Embryonic and induced pluripotent stem cells Part 6
In this video we discuss embryonic and induced pluripotent stem cells. Topics discussed include the origins of cell specialization, the master transcription regulators of pluripotency and the...
By: Ben Garside
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Introduction: What are stem cells, and why are they important? What are the unique properties of all stem cells? What are embryonic stem cells? What are adult stem cells? What are the similarities and differences between embryonic and adult stem cells? What are induced pluripotent stem cells? What are the potential uses of human stem cells and the obstacles that must be overcome before these potential uses will be realized? Where can I get more information?
Induced pluripotent stem cells (iPSCs) are adult cells that have been genetically reprogrammed to an embryonic stem celllike state by being forced to express genes and factors important for maintaining the defining properties of embryonic stem cells. Although these cells meet the defining criteria for pluripotent stem cells, it is not known if iPSCs and embryonic stem cells differ in clinically significant ways. Mouse iPSCs were first reported in 2006, and human iPSCs were first reported in late 2007. Mouse iPSCs demonstrate important characteristics of pluripotent stem cells, including expressing stem cell markers, forming tumors containing cells from all three germ layers, and being able to contribute to many different tissues when injected into mouse embryos at a very early stage in development. Human iPSCs also express stem cell markers and are capable of generating cells characteristic of all three germ layers.
Although additional research is needed, iPSCs are already useful tools for drug development and modeling of diseases, and scientists hope to use them in transplantation medicine. Viruses are currently used to introduce the reprogramming factors into adult cells, and this process must be carefully controlled and tested before the technique can lead to useful treatment for humans. In animal studies, the virus used to introduce the stem cell factors sometimes causes cancers. Researchers are currently investigating non-viral delivery strategies. In any case, this breakthrough discovery has created a powerful new way to "de-differentiate" cells whose developmental fates had been previously assumed to be determined. In addition, tissues derived from iPSCs will be a nearly identical match to the cell donor and thus probably avoid rejection by the immune system. The iPSC strategy creates pluripotent stem cells that, together with studies of other types of pluripotent stem cells, will help researchers learn how to reprogram cells to repair damaged tissues in the human body.
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Charles A. Goldthwaite, Jr., Ph.D.
In 2006, researchers at Kyoto University in Japan identified conditions that would allow specialized adult cells to be genetically "reprogrammed" to assume a stem cell-like state. These adult cells, called induced pluripotent stem cells (iPSCs), were reprogrammed to an embryonic stem cell-like state by introducing genes important for maintaining the essential properties of embryonic stem cells (ESCs). Since this initial discovery, researchers have rapidly improved the techniques to generate iPSCs, creating a powerful new way to "de-differentiate" cells whose developmental fates had been previously assumed to be determined.
Although much additional research is needed, investigators are beginning to focus on the potential utility of iPSCs as a tool for drug development, modeling of disease, and transplantation medicine. The idea that a patient's tissues could provide him/ her a copious, immune-matched supply of pluripotent cells has captured the imagination of researchers and clinicians worldwide. Furthermore, ethical issues associated with the production of ESCs do not apply to iPSCs, which offer a non-controversial strategy to generate patient-specific stem cell lines. As an introduction to this exciting new field of stem cell research, this chapter will review the characteristics of iPSCs, the technical challenges that must be overcome before this strategy can be deployed, and the cells' potential applications to regenerative medicine.
As noted in other chapters, stem cells represent a precious commodity. Although present in embryonic and adult tissues, practical considerations such as obtaining embryonic tissues and isolating relatively rare cell types have limited the large-scale production of populations of pure stem cells (see the Chapter, "Alternate Methods for Preparing Pluripotent Stem Cells" for details). As such, the logistical challenges of isolating, culturing, purifying, and differentiating stem cell lines that are extracted from tissues have led researchers to explore options for "creating" pluripotent cells using existing non-pluripotent cells. Coaxing abundant, readily available differentiated cells to pluripotency would in principle eliminate the search for rare cells while providing the opportunity to culture clinically useful quantities of stem-like cells.
One strategy to accomplish this goal is nuclear reprogramming, a technique that involves experimentally inducing a stable change in the nucleus of a mature cell that can then be maintained and replicated as the cell divides through mitosis. These changes are most frequently associated with the reacquisition of a pluripotent state, thereby endowing the cell with developmental potential. The strategy has historically been carried out using techniques such as somatic cell nuclear transfer (SCNT),1,2 altered nuclear transfer (ANT),3,4 and methods to fuse somatic cells with ESCs5,6 (see "Alternate Methods for Preparing Pluripotent Stem Cells" for details of these approaches). From a clinical perspective, these methods feature several drawbacks, such as the creation of an embryo or the development of hybrid cells that are not viable to treat disease. However, in 2006, these efforts informed the development of nuclear reprogramming in vitro, the breakthrough method that creates iPSCs.
This approach involves taking mature "somatic" cells from an adult and introducing the genes that encode critical transcription factor proteins, which themselves regulate the function of other genes important for early steps in embryonic development (See Fig. 10.1). In the initial 2006 study, it was reported that only four transcription factors (Oct4, Sox2, Klf4, and c-Myc) were required to reprogram mouse fibroblasts (cells found in the skin and other connective tissue) to an embryonic stem celllike state by forcing them to express genes important for maintaining the defining properties of ESCs.7 These factors were chosen because they were known to be involved in the maintenance of pluripotency, which is the capability to generate all other cell types of the body. The newly-created iPSCs were found to be highly similar to ESCs and could be established after several weeks in culture.7,8 In 2007, two different research groups reached a new milestone by deriving iPSCs from human cells, using either the original four genes9 or a different combination containing Oct4, Sox2, Nanog, and Lin28.10 Since then, researchers have reported generating iPSCs from somatic tissues of the monkey11 and rat.12,13
However, these original methods of reprogramming are inefficient, yielding iPSCs in less than 1% of the starting adult cells.14,15 The type of adult cell used also affects efficiency; fibroblasts require more time for factor expression and have lower efficiency of reprogramming than do human keratinocytes, mouse liver and stomach cells, or mouse neural stem cells.1419
Several approaches have been investigated to improve reprogramming efficiency and decrease potentially detrimental side effects of the reprogramming process. Since the retroviruses used to deliver the four transcription factors in the earliest studies can potentially cause mutagenesis (see below), researchers have investigated whether all four factors are absolutely necessary. In particular, the gene c-Myc is known to promote tumor growth in some cases, which would negatively affect iPSC usefulness in transplantation therapies. To this end, researchers tested a three-factor approach that uses the orphan nuclear receptor Esrrb with Oct4 and Sox2, and were able to convert mouse embryonic fibroblasts to iPSCs.20 This achievement corroborates other reports that c-Myc is dispensable for direct reprogramming of mouse fibroblasts.21 Subsequent studies have further reduced the number of genes required for reprogramming,2226 and researchers continue to identify chemicals that can either substitute for or enhance the efficiency of transcription factors in this process.27 These breakthroughs continue to inform and to simplify the reprogramming process, thereby advancing the field toward the generation of patient-specific stem cells for clinical application. However, as the next section will discuss, the method by which transcription factors are delivered to the somatic cells is critical to their potential use in the clinic.
Figure 10.1. Generating Induced Pluripotent Stem Cells (iPSCs).
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10. The Promise of Induced Pluripotent Stem Cells (iPSCs ...
MINNEAPOLIS On December 10, 2011, Portland guard Brandon Roy announced his retirement. He was 27 years old at the time, at the end of just his fifth year in the league. He'd been the NBA Rookie of the Year in 2007 and was a three-time All-Star.
Yet in the face of chronic knee problems, none of that mattered.
Roy retired due to persistent issues in both of his knees. He'd undergone six knee operations, and there was no longer any cartilage remaining in the joints. Trail Blazers team doctors warned him that he should not continue playing and that to do so would have devastating long-term effects.
Not even a year later, and he's announced his comeback. Many teams have expressed interest in signing him, including the Timberwolves.
That's quite the turnaround for a player who was warned that to play basketball any longer might spell difficulties walking later in his life. It's the kind of story where one wonders what detail is missing; the turnaround is too drastic. And in that brief narrative, something was missing: platelet-rich plasma (PRP) therapy.
PRP therapy is a process by which a small quantity of blood is extracted from a patient. The blood is then placed in a centrifuge and spun until it separates into its component parts. Doctors then remove the platelets and inject them back into the patient at the point of injury, peppering the surrounding area with injections for maximum efficacy. The growth factors in platelets are said to promote healing and tissue regeneration, speeding the healing process.
The therapy has been used for nearly a decade, but it's received increased attention in recent years. There's no medical consensus on it yet, and it's still a procedure that's largely relegated to athletes and patients with disposable income. It can cost between $500-$2,000, though prices do vary, and it's rarely covered by insurance.
Dr. Bradley Nelson, a physician at the University of Minnesota School of Medicine, said that the most common use of PRP therapy is for chronic tendinopathy. That's different from the case in Roy's knees, where he's lacking cartilage. Using PRP therapy cases like Roy's, though, is becoming more widespread, but it doesn't have the same healing effects as it does in treating tendinopathy, such as tennis elbow. Recent studies have begun to indicate that PRP can be effective in reducing the pain of arthritis, and using the therapy in such treatments is the newest trend in PRP.
"Some people are injecting (PRP) into the knee joint in patients that have early osteoarthritis, and they can feel better," Nelson said. "It does not grow new cartilage. It does not reverse the course of cartilage damage. It just helps with the pain associated with arthritis."
For a case like Roy's, more experimental stem cell treatments might hold a better chance in actual healing. It's unclear whether Roy has undergone any such stem cell treatments, but he has received PRP therapy in both his hamstring and his knees. In recent years, some of the biggest names in sports have been associated with the therapy, most notably Kobe Bryant. Bryant, who received the treatment in Germany during the summer of 2011, had been suffering from lingering problems with an arthritic joint in his right knee.
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About Blue Horizon Stem Cells
Worlds leader in advanced stem cell therapy
Welcome to the Blue Horizon Stem Cell Therapy Program and Research Center. We are the worlds leading provider of adult and childrens stem cell therapies. Blue Horizon has treated over 500 patients and safely and efficiently performed more than 2,300 procedures. We are the only treatment provider approved and associated with The Wuhan University Department of Medicine.
Experience you can trust
The team at Blue Horizon Stem Cells is experienced in successfully treating conditions such as Alzheimers Disease, Sports Injuries, Spinal Cord Injuries, Cerebral Palsy, Stroke, Diabetes Mellitus, Arthritis, Heart Disease, Autoimmune Disorders, Anti-Aging and many more.
Highest quality treatment at a reasonable price
Blue Horizon Stem Cells has been providing treatments to patients for many years. We are able to provide extremely competitive rates to our patients as we have streamlined our operations and have package options to choose from based upon your needs.
Option of your stem cells or umbilical cord donors
The Blue Horizon Stem Cell Therapy Program ONLY utilizes stem cells from either your own body or umbilical cord donors whom have proceeded through a multiple step testing process that ensures stem cell patient safety. The procedure is virtually painless and for most patients, takes less than a few hours. We have US trained and board certified physicians on staff for your comfort.
At just 21 years old, a devastating motorcycle accident left top athlete Greg Mucci on the sidelines while he worked through a painful recovery from a serious hip injury. After conventional medicine took his recovery as far as it could go, Brian Mehling, M.D., an orthopedic trauma surgeon and founder of Blue Horizon Stem Cells, offered Mucci the opportunity to receive innovative stem cell therapy at his center in Wuhan, China to avoid a hip replacement. Through Dr. Mehlings foundation, the Blue Horizon Charitable Foundation, Mucci received the treatment and now, at age 30, is on the field playing in a semi-pro football league. Watch Greg Muccis story and learn about the amazing health benefits of stem cell treatments.
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