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Objective To investigate the regulation and mechanism of angiotensin II (Ang II) on skeletal muscle cells. Methods C2C12 myoblasts were divided into three groups(Control, Ang II and Ang II+ ARB) according to their treatment with Ang II or Olmesartan. 2% horse serum was used to induce myoblasts differentiated into myotubes. Myotubes average area were detected by immunofluorescence staining, and Western blot was used to test the changes in protein expressions of muscle-specific ubiquitin ligases, myogenic regulatory factors (MRFs) and PI3K / Akt / FOXO1 signaling pathway. Results Immunofluorescence staining showed that the average diameter and area of myotubes decreased after Ang II treatment (P <0. 001) and these phenotypes of myotubes could be markedly reversed (P <0. 01) by Ang II type 1 receptor, olmesartan. Additionally, the protein level of the muscle?specific ubiquitin ligases including MURF1 (P<0. 05) and MAFbx (P<0. 001) were up-regulated induced by Ang II, while the ratio of p?PI3K / PI3K (P<0. 01), p-Akt / Akt (P<0. 001) and p-FOXO1/ FOXO1 (P<0. 01) as well as MRFs including MHC (P<0. 01) and MyoD (P<0. 05) were down?regulaed, and Olmesartan treatment could attenuate the effect of Ang II on myotube proteins. Conclusion Ang II can promote protein degradation and inhibit protein synthesis to induce muscle cell atrophy by inhibiting the phosphorylation of PI3K / Akt / FOXO1 signaling pathway. [ABSTRACT FROM AUTHOR]

Objective: To research the effect of chondroitin sulfate (CS) on the proliferation of myoblasts and the formation of myotube., Methods: The myoblasts at passage 5 were used to prepare the cells suspension (1×108 cells/mL), and the experiment was divided into 4 groups based on CS concentration in the medium:group A (0 μg/mL), group B (50 μg/mL), group C (100 μg/mL), and group D (200 μg/mL). The cell morphology and myotube formation were observed by inverted microscope at 4, 5, and 8 days after treatment; MTT was used to detect the cell proliferation at 6 days, and the number of myotube was calculated by HE staining at 8 days., Results: Cells showed spindle shape after adherent, with ovoid nuclei and dense cytoplasm under inverted microscope. When the cell adherent rate was 90%, cells arranged in whorls swirled and showed long fusiform adherent growth; and then nuclei fusion resulted in formation of multincleated myotubes. At 8 days, most myoblasts fused to form myotube in group A, but less myotube was observed in groups B and C, and the least myotube in group D. The absorbance (A) values of groups A, B, C, and D were 0.045 2±0.004 4, 0.540 4±0.096 7, 0.660 9±0.143 4, and 1.069 0±0.039 0 respectively, showing significant difference between other groups ( P <0.05) except between groups B and C P >0.05). HE staining observation showed that most myoblasts fused to form myotube in group A, but less myotube in groups B and C, and the least myotube in group D. The number of myotube of groups A, B, C, and D were 222.01±30.02, 193.13±42.46, 170.26±11.96, and 136.88±16.78 respectively, showing no significant difference among groups ( F =1.658, P =0.252)., Conclusions: CS can significantly promote the proliferation of myoblast, the promotion is the biggest when CS concentration is 200 μg/mL.