Molecular Neurophysiology and Biophysics Section, Program in Development Neuroscience, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, and.
National Institute of General Medical Sciences, National Institutes of Health, Bethesda, Maryland 20892.
J Neurosci. 2019 Sep 18;39(38):7453-7464. doi: 10.1523/JNEUROSCI.1443-17.2019. Epub 2019 Jul 26.
Fragile X syndrome (FXS) is an inherited intellectual impairment that results from the loss of fragile X mental retardation protein (FMRP), an mRNA binding protein that regulates mRNA translation at synapses. The absence of FMRP leads to neuronal and circuit-level hyperexcitability that is thought to arise from the aberrant expression and activity of voltage-gated ion channels, although the identification and characterization of these ion channels have been limited. Here, we show that FMRP binds the mRNA of the R-type voltage-gated calcium channel Cav2.3 in mouse brain synaptoneurosomes and represses Cav2.3 translation under basal conditions. Consequently, in hippocampal neurons from male and female FMRP KO mice, we find enhanced Cav2.3 protein expression by western blotting and abnormally large R currents in whole-cell voltage-clamp recordings. In agreement with previous studies showing that FMRP couples Group I metabotropic glutamate receptor (GpI mGluR) signaling to protein translation, we find that GpI mGluR stimulation results in increased Cav2.3 translation and R current in hippocampal neurons which is disrupted in FMRP KO mice. Thus, FMRP serves as a key translational regulator of Cav2.3 expression under basal conditions and in response to GpI mGluR stimulation. Loss of regulated Cav2.3 expression could underlie the neuronal hyperactivity and aberrant calcium spiking in FMRP KO mice and contribute to FXS, potentially serving as a novel target for future therapeutic strategies. Patients with fragile X syndrome (FXS) exhibit signs of neuronal and circuit hyperexcitability, including anxiety and hyperactive behavior, attention deficit disorder, and seizures. FXS is caused by the loss of fragile X mental retardation protein (FMRP), an mRNA binding protein, and the neuronal hyperexcitability observed in the absence of FMRP likely results from its ability to regulate the expression and activity of voltage-gated ion channels. Here we find that FMRP serves as a key translational regulator of the voltage-gated calcium channel Cav2.3 under basal conditions and following activity. Cav2.3 impacts cellular excitability and calcium signaling, and the alterations in channel translation and expression observed in the absence of FMRP could contribute to the neuronal hyperactivity that underlies FXS.
脆性 X 综合征（FXS）是一种遗传性智力障碍，由脆性 X 智力低下蛋白（FMRP）缺失引起，FMRP 是一种 mRNA 结合蛋白，可调节突触处的 mRNA 翻译。FMRP 的缺失导致神经元和电路水平的过度兴奋，据认为这是由于电压门控离子通道的异常表达和活性引起的，尽管这些离子通道的鉴定和特征描述受到限制。在这里，我们表明 FMRP 结合了小鼠脑突触体中 R 型电压门控钙通道 Cav2.3 的 mRNA，并在基础条件下抑制 Cav2.3 的翻译。因此，在雄性和雌性 FMRP KO 小鼠的海马神经元中，我们通过 Western blot 发现 Cav2.3 蛋白表达增加，全细胞膜片钳记录中的 R 电流异常增大。与先前表明 FMRP 将 I 组代谢型谷氨酸受体（GpI mGluR）信号与蛋白质翻译偶联的研究一致，我们发现 GpI mGluR 刺激导致海马神经元中 Cav2.3 翻译和 R 电流增加，而在 FMRP KO 小鼠中则受到破坏。因此，FMRP 作为基础条件下和 GpI mGluR 刺激下 Cav2.3 表达的关键翻译调节剂。受调控的 Cav2.3 表达缺失可能是 FMRP KO 小鼠神经元过度兴奋和异常钙峰的基础，并可能导致 FXS，这可能成为未来治疗策略的一个新靶点。脆性 X 综合征（FXS）患者表现出神经元和电路过度兴奋的迹象，包括焦虑和多动行为、注意力缺陷障碍和癫痫发作。FXS 是由脆性 X 智力低下蛋白（FMRP）缺失引起的，FMRP 是一种 mRNA 结合蛋白，而在没有 FMRP 的情况下观察到的神经元过度兴奋可能是由于其调节电压门控离子通道的表达和活性的能力。在这里，我们发现 FMRP 作为基础条件下和活动后电压门控钙通道 Cav2.3 的关键翻译调节剂。Cav2.3 影响细胞兴奋性和钙信号，在没有 FMRP 的情况下观察到的通道翻译和表达的改变可能导致 FXS 所基于的神经元过度兴奋。
