Hematopoietic stem cells in co-culture with mesenchymal stromal cells--modeling the niche compartments in vitro

Biomaterial strategies for controlling stem cell fate via morphogen sequestration

This review explores the role of protein sequestration in the stem cell niche and how it has inspired the design of biomaterials that exploit natural protein sequestration to influence stem cell fate.

Isolation of a novel chronic lymphocytic leukemic (CLL) cell line and development of an in vivo mouse model of CLL

Leukemic cell lines have become important tools for studies of disease providing a monoclonal cell population that can be extensively expanded in vitro while preserving leukemic cellular characteristics. However, studies of chronic lymphocytic leukemia (CLL) have been impeded in part by the lack of continuous human cell lines. CLL cells have a high spontaneous apoptosis rate in vitro and exhibit minimal proliferation in xenograft models. Therefore, there is a need for development of primary CLL cell lines and we describe the isolation of such a line from the bone marrow of a CLL patient (17p deletion and TP53 mutation) which has been in long term culture for more than 12 months with continuous proliferation. The CLL cell line (termed MDA-BM5) which was generated in vitro with continuous co-culture on autologous stromal cells is CD19+CD5+ and shows an identical pattern of somatic hypermutation as determined in the patient's bone marrow (BM), confirming the origin of the cells from the original CLL clone. MDA-BM5 cells were readily transplantable in NOD/SCID gamma null mice (NSG) with disease developing in the BM, liver and spleen. BM cells from quaternary serial transplantation in NSG mice demonstrated the presence of CD19+CD5+ cells with Ig restricted to lambda which is consistent with the original patient cells. These studies describe a new CLL cell line from a patient with del(17p) that provides a unique model for in vitro and in vivo studies.

Importance of cell-cell contact in the therapeutic benefits of cardiosphere-derived cells

Cardiosphere-derived cells (CDCs) effect therapeutic regeneration after myocardial infarction (MI) both in animal models and in humans. Here, we test the hypothesis that cell-cell contact plays a role in mediating the observed therapeutic benefits of CDCs, above and beyond conventional paracrine effects. Human CDCs or vehicle were injected into immunodeficient (SCID) mouse hearts during acute MI. CDC transplantation augmented the proportion of cycling (Ki67(+) ) cardiomyocytes and improved ventricular function. CDC-conditioned media only modestly augmented the percentage of Ki67(+) cardiomyocytes (>control but <CDCs), but did not improve pump function. When neonatal rat ventricular myocytes (NRVMs) were cocultured with human CDCs in vitro, the percentage of cycling NRVMs (Ki67(+) or BrdU(+) nuclei) increased relative to solitary NRVM culture. To further dissect the relative contributions of soluble factors versus contact-dependent mechanisms, we compared CDCs grown with NRVMs in a transwell contact-free system versus admixed coculture. The percentage of cycling NRVMs was higher in admixed coculture than in the contact-free system. Pretreatment with inhibitors of MEK and PI3K, or with β1 integrin neutralizing antibody, blocked the ability of CDCs to promote myocyte cycling. While conditioned media are not inert, direct apposition of CDCs to cardiomyocytes produces greater enhancement of cardiomyocyte proliferation in vitro and in vivo, and improves function post-MI. Intact cardiomyocyte β1 integrin signaling is necessary for the contact-dependent cardioproliferative effects of CDCs.

Fanconi Anemia Mesenchymal Stromal Cells-Derived Glycerophospholipids Skew Hematopoietic Stem Cell Differentiation Through Toll-Like Receptor Signaling

Fanconi anemia (FA) patients develop bone marrow (BM) failure or leukemia. One standard care for these devastating complications is hematopoietic stem cell transplantation. We identified a group of mesenchymal stromal cells (MSCs)-derived metabolites, glycerophospholipids, and their endogenous inhibitor, 5-(tetradecyloxy)-2-furoic acid (TOFA), as regulators of donor hematopoietic stem and progenitor cells. We provided two pieces of evidence that TOFA could improve hematopoiesis-supporting function of FA MSCs: (a) limiting-dilution cobblestone area-forming cell assay revealed that TOFA significantly increased cobblestone colonies in Fanca-/- or Fancd2-/- cocultures compared to untreated cocultures. (b) Competitive repopulating assay using output cells collected from cocultures showed that TOFA greatly alleviated the abnormal expansion of the donor myeloid (CD45.2+Gr1+Mac1+) compartment in both peripheral blood and BM of recipient mice transplanted with cells from Fanca-/- or Fancd2-/- cocultures. Furthermore, mechanistic studies identified Tlr4 signaling as the responsible pathway mediating the effect of glycerophospholipids. Thus, targeting glycerophospholipid biosynthesis in FA MSCs could be a therapeutic strategy to improve hematopoiesis and stem cell transplantation.

Chronic High-Fat Feeding Affects the Mesenchymal Cell Population Expanded From Adipose Tissue but Not Cardiac Atria

Mesenchymal stem cells offer a promising approach to the treatment of myocardial infarction and prevention of heart failure. However, in the clinic, cells will be isolated from patients who may be suffering from comorbidities such as obesity and diabetes, which are known to adversely affect progenitor cells. Here we determined the effect of a high-fat diet (HFD) on mesenchymal stem cells from cardiac and adipose tissues. Mice were fed a HFD for 4 months, after which cardiosphere-derived cells (CDCs) were cultured from atrial tissue and adipose-derived mesenchymal cells (ADMSCs) were isolated from epididymal fat depots. HFD raised body weight, fasted plasma glucose, lactate, and insulin. Ventricle and liver tissue of HFD-fed mice showed protein changes associated with an early type 2 diabetic phenotype. At early passages, more ADMSCs were obtained from HFD-fed mice than from chow-fed mice, whereas CDC number was not affected by HFD. Migratory and clonogenic capacity and release of vascular endothelial growth factor did not differ between cells from HFD- and chow-fed animals. CDCs from chow-fed and HFD-fed mice showed no differences in surface marker expression, whereas ADMSCs from HFD-fed mice contained more cells positive for CD105, DDR2, and CD45, suggesting a high component of endothelial, fibroblast, and hematopoietic cells. Both Noggin and transforming growth factor β-supplemented medium induced an early stage of differentiation in CDCs toward the cardiomyocyte phenotype. Thus, although chronic high-fat feeding increased the number of fibroblasts and hematopoietic cells within the ADMSC population, it left cardiac progenitor cells largely unaffected.

SIGNIFICANCE

Mesenchymal cells are a promising candidate cell source for restoring lost tissue and thereby preventing heart failure. In the clinic, cells are isolated from patients who may be suffering from comorbidities such as obesity and diabetes. This study examined the effect of a high-fat diet on mesenchymal cells from cardiac and adipose tissues. It was demonstrated that a high-fat diet did not affect cardiac progenitor cells but increased the number of fibroblasts and hematopoietic cells within the adipose-derived mesenchymal cell population.

Phenotypic, Morphological and Adhesive Differences of Human Hematopoietic Progenitor Cells Cultured on Murine versus Human Mesenchymal Stromal Cells

Xenogenic transplantation models have been developed to study human hematopoiesis in immunocompromised murine recipients. They still have limitations and therefore it is important to delineate all players within the bone marrow that could account for species-specific differences. Here, we evaluated the proliferative capacity, morphological and physical characteristics of human CD34⁺ hematopoietic stem and progenitor cells (HSPCs) after co-culture on murine or human bone marrow-derived mesenchymal stromal cells (MSCs). After seven days, human CD34⁺CD133^– HSPCs expanded to similar extents on both feeder layers while cellular subsets comprising primitive CD34⁺CD133⁺ and CD133⁺CD34^– phenotypes are reduced fivefold on murine MSCs. The number of migrating HSPCs was also reduced on murine cells suggesting that MSC adhesion influences cellular polarization of HSPC. We used atomic force microscopy-based single-cell force spectroscopy to quantify their adhesive interactions. We found threefold higher detachment forces of human HSPCs from murine MSCs compared to human ones. This difference is related to the N-cadherin expression level on murine MSCs since its knockdown abolished their differential adhesion properties with human HSPCs. Our observations highlight phenotypic, morphological and adhesive differences of human HSPCs when cultured on murine or human MSCs, which raise some caution in data interpretation when xenogenic transplantation models are used.

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.

Concise Review: Stem Cell Microenvironment on a Chip: Current Technologies for Tissue Engineering and Stem Cell Biology

Stem cells have huge potential in many therapeutic areas. With conventional cell culture methods, however, it is difficult to achieve in vivo-like microenvironments in which a number of well-controlled stimuli are provided for growing highly sensitive stem cells. In contrast, microtechnology-based platforms offer advantages of high precision, controllability, scalability, and reproducibility, enabling imitation of the complex physiological context of in vivo. This capability may fill the gap between the present knowledge about stem cells and that required for clinical stem cell-based therapies. We reviewed the various types of microplatforms on which stem cell microenvironments are mimicked. We have assigned the various microplatforms to four categories based on their practical uses to assist stem cell biologists in using them for research. In particular, many examples are given of microplatforms used for the production of embryoid bodies and aggregates of stem cells in vitro. We also categorized microplatforms based on the types of factors controlling the behaviors of stem cells. Finally, we outline possible future directions for microplatform-based stem cell research, such as research leading to the production of well-defined environments for stem cells to be used in scaled-up systems or organs-on-a-chip, the regulation of induced pluripotent stem cells, and the study of the genetic states of stem cells on microplatforms.

SIGNIFICANCE

Stem cells are highly sensitive to a variety of physicochemical cues, and their fate can be easily altered by a slight change of environment; therefore, systematic analysis and discrimination of the extracellular signals and intracellular pathways controlling the fate of cells and experimental realization of sensitive and controllable niche environments are critical. This review introduces diverse microplatforms to provide in vitro stem cell niches. Microplatforms could control microenvironments around cells and have recently attracted much attention in biology including stem cell research. These microplatforms and the future directions of stem cell microenvironment are described.

Engineering the hematopoietic stem cell niche: Frontiers in biomaterial science

Hematopoietic stem cells (HSCs) play a crucial role in the generation of the body's blood and immune cells. This process takes place primarily in the bone marrow in specialized 'niche' microenvironments, which provide signals responsible for maintaining a balance between HSC quiescence, self-renewal, and lineage specification required for life-long hematopoiesis. While our understanding of these signaling mechanisms continues to improve, our ability to engineer them in vitro for the expansion of clinically relevant HSC populations is still lacking. In this review, we focus on development of biomaterials-based culture platforms for in vitro study of interactions between HSCs and their local microenvironment. The tools and techniques used for both examining HSC-niche interactions as well as applying these findings towards controlled HSC expansion or directed differentiation in 2D and 3D platforms are discussed. These novel techniques hold the potential to push the existing boundaries of HSC cultures towards high-throughput, real-time, and single-cell level biomimetic approaches that enable a more nuanced understanding of HSC regulation and function. Their application in conjunction with innovative biomaterial platforms can pave the way for engineering artificial bone marrow niches for clinical applications as well as elucidating the pathology of blood-related cancers and disorders.

Mesenchymal Stem/Stromal Cells Derived from Induced Pluripotent Stem Cells Support CD34(pos) Hematopoietic Stem Cell Propagation and Suppress Inflammatory Reaction

Mesenchymal stem/stromal cells (MSCs) represent a promising cell source for research and therapeutic applications, but their restricted ex vivo propagation capabilities limit putative applications. Substantial self-renewing of stem cells can be achieved by reprogramming cells into induced pluripotent stem cells (iPSCs) that can be easily expanded as undifferentiated cells even in mass culture. Here, we investigated a differentiation protocol enabling the generation and selection of human iPSC-derived MSCs exhibiting relevant surface marker expression profiles (CD105 and CD73) and functional characteristics. We generated such iPSC-MSCs from fibroblasts and bone marrow MSCs utilizing two different reprogramming constructs. All such iPSC-MSCs exhibited the characteristics of normal bone marrow-derived (BM) MSCs. In direct comparison to BM-MSCs our iPSC-MSCs exhibited a similar surface marker expression profile but shorter doubling times without reaching senescence within 20 passages. Considering functional capabilities, iPSC-MSCs provided supportive feeder layer for CD34⁺ hematopoietic stem cells' self-renewal and colony forming capacities. Furthermore, iPSC-MSCs gained immunomodulatory function to suppress CD4⁺ cell proliferation, reduce proinflammatory cytokines in mixed lymphocyte reaction, and increase regulatory CD4⁺/CD69⁺/CD25⁺ T-lymphocyte population. In conclusion, we generated fully functional MSCs from various iPSC lines irrespective of their starting cell source or reprogramming factor composition and we suggest that such iPSC-MSCs allow repetitive cell applications for advanced therapeutic approaches.

The potential of cytotherapeutics in hematologic reconstitution and in the treatment and prophylaxis of graft-versus-host disease. Chapter II: emerging transformational cytotherapies

Hematopoietic stem cell transplantation (HSCT) is a life-saving treatment for inherited anemias, immunodeficiencies or hematologic malignancies. A major complication of allo-HSCT associated with high transplant-related mortality rates is graft-versus-host disease (GvHD). Current and future clinical benefits in HSCT enabled by advances in hematopoietic stem cells, mesenchymal stem cells, Tregs and natural killer cells technologies are reviewed here and discussed. Among these evolutions, based on the need for mesenchymal stem cells to be recruited by an inflammatory environment, the development and use of novel GvHD biomarkers could be explored further to deliver the right pharmaceutical to the right patient at the right time. The successful commercialization of cytotherapeutics to efficiently manage GvHD will create a virtuous ‘halo’ effect for regenerative medicine.

Human adipose-tissue derived stromal cells in combination with hypoxia effectively support ex vivo expansion of cord blood haematopoietic progenitors

The optimisation of haematopoietic stem and progenitor cell expansion is on demand in modern cell therapy. In this work, haematopoietic stem/progenitor cells (HSPCs) have been selected from unmanipulated cord blood mononuclear cells (cbMNCs) due to adhesion to human adipose-tissue derived stromal cells (ASCs) under standard (20%) and tissue-related (5%) oxygen. ASCs efficiently maintained viability and supported further HSPC expansion at 20% and 5% O₂. During co-culture with ASCs, a new floating population of differently committed HSPCs (HSPCs-1) grew. This suspension was enriched with СD34⁺ cells up to 6 (20% O₂) and 8 (5% O₂) times. Functional analysis of HSPCs-1 revealed cobble-stone area forming cells (CAFCs) and lineage-restricted colony-forming cells (CFCs). The number of CFCs was 1.6 times higher at tissue-related O₂, than in standard cultivation (20% O₂). This increase was related to a rise in the number of multipotent precursors - BFU-E, CFU-GEMM and CFU-GM. These changes were at least partly ensured by the increased concentration of MCP-1 and IL-8 at 5% O₂. In summary, our data demonstrated that human ASCs enables the selection of functionally active HSPCs from unfractionated cbMNCs, the further expansion of which without exogenous cytokines provides enrichment with CD34⁺ cells. ASCs efficiently support the viability and proliferation of cord blood haematopoietic progenitors of different commitment at standard and tissue-related O₂ levels at the expense of direct and paracrine cell-to-cell interactions.

Alternative methods in toxicology: CFU assays application, limitation and future prospective

Blood is a fluid connective tissue which plays a vital role for normal body function. It consist different type of blood cells which is continuously reproduce inside the bone marrow from hematopoietic system. Xenobiotics could be specifically toxic to the hematopoietic system and they can cause hematological disorders by disturbing the normal functions. In vitro hematopoietic colony-forming cell assays play a crucial role to evaluate potential toxic effects of new xenobiotics and also helpful in bridging the gap between preclinical toxicology studies in animal models and clinical investigations. Use of these assays in conjunction with, high-throughput screening reduces the cost and time associated with these assays. This article provides a critical view over in vitro hematopoietic colony-forming cell assays in assessment of hematotoxicity.

Biohybrid hematopoietic niche for expansion of hematopoietic stem/progenitor cells by using geometrically controlled fibrous layers

Biohybrid hematopoietic niche for expansion of hematopoietic stem/progenitor cells.

Low intensity pulsed ultrasound enhanced mesenchymal stem cell recruitment through stromal derived factor-1 signaling in fracture healing

Low intensity pulsed ultrasound (LIPUS) has been proven effective in promoting fracture healing but the underlying mechanisms are not fully depicted. We examined the effect of LIPUS on the recruitment of mesenchymal stem cells (MSCs) and the pivotal role of stromal cell-derived factor-1/C-X-C chemokine receptor type 4 (SDF-1/CXCR4) pathway in response to LIPUS stimulation, which are essential factors in bone fracture healing. For in vitro study, isolated rat MSCs were divided into control or LIPUS group. LIPUS treatment was given 20 minutes/day at 37 °C for 3 days. Control group received sham LIPUS treatment. After treatment, intracellular CXCR4 mRNA, SDF-1 mRNA and secreted SDF-1 protein levels were quantified, and MSCs migration was evaluated with or without blocking SDF-1/CXCR4 pathway by AMD3100. For in vivo study, fractured 8-week-old young rats received intracardiac administration of MSCs were assigned to LIPUS treatment, LIPUS+AMD3100 treatment or vehicle control group. The migration of transplanted MSC to the fracture site was investigated by ex vivo fluorescent imaging. SDF-1 protein levels at fracture site and in serum were examined. Fracture healing parameters, including callus morphology, micro-architecture of the callus and biomechanical properties of the healing bone were investigated. The in vitro results showed that LIPUS upregulated SDF-1 and CXCR4 expressions in MSCs, and elevated SDF-1 protein level in the conditioned medium. MSCs migration was promoted by LIPUS and partially inhibited by AMD3100. In vivo study demonstrated that LIPUS promoted MSCs migration to the fracture site, which was associated with an increase of local and serum SDF-1 level, the changes in callus formation, and the improvement of callus microarchitecture and mechanical properties; whereas the blockade of SDF-1/CXCR4 signaling attenuated the LIPUS effects on the fractured bones. These results suggested SDF-1 mediated MSCs migration might be one of the crucial mechanisms through which LIPUS exerted influence on fracture healing.

Influence of a dual-injection regimen, plerixafor and CXCR4 on in utero hematopoietic stem cell transplantation and engraftment with use of the sheep model

BACKGROUND AIMS

Inadequate engraftment of hematopoietic stem cells (HSCs) after in utero HSC transplantation (IUHSCT) remains a major obstacle for the prenatal correction of numerous hereditary disorders. HSCs express CXCR4 receptors that allow homing and engraftment in response to stromal-derived factor 1 (SDF-1) ligand present in the bone marrow stromal niche. Plerixafor, a mobilization drug, works through the interruption of the CXCR4-SDF-1 axis.

METHODS

We used the fetal sheep large-animal model to test our hypotheses that (i) by administering plerixafor in utero before performing IUHSCT to release fetal HSCs and thus vacating recipient HSC niches, (ii) by using human mesenchymal stromal/stem cells (MSCs) to immunomodulate and humanize the fetal BM niches and (iii) by increasing the CXCR4(+) fraction of CD34(+) HSCs, we could improve engraftment. Human cord blood-derived CD34(+) cells and human bone marrow-derived MSCs were used for these studies.

RESULTS

When MSCs were transplanted 1 week before CD34(+) cells with plerixafor treatment, we observed 2.80% donor hematopoietic engraftment. Combination of this regimen with additional CD34(+) cells at the time of MSC infusion increased engraftment levels to 8.77%. Next, increasing the fraction of CXCR4(+) cells in the CD34(+) population albeit transplanting at a late gestation age was not beneficial. Our results show engraftment of both lymphoid and myeloid lineages.

CONCLUSIONS

Prior MSC and HSC cotransplantation followed by manipulation of the CXCR4-SDF-1 axis in IUHSCT provides an innovative conceptual approach for conferring competitive advantage to donor HSCs. Our novel approach could provide a clinically relevant approach for enhancing engraftment early in the fetus.

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.

Effect of stem cell therapy on induced diabetic keratopathy in albino rat

BACKGROUND AND OBJECTIVES

Type 2 diabetes mellitus (DM) is a prevalent disorder. Diabetic keratopathy is a well-known ocular complication secondary to type 2 DM. Topical insulin application did not affect apoptosis and necrosis levels in corneal epithelium. Autologous cell transplantation is not a viable option for diabetic patients with bilateral limbal stem cell deficiency. The present study aimed at assessing the possible effect of hemopoeitic stem cell (HSC) therapy on induced diabetic keratopathy in albino rat.

METHODS AND RESULTS

Fifteen male albino rats were divided into control group of 2 rats, diabetic group of 8 rats receiving single intraperitoneal (IP) injection of 50 mg/kg streptozotocin (STZ). 3 animals were sacrificed 6 weeks following confirmation of diabetes to confirm keratopathy and 5 rats were sacrificed 4 weeks following confirmation of keratopathy. SC therapy group included 5 rats injected with HSCs 6 weeks following confirmation of diabetes and sacrificed 4 weeks following SC therapy. Cord blood collection, stem cells isolation and labeling were performed. Eye specimens were subjected to histological, histochemical, immunohistochemical, morphometric and statistical studies. In diabetic group, the central cornea showed multiple cells with vacuolated cytoplasm and dark nuclei, focal epithelial discontinuity, reduced corneal thickness and less number of layers of corneal and conjunctival epithelia. In stem cell therapy group, few cells with vacuolated cytoplasm and dark nuclei were found in the corneal and conjunctival epithelia with more number of epithelial layers.

CONCLUSIONS

A definite ameliorating effect of HSC therapy was detected on diabetic keratopathy. The therapeutic cells were effective in limiting corneal epithelial changes.

Hematopoietic stem and progenitor cells acquire distinct DNA-hypermethylation during in vitro culture

Hematopoietic stem and progenitor cells (HPCs) can be maintained invitro, but the vast majority of their progeny loses stemness during culture. In this study, we compared DNA-methylation (DNAm) profiles of freshly isolated and culture-expanded HPCs. Culture conditions of CD34⁺ cells - either with or without mesenchymal stromal cells (MSCs) - had relatively little impact on DNAm, although proliferation is greatly increased by stromal support. However, all cultured HPCs - even those which remained CD34⁺ - acquired significant DNA-hypermethylation. DNA-hypermethylation occurred particularly in up-stream promoter regions, shore-regions of CpG islands, binding sites for PU.1, HOXA5 and RUNX1, and it was reflected in differential gene expression and variant transcripts of DNMT3A. Low concentrations of DNAm inhibitors slightly increased the frequency of colony-forming unit initiating cells. Our results demonstrate that HPCs acquire DNA-hypermethylation at specific sites in the genome which is relevant for the rapid loss of stemness during in vitro manipulation.

Over expression of HIF-1α in human mesenchymal stem cells increases their supportive functions for hematopoietic stem cells in an experimental co-culture model

INTRODUCTION

Bone marrow transplantation is a critical approach for the treatment of many hematological disorders. Success of this approach is dependent on many factors the most important of which is the number of hematopoietic stem cells along with an efficient stroma. Co-transplantation of efficient mesenchymal stem cells can greatly improve the outcome of transplantations. Current researches assign a critical role for hypoxia inducible factor (HIF)-1α in protection of various cells and tissues probably through induction of cytokines. To make this feature applicable to human bone marrow-derived mesenchymal stem cells, we manipulated these cells to over express HIF-1α gene.

MATERIALS AND METHODS

Full-length cDNA of human HIF-1α was inserted into human bone marrow mesenchymal stem cells by pcDNA.3.1 non-viral plasmid vector, and the effect of this over expression on production of some hematopoietic growth factors was explored. Moreover, using a co-culture system, the interactive impact of HIF-1α-overexpressed mesenchymal stem cells on hematopoietic stem cells was evaluated. Results Over expression of HIF-1α in mesenchymal stem cells in normoxia increased production of one of the most important hematopoietic growth factors, Stem cell factor (also known as Steel factor or c-kit ligand). HIF-1α overexpression had no effect on production of other hematopoietic growth factors. In co-culture of mesenchymal stem cells-HIF-1α with hematopoietic stem cells, enhancement of colony formation and reduced differentiation of hematopoietic stem cells were observed. Conclusion Over expression of HIF-1α in human bone marrow-derived mesenchymal stem cells can augment the production of some hematopoietic growth factors, and we suggest this response of mesenchymal stem cells could help to improve the outcome of bone marrow transplantation.

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.

Constructing stem cell microenvironments using bioengineering approaches

Within the adult organism, stem cells reside in defined anatomical microenvironments called niches. These architecturally diverse microenvironments serve to balance stem cell self-renewal and differentiation. Proper regulation of this balance is instrumental to tissue repair and homeostasis, and any imbalance can potentially lead to diseases such as cancer. Within each of these microenvironments, a myriad of chemical and physical stimuli interact in a complex (synergistic or antagonistic) manner to tightly regulate stem cell fate. The in vitro replication of these in vivo microenvironments will be necessary for the application of stem cells for disease modeling, drug discovery, and regenerative medicine purposes. However, traditional reductionist approaches have only led to the generation of cell culture methods that poorly recapitulate the in vivo microenvironment. To that end, novel engineering and systems biology approaches have allowed for the investigation of the biological and mechanical stimuli that govern stem cell fate. In this review, the application of these technologies for the dissection of stem cell microenvironments will be analyzed. Moreover, the use of these engineering approaches to construct in vitro stem cell microenvironments that precisely control stem cell fate and function will be reviewed. Finally, the emerging trend of using high-throughput, combinatorial methods for the stepwise engineering of stem cell microenvironments will be explored.

Engraftment Outcomes after HPC Co-Culture with Mesenchymal Stromal Cells and Osteoblasts

Haematopoietic stem cell (HSC) transplantation is an established cell-based therapy for a number of haematological diseases. To enhance this therapy, there is considerable interest in expanding HSCs in artificial niches prior to transplantation. This study compared murine HSC expansion supported through co-culture on monolayers of either undifferentiated mesenchymal stromal cells (MSCs) or osteoblasts. Sorted Lineage(-) Sca-1(+) c-kit(+) (LSK) haematopoietic stem/progenitor cells (HPC) demonstrated proliferative capacity on both stromal monolayers with the greatest expansion of LSK shown in cultures supported by osteoblast monolayers. After transplantation, both types of bulk-expanded cultures were capable of engrafting and repopulating lethally irradiated primary and secondary murine recipients. LSKs co-cultured on MSCs showed comparable, but not superior, reconstitution ability to that of freshly isolated LSKs. Surprisingly, however, osteoblast co-cultured LSKs showed significantly poorer haematopoietic reconstitution compared to LSKs co-cultured on MSCs, likely due to a delay in short-term reconstitution. We demonstrated that stromal monolayers can be used to maintain, but not expand, functional HSCs without a need for additional haematopoietic growth factors. We also demonstrated that despite apparently superior in vitro performance, co-injection of bulk cultures of osteoblasts and LSKs in vivo was detrimental to recipient survival and should be avoided in translation to clinical practice.

SP/drug efflux functionality of hematopoietic progenitors is controlled by mesenchymal niche through VLA-4/CD44 axis

Hematopoiesis is orchestrated by interactions between hematopoietic stem/progenitor cells (HSPCs) and stromal cells within bone marrow (BM) niches. Side population (SP) functionality is a major characteristic of HSPCs related to quiescence and resistance to drugs and environmental stresses. At steady state, SP cells are mainly present in the BM and are mostly absent from the circulation except in stress conditions, raising the hypothesis of the versatility of the SP functionality. However, the mechanism of SP phenotype regulation is unclear. Here we show for the first time that the SP functionality can be induced in lin(-) cells from unmobilized peripheral blood after nesting on mesenchymal stromal cells (MSCs). This MSC-induced SP fraction contains HSPCs as demonstrated by their (i) CD34(+) cell percentage, (ii) quiescent status, (iii) in vitro proliferative and clonogenic potential, (iv) engraftment in NSG (NOD SCID gamma chain) mice and (v) stemness gene expression profile. We demonstrate that SP phenotype acquisition/reactivation by circulating lin(-) cells is dependent on interactions with MSCs through VLA-4/α4β1-integrin and CD44. A similar integrin-dependent mechanism of SP phenotype acquisition in acute myeloid leukemia circulating blasts suggests an extrinsic regulation of ATP-binding cassette-transporter activity that could be of importance for a better understanding of adhesion-mediated chemoresistance mechanisms.

Detection in vitro and quantitative estimation of artificial microterritories which promote osteogenic differentiation and maturation of stromal stem cells

Extracellular matrix can regulate multipotent mesenchymal stromal cells (MMSC) differentiation, with potential applications for tissue engineering. A relief of mineralized bone takes essential effect on MMSC fate. Nevertheless, delicate structure and a hierarchy of niches for stromal stem cells and its quantitative parameters are not practically known. Here, we describe the protocol to define the basic approach providing a guiding for in vitro identification of quantitative features of artificial calcium phosphate niches which promotes osteogenic differentiation and maturation of stromal stem cell.

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.

Exploring the cancer stem cell phenotype with high-throughput screening applications

Several human cancer types consist of diverse cell populations that can differ in their tumor-driving potential. One breakthrough has been the identification of poorly differentiated tumor cells, herein termed cancer stem cells (CSCs). CSCs have been shown to initiate tumors in different model systems and have been implicated in cancer resistance to conventional therapies. The clinical relevance of CSCs has been increasingly recognized, and recent progress in their enrichment and characterization has paved the way for exploring CSC biology with high-throughput screening technologies. This article focuses on functional chemical and RNAi screens that have led to the identification of factors that control the CSC phenotype. Different experimental strategies, current challenges and perspectives in CSC drug discovery are discussed.

Differential effects of mixed lymphocyte reaction supernatant on human mesenchymal stromal cells

The concept that mesenchymal stromal cells (MSCs), a component of the hematopoietic microenvironment, can be a target for alloreactive effector cells in the context of graft-vs-host disease has not been investigated in detail. Mixed lymphocyte reaction (MLR) supernatant was used to mimic the inflammatory milieu induced by an allogeneic immune response in vitro. In addition to phenotype and proliferation, we monitored MSC differentiation, gene expression, and support of CD34(+) hematopoietic stem and progenitor cells after priming with MLR supernatant. Priming of MSCs with MLR supernatant led to an 11-fold decrease in cobblestone area-forming cells in the 4-week coculture (p < 0.05) and a threefold decrease of colony-forming unit macrophage in the colony-forming cell assay (p < 0.05). MSC proliferation over 8 days was increased 2.5-fold (p < 0.05). Osteogenic differentiation was enhanced, while adipogenesis was concurrently suppressed. In addition, the surface expression of HLA-DR and intercellular adhesion molecule-1 was increased 20-fold (p = 0.06) and 45-fold (p < 0.05), respectively. This was associated with increased adhesion of hematopoietic stem and progenitor cells to MLR-treated MSCs. In summary, our data shed light on the dysfunction of the stromal environment during graft-vs-host disease, possibly aggravating cytopenia and leading to an enhanced immunogenicity of MSCs.

Expression of the melanoma cell adhesion molecule in human mesenchymal stromal cells regulates proliferation, differentiation, and maintenance of hematopoietic stem and progenitor cells

The melanoma cell adhesion molecule defines mesenchymal stromal cells in the human bone marrow that regenerate bone and establish a hematopoietic microenvironment in vivo. The role of the melanoma cell adhesion molecule in primary human mesenchymal stromal cells and the maintenance of hematopoietic stem and progenitor cells during ex vivo culture has not yet been demonstrated. We applied RNA interference or ectopic overexpression of the melanoma cell adhesion molecule in human mesenchymal stromal cells to evaluate the effect of the melanoma cell adhesion molecule on their proliferation and differentiation as well as its influence on co-cultivated hematopoietic stem and progenitor cells. Knockdown and overexpression of the melanoma cell adhesion molecule affected several characteristics of human mesenchymal stromal cells related to osteogenic differentiation, proliferation, and migration. Furthermore, knockdown of the melanoma cell adhesion molecule in human mesenchymal stromal cells stimulated the proliferation of hematopoietic stem and progenitor cells, and strongly reduced the formation of long-term culture-initiating cells. In contrast, melanoma cell adhesion molecule-overexpressing human mesenchymal stromal cells provided a supportive microenvironment for hematopoietic stem and progenitor cells. Expression of the melanoma cell adhesion molecule increased the adhesion of hematopoietic stem and progenitor cells to human mesenchymal stromal cells and their migration beneath the monolayer of human mesenchymal stromal cells. Our results demonstrate that the expression of the melanoma cell adhesion molecule in human mesenchymal stromal cells determines their fate and regulates the maintenance of hematopoietic stem and progenitor cells through direct cell-cell contact.

Coculture strategies in bone tissue engineering: the impact of culture conditions on pluripotent stem cell populations

The use of pluripotent stem cell populations for bone tissue regeneration provides many opportunities and challenges within the bone tissue engineering field. For example, coculture strategies have been utilized to mimic embryological development of bone tissue, and particularly the critical intercellular signaling pathways. While research in bone biology over the last 20 years has expanded our understanding of these intercellular signaling pathways, we still do not fully understand the impact of the system's physical characteristics (orientation, geometry, and morphology). This review of coculture literature delineates the various forms of coculture systems and their respective outcomes when applied to bone tissue engineering. To understand fully the key differences between the different coculture methods, we must appreciate the underlying paradigms of physiological interactions. Recent advances have enabled us to extrapolate these techniques to larger dimensions and higher geometric resolutions. Finally, the contributions of bioreactors, micropatterned biomaterials, and biomaterial interaction platforms are evaluated to give a sense of the sophistication established by a combination of these concepts with coculture systems.

Human umbilical cord Wharton's jelly stem cells and its conditioned medium support hematopoietic stem cell expansion ex vivo

Bone marrow mesenchymal stromal cells (BMMSCs) have been used as feeder support for the ex vivo expansion of hematopoietic stem cells (HSCs) but have the limitations of painful harvest, morbidity, and risk of infection to the patient. This prompted us to explore the use of human umbilical cord Wharton's jelly MSCs (hWJSCs) and its conditioned medium (hWJSC-CM) for ex vivo expansion of HSCs in allogeneic and autologous settings because hWJSCs can be harvested in abundance painlessly, are proliferative, hypoimmunogenic, and secrete a variety of unique proteins. In the presence of hWJSCs and hWJSC-CM, HSCs put out pseudopodia-like outgrowths and became highly motile. Time lapse imaging showed that the outgrowths helped them to migrate towards and attach to the upper surfaces of hWJSCs and undergo proliferation. After 9 days of culture in the presence of hWJSCs and hWJSC-CM, MTT, and Trypan blue assays showed significant increases in HSC numbers, and FACS analysis generated significantly greater numbers of CD34(+) cells compared to controls. hWJSC-CM produced the highest number of colonies (CFU assay) and all six classifications of colony morphology typical of hematopoiesis were observed. Proteomic analysis of hWJSC-CM showed significantly greater levels of interleukins (IL-1a, IL-6, IL-7, and IL-8), SCF, HGF, and ICAM-1 compared to controls suggesting that they may be involved in the HSC multiplication. We propose that cord blood banks freeze autologous hWJSCs and umbilical cord blood (UCB) from the same umbilical cord at the same time for the patient for future ex vivo HSC expansion and cell-based therapies.

Bone marrow mesenchymal stem cells in patients with beta thalassemia major: molecular analysis with attenuated total reflection-Fourier transform infrared spectroscopy study as a novel method

Bone marrow mesenchymal stem cells (BM-MSCs) are the main cellular components of the bone marrow, providing a supportive cellular microenvironment to maintain healthy hematopoiesis. β-thalassemia major (β-TM) is characterized by anemia that is caused by a genetic defect in hemoglobin synthesis and results in ineffective erythropoiesis (IE). The alterations in the microenvironment in thalassemic bone marrow during IE can cause changes in BM-MSCs. This study aimed to investigate global structural and compositional changes in BM-MSCs in β-TM that may provide a basis in understanding interactions of hematopoietic stem cells (HSCs)-MSCs in such a pathological bone marrow microenvironment. Following characterization of morphological, immunophenotypical, and differentiation properties, the changes in healthy and thalassemic BM-MSCs before and after bone marrow transplantation (BMT) were examined by attenuated total reflection-Fourier transform infrared (ATR-FTIR). The significant increase in lipid, protein, glycogen, and nucleic acid contents in thalassemic BM-MSCs with respect to healthy BM-MSCs was attributed to enhanced cell proliferation and BM activity during IE. The significant decreases in the content of mentioned macromolecules in post-transplant group BM-MSCs versus pre-transplant BM-MSCs was interpreted as restoring effect of BMT therapy on IE and defective BM microenvironment. These alterations were also supported by ELISA results of erythropoietin (EPO) and growth differentiation factor (GDF15) in bone marrow plasma samples as a reflection of IE and by MTT proliferation assay on BM-MSCs. Based on these changes, sampling groups were discriminated by cluster analysis. These results provide information for the studies that concentrate on interactions between HSCs-MSCs in bone marrow.

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.