title: Photic injury to cultured RPE varies among individual cells in proportion to their endogenous lipofuscin content as modulated by their melanosome content.
abstract: OBJECTIVE
  We determined whether photic stress differentially impairs organelle motility of RPE lipofuscin and melanin granules, whether lethal photic stress kills cells in proportion to lipofuscin abundance, and whether killing is modulated by melanosome content.
  
  
  METHODS
  Motility of endogenous lipofuscin and melanosome granules within the same human RPE cells in primary culture was quantified by real-time imaging during sublethal blue light irradiation. Cell death during lethal irradiation was quantified by dynamic imaging of the onset of nuclear propidium iodide fluorescence. Analyzed were individual cells containing different amounts of autofluorescent lipofuscin, or similar amounts of lipofuscin and a varying content of phagocytized porcine melanosomes, or phagocytized black latex beads (control for light absorbance).
  
  
  RESULTS
  Lipofuscin granules and melanosomes showed motility slowing with mild irradiation, but slowing was greater for lipofuscin. On lethal irradiation, cell death was earlier in cells with higher lipofuscin content, but delayed by the copresence of melanosomes. Delayed death did not occur with black beads, suggesting that melanosome protection was due to properties of the biological granule, not simple screening.
  
  
  CONCLUSIONS
  Greater organelle motility slowing of the more photoreactive lipofuscin granule compared to melanosomes suggests that lipofuscin mediates mild photic injury within RPE cells. With lethal light stress endogenous lipofuscin mediates killing, but the effect is cell autonomous and modulated by coincident melanosome content. Developing methods to quantify the frequency of individual cells with combined high lipofuscin and low melanosome content may have value for predicting the photic stress susceptibility of the RPE monolayer in situ.
authors.affiliation: Department of Ophthalmology, Eye Institute, Medical College of Wisconsin, Milwaukee, Wisconsin, United States.
authors.forename: Mariusz
authors.initials: M
authors.lastname: Zareba
authors.affiliation: Department of Ophthalmology, Eye Institute, Medical College of Wisconsin, Milwaukee, Wisconsin, United States.
authors.forename: Christine M B
authors.initials: CM
authors.lastname: Skumatz
authors.affiliation: Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
authors.forename: Tadeusz J
authors.initials: TJ
authors.lastname: Sarna
authors.affiliation: Department of Ophthalmology, Eye Institute, Medical College of Wisconsin, Milwaukee, Wisconsin, United States.
authors.forename: Janice M
authors.initials: JM
authors.lastname: Burke
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002478:Cells, Cultured; D005131:Eye Injuries / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D008027:Light / Q000009:adverse effects*; D008062:Lipofuscin / Q000378:metabolism*; D020460:Melanosomes / Q000378:metabolism*; D008875:Middle Aged; D055213:Retinal Pigment Epithelium / Q000293:injuries / Q000378:metabolism* / Q000473:pathology
chemical_list: D008062:Lipofuscin
keywords: lipofuscin; melanosome; photic stress; retinal pigment epithelium