nansyajram
المشاركات : 349
تاريخ التسجيل : 19/03/2010
العمر : 1825
 |  موضوع: stem cells and brain research  الجمعة مارس 26, 2010 1:39 pm | |
| Stem Cells and Brain ResearchBy Fred H. Gage
[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]
Almost every day a newspaper article, news magazine piece, or television news story extols the miraculous possibilities of replacing diseased organs with tissue made in the laboratory from stem cells or raises nightmarish specters of unregulated harvesting of stem cells to create clones. The interest in stem cell research recently reached such a fever pitch that when a Korean scientist fabricated claims to have generated new stem cell lines using nuclear transfer technology, the story was covered by the world press on a daily basis. Stem cell research does offer real promise and does raise real concerns, but unfortunately the public has not been adequately informed about the science behind the debate. The hopes and promises for the use of these cells as therapies for devastating and currently untreatable diseases are being counterbalanced by the concerns over the ethical issues associated with the source of the cells. The discussion of stem cells also has been linked to discussions of cloning humans, as well as to the use of fetal tissue for transplantation. Trying to untangle unrelated issues and clarifying what is currently known versus what is believed to be true can help us make informed decisions. An informed public will make rational decisions about the use of stem cells and can provide knowledgeable support in advancing this potentially useful field of biomedical research. So, What Is a Stem Cell? In its simplest form, a stem cell is any cell that can divide and produce a cell like itself (selfrenewal) and produce another progeny that gives rise to a mature cell of any organ of the body— that is, blood, brain, liver, and so on. Some stem cells are “totipotent” cells; that is, they can give rise to a fully developed organism. For instance, a fertilized egg has this potential for about four days. These cells can be produced through human reproduction or in the laboratory through in vitro fertilization (IVF), a life-giving procedure that helps infertile couples conceive a child. Within about eight days after fertilization, the totipotent stem cell divides, matures, and gives rise to more restricted cells called “pluripotent” stem cells. These cells can self-renew and can give rise to any cell of the body. Pluripotent cells have, as far as we understand now, lost the potential to form an organ and certainly cannot form a fully developed organism. This complex cellular development takes place before organs begin to form in the embryo or even before the embryo leaves the fallopian tubes and implants in the uterus. These more restricted pluripotent cells are called embryonic stem (ES) cells and are the focus of both the promise and concern currently being expressed at national and international levels. The promise is based on the fact that these cells can divide indefinitely and may be able to be used to replace missing, damaged, or dying cells in any organ of the developing and adult body. Certain diseases, in which specific types of cells are damaged, as in diabetes, Parkinson’s disease, heart disease, and cancers, are likely to be the first targets for such therapeutic applications. A less well described, but more immediate use of human ES cells is as a tool to understand human disease. ES cells generated from humans with disease can be grown in culture indefinitely and induced to become any cell of the human body. Therefore, the cells can be used to study and discover how diseases begin and develop in human diseased cells. These same cells can then be used to screen drug libraries to find new therapeutic agents that are safe to “normal” human cells and that could prevent the development of the disease. The concern about human cloning is a very different issue and is not supported or encouraged by the public, politicians, ethicists, or scientists. Human cloning would involve taking DNA from one person and putting it in a donor egg that has had its DNA removed. This newly engineered egg would then be implanted in a woman who would carry the resulting child to term. That child would have the same or similar DNA content as the person who originally donated the DNA. This is not only unacceptable on ethical grounds, but all animals that have been generated by this method have been shown to be sick or deformed in some way. Where Can Stem Cells Be Obtained, and How Do Various Types of Stem Cells Differ? Once an embryo implants in the uterus and begins to make specific organs, at about 25 days after fertilization, separate groups of more mature stem cells take up residence in the different organs (blood, skin, brain, etc.) and contribute to making the cells of each organ. These cells remain in the organ throughout life and can be obtained at any time in development as well as in adulthood, but are more abundant early during development, when the fetus is growing. These later cells are called organ-restricted, “multipotent” stem cells (sometimes referred to as adult stem cells, because a limited number remain in and can be isolated from adult organs). Great interest and effort are being put into investigating both ES cells and multipotent stem cells, but it is not clear whether the multipotent (adult stem) cells live as long or are as viable as the pluripotent ES cells. Research shows that multipotent cells are certainly not as versatile or potent as ES cells. Our knowledge is currently too limited for making a decision as to which cells will be the best or most efficacious for which therapy. However, it is quite likely that, through a careful comparison of ES cells and multipotent cells, a clearer understanding will emerge as to the best, safest, and most ethical way to use stem cells for the treatment of human diseases. Pluripotent ES cells can be obtained from the surplus fertilized eggs produced by fertility clinics through IVF. Most of these surplus fertilized eggs are not used and are discarded. This fact contributed to the recent decision in the United Kingdom to approve financial support for the evaluation of new human embryonic cells to develop therapies for human disease. The United States approved a plan permitting the use of a limited number of existing ES cell lines in 2001. In the United States, unregulated research continues to be carried out by private companies using private funding. In 2004 a ballot initiative was passed in California to support human stem cell research in that state by issuance of a bond. The funds are currently tied up in litigation, but planning for a new California Institute of Regenerative Medicine is under way to administer this statewide research effort.While other states are beginning to follow California’s lead, approval of federal support for the generation of new ES cells would guarantee that extensive guidelines could be enforced for federally funded research. Oversight of federally funded research would cover such issues as the source of cells, informed consent, and measures to ensure safety and the ethical use of ES cells. It is important to remember that the information gained from research sponsored by federal funding is open to the public and available for scientists to use for their own studies and potential therapeutic applications. The biomedical research community generally supports the study of ES cells for their potential value in understanding and treating a variety of diseases unresponsive to current therapies, but like most citizens of this country, the scientific community would support fully enforceable guidelines that would permit the best open and ethical information to be obtained. Only by obtaining accurate, responsible, and high-quality information can people make informed decisions and explain our positions to our local and national representative | |
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