DOI: 10.5061/dryad.np5hqbzwb
title: Effects of acute exposure to polystyrene nanoplastics on the channel catfish larvae: Insights from energy metabolism and transcriptomic analysis

description: Microplastics (nanoplastics) pollution has been a major ecological issue
 threatening global aquatic ecosystems. However, knowledge of the adverse
 effects of nanoplastics and the effects on freshwater ecosystems is still
 limited. To understand the impacts of nanoplastics on freshwater
 ecosystems, it is essential to reveal the physiological changes caused by
 nanoplastics in freshwater organisms, especially at their early
 life-history stages. In the present study, the larval channel catfish
 Ietalurus punetaus were exposed to gradient concentrations (0, 5, 10, 25
 and 50 mg/L) of 75-nm polystyrene nanoplastics (PS-NPs) for 24 h or 48 h,
 and changes in contents of energy metabolites, metabolic enzyme activities
 and transcriptome were assessed. The results showed glucose and
 triglyceride contents increased after 24 h of exposure to 10 or 25 mg/L of
 PS-NPs but decreased with increased concentrations or prolonged exposure
 duration. Activities of most metabolic enzymes analyzed decreased in the
 larvae after 48 h of exposure, especially in 25 or 50 mg/L of PS-NPs.
 These suggested that PS-NPs caused huge energy consumption and disturbed
 the energy metabolism in larval fish. Transcriptomic analysis showed that
 48 h of exposure to 50 mg/L PS-NPs affected the expression of
 genes involved in protein digestion and induced response of proteasomes or
 heat shock proteins in the larval I. punetaus. The genes involved in
 peroxisome proliferator-activated receptors (PPAR) pathway and
 biosynthesis of amino acids were activated after the exposure. PS-NPs also
 depressed the expression of the genes involved in gonad development or
 muscle contraction in the larval I. punetaus. Overall, acute exposure to
 75-nm PS-NPs disrupted the energy metabolism by consuming  the
 energy reserves, and affected a series of molecular pathways which may
 further affect the development and survival of fish. This study provided
 the information about adverse effects of nanoplastics on the fish larvae
 and revealed the molecular pathways for the potential adverse outcomes.
description: The channel catfish <em>Ietalurus punetaus
 </em>larvae were obtained from the National
 Genetics and Breeding Center of Channel Catfish (Nanjing, P.R. China) and
 were reared in tanks with aerated tap water at
 26<sup>o</sup>C, a
 dissolved oxygen concentration of about 5.0 mg/L and a 12 h light/dark
 photoperiod. After two-week acclimation and a 24-h fasting, the larvae
 were exposed to 50 mg/L of 75 nm polystyrene nanoplastics for 48 h plus a
 control group without exposure. The
 unlabeled 75-nm PS-NPs particles used in the present study were purchased
 from Baseline Chromtech Research Centre, Tianjin, China.
 After the exposure, the larvae were
 whole-body sampled and the RNAseq was performed. Each group contained
 three replications. Total RNA was isolated from the
 whole-body samples using a miRNA isolation kit (Invitrogen, USA). The
 concentration and integrity of total RNA were determined with a
 bioanalyzer (Nanodrop 2000, Thermo Scientific, USA) and agarose gel
 electrophoresis, respectively. The mRNA was isolated from total RNA using
 oligo(dT) magnetic beads and then broken into fragments. Double-stranded
 cDNAs were generated with reverse transcribed fragments followed by end
 repair and adapter attachment. After PCR amplification, the quality of the
 cDNA library was evaluated using an Agilent bioanalyzer (Agilent, USA) and
 then paired-end sequenced on the Illumina Hiseq X Ten
 platform. Clean reads were obtained by removing reads
 containing poly-N and with low quality using Trimmomatic (v. 0.36). Clean
 reads were mapped to a reference genome using hisat2 (v. 2.2.1.0).
 Expression levels of genes
 were assessed as fragments per kilobase of exon million (FPKM) using
 Cufflinks (v. 2.2.1). For genes from the PS-NPs group and control group,
 FPKMs of each gene were used to conduct DEGs analysis with DESeq R package
 (v. 1.18.0). The thresholds for scanning DEGs were set as P-adjust
 &lt; 0.05 and fold change &gt; 2.