Mitochondrial dysfunction and cellular stress progression after ultraviolet B irradiation in human keratinocytes

Background: Ultraviolet (UV) radiation is the major environmental harmful factor that affects human skin. UVB radiation is known to be a potent inducer of reactive oxygen species (ROS) production and has also been associated with the generation of nitric oxide (NO), all of which have been implicated in various skin disorders. It is well known that mitochondria can also be affected by UVB, leading to alterations in their membrane structure and permeabilization with cytochrome c release, which consequently affects the cell function. However, the loss of keratinocyte mitochondrial function generated by UVB, as well as its kinetics, has not been characterized completely. Methods: We evaluated the effect of UVB irradiation on HaCat cells' mitochondrial function, assessed by membrane potential loss and superoxide anion (O-2(center dot-)) production, correlating with apoptosis, p53 expression, ROS levels and NO production, 0, 6, 12, 24 and 48 h post-irradiation. Results: HaCat cells progressed toward apoptotic cell death as the time post-irradiation increased, with the highest levels found 48 h after irradiation. Increased levels of ROS were observed 6 h after irradiation while high O-2(center dot-) levels and mitochondrial membrane depolarization were detected 12 h post-UVB. Nevertheless, NO production was not significantly increased at any of the evaluated times. Conclusions: The kinetics of mitochondrial dysfunction after UVB irradiation in human keratinocytes progressed in a time post-irradiation-dependent manner, and they are closely related to cell death. However, there are certain levels of apoptosis, although low, in the absence of mitochondrial alterations. In addition, our data suggest that ROS play a greater role in keratinocyte UVB damage than reactive nitrogen species.