Fig. 9.

The methylation status of the POLD1 promoter, the expression levels of POLD1 and E2F1 and the binding affinity of E2F1 to the POLD1 promoter in lymphocytes from healthy people of different ages (n = 14 in 20 ~ years to 70 ~ years group, n = 8 in 80 ~ years and 90 ~ years group). a, b The mRNA expression levels of POLD1 and E2F1 in lymphocytes from healthy people of different ages. GAPDH was used for normalization of the data. Values represent the mean ± SD. c, d The protein expression levels of POLD1 and E2F1 in the lymphocytes of healthy people of different ages. GAPDH was used for normalization of the data. Values represent the mean ± SD. e The percentage of cytosine methylation of CpG site 33–38 of CpG island 3 in the lymphocytes of healthy people of different ages (n = 3 in each group), as measured by bisulfite DNA sequencing analysis. f The methylation levels of the POLD1 promoter in the lymphocytes of healthy people of different ages (n = 3 in each group). g, h The binding affinity of E2F1 for the POLD1 promoter in the lymphocytes from healthy people of different ages. Densitometric analysis of the band intensity in different groups, normalized to the input. The data were compared using one-way ANOVA, with three independent experiments in each group; *p < 0.05, **p < 0.01, *** p < 0.005, vs. the 20 ~ years group