Unrestricted somatic stem cells: interaction with CD34+ cells in vitro and in vivo, expression of homing genes and exclusion of tumorigenic potential

Expression analysis of genes involved in the expansion of hematopoietic stem cells (SCF, Flt3-L, TPO, IL-3, and IL-6) in unrestricted somatic stem cells cultured on fibrin

Umbilical cord blood (UCB) transplantation is a promising therapeutic approach for patients lacking HLA-matched donors. A main limitation to the use of UCB-derived HSCs (UCB-HSCs) is the low number of transplantable cells. Novel culture strategies are being developed to increase the number of HSCs. Unrestricted somatic stem cells (USSCs) have been identified as promising stromal cells for supporting HSC expansion. The current study aimed to explore the effect of fibrin on the expression of hematopoiesis-related genes (SCF, Flt3-L, TPO, IL-3, and IL-6) in USSCs. USSCs were isolated from UCB and characterized by flow cytometry and in vitro multilineage differentiation ability. DAPI staining and the MTT assay were used to assess the effect of fibrin on USSC viability. The cell attachment was evaluated using SEM. qRT-PCR was performed to evaluate the expression of SCF, Flt3-L, TPO, IL-3, and IL-6 in USSCs cultured on 3D fibrin scaffolds. USSCs were positive for CD73, CD105, and CD166 and negative for CD45. Alizarin red and Oil red O stains confirmed calcium deposition and lipid vacuoles in USSCs. Results obtained from DAPI and MTT assays revealed a positive effect of fibrin on USSC viability. Cells cultured on fibrin express significantly higher levels of SCF and TPO compared to those grown in a 2D environment. The positive effect of fibrin on IL-6 levels was reversed. Fibrin did not affect Flt3-L expression and IL-3 mRNA expression was not detected in either group. The results of this study provide the basis for developing further research on the ex vivo expansion of HSCs with USSCs.

The Incorporation of Extracellular Vesicles from Mesenchymal Stromal Cells Into CD34+ Cells Increases Their Clonogenic Capacity and Bone Marrow Lodging Ability

Mesenchymal stromal cells (MSC) may exert their functions by the release of extracellular vesicles (EV). Our aim was to analyze changes induced in CD34⁺ cells after the incorporation of MSC‐EV. MSC‐EV were characterized by flow cytometry (FC), Western blot, electron microscopy, and nanoparticle tracking analysis. EV incorporation into CD34⁺ cells was confirmed by FC and confocal microscopy, and then reverse transcription polymerase chain reaction and arrays were performed in modified CD34⁺ cells. Apoptosis and cell cycle were also evaluated by FC, phosphorylation of signal activator of transcription 5 (STAT5) by WES Simple, and clonal growth by clonogenic assays. Human engraftment was analyzed 4 weeks after CD34⁺ cell transplantation in nonobese diabetic/severe combined immunodeficient mice. Our results showed that MSC‐EV incorporation induced a downregulation of proapoptotic genes, an overexpression of genes involved in colony formation, and an activation of the Janus kinase (JAK)‐STAT pathway in CD34⁺ cells. A significant decrease in apoptosis and an increased CD44 expression were confirmed by FC, and increased levels of phospho‐STAT5 were confirmed by WES Simple in CD34⁺ cells with MSC‐EV. In addition, these cells displayed a higher colony‐forming unit granulocyte/macrophage clonogenic potential. Finally, the in vivo bone marrow lodging ability of human CD34⁺ cells with MSC‐EV was significantly increased in the injected femurs. In summary, the incorporation of MSC‐EV induces genomic and functional changes in CD34⁺ cells, increasing their clonogenic capacity and their bone marrow lodging ability. stem cells2019;37:1357–1368

Rescue of the mucocutaneous manifestations by human cord blood derived nonhematopoietic stem cells in a mouse model of recessive dystrophic epidermolysis bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin blistering disease caused by mutations in COL7A1-encoding type VII collagen (C7). Currently, there is no curative therapy for patients with RDEB. Our previous studies demonstrated that human umbilical cord blood (HUCB) derived unrestricted somatic stem cells (USSCs) express C7 and facilitate wound healing in a murine wounding model. The primary objective of this study is to investigate the therapeutic functions of USSCs in the C7 null (Col7a1(-/-) ) C57BL6/J mice, a murine model of RDEB. We demonstrated that intrahepatic administration of USSCs significantly improved the blistering phenotype and enhanced the life span in the recipients. The injected USSCs trafficked to the sites of blistering and were incorporated in short-term in the recipients' skin and gastrointestinal tract. Consistent with an overall histological improvement in the epidermal-dermal adherence following USSC treatment, the expression of C7 at the basement membrane zone was detected and the previously disorganized integrin α6 distribution was normalized. We also demonstrated that USSCs treatment induced an infiltration of macrophages with a regenerative "M2" phenotype. Our data suggest that HUCB-derived USSCs improved the RDEB phenotype through multiple mechanisms. This study has warranted future clinical investigation of USSCs as a novel and universal allogeneic stem cell donor source in selected patients with RDEB.

Crif1 Promotes Adipogenic Differentiation of Bone Marrow Mesenchymal Stem Cells After Irradiation by Modulating the PKA/CREB Signaling Pathway

Dysfunction of the hematopoietic microenvironment is the main obstacle encountered during hematopoiesis reconstruction in patients with acute hematopoietic radiation syndrome. Bone marrow mesenchymal stem cells (BM-MSCs) play a crucial supporting role in hematopoiesis by maintaining the balance between adipogenic and osteogenic differentiation. In this study, we found that irradiation decreased the colony-forming efficiency of BM-MSCs and impaired the balance between adipogenic and osteogenic differentiation. Following irradiation, BM-MCSs became strongly predisposed to adipogenesis, as evidenced by increased oil red O staining and elevated mRNA and protein levels of the adipogenic markers and transcription factors PPARγ and AP2. Overexpression of the essential adipogenesis regulator Crif1 in BM-MSCs promoted adipogenesis after irradiation exposure by upregulating adipogenesis-related genes, including C/EBPβ, PPARγ, and AP2. We found that Crif1 promoted the phosphorylation of cAMP response element binding protein (CREB) through direct interaction with protein kinase A (PKA)-α. Phosphorylation of CREB was inhibited in Crif1-knockdown BM-MSCs even in the presence of a PKA agonist (db-cAMP) and could be suppressed in Crif1-overexpressing BM-MSCs by a PKAα inhibitor (H-89). These results suggest that Crif1 is an indispensable regulator of PKAα cat that modulates the PKA/CREB signaling pathway to promote adipogenic differentiation of BM-MSCs after irradiation.

Increased Haematopoietic Supportive Function of USSC from Umbilical Cord Blood Compared to CB MSC and Possible Role of DLK-1

Multipotent stromal cells can be isolated from a variety of different tissues in the body. In contrast to stromal cells from the adult bone marrow (BM) or adipose tissue, cord blood (CB) multipotent stromal cells (MSC) are biologically younger. Since first being described by our group, delta like 1 homologue (DLK-1) was determined as a discriminating factor between the distinct cord blood-derived subpopulations: the unrestricted somatic stromal cells (USSC), which lack adipogenic differentiation capacity, and the BM MSC-like CB MSC. In this study, experiments assessing the haematopoiesis-supporting capacity and molecular biological analyses were conducted and clearly confirmed different properties. Compared to CB MSC, USSC lead to a higher expansion of haematopoietic cells and in addition express significantly higher levels of insulin-like growth factor binding protein 1 (IGFBP1), but lower levels of IGF2. The data presented here also indicate that DLK-1 might not be the sole factor responsible for the inhibition of adipogenic differentiation potential in USSC but nevertheless indicates a biological diversity among cord blood-derived stromal cells.

Potential application of cord blood-derived stromal cells in cellular therapy and regenerative medicine

Neonatal stromal cells from umbilical cord blood (CB) are promising alternatives to bone marrow- (BM-) derived multipotent stromal cells (MSCs). In comparison to BM-MSC, the less mature CB-derived stromal cells have been described as a cell population with higher differentiation and proliferation potential that might be of potential interest for clinical application in regenerative medicine. Recently, it has become clear that cord blood contains different stromal cell populations, and as of today, a clear distinction between unrestricted somatic stromal cells (USSCs) and CB-MSC has been established. This classification is based on the expression of DLK-1, HOX, and CD146, as well as functional examination of the adipogenic differentiation potential and the capacity to support haematopoiesis in vitro and in vivo. However, a marker enabling a prospective isolation of the rare cell populations directly out of cord blood is yet to be found. Further analysis may help to reveal even more subpopulations with different properties, which could be useful for the directed application of these cells in preclinical models.

Mechanical characterization of adult stem cells from bone marrow and perivascular niches

Therapies using adult stem cells often require mechanical manipulation such as injection or incorporation into scaffolds. However, force-induced rupture and mechanosensitivity of cells during manipulation is largely ignored. Here, we image cell mechanical structures and perform a biophysical characterization of three different types of human adult stem cells: bone marrow CD34+ hematopoietic, bone marrow mesenchymal and perivascular mesenchymal stem cells. We use micropipette aspiration to characterize cell mechanics and quantify deformation of subcellular structures under force and its contribution to global cell deformation. Our results suggest that CD34+ cells are mechanically suitable for injection systems since cells transition from solid- to fluid-like at constant aspiration pressure, probably due to a poorly developed actin cytoskeleton. Conversely, mesenchymal stem cells from the bone marrow and perivascular niches are more suitable for seeding into biomaterial scaffolds since they are mechanically robust and have developed cytoskeletal structures that may allow cellular stable attachment and motility through solid porous environments. Among these, perivascular stem cells cultured in 6% oxygen show a developed cytoskeleton but a more compliant nucleus, which can facilitate the penetration into pores of tissues or scaffolds. We confirm the relevance of our measurements using cell motility and migration assays and measure survival of injected cells. Since different types of adult stem cells can be used for similar applications, we suggest considering mechanical properties of stem cells to match optimal mechanical characteristics of therapies.

Paracrine molecules of mesenchymal stem cells for hematopoietic stem cell niche

Hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs) are both adult stem cells residing in the bone marrow. MSCs interact with HSCs, they stimulate and enhance the proliferation of HSCs by secreting regulatory molecules and cytokines, providing a specialized microenvironment for controlling the process of hematopoiesis. In this paper we discuss how MSCs contribute to HSC niche, maintain the stemness and proliferation of HSCs, and support HSC transplantation.