Abstract: BACKGROUND: The phosphatidylinositol 3-kinase/serine protein kinase B signaling pathway is closely related to the regulation of cell proliferation, growth, and metabolism. As a traditional Chinese medicine for invigorating the spleen and tonifying the kidney, the active ingredient of Polygonatum sibiricum, Polygonatum sibiricum polysaccharide, has the potential to improve skeletal muscle aging and treat sarcopenia, but the specific molecular mechanism remains unclear.
OBJECTIVE: To investigate the protective effect and mechanism of Polygonatum sibiricum polysaccharide on skeletal muscle aging in sarcopenia mice by regulating the phosphatidylinositol 3-kinase/serine protein kinase B signaling pathway.
METHODS: Forty C57BL/6 male mice were randomly divided into control group, model group, and low-, medium-, and high-dose Polygonatum sibiricum polysaccharide groups. The latter four groups received intraperitoneal injections of 400 mg/kg D-galactose every other day for 12 weeks to establish a sarcopenia model. Modeling and drug administration were performed simultaneously. The low-, medium-, and high-dose Polygonatum sibiricum polysaccharide groups were administered 30, 60, and 120 mg/kg by gavage, respectively, while the control and model groups received an equal volume of normal saline by gavage every other day for 12 consecutive weeks. Physiological functions were assessed by body mass, grip strength, and endurance. Western blot and real-time quantitative PCR were used to detect the expression of phosphatidylinositol 3-kinase/protein kinase B pathway proteins (phosphorylated phosphatidylinositol 3-kinase, phosphatidylinositol 3-kinase, phosphorylated serine protein kinase B, and protein kinase B) and aging-related p21 and p53 proteins and mRNAs in skeletal muscle. Immunofluorescence staining was used to detect the expression of aging-related protein p21. Hematoxylin-eosin staining and Sirius red staining were used to observe myofiber pathology and fibrosis degree.
RESULTS AND CONCLUSION: (1) After 12 weeks of intervention, compared with the control group, body mass, grip strength, and endurance were significantly reduced in the model group (P < 0.01). Compared with the model group, only grip strength showed an upward trend in the low-dose Polygonatum sibiricum polysaccharide group (P < 0.05), while body mass, grip strength, and endurance were all increased in the medium- and high-dose Polygonatum sibiricum polysaccharide groups (P < 0.05 or P < 0.01). (2) Western blot results showed that compared with the control group, the expression levels of phosphorylated phosphatidylinositol 3-kinase/phosphatidylinositol 3-kinase and phosphorylated protein kinase B/protein kinase B proteins were decreased in the model group (P < 0.01). Compared with the model group, there were no significant changes in the low-dose Polygonatum sibiricum polysaccharide group, but these indexes were significantly increased in the medium- and high-dose Polygonatum sibiricum polysaccharide groups (P < 0.01). Compared with the control group, p21 and p53 protein expression was increased in the model group (P < 0.01). Compared with the model group, there was no significant change in p21 and p53 protein expression in the low-dose Polygonatum sibiricum polysaccharide group, but p21 and p53 protein expression was significantly decreased in the medium- and high-dose Polygonatum sibiricum polysaccharide groups (P < 0.01). (3) Real-time quantitative PCR results showed that compared with the control group, p21 and p53 mRNA expression was increased in the model group (P < 0.01). Compared with the model group, there was no significant change in p21 and p53 mRNA expression in the low-dose Polygonatum sibiricum polysaccharide group, but p21 and p53 mRNA expression was significantly decreased in the medium- and high-dose Polygonatum sibiricum polysaccharide groups (P < 0.05 or P < 0.01). (4) Immunofluorescence staining showed that compared with the control group, the mean fluorescence intensity was significantly increased in the model group (P < 0.01). Compared with the model group, the mean fluorescence intensity of p21 was significantly decreased in all Polygonatum sibiricum polysaccharide groups (P < 0.01). (5) Hematoxylin-eosin staining showed that compared with the model group, all doses of Polygonatum sibiricum polysaccharide improved the degree of skeletal muscle cell atrophy and degeneration. (6) Sirius red staining showed that compared with the model group, low-, medium-, and high-dose Polygonatum sibiricum polysaccharide interventions improved skeletal muscle fibrosis. To conclude, these findings indicate that Polygonatum sibiricum polysaccharides can improve the physiological function, pathological changes, and fibrosis degree of skeletal muscle aging in sarcopenia model mice, and its mechanism is related to the regulation of the phosphatidylinositol 3-kinase/protein kinase B signaling pathway.

Key words: polygonatum sibiricum polysaccharide, sarcopenia, skeletal muscle aging, phosphatidylinositol 3-kinase/protein kinase B signaling pathway