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

Shuiliang Shi, Brian J. Kelly, Congrong Wang, Ken Klingler, Albert Chan, George J. Eckert, Stephen B. Trippel

Research output: Contribution to journalArticle

2 Scopus citations

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.

Original languageEnglish (US)
Pages (from-to)567-575
Number of pages9
JournalBiochimica et Biophysica Acta - General Subjects
Volume1862
Issue number3
DOIs
StatePublished - Mar 2018

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Keywords

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

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology

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