Thyroid hormone signaling

我们正在研究PI3K信号对甲状腺激素对大脑发育的生理影响的后果。我们的团队最近在哺乳动物甲状腺激素受体的第二个锌指上发现了两种酪氨酸，它们是刺激PI3K所必需的。当任何一种酪氨酸发生突变时，甲状腺激素对PI3K的刺激都会被阻断，而不会阻止受体与DNA中规范的甲状腺激素反应元件结合，并刺激转录。为了测试直接基因调控和PI3K刺激在大脑发育过程中甲状腺激素作用中的相对重要性，我们用苯丙氨酸取代了其中一种酪氨酸--TRbeta1中的Y147F(TRbeta2中的Y161F)，制造了一个突变的敲入小鼠品系。我们在电压钳下记录了出生后13-17天小鼠海马片CA1神经元的全细胞记录，并测量了突触对刺激Schaffer络脉的反应。突变体的突触可塑性被破坏。然而，突变体中TRB在神经元中的表达和TSHb在垂体中的表达都是正常的，这是由TRB通过直接DNA结合来调节的。总之，甲状腺激素通过PI3K传递的信号对于小鼠海马锥体神经元兴奋性和抑制性突触的生后可塑性的成熟是必不可少的。此外，我们还证明了通过PI3K传递的甲状腺激素信号对突触前介导的突触可塑性有急性影响，我们通过用野生型TRB感染突触前神经元来挽救突变体中的增强来检验这一假说。因此，环境毒物通过PI3K干扰甲状腺激素信号通路可能是环境影响人类认知发育的一个重要机制，我们发现双酚A阻断了这一新的信号通路。我们还发现，突变对神经元兴奋性的影响与RNAseq确定的活性依赖基因表达的变化相匹配。 与谢丽尔·莫伊博士在国防部合作。在北卡罗来纳大学教堂山的精神病学方面，我们正在测试这种突变对经典学习和记忆范例中小鼠行为的影响。

We are investigating the consequences of PI3K signaling for the physiological effects of thyroid hormone on brain development. Our group has recently identified two tyrosines in the second zinc finger of the mammalian thyroid hormone receptor, TR beta, that are essential for stimulation of PI3K. When either tyrosine is mutated, PI3K stimulation by thyroid hormone is blocked without preventing the receptor from binding to canonical thyroid hormone response elements in DNA and stimulating transcription. To test the relative importance of direct gene regulation and PI3K stimulation in thyroid hormone action during brain development, we made a mutant knock-in strain of mice with a phenylalanine replacing one of these tyrosines, Y147F in TRbeta1 (Y161F in TRbeta2). We made whole-cell recordings under voltage-clamp from CA1 neurons in hippocampal slices from postnatal day 13-17 mice, and measured synaptic responses to stimulation of Schaffer collaterals. Synaptic plasticity in the mutants was disrupted. However, TRb expression in the neurons and TSHb expression in pituitary, which is fregulated by TRb through direct DNA binding, are both normal in the mutant. In summary, thyroid hormone signaling through PI3K appears to be essential for maturation of postnatal plasticity of both excitatory and inhibitory synapses on mouse hippocampal pyramidal neurons. In addition we have shown that thyroid hormone signaling through PI3K has acute effects on synaptic plasticity that are mediated presynaptically, and we have tested that hypothesis by rescuing potentiation in the mutant by infecting the presynaptic neurons with wild-type TRb. Thus, disruption of thyroid hormone signaling through PI3K by environmental toxicants could be an important mechanism for environmental effects on human cognitive development, and we have discovered that bisphenol A blocks this novel signaling pathway. We have also found effects of the mutation on neuronal excitability that matches changes in activity-dependent gene expression as determined by RNAseq. In collaboration with Dr. Sheryl Moy in the Dept. Psychiatry at UNC Chapel Hill, we are testing the effects of this mutation on the mice's behavior in classical learning and memory paradigms.