Tanycytes and hypothalamic control of energy metabolism

Abstract

Studies from a number of areas of neuroendocrinology indicate that hypothalamic tanycytes play a key role in control of energy metabolism. First, profound annual changes in gene expression have been identified in these unusual glial cells in seasonal mammals, for example in genes relating to the transport and metabolism of thyroid hormone into the hypothalamus. The consequent changes in local thyroid hormone availability in the hypothalamus have been shown experimentally to regulate annual cycles in energy intake, storage and expenditure in seasonal species. This is reflected in overt seasonal changes in appetite, body fat composition and torpor. Second, studies in laboratory rodents demonstrate that hypothalamic tanycytes possess transport mechanisms and receptors that indicate they have a cellular function as nutrient sensors. Ex vivo studies with organotypic tanycyte cultures confirm that acute changes in nutrient availability alter calcium and purinergic signalling within and between tanycytes. Finally, tanycytes are components of a stem cell niche in the hypothalamus whose activity can be regulated by the nutritional environment. Experimental depletion of cell division in the hypothalamus alters the homeostatic response to nutrient excess in mice raised in high fat diets. These convergent lines of evidence suggest that tanycytes are nutrient and metabolite sensors that impact upon plasticity and neuronal function in the surrounding hypothalamus, and consequently have an important role in energy intake and expenditure.

A unifying hypothesis for control of body weight and reproduction in seasonally breeding mammals

“…30,31 Tanycytes extend into hypothalamic nuclei closely associated with homeostatic appetite regulation and act as gatekeepers for peripheral signals, such as leptin, to regulate metabolic control. 30,31 Tanycytes extend into hypothalamic nuclei closely associated with homeostatic appetite regulation and act as gatekeepers for peripheral signals, such as leptin, to regulate metabolic control.…”

“…Recently, the tanycytes have emerged as an integral part of the hypothalamic networks that control body weight, appetite regulation and energy balance. 30,31 Tanycytes extend into hypothalamic nuclei closely associated with homeostatic appetite regulation and act as gatekeepers for peripheral signals, such as leptin, to regulate metabolic control. 30,31 Tanycytes exhibit high levels of structural plasticity and, importantly, it is photoperiod that strongly affects the structural organisation of tanycytes.…”

“…30,31 Tanycytes extend into hypothalamic nuclei closely associated with homeostatic appetite regulation and act as gatekeepers for peripheral signals, such as leptin, to regulate metabolic control. 30,31 Tanycytes exhibit high levels of structural plasticity and, importantly, it is photoperiod that strongly affects the structural organisation of tanycytes. Under a long photoperiod, tanycytes are densely distributed around the third ventricle of the hypothalamus, forming long radial processes, visualised by immunolabelling for vimentin, which project into the hypothalamic areas controlling body weight regulation.…”

“…22,38,43,103 Although seasonal variation in hypothalamic thyroid hormone Recent years has brought a renewed focus on the role and function of tanycytes as the corridor of communication between the hypothalamus and PT of the pituitary gland. 30,31 Many pathways have been found to be photoperiodically regulated in tanycytes 22 and their role in photoperiodic control cannot be ignored. Most importantly, retinoic acid and Wnt/β-catenin signalling have been found in Siberian hamster and F344 rats with the most prominent changes similar to thyroid hormone signalling.…”

Astrocytes in neuroendocrine systems: An overview

“…Although our understanding of the importance of tanycytes in neuroendocrine function is evolving, in the interest of focus, they will not feature in this review and other recent reviews in this area are available elsewhere. 1,2 Although the pituitary gland contains glial cells with morphological similarities to astrocytes, namely pituicytes, 3 these will not feature in this review.…”