Comparative Analysis of UVA- and UVB-Mediated DNA Damage and Repair in Human Dermal Stem Cells : Confocal Imaging of Skin Biopsies

Abstract

Ultraviolet (UV) radiation from the sun is a major risk factor for skin cancer, including the malignant melanoma (MM). UVA and UVB radiation both reach the Earth’s surface and are therefore of considerable biological relevance. They penetrate human skin to different depths and induce DNA damage. This thesis investigates UV-induced DNA damage in the form of cyclobutane pyrimidine dimers (CPDs) in human skin biopsies. Skin samples obtained from the thigh, axilla, and juvenile foreskin were irradiated with 140 kJ/m2 UVA or 1500 J/m2 UVB and analyzed immediately after irradiation as well as 24 and 48 hours later to assess CPD repair kinetics. The study focused on dermal stem cells (DSCs), which have been discussed as potential cells of origin for MM. Skin sections from all samples were analyzed by immunofluorescence staining following DNase-I digestion. CPDs were detected using the anti-CPD antibody TDM2, while the neural crest marker NGFRp75 was used to identify DSCs. In addition, SOX10, Nestin, and βIII-Tubulin were evaluated as potential DSC markers. Image acquisition was performed using confocal laser scanning microscopy. The results demonstrate that NGFRp75 was the most suitable marker for identifying DSCs in human skin sections in this study. Both UVA and UVB radiation efficiently induced CPDs in skin cells. UVB-irradiation also induced CPDs in NGFRp75-positive cells, which remained detectable for up to 48 hours. These findings suggest that although UVA-radiation represents a substantial risk to DSCs because of its longer wavelength and deeper tissue penetration, UVB can induce persistent DNA damage in dermal NGFRp75-positive cells and may thereby contribute to mutational events involved in MM development.