Insulin-like growth factor binding protein-4 inhibits both basal and IGF-mediated chick pelvic cartilage growth in vitro.
This laboratory has purified a unique insulin-like growth factor binding protein (IGFBP-4) that was previously demonstrated to be inhibitory to bone cell proliferation. In this study, the hypothesis that IGFBP-4 is inhibitory to insulin-like growth factor (IGF) actions on cartilage was tested using the pelvic cartilages of 10-day-old chick embryos as an in vitro model system. Pelvic leaflets were incubated in serum-free medium for 18 h with effectors (BSA, IGF-I, IGF-II, IGFBP-4, or a combination of IGF and IGFBP-4). After the first 8 h, 1.5 microCi [3H]thymidine per well was added. Cartilage growth was assayed by TCA-insoluble [3H]thymidine incorporation into DNA. Additional experiments were conducted under similar conditions to assess the actions of the effectors on cartilage dry weight over a 72 h time period. In separate experiments, serum-free medium conditioned by chick pelvic cartilages for 72 h was assayed for IGF-II by radioreceptorassay, IGF-I by radioimmunoassay, and IGFBP by western ligand analysis. Exogenous IGF addition increased [3H]thymidine incorporation and dry weight of cartilages compared to controls. IGFBP-4 decreased both parameters in basal cartilage growth and also inhibited IGF-mediated cartilage growth. Pelvic cartilages secreted in vitro both IGF-I and IGF-II and a 32-34 kD IGFBP. In conclusion, the IGFs are stimulatory to cartilage growth in vitro and embryonic chick cartilage in vitro produces both IGF-I and II as well as an IGFBP.(ABSTRACT TRUNCATED AT 250 WORDS)
Schiltz
P M
PM
Department of Orthopedic Surgery, Loma Linda University, California.
Mohan
S
S
Baylink
D J
DJ
D000818:Animals; D002352:Carrier Proteins / Q000096:biosynthesis / Q000502:physiology*; D002356:Cartilage / Q000196:embryology / Q000254:growth & development* / Q000378:metabolism; D002642:Chick Embryo; D018974:Insulin-Like Growth Factor Binding Protein 4; D009924:Organ Culture Techniques; D010384:Pelvic Bones / Q000378:metabolism; D013002:Somatomedins / Q000037:antagonists & inhibitors / Q000502:physiology*
D002352:Carrier Proteins; D018974:Insulin-Like Growth Factor Binding Protein 4; D013002:Somatomedins