Department of Physical Therapy, Faculty of Health and Welfare, Prefectural University of Hiroshima, 1-1 Gakuen-cho, Mihara-shi, Hiroshima 723-0053, Japan.
Department of Physical Therapy, Faculty of Health Sciences, Okayama Healthcare Professional Uni- versity, 3-2-18 Daiku, Kita-ku, Okayama-shi, Okayama 700-0913, Japan.
Biomed Res. 2023;44(5):209-218. doi: 10.2220/biomedres.44.209.
Electrical stimulation (ES) is effective for disuse-induced muscle atrophy. However, the acute effect of ES on muscle protein synthesis (MPS) and muscle protein breakdown (MPB) remains unclear. We investigated the effect of a single-session ES treatment on mTORC1 signaling, MPS, and MPB in the soleus muscle of 2-week hindlimb unloaded rats. Sprague Dawley rats (n = 12 male) were randomly divided into control (CON) and hindlimb unloaded (HU) groups. After 2 weeks, the right soleus muscle was percutaneously stimulated and underwent supramaximal isometric contractions. The left soleus muscle served as an internal control. We collected soleus muscle samples 6 h after ES. Two weeks of HU decreased p70S6K and S6rp activation, downstream factors for mTORC1 signaling, and SUnSET method-assessed MPS, but increased the LC3-II/I ratio, an indicator of autophagy. ES on disused muscle successfully activated mTORC1 signaling but did not affect MPS. Contrary, ES decreased ubiquitinated proteins expression and LC3B-II/I ratio. HU might affect mTORC1 activation and MPS differently in response to acute ES possibly due to excessive ROS production caused by ES. Our findings suggest that ES applied to disused skeletal muscles may suppress MPB, but its effect on MPS appears to be attenuated.
电刺激（ES）对废用性肌肉萎缩有效。然而，ES 对肌肉蛋白合成（MPS）和肌肉蛋白分解（MPB）的急性影响仍不清楚。我们研究了单次 ES 治疗对 2 周后肢去负荷大鼠比目鱼肌中 mTORC1 信号、MPS 和 MPB 的影响。雄性 Sprague Dawley 大鼠（n = 12）随机分为对照组（CON）和后肢去负荷组（HU）。2 周后，右侧比目鱼肌经皮刺激并进行最大等长收缩。左侧比目鱼肌作为内部对照。ES 后 6 小时采集比目鱼肌样本。2 周的 HU 降低了 mTORC1 信号的下游因子 p70S6K 和 S6rp 的激活以及 SUnSET 方法评估的 MPS，但增加了自噬的标志 LC3-II/I 比值。ES 对失用肌肉的成功激活了 mTORC1 信号，但没有影响 MPS。相反，ES 降低了泛素化蛋白表达和 LC3B-II/I 比值。HU 可能会因 ES 引起的过多 ROS 产生而以不同的方式影响 mTORC1 激活和 MPS。我们的研究结果表明，ES 应用于失用的骨骼肌可能会抑制 MPB，但对 MPS 的影响似乎减弱了。
