The Role of Short-Chain Fatty Acids, Produced by Anaerobic Bacteria, in the Cystic Fibrosis Airway

Abstract

Rationale: Anaerobic bacteria are present in large numbers in the airways of people with cystic fibrosis (PWCF). In the gut, anaerobes produce short-chain fatty acids (SCFAs) that modulate immune and inflammatory processes.Objectives: To investigate the capacity of anaerobes to contribute to cystic fibrosis (CF) airway pathogenesis via SCFAs.Methods: Samples of 109 PWCF were processed using anaerobic microbiological culture with bacteria present identified by 16S RNA sequencing. SCFA levels in anaerobic supernatants and bronchoalveolar lavage (BAL) were determined by gas chromatography. The mRNA and/or protein expression of two SCFA receptors, GPR41 and GPR43, in CF and non-CF bronchial brushings and 16HBE14o 2 and CFBE41o 2 cells were evaluated using reverse transcription polymerase chain reaction, Western blot analysis, laser scanning cytometry, and confocal microscopy. SCFA-induced IL-8 secretion was monitored by ELISA.Measurements and Main Results: Fifty-seven (52.3%) of 109 PWCF were anaerobe positive. Prevalence increased with age, from 33.3% to 57.7% in PWCF younger (n = 24) and older (n = 85) than 6 years of age. All evaluated anaerobes produced millimolar concentrations of SCFAs, including acetic, propionic, and butyric acids. SCFA levels were higher in BAL samples of adults than in those of children. GPR41 levels were elevated in CFBE41o 2 versus 16HBE14o 2 cells; CF versus non-CF bronchial brushings; and 16HBE14o 2 cells after treatment with cystic fibrosis transmembrane conductance regulator inhibitor CFTR(inh)-172, CF BAL, or inducers of endoplasmic reticulum stress. SCFAs induced a dosedependent and pertussis toxin-sensitive IL-8 response in bronchial epithelial cells, with a higher production of IL-8 in CFBE41o 2 than in 16HBE14o 2 cells.Conclusions: This study illustrates that SCFAs contribute to excessive production of IL-8 in CF airways colonized with anaerobes via up-regulated GPR41.Keywords: anaerobic bacteria; cystic fibrosis; inflammation; short-chain fatty acids Correspondence and requests for reprints should be addressed to Bojana Mirković, Ph

Evidence and role for bacterial mucin degradation in cystic fibrosis airway disease

“…We subsequently found that co-culture of pathogens with an anaerobic bacterial consortium composed of taxa commonly found in the lower airways [3,5,27,28] can facilitate robust pathogen growth using mucins as a sole carbon source. We also confirmed that fermentation-derived metabolites are abundant within expectorated CF patient sputum, consistent with previous studies [14,29]. Finally, we found that genes required for the catabolism of mucin fermentation byproducts are highly expressed by P. aeruginosa in vivo.…”

“…Moreover, we revealed that in vitro mucin fermentation generated high concentrations of SCFAs and amino acids, which were also abundant and bioavailable for P. aeruginosa within patient sputum. Together, these results suggest that the high levels of utilizable metabolites present in sputum reported previously [14,15,29] may be derived from bacterial mucin degradation. In this context, fermentative anaerobes aspirated from the oral cavity that become established in the lower airways may play a central role in the progression of CF lung disease.…”

“…These results, coupled with previous reports of SCFA in bronchoalveolar lavage fluid [14,29] and degraded mucins in CF sputum [18,39], provide compelling evidence that anaerobic organisms can contribute to CF lung disease by degrading mucins and consequently providing utilizable substrates for opportunistic airway pathogens.…”

Innate Immunity of the Lung: From Basic Mechanisms to Translational Medicine

“…Selected examples include: (1) the short-chain fatty acid receptor GPR41, which is present at higher-than-normal levels in bronchial epithelium of cystic fibrosis (CF) patients and is responsible for exaggerated IL-8 induction in these cells in response to short-chain fatty acids from anaerobic bacteria present in CF lungs [29], (2) the fractalkine receptor CX3CR1, which was recently reported to mediate respiratory syncytial virus-induced cytokine production in primary human airway epithelial cells [30], and (3) an isoform of the coxsackievirus and adenovirus receptor CAREx8a, expressed on the apical surface of airway epithelial cells in culture, that enhances adenovirus entry into cells by coopting neutrophils [31]. …”

Genome-Wide Survey of Pseudomonas aeruginosa PA14 Reveals a Role for the Glyoxylate Pathway and Extracellular Proteases in the Utilization of Mucin

“…Son et al (44) demonstrated that genes required for the glyoxylate cycle in P. aeruginosa are highly expressed within sputum derived from CF patients, while others have reported that aceA is more highly expressed in CF P. aeruginosa isolates compared to those derived from non-CF sources when isolates are grown in vitro (45). Notably, acetate has also been found at elevated concentrations within CF sputum and bronchoalveolar lavage fluid (34,46,47). Our data, when considered in the context of the aforementioned studies, support a role for the glyoxylate shunt in respiratory mucin degradation by P. aeruginosa.…”