The expanded CAG repeat in the huntingtin gene as target for therapeutic RNA modulation throughout the HD mouse brain

The aim of these studies was to demonstrate the therapeutic capacity of an antisense oligonucleotide with the sequence (CUG)7 targeting the expanded CAG repeat in huntingtin (HTT) mRNA in vivo in the R6/2 N-terminal fragment and Q175 knock-in Huntington’s disease (HD) mouse models. In a first study, R6/2 mice received six weekly intracerebroventricular infusions with a low and high dose of (CUG)7 and were sacrificed 2 weeks later. A 15–60% reduction of both soluble and aggregated mutant HTT protein was observed in striatum, hippocampus and cortex of (CUG)7-treated mice. This correction at the molecular level resulted in an improvement of performance in multiple motor tasks, increased whole brain and cortical volume, reduced levels of the gliosis marker myo-inositol, increased levels of the neuronal integrity marker N-aceyl aspartate and increased mRNA levels of the striatal marker Darpp-32. These neuroanatomical and neurochemical changes, together with the improved motor performance, suggest that treatment with (CUG)7 ameliorates basal ganglia dysfunction. The HTT-lowering was confirmed by an independent study in Q175 mice using a similar (CUG)7 AON dosing regimen, further demonstrating a lasting reduction of mutant HTT protein in striatum, hippocampus and cortex for up to 18 weeks post last infusion along with an increase in motor activity. Based on these encouraging results, (CUG)7 may thus offer an interesting alternative HTT-lowering strategy for HD.本研究旨在验证序列为(CUG)7的反义寡核苷酸（antisense oligonucleotide）在体内靶向R6/2 N端片段与Q175敲入亨廷顿病（HD）小鼠模型中亨廷顿蛋白（HTT）mRNA的扩增CAG重复序列的治疗潜力。在第一项研究中，R6/2小鼠分为低剂量组与高剂量组，分别接受每周1次、共计6次的(CUG)7脑室内输注，并于末次输注后2周处死。结果显示，经(CUG)7处理的小鼠纹状体（striatum）、海马体（hippocampus）与大脑皮层（cortex）内，可溶性与聚集型突变HTT蛋白水平均降低15%~60%。该分子层面的矫正效应可改善多项运动任务中的行为表现，提升全脑及皮层体积，降低神经胶质增生标志物（gliosis marker）肌醇（myo-inositol）的水平，升高神经元完整性标志物N-乙酰天门冬氨酸（N-acetyl aspartate）的水平，并上调纹状体标志物Darpp-32的mRNA表达水平。上述神经解剖学与神经化学变化，结合运动功能的改善，表明(CUG)7治疗可缓解基底节功能障碍（basal ganglia dysfunction）。后续一项独立研究在Q175小鼠中采用相似的(CUG)7反义寡核苷酸给药方案，证实了HTT蛋白的降低效果，进一步证明末次输注后最长18周内，纹状体、海马体与大脑皮层内的突变HTT蛋白水平持续降低，同时小鼠运动活性有所提升。基于上述令人鼓舞的研究结果，(CUG)7有望成为亨廷顿病的一种极具应用前景的HTT蛋白降低治疗策略。