Neutrophil-Mediated Phagocytic Host Defense Defect in Myeloid Cftr-Inactivated Mice

Abstract

Cystic fibrosis (CF) is a common and deadly inherited disease, caused by mutations in the CFTR gene that encodes a cAMP-activated chloride channel. One outstanding manifestation of the disease is the persistent bacterial infection and inflammation in the lung, which claims over 90% of CF mortality. It has been debated whether neutrophil-mediated phagocytic innate immunity has any intrinsic defect that contributes to the host lung defense failure. Here we compared phagosomal CFTR targeting, hypochlorous acid (HOCl) production, and microbial killing of the neutrophils from myeloid Cftr-inactivated (Myeloid-Cftr−/−) mice and the non-inactivated control (Cftrfl10) mice. We found that the mutant CFTR that lacked Exon-10 failed to target to the neutrophil phagosomes. This dysfunction resulted in impaired intraphagosomal HOCl production and neutrophil microbial killing. In vivo lung infection with a lethal dose of Pseudomonas aeruginosa caused significantly higher mortality in the myeloid CF mice than in the controls. The myeloid-Cftr−/− lungs were deficient in bacterial clearance, and had sustained neutrophilic inflammation and stalled transition from early to late immunity. These manifestations recapitulated the symptoms of human CF lungs. The data altogether suggest that myeloid CFTR expression is critical to normal host lung defense. CFTR dysfunction in neutrophils compromises the phagocytic innate immunity, which may predispose CF lungs to infection.

Neutrophils in cystic fibrosis

“…While the surrounding pro-inflammatory CF microenvironment substantially affects neutrophil phenotype and function, the intrinsic CFTR defect also seems to modulate neutrophil homeostasis and granule release (Pohl et al, 2014). Collectively, CFTR function in neutrophils has been associated with granule exocytosis and phagocytosis, as well as sustained neutrophilic lung inflammation in response to infection (Painter et al, 2006;Bonfield et al, 2012;Ng et al, 2014;Pohl et al, 2014). Intriguingly, the CFTR potentiator ivacaftor was found to modulate leukocyte activation in CF patients (Pohl et al, 2014;Bratcher et al, 2016).…”

“…Therefore, additional studies described that neutrophils migrating into CF airways can adapt to this enriched milieu by positively modulating their G-CSF receptor (CD114) (Makam et al, 2009) and their metabolite transporters, notably for glucose (GLUT1 or SLC2A1) and inorganic phosphate (PiT1 or SLC20A1) when compared to blood neutrophils. Interestingly, by looking directly into airway subsets, CF airway neutrophils displayed further regulation profile in PiT2 (or SLC20A2, another inorganic phosphate transporter) as well as in amino acid transporter (ASCT2 or SLC1A5), involved in the supplementation of essential amino acids regulating mTOR (Nicklin et al, 2009;Laval et al, 2013). Taken together, up-regulation of the anabolic prosurvival mTOR pathway and changes in surface receptors suggest that neutrophils homing to CF lungs undergo a concerted set of reprogramming processes.…”

“…However, in the past decade, combined in vitro and in vivo studies, both in mice and humans, demonstrated that the absence or dysfunction of CFTR in neutrophils impairs bacterial killing and disease outcome (Painter et al, 2006;Bonfield et al, 2012;Ng et al, 2014). These studies also demonstrated the localization of CFTR at the membrane of phagolysosomes, which was shown to be essential for chloride transport and was linked to bacterial protein chlorination during phagocytosis.…”

CFTR Controls the Activity of NF-κB by Enhancing the Degradation of TRADD

“…A second source of induced NFκB activation is calcium accumulation in the endoplasmic reticulum (ER), leading to ER stress [6]. However, it is not just a bacterial effect alone, because NFκB-activated inflammation persists in the infection-suppressed CF airway or in CF lung epithelial cells cultured in the explicit absence of bacteria [7,8]. Therefore, whether inflammation is intrinsic, is caused by bacterial infection, or is caused by both processes, has remained consistently controversial.…”

Consequences of cystic fibrosis transmembrane regulator mutations on inflammatory cells

“…Inhibitor of PI3K, LY294002, increased CF neutrophils apoptosis in 50%, similar to normal patients' neutrophil apoptosis [68]. In addition to prolonged life span, that impairs inflammation resolution, neutrophils carrying CFTR mutations have significantly higher expression of active CD11b and compromised phagocytosis, which predispose CF lungs to infection [61,69].…”