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Angiodiversity and the liver

 Angiodiversity. The microvasculature displays remarkable structural and functional diversity. Angiodiversity occurs along the segments of the vascular tree and in the microvascular beds of different organs ranging from continuous, barrier-forming endothelium to discontinuous, fenestrated endothelia. Endothelial heterogeneity mediates organ-specific differentiation of the microvascular niche comprising various other cell populations besides endothelial cells such as vascular wall cells (pericytes), parenchymal and stromal cells, but also stem cells. Organ-specific differentiation of the microvascular niche is induced by so-called angiokines. Angiokines are cytokines that are produced by endothelial cells and display an organ-specific pattern of secretion. 

Hepatic Angiodiversity. The microvascular bed of the liver represents a prime example of the organ-specific angiodiversity of the microvascular niche. Here, the organ-specific microvascular endothelial cells are called liver sinusoidal endothelial cells (LSEC). LSEC differ from normal endothelial cells by their special morphology including lack of a basement membrane. Pathological changes of these highly specialized, discontinuous liver sinusoids contribute to severe liver diseases such as alcoholic steatohepatitis and liver cirrhosis. During hepatocarcinogenesis and metastasis to the liver, LSEC trans-differentiate towards a capillary phenotype (capillarization). Normal LSEC display a high capacity of endocytosis for clearance of noxious factors from the peripheral blood. To this end they have a complex cytoskeleton with sieve plates and fenestrations and they express a special set of endocytic receptors. LSEC are also involved in regulating portal blood pressure.