SYNAPSINS--POTENTIAL MEDIATORS OF NEUROTROPHIN ACTION

突触素是一类神经元特异的磷酸蛋白家族，在 在突触前调节神经递质释放和短时程增强 可塑性。最近对一些实验系统的研究已经 提供了突触蛋白调节轴突延长的令人信服的证据， 促进突触发生，稳定突触接触。一个更伟大的 对这些营养不良的分子机制的理解 突触素的作用可能导致新的治疗方法的确定 阿尔茨海默病的治疗目标。神经营养因子发挥作用 在神经元分化和生存中的重要作用，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，突触素和神经营养素有一个共同的 参与多个神经元突起。的一大特点 神经营养因子介导的信号转导是丝裂原激活- 活化蛋白(MAP)激酶。我们最近证明了 突触素I是MAP激酶的生理底物，已有研究表明 这种磷酸化调节突触素I之间的相互作用 和肌动蛋白。因为突触素-肌动蛋白的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 建议进一步探讨MAP依赖于激酶的可能性 突触蛋白的磷酸化介导了 神经营养因子。生物化学研究将在哺乳动物和 非洲爪哇突触素亚型识别磷酸化位点和 酶学特性及其生理调节 突触素I和II的磷酸化和去磷酸化(特定目的 1)。依赖磷酸化的结构和功能变化 将描述突触蛋白的特性(具体目标2)。vbl.使用 突触形成的神经元培养模型，对 神经营养因子将在突触素 表达上调或下调，其中磷酸化 位点突变的突触蛋白亚型被重新引入(特定目标3)。 磷酸化状态特异性抗体将被用来识别 的时间变化、区域分布和亚细胞定位 正常情况下突触蛋白I和突触蛋白II的MAP激酶依赖的磷酸化 在体内发育，以及在突触形成期间的细胞培养系统中， 也将被用于研究MAP激酶的分布- 阿尔茨海默病尸检标本中的磷酸化突触素 患者(特定目标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).