SYNAPSINS--POTENTIAL MEDIATORS OF NEUROTROPHIN ACTION

突触蛋白是一类神经元特异性磷酸化蛋白， 在突触前调节神经递质释放和短期 可塑性最近在一些实验系统中的研究表明， 提供了令人信服的证据表明突触蛋白调节轴突伸长， 促进突触发生并稳定突触接触。更大 了解这些营养的分子机制， 突触蛋白的作用可能会导致新的治疗方法的鉴定， 治疗阿尔茨海默病的新靶点神经营养因子发挥作用 在神经元分化和存活中的重要作用，以及更多 最近被证明可以调节突触的功效和活性- 依赖可塑性因此，突触蛋白和神经营养因子有一个共同的 参与许多神经过程。的一大特色 神经营养因子介导的信号转导是有丝分裂原的激活， 活化蛋白激酶（MAP）。我们最近已经证明， 突触蛋白I是MAP激酶生理底物，且已经显示 这种磷酸化作用调节突触蛋白I 和肌动蛋白。由于突触蛋白-肌动蛋白相互作用被认为有助于 突触蛋白对突触形成和维持的影响，我们现在 建议进一步探索MAP激酶依赖性 突触蛋白的磷酸化介导突触蛋白的某些作用， 神经营养素将对哺乳动物和 非洲爪蟾突触蛋白同种型，以确定磷酸化位点， 表征酶学和生理调节 突触蛋白I和II的磷酸化和去磷酸化（特异性目的 1）。 结构和功能的磷酸化依赖性变化 将表征突触蛋白的性质（具体目标2）。使用 突触形成的神经元培养模型， 神经营养因子将在突触素 表达上调或下调，其中磷酸化 重新引入突触蛋白的位点突变的同种型（具体目标3）。 磷酸化状态特异性抗体将用于辨别磷酸化状态。 时间变化、区域分布和亚细胞定位 突触蛋白I和II的MAP激酶依赖性磷酸化 体内发育，以及在突触形成期间的细胞培养系统中， 也将用于检查MAP激酶的分布- 阿尔茨海默病尸检标本中磷酸化突触蛋白的研究 患者（具体目标4）。

Synapsins are a family of neuron-specific phosphoproteins that play a role in presynaptic regulation of neurotransmitter release and short-term plasticity. Recent studies in a number of experimental systems have provided compelling evidence that synapsins modulate axonal elongation, promote synaptogenesis and stabilize synaptic contacts. A greater understanding of the molecular mechanisms which account for these trophic effects of synapsins could lead to the identification of novel therapeutic targets for the treatment of Alzheimer's disease. Neurotrophins play essential roles in neuronal differentiation and survival, and more recently have been shown to regulate synaptic efficacy and activity- dependent plasticity. Thus, synapsins and neurotrophins share a common involvement in a number of neuronal processes. A major feature of neurotrophin-mediated signal transduction is the activation of mitogen- activated protein (MAP) kinase. We have recently demonstrated that synapsin I is a physiological substrate for MAP kinase, and have shown that this phosphorylation regulates the interactions between synapsin I and actin. As synapsin-actin interactions are believed to contribute to the effects of synapsins on synapse formation and maintenance, we now propose to further explore the possibility that MAP kinase-dependent phosphorylation of synapsins mediates some of the actions of the neurotrophins. Biochemical studies will be carried out with mammalian and Xenopus synapsin isoforms to identify the sites of phosphorylation and to characterize the enzymology and the physiological regulation of phosphorylation and dephosphorylation of synapsins I and II (Specific Aim 1). Phosphorylation dependent changes in structural and functional properties of the synapsins will be characterized (Specific Aim 2). Using neuronal culture models for synapse formation, the responsiveness to neurotrophins will be studied under conditions in which synapsin expression has been up or down-regulated, and in which phosphorylation site-mutated isoforms of synapsins are reintroduced (Specific Aim 3). Phosphorylation state-specific antibodies will be utilized to discern the temporal change, regional distribution, and subcellular localization of MAP kinase-dependent phosphorylation of synapsins I and II during normal development in vivo, and in cell culture systems during synapse formation, and will also be used to examine the distribution of MAP kinase- phosphorylated synapsins in post-mortem samples of Alzheimer's disease patients (Specific Aim 4).