Figure 1.

The angiogenic potential of MSC cultures is controversial. (A) Mesodermal Progenitor Cells (MPCs) are CD90-, Nestin+ progenitors of MSCs. These cells remain in a quiescent state presenting a typical fried egg-shape, condensed chromatin and podosomal structures. When mesengenic differentiation is induced, MPCs differentiate into “early MSCs.” Early MSCs slowly proliferate, express Nestin and CD90 (a MSC marker) and modify their shape because of Actin re-organization in focal adhesion complexes. Under persistent stimulation toward mesengenic differentiation, “early MSC” become “late MSC” showing exponentially growth, fibroblastoid shape and the ability to differentiate into skeletal tissues (fat, bone and cartilage). (B) According to this hierarchical model, MPCs can be considered a putative progenitor of the mesenchymal lineage in vivo, being present in the bone marrow mononuclear fraction. When supplemented with media containing FBS, these cells rapidly differentiate toward the mesengenic lineage and form asynchronous and heterogeneous cultures fulfilling the ISCT MSC criteria of definition. The undetected and unpredictable presence of sub-populations of MPCs, in culture could explain the variable angiogenic potential described for MSC in the literature. Conversely, the isolation of MPC and their subsequent differentiation using optimized protocol can allow the generation of synchronized and homogeneous mesenchymal stromal cells with a reproducible angiogenic potential.