Endothelial Cell Heterogeneity and Differentiation

Abstract

The biology of the endothelial cell is a burgeoning area of scientific interest. Once considered relatively inactive and homogenous, endothelial cells in recent years have been shown to be functionally interactive with other cells in many complex ways and to manifest extensive heterogeneity. Early studies of their heterogeneity focussed on such differences as fenestrated vs. non-fenestrated, large vessel vs. capillary, lymphatic vs. vascular. More current studies have investigated the heterogeneity of the cell surface of endothelial cells, particularly microvascular cells, as demonstrated by organ and tissue specificity. Selectivity in the seeding of metastatic cells and site-specificity of lymphocyte homing are examples of preferential adhesion to the endothelial cell surface. Organ specific enzymes such as glutamyl transpeptidase, structural heterogeneity such as the absence or presence of Weibel-Palade bodies, differences in the synthesis of specific cytokines such as IL-6, and variability in the production of vascular regulatory products such as prostaglandins are testimony to the complexity of the endothelium. Several other papers in this volume will stress the internal and structural variability among endothelial cells obtained from different sites, and from different developmental stages.

The original studies reported in this paper have been supported by grants EY 3243 from the National Institutes of Health and a gift from Nova Pharmaceuticals. JP has been supported by a grant from the Deutsche Forschungsgesellschaft.