Chronic pulmonary infections accompanied by persistent neutrophil-dominated inflammation result in severe progressive lung destruction and are the leading causes of morbidity and mortality of CF patients. Our understanding of the mechanistic links between the CFTR mutations and the pathogenesis of infectious and inflammatory pulmonary disease in CF are far from complete.
>To assess the role of CFTR in regulating host innate immune potential in vivo, expression of cftr was knocked-out using CRISPR-Cas9 technology and/or knocked-down by morpholino-modified antisense oligonucleotides in various reporter transgenic lines.
>Exploiting these CFTR-depleted zebrafish models, we investigated the effects of CFTR dysfunction on host innate immune response to infection and tissue injury, and uncovered a number of altered inflammatory processes as critical mechanisms underlying infectious and inflammatory disease in CF.
CF zebrafish exhibit hyper-susceptibility to infection with CF pathogens
Among the deleterious bacteria found in CF airway, Mycobacterium abscessus has emerged as an important respiratory pathogen of major concern in CF centers worldwide. Nevertheless, the specific vulnerability of the CF population to M. abscessus, the potential link with CFTR dysfunction, and how these mycobacteria contribute to progression of lung disease remain unknown. Using CF zebrafish larvae we elucidated the role of CFTR in regulation of innate immunity to M. abscessus infections.
We showed that CF zebrafish exhibit increased susceptibility to M. abscessus infection, resulting in increased mortality and higher bacterial loads, in part due to an inability to generate effective oxidative responses in professional phagocytes. (Bernut et al, 2019, Cell Rep 26:1828-40.e4)
Loss of CFTR function leads an overactive neutrophilic inflammation to tissue injury
It is commonly assumed that the CF-related lung pathology is primarily an infectious disorder: susceptibility to invading pathogens results from airway mucus obstruction and collapse of mucociliary clearance and that the resultant persistent infection drives chronic inflammatory lung damage. However, in CF airways, there is an abnormal inflammatory phenotype often present in absence of detectable infection, raising the question of what drives non-infectious inflammation in CF. Using CF zebrafish, we investigated the effects of CFTR dysfunction on host innate immune response to sterile tissue injury.
We showed that sterile injury leads to high-intensive inflammation, typified by increased then sustained accumulation of neutrophils at wounds: 1) excessive epithelial ROS release drives increased neutrophil recruitment towards wounds; 2) reduction of neutrophil apoptosis and impaired retrograde migration of neutrophils resulting in delayed resolution of inflammation. 3) Therefore, the increased number of neutrophils that mobilized in an uncontrolled manner at wound sites causes persistent inflammation, severe tissue damages, and abnormal tissue repair, which all can be prevented by pharmacological modulation of neutrophilic response using the anti-inflammatory molecule, Tanshinone IIA. (Bernut et al, 2018, J Cyst Fibros June, Vol 17, Sup 3, PS8-9; manuscript in preparation)
