It is estimated that the aging worldwide population will result in over 150 million sufferers of dementia by the year 2050. Currently, there is no treatment available to cure dementia. Numerous treatments are being investigated in clinical trials and there are major research efforts in neurodegenerative diseases and the associated loss of cognitive function. Diseases such as Alzheimer’s (AD), Parkinson’s (PD), Huntington’s (HD), and Amyotrophic Lateral Sclerosis (ALS) are diseases of protein homeostasis, characterized by loss of specific neuronal populations and the presence of inclusion bodies consisting of insoluble, unfolded proteins. Harnessing the full therapeutic potential of stem cells will require full interpretation of signal transduction forces for proliferation, differentiation, and apoptosis. Regardless of the specific path your stem cell research takes, Enzo provides innovative tools to help you realize its full potential.
Stem Cell Classifications
Stem cells are highly unspecialized cells that are the basis for every tissue and organ. Stem cells are characterized by the ability to self-renew and the ability to differentiate. These include embryonic stem (ES) cells, progenitor cells, mesenchymal stem cells (MSCs), neural stem cells (NSCs) and induced pluripotent stem (iPS) cells. The progressive loss of structure, function, and number of neurons, including death of neurons, underlies all neurodegenerative diseases. The current treatment options are limited.
Tissue-Specific Stem Cells
Adult or somatic stem cells are somewhat specialized and are often found in organs that need to continuously replenish themselves including the blood, gut and skin. These types of stem cells have the ability to generate multiple, organ-specific cell types and are described as multipotent. Tissue-specific stem cells are difficult to culture in the laboratory.
Embryonic Stem Cells (ESCs)
Embryonic stem cells (ESCs) are a class of pluripotent cells derived from the inner cell mass of blastocysts that can give rise to almost all types of somatic cells. Initial work at the James A. Thomson laboratory on mouse ESC paved the way for the first successful generation of human ESCs in 1998. . Due to its plasticity and ability for indefinite self-renewal, ESCs offer promising avenues for research in neurodegenerative disorders such as the ones mentioned above. However, there are several risks associated with all novel ESC therapies, such as the risk of immune-rejection as well as teratoma formation due to instability associated with prolonged time in culture. Nevertheless, ESCs are frequently differentiated into neurons and serve as test subjects for novel candidate drugs against these diseases.
Induced Pluripotent Stem Cells (IPSCs)
Induced pluripotent stem cells (iPSCs) are a type of pluripotent stem cell that is artificially derived from a non-pluripotent, adult somatic cell by forcing the expression of genes and transcription factors that maintain embryonic stem cells. By reprogramming adult cells back to pluripotency, this enables the development of an unlimited source of any type of human cell needed for therapeutic purposes. Early experiments with somatic cell nuclear transfer demonstrated that adult nuclei from somatic cells can be reprogrammed upon transfer into an undifferentiated oocyte. Pioneering work by Yamanaka and Takahashi on nuclear reprogramming allows for specific expression of embryonic genes in adult somatic cells to induce embryonic properties in adult cells. These embryonic properties are the ability to self-renew, to form derivatives of all three embryonic germ layers from the progeny of a single cell, and to generate a teratoma. In 2006, Yamanaka and Kazutoshi successfully induced pluripotency in mouse fibroblasts through co-transduction with retroviral vectors for 24 genes implicated in maintaining embryonic stem cells. Despite the potential that iPSCs have as useful tools for drug development and disease modeling, additional research is needed to continue to refine methods to reprogram adult cells into de-differentiated naïve cells and to compel cell-specific developmental fates.
Mesenchymal Stem Cells or Mesenchymal Stromal Cells (MSCs)
Mesenchymal stem cells (MSCs) are traditionally found in the bone marrow and can differentiate into a variety of cell types, including bone, cartilage, fat and possibly even muscle. MSCs have a great capacity for self-renewal while maintaining their multipotency. Therefore, MSCs have enormous therapeutic potential, including tissue repair, and could be an ideal source for cell transplantation in neurodegenerative diseases. Since 1991, the term MSCs has been used to also describe many cell types from diverse tissues varying levels of multipotency. There is concern in the scientific community that are calling for a name change for MSCs due to the variety of cells and tissue-specific cell types that may fall into the MSC category. Unfortunately, MSCs have become the go-to cell type for many unproven stem-cell interventions.
Neural Stem Cells (NSCs)
Neural stem cells (NSCs) can be produced by the dissection of specific brain regions. NSCs are self-renewing, multipotent cells that are more specialized than ESCs as they only generate the radial glial progenitor cells that create the neurons and glia of the nervous system in all animals. Adult NSCs were first discovered in the 1960s and methods were developed so cells can be cultured in vitro as neurospheres. NSCs have also been genetically modified to create immortalized cell lines with increased proliferative potential.
Cellular Therapy for Neurodegenerative Diseases
Stem cell research holds tremendous promise for medical treatments, but scientists still have much to learn about how stem cells, and the specialized cells they generate, work in the body and their capacity for healing.
Alzheimer’s Disease
Scientists have discovered a novel way to convert human skin cells into brain cells, an advancement that offers hope for regenerative medicine and personalized drug discovery and development. Researchers have come up with a recipe for making functional neurons directly from human skin cells, including those taken from patients with AD. The new method offers a critical short step necessary for generating neurons for replacement therapies in the future. The converted neurons are beginning to yield insights into what goes wrong in an Alzheimer’s brain and how diseased neurons would respond to treatment. In earlier approaches to generate neurons from skin cells, those adult cells first had to be returned to an embryonic stem cell state. Those cells are hard to come by - less than one percent of cells are typically reprogrammed successfully. In addition, the entire process is time-consuming, requiring months to coax cells into IS cells and then stimulate them into becoming neurons. While the process was not initially very efficient, scientists at Columbia University refined the protocol, converting about 50 percent of the cells, whereby neurons developed from healthy skin cells could fire and receive signals like normal neurons. The more exciting news was that when the cells were placed into the brains of developing mice, the converted cells were able to connect up to the existing circuitry.
Parkinson’s Disease
Dopamine is a key neurotransmitter that is used to send signals from one neuron to another and is involved in motor control. Patients with Parkinson’s disease (PD) suffer symptoms from dopamine deficits produced by the disease targeting the destruction of dopamine-producing neurons in the substantia nigra. As the disease progresses, patients may present symptoms such as muscle tremors, muscle rigidity, deficits in movement, problems with thinking, and aggregates of a protein called alpha-synuclein in their brains. Currently, the primary treatment modality is supplementing dopamine (Levadopa) to compensate for the deficit in the brain that is produced by the disease destroying dopaminergic neurons. While current medications have proven useful, their efficacy begins to decrease over time as the disease progresses. Therefore, researchers have been looking for alternative strategies to supplement dopamine – one of them is by trying to replace dopaminergic neurons that have been lost by the disease with stem-cell derived dopaminergic neurons. Scientists are working with ESCs and iPSCs and inducing their differentiation into mature dopaminergic cells that can survive and function after transplantation. Thus far, these stem cell transplantation treatments for PD have demonstrated some success in animal models using mouse, rat and monkey brains. Clinical trials have just started using the transplantation of young brain cells from human fetuses into people with PD with the aim of examining the efficacy and minimizing side effects.
Huntington’s Disease
Therapeutic approaches based on stem cells have received considerable attention as potential treatments for HD, which is a fatal, inherited neurodegenerative disorder, caused by progressive loss of GABAergic medium spiny neurons (MSNs) in the striatum of the forebrain. Recent advancement in cellular reprogramming technology provides a unique opportunity to derive iPSCs from a patient’s own cells, making it an ideal cell source for personal stem cell replacement therapy with minimal or no immunological rejection. Transplantation of stem cells or their derivatives in animal models of HD, efficiently improved functions by replacing the damaged or lost neurons. In particular, NSCs for HD treatments have been developed from various sources, such as the brain itself, the SCs, and the somatic cells of HD patients. However, the brain-derived NSCs are difficult to obtain, and the PSCs have to be differentiated into a population of the desired neuronal cells that may cause a risk of tumor formation after transplantation. In contrast, induced NSCs, derived from somatic cells as a new stem cell source for transplantation, are less likely to form tumors. Given that the stem cell transplantation strategy for treatment of HD, as a genetic disease, is to replace the dysfunctional or lost neurons, the correction of mutant genes containing the expanded CAG repeats would be promising.
Amyotrophic Lateral Sclerosis
ALS is a progressive, incurable neurodegenerative disease that targets motor neurons. Several factors contribute to the difficulty in finding effective therapies for ALS. Ninety percent of cases are sporadic, which means they are caused by a combination of genetic mutations and/or presumed environmental variables. Only ten percent of ALS cases are caused by inherited forms of known genes. This diversity of potential causes means that any therapy would only be effective on a certain subset of patients. Furthermore, until recently, there was also no way to test if a drug would even work on motor neurons, the cells affected in ALS, because they couldn’t be obtained in large numbers. Cell-based therapies have generated widespread interest as a potential therapeutic approach but no conclusive results have yet been reported either from pre-clinical or clinical studies. In a leap forward for the field, Harvard scientists derived human induced pluripotent stem cells — mature cells that are manipulated back to a stem cell state — from the skin and blood of ALS patients. This achievement means that the disease can be studied in a laboratory culture dish filled with the cells responsible for this devastating condition, allowing scientists to identify new therapies for ALS.
Future Challenges
Currently, certain bone, skin, and corneal injuries are treated by grafting tissues, usually derived from stem cells. Over the past 50 years, bone marrow transplants have been used to treat diseases such as leukemia and inherited blood disorders. Umbilical cord blood has also been used as an alternative source to bone marrow transplantation. Other promising stem cell treatments are still at a very early experimental stage. Very few stem cell treatments are safe and effective. There are several major challenges that need to be addressed before stem cells can be used to treat a wide range of diseases. Culturing the right type of stem cells is a difficult process. An abundant source of stem cells is needed. Pluripotent ESCs and iPS cells can be grown indefinitely in the lab. However, these procedures are very complex and still need to ensure that these cells can be used safely and routinely. Stem cell treatments would likely need to have a close match between the donor and recipient to reduce the risk of rejection. iPS cells have the potential to be used for personalized patient-specific treatment without the problems of rejection and use of immunosuppressants. Furthermore, a delivery system is needed to target the cells to the right location in the body for successful treatment. Lastly, long-term clinical studies are required to determine the precise therapeutic effect of stem cells.
Summary
Enzo Life Sciences offers a comprehensive
Stem Cell research portfolio. At Enzo, we believe in providing scientists with novel tools that will help stem cell discovery. We have our
SCREEN- WELL® Stem Cell Library, a collection of 130 compounds that can be used for stem cell signaling research and drug screening. Furthermore, our growth factor
protein portfolio includes
Activin-A,
BML-4, and
Wnt3a. We also offer a broad range of
antibodies for use in all areas of stem cell research. Every antibody is backed by our
Worry-Free Antibody Trial program, allowing you to evaluate any of our antibodies of interest for your specific application or species without risk. Please check out our
Stem Cell platform for more information or contact our
Technical support team for future assistance.
