Department of Laboratory Medicine, Institute of Biomedicine, University of Gothenburg, Gothenburg, Sweden.
Department of Paediatrics, Institute of Clinical Sciences, University of Gothenburg, Sweden.
Acta Myol. 2024 Sep;43(3):89-94. doi: 10.36185/2532-1900-558.
We investigated myosin heavy chain (MyHC) isoform expression at early postnatal stages of clinically and genetically confirmed spinal muscular atrophy type 1 (SMA1) patients, in order to study the muscle fibre differentiation compared to age-matched controls at single fibre level.
Open skeletal muscle biopsies were performed from the quadriceps muscle in four SMA1 patients and three age-matched controls. Standard techniques were used for immunohistochemistry of embryonic and foetal MyHCs. Type I, IIa and IIx MyHCs were assessed by applying quadruple immunofluorescence. Western blot was performed to analyse the amount of survival motor neuron (SMN) protein in the muscle samples.
There were profound and early alterations in MyHC expression from 7 days of life compared to age-matched controls. The expression of type IIx MyHC was completely lost in SMA1 and instead developmental isoforms remained highly expressed. Foetal MyHC was still, at 3.5 months of age, expressed in the majority of muscle fibres in SMA1 patients, whereas it was completely downregulated in age-matched controls. The level of SMN protein was reduced in all SMN1 patients.
The abnormal pattern of MyHC expression in postnatal stages of SMA1 was observed early in the newborn period, which may have implications for the effects of gene therapy, since there are clear clinical benefits from early treatment. Whether such aberrant and delayed expression of MyHCs can be completely restored by postnatal gene therapy remains to be studied and may also have implications for new phenotypes that will evolve with new therapies.
我们研究了临床和基因确诊的脊髓性肌萎缩症 1 型（SMA1）患者出生后早期的肌球蛋白重链（MyHC）同工型表达，以便在单细胞水平上研究与年龄匹配的对照相比肌肉纤维分化情况。
对 4 名 SMA1 患者和 3 名年龄匹配的对照者的股四头肌进行开放性骨骼肌活检。采用免疫组织化学技术对胚胎和成体 MyHC 进行染色。通过四重免疫荧光评估 I 型、IIa 型和 IIx 型 MyHC。通过 Western blot 分析肌肉样本中存活运动神经元（SMN）蛋白的含量。
与年龄匹配的对照组相比，从出生后 7 天开始，MyHC 表达出现明显和早期改变。IIx 型 MyHC 的表达在 SMA1 中完全丧失，而发育同工型仍高度表达。在 SMA1 患者中，3.5 个月大时仍有多数肌纤维表达胎儿型 MyHC，而在年龄匹配的对照组中已完全下调。所有 SMN1 患者的 SMN 蛋白水平均降低。
在 SMA1 出生后的阶段观察到异常的 MyHC 表达模式，在新生儿期就已出现，这可能对基因治疗的效果产生影响，因为早期治疗有明显的临床益处。通过产后基因治疗是否可以完全恢复这种异常和延迟的 MyHC 表达，还有待研究，并且可能对新出现的治疗方法也会出现的新表型产生影响。
