Pericytes: pluripotent cells of the blood brain barrier.

Pericytes were described nearly 140 years ago by the French scientist Charles-Marie Benjamin Rouget and were referred to as the Rouget cell. The Rouget cell was renamed primarily due to its anatomical location in the endothelium. Pericytes are important cellular constituents of the capillaries and post capillary venules and are located abluminal to the endothelial cells and luminal to parenchymal cells. They deposit elements of the basal lamina and are totally surrounded by this vascular component. Despite many years of investigation since their discovery, the role of this intriguing cell still remains a mystery, in part, due to the difficulty of studying this cell in vivo, due to the difficulty of isolating pure primary pericytes, and due to the lack of a pericyte specific marker. Pericytes are thought to be local regulatory cells and important to the maintenance of homeostasis and hemostasis. In the brain, pericytes are in active communication with the cells of the neurovascular unit and make fine-tuned regulatory adjustments in response to stress stimuli. These adaptations at the vascular level form the basis for functional and phenotypic changes that include differentiation along mesenchymal and neurological lineages, and lend credence to the supposition that pericytes are multipotential stems cells in the adult brain and in other tissues. This review will consider evidence that pericytes are stem cells derived from historical work and from more recent literature, and will attempt to dispel a number of misconceptions about the pericyte that has lead to confusion in the literature. We will also speculate on the importance of pericyte stem cell activity in survival and DNA repair and how dysregulation of pericyte function may lead to disease.