Maldifassi Maria C, Atienza Gema, Arnalich Francisco, López-Collazo Eduardo, Cedillo Jose L, Martín-Sánchez Carolina, Bordas Anna, Renart Jaime, Montiel Carmen
Departamento de Farmacología y Terapéutica, Facultad de Medicina, Universidad Autónoma de Madrid, IdiPAZ, Madrid, Spain.
Servicio de Medicina Interna, Hospital Universitario "La Paz" de Madrid, IdiPAZ, Madrid, Spain.
PLoS One. 2014 Sep 26;9(9):e108397. doi: 10.1371/journal.pone.0108397. eCollection 2014.
Nicotine stimulation of α7 nicotinic acetylcholine receptor (α7 nAChR) powerfully inhibits pro-inflammatory cytokine production in lipopolysaccharide (LPS)-stimulated macrophages and in experimental models of endotoxemia. A signaling pathway downstream from the α7 nAChRs, which involves the collaboration of JAK2/STAT3 and NF-κB to interfere with signaling by Toll-like receptors (TLRs), has been implicated in this anti-inflammatory effect of nicotine. Here, we identifiy an alternative mechanism involving interleukin-1 receptor-associated kinase M (IRAK-M), a negative regulator of innate TLR-mediated immune responses. Our data show that nicotine up-regulates IRAK-M expression at the mRNA and protein level in human macrophages, and that this effect is secondary to α7 nAChR activation. By using selective inhibitors of different signaling molecules downstream from the receptor, we provide evidence that activation of STAT3, via either JAK2 and/or PI3K, through a single (JAK2/PI3K/STAT3) or two convergent cascades (JAK2/STAT3 and PI3K/STAT3), is necessary for nicotine-induced IRAK-M expression. Moreover, down-regulation of this expression by small interfering RNAs specific to the IRAK-M gene significantly reverses the anti-inflammatory effect of nicotine on LPS-induced TNF-α production. Interestingly, macrophages pre-exposed to nicotine exhibit higher IRAK-M levels and reduced TNF-α response to an additional LPS challenge, a behavior reminiscent of the 'endotoxin tolerant' phenotype identified in monocytes either pre-exposed to LPS or from immunocompromised septic patients. Since nicotine is a major component of tobacco smoke and increased IRAK-M expression has been considered one of the molecular determinants for the induction of the tolerant phenotype, our findings showing IRAK-M overexpression could partially explain the known influence of smoking on the onset and progression of inflammatory and infectious diseases.
尼古丁对α7烟碱型乙酰胆碱受体（α7 nAChR）的刺激可有效抑制脂多糖（LPS）刺激的巨噬细胞以及内毒素血症实验模型中促炎细胞因子的产生。α7 nAChRs下游的一条信号通路涉及JAK2/STAT3和NF-κB的协同作用，以干扰Toll样受体（TLR）的信号传导，该通路与尼古丁的这种抗炎作用有关。在此，我们确定了一种涉及白细胞介素-1受体相关激酶M（IRAK-M）的替代机制，IRAK-M是天然TLR介导的免疫反应的负调节因子。我们的数据表明，尼古丁在人巨噬细胞中在mRNA和蛋白质水平上调IRAK-M的表达，且这种作用是α7 nAChR激活的继发效应。通过使用受体下游不同信号分子的选择性抑制剂，我们提供证据表明，通过单一（JAK2/PI3K/STAT3）或两个汇聚级联反应（JAK2/STAT3和PI3K/STAT3）经由JAK2和/或PI3K激活STAT3对于尼古丁诱导的IRAK-M表达是必需的。此外，用IRAK-M基因特异性小干扰RNA下调这种表达可显著逆转尼古丁对LPS诱导的TNF-α产生的抗炎作用。有趣的是，预先暴露于尼古丁的巨噬细胞表现出更高的IRAK-M水平，并且对额外的LPS刺激的TNF-α反应降低，这种行为让人联想到在预先暴露于LPS的单核细胞或免疫受损脓毒症患者的单核细胞中鉴定出的“内毒素耐受”表型。由于尼古丁是烟草烟雾的主要成分，并且IRAK-M表达增加被认为是诱导耐受表型的分子决定因素之一，我们发现IRAK-M过表达可能部分解释了吸烟对炎症和感染性疾病的发生和进展的已知影响。
