Altered actin and myosin expression in muscle during exposure to microgravity

Area of Science:

• Spaceflight research
• Molecular biology
• Physiology

Background:

• Cardiovascular deconditioning and skeletal muscle atrophy are known effects of microgravity.
• The underlying molecular mechanisms, particularly changes in gene expression, remain unclear.

Purpose of the Study:

• To investigate alterations in contractile protein gene expression in rat heart and skeletal muscles following 14 days of microgravity exposure.
• To identify potential molecular targets contributing to microgravity-induced physiological changes.

Main Methods:

• Rats were subjected to 14 days of microgravity (spaceflight) and compared to a synchronous ground control group.
• Quantitative analysis of myosin heavy chain and alpha-actin mRNA levels in cardiac and skeletal muscles.
• Covariance mapping analysis was used to assess relative mRNA expression.

Main Results:

• No significant differences in myosin protein isoforms or beta-myosin heavy chain mRNA in the heart were observed between groups.
• Covariance mapping revealed differences in beta-myosin heavy chain mRNA relative to rRNA in the heart.
• Skeletal alpha-actin mRNA decreased significantly in the vastus intermedius and lateral gastrocnemius, but not triceps brachii.
• Cytochrome c mRNA decreased only in the vastus intermedius.

Conclusions:

• Microgravity exposure for 14 days induces changes in the pretranslational regulation of contractile protein gene expression in both cardiac and skeletal muscles.
• These molecular changes may contribute to cardiovascular deconditioning and skeletal muscle atrophy observed during spaceflight.