Downregulation of carnitine acetyltransferase by promoter hypermethylation regulates ultraviolet-induced matrix metalloproteinase-1 expression in human dermal fibroblasts

Abstract

Background

Overexposure to ultraviolet (UV) radiation accelerates skin aging, resulting in wrinkle formation, reduced skin elasticity, and hyperpigmentation. UV irradiation induces increased matrix metalloproteinases (MMPs) that degrade collagen in the extracellular matrix. Skin aging is also accompanied by epigenetic alterations such as promoter methylation by DNA methyltransferases, leading to the activation or suppression of gene expression. Although carnitine acetyltransferase (CRAT) is implicated in aging, the effect of UV on the expression of CRAT and regulatory mechanisms of UV-induced MMP-1 expression remain unknown.

Objective

We investigated changes in CRAT expression upon UV irradiation and its effect on MMP-1 expression.

Methods

Primary human dermal fibroblasts were UV irradiated with either control or 5-AZA-dC. CRAT knockdown or overexpression was performed to investigate its effect on MMP-1 expression. The mRNA level was analyzed by quantitative real-time PCR, and protein level by western blotting.

Results

The expression of CRAT was decreased in UV-irradiated human skin in vivo and in human dermal fibroblasts in vitro. CRAT was downregulated upon UV irradiation by hypermethylation, and treatment with 5-Aza-2′-deoxycytidine, a DNA methyltransferase inhibitor, reversed UV-induced downregulation of CRAT. CRAT knockdown activated the JNK, ERK, and p38 MAPK signaling pathways, which increased MMP-1 expression. Stable overexpression of CRAT alleviated UV-induced MMP-1 induction.

Conclusion

CRAT downregulation caused by promoter hypermethylation may play an important role in UV-induced skin aging via upregulation of MMP-1 expression.