Microvessel endothelial cell transdifferentiation: phenotypic characterization

Human dermal microvessel endothelial cells (MEC) have two basic functions: maintenance of tissue homeostasis and facilitation of inflammatory responses. The former requires that the endothelium expresses traits of an epithelium, while inflammatory reactions are associated with intimal disruption. Acute inflammation transiently alters endothelium, whereas chronic inflammation may result in vessel reorganization and MEC mesenchymalization. Foreskin MEC in vitro undergo a similar epithelial-mesenchymal modulation. In the presence of cAMP, cultivated dermal MEC exhibit the structural and functional characteristics of an epithelium. MEC grown in cAMP-deficient medium initially have a "transitional" configuration and are subsequently transformed into mesenchymal cells. If cAMP is replaced by histamine, MEC maintain a stable intermediate transitional configuration. Transitional MEC refed cAMP-supplemented medium revert to an epithelial phenotype, whereas parallel cultures fed cAMP-deficient medium are transformed into mesenchymal cells. Phenotypic modulation can be induced without cell division and thus provides a unique example of direct transdifferentiation. Our data furthermore suggest that this transdifferentiation results in the acquisition of properties usually attributed to cells of the reticuloendothelial system.