Phenotypic diversity in cultured cerebral microvascular endothelial cells

Diversity exists in both the structure and function of the endothelial cells (EC) that comprise the microvasculature of different organs. Studies of EC have been aided by our ability to first isolate and subsequently establish cultures from microvascularized tissue. After the isolation of microvessel endothelial cells (MEC) derived from rat cerebrum, we observed morphologic differences in colonies of cells that grew in primary cultures. The morphologies ranged from a cobblestone phenotype considered typical of EC in culture to elongated and stellate cell appearances. Serially passaged cell lines were established based on two parameters: initially by growth and, seconds, on differences in primary colony morphology using selective weeding techniques. Each culture was examined for the presence of EC-characteristic markers which include Factor-VIII-related antigen, angiotensin-I-converting enzyme activity, collagen type IV synthesis, and PGI2 production. Variable expression of each of these characteristics among the established EC lines was observed. Growth curves established for each of the EC cultures demonstrated differences in both population doubling rates and cell densities at confluence. The endocytic capacity of each EC line was also evaluated. Our ability to isolate and establish a number of morphologically distinct EC cultures indicates that diversity exists within the EC that comprise the cerebral microvasculature. Diversity in the established cell lines suggests either the EC that line the brain microvasculature exist as a mosaic or that morphologically distinct cultures may originate from different microanatomical origins (arteriolar, true capillary, or venular) or may have resulted from cells at different points in their in vitro life spans at the time of isolation.