Aortic endothelial cell heterogeneity in vitro: Lack of association between morphological phenotype and collagen biosynthesis

Previous reports dealing with the characterisation of endothelial cells derived from the same tissue have produced apparently conflicting results in fundamental cellular attributes such as matrix biosynthesis and the ability to form sprouts in vitro. One potential explanation for this discrepancy is that endothelial cells actually comprise a heterogeneous population of cells displaying a significant degree of intra-site variation in phenotype. In order to address this question, we have characterised both cloned and uncloned lines of bovine aortic endothelial cells with respect to (a) their ability to adopt both the cobblestone and sprouting cell phenotypes and (b) matrix biosynthesis by cells displaying these two phenotypes. Data are presented indicating that all of the 18 cloned and 20 uncloned cell lines examined were capable of undergoing a reversible transition between the cobblestone and sprouting cell phenotypes ni response to culture conditions. In all cases, sprouting occurred spontaneously in the presence of either serum or platelet-poor plasma and did not require the addition of exogenous factors to the medium. Twelve lines of cells were examined with respect to protein biosynthesis; these lines produced different types of collagens in differing proportions. The pattern of collagen synthesis displayed by every cell line was stable and did not vary with either passage number or batch of serum. The presence of a 3-D gel of native type I collagen increased specifically the synthesis of type IV collagen by one cell line. However, in four other cell lines, even though total synthesis was increased, the type of proteins secreted by these cells was not altered. Transition from a cobblestone to a sprouting cell phenotype by all five cell lines examined was not accompanied by any changes in the specific types of collagens synthesised by these cells. A decrease in thrombospondin and an increase in type IV collagen secretion was observed in one out of five cell lines. These data are discussed in terms of the possible significance of endothelial cell heterogeneity to the angiogenic response.