Understanding the mechanisms that modulate the effects of mutant Huntingtin lowering in aging Huntington's disease model mice

亨廷顿病(HD)是一种常染色体显性遗传性神经退行性疾病，由 编码一段聚谷氨酰胺(PolyQ)的CAG三联体重复序列在Huntingtin(HTT)中的扩展， HD基因的蛋白质产物。HD突变导致有害的功能获得，可能是通过 毒性RNA转录本和蛋白的表达，以及正常HTT功能的潜在丧失 影响多种细胞功能。正在制定一些降低HTT的策略--第三阶段 检测针对HTT总表达或靶向的反义寡核苷酸(ASO)有效性的临床试验 选择性突变HTT(MHTT)的表达正在进行中，同时使用其他方法(MiRNA)降低Htt 和剪接调制器)目前正在进行安全性/耐受性试验，或将很快开始这种试验。许多人 然而，最初的临床前研究并没有检查老年模型中Htt降低的长期影响。vbl.使用 一种mHTT或总Htt表达受Lac调控的可调控HD小鼠模型 操作员/抑制系统，我们发现全球症状前~50%的Htt下降(开始于3个月前 Htt基因突变或总表达在改善HD小鼠模型中更有利 表型与后来的下降(从6个月或更晚开始)相比，没有 与等位基因特异性相比，降低总Htt表达会产生明显的有害后果 降低mHTT的表达。然而，我们观察到，在老年小鼠中，早期Htt的有益效果 一些HD模型表型的降低有所减弱，但并不是全部。我们假设：(1)大脑区域 对mHTT降低的量和/或时间的反应不同，衰老可能会加剧这种影响，并且 (2)可能需要将mHTT的表达减少50%，以维持细胞和生理的动态平衡 效率随着年龄的增长而下降的功能。来检验这些假说，并提供更好的理解 关于降低mHTT表达如何影响老年小鼠的体内平衡功能，我们提出了三个目标。In(目标) 1)，我们将使用不同的Lac-1菌株来表征全局降低mHTT表达~75%的效果。 可调节的HD小鼠模型，以确定mHTT降低的益处是否可以延长到12个月以上 所有HD小鼠模型表型的年龄。以确定DNA损伤反应和 神经炎症是两种重要的稳态功能，随着年龄的增长而下降，它可以调节mHTT的效果。 在老年小鼠中，我们建议描述(目标2)中的DNA损伤反应，而在(目标3)中，我们 建议表征炎性小体的激活情况并测量脑膜淋巴功能。 MHTT-降低小鼠和对照组。总而言之，这些目标应该为mHTT的程度提供新的见解 降低影响衰老小鼠HD发病机制所需的水平。此外，确定两个与年龄相关的人 与mHTT表达水平和/或HD模型表型相关的通路可能提供新的潜力 HD的治疗靶点有待探索。

Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder 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 HD mutation confers a deleterious gain-of-function, possibly via the expression of both toxic RNA transcripts and protein, together with potential loss of normal HTT function that affects a variety of cellular functions. A number of HTT lowering strategies are being developed–Phase III clinical trials testing the efficacy of anti-sense oligonucleotides (ASOs) targeting either total HTT expression or selectively mutant HTT (mHTT) expression are underway, while Htt lowering using other approaches (miRNA and splicing modulators) are currently in safety/tolerability trials or will begin such trials shortly. Many of the initial preclinical studies, however, did not examine the long-term effects of Htt lowering in aged models. Using a regulatable HD mouse model whose mHtt expression or total Htt expression are controlled via a Lac operator/repressor system, we found that global pre-symptomatic ~50% Htt lowering (starting prior to 3 months of age) of either mutant or total Htt expression was more beneficial in ameliorating HD mouse model phenotypes in comparison to later lowering (starting at 6 months of age or later), and that there were no obvious detrimental consequences from lowering total Htt expression in comparison to the allele-specific lowering of mHtt expression. However, we observed that in older mice, the beneficial effects of earlier Htt lowering were attenuated for some, but not all HD model phenotypes. We hypothesize that: (1) brain regions respond differentially to the amount and/or timing of mHtt lowering, and aging may exacerbate this effect, and (2) >50% reduction of mHtt expression may be needed to maintain homeostatic cellular and physiological functions whose efficiency declines with age. To test these hypotheses, and to provide a better understanding of how lowering mHtt expression affects homeostatic functions in older mice, we propose three aims. In (Aim 1), we will characterize the effects of globally lowering mHtt expression by ~75% using a different strain of Lac- regulatable HD mouse model to determine if the benefits of mHtt lowering can be extended beyond 12 months of age for all HD mouse model phenotypes. To determine if the DNA damage response and neuroimmflamation, two critical homeostatic functions that decline with age, can modulate the effect of mHtt lowering in older mice, we propose to characterize the DNA damage response in (Aim 2), while in (Aim 3), we propose to characterize activation of the inflammasome and measure meningeal lymphatic function in our mHtt-lowered mice and controls. Together, these aims should provide new insight into the degree of mHtt lowering that is needed to impact HD pathogenesis in aging mice. In addition, determining if two age-related pathways correlate with mHtt expression levels and/or HD model phenotypes could provide new potential therapeutic targets to be explored for the treatment of HD.