OC 39.5 - Lung megakaryocytes are tissue resident, arise independent of HSCs, and contribute to recovery in low platelet states.

Background: Platelet-producing megakaryocytes (Mks) are present in the lung, and we have described an immune modulatory phenotype of lung Mks. It is assumed that the extravascular lung Mks are ‘seeded’ from the bone marrow (BM).

Aims: To investigate lung Mk origin and how origin may impact function, we used complementary models to lineage trace lung Mks and their platelets.

Methods: We used CFSE dye given oropharyngeal (OP) to label only lung cells. We detected CFSE+ lung Mks for up to 120 days post administration without any CFSE+ Mks in BM or spleen. We then used a lineage tracing model (MDS1-Cre-ERT2 eYFP) where tamoxifen (TAM) administration induces an eYFP reporter in hematopoietic stem cell (HSC)-derived cells.

Results: Mice were dosed with TAM at 11 months (mos) and sacrificed at 16 mos. Lung Mks had less eYFP than BM Mks. Similarly, we dosed mice with TAM at embryonic day 9.25 and sacrificed them at 12 weeks. The majority of BM Mks were eYFP+/HSC-dependent, while few lung Mks were eYFP+. These data suggest that the majority of lung Mks are not HSC-dependent.
The CFSE OP method labeled lung cells, which enabled us to track lung Mk-derived platelets. We found that 10% of the steady-state platelet pool is lung derived. In a model of thrombocytopenia using diphtheria toxin mediated platelet depletion in PF4-Cre-iDTR mice, we observed a doubling of lung platelets (about 20%).

Conclusion(s): Our studies suggest that lung Mks are tissue resident, self-renewing cells that contribute relatively more platelets following acute Mk/platelet depletion. Future work will focus on using complementary techniques to define lung Mk tissue residence, the developmental origin of lung Mks, and function of lung platelets during health and disease.