TLR5 signalling activates the alternative NF-κB signalling pathway in Cystic Fibrosis bronchial epithelial cells in response to infection with Prevotella histicola.

Abstract

Cystic Fibrosis (CF), caused by mutations affecting the CFTR gene, is characterised by viscid secretions in multiple organ systems. CF airways contain thick mucus, creating a gradient of hypoxia, which promotes the establishment of polymicrobial infection. Such inflammation predisposes to further infection, a self-perpetuating cycle in mediated by NF-{kappa}B. Anaerobic Gram-negative Prevotella spp. are found in sputum from healthy volunteers and CF patients and in CF lungs correlate with reduced levels of inflammation. Prevotella histicola (P.histicola) can suppress murine lung inflammation, however, no studies have examined the role of P.histicola in modulating infection and inflammation in the CF airways. We investigated innate immune signalling and NF-kB activation in CF epithelial cells CFBE41o-in response to clinical stains of P.histicola and Pseudomonas aeruginosa (P.aeruginosa). Toll-Like Receptor (TLR) expressing HEK-293 cells and siRNA assays for TLRs and IKKa were used to confirm signalling pathways. We show that P.histicola infection activated the alternative NF-kB signalling pathway in CF bronchial epithelial cells inducing HIF-1 protein. TLR5 signalling was responsible for the induction of the alternative NF-kB pathway through phosphorylation of IKK. The induction of transcription factor HIF-1 was inversely associated with the induction of the alternative NF-kB pathway and knockdown of IKK partially restored canonical NF-kB activation in response to P.histicola. This study demonstrates that different bacterial species in the respiratory microbiome can contribute differently to inflammation, either by activating inflammatory cascades (P.aeruginosa) or by muting the inflammatory response by modulating similar or related pathways (P.histicola). Further work is required to assess the complex interactions of the lung microbiome in response to mixed bacterial infections and their effects in people with CF.