HS/syndecan modulate proteolytic balance in airway inflammation

Abstract

Persistent tissue injury in chronic airway inflammation is contributed by the unopposed neutrophil elastase (NE) activity. In sputum sols of patients with bronchiectasis, alpha-1-antitrypsin (α1-AT) was found in excess of unopposed NE at molar ratios that averaged 16:1, suggesting the existence of imbalance between protease and anti-protease. Western blot analysis of sputum sol samples however found NE in a supramolecular complex with syndecan-1 and as such, inhibition of NE activity was incomplete even with addition of α1-AT. To confirm that NE binding to heparan sulfate (HS) moieties of syndecan-1 limits the anti-elastase effect, recombinant syndecan-1 was recovered from stable syndecan-1 transfectants of ARH-77 cells. Western ligand blot confirmed that NE bound only to HS moieties of syndecan-1. Inhibition of NE activity by standard additions of α1-AT was incomplete unless syndecan-1 had been deglycanated by heparitinase treatment. SPR analysis revealed that NE binding to HS could be competed out by heparin variants. To test if heparin fragments can displace NE from the complex, heparin oligosaccharides were incubated with sputum sol samples. Western blot analysis indicated that heparin oligosaccharides (dp ≥4) displaced NE from the complex and the displaced NE became accessible to inhibition by endogenous α1-AT. MALDI TOF-MS analysis further revealed subunit composition of the heparin oligosaccharides. Our results therefore suggest the possible use of heparin oligosaccharides in restoring the balance between protease/anti-protease in chronic airway inflammation.