Oral infection with periodontal pathogens induced chronic obstructive pulmonary disease-like lung changes in mice

Abstract

Background: Epidemiological studies have demonstrated that periodontitis is an independent risk factor for chronic obstructive pulmonary disease (COPD). However, the mechanism underlying the association between these two diseases remains unclear. The lung microbiota shares similarities with the oral microbiota, and there is growing evidence to suggest that the lung microbiome could play a role in the pathogenesis of COPD. This study aimed to investigate whether periodontal pathogens could contribute to the pathogenesis of COPD in a mouse model.

Methods: We established mouse models with oral infection by typical periodontal pathogens, porphyromonas gingivalis (Pg group) or fusobacterium nucleatum (Fn group), over a three-month period. Mice that did not receive oral infection were set as the control group (C group). We assessed the level of alveolar bone resorption, lung function, and histological changes in the lungs of the mice. Additionally, we measured the levels of inflammatory factors and tissue damage associated factors in the lung tissues.

Results: Lung function indices, including airway resistance, peak inspiratory/expiratory flow and expiratory flow-50%, were significantly reduced in the Fn group compared to the C group. Additionally, histological examination revealed an increased number of inflammatory cells and bullae formation in the lung tissue sections of the Fn group. Meanwhile, levels of inflammatory factors such as IL-1β, IL-6, IFN-γ, and TNF-α, as well as tissue damage associated factors like matrix metalloproteinase-8 and neutrophil elastase, were significantly elevated in the lung tissue of the Fn group in comparison to the C group. The Pg group also showed similar but milder lung changes compared to the Fn group. Pg or Fn could be detected in the lungs of both oral infected groups.

Conclusion: The results indicated that oral periodontal pathogens infection could induce COPD-like lung changes in mice, and they may play a biological role in the association between periodontitis and COPD.

Keywords: Fusobacterium nucleatum; Porphyromonas gingivalis; Chronic obstructive pulmonary disease; Inflammation; Periodontitis.

Fig. 1

Diagram of the establishment protocol for mouse oral infection models

Fig. 2

Alveolar bone resorption at the maxillary second molars of mice in each group. The average bone resorption was 0.15 ± 0.02 mm (C group), 0.16 ± 0.02 mm (Pg group) and 0.19 ± 0.04 mm (Fn group) separately (C group: control group, Pg group: P.gingivalis oral infection group, Fn group: F.nucleatum oral infection group; * vs. C group, P < 0.05)

Fig. 3

Oral infection with F.nucleatum significantly impairs lung function in mice. The level of Raw was significantly increased in the Fn group compared to the C group. The levels of PIF, PEF, and EF50 in the Fn group were significantly decreased compared to the C group. (C group: control group, Pg group: P.gingivalis oral infection group, Fn group: F.nucleatum oral infection group; Raw: airway resistance, PIF: peak inspiratory flow, PEF: peak expiratory flow, EF50: expiratory flow-50% .* vs C group, P < 0.05)

Fig. 4

Histological manifestations of the mice lung tissues in each group (HE staining). Oral infections with P.gingivalis or F.nucleatum led to increased immune cell infiltration, mucous accumulation and airway wall thickening in lung tissue, features characteristic of the advanced stages of COPD(C group: control group, Pg group: P.gingivalis oral infection group, Fn group: F.nucleatum oral infection group; black arrow: alveolar walls were damaged and fused to form bullae; yellow arrow: inflammatory cells infiltrated around the alveoli; red arrow: the bronchus is infiltrated by a large amount of inflammatory cells)

Fig. 5

P. gingivalis and F. nucleatum detection in the lung tissue of each group by immunofluorescence staining. (A) positive staining for P. gingivalis (red) observed in the Pg group, and no staining was observed in the C group; (B) positive staining for F. nucleatum (green) observed in the Fn group, and no staining was observed in the C group (C group: control group, Pg group: P.gingivalis oral infection group, Fn group: F.nucleatum oral infection group)

Fig. 6

Expression levels of inflammatory factors in the lung tissues of mice in each group. The protein expression level of inflammatory factor IFN-γ, TNF-α and IL-6 were significantly increased both in the Pg group and Fn group, with the levels in the Fn group being significantly higher than those in the Pg group (C group: control group, Pg group: P.gingivalis oral infection group, Fn group: F.nucleatum oral infection group; a: vs. C group, P < 0.05; b: Fn group vs. Pg group, P < 0.05)

Fig. 7

Expression levels of tissue damage associated factors in each group. The tissue damage associated factors NE and MMP-8 in the lung tissues of Pg group and Fn group were both significantly higher than those in the C group (C group: control group, Pg group: P.gingivalis oral infection group, Fn group: F.nucleatum oral infection group; *vs. C group, P < 0.05)