Role of Pneumococcal Autolysin for KLF4 Expression and Chemokine Secretion in Lung Epithelium

Resident microbes shape the vaginal epithelial glycan landscape

Epithelial cells are covered in carbohydrates (glycans). This glycan coat or "glycocalyx" interfaces directly with microbes, providing a protective barrier against potential pathogens. Bacterial vaginosis (BV) is a condition associated with adverse health outcomes in which bacteria reside in direct proximity to the vaginal epithelium. Some of these bacteria, including Gardnerella, produce glycosyl hydrolase enzymes. However, glycans of the human vaginal epithelial surface have not been studied in detail. Here, we elucidate key characteristics of the "normal" vaginal epithelial glycan landscape and analyze the impact of resident microbes on the surface glycocalyx. In human BV, glycocalyx staining was visibly diminished in electron micrographs compared to controls. Biochemical and mass spectrometric analysis showed that, compared to normal vaginal epithelial cells, BV cells were depleted of sialylated N- and O-glycans, with underlying galactose residues exposed on the surface. Treatment of primary epithelial cells from BV-negative women with recombinant Gardnerella sialidases generated BV-like glycan phenotypes. Exposure of cultured VK2 vaginal epithelial cells to recombinant Gardnerella sialidase led to desialylation of glycans and induction of pathways regulating cell death, differentiation, and inflammatory responses. These data provide evidence that vaginal epithelial cells exhibit an altered glycan landscape in BV and suggest that BV-associated glycosidic enzymes may lead to changes in epithelial gene transcription that promote cell turnover and regulate responses toward the resident microbiome.

Krueppel-Like Factor 4 Expression in Phagocytes Regulates Early Inflammatory Response and Disease Severity in Pneumococcal Pneumonia

The transcription factor Krueppel-like factor (KLF) 4 fosters the pro-inflammatory immune response in macrophages and polymorphonuclear neutrophils (PMNs) when stimulated with Streptococcus pneumoniae, the main causative pathogen of community-acquired pneumonia (CAP). Here, we investigated the impact of KLF4 expression in myeloid cells such as macrophages and PMNs on inflammatory response and disease severity in a pneumococcal pneumonia mouse model and in patients admitted to hospital with CAP. We found that mice with a myeloid-specific knockout of KLF4 mount an insufficient early immune response with reduced levels of pro-inflammatory cytokines and increased levels of the anti-inflammatory cytokine interleukin (IL) 10 in bronchoalveolar lavage fluid and plasma and an impaired bacterial clearance from the lungs 24 hours after infection with S. pneumoniae. This results in higher rates of bacteremia, increased lung tissue damage, more severe symptoms of infection and reduced survival. Higher KLF4 gene expression levels in the peripheral blood of patients with CAP at hospital admission correlate with a favourable clinical presentation (lower sequential organ failure assessment (SOFA) score), lower serum levels of IL-10 at admission, shorter hospital stay and lower mortality or requirement of intensive care unit treatment within 28 days after admission. Thus, KLF4 in myeloid cells such as macrophages and PMNs is an important regulator of the early pro-inflammatory immune response and, therefore, a potentially interesting target for therapeutic interventions in pneumococcal pneumonia.

Induction of Krüppel-Like Factor 4 Mediates Polymorphonuclear Neutrophil Activation in Streptococcus pneumoniae Infection

The recruitment and activation of polymorphonuclear neutrophils (PMNs) are of central importance for the elimination of pathogens in bacterial infections. We investigated the Streptococcus pneumoniae-dependent induction of the transcription factor Krüppel-like factor (KLF) 4 in PMNs as a potential regulator of PMN activation. We found that KLF4 expression is induced in human blood-derived PMNs in a time- and dose-dependent manner by wild-type S. pneumoniae and capsule knockout mutants. Unencapsulated knockout mutants induced stronger KLF4 expression than encapsulated wild types. The presence of autolysin LytA-competent (thus viable) pneumococci and LytA-mediated bacterial autolysis were required for KLF4 induction in human and murine PMNs. LyzMcre-mediated knockdown of KLF4 in murine blood-derived PMNs revealed that KLF4 influences pneumococci killing and increases the release of the proinflammatory cytokines tumor necrosis factor α and keratinocyte chemoattractant and decreases the release of the anti-inflammatory cytokine interleukin-10. Thus, S. pneumoniae induces KLF4 expression in PMNs, which contributes to PMN activation in S. pneumoniae infection.

OmpA of Klebsiella pneumoniae ATCC 13883 induces pyroptosis in HEp-2 cells, leading to cell-cycle arrest and apoptosis

Klebsiella pneumoniae is an opportunistic pathogenic bacterium that commonly causes pneumonia in elderly people. OmpA, a toxin that is highly expressed in the outer membrane of the bacterium, is one of the primary factors implicated in the pulmonary pathogenesis of K. pneumoniae. To evaluate the associated pyroptosis mechanism of infection, the ompA gene was cloned, and the protein was expressed, extracted, and used to treat human larynx epithelial cells. We observed that OmpA induces reactive oxygen species production and cell-cycle arrest in the G2/M phase in host cells, leading to subsequent apoptosis. Moreover, OmpA was found to induce IL-1β and IL-18 production in host cells, resulting in caspase-1 activation, which simultaneously stimulated pyroptosis, thus leading to the death of the host cells. We next sought to examine differential gene expression via RNA sequencing to better elucidate the mechanisms associated with these cellular changes, and found that genes associated with these pathways were more highly expressed in OmpA-treated cells than in K. pneumoniae-infected cells. Thus, cell-cycle arrest, apoptosis, and pyroptosis may serve as the primary defenses employed by host cells against OmpA. These results provide novel insights into the host defense against K. pneumoniae infection.

Microinvasion by Streptococcus pneumoniae induces epithelial innate immunity during colonisation at the human mucosal surface

Control of Streptococcus pneumoniae colonisation at human mucosal surfaces is critical to reducing the burden of pneumonia and invasive pneumococcal disease, interrupting transmission, and achieving herd protection. Here, we use an experimental human pneumococcal carriage model (EHPC) to show that S. pneumoniae colonisation is associated with epithelial surface adherence, micro-colony formation and invasion, without overt disease. Interactions between different strains and the epithelium shaped the host transcriptomic response in vitro. Using epithelial modules from a human epithelial cell model that recapitulates our in vivo findings, comprising of innate signalling and regulatory pathways, inflammatory mediators, cellular metabolism and stress response genes, we find that inflammation in the EHPC model is most prominent around the time of bacterial clearance. Our results indicate that, rather than being confined to the epithelial surface and the overlying mucus layer, the pneumococcus undergoes micro-invasion of the epithelium that enhances inflammatory and innate immune responses associated with clearance.

Streptococcus pneumoniae is a common coloniser of the human nasopharynx, but it also causes severe diseases. Here, Weight et al. use an experimental human pneumococcal carriage model to show that bacterial colonisation is associated with invasion of the epithelium and enhancement of immune responses.

Formaldehyde inhibits proliferation of bronchial epithelial cells by down-regulating miR-375

Objective: To study the effect of formaldehyde on the proliferation of human bronchial epithelial cells 16HBE and to explore its mechanism. Methods: MTT assay was used to detect the inhibition rate of formaldehyde-treated 16HBE cells; FCOH + miR-375 group (transfected miR-375 mimics), FCOH + miR-con group (transfected miR-con), FCOH + si-KLF4 group (transfected si-KLF4) and FCOH + si-con group (transfected si-con), were transfected into 16HBE cells by liposome method, then treated with formaldehyde 200 μmol/L for 24 h; qRT-PCR was used to detect the expression of miR-375 in each group; the protein expression of KLF4 in each group was detected by Western blot. The fluorescence activity of each group was detected by dual-fluorescein gene detection assay. Results: Compared with 16HBE cells in Control group, the expression of miR-375 was significantly decreased in FCOH group, cell proliferation was significantly decreased, and KLF4 expression was significantly increased (p < .05). Overexpression of miR-375 and KLF4 knockdown could reverse the inhibition effect of formaldehyde on proliferation of 16HBE cells; KLF4 is a target of miR-375. KLF4 could reverse the promotion of miR-375 on the proliferation of formaldehyde-treated 16HBE cells. Conclusion: Formaldehyde can inhibit the proliferation of human bronchial epithelial cells. The mechanism may be related to the down-regulation of miR-375 targeting KLF4, which will provide support for the treatment of chronic respiratory diseases.

DNA-release by Streptococcus pneumoniae autolysin LytA induced Krueppel-like factor 4 expression in macrophages

The recruitment of myeloid cells to the lung is of utmost importance for the elimination of invading pathogens. We investigated the Streptococcus pneumoniae-dependent induction mechanism of KLF4 in macrophages as a potential regulator of the macrophage immune response. We demonstrated that only viable pneumococci, which have direct contact to the host cells and release LytA-dependent DNA, induced KLF4. Exogenous supplementation of pneumococcal, other bacterial, eukaryotic foreign (human) or self (mouse) DNA to autolysis-deficient pneumococci restored (at least in part) pneumococci-related KLF4 induction. Experiments using TLR9, TRIF and MyD88 knockout macrophages revealed that TLR9, TRIF and MyD88 were partly involved in the S. pneumoniae-induced KLF4 expression. BMMs missing important DNA receptor related molecules (ASC^−/−, STING^−/−) showed no differences in pneumococci-related KLF4 expression. Similar results were observed with IFNAR^−/− BMMs and Type I IFN stimulated cells. LyzMcre mediated knockdown of KLF4 in BMMs resulted in a decreased secretion of proinflammatory cytokines and enhanced IL-10 release. In summary, we showed that pneumococci-related KLF4 induction in macrophages is mediated via a PAMP-DAMP induction mechanism involving a hitherto unknown host cell DNA sensor leading to a more proinflammatory macrophage phenotype.

Human lung ex vivo infection models

Pneumonia is counted among the leading causes of death worldwide. Viruses, bacteria and pathogen-related molecules interact with cells present in the human alveolus by numerous, yet poorly understood ways. Traditional cell culture models little reflect the cellular composition, matrix complexity and three-dimensional architecture of the human lung. Integrative animal models suffer from species differences, which are of particular importance for the investigation of zoonotic lung diseases. The use of cultured ex vivo infected human lung tissue may overcome some of these limitations and complement traditional models. The present review gives an overview of common bacterial lung infections, such as pneumococcal infection and of widely neglected pathogens modeled in ex vivo infected lung tissue. The role of ex vivo infected lung tissue for the investigation of emerging viral zoonosis including influenza A virus and Middle East respiratory syndrome coronavirus is discussed. Finally, further directions for the elaboration of such models are revealed. Overall, the introduced models represent meaningful and robust methods to investigate principles of pathogen-host interaction in original human lung tissue.

Adhesion and invasion of Streptococcus pneumoniae to primary and secondary respiratory epithelial cells

The interaction between Streptococcus pneumoniae (S. pneumoniae) and the mucosal epithelial cells of its host is a prerequisite for pneumococcal disease development, yet the specificity of this interaction between different respiratory cells is not fully understood. In the present study, three areas were examined: i) The capability of the encapsulated S. pneumoniae serotype 3 strain (WU2) to adhere to and invade primary nasal‑derived epithelial cells in comparison to primary oral‑derived epithelial cells, A549 adenocarcinoma cells and BEAS‑2B viral transformed bronchial cells; ii) the capability of the unencapsulated 3.8DW strain (a WU2 derivative) to adhere to and invade the same cells over time; and iii) the ability of various genetically‑unrelated encapsulated and unencapsulated S. pneumoniae strains to adhere to and invade A549 lung epithelial cells. The results of the present study demonstrated that the encapsulated WU2 strain adhesion to and invasion of primary nasal epithelial cells was greatest, followed by BEAS‑2B, A549 and primary oral epithelial cells. By contrast, the unencapsulated 3.8‑DW strain invaded oral epithelial cells significantly more efficiently when compared to the nasal epithelial cells. In addition, unencapsulated S. pneumoniae strains adhered to and invaded the A459 cells significantly more efficiently than the encapsulated strains; this is consistent with previously published data. In conclusion, the findings presented in the current study indicated that the adhesion and invasion of the WU2 strain to primary nasal epithelial cells was more efficient compared with the other cultured respiratory epithelial cells tested, which corresponds to the natural course of S. pneumoniae infection and disease development. The target cell preference of unencapsulated strains was different from that of the encapsulated strains, which may be due to the exposure of cell wall proteins.