Hence the question arises, will it be possible to mobilize the reserve cells of the facial muscles to repair damaged tissue in the heart muscle? Dr. Tzhor and the members of the research group he heads received some hints that the answer to this may be positive.
What does the past of the cells in our body tell us about them? Dr. Eldad Tzhor and research student Itamar Harel, from the Department of Biological Control at the Weizmann Institute of Science, recently succeeded in tracking embryonic and adult stem cells in the skeletal muscles, revealing their developmental origin. These findings are described in an article recently published in the scientific journal Developmental Cell, and they may lead, in the future, to the development of advanced ways to repair damaged heart muscle.
All skeletal muscles work in more or less the same way: the muscle cells are organized into long fibers that contract and relax to move the skeletal components they are attached to. From the delicate eye muscles to the powerful jaw muscles, all 60 muscles that exist and operate in the face work this way. Studies by Dr. Tzhor and other scientists have shown in recent years that the facial muscles develop from separate groups of cells in the fetus, and they grow according to a different development plan than all the other skeletal muscles in the body. In fact, there are differences even between the different groups of facial muscles: a previous study by Dr. Tzhor showed that some of them are closer to a muscle that is not related to the skeleton at all - the heart muscle.
The scientists of the institute decided to examine and discover the developmental origin of the cells that belong to the repair system of the facial muscles. The satellite cells (so called because they are located outside the muscle fiber) are stem cells unique to skeletal muscles. Like adult stem cells, they are kept aside, as a reserve, for replacement and repair. In fact, the development of these cells is delayed: they do not complete the differentiation process until the final stage of a muscle cell, and wait until muscle fibers die of old age or tear as a result of overexertion. At this stage, when the body needs help, it activates the reserve forces available to it. This is the stage in which the satellite cells - called flagellum - return to the development process, become mature and functioning muscle cells, and unite to form fibers - which replace the damaged muscle fibers. Scientists working in different parts of the world have solved, in recent years, the mystery of the embryonic origins of the satellite cells in the body's skeletal muscles, But it was not clear if the head muscles develop in the same way, or if their satellite cells come from a different embryonic source. To answer this question, the scientists decided to map the lineages of cells in the head muscles, from the fetus to after birth, when the mature stem cells appear in their place as satellite cells. For this they had to use several research methods. In the first stage, they transplanted a small number of cells from the area where the head muscle cells are formed in quail embryos, into chicken embryos. The transplanted cells continued to develop in the chick, contributing to the head muscles as well as the satellite cells in these muscles. In the next step, they sought to track cell lineages in mice, using methods of genetic engineering, in combination with fluorescent markers that pass from the mother cells to the daughter cells. Precise tracking of the fluorescent markers carried out in these transgenic mice allowed the scientists to solve the mystery for the first time, and to map the development pathways of different muscles in the head, and of their satellite cells.
The scientists also discovered that the satellite cells of each of the facial muscles develop from the same groups of embryonic cells from which the corresponding muscle develops. In other words, the "reserve forces" of each of the facial muscles come from the same source from which the normal cells developed. These findings rule out the suggestion that the satellite cells come from different sources, such as the bone marrow or blood vessels. One of the outstanding findings that emerged from this study is the common origin of heart muscle cells and facial muscle cells. As surprising as it sounds, these two types of cells start their developmental path from the same embryonic source. Nevertheless, in adulthood they are very different from each other: the heart does not have cells similar to satellite cells that exist in skeletal muscles. Therefore, heart muscle cells that die have no replacement, and the death of such cells can be dangerous.
Hence the question arises, will it be possible to mobilize the reserve cells of the facial muscles to repair damaged tissue in the heart muscle? Dr. Tzhor and the members of the research group he heads received some hints that the answer to this may be positive. Today they are trying to test this direction, and find a way to activate the "genetic software" of the heart in satellite cells taken from the facial muscles, which will allow them to be transformed into heart muscle cells. Using such cells it will be possible to treat, among other things, patients who suffer from heart diseases.
