Aspergillus fumigatus Supernatants Disrupt Bronchial Epithelial Monolayers: Potential Role for Enhanced Invasion in
Katie Dunne1, Emma Reece1, Siobhán McClean2
1Discipline of Clinical Microbiology, School of Medicine, Trinity College Dublin, D02 PN40 Dublin, Ireland.
Abstract:
Aspergillus fumigatus is the most commonly isolated fungus in chronic lung diseases, with a prevalence of up to 60% in cystic fibrosis patients. Despite this, the impact of A. fumigatus colonisation on lung epithelia has not been thoroughly explored. We investigated the influence of A. fumigatus supernatants and the secondary metabolite, gliotoxin, on human bronchial epithelial cells (HBE) and CF bronchial epithelial (CFBE) cells. CFBE (F508del CFBE41o-) and HBE (16HBE14o-) trans-epithelial electrical resistance (TEER) was measured following exposure to A. fumigatus reference and clinical isolates, a gliotoxin-deficient mutant (ΔgliG) and pure gliotoxin. The impact on tight junction (TJ) proteins, zonula occludens-1 (ZO-1) and junctional adhesion molecule-A (JAM-A) were determined by western blot analysis and confocal microscopy. A. fumigatus conidia and supernatants caused significant disruption to CFBE and HBE TJs within 24 h. Supernatants from later cultures (72 h) caused the greatest disruption while ΔgliG mutant supernatants caused no disruption to TJ integrity. The ZO-1 and JAM-A distribution in epithelial monolayers were altered by A. fumigatus supernatants but not by ΔgliG supernatants, suggesting that gliotoxin is involved in this process. The fact that ΔgliG conidia were still capable of disrupting epithelial monolayers indicates that direct cell-cell contact also plays a role, independently of gliotoxin production. Gliotoxin is capable of disrupting TJ integrity which has the potential to contribute to airway damage, and enhance microbial invasion and sensitisation in CF.
Insights
Aspergillus fumigatus disrupts lung epithelial barrier integrity in cystic fibrosis patients. The toxin gliotoxin and direct fungal contact contribute to airway damage and increased infection risk.
Area of Science:
- Microbiology
- Cell Biology
- Pulmonology
Background:
- Aspergillus fumigatus is a common fungal isolate in chronic lung diseases, particularly cystic fibrosis (CF).
- The impact of A. fumigatus colonization on lung epithelial cells remains incompletely understood.
- Investigating epithelial barrier function is crucial for understanding CF pathogenesis.
Purpose of the Study:
- To investigate the effects of A. fumigatus and its metabolite gliotoxin on human bronchial epithelial (HBE) and CF bronchial epithelial (CFBE) cells.
- To determine the role of gliotoxin in disrupting epithelial barrier integrity and tight junctions.
- To assess the contribution of direct fungal contact versus secreted factors in epithelial damage.
Main Methods:
- Exposure of HBE and CFBE cell lines to A. fumigatus isolates, a gliotoxin-deficient mutant (ΔgliG), and purified gliotoxin.
- Measurement of trans-epithelial electrical resistance (TEER) to assess barrier function.
- Analysis of tight junction proteins (ZO-1, JAM-A) using western blotting and confocal microscopy.
Main Results:
- A. fumigatus conidia and supernatants significantly disrupted epithelial tight junctions in both HBE and CFBE cells within 24 hours.
- Supernatants from later cultures (72h) induced the most significant disruption.
- Gliotoxin was identified as a key mediator of this disruption, as ΔgliG mutant supernatants caused no damage.
- Direct contact with ΔgliG conidia also caused disruption, indicating a gliotoxin-independent mechanism.
- Alterations in ZO-1 and JAM-A distribution were observed with A. fumigatus supernatants but not with ΔgliG supernatants.
Conclusions:
- A. fumigatus significantly compromises lung epithelial barrier integrity through both gliotoxin production and direct cell contact.
- Gliotoxin plays a critical role in disrupting tight junctions, potentially contributing to airway damage in CF.
- The findings highlight the dual mechanisms by which A. fumigatus exacerbates lung disease in CF patients.
- Targeting gliotoxin and understanding fungal-epithelial interactions may offer therapeutic strategies for CF lung infections.
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