Tanycyte radial morphology and proliferation are influenced by fibroblast growth factor receptor 1 and high-fat diet.

ABSTRACT

Fibroblast growth factor receptor 1 (FGFR1) is a widely expressed, membrane-bound receptor that transduces extracellular signals from FGF ligands and cadherins, resulting in intracellular signals influencing cellular growth, proliferation, calcium, and transcription. FGF21 and FGF2 stimulate the proliferation of tanycytes, specialized radial astrocytes along the ventricle of the hypothalamus, and influence metabolism. Tanycytes are in a privileged position between the cerebrospinal fluid, the blood supply in the median eminence, and neurons within nuclei in the hypothalamus. The effect of FGFR1 signaling upon tanycyte morphology and metabolism was examined in adult mice with conditional deletion of the Fgfr1 gene using the Fgfr1flox/flox; Nestin-Cre+ line. Loss of Fgfr1 resulted in shorter ß tanycytes along the medial eminence. Control Fgfr1flox/flox littermates and Fgfr1flox/flox, Nestin-Cre+ (Fgfr1 cKO) knockout mice were placed on a 1-month long high-fat diet (HFD) or a normal-fat diet (NFD), to investigate differences in body homeostasis and tanycyte morphology under an obesity inducing diet. We found that FGFR1 is a vital contributor to tanycyte morphology and quantity and that it promotes stem cell maintenance in the hypothalamus and hippocampal dentate gyrus. The Fgfr1 cKO mice developed impaired tolerance to a glucose challenge test on a HFD without gaining more weight than control mice. The combination of HFD and loss of Fgfr1 gene resulted in altered ß and α tanycyte morphology, and reduced stem cell numbers along the third ventricle of the hypothalamus and hippocampus.