Reversible conditional models for Huntington's disease

描述（由申请人提供）：亨廷顿病（HD）是一种显性遗传性疾病，由编码亨廷顿蛋白（Htt）内一段多聚谷氨酰胺（polyQ）的CAG三联体重复扩增引起，亨廷顿蛋白是HD基因的蛋白产物。Htt polyQ延伸的扩展赋予有害的功能获得，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期间的功能障碍可能导致后期发病。或者，在发育过程中起作用的代偿机制可以延迟神经变性和运动/行为症状的发作。我们的总体目标是使用新的可抑制/诱导的敲入小鼠模型HD探索亨廷顿病的进展中的发育表达和补偿的作用，并确定是否有在发展过程中的关键时刻或在不同年龄的成人，当正常htt的表达必须保持。为此，我们正在开发敲入小鼠模型，表达正常（7 Q）或突变（140 Q）版本的小鼠HD基因（Hdh），其启动子内插入乳糖操纵子（LacO）序列。当这些HdhLacO等位基因与编码在小鼠中起作用的细菌乳糖阻遏物（LacIR）的转基因一起表达时，（HdhLacO-3xFLAG-7Q/-; -actin LacIR-tg和HdhLacO-140Q/+;- 肌动蛋白LacIR-tg小鼠），野生型或突变体htt表达可以通过施用或撤回异丙基- D硫代半乳糖苷来开启或关闭（IPTG，乳糖类似物）在小鼠饮用水中的浓度。在目的1中，我们建议通过在HdhLacO-140 Q/+; -actin LacIR-tg小鼠中在受孕时开启突变htt的表达，并在1个月龄时关闭突变htt的表达，来研究发育限制性突变htt表达对成年行为和神经病理表型的影响。同样，我们将在一个月大时开启突变htt表达，以研究补偿在HD发病机制中的作用。在目的2中，我们提出确定在小鼠的生命期间是否存在必须通过在HdhLacO-3xFLAG-7 Q/-; -肌动蛋白LacIR-tg小鼠中在不同年龄关闭正常htt表达来维持正常htt表达的关键时期。此外，为了模拟降低总体Htt表达的治疗功效和安全性（目标3），我们将在一个小鼠模型（HdhLacO-140 Q/LacO-3xFLAG-7 Q; -肌动蛋白LacIR-tg小鼠）中联合收割机两种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体htt表达。 公共卫生相关性：新型亨廷顿病（HD）小鼠模型的开发和应用，可逆转HD基因表达的开启或关闭，使我们能够探索HD发病机制中的发育和代偿机制，并使我们能够评估基于抑制HD基因表达的HD潜在治疗策略的有效性和安全性。

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.