Insulin-like growth factor binding proteins (IGF-BPs) in bovine articular and ovine growth-plate chondrocyte cultures: their regulation by IGFs and modulation of proteoglycan synthesis.
Cultured chondrocytes respond to insulin-like growth factors (IGFs) by increasing the production of proteoglycans and insulin-like growth factor binding proteins (IGF-BPs). To investigate the biological effects of IGFs and IGF-BPs, isolated bovine articular and ovine growth-plate chondrocytes were cultured at high density in the presence of IGF-1, and its truncated form, des (1-3) IGF-I. Both growth factors stimulated the production of IGF-BPs in articular and growth-plate chondrocyte monolayers. Western ligand blots showed that bovine articular chondrocytes released two forms of IGF-BPs into conditioned medium with molecular weights of 29 and 31 kDa. Ovine growth-plate chondrocytes released four different forms of IGF-BPs of approx. 22, 24; 29-30 and 34 kDa. IGF-I and des (1-3) IGF-I stimulated total proteoglycan synthesis by articular chondrocytes up to 1.5-fold. The truncated analogue was more potent at lower concentrations, particularly in stimulating incorporation of newly synthesized proteoglycans into the cell-layer. The maximal stimulation of proteoglycan synthesis in ovine growth-plate chondrocyte culture was 3-fold with des (1-3) IGF-I, while IGF-I enhanced proteoglycan production by only 2-fold over the concentrations used. Our results suggest that endogenous IGF-BPs in chondrocyte cultures act as a part of a feed-back mechanism which diminishes the bioactivity of IGF-I.
Sunic
D
D
Department of Medicine, University of Adelaide, South Australia.
Belford
D A
DA
McNeil
J D
JD
Wiebkin
O W
OW
D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis*; D002356:Cartilage / Q000187:drug effects / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D011509:Proteoglycans / Q000096:biosynthesis*; D012756:Sheep
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D010446:Peptide Fragments; D011509:Proteoglycans; C058957:insulin-like growth factor 1, des-(1-3)-; D007334:Insulin-Like Growth Factor I