What are stem cells?
- They can divide throughout our lifespan, a feature defined as long-term self-renewal.
- They have retained part of the potency of embryonic cells to give rise to multiple cell types
- They can give rise to specialized cell types in a process called differentiation.
What is the role of stem cells?
In our body, cells can function for different amounts of time. For instance, red blood cells live for 4 months, whereas intestinal epithelial cells only live for 1 week. Tissue specific stem cells serve for the continuous replacement of these missing cells. Growth of hairs and nails also relies on stem cells. Other organs, such as the heart or the pancreas, are composed of long-living cells that do not need replacement. These organs typically also lack competent stem cells and thus cannot regenerate well after damage.
Are all stem cells the same?
No, stem cells can be very heterogeneous and might have different potential for maturation. In the adult organism, stem cells could be unipotent or multipotent. Unipotent stem cells differentiate into only one cell type. For example, all spermatogonia become sperms. Multipotent stem cells can differentiate into several cell types from the same tissue. For example, hematopoietic stem cells in our bone marrow give rise to diverse blood cells, but not to muscle or brain cells. In the early embryo, cells are pluripotent, meaning that they can give rise to all cell types of the body, but they lose this feature as development progresses. Researchers have established methods to culture embryonic stem (ES) cells and to induce pluripotent stem (iPS) cells from specialized cells.
What are the major questions in stem cell research?
Researchers want to know what makes stem cells different from the other more specialized cell types of our body. To understand this, studies try to elucidate how stem cells produce specialized cells (differentiation) of the correct type and number to maintain the integrity of tissues (homeostasis). In addition, stimulating stem-cell properties to support tissue regeneration is of great therapeutic interest. For organs with limited regenerative capacity, researchers investigate whether specialized cells can regain some of these stem cells properties. Stem cell research is one of the most fascinating and promising areas of contemporary biology and medicine.
What animal models are used to study stem cells?
Certain animals display astonishing regenerative abilities. Some invertebrate species, such as hydra, flatworms and tunicates, can restore their entire body from a fragment of it. Among vertebrates, salamanders and fish can efficiently replace amputated appendages and complex organs. Among mammals, mice and rats are the most common animal models to study stem cell differentiation, wound healing and tissue homeostasis. Researchers do not yet understand why the natural regenerative capacity varies between species. Beside animal studies, cell culture approaches are fundamental for stem cell research.
Can tissue regeneration occur without stem cells?
Yes, tissue regeneration can also rely on the multiplication of specialized cells to restore the damaged tissue. This process is dependent on the plasticity of specialized cells around the wounded tissue. For example, the liver can recover after partial damage (for example after a hepatectomy) through the proliferation of the remaining liver cells. Among vertebrates, salamanders can regenerate amputated limbs by mobilizing the functional cells in the remaining stump. Understanding how mature tissues are activated in response to injury will provide new insights into developing regenerative therapies.
Why is stem cells research important for regenerative medicine?
Regenerative medicine aims at discovering better ways of helping people after disease or injury. While most traditional therapies provide a punctual solution, the unique properties of stem cells can provide a life-long cure. However, because of the permanent aspect of stem cell therapies, their efficacy and safety have to be assessed very thoroughly. Many promising treatments are thus still being tested in laboratories. Yet, stem cell therapies are already being used, for instance to treat leukemia through bone marrow transplantation or blindness by corneal conjunctivalization through limbus grafting.
What is “stem cell tourism”?
Some clinics are offering “stem cell-based” treatments that allegedly bring anti-aging effects, enhance physical properties, or even cure incurable diseases. If a treatment is not available in Switzerland, it is either because the treatment has no proven efficacy or because its safety has not been established. Consequently, traveling to another country to undergo an experimental treatment (stem cell tourism) can be expensive, ineffective and even dangerous. When considering a stem cell therapy, always gather information from different sources.
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