Effects of zebrafish exposure to high-density polyethylene and polystyrene microplastics at molecular and histological levels

Due to the constant increase of plastic use and production, microplastics (MPs)
\nhave become a contaminant of serious concern for the marine environment.
\nHowever, detailed information about biological pathways affected by the exposure
\nto different MP polymers is still lacking, in particular at transcriptome level. The
\npresent study focused on the identification of the molecular pathways affected by a
\nchronic exposure of zebrafish (Danio rerio) to different concentrations of a
\ncombination of two environmentally relevant MPs for 20 days. Adult zebrafish
\nwere fed daily with dry fish food (control group, N=12) and food supplemented
\nwith a mix of pristine high-density polyethylene and polystyrene microplastics (two
\nexperimental groups: 0.1 and 1 mg/L, N=12 each). The microplastics dimension
\nranged from below 25 μm to 90 μm for both polymers. At the end of the exposure
\nperiod, the liver was dissected and its whole transcriptome analyzed by
\nnext-generation RNA-sequencing technologies on an Illumina platform. In
\naddition, the gastrointestinal tract and the gills were dissected and fixed for
\nhistology and immunohistochemistry. The exposure to polyethylene and
\npolystyrene microplastics affected the liver transcriptome in a dose-dependent way,
\ninducing the differential regulation of specific suites of genes. Histological analyses
\nevidenced changes in the inflammatory response occurring at the two mucosal
\ntissues selected for observation. The correlation of histological alterations with
\ndifferential gene expression will be addressed and discussed. This study provides a
\ncomprehensive transcriptomic dataset useful for ecotoxicological studies on other
\nfish species.