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Biochim Biophys Acta Gen Subj. 2018 Mar;1862(3):567-575. doi: 10.1016/j.bbagen.2017.11.017. Epub 2017 Nov 21.

Human IGF-I propeptide A promotes articular chondrocyte biosynthesis and employs glycosylation-dependent heparin binding.

Author information

1
Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN 46202, United States. Electronic address: shushi@iupui.edu.
2
Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN 46202, United States.
3
Department of Biostatistics, Indiana University School of Medicine, Indianapolis, IN 46202, United States.
4
Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN 46202, United States; Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202, United States; Orthopaedic Surgery Service, Richard L. Roudebush VA Medical Center, Indianapolis, IN 46202, United States.

Abstract

BACKGROUND:

Insulin-like growth factor I (IGF-I) is a key regulator of chondrogenesis, but its therapeutic application to articular cartilage damage is limited by rapid elimination from the repair site. The human IGF-I gene gives rise to three IGF-I propeptides (proIGF-IA, proIGF-IB and proIGF-IC) that are cleaved to create mature IGF-I. In this study, we elucidate the processing of IGF-I precursors by articular chondrocytes, and test the hypotheses that proIGF-I isoforms bind to heparin and regulate articular chondrocyte biosynthesis.

METHODS:

Human IGF-I propeptides and mutants were overexpressed in bovine articular chondrocytes. IGF-I products were characterized by ELISA, western blot and FPLC using a heparin column. The biosynthetic activity of IGF-I products on articular chondrocytes was assayed for DNA and glycosaminoglycan that the cells produced.

RESULTS:

Secreted IGF-I propeptides stimulated articular chondrocyte biosynthetic activity to the same degree as mature IGF-I. Of the three IGF-I propeptides, only one, proIGF-IA, strongly bound to heparin. Interestingly, heparin binding of proIGF-IA depended on N-glycosylation at Asn92 in the EA peptide. To our knowledge, this is the first demonstration that N-glycosylation determines the binding of a heparin-binding protein to heparin.

CONCLUSION:

The biosynthetic and heparin binding abilities of proIGF-IA, coupled with its generation of IGF-I, suggest that proIGF-IA may have therapeutic value for articular cartilage repair.

GENERAL SIGNIFICANCE:

These data identify human pro-insulin-like growth factor IA as a bifunctional protein. Its combined ability to bind heparin and augment chondrocyte biosynthesis makes it a promising therapeutic agent for cartilage damage due to trauma and osteoarthritis.

KEYWORDS:

Biosynthesis; Chondrocyte; E peptide; Glycosylation; Heparin-binding protein; IGF-I propeptide; Insulin-like growth factor (IGF); Protein processing

PMID:
29174671
PMCID:
PMC5801056
DOI:
10.1016/j.bbagen.2017.11.017
[Indexed for MEDLINE]
Free PMC Article

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