No abstract

Bacterial pathogens are a leading cause of lung infections and contribute to acute exacerbations in patients with chronic respiratory diseases. The innate immune system of the respiratory tract controls and prevents colonization of the lung with bacterial pathogens. Forkhead box transcription factor family O (FOXO) transcription factors are key regulators of cellular metabolism, proliferation, and stress resistance. In this study, our aim was to investigate the role of FOXO transcription factors in innate immune functions of respiratory epithelial cells. We show that bacterial pathogens potently activate FOXO transcription factors in cultured human respiratory epithelial cells in vitro. Infection of mice with bacterial pathogens resulted in the activation of FOXO transcription factors in alveolar and bronchial epithelial cells in vivo. Active FOXO was also detectable in human bronchial tissue obtained from subjects with different infection-related lung diseases. Small interfering RNA–mediated knockdown of FOXO in bronchial epithelial cells resulted in reduced expression of factors of the innate immune system such as antimicrobial peptides and proinflammatory cytokines, both under basal conditions and upon infection. FOXO deficiency further affected internalization of Haemophilus influenzae in bronchial epithelial cells. Finally, we show that TLR3 activates innate immune responses in a FOXO-dependent manner. In conclusion, FOXO transcription factors are involved in the cellular responses to bacterial stimuli and act as central regulators of innate immune functions in respiratory epithelial cells.

Chronic obstructive pulmonary disease (COPD) is associated with an increased risk for lung cancer and an aberrant microbiota of the lung. Microbial colonization contributes to chronic neutrophilic inflammation in COPD. Nontypeable Haemophilus influenzae (NTHi) is frequently found in lungs of stable COPD patients and is the major pathogen triggering exacerbations. The epithelial cytokine interleukin-17C (IL-17C) promotes the recruitment of neutrophils into inflamed tissues. The purpose of this study was to investigate the function of IL-17C in the pulmonary tumor microenvironment. We subjected mice deficient for IL-17C (IL-17C) and mice double deficient for Toll-like receptor 2 and 4 (TLR-2/4) to a metastatic lung cancer model. Tumor proliferation and growth as well as the number of tumor-associated neutrophils was significantly decreased in IL-17C and TLR-2/4 mice exposed to NTHi. The NTHi-induced pulmonary expression of IL-17C was dependent on TLR-2/4. In vitro, IL-17C increased the NTHi- and tumor necrosis factor-α-induced expression of the neutrophil chemokines keratinocyte-derived chemokine and macrophage inflammatory protein 2 in lung cancer cells but did not affect proliferation. Human lung cancer samples stained positive for IL-17C, and in non-small cell lung cancer patients with lymph node metastasis, IL-17C was identified as a negative prognostic factor. Our data indicate that epithelial IL-17C promotes neutrophilic inflammation in the tumor microenvironment and suggest that IL-17C links a pathologic microbiota, as present in COPD patients, with enhanced tumor growth.

BackgroundBacterial colonization and recurrent infections of the respiratory tract contribute to the progression of chronic obstructive pulmonary disease (COPD). There is evidence that exacerbations of COPD are provoked by new bacterial strains acquired from the environment. Using a murine model of colonization, we examined whether chronic exposure to cigarette smoke (CS) promotes nasopharyngeal colonization with typical lung pathogens and whether colonization is linked to inflammation in the respiratory tract.MethodsC57BL/6 N mice were chronically exposed to CS. The upper airways of mice were colonized with nontypeable Haemophilus influenzae (NTHi) or Streptococcus pneumoniae. Bacterial colonization was determined in the upper respiratory tract and lung tissue. Inflammatory cells and cytokines were determined in lavage fluids. RT-PCR was performed for inflammatory mediators.ResultsChronic CS exposure resulted in significantly increased numbers of viable NTHi in the upper airways, whereas NTHi only marginally colonized air-exposed mice. Colonization with S. pneumoniae was enhanced in the upper respiratory tract of CS-exposed mice and was accompanied by increased translocation of S. pneumoniae into the lung. Bacterial colonization levels were associated with increased concentrations of inflammatory mediators and the number of immune cells in lavage fluids of the upper respiratory tract and the lung. Phagocytosis activity was reduced in whole blood granulocytes and monocytes of CS-exposed mice.ConclusionsThese findings demonstrate that exposure to CS impacts the ability of the host to control bacterial colonization of the upper airways, resulting in enhanced inflammation and susceptibility of the host to pathogens migrating into the lung.

Chronic diseases of the respiratory tract, such as cystic fibrosis, are associated with mucosal and systemic hypoxia. Innate immune functions of airway epithelial cells are required to prevent and control infections of the lung parenchyma. The transcription factor hypoxia-inducible factor 1a (HIF-1a) regulates cellular adaptation to low oxygen conditions. Here, we show that hypoxia and HIF-1a regulate innate immune mechanisms of cultured human bronchial epithelial cells (HBECs). Exposure of primary HBECs to hypoxia or the prolyl hydroxylase inhibitor dimethyloxaloylglycine (DMOG) resulted in a significantly decreased expression of inflammatory mediators (IL-6, IFN-g-induced protein 10) in response to ligands for TLRs (flagellin, polyI:C) and Pseudomonas aeruginosa, whereas the expression of inflammatory mediators was not affected by hypoxia or DMOG in the absence of microbial factors. Small interfering RNA-mediated knockdown of HIF-1a in HBECs and in the bronchial epithelial cell line Calu-3 resulted in increased expression of inflammatory mediators. The inflammatory response was decreased in lungs of mice stimulated with inactivated P. aeruginosa under hypoxia. These data suggest that hypoxia suppresses the innate immune response of airway epithelial cells via HIF-1a.