Endothelial progenitor cells are bone marrow-derived cells that circulate in the blood and have the ability to differentiate into endothelial cells, the cells that make up the lining of blood vessels. The process by which blood vessels are born de novo from endothelial progenitor cells is known as vasculogenesis. Most of vasculogenesis occurs in utero during embryologic development. Endothelial progenitor cells found in adults are thus related to angioblasts, which are the stem cells that form blood vessels during embryogenesis. Endothelial progenitor cells are thought to participate in pathologic angiogenesis such as that found in retinopathy and tumor growth. While angioblasts have been known to exist for many years, adult endothelial progenitor cells were only characterized in the 1990s after Asahara and colleagues published that a purified population of CD34-expressing cells isolated from the blood of adult mice could differentiate into endothelial cells in vitro. As endothelial progenitor cells are originally derived from the bone marrow, it is thought that various cytokines, growth factors, and hormones cause them to be mobilized from the bone marrow and into the peripheral circulation where they ultimately are recruited to regions of angiogenesis .

Endothelial Progenitor Cell Markers

• Endothelial progenitor cells are thought to express CD34, CD133, CD31, VE-cadherin, VEGFR2, and c-Kit. CD133 and CD34 are often used as markers for selection and purification of these cells because CD133 is not found on mature endothelial cells, and CD34 is not found on the undifferentiated stem cells from which endothelial progenitor cells derive.
• There is emerging evidence that cells that express the combination of CD31, CD45, and Tie-2 may also be a population endothelial progenitor cells.

Relationship to Cardiovascular Outcomes

• There is evidence that circulating endothelial progenitor cells play a role in the repair of damaged blood vessels after a myocardial infarction. In fact, higher levels of circulating endothelial progenitor cells detected in the bloodstream predict for better outcomes and fewer repeat heart attacks. It is hypothesized that endothelial progenitor cells are mobilized after a myocardial infarction, and that they function to restore the lining of blood vessels that are damaged during the heart attack. In a September 2007 news press release by Harvard University, Virna Sales, a researcher in cardiology and surgery at Boston Children's Hospital and Harvard University Medical School and John Mayer, Jr. who is an associate of Surgery Professor, discovered that adult endothelial progenitor stem cells could eventually (within 10 years) be scaffolded with supportive tissue to make pediatric heart valves- for better use in surgically treating cardiac defects.

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