RGS14 regulation of synaptic plasticity in hippocampal neurons

摘要：RGS14是一种多功能信号蛋白，整合了G蛋白、MAPK和 钙/钙调素信号通路。RGS14在大脑中发现，在那里它高度富含树突和脊椎 海马区CA2区锥体神经元的表达。我们发现RGS14作为一种天然的 CA2神经元突触可塑性的抑制因子(长时程增强)。我们的研究表明，异位 将RGS14传递到RGS14不表达的CA1神经元阻断了那里的LTP，提示RGS14 参与共同的信号通路，这些信号通路对两类神经元的突触可塑性至关重要。 与CA1神经元不同，人们对表达RGS14的CA2神经元知之甚少。这个神秘的大脑区域 与社会行为和包括精神分裂症在内的人类神经心理疾病有关， 自闭症/双相情感障碍和癫痫。值得注意的是，我们发现缺乏RGS14(RGS14-KO)的小鼠 与野生型相比，在空间学习和物体识别记忆方面表现出出人意料的增强 产仔，在非海马区依赖行为上没有差异。此外，RGS14-KO小鼠 表达了令人惊讶的强健的新生LTP，并在谷氨酸能突触增强了神经元的兴奋性 CA2，对相邻CA1神经元的可塑性无影响。总而言之，这些发现突显了 理解RGS14调节CA2区LTP和突触可塑性的分子机制(S) 海马神经元。LTP和相关的脊髓可塑性取决于突触后钙的升高，这是由于 谷氨酸激活NMDA/Glun通道和电压门控钙通道Cav1.2，导致 激活CaM和CaMKII信号通路。这些途径反过来又增加了肌动球蛋白驱动的 AMPA/GluA受体囊泡在突触处的运输和插入导致脊柱尺寸增加(即 结构可塑性)。值得注意的是，我们发现RGS14抑制了活性诱导的脊柱钙的升高，抑制了 Cav1.2，结合Ca/CaM，并被CaMKII磷酸化。此外，我们发现RGS14抑制脊椎 与LTP相关的结构可塑性，并作为富含的高分子复合体的一部分存在于大脑中 含有脊椎肌球蛋白(MyoV、MyoVI、MyoII)和肌动蛋白结合蛋白。基于这些观察，我们的 工作假说是，RGS14通过抑制Cav1.2通道抑制脊柱钙离子，并通过 激活肌球蛋白系统(以一种受调控的方式)限制表面AMPA受体。我们进一步建议 RGS14的这些作用受其结合伙伴CaM、CaMKII、H-RAS/Rap2-GTP和Gai1的调控。为了测试 针对这些想法，我们提出了以下实验方案。目的1.确定Ca/CaM结合和CaMKII 磷酸化调节已建立的RGS14功能。目标2：确定RGS14如何调节Cav1.2 并抑制海马神经元突触后钙信号。目标3：确定RGS14如何 影响AMPA受体循环并参与肌动球蛋白系统抑制脊髓可塑性 海马神经元。

SUMMARY: RGS14 is a multifunctional signaling protein that integrates G protein, MAPkinase, and calcium/CaM signaling pathways. RGS14 is found in brain where it is highly enriched in dendrites and spines of pyramidal neurons in hippocampal region CA2. We discovered that RGS14 is critically important as a natural suppressor of synaptic plasticity (long-term potentiation, LTP) in CA2 neurons. Our studies show that ectopic delivery of RGS14 to CA1 neurons where RGS14 is not expressed blocks LTP there, suggesting that RGS14 engages common signaling pathways that are critical for synaptic plasticity in both populations of neurons. Unlike CA1 neurons, little is known about CA2 neurons where RGS14 is expressed. This enigmatic brain region has been implicated in social behavior and human neuro-psychological diseases including schizophrenia, the autism/bipolar disorders, and epilepsy. Remarkably, we have found that mice lacking RGS14 (RGS14-KO) exhibit an unexpected enhancement of spatial learning and object recognition memory compared with wild type littermates, with no differences in non-hippocampal-dependent behaviors. Furthermore, RGS14-KO mice expressed a surprisingly robust nascent LTP with enhanced neuronal excitability at glutamatergic synapses in CA2, with no impact on plasticity in adjacent CA1 neurons. Together, these findings highlight the importance of understanding the molecular mechanism(s) whereby RGS14 regulates LTP and synaptic plasticity within CA2 hippocampal neurons. LTP and associated spine plasticity depends on a rise in postsynaptic calcium due to glutamate activation of NMDA/GluN channels and the voltage-gated calcium channel Cav1.2, which result in activation of CaM and CaMKII signaling pathways. These pathways, in turn, increase actomyosin-driven trafficking and insertion of AMPA/GluA receptor vesicles at the synapse that result in increased spine size (i.e. structural plasticity). Of note, we find that RGS14 suppresses the activity-induced rise in spine calcium, inhibits Cav1.2, binds Ca++/CaM, and is phosphorylated by CaMKII. Furthermore, we find that RGS14 suppresses spine structural plasticity associated with LTP, and exists in brain as part of a high-molecular weight complex enriched with spine myosins (MyoV, MyoVI, MyoII) and actin binding proteins. Based on these observations, our working hypothesis is that RGS14 suppresses spine calcium by inhibiting Cav1.2 channels, and blocks LTP by engaging the actomyosin system (in a regulated way) to limit surface AMPA receptors. We further propose that these actions of RGS14 are regulated by its binding partners CaM, CaMKII, H-Ras/Rap2-GTP and Gai1. To test these ideas, we propose the following experiments. AIM 1. Determine how Ca++/CaM binding and CaMKII phosphorylation modulate established RGS14 functions. AIM 2: Determine how RGS14 regulates Cav1.2 and suppresses postsynaptic calcium signaling in hippocampal neurons. AIM 3: Determine how RGS14 impacts AMPA receptor recycling and engages the actomyosin system to suppress spine plasticity in hippocampal neurons.