Macoch Mélinda, Morzadec Claudie, Génard Romain, Pallardy Marc, Kerdine-Römer Saadia, Fardel Olivier, Vernhet Laurent
UMR INSERM U1085, Institut de Recherche sur la Santé, l'Environnement et le Travail (IRSET), Université de Rennes 1, Rennes, France.
INSERM, Faculté de Pharmacie, Université Paris Sud, Châtenay-Malabry, France; UniverSud, INSERM, UMR-996 "Cytokines, chemokines and immunopathology", Châtenay-Malabry, France.
Free Radic Biol Med. 2015 Nov;88(Pt B):381-390. doi: 10.1016/j.freeradbiomed.2015.02.003. Epub 2015 Feb 11.
Inorganic arsenic, a well-known Nrf2 inducer, exerts immunosuppressive properties. In this context, we recently reported that the differentiation of human blood monocytes into immature dendritic cells (DCs), in the presence of low and noncytotoxic concentrations of arsenic, represses the ability of DCs to release key cytokines in response to different stimulating agents. Particularly, arsenic inhibits the expression of human interleukin-12 (IL-12, also named IL-12p70), a major proinflammatory cytokine that controls the differentiation of Th1 lymphocytes. In the present study, we determined if Nrf2 could contribute to these arsenic immunotoxic effects. To this goal, human monocyte-derived DCs were first differentiated in the absence of metalloid and then pretreated with arsenic just before DC stimulation with lipopolysaccharide (LPS). Under these experimental conditions, arsenic rapidly and stably activates Nrf2 and increases the expression of Nrf2 target genes. It also significantly inhibits IL-12 expression in activated DCs, at both mRNA and protein levels. Particularly, arsenic reduces mRNA levels of IL12A and IL12B genes which encodes the p35 and p40 subunits of IL-12p70, respectively. tert-Butylhydroquinone (tBHQ), a reference Nrf2 inducer, mimics arsenic effects and potently inhibits IL-12 expression. Genetic inhibition of Nrf2 expression markedly prevents the repression of both IL12 mRNA and IL-12 protein levels triggered by arsenic and tBHQ in human LPS-stimulated DCs. In addition, arsenic significantly reduces IL-12 mRNA levels in LPS-activated bone marrow-derived DCs from Nrf2+/+ mice but not in DCs from Nrf2-/- mice. Finally, we show that, besides IL-12, arsenic significantly reduces the expression of IL-23, another heterodimer containing the p40 subunit. In conclusion, our study demonstrated that arsenic represses IL-12 expression in human-activated DCs by specifically stimulating Nrf2 activity.
无机砷是一种著名的Nrf2诱导剂，具有免疫抑制特性。在此背景下，我们最近报道，在低浓度且无细胞毒性的砷存在下，人血单核细胞分化为未成熟树突状细胞（DCs）会抑制DCs对不同刺激剂释放关键细胞因子的能力。特别是，砷会抑制人白细胞介素12（IL-12，也称为IL-12p70）的表达，IL-12是一种主要的促炎细胞因子，可控制Th1淋巴细胞的分化。在本研究中，我们确定Nrf2是否会导致这些砷的免疫毒性作用。为此，首先在没有类金属的情况下使人单核细胞衍生的DCs分化，然后在DCs用脂多糖（LPS）刺激之前用砷进行预处理。在这些实验条件下，砷迅速且稳定地激活Nrf2并增加Nrf2靶基因的表达。它还在mRNA和蛋白质水平上显著抑制活化DCs中IL-12的表达。特别是，砷降低了分别编码IL-12p70的p35和p40亚基的IL12A和IL12B基因的mRNA水平。叔丁基对苯二酚（tBHQ）是一种参考Nrf2诱导剂，可模拟砷的作用并有效抑制IL-12的表达。Nrf2表达的基因抑制明显阻止了砷和tBHQ在人LPS刺激的DCs中引发的IL12 mRNA和IL-12蛋白水平的抑制。此外，砷显著降低了Nrf2+/+小鼠LPS活化的骨髓来源DCs中IL-12的mRNA水平，但在Nrf2-/-小鼠的DCs中则没有。最后，我们表明，除了IL-12之外，砷还显著降低了另一种含p40亚基的异二聚体IL-23的表达。总之，我们的研究表明，砷通过特异性刺激Nrf2活性来抑制人活化DCs中IL-12的表达。
