Abstract Rationale Methicillin-resistant Staphylococcus aureus (MRSA) is the leading cause of both community and hospital-acquired pneumonia in the United States. The emergence of multidrug-resistant bacteria strains leads to an urgent need for alternative treatment strategies. The recently identified NLRP10 (NACHT, leucine-rich repeat LRR, and PYD-containing protein 10) inflammasome is unique because it lacks the ligand-binding/sensing LRR domain, and the role of NLRP10 during MRSA-induced pneumonia remains elusive. Methods Female C57BL/6 wild-type (WT) and NLRP10 knockout (KO) mice were infected with 5 × 107 CFU/75uL of MRSA (USA300 strain) or 2 × 108 CFU/75uL for survival. We stained healthy and pneumonic human and mouse lung sections for myeloid cells (neutrophils and macrophages), non-myeloid cells (epithelial cells), and NLRP10. We performed bronchoalveolar lavage fluid (BALF) phenotyping, quantified cytokines, and chemokines in the BALF and lung tissues, and enumerated bacterial burden in the lungs, liver, and spleen at 12 and 24 hours post-infection. We quantified different granulocyte populations and granulocyte progenitor cells in the blood and bone marrow using flow cytometry and measured neutrophil extracellular killing ability. We constructed bone marrow chimeric mice through lethal irradiation and reconstitution with either WT or NLRP10 KO bone marrow cells. The chimeric mice were infected with MRSA and sacrificed at 24 hours post-infection to quantify the bacterial burden. Lastly, we performed single-cell RNA sequencing to examine the neutrophil populations in the lungs, blood, and bone marrow of the WT and KO mice 12 and 24 hours post-infection. Results NLRP10 is upregulated in human and mouse lungs during pneumonia. Interestingly, the NLPR10 KO mice show decreased mortality following MRSA-induced pneumonia compared to the WT counterparts. We found lower bacterial burdens in the lungs and spleens of the KO mice. Additionally, the KO mice show increased total white blood cells (predominantly neutrophils and macrophages) and cytokines/chemokines (IFN-g, CXCL1, CXCL5, and IL-17A) in the BALF. The NLRP10 KO mice exhibited lower levels of granulocyte progenitor subpopulations but showed higher levels of neutrophil release into the bloodstream. The WT-to-NLRP10 chimeric mice had lower bacterial burden than the WT-to-WT chimera mice. NLRP10 deletion altered the gene expression of neutrophils in the lungs, blood, and bone marrow, and increased extracellular killing of bacteria by neutrophils. Conclusion Deletion of the NLRP10 inflammasome decreases susceptibility to MRSA-induced pneumonia and results in increased neutrophil recruitment and function. Furthermore, NLRP10 deletion modulates granulopoiesis, neutrophil release, and alters neutrophil gene expression in the lungs, blood, and bone marrow. This abstract is funded by: F31HL168986, R01AI180123, R01AI157353, and P20GM130555
Le et al. (Fri,) studied this question.