Skeletal muscle adaptations to microgravity exposure in the mouse

Area of Science:

• Spaceflight and microgravity research
• Skeletal muscle physiology
• Biomedical sciences

Background:

• Microgravity poses risks to skeletal muscle health.
• Understanding muscle changes during spaceflight is crucial for astronaut health and mission success.

Purpose of the Study:

• To investigate the effects of microgravity on murine skeletal muscle fiber size, contractile protein, and enzymatic activity.
• To analyze changes in myosin heavy chain (MHC) isoform expression and citrate synthase activity.

Main Methods:

• Female C57BL/6J mice were subjected to approximately 11 days of spaceflight (SF) or ground control (AEM).
• Immunohistochemistry was used to analyze muscle fiber cross-sectional area and MHC isoform expression.
• Enzymatic analysis assessed citrate synthase activity in muscle tissue.

Main Results:

• Spaceflight significantly reduced muscle fiber cross-sectional area across all fiber types.
• An increase in MHC IIx and MHC IIb isoform expression was observed in the soleus muscle.
• Citrate synthase activity in the gastrocnemius muscle was significantly decreased in spaceflight mice.

Conclusions:

• Microgravity induces significant atrophy in murine skeletal muscle.
• Changes in MHC isoform expression and reduced enzymatic activity suggest functional alterations in muscle.
• These findings highlight the detrimental effects of spaceflight on skeletal muscle and inform countermeasures.