Activity-dependent translation and release of BDNF

描述(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成员，在神经元的存活、分化、回路形成/重建和突触可塑性中发挥基础作用。脑源性神经营养因子功能缺陷与精神障碍、抑郁症和学习记忆障碍有关。BDNF对神经元回路的作用是回路和突触的选择性作用，暗示BDNF蛋白的局部表达/释放可能参与其中。BDNF的初级转录本在两个不同的聚腺苷酸化位点被加工，产生两个BDNF mRNAs池，含有0.35kb和2.85kb的短和长3‘非编码区，但编码相同的BDNF蛋白。长3‘非编码区含有额外的不同序列实体，为BDNF提供了特异的转录后调控。携带短3‘非编码区的BDNF mRNA仅局限于细胞体，而携带长3’非编码区的BDNF mRNA仅存在于树突区。重要的是，长3‘非编码区负责树突状靶向BDNF mRNA，这是由神经元活动增强的。此外，长3‘非编码区抑制了静息神经元中BDNF的翻译，但在树突中经历了活性依赖性的BDNF翻译。BDNF长3‘非编码区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状表达中发挥重要作用。我们推测，长3‘非编码区BDNF mRNA可能介导BDNF在选择性树突区的翻译，以响应局部突触活动，导致突触特异性突触修饰的时空受限的BDNF释放。这项拟议的研究将评估这一令人兴奋的假设，并解决几个关于BDNF的关键问题，这些问题是由长的3‘UTR转录本产生的。最重要的是BDNF蛋白是否通过突触活动从长3‘非编码区转录产物中局部产生，包装成小泡，并从刺激的突触中释放。同样重要的是要知道，从短转录本和长转录本翻译过来的BDNF蛋白在分布、运输和释放方面是否表现不同，以响应局部突触活动。将利用先进的活细胞成像技术解决三个具体问题：(1)长3‘UTR BDNF转录产物是否介导了活性依赖的局部翻译BDNF；(2)从长3’UTR转录产物合成的BDNF蛋白质是否被包装在小泡中，并能定位到突触活动的部位；(3)从长3‘UTR转录产物合成的BDNF蛋白质是否真的能响应突触活动而释放。这些问题的解答将为有关BDNF的产生、运输和分泌的新机制提供支持，该机制可能在突触修饰中发挥重要作用。这项研究的结果可能会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)在大脑发育和功能中起着至关重要的作用，但它是由两个含有一个短的和一个长的3‘非编码区的BDNF mRNA池产生的。本研究将探讨长3‘端非编码区脑源性神经营养因子基因是否在局部翻译和释放脑源性神经营养因子以进行突触修饰。这项研究的结果可能会对我们理解BDNF在正常和疾病大脑中的功能产生重大影响，从而与公共健康直接相关。

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.