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The Effect of Motor Denervation on Skeletal Muscle Stem Cells
Alvin Wong, MD, Joanna Dreux, MSc, Steven Garcia, BA, William Y. Hoffman, MD, Stanley Tamaki, PhD, Jason H. Pomerantz, MD.
University of California San Francisco, San Francisco, CA, USA.

PURPOSE:
Resident stem cells in skeletal muscle (MuSCs) express the transcription factor paired box protein 7 (Pax7) and repair injured muscle. Previous studies have reported MuSC depletion after long-term denervation, possibly explaining the irreversibility of denervation atrophy, but did not quantify Pax7+ cells and did not perform functional studies. It remains unknown to what extent MuSC depletion limits recovery after delayed reinnervation. Determining whether MuSCs in denervated muscle survive and retain regenerative ability would direct future approaches to muscle regeneration in denervation injuries.
METHODS:
A 4mm segment of the left sciatic nerve in three C57Bl6 mice was removed. After three months, the bilateral lower leg muscles were harvested, weighed, and flow cytometry was used to deplete Sca-1/CD31/CD45 and select calcein/VCAM/ITGA7 cells. Pax7 staining confirmed MuSC identity.
RESULTS:
Tibialis anterior muscles weighed 11.9±0.6mg following denervation compared with 49.5±2.5mg (p<0.0001). Two distinct populations of MuSCs expressing either high levels of VCAM (VCAMhigh) or ITGA7 (ITGA7high) were observed. ITGA7high cells were relatively larger than VCAMhigh cells (Figure). >90% of MuSCs isolated from muscles expressed Pax7. Denervated MuSCs expressed higher levels of VCAM. MuSCs as a percentage of total sorted cells was 37.7±7.0% in denervated legs vs. 30.8±3.7% in controls, p<0.23.
CONCLUSION:
Muscle denervation alters MuSC phenotype from quiescence towards activation. Resident MuSCs increase in number 3 months after denervation, and may retain intrinsic regenerative capacity.


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