title: α- and β-crystallins modulate the head group order of human lens membranes during aging.
abstract: OBJECTIVE
  To examine the physical properties of human lens cell membranes as a function of age.
  
  
  METHODS
  The environment of the phospholipid head groups in fiber cell membranes from human lenses, aged 22 to 83 years, was assessed with Laurdan and two-photon confocal microscopy. The effect of mild thermal stress on head group order was studied with lens pairs in which one intact lens was incubated at 50 °C. Dihydrosphingomyelin vesicles were preloaded with Laurdan, α-, β-, or γ-crystallin was added, and surface fluidity was determined.
  
  
  RESULTS
  The membrane head group environment became more fluid with age as indicated by increased water penetration. Furthermore, these changes could be replicated simply by exposing intact human lenses to mild thermal stress; conditions which decreased the concentration of soluble α- and β-crystallins. Vesicle binding experiments showed that α- and β-, but not γ-, crystallins markedly affected head group order.
  
  
  CONCLUSIONS
  The physical properties of cell membranes in the lens nucleus change substantially with age, and α- and β-crystallins may modulate this effect. β-Crystallins may therefore play a role in lens cells, and cells of other tissues, apart from being simple structural proteins. Age-dependent loss of these crystallins may affect membrane integrity and contribute to the dysfunction of lenses in older people.
authors.affiliation: Department of Ophthalmology, Eye and ENT Hospital, Fudan University, Shanghai, China.
authors.forename: Xiangjia
authors.initials: X
authors.lastname: Zhu
authors.forename: Katharina
authors.initials: K
authors.lastname: Gaus
authors.forename: Yi
authors.initials: Y
authors.lastname: Lu
authors.forename: Astrid
authors.initials: A
authors.lastname: Magenau
authors.forename: Roger J W
authors.initials: RJ
authors.lastname: Truscott
authors.forename: Todd W
authors.initials: TW
authors.lastname: Mitchell
mesh_terms: D015081:2-Naphthylamine / Q000031:analogs & derivatives / Q000494:pharmacology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D005456:Fluorescent Dyes / Q000494:pharmacology; D018869:Heat-Shock Response / Q000502:physiology*; D006801:Humans; D007848:Laurates / Q000494:pharmacology; D007908:Lens, Crystalline / Q000187:drug effects / Q000378:metabolism*; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000378:metabolism*; D018613:Microscopy, Confocal; D008875:Middle Aged; D013109:Sphingomyelins / Q000494:pharmacology; D055815:Young Adult; D038201:alpha-Crystallins / Q000502:physiology*; D038204:beta-Crystallins / Q000502:physiology*
chemical_list: C091181:4,5-dihydrosphingomyelin; D005456:Fluorescent Dyes; D007848:Laurates; D008563:Membrane Lipids; D013109:Sphingomyelins; D038201:alpha-Crystallins; D038204:beta-Crystallins; D002784:Cholesterol; D015081:2-Naphthylamine; C065580:laurdan