Zebrafish exposure to high-density polyethylene and polystyrene microplastics: effects on liver transcriptome and gastrointestinal histology

Due to the constant increase of plastic use and production, microplastics (MPs) have become a contaminant of serious concern for the aquatic environment. However, the biological pathways affected by the exposure to different MP polymers still needs to be elucidated, in particular at the ”omic” level. The present study focuses on the identification of the molecular pathways affected by the expo- sure of zebrafish (Danio rerio) to different concentrations of a mixture of two environmentally relevant MPs. Adult zebrafish were fed daily with dry fish food (control group, N=12) and food supplemented with a mix of pristine high-density polyethylene and polystyrene microplas- tics (two experimental groups: 0.1 and 1 mg/L, N=12 each) for 20 days. The MPs dimension ranged from 25 im to 90 im for both polymers. At the end of the exposure period, the fish liver was dissected, and its whole transcriptome was analyzed by next-generation RNA-sequencing technologies on an Illumina platform. In addition, the gastrointestinal tract and the gills were dissected and fixed for histology and immunohistochemistry. The exposure to polyethylene and polystyrene microplastics affected the liver transcriptome in a dose-dependent way, inducing the differential regulation of specific suites of genes compared to the control. Histological analyses evidenced changes in the inflammatory response occurring at the two mucosal tissues selected for observation in the MPs treated fish. The correlation of histological alterations with differential gene expression could represent a useful approach to decipher early warning for effects at higher biological organization. This study provides a comprehensive transcriptomic dataset, useful to understand a wide range of biological pathways affected by MPs exposure as a model for studies on fish also in the field.