The inner surface of blood vessels is lined by a wafer-thin layer of cells known as the endothelium, which forms a crucial barrier between blood and the surrounding tissue. The single-layered cell structure promotes the exchange of oxygen and nutrients, while simultaneously preventing the uncontrolled leakage of blood components. Only when the metabolic needs of the surrounding tissue increase, e.g., during growth, wound healing or tumor development, do endothelial cells abandon this stable cell association in order to divide and form new blood vessels. The signals that trigger this activation have been throroughly studied. Previously, however, little was known about how endothelial cells maintain their stable resting state. This is what scientists at Berlin Institute of Health (BIH) at Charité have now investigated together with an international team of researchers. They have published their findings in the journal Nature Cell Biology.