Abstract — Molecular mechanisms initiating the development of atrophic changes in a mammalian postural muscle remain unclear. We have suggested that AMP-activated protein kinase (AMPK) may play an important role in the regulation of anabolic and catabolic signaling pathways in postural muscle at the initial stage of mechanical unloading, since skeletal muscle inactivation can lead to changes in the balance of intramuscular high-energy phosphates. Beta-guanidinopropionic acid (β-GPA) can act as a modulator of the balance of high-energy phosphates, application of which can reduce the content of intracellular high-energy phosphates. The purpose of this study was to assess signaling pathways of protein synthesis and degradation in rat soleus muscle after preliminary treatment with β-GPA followed by 1-day hindlimb unloading. The experiments were performed on male Wistar rats, which were divided into the following groups: (1) vivarium control (C); (2) vivarium control + β-GPA (C + GPA); (3) 1-day hindlimb unloading (HU); and (4) 1-day hindlimb unloading + β-GPA (HU + GPA). β-GPA was administered daily by intraperitoneal injections (400 mg/kg). The content of the key signaling proteins (AMPK, ACC, p70S6K, 4E-BP1, and FOXO3) was determined by gel electrophoresis followed by immunoblotting. The expression of mRNA of ubiquitin ligases (MuRF1 and MAFbx) was evaluated by real-time PCR. A prevention of reduction in phosphorylation of AMPK, ACC and 4E-BP1 and the return to control values of the increased level of p70S6K phosphorylation were observed in the group with 1-day unloading and β-GPA pretreatment. The phosphorylation of AKT and FOXO3, as well as the expression levels of MuRF1 and MAFbx in the HU + GPA group did not differ from the HU group. The obtained data indicate that the AMPK activity may play an important role in the modulation of anabolic mTORC1-signaling in rat soleus muscle at the early stage of simulated microgravity.

中文翻译：

---

β-GPA 对后肢卸载初期大鼠比目鱼肌合成代谢和分解代谢信号通路标志物的影响

摘要 — 引发哺乳动物姿势肌肉萎缩变化发展的分子机制尚不清楚。我们已经提出 AMP 活化蛋白激酶 (AMPK) 可能在机械卸载的初始阶段在调节姿势肌肉的合成代谢和分解代谢信号通路中发挥重要作用，因为骨骼肌失活会导致肌肉内平衡的变化。高能磷酸盐。β-胍基丙酸（β-GPA）可作为高能磷酸盐平衡的调节剂，应用可降低细胞内高能磷酸盐的含量。本研究的目的是评估大鼠比目鱼肌在用 β-GPA 进行初步治疗和后肢卸载 1 天后蛋白质合成和降解的信号通路。实验在雄性Wistar大鼠上进行，分为以下几组：（1）动物饲养组（C）；(2)动物饲养控制+β-GPA(C+GPA)；(3) 1天后肢卸荷(HU)；(4) 1天后肢卸荷+β-GPA(HU+GPA)。β-GPA 每天通过腹腔注射 (400 mg/kg) 给药。通过凝胶电泳和免疫印迹确定关键信号蛋白（AMPK、ACC、p70S6K、4E-BP1 和 FOXO3）的含量。通过实时PCR评估泛素连接酶（MuRF1和MAFbx）的mRNA表达。在具有 1 天卸载和 β-GPA 预处理的组中观察到 AMPK、ACC 和 4E-BP1 磷酸化减少的预防以及 p70S6K 磷酸化水平增加的控制值恢复。AKT 和 FOXO3 的磷酸化，HU+GPA组MuRF1和MAFbx的表达水平与HU组无差异。获得的数据表明，在模拟微重力的早期阶段，AMPK 活性可能在大鼠比目鱼肌中合成代谢 mTORC1 信号的调节中起重要作用。