title: Human epidermal keratinocytes accumulate superoxide due to low activity of Mn-SOD, leading to mitochondrial functional impairment.
abstract: The energy metabolism of the epidermis has been the subject of controversy; thus we characterized the mitochondrial phenotype of human primary keratinocytes and fibroblasts, in cell culture and in human skin sections. We found that keratinocytes respire as much as fibroblasts, however, maximal activities of the respiratory chain (RC) complexes were 2- to 5-fold lower, whereas expression levels of RC proteins were similar. Maximal activities of aconitase and isocitrate dehydrogenase, two mitochondrial enzymes especially vulnerable to superoxide, were lower than in fibroblasts. Indeed, superoxide anion levels were much higher in keratinocytes, and keratinocytes displayed higher lipid peroxidation levels and a lower reduced glutathione/oxidized glutathione ratio, indicating enhanced oxidative stress. Although superoxide dismutase activity and especially expression of the mitochondrial superoxide dismutase, Mn-SOD, were drastically lower in keratinocytes, explaining the high superoxide levels, glutathione peroxidase activity and protein were almost undetectable in fibroblasts. Catalase activity and hydrogen peroxide levels were similar. In summary, we could show that keratinocytes actively use the mitochondrial RC not only for adenosine 5' triphosphate synthesis but also for the accumulation of superoxide anions, even at the expense of mitochondrial functional capacity, indicating that superoxide-driven mitochondrial impairment might be a prerequisite for keratinocyte differentiation.
authors.affiliation: Institute of Vegetative Physiology, University of Köln, Köln, Germany.
authors.forename: Hue-Tran
authors.initials: HT
authors.lastname: Hornig-Do
authors.forename: Jürgen-Christoph
authors.initials: JC
authors.lastname: von Kleist-Retzow
authors.forename: Katrin
authors.initials: K
authors.lastname: Lanz
authors.forename: Claudia
authors.initials: C
authors.lastname: Wickenhauser
authors.forename: Alexei P
authors.initials: AP
authors.lastname: Kudin
authors.forename: Wolfram S
authors.initials: WS
authors.lastname: Kunz
authors.forename: Rudolf J
authors.initials: RJ
authors.lastname: Wiesner
authors.forename: Matthias
authors.initials: M
authors.lastname: Schauen
mesh_terms: D000154:Aconitate Hydratase / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D002648:Child; D004579:Electron Transport / Q000502:physiology; D004734:Energy Metabolism / Q000502:physiology; D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006801:Humans; D007521:Isocitrate Dehydrogenase / Q000378:metabolism; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism*; D015227:Lipid Peroxidation / Q000502:physiology; D008297:Male; D008928:Mitochondria / Q000502:physiology*; D018384:Oxidative Stress / Q000502:physiology; D013482:Superoxide Dismutase / Q000502:physiology*; D013481:Superoxides / Q000378:metabolism*
chemical_list: D013481:Superoxides; D007521:Isocitrate Dehydrogenase; D013482:Superoxide Dismutase; D000154:Aconitate Hydratase