Mitochondrial DNA depletion causes decreased ROS production and resistance to apoptosis.

Mitochondrial DNA (mtDNA) depletion occurs frequently in many diseases including cancer. The present study was designed in order to examine the hypothesis that mtDNA­depleted cells are resistant to apoptosis and to explore the possible mechanisms responsible for this effect. Parental human osteosarcoma 143B cells and mtDNA­deficient (Rho˚ or ρ˚) 206 cells (derived from 143B cells) were exposed to different doses of solar-simulated ultraviolet (UV) radiation. The effects of solar irradiation on cell morphology were observed under both light and fluorescence microscopes. Furthermore, apoptosis, mitochondrial membrane potential (MMP) disruption and reactive oxygen species (ROS) production were detected and measured by flow cytometry. In both cell lines, apoptosis and ROS production were clearly increased, whereas MMP was slightly decreased. However, apoptosis and ROS production were reduced in the Rho˚206 cells compared with the 143B cells. We also performed western blot analysis and demonstrated the increased release of cytosolic Cyt c from mitochondria in the 143B cells compared with that in the Rho˚206 cells. Thus, we concluded that Rho˚206 cells exhibit more resistance to solar­simulated UV radiation­induced apoptosis at certain doses than 143B cells and this is possibly due to decreased ROS production.

Luteolin decreases the UVA­induced autophagy of human skin fibroblasts by scavenging ROS.

Luteolin (LUT) is a flavone, which is universally present as a constituent of traditional Chinese herbs, and certain vegetables and spices, and has been demonstrated to exhibit potent radical scavenging and cytoprotective properties. Although LUT has various beneficial effects on health, the effects of LUT on the protection of skin remain to be fully elucidated. The present study investigated whether LUT can protect human skin fibroblasts (HSFs) from ultraviolet (UV) A irradiation. It was found that, following exposure to different doses of UVA irradiation, the HSFs exhibited autophagy, as observed by fluorescence and transmission electron microscopy, and reactive oxygen species (ROS) bursts, analyzed by flow cytometry, to differing degrees. Following incubation with micromolar concentrations of LUT, ROS production decreased and autophagy gradually declined. In addition, the expression of hypoxia­inducible factor­1α and the classical autophagy­associated proteins, LC3 and Beclin 1 were observed by western blotting. Western blot analysis showed that the expression levels of HIF­1α, LC3­II and Beclin 1 gradually decreased in the UVA­irradiated HSFs following treatment with LUT. These data indicated that UVA­induced autophagy was mediated by ROS, suggesting the possibility of resistance against UV by certain natural antioxidants, including LUT.