Medical Clinic, Department of Sports Medicine, University Hospital Tübingen, Hoppe-Seyler-Str. 6, 72076, Tübingen, Germany.
Mol Cell Biochem. 2018 Nov;448(1-2):251-263. doi: 10.1007/s11010-018-3330-z. Epub 2018 Feb 14.
Dietary administration of orotic acid (OA), an intermediate in the pyrimidine biosynthetic pathway, is considered to provide a wide range of beneficial effects, including cardioprotection and exercise adaptation. Its mechanisms of action, when applied extracellularly, however, are barely understood. In this study, we evaluated potential effects of OA on skeletal muscle using an in vitro contraction model of electrically pulse-stimulated (EPS) C2C12 myotubes. By analyzing a subset of genes representing inflammatory, metabolic, and structural adaptation pathways, we could show that OA supplementation diminishes the EPS-provoked expression of inflammatory transcripts (interleukin 6, Il6; chemokine (C-X-C Motif) ligand 5, Cxcl5), and attenuated transcript levels of nuclear receptor subfamily 4 group A member 3 (Nr4A3), early growth response 1 (Egr1), activating transcription factor 3 (Atf3), and fast-oxidative MyHC-IIA isoform (Myh2). By contrast, OA had no suppressive effect on the pathogen-provoked inflammatory gene response in skeletal muscle cells, as demonstrated by stimulation of C2C12 myotubes with bacterial LPS. In addition, we observed a suppressive effect of OA on EPS-induced phosphorylation of AMP-activated protein kinase (AMPK), whereas EPS-triggered phosphorylation/activation of the mammalian target of rapamycin (mTOR) was not affected. Finally, we demonstrate that OA positively influences glycogen levels in EP-stimulated myotubes. Taken together, our results suggest that in skeletal muscle cells, OA modulates both the inflammatory and the metabolic reaction provoked by acute contraction. These results might have important clinical implications, specifically in cardiovascular and exercise medicine.
饮食中添加嘧啶生物合成途径的中间产物乳清酸（OA）被认为具有广泛的有益作用，包括心脏保护和运动适应。然而，当其在细胞外应用时，其作用机制几乎不为人知。在这项研究中，我们使用电脉冲刺激（EPS）C2C12 肌管的体外收缩模型评估了 OA 对骨骼肌的潜在影响。通过分析一组代表炎症、代谢和结构适应途径的基因，我们可以表明 OA 补充减少了 EPS 引起的炎症转录物（白细胞介素 6，Il6；趋化因子（C-X-C 基序）配体 5，Cxcl5）的表达，并减弱了核受体亚家族 4 组 A 成员 3（Nr4A3）、早期生长反应 1（Egr1）、激活转录因子 3（Atf3）和快速氧化型 MyHC-IIA 同工型（Myh2）的转录水平。相比之下，OA 对骨骼肌细胞中病原体引起的炎症基因反应没有抑制作用，这是通过用细菌 LPS 刺激 C2C12 肌管来证明的。此外，我们观察到 OA 对 EPS 诱导的 AMP 激活蛋白激酶（AMPK）磷酸化具有抑制作用，而 EPS 触发的哺乳动物雷帕霉素靶蛋白（mTOR）的磷酸化/激活不受影响。最后，我们证明 OA 可正向影响 EP 刺激的肌管中的糖原水平。总之，我们的结果表明，在骨骼肌细胞中，OA 调节急性收缩引起的炎症和代谢反应。这些结果可能具有重要的临床意义，特别是在心血管和运动医学领域。
