Effects of spaceflight on the muscles of the murine shoulder

TLDR

Mechanical loading is essential for musculoskeletal development and maintenance, and its removal—through microgravity, paralysis, or bed rest—causes rapid muscle loss, yet the underlying molecular mechanisms, especially in spaceflight, remain largely unknown. The study aimed to investigate how microgravity affects mouse shoulder muscles during the 15‑day STS‑131, 13‑day STS‑135, and 30‑day Bion‑M1 spaceflight missions. Mice from the STS missions were euthanized within 4 h after landing, while Bion‑M1 mice were euthanized within 14 h, allowing analysis of shoulder muscle changes immediately post‑flight. Results showed that the deltoid muscle was more sensitive to microgravity than rotator cuff muscles; STS‑131 mice exhibited reduced myogenic (Myf5/6) and adipogenic (Pparg, Cebpa, Lep) gene expression, whereas Bion‑M1 mice showed no change or increased expression, indicating muscle‑type specific, rapid molecular responses to short‑duration spaceflight and reloading.

Abstract

Mechanical loading is necessary for the development and maintenance of the musculoskeletal system. Removal of loading via microgravity, paralysis, or bed rest leads to rapid loss of muscle mass and function; however, the molecular mechanisms that lead to these changes are largely unknown, particularly for the spaceflight (SF) microgravity environment. Furthermore, few studies have explored these effects on the shoulder, a dynamically stabilized joint with a large range of motion; therefore, we examined the effects of microgravity on mouse shoulder muscles for the 15-d Space Transportation System (STS)-131, 13-d STS-135, and 30-d Bion-M1 missions. Mice from STS missions were euthanized within 4 h after landing, whereas mice from the Bion-M1 mission were euthanized within 14 h after landing. The motion-generating deltoid muscle was more sensitive to microgravity than the joint-stabilizing rotator cuff muscles. Mice from the STS-131 mission exhibited reduced myogenic (Myf5 and -6) and adipogenic (Pparg, Cebpa, and Lep) gene expression, whereas either no change or an increased expression of these genes was observed in mice from the Bion-M1 mission. In summary, muscle responses to microgravity were muscle-type specific, short-duration SF caused dramatic molecular changes to shoulder muscles and responses to reloading upon landing were rapid.-Shen, H., Lim, C., Schwartz, A. G., Andreev-Andrievskiy, A., Deymier, A. C., Thomopoulos, S. Effects of spaceflight on the muscles of the murine shoulder.