Center of Emphasis in Neurosciences, Texas Tech University Health Sciences Center El Paso, El Paso, TX, USA.
Department of Molecular and Translational Medicine, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center El Paso, El Paso, TX, USA.
Brain. 2020 Jan 1;143(1):69-93. doi: 10.1093/brain/awz373.
Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by homozygous mutation or deletion of the survival motor neuron 1 (SMN1) gene. A second copy, SMN2, is similar to SMN1 but produces ∼10% SMN protein because of a single-point mutation that causes splicing defects. Chronic low levels of SMN cause accumulation of co-transcriptional R-loops and DNA damage leading to genomic instability and neurodegeneration in SMA. Severity of SMA disease correlates inversely with SMN levels. SMN2 is a promising target to produce higher levels of SMN by enhancing its expression. Mechanisms that regulate expression of SMN genes are largely unknown. We report that zinc finger protein ZPR1 binds to RNA polymerase II, interacts in vivo with SMN locus and upregulates SMN2 expression in SMA mice and patient cells. Modulation of ZPR1 levels directly correlates and influences SMN2 expression levels in SMA patient cells. ZPR1 overexpression in vivo results in a systemic increase of SMN levels and rescues severe to moderate disease in SMA mice. ZPR1-dependent rescue improves growth and motor function and increases the lifespan of male and female SMA mice. ZPR1 reduces neurodegeneration in SMA mice and prevents degeneration of cultured primary spinal cord neurons derived from SMA mice. Further, we show that the low levels of ZPR1 associated with SMA pathogenesis cause accumulation of co-transcriptional RNA-DNA hybrids (R-loops) and DNA damage leading to genomic instability in SMA mice and patient cells. Complementation with ZPR1 elevates senataxin levels, reduces R-loop accumulation and rescues DNA damage in SMA mice, motor neurons and patient cells. In conclusion, ZPR1 is critical for preventing accumulation of co-transcriptional R-loops and DNA damage to avert genomic instability and neurodegeneration in SMA. ZPR1 enhances SMN2 expression and leads to SMN-dependent rescue of SMA. ZPR1 represents a protective modifier and a therapeutic target for developing a new method for the treatment of SMA.
脊髓性肌萎缩症（SMA）是一种由生存运动神经元 1（SMN1）基因突变或缺失引起的神经肌肉疾病。第二个拷贝 SMN2 与 SMN1 相似，但由于单点突变导致剪接缺陷，仅产生约 10%的 SMN 蛋白。慢性低水平的 SMN 导致共转录 R-环和 DNA 损伤的积累，从而导致 SMA 中的基因组不稳定性和神经退行性变。SMA 疾病的严重程度与 SMN 水平呈负相关。SMN2 是通过增强其表达产生更高水平 SMN 的有前途的靶标。调节 SMN 基因表达的机制在很大程度上尚不清楚。我们报告锌指蛋白 ZPR1 与 RNA 聚合酶 II 结合，在体内与 SMN 基因座相互作用，并上调 SMA 小鼠和患者细胞中的 SMN2 表达。ZPR1 水平的调节直接与 SMA 患者细胞中 SMN2 表达水平相关并影响其表达水平。体内过表达 ZPR1 导致 SMN 水平的全身性增加，并挽救 SMA 小鼠的严重至中度疾病。ZPR1 依赖性挽救可改善生长和运动功能，并延长 SMA 小鼠的寿命。ZPR1 可减少 SMA 小鼠的神经退行性变并防止源自 SMA 小鼠的培养原代脊髓神经元的变性。此外，我们表明与 SMA 发病机制相关的 ZPR1 低水平导致共转录 RNA-DNA 杂交（R-环）和 DNA 损伤的积累，从而导致 SMA 小鼠和患者细胞中的基因组不稳定性。用 ZPR1 补充可提高 senataxin 水平，减少 R-环积累并挽救 SMA 小鼠、运动神经元和患者细胞中的 DNA 损伤。总之，ZPR1 对于防止共转录 R-环和 DNA 损伤的积累以避免 SMA 中的基因组不稳定性和神经退行性变至关重要。ZPR1 增强 SMN2 表达并导致 SMA 的 SMN 依赖性挽救。ZPR1 代表一种保护性修饰因子和治疗靶点，可开发用于治疗 SMA 的新方法。
