Background Pseudomonas aeruginosa lung infections are a huge problem in ventilator-associated pneumonia, cystic fibrosis (CF) and in chronic obstructive pulmonary disease (COPD) exacerbations. This bacterium secretes virulence factors that may subvert host innate immunity.
Objective We evaluated the effect of P. aeruginosa elastase LasB, an important virulence factor secreted by the type II secretion system, on ion transport, innate immune responses and epithelial repair, both in vitro and in vivo.
Methods Wild-type (WT) or cystic fibrosis transmembrane conductance regulator (CFTR)-mutated epithelial cells (cell lines and primary cells from patients) were treated with WT or ΔLasB pseudomonas aeruginosa O1 (PAO1) secretomes. The effect of LasB and PAO1 infection was also assessed in vivo in murine models.
Results We showed that LasB was the most abundant protein in WT PAO1 secretomes and that it decreased epithelial CFTR expression and activity. In airway epithelial cell lines and primary bronchial epithelial cells, LasB degraded the immune mediators interleukin (IL)-6 and trappin-2, an important epithelial-derived antimicrobial molecule. We further showed that an IL-6/STAT3 signalling pathway was downregulated by LasB, resulting in inhibition of epithelial cell repair. In mice, intranasally instillated LasB induced significant weight loss, inflammation, injury and death. By contrast, we showed that overexpression of IL-6 and trappin-2 protected mice against WT-PAO1-induced death, by upregulating IL-17/IL-22 antimicrobial and repair pathways.
Conclusions Our data demonstrate that PAO1 LasB is a major P. aeruginosa secreted factor that modulates ion transport, immune response and tissue repair. Targeting this virulence factor or upregulating protective factors such as IL-6 or antimicrobial molecules such as trappin-2 could be beneficial in P. aeruginosa-infected individuals.
- airway epithelium
- bacterial infection
- cystic fibrosis
- innate immunity
- respiratory infection
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Contributors VS-C designed and performed experiments, analysed data and wrote part of the manuscript. BV, FB and SK performed ex vivo and in vivo experiments. AH helped perform ex vivo experiments. AC blindly performed histological analysis. ZX provided adenovirus constructs and critically appraised drafts of the document. IS-G and AE provided CF patients bronchial epithelial cells and wrote a section of the manuscript. IG-V helped in the design of the experiments and critically appraised drafts of the document. J-MS designed experiments, provided reagents, analysed data and wrote the manuscript.
Funding ‘Vaincre la Mucoviscidose’ (grants RF 20130500896 and RF 20150501368).
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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