Lienau, J. | Search bioRxiv

bioRxiv2024

IGF1R is protective in pneumococcal pneumonia

BackgroundStreptococcus pneumoniae (S.pn) is the most prevalent causal bacterial pathogen in community-acquired pneumonia. Despite appropriate antimicrobial therapy, pneumococcal pneumonia can progress to acute respiratory distress syndrome where actual therapies are mainly supportive, and the discovery of new molecular targets is needed. ObjectiveTo investigate the role of IGF1R (Insulin-like Growth Factor 1 Receptor) in pneumococcal pneumonia. MethodsIgf1r-deficient (UBC-CreERT2; Igf1rfl/fl) and control (Igf1rfl/fl) mice were infected with 5x106 S.pn (PN36) or PBS (sham infected). Mice were sacrificed 48 h after infection. Pulmonary permeability, local inflammatory response, and pulmonary and extra-pulmonary bacterial loads were analyzed. Further, IGF1R protein expression was determined in human lung tissue after S.pn infection and IGF1 and IGF1R levels were determined serum of pneumonia patients. ResultsIn patients and mice infected with S.pn, IGF1 signaling was significantly altered. Igf1r-deficient mice had significantly increased pulmonary permeability after infection with increased pulmonary inflammatory cytokine levels, while inflammatory cell recruitment was not altered compared to infected Igf1rfl/fl control animals. Pulmonary bacterial load was significantly higher in Igf1r-deficient mice, and histological analysis confirmed increased alveolar edema and necrosis compared to infected Igf1rfl/fl control and sham-infected mice. Ex vivo, S.pn caused a decrease in IGF1R protein expression in human lung tissue. ConclusionOur results demonstrate a significant regulation of IGF1R in ex-vivo infected human lung tissue and in serum of S.pn pneumonia patients. Moreover, pneumonia severity was increased in Igf1r-deficient mice upon S.pn infection compared to Igf1rfl/fl control mice, suggesting that IGF1R plays a protective role in pneumococcal pneumonia.

molecular biology↗

bioRxiv2024

Overventilation-induced airspace acidification increases susceptibility to Pseudomonas pneumonia

Ventilator-associated pneumonia (VAP) is the most frequent nosocomial infection in critically ill patients. Local pH variations affect bacterial growth. Whether airway acidification contributes to the pathogenesis and pathophysiology of Pseudomonas aeruginosa (PA)-induced VAP is currently unknown. This study was undertaken to investigate the role and mechanisms of airspace acidification by mechanical ventilation (MV) in PA-induced VAP. C57BL/6J mice were subjected to high (HVt: 34 mL/kg) or low (LVt: 9 mL/kg) tidal volume MV for 4 h. PA was instilled via the tracheal tube, and animals were allowed to recover from sedation and breathe spontaneously for 24 h following extubation. Fluorescence microscopy was applied to determine alveolar pH in ex vivo perfused and ventilated murine lungs. Bacterial growth and adhesion on cyclically stretched A549 and human alveolar epithelial cells was examined. Upon PA infection, HVt mice showed increased alveolo-capillary permeability, elevated lung and blood leukocyte counts, and higher bacterial load in lungs and extrapulmonary organs as compared to LVt controls. HVt MV induced acidification of alveolar lining fluid (ALF) in lungs and decreased pulmonary expression of Na+/H+ exchanger 1 (NHE1). Inhibition of NHE1 enhanced PA growth in vitro on alveolar epithelial cells and increased pulmonary bacterial loads in LVt-MV mice in vivo. In a novel murine VAP model, key characteristics of PA-VAP were replicated. HVt MV induced mild VILI with acidification of airway lining fluid, increasing susceptibility to PA pneumonia. NHE1 was identified as critical factor for MV-induced airspace acidification, and thus as potential target to combat PA-VAP.

immunology↗