MicroRNAs in Synaptic Plasticity and Behaviors Relevant to Autism

描述(由申请人提供)：我研究的主要目标是促进我们对认知和认知障碍背后的分子和细胞机制的理解。突触蛋白合成的调控已成为突触可塑性和记忆巩固的关键控制点。最近的证据表明，不适当或过度的突触蛋白合成与认知障碍和自闭症的发病机制有关。例如，在结节性硬化症复合体和脆性X综合征中失活的基因产物作为翻译抑制物发挥作用。我们最近提出，失去对突触蛋白合成的正常限制可能会促进异常的突触连接，损害调节认知的神经网络的性能，并导致认知障碍和自闭症的发展。这项应用的广泛、长期的目标是了解microRNAs翻译抑制在突触可塑性、突触连接和与自闭症相关的行为中的作用。MicroRNAs包括一个内源性的20-23个核苷酸的非编码RNAs大家族，通过与靶mRNAs中的互补序列结合来抑制蛋白质的合成。MicroRNAs与大脑发育和神经元存活有关，但对它们在突触过程或行为中的作用知之甚少。有趣的是，脆性X智力低下蛋白(FMRP)与介导microRNAs翻译抑制的分子机制在物理和遗传上相互作用。此外，microRNA表达减少与人类自闭症疾病有关。基于这些观察，我们假设microRNAs调节依赖蛋白质合成的突触可塑性和记忆，并且microRNA介导的翻译抑制的丢失可能导致突触蛋白合成过多，突触连接性改变和自闭症行为表型。我们最近产生了条件基因敲除小鼠，在这些小鼠中，microRNA在出生后的前脑中部分或完全失活。这些microRNA缺陷的小鼠看起来非常正常，在2-3个月大的时候没有表现出神经退化的证据。我们建议分析这些microRNA缺陷小鼠和FMRP缺陷小鼠与自闭症相关的行为缺陷(目标1)，蛋白质合成依赖的突触可塑性和记忆障碍(目标2)，以及突触连接异常(目标3)。在后一个目标中，我们提出了一种新的使用“大脑”小鼠来可视化失去microRNA或FMRP表达对兴奋性突触连接的影响。这些目标的实现将为了解microRNA的功能和自闭症的发病机制提供新的见解。建议的研究是对我的NIMH资助的R01的补充和紧密结合。详细的职业发展计划包括关键的合作和增强的多学科研究技能。K02奖项提供的薪酬支持将有助于我专注于研究和职业发展活动，而不会承担过多的临床责任。 公共卫生相关性：拟议的项目与负责正常认知和行为以及认知和行为障碍的大脑机制直接相关。有待研究的分子途径与自闭症和其他精神障碍的发病机制有关。这些目标的实现将增加我们对导致这些疾病的分子和突触缺陷的了解，并可能确定新的治疗靶点或策略。

DESCRIPTION (provided by applicant): The primary goal of my research is to advance our understanding of the molecular and cellular mechanisms underlying cognition and cognitive disorders. Regulation of synaptic protein synthesis has emerged as a key control point in the consolidation of synaptic plasticity and memory. Recent evidence has implicated inappropriate or excessive synaptic protein synthesis in the pathogenesis of cognitive impairment and autism. For example, the gene products inactivated in tuberous sclerosis complex and fragile X syndrome function as translational repressors. We recently proposed that loss of the normal constraints on synaptic protein synthesis may promote abnormal synaptic connectivity, compromising the performance of neuronal networks mediating cognition, and leading to the development of cognitive impairment and autism. The broad, long-term goals of this application are to understand the role of translational repression by microRNAs in synaptic plasticity, synaptic connectivity and behaviors relevant to autism. MicroRNAs comprise a large family of endogenous 20-23 nucleotide noncoding RNAs that repress protein synthesis by binding to complementary sequences in target mRNAs. MicroRNAs have been implicated in brain development and neuronal survival, but little is known about their roles in synaptic processes or behavior. Intriguingly, the fragile X mental retardation protein (FMRP) interacts physically and genetically with the molecular machinery mediating translational repression by microRNAs. In addition, reduced microRNA expression has been associated with human autistic disorders. Based on these observations, we hypothesize that microRNAs regulate protein synthesis-dependent synaptic plasticity and memory, and that loss of microRNA-mediated translational repression may lead to excessive synaptic protein synthesis, altered synaptic connectivity and autistic behavioral phenotypes. We have recently generated conditional knockout mice in which microRNA expression is partially or completely inactivated in the postnatal forebrain. These microRNA-deficient mice appear grossly normal and display no evidence of neurodegeneration at 2-3 months of age. We propose to analyze these microRNA-deficient mice in parallel with FMRP-deficient mice for behavioral deficits relevant to autism (Aim 1), impairments in protein synthesis-dependent synaptic plasticity and memory (Aim 2), and abnormalities in synaptic connectivity (Aim 3). In the latter Aim, we propose a novel use of "Brainbow" mice to visualize the impact of loss of microRNA or FMRP expression on excitatory synaptic connections. Accomplishment of these Aims should offer new insights into microRNA function and autism pathogenesis. The proposed studies are complementary to and closely integrated with my NIMH-funded R01. The detailed career development plan includes key collaborations and acquisition of enhanced multidisciplinary research skills. The salary support provided by the K02 award will be instrumental in allowing me to focus on research and career development activities without excessive clinical responsibilities. PUBLIC HEALTH RELEVANCE: The proposed project has direct relevance to the brain mechanisms responsible for normal cognition and behavior as well as cognitive and behavioral disorders. The molecular pathways to be investigated have been implicated in the pathogenesis of autism and other mental disorders. Accomplishment of the proposed goals will increase our understanding of the molecular and synaptic defects responsible for these disorders, and possibly identify new therapeutic targets or strategies.