Nitric oxide synthase activation and oxidative stress, but not intracellular zinc dyshomeostasis, regulate ultraviolet B light-induced apoptosis

Abstract

Aims To investigate the role of nitric oxide synthase and intracellular free zinc ion (Zn2+) in regulation of ultraviolet B light (UVB)-induced cell damage and apoptosis. Main methods Real time confocal microscopy measurement was used to determine the changes of intracellular free zinc concentration under different conditions. Cell apoptotic death was determined using fluorescein isothiocyanate (FITC) conjugated-annexin V (ANX5)/PI labeling followed by flow cytometry. Western analysis was used to determine cell apoptosis and eNOS uncoupling. Key findings UVB induced an elevation of Zn2+ within 2 min of exposure. The UVB-induced intracellular Zn2+ elevation was dependent on the increase of constitutive nitric oxide synthase (cNOS) activity and production of superoxide. Removal of Zn2+ with a lower concentration (<25 µM) of N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), a Zn2+-specific chelator, did not induce cell death or prevent cells from UVB-induced apoptosis. However, a higher [TPEN] (> 50 µM) was cytotoxic to cells, but prevented cells from further UVB-induced apoptosis. The higher [TPEN] also induced cNOS uncoupling. Furthermore, treating the cells with a membrane permeable superoxide dismutase (PEG-SOD) inhibited Zn2+ release and reduced apoptotic cell death after UVB treatment. The results demonstrated a complex and dynamic regulation of UVB-induced cell damage. Significance Our findings not only advance our understanding of the correlations between cNOS activation and Zn elevation, but also elucidated the role of cNOS in regulation of oxidative stress and apoptosis upon UVB-irradiation.

Differential roles of nitric oxide synthases in regulation of ultraviolet B light-induced apoptosis

“…However it is not clear how these NOSs were involved in the regulation of UV-induced apoptosis in a contrasting manner. Our recent reports suggested that the UVB-induced activation of constitutive NOS (cNOS), including nNOS and eNOS, in combination of oxidative stress, promoted apoptosis of keratinocytes [4,17]. In this report, we further elucidate the mechanism for coordinative regulation of apoptosis of keratinocytes by the three NOSs after UVB-irradiation.…”

“…Our recently studies suggested that early activation of NOSs promotes apoptotic death of keratinocytes upon UVB-irradiation [4,17]. To further analyze the roles of NOSs in regulation of UVB-induced apoptosis of keratinocytes, we determined the extent of effects of a short or prolonged inhibition of cNOS on UVB-induced caspase 3 activation and apoptosis.…”

Effects of non-toxic zinc exposure on human epidermal keratinocytes

“…The use of zinc-containing topical therapeutics is widespread due to its clear benefit on cutaneous regeneration and on various inflammatory skin conditions 3 . UVB, the main harmful environmental factor in skin, induces intracellular zinc release in keratinocytes, suggesting a functional role of zinc in the UV stress response 15,16 .…”

“…UVB causes skin cell damage directly by inducing the production of cyclobutane pyrimidine dimers (CPDs) and indirectly by triggering the production of reactive species and interfering with cellular redox homeostasis. Importantly, rapid intracellular elevation of zinc levels occurs in keratinocytes after UVB irradiation 15,16 , and the level of MT is higher in the epidermis after acute UV exposure, while the skin of MT knockout mice is more susceptible to UVB 17 . Previously, it was found that solar (i.e., mixed) UV irradiation of keratinocytes exposed to zinc chloride (ZnCl 2 ) enhances cell survival and is able to reduce the immediate DNA damage 18,19 and DNA fragmentation after exposure 20 .…”

Genistein prevents ultraviolet B radiation-induced nitrosative skin injury and promotes cell proliferation

“…The free radical species generated by UVB exposure include the hydroxyl radical ( • OH) [3,4], singlet oxygen ( 1 O 2 ) [5], superoxide radical (O 2 -) [6], and hydrogen peroxide (H 2 O 2 ) [7,8]. Peroxynitrite (ONOO -) and nitric oxide (NO) have been reported to be involved in oxidative skin injury induced by UVB radiation [4,[9][10][11]. In a previous study, we showed that after 24 h of exposure to UVB radiation, development of skin lesions increased because of high levels of NO, which led to lipid peroxidation and nitrotyrosine formation, and cell proliferation decreased determined on the basis of the levels of markers of cell proliferation, proliferating cell nuclear antigen (PCNA) and vascular endothelial growth factor (VEGF) [4,11].…”