Particulate matter stimulates the NADPH oxidase system via AhR-mediated epigenetic modifications

Stimulation of human keratinocytes with particulate matter 2.5 (PM_2.5) elicits complex signaling events, including a rise in the generation of reactive oxygen species (ROS). However, the mechanisms underlying PM_2.5-induced ROS production remain unknown. Here, we show that PM_2.5-induced ROS production in human keratinocytes is mediated via the NADPH oxidase (NOXs) system and the Ca²⁺ signaling pathway. PM_2.5 treatment increased the expression of NOX1, NOX4, and a calcium-sensitive NOX, dual oxidase 1 (DUOX1), in human epidermal keratinocyte cell line. PM_2.5 bound to aryl hydrocarbon receptor (AhR), and this complex bound to promoter regions of NOX1 and DUOX1, suggesting that AhR acted as a transcription factor of NOX1 and DUOX1. PM_2.5 increased the transcription of DUOX1 via epigenetic modification. Moreover, a link between DNA demethylase and histone methyltransferase with the promoter regions of DUOX1 led to an elevation in the expression of DUOX1 mRNA. Interestingly, PM_2.5 increased NOX4 expression and promoted the interaction of NOX4 and Ca²⁺ channels within the cytoplasmic membrane or endoplasmic reticulum, leading to Ca²⁺ release. The increase in intracellular Ca²⁺ concentration activated DUOX1, responsible for ROS production. Our findings provide evidence for a PM_2.5-mediated ROS-generating system network, in which increased NOX1, NOX4, and DUOX1 expression serves as a ROS signal through AhR and Ca²⁺ activation.