Involvement of Tanycytes in the Neuroendocrine Control of Energy Homeostasis

Tanycytes are the hypothalamic glial cells that play a key role in energy homeostasis given their privileged position that allows them to regulate access to peripheral hormones, nutrients and other metabolic signals (i.e., leptin, insulin, grehlin, glucose and amioacids). Currently, there is great interest in elucidating how tanycytes participate in regulating food intake, energy expenditure and hypothalamic neurogenesis. Tanycytes are a specialized type of ependymal cell similar to the radial glia that covers the third ventricle, extending their long processes along the arcuate nucleus (AN) and the median eminence (ME). Interestingly, the AN and ME form an anatomically and functionally important complex (AN-ME) involved in energy homeostasis, fertility and neuroendocrine control of growth hormone and prolactin release. Tanycytes have been proposed to modulate the activity of neuroendocrine neurons, such as orexigenic or anorexigenic neurons, through a metabolic interaction that includes nutritional metabolites and/or growth factors. Although tanycytes respond to glucose and amino acids with increases of intracellular free Ca2+ concentration and can synthesize some neuropeptides, the physiological importance of these cells has not been elucidated. Several responses of tanycytes are coordinated by connexin43 based channels (gap junction channels and hemichannels) and their inhibition affects hypothalamic glucose sensitivity. Tanycytes can adapt their morphology depending on the physiological state of the individual to dynamically control the secretion of neuropeptides in the portal vessels of the ME. They can also undergo modifications to modulate the access of metabolic signals transmitted by the blood to AN neurons and, consequently, generate adaptive responses to acute nutritional challenges. In addition to sending circulating signals from the blood to the cerebro spinal fluid, could also act as "brain scavengers" using the reverse route to eliminate excess toxic proteins generated in patients with neurodegenerative disorders such as Alzheimer's disease, thus protecting the hypothalamus. With recent advances in transcriptomic technology, different neuronal and also tanycytic populations have been identified in the AN-ME complex; thus, the spectrum of functions mediated by these cells is still widening.

The aim of this Research Topic is to gather review articles and original research contributions on the role of tanycytes in neuroendocrine control of energy homeostasis. Potential topics include among others sensing of nutrients, food intake regulation, entrance of hormones to the hypothalamus, release of hormones or neuropeptides, structural modifications of the AN-ME complex, effect of thyroid hormones on tanycytes, identification of different tanycytic sub-populations, relationship with the melanocortin and endocannabinoid systems, gliosis, obesity and hypothalamic neurogenesis.