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Elusive Stem Cells Could Help Repair Blood Vessels

LONDON (UK), September 2018 — A unique source of stem cells in blood helps to build blood vessels according to a new study using mouse embryos, led by researchers at the University College of London Institute of Ophthalmology.

The findings, published in Nature, change our understanding of how blood vessels are made and bring scientists one step closer to using stem cells to grow new blood vessels and repair damaged ones.

Growing and repairing blood vessels is a major goal in treating heart and circulatory diseases in which vessels become damaged, including, for example, coronary heart disease and peripheral arterial disease or some blinding eye diseases.

Until now, scientists thought that new blood vessels in the embryo only grew when existing blood vessel cells divided. The new research shows that stem cells in the bloodstream can develop into endothelial cells — important cells which line all blood vessels.

“These stem cells were previously known to form blood and immune system cells in the fetus. To find that they also generate endothelial cells for new blood vessels in the fetus was unexpected and is hugely exciting,” said lead author Christiana Ruhrberg, Ph.D.

“Our findings may pave the way to resolve a longstanding debate in the scientific community as to whether blood stem cells could be used to promote endothelial regeneration in patients with poor blood supply in their hearts or other organs.”

Stem cells are cells which can differentiate into mature cell types. For decades, researchers have been searching for stem cells in the blood that can develop into endothelial cells, coined “endothelial progenitor cells” because of their potential in regenerative medicine. So far, scientists have disagreed about what they are and what they look like, and whether they truly exist in the blood.

This study provides important new evidence that such a stem cell exists in the blood stream of developing embryos. An important next step will be to track these cells down in humans.

The researchers used fluorescent tags to follow the fate of the stem cells, called erythromyeloid progenitors (EMPs), already known to develop into red blood cells and certain types of immune cells. EMP stem cells grown in a dish developed into endothelial cells as well as red blood cells and immune cells. The EMP stem cells also developed into endothelial cells in mice that were naturally growing in their mother’s womb, and they continued to line blood vessels into adulthood.

“Further research is needed to find out exactly how EMPs and their endothelial cell offspring work and whether they might be used in regenerative medicine. It will also be important to figure out if these cells actively contribute to making new endothelial cells throughout life,” said co-author Alice Plein, Ph.D.

“We initially discovered the EMP origin of endothelial cells in the brain when observing brain-resident immune cells. In a further twist, we found that they also lined more than half of the liver vasculature all the way into adulthood,” added co-author Alessandro Fantin, Ph.D.

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