The role of DNA methylation in UV-induced decrease of TIMP1 and TIMP2 expressions in the human skin

Abstract

Ultraviolet (UV) radiation poses as a harmful threat to the skin because of its mutagenic properties. It causes lesions and mutations to the base sequence of the DNA, potentially altering the vast outcome of gene expressions. Aside from UV-induced DNA damages, which has been extensively studied, UV has been reported to influence the activities of epigenetic regulation by affecting the expression of genome regulators such as DNA methyltransferases (DNMTs). DNMT1 is a gene silencer, that is responsible for the maintenance of DNA methylation and contribution to de novo methylation, and DNMT3A and DNMT3B, de novo methyltransferases, harness the ability to create new methylation patterns. In UV-irradiated skin, the levels of matrix metalloproteinases (MMPs) has been reported to elevate, and the levels of tissue inhibitor of metalloproteinases (TIMPs), an inhibitor of MMPs, to decrease. In this study, we examined the role of DNMT1 in the suppression of TIMP1 and TIMP2 in UV-irradiated human skin. We observed an increase in DNMT1 expression in a time-dependent manner through in vivo and in vitro experimentations using acutely UV-irradiated human skin and UV-irradiated human dermal fibroblasts. To analyze the effect of DNMT1 on TIMP1 and TIMP2 expressions, knockdown and inhibition of DNMT1 were performed. A decrease in DNMT1 expression resulted in an increase in TIMP1 and TIMP2. However, DNMT1 overexpression led to reduced levels of TIMP1 and TIMP2. Lastly, methylation-specific PCR results confirmed greater methylation on the CpG island residing in TIMP2 promoter region in UV-irradiated human dermal fibroblasts. These findings suggest that UV-induced expression of DNMT1 may be responsible for mediating DNA hypermethylation in TIMP, and thus, silencing its expressions, in UV-exposed human skin.