan receptor transcription factor in smooth muscle cell (SMC) (patho)physiology. 4. To reveal functional involvement of these proteins in SMC during atherosclerosis, we performed experiments with mouse models, adjusted either to the characteristics of a secreted protein or to that of an intracellular transcription factor. 5. The secreted protein activin A was studied in mice infected systemically with recombinant adenoviral vehicles, resulting in predominant hepatic expression and subsequent high protein levels in the circulation. 6. To study the role of TR3 in atherosclerosis, we generated transgenic mice in which promoter sequences were applied that direct expression of the transgenes to SMC of the arterial tree. 7. Two approaches were taken to induce the formation of SMC-rich lesions: (i) activation of femoral artery SMC by placement of a loosely fitting cuff; and (ii) ligation of the carotid artery. 8. The aim of the present review is to illustrate the different approaches that can be taken to assess the potential relevance of genes in atherosclerosis in carefully selected mouse models. 9. Based on the results described, we propose that both activin A and TR3 prevent excessive SMC proliferation.

Vasculin, a novel vascular protein differentially expressed in human atherogenesis

Recent suppressive subtractive hybridization analysis on human atherosclerotic plaque-derived RNA revealed genes upregulated in plaques with a thrombus versus stable plaques. Clone SSH6, containing part of a putative open reading frame of an unknown protein, was further investigated. Full-length cDNA, coding for a 473-amino acid (aa) protein, was identified in a vascular smooth muscle cell (SMC) cDNA library. Bioinformatics suggested the presence of multiple SSH6 variants due to alternative splicing of exon 3. Multiple-tissue Northern blot analysis demonstrated a differential expression pattern of these variants, as a ubiquitously expressed SSH6 mRNA missing exon 3, was detected apart from a putative vascular SMC-specific form containing exon 3. Western blot analysis indicated a ubiquitous 35-kDa protein (SSH6-beta), in addition to a 45-kDa protein (vasculin), detected in the vascular wall and in plasma. Analysis of arteries displaying various stages of atherosclerosis indicated that the vasculin/SSH6-beta ratio increases throughout atherogenesis. Immunohistochemical analysis demonstrated cytoplasmic expression of SSH6 gene products in macrophages, endothelial cells, and SMCs. In summary, we identified a novel mRNA/protein, vasculin, in the arterial wall and plasma. The regulated expression of vasculin in plaques suggests a role in atherogenesis. Moreover, its presence in plasma opens perspectives for vasculin as a marker for atherosclerosis.

Arterial smooth muscle cell heterogeneity: implications for atherosclerosis and restenosis development

During atheromatous plaque formation or restenosis after angioplasty, smooth muscle cells (SMCs) migrate from the media toward the intima, where they proliferate and undergo phenotypic changes. The mechanisms that regulate these phenomena and, in particular, the phenotypic modulation of intimal SMCs have been the subject of numerous studies and much debate during recent years. One view is that any SMCs present in the media could undergo phenotypic modulation. Alternatively, the seminal observation of Benditt and Benditt that human atheromatous plaques have the features of a monoclonal or an oligoclonal lesion has led to the hypothesis that a predisposed, medial SMC subpopulation could play a crucial role in the production of intimal thickening. The presence of a distinct SMC population in the arterial wall implies that under normal conditions, SMCs are phenotypically heterogeneous. The concept of SMC heterogeneity is gaining wider acceptance, as shown by the increasing number of publications on this subject. In this review, we discuss the in vitro studies that demonstrate the presence of distinct SMC subpopulations in arteries of various species, including humans. Their specific features and their regulation will be highlighted. Finally, the relevance of an atheroma-prone phenotype to intimal thickening formation will be discussed.

Gene expression profiling of resting and activated vascular smooth muscle cells by serial analysis of gene expression and clustering analysis

Migration and proliferation of vascular smooth muscle cells (SMCs) are key events in atherosclerosis. However, little is known about alterations in gene expression upon transition of the quiescent, contractile SMC to the proliferative SMC. We performed serial analysis of gene expression (SAGE) of cultured, human SMCs, either grown under resting circumstances or activated with an atherogenic stimulus. Analysis of tags, representing 47,209 and 47,259 mRNAs from a library of resting and activated SMCs, respectively, identified 105 tags induced and 52 tags repressed greater than fivefold. To evaluate the relevance in SMC biology of unmatched, regulated tags, we performed hierarchical clustering analysis, based on their expression profiles in public SAGE databases, and clustered these novel genes in distinct groups. The regulation in SMCs was confirmed by Northern blotting for representative genes of these groups. Plasminogen activator inhibitor-2 has not been associated with atherosclerosis before and was localized to atherosclerotic lesions.

Direct binding of Nur77/NAK-1 to the plasminogen activator inhibitor 1 (PAI-1) promoter regulates TNF alpha -induced PAI-1 expression

Plasminogen activator inhibitor 1 (PAI-1) is the main fibrinolysis inhibitor, and high plasma levels are associated with an increased risk for vascular diseases. Inflammatory cytokines regulate PAI-1 through a hitherto unclear mechanism. Using reporter gene analysis, we could identify a region in the PAI-1 promoter that contributes to basal expression as well as to tumor necrosis factor alpha (TNFalpha) induction of PAI-1 in endothelial cells. Using this region as bait in a genetic screen, we could identify Nur77 (NAK-1, TR3, NR4A1) as an inducible DNA-binding protein that binds specifically to the PAI-1 promoter. Nur77 drives transcription of PAI-1 through direct binding to an NGFI-B responsive element (NBRE), indicating monomeric binding and a ligand-independent mechanism. Nur77, itself, is transcriptionally up-regulated by TNFalpha. High expression levels of Nur77 and its colocalization with PAI-1 in atherosclerotic tissues indicate that the described mechanism for PAI-1 regulation may also be operative in vivo.

Protective function of transcription factor TR3 orphan receptor in atherogenesis: decreased lesion formation in carotid artery ligation model in TR3 transgenic mice

BACKGROUND

Smooth muscle cells (SMCs) play a key role in intimal thickening in atherosclerosis and restenosis. The precise signaling pathways by which the proliferation of SMCs is regulated are largely unknown. The TR3 orphan receptor, the mitogen-induced nuclear orphan receptor (MINOR), and the nuclear receptor of T cells (NOT) are a subfamily of transcription factors belonging to the nuclear receptor superfamily and are induced in activated SMCs. In this study, we investigated the role of these transcription factors in SMC proliferation in atherogenesis.

METHODS AND RESULTS

Multiple human vascular specimens at distinct stages of atherosclerosis (lesion types II to V by American Heart Association classification) derived from 14 different individuals were studied for expression of these transcription factors. We observed expression of TR3, MINOR, and NOT in neointimal SMCs, whereas no expression was detected in medial SMCs. Adenovirus-mediated expression of a dominant-negative variant of TR3, which suppresses the transcriptional activity of each subfamily member, increases DNA synthesis and decreases p27(Kip1) protein expression in cultured SMCs. We generated transgenic mice that express this dominant-negative variant or full-length TR3 under control of a vascular SMC-specific promoter. Carotid artery ligation of transgenic mice that express the dominant-negative variant of TR3 in arterial SMCs, compared with lesions formed in wild-type mice, results in a 3-fold increase in neointimal formation, whereas neointimal formation is inhibited 5-fold in transgenic mice expressing full-length TR3.

CONCLUSIONS

Our results reveal that TR3 and possibly other members of this transcription factor subfamily inhibit vascular lesion formation. These transcription factors could serve as novel targets in the treatment of vascular disease.

Prolonged fluid shear stress induces a distinct set of endothelial cell genes, most specifically lung Krüppel-like factor (KLF2)

The endothelium expresses a large repertoire of genes under apparent transcriptional control of biomechanical forces, many of which are neither cell-type nor flow specific. We set out to identify genes that are uniquely flow responsive in human vascular endothelial cells. Transcriptional profiling using commercial DNA microarrays identified 12 of 18 000 genes that were modulated at least 5-fold after 24 hours of steady laminar flow (25 dyne/cm(2)). After a 7-day exposure to unidirectional pulsatile flow (19 +/- 12 dyne/cm(2)), only 3 of 12 remained elevated at least 5-fold. A custom microarray of ~300 vascular cell-related gene fragments was constructed, and expression analysis revealed that many flow-induced genes are also induced by at least one of the following agents: tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), transforming growth factor-beta, vascular endothelial growth factor, or thrombin, indicating a more general role in adaptive or stress responses. Most flow-induced genes were also induced by TNF-alpha but not IL-1beta, suggesting the involvement of reactive oxygen species. A limited panel of genes that are unique for flow-exposed cultures was identified, including lung Krüppel-like factor (LKLF/KLF2) and cytochrome P450 1B1 (CYP1B1). In marked contrast, both these genes were substantially repressed by TNF-alpha. LKLF but not CYP1B1 mRNA was detected exclusively in the vascular endothelium of healthy human aorta by in situ hybridization and appeared to be flow regulated. To date LKLF is the first endothelial transcription factor that is uniquely induced by flow and might therefore be at the molecular basis of the physiological healthy, flow-exposed state of the endothelial cell.

Human sprouty 4, a new ras antagonist on 5q31, interacts with the dual specificity kinase TESK1

The Drosophila melanogaster protein sprouty is induced upon fibroblast growth factor (FGF)- and epidermal growth factor (EGF)-receptor tyrosine kinase activation and acts as an inhibitor of the ras/MAP kinase pathway downstream of these receptors. By differential display RT-PCR of activated vs. resting umbilical artery smooth muscle cells (SMCs) we detected a new human sprouty gene, which we designated human sprouty 4 (hspry4) based on its homology with murine sprouty 4. Hspry4 is widely expressed and Northern blots indicate that different isoforms of hspry4 are induced upon cellular activation. The hspry4 gene maps to 5q31.3. It encodes a protein of 322 amino acids, which, in support of a modulating role in signal transduction, contains a prototypic cysteine-rich region, three, potentially Src homology 3 (SH3) binding, proline-rich regions and a PEST sequence. This new sprouty orthologue can suppress the insulin- and EGF-receptor transduced MAP kinase signaling pathway, but fails to inhibit MAP kinase activation by constitutively active V12 ras. Hspry4 appears to impair the formation of active GTP-ras and exert its activity at the level of wild-type ras or upstream thereof. In a yeast two-hybrid screen, using hspry4 as bait, testicular protein kinase 1 (TESK1) was identified from a human fetal liver cDNA library as a partner of hspry4. The hspry4-TESK1 interaction was confirmed by coimmunoprecipitation experiments and increases by growth factor stimulation. The two proteins colocalize in apparent cytoplasmic vesicles and do not show substantial translocation to the plasma membrane upon receptor tyrosine kinase stimulation.

Trends in genomic analysis of the cardiovascular system

OBJECTIVE

To evaluate the opportunities afforded cardiovascular medicine by the comprehensive and integrative approaches of genomics in cellular physiology. We present a meta-analysis of recently reported results obtained by means of high-throughput technologies (complementary DNA and oligonucleotide arrays, serial analysis of gene expression [SAGE]), as well as more traditional molecular biology approaches (real-time polymerase chain reaction, differential display, and others).

DATA SOURCES

Newly published articles identified on PubMed and additional data provided by authors on-line (where available).

CONCLUSIONS

The impact of genomic analysis on cardiovascular research is already visible. New genes of cardiovascular interest have been discovered, while a number of known genes have been found to be changed in unexpected contexts. The patterns in the variation of expression of many genes correlate well with the models currently used to explain the pathogenesis of cardiovascular diseases. Much more work has yet to be done, however, for the full exploitation of the immense informative potential still dormant in the genomic technologies.

Pathophysiology of plaque instability: insights at the genomic level

Atherosclerosis and plaque rupture represent complex "traits" of unknown cause that involve multiple genes and their variants. Novel genomic technologies provide us with the tools that will allow for the identification of groupings of genes that determine either susceptibility or resistance relative to the development of atherosclerosis and its thromboembolic complications. This information may, in turn, lead to a clearer understanding of the cause and risk for atherosclerosis. Diagnostic tools, as well as preventive and therapeutic strategies, will be derived from such heightened understanding of the disease process. With this chapter, we have presented the current state of knowledge of atherosclerosis genomics.

Identification of genes potentially involved in rupture of human atherosclerotic plaques

Although rupture of an atherosclerotic plaque is the major cause of acute vascular occlusion, the exact molecular mechanisms underlying this process are still poorly understood. In this study, we used suppression subtractive hybridization to make an inventory of genes that are differentially expressed in whole-mount human stable and ruptured plaques. Two libraries were generated, one containing 3000 clones upregulated and one containing 2000 clones downregulated in ruptured plaques. Macroarray analysis of 500 randomly chosen clones showed differential expression of 45 clones. Among the 25 clones that showed at least a 2-fold difference in expression was the gene of perilipin, upregulated in ruptured plaques, and the genes coding for fibronectin and immunoglobulin lambda chain, which were downregulated in ruptured plaques. Reverse transcriptase-polymerase chain reaction analysis on 10 individual ruptured and 10 individual stable plaques showed a striking consistency of expression for the clones SSH6, present in 8 ruptured and 2 stable plaques, and perilipin, expressed in 8 ruptured plaques and completely absent in stable plaques. Localization studies of both perilipin mRNA and protein revealed expression in cells surrounding the cholesterol clefts and in foam cells of ruptured atherosclerotic plaques. No expression was observed in nondiseased artery, and only a few cells in the shoulder region of stable plaques tested positive for perilipin. In conclusion, this study shows that it is possible to identify genes that are differentially expressed in whole-mount stable or ruptured atherosclerotic plaques. This approach may yield several potential regulators of plaque destabilization.

From symptomatic treatments to causative therapy?

The search for genes that predispose individuals to develop common chronic diseases such as asthma, diabetes and Alzheimer's promises to give insights into their molecular pathogenesis. This will lead to the development of therapies that modulate the pathology, rather than the physiology of these diseases. As academia and the pharmaceutical industry increasingly focus on this challenge, the genetic dissection of Alzheimer's is spearheading attempts to shift the therapeutic paradigm away from symptomatic to curative treatments.