Aberrant neuronal excitability of the cerebellum in mouse models of autism spectrum disorder

摘要 孤独症谱系障碍（ASD）是一种常见的神经发育障碍，其特征是缺乏社交能力， 互动，沟通障碍和重复行为的限制模式。在美国，每88名儿童中就有1名 被诊断患有自闭症，这对家庭以及教育和 医疗保健系统。ASD的病因是难以捉摸的，结合了遗传，表观遗传和环境风险。到 迄今为止，ASD的有效治疗是有限的。为了找到创新的解决方案，重要的是要了解 ASD潜在的细胞和分子机制。虽然ASD涉及许多大脑区域，但新兴的 有证据显示，在早期发育阶段，小脑的异常活动可导致自闭症。 小脑整合了多种感觉输入，并连接到不同的大脑区域，这些区域对 认知和情感。在小脑回路中，浦肯野神经元（PNs）接受兴奋性和抑制性信号， 突触输入并生成唯一输出。虽然兴奋为PN放电提供驱动，但放电率 并且模式由GABA能中间神经元（IN）的前馈抑制决定。为了阐明非- 小脑在ASD中的传统作用，我们采用了两种广泛接受的ASD小鼠模型： 一种类似于ASD最常见的遗传形式，脆性X综合征;另一种是自发突变 与ASD的表面有效性在这两种情况下，我们已经发现，由于过度- 在目标1中，我们确定了异常的细胞内分泌抑制的异质性分子基础。 抑制通路中的神经元兴奋性。即，Kv1.2钾通道的下调增加 INs的兴奋性增强，导致突触前过度抑制。超极化表达减少- 激活的环核苷酸门控（HCN）通道降低了PN的内在兴奋性，进一步损害了PN的功能。 小脑皮层的输出活动通过揭示新的分子靶点， 具有低毒性的试剂以矫正ASD模型的细胞、电路和行为表型。在Aim中 2.我们设计了新的化学发生学方法来选择性地操纵IN和PN的兴奋性， 阐明小脑回路在ASD发病机制中的必要性和充分性， 对小鼠ASD样行为进行基因拯救。除了为临床奠定基础外， ASD的干预，该项目将改变我们的区域研究所的研究景观，并锚定 下一代神经科学家的卓越培训平台。

ABSTRACT Autism spectrum disorder (ASD) is a prevalent neurodevelopmental disorder characterized by defective social interaction, impaired communication and restricted patterns of repetitive behaviors. In US, 1 in 88 children are diagnosed with autism, which presents an ever-growing challenge for the families, as well as education and healthcare systems. The etiology of ASD is elusive, combining genetic, epigenetic and environmental risks. To this date, the effective treatment for ASD is limited. To find innovative solutions, it is important to understand the cellular and molecular mechanisms underlying ASD. Although ASD involves many brain regions, emerging evidence suggests that aberrant activity of the cerebellum in the early developmental stage can lead to autism. The cerebellum integrates multiple sensory inputs and connect to diverse brain areas that are important for cognition and affection. Within the cerebellar circuitry, Purkinje neurons (PNs) receive excitatory and inhibitory synaptic inputs and generate the sole output. Although excitation provides the drive for PN firing, the firing rate and patterns are dictated by feedforward inhibition from GABAergic interneurons (INs). To elucidate the non- conventional role of the cerebellum in ASD, we have employed two widely accepted mouse models for ASD: one mimics the most common genetic form of ASD, Fragile X syndrome; and the other is a spontaneous mutation with face validity to ASD. In both cases, we have revealed a significant reduction in the PN activity due to over- inhibition from upstream INs. In Aim 1, we identify heterogeneous molecular underpinnings of the abnormal neuronal excitability in the inhibitory pathway. Namely, downregulation of Kv1.2 potassium channels increases the excitability of INs, resulting in the presynaptic over-inhibition. Decreased expression of hyperpolarization- activated cyclic nucleotide-gated (HCN) channels lowers the intrinsic excitability of PNs, further impairing the output activity from the cerebellar cortex. By revealing the new molecular targets, we develop pharmacological reagents with low toxicity to rectify the cellular, circuitry and behavioral phenotypes of the ASD models. In Aim 2, we design novel chemogenetic approaches to selectively manipulate the excitability of INs and PNs to elucidate the necessity and sufficiency of the cerebellar circuits in mediating the pathogenesis of ASD and instigate genetic rescues for the mouse ASD-like behaviors. In addition to setting foundation for clinical intervention of ASD, this project will transform the research landscape in our regional institute and anchors an exceptional training platform for next generations of neuroscientists.