Stem cells found in the bone marrow can develop and become other types of cells: liver, muscle, or nerve cells. Thus they can fill a severe lack of cells of various types, resulting from damage, or infection
They don't have an independent personality yet, and they haven't started growing up yet. These are stem cells found in the bone marrow. They usually mature, differentiate, and become blood cells of different types, which are released into our blood system. But in emergency situations, in response to an urgent need of the body, they can develop and become other types of cells: liver, muscle, or nerve cells. Thus they can fill a severe lack of cells of various types, resulting from damage, or infection.
But how do the stem cells know about a severe lack of certain cells occurring somewhere in the body? Prof. Zvi Lapidot and Dr. Orit Kolt from the Department of Immunology at the Weizmann Institute of Science found how the liver, when damaged, calls the stem cells for help. "When the liver is damaged, it signals the stem cells in the bone marrow, and they rush to it and help in its healing by joining it themselves as new liver cells," says Prof. Lapidot. The research group led by him discovered that certain molecules involved in the normal development of the liver are produced more strongly when it is damaged. The overabundance of these molecules constitutes a kind of signal that alerts the stem cells and calls them to leave their place in the bone skeleton and migrate to the liver. The scientists identified these signaling molecules, called HGF, MMP-9 and SDF-1 - and described the homing process of the stem cells in the liver.
HGF is a molecule involved in the development of the liver. In some situations it can play a role in the spread of cancer metastases. MMP-9 helps the migration of cells from the blood system into different tissues, including liver tissue. In a damaged liver, the physiological balance is violated and these molecules are produced in too great a quantity. Prof. Lapid's current research shows that large amounts of MMP-9 and HGF molecules cause stem cells to be released from the bone marrow into the bloodstream and navigate their way to the liver. The SDF-1 type molecules function as a kind of emergency transmitter that calls the migrating cells to come to the aid of the damaged liver.
These findings may lead to new insights in the field of transplantation and healing of various internal organs, including the liver. They may also reveal a new pool of stem cells capable - under certain conditions - of turning into liver cells. A few years ago it was common to think that only embryonic stem cells had such abilities. Understanding the way in which bone marrow stem cells can also become liver cells may be an important step towards developing advanced methods for curing liver diseases as well as finding an alternative to using fetal stem cells.
