Duque Sandra I, Arnold W David, Odermatt Philipp, Li Xiaohui, Porensky Paul N, Schmelzer Leah, Meyer Kathrin, Kolb Stephen J, Schümperli Daniel, Kaspar Brian K, Burghes Arthur H M
Department of Molecular and Cellular Biochemistry, Ohio State University Wexner Medical Center, Columbus, OH.
Ann Neurol. 2015 Mar;77(3):399-414. doi: 10.1002/ana.24332. Epub 2015 Feb 9.
Spinal muscular atrophy (SMA) is caused by reduced levels of survival motor neuron (SMN) protein, which results in motoneuron loss. Therapeutic strategies to increase SMN levels including drug compounds, antisense oligonucleotides, and scAAV9 gene therapy have proved effective in mice. We wished to determine whether reduction of SMN in postnatal motoneurons resulted in SMA in a large animal model, whether SMA could be corrected after development of muscle weakness, and the response of clinically relevant biomarkers.
Using intrathecal delivery of scAAV9 expressing an shRNA targeting pig SMN1, SMN was knocked down in motoneurons postnatally to SMA levels. This resulted in an SMA phenotype representing the first large animal model of SMA. Restoration of SMN was performed at different time points with scAAV9 expressing human SMN (scAAV9-SMN), and electrophysiology measurements and pathology were performed.
Knockdown of SMN in postnatal motoneurons results in overt proximal weakness, fibrillations on electromyography indicating active denervation, and reduced compound muscle action potential (CMAP) and motor unit number estimation (MUNE), as in human SMA. Neuropathology showed loss of motoneurons and motor axons. Presymptomatic delivery of scAAV9-SMN prevented SMA symptoms, indicating that all changes are SMN dependent. Delivery of scAAV9-SMN after symptom onset had a marked impact on phenotype, electrophysiological measures, and pathology.
High SMN levels are critical in postnatal motoneurons, and reduction of SMN results in an SMA phenotype that is SMN dependent. Importantly, clinically relevant biomarkers including CMAP and MUNE are responsive to SMN restoration, and abrogation of phenotype can be achieved even after symptom onset.
脊髓性肌萎缩症（SMA）是由存活运动神经元（SMN）蛋白水平降低引起的，这会导致运动神经元丧失。提高SMN水平的治疗策略，包括药物化合物、反义寡核苷酸和scAAV9基因疗法，已在小鼠中证明有效。我们希望确定出生后运动神经元中SMN的减少是否会在大型动物模型中导致SMA，肌肉无力发展后SMA是否可以得到纠正，以及临床相关生物标志物的反应。
通过鞘内注射表达靶向猪SMN1的短发夹RNA（shRNA）的scAAV9，在出生后将运动神经元中的SMN敲低至SMA水平。这产生了一种SMA表型，代表了第一个SMA大型动物模型。在不同时间点用表达人SMN的scAAV9（scAAV9-SMN）进行SMN恢复，并进行电生理测量和病理学检查。
出生后运动神经元中SMN的敲低导致明显的近端无力、肌电图上的纤颤表明有活动性去神经支配，以及复合肌肉动作电位（CMAP）和运动单位数量估计（MUNE）降低，与人类SMA相同。神经病理学显示运动神经元和运动轴突丧失。症状前给予scAAV9-SMN可预防SMA症状，表明所有变化均依赖于SMN。症状发作后给予scAAV9-SMN对表型、电生理指标和病理学有显著影响。
高SMN水平在出生后运动神经元中至关重要，SMN的减少会导致依赖于SMN的SMA表型。重要的是，包括CMAP和MUNE在内的临床相关生物标志物对SMN恢复有反应，即使在症状发作后也可实现表型消除。
