Department of Anatomy, Physiology and Human Biology, School of Human Sciences, The University of Western Australia, Perth, WA, Australia.
Curtin Health Innovation Research Institute, Curtin Medical School, Curtin University, Bentley, WA, Australia.
Skelet Muscle. 2024 Aug 9;14(1):19. doi: 10.1186/s13395-024-00350-6.
Dysferlinopathies are a clinically heterogeneous group of muscular dystrophies caused by gene mutations resulting in deficiency of the membrane-associated protein dysferlin. They manifest post-growth and are characterised by muscle wasting (primarily in the limb and limb-gridle muscles), inflammation, and replacement of myofibres with adipose tissue. The precise pathomechanism for dysferlinopathy is currently unclear; as such there are no treatments currently available. Glucocorticoids (GCs) are widely used to reduce inflammation and treat muscular dystrophies, but when administered to patients with dysferlinopathy, they have unexpected adverse effects, with accelerated loss of muscle strength.
To investigate the mechanistic basis for the adverse effects of GCs in dysferlinopathy, the potent GC dexamethasone (Dex) was administered for 4-5 weeks (0.5-0.75 µg/mL in drinking water) to dysferlin-deficient BLA/J and normal wild-type (WT) male mice, sampled at 5 (Study 1) or 10 months (Study 2) of age. A wide range of analyses were conducted. Metabolism- and immune-related gene expression was assessed in psoas muscles at both ages and in quadriceps at 10 months of age. For the 10-month-old mice, quadriceps and psoas muscle histology was assessed. Additionally, we investigated the impact of Dex on the predominantly slow and fast-twitch soleus and extensor digitorum longus (EDL) muscles (respectively) in terms of contractile function, myofibre-type composition, and levels of proteins related to contractile function and metabolism, plus glycogen.
At both ages, many complement-related genes were highly expressed in BLA/J muscles, and WT mice were generally more responsive to Dex than BLA/J. The effects of Dex on BLA/J mice included (i) increased expression of inflammasome-related genes in muscles (at 5 months) and (ii) exacerbated histopathology of quadriceps and psoas muscles at 10 months. A novel observation was pronounced staining for glycogen in many myofibres of the damaged quadriceps muscles, with large pale vacuolated myofibres, suggesting possible myofibre death by oncosis.
These pilot studies provide a new focus for further investigation into the adverse effects of GCs on dysferlinopathic muscles.
肌营养不良症是一组由基因突变引起的临床异质性肌肉疾病，导致膜相关蛋白 dysferlin 缺乏。它们在生长后表现出来，其特征是肌肉萎缩（主要在四肢和四肢网格肌肉）、炎症和肌纤维被脂肪组织取代。肌营养不良症的精确发病机制目前尚不清楚；因此，目前尚无治疗方法。糖皮质激素（GCs）被广泛用于减轻炎症和治疗肌肉疾病，但当给予肌营养不良症患者时，它们会产生意想不到的不良反应，导致肌肉力量加速丧失。
为了研究 GCs 在肌营养不良症中的不良反应的机制基础，将强效 GC 地塞米松（Dex）以 0.5-0.75μg/mL 的浓度（在饮用水中）连续给药 4-5 周，用于 BLA/J 肌营养不良症缺陷型和正常野生型（WT）雄性小鼠，在 5 个月（研究 1）或 10 个月（研究 2）时取样。进行了广泛的分析。在两个年龄时评估了比目鱼肌中的代谢和免疫相关基因表达，并在 10 个月时评估了股四头肌中的代谢和免疫相关基因表达。对于 10 个月大的小鼠，评估了股四头肌和比目鱼肌的组织学。此外，我们研究了 Dex 对主要是慢肌和快肌比目鱼肌和伸趾长肌（EDL）肌肉（分别）在收缩功能、肌纤维型组成以及与收缩功能和代谢相关的蛋白质水平和糖原方面的影响。
在两个年龄时，BLA/J 肌肉中的许多补体相关基因都高度表达，WT 小鼠通常对 Dex 的反应比 BLA/J 更敏感。Dex 对 BLA/J 小鼠的影响包括（i）肌肉中炎症小体相关基因的表达增加（在 5 个月时）和（ii）10 个月时股四头肌和比目鱼肌的组织病理学恶化。一个新的观察结果是，受损股四头肌肌肉中许多肌纤维的糖原染色明显，有大的苍白空泡化肌纤维，提示可能通过胀亡导致肌纤维死亡。
这些初步研究为进一步研究 GCs 对肌营养不良症肌肉的不良反应提供了新的重点。
