Novel intravital assessment of muscle cytosol H 2 0 2 content supports a key role for motor unit remodelling in sarcopenia.

Sarcopenia; the age‐related loss of muscle mass and function, significantly affects quality of life in the ageing population and has been linked to remodelling and loss of motor units. Reactive oxygen species (ROS) generation, inflammation and FOXO‐dependant muscle atrophy are three key pathways associated with muscle dysfunction and this study focusses on the role of H 2 0 2 in skeletal muscle ageing. The aim was to determine whether increases in H 2 0 2 concentration occur in skeletal muscle fibres from adult (6–8 months) and old (26 months) mice and whether this was confined to denervated fibres, or additionally to healthy muscle fibres. The role of hydrogen peroxide (H 2 0 2 ) in motor unit remodelling was examined using AAV‐mediated transfection of cyto‐Hyper2 (a highly specific H 2 0 2 probe), into muscle of a transgenic Thy‐1 CFP mice. AAV6‐Hyper2 (5×10 10 vg/ml) was directly injected into the anterior tibialis (TA) muscles of mice at 28 days prior to surgical crush of the common peroneal nerve or sham control mice and the TA muscles of these mice were imaged using intravital fluorescence microscopy at 3, 7 and 21 days post‐crush. Electrophysiological approaches are also being utilised to examine the structure and function of fibres and how this changes with ageing. Data from the sequential intravital images from adult mice showed that that the TA muscle fibres following nerve crush had an elevated H 2 0 2 content that was statistically significant (p<0.001) by 3 days post nerve crush which coincided with the time at which neuromuscular junction (NMJ) breakdown occurred at the presynaptic terminus. Complete loss of pre‐synaptic structure of the NMJ was seen by 7 days post‐crush when H 2 0 2 levels remained elevated and when skeletal muscle fibre atrophy was apparent. At 21 days post‐injury, full reinnervation of the muscle had occurred with both pre and post‐synaptic structures intact although there remained some faint AChR clustering. At this time point the muscle fibre H 2 0 2 levels had returned to baseline values. In light of these unique data, current work is examining aged Thy‐1 CFP mice (26 months old) to determine the fibre H 2 0 2 content following nerve injury and the regenerative capacity of the nerves. Potential therapeutic targets are also being examined using RNA‐seq approaches to identify novel sprouting factors and proteins of interest that could be driving these processes. Support or Funding Information This work was funded by the MRC. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .