Thursday, 7 March 2013

Stem Cell

What is a Stem Cell
Blastula with the inner
 cell mass (yellow) where
 ESC are located.
 Stem cells are defined as cells with the unique capacity to self-replicate throughout the entire life of an organism and to differentiate into cells of various tissues. Most cells of the body are specialized and play a well-defined role in the body. For example, brain cells respond to electrical signals from other brain cells and release neurotransmitters; cells of the retina are activated by light, and pancreatic ß-cells produce insulin. These cells, called somatic cells, will never differentiate into other types of cells or even proliferate. By contrast, stem cells are primitive cells that remain undifferentiated until they receive a signal prompting them to become various types of specialized cells.

 Generally speaking, there are two types of stem cells: embryonic stem cells (ESC) and adult stem cells (ASC). ESC are cells extracted from the blastula, the very early embryo, while ASC are stem cells found in the body after birth. The term "adult stem cells" does not refer to a characteristic associated with adulthood, but rather a contrast with the developing embryo. Stem cells in the bone marrow of a newborn baby, for example, or even stem cells found in the umbilical cord are referred to as adult stem cells.

 Although much has been published in the media about ESC and their huge potential for the treatment of various health problems, little has been published about the impressive potential of ASC. When used according to protocols that are tailored for the properties and characteristics of ASC, these latter show similar potential. But most interesting is the natural role of stem cells in the body

 The Stem Cell Theory of Renewal

 What has emerged over the past few years, through a vast body of scientific literature, is the novel view that the process of repair and renewal taking place in the body involves bone marrow stem cells. In brief, when a tissue is subjected to significant stress, stem cells originating from the bone marrow migrate to the tissue, proliferate and differentiate into cells of that tissue, thereby supporting the repair process.1 This natural process of repair has been described in many tissues and organs of the body. It is the natural process of tissue renewal taking place in the body every day of our lives, from the day we are born!

 Let’s briefly describe the process that takes place any time a tissue is exposed to stress and needs assistance. A few hours after an instance of tissue stress or damage, the affected tissue releases a compound called Granulocyte Colony-Stimulating Factor (G-CSF). G-CSF is well known to trigger stem cell release from the bone marrow.2 G-CSF is routinely used prior to cancer treatments involving chemotherapy or radiation. Since such treatments are known to kill all stem cells in the body (requiring stem cell transplantation after the treatment), G-CSF is commonly injected into the cancer patient to trigger stem cell release from the bone marrow in order to harvest and cryo-preserve stem cells. After the treatment, the stem cells are thawed and re-injected in the patient to reconstitute the bone marrow.

 After tissue damage, as its concentration slowly and naturally increases in the blood, G-CSF triggers the release of stem cells from the bone marrow, increasing the number of stem cells circulating in the blood.

 As we will see below, much scientific evidence indicates that this aspect is probably the most crucial part of the whole process. Increasing the number of circulating stem cells means that more stem cells are available to migrate in the damaged tissue.

  Within a few hours after an instance of tissue damage, G-CSF appears in the bloodstream. G-CSF triggers the release of stem cells whose numbers increase in the blood over the next few days. Within 24 hours after the incident, the affected tissue begins secreting SDF-1, which peaks at 72 hours. SDF-1 is the only compound known to attract stem cells. Soon afterward, the affected tissue releases a unique compound called Stromal-Derived Factor-1 (SDF-1).3 SDF-1 is the only compound known to attract stem cells. When SDF-1 binds to CXCR4, the receptor present on the surface of stem cells, this binding process triggers the expression of adhesion molecules on the surface of the cell. Therefore, as SDF-1 diffuses from the affected area to the blood circulation, and as stem cells circulating in the blood travel through the affected tissue, the binding of SDF-1 to CXCR4 triggers the adhesion of stem cells to the capillary wall and – subsequently -- their migration into the tissue.4 When they arrive in the target tissue, stem cells proliferate and then differentiate into cells of that tissue, thereby assisting in the repair of the tissue.

 This whole process has now been demonstrated in numerous studies, where stem cells have been shown to participate to the repair of muscles, bone, pancreas, brain, skin, liver, intestine, lung … virtually every organ and tissue of the body!

In this whole process, the number of stem cells circulating in the bloodstream appears to be the most important factor. When the level of circulating stem cells was measured in the bloodstream of individuals who suffered an injury, the individuals who had the largest number of stem cells on the day of their injury showed the fastest and greatest recovery.7 Likewise, when the number of stem cells was quantified in the bloodstream of nearly 500 individuals, and their health condition was monitored for one year, the individuals with a larger number of stem cells in their blood showed a greater level of health.8 In other words, more stem cells circulating in the bloodstream means more stem cells available to migrate into tissues that might need assistance.

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