Aging human skin shows DNA hypomethylation, which can be reverted by topical melatonin ex vivo

Summary: Abstract Body: DNA methylation has emerged as a key mechanism in cell and tissue aging. This involves DNA methyltransferases (DNMTs) that add methyl groups to cytosine, creating 5-methylcytosine (5-mC), which typically silences gene expression. Conversely, ten-eleven-translocation (TET) proteins convert 5-mC to 5-hydroxymethylcytosine (5-hmC), potentially reactivating previously suppressed genes. Our study explores if these epigenetic changes occur during human skin aging ex vivo, using a “speed aging” organ culture assay of aged, full-thickness female scalp skin (4 healthy donors, aged 43-75 yrs). Quantitative immunohistomorphometry revealed that after 3 days, expression levels of DNMT1, 5-mC and 5-hmC in the epidermis were reduced compared to day 0, showing a progressive DNA hypomethylation observed during “speed aging” ex vivo. Moreover, DNA hypomethylation was maximal in skin of the oldest donors (>65yrs), in line with recognized human skin aging characteristics. Topically applied melatonin (200mM) significantly increased epidermal 5-mC, DNMT1, and TET3 protein expression ex vivo after 3 and/or 6 days, compared to vehicle-treated control skin. Interestingly, the 5-mC response to melatonin treatment was most pronounced in “middle-aged” skin, while DNMT1 and TET3 expression changes did not differ between age groups. Our pilot data suggest that global DNA hypomethylation is a fundamental feature of human skin aging, which may promote the overexpression of aging-associated genes and suppress anti-aging genetic programs. The high-dose topical melatonin, which circumvents its rapid metabolism in the liver, penetrates the skin barrier and can counteract DNA hypomethylation ex vivo. This introduces a new mechanism for how melatonin can be utilized to slow human skin aging. Kinga Linowiecka^{1, 2, 3}, Jérémy Chéret^{2, 3}, Aysun Akhundlu³, Yeqin Dai³, Jing Jing³, Tatiana Gomez-Gomez³, Ramtin Kassir⁴, Jennifer Gherardini², Ralf Paus^{2, 3} 1. Department of Human Biology, Nicolaus Copernicus University in Torun, Torun, Poland. 2. Cutaneon - Skin & Hair Innovations GmbH, Hamburg & Berlin, Germany. 3. Department of Dermatology & Cutaneous Surgery, University of Miami Miller School of Medicine, Miami, FL, United States. 4. Kassir Plastic Surgery, New York, NY, United States. Epidermal Structure and Barrier Function