Endothelial stem cell

Endothelial stem cells (ESCs) are one of three types of stem cells found in bone marrow. They are multipotent, which describes the ability to give rise to many cell types, whereas a pluripotent stem cell can give rise to all types. ESCs have the characteristic properties of a stem cell: self-renewal and differentiation. These parent stem cells, ESCs, give rise to progenitor cells, which are intermediate stem cells that lose potency. Progenitor stem cells are committed to differentiating along a particular cell developmental pathway. ESCs will eventually produce endothelial cells (ECs), which create the thin-walled endothelium that lines the inner surface of blood vessels and lymphatic vessels. ECs were first thought to arise from extraembryonic tissues because blood vessels were observed in the avian and mammalian embryos. However, after histological analysis, it was seen that ECs were in the embryo. This meant that blood vessels come from an intraembryonic source, the mesoderm. ECs derived from stem cells are the beginning of vasculogenesis. Vasculogenesis is the new production of a vascular network from mesodermal progenitor cells. This can be distinguished from angiogenesis, which is the creation of new capillaries from vessels that already exist through the process of splitting or sprouting. This can occur 'in vitro' in embryoid bodies (EB) derived from embryonic stem cells; this process in EB is similar to 'in vivo' vasculogenesis. Important signaling factors for vasculogenesis are TGF-β, BMP4, and VEGF, all of which promote pluripotent stem cells to differentiate into mesoderm, endothelial progenitor cells, and then into mature endothelium. It is well established that insulin-like growth factor (IGF) signaling is important for cell responses such as mitogenesis, cell growth, proliferation, angiogenesis, and differentiation. IGF1 and IGF2 increase the production of ECs in EB. A method that IGF employs to increase vasculogenesis is upregulation of VEGF. Not only is VEGF critical for mesoderm cells to become an EC, but also for EPCs to differentiate into mature endothelium. Understanding this process can lead to further research in vascular regeneration. Stem cells have the unique ability make identical copies of themselves. This property maintains unspecialized and undifferentiated cells within the body. Differentiation is the process by which a cell becomes more specialized. For stem cells, this usually occurs through several stages, where a cell proliferates giving rise to daughter cells that are further specialized. For example, an endothelial progenitor cell (EPC) is more specialized than an ESC, and an EC is more specialized than an EPC. The further specialized a cell is, the more differentiated it is and as a result it is considered to be more committed to a certain cellular lineage. Blood vessels are made of a thin layer of ECs. As part of the circulatory system, blood vessels play a critical role in transporting blood throughout the body. Consequently, ECs have unique functions such as fluid filtration, homeostasis and hormone trafficking. ECs are the most differentiated form of an ESC. Formation of new blood vessels occurs by two different processes: vasculogenesis and angiogenesis. The former requires differentiation of endothelial cells from hemangioblasts and then the further organization into a primary capillary network. The latter occurs when new vessels are built from preexisting blood vessels.