Macrophage Dysfunction in Cystic fibrosis lung disease

Cystic fibrosis (CF) is a life-shortening, autosomal recessive disease caused by loss-of-function mutations in the CFTR gene. The primary cause of morbidity and mortality in CF is respiratory failure following progressive loss of lung function and characterised by recurrent infections and an intense, chronic, neutrophil-dominated inflammatory airway response that is highly excessive relative to the weight of the actual infectious burden. As such, the inflammatory response has been one of the central focuses of CF research for the past 30 years, with an array of studies elucidating the dysregulation of several key immune processes in CF. Macrophages are the most plastic of all immune cells and their immense functional diversity allows them to play a part in orchestrating all major stages of the inflammatory response, from initiation, to resolution and repair. Macrophages, often overlooked in CF research despite their integral role in other chronic inflammatory pathologies, have increasingly become recognised as potential orchestrators of the excessive inflammatory response in CF. The discovery of functional CFTR expression in several immune cells, monocytes and macrophages in particular, has also opened the possibility that some immune cells, much like epithelial cells, are intrinsically dysregulated in CF and pre-programmed to contribute to an excessive inflammatory response. The aim of this project was to investigate the role of macrophages in driving progressive lung disease in CF and gain a better understanding of the mechanisms underlying dysregulation of CF macrophage immune function, with a focus also on the extent of the CFTR-dependent nature of such dysfunction. Another aim was to track longitudinally the effects of novel CFTR modulator therapies, which work to correct the basic underlying defect in CF, on patient inflammation and myeloid function. Whole-blood flow cytometry was used to show that patient circulating monocytes exist in a significantly higher state of activation than non-CF controls and that this correlates with predicted lung function (FVCpp). This activation phenotype was reversed with CFTR modulator (Elexacaftor/Tezacaftor/Ivacaftor) treatment suggesting that such treatment modulates levels of inflammation in patient circulation. CF monocyte-derived macrophages (MDMs) were found to exhibit a hyperinflammatory response to activation with P. aeruginosa LPS and produce elevated levels of several important proinflammatory cytokines by qRT-PCR and ELISA. Given that such cells were cultured for 9 days in the same conditions as non-CF controls, such a phenotype would point towards intrinsic immune dysregulation in the cells. In order to gain a more high-resolution, genome-wide view of transcriptional changes in CF MDMs responding to inflammatory challenge, a highly unbiased approach of global transcriptome profiling was carried out using the cap analysis of gene expression (CAGE) method, which provides additional layers of information regarding promoter usage, enhancer activity and other important regulatory elements that drive gene expression. CAGE sequencing revealed substantial differences in gene expression patterns of CF LPS-treated MDMs compared to non-CF controls, particularly involving genes involved in the immune response, and elucidated a significantly blunted type I IFN signalling response in CF macrophages at 24 hours post-LPS. Such results provide scope for investigating the impact of defective type I IFN signalling in macrophages on bacterial inflammation in CF and also on antiviral immunity, with acute respiratory viral infections representing important, and common, precipitants of pulmonary exacerbation in CF. These findings provide novel insights into macrophages dysfunction in CF and further underline the potential of these cells as a target for novel, and thus far elusive, anti-inflammatory interventional strategies to effectively slow CF lung function decline in combination with novel CFTR modulators and the standard treatment regimen