Reversible conditional models for Huntington's disease

描述(申请人提供)：亨廷顿病(HD)是一种显性遗传性疾病，由HD基因的蛋白质产物亨廷顿(Htt)内编码一段聚谷氨酰胺(PolyQ)的CAG三联体重复序列扩张引起。Htt PolyQ伸展的扩张带来了有害的功能获得，同时正常Htt功能的丧失也可能导致发病。在HD和其他成人起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有助于后来的发病。或者，在发育过程中起作用的代偿机制可以延缓神经退化和运动/行为症状的发生。我们的总体目标是使用新的可抑制/可诱导的敲击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，并确定在发育过程中或在不同年龄是否存在必须维持正常HTT表达的关键时期。为此，我们正在开发敲门小鼠模型，该模型表达正常(7Q)或突变(140Q)的小鼠HD基因(HDH)，其启动子中插入了乳糖操纵子(LACO)序列。当这些HdhLacO等位基因与编码一种细菌乳糖抑制因子(LacIR)的转基因一起表达时，该转基因在小鼠(分别为HdhLacO-3xFLAG-7Q/-；-actin Lacir-TG和HdhLacO-140Q/+；-actin Lacir-TG小鼠)中发挥作用，可以通过在小鼠的饮用水中加入或停止使用异丙基-D硫代半乳糖苷(IPTG，一种乳糖类似物)来开启或关闭野生型或突变型HTT的表达。在目标1中，我们建议在HdhLacO-140Q/+；-actin Lacir-TG小鼠中，通过在受孕时开启突变HTT的表达，并在1月龄时关闭突变HTT的表达，来研究发育受限突变HTT表达对成年行为和神经病理表型的影响。同样，我们将在一个月龄时开启突变型HTT的表达，以研究代偿在HD发病中的作用。在目标2中，我们建议确定在小鼠的生命中是否存在关键时期，此时必须通过关闭HdhLacO-3xFLAG-7Q/-；-actin Lacir-TG小鼠不同年龄的正常hTt表达来维持正常hTt表达。此外，为了模拟降低Htt总体表达的疗效和安全性(目标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。 公共卫生相关性：新的亨廷顿病小鼠模型的开发和应用可以可逆地开启或关闭突变和正常的HD基因表达，将使我们能够探索HD发病机制中的发育和代偿机制，并将使我们能够评估基于抑制HD基因表达的潜在HD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.