Tanycytes: bloodhounds of the metabolic brain

Constant monitoring and fine-tuning of internal body status to maintain energy homeostasis despite changing physiological needs and environmental conditions are essential brain functions. Hypothalamic tanycytes - specialized ependymoglial cells at the interface between the blood and the brain - play crucial roles in this regulation through mechanisms as diverse as sensing and responding to circulating nutrients and metabolic hormones, gating their access or shuttling them into the brain, modulating hypothalamic neuronal function and neuroendocrine communication with peripheral organs, and generating new regulatory neurons. We summarize these mechanisms and emphasize striking recent discoveries that extend beyond energy balance to reproduction and even cognitive aging. These highlight the need for a deeper understanding of the physiological and pathological roles of these unique cells.