Fusobacterium Nucleatum Promotes Pseudomonas Aeruginosa Invasion to Modulate the Inflammatory Cytotoxicity of Pulmonary Epithelial Cells

Abstract BackgroundChronic obstructive pulmonary disease (COPD) is one of the most common and costly respiratory disease and is a leading cause of mortality globally. Inflammatory damage induced by bacterial infections is an important contributor to the etiology of COPD. Fusobacterium nucleatum, a recognized periodontal pathogen, frequently coexists with Pseudomonas aeruginosa in the airway of COPD patients, its amount is negatively correlated with lung function of COPD patients coinfected with P. aeruginosa, but the mechanism of this is still unclear. This study intends to reveal the effect of F. nucleatum on P. aeruginosa-induced inflammatory cytotoxicity of pulmonary epithelial cells to illustrate the underlying mechanism of the above clinical phenomenon.MethodsA549 cells were infected with F. nucleatum and P. aeruginosa simultaneously or sequentially. Bacterial aggregation assay and scanning electron microscopy (SEM) were used to evaluate the interaction between F. nucleatum and P. aeruginosa. Antibiotic protection assay was used to detect bacterial adhesion and invasion. The cellular proliferation and cytotoxic damage were examined through CCK-8 assay, lactate dehydrogenase (LDH) leakage assay and calcein acetoxymethyl ester/propidium iodide (Calcein-AM/PI) staining. Enzyme-linked immunosorbent assay (ELISA) was performed to observe IL-1β, IL-6 and TNF-α expressions.ResultsP. aeruginosa mainly induces IL-1β and IL-6 associated inflammatory cytotoxicity of pulmonary epithelial cells, F. nucleatum mainly initiates high inflammatory proliferation of pulmonary epithelial cells. When pulmonary epithelial cells are simultaneously infected with P. aeruginosa and F. nucleatum, F. nucleatum coaggregates with P. aeruginosa to synergistically invade into pulmonary epithelial cells and transiently resists P. aeruginosa-induced cytotoxic damage to amplify IL-6 and TNF-α associated inflammation in pulmonary epithelial cells. Furthermore, F. nucleatum maintains or even aggravates P. aeruginosa-induced inflammatory cytotoxicity of pulmonary epithelial cells, no matter which were pretreated or subsequentially infected with F. nucleatum.ConclusionsF. nucleatum modulates P. aeruginosa-induced inflammatory cytotoxicity of pulmonary epithelial cells, which may contribute to persistent exacerbation of COPD patients accompanied with P. aeruginosa and F. nucleatum coinfection.