Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene leading to the presence of premature termination codons (PTC). Previous transcriptional studies have shown reduced DMD transcript levels in DMD patient and animal model muscles when PTC are present. Nonsense-mediated decay (NMD) has been suggested to be responsible for the observed reduction, but there is no experimental evidence supporting this claim. In this study, we aimed to investigate the mechanism responsible for the drop in DMD expression levels in the presence of PTC. We observed that the inhibition of NMD does not normalize DMD gene expression in DMD. Additionally, in situ hybridization showed that DMD messenger RNA primarily localizes in the nuclear compartment, confirming that a cytoplasmic mechanism like NMD indeed cannot be responsible for the observed reduction. Sequencing of nascent RNA to explore DMD transcription dynamics revealed a lower rate of DMD transcription in patient-derived myotubes compared to healthy controls, suggesting a transcriptional mechanism involved in reduced DMD transcript levels. Chromatin immunoprecipitation in muscle showed increased levels of the repressive histone mark H3K9me3 in mdx mice compared to wild-type mice, indicating a chromatin conformation less prone to transcription in mdx mice. In line with this finding, treatment with the histone deacetylase inhibitor givinostat caused a significant increase in DMD transcript expression in mdx mice. Overall, our findings show that transcription dynamics across the DMD locus are affected by the presence of PTC, hinting at a possible epigenetic mechanism responsible for this process.

杜氏肌营养不良症 (DMD) 是由DMD基因突变导致提前终止密码子 (PTC) 的存在引起的。先前的转录研究表明，当 PTC 存在时，DMD 患者和动物模型肌肉中的 DMD 转录水平降低。无义介导的衰变（NMD）被认为是观察到的减少的原因，但没有实验证据支持这一说法。在本研究中，我们旨在研究 PTC 存在时DMD表达水平下降的机制。我们观察到 NMD 的抑制不会使 DMD 中的DMD基因表达正常化。此外，原位杂交表明 DMD 信使 RNA 主要定位于核区室，证实像 NMD 这样的细胞质机制确实不能解释观察到的减少。通过对新生 RNA 进行测序来探索DMD转录动态，结果发现，与健康对照相比，患者来源的肌管中DMD转录率较低，这表明转录机制与 DMD 转录水平降低有关。肌肉中的染色质免疫沉淀显示，与野生型小鼠相比， mdx小鼠中抑制性组蛋白标记 H3K9me3 的水平增加，表明mdx小鼠中染色质构象不易转录。与这一发现一致，组蛋白脱乙酰酶抑制剂 givinostat 治疗导致mdx小鼠中 DMD 转录物表达显着增加。 总体而言，我们的研究结果表明，跨DMD位点的转录动态受到 PTC 存在的影响，暗示可能存在导致该过程的表观遗传机制。