UVB irradiation-induced impairment of keratinocytes and adaptive responses to oxidative stress

UVB irradiation of human skin is known to induce pathophysiological processes as oxidative stress and inflammation. HaCaT keratinocytes represent a well-established in vitro model system to investigate the influence of UVB irradiation on cell cultures. It was the aim of these investigations to study the effects of moderate UVB doses on cellular and mitochondrial integrity of HaCaT keratinocytes, biomarkers of oxidative stress and antioxidant protection by superoxide dismutases. F₂-isoprostane concentrations were UVB dose-dependently enhanced reaching a plateau at 50 mJ/cm². Cell viability was reduced and apoptosis was enhanced with increasing UVB doses. The activities of the respiratory chain complexes were practically not altered at lower UVB doses, up to 50 mJ/cm², whereas remarkable decreases, also for the levels of cardiolipin species, were seen at 100 mJ/cm². As an adaptive response to the enhanced oxidative stress, protein levels of MnSOD increased about 3-fold at 50 mJ/cm² and decreased at higher doses. From the data it can be concluded that keratinocytes are sufficiently protected at low UVB doses, whereas higher doses lead to irreversible cell damage.