Objective:To detect DNMT1 protein and m RNA expression levels in epidermis keratinocytes of sun-unexposed area in different age groups and to explore the significance of DNMT1 in the process of human skin aging. Methods:Forty cases of sun-unexposed area specimens of the epidermis were obtained and were divided into 4 groups according to age:children group(0 to14 years old)

youth group(15 to 39 years old)

middle-age group(40 to 59 years old)and elderly group(aged 60 and above). Immunohistochemistry and RT-PCR methods were used to detect the DNMT1 protein and m RNA expression level in each case and the differences of the DNMT1 expression level between each age group were analyzed. Results:DNMT1 mainly expressed in the keratinocytes nuclei;the expression level of DNMT1 in keratinocytes was on the decline from children

youth

middle-aged to elderly group. DNMT1 positive expression rates in epidermis keratinocytes of children group

youth group

middle-age group and elderly group were 84.7%

69.4%

51.1%

12.3% respectively and 23.10

19.30

14.40

3.80 scores(P value of every two groups<0.05). The relative expression levels of DNMT1 m RNA were 1.347

0.817

0.567 and 0.202. The relative expression levels of DNMT1 protein were 1.102

0.494

0.320 and0.088

and the expression levels of DNMT1 was decreased as aging(P value of every two groups<0.05). Conclusion:DNMT1 expression level drops as the growth of the age

and human skin aging may have certain relevance with down-regulated expression of DNMT1.