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GluN2B亚单位的NMDA受体(hi-PR、hi-GluN2B)的突触后特化相结合 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- 对低PR、低GluN2B突触的依赖方式，但协调这种转变的机制，为什么 它如何对电路的可塑性和稳定性做出贡献仍然存在争议，并且是基本的 悬而未决的问题。解决这些问题将确定控制突触的基本机制 这可能会在神经发育和精神障碍中中断。扰乱了 在小鼠体内，Arg/ABL2激酶产生一组hi-Pr，hi-GluN2B突触，并持续到成年早期。这个 这些未成熟突触的持续存在导致出生后40%的海马区突触净损失 21天和42天，并损害突触的可塑性和行为。在这些发现的基础上，我们将确定 突触成熟的新调节者，并决定它们如何调节突触的可塑性和稳定性。 在目标1中，我们将确定激活arg的细胞表面受体，以协调hi-Pr，hi-Pr- GluN2B突触与低PR、低GluN2B突触连接。我们提供了整合素α3β1黏附的初步数据 受体和血小板衍生生长因子受体β(PDGFRβ)作用于Arg上游调控突触 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 遗传上位性和挽救实验，以解决这些受体如何以及在哪里与Arg和 相互调节PR和突触后GluN2B水平。 在目标2中，我们将阐明Arg如何介导突触GluN2B的下调。精氨酸介导的信号转导 是在成熟过程中下调GluN2B的关键。我们鉴定了SHP2酪氨酸磷酸酶和 NMDAR相关蛋白BRAG1在智能障碍中都发生了突变，可能是 Arg和发育中的GluN2B下调。我们将使用生化、基于细胞和遗传的方法 检测Arg如何与SHP2和BRAG1相互作用，下调GluN2B功能。 在目标3中，我们将描述未成熟和成熟突触如何对可塑性和 稳定性。我们将使用单个突触上的模式谷氨酸去掉来测试hi-PR，hi-GluN2B和hi-GluN2B 低PR、低GluN2B突触改变了经历长时程增强(LTP)和长时程 Arg-/-小鼠的抑郁(LTD)。我们将使用活体成像来研究在高海拔时扩大的树突是如何- Arg-/-小鼠的PR、hi-GluN2B皮质突触在可塑性和稳定性方面不同于正常脊椎。 我们的研究将阐明受体通过Arg及其下游靶点作用于 控制突触成熟过程中PR和NMDAR的组成。这些机制的破坏可能是 智力障碍和其他大脑疾病的突触发育、可塑性和稳定性方面的缺陷。

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.