Skeletal muscle “ex vivo” mitochondrial respiration parallels decline in vivo oxidative capacity, cardiorespiratory fitness and muscle strength: the Baltimore Longitudinal Study of Aging.. Homo sapiens

Mitochondrial function in human skeletal muscle declines with aging, possibly because of damage accumulation caused by reactive oxygen species (ROS) produced during oxidative phosphorylation. However, most evidence for such a decline comes from studies based on indirect methods and the clinical relevance of this decline with respect to physical function has not been clearly delineated. We hypothesized that mitochondrial respiration objectively assessed in permeabilized human muscle fibers declines with aging, correlates with phosphocreatine post exercise recovery rate (kPCr) assessed by 31P magnetic resonance spectroscopy (MRS) and with muscle performance and aerobic fitness. Mitochondrial respiration was assessed by high resolution respirometry in saponin-permeabilized fibers from vastus lateralis muscle biopsies of 38 participants from the Baltimore Longitudinal Study of Aging (BLSA) (21 men, age 24-91 years) who also had available measures of peak oxygen consumption (VO2max) from treadmill tests, gait speed in different tasks, 31P magnetic resonance spectroscopy and isokinetic knee extension strength. Results indicated a significant reduction in mitochondrial respiration in older age (p<0.05) that was independent of potential confounders. Mitochondrial respiratory capacity was also associated with VO2max, muscle strength, phosphocreatine post-exercise recovery rate (kPCr), and time in 400m walk (p < 0.05). A moderate negative trend toward significance (p = 0.074) was observed between mitochondrial respiration and BMI. Finally, transcriptional profiling revealed a downregulation of mitochondrial gene networks with aging (p < 0.05). Overall, our findings reinforce the notion that mitochondrial function declines with age and is implicated in the parallel decline of muscle performance and cardiorespiratory fitness. Overall design: RNA obtained from the vastus lateralis of a subset of the participants (N=24), aged 25-84 years (mean= 67 ± 15) was analyzed by Illumina HT-12v4 microarrays, with 4 young (Y, 2M/2F), 5 middle-aged (MA, 2M, 3F), and 14 old (O, 11M, 3F) BLSA participants.