High-level dietary cadmium exposure is associated with global DNA hypermethylation in the gastropod hepatopancreas

Abstract

5-methylcytosine (5mC) is a key epigenetic mark which influences gene expression and phenotype. In vertebrates, this epigenetic mark is sensitive to Cd exposure, but there is no information linking such an event with changes in global 5mC levels in terrestrial gastropods despite their importance as excellentecotoxicological bioindicators of metal contamination. Therefore, we first evaluated total 5mC content in DNA of the hepatopancreas of adult Cantareus aspersus with the aim to determine whether this epigenetic mark is responsive to Cd exposure. The experiment was conducted under laboratory conditions and involved a continuous exposure, multiple dose- and time-point (14, 28, and 56 days) study design. Hepatopancreas cadmium levels were measured using Flame Atomic Absorption Spectrometry and the percentage of 5-mC in samples using an ELISA-based colorimetric assay. Snail death rates were also assessed. Our results, for the first time, reveal the presence of 5mC in C. aspersus and provide evidence for Cd-induced changes in global 5mC levels in DNA of gastropods and mollusks. Although less sensitive than tissue accumulation, DNA methylation levels responded in a dose- and time-dependent manner to dietary cadmium, with exposure dose having a much stronger effect than exposure duration. An obvious trend of increasing 5mC levels was observed starting at 28 days of exposure to the second highest dose and this trend persisted at the two highest treatments for close to one month, when the experiment was terminated after 56 days. Moreover, a strong association was identified between Cd concentrations in the hepatopancreas and DNA methylation levels in this organ. These data indicate an overall trend towards DNA hypermethylation with elevated Cd exposure. No consistent lethal effect was observed, irrespective of time point and Cd-dosage. Overall, our findings suggest that the total 5mC content in DNA of the hepatopancreas of land snails is responsive to sublethal Cd exposure and give new insights into invertebrate environmental epigenetics.

An 112 Days Experiment on Dietary Cadmium Retention in Hepatopancreas in Adult Cantareus aspersus Snails

“…1). The measured values in controls were within the same range with those assessed in one of our previous experiments [1], as well as with those determined in specimens sampled from unpolluted areas [15,16]. The maximum Cd levels observed here are also of interest from an ecotoxicological point of view since they are among the highest values ever reported in C. aspersus.…”

“…In a previous study, were investigated the retention of Cd in adult C. aspersus snails at similar exposure doses, but for shorter durations, namely 14, 28 and 56 days. Interestingly, the dose from which significant increases in hepatopancreas Cd were detected was similar [1].These results suggest the potential existence of threshold level below which these land snails are able to maintain relatively stable cadmium concentrations in the hepatopancreas, which is up to 5 mg/kg d. wt.…”

“…These treatments were abbreviated as 0Cd, 0.02Cd, 0.05Cd, 0.2Cd, 1Cd, 10Cd and 100Cd. The rearing method and the corresponding procedures were similar to those used in our previous experiments [1].…”

“…Cadmium (Cd) contamination in terrestrial environments is a major global issue; it increases year after year with a massive impact on everyday life ranging from ecological sustainability and food security to human health. This trace metal (TM) occurs naturally in the Earth' crust with an abundance of 0.1 -0.5 mg/kg dry weight (mg/kg d. wt) [1].…”

Transgenerational Effects of Copper on a Freshwater Gastropod, Planorbella pilsbryi

“…Additionally, this study demonstrated the presence of a relationship between DNA methylation and multigenerational effects, with DNA methylation decreasing with increasing prednisolone concentration in the F1 (Bal et al 2017). Furthermore, metals such as cadmium have been shown to induce DNA methylation in terrestrial snails, although minimal literature exists linking DNA methylation caused by metal exposure with multigenerational effects (Nica et al 2017).…”