In mammals, a central clock maintains the daily rhythm in accordance with the external environment. At the molecular level, the circadian rhythm is maintained by epigenetic regulation of the Circadian pathway. Here, we tested the role of particulate matter with an aerodynamic diameter ≤ 2.5 μm (PM_2.5) exposure during gestational life on human placental Circadian pathway methylation, as an important molecular target for healthy development. In 407 newborns, we quantified placental methylation of CpG sites within the promoter regions of the following genes: CLOCK, BMAL1, NPAS2, CRY1-2 and PER1-3 using bisulfite-PCR-pyrosequencing. Daily PM_2.5 exposure levels were estimated for each mother's residence, using a spatiotemporal interpolation model. We applied mixed-effects models to study the methylation status of the Circadian pathway genes and in utero PM_2.5 exposure, while adjusting for a priori chosen covariates. In a multi-gene model, placental Circadian pathway methylation was positively and significantly (p < 0.0001) associated with 3rd trimester PM_2.5 exposure. Consequently, the single-gene models showed relative methylation differences [Log(fold change)] in placental NPAS2 (+0.16; p = 0.001), CRY1 (+0.59; p = 0.0023), PER2 (+0.36; p = 0.0005), and PER3 (+0.42; p = 0.0008) for an IQR increase (8.9 μg/m³) in 3rd trimester PM_2.5 exposure. PM_2.5 air pollution, an environmental risk factor leading to a pro-inflammatory state of the mother and foetus, is associated with the methylation pattern of genes in the Circadian pathway. The observed alterations in the placental CLOCK epigenetic signature might form a relevant molecular mechanism through which fine particle air pollution exposure might affect placental processes and foetal development.

在哺乳动物中，中央时钟根据外部环境维持日常节律。在分子水平上，昼夜节律通过昼夜节律途径的表观遗传调控来维持。在这里，我们测试了胎龄期空气动力学直径≤2.5μm（PM _2.5）的微粒物质对人胎盘昼夜节律途径甲基化的作用，作为健康发展的重要分子靶标。在407例新生儿中，我们使用亚硫酸氢盐-PCR-焦磷酸测序对以下基因的启动子区域内CpG位点的胎盘甲基化进行了定量：CLOCK，BMAL1，NPAS2，CRY1-2和PER1-3。每日PM _2.5使用时空插值模型估算每个母亲的住所的暴露水平。我们应用混合效应模型研究了昼夜节律途径基因的甲基化状态和子宫内PM _2.5暴露，同时调整了先验选择的协变量。在多基因模型中，胎盘昼夜节律途径甲基化 与孕晚期PM _2.5暴露呈显着正相关（p <0.0001）。因此，单基因模型显示胎盘NPAS2（+0.16; p  = 0.001），CRY1（+0.59; p  = 0.0023），PER2的相对甲基化差异[Log（倍数变化）]。（+0.36; p  = 0.0005）和PER3（+0.42; p  = 0.0008 ）在孕中期PM _2.5暴露中的IQR增加（8.9μg / m ³）。PM _2.5空气污染是导致母亲和胎儿发炎的一种环境危险因素，与昼夜节律途径中的基因甲基化模式有关。观察到的胎盘CLOCK表观遗传学特征的改变可能形成相关的分子机制，通过该机制，细小颗粒的空气污染暴露可能影响胎盘的发育和胎儿的发育。