Inhaled polystyrene microplastics impaired lung function through pulmonary flora/TLR4-mediated iron homeostasis imbalance

Microplastics (MPs) have been found in the air, human nasal cavity, and lung, suggesting that the respiratory tract is one of the important exposure routes for MPs. The lung is a direct target organ for injury from inhaled MPs, but data on lung injury from longer-term exposure to environmental doses of MPs are limited, and the mechanisms remain unclear. Here, C57BL/6 J mice were treated with 5 μm polystyrene (PS)-MPs by intratracheal instillation (0.6, 3, 15 mg/kg) for 60 days to establish MPs exposure model. We found that PS-MPs lead to increased collagen fibers and decreased lung barrier permeability and lung function in lung tissue. Mechanistically, the abundance of gram-negative bacteria in the pulmonary flora increased after inhalation of PS-MPs, causing lipopolysaccharide (LPS) release. The expression of Toll-like receptor 4 (TLR4), the key receptor of LPS, was increased, and ferroptosis occurred in lung tissue cells. Further in vitro intervention experiments were performed, pulmonary flora/TLR4-induced imbalance of lung iron homeostasis is an important mechanism of PS-MPs-induced lung injury. Our study provides new evidence for lung injury caused by environmental doses of MPs and strategies to prevent it through longer-term dynamic observation.