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Endothelial cells differentiation pathway

In vitro assays of angiogenesis

In vitro models of angiogenesis have focused to date predominantly on migration, proliferation and tubule formation by endothelial cells in response to exogenous inhibitory or stimulatory agents.

Endothelial cells in vitro

One problem with endothelial cell assays is that all endothelial cells are not alike, demonstrating phenotypic differences. Differences have been identified between large vessel-derived endothelial cells, such as human umbilical vein endothelial cells (HUVECs), and endothelial cells of microvascular origin, such as human dermal microvascular endothelial cells (HuDMECs) Not only are there structural differences (e.g. fenestrated vs. sinusoidal) but also organ-associated differences.

For example, brain endothelial cells establish the blood brain barrier and express brain-specific antigens, whereas lymphatic endothelial cells have an augmented receptor density for vascular endothelial growth factor (VEGF)-C . The response to growth factors and inhibitors varies with tissue of origin. Proliferating endothelial cells in culture undergo changes in activation state, karyotype, expression of cell-surface antigens and growth properties This last observation presents a significant limitation to the use of these cells to model in vivo angiogenic events because endothelial cells are normally quiescent in adult blood vessels. There are also species differences that should not be ignored. For example, most human endothelial cells bind Ulex europeus agglutinin I (UEA-I), whereas murine endothelial cells do not.

Assays of endothelial cell proliferation

Cell proliferation assays are easy to perform and highly reproducible, lending themselves to precise quantification Endothelial cells established in culture are capable of cell division. Thus, a number of markers of cell division can be used to assess their proliferation in culture. There are two major classes of proliferation assays: those that determine net cell number and those that evaluate cell-cycle kinetics.