Novel neuroanatomical pathways for thyroid hormone action in the human anterior pituitary.
OBJECTIVE
An increasing number of proteins appear to be involved in thyroid hormone feedback action at the level of the anterior pituitary, but the cell types expressing these proteins are largely unknown. The aim of the present study was to identify cell types in the human anterior pituitary that express type II and type III deiodinase (D2 and D3), the recently described thyroid hormone transporter (MCT8) and thyroid hormone receptor (TR) isoforms by means of double-labeling immunocytochemistry.


RESULTS
We found TR isoforms to be expressed most prominently in gonadotropes and - although to a lesser extent - in thyrotropes, corticotropes, lactotropes and somatotropes. D3 staining showed a distribution pattern that was remarkably similar. By contrast, D2 immunoreactivity was observed exclusively in folliculostellate (FS) cells showing coexpression with human leukocyte antigen (HLA), a marker of major histocompatibility complex (MHC)-class II. MCT8 immunostaining was present in FS cells without HLA coexpression.


CONCLUSIONS
From these results, we propose a novel neuroanatomical model for thyroid hormone feedback on the human pituitary, with a central role for FS cells in thyroid hormone activation, which thus play an important role in the suppression of TSH secretion by circulating thyroxine (T(4)).
Alkemade
Anneke
A
Department of Endocrinology and Metabolism, Academic Medical Center, University of Amsterdam, The Netherlands.
Friesema
Edith C
EC
Kuiper
George G
GG
Wiersinga
Wilmar M
WM
Swaab
Dick F
DF
Visser
Theo J
TJ
Fliers
Eric
E
D000368:Aged; D000911:Antibodies, Monoclonal; D005246:Feedback; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D007150:Immunohistochemistry; D007453:Iodide Peroxidase / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D027501:Monocarboxylic Acid Transporters / Q000378:metabolism; D010903:Pituitary Gland, Anterior / Q000502:physiology*; D011988:Receptors, Thyroid Hormone / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D027981:Symporters; D013963:Thyroid Hormones / Q000502:physiology*; D013974:Thyroxine / Q000378:metabolism
D000911:Antibodies, Monoclonal; D007527:Isoenzymes; D027501:Monocarboxylic Acid Transporters; D011988:Receptors, Thyroid Hormone; C090735:SLC16A2 protein, human; D027981:Symporters; D013963:Thyroid Hormones; D007453:Iodide Peroxidase; D013974:Thyroxine