Exercise stress leads to an acute loss of mitochondrial proteins and disruption of redox control in skeletal muscle of older subjects: An underlying decrease in resilience with aging?

Reactive oxygen species (ROS) are recognized as important signaling molecules in healthy skeletal muscle. Redox sensitive proteins can respond to intracellular changes in ROS by oxidation of reactive thiol groups on cysteine (Cys) residues. Exercise is known to induce the generation of superoxide and nitric oxide, resulting in the activation of several adaptive signaling pathways; however, it has been suggested that aging attenuates these redox-regulated adaptations to acute exercise. In the present study, we used redox proteomics to study the vastus lateralis muscles of Adult (n = 6 male, 6 female; 18-30 yrs) and Old (n = 6 male, 6 female; 64-79 yrs) adults. Participants completed a bout of high intensity cycling exercise consisting of five sets of 2-min intervals performed at 80% maximal aerobic power output (PPO), with 2 min recovery cycling at 40% PPO between sets. Muscle biopsies were collected prior to exercise, and immediately following the first, second, and fifth high intensity interval. Global proteomic analysis indicated differences in abundance of a number of individual proteins between skeletal muscles of Adult and Old subjects at rest with a significant exacerbation of these differences induced by the acute exercise. In particular, we observed an exercise-induced decrease in abundance of mitochondrial proteins in muscles from older subjects only. Redox proteome analysis revealed cysteines from five cytosolic proteins in older subjects with lower oxidation (i.e. greater reduction) than was seen in muscle from the young adults at rest. Redox homeostasis was well maintained in Adult subjects following exercise, but there was significant increase in oxidation of multiple mitochondrial and cytosolic protein cysteines in Old subjects. We also observed that oxidation of peroxiredoxin 3 occurred following exercise in both Adult and Old groups, supporting the possibility that this is a key effector protein for mitochondrial redox signaling. Thus, we show, for the first time that exercise reveals a lack of resilience in muscle of older human participants, that is apparent as a loss of mitochondrial proteins and oxidation of multiple protein cysteines that are not seen in younger subjects. The precise consequences of this redox disruption are unclear, but this likely play a role in the attenuation of multiple adaptations to exercise that are classically seen with aging. Such changes were only seen following the acute stress of exercise., highlighting the need to consider not only basal differences seen during aging but also the difference following physiological challenge.