title: Aging and oxidative stress reduce the response of human articular chondrocytes to insulin-like growth factor 1 and osteogenic protein 1.
abstract: OBJECTIVE
  To determine the effects of aging and oxidative stress on the response of human articular chondrocytes to insulin-like growth factor 1 (IGF-1) and osteogenic protein 1 (OP-1).
  
  
  METHODS
  Chondrocytes isolated from normal articular cartilage obtained from tissue donors were cultured in alginate beads or monolayer. Cells were stimulated with 50-100 ng/ml of IGF-1, OP-1, or both. Oxidative stress was induced using tert-butyl hydroperoxide. Sulfate incorporation was used to measure proteoglycan synthesis, and immunoblotting of cell lysates was performed to analyze cell signaling. Confocal microscopy was performed to measure nuclear translocation of Smad4.
  
  
  RESULTS
  Chondrocytes isolated from the articular cartilage of tissue donors ranging in age from 24 years to 81 years demonstrated an age-related decline in proteoglycan synthesis stimulated by IGF-1 and IGF-1 plus OP-1. Induction of oxidative stress inhibited both IGF-1- and OP-1-stimulated proteoglycan synthesis. Signaling studies showed that oxidative stress inhibited IGF-1-stimulated Akt phosphorylation while increasing phosphorylation of ERK, and that these effects were greater in cells from older donors. Oxidative stress also increased p38 phosphorylation, which resulted in phosphorylation of Smad1 at the Ser(206) inhibitory site and reduced nuclear accumulation of Smad1. Oxidative stress also modestly reduced OP-1-stimulated nuclear translocation of Smad4.
  
  
  CONCLUSIONS
  These results demonstrate an age-related reduction in the response of human chondrocytes to IGF-1 and OP-1, which are 2 important anabolic factors in cartilage, and suggest that oxidative stress may be a contributing factor by altering IGF-1 and OP-1 signaling.
authors.affiliation: University of North Carolina, Chapel Hill, and Wake Forest University School of Medicine, Winston-Salem, North Carolina.
authors.forename: Richard F
authors.initials: RF
authors.lastname: Loeser
authors.forename: Uma
authors.initials: U
authors.lastname: Gandhi
authors.forename: David L
authors.initials: DL
authors.lastname: Long
authors.forename: Weihong
authors.initials: W
authors.lastname: Yin
authors.forename: Susan
authors.initials: S
authors.lastname: Chubinskaya
mesh_terms: D000375:Aging / Q000378:metabolism*; D055419:Bone Morphogenetic Protein 7 / Q000502:physiology*; D002358:Cartilage, Articular / Q000166:cytology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000502:physiology*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D018384:Oxidative Stress
chemical_list: D055419:Bone Morphogenetic Protein 7; D007334:Insulin-Like Growth Factor I