Abstract
To determine the role of denervation and motor unit turnover in the age-related increase in skeletal muscle oxidative stress, the hydrogen peroxide (H2O2) specific, genetically-encoded, fluorescent cyto-HyPer2 probe was expressed in mouse anterior tibialis (AT) muscle and compared with ex vivo measurements of mitochondrial oxidant generation. Crush of the peroneal nerve induced increased mitochondrial peroxide generation, measured in permeabilised AT fibers ex vivo and intra vital confocal microscopy of cyto-HyPer2 fluorescence showed increased cytosolic H2O2 in a sub-set (~24%) of individual fibers associated with onset of fiber atrophy. In comparison, mitochondrial peroxide generation was also increased in resting muscle from old (26 month) mice compared with adult (6–8 month) mice, but no age effect on fiber cytosolic H2O2in vivo was seen. Thus ageing is associated with an increased ability of muscle fibers to maintain cytosolic redox homeostasis in the presence of denervation-induced increase in mitochondrial peroxide generation.
Highlights
Age-related loss of muscle mass and strength is a disabling factor in older subjects for which approaches to prevention and therapeutic intervention are currently limited
We speculated that denervation-induced increases in mitochondrial reactive oxygen species (ROS) production by individual muscle fibers might contribute to the increased ROS generation by muscle mitochondria that has been reported to occur during aging[13,16], but whether such changes occur during motor unit remodelling is unknown
Following previous studies undertaken to transfect skeletal muscle fibers with HyPer using rAAV6 ex vivo[24] and in vivo studies undertaken by Chamberlain and colleagues[27], we examined the efficacy of the AAV6 approach to transfect anterior tibialis (AT) fibers with HyPer[2]
Summary
Age-related loss of muscle mass and strength is a disabling factor in older subjects for which approaches to prevention and therapeutic intervention are currently limited. We speculated that denervation-induced increases in mitochondrial reactive oxygen species (ROS) production by individual muscle fibers might contribute to the increased ROS generation by muscle mitochondria that has been reported to occur during aging[13,16], but whether such changes occur during motor unit remodelling is unknown. Following development of the method, this approach was used to examine the effect of nerve crush (as a model of motor unit turnover) on skeletal muscle cytosolic H2O2 content in vivo in comparison with ex vivo measurements of skeletal muscle mitochondrial peroxide generation obtained using the amplex red technique and to examine both mitochondrial and cytosolic H2O2 content in adult and old mice
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