Developmental and cell type-specific expression of thyroid hormone transporters in the mouse brain and in primary brain cells.
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 T(3)- and T(4)-transport assays into primary astrocytes showed K(M) values of 4.2 and 3.7 μM for T(3) and T(4). Pharmacological inhibition of L-type amino acid transporters by BCH and genetic inactivation of Lat2 reduced astrocytic T(3) uptake to the same extent. BSP, a broad spectrum inhibitor, including Mct8, reduced T(3) uptake further suggesting the cooperative activity of several T(3) transporters in astrocytes.
Institut für Experimentelle Endokrinologie, Charité-Universitätsmedizin, Berlin, Germany.
Doreen
D
Braun
Anita
A
Kinne
Anja U
AU
Bräuer
Remy
R
Sapin
Marc O
MO
Klein
Josef
J
Köhrle
Eva K
EK
Wirth
Ulrich
U
Schweizer
D027182:Amino Acid Transport System y+ / Q000096:biosynthesis / Q000378:metabolism; D027241:Amino Acid Transport System y+L; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism; D001921:Brain / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D018920:Coculture Techniques; D027301:Fusion Regulatory Protein 1, Light Chains / Q000096:biosynthesis / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D057809:HEK293 Cells; D006801:Humans; D026901:Membrane Transport Proteins / Q000172:deficiency / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D027501:Monocarboxylic Acid Transporters; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D027981:Symporters; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*
D027182:Amino Acid Transport System y+; D027241:Amino Acid Transport System y+L; D027301:Fusion Regulatory Protein 1, Light Chains; D026901:Membrane Transport Proteins; D027501:Monocarboxylic Acid Transporters; C518286:SLC7A8 protein, mouse; C484257:Slc16a2 protein, mouse; C518287:Slc7a7 protein, mouse; D027981:Symporters; D014284:Triiodothyronine; D013974:Thyroxine