Impact of Nicotinic Signaling through Astrocytes on Glutamate Synapse Formation

描述（申请人提供）：谷氨酸突触构成大脑中主要的兴奋通路。决定谷氨酸能突触强度的一个关键特征是突触后AMPA受体的激活数量。我们有初步的证据表明，烟碱刺激星形胶质细胞会导致它们释放一种成分，这种成分可以特异性地将AMPA受体招募到神经元的突触后位点，从而使这些先前“沉默”的突触发挥作用。这是完全出乎意料的，并提出了形成兴奋电路的一种新的重要机制。在发育过程中，当谷氨酸突触第一次形成时，星形胶质细胞是普遍和丰富的，并且有大量的？7-含烟碱乙酰胆碱受体（- 7-nAChRs）。自发性烟碱能活性部分通过？7- nachr在发育早期也广泛存在。我们的初步证据表明是这些？7- nachr负责星形细胞对AMPA受体的影响。鉴于星形胶质细胞的早期出现和广泛发生，7-nAChR信号，这样的机制可能对塑造网络形成和功能输出产生深远的影响。第一个特异性目标将在细胞培养中测试尼古丁刺激星形胶质细胞- 7- nachr所释放的成分的突触形成效应。将检查谷氨酸能突触的突触前和突触后成分，评估突触功能，并开始筛选候选成分。第二个特异性目标将在体内验证这一假设，在突变小鼠中使用病毒构建体和gmap - cre系统来确定星形胶质细胞？7- nachr在海马神经元突触后AMPA受体的募集中起关键作用。后续实验将测试星形胶质细胞？7- nachr也对突触可塑性有贡献，重点关注先前研究表明AMPA受体数量增加导致长期增强的位置。除了提供对大脑基本过程的新见解之外，这些研究将具有严重的生物医学意义。发现尼古丁信号影响谷氨酸突触功能等基本特征，如果早期暴露于尼古丁（如二手烟或母乳），可能会使该系统在发育过程中处于高风险状态，要么过早刺激这种调节输入，要么使其脱敏。此外，研究结果将与全球制药公司的目标直接相关。7- nachr在药物设计中没有意识到星形胶质细胞？7- nachr可能具有这种独特而关键的作用。这个R21项目将测试中心假设，并为未来的项目奠定基础，了解星形胶质细胞和尼古丁信号在调节神经系统形态和功能中的作用。

DESCRIPTION (provided by applicant): Glutamatergic synapses comprise the major excitatory pathways in brain. A key feature determining the strength of a glutamatergic synapse is the number of postsynaptic AMPA receptors available for activation. We have preliminary evidence that nicotinic stimulation of astrocytes causes them to release a component that specifically recruits AMPA receptors to postsynaptic sites on neurons, rendering these previously "silent" synapses functional. This is completely unexpected and suggests a new and important mechanism for shaping excitatory circuits. Astrocytes are pervasive and abundant when glutamatergic synapses are first forming during development, and have significant numbers of ?7-containing nicotinic acetylcholine receptors (?7-nAChRs). Spontaneous nicotinic cholinergic activity mediated in part through ?7-nAChRs is also widespread early in development. Our preliminary evidence suggests that it is these ?7-nAChRs that are responsible for the astrocyte effect on AMPA receptors. In view of the early appearance and widespread occurrence of astrocytes and ?7-nAChR signaling, such a mechanism could have profound consequences for shaping network formation and functional output. The first Specific Aim will test in cell culture the synaptogenic effects of components released uniquely by nicotinic stimulation of astrocyte ?7-nAChRs. Pre- and postsynaptic components at glutamatergic synapses will be examined, synaptic function assessed, and a screen of candidate components initiated. The second Specific Aim will test the hypothesis in vivo, using viral constructs and a GFAP-Cre system in mutant mice to determine if astrocyte ?7-nAChRs play a critical role in recruiting postsynaptic AMPA receptors on neurons in the hippocampus. Subsequent experiments will test whether astrocyte ?7-nAChRs also contribute to synaptic plasticity, focusing on locations where previous studies have shown that long-term potentiation results from increased numbers of AMPA receptors. In addition to providing new insight into fundamental processes in the brain, these studies will have serious biomedical implications. Finding that nicotinic signaling influences such basic features as the functionality of glutamatergic synapses may put the system at high risk during development if exposed early on to nicotine, such as through secondhand smoke or maternal milk, either prematurely stimulating or desensitizing this regulatory input. Further, the results will have immediate relevance for pharmaceutical companies globally targeting ?7-nAChRs in drug design without realizing that astrocyte ?7-nAChRs may have this unique and critical role. This R21 project will test the central hypotheses and lay the groundwork for future projects understanding the role of astrocytes and nicotinic signaling in regulating nervous system form and function.