Department of Integrative Physiology, Gunma University Graduate School of Medicine, Maebashi, Japan.
Education and Research Support Center, Gunma University Graduate School of Medicine, Maebashi, Japan.
Front Endocrinol (Lausanne). 2021 Feb 23;12:629100. doi: 10.3389/fendo.2021.629100. eCollection 2021.
Thyroid hormone (TH) plays important roles in the developing brain. TH deficiency in early life leads to severe developmental impairment in the hippocampus. However, the mechanisms of TH action in the developing hippocampus are still largely unknown. In this study, we generated 3,5,3'-tri-iodo-l-thyronine (T)-free neuronal supplement, based on the composition of neuronal supplement 21 (NS21), to examine the effect of TH in the developing hippocampus using primary cultured neurons. Effects of TH on neurons were compared between cultures in this T-free culture medium (-T group) and a medium in which T was added (+T group). Morphometric analysis and RT-qPCR were performed on 7, 10, and 14 days (DIV). On 10 DIV, a decreased dendrite arborization in -T group was observed. Such difference was not observed on 7 and 14 DIV. Brain-derived neurotrophic factor () mRNA levels also decreased significantly in -T group on 10 DIV. We then confirmed protein levels of phosphorylated neurotrophic tyrosine kinase type 2 (NTRK2, TRKB), which is a receptor for BDNF, on 10 DIV by immunocytochemistry and Western blot analysis. Phosphorylated NTRK2 levels significantly decreased in -T group compared to +T group on 10 DIV. Considering the role of BDNF on neurodevelopment, we examined its involvement by adding BDNF on 8 and 9 DIV. Addition of 10 ng/ml BDNF recovered the suppressed dendrite arborization induced by T deficiency on 10 DIV. We show that the lack of TH induces a developmental delay in primary hippocampal neurons, likely caused through a decreased expression. Thus, BDNF may play a role in TH-regulated dendritogenesis.
甲状腺激素（TH）在大脑发育中发挥着重要作用。生命早期的 TH 缺乏会导致海马区严重的发育损伤。然而，TH 在发育中的海马区的作用机制在很大程度上仍不清楚。在这项研究中，我们基于神经元补充剂 21（NS21）的组成，生成了 3,5,3'-三碘-L-甲状腺素（T）自由神经元补充剂，以使用原代培养神经元来研究 TH 在发育中的海马区的作用。在这种无 T 的培养基（-T 组）和添加 T 的培养基（+T 组）中比较了 TH 对神经元的影响。在 7、10 和 14 天（DIV）进行形态计量分析和 RT-qPCR。在 10 DIV 时，-T 组的树突分支减少。在 7 和 14 DIV 时未观察到这种差异。BDNF 的 mRNA 水平在 10 DIV 时也显著降低。然后，我们通过免疫细胞化学和 Western blot 分析在 10 DIV 时证实了 BDNF 的受体磷酸化神经营养酪氨酸激酶 2（NTRK2，TRKB）的蛋白水平。与 +T 组相比，-T 组的磷酸化 NTRK2 水平在 10 DIV 时显著降低。考虑到 BDNF 对神经发育的作用，我们通过在 8 和 9 DIV 添加 BDNF 来检查其参与情况。添加 10 ng/ml BDNF 可恢复 T 缺乏引起的 10 DIV 时树突分支减少。我们表明，缺乏 TH 会导致原代海马神经元发育延迟，这可能是由于表达减少所致。因此，BDNF 可能在 TH 调节的树突发生中发挥作用。
