Molecular Mechanisms of Synapse Development and Plasticity

突触可以通过突触的可塑性改变它们的功效。长时间的突触可塑性(如突触传递的长期增强和长期抑制)是大脑中信息存储和发育过程中建立适当神经回路的重要细胞机制。在这个项目中，我们研究了突触传递长期抑制的机制。我们的研究表明，宏自噬(以下简称自噬)在LTD中起着重要的作用。自噬是一种细胞质成分和细胞器被运送到溶酶体进行降解的细胞过程。自噬可以去除错误折叠或聚集的蛋白质和有缺陷的细胞器。功能失调的自噬与神经疾病有关。自噬对突触的发育和功能也是必不可少的。它能使树突棘(容纳突触后成分的亚细胞结构)发育修剪，调节突触前结构和多巴胺释放，并调节突触后受体的降解。 自体干草是由噬菌体(隔离膜)的形成启动的。吞噬菌体膨胀成自噬小体(双层膜结构)以隔离货物，然后与溶酶体融合成为自溶酶小体，货物在那里被降解。这些过程是由30多个自噬相关(ATG)蛋白和多个信号通路协调的。雷帕霉素复合体的机械靶点1(MTORC1)是哺乳动物细胞中最典型的自噬诱导因子。它通过磷酸化ULK1/2(UNC-51样激酶)和ATG13来抑制自噬的启动。 使用mTOR抑制剂和自噬缺陷的基因敲除小鼠，我们发现自噬通量在LTD过程中发生变化，这反过来导致AMPA受体内吞。在本报告所述期间，我们调查了自噬在LTD中的调控机制，以及自噬如何对LTD做出贡献。我们还检测了自噬通量发生变化的小鼠的行为。 2.精神分裂症危险基因dybindin在精神分裂症突触病理学中的作用机制。Dybindin是一个含有卷曲结构域的蛋白质，最初被发现是一种抗肌营养不良蛋白结合蛋白，后来被发现是溶酶体相关细胞器复合体1(BLOC-1)生物发生的八个亚基之一。Dybindin基因(Dtnbp1)的单核苷酸多态性与精神分裂症的高风险相关，精神分裂症患者死后大脑中一直显示出低水平的dybindin蛋白和mRNAs。我们早期的工作表明，dybindin通过调节树突的发育来促进神经元连通性的建立，树突包括树突(形成兴奋性突触的微小树突)和丝状足突(在年轻神经元中占主导地位的细长突起)。因此，结合障碍可能通过调节树突棘的发育而增加患精神分裂症的风险。 精神疾病通常是由心理压力引起的。在精神分裂症的病因中，压力与遗传风险因素如何相互作用在很大程度上尚不清楚。在本项目中，我们研究了应激对debindin缺失突变小鼠行为的影响。我们发现，对野生型小鼠的行为没有明显影响的温和应激，会在突变小鼠中诱导与精神分裂症症状相关的行为。我们记录了应激小鼠的脑片，发现压力改变了突变小鼠的突触生理，但对野生型小鼠没有影响。在本报告期间，我们研究了应激对SDY小鼠突触生理学的影响。我们还建立了一个双光子显微镜系统来拍摄清醒的、行为正常的小鼠的树突图像。我们将使用这个系统来研究压力是否以及如何影响大脑中树突棘的数量、形态和动力学。

Synapses can change their efficacy through synaptic plasticity. Long-lasting forms of synaptic plasticity (such as long-term potentiation and long-term depression of synaptic transmission) are important cellular mechanisms underlying information storage in the brain and the establishment of proper neural circuits during development. In this project, we investigated the mechanism underlying long-term depression of synaptic transmission. Our study shows that macroautophagy (autophagy hereinafter) plays an important role in LTD. Autophagy is a cellular process by which cytoplasmic components and organelles are delivered to lysosomes for degradation. Autophagy removes misfolded or aggregated proteins and defective organelles. Dysfunctional autophagy has been associated with neurological disorders. Autophagy is also essential for the development and function of synapses. It enables developmental pruning of dendritic spines (subcellular structures accommodating postsynaptic components), regulates presynaptic structure and dopamine release, and regulates degradation of postsynaptic receptors. Autophay is initiated by the formation of a phagophore (the isolation membrane). The phagophore expands into autophagosomes (a double membrane structure) to sequester the cargo, and then fuses with lysosomes to become an autolysosome where the cargo is degraded. These processes are orchestrated by more than 30 autophagy-related (Atg) proteins and multiple signaling pathways. Mechanistic target of rapamycin complex 1 (mTORC1) is the best-characterized regulator of autophagy induction in mammalian cells. It inhibits autophagy initiation by phosphorylating ULK1/2 (Unc-51-like kinase) and Atg13. Using mTOR inhibitors and knockout mice with deficient autophagy, we found that autophagic fluxis changed during LTD and this in turn leads toAMPA receptor endocytosis. During this reporting period, we investigated the mechanism by which autophagy is regulated in LTD and how autophagy contributes to LTD. We also examined the behavior of mice in which autophagic flux is altered. 2. The mechanism by which the schizophrenia risk gene dysbindin contributes to synaptopathology in schizophrenia. Dysbindin is a coiled-coil domain containing protein, initially discovered as a dystrophin-binding protein and later found to be one of eight subunits of biogenesis of lysosome-related organelles complex 1 (BLOC-1). Single-nucleotide polymorphisms of the dysbindin gene (Dtnbp1) have been associated with higher risk for schizophrenia, and the postmortem brains of schizophrenia patients consistently exhibit low levels of dysbindin proteins and mRNAs. Our earlier work shows that dysbindin contributes to the establishment of neuronal connectivity by regulating the development of dendritic protrusions, including dendritic spines (tiny dendritic protrusions where excitatory synapses are formed) and filopodia (long, thin protrusions that predominant in young neurons). Dysbindin, therefore, may confer the risk for schizophrenia by regulating the development of dendritic spines. Psychiatric disease is commonly precipitated by psychological stress. It is largely unclear how stress interacts with genetic risk factors in the etiology of schizophrenia. In this project, we investigated the effect of stress on the behavior of dysbindin null mutant mice. We found that mild stress that does not significantly affect the behavior of wild-type mice induces behaviors that are related to the symptom of schizophrenia in mutant mice. We recorded in the brain slices of stressed mice and found that stress alters synaptic physiology in mutant but not in wild-type mice. During this reporting period, we examined the effect of stress on synaptic physiology in sdy mice. We also set up a two-photon microscopy system to take images of dendritic spines in awake, behaving mice. We will use this system to investigate whether and how stress affects the number, morphology and dynamics of dendritic spines in the brain.