Muscle stem cell adaptations to cellular and environmental stress

Area of Science:

• Cellular Biology
• Regenerative Medicine
• Muscle Physiology

Background:

• Skeletal muscle regeneration relies on a unique population of stem cells called satellite cells.
• These cells maintain a quiescent state but activate upon injury to facilitate muscle repair.
• The absence of functional satellite cells prevents skeletal muscle regeneration.

Purpose of the Study:

• To investigate the role of stress response pathways in skeletal muscle stem cell (satellite cell) function.
• To explore how prolonged quiescence and microenvironmental factors act as selective pressures on satellite cells.
• To propose a cellular stress test model for satellite cell maintenance and muscle regeneration.

Main Methods:

• Review of accumulating evidence on satellite cell stress responses.
• Analysis of pathways involved in satellite cell quiescence and activation.
• Examination of stress-induced responses including DNA damage, heat shock, and environmental stress.

Main Results:

• Satellite cells activate multiple stress response pathways during quiescence and activation.
• Stress response pathways, including the integrated stress response (eIF2α) and mTORC1, regulate satellite cell protein synthesis and quiescence.
• Evidence suggests satellite cells respond to stress not only with survival or death pathways but also with spontaneous activation and fusion.

Conclusions:

• A cellular stress test model is proposed where quiescence and microenvironment maintain satellite cell fitness.
• Fit satellite cells with robust stress responses sustain the stem cell pool for lifelong muscle regeneration.
• Unfit satellite cells are eliminated through spontaneous activation, cell death, or senescence, preserving stem cell pool integrity.