Muscle function decline and mitochondria changes in middle age precede sarcopenia in mice

Area of Science:

• Muscle biology
• Mitochondrial biology
• Aging research

Background:

• Sarcopenia, the loss of muscle mass and strength with aging, is a significant health concern.
• While mitochondrial metabolism is linked to muscle function and disease, its role in muscle aging, specifically mitochondrial topology and dynamics, remains unclear.

Purpose of the Study:

• To investigate the age-dependent changes in mitochondrial distribution and skeletal muscle function in mice.
• To understand the specific alterations in mitochondrial morphology and calcium handling during the aging process.

Main Methods:

• Isolation of muscle fibers from the flexor digitorum brevis of mice across different age groups (juvenile, adult, older).
• Microscopic analysis to assess mitochondrial morphology, distribution, and contact with the sarcoplasmic reticulum.
• Measurement of mitochondrial calcium (Ca2+) resting levels and quantification of mitochondria-to-jSR pairs.

Main Results:

• A fusion-like mitochondrial phenotype and altered orientation (perpendicular to fiber axis) were observed in adult mice compared to juvenile and older groups.
• Increased contact area between the sarcoplasmic reticulum and mitochondria was noted in adult mice.
• Mitochondrial Ca2+ resting levels decreased in adult mice (10-14 months) and significantly increased in older mice, with fewer mitochondria-to-jSR pairs in older mice.

Conclusions:

• Mitochondrial morphology and distribution undergo age-dependent changes, with notable alterations occurring in midlife.
• These mitochondrial changes, including altered calcium handling, precede the full manifestation of sarcopenia.
• The study highlights the critical role of mitochondrial dynamics and topology in the aging skeletal muscle.