Rodrigues Tiago B, Ceballos Ainhoa, Grijota-Martínez Carmen, Nuñez Barbara, Refetoff Samuel, Cerdán Sebastian, Morte Beatriz, Bernal Juan
Instituto de Investigaciones Biomedicas, Consejo Superior de Investigaciones Cientificas and Universidad Autonoma de Madrid, Madrid, Spain ; CRUK, Cambridge Institute and Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom.
PLoS One. 2013 Oct 1;8(10):e74621. doi: 10.1371/journal.pone.0074621. eCollection 2013.
Mutations of the monocarboxylate transporter 8 (MCT8) cause a severe X-linked intellectual deficit and neurological impairment. MCT8 is a specific thyroid hormone (T4 and T3) transporter and the patients also present unusual abnormalities in the serum profile of thyroid hormone concentrations due to altered secretion and metabolism of T4 and T3. Given the role of thyroid hormones in brain development, it is thought that the neurological impairment is due to restricted transport of thyroid hormones to the target neurons. In this work we have investigated cerebral metabolism in mice with Mct8 deficiency. Adult male mice were infused for 30 minutes with (1-(13)C) glucose and brain extracts prepared and analyzed by (13)C nuclear magnetic resonance spectroscopy. Genetic inactivation of Mct8 resulted in increased oxidative metabolism as reflected by increased glutamate C4 enrichment, and of glutamatergic and GABAergic neurotransmissions as observed by the increases in glutamine C4 and GABA C2 enrichments, respectively. These changes were distinct to those produced by hypothyroidism or hyperthyroidism. Similar increments in glutamate C4 enrichment and GABAergic neurotransmission were observed in the combined inactivation of Mct8 and D2, indicating that the increased neurotransmission and metabolic activity were not due to increased production of cerebral T3 by the D2-encoded type 2 deiodinase. In conclusion, Mct8 deficiency has important metabolic consequences in the brain that could not be correlated with deficiency or excess of thyroid hormone supply to the brain during adulthood.
单羧酸转运体8（MCT8）的突变会导致严重的X连锁智力缺陷和神经功能障碍。MCT8是一种特异性甲状腺激素（T4和T3）转运体，由于T4和T3的分泌及代谢改变，患者的甲状腺激素浓度血清谱也呈现异常。鉴于甲状腺激素在脑发育中的作用，人们认为神经功能障碍是由于甲状腺激素向靶神经元的转运受限所致。在这项研究中，我们研究了Mct8缺陷小鼠的脑代谢。成年雄性小鼠经（1-（13）C）葡萄糖灌注30分钟，然后制备脑提取物并用（13）C核磁共振波谱进行分析。Mct8的基因失活导致氧化代谢增加，这表现为谷氨酸C4富集增加，以及谷氨酰胺C4和GABA C2富集增加所观察到的谷氨酸能和GABA能神经传递增加。这些变化与甲状腺功能减退或亢进所产生的变化不同。在Mct8和D2联合失活时观察到谷氨酸C4富集和GABA能神经传递有类似增加，这表明神经传递和代谢活性增加并非由于D2编码的2型脱碘酶使脑内T3生成增加所致。总之，Mct8缺陷在脑中具有重要的代谢后果，这与成年期脑内甲状腺激素供应不足或过量无关。
