8631 Tanycytic TSHR Activation Regulates Blood-Hypothalamus Barrier Plasticity, Ingestive Behavior, Adipose Remodeling, and Body Weight

Abstract Disclosure: L. Cullen: None. H.S. Kannangara: None. R. Witztum: None. J. Burgess: None. S. Miyashita: None. A. Gumerova: None. F. Korkmaz: None. S.L. Sims: None. U. Cheliadinova: None. G. Pevnev: None. O. Moldavski: None. O. Barak: None. S. Rojekar: None. V. Laurencin: None. T. Frolinger: None. T. Yuen: None. K. Goosens: None. W. Zhou: None. V. Ryu: None. M. Zaidi: None. The notion that TSH acts solely on its primary endocrine target, the thyroid gland, has long been challenged (Abe et al., 2003; PMID: 14567913). More recently, however, we and others have used single transcript technology to document, for the first time, Tshr expression in over 173 brain regions and nuclei, particularly hypothalamic tanycytes (eLife, 2022, PMID: 36052994). The latter cells are known to convey metabolic information across the blood-hypothalamus barrier (BHB) and regulate energy homeostasis. To study whether tanycytic TSHRs have a role in the regulation of BHB permeability, ingestive behavior, adipose tissue remodeling and body weight, we first compared BHB vascular permeability of food-deprived and ad libitum-fed Tshr+/- mice and their wild type (WT) littermates. Transmission electron microscopy and immunostaining was used to study the expression of the constitutive tight junction protein claudin-1 and the glycoprotein MECA-32, which are expressed in tanycytes and endothelial cells, respectively. In loss-of-function studies, fasting of Tshr+/- mice and of WT mice significantly increased the organization of tanycytic honeycomb pattern of claudin-1 and MECA-32-associated fenestral diaphragms in the median eminence and arcuate nucleus, suggesting decreased BHB permeability. As a result, peanut butter consumption following fasting was decreased significantly compared to control mice. In gain-of-function studies, intracerebroventricular (ICV) infusions of a highly specific TSHR agonist, MS438, profoundly increased BHB permeability in fasted mice, as evidenced by decreased claudin-1 and MECA-32 immunostaining and significant increases in peanut butter consumption. This was associated with greater loss of fat mass and body weight following food deprivation, as well as increased influx of fatty acids across the BHB, increased NPY expression (as a measure of increased appetite), and increased secretion of ghrelin from the stomach fundus. We further performed c-Fos immunostaining in brain centers regulating ingestive behavior. ICV MS438 significantly decreased c-Fos immunoreactivity in the hypothalamic paraventricular nucleus, arcuate nucleus and the nucleus of the solitary tract. Early studies using CRSIPR/Cas9 to delete Tshrs in tanycytes via ICV injection resulted in reduced body weight following food deprivation. Finally, using PRV152 (injected into fat tissue) and PRV614 (injected into stomach fundus), we colocalized immunostaining in the hypothalamic paraventricular nucleus, and hindbrain raphe pallidus. Collectively, these data establish a new role for tanycytic TSHRs in regulating BHB plasticity, ingestive behavior, adipose tissue remodeling, and body weight through a novel fast-forward circuit involving the hypothalamus, stomach fundus and fat depots. Presentation: 6/3/2024