马球样激酶2对突触稳态的生理及病理性调控作用北大核心CSCD

Plk2(polo-likekinases2),即血清诱导激酶(serum-induciblekinase,Snk)是调节细胞有丝分裂的丝/苏氨酸特异性马球样激酶(polo-likekinases,Plks)家族成员之一,因其具有调节机体稳定,维持内稳态等独特作用而备受关注。Plk2通过泛素蛋白酶体途径参与维持神经突触稳定和调节突触重塑。在阿尔兹海默症及癫痫中发现存在Plk2表达及其调节通路异常,通过对Plk2活性及其上游信号Ca2+及下游底物蛋白SPAR的有效干预将对神经系统疾病的防治提供新思路。     

受体酪氨酸激酶依赖的信号转导在突触可塑性中的研究

突触可塑性对于脑发育过程中的神经环路重构以及学习记忆等脑的高级功能是非常重要的。许多受体酪氨酸激酶家族成员,包括TrkB、ErbB和Eph在神经连接的建立和重构过程中起到核心作用。比如,突触后EphB依赖的信号会导致树突棘的产生和神经递质受体的聚集,而ephrinA引起的EphA4激活可以导致树突棘的回缩。但是,目前对EphA4依赖的树突棘重组和对神经递质受体的调节背后的机制还知之甚少。本文将集中探讨EphA4及其下游的信号通路在神经肌肉接头和中枢神经的突触中,对神经递质受体的调节功能。     

细胞间黏附分子5在树突棘发育和突触可塑性中的研究进展

诸多神经精神性疾病的发生均伴有树突棘发育异常。免疫球蛋白超家族成员细胞间黏附分子5(intercellular adhesion molecule 5,ICAM5)是一个通过抑制树突棘成熟,将其维持在丝状形态的跨膜蛋白,它只表达于端脑兴奋性神经元,可能与树突棘发育、突触可塑性乃至学习记忆密切相关。现综述了ICAM5的发现和特征、分子结构、基因结构、在树突棘发育过程中的作用,以及与脆性X综合征等疾病的关系,试图为阐明发育阶段脑神经元异常树突棘形成的机制提供线索。     

关于mGluR在脆性X综合征发病机制中的研究新进展

脆性X综合征为最常见的遗传性智力低下性疾病之一,是由于FMR1基因异常导致其编码的脆性X智力低下蛋白减少或缺失所致.研究发现脆性X综合征尸解病人和FMR1基因敲除小鼠(KO鼠)神经元树突棘发育不成熟,模型小鼠海马区代谢性谷氨酸受体所触发的长时程抑制(LTD)延长,不成熟的树突棘导致突触功能障碍被认为是脑功能异常的基础.最近的研究表明,应用代谢性谷氨酸受体拮抗剂能改善由FMRP缺失所导致的突触和行为缺陷,表明mGluR功能过度激活可能参与了脆性X综合征的发病过程,但具体机制不明.FMRP是一种mRNA结合蛋白,可作为翻译抑制因子负性调节突触后膜mRNA的翻译和表达.因此推测FMRP缺乏和减少可能导致mGluR激发的mRNA翻译增多,参与神经系统发育的蛋白过度表达,而影响树突棘的发育,但具体机制仍不清楚.本文对mGluR和脆性X综合征的研究历史和最新进展进行了讨论.     

神经元的突触可塑性与学习和记忆

大量研究表明,神经元的突触可塑性包括功能可塑性和结构可塑性,与学习和记忆密切相关.最近,在经过训练的动物海马区,记录到了学习诱导的长时程增强(long term potentiation,LTP),如果用激酶抑制剂阻断晚期LTP,就会使大鼠丧失训练形成的记忆.这些结果指出,LTP可能是形成记忆的分子基础.因此,进一步研究哺乳动物脑内突触可塑性的分子机制,对揭示学习和记忆的神经基础有重要意义.此外,在精神迟滞性疾病和神经退行性疾病患者脑内记录到异常的LTP,并发现神经元的树突棘数量减少,形态上产生畸变或萎缩,同时发现,产生突变的基因大多编码调节突触可塑性的信号通路蛋白,故突触可塑性研究也将促进精神和神经疾病的预防和治疗.综述了突触可塑性研究的最新进展,并展望了其发展前景.     

外周输入依赖的嗅球颗粒细胞的突触结构可塑性

活动依赖的突触结构可塑性是学习和记忆的基础.哺乳动物,尤其是啮齿类动物,具有高度发达的嗅觉系统和惊人的气味学习和记忆能力.本研究以CNGA2敲除而导致外周输入缺失的小鼠为模型,研究嗅球内活动依赖的突触结构可塑性.利用特异性的突触前和突触后标记物,发现外周输入缺失减少了突触标记蛋白突触素(synaptophysin)和抑制性突触标记蛋白桥蛋白(gephyrin)在嗅球外网状层和颗粒细胞层中的表达;兴奋性突触标记蛋白囊泡谷氨酸转运蛋白1(VGluT1)的表达水平只在外网状层中有显著下降,而在颗粒细胞层中没有明显变化.进一步通过活体质粒电转标记嗅球颗粒细胞后发现,CNGA2敲除小鼠颗粒细胞上位于外网状层中的远端树突棘密度显著减小,而位于颗粒细胞层中的近端树突棘密度没有明显变化.这些结果表明颗粒细胞上的树-树突触具有对外周活动依赖的结构可塑性,而轴-树突触则无.     

NMDA受体参与皮层内突触结构和功能的调节

在中枢神经系统内神经细胞的树突棘是突触信息传递的重要部位,树突棘的体积和密度影响神经环路的功能。2007年美国加利福尼亚大学的SilaK．Ultanir等人在皮层NRl亚基（是NMDA受体的必要组分）基因敲除的小鼠上发现NMDA受体对树突棘的发育有重要影响。急性分离出生后三周内小鼠的脑片,用电压钳全细胞记录的方法,发现在皮层2／3层的锥体细胞中,AMPA受体介导的微小兴奋性突触后电流（mEP-SC）的幅度和频率均明显增大。     

与帕金森病相关的LRRK2-PKA-Cofilin信号通路

<正>"二型富亮氨酸重复激酶"(leucine-rich repeat kinase 2,LRRK2)由帕金森基因家族PARK8基因编码,富含于脑纹状体神经元。最近,NIH研究人员发现了LRRK2参与帕金森症的分子机制。敲除LRRK2分子会导致"纹状体投射神经元"(striatal projection neurons,SPNs)蛋白激酶A(PKA)活性降低、细胞骨架蛋白actin的调节子"Cofilin"过磷酸化、"树突棘"密度降低、突触发育迟滞,呈现帕金森症病理学特征。Parisiadou等人发现:敲除Lrrk2基因会导致SPNs树突棘数量剧减、丝状幼稚树突棘显著多于蘑菇状成熟树突棘、PSD95     

竞争机制介导树突棘的协同修剪与成熟

树突棘是中枢神经系统中绝大多数兴奋性突触的突触后位点。在出生后早期,脑内树突棘大量形成;当个体进入青少年期,脑内树突棘总数逐渐减少,这一过程被称为树突棘修剪,并被认为是神经环路精确化的重要过程。在孤独症谱系障碍、精神分裂症等发育性神经系统疾病中被报道存在树突棘修剪的异常。虽然树突棘修剪的现象已被广泛描述,然而介导该过程的分子机制尚待进一步研究。该研究组近期工作发现,在小鼠触须所对应的感觉皮层,树突棘的修剪与成熟是协同发生的,并且受感觉经验的双向调控。进一步研究发现,神经电活动可以引起相邻树突棘对cadherin/catenin细胞黏附复合物的竞争,导致该复合物的重新分布,并使这两个树突棘的命运产生分化:得到cadherin/catenin复合物的树突棘变得更加成熟而相邻失去这些分子的树突棘变小或被修剪。这一cadherin/catenin复合物依赖的竞争机制为树突棘的协同成熟与修剪提供了特异性,对于理解介导神经环路精确化的机制至关重要。     

谷氨酸受体调控树突棘形态可塑性的研究进展

树突棘是神经元之间产生直接联系的部位,其形态可塑性是记忆的结构基础。谷氨酸信息传递是中枢神经信息传递的主要方式,能产生突触传递效率的可塑性,由此引起树突棘形态的可塑性变化。本文从谷氨酸受体途径的角度对树突棘形态可塑性的调控机制做一综述。谷氨酸受体主要通过其下游信号分子调节棘内肌动蛋白动力学蛋白,参与树突棘的形态发生和稳定。该作用在局部受到不同的蛋白、信号分子、激素、mi RNAs的调节,从而参与生理及病理过程。最后,提出展望,研究脑区特异的局部微环境变化对记忆相关疾病病因及治疗探讨有参考价值。     

Critical role of CDK5 and Polo-like kinase 2 in homeostatic synaptic plasticity during elevated activity

Homeostatic plasticity keeps neuronal spiking output within an optimal range in the face of chronically altered levels of network activity. Little is known about the underlying molecular mechanisms, particularly in response to elevated activity. We report that, in hippocampal neurons experiencing heightened activity, the activity-inducible protein kinase Polo-like kinase 2 (Plk2, also known as SNK) was required for synaptic scaling-a principal mechanism underlying homeostatic plasticity. Synaptic scaling also required CDK5, which acted as a "priming" kinase for the phospho-dependent binding of Plk2 to its substrate SPAR, a postsynaptic RapGAP and scaffolding molecule that is degraded following phosphorylation by Plk2. RNAi knockdown of SPAR weakened synapses, and overexpression of a SPAR mutant resistant to Plk2-dependent degradation prevented synaptic scaling. Thus, priming phosphorylation of the Plk2 binding site in SPAR by CDK5, followed by Plk2 recruitment and SPAR phosphorylation-degradation, constitutes a molecular pathway for neuronal homeostatic plasticity during chronically elevated activity.     

Regulation of postsynaptic RapGAP SPAR by Polo-like kinase 2 and the SCFbeta-TRCP ubiquitin ligase in hippocampal neurons

The ubiquitin-proteasome pathway (UPP) regulates synaptic function, but little is known about specific UPP targets and mechanisms in mammalian synapses. We report here that the SCF(beta-TRCP) complex, a multisubunit E3 ubiquitin ligase, targets the postsynaptic spine-associated Rap GTPase activating protein (SPAR) for degradation in neurons. SPAR degradation by SCF(beta-TRCP) depended on the activity-inducible protein kinase Polo-like kinase 2 (Plk2). In the presence of Plk2, SPAR physically associated with the SCF(beta-TRCP) complex through a canonical phosphodegron. In hippocampal neurons, disruption of the SCF(beta-TRCP) complex by overexpression of dominant interfering beta-TRCP or Cul1 constructs prevented Plk2-dependent degradation of SPAR. Our results identify a specific E3 ubiquitin ligase that mediates degradation of a key postsynaptic regulator of synaptic morphology and function.     

Requirement for Plk2 in orchestrated ras and rap signaling, homeostatic structural plasticity, and memory

Ras and Rap small GTPases are important for synaptic plasticity and memory. However, their roles in homeostatic plasticity are unknown. Here, we report that polo-like kinase 2 (Plk2), a homeostatic suppressor of overexcitation, governs the activity of Ras and Rap via coordination of their regulatory proteins. Plk2 directs elimination of Ras activator RasGRF1 and Rap inhibitor SPAR via phosphorylation-dependent ubiquitin-proteasome degradation. Conversely, Plk2 phosphorylation stimulates Ras inhibitor SynGAP and Rap activator PDZGEF1. These Ras/Rap regulators perform complementary functions to downregulate dendritic spines and AMPA receptors following elevated activity, and their collective regulation by Plk2 profoundly stimulates Rap and suppresses Ras. Furthermore, perturbation of Plk2 disrupts Ras and Rap signaling, prevents homeostatic shrinkage and loss of dendritic spines, and impairs proper memory formation. Our study demonstrates a critical role of Plk2 in the synchronized tuning of Ras and Rap and underscores the functional importance of this regulation in homeostatic synaptic plasticity.     

Cyclin-Dependent Kinase 5 Is Involved in the Phosphorylation of Gephyrin and Clustering of GABAA Receptors at Inhibitory Synapses of Hippocampal Neurons

CDK5 has been implicated in neural functions including growth, neuronal migration, synaptic transmission and plasticity of excitatory chemical synapses. Here we report robust effects of CDK5 on phosphorylation of the postsynaptic scaffold protein gephyrin and clustering of inhibitory GABA_A receptors in hippocampal neurons. shRNA-mediated knockdown of CDK5 and pharmacological inhibition of cyclin-dependent kinases reduced phosphorylated gephyrin clusters and postsynaptic γ2-containing GABA_A receptors. Phosphorylation of S270 is antagonized by PP1/PP2a phosphatase and site-directed mutagenesis and in vitro phosphorylation experiments indicate that S270 is a putative CDK5 phosphorylation site of gephyrin. Our data suggest that CDK5 plays an essential role for the stability of gephyrin-dependent GABA_A receptor clusters in hippocampal neurons.     

Chk1 modulates the interaction between myosin phosphatase targeting protein 1 (MYPT1) and protein phosphatase 1cβ (PP1cβ)

Polo-like kinase 1 (Plk1) is an instrumental kinase that modulates many aspects of the cell cycle. Previous investigations have indicated that Plk1 is a target of the DNA damage response, and Plk1 inhibition is dependent on ATM/ATR and Chk1. But the exact mechanism remains elusive. In a proteomic screen to identify Chk1-interacting proteins, we found that myosin phosphatase targeting protein 1 (MYPT1) was present in the immunocomplex. MYPT1 is phosphorylated by CDK1, thus recruiting protein phosphatase 1β (PP1cβ) to dephosphorylate and inactivate Plk1. Here we identified that Chk1 directly interacts with MYPT1 and preferentially phosphorylates MYPT1 at Ser20, which is essential for MYPT1-PP1cβ interaction and subsequent Plk1 dephosphorylation. Phosphorylation of Ser20 is abolished during mitotic damage when Chk1 is inhibited. The degradation of MYPT1 is also regulated by Chk1 phosphorylation. Our results thus unveil the underlying machinery that attenuates Plk1 activity during mitotic damage through Chk1-induced phosphorylation of MYPT1.     

受体、突触和记忆

大脑中神经元突触间的信号传递是由许多神经递质受体介导的。在过去,Richard L．Huganir实验室一直致力于神经递质受体功能调节的分子机制。而最近,该实验室又聚焦到大脑中一种最主要的兴奋性受体的研究——谷氨酸受体。谷氨酸受体主要可以分为两大类：AMPA受体和NMDA受体。AMPA受体主要介导了快速的兴奋性突触传递;而NMDA受体则在神经可塑性和发育中起到重要作用。实验发现,AMPA受体和NMDA受体都可以被一系列的蛋白激酶磷酸化,而磷酸化的水平则直接影响了这些受体的功能特性,包括通道电导和受体膜定位等。AMPA受体磷酸化的水平同时还在学习和记忆的细胞模型中发生改变,如长时程增强（LTP）和长时程抑制（LTD）。此外,AMPA受体中GluR1亚单位的磷酸化对于各种形式的可塑性以及空间记忆的维持有重要的作用。实验室主要研究突触部位谷氨酸受体在亚细胞水平的定位和聚集的分子机制。最近,一系列可以直接或间接与AMPA和NMDA受体相互作用的蛋白质得以发现,其中包括一个新发现的蛋白家族GRIPs（glutamate receptor interacting proteins）。GRIPs可以直接和AMPA受体的GluR2／3亚单位的C端结合。GRIPs包含7个PDZ结构域,可以介导蛋白与蛋白直接的相互连接,从而把各个AMPA受体交互连接在一起并与其他蛋白相连。另外,GluR2亚单位的c端还可以和兴奋性突触中的蛋白激酶C结合蛋白（PICK1）的PDZ结构域相互作用。另外,GluR2亚单位的C端也可以与一种参与膜融合的蛋白NSF相互作用。这些与AMPA受体相互作用的蛋白质对于受体在膜上的运输以及定位有至关重要的作用。同时,受体与PICK1和GRIP的结合对于小脑运动学习中的LTD有重要作用。总体上说,该实验室发现了一系列可以调节神经递质受体功能的分子机制,这些工作提示受体功能的调节可能是?     

Suppression of inhibitory synaptic potentiation by presynaptic activity through postsynaptic GABA(B) receptors in a Purkinje neuron

At inhibitory synapses on a cerebellar Purkinje neuron, the depolarization caused by heterosynaptic climbing fiber activation induces long-lasting potentiation accompanied by an increase in GABA(A) receptor responsiveness. Here we show that activation of a presynaptic inhibitory interneuron during the conditioning postsynaptic depolarization suppresses the potentiation. The suppression is due to postsynaptic GABA(B) receptor activation by GABA released from presynaptic terminals. The results suggest that GABA(B) receptor activation decreases the activity of cAMP-dependent protein kinase through the G(i)/G(o) proteins. The presynaptic activity-dependent suppression of synaptic plasticity is a novel regulatory mechanism of synaptic efficacy at individual synapses and may contribute to the learning and computational ability of the cerebellar cortex.     

Local sharing as a predominant determinant of synaptic matrix molecular dynamics

Recent studies suggest that central nervous system synapses can persist for weeks, months, perhaps lifetimes, yet little is known as to how synapses maintain their structural and functional characteristics for so long. As a step toward a better understanding of synaptic maintenance we examined the loss, redistribution, reincorporation, and replenishment dynamics of Synapsin I and ProSAP2/Shank3, prominent presynaptic and postsynaptic matrix molecules, respectively. Fluorescence recovery after photobleaching and photoactivation experiments revealed that both molecules are continuously lost from, redistributed among, and reincorporated into synaptic structures at time-scales of minutes to hours. Exchange rates were not affected by inhibiting protein synthesis or proteasome-mediated protein degradation, were accelerated by stimulation, and greatly exceeded rates of replenishment from somatic sources. These findings indicate that the dynamics of key synaptic matrix molecules may be dominated by local protein exchange and redistribution, whereas protein synthesis and degradation serve to maintain and regulate the sizes of local, shared pools of these proteins.     

c-Jun N-terminal kinase has a key role in Alzheimer disease synaptic dysfunction in vivo

Altered synaptic function is considered one of the first features of Alzheimer disease (AD). Currently, no treatment is available to prevent the dysfunction of excitatory synapses in AD. Identification of the key modulators of synaptopathy is of particular significance in the treatment of AD. We here characterized the pathways leading to synaptopathy in TgCRND8 mice and showed that c-Jun N-terminal kinase (JNK) is activated at the spine prior to the onset of cognitive impairment. The specific inhibition of JNK, with its specific inhibiting peptide D-JNKI1, prevented synaptic dysfunction in TgCRND8 mice. D-JNKI1 avoided both the loss of postsynaptic proteins and glutamate receptors from the postsynaptic density and the reduction in size of excitatory synapses, reverting their dysfunction. This set of data reveals that JNK is a key signaling pathway in AD synaptic injury and that its specific inhibition offers an innovative therapeutic strategy to prevent spine degeneration in AD.     

Calcium-induced modulation of synaptic transmission

Calcium (Ca²⁺) is a second messenger regulating a wide variety of intracellular processes. Using GABA-and glycinergic synapses as examples, this review analyzes two functions of this unique ion: postsynaptic Ca²⁺-dependent modulation of receptor-operated channels and Ca²⁺-induced retrograde regulation of neurotransmitter release from the presynaptic terminals. Phosphorylation, rapid Ca²⁺-induced modulation via intermediate Ca²⁺-binding proteins, and changes in the number of functional receptors represent the main pathways of short-and long-term plasticity of postsynaptic receptor-operated channel machinery. Retrograde signaling is an example of synaptic modulation triggered by stimulation of postsynaptic cells and mediated via regulation of presynaptic neurotransmitter release. This mechanism provides postsynaptic neurons with efficient tools to control the presynaptic afferents in an activity-dependent mode. Elevation of intracellular Ca²⁺ in a postsynaptic neuron triggers the synthesis of endocannabinoids (derivatives of arachidonic acid). Their retrograde diffusion through the synaptic cleft and consequent activation of presynaptic G-protein coupled to CB1 receptors inhibits the release of neurotransmitter. These mechanisms of double modulation, which include control over the function of postsynaptic ion channels and retrograde suppression of the release machinery, play an important role in Ca²⁺-dependent control of the main excitatory and inhibitory synaptic pathways in the mammalian nervous system.