Omega-3 fatty acids attenuate dendritic cell function via NF-κB independent of PPARγ☆ Eve Draper a,1 , Clare M. Reynolds b,1 , Mary Canavan a , Kingston H. Mills c , Christine E. Loscher a, ⁎ ,2 , Helen M. Roche b,2 a Immunomodulation Research Group, School of Biotechnology, Dublin City University, Dublin 9, Ireland b Nutrigenomics Research Group, UCD Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland c Immune Regulation Research Group, School of Biochemistry and Immunology, Trinity College Dublin, Ireland Received 15 February 2010; received in revised form 14 June 2010; accepted 30 June 2010 Abstract Long-chain n-3 polyunsaturated fatty acids (n-3 PUFA) have been shown to modulate the immune response and have therapeutic effects in inflammatory disorders. PUFA are also peroxisome proliferators-activator receptor-gamma (PPARγ) ligands; a family of ligand-activated transcription factors, which when activated antagonise the pro-inflammatory capability of nuclear factor κB (NF-κB). PPARγ plays a role in dendritic cell (DC) maturation and n-3 PUFA have been shown to affect DC maturation by decreasing activation of NF-κB. While n-3 PUFA can function as PPAR ligands, it is not known whether the NF-κB-mediated immunomodulatory properties of n-3 PUFA are PPARγ-dependent. In this study we examined whether the immunomodulatory effects of n-3 PUFA on DC activation were mediated through activation of PPARγ. Treatment of murine bone marrow derived DCs with docosahexaenoic acid (DHA; 25 μM) and eicosapentaenoic acid (EPA; 25 μM) attenuated LPS-induced DC maturation. This was characterised by suppression of IL-12 production and expression of CD40, CD80, CD86 and MHC II and enhanced production of IL-10 and expression of IL-10R. This was coincident with enhanced PPARγ expression, suppressed NF-κB activity and increased the physical interaction and cellular colocalization between NF-κB with PPARγ. To understand the functional implication of the physical association of PPARγ with NF-κB, we determined whether the specific PPARγ inhibitor, GW9662 could abolish the anti-inflammatory effect of n-3 PUFA Inhibiting PPARγ did not impede the NF-κB-mediated anti-inflammatory cytokine profile induced by EPA and DHA alone. Thus n-3 PUFA activate PPARγ and interact with NF-κB in DC. However, the anti-inflammatory effects of EPA and DHA on DCs are independent of PPARγ. © 2011 Elsevier Inc. All rights reserved. Keywords: Dendritic cells; LC n-3 PUFA; NF-κB; PPARγ 1. Introduction Dendritic cells (DCs) play a critical role in directing adaptive immune responses, including T helper (Th) cell responses. Activation of DCs by inflammatory stimuli, such as lipopolysaccharide (LPS), induces maturation and homing to lymph nodes where DCs present antigen to naïve T cells [1]. This maturation process is characterized by the production of cytokines and by increased expression of major histocompatibility complex (MHC) class II molecules and co- stimulatory molecules (CD40, CD80, CD86). The differentiation of naïve CD4 + T cells into Th cell subsets is determined in part by the cytokines produced by DCs. Interleukin (IL)-12 promotes Th1 differentiation, IL-4 induces Th2 cells, IL-10 promotes the induction of type 1 T regulatory T (Tr1) cells, while IL-23 production by DCs is involved in generating or expansion of IL-17-producing CD4+ T (Th17) cells [2–5]. Since expression of these cytokines, together with the maturation status of the DC have a pivotal role in directing Th cell responses, modulating DC activation can have a profound effect on the quality and quantity of the adaptive immune response. Recently it has been demonstrated that peroxisome prolifera- tors-activator receptor-gamma (PPARγ) affects DC maturation [6]. PPARγ is a ligand-activated transcription factor that antagonises nuclear factor κB (NF-κB), activator protein-1 (AP-1) and signal transducers and activators of transcription factor (STAT) transcrip- tional activity [7]. The phenotypic effects of agonist-induced PPARγ activation on DC maturation are well characterised [6,8,9]. The PPARγ ligand, rosiglitazone, suppresses production of IL-12 and expression of CD80 in DCs [8]. Furthermore, other PPARγ ligands, troglitazone or 15d-PGJ2, decrease DC IL-12 production and increase expression of CD80 and CD40 expression, concomitant with up- regulation of CD86 [6]. Thus, activation of PPARγ in DCs may influence Th cell differentiation and may represent a therapeutic target against T cell-mediated diseases. Available online at www.sciencedirect.com Journal of Nutritional Biochemistry 22 (2011) 784 – 790 ☆ This work was supported by a Basic Research Grant and a Research Frontiers Programme Grant from Science Foundation Ireland and funds from the Food Institutional Research Measure, Department of Agriculture and Food, Ireland. K.H.M is funded by Science Foundation Ireland. ⁎ Corresponding author. Tel.: +353 1 700 5244. E-mail address: christine.loscher@dcu.ie (C.E. Loscher). 1 First authors ED and CMR contributed equally to this work. 2 Last authors HMR and CEL contributed equally to this work. 0955-2863/$ - see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.jnutbio.2010.06.009