Production of binding proteins and role of the insulin-like growth factor I binding protein 3 in human articular cartilage explants.
The aim of this study was to determine the production of insulin-like growth factor binding proteins (IGFBP) and the role of the IGFBP-3 in human normal (n = 2) and osteoarthritic (OA) articular cartilage (n = 14) explants. Binding proteins were studied in the medium by Western ligand blotting and Western blotting. Proteoglycan synthesis under insulin-like growth factor I (IGF-I) stimulation was studied after a pulse of 35SO4(2-) in the presence or absence of added IGFBP-3. Osteoarthritic explants released a doublet of IGFBPs with a 39/43 kDa Mr corresponding to the binding protein 3. Constitutive production from unstimulated OA cartilage was higher than from normal cartilage. IGF-I induced a 20-fold increase and IL-1 a 2-fold increase in IGFBP-3 release. A minor band around 30 kDa was also detectable. Studies of proteoglycan (PG) synthesis showed that the majority of OA cartilage explant samples responded weakly to IGF-I (100 ng/ml) stimulation (+33%), while the others were high responders (+180%). Co-incubation of IGF-I with recombinant (r) IGFBP-3 did not affect the rate of PG synthesis. However, while pre-incubation with rIGFBP3 for 72 h did not change the rate of PG synthesis in the high-responder group, it strongly increased PG synthesis in the low-responder group. This study demonstrates that the ability of IGF-I to enhance proteoglycan synthesis varied among the OA samples and may in part be dependent on the local level of IGFBP-3. This implies pathophysiological considerations in the limits of IGF-I action during the OA process.
Chevalier
X
X
Strangeways Research Laboratory, Cambridge.
Tyler
J A
JA
D000368:Aged; D002358:Cartilage, Articular / Q000378:metabolism*; D046508:Culture Techniques; D006801:Humans; D015151:Immunoblotting; D018969:Insulin-Like Growth Factor Binding Proteins / Q000096:biosynthesis* / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D007375:Interleukin-1 / Q000502:physiology; D010003:Osteoarthritis / Q000378:metabolism*; D011509:Proteoglycans / Q000096:biosynthesis*; D011994:Recombinant Proteins; D013431:Sulfates / Q000378:metabolism
D018969:Insulin-Like Growth Factor Binding Proteins; D007375:Interleukin-1; D011509:Proteoglycans; D011994:Recombinant Proteins; D013431:Sulfates; D007334:Insulin-Like Growth Factor I