Pathophysiology of Transgenic Mouse Models of Huntington's Disease

描述(申请人提供)：亨廷顿病(HD)的致命突变导致亨廷顿蛋白内谷氨酰胺重复序列的扩大，导致神经元功能障碍，通常伴随着选择性神经变性，特别是在纹状体和皮质内。这些神经元和回路的功能障碍发生在疾病表型的发展过程中，远在细胞显著丧失之前。本应用中的实验旨在了解在HD表型进展过程中特定神经元群体中发生的功能变化，并发现新的治疗靶点和方法。我们的工作假设是，导致HD病理的最明显的细胞功能障碍是细胞-自主变化和细胞-细胞相互作用的组合。这种两次打击的假说表明，仅细胞内基因的突变可能不足以导致显著的功能障碍；必须发生其他变化才能导致疾病症状，其中一些包括细胞间突触相互作用的改变。之前，我们研究了纹状体、皮质和皮质纹状体相互作用的变化，因为皮质输入是纹状体的两个主要兴奋性输入之一。然而，在HD表型中，丘脑对纹状体的兴奋性输入可能与皮质输入一样重要。目前尚不清楚丘脑纹状体通路和皮质纹状体通路对纹状体神经元的改变是否有相同或不同的影响。目的1将利用光遗传学来特异性地和单独地激活纹状体谷氨酸能输入到已识别的纹状体神经元亚群，并确定它们对细胞变化的相对贡献。直接和间接纹状体输出通路的中等大小的棘神经元也随着HD表型的进展而显示出独特的、选择性的和复杂的变化。这将影响它们在苍白球和黑质的靶点。据我们所知，HD的纹状体输出还没有任何详细的研究，特别是在小鼠模型中，但它们非常重要，因为它们决定了基底节如何影响丘脑和皮质。目标2将专门检查纹状体输出靶结构的变化，而目标3将以不同的方式操纵纹状体输出途径，以试图对抗随着疾病进展直接和间接途径的不平衡。我们的研究使用最先进的光遗传学技术来特异性地激活或抑制神经元亚类，以及使用遗传技术来移除亚类神经元中突变的Huntingtin基因的表达。总之，这些研究将通过在空间和时间上描绘更多的限制性靶点，为HD的新的和合理的治疗提供基础，并将对了解其他CAG三联体重复疾病和神经退行性疾病具有重要意义。

DESCRIPTION (provided by applicant): The fatal mutation in Huntington's disease (HD) leads to an expanded glutamine repeat within the huntingtin protein which causes neuronal dysfunction typically followed by selective neurodegeneration especially within the striatum and cortex. These dysfunctions in neurons and circuits occur during the development of the disease phenotype, well before there is significant cell loss. The experiments in this application are designed to understand the functional changes that occur in specific populations of neurons during the progression of the HD phenotype and to uncover new targets and approaches for therapies. Our working hypothesis is that the most conspicuous cellular dysfunctions leading to pathology in HD result from a combination of cell- autonomous changes and cell-cell interactions. This two-hit hypothesis implies that mutation of the gene in the cell alone may not be sufficient to cause significant dysfunction; other changes have to occur to cause symptoms of the disease, and some of these include altered intercellular synaptic interactions. Previously, we examined changes in the striatum, the cortex and corticostriatal interactions, as the cortical input is one of the two major excitatory inputs to the striatum. However, the excitatory thalamic input to the striatum may be as important as the cortical input in the HD phenotype. It is presently unclear if both thalamostriatal and corticostriatal pathways contribute equally or differentially to alterations in striatal neurons. Aim 1 will use optogenetics to specifically and separately activate striatal glutamatergic inputs to identified subpopulations of striatal neurons and determine their relative contribution to cellular alterations. Medium-sized spiny neurons of the direct and indirect striatal output pathways also display unique, selective and complex alterations as the HD phenotype progresses. These will affect their targets in globus pallidus and substantia nigra. To our knowledge, striatal outputs in HD have not been studied in any detail, especially in mouse models, yet they are extremely important because they determine how the basal ganglia influence the thalamus and cortex. Aim 2 will specifically examine alterations in striatal output target structures while Aim 3 will manipulate striatal output pathwas differentially in an attempt to counter the imbalance of direct and indirect pathways as the disease progresses. Our studies use state-of-the-art optogenetic techniques to specifically activate or inhibit subclasses of neurons as well as genetic techniques to remove expression of the mutant huntingtin gene in subclasses of neurons. Together, the studies will provide the basis for novel and rational treatments for HD by delineating more restricted targets spatially and temporally and will be relevant for understanding other CAG triplet repeat diseases and neurodegenerative disorders.