Inserm 1185, Fac Med Paris Sud, Université Paris-Saclay, Le Kremlin-Bicêtre, France.
UMS-32, Institut Biomédical de Bicêtre, Le Kremlin-Bicêtre, France.
Neuroscience. 2019 Feb 10;399:12-27. doi: 10.1016/j.neuroscience.2018.12.012. Epub 2018 Dec 19.
The brain-derived neurotrophic factor (BDNF) is a key player in brain functions such as synaptic plasticity, stress, and behavior. Its gene structure in rodents contains 8 untranslated exons (I to VIII) whose expression is finely regulated and which spliced onto a common and unique translated exon IX. Altered Bdnf expression is associated with many pathologies such as depression, Alzheimer's disease and addiction. Through binding to glucocorticoid receptor (GR), glucocorticoids play a pivotal role for stress responses, mood and neuronal plasticity. We recently showed in neuronal primary culture and in the immortalized neuronal-like BZ cells that GR repressed Bdnf expression, notably the bdnf exon IV containing mRNA isoform (Bdnf4) via GR binding to a short 275-bp sequence of Bdnf promoter. Herein, we demonstrate by transient transfection experiments and mutagenesis in BZ cells that GR interacts with an early growth response protein 1 (EGR1) response element (EGR-RE) located in the transcription start site of Bdnf exon IV promoter. Using Chromatin Immunoprecipitation, we find that both GR and EGR1 bind to this promoter sequence in a glucocorticoid-dependent manner and demonstrate by co-immunoprecipitation that GR and EGR1 are interacting physically. Interestingly, EGR1 has been widely characterized as a regulator of brain plasticity. In conclusion, we deciphered a mechanism by which GR downregulates Bdnf expression, identifying a novel functional crosstalk between glucocorticoid pathways, immediate early growth response proteins and Bdnf. As all these factors are well-recognized germane for brain pathophysiology, these findings may have significant implications in neurosciences as well as in therapeutics.
脑源性神经营养因子（BDNF）是大脑功能的关键因子，如突触可塑性、应激和行为等。其在啮齿动物中的基因结构包含 8 个非翻译外显子（I 至 VIII），其表达受到精细调节，并拼接成一个共同的和独特的翻译外显子 IX。BDNF 表达的改变与许多疾病有关，如抑郁症、阿尔茨海默病和成瘾。通过与糖皮质激素受体（GR）结合，糖皮质激素在应激反应、情绪和神经元可塑性中发挥关键作用。我们最近在神经元原代培养物和永生化的神经元样 BZ 细胞中表明，GR 通过与 Bdnf 启动子的短 275bp 序列结合，抑制 Bdnf 表达，特别是包含 mRNA 异构体（Bdnf4）的 bdnf 外显子 IV。在此，我们通过瞬时转染实验和 BZ 细胞中的突变分析证明，GR 与 Bdnf 外显子 IV 启动子转录起始位点处的早期生长反应蛋白 1（EGR1）反应元件（EGR-RE）相互作用。使用染色质免疫沉淀，我们发现 GR 和 EGR1 都以糖皮质激素依赖的方式结合到这个启动子序列上，并通过共免疫沉淀证明 GR 和 EGR1 物理相互作用。有趣的是，EGR1 已被广泛表征为大脑可塑性的调节因子。总之，我们揭示了 GR 下调 Bdnf 表达的机制，确定了糖皮质激素途径、早期生长反应蛋白和 Bdnf 之间的一种新的功能串扰。由于所有这些因素都被认为与大脑病理生理学有关，这些发现可能对神经科学以及治疗学具有重要意义。
