Control of syndecan-1 shedding to limit smoking-related neutrophilic inflammation

Abstract

Deteriorating lung function is common in cigarette smoke related airway inflammation which is caused by unopposed neutrophil elastase (NE) activity that persists and disrupts the protease-anti-protease balance even after the primary cause has subsided. The focus of this work is on syndecan-1 (sdc-1) shedding in the affected airway. Our group has reported that in the sputum sol of patients with bronchiectasis, NE exists as supramolecular complexes with shed sdc-1, which were resistant to inhibition by i1-antitrypsin (11111). We hypothesized that similar mechanisms occur in the airway fluids of patients with chronic obstructive pulmonary disease and that the neutrophilic inflammation would be attenuated by (1) reduction of sdc-1 shedding and/or (2) displacement of NE from the supramolecular complexes.

The first half of this work investigates the mechanism by which the heparan sulphate cleaving enzyme heparanase (HPSE) controls the shedding of sdc-1 from the airway epithelium. Western blot analysis of bronchial aspirates of patients demonstrated abundance of HPSE in the inflammatory airway fluid. With human bronchio-epithelial cells in air-liquid interface culture as model, HPSE activity robustly enhanced sdc-1 shedding as mediated by matrix metalloprotease-7 (MMP-7, matrilysin). This can be explained by the increased affinity of MMP-7 for the sdc-1 core following HPSE treatment of the heparan moiety. A similar increase in binding affinity between sdc-1 core and MMP-7 was also observed in bronchial aspirates of patients with airway inflammation. This points to HPSE inhibition as a strategy to reduce sdc-1 shedding.

The second half of this work focuses on the use of an oligosaccharide heparin mimetic to treat cigarette smoke induced neutrophilic inflammation.

In vitro tests showed that the heparin mimetic could displace NE from supramolecular complexes with sdc-1 in bronchial aspirates of patients with COPD. The displaced NE was then inhibited by endogenous wwwww. The heparin mimetic was also shown to be an inhibitor of HPSE activity and as-such was able to inhibit HPSE induced sdc-1 shedding from human bronchio-epithelial cells in vtiro.

To test the efficacy of using this compound as a treatment for neutrophilic inflammation in the airway, rats were subjected to chronic cigarette smoke exposure and treated with a dry powder preparation of the heparin mimetic. Three consecutive doses of the heparin mimetic decreased both neutrophil count and NE activity in the lung compared to rats treated with carrier alone. Mean linear intercept of lung tissue sections from cigarette smoke exposed rats treated with the heparin mimetic were not different from the sham control group, demonstrating the effective protection of the lung against anatomical damage. Whole body plethysmography suggested improvement in lung function of treated animals compared to rats treated with carrier alone.

This study provides insight on the mechanism by which HPSE modulates sdc-1 shedding and suggests a possible therapeutic for the treatment of neutrophilic inflammation.