Responses of the Proteome and Metabolome in Livers of Zebrafish Exposed Chronically to Environmentally Relevant Concentrations of Microcystin-LR

In this study, for the first time, changes in expressions of proteins and profiles of metabolites in liver of the small, freshwater fish Danio rerio (zebrafish) were investigated after long-term exposure to environmentally relevant concentrations of microcystin-LR (MC-LR). Male zebrafish were exposed via water to 1 or 10 mu g MC-LR/L for 90 days, and iTRAQ-based proteomics and H-1 NMR-based metabolomics were employed. Histopathological observations showed that MC-LR caused damage to liver, and the effects were more pronounced in fish exposed to 10 mu g MC-LR/L. Metabolomic analysis also showed alterations of hepatic function, which included changes in a number of metabolic pathways, including small molecules involved in energy, glucose, lipids, and amino acids metabolism. Concentrations of lactate were significantly greater in individuals exposed to MC-LR than in unexposed controls. This indicated a shift toward anaerobic metabolism, which was confirmed by impaired respiration in mitochondria. Proteomics revealed that MC-LR significantly influenced multiple proteins, including those involved in folding of proteins and metabolism. Endoplasmic reticulum stress contributed to disturbance of metabolism of lipids in liver of zebrafish exposed to MC-LR. Identification of proteins and metabolites in liver of zebrafish responsive to MC-LR provides insights into mechanisms of chronic toxicity of MCs.