Evans William J, Shankaran Mahalakshmi, Smith Edward C, Morris Carl, Nyangau Edna, Bizieff Alec, Matthews Marcy, Mohamed Hussein, Hellerstein Marc
Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA, USA.
Department of Medicine, Duke Medical Center, Durham, NC, USA.
J Physiol. 2021 Dec;599(23):5215-5227. doi: 10.1113/JP282227. Epub 2021 Oct 11.
Boys with Duchenne muscular dystrophy (DMD) experience a progressive loss of functional muscle mass, with fibrosis and lipid accumulation. Accurate evaluation of whole-body functional muscle mass (MM) in DMD patients has not previously been possible and the rate of synthesis of muscle proteins remains unexplored. We used non-invasive, stable isotope-based methods from plasma and urine to measure the fractional rate of muscle protein synthesis (FSR) functional muscle mass (MM), and fat free mass (FFM) in 10 DMD (6-17 years) and 9 age-matched healthy subjects. An oral dose of D creatine in 70% H O was administered to determine MM and FFM followed by daily 70% H O to measure protein FSR. Functional MM was profoundly reduced in DMD subjects compared to controls (17% vs. 41% of body weight, P < 0.0001), particularly in older, non-ambulant patients in whom functional MM was extraordinarily low (<13% body weight). We explored the urine proteome to measure FSR of skeletal muscle-derived proteins. Titin, myosin light chain and gelsolin FSRs were substantially lower in DMD subjects compared to controls (27%, 11% and 40% of control, respectively, P < 0.0001) and were strongly correlated. There were no differences in muscle-derived sarcoplasmic proteins FSRs (creatine kinase M-type and carbonic anhydrase-3) measured in plasma. These data demonstrate that both functional MM, body composition and muscle protein synthesis rates can be quantified non-invasively and are markedly different between DMD and control subjects and suggest that the rate of contractile but not sarcoplasmic protein synthesis is affected by a lack of dystrophin. KEY POINTS: Duchenne muscular dystrophy (DMD) results in a progressive loss of functional skeletal muscle but total body functional muscle mass or rates of muscle protein synthesis have not previously been assessed in these patients. D -creatine dilution was used to measure total functional muscle mass and oral H O was used to examine the rates of muscle protein synthesis non-invasively in boys with DMD and healthy controls using urine samples. Muscle mass was profoundly lower in DMD compared to control subjects, particularly in older, non-ambulant patients. The rates of contractile protein synthesis but not sarcoplasmic proteins were substantially lower in DMD. These results may provide non-invasive biomarkers for disease progression and therapeutic efficacy in DMD and other neuromuscular diseases.
患有杜兴氏肌营养不良症（DMD）的男孩会出现功能性肌肉质量逐渐丧失，并伴有纤维化和脂质堆积。此前，无法对DMD患者的全身功能性肌肉质量（MM）进行准确评估，肌肉蛋白的合成速率也尚未得到研究。我们采用基于稳定同位素的非侵入性方法，从血浆和尿液中测量了10名DMD患者（6 - 17岁）和9名年龄匹配的健康受试者的肌肉蛋白合成分数率（FSR）、功能性肌肉质量（MM）和去脂体重（FFM）。口服一剂溶于70%水的D - 肌酸以测定MM和FFM，随后每日服用70%水以测量蛋白FSR。与对照组相比，DMD受试者的功能性MM显著降低（分别为体重的17%和41%，P < 0.0001），尤其是在年龄较大、无法行走的患者中，其功能性MM极低（<体重的13%）。我们通过探索尿液蛋白质组来测量骨骼肌衍生蛋白的FSR。与对照组相比，DMD受试者的肌联蛋白、肌球蛋白轻链和凝溶胶蛋白的FSR显著降低（分别为对照组的27%、11%和40%，P < 0.0001），且具有强相关性。血浆中测量的肌肉衍生肌浆蛋白FSR（肌酸激酶M型和碳酸酐酶 - 3）没有差异。这些数据表明，功能性MM、身体成分和肌肉蛋白合成速率都可以通过非侵入性方法进行量化，且在DMD患者和对照组之间存在显著差异，这表明缺乏肌营养不良蛋白会影响收缩蛋白而非肌浆蛋白的合成速率。要点：杜兴氏肌营养不良症（DMD）导致功能性骨骼肌逐渐丧失，但此前尚未评估这些患者的全身功能性肌肉质量或肌肉蛋白合成速率。采用D - 肌酸稀释法测量总功能性肌肉质量，并使用口服水通过尿液样本对DMD男孩和健康对照进行非侵入性的肌肉蛋白合成速率检测。与对照受试者相比，DMD患者的肌肉质量显著降低，尤其是在年龄较大、无法行走的患者中。DMD患者收缩蛋白的合成速率显著降低，但肌浆蛋白的合成速率没有降低。这些结果可能为DMD和其他神经肌肉疾病的疾病进展和治疗效果提供非侵入性生物标志物。
