Control of Dendritic and Synaptic Development by Extracellular Cues

描述(由申请人提供)：严重抑郁障碍(MDD)是一种反复发作的精神疾病，大约每6个美国人中就有一个在一生中至少折磨一次。虽然原因可能是多因素的，但MDD的发病与海马区的结构缺陷有关，包括树突形态的变化。在患有MDD的人类和MDD动物模型中，刺激树突状细胞生长的脑源性神经营养因子(BDNF)等神经营养因子的水平都会下降。然而，虽然已知BDNF水平的降低与树突状细胞形态的改变有关，但BDNF刺激树突状细胞生长的潜在信号机制尚不清楚。识别这些途径对于了解树突状细胞发育和突触发生的正常方式以及在MDD发作期间它是如何改变的至关重要。我们的长期目标是确定神经营养因子控制树突发育的细胞内信号，并确定这些信号在正常和抑郁大脑中是如何调节的。这项应用的目的是确定一种关键的神经营养因子BDNF控制树突状细胞形态发生、突触发生和突触结构维持的信号通路。我们的中心假设是，BDNF通过一种协调反应刺激树突状细胞的发育，该反应包括关键蛋白编码基因和非编码microRNAs的基因组调节，后者在抑郁症期间表达发生变化。我们根据已发表和未发表的数据提出了这一假说，这表明增加CREB对蛋白质编码基因和非编码microRNAs的调节对于依赖BDNF的树突状细胞生长和突触发生是必不可少的。这些事件的结合不仅激活了促进树突状细胞生长的途径，也抑制了抑制树突状细胞生长的途径。我们将通过以下具体目标来验证我们的中心假说：1.确定CREB调节的蛋白编码基因在BDNF刺激的树突状细胞生长和突触形成中的需求。2.确定BDNF依赖的树突状细胞生长和突触发生对CREB调控的microRNAs的需求。确定蛋白质编码基因和微RNA在体内正常发育和BDNF表达改变期间的作用。我们将使用生化、遗传学、细胞生物学、行为学和成像方法来解决这些具体目标。这项研究的理论基础是，一旦将BDNF与树突状细胞和脊椎重塑联系起来的关键信号分子变得已知，它们就可以成为治疗和预防MDD的靶点。这些研究具有创新性，因为它们将PI在信号转导方面的专业知识应用于一个关键而未被研究的问题：确定抑郁症期间发生结构变化的分子机制。我们已经得到了我们的顾问雅克·潘克塞普的帮助，他在研究抑郁症模型方面拥有丰富的经验。此外，这些结果预计将对该领域产生广泛的影响，因为树突分枝和棘突形成的异常在包括脆性X综合征、唐氏症和Rett综合征在内的多种形式的精神发育迟滞中都很常见。

DESCRIPTION (PROVIDED BY APPLICANT): Major Depressive Disorder (MDD) is a recurrent mental illness that afflicts approximately 1 in 6 Americans at least once during their lifetime. While the causes are likely to be multi-factoral, the onset of MDD correlates with structural defects in the hippocampus, including alterations in dendritic morphology. The levels of neurotrophic factors like Brain Derived Neurotrophic Factor (BDNF), which stimulates dendritic growth, are decreased in both humans suffering from MDD and in animal models of MDD. However, while the decrease in BDNF levels is known to correlate with alterations in dendritic morphology, the underlying signaling mechanisms by which BDNF stimulates dendritic growth are unknown. Identifying these pathways is critical to understand how dendritic development and synaptogenesis occurs normally and how it is altered during bouts of MDD. Our long-range goal is to identify the intracellular signals by which neurotrophic factors control dendritic development and to determine how these signals are regulated in both normal and depressed brains. The objective of this application is to determine the signaling pathways by which one critical neurotrophic factor, BDNF, controls dendritic morphogenesis, synaptogenesis and the maintenance of synaptic structures. Our central hypothesis is that BDNF stimulates dendritic development via a coordinated response comprised of genomic regulation of both critical protein-coding genes and non-coding microRNAs whose expression are altered during depression. We have formulated this hypothesis on the basis of our published and unpublished data, which shows that an increase CREB dependent regulation of both protein coding genes and non-coding microRNAs are essential for BDNF dependent dendritic growth and synaptogenesis. The combination of these events not only activates pathways that promote dendritic growth but also inhibits pathways that suppress dendritic growth. We will test our central hypothesis with the following Specific Aims: 1. Determine the requirement of CREB regulated protein coding genes in BDNF-stimulated dendritic growth and synaptogenesis. 2. Determine the requirement for CREB regulated micro-RNAs in BDNF dependent dendritic growth and synaptogenesis. Determine the role of protein coding genes and micro-RNAs in vivo during normal development and during periods of altered BDNF expression. We will use biochemical, genetic, cell biological, behavioral and imaging approaches to address these specific aims. The rationale that underlies the proposed research is that once the critical signaling molecules linking BDNF to dendritic and spine remodeling become known they can be targeted for the treatment and prevention of MDD. These studies are innovative because they apply the expertise of the PI in signal transduction to a critical and under examined problem: to identify the molecular mechanisms underlying structural changes occurring during depression. We have enlisted the help of our consultant Jaak Panksepp, who has extensive experience in studying models of depression. Additionally, these results are expected to have a broad impact on the field as abnormalities in dendritic arborization and spinogenesis are common to numerous forms of mental retardation including Fragile X, Down's, and Rett syndromes.