Department of Pharmacology and Physiology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, 185 South Orange Avenue, Newark, NJ 07103, U.S.A.
Biochem J. 2013 Jan 1;449(1):133-42. doi: 10.1042/BJ20120787.
DMD (Duchenne muscular dystrophy) is an incurable rapidly worsening neuromuscular degenerative disease caused by the absence of dystrophin. In skeletal muscle a lack of dystrophin disrupts the recruitment of neuronal NOS (nitric oxide synthase) to the sarcolemma thus affecting NO (nitric oxide) production. Utrophin is a dystrophin homologue, the expression of which is greatly up-regulated in the sarcolemma of dystrophin-negative fibres from mdx mice, a mouse model of DMD. Although cardiomyopathy is an important cause of death, little is known about the NO signalling pathway in the cardiac muscle of DMD patients. Thus we used cardiomyocytes and hearts from two month-old mdx and mdx:utrophin-/- (double knockout) mice (mdx:utr) to study key steps in NO signalling: L-arginine transporters, NOS and sGC (soluble guanylyl cyclase). nNOS did not co-localize with dystrophin or utrophin to the cardiomyocyte membrane. Despite this nNOS activity was markedly decreased in both mdx and mdx:utr mice, whereas nNOS expression was only decreased in mdx:utr mouse hearts, suggesting that utrophin up-regulation in cardiomyocytes maintains nNOS levels, but not function. sGC protein levels and activity remained at control levels. Unexpectedly, L-arginine transporter expression and function were significantly increased, suggesting a novel biochemical compensatory mechanism of the NO pathway and a potential entry site for therapeutics.
DMD（杜氏肌营养不良症）是一种无法治愈的进行性神经肌肉退行性疾病，由肌营养不良蛋白的缺失引起。在骨骼肌中，肌营养不良蛋白的缺乏会破坏神经元 NOS（一氧化氮合酶）向肌膜的募集，从而影响 NO（一氧化氮）的产生。肌联蛋白是肌营养不良蛋白的同源物，mdx 小鼠（DMD 的一种小鼠模型）中肌营养不良蛋白阴性纤维的肌膜中肌联蛋白的表达大大上调。尽管心肌病是死亡的一个重要原因，但 DMD 患者心肌中的 NO 信号通路知之甚少。因此，我们使用来自两个月大的 mdx 和 mdx：utrophin-/-（双敲除）小鼠（mdx：utr）的心肌细胞和心脏来研究 NO 信号通路的关键步骤：L-精氨酸转运体、NOS 和 sGC（可溶性鸟苷酸环化酶）。nNOS 与肌营养不良蛋白或肌联蛋白没有共定位到心肌细胞膜上。尽管如此，nNOS 活性在 mdx 和 mdx：utr 小鼠中均显著降低，而 nNOS 表达仅在 mdx：utr 小鼠心脏中降低，表明肌联蛋白在心肌细胞中的上调维持了 nNOS 的水平，但不维持其功能。sGC 蛋白水平和活性保持在对照水平。出乎意料的是，L-精氨酸转运体的表达和功能显著增加，提示 NO 途径存在新的生化代偿机制，可能是治疗的潜在靶点。
