Role of mesenchymal stromal/stem cells in regulation of hemotoration in 3D in vitro culture

The article is devoted to studying the role of mesenchymal stromal cells in formation of microenvironment for hematopoietic stem cells under the conditions mimicking physiological bone remodeling in presence of artificial three-dimensional matrices (Ra = 2-3 μm). The study was carried out using experimental samples of artificial implants obtained in electrolyte from hydroxyapatite nanoparticles (HAP) produced at the Institute of Strength Physics and Materials Science (Siberian Branch of the Russian Academy of Sciences). The work included cultural and instrumental research techniques. Phenotypic profile of cells was assessed by flow cytometry. Determination of cytokine/chemokine levels from cell culture supernatants was assessed by flow fluorimetry. Detection of hematopoietic cells in the vision fields, as well as areas of extracellular matrix mineralization was carried out by means of cytomorphometry.

It was revealed that the 3D matrices with a calcium phosphate coating initiate the in vitro formation of specific microenvironment of MSCs, resulting in the increased numbers of HSCs with the CD45⁺CD34⁺ phenotype (at 14 days), an increased number of cells with hematopoietic morphology and evolving foci of extracellular matrix mineralization of the (at 21 days). Changed numbers of hematopoietic cells per vision field occurred, mainly, due to indirect effect of hematopoietic factors (SCF and G-CSF), along with decrease of proapoptotic factor TRAIL. It was also found that MSCs reduce the level of proinflammatory cytokines (IFNγ, TNFα, IP-10, IL-2, IL-6) in culture medium in the presence of artificial 3D calcium-phosphate-coated matrices. The revealed features of MSC functioning under the conditions simulating physiological bone remodeling, upon co-cultures with three-dimensional matrices (Ra = 2-3 μm), have shown a significant effect of MSCs upon regulation of HSCs by local microenvironment, through distinct modulating effects of cytokines, chemokines, and growth factors that provide intercellular interactions. Development of extracellular matrix mineralization areas during MSC cultivation in the presence of 3D matrices imitating mineral substance of bone tissue also indicates the formation of osteoblastic niches under the in vitro cultivation conditions.

The results obtained are important in order to assess functions of hematopoietic niches and the role of MSCs in their development and maintenance of the microenvironment.

The results obtained may find practical application in development of new classes of medical devices able to provide effective osseointegration.