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Stem cells - embryonic, fetal, adult,
Stem cells have two qualities that do not have the other
cells: their ability to multiply indefinitely in culture in vitro, provided they are left in an undifferentiated state and their ability to distinguish when they are offered relevant factors.
Present in the umbilical embryo, fetus and cord, or individuals born - called ... an adult.
These features allow us to consider the therapeutic use of
human stem cells to treat currently incurable diseases. However, the study and / or the use of human embryonic stem cells, which could meet the most interesting ethical issues related to the fact that their production necessarily involves the destruction of the embryo from which they came. The ensuing debate has gone on for years and ethics still unfinished.
In this debate, the legislation requires a response that varies between countries, but also in terms of time of its promulgation.
In France, the National Consultative Ethics Committee (
CCNE) in its draft revision of the bioethics law in January 2000, recognizes the
embryo as a potential human being must be respected at all [...] considered the duty of society is to promote therapeutic progress and to accelerate the improvement of prevention and treatment of diseases currently incurable or hardly curable [...] and advocates a very controlled use of surplus embryos from in vitro fertilization as a source of stem cells.
Until July 2004, French law prohibits the use of these embryos even for research. It allowed for decades, creating lines of stem cells from
embryos or fetuses as a result of natural or induced abortions.
In July 2004 the law on bioethics, Parliament allowed the researchers to use surplus embryos are no longer subject to the parents - and this, in a highly regulated environment, for a trial period of five years or less, provided that both parents have given their consent.
In Europe, many countries have this right for years (Belgium, Denmark, Finland, Greece, Holland, Sweden and Great Britain), which has led to increased research in this extremely scalable.
In the U.S., the situation is very complex and depends on the fact that
research is conducted under the auspices of the federal and local institutions with surplus embryos obtained before or after the election of President Bush in 2000, or if financed by public or private. ..
Embryonic stem cells, located in the inner cell mass of early embryos (see figure below), are exceptional in that they are involved in the construction of all tissues of the future individual. This totipotency to qualify for the repair of all tissues and allows them to provide information at the time unparalleled in embryonic development and its genetic control ...
Diagram of a 5-day blastocyst (0.14 mm)
For its part, fetal or adult stem cells, found in small quantities in all tissues (ensuring maintenance), have no such universality are only multipotent, although most show no thought multipotent stem cells as the study of tissue Fat has been demonstrated.
The benefits of
adult adipose tissue
Adipose tissue is easy to take with liposuction, and a person, although thin, can easily provide a liter.
It contains stem cells that have the interest to grow faster than those obtained from other adult tissues such as bone marrow or brain, for example.
These stem cells differentiate into fat cells, but also in vitro in cells of muscle, bone and nerve cells, too, that was not expected given that nerve cells derived from the epidermis, while the fat cells of the mesoderm.
Every so often, I could free these autologous cells to restore rejection. And anyone could propose engagement, which carries a genetic defect to prevent autograft.
Preliminary studies in mice have opened in this way.
Progress between April and June 2004 in mice
Researchers working on adult stem cells from adipose tissue of mice during this spring, has won three major successes:
- The repair of the fracture
We could go on in vitro differentiation of mouse cells into stem cells and bone cartilage fat. Michael Longaker and his team at Stanford University in California, has managed to do in mice in vivo: perform the surgery, the repair of the fracture is too large for each of which have been applied to adult ASC, located in a biodegradable polymer apatite (a natural constituent of bone tissue). Fractures of the control mice were not mistreated.
Twelve weeks later, the stem cells that differentiate into full 70 to 90% of the mice treated fractures. In comparison, in control mice was evident that a disorganized tissue and above only less than 10% of cases.
For now, clinical trials on humans, to try to repair severe fractures, using only stem cells from bone marrow.
- The expression of cardiac muscle-specific proteins
We knew we obtain the expression of specific proteins of the cardiac muscle (myosin heavy chain and troponin 1) from adipose stem cells cultured in vitro. John Fraser and macropores biotechnology company has just demonstrated the feasibility of in vivo, mice were injected with impairment of the myocardium, a simple saline solution, or a million of ASC-induced, c 'words had always been the differentiation factors . The second group of mice, including the myocardium, the two began to express specific proteins of the heart muscle.
- Differentiation in vitro: towards the
nerve cells
The researchers knew obtain cells in vitro that resemble nerve cells from adipose stem cells and a cocktail of growth factors and inducing agents.
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Kristine Safford and Henry Rice (pictured above), the Medical Center of Duke University (USA, North Carolina) have recently demonstrated, once again, in vitro, these cells work well in nerve cells: the effect of specific proteins expressed in like proteins of neurotransmitter receptors.
Therefore, the
NMDA, a mimic of the neurotransmitter glutamate, has the distinction of killing the nerve cells when present in excessive amounts, resulting in the countryside, once bound to the receptors of glutamate, an excitatory effect as well. However, NMDA has the same lethal effect on the induced stem cells shows that the message, and its surface expressed NMDA glutamate receptors are able to capture.
The next step is to study in vivo in an animal model of introducing these cells induced.
Perspectives
In light of these initial findings, it appears that adult stem cells from adipose tissue, which have the advantage of being available in quantity and has no ethical debate, which has been promised a bright future in the reconstruction of damaged or lost tissue.
These results also show that the tissues are required to provide more varied types of these cells naturally move in that they provide adequate differentiation factors.
But there are hundreds of different cell types in humans, and it is unlikely that stem cells only from the types of fat, or other adult stem cells, enough for all types of cells. This result does not seem accessible only through the expansion and diversification of sources of stem cells available.
Thus, Britain in May 2004 has created a bank of stem cells available to researchers throughout the world, host and maintain all types of stem cells will be able to isolate that are embryonic, fetal or adult.
As a research cell bank is being exploited? Some ideas include:
The identification of acceleration and almost industrial differentiation through a detection system available today, and detection comparable to
microarrays.
The creation of mutant lines of embryos from very young embryos was released as part of IVF when deleterious mutations. These lines are to better understand and cure these genetic diseases, and possibly a treatment day.
Identified in the gene of the mouse Nanog love, active in embryonic stem cells, their multiplication triggers indefinitely, preventing their differentiation. Totipotent embryonic cells, in contact with the product of this gene, which may soon offer - and very cheap, because from a single embryo - millions of others. And if possible one day to re-activate this gene in adult stem cells, he would return to its
totipotent, ie a type of embryonic stem cells and ethical issues raised by the use of human embryos no longer arise.
Recent results of research in the field of stem cells used to assess its subsequent use for therapeutic purposes. The limits of this revolution in medicine will not only be dictated by science, but also the answers to ethical questions. A debate involving all actors of society is in progress and the development of the recent legislation was not the end. There is no doubt that the use of stem cells, limits the possibility remains defined by the advancement of knowledge, but also the evolution of society.
