Regulation of BDNF and TrkB Isoforms, their Signaling and Synaptic Modulation

脑源性神经营养因子(BDNF)及其受体(TrkB)在神经元和突触的发育和突触连接的调节中起着关键作用。BDNF表达或TrkB信号的变化深刻地影响突触的发育和可塑性。此外，偏离BDNF和TrkB亚型的最佳水平可能会对大脑功能造成严重后果，因为这可能会改变突触/神经元功能。BDNF已被广泛研究，但对其异构体的调节和生物活性知之甚少。同样，对TrkB亚型的调控也不是很清楚。我整个研究计划的长期目标是了解神经营养因子(NGF和BDNF)及其异构体和受体在转录、翻译后和运输水平上的表达和活性是如何调节的，以促进我们对突触发育、可塑性和功能的基本机制的了解。在这项发现拨款的五年中，我将研究调节BDNF和TrkB异构体表达的机制，以及这些异构体如何影响信号和突触。BDNF和TrkB分别以三种不同的生物活性亚型存在。这些异构体的相对水平在转录后受到调节。然而，其机制尚不清楚。我们建议研究特定的miRNAs和RNA结合蛋白在调节TrkB全长异构体(TrkB-FL)中的作用，以及特定的蛋白酶在调节BDNF异构体中的作用。此外，我们还将研究干扰这些调节因子对培养神经元中BDNF/TrkB信号以及脊髓密度和形态的影响。最后，我们将研究截短的BDNF亚型，其受体结合、信号转导和生物活性尚未确定。我们的短期目标是：1)通过检测TrkB RNA结合因子(蛋白质、miRNA)及其对信号转导和脊柱测量的影响来探讨TrkB-FL的调节；2)研究特定蛋白酶对BDNF异构体的调节以及对信号转导和脊柱测量的影响；以及3)确定截短的BDNF异构体的生物学活性。意义：我的研究计划解决了我们对BDNF生物学理解上的严重差距。神经营养因子的生物合成和功能以及它们如何信号在许多水平上受到调节，其中一些尚未被研究。了解proBDNF的蛋白降解过程、TrkB-FL水平的转录后调节、神经营养素异构体的生物学作用和活性、它们的信号特性以及它们对神经元和突触的影响，对于我们了解突触和脑的发育、调节和功能是至关重要的。这项研究的结果将导致对日常大脑功能，如学习和记忆及其在精神、神经发育和神经退行性疾病中的失调的新的科学和医学理解。

Brain-derived neurotrophic factor (BDNF) and its receptor (TrkB) play a key role in neuronal and synaptic development and regulation of synaptic connectivity. Changes in BDNF expression or TrkB signalling profoundly impact synaptic development and plasticity. Moreover, deviations from optimal levels of BDNF and TrkB isoforms have severe consequences for brain function, as this can alter synaptic/neuronal function. BDNF is well studied, but less is known about the regulation and biological activity of its isoforms. Similarly, the regulation of TrkB isoforms is not well understood. The long-term goal of my overall research program is to understand how expression and activity of neurotrophins (NGF and BDNF) and their isoforms and receptors are regulated at the transcriptional, post-translational and trafficking levels, to advance our knowledge of basic mechanisms of synapse development, plasticity and function. During the five years of this Discovery Grant, I will study the mechanisms that regulate BDNF and TrkB isoform expression, and how those isoforms impact signaling and synapses. BDNF and TrkB are each found in three isoforms with differing biological activities. Relative levels of these isoforms are regulated post-transcriptionally. However, the mechanisms are unclear. We propose to investigate the role of specific miRNAs and RNA binding proteins in the regulation of the full-length isoform of TrkB (TrkB-FL) and the role of specific proteases in the regulation of BDNF isoforms. Furthermore, we will study the effects of perturbing these regulatory factors on BDNF/TrkB signaling and spine density and morphology in cultured neurons. Lastly, we will study the truncated BDNF isoform, whose receptor binding, signaling and biological activity are uncharacterized. Our Short-Term Objectives are: 1) To explore TrkB-FL regulation by examining TrkB RNA binding factors (protein, miRNA) and their effects on signal transduction and spine measures; 2) To study the regulation of BDNF isoforms by specific proteases and the effects on signal transduction and spine measures; and 3) To determine the biological activity of the truncated BDNF isoform. Significance: My program of research addresses critical gaps in our understanding of BDNF biology. The biosynthesis and function of neurotrophins and how they signal are regulated at many levels, some of which have not been investigated. Understanding the regulation of proteolytic processing of proBDNF, the post-transcriptional regulation of TrkB-FL levels, the biological roles and activities of neurotrophin isoforms, their signalling properties and their effects on neurons and synapses, is critical to our fundamental knowledge of synapse and brain development, regulation and function. The results of this study will lead to new scientific and medical understanding of everyday brain functions such as learning and memory and its dysregulation in psychiatric, neurodevelopmental and neurodegenerative diseases.