Modification of the Properties of Extracellular Matrix of Senescent Mesenchymal Stem Cells.

Cell senescence leads to changes in the secretory activity of mesenchymal stem cells (MSC), including proteins of extracellular matrix (ECM). Here we studied the regulatory properties of ECM of senescent MSC in a model with endothelial cells (EC). EC were seeded onto a decellularized extracellular matrix of senescent MSC. Changes in cell morphology and a decrease in cell growth were observed. In addition, increased production of inflammatory chemokines MCP-1 and GROα and reduced synthesis of proangiogenic growth factor FGF-2 were revealed. Analysis of ECM showed quantitative and qualitative changes, including fibronectin layer morphology, total protein content, and concentration of deposited growth factors such as VEGF. Thus, our work demonstrates that senescence of MSC can lead to modification of the effects of their ECM on EC activity.

Short-Term Interaction with Endothelial Cells Enhances Angiogenic Activity of Growth-Arrested Mesenchymal Stromal Cells In Vitro and In Ovo.

We compared angiogenic effects of conditioned medium from mesenchymal stromal cell (MSC) monoculture and co-culture of MSC with endothelial cells (EC). Conditioned medium from 24-h EC-MSC co-cultures significantly stimulated the proliferation and migration of EC in monoculture and growth of the vascular network of the chorioallantoic membrane of the quail embryo in ovo in comparison with the conditioned medium from MSC monoculture. Conditioned medium from the co-culture contained increased levels of angiogenic factors (FGF-2, MCP-1, PDGF-AB/BB, IL-6, IL-8, etc.), which could explain the revealed effects. We hypothesized that a similar mechanism of EC-mediated enhancement of functional activity of MSC could be involved in reparative angiogenesis in the target tissues in vivo.

Osteogenic Commitment of MSC Is Enhanced after Interaction with Umbilical Cord Blood Mononuclear Cells In Vitro.

The effectiveness of stroma-dependent expansion of hematopoietic cells ex vivo may depend on the level of commitment of multipotent mesenchymal stromal cells (MSC). Markers of MSC osteodifferentiation and the level of soluble hematopoiesis regulators were determined during their interaction with umbilical cord blood mononuclears. After 72-h co-culturing, an increase in the expression of ALPL and alkaline phosphatase activity was revealed. In conditioned medium of co-cultures, the levels of osteopontin and osteoprotegerin were elevated and the levels of osteocalcin and sclerostin were reduced. Co-culturing of umbilical cord blood mononuclears with osteocommitted MSC was accompanied by more pronounced increase in the concentration of both positive (GM-CSF and G-CSF) and negative (IP-10, MIP-1α, and MCP-3) regulators of hematopoiesis. Thus, umbilical cord blood mononuclears induced the formation of early osteogenic progenitor phenotype in MSC ex vivo, providing the microenvironmental conditions necessary to support hematopoiesis. Preliminary osteocommitted MSC were more sensitive to the effect of umbilical cord blood mononuclears.

Functional Activity of Non-Proliferating Mesenchymal Stromal Cells Cultured at Different Densities.

We analyzed the state of intracellular compartments and production of cytokines in MSC depending on the culture density. MSC were growth-arrested with mitomycin C and seeded at a density of 300-7000 cell/cm2. MSC in low-density cultures had 2-fold higher levels of transmembrane mitochondrial potential (MitoTracker Red) and endogenous ROS (CMH2DCFDA), lysosomal compartments were less acidified (LysoTracker Green DND26), the production of immunoregulatory and angiogenic mediators VEGF, IL-6, IL-8, MCP-1, TGF-ß was more intensive. It was assumed that culture density can be an effective tool for phenotypic polarization of MSC providing directional changes in their properties.

Сord blood hematopoietic stem cells ex vivo enhance the bipotential commitment of adipose mesenchymal stromal progenitors.

AIMS: Stroma-dependent ex vivo expansion of hematopoietic stem progenitor cells (HSPCs) is a valid approach for cell therapy needs. Our goal was to verify whether HSPCs can affect stromal cells to optimize their functions during ex vivo expansion. MAIN METHODS: HSPCs from cord blood (cb) were cocultured with growth-arrested adipose mesenchymal stromal cells (MSCs). Commitment-related transcriptional and secretory profiles as well as hematopoiesis-supportive activity of intact and osteo-induced MSCs were examined. KEY FINDINGS: During expansion, cbHSPCs affected the functional state of MSCs, contributing to the formation of early stromal progenitors with a bipotential osteo-adipogenic profile. This was evidenced by the upregulation of certain MSC genes of osteo- and adipodifferentiation (ALPL, RUNX2, BGLAP, CEBPA, ADIPOQ), as well as by elevated alkaline phosphatase activity and altered osteoprotein patterns. Joint paracrine profiles upon coculture were characterized by a balance of "positive" (GM-SCF) and "negative" (IP-10, MIP-1α, MCP-3) myeloid regulators, effectively supporting expansion of both committed and primitive cbHSPCs. Short-term (72 h) osteoinduction prior to coculture resulted in more pronounced shift of the bipotential transcriptomic and osteoprotein profiles. The increased proportions of late primitive CD133-/CD34+cbHSPCs and unipotent CFUs suggested that cbHSPCs after expansion on osteo-MSCs were more committed versus cbHSPCs from coculture with non-differentiated MSCs. SIGNIFICANCE: During ex vivo expansion, cbHSPCs can drive the bipotential osteo-adipogenic commitment of MSCs, providing a specific hematopoiesis-supportive milieu. Short-term preliminary osteo-induction enhanced the development of the bipotential profile, leading to more pronounced functional polarization of cbHSPCs, which may be of interest in an applied context.

Differential Expression of Bipotent Commitment-Related Genes in Multipotent Mesenchymal Stromal Cells at Different O2 Levels.

The transcriptomic profile associated with osteo- and adipogenic differentiation in growth-arrested multipotent mesenchymal stromal cells (MSCs) from human adipose tissue was analyzed in vitro at 20% (standard laboratory) and 5% (tissue-related) O2 levels. Compared with day 7, at 5% O2 on day 14 spontaneous upregulation of osteo- (RUNX2, SP7, BGLAP, and SPP1) and adipogenic differentiation (CEBPA, PPARG, and ADIPOQ) genes in MSCs was observed (p < 0.05). Thus, upon expansion under tissue-related O2, MSCs demonstrated a bipotent transcriptomic profile, which may contribute to the improvement of their hematopoiesis-supportive function.

[EFFECTS OF HYPOXIA AND GROWTH FACTORS ON THE ANGIOGENIC ACTIVITY OF MULTIPOTENT MESENCHYMAL STROMAL CELLS].

The effects of fetal calf serum (FCS) growth factor concentration and cell growth phase on production of angiogenic mediators by mesenchymal stromal cells (MSCs) at different O2 levels (20 and 5%) was studied. For this purpose vascular endothelial growth factor (VEGF-A) production was measured in MSC-conditioned medium (CM); besides, branching vessels as well as vessel end points (ramification) in the chorioallantoic membrane of Japanese quail eggs (Coturnix coturnix japonica) were counted following MSC-CM application. During the standard cultivation (20% O2; 10% FCS) the total number of vessels was 1.6 times higher comparing with hypoxic condition (5% O2; 10% FCS) due to increase in ramification, the number of branching vessels did not change. Maximal (double) increase in the total vessel number was observed when CM from MSCs after hypoxia plus serum deprivation was added. VEGF-A synthesis linearly increased with FCS concentration both at 20% and 5% O2. In all cases VEGF-A level was higher at hypoxia. No direct correlation between the VEGF-A concentration and total number of vessels was noted indicating that hypoxia possibly stimulates synthesis of additional angiogenic factors to enhance vascular growth despite the drastic serum deprivation. At 20% oxygen, exponentially growing MSCs showed the highest angiogenic activity and the ramification increased in 1.6 times. Depending on O2, MSCs produced angiogenic factors required at different stages of vascularization. Specifically, mediators of ramification were accumulated in the standard conditions (20% O2) and factors stimulating growth of branching vessels--in hypoxia.