Impact of excitatory synapse maturation on synaptic plasticity and stability

围产期脑内未成熟的兴奋性突触含有高释放概率（Pr）的突触前终末 与含有GluN 2B亚基的NMDA受体（hi-Pr，hi-GluN 2B）的突触后特化偶联 突触）。二十多年来，我们已经知道这些未成熟的突触在一种活动中成熟- 低Pr，低GluN 2B突触的依赖方式，但协调这种过渡的机制，为什么它 发生，以及它如何有助于电路的可塑性和稳定性仍然存在争议， 没有答案的问题解决这些问题将确定控制突触的基本机制 在神经发育和精神疾病中可能被破坏。破坏 小鼠中的Arg/GluN 2激酶产生持续到成年早期的hi-Pr、hi-GluN 2B突触群。的 这些未成熟突触的持续存在导致出生后海马突触的净损失>40%。 （P）21和P42天，并且损害突触可塑性和行为。根据这些发现，我们将确定 新的调节突触成熟，并确定他们如何调节突触可塑性和稳定性。 在目的1中，我们将鉴定激活Arg以协调从hi-Pr、hi-Pr成熟的细胞表面受体。 GluN 2B突触到低Pr、低GluN 2B突触。我们提供了整合素α3β1粘附的初步数据， 受体和血小板衍生生长因子受体β（PDGFRβ）作用于Arg上游，控制突触 功能和稳定性。我们将在突触前和突触后神经元中使用选择性基因失活， 遗传上位性和拯救实验，以解决这些受体如何以及在何处与Arg相互作用， 彼此调节Pr和突触后GluN 2B水平。 在目标2中，我们将阐明精氨酸如何介导GluN 2B在突触下调。Arg介导信号 是在成熟过程中下调GluN 2B的关键。我们鉴定了SHP 2酪氨酸磷酸酶和 NMDAR相关蛋白BRAG 1，两者在智力残疾中突变，可能是 Arg和发育性GluN 2B下调。我们将使用生物化学、细胞和遗传学方法 以测试Arg如何与SHP 2和BRAG 1相互作用以下调GluN 2B功能。 在目标3中，我们将描述不成熟和成熟突触对可塑性的不同贡献， 稳定我们将在单个突触上使用模式化的谷氨酸释放来测试hi-Pr，hi-GluN 2B和 低Pr、低GluN 2B突触改变了长时程增强（LTP）和长时程增强（LTP）的能力。 在arg-/-小鼠中的抑郁症（LTD）。我们将使用体内成像来研究在高血压时， Arg-/-小鼠的Pr，hi-GluN 2B皮质突触在可塑性和稳定性方面不同于正常脊髓。 我们的研究将阐明受体通过Arg及其下游靶点发挥作用的机制， 控制突触成熟过程中Pr和NMDAR的组成。这些机制的破坏可能导致 智力残疾和其他脑部疾病中突触发育、可塑性和稳定性的缺陷。

Immature excitatory synapses in the perinatal brain contain high release probability (Pr) presynaptic terminals coupled to postsynaptic specializations with GluN2B subunit-containing NMDA receptors (hi-Pr, hi-GluN2B synapses). For over two decades, we have known that these immature synapses mature in an activity- dependent manner to low-Pr, low-GluN2B synapses, but the mechanisms that coordinate this transition, why it occurs, and how it contributes to circuit plasticity and stability remain controversial and are fundamental unanswered questions. Addressing these issues will identify basic mechanisms that control synapse development and that may be disrupted in neurodevelopmental and psychiatric disorders. Disruption of the Arg/Abl2 kinase in mice yields a population of hi-Pr, hi-GluN2B synapses that persist into early adulthood. The persistence of these immature synapses drives a >40% net loss of hippocampal synapses between postnatal day (P) 21 and P42, and impairs synaptic plasticity and behavior. Building on these findings, we will identify new regulators of synapse maturation, and determine how they regulate synaptic plasticity and stability. In Aim 1, we will identify the cell surface receptors that activate Arg to coordinate the maturation from hi-Pr, hi- GluN2B synapses to low-Pr, low-GluN2B synapses. We provide preliminary data that integrin α3β1 adhesion receptor and platelet-derived growth factor receptor β (PDGFRβ) act upstream of Arg to control synapse function and stability. We will use selective gene inactivation in the pre- and postsynaptic neurons along with genetic epistasis and rescue experiments to address how and where these receptors interact with Arg and each other to regulate Pr and postsynaptic GluN2B levels. In Aim 2, we will elucidate how Arg mediates GluN2B downregulation at the synapse. Arg-mediated signaling is critical to downregulate GluN2B during maturation. We identified the SHP2 tyrosine phosphatase and the NMDAR-associated protein BRAG1, both mutated in intellectual disability, as likely functional links between Arg and developmental GluN2B downregulation. We will use biochemical, cell-based, and genetic approaches to test how Arg interacts with SHP2 and BRAG1 to downregulate GluN2B function. In Aim 3, we will characterize how immature and mature synapses differentially contribute to plasticity and stability. We will use patterned glutamate uncaging at single synapses to test whether hi-Pr, hi-GluN2B and low-Pr, low-GluN2B synapses have altered ability to undergo long-term potentiation (LTP) and long-term depression (LTD) in arg–/– mice. We will use in vivo imaging to examine how enlarged dendritic spines at hi- Pr, hi-GluN2B cortical synapses in arg–/– mice differ from normal spines in their plasticity and stability. Our studies will elucidate the mechanisms by which receptors act through Arg and its downstream targets to control Pr and NMDAR composition during synapse maturation. Disruption of these mechanisms may underlie the defects in synapse development, plasticity, and stability in intellectual disability and other brain disorders.