The Pro-Inflammatory Phenotype of Human Macrophages is Restricted by the Activity of the Orphan Nuclear Receptor Nurr1

Abstract The nuclear receptor related 1 protein (Nurr1) is a member of the orphan nuclear hormone receptor family whose expression has been associated with several inflammatory diseases. Macrophages are key regulators of the inflammatory processes, yet information about the role of Nurr1 in human macrophages is limited. In the present study we examined the expression and activity of Nurr1 in steady state and activated human monocyte-derived macrophages. Pro- and anti-inflammatory macrophages were derived in vitro by culture of blood monocytes with the hematopoietic cytokines GM-CSF and M-CSF, respectively. Nurr1 expression was predominant in macrophages with a pro-inflammatory phenotype. Accordingly, its expression was induced by a variety of inflammatory stimuli such as TLR-2, -3 and -4 ligands, TNF, IFN-β, and IL-4. Pro-inflammatory macrophages exposed to the Nurr1 agonist C-DIM12 decreased their production of IL-1β, IL-6, and reactive oxygen species. Conversely, Nurr1 deficient macrophages produced enhanced levels of IL-6. Mechanistically, Nurr1 agonists partially abrogated the activation of the NF-κB signaling pathway in pro-inflammatory macrophages exposed to LPS, rendering cells with a lower rate of NF-κB p65 nuclear translocation. These results suggest that Nurr1 expression is linked with the pro-inflammatory phenotype of human macrophages where it may constitute a brake to attenuate the synthesis of inflammatory mediators. Supported by grants from Secretaria de Educación Pública-Consejo Nacional de Ciencia y Tecnología (SEP-CONACYT, #A1-S-9430)