NR4A1 (Nur77) Deletion Polarizes Macrophages Toward an Inflammatory Phenotype and Increases Atherosclerosis

Division of Inflammation Biology, La Jolla Institute for Allergy and Immunology, CA 92037, USA.
Circulation Research (Impact Factor: 11.02). 12/2011; 110(3):416-27. DOI: 10.1161/CIRCRESAHA.111.253377
Source: PubMed


NR4A1 (Nur77) is a nuclear receptor that is expressed in macrophages and within atherosclerotic lesions, yet its function in atherosclerosis is unknown.
Nur77 regulates the development of monocytes, particularly patrolling Ly6C(-) monocytes that may be involved in resolution of inflammation. We sought to determine how absence of nuclear receptor subfamily 4, group A, member 1 (NR4A1) in hematopoietic cells affected atherosclerosis development.
Nur77(-/-) chimeric mice on a Ldlr(-/-) background showed a 3-fold increase in atherosclerosis development when fed a Western diet for 20 weeks, despite having a drastic reduction in Ly6C(-) patrolling monocytes. In a second model, mice deficient in both Nur77 and ApoE (ApoE(-/-)Nur77(-/-)) also showed increased atherosclerosis after 11 weeks of Western diet. Atherosclerosis was associated with a significant change in macrophage polarization toward a proinflammatory phenotype, with high expression of tumor necrosis factor-α and nitric oxide and low expression of Arginase-I. Moreover, we found increased expression of toll-like receptor 4 mRNA and protein in Nur77(-/-) macrophages as well as increased phosphorylation of the p65 subunit of NFκB. Inhibition of NFκB activity blocked excess activation of Nur77(-/-) macrophages.
We conclude that the absence of Nur77 in monocytes and macrophages results in enhanced toll-like receptor signaling and polarization of macrophages toward a proinflammatory M1 phenotype. Despite having fewer monocytes, Nur77(-/-) mice developed significant atherosclerosis when fed a Western diet. These studies indicate that Nur77 is a novel target for modulating the inflammatory phenotype of monocytes and macrophages and may be important for regulation of atherogenesis.

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    • "An increasing number of evidence suggest that NR4A receptors are highly expressed in advanced atherosclerotic lesions and injury induced vasculature [27]. Additionally, Nur77 deficiency has recently been shown to promote the development of atherosclerotic lesions in Apo-E knockout mice fed with a high fat diet through modulating inflammatory responses in microphages [31], further implicating their important roles in vascular diseases. Since ET-1 is highly expressed in human atherosclerotic lesions [8] [9], it is speculated that Nur77 deficiency may cause a higher expression of ET-1 and this may partially contribute to the increased atherosclerotic formation in Nur77 knockout mice. "
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    ABSTRACT: Endothelin-1 (ET-1) produced by vascular endothelial cells plays essential roles in the regulation of vascular tone and development of cardiovascular diseases. The objective of this study is to identify novel regulators implicated in the regulation of ET-1 expression in vascular endothelial cells (ECs). By using quantitative real-time PCR (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA), we show that either ectopic expression of orphan nuclear receptor Nur77 or pharmacological activation of Nur77 by 6-mercaptopurine (6-MP) substantially inhibits ET-1 expression in human umbilical vein endothelial cells (HUVECs), under both basal and thrombin-stimulated conditions. Furthermore, thrombin-stimulated ET expression is significantly augmented in both Nur77 knockdown ECs and aort from Nur77 knockout mice, suggesting that Nur77 is a negative regulator of ET-1 expression. Inhibition of ET-1 expression by Nur77 occurs at gene transcriptional levels, since Nur77 potently inhibits ET-1 promoter activity, without affecting ET-1 mRNA stability. As shown in electrophoretic mobility shift assay (EMSA), Nur77 overexpression markedly inhibits both basal and thrombin-stimulated transcriptional activity of AP-1.Mechanistically, we demonstrate that Nur77 specially interacts with c-Jun and inhibits AP-1 dependent c-Jun promoter activity,which leads to a decreased expression of c-Jun, a critical component involved in both AP-1 transcriptional activity and ET-1 expression in ECs. These findings demonstrate that Nur77 is a novel negative regulator of ET-1 expression in vascular ECs through an inhibitory interaction with the c-Jun/AP-1 pathway. Activation of Nur77 may represent a useful therapeutic strategy for preventing certain cardiovascular diseases, such as atherosclerosis and pulmonary artery hypertension.
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    • "The domain structure of NR4A1 is similar to other nuclear receptors, containing an N-terminal activating function-1 domain, a zinc finger DNA-binding domain and a C-terminal ligand-binding domain (16,17). NR4A1 is reported to have multiple biological functions, regulating cell proliferation, differentiation, apoptosis, development, metabolism and immunity (16,18–20). The receptor exerts these physiological functions through expression regulation, post-translational modification and subcellular localization (21). "
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    • "An emerging literature suggests a previously unrecognized role for nonclassical Ly6C À monocytes during tissue injury. These cells patrol the luminal side of the endothelium and extravasate in response to both septic and aseptic tissue injury (Auffray et al., 2007), and recent work suggests that these cells may serve as precursors for alternatively activated macrophages (Auffray et al., 2009;Nahrendorf et al., 2007), playing a protective or anti-inflammatory role during tissue injury (Hamers et al., 2012;Hanna et al., 2012). However, the relative contribution of classical Ly6C + compared with nonclassical Ly6C À monocytes to tissue injury and repair is incompletely understood. "
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