Megakaryocytes (MK) are responsible for platelet biogenesis, which is thought to occur canonically in the adult bone marrow (BM) and in the fetal liver during development. However, emerging evidence highlights the lung as a previously underappreciated residence for MKs that may significantly contribute to circulating platelet mass. While a diversity of cells specific to the BM are known to promote the maturation and trafficking of MKs, little investigation into the impact of the lung niche on the development and function of MKs has been done. Here, we describe the application of single cell RNA sequencing (scRNA-Seq) coupled with histological, ploidy and flow cytometric analyses to profile primary MKs derived from syngeneic mouse lung and hematopoietic tissues. Transcriptional profiling demonstrated that lung MKs have a unique signature distinct from their hematopoietic counterparts with lung MKs displaying enrichment for maturation markers, potentially indicating a propensity for more efficient platelet production. Reciprocally, fetal lung MKs also showed the robust expression of cytokines and growth factors known to promote lung development. Lastly, lung MKs possess an enrichment profile skewed towards roles in immunity and inflammation. These findings highlight the existence of a lung-specific MK phenotype and support the notion that the lung plays an independent role in the development and functional maturation of MKs.
In addition to MKs, the lung houses many resident hematopoietic cells, including hematopoietic stem and progenitor cells (HSPCs). The existence of lung HSPCs suggests that the differentiation and development of lung resident hematopoietic cells may occur in-situ. To investigate the potential role the lung has in instructing site specific hematopoiesis, we employed explant cultures of murine and human fetal lungs. This displayed adherent endothelial cells transitioning into floating hematopoietic cells, suggesting that the fetal lung is a source of hemogenic endothelial cells that have the functional capacity to undergo endothelial to hematopoietic transition (EHT) to produce HSPCs. Flow cytometric and functional assessment of fetal lung explants showed the production of HSPCs that expressed key EHT and pre-HSPC markers. Expression profiles revealed by scRNA-Seq and small molecule modulation demonstrated that fetal lung EHT is reliant on canonical EHT signaling pathways. These findings suggest that functional HECs are present in the fetal lung, thus establishing this location as a potential extramedullary site of de-novo hematopoiesis. Overall, these findings suggest that the lung may have a greater role in instructing tissue specific hematopoiesis and/or overall hematopoietic development.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/45505 |
| Date | 23 January 2023 |
| Creators | Yeung, Anthony Kok Wai |
| Contributors | Murphy, George J. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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