Massage Induces an Increase in DNA Synthesis and Satellite Cell Number in Rat Muscle Recovering from Atrophy
Authors: Hayek Amanda M , Confides Amy L , Abshire Sarah M , Miller Benjamin , Hamilton Karyn , Baeverstad Kathryn A , Peelor Frederick , Butterfield Timothy A , Dupont‐Versteegden Esther E 
Published: November 2023

BackgroundMassage of skeletal muscle is associated with many benefits, but very few mechanisms are currently identified. Massage in the form of cyclic compressive loading (CCL) results in an immunomodulatory effect on injured and uninjured muscles, but its effect on muscle size is unclear. We have recently shown that muscle fiber cross sectional area and protein synthesis were elevated in response to CCL in rats that were recovering from atrophy. Surprisingly, it was also found that DNA synthesis was elevated with CCL in muscles undergoing regrowth after disuse. It is currently unknown which cell type in muscle would be undergoing DNA replication in response to massage, but we recently found that satellite cells are elevated after one bout of CCL in unperturbed rats. Therefore, the goal of this investigation was to identify which cells were increased in number to account for the observed elevation in DNA synthesis; we hypothesize that satellite cell number is greater in the massaged limb.MethodsMale Fisher 344‐BN rats (10 months) were divided into 4 groups (n=8): weight bearing (WB), hindlimb suspended for 14 days (HS), HS and reloaded for 7 days (RE), and RE with 4 bouts of massage applied every other day during the reloading period (REM) starting the first bout at the moment of reloading; right gastrocnemius muscles were subjected to CCL. Muscles were collected and frozen 24 hours after the last bout of CCL. Muscle sections were cut and immunohistochemistry was performed to identify myonuclei (dystrophin and DAPI), M2 macrophages (ED2+), satellite cells (Pax7+), endothelial cells (Lectin+), and fibroblasts (TCF4+). Cell types and myonuclei were visualized using Axiovision image analysis software (Zeiss) and expressed per fiber number.ResultsNo significant differences were observed for ED2, TCF4, or lectin positive cells with HS, RE, or with massage during RE, indicating that these cells types had not changed in number and likely did not explain the increase in DNA synthesis with massage. Satellite cell number (Pax7+) was significantly decreased with HS, was restored with reloading, and was significantly elevated with massage compared to weight bearing and reloading, suggesting that this cell type was responsible for the observed DNA synthesis. However, the number of myonuclei and centrally located nuclei was not changed under any condition.ConclusionResults indicate that the observed increase in DNA synthesis with massage during muscle regrowth after atrophy could be explained by satellite cell proliferation. Since no increase in myonuclear count was found, we suggest that these satellite cells likely do not contribute to new myonuclei, but rather could be involved in the modulation of the extracellular matrix.Support or Funding InformationThis research was funded by NIH grant AG042699. Amanda Hayek received funding from the STRIDE Undergraduate Summer Research Fellowship supported by the American Physiological Society and NHLBI, 1 R25 HL115473‐01.