Increase in net activity of serine proteinases but not gelatinases after local endotoxin exposure in the peripheral airways of healthy subjects.

Margaretha E Smith,Steven Bozinovski,Ingemar Qvarfordt,Gary P Anderson,Pernilla Glader,Margareta Sjöstrand,Anders Lindén,Carina Malmhäll,Pieter S Hiemstra,Per Venge

doi:10.1371/journal.pone.0075032

Abstract

We tested the hypothesis that activation of the innate immune response induces an imbalance in the proteolytic homeostasis in the peripheral airways of healthy subjects, towards excess serine or gelatinase proteinase activity. During bronchoscopy, 18 healthy human subjects underwent intra-bronchial exposure to endotoxin and contra-lateral exposure to vehicle. Bronchoalveolar lavage (BAL) samples were harvested 24 or 48 hours (h) later. We quantified archetype proteinases, anti-proteinases, inflammatory BAL cells, and, importantly, total plus net proteinase activities using functional substrate assays. As expected, endotoxin exposure increased the concentrations of polymorphonuclear leukocytes (PMN's) and macrophages, of proteinases and the anti-proteinases tissue inhibitor of metalloproteinase-1, α-1-antitrypsin and, to a lesser extent, secretory leukoproteinase inhibitor, at both time points. Notably, at these time points, endotoxin exposure substantially increased the quantitative NE/SLPI ratio and the net serine proteinase activity corresponding to neutrophil elastase (NE). Endotoxin exposure also increased the total gelatinase activity corresponding to matrix metalloproteinase (MMP)-9; an activity dominating over that of MMP-2. However, endotoxin exposure had no impact on net gelatinolytic activity at 24 or 48 h after exposure. Thus, local activation of the innate immune response induces an imbalance towards increased net serine proteinase activity in the proteolytic homeostasis of the peripheral airways in healthy subjects. Hypothetically, this serine proteinase activity can contribute to tissue remodelling and hypersecretion via NE from PMN's, if it is triggered repeatedly, as might be the case in chronic inflammatory airway disorders.

Highlights

A well-maintained balance between the local serine proteinases, gelatinases and their inhibitors is believed to be critical for preserving tissue structure and function in the airways, as well as for coordinating the collective immune responses from structural and inflammatory cells to maintain host defence [1,2,3,4,5,6,7]
We tested the hypothesis that activation of the innate immune response induces an imbalance in the proteolytic homeostasis in the peripheral airways, towards excess serine proteinase or gelatinase activity
We found that after activation of the innate immune response with the tolllike receptor (TLR)-4 agonist endotoxin, healthy human subjects displays an imbalance in the proteolytic homeostasis in the peripheral airways, towards an increase in the net activity for serine proteinases but not gelatinases

Summary

Introduction

A well-maintained balance between the local serine proteinases, gelatinases and their inhibitors is believed to be critical for preserving tissue structure and function in the airways, as well as for coordinating the collective immune responses from structural and inflammatory cells to maintain host defence [1,2,3,4,5,6,7]. Even though there is accumulating evidence that the maintenance of the proteolytic homeostasis is involved and altered in several chronic airway disorders, surprisingly little is known about more holistic and functional aspects of the proteolytic homeostasis in the airways of healthy human subjects [1,2,3,19] One reason for this may be that previous investigators have tended to focus on isolated molecular aspects of the proteolytic homeostasis, without assessing other principal components or total and net proteinase activities in the airways [1,2,3,19,20]. By limiting their study to samples of induced sputum instead of bronchoalveolar lavage (BAL), the authors of these studies may have missed events unique for the peripheral airways

Methods

Results

Conclusion