RGS14 Regulation of CaM/CaMKII Signaling in Hippocampal CA2 Synaptic Plasticity

描述(由申请人提供)： 在人类中，海马区的突触可塑性与编码情景记忆和认知高度相关，这种神经元加强/削弱突触输入的能力在CA3-CA1突触中已经得到了很好的研究。来自CA3 Schaffer侧支的输入在CA2和CA1锥体神经元的近端树突上形成突触，但CA2神经元抵制长时程增强(LTP)，LTP是突触连接的加强，遵循在CA1神经元中产生LTP的方案。调控CA2区神经元可塑性的分子机制以及CA2区在整个海马区功能和行为中的作用尚不清楚。G蛋白信号转导调节因子14(RGS14)是一种信号蛋白，在CA2锥体神经元的树突和棘中高度丰富，是LTP的天然抑制因子。缺乏RGS14 mRNA/蛋白(RGS14-KO)的小鼠显示出对CA2区LTP的强健和新生能力，而对CA1区的可塑性没有影响。与野生型小鼠相比，RGS14-KO小鼠还增强了对海马体依赖的学习和记忆。综上所述，这些数据表明，RGS14是CA2突触可塑性和学习记忆的天然抑制因子。然而，RGS14限制CA2区LTP的机制(S)尚不清楚。RGS14是一个复杂的支架/效应器，它整合了G蛋白和H-RAS/MAPK信号通路来抑制ERK信号。MEK抑制剂的应用一直阻止在RGS14-KO小鼠CA2区观察到的新生LTP。以前的工作表明，健壮的钙处理和挤出是CA2区缺乏可塑性的基础，但直到最近，还没有明确的RGS14和钙信号之间与可塑性相关的联系。新的数据显示，RGS14以钙依赖的方式与关键的细胞内钙调素(CaM)相互作用。典型的活性依赖性可塑性诱导需要突触后钙离子内流。钙离子内流后，钙离子结合CaM(钙/钙调素)启动LTP诱导所需的几个下游信号级联反应。具体来说，CaM激活CaM依赖的蛋白激酶II(CaMKII)和PKA。新的证据表明，RGS14也被CaMKII磷酸化。基于这些发现，我的工作假设是，CaM与RGS14的结合和CaMKII的磷酸化改变了其已知的功能，RGS14与已知的钙激活途径相互作用，抑制了CA2区的LTP。我将从以下几个具体目标来检验这一假设。在目标1中，我将测试CaM结合和CaMKII磷酸化如何调节RGS14的活性。在目标2中，我将确定RGS14与CaM和CaMKII的相互作用如何影响CA2区LTP的诱导。

DESCRIPTION (provided by applicant): Synaptic plasticity within the hippocampus is highly correlated with encoding episodic memories and cognition in humans, and this ability of neurons to strengthen/weaken synaptic inputs has been well studied at CA3-CA1 synapses. Inputs from CA3 Schaffer collaterals form synapses on proximal dendrites of both CA2 and CA1 pyramidal neurons, but CA2 neurons resist long-term potentiation (LTP), the strengthening of synaptic connections, following protocols that produce LTP in CA1 neurons. The molecular mechanisms regulating plasticity in CA2 neurons and the role of area CA2 in overall hippocampal function and behavior are not known. Regulator of G Protein Signaling 14 (RGS14) is a signaling protein that is highly enriched in the dendrites and spines of CA2 pyramidal neurons that is a natural suppressor of LTP. Mice lacking RGS14 mRNA/protein (RGS14-KO) display a robust and nascent capacity for LTP in CA2, with no effect on plasticity in area CA1. RGS14-KO mice also have enhanced hippocampal-dependent learning and memory relative to wild- type littermates. Taken together, these data show that RGS14 is a natural suppressor of CA2 synaptic plasticity and learning and memory. However, the mechanism(s) by which RGS14 limits LTP in area CA2 are not understood. RGS14 is a complex scaffold/effector that integrates G protein and H-Ras/MAPK signaling pathways to suppress ERK signaling. Consistently, application of a MEK inhibitor blocks the nascent LTP observed in area CA2 of RGS14-KO mice. Previous work had suggested robust calcium handling and extrusion underlie the lack of plasticity observed in area CA2, but until very recently, no defined connection between RGS14 and calcium signaling relevant to plasticity. New data shows that RGS14 interacts with the key intracellular calcium sensor calmodulin (CaM) in a calcium-dependent manner. Postsynaptic calcium entry is required for typical activity- dependent plasticity induction. Following calcium influx, calcium binds CaM (Ca2+/CaM) to initiate several downstream signaling cascades required for LTP induction. Specifically, CaM activates CaM-dependent protein kinase II (CaMKII) and PKA. New evidences shows RGS14 is phosphorylated by CaMKII as well. Based on these findings, my working hypothesis is that CaM binding to and CaMKII phosphorylation of RGS14 alter its known functions, and RGS14 interacts with known calcium-activated pathways to suppress LTP in area CA2. I will test this hypothesis in the following specific aims. In aim 1, I will test how CaM binding and CaMKII phosphorylation modulate RGS14 activiy. In aim 2, I will determine how RGS14 interactions with CaM and CaMKII impact LTP induction in area CA2.