RGS14 regulation of synaptic plasticity in hippocampal neurons

RGS 14是一种多功能信号蛋白，它整合了G蛋白、MAP激酶和 钙/CaM信号通路。RGS 14存在于大脑中，在那里它在树突和棘中高度富集 海马CA 2区锥体神经元。我们发现RGS 14作为一种天然的 CA 2神经元中突触可塑性（长时程增强，LTP）的抑制剂。我们的研究表明异位妊娠 将RGS 14递送到不表达RGS 14的CA 1神经元阻断了那里的LTP，这表明RGS 14 参与共同的信号通路，这对两种神经元群体的突触可塑性至关重要。 与CA 1神经元不同，对表达RGS 14的CA 2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RGS 14的小鼠（RGS 14-KO） 显示出与野生型相比空间学习和物体识别记忆的意外增强 同窝仔，在非海马依赖性行为方面没有差异。此外，RGS 14-KO小鼠 表达了一个令人惊讶的强大的新生LTP与增强的神经元兴奋性在海马神经元突触， CA 2，对邻近CA 1神经元的可塑性没有影响。总之，这些发现强调了 了解RGS 14调节CA 2内LTP和突触可塑性的分子机制 海马神经元LTP和相关的脊柱可塑性取决于突触后钙的升高， 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CaMK II信号通路。这些通路反过来增加肌动蛋白驱动的 AMPA/GluA受体囊泡在突触处的运输和插入导致棘大小增加（即， 结构塑性）。值得注意的是，我们发现RGS 14抑制活动诱导的脊椎钙升高， Cav1.2结合Ca++/CaM，并被CaMKII磷酸化。此外，我们发现RGS 14抑制脊柱， 与LTP相关的结构可塑性，并作为高分子量复合物的一部分存在于大脑中， 与棘肌球蛋白（MyoV，MyoVI，MyoII）和肌动蛋白结合蛋白。根据这些观察，我们 工作假设是RGS 14通过抑制Cav1.2通道来抑制脊柱钙，并通过 接合肌动球蛋白系统（以调节的方式）以限制表面AMPA受体。我们进一步建议， RGS 14的这些作用受其结合配偶体CaM、CaMKII、H-Ras/Rap 2-GTP和Gai 1调节。测试 这些想法，我们提出以下实验。AIM 1.确定Ca++/CaM结合和CaMKII 磷酸化调节已建立的RGS 14功能。目的2：确定RGS 14如何调节Cav1.2 并抑制海马神经元中的突触后钙信号。目标3：确定RGS 14 影响AMPA受体再循环，并参与肌动球蛋白系统，以抑制脊柱可塑性， 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.