Reversible conditional models for Huntington's disease

描述（由申请人提供）：亨廷顿舞蹈病（HD）是一种显性遗传性疾病，由亨廷顿舞蹈病基因的蛋白产物亨廷顿舞蹈病蛋白（Htt）中编码一段聚谷氨酰胺（polyQ）的CAG三重重复扩增引起。Htt polyQ拉伸的扩张会带来有害的功能获得，而同时正常Htt功能的丧失也可能导致发病。在HD和其他成人发病的神经退行性疾病中，越来越多的证据表明发育过程中的功能障碍可能导致后来的发病机制。或者，在发育过程中起作用的代偿机制可以延缓神经变性和运动/行为症状的发生。我们的总体目标是使用新的抑制/诱导敲入HD小鼠模型来探索发育表达和代偿在亨廷顿病进展中的作用，并确定在发育期间或成人不同年龄是否存在必须维持正常htt表达的关键时期。为此，我们正在开发敲入小鼠模型，表达正常（7Q）或突变（140Q）版本的小鼠HD基因（Hdh），在其启动子中插入乳糖操作符（LacO）序列。当这些HdhLacO等位基因与编码细菌乳糖抑制因子（LacIR）的转基因基因一起表达时（分别为HdhLacO- 3xflag - 7q /- -actin LacIR-tg和HdhLacO- 140q /+； -actin LacIR-tg小鼠），野生型或突变型的htt表达可以通过在小鼠饮用水中添加或提取异丙基- D硫代半乳糖苷（IPTG，一种乳糖类似物）来开启或关闭。在第1项研究中，我们提出在HdhLacO-140Q/+中，通过在受孕时开启突变体htt的表达，并在1月龄时关闭突变体htt的表达，来研究发育受限突变体htt表达对成人行为和神经病理表型的影响；-actin LacIR-tg小鼠。同样，我们将在1月龄时开启突变体htt表达，以研究代偿在HD发病机制中的作用。在Aim 2中，我们建议通过关闭HdhLacO-3xFLAG-7Q/-中不同年龄的正常htt表达来确定小鼠生命中是否存在必须维持正常htt表达的关键时期；-actin LacIR-tg小鼠。此外，为了模拟降低整体Htt表达的治疗效果和安全性（Aim 3），我们将在一个小鼠模型（HdhLacO-140Q/LacO-3xFLAG-7Q； -actin LacIR-tg小鼠）中结合两个laco修饰的Hdh等位基因，并在6个月或1岁时抑制正常和突变的Htt表达。

DESCRIPTION (provided by applicant): Huntington's disease (HD) is a dominant hereditary disease that is caused by the expansion of a CAG triplet repeat encoding a stretch of polyglutamine (polyQ) within Huntingtin (Htt), the protein product of the HD gene. The expansion of the Htt polyQ stretch confers a deleterious gain-of-function while simultaneous loss of normal Htt function can also contribute to pathogenesis. In HD and other adult onset neurodegenerative diseases, evidence is accumulating suggesting that dysfunction during development can contribute to later pathogenesis. Alternatively, compensatory mechanisms acting during development can delay the onset of neurodegeneration and motor/behavioral symptoms. Our overall objective is to use novel repressible/inducible knockin mouse models for HD to explore the role of developmental expression and compensation in the progression of Huntington's disease, and to determine if there are critical times during development or at different ages in the adult, when normal htt expression must be maintained. To this end, we are developing knockin mouse models that express either normal (7Q) or mutant (140Q) versions of the mouse HD gene (Hdh) that have lactose operator (LacO) sequences inserted within their promoters. When these HdhLacO alleles are expressed together with a transgene encoding a version of the bacterial lactose repressor (LacIR) that functions in mice (HdhLacO-3xFLAG-7Q/-; -actin LacIR-tg and HdhLacO-140Q/+; -actin LacIR-tg mice, respectively), wild-type or mutant htt expression can be turned-on or turned-off by administering or withdrawing isopropyl - D thiogalactoside (IPTG, a lactose analog) in the mouse's drinking water. In Aim 1, we propose to study the consequences of developmentally-restricted mutant htt expression on adult behavioral and neuropathological phenotypes by turning-on the expression of mutant htt at conception, and turning-off mutant htt expression at 1 month of age in HdhLacO-140Q/+; -actin LacIR-tg mice. Similarly, we will turn-on mutant htt expression at one month of age to study the role of compensation in HD pathogenesis. In Aim 2, we propose to determine if there are critical periods during the life of the mouse when normal htt expression must be maintained by turning-off normal htt expression at different ages in HdhLacO-3xFLAG-7Q/-; -actin LacIR-tg mice. Moreover, to model the therapeutic efficacy and safety of reducing overall Htt expression (Aim 3), we will combine both LacO-modified Hdh alleles in one mouse model (HdhLacO-140Q/LacO-3xFLAG-7Q; -actin LacIR-tg mice), and suppress both normal and mutant htt expression at 6 months or 1 year of age. PUBLIC HEALTH RELEVANCE: The development and application of new mouse models for Huntington's disease (HD) that can reversible turn-on or turn-off mutant and normal HD gene expression will enable us to explore developmental and compensatory mechanisms in HD pathogenesis, and will allow us to evaluate the efficacy and safety of potential therapeutic strategies for HD that are based on suppressing HD gene expression.