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Abstract
Macrophage dysfunction is fundamentally related to altered immunity in cystic fibrosis (CF). How genetic deficits in the cystic fibrosis transmembrane conductance regulator (CFTR) lead to these defects remains unknown. Rapid advances in genomic editing such as the clustered regularly interspaced short palindromic repeats associated protein 9 (CRISPR/Cas9) system provide new tools for scientific study. We aimed to create a stable CFTR knockout (KO) in human macrophages in order to study how CFTR regulates macrophage function. Peripheral blood monocytes were isolated from non-CF healthy volunteers and differentiated into monocyte-derived macrophages (MDMs). MDMs were transfected with a CRISPR Cas9 CFTR KO plasmid. CFTR KO efficiency was verified and macrophage halide efflux, phagocytosis, oxidative burst, apoptosis, and cytokine functional assays were performed. CFTR KO in human MDMs was efficient and stable after puromycin selection. CFTR KO was confirmed by CFTR mRNA and protein expression. CFTR function was abolished in CFTR KO MDMs. CFTR KO recapitulated known defects in human CF MDM (CFTR class I/II variants) dysfunction including (1) increased apoptosis, (2) decreased phagocytosis, (3) reduced oxidative burst, and (4) increased bacterial load. Activation of the oxidative burst via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase assembly was diminished in CFTR KO MDMs (decreased phosphorylated p47phox). Cytokine production was unchanged or decreased in response to infection in CFTR KO MDMs. In conclusion, we developed a primary human macrophage CFTR KO system. CFTR KO mimics most pathology observed in macrophages obtained from persons with CF, which suggests that many aspects of CF macrophage dysfunction are CFTR-dependent and not just reflective of the CF inflammatory milieu.
Highlights
Cystic fibrosis (CF) is a multi-system disorder characterized by chronic polymicrobial pulmonary infections that lead to progressive morbidity [1]
We found that KO was more effective in differentiated macrophages compared to monocytes during preliminary experiments
cystic fibrosis transmembrane conductance regulator (CFTR) function was abolished in CFTR KO monocyte-derived macrophages (MDMs) compared to untreated vector control non-cystic fibrosis (CF) MDMs (Figure 2E)
Summary
Cystic fibrosis (CF) is a multi-system disorder characterized by chronic polymicrobial pulmonary infections that lead to progressive morbidity [1]. CF pathophysiology results from variants in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which lead to absent or dysfunctional CFTR protein expression. While the persistence of pathogens in CF is multi-factorial, recent evidence suggest that alterations in the innate immune system are critically related to both acute and chronic infections in CF. The overall relationship between CFTR deficits and immune function remains poorly defined. We aimed to create a stable CFTR knockout (KO) in human macrophages to study how CFTR regulates macrophage function. We hypothesized that macrophage effector functions are directly dependent on CFTR and a CFTR KO would reflect the functional macrophage deficits observed in primary human CF macrophages with CFTR (class I/II) variants that result in little or no CFTR protein expression
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