Effects of acute exposure to polystyrene nanoplastics on the channel catfish larvae: Insights from energy metabolism and transcriptomic analysis

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.