Dissecting neutrophilic inflammation in cystic fibrosis lung disease: the role of chitinases
Final Report Abstract
The aim of the project was to study the role of chitinases in cystic fibrosis /CF) lung disease. Chitinases are enzymes that cleaves chitin, which is one of the major components in the cell wall of fungal pathogens. In the first part of this project, we focussed on chitinase activity in patients with CF (PwCF) and we were able to show that chitinases are elevated in blood of PwCF compared to healthy controls and / or other chronic diseases that are associated with increased levels of chitinase activity such as asthma and Gaucher disease. PwCF colonized with Candida (C.) albicans had higher chitinase levels in blood and in the airways than those without, while stratification for Aspergillus (A.) fumigatus – both being the most common fungi isolated from the airways of PwCF – showed no difference. Hence, chronic infection with C. albicans results in increased secretion and activation of chitinases in PwCF. But this presses the question to why PwCF are more susceptible to fungal pathogens, especially to C. albicans. We found that the airway environment with high levels of proteases that are mainly secreted by neutrophils are counterproductive by cleaving and inactivating chitinases and thereby dampening the antifungal activity of the chitinases. Furthermore, in our population of PwCF, a single nucleotide polymorphism in the CHIT1 gene that is associated with deficiency of the chitinase chitotriosidase significantly correlated with chronic infection with C. albicans. These findings may partly explain why – at least a part of – PwCF are more susceptible to fungal pathogens, especially to C. albicans. In the second part of this project, we asked if there is also a difference in the recognition of or in the response to fungal pathogens. In our analyses, a receptor for β-glucan – another major component of the fungal cell wall - dectin-1 was altered in CF cells with lower intracellular expression in neutrophils and bronchial epithelial cells compared to healthy control cells. This also resulted in lower binding of fungal PAMPs in CF compared to healthy control cells which might result in insufficient immune response and therefore decreased clearance of fungal pathogens. However, while main components of the dectin-1 signalling cascade were also decreased in neutrophils from PwCF compared to healthy controls, treatment with fungal pathogens and PAMPs had no significant impact on the secretion of the main pro-inflammatory cytokine IL-8 in both, CF and healthy control cells. Particularly for the second part of this project, many questions are yet to be answered. Future investigation will focus on as why PwCF are more prone to be chronically infected by fungal pathogens. As shown in our project, the proinflammatory and proteolytic environment within the airways of PwCF definitely play a key role. However, there might also be a link between the defect of the CFTR channel and regulation of the expression of PRRs. Further experiments including CFTR-targeted approaches and more detailed analysis on the PRRs and the respective signalling pathways will have to be conducted.
Publications
- Chitinase activation in patients with fungus-associated cystic fibrosis lung disease. J Allergy Clin Immunol. 2016 Oct;138(4):1183-1189.e4
Hector A, Chotirmall SH, Lavelle GM, Mirković B, Horan D, Eichler L, Mezger M, Singh A, Ralhan A, Berenbrinker S, Mack I, Ensenauer R, Riethmüller J, Graepler-Mainka U, Murray MA, Griese M, McElvaney NG, Hartl D
(See online at https://doi.org/10.1007/s11046-017-0184-y) - Fungal Pathogens in CF Airways: Leave or Treat? Mycopathologia. 2018 Feb;183(1):119-137. Epub 2017 Aug 2
Singh A, Ralhan A, Schwarz C, Hartl D, Hector A
(See online at https://doi.org/10.1007/s11046-017-0184-y)
