Molecular mechanisms of synapse loss

描述（由申请人提供）：神经元连接的正确发育取决于精确控制突触形成和消除之间的平衡。这些相反的过程也在突触可塑性、学习和记忆中发挥重要作用。然而，与目前关于突触发生的丰富数据相比，对中枢突触丧失的分子事件知之甚少。我们最近发现了一种新的突触丢失机制，其中心是血清诱导激酶（SNK），一种波罗家族的丝氨酸-苏氨酸蛋白激酶。在皮层和海马中，短暂的SNK由突触活动诱导，随后促进兴奋性突触和树突棘（CMS中兴奋性突触的主要位点）的丧失。SNK通过磷酸化和泛素依赖性降解特定的突触后底物（如SPAR，树突棘的重要形态原）对突触发挥作用。由于SNK调节突触和棘的数量，结构和组成，这种激酶可能对塑造神经元的长期功能特性很重要。我们已经确定了SNK的一个额外的潜在底物，丰富的突触后Ras调节剂SynGAP。Ras信号传导对于包括突触可塑性、发育和保护免受兴奋性毒性损伤在内的多种神经生物学过程至关重要。在目标1中将采用生物化学和分子方法来确定SynGAP和SNK是否物理相互作用以及SynGAP是否是SNK的直接磷酸化底物。目的2：在体外研究SNK和SynGAP之间的功能关系，并确定SNK是否调节神经元中的SynGAP和Ras。最后，一个假定的SNK/SynGAP/Ras调节网络在调节树突棘形态的作用将在目标3中讨论。本提案中描述的实验对于理解SNK作用的机制至关重要，并且可能在突触可塑性、突触发育和病理性突触丧失领域产生广泛影响。阐明这些途径可能具有临床意义，并与公共卫生高度相关，因为新皮质突触丢失是人类神经退行性变的标志，并且是许多形式的痴呆症中认知下降的主要相关因素。

DESCRIPTION (provided by applicant): The proper development of neuronal connections depends on precisely controlling the balance between formation and elimination of synapses. These opposing processes also play important roles in synaptic plasticity, learning and memory. Compared to the current wealth of data regarding synaptogenesis, however, relatively little is known about the molecular events underlying the loss of central synapses. We have recently identified a novel mechanism of synapse loss centered on the serum-inducible kinase (SNK), a serine-threonine protein kinase of the polo family. In cortex and hippocampus, the short-lived SNK is induced by synaptic activity and subsequently promotes loss of excitatory synapses and dendritic spines (the primary loci of excitatory synapses in the CMS). SNK exerts its effect on synapses via the phosphorylation- and ubiquitin-dependent degradation of specific postsynaptic substrates such as SPAR, an important morphogen for dendritic spines. Because SNK regulates the number, structure and composition of synapses and spines, this kinase is likely to be important for shaping the long-term functional properties of neurons. We have identified an additional potential substrate of SNK, the abundant postsynaptic Ras regulator SynGAP. Ras signaling is of critical importance for a wide variety of neurobiological processes including synaptic plasticity, development, and protection from excitotoxic insults. Biochemical and molecular approaches will be employed in Aim 1 to determine whether SynGAP and SNK physically interact and whether SynGAP is a direct phosphorylation substrate of SNK. In Aim 2 we will analyze the functional relationship between SNK and SynGAP in vitro and determine whether SNK regulates SynGAP and Ras in neurons. Finally, the role of a putative SNK/SynGAP/Ras regulatory network in regulating dendritic spine morphology will be addressed in Aim 3. The experiments described in this proposal are essential for understanding the mechanisms of SNK action and may have broad impact in the fields of synaptic plasticity, synapse development, and pathological synapse loss. Elucidating these pathways is likely to be of clinical significance and highly relevant to public health in view of the fact that neocortical synapse loss is a hallmark of human neurodegeneration and is the major correlate of cognitive decline in many forms of dementia.