Three-Dimensional Environment Sustains Hematopoietic Stem Cell Differentiation into Platelet-Producing Megakaryocytes.

Hematopoietic stem cells (HSC) differentiate into megakaryocytes (MK), whose function is to release platelets. Attempts to improve in vitro platelet production have been hampered by the low amplification of MK. Providing HSC with an optimal three-dimensional (3D) architecture may favor MK differentiation by mimicking some crucial functions of the bone marrow structure. To this aim, porous hydrogel scaffolds were used to study MK differentiation from HSC as well as platelet production. Flow cytometry, qPCR and perfusion studies showed that 3D was suitable for longer kinetics of CD34+ cell proliferation and for delayed megakaryocytic differentiation far beyond the limited shelf-life observed in liquid culture but also increased production of functional platelets. We provide evidence that these 3D effects were related to 1) persistence of MK progenitors and precursors and 2) prolongation of expression of EKLF and c-myb transcription factors involved in early MK differentiation. In addition, presence of abundant mature MK with increased ploidy and impressive cytoskeleton elongations was in line with expression of NF-E2 transcription factor involved in late MK differentiation. Platelets produced in flow conditions were functional as shown by integrin αIIbβ3 activation following addition of exogenous agonists. This study demonstrates that spatial organization and biological cues synergize to improve MK differentiation and platelet production. Thus, 3D environment constitutes a powerful tool for unraveling the physiological mechanisms of megakaryopoiesis and thrombopoiesis in the bone marrow environment, potentially leading to an improved amplification of MK and platelet production.