Differential cellular uptake and trafficking of nanoplastics in two hemocyte subpopulations of mussels Perna viridis

Abstract

Nanoplastics (NPs) could be ingested by bivalves and translocated to their hemocytes, which played critical roles in immune-defense. In this study, highly fluorescent aggregation-induced emission nanoplastics (AIE-NPs) of two sizes (50 nm and 200 nm) were utilized to explore the dynamic systems of cellular uptake, intracellular trafficking, and ultimate localization in the granulocyte and agranulocyte subpopulations of hemocytes in the green mussels Perna viridis. We firstly revealed their differential cellular uptake and trafficking of nanoplastics in two hemocyte subpopulation systems. Specifically, agranulocytes performed relatively faster uptake rate for nanoplastics of two sizes, whereas granulocytes had about tenfold higher accumulation capacity. Unexpectedly, there was little removal of nanoplastics in the two subpopulation systems, and such persistence probably could trigger more severe cytotoxicity. Considerable amounts of 200 nm NPs without plasma membrane wrapping were present in the agranulocytes, which may be related to their unique caveolae-mediated uptake pathway. We further demonstrated that the internalized NPs accelerated the differentiation of agranulocytes into granulocytes with higher immunoreactivity, which may be a crucial detoxification mechanism. Our results highlighted the size-driven fate of NPs in different subpopulations of mussel hemocytes, contributing to a more comprehensive understanding of the toxicity of NPs to aquatic organisms.