With age, skeletal muscle mitochondria lose their oxidative capacity and their ability to respond to energy demand. These phenomena can lead to a reduction in skeletal muscle oxygen consumption, atrophy, and increased risk of developing age-related diseases such as sarcopenia. Whether age-derived changes in mitochondrial function correspond to morphological changes in the mitochondrial reticulum remains unknown. Our objective is to investigate age-related changes in mitochondrial morphology and function using primary skeletal muscle cells derived from healthy young and old men. Primary skeletal muscle progenitor cells (SkM) derived from the Rectus abdominis muscle of healthy active 18-19-year-old men (Young), and 66-69-year-old men (Old) were obtained from Cook MyoSite Inc. (Pittsburgh, PA). Mitochondrial morphology was analyzed in live cells using confocal microscopy. Oxygen Consumption Rate (OCR) was measured in intact cells using the extracellular flux assay and a Seahorse analyzer (Agilent Technologies; Santa Clara, CA). Seahorse Cell Mito Stress Test of primary cells derived from Young revealed a higher Basal and Maximal OCR compared to Old (Basal: 23.20 ± 1.49 vs. 11.34 ± 2.31; Maximal: 41.50 ± 4.72 vs. 18.36 ± 1.65 pmol/min/protein). Young also had higher ATP production and Spare Respiratory Capacity (ATP: 19.08 ± 1.21 vs. 9.19 ± 2.10; SRC: 18.30 ± 3.47 vs. 7.03 ± 1.29 pmol/min/protein). No differences were revealed in morphology (Individuals: 37.80 ± 23.18 vs. 46.67 ± 22.43 counts; Networks: 10.20 ± 2.48 vs. 15.33 ± 5.75 counts; Mean Branches per Network: 15.52 ± 6.41 vs. 11.27 ± 3.67 counts). These preliminary results show primary skeletal muscle progenitor cells derived from old donors have lower respiration, produce less ATP, and have a reduced capacity to adapt to energy demands when compared to SkM derived from young donors. Further analyses can give us an insight into human skeletal muscle-derived cellular physiological capacity. Technology to observe human muscle mitochondrial dysfunction in vitro helps us understand the effects of aging on skeletal muscle mitochondria and whole-body declines of resting and exercise metabolic rates. Studies on aging individuals will be required to determine if predicted decrements in energy coupling efficiency occur with aging in vivo.
