Genomic profiling using RNAseq to identify key drivers of sarcopenia and motor unit turnover in murine skeletal muscle
Authors: Staunton Caroline Amy , Vasilaki Aphrodite , Barrett‐Jolley Richard , McArdle Anne , Jackson Malcolm 
Published: June 2021

Sarcopenia; the age‐related loss of skeletal muscle mass and function, significantly affects quality of life in the aging population and has been linked to remodelling and loss of motor units. Throughout the life course, there is evidence for motor unit turnover through cycles of denervation and reinnervation of individual muscle fibres and at more advanced ages this process may breakdown. The mechanisms that underlie these processes are unclear, but are believed to be multifactorial which has confounded efforts to identify primary mechanisms.The aim of this study was to determine the gene expression profiles in the anterior tibialis muscle of adult (6–8 months) and old (26 months) mice before and 3 days after peroneal nerve crush surgery. We achieved this with RNA deep sequencing and parallel histological, molecular and electrophysiological assessments of muscle pathophysiology.Nerve crush injury was used to mimic motor unit remodelling at the neuromuscular junctions since the crush injury damages all axons, but the endoneurial tubes are preserved which alongside the Schwann cell basal laminae which remains, enables axonal elongation and facilitates reinnervation. Samples were examined at 3 days post‐crush since this at time point there was complete loss of pre‐synaptic input to the neuromuscular junctions and hence putatively a time when sprouting factors and nerve regenerative proteins are being transcribed. Using paired‐end 2×75 base pair sequencing we generated data from >280 M clusters per lane (n=5/treatment).In total, 16 differentially expressed genes (DEGs) were found in the AT muscle in response to age. 1448 DEGs were changed in the muscle of adult mice in response to nerve crush in comparison with 644 DEGs identified in the muscle of old mice in response to nerve crush.The protein coding DEG (adjusted for by False Discovery Rate <0.05 and 1.4log2 fold change) were then examined and those with highest and lowest fold changes from each treatment contrasts were investigated using DAVID and Ingenuity Pathway Analysis (IPA) to reveal key upstream regulators as well as canonical pathways for each contrast. Several DEGs were revealed across the different contrasts and of particular interest ZCCHC17 (previously reported as a master regulator of synaptic gene expression in Alzheimer's disease) was altered with age in response to crush. Key pathways affected by aging and nerve crush included P13K‐Akt signalling, NFkB signalling, Schwann cell guidance, axonal guidance and extension.These findings provide a novel insight into the effects of aging on the response of muscle to nerve crush. Further studies are underway to identify the specific signalling pathways involved. These results reveal potential therapeutic targets that could aid the regenerative capacity of aging skeletal muscle.Support or Funding InformationThis work was funded by the UK Medical Research Council.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.