UVA irradiation increases ferrous iron release from human skin fibroblast and endothelial cell ferritin: Consequences for cell senescence and aging.

UVA irradiation of human dermal fibroblasts and endothelial cells induces an immediate transient increase in cytosolic Fe(II), as monitored by the fluorescence Fe(II) reporters, FeRhonox1 in cytosol and MitoFerroGreen in mitochondria. Both superoxide dismutase (SOD) inhibition by tetrathiomolybdate (ATM) and catalase inhibition by 3-amino-1, 2, 4-triazole (ATZ) increase and prolong the cytosolic Fe(II) signal after UVA irradiation. SOD inhibition with ATM also increases mitochondrial Fe(II). Thus, mitochondria do not source the UV-dependent increase in cytosolic Fe(II), but instead reflect and amplify raised cytosolic labile Fe(II) concentration. Hence control of cytosolic ferritin iron release is key to preventing UVA-induced inflammation. UVA irradiation also increases dermal endothelial cell HO, as monitored by the adenovirus vector Hyper-DAAO-NES(HyPer). These UVA-dependent changes in intracellular Fe(II) and HO are mirrored by increases in cell superoxide, monitored with the luminescence probe L-012. UV-dependent increases in cytosolic Fe(II), HO and L-012 chemiluminescence are prevented by ZnCl (10 μM), an effective inhibitor of Fe(II) transport via ferritin's 3-fold channels. Quercetin (10 μM), a potent membrane permeable Fe(II) chelator, abolishes the cytosolic UVA-dependent FeRhonox1, Fe(II) and HyPer, HO and increase in MitoFerroGreen Fe(II) signals. The time course of the quercetin-dependent decrease in endothelial HO correlates with the decrease in FeRhox1 signal and both signals are fully suppressed by preloading cells with ZnCl. These results confirm that antioxidant enzyme activity is the key factor in controlling intracellular iron levels, and hence maintenance of cell antioxidant capacity is vitally important in prevention of skin aging and inflammation initiated by labile iron and UVA.