Novel cellular effects of ultrafine particulate matter from an underground railway station uncovered through RNAseq

Abstract

Background: In underground railways, airborne particulate matter (PM) concentrations are significantly elevated compared to outdoors. Underground PM is especially rich in iron and transition metals; in the ultrafine fraction (UFPM; diameter Aim: To analyse cellular responses to underground UFPM beyond the constrained range of markers commonly used. Methods: UFPM was collected from a European underground station. UFPM-induced antioxidant response element (ARE) activation by the transcription factor Nrf2 was measured in a reporter epithelial cell line transiently transfected with an Nrf2-binding ARE-luciferase construct. Healthy-donor primary bronchial epithelial cells (PBECs) were cultured at air-liquid interface (ALI) to form mucociliary cultures, and exposed to 25µg/ml UFPM for 6h/24h. RNAseq was performed to identify differentially expressed genes (DEGs) following UFPM exposure. Results: An antioxidant response to underground UFPM was seen with significant activation of ARE after 24h UFPM exposure. In PM-exposed ALI cultures, after 6h there were 52 DEGs (13 up/39 down), particularly associated with epithelial maintenance, whereas after 24h there were 23 DEGs (17 up/6 down), notably relating to redox homeostasis and metal binding. There was prolonged up-regulation of several members of the metal-binding antioxidant metallothionein (MT) family, partially responsive to iron chelation (desferrioxamine) and ROS scavenging (N-acetylcysteine). Conclusion: These data suggest time-dependent responses to metal-rich UFPM and highlight novel markers of exposure to PM constitutents, such as MTs.