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Rapid switch‐off of the human myosin heavy chain IIX gene after heavy load muscle contractions is sustained for at least four days
Author(s) -
Andersen J. L.,
GruschyKnudsen T.
Publication year - 2018
Publication title -
scandinavian journal of medicine and science in sports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.575
H-Index - 115
eISSN - 1600-0838
pISSN - 0905-7188
DOI - 10.1111/sms.12914
Subject(s) - myosin , medicine , gene isoform , endocrinology , in situ hybridization , biology , skeletal muscle , major histocompatibility complex , glycogen , messenger rna , gene , microbiology and biotechnology , biochemistry
Long‐term heavy load contractions decrease the relative amount of the myosin heavy chain ( MHC ) IIX isoform in human skeletal muscle, but the timing of the down‐regulation in the short term is unknown. Untrained subjects performed two resistance bouts, in two consecutive days, with one leg, the other leg serving as a control (age 24±1, n=5). Muscle biopsies were obtained in both legs before, immediately after, and 24, 54, and 96 hours after exercise. Serial cryosection analysis combined immunohistochemistry and ATP ase histochemistry with In Situ hybridization to identify the distribution of MHC isoforms and their corresponding transcripts, enabling identification of transitional fibers. Fibers positive solely for MHC IIX mRNA decreased in the exercised leg throughout the study period. At 96 hours post‐exercise, no fibers solely expressed MHC IIX mRNA . In contrast, the number of fibers expressing MHC IIA mRNA increased throughout the study period. The percentage of fibers expressing mRNA for MHC I was unchanged in both legs at all time points. Pronounced depletion of glycogen in the MHC IIX fibers of the exercised leg verifies that the type IIX fibers were active during the heavy load contractions. Major mismatch between MHC at the mRNA and protein levels was only found in the fibers of the exercised leg. These data provide unequivocal in situ evidence of an immediate shutdown of the MHC IIX gene after resistance exercise. A further novel finding was that the silencing of the MHC IIX gene is sustained at least 4 days after removal of the stimulus.