Intrinsic Stem Cell Research Articles

Sorting, identification and enrichment of side population cells in acute monocytic leukemia THP-1 Cells

Objective To assay and determine whether the human acute monocytic leukemia cell line THP-1 contains side populations (SP) cells, and to increase the proportion of SP cells using cytarabine (Ara-C). Methods Fluorescent microscope and flow cytometry (FCM) were employed for detecting the percentage of SP cells in THP-1 cells.Then, SP and non-SP (NSP) subpopulations were collected and identified.Finally, THP-1 cells were incubated with different concentrations of Ara-C for 24 hours and detected the proportion of SP cells, respectively. Results The results demonstrated that the percentage of SP cells was (1.81±0.99)% in THP-1 cells.A majority of the SP cells remained in the G0/G1 phase, and the expressions of CD34+ and CD34+ CD38- and the proliferative ability of the SP cells were higher than those of NSP cells (P<0.05). The mRNA expression of multidrug resistance genes (ABCG2, ABCB1), apoptosis regulation genes (Bcl-2) and the Bcl-2/Bax ratio of SP cells were higher than those of NSP cells.SP cells have been shown to be more tumorigenic than NSP cells.After co-culture with Ara-C, the proportion of SP cells increased significantly and presented in a concentration-dependent manor. Conclusions All of these findings suggest that the THP-1 cell line contains SP cells and the SP cells possess some intrinsic stem cell properties.The proportion of SP cells can be increased when co-cultured with Ara C, and this technique is a useful and important application for the study of LSCs. Key words: THP-1 cell line; Leukemia stem cells; Side population cells; Ara-C

Intrinsic pluripotent stem cells, Muse cells, are a primary source of iPS cells in human fibroblasts

We found a novel type of pluripotent stem cells Multilineage differentiating Stress Enduring (Muse) cells (Kuroda et al., PNAS, 2010). They reside in adult mesenchymal tissues or cultured fibroblasts and can be isolated as cells double positive for mesenchymal marker CD105 and human ES cell marker SSEA‐3. Muse cells express pluripotency markers, self‐renew and exhibit triploblastic differentiation from a single cell but are not immortal in culture or tumorigenic in vivo. Recently, we found that Muse cells are a primary source of iPS cells in human fibroblasts (Wakao et al., PNAS, 2011). When human fibroblasts were separated into Muse and non‐Muse cells and transduced with Oct3/4, Sox2, Klf4, and c‐Myc, iPS cells were generated exclusively from Muse cells, but never from non‐Muse cells. Epigenetic alterations were not seen in non‐Muse cells and some of the major pluripotency markers were not expressed for the entire period of generation, suggesting that Muse cells that are already pluripotent selectively become iPS cells by acquiring tumorigenic proliferative activity, whereas the remaining cells make no contribution to the generation of iPS cells.

Sorting, identification and enrichment of side population cells in THP-1 acute monocytic leukemia cells

The objective of the present study was to examine and determine whether the human acute monocytic leukemia cell line THP-1 contains side population (SP) cells, and, if so, to increase the proportion of SP cells using arabinosylcytosine (Ara-C). Fluorescent microscopy and flow cytometry were employed to detect the percentage of SP cells in THP-1 cells. Then, SP and non-SP (NSP) cell subpopulations were collected and identified. THP-1 cells were incubated with different concentrations of Ara-C for 24 h and the proportion of SP cells was detected. Our results demonstrated that the percentage of SP cells was 1.81 ± 0.99% in THP-1 cells. A majority of the SP cells remained in the G₀/G₁ phase, and the expression of CD34⁺ and CD34⁺CD38⁻ and the proliferation ability of the SP cells were higher compared to NSP cells (P<0.05). The mRNA expression of multidrug resistance genes (ABCG2 and ABCB1), apoptosis regulation genes (Bcl-2) and the Bcl-2/Bax value of SP cells were higher than those of NSP cells. SP cells have been shown to be more tumorigenic than NSP cells. Following co-culture with Ara-C, the proportion of SP cells increased significantly and subsequently the Ara-C concentration increased. These findings suggest that the THP-1 cell line contains SP cells and that SP cells possess certain intrinsic stem cell properties and may contain a larger proportion of leukemia stem cells (LSCs). The concentrations of SP cells can be increased with Ara-C by co-culture, and this technique is a useful and important application for the study of LSCs.

Mesenchymal stem cells in neurological diseases

Due to the limited capacity of the CNS for regeneration, more effective treatment of chronic degenerative and inflammatory neurological conditions, but also of acute neuronal damage from injuries or cerebrovascular diseases, could be only achieved, theoretically at least, by stem cells that may have the potential to either regenerate or to support the survival of the existing, partially damaged, cells. A small number of stem cells are found in the adult brain in very specific regions, but this intrinsic stem cell repertoire is rather small and does not contribute significantly to the repair of damaged tissues. Transplantation of stem cells has long been suggested as a possible logical approach for repair of the damaged nervous system. Embryonic cells carrying the pluripotent and self-renewal properties represent the prototype of stem cells, but there are additional somatic stem cells that may be harvested and expanded from various tissues during adult life, such as the mesenchymal stem cells (MSC), which offer several practical advantages for the clinical application. MSC can be obtained from every adult and there are effective culture protocols for their expansion to large numbers for clinical uses. They seem to carry fewer risks for malignancies and some initial indications of their short-term safety (upon system delivery), in clinical settings, exist in the literature. Therefore, in most of the registered clinical trials with stem cells, MSC is the primary stem cell population used. This review summarizes the rationale, the mechanisms and the worldwide clinical experience with MSC, in neurological and other diseases.

The cardiac atrial appendage stem cell: a new and promising candidate for myocardial repair

Considerable shortcomings in the treatment of myocardial infarction (MI) still exist and therefore mortality remains high. Cardiac stem cell (CSC) therapy is a promising approach for myocardial repair. However, identification and isolation of candidate CSCs is mainly based on the presence or absence of certain cell surface markers, which suffers from some drawbacks. In order to find a more specific and reliable identification and isolation method, we investigated whether CSCs can be isolated based on the high expression of aldehyde dehydrogenase (ALDH). An ALDH(+) stem cell population, the cardiac atrial appendage stem cells (CASCs), was isolated from human atrial appendages. CASCs possess a unique phenotype that is clearly different from c-kit(+) CSCs but that seems more related to the recently described cardiac colony-forming-unit fibroblasts. Based on immunophenotype and in vitro differentiation studies, we suggest that CASCs are an intrinsic stem cell population and are not mobilized from bone marrow or peripheral blood. Indeed, they possess a clonogenicity of 16% and express pluripotency-associated genes. Furthermore, compared with cardiosphere-derived cells, CASCs possess an enhanced cardiac differentiation capacity. Indeed, differentiated cells express the most important cardiac-specific genes, produce troponin T proteins, and have an electrophysiological behaviour similar to that of adult cardiomyocytes (CMs). Transplanting CASCs in the minipig MI model resulted in extensive cardiomyogenic differentiation without teratoma formation. We have identified a new human CSC population able to differentiate into functional CMs. This opens interesting perspectives for cell therapy in patients with ischaemic heart disease.

Embryonic stem cells and inducible pluripotent stem cells: two faces of the same coin?

Embryonic stem cells (ESCs) are derived from the inner cell mass of the blastocysts and are characterized by the ability to renew themselves (self-renewal) and the capability to generate all the cells within the human body. In contrast, inducible pluripotent stem cells (iPSCs) are generated by transfection of four transcription factors in somatic cells. Like embryonic stem cells, they are able to self-renew and differentiate. Because of these features, both ESCs and iPSCs, are under intense clinical investigation for cell-based therapy. In this review, we revisit stem cell biology and add a new layer of complexity. In particular, we will highlight some of the complexities of the system, but also where there may be therapeutic potential for modulation of intrinsic stem cells and where particular caution may be needed in terms of cell transplantation therapies.

Potential Treatment Strategies For Enhancing Neuroplasticity and Regeneration After Ischemic Stroke

Strokes are a major cause of death and result in a drastic reduction in quality of life. Novel therapeutic strategies for patients suffering from stroke are thus required. Two possible strategies can be proposed for treating ischemic stroke: enhancing neuroplasticity, allowing the surviving neuronal cells to compensate for stroke-related impairment through brain reorganization, sprouting and rewiring of neuronal cells, or regeneration of neuronal cells, including enhancement of intrinsic neurogenesis and stem cell transplantation therapy with neural stem cells, embryonic stem cells or induced pluripotent stem cells. Endogenous neurogenesis or transplanted neural stem cells, embryonic stem cells or induced pluripotent stem cell-derived cells are able to not only supply newborn neurons integrated into a damaged neuronal network, but also produce growth factors into the recovering brains. These secretory factors enhance sprouting and angiogenesis and may be important in neuroplasticity and recovery in the poststroke brain.

Worldwide status of clinical experimentation with stem cells in neurologic diseases

The adult brain contains small numbers of stem cells in restricted areas, but this intrinsic stem cell repertoire is small and does not contribute substantially to regeneration of damaged neurons. Transplantation of stem cells has long been suggested as a possible logical approach for CNS repair. Embryonic stem cells (ESC) possessing pluripotent and self-renewal properties represent the stem cell prototype1 and have a tremendous transdifferentiation ability and, therefore, the potential for neural cell replacement. However, the transplantation of undifferentiated ESCs cannot provide a first-line option for clinical applications since it is associated with a high risk of potential carcinomatous transformation. There are additional somatic stem cells that may be easily harvested and expanded from various tissues during adult life, such as neuronal (NSC) and mesenchymal stem cells (MSC).2 Fetal NSC, despite the advantage of being naturally “neuralized,” are accompanied by numerous ethical, scientific, and legislative hurdles upon transplantation into the human adult brain.3 MSC, which exert immunomodulatory effects and secrete various neurotrophic factors, are easier to obtain (usually from the bone marrow) and their use is not beset by contentious ethical issues.2 As these cells seem to be able to pass the blood–brain barrier, no invasive intracerebral surgery is required and peripheral systemic administration or injection into the CSF compartment have been proven safe and efficient ways for cell delivery in humans.4 In vitro experiments provided the initial proof for differentiation (or transdifferentiation) of embryonic and adult type somatic stem cells into cells of the neuronal lineage.5 Additional (and more convincing) proof was provided by animal studies. Over the past decade, clinching evidence has emerged regarding the capability of various stem cell populations to induce regeneration in animal models of neurologic disorders such as Parkinson disease (PD), Huntington disease (HD), multiple system atrophy (MSA), …

Myeloproliferative disorders in older people

SummaryThe term myeloproliferative disorders (MPDs) describes a group of conditions in which an intrinsic stem cell defect is present in the bone marrow. This leads to hypercellularity in one or more of the myeloid cell lines (red blood cells, platelets, granulocytes and their precursors), or increased bone marrow fibrosis. MPDs are rare; combined annual incidence is 6 per 100,000.MPDs may present in asymptomatic patients as an incidental finding, or may be associated with constitutional features such as weight loss, sweats or lethargy. Splenomegaly is common but lymphadenopathy is not a feature. The most significant complications are: arterial thrombosis, venous thrombosis, secondary marrow fibrosis and transformation to acute myeloblastic leukaemia (AML). Treatment aims to reduce the risk of such complications.Recent advances in the understanding of the pathogenesis of these disorders have radically changed the approach to the diagnosis of MPD and are the focus of new treatment developments.

MEIS1 Is Required for the Maintenance of Long Term Hematopoietic Stem Cells Wherein It Regulates Quiescence

Abstract 551Normal hematopoiesis is maintained by long-term hematopoietic stem cells (LT-HSCs) that are defined by their extensive self-renewal and multipotency. Self-renewal of LT-HSCs in turn is regulated by a complex network of intrinsic and extrinsic factors. The transcription factor MEIS1 is highly expressed in hematopoietic stem and progenitor cells and also in several leukemias, suggesting that MEIS1 might be important in regulating self-renewal. However, the role of MEIS1 in normal hematopoiesis has not been defined. To determine the role of MEIS1 in hematopoiesis, we studied conditional knockout mice. We generated transgenic mice bearing loxp sites flanking the homeodomain of MEIS1. The MEIS1-floxed mice were then bred to Rosa26-CreERT2 mice, the latter expressing cre-recombinase ubiquitously, that can be activated by estrogen or its analog Tamoxifen (Tam). Efficient, complete recombination was achieved in vivo by treating MEIS1-f/f-Cre (homozygous for MEIS1-flox) mice with Tam and in vitro by treating bone marrow cells with 4-hydroxy tamoxifen. Loss of MEIS1 expression was detected by QRT-PCR and western blotting. To determine the role of MEIS1 in the maintenance of adult hematopoiesis, MEIS1-f/f-Cre and control mice were treated with Tam and MEIS1 deletion confirmed by PCR. At three weeks post deletion, bone marrow analysis showed a significant reduction in the number of LT-HSCs defined as lin-/c-Kit+/Sca1+/CD48−/CD150+ in the MEIS1-depleted mice compared to controls (0.012% compared to 0.037%, N=6, p<0.05, t-test). However, the progenitor populations were unaffected by MEIS1 deletion. Over a period of 12 weeks of observation, the mice did not show any signs of distress and the peripheral blood counts of the experimental and control mice remained normal, indicating that short term hematopoiesis was not affected. Cell cycle analysis of LT-HSCs showed that MEIS1 deletion resulted in a significant shift of cells from G0 to G1 phase (G0 and G1 proportions respectively, 81.75±3.25% and 9.40±3% for control and 56.10±0.873% and 31.17±1.5% for MEIS1-deleted). To determine the effects of MEIS1 loss on intrinsic hematopoietic stem cell function, we performed competitive repopulation assays. Bone marrow cells harvested from MEIS1-f/f-Cre or MEIS1-f/+-Cre (control) mice were combined with equal numbers of bone marrow cells from BoyJ mice and transplanted via tail vein injection into lethally irradiated BoyJ mice. Four weeks after transplant, recipients were treated with Tam or vehicle for 5 days and deletion of MEIS1 confirmed by PCR on peripheral blood. Peripheral blood of recipient mice was analyzed at 1, 4, 8, 12 and 16 weeks after treatment and relative chimerism assessed by flow cytometry. At 1 and 4 weeks after treatment, the chimerism in the MEIS1 deleted group (Tam treated MEIS1-f/f-CreER) and the control groups (Tam treated MEIS1-f/+-CReER and vehicle treated MEIS1-f/f-CreER) was comparable (41%, 40.5% and 41.5% respectively, average, N=5 to 8). However, by 8 weeks after treatment, the MEIS1 deleted group showed a significant decline in chimerism compared to controls (18.2% compared to 43.1% and 35.1% respectively, p<0.02, t-test) and at 16 weeks the chimerism in the MEIS1-deleted group declined further (11.1% compared to 40.2% and 35.0% respectively, p<0.001). Subpopulation analysis showed loss of chimerism in granulocytes and in B and T lymphocytes. The latency and breadth of the effect of MEIS1 loss suggested an effect on the hematopoietic stem cell population. Indeed, bone marrow analysis of transplant recipients showed near complete loss of LT-HSC chimerism (3% compared to 70.25% and 75.6% respectively, p<0.001). Finally, we performed gene expression profiling on lineage negative bone marrow cells with and without MEIS1 deletion. Results showed that loss of MEIS1 was associated with decreased expression of hypoxia-responsive genes. Collectively, these results indicate that MEIS1 is required for the maintenance of the pool of LT-HSCs. Loss of MEIS1 promotes cycling and exhaustion of LT-HSCs. Further, we propose that activation of the hypoxia-response pathway may be one of the mechanisms by which MEIS1 exerts its effects on hematopoietic stem cells. Disclosures:No relevant conflicts of interest to declare.

Low-dose Erythropoietin reduces risk of heart failure induced by anti-cancer therapy

Heart disease can be caused by many different insults and injuries and often terminates in death from heart failure, an inability of the heart muscle to adequately supply blood to the body. A major aim in today's research is to define novel therapeutic strategies to limit myocardial damage and to enhance the ability of the heart muscle to regenerate and to heal itself. The anti-cancer drug doxorubicin (DOX) is used to treat a broad range of cancers but is limited in its use by severe side effects, most notably heart failure [1]. STAT3 is an important factor that promotes survival and migration of many tumor cell types and its pharmacological blockade hold good promise as a novel anti-cancer strategy [2, 3]. However, likewise to DOX, blocking STAT3 in the heart has been associated with heart failure in various experimental models [4, 5]. In our latest work, we found that low-doses of erythropoietin (EPO), a cytokine with multiple functions best known for its role to control the production of red blood cells, reduces the risk of heart failure mediated by DOX treatment or STAT3 blockade [6]. Our findings suggest that treatment with low-doses (hematocrit-inactive) synthetic EPO (CERA) during DOX treatment or STAT3 blockade is able to preserve the ability of cardiac progenitor cells to repair the vasculature of the heart and thereby to attenuate myocardial injury [6]. Recent studies have shown that the heart possesses intrinsic cardiac stem or progenitor cells that can contribute to regeneration and healing during disease and aging [7]. Little is known about the molecules and pathways that regulate stem cell proliferation and differentiation. In order to obtain a better understanding how the cardiac microenvironment impacts on the endogenous regeneration system of the adult heart, we studied phenotypic alterations of resident cardiac progenitor cells (identified by the expression of Sca-1) in heart failure as a consequence of DOX treatment or genetic ablation of STAT3 in cardiac muscle cells. We observed that in both heart failure models, cardiac progenitor cells displayed an impaired ability to form new blood vessels essential for oxygen delivery to the heart muscle[6]. Both models also exhibited reduced production of EPO in the heart muscle[6]. Interestingly, we found that cardiac progenitor cells bind EPO within the cardiac microenvironment, a feature that seems to be required to maintain the ability to differentiate into new blood vessels[6]. Importantly, administration of the synthetic EPO derivative CERA at a low-dosage (hematocrit-inactive) restored or preserved the endothelial differentiation potential of cardiac progenitor cells in mice with depleted STAT3 or in mice obtaining DOX treatment. Moreover, CERA preserved heart blood vessels and cardiac function in both mouse models[6]. Our data imply that short-term EPO administration at low-doses seems an attractive avenue to pursue for protecting the heart against chemotherapy-induced failure and might even have broader applications in cardiac regeneration[6]. However, further evaluation of EPO in tumor research is required, especially with regard to its effect on tumor growth and anti-tumor treatment strategies.

Cardiac Regeneration by Intrinsic Cardiac Stem Cells

Cardiac Regeneration by Intrinsic Cardiac Stem Cells

Eradication of breast cancer cells in patients with distant metastasis: the finishing touches?

Cytotoxic agents are significantly active in breast cancer cells, but their usefulness has been limited in treating metastatic breast cancer (MBC). This has facilitated the development of an approach using molecular-targeted agents. Intrinsic subtypes including luminal A, luminal B, human epidermal growth factor receptor type 2 (HER2)-enriched, basal-like, and claudin-low tumors exhibit original drug responsiveness and clinical prognosis. Anti-HER2 treatments, trastuzumab or lapatinib, have demonstrated clinically significant efficacy. Poly ADP-ribose polymerase-1 inhibitors act against BRCA1-disabled breast cancer. Cancer stem cells could be the major obstacle to achieving a cure in systemic treatment. Extensive investigations are underway to develop novel agents that act on the genes or signaling of Hedgehog, Wnt, and Notch, which regulate cancer stem cells. Cancer cells undergo epithelial-mesenchymal transition (EMT) and acquire invasive properties. Breast cancer cells alter their phenotype in blood and bone marrow, e.g., circulating tumor cells or disseminated tumor cells. Cancer stem cells, like normal stem cells, may exist at niches in bone marrow. To achieve a cure for MBC, it is necessary to disrupt cancer stem cell-niche interactions or eradicate cancer stem cells. Traditional treatments with cytotoxic or endocrine agents require development in relation to intrinsic subtypes, stem cells, or EMT.

Restraining Stem Cell Niche Plasticity: A New Talent of Eph Receptors

Multiple Eph receptor tyrosine kinases and ephrin ligands are expressed in stem cells and their niches, where their complex roles are under intense investigation. Nomura et al. (2010) reveal an unexpected function of Eph signaling in suppressing cell fate plasticity of niche cells in the adult brain.

EphB Signaling Controls Lineage Plasticity of Adult Neural Stem Cell Niche Cells

Stem cells remain in specialized niches over the lifespan of the organism in many organs to ensure tissue homeostasis and enable regeneration. How the niche is maintained is not understood, but is probably as important as intrinsic stem cell self-renewal capacity for tissue integrity. We here demonstrate a high degree of phenotypic plasticity of the two main niche cell types, ependymal cells and astrocytes, in the neurogenic lateral ventricle walls in the adult mouse brain. In response to a lesion, astrocytes give rise to ependymal cells and ependymal cells give rise to niche astrocytes. We identify EphB2 forward signaling as a key pathway regulating niche cell plasticity. EphB2 acts downstream of Notch and is required for the maintenance of ependymal cell characteristics, thereby inhibiting the transition from ependymal cell to astrocyte. Our results show that niche cell identity is actively maintained and that niche cells retain a high level of plasticity.

Efficacy of the coadministration of granulocyte colony-stimulating factor and stem cell factor in the activation of intrinsic cells after spinal cord injury in mice

Granulocyte colony-stimulating factor (G-CSF) is a hematopoietic cytokine that induces undifferentiated stem cells from the bone marrow (BM) into the peripheral blood. Stem cell factor (SCF) is also a hematopoietic cytokine that stimulates the differentiation and proliferation of neural stem cells and has neuroprotective effects. In cerebrally infarcted mice, the combination of G-CSF and SCF promotes the differentiation of BM-derived cells into neural cells, stimulates the proliferation of intrinsic neural stem cells, and improves motor function. The object of this study was to investigate the effects of these cytokines on BM stem cells, intrinsic cells, and motor function recovery in spinal cord-injured mice. For marking BM-derived cells, the authors induced contusive spinal cord injury in mice transplanted with BM cells from green fluorescent protein (GFP)-transgenic mice after whole-body irradiation. These mice were treated with G-CSF and SCF in the subacute injury phase. Bromodeoxyuridine (BrdU) was injected into these mice to label proliferating cells. The cell numbers and phenotype of the BM-derived cells were evaluated, and the change in intrinsic cells (proliferation, accumulation, and differentiation) was noted using immunohistological analysis at 4 weeks postinjury (wpi). A behavior analysis was conducted until 12 wpi using the Basso, Beattie, Bresnahan locomotor rating scale. In the SCF + G-CSF group, improvement in hindlimb motor function was significantly greater than in the SCF group, G-CSF group, and sham-treatment (vehicle) group after 8 wpi. At 4 wpi, the number of GFP+ BM-derived cells induced in the lesion did not significantly differ between groups. At 4 wpi, the authors evaluated perilesional GFP− intrinsic spinal cord cells. The number of GFP− and F4/80+ cells was significantly greater in the SCF + G-CSF group than in the other 3 groups. As compared with the sham group, the number of NG2+/BrdU+ cells was significantly increased in the SCF + G-CSF group. In this study, the combined administration of SCF and G-CSF in traumatic spinal cord injury not only improved motor function, but also induced the accumulation of intrinsic microglia and the active proliferation of intrinsic oligodendrocyte precursor cells.

Syndromes myélodysplasiques érythroblastopéniques

Myelodysplastic syndrome with erythroid hypoplasia or erythroblastopenia has not yet been clearly defined, and in most patients it is mistaken for acquired pure red cell aplasia. Including one additional patient reported in this article, a literature review revealed only 50 cases over the last 20 years. These patients were predominantly elderly males, all required regular packed red cell transfusions, and they had a poor prognosis, mainly because of acute transformation. The mechanisms of erythroid aplasia remain unclear. However, recent data suggest the association of an intrinsic stem cell defect with immunological implication.

The influence of collagen film nanostructure on pulmonary stem cells and collagen–stromal cell interactions

We have recently identified a rare subpopulation of lung colony cells with the characteristics of pulmonary stem cells, and discovered that stem cell colonies grew preferentially on type I collagen films in a serum-free medium. In order to further optimize culture conditions and determine stem cell growth in relation to microenvironments (including the stroma, medium and nanostructures of type I collagen films), both primary and pre-sorted stem cells were cultured on the type I collagen films with controllable degree of polymerization and film thickness, as confirmed by an atomic force microscope and surface profiler. We found that in a primary culture, the spreading of stromal cells is greatly restrained and both the size and number of colonies are significantly reduced on highly polymerized collagen films. In contrast, in a pre-sorted stem cell culture without stromal cells, the intrinsic stem cell properties and cell number are independent of the degree of collagen polymerization. Our results indicate that the nanostructures of type I collagen films primarily affect stem colony formation through the collagen–stroma interactions. In those cases, collagen film thickness shows no effect on colony formation.

Endothelial progenitors encapsulated in bioartificial niches are insulated from systemic cytotoxicity and are angiogenesis competent

Intrinsic stem cells (SC) participate in tissue remodeling and regeneration in various diseases and following toxic insults. Failure of tissue regeneration is in part attributed to lack of SC protection from toxic stress of noxious stimuli, thus prompting intense research efforts to develop strategies for SC protection and functional preservation for in vivo delivery. One strategy is creation of artificial SC niches in an attempt to mimic the requirements of endogenous SC niches by generating scaffolds with properties of extracellular matrix. Here, we investigated the use of hyaluronic acid (HA) hydrogels as an artificial SC niche and examined regenerative capabilities of encapsulated embryonic endothelial progenitor cells (eEPC) in three different in vivo models. Hydrogel-encapsulated eEPC demonstrated improved resistance to toxic insult (adriamycin) in vitro, thus prompting in vivo studies. Implantation of HA hydrogels containing eEPC to mice with adriamycin nephropathy or renal ischemia resulted in eEPC mobilization to injured kidneys (and to a lesser extent to the spleen) and improvement of renal function, which was equal or superior to adoptively transferred EPC by intravenous infusion. In mice with hindlimb ischemia, EPC encapsulated in HA hydrogels dramatically accelerated the recovery of collateral circulation with the efficacy superior to intravenous infusion of EPC. In conclusion, HA hydrogels protect eEPC against adriamycin cytotoxicity and implantation of eEPC encapsulated in HA hydrogels supports renal regeneration in ischemic and cytotoxic (adriamycin) nephropathy and neovascularization of ischemic hindlimb, thus establishing their functional competence and superior capabilities to deliver stem cells stored in and released from this bioartificial niche.

Strategies for ensuring that regenerative cardiomyocytes function properly and in cooperation with the host myocardium

In developed countries, in which people have nutrient-rich diets, convenient environments, and access to numerous medications, the disease paradigm has changed. Nowadays, heart failure is one of the major causes of death. In spite of this, the therapeutic efficacies of medications are generally unsatisfactory. Although whole heart transplantation is ideal for younger patients with heart failure, many patients are deemed to be unsuitable for this type of surgery due to complications and/or age. The need for therapeutic alternatives to heart transplantation is great. Regenerative therapy is a strong option. For this purpose, several cell sources have been investigated, including intrinsic adult stem or progenitor cells and extrinsic pluripotent stem cells. Most intrinsic stem cells seem to contribute to a regenerative environment via paracrine factors and/or angiogenesis, whereas extrinsic pluripotent stem cells are unlimited sources of cardiomyocytes. In this review, we summarize the various strategies for using regenerative cardiomyocytes including our recent progressions: non-genetic approaches for the purification of cardiomyocytes and efficient transplantation. We expect that use of intrinsic and extrinsic stem cells in combination will enhance therapeutic effectiveness.