Pericyte Biology: Development, Homeostasis, and Disease.

In the nineteenth century, a French researcher, Charles-Marie Benjamin Rouget, revealed a population of contractile cells associated with small blood vessels, which were initially named after him as the Rouget cells. In the twentieth century, a German scientist, Karl Wilhelm Zimmermann, called these cells "pericytes" due to their anatomical position located in a perivascular position. The word pericyte was derived from "peri" meaning "around" and "cyte" from the word "kytos" (cell), illustrating a cell encircling a blood vessel. Until now, pericytes are still identified partially based on their specific anatomical location and morphology. Pericytes are present in all vascularized tissues, surrounding blood vessel walls. They encircle endothelial cells and communicate with them along the length of the blood vessels by paracrine signaling and physical contacts. Previously, the accurate distinction of pericytes from other perivascular cells was difficult, as electron and light microscopy were the sole available techniques capable to image these cells, limiting the information acquired from those works. This resulted in the misleading assumption that pericytes are merely inert supporting cells, limited exclusively to the physiological function of vascular stability. In the last 10 years, the combination of fluorescent and confocal microscopy with genetic state-of-art techniques, such as fate lineage tracing, enabled remarkable progress in the discovery of multiple novel essential functions for pericytes in health and disease, before unexpected. Recently, the rapidly expanding understanding of the pathophysiological roles of pericytes drew the attention of several research groups. Now, we know, for instance, that pericytes may play immune functions: attract innate leukocytes to exit via sprouting blood vessels, regulate lymphocyte activation, and contribute to the clearance of toxic by-products, having direct phagocytic activity. Pericytes also may behave as stem cells, forming other cell populations, as well as regulate the behavior of other stem cells in their niches. Very little is known about the exact identity of pericyte ancestors within developing tissues, and there is evidence for multiple distinct developmental sources. Pericytes differ in their embryonic origins between tissues and also within the same organ. Importantly, pericytes from distinct tissues may differ in their distribution, morphology, expression of molecular markers, plasticity, and functions; and, even within the same organ, there are various pericyte subpopulations. This book describes the major contributions of pericytes to different organ biology in physiological and pathological conditions. Further insights into the biology of pericytes will have important implications for our understanding of organ development, homeostasis, and disease. This book's initial title was "Pericyte Biology: Development, Homeostasis, and Disease." However, due to the current great interest in this topic, we were able to assemble more chapters than would fit in one book, covering pericyte biology under distinct circumstances. Therefore, the book was subdivided into three volumes entitled: "Pericyte Biology: Novel Concepts," "Pericyte Biology in Different Organs," and "Pericyte Biology in Disease." Here, we present a selected collection of detailed chapters on what we know so far about pericytes. More than 30 chapters written by experts in the field summarize our present knowledge on pericyte biology. Here, we present a selected collection of detailed chapters on what we know so far about pericytes. More than 30 chapters written by experts in the field summarize our present knowledge on pericyte biology.