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Insulin-like growth factor binding protein-4 inhibits both basal and IGF-mediated chick pelvic cartilage growth in
P M Schiltz1, S Mohan, D J Baylink
1Department of Orthopedic Surgery, Loma Linda University, California.
Abstract:
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)
Insights
Insulin-like growth factor binding protein-4 (IGFBP-4) inhibits cartilage growth and insulin-like growth factor (IGF) actions on cartilage. Embryonic chick cartilage produces IGFs and IGFBP, indicating their roles in cartilage development.
Area of Science:
- Biochemistry
- Developmental Biology
- Cell Biology
Background:
- Insulin-like growth factor binding protein-4 (IGFBP-4) is known to inhibit bone cell proliferation.
- The role of IGFBP-4 in regulating insulin-like growth factor (IGF) actions on cartilage remains unclear.
Purpose of the Study:
- To investigate the inhibitory effects of IGFBP-4 on IGF actions in embryonic chick cartilage.
- To determine if IGFBP-4 affects basal cartilage growth.
Main Methods:
- In vitro culture of embryonic chick pelvic cartilages.
- Assay of cartilage growth via [3H]thymidine incorporation and dry weight measurement.
- Quantification of IGF-I, IGF-II, and IGFBP in conditioned medium using radioimmunoassay, radioreceptorassay, and western ligand analysis.
Main Results:
- Exogenous IGF-I and IGF-II significantly increased cartilage [3H]thymidine incorporation and dry weight.
- IGFBP-4 inhibited both basal cartilage growth and IGF-mediated growth.
- Embryonic chick cartilage secreted IGF-I, IGF-II, and an IGFBP (32-34 kD).
Conclusions:
- IGFs are potent stimulators of cartilage growth in vitro.
- IGFBP-4 acts as an inhibitor of both basal and IGF-stimulated cartilage growth.
- Embryonic chick cartilage actively produces and secretes IGFs and IGFBPs, suggesting autocrine/paracrine roles in development.