Developmental and cell type-specific expression of thyroid hormone transporters in the mouse brain and in primary brain cells

• Published in: Glia Vol. 59; no. 3; pp. 463 - 471
• Main Authors: Braun, Doreen, Kinne, Anita, Bräuer, Anja U., Sapin, Remy, Klein, Marc O., Köhrle, Josef, Wirth, Eva K., Schweizer, Ulrich
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.03.2011
• Subjects: Amino Acid Transport System y+ - biosynthesis; Amino Acid Transport System y+ - metabolism; Amino acids; Animals; Animals, Newborn; astrocyte; Astrocytes; Astrocytes - cytology; Astrocytes - metabolism; blood-brain-barrier; Brain; Brain - cytology; Brain - growth & development; Brain - metabolism; Cell culture; Cell Line; Cells, Cultured; Coculture Techniques; development; Endothelial cells; Fusion Regulatory Protein 1, Light Chains - biosynthesis; Fusion Regulatory Protein 1, Light Chains - metabolism; Gene Expression Regulation, Developmental - physiology; HEK293 Cells; Humans; Immunocytochemistry; Membrane Transport Proteins - deficiency; Membrane Transport Proteins - genetics; Mental retardation; Mice; Mice, Inbred C57BL; Mice, Knockout; Microglia; Microvasculature; mRNA; Myelination; neuron; Neurons; Neurons - cytology; Neurons - metabolism; Protein Transport - physiology; Thyroid hormones; Thyroxine; Thyroxine - metabolism; Triiodothyronine - metabolism; Western blotting
• ISSN: 0894-1491; 1098-1136; 1098-1136
• DOI: 10.1002/glia.21116

Cellular thyroid hormone uptake and efflux are mediated by transmembrane transport proteins. One of these, monocarboxylate transporter 8 (MCT8) is mutated in Allan‐Herndon‐Dudley syndrome, a severe mental retardation associated with abnormal thyroid hormone constellations. Since mice deficient in Mct8 exhibit a milder neurological phenotype than patients, we hypothesized that alternative thyroid hormone transporters may compensate in murine brain cells for the lack of Mct8. Using qPCR, Western Blot, and immunocytochemistry, we investigated the expression of three different thyroid hormone transporters, i.e., Mct8 and L‐type amino acid transporters Lat1 and Lat2, in mouse brain. All three thyroid hormone transporters are expressed from corticogenesis and peak around birth. Primary cultures of neurons and astrocytes express Mct8, Lat1, and Lat2. Microglia specifically expresses Mct10 and Slco4a1 in addition to high levels of Lat2 mRNA and protein. As in vivo, a brain microvascular endothelial cell line expressed Mct8 and Lat1. 158N, an oligodendroglial cell line expressed Mct8 protein, consistent with delayed myelination in MCT8‐deficient patients. Functional T3‐ and T4‐transport assays into primary astrocytes showed KM values of 4.2 and 3.7 μM for T3 and T4. Pharmacological inhibition of L‐type amino acid transporters by BCH and genetic inactivation of Lat2 reduced astrocytic T3 uptake to the same extent. BSP, a broad spectrum inhibitor, including Mct8, reduced T3 uptake further suggesting the cooperative activity of several T3 transporters in astrocytes. © 2010 Wiley‐Liss, Inc.