Glial cells in the brain control the thyroid axis

Tanycates (red) in the wall of the third brain ventricle project with long fibers into neighboring brain centers. Blue: cell nucleus. Green: fenestrated blood vessels.

The brain contains a remarkable variety of cell types. Only in the 1950s a special type of glial cells was discovered that has a strikingly elongated cell form suggesting the name tanycyte, according to the Greek work for elongated („tanus“). Tanycytes are located in the wall of the brain ventricles and send their long processes into neighboring brain centers that control vital body functions, such as blood pressure, body temperature, or the endocrine system. Besides location and cell form, little was known about these cells. However, recently evidence emerged that tanycytes are involved in the regulation of body weight and sexual hormones. Now a group headed by Dr. Müller-Fielitz and Prof. Schwaninger (Institute for Experimental and Clinical Pharmacology and Toxicology) at the University of Lübeck reports that tanycytes play an important role in the regulation of the thyroid axis.

The brain controls thyroid function by releasing TRH, a small hormone. However, TRH not only acts on the thyroid axis but also activates adjacent tanycytes according to the data of Müller-Fielitz, Schwaninger and colleagues. Being activated tanycytes inhibit the further release of TRH from the brain. An unexpected finding of the study was the way in which tanycytes modulate hormone release. According to the authors, tanycytes seem to block the outflow of TRH by shielding blood vessels and by degrading TRH. In summary, tanycytes function as a brake in the thyroid axis. At the moment it is still unclear whether tanycytes could also be responsible for clinical disorders of thyroid function. Beyond thyroid axis function, an important aspect lies in the toolbox generated by the study that allows studying tanycytes and that might help to elucidate the functions of this enigmatic cell type.

Publication:

Tanycytes control the hormonal output of the hypothalamic-pituitary-thyroid axis.

Müller-Fielitz H, Stahr M, Bernau M, Richter M, Abele S, Krajka V, Benzin A, Wenzel J, Kalies K, Mittag J, Heuer H, Offermanns S, Schwaninger M. Nat Commun. 2017 Sep 7;8(1):484. doi: 10.1038/s41467-017-00604-6.