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Midkine is expressed and differentially processed during COPD exacerbations and ventilator-associated pneumonia associated with Staphylococcus aureus infection.

Journal article
Authors Helena M Linge
Cecilia Andersson
Sara L Nordin
Anders I Olin
Ann-Cathrine Petersson
Matthias Mörgelin
Amanda Welin
Johan Bylund
Leif Bjermer
Jonas Erjefält
Arne Egesten
Published in Molecular medicine (Cambridge, Mass.)
Volume 19
Pages 314-323
ISSN 1528-3658
Publication year 2013
Published at Institute of Medicine, Department of Rheumatology and Inflammation Research
Pages 314-323
Language en
Links static.smallworldlabs.com/molmedcom...
Subject categories Medical microbiology

Abstract

Staphylococcus aureus is sometimes isolated from the airways during acute exacerbations of chronic obstructive pulmonary disease (COPD) but more commonly recognized as a cause of ventilator-associated pneumonia (VAP). Antimicrobial proteins, among them midkine (MK), are an important part of innate immunity in the airways. In this study, the levels and possible processing of MK in relation to S. aureus infection of the airways were investigated, comparing COPD and VAP, thus comparing a state of disease with preceding chronic inflammation and remodeling (COPD) with acute inflammation (i.e. VAP). MK was detected in the small airways and alveoli of COPD lung tissue but less so in normal lung tissue. MK at below micromolar concentrations killed S. aureus in vitro. Proteolytic processing of MK by the staphylococcal metalloprotease AL but not cysteine protease SA, resulted in impaired bactericidal activity. Degradation was foremost seen in the COOH-terminal portion of the molecule that harbors high bactericidal activity. In addition, MK was detected in sputum from patients suffering from VAP caused by S. aureus but less so in sputum from COPD-exacerbations associated with the same bacterium. Recombinant MK was degraded more rapidly in sputum from the COPD patients than from the VAP patients and a greater proteolytic activity in COPD sputum was confirmed by zymography. Taken together, proteases of both bacteria and the host contribute to degradation of the antibacterial protein MK, resulting in an impaired defense of the airways, in particular in COPD where the state of chronic inflammation could be of importance.

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