Using Drosophila to Characterize the Molecular Pathogenesis of Autism

描述(由申请人提供)：定义自闭症和自闭症谱系障碍(ASD)中功能失调的分子通路是了解其发病机制和开发未来治疗方法的关键。在阿尔茨海默病和帕金森病中，在5%-10%的遗传病例中对单基因突变的鉴定揭示了核心分子通路的改变，包括在更大类别的散发性病例中。一个关键的问题是，根据最近发现的定义突变和从头开始的基因组拷贝数变异，是否会出现类似的自闭症分子通路(S)，这些突变和从头基因组拷贝数变异占自闭症的10%-20%。在这里，我们建议利用在果蝇中可用的遗传操作来探索与自闭症相关的内体蛋白NHE9(Na+/H+交换器9)将神经元活动的改变与突触连接的改变相结合的机制。NHE9是几个新发现的遗传联系之一，表明异常的内体运输和突触生长可能易患自闭症。我实验室的工作最近描述了果蝇的突触生长和可塑性途径，突触后靶点以依赖活动的方式释放逆行信号，触发突触成熟和生长。这些生长信号通过突触前内体通路的运输来处理和调节。我们假设，NHE9的突变通过破坏内体的pH改变了内体的形成，或内体隔间的配体-受体结合，导致突触生长信号异常和脑连接中的活性依赖缺陷，这可能导致自闭症行为。内涵体表现出从早期(pH~6.5)到溶酶体(pH~4.5)的渐进式酸化，这是内化的配体-受体复合体和细胞黏附蛋白降解和循环所必需的。与液泡V-ATPase一起，NHE9被预测为内体pH的关键分子决定因素，因为它允许早期信号内体通过将H+离子输送出这个隔室而保持相对基本的状态，在这个隔室中，配体-受体对可以保持连接并传递突触生长信号。我们将确定NHE9突变体中是否存在内体转运缺陷，以及NHE9的活性是否可能与其他ASD突变体有关，这些突变体包括突触细胞黏附蛋白，如Neuresin和Neuroluin。新接触部位的产生可能需要通过内体系统移除或回收表面神经毒素和神经连接蛋白，这一过程可能需要NHE9。将这些看似无关的蛋白质中的共同突触缺陷联系起来，可能会揭示一条保守的分子途径，这条途径在自闭症中是功能失调的。

DESCRIPTION (provided by applicant): Defining molecular pathways that are dysfunctional in autism and autistic spectrum disorders (ASDs) is key to understanding their pathogenesis and developing future therapeutics. In Alzheimer's and Parkinson's Disease, identification of single gene mutations in the 5-10% of genetic cases have revealed core molecular pathways that are altered, including in the larger category of sporadic cases. A key question is whether a similar molecular pathway(s) will emerge for autism based on the recent identification of defined mutations and de novo genome copy number variations that account for 10-20% of ASDs. Here, we propose to take advantage of genetic manipulations available in Drosophila to explore the mechanisms by which the autism-associated endosomal protein, NHE9 (Na+/H+ exchanger 9), couples alterations in neuronal activity to modifications of synaptic connectivity. NHE9 is one of several newly identified genetic links that indicate abnormal endosomal trafficking and synaptic growth may predispose to autism. Work from my lab has recently characterized a synaptic growth and plasticity pathway in Drosophila where postsynaptic targets release retrograde signals in an activity-dependent manner, triggering synaptic maturation and growth. These growth signals are processed and regulated through trafficking in the presynaptic endosomal pathway. We hypothesize that mutations in NHE9 alter endosomal formation, or ligand-receptor association in endosomal compartments, through disruption of endosomal pH, leading to abnormal synaptic growth signaling and activity-dependent defects in brain wiring that might contribute to autistic behavior. Endosomes exhibit a progressive acidification from early endosomes (pH ~6.5) to lysosomes (pH ~4.5) that is essential for degradation and recycling of internalized ligand-receptor complexes and cell adhesion proteins. Together with the vacuolar V-ATPase, NHE9 is predicted to be the key molecular determinant of endosomal pH by allowing early signaling endosomes to remain relatively basic by transporting H+ ions out of this compartment, where ligand-receptor pairs can remain attached and transmit synaptic growth signals. We will determine if endosomal trafficking defects are present in NHE9 mutants, and whether NHE9 activity may be linked to other ASD mutants that include synaptic cell adhesion proteins like Neurexin and Neuroligin. The generation of new contact sites is likely to require removal or recycling of surface Neurexin and Neuroligin through the endosomal system, a process that may require NHE9. Linking a common synaptic defect in these seemingly unrelated proteins may reveal a conserved molecular pathway that is dysfunctional in autism.