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The effect of insulin-like growth factor (IGF) and of human serum on steps in proteoglycan synthesis
Insights
Insulin-like growth factor (IGF) stimulates proteoglycan synthesis in embryonic chick cartilage by increasing glycosaminoglycan chain production. IGF may also promote synthesis of other sugar chains, impacting cartilage development.
Area of Science:
- Developmental Biology
- Biochemistry
- Cell Biology
Background:
- Proteoglycans (PG) are crucial for cartilage structure and function.
- Insulin-like growth factor (IGF) is known to influence cartilage development.
- Understanding IGF's role in PG synthesis is key to cartilage biology.
Purpose of the Study:
- To investigate the effect of IGF on proteoglycan synthesis in embryonic chick pelvic cartilage.
- To determine the specific mechanisms by which IGF influences glycosaminoglycan (GAG) chain synthesis.
- To explore the role of serum in modulating precursor uptake.
Main Methods:
- Incubation of embryonic chick pelvic cartilages with varying concentrations of IGF and human serum.
- Utilizing radiolabeled precursors (L-[3-3H]serine, D-[6-3H]glucosamine, [35S]Na2SO4) to track proteoglycan synthesis.
- Analysis of glycosaminoglycan chain incorporation and precursor uptake.
Main Results:
- IGF dose-dependently stimulated D-[6-3H]glucosamine incorporation into GAG chains.
- IGF did not stimulate L-[3-3H]serine incorporation into PG molecules, despite increased precursor uptake.
- [35S]Na2SO4 incorporation remained unaffected by IGF.
- Serum enhanced the uptake of all tested precursors into tissue-bound GAGs.
Conclusions:
- IGF stimulates proteoglycan synthesis, potentially by elongating existing chondroitin sulfate chains.
- IGF may also promote the synthesis of other sugar chains like keratan sulfate and oligosaccharides.
- Serum plays a role in enhancing precursor uptake for GAG synthesis in cartilage.
Abstract:
Embryonic chick pelvic cartilages were incubated in the presence of insulin like growth factor (IGF) (1 - 100 microunits/ml), as well as normal human serum (5%), with radiolabelled precursors of proteoglycan (PG) synthesis: L-[3-3H]serine, D-[6-3H]glucosamine and [35S]Na2SO4. IGF alone (1 - 15 microunits/ml), stimulated in a dose-dependent manner D-[6-3H]glucosamine incorporation into tissue-bound and soluble isolated glycosaminoglycan (GAG) chains. L-[3-3H]serine incorporation into PG molecules was not stimulated by IGF (1 - 100 microunits/ml), despite the increase in the uptake of this precursor into intact cartilage. [35S]Na2SO4 incorporation was unaffected by IGF. Serum promoted the uptake of all three precursors into tissue-bound glycosaminoglycans. It was postulated that IGF could stimulate proteoglycan synthesis not only by elongating existing chondroitin sulphate chains but also by increased synthesis of other sugar chains e.g. keratan sulphate and oligosaccharides.