Dietary methylmercury alters the proteome in Atlantic salmon (Salmo salar) kidney

Methylmercury (MeHg) is an environmental contaminant most known for its severe neurotoxic effects. Although accumulation of MeHg tends to be several folds higher in kidney compared to other tissues, studies on nephrotoxic effects are almost non-existing. In this study we aim to investigate the toxicity of dietary MeHg in kidney of Atlantic salmon (Salmo salar).

Atlantic salmon were exposed to dietary MeHg for a period of 8 weeks, before the fish were euthanized and kidney was sampled for proteomic and real time RT-PCR analysis, as well as for mercury determination. Protein separation was done with 2-D PAGE, and differentially regulated spots were picked for analysis using liquid chromatography MS/MS analysis. Moreover, whole blood and liver tissue were sampled for mercury determination and real time RT-PCR (liver).

MeHg exposed fish accumulated significantly more mercury (Hg) than control fish. The proteomic analysis revealed differential abundance of 26 spots in the kidney, and 14 of these protein spots were successfully identified. The proteins identified indicated effects of MeHg on; metabolism, inflammation, oxidative stress, protein-folding, and cell-structural components. Gene expression analysis of selected markers revealed few differentially regulated transcripts in kidney and liver in the exposed fish compared to the control fish. However, the affected transcripts indicated a disruption in the expression of two metabolic markers due to MeHg exposure in liver.

This study suggests that dietary MeHg has similar effects in kidney as previously shown for other tissues in fish. The effects observed were in markers for oxidative stress, inflammation and energy metabolism. The identification of proteomic markers in this study provides a basis for a better understanding of MeHg-induced nephrotoxicity in fish.