Impact of Nicotinic Signaling through Astrocytes on Glutamate Synapse Formation

通过星形胶质细胞的烟碱信号传导对谷氨酸突触形成的影响

• 批准号: 8359365
• 负责人: Darwin K BERG
• 金额: $ 23.25万
• 依托单位: UNIVERSITY OF CALIFORNIA, SAN DIEGO
• 依托单位国家: 美国
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-06-01 至 2014-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8359365
• 关键词: AMPA Receptors; Adult; Appearance; Astrocytes; Behavioral; Biological; Biological Neural Networks; Brain; Calcium; Cell Culture Techniques; Cells; Conditioned Culture Media; Dementia; Development; Drug Design; Drug Industry; Engineering; Environmental Tobacco Smoke; Future; Generations; Glial Fibrillary Acidic Protein; Glutamate Transporter; Glutamates; Hippocampus (Brain); Knock-out; Life; Location; Long-Term Potentiation; Mediating; Milk; Molecular; Mus; Mutant Strains Mice; N-Methyl-D-Aspartate Receptors; NR1 gene; Nervous system structure; Neuroglia; Neurons; Nicotine; Nicotinic Receptors; Output; Pathway interactions; Permeability; Pharmacologic Substance; Play; Process; RNA Interference; Recruitment Activity; Role; Shapes; Signal Transduction; Site; Slice; Specific qualifier value; Synapses; Synaptic plasticity; System; TNF gene; Testing; Therapeutic Intervention; Thinking; Time; Viral; Wild Type Mouse; base; cholinergic; coping; functional status; high risk; in vivo; insight; loss of function; nervous system disorder; patch clamp; postsynaptic; presynaptic; receptor; relating to nervous system; research study; synaptic function; synaptogenesis

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. PUBLIC HEALTH RELEVANCE: Astrocytes are cells which are nearly 5 times more abundant than neurons in brain and express receptors that can be stimulated by nicotine. Our preliminary results suggest that nicotinic stimulation of astrocytes has profound effects on the formation of glutamatergic synapses, the principal form of excitatory connections between neurons. This proposal will determine when and how this occurs, and in so doing, will not only make major advances in our understanding of brain development but will also have biomedical consequences by revealing circuits and processes vulnerable to nicotine but possibly amenable to therapeutic intervention.

描述（由申请人提供）：谷氨酸突触构成大脑中的主要兴奋通路。决定谷氨酸能突触强度的一个关键特征是可用于激活的突触后 AMPA 受体的数量。我们有初步证据表明，烟碱刺激星形胶质细胞会导致它们释放一种成分，专门将 AMPA 受体招募到神经元的突触后位点，使这些以前“沉默”的突触发挥功能。这是完全出乎意料的，并提出了一种塑造兴奋回路的新的重要机制。当谷氨酸能突触在发育过程中首次形成时，星形胶质细胞是普遍且丰富的，并且具有大量含α7的烟碱乙酰胆碱受体（α7-nAChR）。部分通过 α7-nAChR 介导的自发烟碱胆碱能活性在发育早期也广泛存在。我们的初步证据表明，正是这些 ?7-nAChR 导致了星形胶质细胞对 AMPA 受体的影响。鉴于星形胶质细胞和α7-nAChR信号传导的早期出现和广泛存在，这种机制可能对塑造网络形成和功能输出产生深远的影响。第一个具体目标将在细胞培养物中测试星形胶质细胞 α7-nAChR 的烟碱刺激所独特释放的成分的突触生成效应。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，并启动候选成分的筛选。第二个具体目标将在体内测试这一假设，在突变小鼠中使用病毒构建体和 GFAP-Cre 系统，以确定星形胶质细胞 α7-nAChR 是否在招募海马神经元上的突触后 AMPA 受体方面发挥关键作用。随后的实验将测试星形胶质细胞 ?7-nAChR 是否也有助于突触可塑性，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，这些研究还将产生严重的生物医学影响。发现烟碱信号传导影响谷氨酸能突触功能等基本特征，如果早期接触尼古丁（例如通过二手烟或母乳），可能会使系统在发育过程中处于高风险，从而过早刺激或使这种调节输入变得不敏感。此外，这些结果对于全球在药物设计中以 α7-nAChR 为目标的制药公司具有直接意义，而没有意识到星形胶质细胞 α7-nAChR 可能具有这种独特而关键的作用。该 R21 项目将测试中心假设，并为未来了解星形胶质细胞和烟碱信号传导在调节神经系统形式和功能中的作用的项目奠定基础。 公共健康相关性：星形胶质细胞的数量比大脑中神经元的数量近 5 倍，并且表达可被尼古丁刺激的受体。我们的初步结果表明，星形胶质细胞的烟碱刺激对谷氨酸突触的形成具有深远的影响，谷氨酸突触是神经元之间兴奋性连接的主要形式。该提议将确定这种情况何时以及如何发生，这样做不仅将在我们对大脑发育的理解方面取得重大进展，而且还将通过揭示易受尼古丁影响但可能适合治疗干预的回路和过程来产生生物医学后果。