Tanycyte Gene Expression Dynamics in the Regulation of Energy Homeostasis

Abstract

Animal survival relies on a constant balance between energy supply and energy expenditure, which is controlled by several neuroendocrine functions that integrate metabolic information and adapt the response of the organism to physiological demands. Polarized ependymoglial cells lining the floor of the third ventricle and sending a single process within metabolic hypothalamic parenchyma, tanycytes are henceforth described as key components of the hypothalamic neural network controlling energy balance. Their strategic position and peculiar properties convey them diverse physiological functions ranging from blood/brain traffic controllers, metabolic modulators, and neural stem/progenitor cells. At the molecular level, these functions rely on an accurate regulation of gene expression. Indeed, tanycytes are characterized by their own molecular signature which is mostly associated to their diverse physiological functions, and the detection of variations in nutrient/hormone levels leads to an adequate modulation of genetic profile in order to ensure energy homeostasis. The aim of this review is to summarize recent knowledge on the nutritional control of tanycyte gene expression.

Triiodothyronine secretion in early thyroid failure: The adaptive response of central feedforward control

“…TSH dependency of T3 production has been supported by in vitro and in vivo studies but was only recently incorporated into a model of hypothalamic-pituitary-thyroid regulation. 33 Because intracellular T3 concentrations are not readily measurable in humans, intracellular T3-regulating processes were not directly observable. Mathematically connecting chains of physiological events may generate unforeseen hypotheses, which then can be clinically assessed.…”

“…31,32 Central regulation involving TRH and tanycytes is also incompletely understood and could only be partly implemented. 33 Because intracellular T3 concentrations are not readily measurable in humans, intracellular T3-regulating processes were not directly observable. 34 While our approach integrates central and local control, thereby denying an autonomy exclusively assigned to local control elements, it does not diminish the importance of their modulatory role in various tissues.…”

Targeting Tanycytes: Balance between Efficiency and Specificity

“…Indeed, the complete characterization of the different tanycyte subgroups is needed. While this classification currently defines 4 subgroups with specific markers for each of them, recent advances clearly showed that > 4 subgroups may be defined (see review [4]). In addition, according to their location along the ventricle wall, tanycytes likely interact with different neural cell types and different neuronal populations: this variable "connectivity" certainly has an impact on their transcriptomic profiles resulting in different subgroups with different functions.…”

“…Since their characterization by Horstmann [1], tanycytes are now considered as key cells in the regulation of numerous physiological functions, ranging from reproduction to energy balance [2][3][4]. Elongated unipolar ependymoglial cells lining the bottom and the lateral wall of the third ventricle, they send a long radial process to connect blood-brain barrier capillaries in the mediobasal hy-pothalamus and the fenestrated capillaries of the hypothalamo-hypophysial portal system in the median eminence [5][6][7].…”

“…Along the third ventricle, tanycytes are born around E19 in rat brain, but some of them continue to be generated and to mature during the first and the second postnatal week [26]. Interestingly, tanycytes maintain the expression of numerous radial glial cell markers such as Nestin, Glast, or Rax [2,4,24]. Most importantly, they also maintain their capacity not only to proliferate in the postnatal brain to renew part of the tanycyte population but also to generate other neural cells including glial cells and neurons that will be involved in the same regulatory systems as tanycytes [20][21][22][23].…”