Thyroid hormone signaling

我们正在研究PI3K信号在甲状腺激素对大脑发育的生理影响中的作用。我们的研究小组最近在哺乳动物甲状腺激素受体TR β的第二个锌指中发现了两个酪氨酸，这两个酪氨酸对刺激PI3K至关重要。当任何一种酪氨酸发生突变时，甲状腺激素对PI3K的刺激被阻断，但不会阻止受体与DNA中典型甲状腺激素反应元件结合并刺激转录。为了测试在大脑发育过程中，直接基因调控和PI3K刺激在甲状腺激素作用中的相对重要性，我们制作了一种突变敲入菌株，用苯丙氨酸取代其中一种酪氨酸，即TRbeta1中的Y147F （TRbeta2中的Y161F）。我们在电压钳下对出生13-17天的小鼠海马CA1神经元切片进行全细胞记录，并测量突触对Schaffer侧枝刺激的反应。突变体的突触可塑性被破坏。然而，TRb在神经元中的表达和TSHb在垂体中的表达在突变体中都是正常的，而TSHb通过DNA直接结合调节垂体中TSHb的表达。实验正在进行，以确定突触可塑性的确切缺陷。总之，甲状腺

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. Experiments are underway to determine the exact defect in synaptic plasticity. In summary, thyroid hormone signaling through PI3K appears to be essential for postnatal plasticity of both excitatory and inhibitory synapses on mouse hippocampal pyramidal neurons. 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. 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.