The Effects Of Cadmium On The DNA Methylation In Mouse Tissues And Early Embryos

With the development of the industry, the environmental problem caused by cadmium pollution get more and more attention. Organization and reproductive toxicity of cadmium and the impact on embryonic development had become the hot research. But the molecular mechanism of cadmium toxicity is still unclear. Chronic cadmium poisoning was due to long-term consumption of food containing cadmium, and long-term consumptbn of cadmium pollution water. It is a locally systemic disease. In this research, mice were free to drink water containing cadmium chloride (64 mg/L), which was used as the animal model. By detecting the effect of cadmium on genomic DNA methylation and imprinting genes DNA methylation in liver, kidney ovary and embryo with early stage, cadmium toxicity associated with epigenetic was explored.1. Effects of cadmium on gene expression of DNMTs and MTs in some tissueTo study the effect of cadmium on gene expression of DNMTs and MTs, RT-PCR was used to examine the mRNA levels of DNMT1o, DNMT1s, DNMT3a, DNMT3b,MT-Ⅰ and MT-Ⅱ in liver, kidney and ovary of mice which were free to drink cadmium chloride (64 mg/L) water for 35 days. The results showed that the expression level of Dnmtls and Dnmt3b were significantly increased in the liver of cadmium treatment group, while MTs was increased without significant However, cadmium had no significant effect on the expression of DNMTs in kidney and ovary, and the effect of cadmium on the expression of MTs in kidney and ovary was slight The results indicated that the effect of cadmium on the expression of DNMTs and MTs was mainly in the liver but not in the kidney and ovary.2. Effects of cadmium on DNA methylation in mouse liver, kidney and ovaryMice were free to drink water containg cadmium chloride (64 mg/L) for 35 days. And liver, kidney and ovary were collected. ELIS A and BSP were respectively used to examine the genomic DNA methylation and single gene DNA methylation including H19, LIN El and MT. The results showed that cadmium resulted in the slight changes of genomic DNA methylaiton in liver, kidney and ovary without significant There were no significant changes in LINE1 and MT DNA methylation LINE1 maintained hypermethylation, while MT was hypo methylation in all samples. Cadmium exposure resulted in significant decrease of H19 methylation in liver. It was 29.74%±3.05% in cadmium treatment group, while it was 39.11%±2.67% in control. As for kidney, H19 methylation was significantly increased to 45.24%±2.98%, comparing with 28.2%±3.23% in the control group. Also cadmium exposure can cause ovary H19 methylation level rise, but the result is not significant, the control group: 34.67%±3.97%, the cadmium treatment group:42.08%±2.37%(p>0.05). The results show that female straight drinking water containing cadmium for 35d won’t directly affect the level of genomic DNA methylation as well as the LINE1 and MT DNA methylation level in liver, kidney and ovary, but the impact on DNA methylation of H19 is site specific.3. Effects of cadmium on the DNA methylation of embryo at the early stageTo understand the effects of cadmium on early embryonic DNA methylation, BSP and COBRA were used to examine the DNA methylation of the imprinted genes and retrotransposon LINE1 gene in the early embryos from pregnant mice which were free to drink cadmium chloride (64 mg/L) water for 2 days. The results showed that H19 DNA methylation was significantly reduced to 15.44%±1.58% in cadmium treatment group, while it was 48.97%±1.66% in control group. Enzyme digestion results further confirmed it. Peg3 was hypomethylation in both groups. LINE1 DNA methylation in the control group and in the treatment group were 34.85%±1.79% and 39.39%±1.52%, respectively. This suggested that cadmium exposure to pregnant mice would directly result in abnormal DNA methylation of H19, paternal imprinted gene, but it has no significant effect on Peg3, maternally imprinted gene, and LINE1.4. ConclusionCadmium exposure can affect DNA methylation patterns in mouse early embryos; Early cadmium exposure can affect DNA methylation patterns in mouse liver and kidney, but have less effect on DNA methylation patterns in the ovaries.