Polystyrene Nanoplastics Disrupt Lateral Line Neuromasts and Impair Flow-Guided Behaviors in Zebrafish.

Nanoplastics (NPs) are pervasive aquatic pollutants; however, their effects on fish mechanosensory function remain poorly understood. This study investigated the impacts of polystyrene NPs (PS-NPs) on the lateral line system of zebrafish (Danio rerio) across life stages by integrating hydrodynamic behavioral assays with cellular, ultrastructural, transcriptomic, and protein-level analyses. Our results showed that PS-NP exposure significantly impaired flow-guided behaviors and hydrodynamic sensing in both life stages. Adult zebrafish exhibited reduced trajectory linearity and directional precision during rheotaxis, while larvae showed compromised spatial stability and elevated angular motion under vortex-flow conditions. These functional alterations were accompanied by reduced DASPEI-positive hair-cell counts, increased apoptosis, shortened kinocilia, and disorganization and partial loss of apical hair bundles. Integrated bulk and single-cell RNA sequencing revealed consistent perturbations in pathways related to mitochondrial bioenergetics, glutathione metabolism, AMPK/mTOR-associated signaling, cytoskeletal organization, and vesicle trafficking. Whole-larva protein analysis further showed increased LC3B and ACSL4 abundance and decreased GPX4 abundance, consistent with autophagy- and ferroptosis-associated molecular alterations. In conclusion, these results identify the lateral line as a sensitive target of NP exposure and suggest that PS-NPs may impair hydrodynamic sensing through neuromast structural damage and metabolic-redox dysregulation.