The Role of H²O² as a Mediator of UVB-induced Apoptosis in Keratinocytes

Abstract

Apoptosis is an active form of cell death that is initiated by a variety of stimuli, including reactive oxygen species (ROS) and ultraviolet (UV) radiation. Previously, it has been reported that UVB-irradiation of keratinocytes leads to intracellular generation of hydrogen peroxide (H²O²) and that antioxidants can inhibit ROS-induced apoptosis. Although both UVB-irradiation and H²O²-incubation led to increased intracellular H²O² levels, the antioxidants catalase and glutathione monoester (GME), inhibited apoptosis only when induced by H²O², not by UVB. Furthermore, extracellular signal-regulated kinase (ERK), a prominent member of the mitogen-activated protein kinase (MAPK) family, was found to be activated by treatment with both UVB and H²O². Inhibition of ERK phosphorylation by pre-treatment with PD98059 resulted in enhanced apoptosis after H²O²-exposure. However, no significant difference of apoptosis was observed between cells with and without inhibitor pre-treatment upon UVB-irradiation. DNA damage in the form of cyclobutane pyrimidine dimers was observed after exposure to UVB, but no photoproducts were found in H²O²-treated cells. These results suggest a ROS-independent pathway of UVB-induced apoptosis. Although UVB-irradiation causes moderate increase in H²O², the generation of H²O² does not contribute to the induction of apoptosis. Moreover, activation of ERK only blocks H²O²-dependent apoptosis but has no impact on UVB-induced apoptosis.

• Antioxidant
• Apoptosis
• ERK
• HO
• Poly(ADP-ribose)
• UVB