Stem Cell-based Regenerative Medicine Research Articles

Glycoengineering of HCELL, the Human Bone Marrow Homing Receptor: Sweetly Programming Cell Migration

The successful clinical implementation of adoptive cell therapeutics, including bone marrow transplantation and other stem cell-based treatments, depends critically on the ability to deliver cells to sites where they are needed. E-selectin, an endothelial C-type lectin, binds sialofucosylated carbohydrate determinants on its pertinent ligands. This molecule is expressed in a constitutive manner on bone marrow and dermal microvascular endothelium, and inducibly on post-capillary venules at all sites of tissue injury. Engagement of E-selectin with relevant ligand(s) expressed on circulating cells mediates initial "tethering/rolling" endothelial adhesive interactions prerequisite for extravasation of blood-borne cells at any target tissue. Most mammalian cells express high levels of a transmembrane glycoprotein known as CD44. A specialized glycoform of CD44 called "Hematopoietic Cell E-/L-selectin Ligand" (HCELL) is a potent E-selectin ligand expressed on human cells. Under native conditions, HCELL expression is restricted to human hematopoietic stem/progenitor cells. We have developed a technology called "Glycosyltransferase-Programmed Stereosubstitution" (GPS) for custom-modifying CD44 glycans to create HCELL on the surface of living cells. GPS-based glycoengineering of HCELL endows cell migration to endothelial beds expressing E-selectin. Enforced HCELL expression targets human mesenchymal stem cell homing to marrow, licensing transendothelial migration without chemokine signaling via a VLA-4/VCAM-1-dependent "Step 2-bypass pathway." This review presents an historical framework of the homing receptor concept, and will describe the discovery of HCELL, its function as the bone marrow homing receptor, and how enforced expression of this molecule via chemical engineering of CD44 glycans could enable stem cell-based regenerative medicine and other adoptive cell therapeutics.

Telomere dysfunction and cell cycle checkpoints in hematopoietic stem cell aging

Stem cells are believed to be closely associated with tissue degeneration during aging. Studies of human genetic diseases and gene-targeted animal models have provided evidence that functional decline of telomeres and deregulation of cell cycle checkpoints contribute to the aging process of tissue stem cells. Telomere dysfunction can induce DNA damage response via key cell cycle checkpoints, leading to cellular senescence or apoptosis depending on the tissue type and developmental stage of a specific stem cell compartment. Telomerase mutation and telomere shortening have been observed in a variety of hematological disorders, such as dyskeratosis congenital, aplastic anemia, myelodysplastic syndromes and leukemia, in which the hematopoietic stem cells (HSC) are a major target during the pathogenesis. Moreover, telomere dysfunction is able to induce both cell-intrinsic checkpoints and environmental factors limiting the self-renewal capacity and differentiation potential of HSCs. Crucial components in the cascade of DNA damage response, including ataxia telangiectasia mutated, CHK2, p53, p21 and p16/p19(ARF), play important roles in HSC maintenance and self-renewal in the scenarios of both sufficient telomere reserve and dysfunctional telomere. Therefore, a further understanding of the molecular mechanisms underlying HSC aging may help identity new therapeutic targets for stem cell-based regenerative medicine.

Nasal Septum-Derived Multipotent Progenitors: A Potent Source for Stem Cell-Based Regenerative Medicine

Thus far, autologous adult stem cells have attracted great attention for clinical purposes. In this study, we aimed at identifying and comprehensively characterizing a subpopulation of multipotent cells within human nasal septal cartilage. We also conducted a comparative investigation with other well-established stem cells such as bone marrow-mesenchymal stem cells, adipose tissue-mesenchymal stem cells, and unrestricted somatic stem cells. The isolated clonal population was characterized using immunofluorescence, flow cytometry, reverse transcriptase, and real-time polymerase chain reaction. Nasal septal progenitors (NSP) expressed critical pluripotency and mesoectodermal stem cell markers. They also shared many characteristics with MSC in expression of CD90, CD105, CD106, CD166, and HLA-ABC and lack of expression of CD34, CD45, and HLA-DR. NSP distinctly presented CD133 (Prominin-1). These cells could proliferate rapidly in vitro with a higher clonogenic potential and showed a longer lifespan than other studied cells. This population bears some other multipotent properties in showing a high capacity to be differentiated into other lineages including chondrocytes, osteocytes, and neural-like cell types. Another strong/positive feature of this population was their ability to be safely expanded ex vivo with no susceptibility to chromosomal abnormality or tumorigenicity both in vitro and in vivo. In conclusion, NSP could be considered as an alternative autologous cell source that can bring them to the top of therapeutic applications.

Skeletal Myoblasts for Cardiac Repair

Stem cells provide an alternative curative intervention for the infarcted heart by compensating for the cardiomyocyte loss subsequent to myocardial injury. The presence of resident stem and progenitor cell populations in the heart, and nuclear reprogramming of somatic cells with genetic induction of pluripotency markers are the emerging new developments in stem cell-based regenerative medicine. However, until safety and feasibility of these cells are established by extensive experimentation in in vitro and in vivo experimental models, skeletal muscle-derived myoblasts, and bone marrow cells remain the most well-studied donor cell types for myocardial regeneration and repair. This article provides a critical review of skeletal myoblasts as donor cells for transplantation in the light of published experimental and clinical data, and indepth discussion of the advantages and disadvantages of skeletal myoblast-based therapeutic intervention for augmentation of myocardial function in the infarcted heart. Furthermore, strategies to overcome the problems of arrhythmogenicity and failure of the transplanted skeletal myoblasts to integrate with the host cardiomyocytes are discussed.

E0230 The effect of co-culturing with native cardiomyocytes on ascorbic acid-induced cardiomyogenic differentiation in embryonic stem cells

ObjectiveAscorbic acid has been reported to promote the differentiation of embryonic stem cells (ESCs) into cardiomyocytes (CMs). However, appropriate culture protocols are needed to improve the differentiation efficiency and produce...

Targeting of Embryonic Stem Cells by Peptide-Conjugated Quantum Dots

BackgroundTargeting stem cells holds great potential for studying the embryonic stem cell and development of stem cell-based regenerative medicine. Previous studies demonstrated that nanoparticles can serve as a robust platform for gene delivery, non-invasive cell imaging, and manipulation of stem cell differentiation. However specific targeting of embryonic stem cells by peptide-linked nanoparticles has not been reported.Methodology/Principal FindingsHere, we developed a method for screening peptides that specifically recognize rhesus macaque embryonic stem cells by phage display and used the peptides to facilitate quantum dot targeting of embryonic stem cells. Through a phage display screen, we found phages that displayed an APWHLSSQYSRT peptide showed high affinity and specificity to undifferentiated primate embryonic stem cells in an enzyme-linked immunoabsorbent assay. These results were subsequently confirmed by immunofluoresence microscopy. Additionally, this binding could be completed by the chemically synthesized APWHLSSQYSRT peptide, indicating that the binding capability was specific and conferred by the peptide sequence. Through the ligation of the peptide to CdSe-ZnS core-shell nanocrystals, we were able to, for the first time, target embryonic stem cells through peptide-conjugated quantum dots.Conclusions/SignificanceThese data demonstrate that our established method of screening for embryonic stem cell specific binding peptides by phage display is feasible. Moreover, the peptide-conjugated quantum dots may be applicable for embryonic stem cell study and utilization.

New concepts for reconstruction of retinal and pigment epithelial tissues

The rise of stem cell-based regenerative medicine has created great hopes for novel therapies for major blinding diseases. Intensive relevant research is grounded on a deep cellular and molecular knowledge of the complex embryonic development of the neural retina and retinal pigmented epithelium (RPE) from the eye vesicle. This research similarly relies on a long history of transdifferentiation studies, having revealed an innate capacity to regenerate a more or less complete retinal tissue from RPE. To analyze principles of self-organization that govern retinal tissue (re-)construction under normal or regenerative conditions on a ‘cell-by-cell’ basis, the reaggregate approach of dispersed embryonic progenitor cells into retinotypic cellular spheres has been instrumental. Based on this knowledge, a multitude of fascinating studies using embryonic, induced pluripotent, adult stem cells, or permanent cell lines from various species have been carried out over the past two decades, and directed production of human retinal and RPE cell types has become possible. Moreover, reconstruction of complete retinal tissue, of functioning RPE monolayers, or even eye-like structures has become feasible. After their implantation into appropriate animal models for blinding diseases, some functional recovery has been observed. Here, we review some historical, cellular and molecular perspectives of this vast research program.

Stem Cell Based Regenerative Medicine: Is Russia Taking the Lead? A Case Study from St. Petersburg

The recent scientific breakthroughs in genetics have lead to a thriving stem cell industry transforming the way medicine is practiced. This article discusses these developments and presents a case study of Russian research institute in St. Petersburg which is doing state of the art stem cell trials providing successful treatment of blood vessel disease andbone fractures. The potential impact of stem cell technology on regenerative medicine is discussed, the potential convergence of nanoparticle science and its contribution to stem cell research is discussed, and the dynamics of the stem cell industry is presented.

Human mesenchymal stem cell differentiation on self-assembled monolayers presenting different surface chemistries

Human mesenchymal stem cells (hMSCs) have tremendous potential as a cell source for regenerative medicine due to their capacity for differentiation into a wide range of connective tissue cell types. Although significant progress has been made in the identification of defined growth factor conditions to induce lineage commitment, the effect of underlying biomaterial properties on functional differentiation is far less understood. Here we conduct a systematic assessment of the role for surface chemistry on cell growth, morphology, gene expression and function during hMSC commitment along osteogenic, chondrogenic and adipogenic lineages. Using self-assembled monolayers of ω-functionalized alkanethiols on gold as model substrates, we demonstrate that biomaterial surface chemistry differentially modulates hMSC differentiation in a lineage-dependent manner. These results highlight the importance of initial biomaterial surface chemistry on long-term functional differentiation of adult stem cells, and suggest that surface properties are a critical parameter that must be considered in the design of biomaterials for stem cell-based regenerative medicine strategies.

Introducing Transcription Factors to Multipotent Mesenchymal Stem Cells: Making Transdifferentiation Possible

Multipotent mesenchymal stem cells (MSCs) represent a promising autologous source for regenerative medicine. Because MSCs can be isolated from adult tissues, they represent an attractive cell source for autologous transplantation. A straightforward therapeutic strategy in the field of stem cell-based regenerative medicine is the transplantation of functional differentiated cells as cell replacement for the lost or defective cells affected by disease. However, this strategy requires the capacity to regulate stem cell differentiation toward the desired cell fate. This therapeutic approach assumes the capability to direct MSC differentiation toward diverse cell fates, including those outside the mesenchymal lineage, a process termed transdifferentiation. The capacity of MSCs to undergo functional transdifferentiation has been questioned over the years. Nonetheless, recent studies support that genetic manipulation can serve to promote transdifferentiation. Specifically, forced expression of certain transcription factors can lead to reprogramming and alter cell fate. Using such a method, fully differentiated lymphocytes have been reprogrammed to become macrophages and, remarkably, somatic cells have been reprogrammed to become embryonic stem-like cells. In this review, we discuss the past and current research aimed at transdifferentiating MSCs, a process with applications that could revolutionize regenerative medicine.

AICAR activates the pluripotency transcriptional network in embryonic stem cells and induces KLF4 and KLF2 expression in fibroblasts

BackgroundPluripotency, the property of a cell to differentiate into all cellular types of a given organism, is central to the development of stem cell-based therapies and regenerative medicine. Stem cell pluripotency is the result of the orchestrated activation of a complex transcriptional network characterized by the expression of a set of transcription factors including the master regulators of pluripotency Nanog and Oct4. Recently, it has been shown that pluripotency can be induced in somatic cells by viral-mediated expression of the transcription factors Oct3/4, Sox2, Klf4, and c-Myc.ResultsHere we show that 5-Aminoimidazole-4-carboxamide-1-b-riboside (AICAR) is able to activate the molecular circuitry of pluripotency in mouse embryonic stem cells (mESC) and maintain Nanog and Oct4 expression in mESC exposed to the differentiating agent retinoic acid. We also show that AICAR is able to induce Klf4, Klf2 and Myc expression in both mESC and murine fibroblasts.ConclusionAICAR is able to activate the molecular circuitry of pluripotency in mESC and to induce the expression of several key regulators of pluripotency in somatic cells. AICAR is therefore a useful pharmacological entity for studying small molecule mediated induction of pluripotency.

Deconstructing Stem Cell Tumorigenicity: A Roadmap to Safe Regenerative Medicine

Many of the earliest stem cell studies were conducted on cells isolated from tumors rather than from embryos. Of particular interest was research on embryonic carcinoma cells (EC), a type of stem cell derived from teratocarcinoma. The EC research laid the foundation for the later discovery of and subsequent work on embryonic stem cells (ESC). Both ESC isolated from the mouse (mESC) and then later from humans (hESC) shared not only pluripotency with their EC cousins, but also robust tumorigenicity as each readily form teratoma. Surprisingly, decades after the discovery of mESC, the question of what drives ESC to form tumors remains largely an open one. This gap in the field is particularly serious as stem cell tumorigenicity represents the key obstacle to the safe use of stem cell-based regenerative medicine therapies. Although some adult stem cell therapies appear to be safe, they have only a very narrow range of uses in human disease. Our understanding of the tumorigenicity of human induced pluripotent stem cells (IPSC), perhaps the most promising modality for future patient-specific regenerative medicine therapies, is rudimentary. However, IPSC are predicted to possess tumorigenic potential equal to or greater than that of ESC. Here, the links between pluripotency and tumorigenicity are explored. New methods for more accurately testing the tumorigenic potential of IPSC and of other stem cells applicable to regenerative medicine are proposed. Finally, the most promising emerging approaches for overcoming the challenges of stem cell tumorigenicity are highlighted.

Regulation of Cell Cytoskeleton and Membrane Mechanics by Electric Field: Role of Linker Proteins

Cellular mechanics is known to play an important role in the cell homeostasis including proliferation, motility, and differentiation. Significant variation in the mechanical properties between different cell types suggests that control of the cell metabolism is feasible through manipulation of the cell mechanical parameters using external physical stimuli. We investigated the electrocoupling mechanisms of cellular biomechanics modulation by an electrical stimulation in two mechanically distinct cell types—human mesenchymal stem cells and osteoblasts. Application of a 2 V/cm direct current electric field resulted in approximately a twofold decrease in the cell elasticity and depleted intracellular ATP. Reduction in the ATP level led to inhibition of the linker proteins that are known to physically couple the cell membrane and cytoskeleton. The membrane separation from the cytoskeleton was confirmed by up to a twofold increase in the membrane tether length that was extracted from the cell membrane after an electrical stimulation. In comparison to human mesenchymal stem cells, the membrane-cytoskeleton attachment in osteoblasts was much stronger but, in response to the same electrical stimulation, the membrane detachment from the cytoskeleton was found to be more pronounced. The observed effects mediated by an electric field are cell type- and serum-dependent and can potentially be used for electrically assisted cell manipulation. An in-depth understanding and control of the mechanisms to regulate cell mechanics by external physical stimulus (e.g., electric field) may have great implications for stem cell-based tissue engineering and regenerative medicine.

Epigenetic regulation of stem cell fate

Stem cell-based regenerative medicine holds great promise for repair of diseased tissue. Modern directions in the field of epigenetic research aimed to decipher the epigenetic signals that give stem cells their unique ability to self-renew and differentiate into different cell types. However, this research is only the tip of the iceberg when it comes to writing an 'epigenetic instruction manual' for the ramification of molecular details of cell commitment and differentiation. In this review, we discuss the impact of the epigenetic research on our understanding of stem cell biology.

Establishment of a Labeling System for Hematopoietic Stem Cells by Nucleostemin Enhancer/Promoter-GFP Transgenic Mice.

A labeling system for tissue stem cells is a powerful tool for stem cell research and for development of stem cell-based regenerative medicine to human disease. Here we generated transgenic mice expressing green fluorescent protein (GFP) under control of enhancer/promoter activity to Nucleostemin (NS) gene. NS, a nucleolar GTP-binding protein, expresses at high levels in embryonic stem cells and neural stem cells, suggesting that NS expresses in various tissue stem cells. In fact, we found that NS highly expressed in mouse immature hematopoietic cells containing hematopoietic stem cells (HSCs) and progenitor cells compared with differentiated hematopoietic cells. To examine whether HSCs could be labeled by using enhancer/promoter activity to NS gene, we generated transgenic mice harboring putative genomic enhancer/promoter region of NS gene followed by GFP cDNA-polyA in the 3′ end (NS-GFP tg mice). Fluorescence activated cell sorting (FACS) analysis indicated that most bone marrow (BM) mononuclear cells (MNCs) showed green fluorescence in NS-GFP tg mice. To validate the relationship between fluorescent intensity of GFP and expression levels of endogenous NS mRNA, BM MNCs from NS-GFP tg mice were separated into four fractions depending on their fluorescent intensity (i.e., GFP−, GFP+, GFP++, and GFP+++) by FACS, and these cells were subjected to quantitative real-time PCR analysis. The fluorescent intensity of GFP certainly reflected the amount of endogenous NS mRNA, indicating that the enhancer/promoter region used in this study is sufficient for monitoring the expression levels of endogenous NS mRNA in vivo. We next characterized expression levels of cell-surface markers on the four fractions of BM MNCs. FACS analysis showed that the GFP+++ cells, but not the other cell populations, lost the expression of mature hematopoietic cell markers (myeloid, B cells, T cells and erythroid cells). The fluorescent intensity of GFP in c-Kit+ Sca-1+ Lineage− (KSL) cells, which represent a primitive hematopoietic cell fraction containing HSCs and progenitor cells, was much higher than that in the other cell populations, indicating that the immature hematopoietic cells highly express GFP. To investigate the biological properties of the GFP-high expressing cells, we further performed colony-forming assay in vitro and BM transplantation assay in vivo. When the sorted BM MNCs were cultured in methylcellulose medium supplemented with cytokines, GFP+++ cells showed the highest number of colony formation. To assess the repopulating capacity as stem cell function, the sorted BM MNCs were transplanted into irradiated recipient mice. Notably, only GFP+++ cells had long-term reconstitution capacity of hematopoiesis in the recipient mice on the competitive reconstitution assay. In addition, the GFP+++ cells that were sorted from the GFP+++ cells-transplanted mouse retained the reconstitution capacity after secondary BM transplantation. The reconstitutive capacity of the GFP+++ cells into multi-lineages was confirmed by detection of donor-derived B, T, and myeloid cells in the recipient mice. These results demonstrate that HSCs with self-renewal capacity and differentiation potential for multi-lineages are enriched in GFP+++ cell population. The NS-GFP tg mouse system may provide a useful tool for effective enrichment of HSCs in combination with other cell-surface markers for HSCs.

Adaptor Protein Lnk Negatively Controls the Likelihood of Self-Renewal in Hematopoietic Stem Cells.

Great progresses are promised for the development of stem cell-based regenerative medicine if we can manipulate stem cell self-renewal. Thus, one of the central tasks in stem cell biology is to understand how stem cell fate is determined. Hematopoietic stem cells (HSCs) are the best studied stem cells. Their in vivo self-renewal has been extensively studied, but its in vitro recapitulation remains so difficult. We previously reported that HSCs undergo asymmetrical self-renewal division in culture with stem cell factor (SCF) and thrombopoietin (TPO). Since then, we have sought any condition in which HSCs can symmetrically self-renew. We now report in vitro symmetrical self-renewal division of HSCs in the absence of Lnk. Lnk is an adaptor protein containing praline-rich domain, pleckstrin homology domain, and Src homology domain. Lnk-deficient mice have over 10-fold HSCs due to increased self-renewal capacity. CD34−Kit+Sca-1+Lin− cells were purified from bone marrow of wild-type or Lnk-deficient B6 mice, and were subjected to serum-free single cell cultures in the presence of a variety of cyokines. We found that Lnk-deficient CD34−Kit+Sca-1+Lin− cells are hypersensitive to TPO. Repopulating activity in 40 CD34−Kit+Sca-1+Lin− cells from Lnk-deficient mice increased after 3 day-culture with TPO or with SCF and TPO, but not after 3 day-culture with SCF. In contrast, repopulating activity in 40 CD34−Kit+Sca-1+Lin− cells from wild type mice did not significantly change after 3 day-culture with SCF, TPO, or SCF and TPO. Moreover, paired daughter cell-experiments clearly showed that Lnk-deficient, but not wild-type long-term repopulating cells are able to undergo symmetrical self-renewal division at least once in the presence of SCF and TPO. These data suggest that Lnk acts just like a tuner in the regulation of HSC self-renewal downstream of TPO/Mpl signaling. We further investigated TPO-mediated signal transduction pathways in CD34−Kit+Sca-1+Lin− cells. To this end, we developed a novel assay which allowed us to analyze signal transduction in a very limited number of cells. We detected enhanced up-regulation of STAT5 and Akt pathways, and inversely enhanced down-regulation of p38 MAPK pathway in Lnk-deficient CD34−Kit+Sca-1+Lin− cells, as compared with normal ones. These data suggest that these combinational changes in signal transduction lead to initiation of self-renewal in HSCs. We propose that stem cell self-renewal is determined by a balance of positive and negative signals in multiple signal transduction pathways rather than by any particular self-renewal signals.

Nonhuman primate embryonic stem cells as a preclinical model for hematopoietic and vascular repair

Stem cell-based regenerative medicine therapies have been touted recently as a novel therapeutic approach to treat and cure a wide range of diseases. Both adult and embryonic stem (ES) cells can serve as important sources of precursor cells to derive more mature cells potentially utilized for clinical applications. Nonhuman primates have proven useful as a preclinical model, as demonstrated in studies of hematopoietic cell transplantation, gene therapy, and other areas. The derivation of nonhuman primate ES cells now provides an optimal resource to characterize and test ES cell-based therapies prior to trials with human ES cells. This review describes work to define strategies and mechanisms to derive blood and endothelial cells from nonhuman primate ES cells isolated from various species. Preclinical testing that solely relies on studies of putative therapeutic cells derived from mouse ES cells transplanted into other mice, or analyses of human ES cell-derived cells transplanted into immunodeficient or immunosuppressed rodents may not be predictive of efficacy in subsequent human trials. However, future testing using nonhuman primate ES cell-derived therapeutic cells done as an allogeneic transplant may best predict success for subsequent studies using human ES cells. Therefore, additional research on nonhuman primate ES cells, in addition to work on mouse and human ES cells, is greatly needed to facilitate clinical translation of new stem cell treatments.