Muscle and neuromuscular junctions in spinal muscular atrophy

描述（由申请人提供）：脊髓性肌萎缩症（SMA）是一种目前无法治疗的常染色体隐性运动神经元疾病，是婴儿死亡的主要遗传原因。SMA是由存活运动神经元（SMN）蛋白缺乏引起的。我们的长期研究目标是了解SMA的潜在发病机制，以便制定有效的治疗策略。最近的研究表明，SMA的开始是由于肌肉和运动神经末梢的内在异常；然而，这些缺陷的性质尚不清楚。组蛋白去乙酰化酶（HDAC）抑制剂已被证明可以提高SMA小鼠的存活率；但目前尚不清楚这些药物如何改善肌肉和/或运动神经元的功能。在对SMA小鼠的初步研究中，我们已经表明，在小鼠非常虚弱的时候，几乎没有结构性的去神经支配。然而，存在广泛的未成熟和萎缩肌纤维以及简化的神经肌肉连接（NMJs）。用pan- HDAC抑制剂治疗的小鼠显示出存活时间的显著延长，运动功能的增加，肌纤维的大小和成熟度的改善，而运动神经元的数量没有变化。基于这些初步数据，我们假设SMN缺乏导致肌肉成熟停滞和/或NMJ传递失败，这可以通过HDAC抑制剂克服，从而加速SMA运动单元的发展。我们进一步假设，HDAC亚型特异性药物将对SMA运动单元产生不同的生物学效应，这将为这些化合物的治疗机制提供重要的见解。我们将通过以下方式检验这些假设：1)通过研究培养的SMA肌肉细胞和挽救条理性SMA小鼠肌肉组织中特异性SMN的表达，确定肌肉发育缺陷是否会导致SMA； 2)通过检测SMA小鼠NMJs的电生理和形态学，确定SMA的无力是否由于神经肌肉传递障碍所致；3)表征HDAC抑制剂促进肌肉和NMJ成熟的能力，并通过使用广泛活性和HDAC-异型特异性HDAC抑制剂治疗SMA肌肉细胞和SMA小鼠来改善SMA。公共卫生相关性：这项工作对公共卫生很重要，因为脊髓性肌萎缩症是婴儿死亡的主要遗传原因，目前无法治愈。在本项目中，我们计划明确肌肉和运动神经元末端在SMA发病机制中的作用，并探索组蛋白去乙酰化酶抑制剂的治疗机制。这些研究将提供重要的见解，哪些组织和分子是治疗SMA所必需的，因此将指导未来开发这种疾病的治疗方法。

DESCRIPTION (provided by applicant): Spinal muscular atrophy (SMA) is a currently untreatable, autosomal recessive motor neuron disease that is the leading inherited cause of infant mortality. SMA is caused by deficiency of the survival motor neuron (SMN) protein. Our long term research goal is to understand the underlying pathogenesis of SMA in order to develop effective treatment strategies for this disease. Recent studies suggest that SMA begins because of intrinsic abnormalities of both muscle and motor nerve terminals; however the nature of these defects remains unknown. Histone deacetylase (HDAC) inhibitors have been shown to increase survival of SMA mice; but it is unclear how these drugs improve muscle and/or motor neuron function. In preliminary studies in SMA mice, we have shown that at a time when the mouse is profoundly weak, there is little structural denervation. However there are widespread immature and hypotrophic myofibers as well as simplified neuromuscular junctions (NMJs). Mice treated with a pan- HDAC inhibitor show a substantial extension of survival, increase in motor function, and improvement in the size and maturity of myofibers, without a change in motor neuron number. Based on these preliminary data, we hypothesize that SMN deficiency causes an arrest of muscle maturation and/or a failure of NMJ transmission that can be overcome with HDAC inhibitors, which accelerate the development of the SMA motor unit. We further hypothesize that HDAC isoform-specific drugs will have distinct biological effects on the SMA motor unit that will provide crucial insights into the therapeutic mechanism of these compounds. We will test these hypotheses by: 1) establishing whether or not a defect of muscle development contributes to SMA by studying cultured SMA muscle cells and by rescuing SMN expression specifically in muscle tissue in conditional SMA mice, 2) determining whether or not weakness in SMA is due to an impairment of neuromuscular transmission by examining the electrophysiology and morphology of the NMJs in SMA mice, and 3) characterizing the ability of HDAC inhibitors to facilitate muscle and NMJ maturation and ameliorate SMA in mice by treating SMA muscle cells and SMA mice with broadly active and HDAC-isoform specific HDAC inhibitors. PUBLIC HEALTH RELEVANCE: This work is important for public health because spinal muscular atrophy is the leading inherited cause of infant mortality and is currently untreatable. In this project, we plan to define the roles of muscle and motor neuron terminals in the pathogenesis of SMA and to explore the therapeutic mechanism of histone deacetylase inhibitors. These studies will provide important insights about what tissue and molecules are necessary to target therapeutically in SMA and will therefore guide future efforts to develop treatment for this disease.