Polystyrene nanoplastics and benzo(a)pyrene synergistically induce lung fibrosis and inflammation via relaxin signalling in mice

Micro- and nanoplastics (MNPs) are emerging pollutants that can carry harmful substances like benzo(a)pyrene, posing potential health risks. While the harmful effects of nanoplastics on the lungs are known, how they interact with benzo(a)pyrene to affect cellular communication remains unclear. In our study, We explore this interplay using a 16-week mouse model exposed to environmentally relevant doses of polystyrene nanoplastics, benzo(a)pyrene, or a combination of both. We find that only the combined exposure leads to significant lung damage, characterized by severe inflammation and tissue scarring, which are not seen with single exposures. This combined exposure also increases oxidative stress and reduces antioxidant defenses in the lungs. Furthermore, we notice increased levels of inflammation-related molecules and markers of lung tissue damage, confirming a more severe toxic effect. Transcriptomic analysis highlights the involvement of the Relaxin signaling pathway, which influences inflammatory and tissue damage processes through PI3K-AKT and MAPK cascades; Relaxin4 activated PLC-IP3R, opening ER calcium channels and raising cytosolic Ca²⁺, which triggered macrophage extracellular trap (MET) formation. Additionally, a macrophage-MLE-12 co-culture system confirmed that Mix-induced METs are linked to the exacerbation of alveolar inflammation and the progression of pulmonary fibrosis. Our findings reveal novel molecular connections that explain how these pollutants worsen lung health, suggesting that targeting the identified signaling pathways could offer a potential approach to mitigating these harmful effects.