Department of Genetic Medicine, Weill Cornell Medical College, New York, New York, USA.
Hum Gene Ther. 2020 Aug;31(15-16):819-827. doi: 10.1089/hum.2019.363.
Friedreich's ataxia (FA), an autosomal recessive disorder caused by a deficiency in the expression of frataxin (FXN), is characterized by progressive ataxia and hypertrophic cardiomyopathy. Although cardiac dysfunction is the most common cause of mortality in FA, the cardiac disease remains subclinical for most of the clinical course because the neurologic disease limits muscle oxygen demands. Previous knockout mouse models exhibit fatal cardiomyopathy similar to human FA, but in contrast to the human condition, untreated mice become moribund by 2 months of age, unlike humans where the cardiac disease often does not manifest until the third decade. The study was designed to create a mouse model for early FA disease relevant to the time for which a gene therapy would likely be most effective. To generate a cardiac-specific mouse model of FA cardiomyopathy similar to the human disease, we used a cardiac promoter (αMyhc) driving CRE recombinase cardiac-specific excision of exon 4 to generate a mild, cardiac-specific FA model that is normal at rest, but exhibits the cardiac phenotype with stress. The hearts of αMyhc mice had decreased levels of FXN and activity of the mitochondrial complex II/complex IV respiratory chain. At rest, αMyhc mice exhibited normal cardiac function as assessed by echocardiographic assessment of ejection fraction and fractional shortening, but when the heart was stressed chemically with dobutamine, αMyhc mice compared with littermate control mice had a 62% reduction in the stress ejection fraction ( < 2 × 10) and 71% reduction in stress-related fractional shortening ( < 10). When assessing functional cardiac performance using running on an inclined treadmill, αMyhc mice stayed above the midline threefold less than littermate controls ( < 0.02). A one-time intravenous administration of 10 genome copies of AAVrh.10hFXN, an adeno-associated virus (AAV) serotype rh10 gene transfer vector expressing human , corrected the stress-induced ejection fraction and fractional shortening phenotypes. Treated αMyhc mice exhibited exercise performance on a treadmill indistinguishable from littermate controls ( > 0.07). These αMyhc mice provide an ideal model to study long-term cardiac complications due to FA and AAV-mediated gene therapy correction of stress-induced cardiac phenotypes typical of human FA.
弗里德赖希共济失调（FA）是一种常染色体隐性遗传病，由 frataxin（FXN）表达缺陷引起，其特征是进行性共济失调和肥厚型心肌病。尽管心脏功能障碍是 FA 患者最常见的死亡原因，但由于神经系统疾病限制了肌肉的氧气需求，大多数情况下心脏疾病在临床过程中仍处于亚临床状态。先前的 knockout 小鼠模型表现出类似于人类 FA 的致命性心肌病，但与人类情况不同的是，未经治疗的小鼠在 2 个月大时就会濒死，而在人类中，这种心脏病通常直到第三十年才会出现。本研究旨在创建一种与基因治疗最有效的时间相关的早期 FA 疾病的小鼠模型。为了生成类似于人类疾病的 FA 心肌病的心脏特异性小鼠模型，我们使用心脏启动子（αMyhc）驱动 CRE 重组酶对心脏特异性外显子 4 进行切除，从而产生一种轻度的、心脏特异性的 FA 模型，该模型在休息时正常，但在应激时表现出心脏表型。αMyhc 小鼠的心脏 FXN 水平降低，线粒体复合物 II/复合物 IV 呼吸链的活性降低。在休息时，αMyhc 小鼠的心脏功能通过射血分数和缩短分数的超声心动图评估正常，但当心脏受到化学刺激多巴酚丁胺时，αMyhc 小鼠与同窝对照小鼠相比，应激射血分数降低了 62%（ < 2×10），应激相关缩短分数降低了 71%（ < 10）。在用倾斜跑步机跑步评估功能性心脏性能时，αMyhc 小鼠的中线以上停留时间是同窝对照小鼠的三倍（ < 0.02）。单次静脉注射 10 个基因组拷贝的 AAVrh.10hFXN，一种腺相关病毒（AAV）血清型 rh10 基因转移载体，表达人类 ，纠正了应激诱导的射血分数和缩短分数表型。经过治疗的αMyhc 小鼠在跑步机上的运动表现与同窝对照小鼠无异（ > 0.07）。这些αMyhc 小鼠为研究由于 FA 引起的长期心脏并发症以及 AAV 介导的基因治疗纠正人类 FA 典型的应激诱导心脏表型提供了理想的模型。
