Human mesenchymal stromal cells regulate initial self-renewing divisions of hematopoietic progenitor cells by a beta1-integrin-dependent mechanism

Extracellular matrix-induced signaling pathways in mesenchymal stem/stromal cells

The extracellular matrix (ECM) is a crucial component of the stem cell microenvironment, or stem-cell niches, and contributes to the regulation of cell behavior and fate. Accumulating evidence indicates that different types of stem cells possess a large variety of molecules responsible for interactions with the ECM, mediating specific epigenetic rearrangements and corresponding changes in transcriptome profile. Signals from the ECM are crucial at all stages of ontogenesis, including embryonic and postnatal development, as well as tissue renewal and repair. The ECM could regulate stem cell transition from a quiescent state to readiness to perceive the signals of differentiation induction (competence) and the transition between different stages of differentiation (commitment). Currently, to unveil the complex networks of cellular signaling from the ECM, multiple approaches including screening methods, the analysis of the cell matrixome, and the creation of predictive networks of protein-protein interactions based on experimental data are used. In this review, we consider the existing evidence regarded the contribution of ECM-induced intracellular signaling pathways into the regulation of stem cell differentiation focusing on mesenchymal stem/stromal cells (MSCs) as well-studied type of postnatal stem cells totally depended on signals from ECM. Furthermore, we propose a system biology-based approach for the prediction of ECM-mediated signal transduction pathways in target cells. Video Abstract.

Expanding hematopoietic stem cell ex vivo: recent advances and technical considerations

Hematopoietic stem cells (HSCs) are the most primitive cell type in the hematopoietic hierarchy, which are responsible for sustaining the lifelong production of mature blood and immune cells. Due to their superior long-term regenerative capacity, HSC therapies such as stem cell transplantation have been used in a broad range of hematologic disorders. However, the rarity of this population in vivo considerably limits its clinical applications and large-scale analyses such as screening and safety studies. Therefore, ex vivo culture methods that allow long-term expansion and maintenance of functional HSCs are instrumental in overcoming the difficulties in studying HSC biology and improving HSC therapies. In this perspective, we discuss recent advances and technical considerations for three ex vivo HSC expansion methods including 1) polyvinyl alcohol-based HSC expansion, 2) mesenchymal stromal cell-HSC co-culture, and 3) two-/three-dimensional hydrogel HSC culture. This review summarizes the presentations and discussions from the 2022 International Society for Experimental Hematology (ISEH) Annual Meeting New Investigator Technology Session.

Alterations of bovine nucleus pulposus cells with aging

Aging is one of the major etiological factors driving intervertebral disc (IVD) degeneration, the main cause of low back pain. The nucleus pulposus (NP) includes a heterogeneous cell population, which is still poorly characterized. Here, we aimed to uncover main alterations in NP cells with aging. For that, bovine coccygeal discs from young (12 months) and old (10-16 years old) animals were dissected and primary NP cells were isolated. Gene expression and proteomics of fresh NP cells were performed. NP cells were labelled with propidium iodide and analysed by flow cytometry for the expression of CD29, CD44, CD45, CD146, GD2, Tie2, CD34 and Stro-1. Morphological cell features were also dissected by imaging flow cytometry. Elder NP cells (up-regulated bIL-6 and bMMP1 gene expression) presented lower percentages of CD29+, CD44+, CD45+ and Tie2+ cells compared with young NP cells (upregulated bIL-8, bCOL2A1 and bACAN gene expression), while GD2, CD146, Stro-1 and CD34 expression were maintained with age. NP cellulome showed an upregulation of proteins related to endoplasmic reticulum (ER) and melanosome independently of age, whereas proteins upregulated in elder NP cells were also associated with glycosylation and disulfide bonds. Flow cytometry analysis of NP cells disclosed the existence of 4 subpopulations with distinct auto-fluorescence and size with different dynamics along aging. Regarding cell morphology, aging increases NP cell area, diameter and vesicles. These results contribute to a better understanding of NP cells aging and highlighting potential anti-aging targets that can help to mitigate age-related disc disease.

Glucose Metabolism and Aging of Hematopoietic Stem and Progenitor Cells

Comprehensive proteomics studies of human hematopoietic stem and progenitor cells (HSPC) have revealed that aging of the HSPC compartment is characterized by elevated glycolysis. This is in addition to deregulations found in murine transcriptomics studies, such as an increased differentiation bias towards the myeloid lineage, alterations in DNA repair, and a decrease in lymphoid development. The increase in glycolytic enzyme activity is caused by the expansion of a more glycolytic HSPC subset. We therefore developed a method to isolate HSPC into three distinct categories according to their glucose uptake (GU) levels, namely the GU^high, GU^inter and GU^low subsets. Single-cell transcriptomics studies showed that the GU^high subset is highly enriched for HSPC with a differentiation bias towards myeloid lineages. Gene set enrichment analysis (GSEA) demonstrated that the gene sets for cell cycle arrest, senescence-associated secretory phenotype, and the anti-apoptosis and P53 pathways are significantly upregulated in the GU^high population. With this series of studies, we have produced a comprehensive proteomics and single-cell transcriptomics atlas of molecular changes in human HSPC upon aging. Although many of the molecular deregulations are similar to those found in mice, there are significant differences. The most unique finding is the association of elevated central carbon metabolism with senescence. Due to the lack of specific markers, the isolation and collection of senescent cells have yet to be developed, especially for human HSPC. The GU^high subset from the human HSPC compartment possesses all the transcriptome characteristics of senescence. This property may be exploited to accurately enrich, visualize, and trace senescence development in human bone marrow.

Rebuilding the hematopoietic stem cell niche: Recent developments and future prospects

Hematopoietic stem cells (HSCs) have proven their clinical relevance in stem cell transplantation to cure patients with hematological disorders. Key to their regenerative potential is their natural microenvironment - their niche - in the bone marrow (BM). Developments in the field of biomaterials enable the recreation of such environments with increasing preciseness in the laboratory. Such artificial niches help to gain a fundamental understanding of the biophysical and biochemical processes underlying the interaction of HSCs with the materials in their environment and the disturbance of this interplay during diseases affecting the BM. Artificial niches also have the potential to multiply HSCs in vitro, to enable the targeted differentiation of HSCs into mature blood cells or to serve as drug-testing platforms. In this review, we will introduce the importance of artificial niches followed by the biology and biophysics of the natural archetype. We will outline how 2D biomaterials can be used to dissect the complexity of the natural niche into individual parameters for fundamental research and how 3D systems evolved from them. We will present commonly used biomaterials for HSC research and their applications. Finally, we will highlight two areas in the field of HSC research, which just started to unlock the possibilities provided by novel biomaterials, in vitro blood production and studying the pathophysiology of the niche in vitro. With these contents, the review aims to give a broad overview of the different biomaterials applied for HSC research and to discuss their potentials, challenges and future directions in the field. STATEMENT OF SIGNIFICANCE: Hematopoietic stem cells (HSCs) are multipotent cells responsible for maintaining the turnover of all blood cells. They are routinely applied to treat patients with hematological diseases. This high clinical relevance explains the necessity of multiplication or differentiation of HSCs in the laboratory, which is hampered by the missing natural microenvironment - the so called niche. Biomaterials offer the possibility to mimic the niche and thus overcome this hurdle. The review introduces the HSC niche in the bone marrow and discusses the utility of biomaterials in creating artificial niches. It outlines how 2D systems evolved into sophisticated 3D platforms, which opened the gateway to applications such as, expansion of clinically relevant HSCs, in vitro blood production, studying niche pathologies and drug testing.

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.

Effects of protein malnutrition on hematopoietic regulatory activity of bone marrow mesenchymal stem cells

Protein malnutrition causes anemia and leukopenia as it reduces hematopoietic precursors and impairs the production of mediators that regulate hematopoiesis. Hematopoiesis occurs in distinct bone marrow niches that modulate the processes of differentiation, proliferation and self-renewal of hematopoietic stem cells (HSCs). Mesenchymal stem cells (MSCs) contribute to the biochemical composition of bone marrow niches by the secretion of several growth factors and cytokines, and they play an important role in the regulation of HSCs and hematopoietic progenitors. In this study, we investigated the effect of protein malnutrition on the hematopoietic regulatory function of MSCs. C57BL/6NTaq mice were divided into control and protein malnutrition groups, which received, respectively, a normal protein diet (12% casein) and a low protein diet (2% casein). The results showed that protein malnutrition altered the synthesis of SCF, TFG-β, Angpt-1, CXCL-12, and G-CSF by MSCs. Additionally, MSCs from the protein malnutrition group were not able to maintain the lymphoid, granulocytic and megakaryocytic-erythroid differentiation capacity compared to the MSCs of the control group. In this way, the comprehension of the role of MSCs on the regulation of the hematopoietic cells, in protein malnutrition states, is for the first time showed. Therefore, we infer that hematopoietic alterations caused by protein malnutrition are due to multifactorial alterations and, at least in part, the MSCs' contribution to hematological impairment.

Molecular Insights into the Potential of Extracellular Vesicles Released from Mesenchymal Stem Cells and Other Cells in the Therapy of Hematologic Malignancies

Hematologic cancer encompasses the heterogeneous group of neoplasms that affect different stages of blood cell linages. Despite the significant improvements made in the new modalities of anticancer therapy, many forms of blood cancer remain untreatable, putting the afflicted patients at high risk of death. Therefore, there has been an urgent need for novel therapy to improve the clinical outcomes of patients with blood cancer. Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have been reported to possess an anticancer activity. This review discusses (i) the therapeutic potential of MSC-EVs against blood cancer, (ii) the possibility of using EVs from sources other than MSCs as a mean for blood cancer vaccination and drug delivery, and (iii) areas to be optimized for MSC-EV-based clinical application on blood malignancies.

Hypermethylation-mediated downregulation of long non-coding RNA MEG3 inhibits osteogenic differentiation of bone marrow mesenchymal stem cells and promotes pediatric aplastic anemia

BACKGROUND

The reduced osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) is the typical characteristics of pediatric aplastic anemia (AA) pathogenesis. Long non-coding RNA MEG3 is reported to promote osteogenic differentiation of BMSCs via inducing BMP4 expression.

OBJECTIVE

This study aims to investigate the mechanism of DNMT1/MEG3/BMP4 pathway in osteogenic differentiation of BMSCs in pediatric AA.

METHODS

BMSCs were isolated and purified from bone marrows of pediatric AA patients (n = 5) and non-AA patients (n = 5). The expression of DNMT1, MEG3, and BMP4 in isolated BMSCs was detected using quantitative real-time PCR and western blot analysis. Osteogenic differentiation was determined using Alizarin red staining. The methylation of MEG3 promoter and the interaction between DNMT1 and MEG3 promoter were detected using methylation-specific PCR and chromatin immunoprecipitation assay, respectively.

RESULTS

Lowly expressed MEG3 and BMP4 and highly expressed DNMT1 were observed in BMSCs of pediatric AA patients. The overexpression of MEG3 promoted osteogenic differentiation of BMSCs. Luciferase reporter assay showed that MEG3 overexpression increased transcriptional activity of BMP4. The inhibitor of methylation, 5-azacytidine, suppressed DNMT1 expression and reduced methylation of MEG3 promoter. Overexpression of DNMT1 increased the binding between DNMT1 and MEG3 promoter. The simultaneous overexpression of DNMT1 and MEG3 restored the inhibition of osteogenic differentiation caused by DNMT1 overexpression alone.

CONCLUSIONS

Our findings indicated that DNMT1 mediated the hypermethylation of MEG3 promoter in BMSCs, and DNMT1/MEG3/BMP4 pathway modulated osteogenic differentiation of BMSCs in pediatric AA.

In Vitro Modeling of Non-Solid Tumors: How Far Can Tissue Engineering Go?

In hematological malignancies, leukemias or myelomas, malignant cells present bone marrow (BM) homing, in which the niche contributes to tumor development and drug resistance. BM architecture, cellular and molecular composition and interactions define differential microenvironments that govern cell fate under physiological and pathological conditions and serve as a reference for the native biological landscape to be replicated in engineered platforms attempting to reproduce blood cancer behavior. This review summarizes the different models used to efficiently reproduce certain aspects of BM in vitro; however, they still lack the complexity of this tissue, which is relevant for fundamental aspects such as drug resistance development in multiple myeloma. Extracellular matrix composition, material topography, vascularization, cellular composition or stemness vs. differentiation balance are discussed as variables that could be rationally defined in tissue engineering approaches for achieving more relevant in vitro models. Fully humanized platforms closely resembling natural interactions still remain challenging and the question of to what extent accurate tissue complexity reproduction is essential to reliably predict drug responses is controversial. However, the contributions of these approaches to the fundamental knowledge of non-solid tumor biology, its regulation by niches, and the advance of personalized medicine are unquestionable.

Quantitative Efficacy and Fate of Mesenchymal Stromal Cells Targeted to Cardiac Sites by Radiofrequency Catheter Ablation

Engraftment and functional integration of stem cells or stem cell-derived cells within cardiac tissue is an important prerequisite for cell replacement therapy aiming at the treatment of heart disease. Recently, a novel intravenous approach for application of mesenchymal stromal cells (MSCs) to cardiac sites has been established using radiofrequency catheter ablation (RFCA)-guided targeting, bypassing the need for open chest surgery or direct myocardial cell injection. However, little is known about the quantitative efficacy and longevity of this strategy. We performed selective power-controlled RFCA with eight ablation pulses (30 W, 60 s each) to induce heat-mediated lesions at the right atrial appendices (RAAs) of pigs. Different concentrations of human bone marrow-derived MSCs (10⁵ to 1.6 × 10⁶ cells/kg bodyweight) labeled with superparamagnetic iron oxide (SPIO) particles were infused intravenously in nine pigs one d after RFCA treatment and hearts were explanted 8 d later to quantify the number of engrafted cells. Prussian blue staining revealed high numbers of SPIO-labeled cells in areas surrounding the RFCA-induced lesions. Cell numbers were evaluated by quantitative real-time polymerase chain reaction using specific primers for human MSCs (hMSCs), which indicated that up to 10⁶ hMSCs, corresponding to ∼3.9% of the systemically applied human cells, engrafted within the RAAs of RFCA-treated pigs. Of note, infused hMSCs were observed in nontargeted organs, as well, but appeared at very low concentrations. To assess long-term deposition of MSCs, RAAs of three pigs were analyzed after 6 months, which revealed few persisting hMSCs at targeted sites. RFCA-mediated targeting of MSCs provides a novel minimal invasive strategy for cardiac stem cell engraftment. Qualitative and quantitative results of our large animal experiments indicate an efficient guidance of MSCs to selected cardiac regions, although only few cells remained at targeted sites 6 mo after cell transplantation.

Decitabine promotes apoptosis in mesenchymal stromal cells isolated from patients with myelodysplastic syndromes by inducing reactive oxygen species generation

Myelodysplastic syndromes (MDSs) are a group of clonal disorders of hematopoietic stem cells, resulting in ineffective hematopoiesis. Previous studies have reported that decitabine (DAC) plays an essential role in cell cycle arrest and cell death induction in multiple cell types. Nevertheless, the effect of decitabine on mesenchymal stromal cells derived from bone marrow of patients with MDSs is not completely clarified. Here, we explored the apoptotic and anti-proliferative effect of DAC on MSCs isolated from patients with MDSs. Treatment with DAC inhibited cell growth in a concentration- and time-dependent manner by inducing apoptosis. We found a positive relationship between cell death triggered by DAC in MSCs and the death receptor family members Fas and FasL mRNA and protein levels (***P < 0.00085), cleaved caspase (-3, -8, and -9) activity, and mitochondrial membrane potential reduction. Additionally, DAC-induced apoptosis was inhibited by Kp7-6, a FasL/Fas antagonist, indicating a crucial role of FasL/Fas, a cell death receptor, in mediating the apoptotic effect of DAC. DAC also induced reactive oxygen species (ROS) generation in MSCs derived from MDSs patients (*P = 0.038). Furthermore, N-acetyl-L-cysteine (NAC), a widely accepted ROS scavenger, efficiently reversed DAC-induced apoptosis by inhibiting ROS generation (***P < 0.00051) in mitochondria and restoring mitochondrial membrane potential. Furthermore, ROS production was found to be a consequence of caspase activation via caspases inhibition. Our data imply that DAC triggers ROS production in human MSCs, which serves as a crucial factor for mitochondrial membrane potential reduction, and DAC induces cell death prior to FasL/Fas stimulation.

Ally to adversary: mesenchymal stem cells and their transformation in leukaemia

Mesenchymal stem cells (MSC) are the key regulators of hematopoiesis. Owing to their dynamic nature; MSC differentiate into various lineages that further constitute the niche which are required for maintenance of the hematopoietic stem cells (HSC). A plethora of growth factors and cytokines secreted by MSC are essential for regulating the homeostasis within the niche in terms of cycling and quiescence of HSC. Additionally, there is a strong evidence suggesting the role of MSC in transformation of the niche to favour survival of leukemic cells. Regulation of HSC by MSC via BMP, Wnt, Notch and Sonic Hedgehog signalling has been well elaborated, however the modulation of MSC by HSC/LSC is yet unresolved. The cross talk between the HSC and MSC via paracrine or autocrine mechanisms is essential for the transformation. There are some reports implicating cell adhesion molecules, growth factors and cytokines; in modulation of MSC function and differentiation. The role of exosome mediated modulation has also been reported in the context of MSC transformation however, much needs to be done to understand this phenomenon in the present context. Similarly, the role of circulating nucleic acids, a well-studied molecular phenomenon in other tumours, requires attention in their potential role in crosstalk between MSC and HSC. This review underlines the current understanding of the physiological and pathophysiological roles of MSC and its transformation in diseased state, laying stress on developing further understanding of MSC regulation for development of the latter as therapeutic targets.

Hematopoietic Niche - Exploring Biomimetic Cues to Improve the Functionality of Hematopoietic Stem/Progenitor Cells

The adult bone marrow (BM) niche is a complex entity where a homeostatic hematopoietic system is maintained through a dynamic crosstalk between different cellular and non-cellular players. Signaling mechanisms triggered by cell-cell, cell-extracellular matrix (ECM), cell-cytokine interactions, and local microenvironment parameters are involved in controlling quiescence, self-renewal, differentiation, and migration of hematopoietic stem/progenitor cells (HSPC). A promising strategy to more efficiently expand HSPC numbers and tune their properties ex vivo is to mimic the hematopoietic niche through integration of adjuvant stromal cells, soluble cues, and/or biomaterial-based approaches in HSPC culture systems. Particularly, mesenchymal stem/stromal cells (MSC), through their paracrine activity or direct contact with HSPC, are thought to be a relevant niche player, positioning HSPC-MSC co-culture as a valuable platform to support the ex vivo expansion of hematopoietic progenitors. To improve the clinical outcome of hematopoietic cell transplantation (HCT), namely when the available HSPC are present in a limited number such is the case of HSPC collected from umbilical cord blood (UCB), ex vivo expansion of HSPC is required without eliminating the long-term repopulating capacity of more primitive HSC. Here, we will focus on depicting the characteristics of co-culture systems, as well as other bioengineering approaches to improve the functionality of HSPC ex vivo.

Pericytes, integral components of adult hematopoietic stem cell niches

The interest in perivascular cells as a niche for adult hematopoietic stem cells (HSCs) is significantly growing. In the adult bone marrow (BM), perivascular cells and HSCs cohabit. Among perivascular cells, pericytes are precursors of mesenchymal stem/stromal cells (MSCs) that are capable of differentiating into osteoblasts, adipocytes and chondrocytes. In situ, pericytes are recognised by their localisation to the abluminal side of the blood vessel wall and closely associated with endothelial cells, in combination with the expression of markers such as CD146, neural glial 2 (NG2), platelet derived growth factor receptor β (PDGFRβ), α-smooth muscle actin (α-SMA), nestin (Nes) and/or leptin receptor (LepR). However, not all pericytes share a common phenotype: different immunophenotypes can be associated with distinct mesenchymal features, including hematopoietic support. In adult BM, arteriolar and sinusoidal pericytes control HSC behaviour, maintenance, quiescence and trafficking through paracrine effects. Different groups identified and characterized hematopoietic supportive pericyte subpopulations using various markers and mouse models. In this review, we summarize recent work performed by others to understand the role of the perivascular niche in the biology of HSCs in adults, as well as their importance in the development of therapies.

Beyond the Niche: Myelodysplastic Syndrome Topobiology in the Laboratory and in the Clinic

We review the murine and human microenvironment and hematopoietic stem cell niche in the context of intact bone marrow architecture in man and mouse, both in normal and in myelodysplastic syndrome marrow. We propose that the complexity of the hematopoietic stem cell niche can usefully be approached in the context of its topobiology, and we provide a model that incorporates in vitro and in vivo models as well as in situ findings from intact human marrow to explain the changes seen in myelodysplastic syndrome patients. We highlight the clinical application of the study of the bone marrow microenvironment and its topobiology in myelodysplastic syndromes.

Chondrogenic cells respond to partial-thickness defects of articular cartilage in adult rats: an in vivo study

The purpose of this study was to establish a partial-thickness articular cartilage defects model in adult rats and explore the respond of chondrogenic cells to the cartilage injury. Forty-five adult Sprague-Dawley rats were divided into operated group, sham-operated group and control group. Partial-thickness cartilage defects were created on the weight-bearing region of femoral condyles by a converted ophthalmic knife. Rats were exposed to 5-bromo-2'-deoxyuridine (BrdU) for five consecutive days and were sacrificed 1, 2 and 4 weeks after surgery. Evaluations of macroscopic and histological changes were made. Chondrocyte apoptosis was evaluated by TUNEL assay. Immunofluorescence staining of CD105 and BrdU, double staining of CD105/integrin α5β1 and CD105-positive cells counting were performed for evaluations of cells around the defects. Cartilage softening and fibrillation with chondrocyte apoptosis were observed around the injury site after surgery. Results of histological scores indicated no significant difference between one time point and a successive time point for either group. CD105-positive cells and BrdU-label-retaining cells were observed around the linear injury. And cells counting showed the number of CD105-positive cells increased at later time points (P < 0.05). Immunofluorescence double staining demonstrated co-localization of CD105 and integrin α5β1 in activated cells around the defects. We establish a partial-thickness cartilage defects model in adult rats and demonstrate this injury may lead to activation of putative progenitor cells. In addition, the activated cells express integrin α5β1 specially, which may help in early discovery of osteoarthritis.

BMSCs and hematopoiesis

Recent discoveries have significantly expanded our previous knowledge about the role of bone marrow mesenchymal stem cells (BMSCs) in hematopoiesis. BMSCs and their derivatives modulate blood production and immunity at different levels but a prominent role has emerged for BMSCs in the regulation of hematopoietic stem and progenitor cells (HSPCs). Additionally, BMSC-like cells regulate B and T cell lymphopoiesis and also probably myelopoiesis. Furthermore, BMSCs might also exhibit key regulatory properties in non-physiological conditions. BMSCs in extramedullary sites might provide a permissive microenvironment to allow for transient hematopoiesis. BMSCs might be also involved in the manifestation and/or the development of hematopoietic diseases, as stemming from their emerging roles in the progression of hematological malignancies. Here we review some key molecular pathways, adhesion molecules and ligand/receptor interactions that mediate the crosstalk between BMSCs and hematopoietic stem cells (HSCs) in health and disease. The development of novel markers to visualize and isolate individual cells will help to dissect the stromal-hematopoietic interplay.

Arsenic trioxide regulates adipogenic and osteogenic differentiation in bone marrow MSCs of aplastic anemia patients through BMP4 gene

The typical pathological feature of aplastic anemia (AA) is the rise in the number of fat cells and the reduction of osteoblasts in bone marrow. However, both fat cells and osteobalsts in bone marrow are derived from the mesenchymal stem cells (MSCs). Generally, the adipogenic and osteogenic differentiation is a dynamic and balanceable process. The imbalance of the adipogenic and osteogenic differentiation may participate in the occurrence and progress of many diseases. Arsenic trioxide (ATO) could induce differentiation and apoptosis in tumor cells. In this study, Oil Red-O and Alizarin red were used to detect the adipogenic and osteogenic differentiation. The ability of adipogenic differentiation is much higher, whereas the osteogenic differentiation is much lower in the MSCs of AA patients compared with healthy controls. ATO inhibits adipogenic differentiation and promotes osteogenic differentiation in the MSC of AA patients. The expression of BMP4 is increased with ATO treatment. The ability of adipogenic differentiation is decreased, whereas the osteogenic differentiation is increased after transfection of BMP4 gene into the MSCs of AA patients. This study shows that ATO regulates the adipogenic and osteogenic differentiation balance of MSCs in AA, which provides a theoretical basis for the adjunctive therapy of ATO on AA. The BMP4 gene is involved in the ATO regulation of adipogenic and osteogenic differentiation balance, which provides a new target for the treatment of AA.

Stage-specific control of stem cell niche architecture in the Drosophila testis by the posterior Hox gene Abd-B

A fundamental question in biology is how complex structures are maintained after their initial specification. We address this question by reviewing the role of the Hox gene Abd-B in Drosophila testis organogenesis, which proceeds through embryonic, larval and pupal stages to reach maturation in adult stages. The data presented in this review highlight a cell- and stage-specific function of Abd-B, since the mechanisms regulating stem cell niche positioning and architecture at different stages seem to be different despite the employment of similar factors. In addition to its described role in the male embryonic gonads, sustained activity of Abd-B in the pre-meiotic germline spermatocytes during larval stages is required to maintain the architecture of the stem cell niche by regulating βPS-integrin localization in the neighboring somatic cyst cells. Loss of Abd-B is associated with cell non-autonomous effects within the niche, leading to a dramatic reduction of pre-meiotic cell populations in adult testes. Identification of Abd-B target genes revealed that Abd-B mediates its effects by controlling the activity of the sevenless ligand Boss via its direct targets Src42A and Sec63. During adult stages, when testis morphogenesis is completed with the addition of the acto-myosin sheath originating from the genital disc, stem cell niche positioning and integrity are regulated by Abd-B activity in the acto-myosin sheath whereas integrin acts in an Abd-B independent way. It seems that the occurrence of new cell types and cell interactions in the course of testis organogenesis made it necessary to adapt the system to the new cellular conditions by reusing the same players for testis stem cell niche positioning in an alternative manner.

Mesenchymal stromal cell density is increased in higher grade myelodysplastic syndromes and independently predicts survival

OBJECTIVES

We retrospectively tested the prognostic and diagnostic significance of CD271+ mesenchymal stromal cell (MSC) density in cytopenic patients who underwent bone marrow biopsy to evaluate for myelodysplastic syndromes (MDS).

METHODS

CD271+ MSC density was quantitated by automated image analysis of tissue microarray cores in 125 cytopenic patients: 40 lower grade MDS (<5% marrow blasts), 24 higher grade MDS, and 61 benign.

RESULTS

CD271+ MSC density was increased in higher grade MDS compared with benign (P = .006) and lower grade MDS (P = .02). CD271+ MSC density was predictive of survival among patients with MDS independent of Revised International Prognostic Scoring System (IPSS-R), history of transfusion, therapy-related MDS, and fibrosis (hazard ratio, 3.4; P < .001). Among low or intermediate IPSS-R patients, median survival was significantly shorter in the high CD271+ MSC density group (47 vs 18 months, P < .02).

CONCLUSIONS

High CD271+ MSC density is characteristic of higher grade MDS and is associated with poor risk independent of known prognostic factors.

Standardization of Good Manufacturing Practice-compliant production of bone marrow-derived human mesenchymal stromal cells for immunotherapeutic applications

BACKGROUND AIMS

Human mesenchymal stem or stromal cells (MSCs) represent a potential resource not only for regenerative medicine but also for immunomodulatory cell therapies. The application of different MSC culture protocols has significantly hampered the comparability of experimental and clinical data from different laboratories and has posed a major obstacle for multicenter clinical trials. Manufacturing of cell products for clinical application in the European Community must be conducted in compliance with Good Manufacturing Practice and requires a manufacturing license. In Germany, the Paul-Ehrlich-Institut as the Federal Authority for Vaccines and Biomedicines is critically involved in the approval process.

METHODS

This report summarizes a consensus meeting between researchers, clinicians and regulatory experts on standard quality requirements for MSC production.

RESULTS

The strategy for quality control testing depends on the product's cell composition, the manufacturing process and the indication and target patient population. Important quality criteria in this sense are, among others, the immunophenotype of the cells, composition of the culture medium and the risk for malignant transformation, as well as aging and the immunosuppressive potential of the manufactured MSCs.

CONCLUSIONS

This position paper intends to provide relevant information to interested parties regarding these criteria to foster the development of scientifically valid and harmonized quality standards and to support approval of MSC-based investigational medicinal products.

Functional assessment of hematopoietic niche cells derived from human embryonic stem cells

To evaluate hematopoietic niche cell populations isolated from human embryonic stem cells (hESCs), we tested the ability of hESC-derived stromal lines to support CD34(+) umbilical cord blood (UCB)- and hESC-derived CD34(+)45(+) cells in long-term culture initiating cell (LTC-IC) assays. Specifically, these hematopoietic populations were cocultured with hESC-derived mesenchymal stromal cells (hESC-MSCs) and hESC-derived endothelial cells (hESC-ECs), and then assessed for their LTC-IC potential in comparison to coculture with bone marrow (BM)-derived MSCs and the mouse stromal line M2-10B4. We found that the hESC-derived stromal lines supported LTC-ICs from UCB similar to M2-10B4 cells and better than BM-MSCs. However, none of the stromal populations supported LTC-IC from hESC-derived CD34(+)45(+) cells. Engraftment data using the output from LTC-IC assays showed long-term repopulation (12 weeks) of NSG mice to correlate with LTC-IC support on a given stromal layer. Therefore, hESC-derived stromal lines can be used to efficiently evaluate putative hematopoietic stem/progenitor cells derived from hESCs or other cell sources.

High fat diet rapidly suppresses B lymphopoiesis by disrupting the supportive capacity of the bone marrow niche

The bone marrow (BM) niche is the primary site of hematopoiesis, and cues from this microenvironment are critical to maintain hematopoiesis. Obesity increases lifetime susceptibility to a host of chronic diseases, and has been linked to defective leukogenesis. The pressures obesity exerts on hematopoietic tissues led us to study the effects of a high fat diet (HFD: 60% Kcal from fat) on B cell development in BM. Seven week old male C57Bl/6J mice were fed either a high fat (HFD) or regular chow (RD) diet for periods of 2 days, 1 week and 6 weeks. B-cell populations (B220+) were not altered after 2 d of HFD, within 1 w B-cell proportions were reduced by −10%, and by 6 w by −25% as compared to RD (p<0.05). BM RNA was extracted to track the expression of B-cell development markers Il-7, Ebf-1 and Pax-5. At 2 d, the expression of Il-7 and Ebf-1 were reduced by −20% (p = 0.08) and −11% (p = 0.06) whereas Pax-5 was not significantly impacted. At one week, however, the expressions of Il-7, Ebf-1, and Pax-5 in HFD mice fell by -19%, −20% and −16%, and by six weeks were further reduced to −23%, −29% and −34% as compared to RD (p<0.05 for all), a suppression paralleled by a +363% increase in adipose encroachment within the marrow space (p<0.01). Il-7 is a critical factor in the early B-cell lineage which is secreted by supportive cells in the BM niche, and is necessary for B-cell commitment. These data indicate that BM Il-7 expression, and by extension B-cell differentiation, are rapidly impaired by HFD. The trend towards suppressed expression of Il-7 following only 2 d of HFD demonstrates how susceptible the BM niche, and the cells which rely on it, are to diet, which ultimately could contribute to disease susceptibility in metabolic disorders such as obesity.

MiR-134-mediated β1 integrin expression and function in mesenchymal stem cells

The composition of the hematopoietic stem cell (HSC) niche within the bone marrow is highly dynamic, tightly regulated, and of importance for various HSC properties. Integrins are important molecules within this niche that influence those properties through the interactions of HSCs and mesenchymal stem cells (MSCs). Here we investigated the function of miR-134 in integrin regulation in MSCs. In MSCs, miR-134 post-transcriptionally regulated β1 integrin expression. This negative regulation of β1 integrin was mediated by the binding of miR-134 to its 3' untranslated region, which contains two conserved binding sites for miR-134. The miR-134-mediated silencing of β1 integrin in MSCs was shown by atomic force microscopy to decrease the adhesion of 32D cells to MSCs transfected with miR-134. Furthermore, the adhesion of MSCs to fibronectin was reduced after transfection with miR-134. MSCs from patients with myelodysplastic syndrome (MDS) revealed highly significant miR-134 overexpression compared with MSCs from healthy bone marrow donors. MSCs from MDS patients showed lower β1 integrin protein, but not lower mRNA, expression, suggesting post-transcriptional regulation. The present study demonstrates miR-134-mediated negative regulation of β1 integrin that influences cell adhesion to and of MSCs. These results further contribute to our understanding of the complexity of MDS.

Diabetes impairs the interactions between long-term hematopoietic stem cells and osteopontin-positive cells in the endosteal niche of mouse bone marrow

Hematopoietic stem cells (HSCs) are maintained, and their division/proliferation and quiescence are regulated in the microenvironments, niches, in the bone marrow. Although diabetes is known to induce abnormalities in HSC mobilization and proliferation through chemokine and chemokine receptors, little is known about the interaction between long-term HSCs (LT-HSCs) and osteopontin-positive (OPN) cells in endosteal niche. To examine this interaction, LT-HSCs and OPN cells were isolated from streptozotocin-induced diabetic and nondiabetic mice. In diabetic mice, we observed a reduction in the number of LT-HSCs and OPN cells and impaired expression of Tie2, β-catenin, and N-cadherin on LT-HSCs and β1-integrin, β-catenin, angiopoietin-1, and CXCL12 on OPN cells. In an in vitro coculture system, LT-HSCs isolated from nondiabetic mice exposed to diabetic OPN cells showed abnormal mRNA expression levels of Tie2 and N-cadherin. Conversely, in LT-HSCs derived from diabetic mice exposed to nondiabetic OPN cells, the decreased mRNA expressions of Tie2, β-catenin, and N-cadherin were restored to normal levels. The effects of diabetic or nondiabetic OPN cells on LT-HSCs shown in this coculture system were confirmed by the coinjection of LT-HSCs and OPN cells into bone marrow of irradiated nondiabetic mice. Our results provide new insight into the treatment of diabetes-induced LT-HSC abnormalities and suggest that the replacement of OPN cells may represent a novel treatment strategy.

Mesenchymal Stem Cell Insights: Prospects in Hematological Transplantation

Adult stem cells have been proven to possess tremendous potential in the treatment of hematological disorders, possibly in transplantation. Mesenchymal stem cells (MSCs) are a heterogeneous group of cells in culture, with hypoimmunogenic character to avoid alloreactive T-cell recognition as well as inhibition of T-cell proliferation. Numerous experimental findings have shown that MSCs also possess the ability to promote engraftment of donor cells and to accelerate the speed of hematological recovery. Despite that the exact mechanism remains unclear, the therapeutic ability of MSCs on hematologic transplantation have been tested in preclinical trials. Based on encouraging preliminary findings, MSCs might become a potentially efficacious tool in the therapeutic options available to treat and cure hematological malignancies and nonmalignant disorders. The molecular mechanisms behind the real efficacy of MSCs on promoting engraftment and accelerating hematological recovery are awaiting clarification. It is hypothesized that direct cell-to-cell contact, paracrine factors, extracellular matrix scaffold, BM homing capability, and endogenous metabolites of immunologic and nonimmunologic elements are involved in the interactions between MSCs and HSCs. This review focuses on recent experimental and clinical findings related to MSCs, highlighting their roles in promoting engraftment, hematopoietic recovery, and GvHD/graft rejection prevention after HSCT, discussing the potential clinical applications of MSC-based treatment strategies in the context of hematological transplantation.

Novel aspects of parenchymal-mesenchymal interactions: from cell types to molecules and beyond

Mesenchymal stem or stromal cells (MSCs) were initially isolated from the bone marrow and received their name on the basis of their ability to differentiate into multiple lineages such as bone, cartilage, fat and muscle. However, more recent studies suggest that MSCs residing in perivascular compartments of the small and large blood vessels play a regulatory function supporting physiologic and pathologic responses of parenchymal cells, which define the functional representation of an organ or tissue. MSCs secrete or express factors that reach neighbouring parenchymal cells via either a paracrine effect or a direct cell-to-cell interaction promoting functional activity, survival and proliferation of the parenchymal cells. Previous concept of 'epithelial-stromal' interactions can now be widened. Given that MSC can also support hematopoietic, neuronal and other non-epithelial parenchymal lineages, terms 'parenchymal-stromal' or 'parenchymal-mesenchymal' interactions may better describe the supportive or 'trophic' functions of MSC. Importantly, in many cases, MSCs specifically provide supportive microenvironment for the most primitive stem or progenitor populations and therefore can play a role as 'stem/progenitor niche' forming cells. So far, regulatory roles of MSCs have been reported in many tissues. In this review article, we summarize the latest studies that focused on the supportive function of MSC. This thread of research leads to a new perspective on the interactions between parenchymal and mesenchymal cells and justifies a principally novel approach for regenerative medicine based on co-application of MSC and parenchymal cell for the most efficient tissue repair.

Mesenchymal stem cell: keystone of the hematopoietic stem cell niche and a stepping-stone for regenerative medicine

Mesenchymal stem cells (MSCs) are self-renewing precursor cells that can differentiate into bone, fat, cartilage, and stromal cells of the bone marrow. Recent studies suggest that MSCs themselves are critical for forming a niche that maintains hematopoietic stem cells (HSCs). The ease by which human MSC-like and stromal progenitor cells can be isolated from the bone marrow and other tissues has led to the rapid development of clinical investigations exploring their anti-inflammatory properties, tissue preservation capabilities, and regenerative potential. However, the identity of genuine MSCs and their specific contributions to these various beneficial effects have remained enigmatic. In this article, we examine the definition of MSCs and discuss the importance of rigorously characterizing their stem cell activity. We review their role and that of other putative niche constituents in the regulation of bone marrow HSCs. Additionally, how MSCs and their stromal progeny alter immune function is discussed, as well as potential therapeutic implications.

Evaluation of umbilical cord blood CD34 (+) hematopoietic stem cell expansion in co-culture with bone marrow mesenchymal stem cells in the presence of TEPA

BACKGROUND

During the last three decades hematopoietic stem cells (HSC) have become a standard protocol for the treatment of many hematologic malignancies and non-malignant disorders. Umbilical cord blood (UCB), as a source of HSCs, has many advantages compared with other sources. One major drawback in using this source in treatment of adult patients is the low HSC dose available. Ex vivo expansion of HSCs is a solution to overcome this limitation. In this study we used TEPA, as a Cu chelator, and human bone marrow (BM) mesenchymal stem cells (MSCs) to investigate expansion rate of UCB-HSCs.

MATERIALS AND METHODS

CB-HSCs were isolated using miniMACS magnetic separation system. We cultured the enriched CD34(+)cells in various conditions: culture condition A, supplemented only with recombinant cytokines; culture condition B, supplemented with BM-MSCs as a cell feeder layer and recombinant cytokines; culture condition C, supplemented with recombinant cytokines and TEPA; culture condition D, supplemented with recombinant cytokines, BM-MSCs as a cell feeder layer and TEPA. In order to evaluate the HSC expansion, we performed cell count, analysis of CD34(+) expression by flow cytometry, and colony-forming cell assay on Day 10 after culture.

RESULTS

The most fold increase in CD34(+) cell, total cell, and total colony numbers was observed in culture condition D (110.11 ± 15.3, 118.5 ± 21, and 172.9 ± 44.7, respectively) compared to other conditions.

CONCLUSION

The results showed that co-culture of HSCs with BM-MSCs in the presence of copper chelating agent (TEPA) could dramatically increase expansion rate of UCB-HSCs. Therefore, this strategy could be useful for HSC expansion.

Distinctive contact between CD34+ hematopoietic progenitors and CXCL12+ CD271+ mesenchymal stromal cells in benign and myelodysplastic bone marrow

Mesenchymal stromal cells (MSCs) support hematopoiesis and are cytogenetically and functionally abnormal in myelodysplastic syndrome (MDS), implying a possible pathophysiologic role in MDS and potential utility as a diagnostic or risk-stratifying tool. We have analyzed putative MSC markers and their relationship to CD34+ hematopoietic stem/progenitor cells (HSPCs) within intact human bone marrow in paraffin-embedded bone marrow core biopsies of benign, MDS and leukemic (AML) marrows using tissue microarrays to facilitate scanning, image analysis and quantitation. We found that CD271+, ALP+ MSCs formed an extensive branching perivascular, periosteal and parenchymal network. Nestin was brightly positive in capillary/arteriolar endothelium and occasional subendothelial cells, whereas CD146 was most brightly expressed in SMA+ vascular smooth muscle/pericytes. CD271+ MSCs were distinct by double immunofluorescence from CD163+ macrophages and were in close contact with but distinct from brightly nestin+ and from brightly CD146+ vascular elements. Double immunofluorescence revealed an intimate spatial relationship between CD34+ HSPCs and CD271+ MSCs; remarkably, 86% of CD34+ HSPCs were in direct contact with CD271+ MSCs across benign, MDS and AML marrows, predominantly in a perivascular distribution. Expression of the intercrine chemokine CXCL12 was strong in the vasculature in both benign and neoplastic marrow, but was also present in extravascular parenchymal cells, particularly in MDS specimens. We identified these parenchymal cells as MSCs by ALP/CXCL12 and CD271/CXCL12 double immunofluorescence. The area covered by CXCL12+ ALP+ MSCs was significantly greater in MDS compared with benign and AML marrow (P=0.021, Kruskal-Wallis test). The preservation of direct CD271+ MSC/CD34+ HSPC contact across benign and neoplastic marrow suggests a physiologically important role for the CD271+ MSC/CD34+ HSPC relationship and possible abnormal exposure of CD34+ HSPCs to increased MSC CXCL12 expression in MDS.

Support of concept that migrating progenitor cells from stem cell niches contribute to normal regeneration of the adult mammal intervertebral disc: a descriptive study in the New Zealand white rabbit

STUDY DESIGN

Descriptive experimental study performed in rabbits of 2 age groups.

OBJECTIVE

To study and investigate presence of prechondrocytic cells and cell migration routes (MR) in the intervertebral disc (IVD) region to gain knowledge about the normal IVD regeneration pattern.

SUMMARY OF BACKGROUND DATA

Disc degeneration is thought to play a major role in patients with chronic lumbar pain. Regeneration processes and cell migration within the IVD have been sparsely described. Therefore, it is of interest to increase knowledge of these processes in order to understand pathological conditions of the IVD.

METHODS

At the beginning of the experiment, 5-bromo-2-deoxyuridine (BrdU) in vivo labeling was performed in 2 groups of rabbits, 3 and 9 months old (total 27 rabbits). BrdU is incorporated into DNA during mitosis, and then it is gradually diluted with each cell division until it finally disappears. Incorporation of BrdU was then visualized by immunohistochemistry (IHC) at different time points providing cell division pattern and presence of slow-cycling cells in the IVD region. IVD tissue was investigated by IHC for growth and differentiation factor-5 (GDF5), SOX9 (chondrogenic lineage markers), SNAIL homolog 1 (SNAI1), SNAIL homolog 2 (SLUG) (migration markers), and β1-INTEGRIN (cellular adhesion marker). In addition, GDF5, SOX9, and BMPRIB expression were investigated on genetic level.

RESULTS

BrdU cells were observed in early time points in the IVD niche, adjacent to the epiphyseal plate, at later time points mainly in outer region of the annulus fibrosus for both age groups of rabbits, indicating a gradual migration of cells. The presence of SLUG, SNAI1, GDF5, SOX9, and β1-INTEGRIN was found in same regions.

CONCLUSION

The results suggest a cellular MR from the IVD stem cell niche toward the annulus fibrosus and the inner parts of the IVD. These findings may be of importance for understanding IVD regenerative mechanisms and for future development of biological treatment strategies.

Shaping the niche: lessons from the Drosophila testis and other model systems

Stem cells are fascinating, as they supply the cells that construct our adult bodies and replenish, as we age, worn out, damaged, and diseased tissues. Stem cell regulation relies on intrinsic signals but also on inputs emanating from the neighbouring niche. The Drosophila testis provides an excellent system for studying such processes. Although recent advances have uncovered several signalling, cytoskeletal and other factors affecting niche homeostasis and testis differentiation, many aspects of niche regulation and maintenance remain unsolved. In this review, we discuss aspects of niche establishment and integrity not yet fully understood and we compare it to the current knowledge in other model systems such as vertebrates and plants. We also address specific questions on stem cell maintenance and niche regulation in the Drosophila testis under the control of Hox genes. Finally, we provide insights on the striking functional conservation of homologous genes in plants and animals and their respective stem cell niches. Elucidating conserved mechanisms of stem cell control in both lineages could reveal the importance underlying this conservation and justify the evolutionary pressure to adapt homologous molecules for performing the same task.

Reconstruction of hematopoietic inductive microenvironment after transplantation of VCAM-1-modified human umbilical cord blood stromal cells

The hematopoietic inductive microenvironment (HIM) is where hematopoietic stem/progenitor cells grow and develop. Hematopoietic stromal cells were the key components of the HIM. In our previous study, we had successfully cultured and isolated human cord blood–derived stromal cells (HUCBSCs) and demonstrated that they could secret hemopoietic growth factors such as GM-CSF, TPO, and SCF. However, it is still controversial whether HUCBSCs can be used for reconstruction of HIM. In this study, we first established a co-culture system of HUCBSCs and cord blood CD34⁺ cells and then determined that using HUCBSCs as the adherent layer had significantly more newly formed colonies of each hematopoietic lineage than the control group, indicating that HUCBSCs had the ability to promote the proliferation of hematopoietic stem cells/progenitor cells. Furthermore, the number of colonies was significantly higher in vascular cell adhesion molecule-1 (VCAM-1)-modified HUCBSCs, suggesting that the ability of HUCBSCs in promoting the proliferation of hematopoietic stem cells/progenitor cells was further enhanced after having been modified with VCAM-1. Next, HUCBSCs were infused into a radiation-damaged animal model, in which the recovery of hematopoiesis was observed. The results demonstrate that the transplanted HUCBSCs were “homed in” to bone marrow and played roles in promoting the recovery of irradiation-induced hematopoietic damage and repairing HIM. Compared with the control group, the HUCBSC group had significantly superior effectiveness in terms of the recovery time for hemogram and myelogram, CFU-F, CFU-GM, BFU-E, and CFU-Meg. Such differences were even more significant in VCAM-1-modified HUCBSCs group. We suggest that HUCBSCs are able to restore the functions of HIM and promote the recovery of radiation-induced hematopoietic damage. VCAM-1 plays an important role in supporting the repair of HIM damage.

Bone marrow mesenchymal stem cells: biological properties and their role in hematopoiesis and hematopoietic stem cell transplantation

Mesenchymal stem cells (MSCs) are multipotent adult stem cells that are present in practically all tissues as a specialized population of mural cells/pericytes that lie on the abluminal side of blood vessels. Originally identified within the bone marrow (BM) stroma, not only do they provide microenvironmental support for hematopoietic stem cells (HSCs), but can also differentiate into various mesodermal lineages. MSCs can easily be isolated from the BM and subsequently expand in vitro and in addition they exhibit intriguing immunomodulatory properties, thereby emerging as attractive candidates for various therapeutic applications. This review addresses the concept of BM MSCs via a hematologist's point of view. In this context it discusses the stem cell properties that have been attributed to BM MSCs, as compared to those of the prototypic hematopoietic stem cell model and then gives a brief overview of the in vitro and vivo features of the former, emphasizing on their immunoregulatory properties and their hematopoiesis-supporting role. In addition, the qualitative and quantitative characteristics of BM MSCs within the context of a defective microenvironment, such as the one characterizing Myelodysplastic Syndromes are described and the potential involvement of these cells in the pathophysiology of the disease is discussed. Finally, emerging clinical applications of BM MSCs in the field of hematopoietic stem cell transplantation are reviewed and potential hazards from MSC use are outlined.

Oxygen tension plays a critical role in the hematopoietic microenvironment in vitro

BACKGROUND

In the bone marrow mesenchymal stromal cells and osteoblasts form functional niches for hematopoietic stem and progenitor cells. This microenvironment can be partially mimicked using in vitro co-culture systems. In this study, we examined the oxygen tension in three distinct compartments in a co-culture system of purified CD34(+) cells and mesenchymal stromal cells with regard to different spatial localizations.

DESIGN AND METHODS

Hypoxic cells in the co-culture were visualized by pimonidazole staining. Hematopoietic cell distribution, and functional and phenotypic characteristics were analyzed by flow cytometry. The secretion of vascular endothelial growth factor and stromal-derived factor-1 by mesenchymal stromal cells in low oxygen co-cultures was determined by an enzyme-linked immunosorbent assay. The effect of co-culture medium on the hematopoietic cell migration potential was tested in a transwell assay.

RESULTS

In co-cultures under atmospheric oxygen tension, regions of low oxygen tension could be detected beneath the feeder layer in which a reservoir of phenotypically more primitive hematopoietic cells is located in vitro. In low oxygen co-culture, the adhesion of hematopoietic cells to the feeder layer was decreased, whereas hematopoietic cell transmigration beneath mesenchymal stromal cells was favored. Increased vascular endothelial growth factor-A secretion by mesenchymal stromal cells under low oxygen conditions, which increased the permeability of the monolayer, was responsible for this effect. Furthermore, vascular endothelial growth factor-A expression in low oxygen mesenchymal stromal cells was induced via hypoxia-inducible factor signaling. However, stromal cell-derived factor-1 secretion by mesenchymal stromal cells was down-regulated under low oxygen conditions in a hypoxia-inducible factor-independent manner.

CONCLUSIONS

We demonstrate for the first time that differences in oxygen tension cause selective modification of hematopoietic cell and mesenchymal stromal cell interactions in a co-culture system, thus confirming that oxygen tension plays a critical role in the interaction between hematopoietic cells and the niche environment.

Intrinsic growth deficiencies of mesenchymal stromal cells in myelodysplastic syndromes

Myelodysplastic syndromes (MDSs) are clonal disorders of hematopoietic stem cells (HSCs) characterized by ineffective hematopoiesis. MDSs are responsible for 1 or several peripheral cytopenias. The evidence accumulated in recent years demonstrates that in addition to HSC defects, a particular role is also played by stromal microenvironment dysfunctions, which mediate the direct contact with hematopoietic precursor cells (HPCs). These interactions help regulate different adhesion-related processes, such as progenitor cell proliferation, apoptosis, clonogenic growth, and maintenance in in vitro cultures. As previously reported, these interactions are responsible for altering the microenvironment in MDS. Herein, we present a novel selection protocol for obtaining a standards-compliant mesenchymal stromal cell (MSC) preparation. This method allowed us to comparatively analyze 2 subpopulations of bone marrow MSCs (BM-MSCs) in terms of their adhesion profiles and growth abilities: BM-MSCs selected from MDS settings and their normal counterparts. Functional assays revealed that the MSCs from MDS are intrinsically pathological, thus showing a continuous decline of proliferation and a reduced clonogenic capacity during 14 days of culture and in the absence of signals from hematopoietic cells. The MSC growth defects were significantly correlated with decreases in CD44 adhesion molecules and CD49e (α5-integrin).

MicroRNA expression during osteogenic differentiation of human multipotent mesenchymal stromal cells from bone marrow

MicroRNAs comprise a group of non-coding small RNAs (17-25 nt) involved in post-transcriptional regulation that have been identified in various plants and animals. Studies have demonstrated that miRNAs are associated with stem cell self-renewal and differentiation and play a key role in controlling stem cell activities. However, the identification of specific miRNAs and their regulatory roles in the differentiation of multipotent mesenchymal stromal cells (MSCs) have so far been poorly defined. We isolated and cultured human MSCs and osteo-differentiated MSCs from four individual donors. miRNA expression in MSCs and osteo-differentiated MSCs was investigated using miRNA microarrays. miRNAs that were commonly expressed in all three MSC preparations and miRNAs that were differentially expressed between MSCs and osteo-differentiated MSCs were identified. Four underexpressed (hsa-miR-31, hsa-miR-106a, hsa-miR-148a, and hsa-miR-424) and three novel overexpressed miRNAs (hsa-miR-30c, hsa-miR-15b, and hsa-miR-130b) in osteo-differentiated MSCs were selected and their expression were verified in samples from the fourth individual donors. The putative targets of the miRNAs were predicted using bioinformatic analysis. The four miRNAs that were underexpressed in osteo-differentiated MSCs were predicted to target RUNX2, CBFB, and BMPs, which are involved in bone formation; while putative targets for miRNAs overexpressed in osteo-differentiated MSCs were MSC maker (e.g., CD44, ITGB1, and FLT1), stemness-maintaining factor (e.g., FGF2 and CXCL12), and genes related to cell differentiation (e.g., BMPER, CAMTA1, and GDF6). Finally, hsa-miR-31 was selected for target verification and function analysis. The results of this study provide an experimental basis for further research on miRNA functions during osteogenic differentiation of human MSCs.

Automated live cell imaging systems reveal dynamic cell behavior

Automated time-lapsed microscopy provides unique research opportunities to visualize cells and subcellular components in experiments with time-dependent parameters. As accessibility to these systems is increasing, we review here their use in cell science with a focus on stem cell research. Although the use of time-lapsed imaging to answer biological questions dates back nearly 150 years, only recently have the use of an environmentally controlled chamber and robotic stage controllers allowed for high-throughput continuous imaging over long periods at the cell and subcellular levels. Numerous automated imaging systems are now available from both companies that specialize in live cell imaging and from major microscope manufacturers. We discuss the key components of robots used for time-lapsed live microscopic imaging, and the unique data that can be obtained from image analysis. We show how automated features enhance experimentation by providing examples of uniquely quantified proliferation and migration live cell imaging data. In addition to providing an efficient system that drastically reduces man-hours and consumes fewer laboratory resources, this technology greatly enhances cell science by providing a unique dataset of temporal changes in cell activity.

Towards a quantitative understanding of stem cell-niche interaction: experiments, models, and technologies

Here we report about an interdisciplinary workshop focusing on the effects of the local growth-environment on the regulation of stem cell development. Under the title "Towards a quantitative understanding of stem cell/ niche interaction: Experiments, models, and technologies", 33 experts from eight countries discussed current knowledge, new experimental and theoretical results as well as innovative measurement technologies. Specifically, the workshop addressed the following questions: What defines a stem cell niche? What are functional/regulatory characteristics of stem cell- microenvironment interactions? What experimental systems and technologies for quantifying niche function are available? As a consensus result it was recorded that there is no unique niche architecture across tissues but that there are generic principles of niche organization guaranteeing a proper function of stem cells. This functional aspect, as the major defining criterion, leads to the conclusion that stem cells and their niches need to be considered as an inseparable pair with implications for their experimental assessment: To be able to study any of those two components, the other component has to be accounted for. In this context, a number of classical in vitro assays using co-cultures of stem and stroma cells, but also new, specifically bioengineered culture systems have been discussed with respect to their advantages and disadvantages. Finally, there was a general agreement that the comprehensive understanding of niche-mediated stem cell regulation will, due to the complexity of involved mechanisms, require an interdisciplinary, systems biological approach. In addition to cell and molecular biology, biochemistry, biophysics and bioengineering also bioinformatics and mathematical modeling will play a major role in the future of this field.

Pleiotrophin regulates the expansion and regeneration of hematopoietic stem cells

Hematopoietic stem cell (HSC) self-renewal is regulated by both intrinsic and extrinsic signals. Although some of the pathways that regulate HSC self-renewal have been uncovered, it remains largely unknown whether these pathways can be triggered by deliverable growth factors to induce HSC growth or regeneration. Here we show that pleiotrophin, a neurite outgrowth factor with no known function in hematopoiesis, efficiently promotes HSC expansion in vitro and HSC regeneration in vivo. Treatment of mouse bone marrow HSCs with pleiotrophin caused a marked increase in long-term repopulating HSC numbers in culture, as measured in competitive repopulating assays. Treatment of human cord blood CD34(+)CDCD38(-)Lin(-) cells with pleiotrophin also substantially increased severe combined immunodeficient (SCID)-repopulating cell counts in culture, compared to input and cytokine-treated cultures. Systemic administration of pleiotrophin to irradiated mice caused a pronounced expansion of bone marrow stem and progenitor cells in vivo, indicating that pleiotrophin is a regenerative growth factor for HSCs. Mechanistically, pleiotrophin activated phosphoinositide 3-kinase (PI3K) signaling in HSCs; antagonism of PI3K or Notch signaling inhibited pleiotrophin-mediated expansion of HSCs in culture. We identify the secreted growth factor pleiotrophin as a new regulator of both HSC expansion and regeneration.

Bone marrow stromal cell interaction reduces syndecan-1 expression and induces kinomic changes in myeloma cells

CD138 (Syndecan 1) is a heparan sulfate proteoglycan that concentrates heparan sulfate-binding growth factors on the surface of normal and malignant plasma cells (multiple myeloma, MMC). Recent studies have shown the presence of a CD138-negative fraction of MMC within myelomatous bone marrow (BM). We employed kinome array technology to characterize this fraction at a molecular level, using a myeloma cell line model. Compared to CD138-positive cells, CD138-negative MMC showed (i) a reduced activity of kinases involved in cell cycle progression, in agreement with a decreased labeling index and (ii) reduced Rho signaling to F-actin. Interestingly, CD138 mRNA and protein expression was reduced upon interaction of MM cells with stromal cell lines and primary mesenchymal cultures, which was accompanied by the acquisition of an increased Bcl6/Blimp1 ratio. Co-culture induced an increased activity of kinases involved in adhesion and a decreased S-phase transition in both CD138-positive and -negative fractions. In addition, CD138-negative MMC demonstrated an increased STAT3 and ERK1/2 activation compared to CD138+ MMC, in agreement with a lower sensitivity to compound exposure. The presence of a less mature, more resistant CD138-negative myeloma cell fraction within bone marrow microniches might contribute to high incidence of relapse of Myeloma patients.