ROLE OF TANYCYTES IN THE NON-CLASSICAL FEEDBACK REGULATION OF THE HYPOTHALAMIC-PITUITARY-THYROID AXIS

松弛细胞是排列在第三脑室的特殊神经胶质细胞。这些细胞表达通过运输、转化和失活激素向中枢神经系统供应活性甲状腺激素的遗传库。它们的塑形过程覆盖了下丘脑的毛细血管，似乎对正中隆起(ME)的荷尔蒙释放很重要。然而，人们对这种细胞的生理功能知之甚少，尤其是在调节下丘脑-垂体-甲状腺(HPT)轴方面。为了提高对松弛细胞生理功能的了解，我们建立了基于rAAV的新工具来研究体内松弛细胞。有了这些工具，我们能够表达基因，编码蛋白质，如[Ca~(2+)]i传感器GCamP6s、Cre重组酶或其他，特别是在柔韧细胞中。使用这些工具，我们已经能够确定TRH是通过受体TRH-R1在β-张力细胞中GαQ/11途径的特异性激活物。抑制这一途径可降低血浆基础TSH水平，提示伸展细胞在调节HPT轴中起重要作用。我们假设了一种新的非经典反馈机制，该机制是由促甲状腺激素释放激素和甲状腺激素诱导的强细胞终足的形态变化所介导的。在本项目中，我们将研究这一假说，并进一步描述伸展细胞在HPT轴中的作用。具体地说，我们将研究1)HPT激素对TRH诱导的张力细胞钙反应的影响，2)对张力细胞的形态和基因表达的影响，以及3)这些假定的变化对TRH释放和HPT功能的影响。因此，我们的目标是确定伸展细胞在非经典甲状腺激素调节中的作用。

Tanycytes are specialised glial cells lining the 3rd ventricle. These cells express the genetic repertoire to supply active thyroid hormones to the CNS by transporting, converting and inactivating hormones. Their plastic processes cover capillaries in the hypothalamus and seem to be important for the hormonal release in the median eminence (ME). However, only little is known about the physiological functions of this cell type, especially in the regulation of the hypothalamic-pituitary-thyroid (HPT) axis. To improve the knowledge of the physiological function of tanycytes we have established new rAAV-based tools to investigate tanycytes in vivo. With these tools we are able to express genes, encoding proteins like the [Ca2+]i sensor GCamP6s, the Cre-recombinase or others, specifically in tanycytes. Using these tools we have been able to identify TRH as a specific activator of the G alpha q/11-pathway in beta-tanycytes via the receptor TRH-R1. An inhibition of this pathway decreased basal TSH levels in plasma suggesting an important role of tanycytes in regulating the HPT axis. We postulate a new non-classical feedback mechanism that is mediated by morphological changes of tanycytic endfeet and is induced by TRH and thyroid hormones. In the present project we will investigate this hypothesis and further characterise the role of tanycytes in the HPT axis. Specifically, we will investigate 1) the effects of the HPT hormones on the TRH-induced calcium response in tanycytes, 2) on the morphology and gene expression in tanycytes as well as 3) the impact of these postulated changes on TRH release and HPT function. Thus, we aim to define the role of tanycytes in the non-classical thyroid hormone regulation.