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Endothelial progenitor cells are produced in the bone marrow and travel through the blood stream. They repair damage done to the lining of blood vessels and the heart after tissue has died. Progenitor cells are a type of stem cell that can differentiate into several closely related cell types. The amount of these cells circulating in the bloodstream can help indicate how quickly a person will recover from a heart attack or stroke. Endothelial progenitor cells may also have the ability to begin building new blood vessels in areas where the vessels have been damaged beyond repair.
The endothelium is a specialized type of epithelium, or skin tissue, that lines the entire circulatory system; it helps the blood to flow smoothly by providing a smooth surface and preventing clotting on blood vessel walls. Endothelial progenitor cells are present in the blood in low numbers under normal circumstances, but increase in response to stress damage to the endothelium. During a heart attack or stroke, some tissues of the body become ischemic meaning that they have no blood flow and cells begin to die. Endothelial progenitor cells then travel to these damaged areas before finally differentiating into mature endothelium cells and replacing dead cells.
Endothelial progenitor cells are called pluripotent stem cells rather than totipotent unlike the stem cells that are most commonly discussed. This means that they can become several different cell types — plural potential — but not all cell types — total potential. In adults, they function similarly to the angioblasts that are responsible for formation of blood vessels in embryos, although they may be less adaptable.
Some studies have shown that stroke patients with more endothelial progenitor cells had a better chance of avoiding repeat heart attacks. Trials are also being done that find promising results in using these cells in the treatment of peripheral artery disease. Since the level of these cells increases when damage is present, doctors can also analyze the number of these cells to determine the risk of heart disease in a patient.
Early studies found that these cells do not make up the lining of newly formed blood vessels in adults. More recent studies have shown evidence that endothelial progenitor cells are important to the development of tumors and in allowing tumor cells to metastasize, or travel to other areas of the body. These studies found these cells actually present in the blood vessels of tumors. They have also found that tumors grow more slowly if the endothelial progenitor cells are removed from bone marrow before they can be released into the blood stream.