E.R. Andreeva, I.V. Andrianova, P.I. Bobyleva, L.B. Buravkova, E.V. Maslova, Yu.A. Pomanov
The concept of the hematopoietic niche suggests that the existence of hematopoietic stem cells is provided by the close relationship with the microenvironment, which consists of different cell types (stromal, endothelial, macrophages, etc.). In the present study the comparative analysis of hematopoiesis-supporting properties of two human stromal cell types: fetal fibroblasts (fFBs) and multipotent mesenchymal stromal cells (MMSCs), as well as the influence of the oxygen content in the culture medium on the interaction of stromal and hematopoietic cellswas carried out. Stromal cells and cbMNCs were cocultured 14 days at 20 % and 5 % O2. The cbMNCs colony forming capacity was assessed by formation of committed hematopoietic precursors colonies (CFU) in a selective medium MetoCult N4534. Colonies of progenitor cells on stromal layers were detected by staining with crystal violet. After 72 hours in coculture with MMSCs, mononuclear cells from umbilical cord blood (cbMNCs) maintained the same number of colony forming units (CFU) as compare with initial cbMNC suspension, at 5% O2 the number of CFU was 30 % higher than in 20 % O2 (p <0.05). The number CFU in cbMNCs after coculture with fFBs decreased and a stimulatory effect of low oxygen was not observed. CbMNCs, that were adhered to stromal feeders, formed colonies of undifferentiated progenitors after 2 weeks of cocultivation with MMSCs both at 20 % and at 5 % O2. Similar colonies were not found on fFBs.
Thus, this study demonstrated that stromal cells of different origin differed in their ability to maintain the capacity of cbMNCs to form colonies of committed hematopoietic precursors in semisolid selective medium and undifferentiated precursor colonies on the stromal feeders. It is assumed that the implementation of hematopoiesis-inducing activity of stromal cells is determined by a complex regulatory factors, such as the presence of biologically active substances in the culture medium, as well as can be modified by the physical factor of the microenvironment like the partial O2 pressure.