Nuclear Receptors Nur77, Nurr1, and NOR-1 Expressed in Atherosclerotic Lesion Macrophages Reduce Lipid Loading and Inflammatory Responses

Abstract

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 ␣. Lentiviral overexpression of Nur77, Nurr1, or NOR-1 reduces expression and production of interleukin (IL)-1␤ and IL-6 proinflammatory cytokines and IL-8, macrophage inflammatory protein-1␣ and -1␤ 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. A therosclerosis is a chronic inflammatory disease involving deregulation of both the immune system and lipid metabolism. 1,2 Macrophages, imperative in the innate immune system, are involved in the initiation, progression, and rupture of atherosclerotic lesions as well as in the initiation of smooth muscle cell (SMC)-rich pathologies like restenosis. 3,4 At the onset of atherosclerosis, monocytes are locally recruited to the arterial vessel wall, where these cells differentiate into macrophages. These intimal macrophages ingest modified lipid particles and become lipid-laden foam cells that form a so-called fatty streak. In advanced atherosclerotic lesions, macrophages are localized primarily around a central lipid core and at the shoulder region of the plaque. At the latter site, which is known to be prone to rupture, these cells may be involved in destabilization of the lesion. 5 Throughout the progression of atherosclerosis, macrophages produce proinflammatory cytokines, chemokines, growth factors, and matrix-degrading enzymes and are consequently crucial in the chronic inflammatory process in the diseased vessel wall. 6,7 Detailed knowledge on the molecular mechanisms involved in the inflammatory and metabolic processes in macrophages is essential to develop novel drug therapies against atherosclerosis. We hypothesized that NR4A nuclear receptors are key regulatory factors involved in modulation of these specific processes in macrophages. Conclusion-NR4A-factorsThe NR4A nuclear hormone receptors were first described as early response transcription factors expressed on stimulation by growth factors. 8 -...

Adenosine Modulates NR4A Orphan Nuclear Receptors To Attenuate Hyperinflammatory Responses in Monocytic Cells

“…However, specific factors driving differentiation may play an important role, as evident by enhanced MHC class II (HLA-DR) surface expression in NR4A2-depleted cells differentiated using LPS alone in the absence of IFN-g. These data expand recent reports that identify NR4A receptors as effector molecules of TLR and cytokine signaling in human and murine macrophage cells and as important regulators of cellular differentiation (15)(16)(17)(18)40). Treatment of macrophages with LPS, cytokines, or oxidized lipids triggers the transcriptional induction of all three NR4A receptors, and functional studies primarily demonstrate anti-inflammatory and reparative functions for NR4A1 receptors in these cells (16,41).…”

Orphan Nuclear Receptor Nurr1 as a Potential Novel Marker for Progression in Human Prostate Cancer

“…Only a few direct target genes, such as vascular endothelial growth factor (VEGF)-A, have been identified to date (Pols et al, 2007;Zhao and Bruemmer, 2010;Zeng et al, 2006). Specific ligands for the NR4A family of transcription factors have not been identified, classifying them as orphan nuclear receptors (Bonta et al, 2006). Furthermore, gene expression of NR4A members is induced by various growth factors and cytokines in a variety of cell types (Pei et al, 2005;Nomiyama et al, 2006).…”

The Orphan Nuclear Receptor Nur77 Suppresses Endothelial Cell Activation Through Induction of IκBα Expression

“…19 Furthermore, the expression of NR4A receptors in atherosclerotic lesion macrophages underlines the importance of these transcription factors in plaque progression. 22 Indeed, overexpression of Nur77 in macrophages has been shown to inhibit inflammatory cytokine expression and reduce oxidized LDL uptake in these cells. 22 Moreover, 6-mercaptopurine, which is used clinically in the treatment of leukemia and inflammatory bowel disease, has been shown to enhance the transcriptional activity of Nur77, 23,24 attenuate smooth muscle cell proliferation, and prevent cuff injury-induced neointimal formation in a mouse model in a Nur77-dependent manner.…”