Maternal-Derived Polystyrene Nanoplastics Impair Early Retinal Development in Zebrafish ( Danio rerio )

The ubiquitous presence of nanoplastics (NPs) has drawn widespread attention for their accumulation in reproductive tissues, posing latent threats to the delicate retina. Nevertheless, the transgenerational effects of maternally transferred NPs on embryonic retinal morphogenesis and functional development remain largely uncharacterized. Here, we microinjected 60 nm polystyrene NPs (PS-NPs) into the animal pole of zebrafish zygotes to simulate maternal exposure. PS-NP exposure caused pronounced effects in zebrafish larvae at 3 days postfertilization (dpf). At this key developmental stage, exposed larvae developed microphthalmia. Confocal imaging revealed that PS-NPs were broadly distributed across retinal layers, with a preferential accumulation in the vicinity of photoreceptor region. Histological analysis revealed significant thinning of the photoreceptor outer segments (OS) accompanied by marked morphological abnormalities. Transmission electron microscopy confirmed substantial OS shortening and disorganization of disc structures, characterized by reduced disc thickness, increased spacing, and decreased flatness. In addition, mitochondrial swelling with disrupted cristae was observed, along with alterations in retinal pigment epithelium (RPE) melanosomes. Immunofluorescence analysis also indicated aberrant signal expression across multiple retinal cell types, including photoreceptors and RPE cells. Transcriptome profiling revealed that differentially expressed genes were significantly enriched in key visual cycle-related pathways, particularly those associated with retinol binding. These findings were corroborated by gene set enrichment analysis (GSEA) and reverse transcription quantitative polymerase chain reaction (RT-qPCR) validation. Additional RT-qPCR assays indicated activation of oxidative stress and inflammatory pathways. Notably, OS thickness remained significantly reduced compared with controls at 14 dpf, while some phenotypic abnormalities gradually diminished at later developmental stages (5, 10, and 14 dpf). Collectively, these results support a model in which the RPE-OS functional unit represents a primary target of 60 nm PS-NPs. Both direct physical damage and subsequent oxidative stress and inflammatory responses likely contribute to its dysfunction, ultimately impairing RPE function, disrupting OS renewal, and promoting photoreceptor degeneration. These findings highlight the potential visual risks associated with maternally derived nanoparticle exposure.