Identification and isolation from either adult human bone marrow or G-CSF-mobilized peripheral blood of CD34(+)/CD133(+)/CXCR4(+)/ Lin(-)CD45(-) cells, featuring morphological, molecular, and phenotypic characteristics of very small embryonic-like (VSEL) stem cells

The Phoenix of stem cells: pluripotent cells in adult tissues and peripheral blood

Pluripotent stem cells are defined as cells that can generate cells of lineages from all three germ layers, ectoderm, mesoderm, and endoderm. On the contrary, unipotent and multipotent stem cells develop into one or more cell types respectively, but their differentiation is limited to the cells present in the tissue of origin or, at most, from the same germ layer. Multipotent and unipotent stem cells have been isolated from a variety of adult tissues, Instead, the presence in adult tissues of pluripotent stem cells is a very debated issue. In the early embryos, all cells are pluripotent. In mammalians, after birth, pluripotent cells are maintained in the bone-marrow and possibly in gonads. In fact, pluripotent cells were isolated from marrow aspirates and cord blood and from cultured bone-marrow stromal cells (MSCs). Only in few cases, pluripotent cells were isolated from other tissues. In addition to have the potential to differentiate toward lineages derived from all three germ layers, the isolated pluripotent cells shared other properties, including the expression of cell surface stage specific embryonic antigen (SSEA) and of transcription factors active in the early embryos, but they were variously described and named. However, it is likely that they are part of the same cell population and that observed diversities were the results of different isolation and expansion strategies. Adult pluripotent stem cells are quiescent and self-renew at very low rate. They are maintained in that state under the influence of the "niche" inside which they are located. Any tissue damage causes the release in the blood of inflammatory cytokines and molecules that activate the stem cells and their mobilization and homing in the injured tissue. The inflammatory response could also determine the dedifferentiation of mature cells and their reversion to a progenitor stage and at the same time stimulate the progenitors to proliferate and differentiate to replace the damaged cells. In this review we rate articles reporting isolation and characterization of tissue resident pluripotent cells. In the attempt to reconcile observations made by different authors, we propose a unifying picture that could represent a starting point for future experiments.

Stem Cells and Organs-on-chips: New Promising Technologies for Human Infertility Treatment

Having biological children remains an unattainable dream for most couples with reproductive failure or gonadal dysgenesis. The combination of stem cells with gene editing technology and organ-on-a-chip models provides a unique opportunity for infertile patients with impaired gametogenesis caused by congenital disorders in sex development or cancer survivors. But how will these technologies overcome human infertility? This review discusses the regenerative mechanisms, applications, and advantages of different types of stem cells for restoring gametogenesis in infertile patients, as well as major challenges that must be overcome before clinical application. The importance and limitations of in vitro generation of gametes from patient-specific human-induced pluripotent stem cells (hiPSCs) will be discussed in the context of human reproduction. The potential role of organ-on-a-chip models that can direct differentiation of hiPSC-derived primordial germ cell-like cells to gametes and other reproductive organoids is also explored. These rapidly evolving technologies provide prospects for improving fertility to individuals and couples who experience reproductive failure.

Industrialized GMP Production of CD34+ Cells (ProtheraCytes®) at Clinical Scale for Treatment of Ischemic Cardiac Diseases Is Feasible and Safe

Regenerative medicine now needs to pass a crucial turning point, from academic research to the market. Several sources/types of cells have been experimented with, more or less successfully. CD34⁺ cells have demonstrated multipotent or even pluripotent capacities, making them good candidates for regenerative medicine, particularly for treating heart diseases. Strongly encouraged by the results we achieved in a pilot study using CD34⁺ stem cells in patients with poor-prognosis acute myocardial infarcts (AMIs), we soon began the development of an industrialized platform making use of a closed automated device (StemXpand^®) and a disposable kit (StemPack^®) for the large-scale expansion of CD34⁺ cells with reproducible good manufacturing practice (GMP). This scalable platform can produce expanded CD34⁺ cells (ProtheraCytes^®) of sufficient quality that, interestingly, express early markers of the cardiac and endothelial pathways and early cardiac-mesoderm markers. They also contain CD34⁺ pluripotent cells characterized as very small embryonic-like stem cells (VSELs), capable of differentiating under appropriate stimuli into different tissue lineages, including endothelial and cardiomyocytic ones.

Small blood stem cells for enhancing early osseointegration formation on dental implants: a human phase I safety study

Background

Small blood stem cells (SB cells), isolated from human peripheral blood, demonstrated the ability to benefit bone regeneration and osseointegration. The primary goal of our study is to examine the safety and tolerability of SB cells in dental implantation for human patients with severe bone defects.

Methods

Nine patients were enrolled and divided into three groups with SB cell treatment doses of 1 × 10⁵, 1 × 10⁶, and 1 × 10⁷ SB cells, and then evaluated by computed tomography (CT) scans to assess bone mineral density (BMD) by Hounsfield units (HU) scoring. Testing was conducted before treatment and on weeks 4, 6, 8, and 12 post dental implantation. Blood and comprehensive chemistry panel testing were also performed.

Results

No severe adverse effects were observed for up to 6-month trial. Grade 1 leukocytosis, anemia, and elevated liver function were observed, but related with the patient’s condition or the implant treatment itself and not the transplantation of SB cells. The levels of cytokines and chemokines were detected by a multiplex immunological assay. Elevated levels of eotaxin, FGF2, MCP-1, MDC, and IL17a were found among patients who received SB cell treatment. This observation suggested SB cells triggered cytokines and chemokines for local tissue repair. To ensure the efficacy of SB cells in dental implantation, the BMD and maximum stresses via stress analysis model were measured through CT scanning. All patients who suffered from severe bone defect showed improvement from D3 level to D1 or D2 level. The HU score acceleration can be observed by week 2 after guided bone regeneration (GBR) and prior to dental implantation.

Conclusions

This phase I study shows that treatment of SB cells for dental implantation is well tolerated with no major adverse effects. The use of SB cells for accelerating the osseointegration in high-risk dental implant patients warrants further phase II studies.

Trial registration

Taiwan Clinical Trial Registry (SB-GBR001) and clinical trial registry of the United States (NCT04451486).

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02461-z.

A Novel Type of Stem Cells Double-Positive for SSEA-3 and CD45 in Human Peripheral Blood

Peripheral blood (PB) contains several types of stem/progenitor cells, including hematopoietic stem and endothelial progenitor cells. We identified a population positive for both the pluripotent surface marker SSEA-3 and leukocyte common antigen CD45 that comprises 0.04% ± 0.003% of the mononuclear cells in human PB. The average size of the SSEA-3(+)/CD45(+) cells was 10.1 ± 0.3 µm and ∼22% were positive for CD105, a mesenchymal marker; ∼85% were positive for CD19, a B cell marker; and ∼94% were positive for HLA-DR, a major histocompatibility complex class II molecule relevant to antigen presentation. These SSEA-3(+)/CD45(+) cells expressed the pluripotency markers Nanog, Oct3/4, and Sox2, as well as sphingosine-1-phosphate (S1P) receptor 2, and migrated toward S1P, although their adherence and proliferative activities in vitro were low. They expressed NeuN at 7 d, Pax7 and desmin at 7 d, and alpha-fetoprotein and cytokeratin-19 at 3 d when supplied to mouse damaged tissues of the brain, skeletal muscle and liver, respectively, suggesting the ability to spontaneously differentiate into triploblastic lineages compatible to the tissue microenvironment. Multilineage-differentiating stress enduring (Muse) cells, identified as SSEA-3(+) in tissues such as the bone marrow and organ connective tissues, express pluripotency markers, migrate to sites of damage via the S1P-S1P receptor 2 system, and differentiate spontaneously into tissue-compatible cells after homing to the damaged tissue where they participate in tissue repair. After the onset of acute myocardial infarction and stroke, patients are reported to have an increase in the number of SSEA-3(+) cells in the PB. The SSEA-3(+)/CD45(+) cells in the PB showed similarity to tissue-Muse cells, although with difference in surface marker expression and cellular properties. Thus, these findings suggest that human PB contains a subset of cells that are distinct from known stem/progenitor cells, and that CD45(+)-mononuclear cells in the PB comprise a novel subpopulation of cells that express pluripotency markers.

Bone Marrow-Derived VSELs Engraft as Lung Epithelial Progenitor Cells after Bleomycin-Induced Lung Injury

BACKGROUND

Alveolar type 2 (AT2) cells and bronchioalveolar stem cells (BASC) perform critical regenerative functions in response to lung damage. Published data show that nonhematopoietic, bone marrow-derived "very small embryonic-like stem cells" (VSELs) can differentiate in vivo into surfactant protein C (SPC)-producing AT2 cells in the lung. Here, we test directly whether VSEL-derived BASC and AT2 cells function to produce differentiated progeny.

METHODS

using a reporter mouse in which the H2B-GFP fusion protein is driven from the murine SPC promoter, we tested whether bone marrow-derived VSELs or non-VSEL/nonhematopoietic stem cells (non-VSEL/non-HSCs) can differentiate into AT2 and BASC cells that function as progenitor cells. Immediately following bleomycin administration, WT recipient mice underwent intravenous administration of VSELs or non-VSEL/non-HSCs from SPC H2B-GFP mice. GFP+ AT2 and BASC were isolated and tested for progenitor activity using in vitro organoid assays.

RESULTS

after 21 days in vivo, we observed differentiation of VSELs but not non-VSEL/non-HSCs into phenotypic AT2 and BASC consistent with previous data in irradiated recipients. Subsequent in vitro organoid assays revealed that VSEL-derived AT2 and BASC maintained physiological potential for differentiation and self-renewal.

CONCLUSION

these findings prove that VSELs produce functional BASC and AT2 cells, and this may open new avenues using VSELs to develop effective cell therapy approaches for patients with lung injury.

Mesenchymal Stem Cell Transplantation for Ischemic Diseases: Mechanisms and Challenges

Ischemic diseases are conditions associated with the restriction or blockage of blood supply to specific tissues. These conditions can cause moderate to severe complications in patients, and can lead to permanent disabilities. Since they are blood vessel-related diseases, ischemic diseases are usually treated with endothelial cells or endothelial progenitor cells that can regenerate new blood vessels. However, in recent years, mesenchymal stem cells (MSCs) have shown potent bioeffects on angiogenesis, thus playing a role in blood regeneration. Indeed, MSCs can trigger angiogenesis at ischemic sites by several mechanisms related to their trans-differentiation potential. These mechanisms include inhibition of apoptosis, stimulation of angiogenesis via angiogenic growth factors, and regulation of immune responses, as well as regulation of scarring to suppress blood vessel regeneration when needed. However, preclinical and clinical trials of MSC transplantation in ischemic diseases have shown some limitations in terms of treatment efficacy. Such studies have emphasized the current challenges of MSC-based therapies. Treatment efficacy could be enhanced if the limitations were better understood and potentially resolved. This review will summarize some of the strategies by which MSCs have been utilized for ischemic disease treatment, and will highlight some challenges of those applications as well as suggesting some strategies to improve treatment efficacy.

Differential Expression of the Tetraspanin CD9 in Normal and Leukemic Stem Cells

Simple Summary

Before their use in regenerative medicine, stem cells need to be expanded to obtain sufficient cells for the efficient reparation of the injured tissues. This expansion must not affect their integrity. Regarding the role played by different receptors, we observed that, during their expansion, the number of promising pluripotent stem cells found in adult tissues, i.e., very small embryonic-like stem cells (VSELs), which express the CD9 receptor, decreased. This is due to their higher mortality rate compared to that of those not expressing CD9, which can lead to low regenerative efficiency for injured tissues. Interestingly, this could be overcome by the addition of a specific growth factor, allowing the re-establishment of their function. Finally, we found that the expression of this receptor is also deregulated in cells phenotypically identical to VSELs isolated from leukemic patients, which attests to the instability of its expression and may explain disease progression.

Abstract

CD9 plays a crucial role in cellular growth, mobility, and signal transduction, as well as in hematological malignancy. In myeloid neoplasms, CD9 is involved in the altered interactions between leukemic and stromal cells. However, apart from its role in CD34⁺ progenitors and myeloid and megakaryocytic differentiation, its function in normal and leukemic pluripotent cells has not yet been determined. Very small embryonic-like stem cells (VSELs) are promising pluripotent stem cells found in adult tissues that can be developed for safe and efficient regenerative medicine. VSELs express different surface receptors of the highest importance in cell functioning, including CD9, and can be effectively mobilized after organ injury or in leukemic patients. In the present study, we observed that CD9 is among the most expressed receptors in VSELs under steady-state conditions; however, once the VSELs are expanded, CD9⁺ VSELs decrease and are more apoptotic. CD9^– VSELs had no proliferative improvement in vitro compared to those that were CD9⁺. Interestingly, the addition of SDF-1 induced CD9 expression on the surface of VSELs, as observed by flow cytometry, and improved their migration. In addition, we observed, in the phenotypically identical VSELs present in the peripheral blood of patients with myeloproliferative neoplasms, compared to healthy subjects, a significantly higher number of CD9⁺ cells. However, in their hematopoietic stem cell (HSC) counterparts, the expression remained comparable. These results indicate that, likewise, in progenitors and mature cells, CD9 may play an important function in normal and malignant VSELs. This could explain the refractoriness observed by some groups of expanded stem cells to repairing efficiently damaged tissue when used as a source in cell therapies. Understanding the function of the CD9 receptor in normal and malignant CD34⁺ and VSELs, along with its relationship with the CXCR4/SDF-1 pathway, will enable advances in the field of adult pluripotent cell usage in regenerative medicine and in their role in leukemia.

Potential Mechanisms and Perspectives in Ischemic Stroke Treatment Using Stem Cell Therapies

Ischemic stroke (IS) remains one of the major causes of death and disability due to the limited ability of central nervous system cells to regenerate and differentiate. Although several advances have been made in stroke therapies in the last decades, there are only a few approaches available to improve IS outcome. In the acute phase of IS, mechanical thrombectomy and the administration of tissue plasminogen activator have been widely used, while aspirin or clopidogrel represents the main therapy used in the subacute or chronic phase. However, in most cases, stroke patients fail to achieve satisfactory functional recovery under the treatments mentioned above. Recently, cell therapy, especially stem cell therapy, has been considered as a novel and potential therapeutic strategy to improve stroke outcome through mechanisms, including cell differentiation, cell replacement, immunomodulation, neural circuit reconstruction, and protective factor release. Different stem cell types, such as mesenchymal stem cells, marrow mononuclear cells, and neural stem cells, have also been considered for stroke therapy. In recent years, many clinical and preclinical studies on cell therapy have been carried out, and numerous results have shown that cell therapy has bright prospects in the treatment of stroke. However, some cell therapy issues are not yet fully understood, such as its optimal parameters including cell type choice, cell doses, and injection routes; therefore, a closer relationship between basic and clinical research is needed. In this review, the role of cell therapy in stroke treatment and its mechanisms was summarized, as well as the function of different stem cell types in stroke treatment and the clinical trials using stem cell therapy to cure stroke, to reveal future insights on stroke-related cell therapy, and to guide further studies.

Characterization and Isolation of Very Small Embryonic-like (VSEL) Stem Cells Obtained from Various Human Hematopoietic Cell Sources

Stem cell transplantation is one of the available treatments for leukemia, lymphoma, hereditary blood diseases and bone marrow failure. Bone marrow (BM), peripheral blood progenitor cells (PBPC), and cord blood (CB) are the predominant sources of stem cells. Recently a new type of stem cell with a pluripotent potential has been identified. These cells were named "very small embryonic like stem cells (VSELs)". It is claimed that VSEL stem cells can be found in adult BM, peripheral blood (PB), CB and other body tissues. This study is designed to characterize and isolate VSEL stem cells from different human hematopoietic sources; CB, PB and apheresis material (PBPC). VSEL stem cells were isolated from MNC and erythrocyte layers for all materials by using centrifugation and ficoll gradient method. We determined embryonic markers by flow cytometry, immunofluorescence and western blotting methods. Results from western blotting and immunofluorescence show high level of NANOG and OCT4 protein expression in PB, apheresis material and CB. Immunofluorescence images showed cytoplasmic and nuclear presence of these proteins. Flow cytometry results exhibited a higher expression of VSELs markers on debris area than CD45- population and higher expression on CB than PB. As a result, these findings have shown that it is necessary to investigate the function of pluripotent stem cell markers in differentiated adult cells. We further conclude that erythrocyte lysis method had the highest cell recovery amount among erythrocyte lysis and ficoll gradient methods. Consequently, this study gives us new information and viewpoints about expression of pluripotent stem cell (PSC) markers in adult tissues.

Key Success Factors for Regenerative Medicine in Acquired Heart Diseases

Stem cell therapy offers a breakthrough opportunity for the improvement of ischemic heart diseases. Numerous clinical trials and meta-analyses appear to confirm its positive but variable effects on heart function. Whereas these trials widely differed in design, cell type, source, and doses reinjected, cell injection route and timing, and type of cardiac disease, crucial key factors that may favour the success of cell therapy emerge from the review of their data. Various types of cell have been delivered. Injection of myoblasts does not improve heart function and is often responsible for severe ventricular arrythmia occurrence. Using bone marrow mononuclear cells is a misconception, as they are not stem cells but mainly a mix of various cells of hematopoietic lineages and stromal cells, only containing very low numbers of cells that have stem cell-like features; this likely explain the neutral results or at best the modest improvement in heart function reported after their injection. The true existence of cardiac stem cells now appears to be highly discredited, at least in adults. Mesenchymal stem cells do not repair the damaged myocardial tissue but attenuate post-infarction remodelling and contribute to revascularization of the hibernated zone surrounding the scar. CD34+ stem cells - likely issued from pluripotent very small embryonic-like (VSEL) stem cells - emerge as the most convincing cell type, inducing structural and functional repair of the ischemic myocardial area, providing they can be delivered in large amounts via intra-myocardial rather than intra-coronary injection, and preferentially after myocardial infarct rather than chronic heart failure.

The Blood Circulating Rare Cell Population. What is it and What is it Good For?

Blood contains a diverse cell population of low concentration hematopoietic as well as non-hematopoietic cells. The majority of such rare cells may be bone marrow-derived progenitor and stem cells. This paucity of circulating rare cells, in particular in the peripheral circulation, has led many to believe that bone marrow as well as other organ-related cell egress into the circulation is a response to pathological conditions. Little is known about this, though an increasing body of literature can be found suggesting commonness of certain rare cell types in the peripheral blood under physiological conditions. Thus, the isolation and detection of circulating rare cells appears to be merely a technological problem. Knowledge about rare cell types that may circulate the blood stream will help to advance the field of cell-based liquid biopsy by supporting inter-platform comparability, making use of biological correct cutoffs and “mining” new biomarkers and combinations thereof in clinical diagnosis and therapy. Therefore, this review intends to lay ground for a comprehensive analysis of the peripheral blood rare cell population given the necessity to target a broader range of cell types for improved biomarker performance in cell-based liquid biopsy.

Role of Adult Tissue-Derived Pluripotent Stem Cells in Bone Regeneration

Background

Bone marrow-derived mononuclear cells (BM-MNC) consist of a heterogeneous mix of mesenchymal stem cells (MSC), hematopoietic progenitor cells (HPC), endothelial progenitor cells (EPC), monocytes, lymphocytes and pluripotent stem cells. Whereas the importance of MSC and EPC has been well documented in bone healing and regeneration studies, the role of pluripotent stem cells is still poorly understood. In the present study we evaluated if and how Very Small Embryonic Like cells (VSEL), isolated from rat BM-MNC, contribute to bone healing.

Methods

Large bone defects were made in the femurs of 38 Sprague Dawley female rats and treated with β-TCP scaffold granules seeded with male VSEL; BM-MNC, VSEL-depleted BM-MNC or scaffold alone, and bone healing was evaluated at 8 weeks post-surgery.

Results

Bone healing was significantly increased in defects treated with VSEL and BM-MNC, compared to defects treated with VSEL-depleted BM-MNC. Donor cells were detected in new bone tissue, in all the defects treated with cells, and in fibrous tissue only in defects treated with VSEL-depleted BM-MNC. The number of CD68+ cells was the highest in the VSEL-depleted group, whereas the number of TRAP positive cells was the lowest in this group.

Conclusions

Based on the results, we can conclude that VSEL play a role in BM-MNC induced bone formation. In our rat femur defect model, in defects treated with VSEL-depleted BM-MNC, osteoclastogenesis and bone formation were decreased, and foreign body reaction was increased.

Similar Population of CD133+ and DDX4+ VSEL-Like Stem Cells Sorted from Human Embryonic Stem Cell, Ovarian, and Ovarian Cancer Ascites Cell Cultures: The Real Embryonic Stem Cells?

A population of small stem cells with diameters of up to 5 μm resembling very small embryonic-like stem cells (VSELs) were sorted from human embryonic stem cell (hESC) cultures using magnetic-activated cell sorting (MACS) based on the expression of a stem-cell-related marker prominin-1 (CD133). These VSEL-like stem cells had nuclei that almost filled the whole cell volume and expressed stem-cell-related markers (CD133, SSEA-4) and markers of germinal lineage (DDX4/VASA, PRDM14). They were comparable to similar populations of small stem cells sorted from cell cultures of normal ovaries and were the predominant cells in ascites of recurrent ovarian cancer. The sorted populations of CD133+ VSEL-like stem cells were quiescent in vitro, except for ascites, and were highly activated after exposure to valproic acid and follicle-stimulating hormone (FSH), indicating a new tool to study these cells in vitro. These VSEL-like stem cells spontaneously formed clusters resembling tumour-like structures or grew into larger, oocyte-like cells and were differentiated in vitro into adipogenic, osteogenic and neural lineages after sorting. We propose the population of VSEL-like stem cells from hESC cultures as potential original embryonic stem cells, which are present in the human embryo, persist in adult human ovaries from the embryonic period of life and are involved in cancer manifestation.

Autologous activated platelet-rich plasma injection into adult human ovary tissue: molecular mechanism, analysis, and discussion of reproductive response

In clinical infertility practice, one intractable problem is low (or absent) ovarian reserve which in turn reflects the natural oocyte depletion associated with advancing maternal age. The number of available eggs has been generally thought to be finite and strictly limited, an entrenched and largely unchallenged tenet dating back more than 50 years. In the past decade, it has been suggested that renewable ovarian germline stem cells (GSCs) exist in adults, and that such cells may be utilized as an oocyte source for women seeking to extend fertility. Currently, the issue of whether mammalian females possess such a population of renewable GSCs remains unsettled. The topic is complex and even agreement on a definitive approach to verify the process of 'ovarian rescue' or 're-potentiation' has been elusive. Similarities have been noted between wound healing and ovarian tissue repair following capsule rupture at ovulation. In addition, molecular signaling events which might be necessary to reverse the effects of reproductive ageing seem congruent with changes occurring in tissue injury responses elsewhere. Recently, clinical experience with such a technique based on autologous activated platelet-rich plasma (PRP) treatment of the adult human ovary has been reported. This review summarizes the present state of understanding of the interaction of platelet-derived growth factors with adult ovarian tissue, and the outcome of human reproductive potential following PRP treatment.

Stem cells in Osteoporosis: From Biology to New Therapeutic Approaches

Osteoporosis is a systemic disease that affects the skeleton, causing reduction of bone density and mass, resulting in destruction of bone microstructure and increased risk of bone fractures. Since osteoporosis is a disease affecting the elderly and the aging of the world's population is constantly increasing, it is expected that the incidence of osteoporosis and its financial burden on the insurance systems will increase continuously and there is a need for more understanding this condition in order to prevent and/or treat it. At present, available drug therapy for osteoporosis primarily targets the inhibition of bone resorption and agents that promote bone mineralization, designed to slow disease progression. Safe and predictable pharmaceutical means to increase bone formation have been elusive. Stem cell therapy of osteoporosis, as a therapeutic strategy, offers the promise of an increase in osteoblast differentiation and thus reversing the shift towards bone resorption in osteoporosis. This review is focused on the current views regarding the implication of the stem cells in the cellular and physiologic mechanisms of osteoporosis and discusses data obtained from stem cell-based therapies of osteoporosis in experimental animal models and the possibility of their future application in clinical trials.

Prolonged Growth Hormone/Insulin/Insulin-like Growth Factor Nutrient Response Signaling Pathway as a Silent Killer of Stem Cells and a Culprit in Aging

The dream of slowing down the aging process has always inspired mankind. Since stem cells are responsible for tissue and organ rejuvenation, it is logical that we should search for encoded mechanisms affecting life span in these cells. However, in adult life the hierarchy within the stem cell compartment is still not very well defined, and evidence has accumulated that adult tissues contain rare stem cells that possess a broad trans-germ layer differentiation potential. These most-primitive stem cells-those endowed with pluripotent or multipotent differentiation ability and that give rise to other cells more restricted in differentiation, known as tissue-committed stem cells (TCSCs) - are of particular interest. In this review we present the concept supported by accumulating evidence that a population of so-called very small embryonic-like stem cells (VSELs) residing in adult tissues positively impacts the overall survival of mammals, including humans. These unique cells are prevented in vertebrates from premature depletion by decreased sensitivity to growth hormone (GH), insulin (INS), and insulin-like growth factor (IGF) signaling, due to epigenetic changes in paternally imprinted genes that regulate their resistance to these factors. In this context, we can envision nutrient response GH/INS/IGF signaling pathway as a lethal factor for these most primitive stem cells and an important culprit in aging.

A Novel View of the Adult Stem Cell Compartment From the Perspective of a Quiescent Population of Very Small Embryonic-Like Stem Cells

Evidence has accumulated that adult hematopoietic tissues and other organs contain a population of dormant stem cells (SCs) that are more primitive than other, already restricted, monopotent tissue-committed SCs (TCSCs). These observations raise several questions, such as the developmental origin of these cells, their true pluripotent or multipotent nature, which surface markers they express, how they can be efficiently isolated from adult tissues, and what role they play in the adult organism. The phenotype of these cells and expression of some genes characteristic of embryonic SCs, epiblast SCs, and primordial germ cells suggests their early-embryonic deposition in developing tissues as precursors of adult SCs. In this review, we will critically discuss all these questions and the concept that small dormant SCs related to migratory primordial germ cells, described as very small embryonic-like SCs, are deposited during embryogenesis in bone marrow and other organs as a backup population for adult tissue-committed SCs and are involved in several processes related to tissue or organ rejuvenation, aging, and cancerogenesis. The most recent results on successful ex vivo expansion of human very small embryonic-like SC in chemically defined media free from feeder-layer cells open up new and exciting possibilities for their application in regenerative medicine.

Delineating the effects of 5-fluorouracil and follicle-stimulating hormone on mouse bone marrow stem/progenitor cells

Background

Pluripotent, Lin^–/CD45^–/Sca-1⁺ very small embryonic-like stem cells (VSELs) in mouse bone marrow (BM) are resistant to total body radiation because of their quiescent nature, whereas Lin^–/CD45⁺/Sca-1⁺ hematopoietic stem cells (HSCs) get eliminated. In the present study, we provide further evidence for the existence of VSELs in mouse BM and have also examined the effects of a chemotherapeutic agent (5-fluorouracil (5-FU)) and gonadotropin hormone (follicle-stimulating hormone (FSH)) on BM stem/progenitor cells.

Methods

VSELs and HSCs were characterized in intact BM. Swiss mice were injected with 5-FU (150 mg/kg) and sacrificed on 2, 4, and 10 days (D2, D4, and D10) post treatment to examine changes in BM histology and effects on VSELs and HSCs by a multiparametric approach. The effect of FSH (5 IU) administered 48 h after 5-FU treatment was also studied. Bromodeoxyuridine (BrdU) incorporation, cell cycle analysis, and colony-forming unit (CFU) assay were carried out to understand the functional potential of stem/progenitor cells towards regeneration of chemoablated marrow.

Results

Nuclear OCT-4, SCA-1, and SSEA-1 coexpressing LIN^–/CD45^– VSELs and slightly larger LIN^–/CD45⁺ HSCs expressing cytoplasmic OCT-4 were identified and comprised 0.022 ± 0.002 % and 0.081 ± 0.004 % respectively of the total cells in BM. 5-FU treatment resulted in depletion of cells with a 7-fold reduction by D4 and normal hematopoiesis was re-established by D10. Nuclear OCT-4 and PCNA-positive VSELs were detected in chemoablated bone sections near the endosteal region. VSELs remained unaffected by 5-FU on D2 and increased on D4, whereas HSCs showed a marked reduction in numbers on D2 and later increased along with the corresponding increase in BrdU uptake and upregulation of specific transcripts (Oct-4A, Oct-4, Sca-1, Nanog, Stella, Fragilis, Pcna). Cells that survived 5-FU formed colonies in vitro. Both VSELs and HSCs expressed FSH receptors and FSH treatment enhanced hematopoietic recovery by 72 h.

Conclusion

Both VSELs and HSCs were activated in response to the stress created by 5-FU and FSH enhanced hematopoietic recovery by at least 72 h in 5-FU-treated mice. VSELs are the most primitive pluripotent stem cells in BM that self-renew and give rise to HSCs under stress, and HSCs further divide rapidly and differentiate to maintain homeostasis. The study provides a novel insight into basic hematopoiesis and has clinical relevance.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0311-6) contains supplementary material, which is available to authorized users.

Identification of New Rat Bone Marrow-Derived Population of Very Small Stem Cell with Oct-4A and Nanog Expression by Flow Cytometric Platforms

Very small embryonic-like stem cells (VSELs) represent a unique rare population of adult stem cells (SCs) sharing several structural, genetic, biochemical, and functional properties with embryonic SCs and have been identified in several adult murine and human tissues. However, rat bone marrow- (BM-) derived SCs closely resembling murine or human VSELs have not been described. Thus, we employed multi-instrumental flow cytometric approach including classical and imaging cytometry and we established that newly identified population of nonhematopoietic cells expressing CD106 (VCAM-I) antigen contains SCs with very small size, expressing markers of pluripotency (Oct-4A and Nanog) on both mRNA and protein levels that indicate VSEL population. Based on our experience in both murine and human VSEL isolation procedures by fluorescence-activated cell sorting (FACS), we also optimized sorting protocol for separation of CD45⁻/Lin⁻/CD106⁺ rat BM-derived VSELs from wild type and eGFP-expressing rats, which are often used as donor animals for cell transplantations in regenerative studies in vivo. Thus, this is a first study identifying multiantigenic phenotype and providing sorting protocols for isolation VSELs from rat BM tissue for further examining of their functional properties in vitro as well as regenerative capacity in distinct in vivo rat models of tissue injury.

Human Very Small Embryonic-Like Stem Cells Are Present in Normal Peripheral Blood of Young, Middle-Aged, and Aged Subjects

The purpose of our study was to determine whether the number of human very small embryonic-like stem cells (huVSELs) would vary depending on the age of humans. HuVSELs frequency was evaluated into the steady-state (SS) peripheral blood (PB) of healthy volunteers using flow cytometry analysis. Their numbers were compared with volunteers' age. Blood samples were withdrawn from 28 volunteers (age ranging from 20 to 70 years), who were distributed among three groups of age: “young” (mean age, 27.8 years), “middle” (mean age, 49 years), and “older” (mean age, 64.2 years). Comparing the three groups, we did not observe any statistically significant difference in huVSELs numbers between them. The difference in mRNA expression for PSC markers as SSEA-4, Oct-4, Nanog, and Sox2 between the three groups of age was not statistically significant. A similar frequency of huVSELs into the SS-PB of young, middle-aged, and aged subjects may indicate that the VSELs pool persists all along the life as a reserve for tissue repair in case of minor injury and that there is a continuous efflux of these cells from the BM into the PB.

Making gametes from pluripotent stem cells--a promising role for very small embryonic-like stem cells

The urge to have one's own biological child supersedes any desire in life. Several options have been used to obtain gametes including pluripotent stem cells (embryonic ES and induced pluripotent iPS stem cells); gonadal stem cells (spermatogonial SSCs, ovarian OSCs stem cells), bone marrow, mesenchymal cells and fetal skin. However, the field poses a huge challenge including inefficient existing protocols for differentiation, epigenetic and genetic changes associated with extensive in vitro manipulation and also ethical/regulatory constraints. A tremendous leap in the field occurred using mouse ES and iPS cells wherein they were first differentiated into epiblast-like cells and then primordial germ cell-like cells. These on further development produced sperm, oocytes and live offspring (had associated genetic problems). Evidently differentiating pluripotent stem cells into primordial germ cells (PGCs) remains a major bottleneck. Against this backdrop, we propose that a novel population of pluripotent stem cells termed very small embryonic-like stem cells (VSELs) may serve as an alternative, potential source of autologus gametes, keeping in mind that they are indeed PGCs surviving in adult mammalian ovaries and testes. Both VSELs and PGCs are pluripotent, relatively quiescent because of epigenetic modifications of parentally imprinted genes loci like Igf2-H19 and KCNQ1p57, share several markers like Stella, Fragilis, Mvh, Dppa2, Dppa4, Sall4, Blimp1 and functional receptors. VSELs are localized in the basement membrane of seminiferous tubules in testis and in the ovary surface epithelium. Ovarian stem cells from mouse, rabbit, sheep, marmoset and humans (menopausal women and those with premature ovarian failure) spontaneously differentiate into oocyte-like structures in vitro with no additional requirement of growth factors. Thus a more pragmatic option to obtain autologus gametes may be the pluripotent VSELs and if we could manipulate them in vivo - existing ethical and epigenetic/genetic concerns associated with in vitro culture may also be minimized. The field of oncofertility may undergo a sea-change and existing strategies of cryopreservation of gametes and gonadal tissue for fertility preservation in cancer patients will necessitate a revision. However, first the scientific community needs to arrive at a consensus about VSELs in the gonads and then work towards exploiting their potential.

Expression and differentiation between OCT4A and its Pseudogenes in human ESCs and differentiated adult somatic cells

The POU5F1 gene codes for the OCT4 transcription factor, which is one of the key regulators of pluripotency. Its transcription, alternative splicing, and alternative translation leading to the synthesis of the active, nuclear localized OCT4A has been described in detail. Much less, however, is known about actively transcribed OCT4 pseudogenes, several of which display high homology to OCT4A and can be expressed and translated into proteins. Using RT-PCR followed by pseudogene-specific restriction digestion, cloning, and sequencing we discriminate between OCT4A and transcripts for pseudogenes 1, 3 and 4. We show that expression of OCT4 and its pseudogenes follows a developmentally-regulated pattern in differentiating hESCs, indicating a tight regulatory relationship between them. We further demonstrate that differentiated human cells from a variety of tissues express exclusively pseudogenes. Expression of OCT4A can, however be triggered in adult differentiated cells by oxygen and FGF2-dependent mechanisms.

Human and murine very small embryonic-like cells represent multipotent tissue progenitors, in vitro and in vivo

The purpose of this study was to determine the lineage progression of human and murine very small embryonic-like (HuVSEL or MuVSEL) cells in vitro and in vivo. In vitro, HuVSEL and MuVSEL cells differentiated into cells of all three embryonic germ layers. HuVSEL cells produced robust mineralized tissue of human origin compared with controls in calvarial defects. Immunohistochemistry demonstrated that the HuVSEL cells gave rise to neurons, adipocytes, chondrocytes, and osteoblasts within the calvarial defects. MuVSEL cells were also able to differentiate into similar lineages. First round serial transplants of MuVSEL cells into irradiated osseous sites demonstrated that ∼60% of the cells maintained their VSEL cell phenotype while other cells differentiated into multiple tissues at 3 months. Secondary transplants did not identify donor VSEL cells, suggesting limited self renewal but did demonstrate VSEL cell derivatives in situ for up to 1 year. At no point were teratomas identified. These studies show that VSEL cells produce multiple cellular structures in vivo and in vitro and lay the foundation for future cell-based regenerative therapies for osseous, neural, and connective tissue disorders.

Antidepressant fluoxetine and its potential against colon tumors

Colon cancer is one of the most common tumors worldwide, with increasing incidence in developing countries. Patients treated with fluoxetine (FLX) have a reduced incidence of colon cancer, although there still remains great controversy about the nature of its effects. Here we explore the latest achievements related to FLX treatment and colon cancer. Moreover, we discuss new ideas about the mechanisms of the effects of FLX treatment in colon cancer. This leads to the hypothesis of FLX arresting colon tumor cells at the at G₁ cell-cycle phase through a control of the tumor-related energy generation machinery. We believe that the potential of FLX to act against tumor metabolism warrants further investigation.

The proper criteria for identification and sorting of very small embryonic-like stem cells, and some nomenclature issues

Evidence has accumulated that both murine and human adult tissues contain early-development stem cells with a broader differentiation potential than other adult monopotent stem cells. These cells, being pluripotent or multipotent, exist at different levels of specification and most likely represent overlapping populations of cells that, depending on the isolation strategy, ex vivo expansion protocol, and markers employed for their identification, have been given different names. In this review, we will discuss a population of very small embryonic-like stem cells (VSELs) in the context of other stem cells that express pluripotent/multipotent markers isolated from adult tissues as well as review the most current, validated working criteria on how to properly identify and isolate these very rare cells. VSELs have been successfully purified in several laboratories; however, a few have failed to isolate them, which has raised some unnecessary controversy in the field. Therefore, in this short review, we will address the most important reasons that some investigators have experienced problems in isolating these very rare cells and discuss some still unresolved challenges which should be overcome before these cells can be widely employed in the clinic.

Very small embryonic-like stem-cell optimization of isolation protocols: an update of molecular signatures and a review of current in vivo applications

As the theory of stem cell plasticity was first proposed, we have explored an alternative hypothesis for this phenomenon: namely that adult bone marrow (BM) and umbilical cord blood (UCB) contain more developmentally primitive cells than hematopoietic stem cells (HSCs). In support of this notion, using multiparameter sorting we were able to isolate small Sca1(+)Lin(-)CD45(-) cells and CD133(+)Lin(-)CD45(-) cells from murine BM and human UCB, respectively, which were further enriched for the detection of various early developmental markers such as the SSEA antigen on the surface and the Oct4 and Nanog transcription factors in the nucleus. Similar populations of cells have been found in various organs by our team and others, including the heart, brain and gonads. Owing to their primitive cellular features, such as the high nuclear/cytoplasm ratio and the presence of euchromatin, they are called very small embryonic-like stem cells (VSELs). In the appropriate in vivo models, VSELs differentiate into long-term repopulating HSCs, mesenchymal stem cells (MSCs), lung epithelial cells, cardiomyocytes and gametes. In this review, we discuss the most recent data from our laboratory and other groups regarding the optimal isolation procedures and describe the updated molecular characteristics of VSELs.

Very small embryonic-like stem cells (VSELs) represent a real challenge in stem cell biology: recent pros and cons in the midst of a lively debate

The concept that adult tissue, including bone marrow (BM), contains early-development cells with broader differentiation potential has again been recently challenged. In response, we would like to review the accumulated evidence from several independent laboratories that adult tissues, including BM, harbor a population of very rare stem cells that may cross germ layers in their differentiation potential. Thus, the BM stem cell compartment hierarchy needs to be revisited. These dormant, early-development cells that our group described as very small embryonic-like stem cells (VSELs) most likely overlap with similar populations of stem cells that have been identified in adult tissues by other investigators as the result of various experimental strategies and have been given various names. As reported, murine VSELs have some pluripotent stem cell characteristics. Moreover, they display several epiblast/germline markers that suggest their embryonic origin and developmental deposition in adult BM. Moreover, at the molecular level, changes in expression of parentally imprinted genes (for example, Igf2–H19) and resistance to insulin/insulin-like growth factor signaling (IIS) regulates their quiescent state in adult tissues. In several emergency situations related to organ damage, VSELs can be activated and mobilized into peripheral blood, and in appropriate animal models they contribute to tissue organ/regeneration. Interestingly, their number correlates with lifespan in mice, and they may also be involved in some malignancies. VSELs have been successfully isolated in several laboratories; however, some investigators experience problems with their isolation.

Do pluripotent stem cells exist in adult mice as very small embryonic stem cells?

Very small embryonic-like stem cells (VSELs) isolated from bone marrow (BM) have been reported to be pluripotent. Given their nonembryonic source, they could replace blastocyst-derived embryonic stem cells in research and medicine. However, their multiple-germ-layer potential has been incompletely studied. Here, we show that we cannot find VSELs in mouse BM with any of the reported stem cell potentials, specifically for hematopoiesis. We found that: (1) most events within the "VSEL" flow-cytometry gate had little DNA and the cells corresponding to these events (2) could not form spheres, (3) did not express Oct4, and (4) could not differentiate into blood cells. These results provide a failure to confirm the existence of pluripotent VSELs.

Stem cell recruitment after injury: lessons for regenerative medicine

Tissue repair and regeneration are thought to involve resident cell proliferation as well as the selective recruitment of circulating stem and progenitor cell populations through complex signaling cascades. Many of these recruited cells originate from the bone marrow, and specific subpopulations of bone marrow cells have been isolated and used to augment adult tissue regeneration in preclinical models. Clinical studies of cell-based therapies have reported mixed results, however, and a variety of approaches to enhance the regenerative capacity of stem cell therapies are being developed based on emerging insights into the mechanisms of progenitor cell biology and recruitment following injury. This article discusses the function and mechanisms of recruitment of important bone marrow-derived stem and progenitor cell populations following injury, as well as the emerging therapeutic applications targeting these cells.

Small SSEA-4-positive cells from human ovarian cell cultures: related to embryonic stem cells and germinal lineage?

Background

It has already been found that very small embyronic-like stem cells (VSELs) are present in adult human tissues and organs. The aim of this study was to find if there exists any similar population of cells in cell cultures of reproductive tissues and embryonic stem cells, and if these cells have any relation to pluripotency and germinal lineage.

Methods and results

Here we report that a population of small SSEA-4-positive cells with diameters of up to 4 μm was isolated by fluorescence-activated cell sorting (FACS) from the human ovarian cell cultures after enzymatic degradation of adult cortex tissues. These small cells – putative ovarian stem cells – were also observed during cell culturing of up to 6 months and more. In general, small putative ovarian stem cells, isolated by FACS, showed a relatively low gene expression profile when compared to human embryonic stem cells (hESCs) and human adult fibroblasts; this may reflect the quiescent state of these cells. In spite of that, small putative ovarian stem cells expressed several genes related to primordial germ cells (PGCs), pluripotency and germinal lineage, including VASA. The PGC-related gene PRDM1 was strongly expressed in small putative ovarian stem cells; in both hESCs and fibroblasts it was significantly down-regulated. In addition, putative ovarian stem cells expressed other PGC-related genes, such as PRDM14 and DPPA3. Most of the pluripotency and germinal lineage-related genes were up-regulated in hESCs (except VASA). When compared to fibroblasts, there were several pluripotency-related genes, which were up-regulated in small putative ovarian stem cells. Similar populations of small cells were also isolated by FACS from human testicular and hESC cultures.

Conclusions

Our results confirm the potential embryonic-like character of small putative stem cells isolated from human adult ovaries and their possible relation to germinal lineage.

Very small embryonic-like cells: biology and function of these potential endogenous pluripotent stem cells in adult tissues

Very small embryonic-like cells (VSELs), found in murine bone marrow and other adult tissues, are small, non-hematopoietic cells expressing markers of pluripotent embryonic and primordial germ cells. A similar cell type in humans has begun to be characterized, though with a slightly different phenotype and surface markers. Consistent with expression of pluripotency genes, murine VSELs differentiate into cell types from three germ-layer lineages in vitro, though pluripotency has yet to be shown at the single-cell level or in vivo. VSELs appear to be quiescent under steady state conditions, apparently due to partially erased imprinting and overexpression of cell cycle inhibitory genes. In vivo, VSELs can enter the cell cycle under stress conditions, but which factors regulate quiescence versus proliferation and self-renewal versus differentiation are as yet unknown, and in vitro conditions that induce proliferation and self-renewal have yet to be defined. Future experiments are needed to address whether a VSEL niche actively regulates quiescence in vivo or quiescence is cell autonomous under steady state conditions. Insights into these mechanisms may help to address whether or not VSELs could play a role in regenerative medicine in the future.

Isolation of small SSEA-4-positive putative stem cells from the ovarian surface epithelium of adult human ovaries by two different methods

The adult ovarian surface epithelium has already been proposed as a source of stem cells and germinal cells in the literature, therefore it has been termed the “germinal epithelium”. At present more studies have confirmed the presence of stem cells expressing markers of pluripotency in adult mammalian ovaries, including humans. The aim of this study was to isolate a population of stem cells, based on the expression of pluripotency-related stage-specific embryonic antigen-4 (SSEA-4) from adult human ovarian surface epithelium by two different methods: magnetic-activated cell sorting and fluorescence-activated cell sorting. Both methods made it possible to isolate a similar, relatively homogenous population of small, SSEA-4-positive cells with diameters of up to 4 μm from the suspension of cells retrieved by brushing of the ovarian cortex biopsies in reproductive-age and postmenopausal women and in women with premature ovarian failure. The immunocytochemistry and genetic analyses revealed that these small cells—putative stem cells—expressed some primordial germ cell and pluripotency-related markers and might be related to the in vitro development of oocyte-like cells expressing some oocyte-specific transcription factors in the presence of donated follicular fluid with substances important for oocyte growth and development. The stemness of these cells needs to be further researched.

Antiproliferative effects of fluoxetine on colon cancer cells and in a colonic carcinogen mouse model

The antidepressant fluoxetine has been under discussion because of its potential influence on cancer risk. It was found to inhibit the development of carcinogen-induced preneoplastic lesions in colon tissue, but the mechanisms of action are not well understood. Therefore, we investigated anti-proliferative effects, and used HT29 colon tumor cells in vitro, as well as C57BL/6 mice exposed to intra-rectal treatment with the carcinogen N-methyl-N’-nitro-N-nitrosoguanidine (MNNG) as models. Fluoxetine increased the percentage of HT29 cells in the G₀/G₁ phase of cell-cycle, and the expression of p27 protein. This was not related to an induction of apoptosis, reactive oxygen species or DNA damage. In vivo, fluoxetine reduced the development of MNNG-induced dysplasia and vascularization-related dysplasia in colon tissue, which was analyzed by histopathological techniques. An anti-proliferative potential of fluoxetine was observed in epithelial and stromal areas. It was accompanied by a reduction of VEGF expression and of the number of cells with angiogenic potential, such as CD133, CD34, and CD31-positive cell clusters. Taken together, our findings suggest that fluoxetine treatment targets steps of early colon carcinogenesis. This confirms its protective potential, explaining at least partially the lower colon cancer risk under antidepressant therapy.

Very small embryonic/epiblast-like stem cells (VSELs) and their potential role in aging and organ rejuvenation--an update and comparison to other primitive small stem cells isolated from adult tissues

Very small embryonic-like stem cells (VSELs) are a population of developmentally early stem cells residing in adult tissues. These rare cells, which are slightly smaller than red blood cells, i) become mobilized during stress situations into peripheral blood, ii) are enriched in the Sca1⁺Lin⁻CD45⁻ cell fraction in mice and the CD133⁺ Lin⁻CD45⁻ cell fraction in humans, iii) express markers of pluripotent stem cells (e.g., Oct4, Nanog, and SSEA), and iv) display a distinct morphology characterized by a high nuclear/cytoplasmic ratio and undifferentiated chromatin. Recent evidence indicates that murine VSELs are kept quiescent in adult tissues and protected from teratoma formation by epigenetic modification of imprinted genes that regulate insulin/insulin like growth factor signaling (IIS). The successful reversal of these epigenetic changes in VSELs that render them quiescent will be crucial for efficient expansion of these cells. The most recent data in vivo from our and other laboratories demonstrated that both murine and human VSELs exhibit some characteristics of long-term repopulating hematopoietic stem cells (LT-HSCs), are at the top of the hierarchy in the mesenchymal lineage, and may differentiate into organ-specific cells (e.g., cardiomyocytes). Moreover, as recently demonstrated the number of these cells positively correlates in several murine models with longevity. Finally, while murine BM-derived VSELs have been extensively characterized more work is needed to better characterize these small cells at the molecular level in humans.

Potential for a pluripotent adult stem cell treatment for acute radiation sickness

Accidental radiation exposure and the threat of deliberate radiation exposure have been in the news and are a public health concern. Experience with acute radiation sickness has been gathered from atomic blast survivors of Hiroshima and Nagasaki and from civilian nuclear accidents as well as experience gained during the development of radiation therapy for cancer. This paper reviews the medical treatment reports relevant to acute radiation sickness among the survivors of atomic weapons at Hiroshima and Nagasaki, among the victims of Chernobyl, and the two cases described so far from the Fukushima Dai-Ichi disaster. The data supporting the use of hematopoietic stem cell transplantation and the new efforts to expand stem cell populations ex vivo for infusion to treat bone marrow failure are reviewed. Hematopoietic stem cells derived from bone marrow or blood have a broad ability to repair and replace radiation induced damaged blood and immune cell production and may promote blood vessel formation and tissue repair. Additionally, a constituent of bone marrow-derived, adult pluripotent stem cells, very small embryonic like stem cells, are highly resistant to ionizing radiation and appear capable of regenerating radiation damaged tissue including skin, gut and lung.

A comparison of stem cells for therapeutic use

A critical comparison of the attributes of several types of stem cells is presented, with particular emphasis on properties that are critical for the application of these cells for therapeutic purposes. The importance of an autologous source of pluripotent stem cells is stressed. It is apparent that two sources currently exist for non-embryonic pluripotent stem cells--very small embryonic-like stem cells (VSELs) and induced pluripotent stem cells (iPS). The impact of the emerging iPS research on therapy is considered.

The great migration of bone marrow-derived stem cells toward the ischemic brain: therapeutic implications for stroke and other neurological disorders

Accumulating laboratory studies have implicated the mobilization of bone marrow (BM)-derived stem cells in brain plasticity and stroke therapy. This mobilization of bone cells to the brain is an essential concept in regenerative medicine. Over the past ten years, mounting data have shown the ability of bone marrow-derived stem cells to mobilize from BM to the peripheral blood (PB) and eventually enter the injured brain. This homing action is exemplified in BM stem cell mobilization following ischemic brain injury. Various BM-derived cells, such as hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), endothelial progenitor cells (EPCs) and very small embryonic-like cells (VSELs) have been demonstrated to exert therapeutic benefits in stroke. Here, we discuss the current status of these BM-derived stem cells in stroke therapy, with emphasis on possible cellular and molecular mechanisms of action that mediate the cells' beneficial effects in the ischemic brain. When possible, we also discuss the relevance of this therapeutic regimen in other central nervous system (CNS) disorders.

Bone marrow stem cell mobilization in stroke: a 'bonehead' may be good after all!

Mobilizing bone cells to the head, astutely referred to as 'bonehead' therapeutic approach, represents a major discipline of regenerative medicine. The last decade has witnessed mounting evidence supporting the capacity of bone marrow (BM)-derived cells to mobilize from BM to peripheral blood (PB), eventually finding their way to the injured brain. This homing action is exemplified in BM stem cell mobilization following ischemic brain injury. Here, I review accumulating laboratory studies implicating the role of therapeutic mobilization of transplanted BM stem cells for brain plasticity and remodeling in stroke.

Hematopoietic differentiation of umbilical cord blood-derived very small embryonic/epiblast-like stem cells

A population of CD133⁺lin⁻CD45⁻ very small embryonic-like stem cells (VSELs) has been purified by multiparameter sorting from umbilical cord blood (UCB). In order to speed up isolation of these cells, we employed anti-CD133-conjugated paramagnetic beads followed by staining with Aldefluor to detect aldehyde dehydrogenase (ALDH) activity; we subsequently sorted CD45⁻/GlyA⁻/CD133⁺/ALDH^high and CD45⁻/GlyA⁻/CD133⁺/ALDH^low cells, which are enriched for VSELs, and CD45⁺/GlyA⁻/CD133⁺/ALDH^high and CD45⁺/GlyA⁻/CD133⁺/ALDH^low cells, which are enriched for hematopoietic stem/progenitor cells (HSPCs). While freshly isolated CD45⁻ VSELs did not grow hematopoietic colonies, the same cells, when activated/expanded over OP9 stromal support, acquired hematopoietic potential and grew colonies composed of CD45⁺ hematopoietic cells in methylcellulose cultures. We also observed that CD45⁻/GlyA⁻/CD133⁺/ALDH^high VSELs grew colonies earlier than CD45⁻/GlyA⁻/CD133⁺/ALDH^low VSELs, which suggests that the latter cells need more time to acquire hematopoietic commitment. In support of this possibility, real-time PCR analysis confirmed that, while freshly isolated CD45⁻/GlyA⁻/CD133⁺/ALDH^high VSELs express more hematopoietic transcripts (e.g., c-myb), CD45⁻/GlyA⁻/CD133⁺/ALDH^low VSELs exhibit higher levels of pluripotent stem cell markers (e.g., Oct-4). More importantly, hematopoietic cells derived from VSELs that were co-cultured over OP9 support were able to establish human lympho-hematopoietic chimerism in lethally irradiated NOD/SCID mice 4–6 weeks after transplantation. Overall, our data suggest that UCB-VSELs correspond to the most primitive population of HSPCs in UCB.