PB0729 - Lung megakaryocyte compartment expands in response to LPS-induced acute lung injury

Background: While megakaryocytes primarily reside in the bone marrow, there is increased interest in the lung as a thrombopoietic niche with recent evidence of the of megakaryocytes in the pulmonary vasculature. These lung megakaryocytes can reconstitute the platelet pool of c-mpl-/- mice and have an immunogenic transcriptome. A separate study further established their potential role in immunity and described their ability to internalize E. coli and present antigen to T-cells. Platelets are also recognized as immune effectors and have been implicated in pathogenesis of acute respiratory distress syndrome (ARDS), a complex disease process orchestrated by inflammatory and endothelial cells in response to lung insult, such as acute lung injury (ALI).

Aims: Based on current evidence suggesting that megakaryocytes participate in lung immunity, we aim to demonstrate a connection between lung megakaryocytes and ALI/ARDS.

Methods: We sought to investigate the effect of acute lung injury (ALI) on the lung megakaryocyte compartment in a lipopolysaccharide (LPS) model of ALI. ALI was induced in mice by intra-tracheal injection of 1.6 mg/kg LPS or vehicle. We profiled the lung megakaryocyte and neutrophil (defined as Ly6g+) compartments using flow cytometry and immunocytochemistry over 24, 48, 72, and 168 hours.

Results: At 24 hours, lung cellularity has increased including neutrophils, consistent with a localized inflammation in the LPS-induced ALI model. By 48 hours lung cellularity expansion continues, and megakaryocyte count after ALI is increased compared to vehicle. Surprisingly, at 72 hours after ALI, megakaryocyte expansion slows as compared to total lung cellularity expansion, coinciding with a mild thrombocytopenia. Homeostasis returns after 168 hours, but the lung compartment and megakaryocyte counts remain elevated.

Conclusion(s): These data are the first evidence that the lung megakaryocyte compartment fluctuates in response to LPS-induced ALI, therefore, we will next focus on their role in ALI/ARDS pathogenesis.