Eccentric exercise facilitates mesenchymal stem cell appearance in skeletal muscle.

Area of Science:

• Muscle physiology and regeneration
• Stem cell biology
• Exercise-induced adaptations

Background:

• Eccentric contractions cause muscle injury, activating satellite stem cells for regeneration.
• The role of alternative myogenic progenitors beyond satellite cells in exercise response is unclear.

Purpose of the Study:

• To investigate the accumulation of stem cells in skeletal muscle post-exercise.
• To determine the role of alpha7 integrin in regulating these stem cells.
• To characterize the identity and function of exercise-induced stem cells.

Main Methods:

• Evaluation of stem cell antigen-1 (Sca-1) positive, CD45 negative cells in wild type and alpha7 integrin transgenic mice after eccentric exercise.
• Characterization of Sca-1+CD45- cells using in vitro strain and marker analysis.
• Transplantation of identified stem cells into wild type muscle.

Main Results:

• Sca-1+CD45- stem cells doubled in wild type muscle 24 hours post-exercise.
• Alpha7 integrin regulated Sca-1+ cell presence, with expansion in alpha7 integrin transgenic muscle.
• Exercise-induced Sca-1+CD45- cells were identified as mesenchymal-like stem cells (mMSCs), primarily pericytes.
• In vitro strain with laminin upregulated mMSC markers, suggesting a mechanism for accumulation.
• Transplanted mMSCs increased satellite cells and aided muscle fiber formation.

Conclusions:

• Mesenchymal-like stem cells (mMSCs) rapidly accumulate in skeletal muscle post-exercise in an alpha7 integrin-dependent manner.
• These mMSCs represent an early event potentially vital for skeletal muscle repair and growth.
• Alpha7 integrin and/or mMSCs may be targets for therapeutic strategies against muscle atrophy.