Regulation of inhibitory synapse function by Neuroligin 2 membrane dynamics, trafficking and phosphorylation

神经细胞通过称为突触的特殊细胞-细胞接触部位相互通信。在突触前一侧，输入神经元释放神经递质，激活位于突触后侧接收神经元上的特殊神经递质受体。突触在大脑信号传递中既有兴奋(激活)的作用，也有抑制(失活)的作用。对于大脑的良好运作，重要的是突触的正确形成，即突触前和突触后的一侧准确地相互对立，并且大脑活动受到适当的调节。如果突触在发育过程中没有正确连接，或者在以后的生活中出现错误，这可能会导致毁灭性的神经精神障碍和神经退行性大脑疾病，如精神分裂症、自闭症和阿尔茨海默病。神经连接蛋白家族在突触的形成和维持中起着关键作用。它们位于突触后侧的膜上，通过与突触前侧的Neuresin蛋白结合，连接突触裂隙。神经连接蛋白-2(NL2)特异性地位于抑制性突触上，在那里诱导蛋白Gen聚集形成支架。我们中枢神经系统的主要抑制性神经递质受体，GABA-A受体，然后被吉普林和LHFPL4稳定在突触上。突触可以根据神经活动的变化改变其强度，这是学习和记忆等关键大脑功能的重要特性，也是维持兴奋和抑制之间的平衡的重要属性。突触的反应强度可以通过改变支架的大小和连接的神经递质受体的数量来调节。通过其稳定突触的作用，NL2很可能是突触后膜上GABA-A受体数量的关键调节因子，从而调节大脑中抑制性突触的强度和信息处理。然而，关于控制突触上NL2数量的分子机制，或者它动态地进入和离开突触的分子机制，我们知之甚少。我们有初步的数据表明，大脑活动通过从突触释放NL2并摄取到细胞内(这个过程被称为内吞作用)，导致细胞表面NL2数量的变化。我们还发现了一些与NL2相互作用的新蛋白质，这些蛋白质可能参与了NL2在突触处的稳定，或者调节了NL2进入细胞是循环到突触还是被送去破坏。然而，目前还不清楚大脑活动是如何影响这些过程的，反过来，突触上NL2数量的变化又是如何影响突触强度的。因此，我们的研究旨在回答以下相关问题：-在什么生理相关的条件下，NL2在突触的稳定性发生变化？-NL2的各种结合伙伴如何调节其在突触的稳定性，以及它的内吞、循环和降解？-突触中NL2数量的变化如何影响抑制性突触的强度？最终，通过了解抑制性突触是如何形成和调节的分子，我们将更好地了解大脑中的连接是如何被控制的。此外，由于突触功能障碍与许多神经退行性疾病和神经精神疾病有关，我们拟议的工作也可能导致对癫痫、中风、阿尔茨海默病、亨廷顿病和精神分裂症等疾病的更好理解，并可能提出治疗干预的目标。对我们研究NL2的过程的详细了解，也将对其他神经连接蛋白、突触膜蛋白和非神经元细胞中的膜蛋白产生影响。因此，我们的研究可能有助于理解基本的细胞生物学原理，特别是大脑中的连接是如何形成和维持的。

Nerve cells communicate with each other via specialised cell-cell contact sites called synapses. On the presynaptic side the input neuron releases neurotransmitters that activate specialised neurotransmitter receptors located on the receiving neuron at the postsynaptic side. Synapses can have either an excitatory (activating) or an inhibitory (inactivating) role in brain signalling. For the brain to function well, it is important that synapses are formed correctly, i.e. the pre- and postsynaptic side are precisely apposed to each other, and that brain activity is properly regulated. If synapses do not wire correctly during development or go wrong later in life this can lead to devastating neuropsychiatric and neurodegenerative brain disorders like Schizophrenia, autism and Alzheimer's disease, respectively. The protein family of Neuroligins play a key role in synapse formation and maintenance. They are positioned in the membrane of the postsynaptic side and, by binding the protein Neurexin at the presynaptic side, bridge the synaptic cleft. Neuroligin-2 (NL2) is specifically located at the inhibitory synapse, where it induces clustering of the protein gephyrin to form a scaffold. The main inhibitory neurotransmitter receptor of our central nervous system, the GABA-A receptor, is then stabilised at the synapse by gephyrin and LHFPL4. Synapses can change their strength in response to changes in neural activity, an important property for key brain functions such as learning and memory, and for maintaining the balance between excitation and inhibition. The strength of the response at a synapse can be regulated by altering the size of the scaffold and the number of attached neurotransmitter receptors. Through its role in stabilising the synapse, NL2 is likely to be a key regulator of the number of GABA-A receptors in the postsynaptic membrane, and thus of inhibitory synapse strength and information processing in the brain. Little is known, however, about the molecular mechanisms that control NL2 number at the synapse, or its dynamic movement into and out of the synapse.We have initial data suggesting that brain activity causes a change in the amount of NL2 on the cell surface, through its release from the synapse and uptake into the cell (a process called endocytosis). We have also identified a number of novel proteins that interact with NL2 and may be involved with either its stabilisation at the synapse, or regulating whether NL2 taken into the cell is recycled to the synapse or sent for destruction. It is, however, still unknown how brain activity affects these processes, and reciprocally how alterations of NL2 number at the synapse affects its strength. Our research is therefore aimed at answering the following related questions:- Under what physiologically relevant conditions is the stability of NL2 at the synapse altered?- How do the various binding partners of NL2 regulate its stability at the synapse, as well as its endocytosis, recycling and degradation?- How do changes in the amount of NL2 at the synapse affect the strength of the inhibitory synapse?Ultimately, by gaining molecular insight into how inhibitory synapses are formed and regulated, we will better understand how wiring in the brain is controlled. In addition, since synaptic dysfunction is implicated in many neurodegenerative and neuropsychiatric diseases, our proposed work may also lead to an improved understanding of diseases such as epilepsy, stroke, Alzheimer's disease, Huntington's disease and schizophrenia, and may suggest targets for therapeutic intervention. A detailed understanding of the processes that we study for NL2, will also have implications for other Neuroligins, synaptic membrane proteins, and membrane proteins in non-neuronal cells. Thus, our research may contribute to understanding basic cell biological principles as well as specifically how connections in the brain are formed and maintained.