Mesenchymal stromal cells as components of the hematopoietic microenvironment

Mesenchymal stromal cells (MSCs) located in the organs of embryonic and definitive hematopoiesis play a key role in organizing the hematopoietic microenvironment. Their regulatory effect on hematopoietic cells is associated mainly with paracrine production of cytokines and chemoattractants and with direct cell-to-cell interactions. In addition, MSCs are precursors of other cellular components of the hematopoietic niche, which also contribute to the maintenance of hematopoiesis. Data from many studies indicate a correlation of the hematopoietic activity of an organ at a particular developmental stage with the content and properties of MSCs. In the organs of embryonic hematopoiesis (such as placenta, liver, spleen), MSCs have signs of functional immaturity, in particular, a high capacity for proliferation with weak differentiation potential. Perhaps, organ and age differences in the properties of MSCs reflect the process of maturation of the hematopoietic niche during ontogenesis. In the prenatal period, the role of MSCs in the organization of the microenvironment may consist mainly in the trophic effect on hematopoietic cells, and in the postnatal period - in differentiation into specialized components of the stroma. Diseases of the blood system, such as aplastic anemia, myelodysplastic syndrome, acute leukemia, in many cases are accompanied by a decrease in the proliferative and osteogenic potential of MSCs and impairment of their ability to produce regulatory molecules. These changes, which worsen the quality of the hematopoietic niche formed by MSCs, may cause hematopoiesis disorders or contribute to their progression. A promising approach to the therapy of these diseases is the restoration of the pathologically altered hematopoietic microenvironment by transplantation of donor MSCs or pharmacological impact on the patient's own MSCs.