Pseudomonas aeruginosa Ventilator-Associated Pneumonia Induces Lung Injury through TNF-α/c-Jun NH2-Terminal Kinase Pathways

Ventilator-associated pneumonia (VAP) is a common nosocomial infection among intensive care unit (ICU) patients. Pseudomonas aeruginosa (PA) is the most common multidrug-resistant Gram-negative pathogen and VAP caused by PA carries a high rate of morbidity and mortality. This study examined the molecular mechanism of PA VAP-induced lung injury. C57BL/6 wild-type (WT) mice and JNK1 knockout (JNK1(-/-)) mice received mechanical ventilation (MV) for 3 h at 2 days after receiving nasal instillation of PA. The WT and JNK1(-/-) mice also received MV after the induction of lung injury by instillation of supernatants from PA-stimulated alveolar macrophages (AMs). AMs isolated from WT, I kappa B-kinase (IKK) beta(Delta Mye) (IKK beta was selectively deleted in macrophages), and JNK1(-/-) mice were ex vivo stimulated with live PA and supernatants were collected for cytokine assay. Intranasal instillation of 10(6) PA enhanced MV-induced NF-kappa B DNA binding activity in the lungs and nitrite levels in BALF. MV after PA instillation significantly increased the expression of ICAM and VCAM in the lungs and TNF-alpha, IL-1 beta, and IL-6 levels in bronchoalveolar lavage fluid (BALF) of WT mice, but not in JNK1(-/-) mice. MV after supernatant instillation induced more total protein concentration in BALF and neutrophil sequestration in the lungs in WT mice than JNK1(-/-) mice and cytokine assay of supernatants indicated that TNF-alpha is a critical regulator of PA VAP-induced lung injury. Ex vivo PA stimulation induced TNF-alpha production by AMs from WT as well as JNK1(-/-) mice but not IKK beta(Delta Mye) mice. In summary, PA colonization plays an important role in PA VAP-induced lung injury through the induction of JNK1-mediated inflammation. These results suggest that the pathogenesis mechanism of PA VAP involves production of TNF-alpha through activation of IKK/NF-kappa B pathways in AMs and JNK signaling pathway in the lungs.