Single-Cell Tracking By Time Lapse Imaging Confirms Thrombopoietin Promotes Megakaryocytic-Erythroid Progenitor Self Renewal, but Does Not Instruct Lineage Commitment

The molecular mechanisms underlying lineage commitment of stem and progenitor cells have implications for deriving specific cell types in vitro for regenerative medicine purposes. Current approaches to derive transfusable amounts of erythrocytes and platelets fall short of producing physiologically relevant amounts of each cell type. Thrombopoietin (TPO), commonly used in culture systems to increase platelet yield from cultured megakaryocytes, increases megakaryocyte (Mk) numbers and promotes platelet production. With the goal of generating adequate quantities of transfusion products in mind, establishing differentiation cultures that start with highly purified progenitors with Mk and E lineage potential as well as expansion potential is a very attractive option. However, a pervasive misconception exists that supplementing MEP cultures with TPO will increase the frequency with which the MEP produce megakaryocyte-committed daughter cells, thereby increasing the pool of lineage-restricted progenitor cells with high expansion capacity that ultimately yield higher numbers of transfusable platelets. We investigated whether TPO plays a role in instructing Megakaryocytic-Erythroid Progenitor (MEP) [1] commitment to the Mk lineage utilizing our previously presented time-lapse imaged colony forming unit assay and cell tracking approach [2]. This allowed us to calculate the frequency with which MEP give rise to lineage restricted progenitors in control conditions (with SCF, IL3, IL6, EPO, and TPO) compared to conditions lacking TPO to test the hypothesis that absence of TPO may diminish the frequency with which MEP give rise to Mk-restricted progenitors.