Activity-dependent translation and release of BDNF

描述（由申请人提供）：脑源性神经营养因子（BDNF）是神经营养因子家族的一员，在神经元存活、分化、回路形成/重建和突触可塑性中起重要作用。BDNF功能的缺陷与精神疾病、抑郁症和学习记忆缺陷有关。BDNF对神经元回路的作用是回路和突触选择性作用，暗示BDNF蛋白的局部表达/释放的潜在参与。主要的BDNF转录物在两个可选择的多聚腺苷酸化位点加工，产生两个BDNF mRNA库，其具有0.35 kb和2.85 kb的短和长3 'UTR，但编码相同的BDNF蛋白。长的3 'UTR包含额外的不同序列实体，其提供BDNF的特异性转录后调节。携带短3 'UTR的BDNF mRNA局限于细胞体中，而携带长3' UTR的BDNF mRNA存在于树突状区域中。重要的是，长的3 'UTR负责BDNF mRNA的树突靶向，这是由神经元活性增强。此外，长的3 'UTR被发现在静息神经元中抑制BDNF翻译，但在树突中经历活性依赖性BDNF翻译。BDNF长3 'UTR的缺失导致树突棘发育和可塑性的缺陷，表明BDNF通过长转录本在树突表达中的重要作用。我们假设长3 'UTR BDNF mRNA可能介导BDNF在选择性树突区域的翻译，以响应局部突触活动，导致时空限制的BDNF释放突触特异性修饰突触。这项研究将评估这一令人兴奋的假设，并解决有关长3 'UTR转录产生的BDNF的几个关键问题。最重要的是BDNF蛋白是否是通过突触活动从长3 'UTR转录本局部产生的，包装成囊泡，并从刺激的突触释放。同样重要的是要知道从短和长转录本翻译的BDNF蛋白是否在它们的分布、运输和释放方面对局部突触活动有不同的表现。进一步的活细胞成像将解决三个具体问题：（1）长3 'UTR BDNF转录本是否介导BDNF的活性依赖性定位翻译;（2）由长3' UTR转录本合成的BDNF蛋白是否包装在囊泡中，并定位于突触活动的位点;（3）从长3 'UTR转录本合成的BDNF蛋白是否真的可以响应突触活动而释放。这些问题的答案将提供一个新的机制有关BDNF的生产，运输和分泌，可能在突触修饰中发挥重要作用的支持。这项研究的结果可能对我们理解正常和疾病大脑中BDNF功能的分子和细胞机制产生重大影响。 公共卫生相关性：脑源性神经营养因子（BDNF）在脑发育和功能中起着至关重要的作用，但它是由两个含有短和长3 'UTR的BDNF mRNA库产生的。本研究将评估长3 'UTR BDNF mRNA是否介导BDNF的局部翻译和释放用于突触修饰。这项研究的结果可能会对我们理解正常和疾病大脑中的BDNF功能产生重大影响，从而与公共卫生直接相关。

DESCRIPTION (provided by applicant): Brain derived neurotrophic factor (BDNF), a member of the neurotrophin family, plays fundamental roles in neuronal survival, differentiation, circuitr formation/reconstruction, and synaptic plasticity. Deficiency in BDNF functions has been implicated in psychiatric disorders, depression, and learning-memory deficits. BDNF actions on neuronal circuitry are circuitry- and synapse-selective actions, implicating a potential involvement of localized expression/release of BDNF proteins. The primary BDNF transcript is processed at two alternative polyadenylation sites, giving rise to two pools of BDNF mRNAs harboring a short and a long 3'UTR of 0.35 kb and 2.85 kb but encoding the same BDNF protein. The long 3'UTR contains additional distinct sequence entities, which offer specific posttranscriptional regulation of BDNF. BDNF mRNA bearing the short 3'UTR is restricted in the cell body whereas that bearing long 3'UTR is present in the dendritic region. Importantly, the long 3'UTR is responsible for dendritic targeting of BDNF mRNA, which is enhanced by neuronal activity. Furthermore, the long 3'UTR was found to repress BDNF translation in resting neurons but undergoes activity-dependent BDNF translation in dendrites. Loss of the BDNF long 3'UTR results in defects in dendritic spine development and plasticity, indicating an important role for dendritic expression of BDNF through the long transcripts. We hypothesize that the long 3'UTR BDNF mRNA may mediate translation of BDNF in selective dendritic regions in response to local synaptic activities, leading to spatiotemporally restricted BDNF release for synapse-specific modification of synapses. This proposed study will evaluate this exciting hypothesis and address several crucial issues concerning BDNF generated from the long 3'UTR transcripts. Of most importance is whether BDNF protein is locally produced from long 3'UTR transcripts by synaptic activity, packed into vesicles, and released from stimulated synapses. It is also important to know if BDNF proteins translated from the short and long transcripts behave differentially in terms of their distribution, trafficking, and release in respose to local synaptic activity. Advanced live cell imaging will be performed to address three specific questions: (1) whether the long 3'UTR BDNF transcripts mediate activity-dependent localized translation of BDNF; (2) whether BDNF proteins synthesized from the long 3'UTR transcripts are packed in vesicles, and can localize to the site of synaptic activities; (3) whether BDNF proteins synthesized from the long 3'UTR transcripts can actually be released in response to synaptic activities. Answers to these questions will provide the support to a novel mechanism concerning BDNF production, trafficking, and secretion that may play an important role in synaptic modifications. Results from this study could have a major impact on our understanding of the molecular and cellular mechanisms underlying BDNF functions in normal and disease brains. PUBLIC HEALTH RELEVANCE: Brain derived neurotrophic factor (BDNF) plays a crucial role in brain development and functions but is produced from two pools of BDNF mRNAs harboring a short and a long 3'UTR. This study will evaluate if the long 3'UTR BDNF mRNA mediate local translation and release of BDNF for synaptic modification. Results from this study could have a major impact on our understanding of BDNF functions in normal and disease brains, thus having direct relevance to public health.