Very small embryonic-like stem cells with maximum regenerative potential get discarded during cord blood banking and bone marrow processing for autologous stem cell therapy

A Simplified and Effective Approach for the Isolation of Small Pluripotent Stem Cells Derived from Human Peripheral Blood

Pluripotent stem cells are key players in regenerative medicine. Embryonic pluripotent stem cells, despite their significant advantages, are associated with limitations such as their inadequate availability and the ethical dilemmas in their isolation and clinical use. The discovery of very small embryonic-like (VSEL) stem cells addressed the aforementioned limitations, but their isolation technique remains a challenge due to their small cell size and their efficiency in isolation. Here, we report a simplified and effective approach for the isolation of small pluripotent stem cells derived from human peripheral blood. Our approach results in a high yield of small blood stem cell (SBSC) population, which expresses pluripotent embryonic markers (e.g., Nanog, SSEA-3) and the Yamanaka factors. Further, a fraction of SBSCs also co-express hematopoietic markers (e.g., CD45 and CD90) and/or mesenchymal markers (e.g., CD29, CD105 and PTH1R), suggesting a mixed stem cell population. Finally, quantitative proteomic profiling reveals that SBSCs contain various stem cell markers (CD9, ITGA6, MAPK1, MTHFD1, STAT3, HSPB1, HSPA4), and Transcription reg complex factors (e.g., STAT5B, PDLIM1, ANXA2, ATF6, CAMK1). In conclusion, we present a novel, simplified and effective isolating process that yields an abundant population of small-sized cells with characteristics of pluripotency from human peripheral blood.

A chemically defined biomimetic surface for enhanced isolation efficiency of high-quality human mesenchymal stromal cells under xenogeneic/serum-free conditions

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) are one of the most frequently used cell types in regenerative medicine and cell therapy. Generating sufficient cell numbers for MSC-based therapies is constrained by (i) their low abundance in tissues of origin, which imposes the need for significant ex vivo cell expansion; (ii) donor-specific characteristics, including MSC frequency/quality, that decline with disease state and increasing age; and (iii) cellular senescence, which is promoted by extensive cell expansion and results in decreased therapeutic functionality. The final yield of a manufacturing process is therefore primarily determined by the applied isolation procedure and its efficiency in isolating therapeutically active cells from donor tissue. To date, MSCs are predominantly isolated using media supplemented with either serum or its derivatives, which poses safety and consistency issues.

METHODS

To overcome these limitations while enabling robust MSC production with constant high yield and quality, the authors developed a chemically defined biomimetic surface coating called isoMATRIX (denovoMATRIX GmbH, Dresden, Germany) and tested its performance during isolation of MSCs.

RESULTS

The isoMATRIX facilitates the isolation of significantly higher numbers of MSCs in xenogeneic (xeno)/serum-free and chemically defined conditions. The isolated cells display a smaller cell size and higher proliferation rate than those derived from a serum-containing isolation procedure and a strong immunomodulatory capacity. The high proliferation rates can be maintained up to 5 passages after isolation and cells even benefit from a switch towards a proliferation-specific MSC matrix (myMATRIX MSC) (denovoMATRIX GmbH, Dresden, Germany).

CONCLUSION

In sum, isoMATRIX promotes enhanced xeno/serum-free and chemically defined isolation of human MSCs and supports consistent and reliable cell performance for improved stem cell-based therapies.

Application of Stem Cell Therapy for Infertility

Infertility creates an immense impact on the psychosocial wellbeing of affected couples, leading to poor quality of life. Infertility is now considered to be a global health issue affecting approximately 15% of couples worldwide. It may arise from factors related to the male (30%), including varicocele, undescended testes, testicular cancer, and azoospermia; the female (30%), including premature ovarian failure and uterine disorders; or both partners (30%). With the recent advancement in assisted reproduction technology (ART), many affected couples (80%) could find a solution. However, a substantial number of couples cannot conceive even after ART. Stem cells are now increasingly being investigated as promising alternative therapeutics in translational research of regenerative medicine. Tremendous headway has been made to understand the biology and function of stem cells. Considering the minimum ethical concern and easily available abundant resources, extensive research is being conducted on induced pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSC) for their potential application in reproductive medicine, especially in cases of infertility resulting from azoospermia and premature ovarian insufficiency. However, most of these investigations have been carried out in animal models. Evolutionary divergence observed in pluripotency among animals and humans requires caution when extrapolating the data obtained from murine models to safely apply them to clinical applications in humans. Hence, more clinical trials based on larger populations need to be carried out to investigate the relevance of stem cell therapy, including its safety and efficacy, in translational infertility medicine.

SSEA-4 Antigen Is Expressed on Rabbit Lymphocyte Subsets

SSEA-4 antigen can be mainly found in embryos and embryonic stem cells. However, its expression has been observed also in adult stem and progenitor cells, or even in some differentiated cells. Moreover, we found a considerable number of SSEA-4 positive (SSEA-4+) cells within the rabbit peripheral blood and bone marrow mononuclear cells (PBMCs and BMMCs) in our previous study. Since no information about such cells can be found anywhere in the literature, the aim of this study was to identify their origin. At first, phenotypic analyses of fresh rabbit PBMCs and BMMCs were performed using flow cytometry and specific antibodies against SSEA-4 and leukocyte subsets. Then, SSEA-4+ were enriched using magnetic activated cell sorting (MACS) and analyzed for their phenotype using qPCR. We found significant SSEA-4+ cell population in PBMCs (~50%) and BMMCs (~20%). All those cells co-expressed CD45 and a majority of them also expressed B-cell marker (IgM; 50% of SSEA-4+ PBMCs and 60% of SSEA-4+ BMMCs). Increased (p < 0.05) expression of SSEA-4, CD45 and B-cell markers (IgM, CD79α and MHCII) were also noticed by qPCR in SSEA-4+ cells enriched via MACS (with efficiency over 80%). Both methods did not detect significant expression of monocyte or T-cell markers. In conclusion, SSEA-4+ cells in rabbit blood and bone marrow are of hematopoietic origin and probably belong to B-lineage cells as possessing the phenotype of B lymphocytes. However, the true function of SSEA-4 antigen in these cells should be explored by further studies.

Quest for Pan-Cancer Diagnosis/Prognosis Ends with HrC Test Measuring Oct4A in Peripheral Blood

Cancer is a devastating disease whose incidence has increased in recent times and early detection can lead to effective treatment. Existing detection tools suffer from low sensitivity and specificity, and are high cost, invasive and painful procedures. Cancers affecting different tissues, ubiquitously express embryonic markers including Oct-4A, whose expression levels have also been correlated to staging different types of cancer. Cancer stem cells (CSCs) that initiate cancer are possibly the 'transformed' and pluripotent very small embryonic-like stem cells (VSELs) that also express OCT-4A. Excessive self-renewal of otherwise quiescent, pluripotent VSELs in normal tissues possibly initiates cancer. In an initial study on 120 known cancer patients, it was observed that Oct-4A expression in peripheral blood correlated well with the stage of cancer. Based on these results, we developed a proprietary HrC scale wherein fold change of OCT-4A was linked to patient status - it is a numerical scoring system ranging from non-cancer (0-2), inflammation (>2-6), high-risk (>6-10), stage I (>10-20), stage II (>20-30), stage III (>30-40), and stage IV (>40) cancers. Later the scale was validated on 1000 subjects including 500 non-cancer and 500 cancer patients. Ten case studies are described and show (i) HrC scale can detect cancer, predict and monitor treatment outcome (ii) is superior to evaluating circulating tumor cells and (iii) can also serve as an early biomarker. HrC method is a novel breakthrough, non-invasive, blood-based diagnostic tool that can detect as well as classify solid tumors, hematological malignancies and sarcomas, based on their stage.

Adult tissue-resident stem cells-fact or fiction?

Life-long tissue homeostasis of adult tissues is supposedly maintained by the resident stem cells. These stem cells are quiescent in nature and rarely divide to self-renew and give rise to tissue-specific “progenitors” (lineage-restricted and tissue-committed) which divide rapidly and differentiate into tissue-specific cell types. However, it has proved difficult to isolate these quiescent stem cells as a physical entity. Recent single-cell RNAseq studies on several adult tissues including ovary, prostate, and cardiac tissues have not been able to detect stem cells. Thus, it has been postulated that adult cells dedifferentiate to stem-like state to ensure regeneration and can be defined as cells capable to replace lost cells through mitosis. This idea challenges basic paradigm of development biology regarding plasticity that a cell enters point of no return once it initiates differentiation. The underlying reason for this dilemma is that we are putting stem cells and somatic cells together while processing for various studies. Stem cells and adult mature cell types are distinct entities; stem cells are quiescent, small in size, and with minimal organelles whereas the mature cells are metabolically active and have multiple organelles lying in abundant cytoplasm. As a result, they do not pellet down together when centrifuged at 100–350g. At this speed, mature cells get collected but stem cells remain buoyant and can be pelleted by centrifuging at 1000g. Thus, inability to detect stem cells in recently published single-cell RNAseq studies is because the stem cells were unknowingly discarded while processing and were never subjected to RNAseq. This needs to be kept in mind before proposing to redefine adult stem cells.

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.

Pluripotent Stem (VSELs) and Progenitor (EnSCs) Cells Exist in Adult Mouse Uterus and Show Cyclic Changes Across Estrus Cycle

We have earlier reported pluripotent, very small embryonic-like stem cells (VSELs) and slightly bigger endometrial stem cells (EnSCs) in adult mouse uterus and their regulation by gonadotropin and steroid hormones. VSELs can differentiate into cells of all three lineages in vitro; however, they neither expand readily in vitro nor compliment a developing embryo. In the present study, a robust protocol is described to enrich uterine stem/progenitor cells along with their characterization and variation across estrus cycle. After enzymatic digestion of adult mouse uterus, single-cell suspension obtained was spun at 1000 rpm (250 g) to pellet majority of cells. Stem cells remain buoyant at this speed and were pelleted by spinning supernatant at 3000 rpm (1000 g). Spherical, darkly stained VSELs (2-6 μm) with high nucleo-cytoplasmic ratio and EnSCs (> 6 μm) expressed OCT-4, NANOG, SSEA-1, SCA-1, and c-KIT. OCT-4-positive cells co-expressed SSEA-1, ERα, ERβ, PR, and FSHR. Transcripts specific for pluripotent state (Oct-4, Oct-4a, Sox-2, Nanog), primordial germ cells (Stella, Fragilis), and receptors for pituitary and steroid hormones (ERα, ERβ, PR, FSHR 1 and 3) were studied by RT-PCR in 3000 rpm pellet. Cell pellet collected at 3000 rpm showed 10-fold enrichment of VSELs (2-6 μm, viable cells with surface phenotype of LIN-CD45-SCA-1+) by flow cytometry and upregulation of pluripotent transcripts by qRT-PCR compared with 1000 rpm pellet. VSELs were maximal during estrus and metestrus phases of estrus cycle. To conclude, VSELs/EnSCs can be enriched from adult uterus using the strategy described here, vary in numbers across estrus cycle, and are vulnerable to endocrine disruption as they express steroid receptors.

Ovary does harbor stem cells - size of the cells matter!

A recent study published in the journal Nature Communications from Karolinska Institute, Sweden was unable to detect stem cells in adult human ovarian cortex by single-cell RNAseq and by studying cell surface antigen profiles by flow cytometry studies. Their findings are startling since stem cells have been well characterized in the adult mammalian ovary of several species including mouse, rabbit, monkey, sheep, pig and humans. Ovarian stem cells include pluripotent, very small embryonic-like stem cells (VSELs) and slightly bigger ovarian stem cells (OSCs) which are easily visualized in smears obtained by gently scraping the ovary surface. The potential of ovarian stem cells to differentiate into oocyte-like structures in vitro and also resulting in the birth of mouse pups has been reported. A possible role of ovarian VSELs in initiation of ovarian cancers has also been delineated. The ovarian stem cells can also be collected by enzymatic digestion of ovarian tissue for various studies, taking care to always pellet the cells suspension at 1000 g since this high speed is required to collect the small-sized stem cell populations (VSELs & OSCs) with high nucleo-cytoplasmic ratio. These stem cells invariably get discarded when cells suspension is spun at lower speed. The cells were spun at 300 g for various experiments in the Karolinska study and this is the underlying reason for their negative results. Stem cells were inadvertently and unknowingly discarded and never got analyzed by single-cell RNAseq and flow cytometry experiments. To conclude, stem cells surely exist in adult mammalian ovary and their role during neo-oogenesis and primordial follicle assembly under physiological conditions is currently being investigated.

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.

Pluripotent Very Small Embryonic-Like Stem Cells in Adult Testes - An Alternate Premise to Explain Testicular Germ Cell Tumors

Developmental exposure to endocrine disruptors has resulted in the increased incidence of infertility and testicular germ cell tumors (T2GCT) in young men residing in developed countries. Unlike T1GCT (infants and young children) and T3GCT (aged men), T2GCT arise from CIS/GCNIS that develops from pre-CIS. Pre-CIS represents undifferentiated, growth-arrested gonocytes that persist in fetal testes due to endocrine disruption. However, whether pre-CIS truly exist, do CIS develop into T2GCT, why no CIS in T1GCT/T3GCT, why germ cell tumors (GCT) also occur along midline at extra-gonadal sites, why T1GCT show partial erasure and T2GCT show complete erasure of genomic imprints are open questions that are awaiting answers. We propose that rather than pre-CIS, pluripotent, very small embryonic-like stem cells (VSELs) get affected by exposure to endocrine disruption. Since VSELs are developmentally equivalent to primordial germ cells (PGCs), T2GCT cells show complete erasure of genomic imprints and CIS represents growth-arrested clonally expanding stem/progenitor cells. PGCs/VSELs migrate along the midline to various organs and this explains why GCT occur along the midline, T1GCT show partial erasure of imprints as they develop from migrating PGCs. T3GCT possibly reflects effects of aging due to compromised differentiation and expansion of pre-meiotic spermatocytes. Absent spermatogenesis in pre-pubertal and aged testes explains absence of CIS in T1GCT and T3GCT. Endocrine disruptors possibly alter epigenetic state of VSELs and thus rather than maintaining normal tissue homeostasis, VSELs undergo increased proliferation and compromised differentiation resulting in reduced sperm count, infertility and TGCT. This newly emerging understanding offers alternate premise to explain TGCT and warrants further exploration.

Isolation of clinically relevant concentrations of bone marrow mesenchymal stem cells without centrifugation

BACKGROUND

This study examined the quality of bone marrow aspirates extracted using a novel, FDA cleared method to optimally target cells from the inner cortical iliac bone surface without the need for centrifugation. This method employs small draws from a single puncture that promote only lateral flow from multiple sites (SSLM method). The study utilized the Marrow Cellutions bone marrow aspiration system (MC system) which is based on the SSLM method and compared the MC system directly to bone marrow concentrates (BMAC) generated by centrifugation of aspirates harvested with a standard aspiration needle.

METHODS

Three direct comparisons were conducted evaluating the SSLM draws and BMACs derived from the same patient from contralateral iliac crests. The levels of TNCs/mL, CD34+ cells/mL, CD117+ cells/mL, and CFU-f/mL were compared between the various bone marrow preparations. The cellular content of a series of SSLM draws was also analyzed to determine the total nucleated cell (TNC) count and the concentration of mesenchymal stem/progenitor cells as measured by colony forming unit fibroblasts (CFU-f).

RESULTS

In direct comparisons with BMAC systems, SSLM draws yielded significantly higher CFU-f concentrations and comparable concentrations of CD34+ and CD117+ cells. In addition, the average quantity of TNCs/mL in a series of 30 patients utilizing the SSLM draw was 35.2 × 10⁶ ± 17.1 × 10⁶ and the average number of CFU-f/mL was 2885 ± 1716. There were small but significant correlations between the TNCs/mL and the CFU-fs/mL using the SSLM method as well as between the age of the patient and the CFU-fs/mL.

CONCLUSIONS

The MC Device, using the SSLM draw technique, produced concentrations of CFU-fs, CD34+ cells and CD117+ cells that were comparable or greater to BMACs derived from the same patient. Given the rapid speed and simplicity of the MC Device, we believe this novel system possesses significant practical advantages to other currently available centrifugation based systems.

Isolation of a novel embryonic stem cell cord blood-derived population with in vitro hematopoietic capacity in the presence of Wharton's jelly-derived mesenchymal stromal cells

BACKGROUND

Recent studies highlight the existence of a population of cord blood (CB)-derived stem cells that bare embryonic features (very small embryonic-like stem cells [VSELs]) as the most primitive CB-stem cell population. In the present study, we present for the first time a novel and high purity isolation method of VSELs with in vitro hematopoietic capacity in the presence of Wharton's jelly-derived mesenchymal stromal cells (WJ-MSCs).

METHODS

The experimental procedure includes isolation upon gradually increased centrifugation spins and chemotaxis to Stromal cell-derived factor 1a (SDF-1a). Τhis cell population is characterized with flow cytometry, alkaline phosphatase (ALP) staining and qRT-PCR. The functional role of the isolated VSELs is assayed following co-culture with WJ-MSCs or bone marrow-derived mesenchymal stromal cells (BM-MSCs), whereas the stimulation of the quiescent VSEL population is verified via cell cycle analysis. The in vitro hematopoietic capacity is evaluated in methylcellulose cultures and also through induction of erythroid differentiation.

RESULTS

The final isolated subpopulation is characterized as a small-sized CD45/Lineage-/CXCR4+/CD133+/SSEA-4+cell population, positive in ALP staining and overexpressing the Oct3/4, Nanog and Sox-2 transcription factors. Upon the co-culture with MSCs, a stimulation of the quiescent VSEL population is observed. An impressive increase in the co-expression of the CD34+/CD45+ markers is observed following the co-culture with the WJ-MSCs, which is confirmed by the intense clonogenic ability suggesting in vitro differentiation toward all of the hematopoietic cell lineages and successful differentiation toward erythrocytes.

DISCUSSION

Conclusively, we propose a novel, rapid and rather simplified isolation method of CB-VSELs, capable of in vitro hematopoiesis.

Novel Insights into Adult and Cancer Stem Cell Biology

Adult tissues are thought to harbor two populations of "dormant" and "actively dividing" stem cells. Quiescent stem cells undergo rare asymmetric cell divisions (ACDs) through which they self-renew and give rise to tissue-committed "progenitors" of distinct fate and "progenitors" in turn undergo symmetric cell divisions (SCDs) and clonal expansion. However, quiescent stem cells have not been demonstrated in adult tissues such as skin, testis, liver, and brain. After surgical removal of part of liver and pancreas-adult differentiated cells divide and regenerate and a possible role of stem cells remains doubtful. Long-term repopulating hematopoietic stem cells are quiescent in nature but ACD has not been convincingly demonstrated even among them. Attempts by various groups to identify a common stemness program that ensures self-renewal among different kinds of stem cells have also remained futile. Uncontrolled self-renewal and compromised differentiation of stem cells possibly initiate leukemia/cancer, but the identity of leukemic stem cells and whether cancer stem cells arise by epithelial-mesenchymal transition (EMT) in solid tumors are all open-ended questions that need greater clarity. Acceptance of the presence of very small embryonic-like stem cells (VSELs) in adult tissues could clarify several of these existing dilemmas in the field. Data are compiled showing that VSELs undergo ACD in the hematopoietic system, testis, ovary, uterus, and pancreas, whereas tissue-committed progenitors undergo SCD and clonal expansion. VSELs possess similar overlapping stemness program as in embryonic stem cells, embryonic carcinoma cells, embryonic germ cells, induced pluripotent stem cells, and primordial germ cells. VSELs and leukemic and cancer cells express overlapping embryonic markers. Uncontrolled proliferation of VSELs and compromised differentiation possibly initiate leukemia. Process of EMT and initiation of solid tumor from VSELs (located among the epithelial cells) are indeed two distinct and parallel events. To conclude, VSELs provide explanation to several confounding aspects of adult stem cell biology.

Novel View on Umbilical Cord Blood and Maternal Peripheral Blood-an Evidence for an Increase in the Number of Circulating Stem Cells on Both Sides of the Fetal-Maternal Circulation Barrier

Umbilical cord blood (UCB) is a rich source of stem cells, including hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs), endothelial progenitors cells (EPCs), and very small embryonic-like stem cells (VSELs). These cells most likely are mobilized into UCB in response to hypoxia and delivery stress. We have hypothesized that they may play a role in repairing certain tissue/organ injuries that occur in the newborn child after delivery. Here we asked whether delivery also mobilizes stem cells into maternal blood, as the mother also experiences hypoxia and several types of internal tissue injuries, particularly in the reproductive tract. We observed that the number of HSCs, MSCs, EPCs, and VSELs increases in maternal blood at 24 h after physiological delivery (n = 17). Based on this observation, we propose that delivery stress is associated with an increase in the number of circulating stem cells, not only on the fetal side but also on the maternal side of the fetal–maternal circulatory barrier.

Limbal niche cells are a potent resource of adult mesenchymal progenitors

Limbal niche cells located in the limbal Palisades of Vogt are mesenchymal stem cells that reside next to limbal basal epithelial cells. Limbal niche cells are progenitors that express embryonic stem cell markers such as Nanog, Nestin, Oct4, Rex1, Sox2 and SSEA4, mesenchymal cell markers such as CD73, CD90 and CD105, and angiogenesis markers such as Flk-1, CD31, CD34, VWF, PDGFRβ and α-SMA, but negative for CD45. In addition, the stemness of limbal niche cells can be maintained during their cell culture in a three-dimension environment. Furthermore, expanded limbal niche cells have the capability to undergo adipogenesis, chondrogenesis, osteogenesis and endogenesis in vitro, indicating that they are in fact a valuable resource of adult progenitors. Furthermore studies on how the limbal niche cells regulate the aforementioned stemness and corneal fate decision are warranted, as those investigations will shed new light on how mesenchymal progenitors reverse limbal stem cell deficiency and lead to new methods for limbal niche cell treatment.

Subcellular localisation of the stem cell markers OCT4, SOX2, NANOG, KLF4 and c-MYC in cancer: a review

The stem cell markers octamer-binding transcription factor 4, sex-determining region Y-box 2, NANOG, Kruppel-like factor 4 and c-MYC are key factors in inducing pluripotency in somatic cells, and they have been used to detect cancer stem cell subpopulations in a range of cancer types. Recent literature has described the subcellular localisation of these markers and their potential implications on cellular function. This is a relatively complex and unexplored area of research, and the extent of the effect that subcellular localisation has on cancer development and growth is largely unknown. This review analyses this area of research in the context of the biology of stem cells and cancer and explores the potential modulating effect of subcellular localisation of these proteins as supported by the literature.

Mouse Bone Marrow VSELs Exhibit Differentiation into Three Embryonic Germ Lineages and Germ & Hematopoietic Cells in Culture

Very small embryonic-like stem cells (VSELs) have been reported in various adult tissues, express pluripotent and primordial germ cells (PGCs) specific markers, are mobilized under stress/disease conditions, give rise to tissue committed progenitors and thus help regenerate and maintain homeostasis. The aim of the present study was to evaluate in vitro differentiation potential of VSELs using a quantitative approach. VSELs were collected from mouse bone marrow after 4 days of 5-fluorouracil (5-FU, 150 mg/Kg) treatment, further enriched by size based filtration and cultured on a feeder support in the presence of specific differentiation media. Cultured VSELs were found to differentiate into all three embryonic germ cell lineages, germ and hematopoietic cells after 14 days in culture. This was confirmed by studying Nestin, PDX-1, NKX2.5, DAZL, CD45 and other markers expression by various approaches. Very small, CD45 negative cells collected and enriched from GFP positive 5-FU treated mice bone marrow transitioned into CD45 positive cells in vitro thus demonstrating that VSELs can give rise to hematopoietic stem cells (HSCs). We envision that VSELs may be responsible for plasticity and ability of bone marrow cells to give rise to non-hematopoietic tissue progenitors of all 3 germ layers. Moreover the ability of VSELs to differentiate into germ cells as well as all the three lineages provides further evidence to support their pluripotent state and confirms developmental link between bone marrow VSELs and PGCs. The property of quiescence, no risk of teratoma formation and autologus source, make pluripotent VSELs a potential candidate to facilitate endogenous regeneration compared to cell replacement strategy envisioned using embryonic and induced pluripotent stem cells.

Differentiation of human umbilical cord Wharton's jelly-derived mesenchymal stem cells into endometrial cells

BACKGROUND

Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs) are a novel and promising strategy for tissue engineering because of their ability to differentiate into many cell types. We characterized the differentiation of WJ-MSCs into endometrial epithelial cell (EEC)-like and endometrial stromal cell (ESC)-like cells and assessed the effect of 17β-estradiol and 8-Br-cAMP on the differentiation system.

METHODS

WJ-MSCs were treated in two ways to differentiate into EEC-like and ESC-like cells respectively: cocultured with ESCs in control/differentiation medium (17β-estradiol, growth factors); and cultured in control/differentiation medium (8-Br-cAMP alone or 8-Br-cAMP plus 17β-estrogen and growth factors). Three signaling pathway inhibitors (SB203580, PD98059, H89) were used to investigate the mechanism of WJ-MSC differentiation into ESC-like cells. Immunofluorescence, western blot and flow cytometry analyses were used to analyze expression of epithelial markers and stromal cell markers. Enzyme-linked immunosorbent assays were used to test the production of secretory proteins associated with the differentiation of ESC-like cells.

RESULTS

17β-estradiol at 1 μM downregulated vimentin and CD13 and upregulated cytokeratin and CD9 proteins, promoting the differentiation of WJ-MSCs into EEC-like cells in the coculture system. 8-Br-cAMP at 0.5 mM upregulated vimentin and CD13 and downregulated CK and CD9, promoting the differentiation of WJ-MSCs into ESC-like cells. Prolactin (PRL) and insulin-like growth factor-binding protein 1 (IGFBP1) were upregulated and the protein kinase A (PKA) signaling pathway was activated, whereas extracellular signal-regulated (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) were not affected.

CONCLUSIONS

17β-estradiol at 1 μM is a good inducer for facilitating the differentiation of WJ-MSCs into EEC-like cells. 8-Br-cAMP plus estrogen and growth factors can induce the differentiation of WJ-MSCs into ESC-like cells. During the differentiation of WJ-MSCs into ESC-like cells, PRL and IGFBP1 were upregulated by the treatment and the PKA signaling pathway was activated, whereas ERK1/2 and p38 MAPK were not affected. These findings suggest a promising approach to the treatment of endometrial damage and other endometrial diseases and suggest new applications for WJ-MSCs in clinical practice.

HIF-2α and Oct4 have synergistic effects on survival and myocardial repair of very small embryonic-like mesenchymal stem cells in infarcted hearts

Poor cell survival and limited functional benefits have restricted mesenchymal stem cell (MSC) efficacy for treating myocardial infarction (MI), suggesting that a better understanding of stem cell biology is needed. The transcription factor HIF-2α is an essential regulator of the transcriptional response to hypoxia, which can interact with embryonic stem cells (ESCs) transcription factor Oct4 and modulate its signaling. Here, we obtained very small embryonic-like mesenchymal stem cells (vselMSCs) from MI patients, which possessed the very small embryonic-like stem cells' (VSELs) morphology as well as ESCs' pluripotency. Using microarray analysis, we compared HIF-2α-regulated gene profiles in vselMSCs with ESC profiles and determined that HIF-2α coexpressed Oct4 in vselMSCs similarly to ESCs. However, this coexpression was absent in unpurified MSCs (uMSCs). Under hypoxic condition, vselMSCs exhibited stronger survival, proliferation and differentiation than uMSCs. Transplantation of vselMSCs caused greater improvement in cardiac function and heart remodeling in the infarcted rats. We further demonstrated that HIF-2α and Oct4 jointly regulate their relative downstream gene expressions, including Bcl2 and Survivin; the important pluripotent markers Nanog, Klf4, and Sox2; and Ang-1, bFGF, and VEGF, promoting angiogenesis and engraftment. Importantly, these effects were generally magnified by upregulation of HIF-2α and Oct4 induced by HIF-2α or Oct4 overexpression, and the greatest improvements were elicited after co-overexpressing HIF-2α and Oct4; overexpressing one transcription factor while silencing the other canceled this increase, and HIF-2α or Oct4 silencing abolished these effects. Together, these findings demonstrated that HIF-2α in vselMSCs cooperated with Oct4 in survival and function. The identification of the cooperation between HIF-2α and Oct4 will lead to deeper characterization of the downstream targets of this interaction in vselMSCs and will have novel pathophysiological implications for the repair of infarcted myocardium.

Endogenous, very small embryonic-like stem cells: critical review, therapeutic potential and a look ahead

BACKGROUND

Both pluripotent very small embryonic-like stem cells (VSELs) and induced pluripotent stem (iPS) cells were reported in 2006. In 2012, a Nobel Prize was awarded for iPS technology whereas even today the very existence of VSELs is not well accepted. The underlying reason is that VSELs exist in low numbers, remain dormant under homeostatic conditions, are very small in size and do not pellet down at 250-280g. The VSELs maintain life-long tissue homeostasis, serve as a backup pool for adult stem cells and are mobilized under stress conditions. An imbalance in VSELs function (uncontrolled proliferation) may result in cancer.

SEARCH METHODS

The electronic database 'Medline/Pubmed' was systematically searched with the subject heading term 'very small embryonic-like stem cells'.

OBJECTIVE AND RATIONALE

The most primitive stem cells that undergo asymmetric cell divisions to self-renew and give rise to progenitors still remain elusive in the hematopoietic system and testes, while the presence of stem cells in ovary is still being debated. We propose to review the available literature on VSELs, the methods of their isolation and characterization, their ontogeny, how they compare with embryonic stem (ES) cells, primordial germ cells (PGCs) and iPS cells, and their role in maintaining tissue homeostasis. The review includes a look ahead on how VSELs will result in paradigm shifts in basic reproductive biology.

OUTCOMES

Adult tissue-specific stem cells including hematopoietic, spermatogonial, ovarian and mesenchymal stem cells have good proliferation potential and are indeed committed progenitors (with cytoplasmic OCT-4), which arise by asymmetric cell divisions of pluripotent VSELs (with nuclear OCT-4). VSELs are the most primitive stem cells and postulated to be an overlapping population with the PGCs. Rather than migrating only to the gonads, PGCs migrate and survive in various adult body organs throughout life as VSELs. VSELs express both pluripotent and PGC-specific markers and are epigenetically and developmentally more mature compared with ES cells obtained from the inner cell mass of a blastocyst-stage embryo. As a result, VSELs readily differentiate into three embryonic germ layers and spontaneously give rise to both sperm and oocytes in vitro. Like PGCs, VSELs do not divide readily in culture, nor produce teratoma or integrate in the developing embryo. But this property of being relatively quiescent allows endogenous VSELs to survive various kinds of toxic insults. VSELs that survive oncotherapy can be targeted to induce endogenous regeneration of non-functional gonads. Transplanting healthy niche (mesenchymal) cells have resulted in improved gonadal function and live births.

WIDER IMPLICATIONS

Being quiescent, VSELs possibly do not accumulate genomic (nuclear or mitochondrial) mutations and thus may be ideal endogenous, pluripotent stem cell candidates for regenerative and reproductive medicine. The presence of VSELs in adult gonads and the fact that they survive oncotherapy may obviate the need to bank gonadal tissue for fertility preservation prior to oncotherapy. VSELs and their ability to undergo spermatogenesis/neo-oogenesis in the presence of a healthy niche will help identify newer strategies toward fertility restoration in cancer survivors, delaying menopause and also enabling aged mothers to have better quality eggs.

In vitro and in vivo analysis of human fibroblast reprogramming and multipotency

Multipotent stem cells have potential therapeutic roles in the treatment of Duchenne muscular dystrophy (DMD). However, the limited access to stem cell sources restricts their clinical application. To address this issue, we established a simple in vitro epigenetic reprogramming technique in which skin fibroblasts are induced to dedifferentiate into multipotent cells. In this study, human fibroblasts were isolated from circumcised adult foreskin and were reprogrammed by co-culture for 72 h with fish oocyte extract (FOE) in serum-free medium. The cells were then observed and analyzed by immunofluorescence staining, flow cytometry and in vitro differentiation assays. Then FOE-treated human fibroblasts were transplanted by tail vein injection into irradiated mdx mice, an animal model of DMD. Two months after injection, the therapeutic effects of FOE-treated fibroblasts on mdx skeletal muscle were evaluated by serum creatine kinase (CK) activity measurements and by immunostaining and RT-PCR of human dystrophin expression. The results indicated that the reprogrammed fibroblasts expressed higher levels of the pluripotent antigen markers SSEA-4, Nanog and Oct-4, and were able to differentiate in vitro into adipogenic cells, osteoblastic cells, and myotube-like cells. Tail vein injection of FOE-treated fibroblasts into irradiated mdx mice slightly reduced serum CK activity and the percentage of centrally nucleated myofibers two months after cell transplantation. Furthermore, we confirmed human dystrophin protein and mRNA expression in mdx mouse skeletal muscle. These data demonstrated that FOE-treated fibroblasts were multipotent and could integrate into mdx mouse myofibers through the vasculature.

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.

Very Small Embryonic-Like Stem Cells: A Potential Developmental Link Between Germinal Lineage and Hematopoiesis in Humans

It has been suggested that hematopoietic stem/progenitor cells (HSPCs) could become specified from a population of migrating primordial germ cells (PGCs), precursors of gametes, during embryogenesis. Some recent experimental data demonstrated that the cell population that is usually considered to be PGCs, moving toward the gonadal ridges of an embryo, contains a subset of cells coexpressing several germ cell and hematopoietic markers and possessing hematopoietic activity. Experimental data showed that bone morphogenetic protein 4 (BMP4) generates PGCs from mouse bone marrow-derived pluripotent stem cells. Interestingly, functional reproductive hormone receptors have been identified in HSPCs, thus indicating their potential role in reproductive function. Several reports have demonstrated fertility restoration and germ cell generation after bone marrow transplantation in both animal models and humans. A potential link between HSPCs and germinal lineage might be represented by very small embryonic-like stem cells (VSELs), which have been found in adult human bone marrow, peripheral blood, and umbilical cord blood, express a specific pattern of pluripotency, germinal lineage, and hematopoiesis, and are proposed to persist in adult tissues and organs from the embryonic period of life. Stem cell populations, similar to VSELs, expressing several genes related to pluripotency and germinal lineage, especially to PGCs, have been discovered in adult human reproductive organs, ovaries and testicles, and were related to primitive germ cell-like cell development in vitro, thus supporting the idea of VSELs as a potential link between germinal lineage and hematopoiesis.

Identification and Characterization of Lineage(-)CD45(-)Sca-1(+) VSEL Phenotypic Cells Residing in Adult Mouse Bone Tissue

Murine bone marrow (BM)-derived very small embryonic-like stem cells (BM VSELs), defined by a lineage-negative (Lin(-)), CD45-negative (CD45(-)), Sca-1-positive (Sca-1(+)) immunophenotype, were previously reported as postnatal pluripotent stem cells (SCs). We developed a highly efficient method for isolating Lin(-)CD45(-)Sca-1(+) small cells using enzymatic treatment of murine bone. We designated these cells as bone-derived VSELs (BD VSELs). The incidences of BM VSELs in the BM-derived nucleated cells and that of BD VSELs in bone-derived nucleated cells were 0.002% and 0.15%, respectively. These BD VSELs expressed a variety of hematopoietic stem cell (HSC), mesenchymal stem cell (MSC), and endothelial cell markers. The gene expression profile of the BD VSELs was clearly distinct from those of HSCs, MSCs, and ES cells. In the steady state, the BD VSELs proliferated slowly, however, the number of BD VSELs significantly increased in the bone after acute liver injury. Moreover, green fluorescent protein-mouse derived BD VSELs transplanted via tail vein injection after acute liver injury were detected in the liver parenchyma of recipient mice. Immunohistological analyses suggested that these BD VSELs might transdifferentiate into hepatocytes. This study demonstrated that the majority of the Lin(-)CD45(-)Sca-1(+) VSEL phenotypic cells reside in the bone rather than the BM. However, the immunophenotype and the gene expression profile of BD VSELs were clearly different from those of other types of SCs, including BM VSELs, MSCs, HSCs, and ES cells. Further studies will therefore be required to elucidate their cellular and/or SC characteristics and the potential relationship between BD VSELs and BM VSELs.

VSELs may obviate cryobanking of gonadal tissue in cancer patients for fertility preservation

Background

Infertility is an undesirable side effect and gonadal tissue banking is advocated in young cancer patients who are unable to preserve embryos or gametes prior to oncotherapy to achieve biological parenthood later on. Banking gonadal tissue is challenging and protocols to mature gametes in vitro are not yet clinically established. Transplanting ovarian cortical tissue at hetero-or orthotopic sites in women and bone marrow transplantation (BMT) in both men and women has resulted in spontaneous recovery of fertility, pregnancy and live births. Various studies in humans and mice suggest that genetic origin of offspring after BMT is similar to transplanted patient and not the donor. Thus the source of oocytes/sperm which result in spontaneous pregnancies still remains contentious.

Findings

Very small embryonic-like stem cells (VSELs) have been reported in adult human testis and ovary, in azoospermic testicular biopsies from survivors of childhood cancer and also in women with premature ovarian failure and menopause. VSELs survive chemotherapy because of their quiescent nature and can be detected in chemoablated mice gonads at protein and mRNA level and also by flow cytometry. Surviving VSELs spontaneously differentiate into oocyte-like structures and sperm when inhibitory factors are overcome in vitro. Transplantation of mesenchymal cells (isolated from different sources) has led to regeneration of chemoablated mouse gonads and also live births. Spermatogenesis is also restored from endogenous stem cells on inter-tubular transplantation of Sertoli cells in chemoablated mouse testis.

Conclusions

Endogenous VSELs (which survive oncotherapy) can possibly regenerate non-functional gonads in cancer survivors when exposed to a healthy niche in vitro or in vivo (by way of transplanting mesenchymal cells which secrete trophic factors required for endogenous VSELs to differentiate into gametes). Presence of VSELs can also explain spontaneous pregnancies after BMT and cortical tissue transplantation (at heterotopic or orthotopic sites). This understanding once verified and accepted by the scientific community could obviate the need to remove whole ovary or testicular biopsy for cryopreservation prior to oncotherapy.

Different Tissue-Derived Stem Cells: A Comparison of Neural Differentiation Capability

BACKGROUND

Stem cells are capable of self-renewal and differentiation into a wide range of cell types with multiple clinical and therapeutic applications. Stem cells are providing hope for many diseases that currently lack effective therapeutic methods, including strokes, Huntington's disease, Alzheimer's and Parkinson's disease. However, the paucity of suitable cell types for cell replacement therapy in patients suffering from neurological disorders has hampered the development of this promising therapeutic approach.

AIM

The innovative aspect of this study has been to evaluate the neural differentiation capability of different tissue-derived stem cells coming from different tissue sources such as bone marrow, umbilical cord blood, human endometrium and amniotic fluid, cultured under the same supplemented media neuro-transcription factor conditions, testing the expression of neural markers such as GFAP, Nestin and Neurofilaments using the immunofluorescence staining assay and some typical clusters of differentiation such as CD34, CD90, CD105 and CD133 by using the cytofluorimetric test assay.

RESULTS

Amniotic fluid derived stem cells showed a more primitive phenotype compared to the differentiating potential demonstrated by the other stem cell sources, representing a realistic possibility in the field of regenerative cell therapy suitable for neurodegenerative diseases.

Multilayered Magnetic Gelatin Membrane Scaffolds

A versatile approach for the design and fabrication of multilayer magnetic scaffolds with tunable magnetic gradients is described. Multilayer magnetic gelatin membrane scaffolds with intrinsic magnetic gradients were designed to encapsulate magnetized bioagents under an externally applied magnetic field for use in magnetic-field-assisted tissue engineering. The temperature of the individual membranes increased up to 43.7 °C under an applied oscillating magnetic field for 70 s by magnetic hyperthermia, enabling the possibility of inducing a thermal gradient inside the final 3D multilayer magnetic scaffolds. On the basis of finite element method simulations, magnetic gelatin membranes with different concentrations of magnetic nanoparticles were assembled into 3D multilayered scaffolds. A magnetic-gradient-controlled distribution of magnetically labeled stem cells was demonstrated in vitro. This magnetic biomaterial-magnetic cell strategy can be expanded to a number of different magnetic biomaterials for various tissue engineering applications.

Molecular and phenotypic characterization of CD133 and SSEA4 enriched very small embryonic-like stem cells in human cord blood

Very small embryonic-like stem cells (VSELs) are immature primitive cells residing in adult and fetal tissues. This study describes enrichment strategy and molecular and phenotypic characterization of human cord blood VSELs. Flow cytometry analysis revealed that a majority of VSELs (LIN(-)/CD45(-)/CD34(+)) were present in the red blood cell (RBC) pellet after Ficoll-Hypaque centrifugation in contrast to the hematopoietic stem cells (LIN(-)/CD45(+)/CD34(+)) in the interphase layer. Thus, after lyses of RBCs, VSELs were enriched using CD133 and SSEA4 antibodies. These enriched cells were small in size (4-6 μm), spherical, exhibited telomerase activity and expressed pluripotent stem cell (OCT4A, OCT4, SSEA4, NANOG, SOX2, REX1), primordial germ cell (STELLA, FRAGILIS) as well as primitive hematopoietic (CD133, CD34) markers at protein and transcript levels. Heterogeneity was noted among VSELs based on subtle differences in expression of various markers studied. DNA analysis and cell cycle studies revealed that a majority of enriched VSELs were diploid, non-apoptotic and in G0/G1 phase, reflecting their quiescent state. VSELs also survived 5-fluorouracil treatment in vitro and treated cells entered into cell cycle. This study provides further support for the existence of pluripotent, diploid and relatively quiescent VSELs in cord blood and suggests further exploration of the subpopulations among them.

Regenerative Therapy and Immune Modulation Using Umbilical Cord Blood-Derived Cells

Since the first cord blood transplantation in 1988, umbilical cord blood has become an important option as a source of cells for hematopoietic transplantation. Beyond its role in regenerating the blood and immune systems to treat blood diseases and inherited metabolic disorders, the role of nonhematopoietic progenitor cells in cord blood has led to new and emerging uses of umbilical cord blood in regenerative therapy and immune modulation. In this review, we provide an update on the clinical and preclinical studies using cord blood-derived cells such as mesenchymal stromal cells, endothelial-like progenitor cells, and others. We also provide insight on the use of cord blood cells as vehicles for the delivery of therapeutic agents through gene therapy and microvesicle-associated strategies. Moreover, cord blood can provide essential reagents for regenerative applications. Clinical activity using cord blood cells is increasing rapidly and this review aims to provide an important update on the tremendous potential within this fast-moving field.

Intricacies of Pluripotency

Pluripotent stem cells have the potential to differentiate into 200 odd cell types present in adult body. Pluripotent stem cells available for regenerative medicine include embryonic stem (ES) cells, induced pluripotent stem (iPS) cells and very small ES-like stem (VSELs) cells. Nuclear OCT-4 is one of the crucial factors that dictate pluripotent state. Compared to ES/iPS cells grown in Petri dish, VSELs exist in adult body organs and results are emerging to suggest that they may have better potential to regenerate adult organs. This is because of their distinct epigenetic status as they are closer to the primordial germ cells from the epiblast-stage embryo compared to inner cell mass from which ES cells are obtained in vitro. We need to make special efforts to study them as they are very small in size and tend to get lost during processing. VSELs exist in adult organs, get mobilized in response to stress, undergo asymmetric cell divisions to give rise to tissue specific progenitors which further differentiate into various cell types and are possibly better candidates for regenerative medicine because they have no associated risk of tumor formation or immunological rejection. They are possibly also the ‘embryonic remnants’ in adult organs responsible for initiating cancer. Thus, rather than not accepting VSELs because they neither form teratoma nor divide in vitro like ES cells, it is time that scientific community should think of revising the definition of the term ‘pluripotency’.

Very small embryonic-like stem cells are involved in pancreatic regeneration and their dysfunction with age may lead to diabetes and cancer

Mouse pancreas has a remarkable ability to regenerate after partial pancreatectomy, and several investigators have studied the underlying mechanisms involved in this regeneration process; however, the field remains contentious. Elegant lineage-tracing studies undertaken over a decade have generated strong evidence against neogenesis from stem cells and in favor of reduplication of pre-existing islets. Ductal epithelium has also been implicated during regeneration. We recently provided direct evidence for the possible involvement of very small embryonic-like stem cells (VSELs) during regeneration after partial pancreatectomy in mice. VSELs were first reported in pancreas in 2008 and are mobilized in large numbers after treating mice with streptozotocin and in patients with pancreatic cancer. VSELs can be detected in mouse pancreas as small-sized LIN⁻/CD45⁻/SCA-1⁺ cells (3 to 5 μm), present in small numbers (0.6%), which express nuclear Oct-4 (octamer-binding transcription factor 4) and other pluripotent markers along with their immediate descendant ‘progenitors’, which are slightly bigger and co-express Oct-4 and PDX-1. VSELs and the progenitors get mobilized in large numbers after partial pancreatectomy and regenerate both pancreatic islets and acinar cells. In this review, we deliberate upon possible reasons why VSELs have eluded scientists so far. Because of their small size, VSELs are probably unknowingly and inadvertently discarded during processing. Similar to menopause and related loss of ovarian function, type 2 diabetes mellitus occurs because of a decline in beta-cell function possibly resulting from an age-related compromised niche which does not allow VSELs to maintain normal homeostasis. As suggested earlier for ovarian cancers, the presence of Oct-4 and other pluripotent markers in pancreatic cancers is suggestive of VSELs as the possible cancer-initiating stem cells. Several issues raised in the review require urgent confirmation and thus provide scope for further research before arriving at a consensus on the fundamental role played by VSELs in normal pancreas biology and during regeneration, aging, and cancer. In the future, such understanding may allow manipulation of endogenous VSELs to our advantage in patients with diabetes and also to treat cancer.

Very small embryonic-like stem cells are the elusive mouse endometrial stem cells--a pilot study

Background

Endometrium undergoes dramatic growth, breakdown and regeneration throughout reproductive period in mammals. Stem cells have been implicated in the process however their origin, nature, anatomical localization and characterization still remain obscure. Classical concept of presence of stem cells in the basal layer of endometrium was recently challenged when side population and label retaining cells were found to be distributed throughout endometrium. We have earlier reported very small embryonic-like stem cells (VSELs) in adult mammalian ovary and testis as a small population of cells with nuclear OCT-4 along with progenitors (spermatogonial stem cells and ovarian germ stem cells) with cytoplasmic OCT-4. Present study was undertaken to gauge presence of VSELs in bilaterally ovariectomized mouse uterus and their modulation by hormones.

Methods

Bilaterally ovariectomized mice were subjected to sequential estradiol and progesterone treatment in order to induce proliferation, differentiation and remodeling (regeneration). Stem cells were studied in tissue smears after H & E staining and after sorting using SCA-1 by immuno-localization and qRT-PCR studies (Oct-4A, Nanog and Sca-1). Flow cytometry studies were also undertaken to confirm the presence of VSELs in mouse uterus.

Results

Two distinct populations of stem cells with dark stained nucleus and high nucleo-cytoplasmic ratio were detected in ovariectomized mouse uterus. These cells were sorted using SCA-1 and comprised smaller VSELs with nuclear expression of OCT-4 and slightly bigger, more abundant progenitors termed as endometrial stem cells (EnSCs) with cytoplasmic OCT-4. RT-PCR studies showed presence of pluripotent transcripts (Oct-4, Sca-1) and flow cytometry confirmed the presence of 0.069% of LIN-/CD45-/SCA-1+ VSELs. These stem cells were distinctly regulated during endometrial growth, differentiation and regeneration as evidenced by qRT-PCR results.

Conclusions

VSELs are present in normal uterus and also under conditions of atrophy induced by bilateral ovariectomy. Marked increase in EnSCs is associated with endometrial growth and regeneration. Further studies are warranted to define the niche for these stem cells and whether EnSCs arising from the pluripotent VSELs are common progenitors for epithelial and stromal cells or not remains to be addressed. Results of the present study will help in better understanding of endometrial pathologies and their management in the future.

Electronic supplementary material

The online version of this article (doi:10.1186/s13048-015-0138-2) contains supplementary material, which is available to authorized users.

Hematopoietic stem/progenitor cells express several functional sex hormone receptors-novel evidence for a potential developmental link between hematopoiesis and primordial germ cells

Evidence has accumulated that hematopoietic stem progenitor cells (HSPCs) share several markers with the germline, a connection supported by reports that prolactin, androgens, and estrogens stimulate hematopoiesis. To address this issue more directly, we tested the expression of receptors for pituitary-derived hormones, such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH), on purified murine bone marrow (BM) cells enriched for HSPCs and tested the functionality of these receptors in ex vivo signal transduction studies and in vitro clonogenic assays. We also tested whether administration of pituitary- and gonad-derived sex hormones (SexHs) increases incorporation of bromodeoxyuridine (BrdU) into HSPCs and expansion of hematopoietic clonogenic progenitors in mice and promotes recovery of blood counts in sublethally irradiated animals. We report for the first time that HSPCs express functional FSH and LH receptors and that both proliferate in vivo and in vitro in response to stimulation by pituitary SexHs. Furthermore, based on our observations that at least some of CD45(-) very small embryonic-like stem cells (VSELs) may become specified into CD45(+) HSPCs, we also evaluated the expression of pituitary and gonadal SexHs receptors on these cells and tested whether these quiescent cells may expand in vivo in response to SexHs administration. We found that VSELs express SexHs receptors and respond in vivo to SexHs stimulation, as evidenced by BrdU accumulation. Since at least some VSELs share several markers characteristic of migrating primordial germ cells and can be specified into HSPCs, this observation sheds new light on the BM stem cell hierarchy.

Application of a novel population of multipotent stem cells derived from skin fibroblasts as donor cells in bovine SCNT

Undifferentiated stem cells are better donor cells for somatic cell nuclear transfer (SCNT), resulting in more offspring than more differentiated cells. While various stem cell populations have been confirmed to exist in the skin, progress has been restricted due to the lack of a suitable marker for their prospective isolation. To address this fundamental issue, a marker is required that could unambiguously prove the differentiation state of the donor cells. We therefore utilized magnetic activated cell sorting (MACS) to separate a homogeneous population of small SSEA-4⁺ cells from a heterogeneous population of bovine embryonic skin fibroblasts (BEF). SSEA-4⁺ cells were 8-10 μm in diameter and positive for alkaline phosphatase (AP). The percentage of SSEA-4⁺ cells within the cultured BEF population was low (2-3%). Immunocytochemistry and PCR analyses revealed that SSEA-4⁺ cells expressed pluripotency-related markers, and could differentiate into cells comprising all three germ layers in vitro. They remained undifferentiated over 20 passages in suspension culture. In addition, cloned embryos derived from SSEA-4 cells showed significant differences in cleavage rate and blastocyst development when compared with those from BEF and SSEA-4⁻ cells. Moreover, blastocysts derived from SSEA-4⁺ cells showed a higher total cell number and lower apoptotic index as compared to BEF and SSEA-4^– derived cells. It is well known that nuclei from pluripotent stem cells yield a higher cloning efficiency than those from adult somatic cells, however, pluripotent stem cells are relatively difficult to obtain from bovine. The SSEA-4⁺ cells described in the current study provide an attractive candidate for SCNT and a promising platform for the generation of transgenic cattle.

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.

Very small embryonic-like stem cells are involved in regeneration of mouse pancreas post-pancreatectomy

Introduction

Despite numerous research efforts, mechanisms underlying regeneration of pancreas remains controversial. Views are divided whether stem cells are involved during pancreatic regeneration or it involves duplication of pre-existing islets or ductal cells or whether pancreatic islet numbers are fixed by birth or they renew throughout life. Pluripotent embryonic stem (ES) and induced pluripotent stem (iPS) cells have been used by several groups to regenerate diabetic mouse pancreas but the beneficial effects are short-lived. It has been suggested that cells obtained after directed differentiation of ES/iPS cells resemble fetal and not their adult counterparts; thus are functionally different and may be of little use to regenerate adult pancreas. A novel population of pluripotent very small embryonic-like stem cells (VSELs) exists in several adult body tissues in both mice and humans. VSELs have been reported in the mouse pancreas, and nuclear octamer-binding transcription factor 4 (OCT-4) positive, small-sized cells have also been detected in human pancreas. VSELs are mobilized into peripheral blood in streptozotocin treated diabetic mice and also in patients with pancreatic cancer. This study aimed to evaluate whether VSELs are involved during regeneration of adult mouse pancreas after partial pancreatectomy.

Methods

Mice were subjected to partial pancreatectomy wherein almost 70% of pancreas was surgically removed and residual pancreas was studied on Days 1, 3 and 5 post-surgery.

Results

VSELs were detected in Hematoxylin and Eosin stained smears of pancreatic tissue as spherical, small sized cells with a large nucleus surrounded by a thin rim of cytoplasm and could be sorted as LIN-/CD45-/SCA-1+ cells by flow cytometry. Results reveal that although neutrophils with multi-lobed nuclei are mobilized into the pancreas on day 1 after pancreatectomy, by day 5 VSELs with spherical nuclei, high nucleo-cytoplasmic ratio and nuclear OCT-4 are mobilized into the residual pancreas. VSELs undergo differentiation and give rise to PDX-1 and OCT-4 positive progenitors which possibly regenerate both acinar cells and islets.

Conclusions

Results provide direct evidence supporting the presence of VSELs in adult mouse pancreas and their role during regeneration. VSELs are an interesting alternative to ES/iPS cells to regenerate a diabetic pancreas in future.

Expression of the erythropoietin receptor by germline-derived cells - further support for a potential developmental link between the germline and hematopoiesis

BACKGROUND

Expressing several markers of migrating primordial germ cells (PGCs), the rare population of quiescent, bone marrow (BM)-residing very small embryonic-like stem cells (VSELs) can be specified like PGCs into hematopoietic stem/progenitor cells (HSPCs). These two properties of VSELs support the possibility of a developmental origin of HSPCs from migrating PGCs.

METHODS

To address a potential link between VSELs and germ line cells we analyzed by RT-PCR and FACS expression of erythropoietin receptor (EpoR) on murine bone marrow- and human umbilical cord blood-derived VSELs, murine and human teratocarcinoma cell lines and human ovarian cancer cells. A proper gating strategy and immunostaining excluded from FACS analysis potential contamination by erythroblasts. Furthermore, the transwell chemotaxis assays as well as adhesion and signaling studies were performed to demonstrate functionality of erythropoietin - EpoR axes on these cells.

RESULTS

We report here that murine and human VSELs as well as murine and human teratocarcinoma cell lines and ovarian cancer cell lines share a functional EpoR.

CONCLUSIONS

Our data provide more evidence of a potential developmental link between germline cells, VSELs, and HSCs and sheds more light on the developmental hierarchy of the stem cell compartment in adult tissues.

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.

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.

Recovery of CD45(-)/Lin(-)/SSEA-4(+) very small embryonic-like stem cells by cord blood bank standard operating procedures

BACKGROUND AIMS

Very small embryonic-like (VSEL) stem cells are a rare cell population present in bone marrow, cord blood and other tissues that displays a distinct small cell size and the ability to give rise to cells of the three germ layers. VSEL stem cells were reported to be discarded in the red blood cell fraction by Ficoll-Paque density gradient centrifugation during the processing of bone marrow and cord blood specimens. However, most cord blood banks do not include density gradient centrifugation in their procedures while red blood cells are removed by Hespan sedimentation following the Cord Blood Transplantation Study cord blood bank standard operating procedures (COBLT SOP). To clarify the retention of VSEL stem cells, we investigated the recovery of VSEL stem cells following COBLT SOP guidelines.

METHODS

The recovery of CD45(-)/Lin(-)/SSEA-4(+) VSEL stem cells of umbilical cord blood was examined by flow cytometry before and after COBLT SOP processing, and relative expression of pluripotent genes was analyzed by quantitative polymerase chain reaction.

RESULTS

CD45(-)/Lin(-)/SSEA-4(+) VSEL stem cells were mostly recovered in the final products following COBLT SOP guidelines. The expression of pluripotent genes could be maintained at >80% in products after hetastarch (Hespan; B. Braun Medical Inc., Irvine, CA, USA) processing.

CONCLUSIONS

The rare sub-population of CD45(-)/Lin(-)/SSEA-4(+) VSEL stem cells survived after Hespan sedimentation. This finding suggests that umbilical cord blood units cryopreserved by COBLT SOP in cord blood banks should retain most VSEL stem cells present in the un-processed specimens.