Pulmonary megakaryocytes orchestrate host defense via PcrV-induced NF-κB signaling in Pseudomonas aeruginosa infection

BACKGROUND: Megakaryocytes, beyond their classical role in platelet formation, are increasingly recognized as immune modulators. This study aimed to investigate the function and activation mechanisms of megakaryocytes during Pseudomonas aeruginosa (PA) infection, focusing on their interaction with bacterial toxins and innate immune pathways. METHODS: This study evaluated the response of pulmonary megakaryocytes to PA-induced acute pneumonia in mice. Specifically, the activation status of pulmonary megakaryocytes was determined by flow cytometry and sorting, followed by RNA sequencing, combining Gene Ontology and Gene Set Enrichment Analysis. The expression of pro-inflammatory cytokines and chemokines within megakaryocytes after PA infection were detected by qPCR and fluorescent confocal imaging. The effect of megakaryocytes on the chemotaxis and recruitment of neutrophils and monocytes was demonstrated using chemotaxis assays. Additionally, purified PA toxins were injected into the lungs of mice in vivo or added to flow-sorted cells in vitro in order to induce inflammation and evaluate the response of megakaryocytes to a single PA toxin. The activation status of intracellular signaling pathways was verified through inhibitor-mediated blocking experiments. RESULTS: PA infection significantly activates megakaryocytes, which promote the recruitment of phagocytes and enhance the host's defense against PA infection. The innate immune response in the lungs was diminished during the early stages of PA infection among the megakaryocytes depleted mice, resulting in increased bacterial load and higher mortality. Flow cytometry sorting followed by RNA sequencing indicated that megakaryocytes exhibit a typical pro-inflammatory phenotype, along with NF-κB pathways activation. Furthermore, the PA toxin PcrV was identified as a key NF-κB activator on megakaryocytes, as demonstrated by increased expression of inflammatory markers and chemokines in response to PcrV. Inhibition of NF-κB signaling attenuated this pro-inflammatory phenotype of megakaryocytes. CONCLUSIONS: This study provides new insights into how megakaryocytes shape the cytokine and chemokine landscape in the lung during PA infection. It highlights the intrinsic interactions between megakaryocytes and phagocytes during pathogen invasion, suggests that managing megakaryocyte activity could be a new strategy to enhance immune defense.