Institut für Biochemie und Molekularbiologie, Medizinische Fakultät, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany.
The Department of Physiology and Cell Biology, Faculty of Health Sciences, The Regenerative Medicine and Stem Cell (RMSC) Research Center and the Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Thyroid. 2022 Jul;32(7):860-870. doi: 10.1089/thy.2021.0643. Epub 2022 Apr 26.
Monocarboxylate transporter 8 (MCT8) deficiency is a rare genetic disease leading to a severe developmental delay due to a lack of thyroid hormones (THs) during critical stages of human brain development. Some MCT8-deficient patients are not as severely affected as others. Previously, we hypothesized that these patients' mutations do not affect the functionality but destabilize the MCT8 protein, leading to a diminished number of functional MCT8 molecules at the cell surface. We have already demonstrated that the chemical chaperone sodium phenylbutyrate (NaPB) rescues the function of these mutants by stabilizing their protein expression in an overexpressing cell system. Here, we expanded our previous work and used iPSC (induced pluripotent stem cell)-derived brain microvascular endothelial-like cells (iBMECs) as a physiologically relevant cell model of human origin to test for NaPB responsiveness. The effects on mutant MCT8 expression and function were tested by Western blotting and radioactive uptake assays. We found that NaPB rescues decreased mutant MCT8 expression and restores transport function in iBMECs carrying patient's mutation MCT8-P321L. Further, we identified MCT10 as an alternative TH transporter in iBMECs that contributes to triiodothyronine uptake, the biological active TH. Our results indicate an upregulation of MCT10 after NaPB treatment. In addition, we detected an increase in thyroxine (T4) uptake after NaPB treatment that was not mediated by rescued MCT8 but an unidentified T4 transporter. We demonstrate that NaPB is suitable to stabilize a pathogenic missense mutation in a human-derived cell model. Further, it activates TH transport independent of MCT8. Both options fuel future studies to investigate repurposing the Food and Drug Administration-approved drug NaPB in selected cases of MCT8 deficiency.
单羧酸转运蛋白 8（MCT8）缺乏症是一种罕见的遗传性疾病，由于人类大脑发育关键阶段缺乏甲状腺激素（THs），导致严重的发育迟缓。一些 MCT8 缺乏症患者的病情没有其他患者那么严重。此前，我们假设这些患者的突变不会影响其功能，而是使 MCT8 蛋白不稳定，导致细胞表面功能性 MCT8 分子数量减少。我们已经证明，化学伴侣苯丁酸钠（NaPB）通过稳定过表达细胞系中这些突变体的蛋白表达来恢复其功能。在这里，我们扩展了之前的工作，使用 iPSC（诱导多能干细胞）衍生的脑微血管内皮样细胞（iBMECs）作为一种源自人类的生理相关细胞模型，来测试 NaPB 的反应性。通过 Western blot 和放射性摄取测定来测试突变体 MCT8 表达和功能的变化。我们发现 NaPB 可挽救突变型 MCT8 表达的减少，并恢复携带患者突变 MCT8-P321L 的 iBMECs 中的转运功能。此外，我们发现 MCT10 是 iBMECs 中另一种替代 TH 转运体，可促进三碘甲状腺原氨酸（T3）摄取，即具有生物活性的 TH。我们的结果表明，NaPB 处理后 MCT10 的表达上调。此外，我们在 NaPB 处理后检测到甲状腺素（T4）摄取增加，这不是由挽救的 MCT8 介导的，而是由未鉴定的 T4 转运体介导的。我们证明 NaPB 适合稳定人源细胞模型中的致病性错义突变。此外，它可以独立于 MCT8 激活 TH 转运。这两种选择都为未来的研究提供了依据，以研究在选定的 MCT8 缺乏症病例中重新利用已获美国食品和药物管理局批准的药物 NaPB。
