Bone and muscle tissues are closely linked anatomically, functionally, and metabolically. Skeletal muscles influence biochemical processes in bone tissue through mechanical loading and signaling molecules, while bone cells regulate muscle function through their mediators. A key process in maintaining bone strength is bone mineralization, in which numerous proteins are involved, including the vitamin D receptor, osteocalcin, fibroblast growth factor 23, and alkaline phosphatase. With aging, bone and muscle mass decline, increasing the risk of osteoporosis and sarcopenia. Osteoporosis is a metabolic bone disease characterized by reduced bone density and altered microarchitecture, while sarcopenia is a skeletal muscle disease characterized by the loss of muscle mass, strength, and physical performance. Because changes in bone and muscle often occur simultaneously and are linked through biochemical communication, increasing attention has been directed to osteosarcopenia.
The aim of this study was to determine, based on gene expression, whether bone mineralization is altered in sarcopenia and whether these changes are reflected in clinical indicators of sarcopenia, such as reduced handgrip strength and reduced muscle mass. We focused on genes involved in bone mineralization and calcium and phosphate metabolism.
Gene expression was measured in 58 bone tissue samples obtained from women with osteoporotic fractures, with or without sarcopenia. Total RNA was isolated from the bone samples, and its concentration and integrity were assessed. Following reverse transcription into cDNA, we measured the expression of the VDR, BGLAP, FGF23, and ALPL genes using RT-qPCR and normalized the results to the reference gene RPLP0. Statistical analysis was performed to compare gene expression between the osteoporosis and osteosarcopenia groups and to evaluate its association with clinical indicators of sarcopenia.
RNA was successfully isolated from all 58 bone samples. The mean RNA concentration was 466,6 ng/µL, and the average purity was 1,98. Adequate RNA integrity (RIN > 3,5) was achieved in 32 of the 58 samples (55,2 %). The results showed significantly higher BGLAP expression and marginally significantly higher FGF23 expression in patients with osteosarcopenia, whereas no significant differences were observed for VDR and ALPL. In patients with osteosarcopenia, a statistically significant negative correlation was found between ALPL expression and the percentage of lean body mass. These findings suggest that sarcopenia may be associated with altered expression of certain genes involved in bone mineralization.
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