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BACKGROUND: Research evidence shows that skeletal muscle contractile activity can induce ribosomal biogenesis, which plays an important role in the control of skeletal muscle mass. OBJECTIVE: To review the main mechanism of ribosome biogenesis in skeletal muscle hypertrophy, upstream regulatory signals of ribosomal biogenesis in skeletal muscle, and effect of exercise on ribosomal biogenesis, and to explore the ribosome biogenesis mechanism of exercise-induced skeletal muscle hypertrophy. METHODS: Relevant studies about exercise, skeletal muscle hypertrophy and ribosome biogenesis in CNKI, Wanfang, and PubMed databases were searched. The key words were “exercise, resistance training, skeletal muscle hypertrophy, protein synthesis, ribosome biogenesis” in English and Chinese. Relevant literatures published from 1999 to 2019 were searched and screened according to inclusion and exclusion criteria. RESULTS AND CONCLUSION: (1) Ribosome biogenesis as a main source of translational capacity plays an important role in muscle growth. (2) A single bout of resistance exercise can promote the ribosome biogenesis. However, cumulative bouts of resistance exercise eventually lead to the accumulation of mature rRNAs, leading to increased concentration of total RNA, which promote the growth of skeletal muscle. (3) Ribosome biogenesis may be the key molecular mechanism for the regulation of skeletal muscle hypertrophy induced by resistance training. (4) Moderate-volume resistance training led to adaptations to resistance training. This hypertrophy was associated with volume-dependent regulation of total RNA. This suggests that ribosomal biogenesis regulates the dose-effect relationship between training volume and muscle hypertrophy.
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Objective To establish an overload-induced hypertrophy model in aged rats by severing the distal tendon of gastrocnemius muscle, and to investigate the effect of vitamin D on overload-induced hypertrophy and the related mechanism. Methods A total of 20 male rats (24 months old) underwent tenotomy of the achilles tendon of the gastrocnemius muscle in the left hind limb; and a control sham operation was performed on the right hind limb. The rats were randomly divided into control group and experimental group. Experimental group received 1 000 IU/kg of vitamin D by intragastric administration, and the control group was given soybean oil. The animals were sacrificed one week later, the blood samples were collected, and the left, right hind musculus plantaris tissues were weighed and kept in liquid nitrogen. ELISA assay was used to examine serum 25(OH)D level and vitamin D receptor (VDR) in the skeletal muscle. Western blotting analysis was used to examine mTOR, rpS6 protein and their phosphorylation. Results The food intake and body mass were not significantly different between the two groups. Compared with the control side, vitamin D supplement significantly increased the muscle mass of the overload side in both groups (P<0. 05); and the mass of the overload side in the vitamin D supplement group was significantly higher than that in the control group (P<0. 05), while the mases were not significantly different for the sham sides in the two groups. The results of ELISA assay showed that vitamin D supplement significantly increased serum 25(OH)D levels in rats compared with the control group (P< 0. 05), and significantly promoted the expression of VDR in the overload side compared with the Sham side (P<0. 05), while there was no significant difference between the two sides in the control group. Western blotting analysis showed that p-rpS6/rpS6 and p-mTOR/mTOR ratios in the overload sides were higher than those in the Sham sides, but significant difference was only found for the vitamin D supplement group (P<0. 05). Conclusion Tenotomy of the achilles tendon of the gastrocnemius muscle can effectively promote the skeletal muscle hypertrophy in aging rats, and vitamin D supplement can further enhance overload-induced skeletal muscle hypertrophy, which might be related to VDR expression in skeletal muscle and protein synthesis protein mTOR and rpS6.
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[Objective]The influence of electroacupuncture (EA) stimulation on physical inactivity is not clear. This study aimed to investigate the effects of EA on the recovery of mouse soleus muscle atrophy induced by hindlimb suspension (HS).<BR>[Methods]We used 8-week-old male ICR mice (n = 20). The mice were divided into 4 groups:the No treatment group (NT, n = 5), HS group (HS, n = 5), Control group (CT, n = 5), and Reloading-with-EA-stimulation group (EA, n = 5). HS mice were suspended for up to 14 days. CT and EA mice were reloaded for an additional 14 days after the HS for 14 days. The HS method used a modified version of an apparatus used in a previous study. EA mice received EA every other day immediately after reloading and were stimulated in the triceps surae muscle at 10 Hz for 30 min with a stainless steel needle. The weight, muscle fiber area size and number of macrophages in the soleus muscle were analyzed.<BR>[Results]The number of skeletal muscle macrophages was increased significantly in EA mice compared with that in CT mice (P < 0.01). The soleus muscle weight and muscle fiber cross-sectional area were decreased in HS mice compared with NT mice (P < 0.01). However, the muscle weight of EA and CT mice increased significantly compared with that of HS mice (P < 0.01). In addition, the muscle weight of EA mice was significantly higher than that of CT mice (P < 0.01), without a significant difference in muscle fiber cross-sectional area between CT and EA mice. <BR>[Conclusion]These results indicate that EA was effective in facilitating the recovery of skeletal muscle atrophy in mice. In addition, resolution of the skeletal muscle atrophy suggested the satellite cell activation by macrophages, because macrophages invaded the skeletal muscle after EA stimulation.