Stem cells: the magic brew

A systems approach to blood disorders

A systems approach to blood diseases can help make essential contributions to our ability to diagnose, treat, and perhaps even prevent common diseases in humans. Using blood as a window, one can study health and disease through this unique tool box with reactive biological fluids that mirrors the prevailing hemodynamics of the vessel walls and the various blood cell types. Many blood diseases, rare and common, can and have been exploited using systems biology approaches with successful results and therefore ideal models for systems medicine. More importantly, hematopoiesis offers one of the best studied systems with insight into stem cell biology, cellular interaction, development; linage programming and reprogramming that are influenced every day by the most mature and understood regulatory networks.

Directed neural differentiation of induced pluripotent stem cells from non-human primates

Induced pluripotent stem cells (iPS cells) are important for the future development of regenerative medicine involving autologous cell therapy. Before autologous cell therapy can be applied to human patients, suitable animal models must be developed, and in this context non-human primate models are critical. We previously characterized several lines of marmoset iPS cells derived from newborn skin fibroblasts. In the present studies, we explored methods for the directed differentiation of marmoset iPS cells in the neuroectodermal lineage. In this process we used an iterative process in which combinations of small molecules and protein factors were tested for their effects on mRNA levels of genes that are markers for the neuroectodermal lineage. This iterative process identified combinations of chemicals/factors that substantially improved the degree of marker gene expression over the initially tested combinations. This approach should be generally valuable in the directed differentiation of pluripotent cells for experimental cell therapy.

Tumourigenic characteristics of embryonal carcinoma cells as a model for studying tumour progression of human embryonic stem cells

OBJECTIVES

The objective of this study was to compare tumourigenic characteristics of human embryonic stem cells (HESCs) and embryonal carcinoma cells (ECCs) to identify a robust and simple model for studying certain aspects of cell transformation and tumourigenesis, in tumour progression of HESCs.

MATERIALS AND METHODS

SSEA-3 positive ECCs (NTERA-2) cells were identified and compared to HESCs (ch HES-20) in terms of pluripotency and differentiation capacity, growth characteristics, gene expression profiles and signalling pathways.

RESULTS

Our results showed that NTERA-2 cells shared similarities in expression markers of pluripotency to ch HES-20 cells. However, NTERA-2 cells also expressed some markers of differentiation and had a tendency to differentiate towards ectodermal endpoints. We identified NTERA-2 cells with higher S-phase fraction in cell cycle distribution, anti-apoptosis markers and robust self-renewal ability, compared to ch HES-20 cells. Microarray analysis and real-time PCR results showed that some oncogenes were up-regulated and tumour-suppression genes were down-regulated, whereas pluripotency-related genes were up-regulated and differentiation-related genes were down-regulated, and that Wnt and Notch signalling pathways were activated during progression from ES cells to EC cells.

CONCLUSION

Tumourigenic characteristics of ECCs may provide a valuable insight into possible tumour progression of HESCs.

The combination of inhibitors of FGF/MEK/Erk and GSK3β signaling increases the number of OCT3/4- and NANOG-positive cells in the human inner cell mass, but does not improve stem cell derivation

In embryonic stem cell culture, small molecules can be used to alter key signaling pathways to promote self-renewal and inhibit differentiation. In mice, small-molecule inhibition of both the FGF/MEK/Erk and the GSK3β pathways during preimplantation development suppresses hypoblast formation, and this results in more pluripotent cells of the inner cell mass (ICM). In this study, we evaluated the effects of different small-molecule inhibitors of the FGF/MEK/Erk and GSK3β pathway on embryo preimplantation development, early lineage segregation, and subsequent embryonic stem cell derivation in the humans. We did not observe any effect on blastocyst formation, but small-molecule inhibition did affect the number of OCT3/4- and NANOG-positive cells in the human ICM. We found that combined inhibition of the FGF/MEK/Erk and GSK3β pathways by PD0325901 and CHIR99021, respectively, resulted in ICMs containing significantly more OCT3/4-positive cells. Inhibition of FGF/MEK/Erk alone as well as in combination with inhibition of GSK3β significantly increased the number of NANOG-positive cells in blastocysts possessing good-quality ICMs. Secondly, we verified the influence of this increased pluripotency after 2i culture on the efficiency of stem cell derivation. Similar human embryonic stem cell (hESC) derivation rates were observed after 2i compared to control conditions, resulting in 2 control hESC lines and 1 hESC line from an embryo cultured in 2i conditions. In conclusion, we demonstrated that FGF/MEK/Erk and GSK3β signaling increases the number of OCT3/4- and NANOG-positive cells in the human ICM, but does not improve stem cell derivation.

Genome-wide profiling of pluripotent cells reveals a unique molecular signature of human embryonic germ cells

Human embryonic germ cells (EGCs) provide a powerful model for identifying molecules involved in the pluripotent state when compared to their progenitors, primordial germ cells (PGCs), and other pluripotent stem cells. Microarray and Principal Component Analysis (PCA) reveals for the first time that human EGCs possess a transcription profile distinct from PGCs and other pluripotent stem cells. Validation with qRT-PCR confirms that human EGCs and PGCs express many pluripotency-associated genes but with quantifiable differences compared to pluripotent embryonic stem cells (ESCs), induced pluripotent stem cells (IPSCs), and embryonal carcinoma cells (ECCs). Analyses also identified a number of target genes that may be potentially associated with their unique pluripotent states. These include IPO7, MED7, RBM26, HSPD1, and KRAS which were upregulated in EGCs along with other pluripotent stem cells when compared to PGCs. Other potential target genes were also found which may contribute toward a primed ESC-like state. These genes were exclusively up-regulated in ESCs, IPSCs and ECCs including PARP1, CCNE1, CDK6, AURKA, MAD2L1, CCNG1, and CCNB1 which are involved in cell cycle regulation, cellular metabolism and DNA repair and replication. Gene classification analysis also confirmed that the distinguishing feature of EGCs compared to ESCs, ECCs, and IPSCs lies primarily in their genetic contribution to cellular metabolism, cell cycle, and cell adhesion. In contrast, several genes were found upregulated in PGCs which may help distinguish their unipotent state including HBA1, DMRT1, SPANXA1, and EHD2. Together, these findings provide the first glimpse into a unique genomic signature of human germ cells and pluripotent stem cells and provide genes potentially involved in defining different states of germ-line pluripotency.

Nonhuman primate induced pluripotent stem cells in regenerative medicine

Among the various species from which induced pluripotent stem cells have been derived, nonhuman primates (NHPs) have a unique role as preclinical models. Their relatedness to humans and similar physiology, including central nervous system, make them ideal for translational studies. We review here the progress made in deriving and characterizing iPS cell lines from different NHP species. We focus on iPS cell lines from the marmoset, a small NHP in which several human disease states can be modeled. The marmoset can serve as a model for the implementation of patient-specific autologous cell therapy in regenerative medicine.

Transforming growth factor-beta superfamily in mouse embryonic stem cell self-renewal

Embryonic stem (ES) cells are pluripotent cells that maintain the capability of undifferentiated self-renewal in culture. As mouse ES cells have the capacity to give rise to all the tissues of the body, they are an excellent developmental biology model system and a model for regenerative therapies. The extracellular cues and the intracellular signaling cascades that regulate ES cell self-renewal and cell-fate choices are complex and actively studied. Many developmental signaling pathways regulate the ES cell phenotype, and their intracellular programs interact to modulate the gene networks controlling ES cell pluripotency. This review focuses on the current understanding and outstanding questions of the roles of the transforming growth factor-beta-related signaling pathways in regulating pluripotency and differentiation of mouse ES cells. The complex dichotomic roles of bone morphogenetic protein signaling in maintaining the undifferentiated state and also inducing specific cell fates will be reviewed. The emerging roles of Nodal signaling in ES cell self-renewal will also be discussed.

Translational prospects for human induced pluripotent stem cells

The pace of research on human induced pluripotent stem (iPS) cells is frantic worldwide, based on the enormous therapeutic potential of patient-specific pluripotent cells free of the ethical and political issues that plagued human embryonic stem cell research. iPS cells are now relatively easy to isolate from somatic cells and reprogramming can be accomplished using nonmutagenic technologies. Access to iPS cells is already paying dividends in the form of new disease-in-a-dish models for drug discovery and as scalable sources of cells for toxicology. For translation of cell therapies, the major advantage of iPS cells is that they are autologous, but for many reasons, perfect immunologic tolerance of iPS-based grafts should not be assumed. This article focuses on the functional identity of iPS cells, anticipated safety and technical issues in their application, as well as a survey of the progress likely to be realized in clinical applications in the next decade.

Comparative proteomics of human embryonic stem cells and embryonal carcinoma cells

Pluripotent human embryonic stem cells (ESCs) can be differentiated in vitro into a variety of cells which hold promise for transplantation therapy. Human embryonal carcinoma cells (ECCs), stem cells of human teratocarcinomas, are considered a close but malignant counterpart to human ESCs. In this study, a comprehensive quantitative proteomic analysis of ESCs and ECCs was carried out using the iTRAQ method. Using two-dimensional LC and MS/MS analyses, we identified and quantitated approximately 1800 proteins. Among these are proteins associated with pluripotency and development as well as tight junction signaling and TGFbeta receptor pathway. Nearly approximately 200 proteins exhibit more than twofold difference in abundance between ESCs and ECCs. Examples of early developmental markers high in ESCs include beta-galactoside-binding lectin, undifferentiated embryonic cell transcription factor-1, DNA cytosine methyltransferase 3beta isoform-B, melanoma antigen family-A4, and interferon-induced transmembrane protein-1. In contrast, CD99-antigen (CD99), growth differentiation factor-3, cellular retinoic acid binding protein-2, and developmental pluripotency associated-4 were among the highly expressed proteins in ECCs. Several proteins that were highly expressed in ECCs such as heat shock 27 kDa protein-1, mitogen-activated protein kinase kinase-1, nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor like-2, and S100 calcium-binding protein-A4 have also been attributed to malignancy in other systems. Importantly, immunocytochemistry was used to validate the proteomic analyses for a subset of the proteins. In summary, this is the first large-scale quantitative proteomic study of human ESCs and ECCs, which provides critical information about the regulators of these two closely related, but developmentally distinct, stem cells.

Mouse fibroblasts lacking RB1 function form spheres and undergo reprogramming to a cancer stem cell phenotype

Activation of the RB1 pathway triggers the cell-cycle arrest that mediates cell-cell contact inhibition. Accordingly, mutation of all three RB1 family members leads to loss of contact inhibition and outgrowth of fibroblasts into spheres where cell-cell contacts predominate. We present evidence that such outgrowth triggers reprogramming to generate cells with properties of cancer stem cells. Fibroblasts with only a single RB1 mutation remain contact inhibited; however, if this contact inhibition is bypassed by forcing the RB1(-/-) cells to form spheres in suspension, cells with properties of cancer stem cells are also generated. These cells not only form tumors in nude mice but also generate differentiated cells. We propose that contact inhibition imposed by the RB1 pathway performs an unexpected tumor suppressor function by preventing cell outgrowth into structures where cells with properties of cancer stem cells can be generated from differentiated somatic cells in advancing cancers.

Induction of pluripotent stem cells from primary human fibroblasts with only Oct4 and Sox2

Ectopic expression of defined sets of genetic factors can reprogram somatic cells to induced pluripotent stem (iPS) cells that closely resemble embryonic stem (ES) cells. The low efficiency with which iPS cells are derived hinders studies on the molecular mechanism of reprogramming, and integration of viral transgenes, in particular the oncogenes c-Myc and Klf4, may handicap this method for human therapeutic applications. Here we report that valproic acid (VPA), a histone deacetylase inhibitor, enables reprogramming of primary human fibroblasts with only two factors, Oct4 and Sox2, without the need for the oncogenes c-Myc or Klf4. The two factor-induced human iPS cells resemble human ES cells in pluripotency, global gene expression profiles and epigenetic states. These results support the possibility of reprogramming through purely chemical means, which would make therapeutic use of reprogrammed cells safer and more practical.

Kruppel-like factor 4 is essential for inflammatory monocyte differentiation in vivo

Several members of the Kruppel-like factor (KLF) family of transcription factors play important roles in differentiation, survival, and trafficking of blood and immune cell types. We demonstrate in this study that hematopoietic cells from KLF4(-/-) fetal livers (FL) contained normal numbers of functional hematopoietic progenitor cells, were radioprotective, and performed as well as KLF4(+/+) cells in competitive repopulation assays. However, hematopoietic "KLF4(-/-) chimeras" generated by transplantation of KLF4(-/-) fetal livers cells into lethally irradiated wild-type mice completely lacked circulating inflammatory (CD115(+)Gr1(+)) monocytes, and had reduced numbers of resident (CD115(+)Gr1(-)) monocytes. Although the numbers and function of peritoneal macrophages were normal in KLF4(-/-) chimeras, bone marrow monocytic cells from KLF4(-/-) chimeras expressed lower levels of key trafficking molecules and were more apoptotic. Thus, our in vivo loss-of-function studies demonstrate that KLF4, previously shown to mediate proinflammatory signaling in human macrophages in vitro, is essential for differentiation of mouse inflammatory monocytes, and is involved in the differentiation of resident monocytes. In addition, inducible expression of KLF4 in the HL60 human acute myeloid leukemia cell line stimulated monocytic differentiation and enhanced 12-O-tetradecanoylphorbol 13-acetate induced macrophage differentiation, but blocked all-trans-retinoic acid induced granulocytic differentiation of HL60 cells. The inflammation-selective effects of loss-of-KLF4 and the gain-of-KLF4-induced monocytic differentiation in HL60 cells identify KLF4 as a key regulator of monocytic differentiation and a potential target for translational immune modulation.

Stem-cell approaches for kidney repair: choosing the right cells

With the increasing rate of end-stage renal failure and limited alternatives for its treatment, stem cell (SC) therapy for kidney injury is urgently needed. Choosing the right SC type is the critical step in realizing the potential of this therapeutic approach. Four possible sources of SCs are envisioned for the development of this type of treatment: (i) bone-marrow-derived SCs (BMSCs), (ii) renal adult SCs, (iii) embryonic SCs and (iv) fetal renal SCs. We suggest that resident SCs recently identified in the Bowman's capsule of adult human kidneys might prospectively be the ideal cell type for treatment of both acute and chronic renal injury because they display the potential to differentiate into multiple types of renal cells. However, BMSCs also represent an attractive alternative, especially for the treatment of patients affected by acute renal failure.

Inter-cellular adhesion disruption and the RAS/RAF and beta-catenin signalling in lung cancer progression

Cadherin cell adhesion molecules play an essential role in creating tight intercellular association and their loss has been correlated with poor prognosis in human cancer. Mutational activation of protein kinases and loss of cell adhesion occur together in human lung adenocarcinoma but how these two pathways interconnect is only poorly understood. Mouse models of human lung adenocarcinoma with oncogene expression targeted to subtypes of lung epithelial cells led to formation of adenomas or adenocarcinomas that lacked metastatic potential. Conditional genetic abrogation of epithelial tumour cell adhesion in mice with benign lung tumours induced by oncogenic RAF kinase has been demonstrated to induce intratumourous vascularization (angiogenic switch), progression to invasive adenocarcinoma and micrometastasis. Importantly, breaking cell adhesion in benign oncogene-driven lung tumour cells activated beta-catenin signalling and induced the expression of several genes that are normally expressed in intestine rather than the lung. I will discuss potential routes to nuclear beta-catenin signalling in cancer and how nuclear beta-catenin may epigenetically alter the plasticity of tumour cells during malignant progression.

Hematopoiesis: an evolving paradigm for stem cell biology

Establishment and maintenance of the blood system relies on self-renewing hematopoietic stem cells (HSCs) that normally reside in small numbers in the bone marrow niche of adult mammals. This Review describes the developmental origins of HSCs and the molecular mechanisms that regulate lineage-specific differentiation. Studies of hematopoiesis provide critical insights of general relevance to other areas of stem cell biology including the role of cellular interactions in development and tissue homeostasis, lineage programming and reprogramming by transcription factors, and stage- and age-specific differences in cellular phenotypes.

Epigenetic reprogramming in embryonic and foetal development upon somatic cell nuclear transfer cloning

The birth of ‘Dolly’, the first mammal cloned from an adult donor cell, has sparked a flurry of research activities to improve cloning technology and to understand the underlying mechanism of epigenetic reprogramming of the transferred somatic cell nucleus. Especially in ruminants, somatic cell nuclear transfer (SCNT) is frequently associated with pathological changes in the foetal and placental phenotype and has significant consequences for development both before and after birth. The most critical factor is epigenetic reprogramming of the transferred somatic cell nucleus from its differentiated status into the totipotent state of the early embryo. This involves an erasure of the gene expression program of the respective donor cell and the establishment of the well-orchestrated sequence of expression of an estimated number of 10 000–12 000 genes regulating embryonic and foetal development. The following article reviews the present knowledge on the epigenetic reprogramming of the transferred somatic cell nucleus, with emphasis on DNA methylation, imprinting, X-chromosome inactivation and telomere length restoration in bovine development. Additionally, we briefly discuss other approaches towards epigenetic nuclear reprogramming, including the fusion of somatic and embryonic stem cells and the overexpression of genes crucial in the formation and maintenance of the pluripotent status. Improvements in our understanding of this dramatic epigenetic reprogramming event will be instrumental in realising the great potential of SCNT for basic biological research and for various agricultural and biomedical applications.