Aryl hydrocarbon receptor-dependent enrichment of a megakaryocytic precursor with a high potential to produce proplatelets

Abstract

The mechanisms regulating megakaryopoiesis and platelet production (thrombopoiesis) are still incompletely understood. Identification of a progenitor with enhanced thrombopoietic capacity would be useful to decipher these mechanisms and to improve our capacity to produce platelets in vitro. Differentiation of peripheral blood CD34+cells in the presence of bone marrow-humanmesenchymal stromal cells (MSCs) enhanced the production of proplatelet-bearing megakaryocytes (MKs) and platelet-like elements. This was accompanied by enrichment in aMKprecursor population exhibiting an intermediate level of CD41 positivity while maintaining its expression of CD34. Following sorting and subculture with MSCs, this CD34+CD41low population was able to efficiently generate proplatelet-bearing MKs and platelet-like particles. Similarly, StemRegenin 1 (SR1), an antagonist of the aryl hydrocarbon receptor (AhR) transcription factor known to maintain CD34 expression of progenitor cells, led to an enriched CD34+CD41low fraction and to an increased capacity to generate proplatelet-producing MKs and platelet-like elements ultrastructurally and functionally similar to circulating platelets. The effect of MSCs, like that of SR1, appeared to be mediated by an AhR-dependent mechanism because both culture conditions resulted in repression of its downstream effector CYP1B1. This newly described isolation of a precursor exhibiting strong MK potential could be exploited to study normal and abnormal thrombopoiesis and for in vitro platelet production.