title: Cell-density-dependent changes in mitochondrial membrane potential and reactive oxygen species production in human skin cells post sunlight exposure.
abstract: BACKGROUND
  Solar ultraviolet radiation (UVR) is the principal etiological factor in skin carcinogenesis. In vivo and in vitro studies have demonstrated previously that oxidative DNA damage, mitochondrial mass and mitochondrial membrane potential (MMP) changes are associated with skin cell response to UVR stress.
  
  
  METHODS
  Spontaneously immortalized human skin keratinocytes were irradiated with increasing sub-lethal doses of simulated sunlight irradiation (SSI) using a Q-Sun solar simulator. The effects of SSI on reactive oxygen species (ROS) formation, mitochondrial mass and MMP were then determined.
  
  
  RESULTS
  SSI induced mitochondrial mass increase post low SSI (0.25-2.5 J/cm²), whereas higher SSI doses (5.0 and 7.5 J/cm²) decreased mitochondrial mass. Mitochondrial mass increased with time post 5.0 J/cm² irradiation and all changes in mass were independent of cell density status. Changes in ROS and MMP were cell density dependent. Additionally, an inverted dose-dependent decrease in ROS formation was observed 3 h post SSI with the lower SSI dose (0.25 J/cm²).
  
  
  CONCLUSIONS
  Observations from the present study suggest that changes in the cell's microenvironment (modeled through varying cell density) influence changes in MMP and ROS detoxifying responses in sun-exposed skin cells.
authors.affiliation: Mitochondrial Biology & Radiation Research, School of Science, Institute of Technology Sligo, Ash Lane, Sligo, Ireland. lucienemz@gmail.com
authors.forename: Luciene M
authors.initials: LM
authors.lastname: Zanchetta
authors.forename: David
authors.initials: D
authors.lastname: Kirk
authors.forename: Fiona
authors.initials: F
authors.lastname: Lyng
authors.forename: James
authors.initials: J
authors.lastname: Walsh
authors.forename: James E J
authors.initials: JE
authors.lastname: Murphy
mesh_terms: D002452:Cell Count; D002461:Cell Line, Transformed; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism* / Q000473:pathology; D053078:Membrane Potential, Mitochondrial / Q000528:radiation effects*; D008928:Mitochondria / Q000378:metabolism / Q000473:pathology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012867:Skin / Q000378:metabolism* / Q000473:pathology; D013472:Sunlight / Q000009:adverse effects*; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D017382:Reactive Oxygen Species