Environmental pollution in the form of particulate matter <2.5 μm (PM2.5) is a major risk factor for diseases such as lung cancer, chronic respiratory infections, and major cardiovascular diseases. Our goal was to show that PM2.5 eliciting a proinflammatory response activates the immune‐pineal axis, reducing the pineal synthesis and increasing the extrapineal synthesis of melatonin. Herein, we report that the exposure of rats to polluted air for 6 hours reduced nocturnal plasma melatonin levels and increased lung melatonin levels. Melatonin synthesis in the lung reduced lipid peroxidation and increased PM2.5 engulfment and cell viability by activating high‐affinity melatonin receptors. Diesel exhaust particles (DEPs) promoted the synthesis of melatonin in a cultured cell line (RAW 264.7 cells) and rat alveolar macrophages via the expression of the gene encoding for AANAT through a mechanism dependent on activation of the NFκB pathway. Expression of the genes encoding AANAT, MT1, and MT2 was negatively correlated with cellular necroptosis, as disclosed by analysis of Gene Expression Omnibus (GEO) microarray data from the human alveolar macrophages of nonsmoking subjects. The enrichment score for antioxidant genes obtained from lung gene expression data (GTEx) was significantly correlated with the levels of AANAT and MT1 but not the MT2 melatonin receptor. Collectively, these data provide a systemic and mechanistic rationale for coordination of the pineal and extrapineal synthesis of melatonin by a standard damage‐associated stimulus, which activates the immune‐pineal axis and provides a new framework for understanding the effects of air pollution on lung diseases.

The phenotype of primary cells in culture varies according to the donor environmental condition. We recently showed that the time of the day imposes a molecular program linked to the inflammatory response that is heritable in culture. Here we investigated whether microRNAs (miRNAs) would show differential expression according to the time when cells were obtained, namely daytime or nighttime. Cells obtained from explants of cremaster muscle and cultivated until confluence (∼20 days) presented high CD133 expression. Global miRNA expression analysis was performed through deep sequencing in order to compare both cultured cells. A total of 504 mature miRNAs were identified, with a specific miRNA signature being associated to the light versus dark phase of a circadian cycle. miR-1249 and miR-129-2-3p were highly expressed in daytime cells, while miR-182, miR-96-5p, miR-146a-3p, miR-146a-5p, and miR-223-3p were highly expressed in nighttime cells. Nighttime cells are regulated for programs involved in cell processes and development, as well as in the inflammation, cell differentiation and maturation; while daytime cells express miRNAs that control stemness and cytoskeleton remodeling. In summary, the time of the day imposes a differential profile regarding to miRNA signature on CD133(+) cells in culture. Understanding this daily profile in the phenotype of cultured cells is highly relevant for clinical outputs, including cellular therapy approaches. J. Cell. Physiol. 231: 1953-1963, 2016. © 2016 Wiley Periodicals, Inc.