Department of Pathology, School of Medicine, University of Washington, Seattle, WA 98195, USA.
Skelet Muscle. 2013 Aug 1;3(1):20. doi: 10.1186/2044-5040-3-20.
Presently, there is no effective treatment for the lethal muscle wasting disease Duchenne muscular dystrophy (DMD). Here we show that increased sphingosine-1-phoshate (S1P) through direct injection or via the administration of the small molecule 2-acetyl-4(5)-tetrahydroxybutyl imidazole (THI), an S1P lyase inhibitor, has beneficial effects in acutely injured dystrophic muscles of mdx mice.
We treated mdx mice with and without acute injury and characterized the histopathological and functional effects of increasing S1P levels. We also tested exogenous and direct administration of S1P on mdx muscles to examine the molecular pathways under which S1P promotes regeneration in dystrophic muscles.
Short-term treatment with THI significantly increased muscle fiber size and extensor digitorum longus (EDL) muscle specific force in acutely injured mdx limb muscles. In addition, the accumulation of fibrosis and fat deposition, hallmarks of DMD pathology and impaired muscle regeneration, were lower in the injured muscles of THI-treated mdx mice. Furthermore, increased muscle force was observed in uninjured EDL muscles with a longer-term treatment of THI. Such regenerative effects were linked to the response of myogenic cells, since intramuscular injection of S1P increased the number of Myf5nlacz/+ positive myogenic cells and newly regenerated myofibers in injured mdx muscles. Intramuscular injection of biotinylated-S1P localized to muscle fibers, including newly regenerated fibers, which also stained positive for S1P receptor 1 (S1PR1). Importantly, plasma membrane and perinuclear localization of phosphorylated S1PR1 was observed in regenerating muscle fibers of mdx muscles. Intramuscular increases of S1P levels, S1PR1 and phosphorylated ribosomal protein S6 (P-rpS6), and elevated EDL muscle specific force, suggest S1P promoted the upregulation of anabolic pathways that mediate skeletal muscle mass and function.
These data show that S1P is beneficial for muscle regeneration and functional gain in dystrophic mice, and that THI, or other pharmacological agents that raise S1P levels systemically, may be developed into an effective treatment for improving muscle function and reducing the pathology of DMD.
目前，杜氏肌营养不良症（DMD）这种致命的肌肉消耗性疾病尚无有效的治疗方法。在这里，我们发现通过直接注射或施用小分子 2-乙酰基-4(5)-四羟基丁基咪唑（THI），即 S1P 裂解酶抑制剂，增加鞘氨醇-1-磷酸（S1P）可以对 mdx 小鼠的急性损伤性肌肉产生有益作用。
我们用和不用急性损伤处理 mdx 小鼠，并对增加 S1P 水平的组织病理学和功能影响进行了描述。我们还测试了外源性和直接给予 S1P 对 mdx 肌肉的影响，以研究 S1P 促进肌肉再生的分子途径。
THI 的短期治疗显著增加了急性损伤的 mdx 肢体肌肉中的纤维大小和伸趾长肌（EDL）肌肉比特定力。此外，在 THI 处理的 mdx 小鼠的损伤肌肉中，纤维化和脂肪沉积的积累减少，这是 DMD 病理学和受损肌肉再生的标志。此外，用 THI 进行更长期的治疗后，未受伤的 EDL 肌肉的力量也得到了增强。这种再生作用与成肌细胞的反应有关，因为 S1P 的肌内注射增加了 Myf5nlacz/+阳性成肌细胞的数量和受伤的 mdx 肌肉中新生的肌纤维。生物素化 S1P 的肌内注射定位于肌肉纤维，包括新生的再生纤维，这些纤维也对 S1P 受体 1（S1PR1）呈阳性染色。重要的是，在 mdx 肌肉的再生肌纤维中观察到质膜和核周磷酸化 S1PR1 的定位。成肌细胞内 S1P 水平、S1PR1 和磷酸化核糖体蛋白 S6（P-rpS6）的增加以及 EDL 肌肉比特定力的升高表明，S1P 促进了调节骨骼肌质量和功能的合成代谢途径的上调。
这些数据表明，S1P 有利于 DMD 小鼠的肌肉再生和功能改善，THI 或其他全身性增加 S1P 水平的药物可能被开发成一种有效的治疗方法，以改善肌肉功能并减少 DMD 的病理。
