Department of Medical Physiology and Biophysics, School of Medicine, University of Seville, 41009 Seville, Spain.
Hum Mol Genet. 2021 May 17;30(8):629-643. doi: 10.1093/hmg/ddab065.
Spinal muscular atrophy (SMA) is an autosomal recessive degenerative motor neuron disease characterized by symmetrical muscle weakness and atrophy of limb and trunk muscles being the most severe genetic disease in children. In SMA mouse models, motor nerve terminals display neurotransmitter release reduction, endocytosis decrease and mitochondria alterations. The relationship between these changes is, however, not well understood. In the present study, we investigated whether the endocytosis impairment could be related to the functional alteration of the presynaptic mitochondria during action potential (AP) firing. To this aim, we generated a Synaptophysin-pHluorin (SypHy) transgenic mouse, crossed it with Taiwanese SMA mice, and recorded exo- and endocytosis and mitochondria Ca2+ signaling in real-time at ex vivo motor nerve terminals of Taiwanese-SypHy mice. The experiments were performed at the beginning of the motor symptoms to get an integrated view of the nerve terminal's functional state before degeneration. Our electrophysiological and live imaging results demonstrated that the mitochondria's capacity to increase matrix-free Ca2+ in SMA mice was significantly limited during nerve AP firing, except when the rate of Ca2+ entry to the cytosol was considerably reduced. These results indicate that both the mitochondrial Ca2+ signaling alterations and the secretion machinery defects are significant players in the dysfunction of the presynaptic terminal in SMA.
脊髓性肌萎缩症（SMA）是一种常染色体隐性退行性运动神经元疾病，其特征是对称性肌无力和四肢及躯干肌肉萎缩，是儿童中最严重的遗传疾病。在 SMA 小鼠模型中，运动神经末梢显示神经递质释放减少、内吞作用减少和线粒体改变。然而，这些变化之间的关系尚不清楚。在本研究中，我们研究了内吞作用的损伤是否与动作电位（AP）放电过程中突触前线粒体的功能改变有关。为此，我们生成了一个突触小体蛋白-pH 荧光蛋白（SypHy）转基因小鼠，将其与台湾 SMA 小鼠杂交，并在台湾-SypHy 小鼠的离体运动神经末梢实时记录外显和内吞作用以及线粒体 Ca2+信号。这些实验是在运动症状开始时进行的，以便在神经末梢退化之前获得对其功能状态的综合观察。我们的电生理和实时成像结果表明，在 SMA 小鼠的神经 AP 放电过程中，线粒体增加基质游离 Ca2+的能力显著受限，除非细胞溶质中 Ca2+进入的速率大大降低。这些结果表明，线粒体 Ca2+信号改变和分泌机制缺陷都是 SMA 中突触前末梢功能障碍的重要因素。
