Shed syndecan-1 restricts neutrophil elastase from α1- antitrypsin in neutrophilic airway inflammation

Abstract

Persistent proteolytic imbalance in chronic inflammatory diseases has been ascribed to neutrophil elastase (NE)/antielastase imbalance in wound fluids. In sputum sols of patients with bronchiectasis, we found unopposed NE activity, despite overwhelming excess of the physiological antielastase, α1-antitrypsin (α1-AT). Western blot analysis found NE in a supramolecular complex with shed ectodomains of syndecan (Syn)-1 in sputum sol samples and, as such, inhibition of NE activity was incomplete, even with addition of exogenous α1-AT. To confirm that NE binding to heparan sulfate (HS) components of Syn-1 limits the antielastase effect, recombinant human Syn-1 was recovered from stable Syn-1 transfectants of a human B-lymphoid cell line (ARH-77). Western ligand blot confirmed that NE bound to HS moieties and α1-AT to the core protein of the recombinant product. Inhibition of NE activity by standard additions of α1-AT was incomplete unless Syn-1 had been deglycanated by heparitinase treatment. Surface plasmon resonance analysis revealed that NE binding to HS (equilibrium dissociation constant, ∼14 nM) could be outcompeted by heparin variants. We conclude that the HS moiety of shed Syn-1 binds and restricts NE from inhibition by α1-AT.