The critical component to establish in vitro BBB model: Pericyte

The blood-brain barrier (BBB), a highly regulated membranous barrier of brain capillaries, consists of an intricate network of tight junctions (TJs) that segregate the central nervous system (CNS) from systemic blood circulation and maintain a delicate homeostasis of the CNS environment. While endothelial cells (ECs) of brain capillaries are clearly the principal cellular element of BBB, the formation and regulation of intact BBB structure appear to require the interactions of endothelial cells with other cellular components. Astrocytes, one of the major non-neural cells in the brain, associate closely and interact with capillary endothelial cells during the angiogenesis and BBB development. Current in vitro cellular models for the study of BBB functions often incorporate astrocytes with endothelial cells. However, another foremost cell type, CNS pericyte, which intimately embraces brain capillary endothelium, attracts relatively little attention for its role in developing the in vitro BBB system. This review will analyze the critical functions of pericytes in angiogenesis in various systems and discuss the relevance of these functions in mediating the development, maintenance, and regulation of BBB. The author will also discuss the functional role of actin in both ECs and pericytes, and further elaborate the molecular mechanisms of BBB permeability regulation that involves the transduction pathway-mediated actin remodeling process. Finally, the rationale of incorporating pericytes for establishing a better in vitro BBB model will be emphasized.