Embryonic stem cells for basic research and potential clinical applications in cardiology

Engineered stem cells targeting multiple cell surface receptors in tumors

Multiple stem cell types exhibit inherent tropism for cancer, and engineered stem cells have been used as therapeutic agents to specifically target cancer cells. Recently, stem cells have been engineered to target multiple surface receptors on tumor cells, as well as endothelial and immune cells in the tumor microenvironment. In this review, we discuss the rationales and strategies for developing multiple receptor-targeted stem cells, their mechanisms of action, and the promises and challenges they hold as cancer therapeutics.

Stem Cell-Based Therapies for Cancer

Stem cell-based therapeutic strategies have emerged as very attractive treatment options over the past decade. Stem cells are now being utilized as delivery vehicles especially in cancer therapy to deliver a number of targeted proteins and viruses. This chapter aims to shed light on numerous studies that have successfully employed these strategies to target various cancer types with a special emphasis on numerous aspects that are critical to the success of future stem cell-based therapies for cancer.

Fam40b is required for lineage commitment of murine embryonic stem cells

FAM40B (STRIP2) is a member of the striatin-interacting phosphatase and kinase (STRIPAK) complex that is involved in the regulation of various processes such as cell proliferation and differentiation. Its role for differentiation processes in embryonic stem cells (ESCs) is till now completely unknown. Short hairpin RNA (shRNA)-mediated silencing of Fam40b expression in ESCs and differentiating embryoid bodies (EBs) led to perturbed differentiation to embryonic germ layers and their derivatives including a complete abrogation of cardiomyogenesis. Pluripotency factors such as Nanog, Oct4 and Sox2 as well as epigenetic factors such as histone acetyltransferase type B (HAT1) and DNA (cytosine-5)-methyltransferase 3-β (Dnmt3b) were highly upregulated in Fam40b knockdown EBs as compared with control and scrambled EBs. To examine the relevance of Fam40b for development in vivo, Fam40b was knocked down in developing zebrafish. Morpholino-mediated knockdown of Fam40b led to severe abnormalities of the cardiovascular system, including an impaired expression of ventricular myosin heavy chain (vmhc) and of cardiac myosin light chain 2 (cmlc2) in the heart. We identified the gene product of Fam40b in ESCs as a perinuclear and nucleolar protein with a molecular weight of 96 kDa. We conclude that the expression of Fam40b is essential for the lineage commitment of murine embryonic stem cells (mESCs) into differentiated somatic cells via mechanisms involving pluripotency and epigenetic networks.

Biological, immunological and regenerative characteristics of placenta-derived mesenchymal stem cell isolated using a time-gradient attachment method

It has been verified that placenta contains multi-lineage mesenchymal stem cells (MSCs). We have used a time-gradient attachment method to isolate placenta-derived MSCs (PMSCs). The morphology, differentiation potential, immunogenicity and xenogenic reconstruction potential of these PMSCs were examined. The results showed that PMSCs isolated using the time-gradient attachment method showed higher potential of in vitro proliferation and multi-lineage differentiation. PMSCs isolated using the time-gradient attachment method showed a low immunogenicity. HLA-A gene fragment and no HLA-DR gene fragment were detected in PMSCs isolated using the time-gradient attachment method, and the mixed lymphocyte reaction (MLR) assay identified that these cells inhibited the proliferation of the allogeneic T-lymphocytes induced by PHA. The transplantation in calvaria of rats showed that PMSCs had the higher xenogenic reconstruction potential. Finally, the significance of PMSCs isolated using the time-gradient attachment method in experimental and clinical applications is discussed.

In vitro differentiation of rat embryonic stem cells into functional cardiomyocytes

The recent breakthrough in the generation of rat embryonic stem cells (rESCs) opens the door to application of gene targeting to create models for the study of human diseases. In addition, the in vitro differentiation system from rESCs into derivatives of three germ layers will serve as a powerful tool and resource for the investigation of mammalian development, cell function, tissue repair, and drug discovery. However, these uses have been limited by the difficulty of in vitro differentiation. The aims of this study were to establish an in vitro differentiation system from rESCs and to investigate whether rESCs are capable of forming terminal-differentiated cardiomyocytes. Using newly established rESCs, we found that embryoid body (EB)-based method used in mouse ESC (mESC) differentiation failed to work for the serum-free cultivated rESCs. We then developed a protocol by combination of three chemical inhibitors and feeder-conditioned medium. Under this condition, rESCs formed EBs, propagated and differentiated into three embryonic germ layers. Moreover, rESC-formed EBs could differentiate into spontaneously beating cardiomyocytes after plating. Analyses of molecular, structural, and functional properties revealed that rESC-derived cardiomyocytes were similar to those derived from fetal rat hearts and mESCs. In conclusion, we successfully developed an in vitro differentiation system for rESCs through which functional myocytes were generated and displayed phenotypes of rat fetal cardiomyocytes. This unique cellular system will provide a new approach to study the early development and cardiac function, and serve as an important tool in pharmacological testing and cell therapy.

Global transcriptomic analysis of murine embryonic stem cell-derived brachyury(+) (T) cells

Brachyury(+) mesodermal cell population with purity over 79% was obtained from differentiating brachyury embryonic stem cells (ESC) generated with brachyury promoter driven enhanced green fluorescent protein and puromycin-N-acetyltransferase. A comprehensive transcriptomic analysis of brachyury(+) cells enriched with puromycin application from 6-day-old embryoid bodies (EBs), 6-day-old control EBs and undifferentiated ESCs led to identification of 1573 uniquely up-regulated and 1549 uniquely down-regulated transcripts in brachyury(+) cells. Furthermore, transcripts up-regulated in brachyury(+) cells have overrepresented the Gene Ontology annotations (cell differentiation, blood vessel morphogenesis, striated muscle development, placenta development and cell motility) and Kyoto Encyclopedia of Genes and Genomes pathway annotations (mitogen-activated protein kinase signaling and transforming growth factor beta signaling). Transcripts representing Larp2 and Ankrd34b are notably up-regulated in brachyury(+) cells. Knockdown of Larp2 resulted in a significantly down-regulation BMP-2 expression, and knockdown of Ankrd34b resulted in alteration of NF-H, PPARγ and PECAM1 expression. The elucidation of transcriptomic signatures of ESCs-derived brachyury(+) cells will contribute toward defining the genetic and cellular identities of presumptive mesodermal cells. Furthermore, there is a possible involvement of Larp2 in the regulation of the late mesodermal marker BMP-2. Ankrd34b might be a positive regulator of neurogenesis and a negative regulator of adipogenesis.

Sphingosine 1-phosphate regulation of extracellular signal-regulated kinase-1/2 in embryonic stem cells

Recent evidence suggests that sphingosine 1-phosphate (S1P) regulates self-renewal of human embryonic stem (ES) cells and differentiation of mouse embryoid bodies (derived from mouse ES cells) to cardiomyocytes. We have investigated the role of S1P in regulating ERK-1/2 signaling in mouse ES cells. In this regard, we found that both mouse ES-D3 and CGR8 cells express S1P(1), S1P(2), S1P(3), and S1P(5) but lack S1P(4). The treatment of ES cells with S1P induced the activation of ERK-1/2 via a mechanism that was not mediated by S1P(1), S1P(2), or S1P(3). This was based on: (i) the failure of S1P(1), S1P(2), or S1P(3) antagonists to inhibit S1P-stimulated ERK-1/2 activation and (ii) the failure of SEW 2871 (S1P(1) receptor agonist) to stimulate ERK-1/2 activation. The treatment of ES cells with phytosphingosine 1-phosphate (phyto-S1P), which we show here is an agonist of the S1P(5) receptor, stimulated ERK-1/2 activation. These findings therefore suggest that S1P(5) may mediate the effects of S1P in terms of regulating ERK-1/2 signaling in ES cells. The S1P-dependent activation of ERK-1/2 was sensitive to inhibition by pertussis toxin (uncouples the G-protein, G(i) from GPCR), bisindolylmaleimide I (PKC inhibitor), and PP2 (c-Src inhibitor), but was not reduced by LY29004 (PI3K inhibitor) suggesting that S1P uses G(i)-, PKC-, and c-Src-dependent mechanisms to activate the ERK-1/2 pathway in ES cells.

Preconditioning and stem cell survival

The harsh ischemic and cytokine-rich microenvironment in the infarcted myocardium, infiltrated by the inflammatory and immune cells, offers a significant challenge to the transplanted donor stem cells. Massive cell death occurs during transplantation as well as following engraftment which significantly lowers the effectiveness of the heart cell therapy. Various approaches have been adopted to overcome this problem nevertheless with multiple limitations with each of these current approaches. Cellular preconditioning and reprogramming by physical, chemical, genetic, and pharmacological manipulation of the cells has shown promise and "prime" the cells to the "state of readiness" to withstand the rigors of lethal ischemia in vitro as well as posttransplantation. This review summarizes the past and present novel approaches of ischemic preconditioning, pharmacological and genetic manipulation using preconditioning mimetics, recombinant growth factor protein treatment, and reprogramming of stem cells to overexpress survival signaling molecules, microRNAs, and trophic factors for intracrine, autocrine, and paracrine effects on cytoprotection.

Stem cells as tools in regenerative therapy for retinal degeneration

OBJECTIVE

To describe the use of stem cells (SCs) for regeneration of retinal degenerations. Regenerative medicine intends to provide therapies for severe injuries or chronic diseases where endogenous repair does not sufficiently restore the tissue. Pluripotent SCs, with their capacity to give rise to specialized cells, are the most promising candidates for clinical application. Despite encouraging results, a combination with up-to-date tissue engineering might be critical for ultimate success.

DESIGN

The focus is on the use of SCs for regeneration of retinal degenerations. Cell populations include embryonic, neural, and bone marrow-derived SCs, and engineered grafts will also be described.

RESULTS

Experimental approaches have successfully replaced damaged photoreceptors and retinal pigment epithelium using endogenous and exogenous SCs.

CONCLUSIONS

Stem cells have the potential to significantly impact retinal regeneration. A combination with bioengineering may bear even greater promise. However, ethical and scientific issues have yet to be solved.

Global transcriptome analysis of murine embryonic stem cell-derived cardiomyocytes

Microarray analysis reveals that the specific pattern of gene expression in cardiomyocytes derived from embryonic stem cells reflects the biological, physiological and functional processes occurring in mature cardiomyocytes.

Background

Characterization of gene expression signatures for cardiomyocytes derived from embryonic stem cells will help to define their early biologic processes.

Results

A transgenic α-myosin heavy chain (MHC) embryonic stem cell lineage was generated, exhibiting puromycin resistance and expressing enhanced green fluorescent protein (EGFP) under the control of the α-MHC promoter. A puromycin-resistant, EGFP-positive, α-MHC-positive cardiomyocyte population was isolated with over 92% purity. RNA was isolated after electrophysiological characterization of the cardiomyocytes. Comprehensive transcriptome analysis of α-MHC-positive cardiomyocytes in comparison with undifferentiated α-MHC embryonic stem cells and the control population from 15-day-old embryoid bodies led to identification of 884 upregulated probe sets and 951 downregulated probe sets in α-MHC-positive cardiomyocytes. A subset of upregulated genes encodes cytoskeletal and voltage-dependent channel proteins, and proteins that participate in aerobic energy metabolism. Interestingly, mitosis, apoptosis, and Wnt signaling-associated genes were downregulated in the cardiomyocytes. In contrast, annotations for genes upregulated in the α-MHC-positive cardiomyocytes are enriched for the following Gene Ontology (GO) categories: enzyme-linked receptor protein signaling pathway (GO:0007167), protein kinase activity (GO:0004672), negative regulation of Wnt receptor signaling pathway (GO:0030178), and regulation of cell size (O:0008361). They were also enriched for the Biocarta p38 mitogen-activated protein kinase signaling pathway and Kyoto Encyclopedia of Genes and Genomes (KEGG) calcium signaling pathway.

Conclusion

The specific pattern of gene expression in the cardiomyocytes derived from embryonic stem cells reflects the biologic, physiologic, and functional processes that take place in mature cardiomyocytes. Identification of cardiomyocyte-specific gene expression patterns and signaling pathways will contribute toward elucidating their roles in intact cardiac function.

Human adult skeletal muscle stem cells differentiate into cardiomyocyte phenotype in vitro

Cell transplantation to repair or regenerate injured myocardium is a new frontier in the treatment of cardiovascular disease. Most studies on stem cell transplantation therapy in both experimental heart infarct and in phase-I human clinical trials have focused on the use of undifferentiated stem cells. Based on our previous observations demonstrating the presence of multipotent progenitor cells in human adult skeletal muscle, in this study we investigated the capacity of these progenitors to differentiate into cardiomyocytes. Here we show an efficient protocol for the cardiomyogenic differentiation of human adult skeletal muscle stem cells in vitro. We found that treatment with Retinoic Acid directed cardiomyogenic differentiation of skeletal muscle stem cells in vitro. After Retinoic Acid treatment, cells expressed cardiomyocyte markers and acquired spontaneous contraction. Functional assays exhibited cardiac-like response to increased extracellular calcium. When cocultured with mouse cardiomyocytes, Retinoic Acid-treated skeletal muscle stem cells expressed connexin43 and when transplanted into ischemic heart were detectable even 5 weeks after injection. Based on these results, we can conclude that human adult skeletal muscle stem cells, if opportunely treated, can transdifferentiate into cells of cardiac lineage and once injected into infarcted heart can integrate, survive in cardiac tissue and improve the cardiac function.

Review: ex vivo engineering of living tissues with adult stem cells

Adult stem cells have the potential to revolutionize regenerative medicine with their unique abilities to self-renew and differentiate into various phenotypes. This review examines progress and challenges in ex vivo tissue engineering with adult stem cells. These rare cells are harvested from a variety of tissues, including bone marrow, adipose, skeletal muscle, and placenta, and differentiate into cells of their own lineage and in some cases atypical lineages. Insight into the stem cell niche leads to the identification of matrix components, soluble factors, and physiological conditions that enhance the ex vivo amplification and differentiation of stem cells. Scaffolds composed of metals, naturally occurring materials, and synthetic polymers organize stem cells into complex spatial groupings that mimic native tissue. Cell signals from covalently bound ligands and slowly released regulatory factors in scaffolds direct stem cell fate. Future advances in stem cell biology and scaffold design will ultimately improve the efficacy of tissue substitutes as implants, in research, and as extracorporeal devices.

Identification of small signalling molecules promoting cardiac-specific differentiation of mouse embryonic stem cells

Identification of signalling cascades involved in cardiomyogenesis is crucial for optimising the generation of cardiomyocytes from embryonic stem cells (ES cells) (in vitro). We used a transgenic ES cell lineage expressing enhanced green fluorescent protein (EGFP) under the control of the alpha-myosin heavy chain (alpha-MHC) promoter (palphaMHC-EGFP) to investigate the effects of 33 small molecules interfering with several signalling cascades on cardiomyogenesis. Interestingly, the L-Type Ca2+ channel blocker Verapamil as well as Cyclosporin, an inhibitor of the protein phosphatase 2B, exerted the most striking pro-cardiomyogenic effect. Forskolin (adenylate cyclase stimulator) exerted the most striking anti-cardiomyogenic effect. The cardiomyogenic effect of Cyclosporin and Verapamil correlated with an expression of early cardiac markers Nkx2.5 and GATA4. Compared to the effects on late developmental stage embryoid bodies (EBs) stimulation of early developmental stage EBs (1-day old) with Verapamil or Cyclosporin for 48 h resulted in a potent cardiomyogenic effect. Accordingly, enhanced expression of alpha-MHC mRNA and EGFP mRNA was observed after stimulation of the early developmental stage EBs for 48 h. No expression of alpha-smooth muscle actin or platelet endothelial cell adhesion molecule-1 (PECM-1) as well as of neuronal genes (Nestin, Neurofilament H) has been observed demonstrating a preferentially pro-cardiomyogenic effect by both molecules.

Cardiovascular genomics: a current overview of in vivo and in vitro studies

The cardiovascular system is the first system that is developed in the embryo. The cardiovascular development is a complex process involving the coordination, differentiation, and interaction of distinct cell lineages to form the heart and the diverse array of arteries, veins, and capillaries required to supply oxygen and nutrients to all tissues. Embryonic stem cells have been proposed as an interesting model system to investigate molecular and cellular mechanisms involved in mammalian development. The present review is focused on extrinsic soluble factors, intrinsic transcription factors, receptors, signal transduction pathways, and genes regulating the development of cardiovascular system in vivo and in vitro. Special emphasis has been given to cardiovascular genomics including gene expression studies on the cardiovascular system under developmental and pathophysiological conditions.