Stapleton David I, Lau Xianzhong, Flores Marcelo, Trieu Jennifer, Gehrig Stefan M, Chee Annabel, Naim Timur, Lynch Gordon S, Koopman René
Department of Physiology, The University of Melbourne, Melbourne, Victoria, Australia.
PLoS One. 2014 Mar 13;9(3):e91514. doi: 10.1371/journal.pone.0091514. eCollection 2014.
Duchenne muscular dystrophy (DMD) is a severe, genetic muscle wasting disorder characterised by progressive muscle weakness. DMD is caused by mutations in the dystrophin (dmd) gene resulting in very low levels or a complete absence of the dystrophin protein, a key structural element of muscle fibres which is responsible for the proper transmission of force. In the absence of dystrophin, muscle fibres become damaged easily during contraction resulting in their degeneration. DMD patients and mdx mice (an animal model of DMD) exhibit altered metabolic disturbances that cannot be attributed to the loss of dystrophin directly. We tested the hypothesis that glycogen metabolism is defective in mdx dystrophic mice.
Dystrophic mdx mice had increased skeletal muscle glycogen (79%, (P<0.01)). Skeletal muscle glycogen synthesis is initiated by glycogenin, the expression of which was increased by 50% in mdx mice (P<0.0001). Glycogen synthase activity was 12% higher (P<0.05) but glycogen branching enzyme activity was 70% lower (P<0.01) in mdx compared with wild-type mice. The rate-limiting enzyme for glycogen breakdown, glycogen phosphorylase, had 62% lower activity (P<0.01) in mdx mice resulting from a 24% reduction in PKA activity (P<0.01). In mdx mice glycogen debranching enzyme expression was 50% higher (P<0.001) together with starch-binding domain protein 1 (219% higher; P<0.01). In addition, mdx mice were glucose intolerant (P<0.01) and had 30% less liver glycogen (P<0.05) compared with control mice. Subsequent analysis of the enzymes dysregulated in skeletal muscle glycogen metabolism in mdx mice identified reduced glycogenin protein expression (46% less; P<0.05) as a possible cause of this phenotype.
We identified that mdx mice were glucose intolerant, and had increased skeletal muscle glycogen but reduced amounts of liver glycogen.
杜氏肌营养不良症（DMD）是一种严重的遗传性肌肉萎缩疾病，其特征为进行性肌肉无力。DMD由肌营养不良蛋白（dmd）基因突变引起，导致肌营养不良蛋白水平极低或完全缺失，而肌营养不良蛋白是肌肉纤维的关键结构元件，负责力量的正确传递。在缺乏肌营养不良蛋白的情况下，肌肉纤维在收缩过程中容易受损，导致其退化。DMD患者和mdx小鼠（DMD的动物模型）表现出代谢紊乱，但这种紊乱不能直接归因于肌营养不良蛋白的缺失。我们检验了mdx营养不良小鼠糖原代谢存在缺陷的假设。
营养不良的mdx小鼠骨骼肌糖原增加（79%，P<0.01）。骨骼肌糖原合成由糖原素启动，mdx小鼠中糖原素的表达增加了50%（P<0.0001）。与野生型小鼠相比，mdx小鼠的糖原合酶活性高12%（P<0.05），但糖原分支酶活性低70%（P<0.01）。糖原分解的限速酶糖原磷酸化酶在mdx小鼠中的活性低62%（P<0.01），这是由于蛋白激酶A（PKA）活性降低24%所致（P<0.01）。在mdx小鼠中，糖原脱支酶表达高50%（P<0.001），淀粉结合域蛋白1高219%（P<0.01）。此外，与对照小鼠相比，mdx小鼠葡萄糖耐量受损（P<0.01），肝糖原减少30%（P<0.05）。随后对mdx小鼠骨骼肌糖原代谢失调的酶进行分析，发现糖原素蛋白表达降低（减少46%；P<0.05）可能是这种表型的一个原因。
我们发现mdx小鼠葡萄糖耐量受损，骨骼肌糖原增加，但肝糖原量减少。
