Effects of Simulated Sunlight in Human Skin Equivalents

Abstract

In the past years, almost three million cases of nonmelanoma skin cancer and 132.000 cases of melanoma cancer were registered [21]. Moreover, previous investigations projected an increase between 2-4% per year of skin cancer due to the tanning trend [24]. Consequently, this is a big challenge for society and governments. Exposure to UV radiation has been the subject of research over the last years because of its relationship with skin cancer. Nevertheless, the biological effects of sunlight as a whole have not yet been studied. This led us to examine the biological effects of the simultaneous exposure of UVA, UVB, VIS and IRA (sunlight) in human skin. This thesis aimed to investigate tissue morphology and damage, proteolytic activity and the expression of dermal ECM components, as well as epidermal proliferation and early differentiation in human skin equivalents (fdmSEs) after exposure to 1 MED of simulated sunlight (simultaneous combination of UV, visible and infrared light) and UV radiation. To study the effects of the irradiations in human skin, skin equivalents with an authentic in vivo like dermal and epidermal tissue were used. No morphological changes were detected by traditional Hematoxylin and Eosin staining. Additionally, epidermal differentiation and ECM composition proteins did not seem to be altered by this single irradiation, although epidermal proliferation was differentially affected by the different irradiations, where experimental sunlight gave distinct and rapid damage-recovery pattern. DNA damage was studied by the detection of Cyclobutane Pyrimidine Dimers (CPDs), showing the highest induction with simulated sunlight immediately after the irradiation when compared to UVB treated samples, which rapidly declined 24 hours after the exposure. Proteolytic activity was measured using Enzyme-Linked Immunosorbent Assays (ELISA), indicating the highest MMP-1 and MMP-3 secretion through experimental sunlight in the skin equivalents. MMPs secretion on normal human keratinocytes cultures was also examined. Interestingly, the ELISA there showed a high MMP-1, MMP-3 induction, and an MMP-2 degradation after the irradiations. These results point out the similarities and differences in 2D and 3D cultures attributed to the complex signalling of our skin equivalents. From our results, we can conclude that there is indeed a difference between experimental sunlight and UV radiation, causing induction of damage, a differential proliferative response as well as increased proteolytic activity by MMP-1, MMP-3.