The researchers demonstrate that Cystic fibrosis (CF) neutrophils have prolonged survival secondary to decreased apoptosis, and this is likely a primary defect in CF neutrophils. Increased neutrophil extracellular traps (NET) formation by CF neutrophils is a consequence of a failure to engage in apoptosis and can be targeted by CDKi drugs.
An intrinsic delay in neutrophil apoptosis enhances NET formation in CF and consequently inflammation, representing a novel target for the development of future anti-inflammatory therapies.
Cystic fibrosis (CF) lung disease is defined by large numbers of neutrophils and associated damaging products in the airway. Delayed neutrophil apoptosis is described in CF although it is unclear whether this is a primary neutrophil defect or a response to chronic inflammation.
NETs are a powerful proinflammatory stimulus to macrophages, with CF-derived macrophages being hyper-responsive to NET stimulation.
Increased levels of neutrophil extracellular traps (NETs) have been measured in CF and we aimed to investigate the causal relationship between these phenomena and their potential to serve as a driver of inflammation.
Researchers hypothesized that the delay in apoptosis in CF is a primary defect and preferentially allows CF neutrophils to form NETs, contributing to inflammation.
Blood neutrophils were isolated from patients with CF, CF pigs, and appropriate controls. Neutrophils were also obtained from patients with CF before and after commencing ivacaftor.
Apoptosis was assessed by morphology and flow cytometry. The NET formation was determined by fluorescent microscopy and DNA release assays. NET interaction with macrophages was examined by measuring cytokine generation with ELISA and qRT-PCR.
CF neutrophils live longer due to decreased apoptosis. This was observed in both cystic fibrosis transmembrane conductance regulator (CFTR) null piglets and patients with CF and furthermore was reversed by ivacaftor (CFTR potentiator) in patients with gating (G551D) mutations.
CF neutrophils formed more NETs and this was reversed by cyclin-dependent kinase inhibitor exposure. NETs provided a proinflammatory stimulus to macrophages, which was enhanced in CF.
CF neutrophils have a prosurvival phenotype that is associated with an absence of CFTR function and allows increased NET production, which can in turn induce inflammation. Augmenting neutrophil apoptosis in CF may allow more appropriate neutrophil disposal, decreasing NET formation and thus inflammation.