XIAP Gene Therapy in Huntington's Disease

描述（由主要研究者提供）：亨廷顿病（HD）是一种常染色体显性遗传神经退行性疾病，通常是致命的，无法治疗，并导致严重的运动障碍，认知和神经精神异常。HD是由亨廷顿基因（mhtt）中多聚谷氨酰胺重复序列的病理性扩增引起的，导致主要是纹状体中型多棘神经元的最终损失，尽管也可能发生其他脑区域的功能障碍和/或变性。虽然mht诱导的神经退行性变的机制仍然未知，但细胞凋亡（程序性细胞死亡）已在各种先前研究中作为潜在的介导者出现。X连锁凋亡抑制蛋白（XIAP）是凋亡抑制蛋白家族中最强的成员，已知其可结合并阻断凋亡效应子的功能，包括半胱天冬酶和线粒体细胞死亡蛋白Smac和Omi。我们长期以来一直使用腺相关病毒（AAV）载体作为神经退行性疾病的基因转移剂，最近报道了在帕金森病基因治疗的首次人体试验中使用AAV。基于此，我们收到了一份试点申请R21 NS 055003，以检查纹状体中AAV-XIAP基因疗法作为HD新疗法的潜力。我们现在已经证明纹状体内AAV-XIAP可以逆转HD的N171- 82 Q和YAC 128转基因小鼠模型中的运动功能障碍。N171小鼠的正常缩短的寿命也显著延长了20%，而在正常寿命的YAC 128小鼠中证明了神经变性的统计学完全预防。虽然该试验数据沿着细胞培养研究强烈支持AAV-XIAP作为潜在基因治疗剂的潜力，但在此我们提出解决几个重要的剩余问题，这些问题对于理解HD的发病机制以及将AAV-XIAP特异性转化为临床基因治疗剂都具有重要意义。目的1将进一步阐明AAV-XIAP介导的神经保护的广度和机制。由于死亡被用作初步N171研究的终点，因此未进行组织学分析，因此我们将确定AAV-XIAP在死亡前对该细胞系中神经病理学的影响。我们还将使用缺乏某些特定功能的XIAP点突变体来探索XIAP介导的神经保护的潜在机制，以便更好地定义可能成为HD中新型神经保护疗法的靶向途径。在N171和YAC 128模型中，运动功能在报告的神经元变性正常发生的年龄之前改善至野生型水平。这表明XIAP对神经元功能障碍的改善不同于神经元保护作用。目的2将使用纹状体切片和一种新的转基因HD小鼠来确定XIAP对HD纹状体神经元中多巴胺受体信号传导的影响。最后，目标3将解决某些剩余的问题，这些问题将为AAV-XIAP用于HD的潜在人体临床试验提供信息。这项研究将有助于将AAV-XIAP开发成人类治疗药物，并为开发逆转HD中神经元功能障碍和/或损失的药物提供新的信息。

DESCRIPTION (provided by principal investigator): Huntington's disease (HD) is a autosomal dominant neurodegenerative disorder which is normally fatal and untreatable and results in a severe movement disorder, cognitive and neuropsychiatric abnormalities. HD is caused by a pathological expansion of polyglutamine repeats in the Huntingtin gene (mhtt), resulting in the eventual loss predominantly of striatal medium spiny neurons although dysfunction and/or degeneration of other brain regions can occur as well. While the mechanism of mhtt-induced neurodegeneration remains unknown, apoptosis (programmed cell death) has emerged as a potential mediator in a variety of prior studies. X-linked inhibitor of apoptosis (XIAP) is the most potent member of a family of apoptosis inhibitor proteins, which is known to bind to and block the function of effectors of apoptosis including caspases and mitochondrial cell death proteins Smac and Omi. We have long used the adeno-associated virus (AAV) vector as a gene transfer agent for neurodegenerative diseases and have recently reported the use of AAV in the first human trial of gene therapy for Parkinson's disease. Based upon this, we received a pilot application R21 NS055003 to examine the potential of AAV-XIAP gene therapy in the striatum as a novel therapy for HD. We have now demonstrated that intrastriatal AAV-XIAP can reverse motor dysfunction in both the N171-82Q and YAC128 transgenic mouse models of HD. The normally shortened lifespan of N171 mice were also significantly extended by 20% while statistically complete prevention of neurodegeneration was demonstrated in the normal lifespan YAC128 mice. While this pilot data along with cell culture studies strongly supports the potential of AAV-XIAP as a potential gene therapy agent, here we propose to address several important remaining questions which have significance for both understanding the pathogenesis of HD as well as specifically translating AAV-XIAP into a clinical gene therapy agent. Aim 1 will further address the breadth and mechanism of AAV-XIAP-mediated neuro protection. Since death was used as an endpoint for the pilot N171 study, histological analysis was not performed so we will determine the effect of AAV-XIAP on neuropathology in this line just prior to death. We will also use XIAP point mutants lacking certain specific functions to explore potential mechanisms of XIAP-mediated neuro protection in order to better define pathways which may be targeted for novel neuro protective therapeutics in HD. In both N171 and YAC128 models, motor function was improved to wild-type levels prior to the reported age at which neuro degeneration normally ensues. This suggests an improvement in neuronal dysfunction by XIAP distinct from neuro protective effects. Aim 2 will use both striatal slices and a novel transgenic HD mouse to determine the effect of XIAP on dopamine receptor signaling in HD striatal neurons. Finally, aim 3 will address certain remaining questions which would inform a potential human clinical trial of AAV-XIAP for HD. This study should help develop AAV-XIAP into a human therapeutic and provide novel information to develop drugs to reverse neuronal dysfunction and/or loss in HD.