Neuron-derived orphan receptor-1 (NOR-1) is induced by thrombin and mediates vascular endothelial cell growth

Upregulation of NOR-1 in calcified human vascular tissues: impact on osteogenic differentiation and calcification

Cardiovascular calcification is a significant public health issue whose pathophysiology is not fully understood. NOR-1 regulates critical processes in cardiovascular remodeling, but its contribution to ectopic calcification is unknown. NOR-1 was overexpressed in human calcific aortic valves and calcified atherosclerotic lesions colocalizing with RUNX2, a factor essential for osteochondrogenic differentiation and calcification. NOR-1 and osteogenic markers were upregulated in calcifying human valvular interstitial cells (VICs) and human vascular smooth muscle cells (VSMCs). Gain- and loss-of-function approaches demonstrated that NOR-1 negatively modulates the expression of osteogenic genes relevant for the osteogenic transdifferentiation (RUNX2, IL-6, BMP2, and ALPL) and calcification of VICs. VSMCs from transgenic mice overexpressing NOR-1 in these cells (TgNOR-1VSMC) expressed lower basal levels of osteogenic genes (IL-6, BMP2, ALPL, OPN) than cells from WT littermates, and their upregulation by a high-phosphate osteogenic medium (OM) was completely prevented by NOR-1 transgenesis. Consistently, this was associated with a dramatic reduction in the calcification of both transgenic VSMCs and aortic rings from TgNOR-1VSMC mice exposed to OM. Atherosclerosis and calcification were induce in mice by the administration of AAV-PCSK9D374Y and a high-fat/high-cholesterol diet. Challenged-TgNOR-1VSMC mice exhibited decreased vascular expression of osteogenic markers, and both less atherosclerotic burden (assessed in whole aorta and lesion size in aortic arch and brachiocephalic artery) and less vascular calcification (assessed either by near-infrared fluorescence imaging or histological analysis) than WT mice. Our data indicate that NOR-1 negatively modulates the expression of genes critically involved in the osteogenic differentiation of VICs and VSMCs, thereby restraining ectopic cardiovascular calcification.

SOX17 is a Critical Factor in Maintaining Endothelial Function in Pulmonary Hypertension by an Exosome-Mediated Autocrine Manner

Endothelial dysfunction is considered a predominant driver for pulmonary vascular remodeling in pulmonary hypertension (PH). SOX17, a key regulator of vascular homoeostasis, has been found to harbor mutations in PH patients, which are associated with PH susceptibility. Here, this study explores whether SOX17 mediates the autocrine activity of pulmonary artery ECs to maintain endothelial function and vascular homeostasis in PH and its underlying mechanism. It is found that SOX17 expression is downregulated in the endothelium of remodeled pulmonary arteries in IPH patients and SU5416/hypoxia (Su/hypo)-induced PH mice as well as dysfunctional HPAECs. Endothelial knockdown of SOX17 accelerates the progression of Su/hypo-induced PH in mice. SOX17 overexpression in the pulmonary endothelium of mice attenuates Su/hypo-induced PH. SOX17-associated exosomes block the proliferation, apoptosis, and inflammation of HPAECs, preventing pulmonary arterial remodeling and Su/hypo-induced PH. Mechanistic analyses demonstrates that overexpressing SOX17 promotes the exosome-mediated release of miR-224-5p and miR-361-3p, which are internalized by injured HPAECs in an autocrine manner, ultimately repressing the upregulation of NR4A3 and PCSK9 genes and improving endothelial function. These results suggest that SOX17 is a key gene in maintaining endothelial function and vascular homeostasis in PH through regulating exosomal miRNAs in an autocrine manner.

Comprehensive insights into the function and molecular and pharmacological regulation of neuron-derived orphan receptor 1, an orphan receptor

Neuron-derived orphan receptor 1 (NOR1), also called nuclear receptor subfamily 4 group A member 3 (NR4A3), is a nuclear receptor belonging to the NR4A family. Since no endogenous ligand has been identified to date, NOR1 is also referred to as an orphan receptor. NOR1 is expressed in a variety of cells and tissues, including neurons, vascular smooth muscle cells, T lymphocytes, dendritic cells, tumor cells, heart, liver, and pancreas. Because NOR1 was first identified in apoptotic neurons, it is functionally associated with the regulation of cell migration and the growth of neuronal synapses. In-depth studies have shown that NOR1 can be edited by the immediate early gene and functions as a transcription factor. NOR1 has been shown to be rapidly induced by a number of stimulants including growth factors, fatty acids, and neurotransmitters. Elevated NOR1 levels may be involved in a number of pathophysiological processes. These include regulation of cellular apoptosis and regeneration, neuron formation, contextual fearing memory, inflammation, vascular smooth muscle proliferation, insulin secretion, and tumor development, whereby NOR1 mediates the pathogenesis of numerous diseases such as cerebral ischemia, depression, post-traumatic stress disorder, atherosclerosis, abdominal aortic aneurysm, cardiac hypertrophy, diabetes, osteoarthritis, rheumatoid arthritis, and cancer. However, to date, comprehensive insights into the function of NOR1 are not available in sources published online. In this review, we provide a brief overview of the function and molecular and pharmacological regulation of NOR1 in various pathological or physiological conditions to advance the development of NOR1 as a novel target for disease treatment.

Nuclear receptor NOR-1 (Neuron-derived Orphan Receptor-1) in pathological vascular remodelling and vascular remodelling

Vascular cells and their interaction with inflammatory cells and the immune system play a key role in pathological vascular remodeling. A large number of genes and proteins regulated in a coordinated manner by a small number of transcription factors are involved in this process. In recent years, research on a small subfamily of transcription factors, the NR4A subfamily, has had a major impact on our understanding of vascular biology. The NR4A1 (Nur77), NR4A2 (Nurr1) and NR4A3 (NOR-1) receptors are products of early response genes whose expression is induced by multiple pathophysiological and physical stimuli. Their wide distribution in different tissues and cells places them in the control of numerous processes such as cell differentiation, proliferation, survival and apoptosis, as well as inflammation and the metabolism of lipids and carbohydrates. This review analyzes the role of these receptors, particularly NOR-1, in pathological vascular remodeling associated with atherosclerosis, abdominal aortic aneurysm and pulmonary arterial hypertension.

MiR-34a-3p suppresses pulmonary vascular proliferation in acute pulmonary embolism rat by targeting DUSP1

BACKGROUND

Acute pulmonary embolism (APE) is a prevalent reason of cardiovascular morbidity and mortality. Recent studies have underscored the positive effects of microRNAs (miRNAs) on many diseases. The present study aimed to identify the critical miRNA with differential expressions and explore its role in APE.

METHODS

The critical miRNA with its target gene was screened by bioinformatics analysis. Their binding relationship was analyzed by TargetScan, Dual-luciferase reporter and RNA pull-down assays. A rat model of APE was established by self-blood coagulum. Human pulmonary artery smooth muscle cells (PASMCs) were exposed to platelet-derived growth factor (PDGF-BB) for excessive proliferation, and transfected with miR-34a-3p mimic. Mean pulmonary arterial pressure (mPAP) of rat was measured, and the pulmonary tissues were used for the pathological observation by Hematoxylin-Eosin (H&E) staining. Cell viability and proliferation were detected by Cell Counting Kit-8 (CCK-8) and EdU assays. The expressions of miR-34a-3p with its target genes (including dual-specificity phosphatase-1 (DUSP1)), neuron-derived orphan receptor-1 (NOR-1) and proliferating cell nuclear antigen (PCNA) were determined by quantitative reverse transcription polymerase chain reaction (RT-qPCR) or/and Western blot.

RESULTS

MiR-34a-3p expression was down-regulated in APE patients, which attenuated the increment of mPAP and thickening of the pulmonary arterial walls in APE rats, accompanied with regulation of NOR-1 and PCNA levels. MiR-34a-3p suppressed DUSP1 expression by directly binding to its 3'-untranslated region (UTR), and attenuated cell viability, proliferation, and the expressions of NOR-1 and PCNA in PDGF-BB-induced PASMCs by inhibiting DUSP1 expression.

CONCLUSION

Up-regulated miR-34a-3p negatively regulates DUSP1 expression to inhibit PASMC proliferation, which, thus, may act on APE treatment by negatively regulating pulmonary vascular proliferation.

NR4A3: A Key Nuclear Receptor in Vascular Biology, Cardiovascular Remodeling, and Beyond

The mechanisms committed in the activation and response of vascular and inflammatory immune cells play a major role in tissue remodeling in cardiovascular diseases (CVDs) such as atherosclerosis, pulmonary arterial hypertension, and abdominal aortic aneurysm. Cardiovascular remodeling entails interrelated cellular processes (proliferation, survival/apoptosis, inflammation, extracellular matrix (ECM) synthesis/degradation, redox homeostasis, etc.) coordinately regulated by a reduced number of transcription factors. Nuclear receptors of the subfamily 4 group A (NR4A) have recently emerged as key master genes in multiple cellular processes and vital functions of different organs, and have been involved in a variety of high-incidence human pathologies including atherosclerosis and other CVDs. This paper reviews the major findings involving NR4A3 (Neuron-derived Orphan Receptor 1, NOR-1) in the cardiovascular remodeling operating in these diseases.

SMARCB1 Promotes Ubiquitination and Degradation of NR4A3 via Direct Interaction Driven by ROS in Vascular Endothelial Cell Injury

Nuclear receptor subfamily 4 group A member 3 (NR4A3) protects the vascular endothelial cell (VEC) against hypoxia stress, whose expression is primarily reported to be governed at a transcriptional level. However, the regulation of NR4A3 in the protein level is largely unknown. Here, we report that NR4A3 protein abundance is decreased immensely in VEC injury induced by reoxygenation after oxygen-glucose deprivation (OGD-R), which is significantly blocked by the administration of the antioxidative steroid TRIOL. Moreover, the notable improvement of NR4A3 and the alleviation of pulmonary endothelial barrier hyperpermeability induced by acute hypobaric hypoxia in cynomolgus monkeys are also observed after TRIOL administration. The overproduction of reactive oxygen species (ROS) decreases NR4A3 protein abundance in VEC under OGD-R condition, which is reversed by TRIOL and N-acetylcysteine (NAC). TRIOL dose-dependently increases the NR4A3 protein level by inhibiting ubiquitination and ubiquitin proteasome system- (UPS-) mediated degradation rather than promoting its transcription. Using yeast two-hybrid screening, we further identify the interaction between NR4A3 and SWI/SNF-related matrix-associated actin-dependent regulator of chromatin subfamily B member 1 (SMARCB1), and the DNA-binding domain of NR4A3 is required for this interaction. Knockdown of SMARCB1 reduces ubiquitination and degradation of NR4A3, suggesting the proubiquitylation effect of this interaction which is enhanced by ROS in VEC injury induced by OGD-R. In summary, our study here for the first time reveals a posttranslational regulation in SMARCB1-mediated NR4A3 protein degradation which is driven by ROS, providing further understanding of the impaired regulation of NR4A3-mediated prosurvival pathways under pathological condition in VEC.

Augmentation of Nr4a3 and Suppression of Fshb Expression in the Pituitary Gland of Female Annexin A5 Null Mouse

GnRH enhances the expression of annexin A5 (ANXA5) in pituitary gonadotropes, and ANXA5 enhances gonadotropin secretion. However, the impact of ANXA5 regulation on the expression of pituitary hormone genes remains unclear. Here, using quantitative PCR, we demonstrated that ANXA5 deficiency in female mice reduced the expression of Fshb and Gh in their pituitary glands. Transcriptome analysis confirmed a specific increase in Nr4a3 mRNA expression in addition to lower levels of Fshb expression in ANXA5-deficient female pituitary glands. This gene was then found to be a GnRH-inducible immediate early gene, and its increased expression caused protein to accumulate in the nucleus after administration of a GnRH agonist in LβT2 cells, which are an in vitro pituitary gonadotrope model. The increase in ANXA5 protein levels in LβT2 cells clearly suppressed Nr4a3 expression. siRNA-mediated inhibition of Nr4a3 expression increased Fshb expression. The results revealed that GnRH stimulates Nr4a3 and Anxa5 sequentially. NR4A3 suppression of Fshb may be necessary for later massive secretion of FSH by GnRH in gonadotropes, and Nr4a3 would be negatively regulated by ANXA5 to increase FSH secretion.

Neuron-derived orphan receptor-1 modulates cardiac gene expression and exacerbates angiotensin II-induced cardiac hypertrophy

Hypertensive cardiac hypertrophy (HCH) is a common cause of heart failure (HF), a major public health problem worldwide. However, the molecular bases of HCH have not been completely elucidated. Neuron-derived orphan receptor-1 (NOR-1) is a nuclear receptor whose role in cardiac remodelling is poorly understood. The aim of the present study was to generate a transgenic mouse over-expressing NOR-1 in the heart (TgNOR-1) and assess the impact of this gain-of-function on HCH. The CAG promoter-driven transgenesis led to viable animals that over-expressed NOR-1 in the heart, mainly in cardiomyocytes and also in cardiofibroblasts. Cardiomyocytes from TgNOR-1 exhibited an enhanced cell surface area and myosin heavy chain 7 (Myh7)/Myh6 expression ratio, and increased cell shortening elicited by electric field stimulation. TgNOR-1 cardiofibroblasts expressed higher levels of myofibroblast markers than wild-type (WT) cells (α 1 skeletal muscle actin (Acta1), transgelin (Sm22α)) and were more prone to synthesise collagen and migrate. TgNOR-1 mice experienced an age-associated remodelling of the left ventricle (LV). Angiotensin II (AngII) induced the cardiac expression of NOR-1, and NOR-1 transgenesis exacerbated AngII-induced cardiac hypertrophy and fibrosis. This effect was associated with the up-regulation of hypertrophic (brain natriuretic peptide (Bnp), Acta1 and Myh7) and fibrotic markers (collagen type I α 1 chain (Col1a1), Pai-1 and lysyl oxidase-like 2 (Loxl2)). NOR-1 transgenesis up-regulated two key genes involved in cardiac hypertrophy (Myh7, encoding for β-myosin heavy chain (β-MHC)) and fibrosis (Loxl2, encoding for the extracellular matrix (ECM) modifying enzyme, Loxl2). Interestigly, in transient transfection assays, NOR-1 drove the transcription of Myh7 and Loxl2 promoters. Our findings suggest that NOR-1 is involved in the transcriptional programme leading to HCH.

miR‑106b‑5p modulates acute pulmonary embolism via NOR1 in pulmonary artery smooth muscle cells

Acute pulmonary embolism (APE) is a common cause of acute cardiovascular failure and has a high morbidity and mortality rate. Inhibiting the excessive proliferation and migration of pulmonary artery smooth muscle cells (PASMCs) is a potential treatment strategy following an APE. Various microRNAs (miRNAs/miRs) have been shown to regulate cell proliferation, apoptosis and other physiological processes. However, the specific mechanisms underlying the action of multiple miRNAs are still not understood in APE. In the present study, the role of miR‑106b‑5p on APE was demonstrated in platelet‑derived growth factor (PDGF)‑induced PASMCs in vitro and in an APE‑mouse model in vivo. The results showed that miR‑106b‑5p expression was downregulated in PDGF‑induced PASMCs and APE mice, and NOR1 levels were upregulated. Proliferating cell nuclear antigen (PCNA) expression levels in cells and proliferation of PASMCs proliferation and migration were reduced following treatment with miR‑106b‑5p agomiR, and increased following treatment with miR‑106b‑5p antagomiR. miR‑106b‑5p targeted the 3' untranslated region of NOR‑1 mRNA and reduced NOR1 expression. NOR1 overexpression reversed the effects of miR‑106‑5p on PDGF‑induced PASMCs. The functional roles of miR‑106b‑5p in PDGF‑induced PASMCs and an APE mouse‑model, and the underlying molecular mechanisms were evaluated. AgomiR‑106b‑5p improved APE‑induced mortality and pulmonary vascular proliferation in mice. These data suggest that miR‑106‑5p is a novel regulator of proliferation of PASMCs and of pulmonary vascular remodeling through PDGF‑induced PASMCs in an APE mouse model via targeting NOR1. These results expand the understanding of the pathogenesis underlying APE and highlight potential novel therapeutic targets.

Endothelial HNF4α potentiates angiogenic dysfunction via enhancement of vascular endothelial growth factor resistance in T2DM

Although both hyperprocoagulant status, characterized by elevated thrombin levels, and vascular endothelial growth factor (VEGF) resistance, marked by attenuated expression of VEGFR2 (also called FLK1 or KDR), are known to contribute importantly to an increased risk of vascular events in diabetes mellitus type 2 (T2DM), it remains obscure whether these two biological events regulate angiogenic response in a coordinated manner. We show here that endothelial expression of hepatocyte nuclear factor 4α (HNF4α) was significantly upregulated in rodents and humans with T2DM, and HNF4α upregulation by thrombin was dependent on activation of multiple pathways, including protein kinase B, c-Jun N-terminal kinase, p38, oxidative stress, protein kinase C, and AMPK (5'-adenosine monophosphate (AMP)-activated protein kinase). Functionally, HNF4α inhibited VEGF-mediated endothelial proliferation and migration, and blunted VEGF-stimulated in vitro angiogenesis, thus rendering endothelial cells unresponsive to established angiogenic VEGF stimulation. Mechanistically, HNF4α potentiated the endothelial VEGF resistance through the direct transcriptional repression of FLK1 gene. From a therapeutic standpoint, overexpression of the exogenous FLK1 successfully rescued HNF4α-inhibited angiogenic response to VEGF and potentiated VEGF-stimulated in vitro tube formation. Considering a strong association between HNF4A deregulation and increased risk of T2DM, our findings suggest that HNF4α may act as a critical converging point linking hyperprocoagulant condition to VEGF resistance in diabetic ECs, and repression of FLK1 expression by thrombin-induced HNF4α mediates, at least partially, the vascular dysfunction caused by T2DM.

The nuclear receptor NOR-1 modulates redox homeostasis in human vascular smooth muscle cells

The nuclear receptor NOR-1 (Neuron-derived Orphan Receptor-1) has recently been involved in vascular remodeling and coronary artery disease, however, to date, only a few NOR-1 target genes have been described. We aimed to identify genes regulated by NOR-1 in human vascular smooth muscle cells (VSMC). Lentiviral overexpression of NOR-1 increases reactive oxygen species (ROS) in human VSMC. In accordance, NOR-1 strongly increased NADPH oxidase NOX1 mRNA and protein levels, while NOR-1 silencing significantly reduced NOX1 expression. Luciferase reporter, site-directed mutagenesis and EMSA studies identified two nerve growth factor-induced clone B (NGFI-B)-response elements (NBREs) in NOX1 promoter as essential elements for NOR-1 responsiveness. NOR-1 and NOX1 were co-expressed by VSMC in human atherosclerotic lesions, and NOX1 knockdown counteracted the increased ROS production and cell migration induced by NOR-1 overexpression. NOR-1 also modulated the expression of other enzymes involved in cellular redox status, in particular, upregulated superoxide dismutase-1 (SOD1) and SOD3 while downregulated SOD2 and NOX4. NOR-1 induced SOD1 and SOD3 transcriptional activity and participated in the modulation of SOD3 by inflammatory stimuli. By contrast, NOR-1 impaired SOD2 transcription antagonizing NFκB signaling. These results indicate that NOR-1 induces NOX1 in human VSMC and participates in the complex gene networks regulating oxidative stress and redox homeostasis in the vasculature.

Stimulation of KLF14/PLK1 pathway by thrombin signaling potentiates endothelial dysfunction in Type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) promotes a high oxidative stress and hypercoagulable state that drives microvascular injury and multiple-organ abnormality. Elevated thrombin activity underlies T2DM-linked endothelial dysfunction, but the mechanistic links between T2DM/oxidative stress axis and thrombin-associated endothelial pathologies are incompletely understood. In this work, immunohistochemical studies and quantitative analysis using isolated endothelial cells (ECs) identified accumulated Kru¨ppel-like family of transcription factor 14 (KLF14) deposits in ECs from multiple organs as distinct features of T2DM mice. KLF14 upregulation in ECs, which was stimulated by thrombin treatment, was dependent on multiple pathways including calcium mobilization, activation of PKC and AMPK pathways. Functionally, inhibition of endogenous KLF14 expression significantly attenuated thrombin-induced endotheliocyte proliferation, endothelial cell migration and oxidative stress. Molecularly, by directly binding the promoter, KLF14 functions as a transcriptional activator of PLK1, a polo-like kinase whose overexpression induced excessive reactive oxygen species (ROS) production. Transient knockdown of PLK1 was sufficient to suppress KLF14 overexpression-potentiated endothelial dysfunction. Collectively, these data provide proof of concept that deregulation of KLF14/PLK1 cascade plays a key role in thrombin-induced endothelial dysfunction and targeting KLF14 or PLK1 may limit thrombin-associated pathologies in T2DM patients.

The nuclear receptor NOR-1/NR4A3 regulates the multifunctional glycoprotein vitronectin in human vascular smooth muscle cells

The nuclear receptor NOR-1 (NR4A3) has recently been involved in the regulation of extracellular matrix (ECM) proteins associated with neointimal thickening and the vascular control of hemostasis. We sought to find as-yet unidentified NOR-1 target genes in human vascular smooth muscle cells (VSMCs). An in silico analysis identified putative NOR-1 response elements in the proximal promoter region of several genes encoding for ECM proteins, including vitronectin (VTN). Lentiviral overexpression of NOR-1 strongly increased VTN mRNA and protein levels, whereas NOR-1 silencing significantly reduced VTN expression. Deletion and site-directed mutagenesis studies, as well as EMSA and chromatin immunoprecipitation, identified the NBRE(-202/-195) site in the VTN promoter as an essential element for NOR-1 responsiveness. Furthermore, NOR-1 and VTN colocalized in VSMCs in human atherosclerotic lesions. VTN levels were increased in cell supernatants from VSMCs that overexpress NOR-1. Cell supernatants from VSMCs overexpressing NOR-1 induced cell migration to a greater extent than supernatants from control cells, and this effect was attenuated when cell supernatants were preincubated with anti-VTN blocking antibodies or VTN was silenced in supernatant-generating cells. These results indicate that VTN is a target of NOR-1 and suggest that this multifunctional glycoprotein may participate in vascular responses mediated by this nuclear receptor.-Martí-Pàmies, I., Cañes, L., Alonso, J., Rodríguez, C., Martínez-González, J. The nuclear receptor NOR-1/NR4A3 regulates the multifunctional glycoprotein vitronectin in human vascular smooth muscle cells.

Surgery increases cell death and induces changes in gene expression compared with anesthesia alone in the developing piglet brain

In a range of animal species, exposure of the brain to general anaesthesia without surgery during early infancy may adversely affect its neural and cognitive development. The mechanisms mediating this are complex but include an increase in brain cell death. In humans, attempts to link adverse cognitive development to infantile anaesthesia exposure have yielded ambiguous results. One caveat that may influence the interpretation of human studies is that infants are not exposed to general anaesthesia without surgery, raising the possibility that surgery itself, may contribute to adverse cognitive development. Using piglets, we investigated whether a minor surgical procedure increases cell death and disrupts neuro-developmental and cognitively salient gene transcription in the neonatal brain. We randomly assigned neonatal male piglets to a group who received 6h of 2% isoflurane anaesthesia or a group who received an identical anaesthesia plus 15 mins of surgery designed to replicate an inguinal hernia repair. Compared to anesthesia alone, surgery-induced significant increases in cell death in eight areas of the brain. Using RNAseq data derived from all 12 piglets per group we also identified significant changes in the expression of 181 gene transcripts induced by surgery in the cingulate cortex, pathway analysis of these changes suggests that surgery influences the thrombin, aldosterone, axonal guidance, B cell, ERK-5, eNOS and GABA_A signalling pathways. This suggests a number of novel mechanisms by which surgery may influence neural and cognitive development independently or synergistically with the effects of anaesthesia.

NOR-1/NR4A3 regulates the cellular inhibitor of apoptosis 2 (cIAP2) in vascular cells: role in the survival response to hypoxic stress

Vascular cell survival is compromised under pathological conditions such as abdominal aortic aneurysm (AAA). We have previously shown that the nuclear receptor NOR-1 is involved in the survival response of vascular cells to hypoxia. Here, we identify the anti-apoptotic protein cIAP2 as a downstream effector of NOR-1. NOR-1 and cIAP2 were up-regulated in human AAA samples, colocalizing in vascular smooth muscle cells (VSMC). While NOR-1 silencing reduced cIAP2 expression in vascular cells, lentiviral over-expression of this receptor increased cIAP2 mRNA and protein levels. The transcriptional regulation of the human cIAP2 promoter was analyzed in cells over-expressing NOR-1 by luciferase reporter assays, electrophoretic mobility shift analysis and chromatin immunoprecipitation, identifying a NGFI-B site (NBRE-358/-351) essential for NOR-1 responsiveness. NOR-1 and cIAP2 were up-regulated by hypoxia and by a hypoxia mimetic showing a similar time-dependent pattern. Deletion and site-directed mutagenesis studies show that NOR-1 mediates the hypoxia-induced cIAP2 expression. While NOR-1 over-expression up-regulated cIAP2 and limited VSMC apoptosis induced by hypoxic stress, cIAP2 silencing partially prevented this NOR-1 pro-survival effect. These results indicate that cIAP2 is a target of NOR-1, and suggest that this anti-apoptotic protein is involved in the survival response to hypoxic stress mediated by NOR-1 in vascular cells.

The nuclear receptor NOR-1 regulates the small muscle protein, X-linked (SMPX) and myotube differentiation

Recent works have highlighted the role of NOR-1 in both smooth and skeletal muscle, and have proposed this nuclear receptor as a nexus that coordinates muscle performance and metabolic capacity. However, no muscle specific genes regulated by NOR-1 have been identified so far. To identify NOR-1 target genes, we over-expressed NOR-1 in human vascular smooth muscle cells (VSMC). These cells subjected to sustained over-expression of supraphysiological levels of NOR-1 experienced marked phenotypic changes and up-regulated the skeletal muscle protein X-linked (SMPX), a protein typically expressed in striated muscle and associated to cell shape. By transcriptional studies and DNA-protein binding assays, we identified a non-consensus NBRE site in human SMPX promoter, critical for NOR-1 responsiveness. The expression of SMPX was higher in human skeletal muscle myoblasts (HSMM) than in human VSMC, and further increased in HSMM differentiated to myotubes. NOR-1 silencing prevented SMPX expression in HSMM, as well as their differentiation to myotubes, but the up-regulation of SMPX was dispensable for HSMM differentiation. Our results indicate that NOR-1 regulate SMPX in human muscle cells and acts as a muscle regulatory factor, but further studies are required to unravel its role in muscle differentiation and hypertrophy.

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.

miR-17 and -20a Target the Neuron-Derived Orphan Receptor-1 (NOR-1) in Vascular Endothelial Cells

Neuron-derived orphan receptor-1 (NOR-1) plays a major role in vascular biology by controlling fibroproliferative and inflammatory responses. Because microRNAs (miRNAs) have recently emerged as key players in the regulation of gene expression in the vasculature, here we have investigated the regulation of NOR-1 by miRNAs in endothelial cells. Computational algorithms suggest that NOR-1 could be targeted by members of the miR-17 family. Accordingly, ectopic over-expression of miR-17 or miR-20a in endothelial cells using synthetic premiRNAs attenuated the up-regulation of NOR-1 expression induced by VEGF (as evidenced by real time PCR, Western blot and immunocitochemistry). Conversely, the antagonism of these miRNAs by specific antagomirs prevented the down-regulation of NOR-1 promoted by miR-17 or miR-20a in VEGF-stimulated cells. Disruption of the miRNA-NOR-1 mRNA interaction using a custom designed target protector evidenced the selectivity of these responses. Further, luciferase reporter assays and seed-sequence mutagenesis confirmed that miR-17 and -20a bind to NOR-1 3’-UTR. Finally, miR-17 and -20a ameliorated the up-regulation of VCAM-1 mediated by NOR-1 in VEGF-stimulated cells. Therefore, miR-17 and -20a target NOR-1 thereby regulating NOR-1-dependent gene expression.

Neuron-derived orphan receptor 1 promoted human pulmonary artery smooth muscle cells proliferation

AIMS

As a transcription factor of the nuclear receptor superfamily, neuron-derived orphan receptor 1 (NOR1) is induced rapidly in response to various extracellular stimuli. But, it is still unclear its role in pulmonary artery smooth muscle cells proliferation.

MATERIALS AND METHODS

Human PASMCs were cultured in vitro and stimulated by serum. The special antisense oligodeoxynucleotides (AS-ODNs) were used to knockdown human NOR1 gene expression. Real-time PCR and Western-blot were used to evaluate the gene expression and protein levels.

RESULTS

Fetal bovine serum (FBS) induced human PASMCs proliferation in a dose dependent manner. Furthermore, FBS promoted NOR1 gene expression in a dose dependent manner and a time dependent manner. 10% FBS induced a maximal NOR1 mRNA levels at 2 h. FBS also induced a significant higher NOR1 protein levels as compared with control. The NOR1 over-expressed plasmid significantly promoted DNA synthesis and cells proliferation. Moreover, the special AS-ODNs against human NOR1 not only prevented NOR1 expression but also inhibited DNA synthesis and cells proliferation significantly. The NOR1 over-expression plasmid could up-regulate cyclin D1 expression markedly, but the AS-ODNs inhibited cyclin D1 expression significantly.

CONCLUSION

So, we concluded that NOR1 could promote human PASMCs proliferation. Cyclin D1 might be involved in this process.

NR4A receptors up-regulate the antiproteinase alpha-2 macroglobulin (A2M) and modulate MMP-2 and MMP-9 in vascular smooth muscle cells

Matrix metalloproteinases (MMPs) are associated with tissue remodelling and repair. In non-vascular tissues, NR4A receptors have been involved in the regulation of MMPs by transcriptional repression mechanisms. Here, we analyse alternative mechanisms involving NR4A receptors in the modulation of MMP activity in vascular smooth muscle cells (VSMC). Lentiviral overexpression of NR4A receptors (NOR-1, Nurr1 and Nur77) in human VSMC strongly decreased MMP-2 and MMP-9 activities (analysed by zymography and DQ-gelatin assays) and protein levels. NR4A receptors also down-regulated MMP-2 mRNA levels. Real-time PCR analysis evidenced that alpha-2-macroglobulin (A2M), but not other MMP inhibitors (TIMP-1 and TIMP-2) were up-regulated in NR4A-transduced cells. Interestingly, A2M was expressed in human vascular tissues including the smooth muscle media layer. While NR4A receptors increased A2M expression and secretion in VSMC, NR4A knockdown significantly reduced basal A2M expression in these cells. The direct transcriptional regulation of the human A2M promoter by NR4A receptors was characterised in luciferase reporter assays, electrophoretic mobility shift assays and by chromatin immunoprecipitation, identifying a NGFI-B response element (NBRE-71/-64) essential for the NR4A-mediated induction. The blockade of A2M partially prevented the reduction of MMPs activity observed in NR4A-transduced cells. Although mouse A2M promoter was unresponsive to NR4A receptors, vascular MMP expression was attenuated in transgenic mice over-expressing human NOR-1 in VSMC challenged with lipopolysaccharide. Our results show that the pan-proteinase inhibitor A2M is expressed in the vasculature and that NR4A receptors modulate VSMC MMP activity by several mechanisms including the up-regulation of A2M.

NOR-1 modulates the inflammatory response of vascular smooth muscle cells by preventing NFκB activation

Recent work has highlighted the role of NR4A receptors in atherosclerosis and inflammation. In vascular smooth muscle cell (VSMC) proliferation, however, NOR-1 (neuron-derived orphan receptor-1) exerts antagonistic effects to Nur77 and Nurr1. The aim of this study was to analyse the effect of NOR-1 in VSMC inflammatory response. We assessed the consequence of a gain-of-function of this receptor on the response of VSMC to inflammatory stimuli. In human VSMC, lentiviral over-expression of NOR-1 reduced lipopolysaccharide (LPS)-induced up-regulation of cytokines (IL-1β, IL-6 and IL-8) and chemokines (MCP-1 and CCL20). Similar effects were obtained in cells stimulated with TNFα or oxLDL. Conversely, siRNA-mediated NOR-1 inhibition significantly increased the expression of pro-inflammatory mediators. Interestingly, in the aortas from transgenic mice that over-express human NOR-1 in VSMC (TgNOR-1), the up-regulation of cytokine/chemokine by LPS was lower compared to wild-type littermates. Similar results were obtained in VSMC from transgenic animals. NOR-1 reduced the transcriptional activity of NFκB sensitive promoters (in transient transfections), and the binding of NFκB to its responsive element (in electrophoretic mobility shift assays). Furthermore, NOR-1 prevented the activation of NFκB pathway by decreasing IκBα phosphorylation/degradation and inhibiting the phosphorylation and subsequent translocation of p65 to the nucleus (assessed by Western blot and immunocytochemistry). These effects were associated with an attenuated phosphorylation of ERK1/2, p38 MAPK and Jun N-terminal kinase, pathways involved in the activation of NFκB. In mouse challenged with LPS, the activation of the NFκB signalling was also attenuated in the aorta from TgNOR-1. Our data support a role for NOR-1 as a negative modulator of the acute response elicited by pro-inflammatory stimuli in the vasculature.

MASP-1 induces a unique cytokine pattern in endothelial cells: a novel link between complement system and neutrophil granulocytes

Microbial infection urges prompt intervention by the immune system. The complement cascade and neutrophil granulocytes are the predominant contributors to this immediate anti-microbial action. We have previously shown that mannan-binding lectin-associated serine protease-1 (MASP-1), the most abundant enzyme of the complement lectin pathway, can induce p38-MAPK activation, NFkappaB signaling, and Ca²⁺-mobilization in endothelial cells. Since neutrophil chemotaxis and transmigration depends on endothelial cell activation, we aimed to explore whether recombinant MASP-1 (rMASP-1) is able to induce cytokine production and subsequent neutrophil chemotaxis in human umbilical vein endothelial cells (HUVEC). We found that HUVECs activated by rMASP-1 secreted IL-6 and IL-8, but not IL-1alpha, IL-1ra, TNFalpha and MCP-1. rMASP-1 induced dose-dependent IL-6 and IL-8 production with different kinetics. rMASP-1 triggered IL-6 and IL-8 production was regulated predominantly by the p38-MAPK pathway. Moreover, the supernatant of rMASP-1-stimulated HUVECs activated the chemotaxis of neutrophil granulocytes as an integrated effect of cytokine production. Our results implicate that besides initializing the complement lectin pathway, MASP-1 may activate neutrophils indirectly, via the endothelial cells, which link these effective antimicrobial host defense mechanisms.

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.

MicroRNA-638 is highly expressed in human vascular smooth muscle cells and inhibits PDGF-BB-induced cell proliferation and migration through targeting orphan nuclear receptor NOR1

AIMS

Aberrant vascular smooth muscle cell (VSMC) proliferation and migration contribute significantly to the development of vascular pathologies, such as atherosclerosis and restenosis. MicroRNAs have recently emerged as critical modulators in cellular processes and the purpose of this study is to identify novel miRNA regulators implicated in human aortic VSMC proliferation and migration.

METHODS AND RESULTS

To identify miRNAs that are differentially expressed in human VSMCs, we performed miRNA microarray analysis in human aortic smooth muscle cells (SMCs) at different time points after platelet-derived growth factor (PDGF) stimulation. Here, we identified microRNA-638 (miR-638) as a transcript that was one of the most significantly down-regulated in human VSMCs after PDGF stimulation. Furthermore, we confirmed, by Quantitative RT-PCR, that miR-638 is highly expressed in human VSMCs, and its expression is markedly down-regulated in a dose- and time-dependent manner upon PDGF treatment. Consistent with a critical role in SMC proliferation, we found that miR-638 expression was significantly up-regulated in human VSMCs cultured in differentiation medium, a condition that inhibits SMC proliferation. Furthermore, we identified the orphan nuclear receptor NOR1 as a downstream target gene product of miR-638 and down-regulation of NOR1 is critical for miR-638-mediated inhibitory effects on PDGF-induced cyclin D1 expression, cell proliferation, and migration in human aortic SMCs.

CONCLUSION

These results indicate that miR-638 is a key molecule in regulating human VSMC proliferation and migration by targeting the NOR1/cyclin D pathway and suggest that specific modulation of miR-638 in human VSMCs may represent an attractive approach for the treatment of proliferative vascular diseases.

Over-expression of neuron-derived orphan receptor-1 (NOR-1) exacerbates neointimal hyperplasia after vascular injury

We have previously shown that NOR-1 (NR4A3) modulates the proliferation and survival of vascular cells in culture. However, in genetically modified animal models, somewhat conflicting results have been reported concerning the involvement of NOR-1 in neointimal formation after vascular injury. The aim of this study was to generate a transgenic mouse model over-expressing NOR-1 in smooth muscle cells (SMCs) and assess the consequence of a gain of function of this receptor on intimal hyperplasia after vascular injury. The transgene construct (SM22-NOR1) was prepared by ligating the full-length human NOR-1 cDNA (hNOR-1) and a mouse SM22α minimal promoter able to drive NOR-1 expression to SMC. Two founders were generated and two stable transgenic mouse lines (TgNOR-1) were established by backcrossing the transgene-carrying founders with C57BL/6J mice. Real-time PCR and immunohistochemistry confirmed that hNOR-1 was mainly targeted to vascular beds such as aorta and carotid arteries, and was similar in both transgenic lines. Vascular SMC from transgenic animals exhibit increased NOR-1 transcriptional activity (assessed by electrophoretic mobility shift assay and luciferase assays), increased mitogenic activity (determined by [(3)H]-thymidine incorporation; 1.58-fold induction, P < 0.001) and increased expression of embryonic smooth muscle myosin heavy chain (SMemb) than wild-type cells from control littermates. Using the carotid artery ligation model, we show that neointima formation was increased in transgenic versus wild-type mice (2.36-fold induction, P < 0.01). Our in vivo data support a role for NOR-1 in VSMC proliferation and vascular remodelling. This NOR-1 transgenic mouse could be a useful model to study fibroproliferative vascular diseases.

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.

Tissue factor pathway inhibitor 2 is induced by thrombin in human macrophages

Tissue factor pathway inhibitor 2 (TFPI2) is a serine protease inhibitor critical for the regulation of extracellular matrix remodeling and atherosclerotic plaque stability. Previously, we demonstrated that TFPI2 expression is increased in monocytes from patients with familial combined hyperlipidemia (FCH). To gain insight into the molecular mechanisms responsible for this upregulation, we examined TFPI2 expression in THP-1 macrophages exposed to lipoproteins and thrombin. Our results showed that TFPI2 expression was not affected by treatment with very low density lipoproteins (VLDL), but was induced by thrombin (10 U/ml) in THP-1 (1.9-fold increase, p<0.001) and human monocyte-derived macrophages (2.3-fold increase, p<0.005). The specificity of the inductive effect was demonstrated by preincubation with the thrombin inhibitors hirudin and PPACK, which ablated thrombin effects. TFPI2 induction was prevented by pre-incubation with MEK1/2 and JNK inhibitors, but not by the EGF receptor antagonist AG1478. In the presence of parthenolide, an inhibitor of NFκB, but not of SR-11302, a selective AP-1 inhibitor, thrombin-mediated TFPI2 induction was blunted. Our results also show that thrombin treatment increased ERK1/2, JNK and IκBα phosphorylation. Finally, we ruled out the possibility that TFPI2 induction by thrombin was mediated by COX-2, as preincubation with a selective COX-2 inhibitor did not prevent the inductive effect. In conclusion, thrombin induces TFPI2 expression by a mechanism involving ERK1/2 and JNK phosphorylation, leading finally to NFkB activation. In the context of atherosclerosis, thrombin-induced macrophage TFPI2 expression could represent a means of avoiding excessive activation of matrix metalloproteases at sites of inflammation.

Down-regulation of CREB-binding protein expression inhibits thrombin-induced proliferation of endothelial cells: possible relevance to PDGF-B

Thrombin acts as a potent mitogenic factor for ECs (endothelial cells) by the release of several growth factors, including PDGF-B (platelet-derived growth factor-B). CBP (CREB-binding protein), which functions as a transcriptional coactivator, links the changes in the extracellular stimuli with alterations in gene expression. Therefore, we hypothesized that CBP could mediate thrombin-induced proliferation of ECs via PDGF-B-dependent way. Short hairpin RNA was used to down-regulate the expression of CBP in ECs. CBP and PDGF-B levels were analysed by real-time RT-PCR and Western blot. To evaluate ECs proliferation, cell cycle and DNA synthesis were analysed by flow cytometry and BrdU (bromodeoxyuridine) incorporation assay, respectively. PDGF-B was involved in the mitogenic effect of thrombin on ECs. Down-regulation of CBP attenuated ECs proliferation and inhibited cell cycle progression induced by thrombin. Silencing CBP expression also suppressed thrombin-induced PDGF-B expression in ECs. Mitogenic activity of thrombin was impaired by silencing CBP expression in ECs. This inhibitory effect was, in part, related to the inability to up-regulate PDGF-B expression in ECs. CBP could be regarded as a potential therapeutic target for vascular injury.

Fibulin-5 is up-regulated by hypoxia in endothelial cells through a hypoxia-inducible factor-1 (HIF-1α)-dependent mechanism

Hypoxia modulates gene expression and affects multiple aspects of endothelial cell biology. Fibulin-5 (FBLN5) is an extracellular matrix protein essential for elastic fiber assembly and vasculogenesis that participates in vascular remodeling and controls endothelial cell adhesion, motility, and proliferation. In this context, we aimed to analyze FBLN5 regulation by hypoxia in endothelial cells. Hypoxia (1% O(2)) increased FBLN5 mRNA levels in endothelial cells in a time-dependent manner. Maximal induction (∼2.5-fold) was achieved after 24 h of hypoxia. This effect paralleled an increase in both intracellular and extracellular FBLN5 protein levels. The increase in FBLN5 mRNA levels observed in hypoxic cells was blocked by inhibitors of the PI3K/Akt/mTOR pathway (LY294002 and rapamycin) and mimicked by dimethyl oxal glycine, which prevents proline hydroxylase-mediated degradation of HIF-1α. Silencing of HIF-1α completely prevented hypoxia-induced FBLN5 up-regulation. Accordingly, both hypoxia and HIF-1α overexpression increased FBLN5 transcriptional activity. Serial promoter deletion and mutagenesis studies revealed the involvement of a putative hypoxia response element (HRE) located at -78 bp. In fact, EMSA and ChIP assays demonstrated increased HIF-1 binding to this site in hypoxic cells. Interestingly, the rate of endothelial cells undergoing apoptosis in cultures exposed to hypoxia increased in FBLN5 knockdown cells, suggesting that hypoxia-induced FBLN5 expression contributes to preserve cell survival. These results provide evidence that HIF-1 signaling underlies the increase of FBLN5 expression elicited by hypoxia in endothelial cells and suggest that FBLN5 induction could be involved in the adaptive survival response of endothelial cells to hypoxia.

NR4A orphan nuclear receptors: transcriptional regulators of gene expression in metabolism and vascular biology

Members of the nuclear hormone receptor superfamily, including the peroxisome proliferator-activated receptor and the liver X receptor subfamilies, orchestrate transcriptional networks involved in the control of metabolism and the development of vascular disease. In addition to these well-characterized ligand-activated transcription factors, the nuclear receptor (NR) superfamily comprises many orphan receptors, whose ligands and physiological functions remain unknown. Among this group of orphan receptors is the NR4A subfamily, including Nur77 (NR4A1), Nurr1 (NR4A2), and NOR1 (NR4A3). These orphan NRs constitute an evolutionary ancient and highly conserved group of transcription factors. In contrast to other members of the superfamily, NR4A receptors function as ligand-independent transcription factors and immediate- or early-response genes, which are rapidly induced by a pleiotropy of environmental cues. Early functional studies have pointed to a critical role of NR4A receptors in regulating differentiation, proliferation, and apoptosis. More recent research has characterized NR4A receptors as key transcriptional regulators of glucose and lipid homeostasis, adipogenesis, inflammation, and vascular remodeling. In this review, we will summarize recent advances in understanding the molecular biology and physiological functions of NR4A receptors and discuss their role in the transcriptional control of metabolism and vascular remodeling.

Minireview: Nuclear hormone receptor 4A signaling: implications for metabolic disease

Numerous members of the nuclear hormone receptor (NR) superfamily have been demonstrated to regulate metabolic function in a cell- and tissue-specific manner. This review brings together recent studies that have associated members of the NR superfamily, the orphan NR4A subgroup, with the regulation of metabolic function and disease. The orphan NR4A subgroup includes Nur77 (NR4A1), Nurr1 (NR4A2), and Nor-1 (NR4A3). Expression of these receptors is induced in multiple tissues by a diverse range of stimuli, including stimuli associated with metabolic function, such as: β-adrenoceptor agonists, cold, fatty acids, glucose, insulin, cholesterol, and thiazolidinediones. In vitro and in vivo gain- and loss-of-function studies in major metabolic tissues (including skeletal muscle, adipose, and liver cells and tissues) have associated the NR4A subgroup with specific aspects of lipid, carbohydrate, and energy homeostasis. Most excitingly, although these orphan receptors do not have known endogenous ligands, several small molecule agonists have recently been identified. The preliminary studies reviewed in this manuscript suggest that therapeutic exploitation of the NR4A subgroup may show utility against dyslipidemia, obesity, diabetes, and cardiovascular disease.

The hypoxia-inducible factor 1/NOR-1 axis regulates the survival response of endothelial cells to hypoxia

Hypoxia induces apoptosis but also triggers adaptive mechanisms to ensure cell survival. Here we show that the prosurvival effects of hypoxia-inducible factor 1 (HIF-1) in endothelial cells are mediated by neuron-derived orphan receptor 1 (NOR-1). The overexpression of NOR-1 decreased the rate of endothelial cells undergoing apoptosis in cultures exposed to hypoxia, while the inhibition of NOR-1 increased cell apoptosis. Hypoxia upregulated NOR-1 mRNA levels in a time- and dose-dependent manner. Blocking antibodies against VEGF or SU5614 (a VEGF receptor 2 inhibitor) did not prevent hypoxia-induced NOR-1 expression, suggesting that NOR-1 is not induced by the autocrine secretion of VEGF in response to hypoxia. The reduction of HIF-1 alpha protein levels by small interfering RNAs, or by inhibitors of the phosphatidylinositol-3 kinase (PI3K)/Akt pathway or mTOR, significantly counteracted hypoxia-induced NOR-1 upregulation. Intracellular Ca(2+) was involved in hypoxia-induced PI3K/Akt activation and in the downstream NOR-1 upregulation. A hypoxia response element mediated the transcriptional activation of NOR-1 induced by hypoxia as we show by transient transfection and chromatin immunoprecipitation assays. Finally, the attenuation of NOR-1 expression reduced both basal and hypoxia-induced cIAP2 (cellular inhibitor of apoptosis protein 2) mRNA levels, while NOR-1 overexpression upregulated cIAP2. Therefore, NOR-1 is a downstream effector of HIF-1 signaling involved in the survival response of endothelial cells to hypoxia.

p38 MAPK contributes to angiotensin II-induced COX-2 expression in aortic fibroblasts from normotensive and hypertensive rats

OBJECTIVE

To investigate the effect of angiotensin II on cyclooxygenase-2 (COX-2) expression in aortic adventitial fibroblasts from normotensive [Wistar-Kyoto (WKY)] rats and spontaneously hypertensive rats (SHRs).

METHODS

Protein expression was determined by western blot, mRNA levels by real-time PCR, transcriptional activity by luciferase assays, superoxide anion (O2*-) production by dihydroethidine fluorescence and prostaglandin E2 by enzyme immunoassay.

RESULTS

Angiotensin II (0.1 micromol/l, 0.5-6 h) time dependently induced COX-2 protein expression, this effect being transient in fibroblasts from WKY rats and maintained over time in SHRs. Angiotensin II effect was abolished by valsartan (1 micromol/l), an angiotensin II type 1 receptor antagonist. Angiotensin II-induced prostaglandin E2 production was reduced by valsartan and the COX-2 inhibitor NS398 (1 micromol/l). Angiotensin II increased O2*- production more in SHR than WKY rats. This increase was reduced by apocynin (30 micromol/l) and allopurinol (10 micromol/l), respective nicotinamide adenine dinucleotide phosphate (NADPH) and xanthine oxidase inhibitors. However, angiotensin II-induced COX-2 expression was unaffected by apocynin, allopurinol, tempol (1 mmol/l) or catalase (1000 U/ml). Angiotensin II (2-30 min) induced p38 mitogen-activated protein kinase (MAPK) phosphorylation, transiently in WKY rats but sustained in SHRs. The p38 inhibitor SB203580 (10 micromol/l) reduced angiotensin II-induced COX-2 protein and mRNA levels. The angiotensin II effect was not prevented by inhibition of mRNA synthesis, and angiotensin II was unable to modulate COX-2 transcriptional activity.

CONCLUSIONS

Angiotensin II increases COX-2 expression in aortic fibroblasts through mechanisms including p38 MAPK pathway, independent of reactive oxygen species production and nonmediated by COX-2 transcriptional activity modulation. The sustained angiotensin-induced p38 MAPK activation in SHR cells might be related to the maintained COX-2 expression in this strain.

The orphan nuclear receptor, NOR-1, a target of beta-adrenergic signaling, regulates gene expression that controls oxidative metabolism in skeletal muscle

beta 1-3-Adrenoreceptor (AR)-deficient mice are unable to regulate energy expenditure and develop diet-induced obesity on a high-fat diet. We determined previously that beta2-AR agonist treatment activated expression of the mRNA encoding the orphan nuclear receptor, NOR-1, in muscle cells and plantaris muscle. Here we show that beta2-AR agonist treatment significantly and transiently activated the expression of NOR-1 (and the other members of the NR4A subgroup) in slow-twitch oxidative soleus muscle and fast-twitch glycolytic tibialis anterior muscle. The activation induced by beta-adrenergic signaling is consistent with the involvement of protein kinase A, MAPK, and phosphorylation of cAMP response element-binding protein. Stable cell lines transfected with a silent interfering RNA targeting NOR-1 displayed decreased palmitate oxidation and lactate accumulation. In concordance with these observations, ATP production in the NOR-1 silent interfering RNA (but not control)-transfected cells was resistant to (azide-mediated) inhibition of oxidative metabolism and expressed significantly higher levels of hypoxia inducible factor-1alpha. In addition, we observed the repression of genes that promote fatty acid oxidation (peroxisomal proliferator-activated receptor-gamma coactivator-1alpha/beta and lipin-1alpha) and trichloroacetic acid cycle-mediated carbohydrate (pyruvate) oxidation [pyruvate dehydrogenase phosphatase 1 regulatory and catalytic subunits (pyruvate dehydrogenase phosphatases-1r and -c)]. Furthermore, we observed that beta2-AR agonist administration in mouse skeletal muscle induced the expression of genes that activate fatty acid oxidation and modulate pyruvate use, including PGC-1alpha, lipin-1alpha, FOXO1, and PDK4. Finally, we demonstrate that NOR-1 is recruited to the lipin-1alpha and PDK-4 promoters, and this is consistent with NOR-1-mediated regulation of these genes. In conclusion, NOR-1 is necessary for oxidative metabolism in skeletal muscle.