Genome-wide screening of CpG island methylation changes induced by low-dose X-ray radiation in mice / 南方医科大学学报

<p><b>OBJECTIVE</b>To study the methylation changes in promoter CpG islands induced by low-dose X-ray radiation (LDR).</p><p><b>METHODS</b>Twenty male BALB/c mice were randomly divided into control and fractionated radiation group exposed to 6 MV X-ray for 10 days (0.05 Gy/day). All the mice were sacrificed 2 h after the last radiation on day 10, and blood samples were collected for detecting DNA methylation changes using Roche-NimbleGen mouse DNA methylation 3×720K Promoter Plus CpG Island Array. MeDIP-qPCR was used to further validate the methylation status of specific genes.</p><p><b>RESULTS</b>A total of 811 genes were found to show specific hypermethylation in fractional radiation group as compared with the control group, involving almost all the main biological processes by GO analysis. Eight candidate genes (Rad23b, Tdg, Ccnd1, Ddit3, Llgl1, Rasl11a, Tbx2, and Slc6a15) were confirmed to be hypermethylated in LDR samples by MeDIP-qPCR, consistent with the results of the methylation chip study.</p><p><b>CONCLUSION</b>LDR induces promoter hypermethylation on specific genes, which may contribute to radiation-induced pathogenesis.</p>

Protective effects of EGCG against methylation changes induced by low dose radiation / 中华放射医学与防护杂志

Objective To investigate the role of epigallocatechin gallate ( EGCG) in reversing the CpG island methylation of Rad23b and Ddit3 gene promoter and its mRNA expression induced by 0?5 Gy X-rays. Methods Thirty BALB/c male mice were randomly divided into 6 groups: control group, irradiation group, low/high dose of EGCG group, low/high dose of EGCG with irradiation group. For the irradiation group, mice were fractionally exposed with 6 MV X-rays for 10 d (0?05 Gy/d × 10 d). 2 hours after the final irradiation, all mice were killed and such tissues as blood, kidney, liver, spleen, brain, and lung were collected. Methylation and expression levels of Rad23b and Ddit3 were measured by bisulfate sequencing primers ( BSP) and Real-time PCR, respectively. Results Compare to the control group, Rad23b was hypermethylated in PBMC, liver, spleen, brain and lung (t= -20?19, -14?80, -12?05,-28?42, -12?58, P<0?05) in the irradiation group. Meanwhile, its mRNA expression level was down-regulated in PBMC, liver, brain and lung (t=25?25, 17?43, 11?53, 22?85, P<0?05). Similarly, a significant hypermethylation change of Ddit3 was observed in PBMC, liver and lung after irradiation ( t=-52?89, -20?31, -3?85, P<0?05) so that the mRNA expression of Ddit3 decreased in PBMC and liver ( t = 11?89, 16?52, P < 0?05 ). Compared to the irradiation group, EGCG with different concentrations of 10, 20 mg/kg significantly reduced the methylation level of Rad23b and Ddit3 ( t =-13?39-7?99, P<0?05), and induced re-expression of mRNA (t= -34?02 - -2?89, P<0?05). This change was more notable in the irradiation group with the high dose of EGCG. Conclusions As a natural drug, EGCG may play an important role in affecting DNA methylation and hence protects DNA from radiation damage.

Genome-wide DNA methylation changes induced by low dose radiation in mouse / 中华放射医学与防护杂志

Objective To study the whole genome DNA methylation changes induced by low dose radiation (LDR) in mouse,and mRNA expression profiles of DNMT1 and MBD2 in peripheral blood mononuclear cell (PBMC) and tissues.Methods Thirty male BALB/c mice were randomly divided into 3 groups:control,single exposure (0.5 Gy),and fractionated exposure of 6 MV X-rays for 10 d (0.05 Gy/d × 10 d).Control mice were sham-treated.To determine the immediate (early) effect of irradiation,15 mice (5/group) were sacrificed 2 h after the last irradiation.The other 15 mice were sacrificed 1 month after the last irradiation (delayed effect).Before sacrifice,blood was sampled immediately.Kidney,liver,spleen,brain and lung tissues were collected.A global DNA methylation quantification Kit and highperformance liquid chromatography (HPLC) were used to investigate the methylation level in blood DNA.The expressions of DNMT1 and MBD2 were determined by RT-PCR.Results For the early effects of irradiation,as compared with controls,fractionated exposure to X-ray irradiation led to the significant depression of global DNA methylation level in blood (t =10.19 and 8.93,P ＜ 0.05).DNMT1 and MBD2 mRNA were down-regulated in PBMC,kidney and liver (t =5.06,3.01,3.97,12.25,3.50 and 3.73,P ＜0.05),and MBD2 was also down-regulated in spleen (t =3.03,P ＜ 0.05).However,no changes were observed in single exposed group.As for the delayed effects,the methylation levels of blood were not changed in the single or fractionated exposed groups,and only MBD2 mRNA was down-regulated in PBMC and brain of fractionated exposed group (t =3.52 and 2.85,P ＜ 0.05).Conclusions Fractionated LDR exposure can induce genome DNA hypomethylation,which is tissue-specific,and may be related with down-regulation of DNMT1 and MBD2.