Muscle Memory and a New Cellular Model for Muscle Atrophy and Hypertrophy 

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23rd annual ECSS Congress Dublin/Ireland, July 4-7 2018
Muscle Memory and a New Cellular Model for Muscle Atrophy and Hypertrophy
Author: Gundersen, K.
University of Oslo
Abstract:
We suggest that skeletal muscle fibres display the hallmarks of a cellular memory, entailing encoding, storing and retrieving
information.
The muscle cells are the largest cells in the body and are served by multiple nuclei. The classical cell biological model for muscle
atrophy has implied that during atrophy, muscle nuclei are lost by apoptosis as to maintain a constant cytoplasmic domain volume for each nucleus. Similarly, during hypertrophy, nuclei are recruited form satellite cells that fuse with pre-existing muscle fibres. Although supported by a large body of literature, newer more precise methods, indicate that this model is not correct.
In particular, direct observations of myonuclei by in vivo time laps microscopy indicates that nuclei are not lost during atrophy. Thus,
the number of nuclei reflect the previous size of the muscle fibre, and not its atrophic state. The number of nuclei then represents a
long lasting cytoarchitectural imprint or "memory" of the original fibre size.
Newer methods have confirmed that nuclei from satellite cells are added during de novo hypertrophy, and that also these nuclei are
maintained during subsequent disuse atrophy, serving as a cytoarchitectural "memory" of a previous hypertrophy. The muscles with an elevated number of myonuclei induced either by previous steroid exposure or exercise (encoding), grow faster with retraining
(retrieval), even after a prolonged period of detraining (storage). In humans the memory storage could be very long lasting since our
myonuclei probably have half-lives in excess of 15 years. Our findings might have implications for doping rules, and for training
advice. It might be beneficial to do early strength exercise since myonuclei are more easily recruited in younger than in old individuals.

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