Professor Toshio Ito: A clairvoyant in pericyte biology

Ito cells are liver-specific pericytes which were first described as Fett Speicherung Zellen, the fat-storing cells encircling outside sinusoidal endothelial cells, in 1951 by the late professor Toshio Ito. His pioneering approaches for morphological characterization of the cells stimulate investigators to further examine their functional roles in liver homeostasis: a body of evidence has been accumulated in recent years showing that the cells play a crucial role in storage and delivery of vitamin A, regulation of sinusoidal tone and local blood supply, and tissue repair and fibrosis. It is now widely accepted that microvascular pericytes including Ito cells serve as a key player that controls angiogenesis. Furthermore, recent studies support a concept that Ito cells constitutes a bridging apparatus mediating bidirectional metabolic interactions between sinusoids and hepatocytes, utilizing prostanoids and/or gaseous mediators such as nitric oxide and carbon monoxide as signaling molecules. This article reviews researches on this liver-specific pericyte and its leading roles in recent development of pericyte biology.