Embryonic stem cell research. The case for

Engineering of the embryonic and adult stem cell niches

CONTEXT

Stem cells have the potential to generate a renewable source of cells for regenerative medicine due to their ability to self-renew and differentiate to various functional cell types of the adult organism. The extracellular microenvironment plays a pivotal role in controlling stem cell fate responses. Therefore, identification of appropriate environmental stimuli that supports cellular proliferation and lineage-specific differentiation is critical for the clinical application of the stem cell therapies.

EVIDENCE ACQUISITION

Traditional methods for stem cells culture offer limited manipulation and control of the extracellular microenvironment. Micro engineering approaches are emerging as powerful tools to control stem cell-microenvironment interactions and for performing high-throughput stem cell experiments.

RESULTS

In this review, we provided an overview of the application of technologies such as surface micropatterning, microfluidics, and engineered biomaterials for directing stem cell behavior and determining the molecular cues that regulate cell fate decisions.

CONCLUSIONS

Stem cells have enormous potential for therapeutic and pharmaceutical applications, because they can give rise to various cell types. Despite their therapeutic potential, many challenges, including the lack of control of the stem cell microenvironment remain. Thus, a greater understanding of stem cell biology that can be used to expand and differentiate embryonic and adult stem cells in a directed manner offers great potential for tissue repair and regenerative medicine.

Controlled-size embryoid body formation in concave microwell arrays

Embryonic stem (ES) cells hold great potential as a renewable cell source for regenerative medicine and cell-based therapy. Despite the potential of ES cells, conventional stem cell culture methods do not enable the control of the microenvironment. A number of microscale engineering approaches have been recently developed to control the extracellular microenvironment and to direct embryonic stem cell fate. Here, we used engineered concave microwell arrays to regulate the size and shape of embryoid bodies (EBs)-cell aggregate intermediates derived from ES cells. Murine ES cells were aggregated within concave microwells, and their aggregate sizes were controlled by varying the microwell widths (200, 500, and 1000 mum). Differentiation of murine ES cells into three germ layers was assessed by analyzing gene expression. We found that ES cell-derived cardiogenesis and neurogenesis were strongly regulated by the EB size, showing that larger concave microwell arrays induced more neuronal and cardiomyocyte differentiation than did smaller microwell arrays. Therefore, this engineered concave microwell array could be a potentially useful tool for controlling ES cell behavior.

Isolation and characterization of hepatic stem cells, or "oval cells," from rat livers

The pace of research on the potential therapeutic uses of liver stem cells or "oval cells" has accelerated significantly in recent years. Concurrent advancements in techniques for the isolation and characterization of these cells have helped fuel this research. Several models now exist for the induction of oval cell proliferation in rodents. Protocols for the isolation and culture of these cells have evolved to the point that they may be set up in any laboratory equipped for cell culture. The advent of magnetic cell sorting has eliminated reliance on expensive flow cytometric sorting equipment to generate highly enriched populations of oval cells. Our laboratory has had much success in using the oval cell surface marker Thy-1 in combination with magnetic sorting to produce material suitable for testing the influence of a myriad of chemical signaling molecules on the oval cell phenotype. This chapter will describe our basic strategy for oval cell induction and isolation. Additionally, two in vitro procedures are described which the reader may find useful in the early stages of developing an oval cell research project.

Human embryonic stem cells for cardiomyogenesis

Myocardial cell replacement strategies are emerging as novel therapeutic paradigms for heart failure but are hampered by the paucity of sources for human cardiomyocytes. Human embryonic stem cells (hESC) are pluripotent stem cell lines derived from human blastocysts that can be propagated, in culture, in the undifferentiated state under special conditions and coaxed to differentiate into cell derivatives of all three germ layers, including cardiomyocytes. The current review describes the derivation and properties of the hESC lines and the different cardiomyocyte differentiation system established so far using these cells. Data regarding the structural, molecular, and functional properties of the hESC-derived cardiomyocytes is provided as well as description of the methods used to achieve cardiomyocyte enrichment and purification in this system. The possible applications of this unique differentiation system in several cardiovascular research and applied areas are discussed. Specific emphasis is put on the descriptions of the efforts performed to date to assess the feasibility of this emerging technology in the fields of cardiac cell replacement therapy and tissue engineering. Finally, the obstacles remaining on the road to clinical translation are described as well as the steps required to fully harness the potential of this new technology.

Stem cells and their potential relevance to paediatric cardiology

Basic scientists, as well as cardiologists, are caught by the idea of curing ischaemic heart disease with cardiac progenitor or stem cells. This short review provides an overview of our current knowledge on the potential use of stem cells for cardiac disease. Since, in infants and children, aetiologies and pathomechanisms of critical cardiac disease are fundamentally different from those in adults, we will also address the question as to whether such young patients could be a therapeutic target at all, and in which respect it may be necessary to view treatment with stem cells from a different stance in the developing organism.

Stem cells: new tools in gastroenterology and hepatology

Stem cells play a key role in tissue homeostasis and renewal after damage, so learning more about them may become a sort of 'Pandora's box', which when opened will make it possible to clarify the nature and the pathophysiology of several human diseases and to find new treatments for pathologies, such as cancers, degenerative, autoimmune and genetic disorders, that are currently untreatable. The characteristics of the gastrointestinal tract and of the liver, in terms of genesis and regeneration and their special relationship with the haemolymphopoietic system, allow stem cell research to outline interesting therapeutic perspectives in these fields. We aim to summarize the knowledge acquired on gastrointestinal and hepatic stem cell biology, focusing attention on the issues that remain to be addressed, and to present the main perspectives of treatment offered by these 'new tools' in gastroenterology and hepatology.

Derivation and potential applications of human embryonic stem cells

Embryonic stem cells are pluripotent cell lines that are derived from the blastocyst-stage early mammalian embryo. These unique cells are characterized by their capacity for prolonged undifferentiated proliferation in culture while maintaining the potential to differentiate into derivatives of all three germ layers. During in vitro differentiation, embryonic stem cells can develop into specialized somatic cells, including cardiomyocytes, and have been shown to recapitulate many processes of early embryonic development. The present review describes the derivation and unique properties of the recently described human embryonic stem cells as well as the properties of cardiomyocytes derived using this unique differentiating system. The possible applications of this system in several cardiac research areas, including developmental biology, functional genomics, pharmacological testing, cell therapy, and tissue engineering, are discussed. Because of their combined ability to proliferate indefinitely and to differentiate to mature tissue types, human embryonic stem cells can potentially provide an unlimited supply of cardiomyocytes for cell therapy procedures aiming to regenerate functional myocardium. However, many obstacles must still be overcome on the way to successful clinical utilization of these cells.

Embryonic stem cells: advances toward potential therapeutic use

Established lines of human pluripotent stem cells provide a convenient tool for investigating cell differentiation in a way that is pertinent to human embryonic development, providing insights into the causes of birth defects and diseases such as cancer that involve aberrant cell proliferation and differentiation. In principle, human pluripotent stem cells, including embryonic stem and embryonic germ cells, are capable of differentiating into all of the cell types that are present in the adult human. They therefore have the potential to provide a source of tissues for replacement in diseases in which native cell types are inactivated or destroyed. Intense media and public interest has surrounded the announcement of human pluripotent stem cells derivation, focusing on the ethical implications of embryo-related work and on the prospects of an unlimited source of tissues for transplantation-based treatments. Recent studies have focused on identifying method for culture of these cells and inducing their differentiation into specific cell types.

Hemoglobin switching and modulation: genes, cells, and signals

A detailed understanding of hemoglobin production in erythroid cells is of fundamental clinical importance for the treatment of hemoglobinopathies. Several hundred scientific reports and dozens of reviews describe this intriguing topic of research. Early studies demonstrated the temporal nature of a hemoglobin-switching phenomenon during development in the circulating erythrocytes of humans. The focus then shifted from descriptive to experimental analyses and model systems in an effort to define the switching mechanisms. The application of molecular biology in those experimental models has been a primary focus for the last two decades. Today, advances in the fields of stem cell biology and signal transduction are being integrated with those genetic studies. Genomic and proteomic approaches are also being developed to provide a more robust description of the biologic variables involved. This review highlights recent advances in erythroid genetics and cellular biology with an emphasis upon the modulation of fetal hemoglobin expression during the maturation of adult human erythrocytes.