Effect of Low-Dose Cadmium Exposure on DNA Methylation in the Endangered European Eel

There is increasing evidence that epigenetics can play a key role in the etiology of diseases engendered by chronic pollutant exposure. Although epigenetics has received significant attention in the field of biomedicine during the last years, epigenetics research is surprisingly very limited in ecotoxicology. The aim of the present study was to investigate the possible effects of low-dose cadmium exposure on the DNA methylation profile in a critically endangered fish species, the European eel. Eels were exposed to environmentally realistic concentrations of cadmium (0.4 and 4 mu g.L-1) during 45 days. The global CpG methylation status of eel liver was determined by means of a homemade ELISA assay. We then used a methylation-sensitive arbitrarily primed PCR method to identify genes that are differentially methylated between control and Cd-exposed eels. Our results show that cadmium exposure is associated with DNA hypermethylation and with a decrease in total RNA synthesis. Among hypermethylated sequences identified, several fragments presented high homologies with genes encoding for proteins involved in intracellular trafficking, lipid biosynthesis, and phosphatidic acid signaling pathway. In addition, few fragments presented high homologies with retrotransposon-like sequences. Our study illustrates how DNA methylation can be involved in the chronic stress response to Cd in fish.