Co-culture of hematopoietic stem/progenitor cells with human osteblasts favours mono/macrophage differentiation at the expense of the erythroid lineage

The hematopoietic microenvironment: a network of niches for the development of all blood cell lineages

Blood cell formation (hematopoiesis) takes place mainly in the bone marrow, within the hematopoietic microenvironment, composed of a number of different cell types and their molecular products that together shape spatially organized and highly specialized microstructures called hematopoietic niches. From the earliest developmental stages and throughout the myeloid and lymphoid lineage differentiation pathways, hematopoietic niches play a crucial role in the preservation of cellular integrity and the regulation of proliferation and differentiation rates. Current evidence suggests that each blood cell lineage develops under specific, discrete niches that support committed progenitor and precursor cells and potentially cooperate with transcriptional programs determining the gradual lineage commitment and specification. This review aims to discuss recent advances on the cellular identity and structural organization of lymphoid, granulocytic, monocytic, megakaryocytic, and erythroid niches throughout the hematopoietic microenvironment and the mechanisms by which they interconnect and regulate viability, maintenance, maturation, and function of the developing blood cells.

The Role of Genetically Modified Human Feeder Cells in Maintaining the Integrity of Primary Cultured Human Deciduous Dental Pulp Cells

Tissue-specific stem cells exist in tissues and organs, such as skin and bone marrow. However, their pluripotency is limited compared to embryonic stem cells. Culturing primary cells on plastic tissue culture dishes can result in the loss of multipotency, because of the inability of tissue-specific stem cells to survive in feeder-less dishes. Recent findings suggest that culturing primary cells in medium containing feeder cells, particularly genetically modified feeder cells expressing growth factors, may be beneficial for their survival and proliferation. Therefore, the aim of this study was to elucidate the role of genetically modified human feeder cells expressing growth factors in maintaining the integrity of primary cultured human deciduous dental pulp cells. Feeder cells expressing leukemia inhibitory factor, bone morphogenetic protein 4, and basic fibroblast growth factor were successfully engineered, as evidenced by PCR. Co-culturing with mitomycin-C-treated feeder cells enhanced the proliferation of newly isolated human deciduous dental pulp cells, promoted their differentiation into adipocytes and neurons, and maintained their stemness properties. Our findings suggest that genetically modified human feeder cells may be used to maintain the integrity of primary cultured human deciduous dental pulp cells.

Niche-directed therapy in acute myeloid leukemia: optimization of stem cell competition for niche occupancy

Acute myeloid leukemia (AML) is an aggressive malignancy of stem cell origin that contributes to significant morbidity and mortality. The long-term prognosis remains dismal given the high likelihood for primary refractory or relapsed disease. An essential component of relapse is resurgence from the bone marrow. To date, the murine hematopoietic stem cell (HSC) niche has been clearly defined, but the human HSC niche is less well understood. The design of niche-based targeted therapies for AML must account for which cellular subsets compete for stem cell occupancy within respective bone marrow microenvironments. In this review, we highlight the principles of stem cell niche biology and discuss translational insights into the AML microenvironment as of 2021. Optimization of competition for niche occupancy is important for the elimination of measurable residual disease (MRD). Some of these novel therapeutics are in the pharmacologic pipeline for AML and may be especially useful in the setting of MRD.

An Overview of Different Strategies to Recreate the Physiological Environment in Experimental Erythropoiesis

Human erythropoiesis is a complex process leading to the production of mature, enucleated erythrocytes (RBCs). It occurs mainly at bone marrow (BM), where hematopoietic stem cells (HSCs) are engaged in the early erythroid differentiation to commit into erythroid progenitor cells (burst-forming unit erythroid (BFU-E) and colony-forming unit erythroid (CFU-E)). Then, during the terminal differentiation, several erythropoietin-induced signaling pathways trigger the differentiation of CFU-E on successive stages from pro-erythroblast to reticulocytes. The latter are released into the circulation, finalizing their maturation into functional RBCs. This process is finely regulated by the physiological environment including the erythroblast-macrophage interaction in the erythroblastic island (EBI). Several human diseases have been associated with ineffective erythropoiesis, either by a defective or an excessive production of RBCs, as well as an increase or a hemoglobinization defect. Fully understanding the production of mature red blood cells is crucial for the comprehension of erythroid pathologies as well as to the field of transfusion. Many experimental approaches have been carried out to achieve a complete differentiation in vitro to produce functional biconcave mature RBCs. However, the various protocols usually fail to achieve enough quantities of completely mature RBCs. In this review, we focus on the evolution of erythropoiesis studies over the years, taking special interest in efforts that were made to include the microenvironment and erythroblastic islands paradigm. These more physiological approaches will contribute to a deeper comprehension of erythropoiesis, improve the treatment of dyserythropoietic disorders, and break through the barriers in massive RBCs production for transfusion.

Humanized Culture Medium for Clinical-Grade Generation of Erythroid Cells from Umbilical Cord Blood CD34+ Cells

Purpose: Transfusion of red blood cells (RBCs) is a supportive and common treatment in surgical care, trauma, and anemia. However, in vivo production of RBC seems to be a suitable alternative for blood transfusions due to the limitation of blood resources, the possibility of disease transmission, immune reactions, and the presence of rare blood groups. Cell cultures require serum-free or culture media supplemented with highly expensive animal serum, which can transmit xenoviruses. Platelet lysate (PL) can be considered as a suitable alternative containing a high level of growth factors and a low production cost.

Methods: Three-step culture media supplemented with PL or fetal bovine serum (FBS) were used for proliferation and differentiation of CD34⁺ umbilical cord blood stem cells to erythrocytes in co-culture with bone marrow mesenchymal stem cells (BM-MSCs). The cells were cultivated for 15 days and cell proliferation and expansion were assessed using cell counts at different days. Erythroid differentiation genes, CD71 and glycophorin A expression levels were evaluated.

Results: Maximum hematopoietic stem cells (HSCs) proliferation was observed on day 15 in PL-containing medium (99±17×10³-fold). Gene expression and surface markers showed higher differentiation of cells in PL-containing medium.

Conclusion: The results of this study indicate that PL can enhance erythroid proliferation and differentiation of CD34⁺ HSCs. PL can also be used as a proper alternative for FBS in the culture medium and HSCs differentiation.

Decellularized Wharton jelly matrix: a biomimetic scaffold for ex vivo hematopoietic stem cell culture

Hematopoietic stem progenitor cells (HSPCs) reside in the bone marrow (BM) hematopoietic "niche," a special 3-dimensional (3D) microenvironment that regulates HSPC self-renewal and multipotency. In this study, we evaluated a novel 3D in vitro culture system that uses components of the BM hematopoietic niche to expand umbilical cord blood (UCB) CD34+ cells. We developed this model using decellularized Wharton jelly matrix (DWJM) as an extracellular matrix (ECM) scaffold and human BM mesenchymal stromal cells (MSCs) as supporting niche cells. To assess the efficacy of this model in expanding CD34+ cells, we analyzed UCB CD34+ cells, following culture in DWJM, for proliferation, viability, self-renewal, multilineage differentiation, and transmigration capability. We found that DWJM significantly expanded UCB HSPC subset. It promoted UCB CD34+ cell quiescence, while maintaining their viability, differentiation potential with megakaryocytic differentiation bias, and clonogenic capacity. DWJM induced an increase in the frequency of c-kit+ cells, a population with enhanced self-renewal ability, and in CXCR4 expression in CD34+ cells, which enhanced their transmigration capability. The presence of BM MSCs in DWJM, however, impaired UCB CD34+ cell transmigration and suppressed CXCR4 expression. Transcriptome analysis indicated that DWJM upregulates a set of genes that are specifically involved in megakaryocytic differentiation, cell mobility, and BM homing. Collectively, our results indicate that the DWJM-based 3D culture system is a novel in vitro model that supports the proliferation of UCB CD34+ cells with enhanced transmigration potential, while maintaining their differentiation potential. Our findings shed light on the interplay between DWJM and BM MSCs in supporting the ex vivo culture of human UCB CD34+ cells for use in clinical transplantation.

Paracrine Factors Released by Osteoblasts Provide Strong Platelet Engraftment Properties

Ex vivo expansion of hematopoietic stem cell (HSCs) and progenitors may one day overcome the slow platelet engraftment kinetics associated with umbilical cord blood transplantation. Serum-free medium conditioned with osteoblasts (i.e., osteoblast-conditioned medium [OCM]) derived from mesenchymal stromal cells (MSC) was previously shown to increase cell growth and raise the levels of human platelets in mice transplanted with OCM-expanded progenitors. Herein, we characterized the cellular and molecular mechanisms responsible for these osteoblast-derived properties. Limiting dilution transplantation assays revealed that osteoblasts secrete soluble factors that synergize with exogenously added cytokines to promote the production of progenitors with short-term platelet engraftment activities, and to a lesser extent with long-term platelet engraftment activities. OCM also modulated the expression repertoire of cell-surface receptors implicated in the trafficking of HSC and progenitors to the bone marrow. Furthermore, OCM contains growth factors with prosurvival and proliferation activities that synergized with stem cell factor. Insulin-like growth factor (IGF)-2 was found to be present at higher levels in OCM than in control medium conditioned with MSC. Inhibition of the IGF-1 receptor, which conveys IGF-2' intracellular signaling, largely abolished the growth-promoting activity of OCM on immature CD34⁺ subsets and progenitors in OCM cultures. Finally, IGF-1R effects appear to be mediated in part by the coactivator β-catenin. In summary, these results provide new insights into the paracrine regulatory activities of osteoblasts on HSC, and how these can be used to modulate the engraftment properties of human HSC and progenitors expanded in culture. Stem Cells 2019;37:345-356.

Calcium-Infiltrated Biphasic Hydroxyapatite Scaffolds for Human Hematopoietic Stem Cell Culture

Long-term in vitro expansion of hematopoietic stem cells (HSCs), while maintaining their functionality and multilineage differentiation potential, is still challenging. In this study, three-dimensional (3D) high-porosity hydroxyapatite (HA) foams have been designed to closely mimic the chemistry and physical structure of cancellous bone. Furthermore, calcium oxide was distributed in the HA ceramics to provide surface calcium ion release, hypothesizing that a local surface calcium gradient supports HSC localization and maintenance. Primary human HSCs and osteoblasts were cocultured for 6 weeks. Controls were cultured in two-dimensional dishes, while scaffold cultures were performed with calcium nitrate-infiltrated HA scaffolds and untreated HA scaffolds. Cells were analyzed for surface markers by flow cytometry, metabolic activity, and hematopoietic multilineage differentiation potential. The release of calcium into culture medium was also determined. The implementation of HA scaffolds had a positive effect on erythrocyte colony formation capacity of HSCs, with an increased osteoblast fraction observed when compared to control cultures without scaffolds. The presentation of scaffolds did not affect metabolic turnover when compared to control cultures. In conclusion, 3D open-porous HA scaffolds provide a bone-like structure and enable the long-term maintenance of primary HSCs.

Human Bone Marrow Mesenchymal Stromal Cell-Derived Osteoblasts Promote the Expansion of Hematopoietic Progenitors Through Beta-Catenin and Notch Signaling Pathways

Coculture of hematopoietic stem cells (HSC) with primary stromal cells from HSC niches supports the maintenance and expansion of HSC and progenitors ex vivo. However, a major drawback is the availability of primary human samples for research and clinical applications. We investigated the use of in vitro derived osteoblasts as a new source of feeder cells and characterized the molecular pathways that mediate their growth-promoting activities. First, we compared the growth and differentiation modulating activities of mesenchymal stromal cells (MSC)-derived osteoblasts (M-OST) with those of their undifferentiated precursor on umbilical cord blood (UCB) progenitors. Feeder-free cultures were also included as baseline control. Cell growth and expansion of hematopoietic progenitors were significantly enhanced by both feeder cell types. However, progenitor cell growth was considerably greater with M-OST. Coculture also promoted the maintenance of immature CD34⁺ progenitor subsets and modulated in a positive fashion the expression of several homing-related cell surface receptors, in a feeder-specific fashion. Serial transplantation experiments revealed that M-OST coculture supported the maintenance of long-term lympho-myeloid reconstituting HSC that provided engraftment levels that were generally superior to those from MSC cocultures. Mechanistically, we found that coculture with M-OST was associated with enhanced beta-catenin (β-Cat) activity in UCB cells and that abrogation of β-Cat/T-cell factor activity blunted the growth-promoting activity of the M-OST coculture. Conversely, Notch inhibition reduced UCB cell expansion, but to a much lesser extent. In conclusion, this study demonstrates that M-OST are excellent feeder cells for HSC and progenitors, and it identifies key molecular pathways that are responsible for the growth-enhancing activities of osteoblasts on UCB progenitors.

miR-494-3p overexpression promotes megakaryocytopoiesis in primary myelofibrosis hematopoietic stem/progenitor cells by targeting SOCS6

Primary myelofibrosis (PMF) is a chronic Philadelphia-negative myeloproliferative neoplasm characterized by hematopoietic stem cell-derived clonal myeloproliferation, involving especially the megakaryocyte lineage. To better characterize how the altered expression of microRNAs might contribute to PMF pathogenesis, we have previously performed the integrative analysis of gene and microRNA expression profiles of PMF hematopoietic stem/progenitor cells (HSPCs), which allowed us to identify miR-494-3p as the upregulated microRNA predicted to target the highest number of downregulated mRNAs.To elucidate the role of miR-494-3p in hematopoietic differentiation, in the present study we demonstrated that miR-494-3p enforced expression in normal HSPCs promotes megakaryocytopoiesis. Gene expression profiling upon miR-494-3p overexpression allowed the identification of genes commonly downregulated both after microRNA overexpression and in PMF CD34+ cells. Among them, suppressor of cytokine signaling 6 (SOCS6) was confirmed to be a miR-494-3p target by luciferase assay. Western blot analysis showed reduced level of SOCS6 protein as well as STAT3 activation in miR-494-3p overexpressing cells. Furthermore, transient inhibition of SOCS6 expression in HSPCs demonstrated that SOCS6 silencing stimulates megakaryocytopoiesis, mimicking the phenotypic effects observed upon miR-494-3p overexpression. Finally, to disclose the contribution of miR-494-3p upregulation to PMF pathogenesis, we performed inhibition experiments in PMF HSPCs, which showed that miR-494-3p silencing led to SOCS6 upregulation and impaired megakaryocyte differentiation.Taken together, our results describe for the first time the role of miR-494-3p during normal HSPC differentiation and suggest that its increased expression, and the subsequent downregulation of its target SOCS6, might contribute to the megakaryocyte hyperplasia commonly observed in PMF patients.

Impact of osteoblast maturation on their paracrine growth enhancing activity on cord blood progenitors

BACKGROUND

Osteoblasts possess strong growth modulatory activity on haematopoietic stem cells and progenitors. We sought to characterise the growth and differentiation modulatory activities of human osteoblasts at distinct stages of maturation on cord blood (CB) progenitors in the context of osteoblast conditioned medium (OCM).

METHODS

OCM was produced from MSC-derived osteoblasts (M-OST) at distinct stages of maturation. The growth modulatory activities of the OCM were tested on CB CD34⁺ cells using different functional assays.

RESULTS

OCMs raised the growth of CB cells and expansion of CD34⁺ cells independently of the maturation status of M-OST. However, productions of immature CB cells including committed and multipotent progenitors were superior with OCM produced with immature osteoblasts. Osteogenic differentiation was accompanied by the upregulation of IGFBP-2, by several members of the Angpt-L family of growth factor, and by the Notch ligands Dll-1 and Dll-4. However, the growth activity of OCM and the in vivo engraftment properties of OCM-expanded CB cells were retained after IGFBP-2 neutralisation. Similarly, OCM-mediated expansion of CB myeloid progenitors was largely independent of Notch signalling.

CONCLUSIONS

These results demonstrate that immature osteoblasts possess greater regulatory activity over haematopoietic progenitors, and that this activity is not entirely dependent on Notch signalling.

Integrative analysis of copy number and gene expression data suggests novel pathogenetic mechanisms in primary myelofibrosis

Primary myelofibrosis (PMF) is a Myeloproliferative Neoplasm (MPN) characterized by megakaryocyte hyperplasia, progressive bone marrow fibrosis, extramedullary hematopoiesis and transformation to Acute Myeloid Leukemia (AML). A number of phenotypic driver (JAK2, CALR, MPL) and additional subclonal mutations have been described in PMF, pointing to a complex genomic landscape. To discover novel genomic lesions that can contribute to disease phenotype and/or development, gene expression and copy number signals were integrated and several genomic abnormalities leading to a concordant alteration in gene expression levels were identified. In particular, copy number gain in the polyamine oxidase (PAOX) gene locus was accompanied by a coordinated transcriptional up-regulation in PMF patients. PAOX inhibition resulted in rapid cell death of PMF progenitor cells, while sparing normal cells, suggesting that PAOX inhibition could represent a therapeutic strategy to selectively target PMF cells without affecting normal hematopoietic cells' survival. Moreover, copy number loss in the chromatin modifier HMGXB4 gene correlates with a concomitant transcriptional down-regulation in PMF patients. Interestingly, silencing of HMGXB4 induces megakaryocyte differentiation, while inhibiting erythroid development, in human hematopoietic stem/progenitor cells. These results highlight a previously un-reported, yet potentially interesting role of HMGXB4 in the hematopoietic system and suggest that genomic and transcriptional imbalances of HMGXB4 could contribute to the aberrant expansion of the megakaryocytic lineage that characterizes PMF patients.

Differential ability of MSCs isolated from placenta and cord as feeders for supporting ex vivo expansion of umbilical cord blood derived CD34(+) cells

INTRODUCTION

Ex vivo expansion of umbilical cord blood (UCB) is attempted to increase cell numbers to overcome the limitation of cell dose. Presently, suspension cultures or feeder mediated co-cultures are performed for expansion of hematopoietic stem cells (HSCs). Mesenchymal stem cells (MSCs) have proved to be efficient feeders for the maintenance of HSCs. Here, we have established MSCs-HSCs co-culture system with MSCs isolated from less invasive and ethically acceptable sources like umbilical cord tissue (C-MSCs) and placenta (P-MSCs). MSCs derived from these tissues are often compared with bone marrow derived MSCs (BM-MSCs) which are considered as a gold standard. However, so far none of the studies have directly compared C-MSCs with P-MSCs as feeders for ex vivo expansion of HSCs. Thus, we for the first time performed a systematic comparison of hematopoietic supportive capability of C and P-MSCs using paired samples.

METHODS

UCB-derived CD34(+) cells were isolated and co-cultured on irradiated C and P-MSCs for 10 days. C-MSCs and P-MSCs were isolated from the same donor. The cultures comprised of serum-free medium supplemented with 25 ng/ml each of SCF, TPO, Flt-3 L and IL-6. After 10 days cells were collected and analyzed for phenotype and functionality.

RESULTS

C-MSCs and P-MSCs were found to be morphologically and phenotypically similar but exhibited differential ability to support ex vivo hematopoiesis. Cells expanded on P-MSCs showed higher percentage of primitive cells (CD34(+)CD38(-)), CFU (Colony forming unit) content and LTC-IC (Long term culture initiating cells) ability. CD34(+) cells expanded on P-MSCs also exhibited better in vitro adhesion to fibronectin and migration towards SDF-1α and enhanced NOD/SCID repopulation ability, as compared to those grown on C-MSCs. P-MSCs were found to be closer to BM-MSCs in their ability to expand HSCs. P-MSCs supported expansion of functionally superior HSCs by virtue of reduction in apoptosis of primitive HSCs, higher Wnt and Notch activity, HGF secretion and cell-cell contact. On the other hand, C-MSCs facilitated expansion of progenitors (CD34(+)CD38(+)) and differentiated (CD34(-)CD38(+)) cells by secretion of IL1-α, β, MCP-2, 3 and MIP-3α.

CONCLUSIONS

P-MSCs were found to be better feeders for ex vivo maintenance of primitive HSCs with higher engraftment potential than the cells expanded with C-MSCs as feeders.

Foundational concepts of cell fate conversion to the hematopoietic lineage

Direct conversion of cellular fate provides a potential approach to generate cells of the hematopoietic lineage without the requisite reversion to a pluripotent state via somatic cell reprogramming. The utilization of this technology has enabled transcription factor-mediated conversion of somatic cell types to primitive and mature hematopoietic cells. Recent studies demonstrate that the direct conversion of somatic cells to the hematopoietic lineage likely requires the use of pioneer transcription factors to establish an accessible chromatin state that is responsive to enforced expression of hematopoietic-specific transcription factors, in combination with appropriate culture conditions that facilitate reprogramming. Developing adaptable, experimental strategies that incorporate these parameters should enable the efficient generation of human hematopoietic cells with translational potential.