TrkB Agonist(s), a Potential Therapy for Autism Spectrum Disorders

描述（由申请人提供）：自闭症是一种复杂的发育障碍，会导致社交和沟通方面的问题。症状通常在三岁之前开始，并可能导致从婴儿期到成年期发展的许多不同技能的延迟或问题。自闭症被认为是自闭症谱系障碍（ASD）的一部分，自闭症谱系障碍是一组具有相似特征的障碍。ASD的诊断是基于语言和非语言沟通技能和社会互动的障碍，以及受限制的，重复的和刻板的行为模式，其影响范围从轻度到严重致残。除了典型的特发性自闭症之外，自闭症还常伴有先天性自闭症、先天性自闭症、Rett综合征（RTT）和其他几种遗传性疾病，包括唐氏综合征、脆性X染色体智力低下。虽然ASD是一种多因素疾病，但据推测兴奋性和抑制性突触传递的不平衡（E/I不平衡）可能是该疾病的核心病理生理学基础。神经连接蛋白1（NRXN 1）、神经连接蛋白3和4（NLGN 3/4）、SHANK 3、PTEN等基因的突变与自闭症有关。此外，在自闭症患者中也发现了脑源性神经营养因子（BDNF）的调节改变。在RTT小鼠模型（即，MeCP 2敲除小鼠（- /y小鼠），BDNF表达显示显著降低，并且通过转基因使BDNF表达升高约2倍，减弱MeCP 2敲除小鼠表型。在本申请中，我们假设BDNF信号传导的激活可能不仅有益于RTT，而且有益于其他ASD。此外，在我们的人胚胎干细胞（ESC）衍生的MeCP 2缺陷的人神经元模型中，我们观察到显著增强的GABA能神经传递，这表明由于MeCP 2缺陷导致的E/I失衡，这表明我们的人RTT模型可能在其他ASD中具有广泛的意义。BDNF重组蛋白在治疗性干预中的应用尚未成功，因为BDNF以高亲和力结合细胞外胆固醇，这阻止了其分布到不同组织。此外，许多TrkB激动剂分子不穿过血脑屏障。最近，我们的合作者，埃默里大学的Keqiang Ye博士团队的工作发现了一些小分子化合物，它们可以有效激活小鼠大脑中的TrkB激活，并在通过腹膜内注射或口服外周应用时引起一系列神经保护作用。我们发现，这些化合物，类似于BDNF，是神经保护，甚至在血清饥饿或氧化应激条件下培养的人类神经元。在本申请中，我们提出进行临床前研究以确定小分子TrkB激动剂是否可用于治疗ASD。我们将利用MeCP 2 null（-/y）小鼠和MeCP 2缺陷型神经元进行包括行为、电生理和基因表达分析的综合分析，以确定TrkB激动剂在ASD中的作用。通过这项研究，我们希望评估我们的TrkB激动剂是否可能用作ASD的治疗干预。 公共卫生相关性：自闭症是一种复杂的发育障碍，会导致社交和沟通方面的问题，它被认为是自闭症谱系障碍（ASD）的一部分，自闭症谱系障碍是一组具有相似特征的障碍。在ASD之一Rett综合征（RTT）中，BDNF表达显示在小鼠模型中显著降低（即，MeCP 2敲除（-/y）小鼠），并且通过转基因使BDNF表达升高约两倍减弱MeCP 2敲除小鼠表型。在本申请中，我们假设通过小分子TrkB激动剂激活BDNF信号传导不仅可以使RTT受益，而且还可以使其他ASD受益。

DESCRIPTION (provided by applicant): Autism is a complex developmental disorder that causes problems with social interaction and communication. Symptoms usually start before age three and can cause delays or problems in many different skills that develop from infancy to adulthood. Autism is considered as part of the autism spectrum disorders (ASDs), a group of disorders with similar features. ASDs are diagnosed based on impairment in verbal and nonverbal communication skills and social interactions, and restricted, repetitive and stereotyped patterns of behavior, which can range in impact from mild to significantly disabling. In addition to the classical idiopathic autism, Asperberg's syndrome, Rett syndrome (RTT) and several other genetic disorders including Down's syndrome, Fragile X mental retardation are frequently associated with autism. Although ASD is a multi-factorial disease, it is postulated that an imbalance of excitatory and inhibitory synaptic transmission (E/I imbalance) may underlie the core pathophysiology of the disorder. Mutations of genes such as neurexin 1 (NRXN1), neuroligin3 and 4 (NLGN3/4), SHANK3, PTEN have been associated with autism. In addition, altered regulation of brain derived neurotrophic factor (BDNF) has also been found in autistic patients. In RTT mouse models (i.e., MeCP2 null (- /y) mouse), BDNF expression is shown to be substantially reduced, and elevation of BDNF expression by about two fold via transgenesis, attenuates the MeCP2 knockout mice phenotype. In this application, we hypothesize that activation of BDNF signaling may benefit not only RTT but also other ASDs. Furthermore, in our human embryonic stem cell (ESC)-derived MeCP2 deficient human neuronal model, we observed dramatically enhanced GABAergic neurotransmission, an indication of E/I imbalance due to MeCP2 deficiency, suggesting that our human RTT model might have broad implications in other ASDs. The application of BDNF recombinant protein in therapeutic intervention has not been successful, because BDNF binds to extracellular cholesterol with high affinity which prevents its distribution to different tissues. Moreover, number of TrkB agonist molecules does not cross blood-brain-barrier. Recently, work by our collaborator, Dr. Keqiang Ye's group at Emory University, uncovered a number of small molecule compounds that can effectively activate TrkB activation in the mouse brain and elicit a series of neuroprotective effects when applied peripherally via intra-peritoneal injection or oral ingestion. We showed that these compounds, similar to BDNF, are neuroprotective even for cultured human neurons in serum-starvation or oxidative stress conditions. In this application, we propose to carry out preclinical studies to determine whether the small molecule TrkB agonist(s) can be used for the treatment of ASDs. We will utilize both MeCP2 null (-/y) mice and MeCP2 deficient neurons to perform a comprehensive analysis comprising of behavioral, electrophysiological and gene expression analyses to determine the effects of TrkB agonists in ASDs. Through this study, we hope to evaluate whether our TrkB agonist(s) could be potentially used as a therapeutic intervention for ASDs. PUBLIC HEALTH RELEVANCE: Autism is a complex developmental disorder that causes problems with social interaction and communication, and it is considered as part of the autism spectrum disorders (ASDs), a group of disorders with similar features. In one of the ASDs, Rett syndrome (RTT), BDNF expression is shown to be substantially reduced in mouse models (i.e., MeCP2 null (-/y) mouse), and elevation of BDNF expression by about two fold via transgenesis attenuates the MeCP2 knockout mice phenotype. In this application, we hypothesize that activation of BDNF signaling through small molecule TrkB agonist(s) may benefit not only RTT but also other ASDs.