突触亚群形成及其环路功能组建与情感障碍行为的基础

Neuroligin (NL) is a postsynaptic membrane protein expressed in brain and mediates synaptogesis. Neuroligin family protein 1 and 3 can induce excitatory immature synapse formation while NL2 exclusively induce inhibitory synapses. Yet their function in specific neuronal types is beyond understanding. Dysfunctions of the NL proteins such as deletion or point mutation have been found involved in autism spectrum disorders (ASD), which has been proved in multiple NL deficient mouse models. In most of the models including the human autism-linked NL3 mutation mice, there are social interaction defects, memory impairment and repetitive behaviors being observed. Researchers also found the excitatory/inhibitory synapse ratio altered in those mice, as well as NMDA receptor (NMDAR) subunit composition changed. It raises an interesting probability that NL may have specific affinity in recruiting NMDAR subtypes, in which the defects may lead to imbalanced E/I ratio and finally caused ASD-like symptoms. Although the exact neuronal circuit controlling the social interaction behavior has not been clearly elucidated, it is undoubted that cortex, especially prefrontal lobe of cortex, plays an important role in emotional convergence and processing. There are also cumulative evidences suggesting the involvement of cortical abnormalities in ASD patient social defects, including thickened cortex and impaired uncinate fasciculus and inferior longitudinal fasciculus connectivities. In NL deficient mice, the main findings in E/I ratio imbalance, abnormal neuronal activities are also from the cortical region. However, the exact neuronal circuit has not been mapped out, neither the mechanistic linkage between altered E/I ratio and behavioral symptoms. Here we are planning to use the NL1,3 double knockout mice and NL2 knockout mice as the animal models to investigate the linkage between synapse architecture, socio-emotional circuitry formation and eventually behavioral outputs. We will check how NL contributes to synapse subtype organization in different type of neurons by examining the E/I ratio in different cortical neurons and their electrophysiological read outs. We will then setup to check how these specific E/I ratio changes would affect regional circuitry connectivity and synchronization in cortex, especially in prefrontal lobe region. Down to the detailed molecular mechanisms, we will identify the linkage protein between NL and NMDARs. We are interested in finding out the spatial and temporal consequences in NL’s recruitment of NMDARs into newly formed synapses, and elucidating the functional specificity between NL family members and NMDAR subtypes. Finally, we plan to find possible circuitry involved in the NL mice social defects by using in vivo electrophysiology and in utero electroporation approaches. Three-chambered social tests would also be conducted to check if rescue of NL protein level would reestablish the circuitry and bring the mice into normal.

疾病遗传学研究发现Neuroligin（NL）基因突变与人类孤独症谱系障碍（ASD）密切相关。NL家族蛋白（NL1-4）是突触后膜的细胞粘附因子，NL1/3和NL2分别选择性参与兴奋性突触和抑制性突触的形成。NL缺陷或表达异常小鼠常有类似ASD的行为异常，皮层神经元兴奋性与抑制性突触的比例以及突触NMDA受体亚单位组成改变。然而，能有效将分子和突触与行为衔接起来的环路水平研究依然是重要缺环。本项目拟采用NL1 /3和NL2基因缺陷小鼠，从分析对皮层椎体神经元和中间神经元的兴奋性突触和抑制性突触亚群形成和功能的影响入手，阐明与特定突触亚群形成和功能相关的若干关键分子机制；研究这些NL基因缺陷小鼠前额叶皮层环路功能异常及特征，建立与相应亚群突触功能失调的关联；并探索通过胚胎电转和成年皮层病毒感染导入NL，观察亚群突触、环路功能及行为的重建。该项目的研究将有助于对相关精神疾病神经环路机制的理解。

神经连接素（Neuroligin, NL）是定位于突触后的膜蛋白，介导神经突触形成并参与突触功能。疾病遗传学研究发现NL基因突变与人类孤独症谱系障碍（ASD）密切相关。NL 缺陷小鼠常有类似人类ASD 的行为异常、皮层神经元兴奋性与抑制性突触的比例以及突触NMDA 受体亚单位组成改变。然而，能将分子和突触与行为学有效衔接起来的环路水平研究依然是重要缺环。本项目主要利用NL基因敲减、基因缺陷及基因突变敲入小鼠，从分析对皮层锥体神经元和中间神经元的兴奋性突触和抑制性突触亚群形成和功能的影响入手，阐明NL与特定突触亚群形成和功能相关的分子机制；研究NL孤独症模型小鼠前额叶皮层环路功能异常及特征，并建立其与相应亚群突触功能失调的关联；并探索通过药理及光遗传学操纵特定神经元活性，观察对NL孤独症小鼠亚群突触、环路功能及行为的重建。本项目研究发现：1）不同NL对于不同神经元的不同突触亚群存在差异性调节；2）NL可通过影响Akt信号通路调节神经元发育；3）在突触内NMDA受体转运存在亚单位特异性转运并受神经元活动调节；4）在NL诱导的新生突触内，PICK1可通过招募AMPA受体促进突触成熟。重要的是，在环路建构和功能上我们还发现：1）在NL R451C KI小鼠中，小鼠产生社交行为时其前额叶皮层（mPFC）神经元激活有所减弱，其锥体神经元NMDA受体功能低下且抑制性神经元兴奋性降低，mPFC整体神经震荡功能紊乱，从而进一步导致小鼠社交缺陷；2）我们利用药理及光遗传学操控手段，发现可对mPFC神经元活性及环路功能进行重塑，并拯救小鼠社交行为缺陷。因此，该项目阐明了特定亚群突触缺陷与mPFC环路功能及社会行为异常的因果关系，研究成果加深了对孤独症社会情感障碍发病之神经环路机制的理解，并提供了孤独症治疗的新的可能方向。