Lysosomal dependent transcytosis of polystyrene nanoplastics within macrophages

As emerging pollutants, nanoplastics (NPs) have emerged as significant environmental pollutants with potential health risks and have been largely investigated owing to their distinctive physicochemical properties and ubiquitous environmental distribution. However, research on the intracellular complete migration of NPs is limited, particularly with respect to exocytosis. Here, we exposed human macrophages to polystyrene nanoplastics (PS-NPs) and observed that PS-NPs induced the accumulation of lysosomes within the cells and lead to an increase in their contents. Additionally, PS-NPs co-localized with lysosomes and triggered lysosomal activation. Using a previously established method for PS-NPs adsorption to intracellular proteins and employing proteomic and bioinformatic approaches, we confirmed that after entering the cell, PS-NPs predominantly adsorbed proteins related to the lysosomal pathway, and stably adsorbed the key lysosomal protein cathepsin D (CTSD). Further studies identified that PS-NPs induced lysosomal exocytosis, during which the lysosomal-specific mature-CTSD adsorbed onto PS-NPs and was co-released from the cell. This process was mediated by Ca²⁺. In summary, this study elucidated the lysosome-dependent transcytosis of PS-NPs and established a novel method for verifying lysosomal exocytosis using mature-CTSD as a marker.