The effect of disuse and reloading on muscle ribosome biogenesis

Introduction: Muscle wasting can occur as a result of muscle disuse in disease and non-disease states, often seen in cancer patients and patients undergoing chemotherapy. Muscle mass is regulated by the balanced relationship between muscle protein synthesis and protein degradation. While muscle atrophy remains a significant issue, the cellular and molecular processes involved in muscle wasting are not completely understood. Understanding the mechanisms of muscle loss by disuse may lead to novel therapeutic targets towards mitigation of muscle loss during limb immobilization, and potentially accelerating muscle mass recovery during return to ambulation. Ribosome biogenesis, the cellular process of synthesizing new ribosomes, has been shown to be a key player in skeletal muscle growth and maintenance. Given that ribosome abundance plays a central role in muscle mass, we hypothesize that disuse causes reduced ribosomal RNA (rRNA) due to impaired muscle ribosome biogenesis and reloading causes an increase in ribosome biogenesis, preceding muscle regrowth Methods: Sixteen 12-week-old C57Bl6/J mice (8 males and 8 females) underwent unilateral limb immobilization over two time intervals (3 days and 7 days). Additionally, a second cohort of mice (11 males and 12 females) underwent 7 days of unilateral immobilization and 3 or 7 days of reloading (return to ambulation). RNA was extracted using Direct-zol RNA Miniprep Kit. Results: During disuse, at 3 days (3D), female control (CON) and immobilized (EXP) gastrocnemius weights displayed a mean of 90.53 ± 7.29mg (CON) and 87.48 ± 8.50mg (EXP), (p=0.4660). At 7 days (7D), female gastrocnemius mean weights were 96.68 ± 1.92 mg (CON) and 75.93 ± 6.39 mg (EXP), (p=0.0145). 3D male gastrocnemius weights displayed a mean of 131.83 ± 10.96 mg (CON) and 123.98 ± 5.82 mg (EXP), (p=0.1093). 7D males displayed 137.18 ± 7.03 mg (CON) and 113.18 ± 4.98 mg (EXP), (p= 0.0147). We then measured total RNA, as a readout of ribosome RNA (rRNA). After 3 days, total RNA per mg of tissue was 86.85 ± 13.45% compared to the respective CON leg in females (p=0.4068), and 90.25 ± 13.07% in males (p=0.2533). At 7D, total RNA per mg of tissue was 100.05 ± 14.64% in EXP leg compared to CON leg in females (p=0.9947), and 79.99 ± 9.73% in males (p=0.1340). During reloading, gastrocnemius muscle mass was 98.1 ± 3.82 mg (CON) and 81.48 ± 4.03 mg (EXP) at 3D reloading following the 7D of disuse in females (p<0.0001), and 136.98 ± 8.87 mg (CON) and 116.05 ± 11.12 mg (EXP) in males (p<0.0001). After 7D reloading, muscle mass was 94.17 ± 5.71 mg (CON) and 84.28 ± 7.81 mg (EXP) in females (p=0.0754), and 136.68 ± 9.86 mg (CON) and 122.04 ± 9.71 mg (EXP) in males (p=0.0138). At 3D reloading, total RNA per mg of tissue was 113.33 ± 19.87% in EXP leg compared to CON leg in females (p=0.3320), and 96.78 ± 8.14% in males (p=0.5817). At 7D reloading, total RNA per mg of tissue was 111.72 ± 9.89% in EXP leg compared to CON leg in females (p=0.1143) and 97.01 ± 9.43% in males (p=0.6160). Conclusion: Our preliminary data demonstrates that muscle mass is rapidly reduced in both male and female immobilized limbs. Ribosomal RNA is also rapidly reduced during disuse, although not statistically significant when analyzing each sex in isolation. Ribosomal RNA loss appears to precede muscle loss and is rapidly recovered during reloading, also preceding muscle regrowth. Ribosomal mass contributes to muscle atrophy and regrowth from atrophy. Next, we will proceed to measure markers of ribosome biogenesis. 1R15AR083675-01 80NSSC20M0124 This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.