https://orcid.org/0000-0002-6263-4776
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Madison R Barshick, Madison L Gonzalez, Nicolas I Busse, Patricia J Helsel, Sally E Johnson, The initial delay to mitotic activity in primary cultures of equine satellite cells is reduced by combinations of growth factors, Journal of Animal Science, Volume 100, Issue 8, August 2022, skac140, https://doi.org/10.1093/jas/skac140
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Abstract
Satellite cell (SC) activation is defined as the time frame during which the stem cell becomes poised to reenter G1 of the cell cycle. The growth factors and events leading to full mitotic activation in equine SCs remain largely unknown. Insulin-like growth factor I (IGF-I), hepatocyte growth factor (HGF), and fibroblast growth factor 2 (FGF2) are sequentially transcribed during the muscle repair and recovery period following strenuous exercise in adult horses. Expression of IGF-I occurs within 24 h of the postexercise recovery period suggesting it may affect early SC actions. As a first step, gluteus medius muscle cryosections from adult horses (n = 9) were examined for the presence of central nuclei (CN), a marker of SC addition to the fiber. Results demonstrate few CN fibers prior to exercise with a 3-fold increase (P = 0.05) 24 h postexercise. Cultures of SC (n = 4 isolates) were treated with 100 ng/mL IGF-I for varying times prior to measurement of myogenic events. Results demonstrate that IGF-I does not affect the initial lag period, proliferation, or subsequent differentiation of equine SC in vitro (P > 0.05). However, media containing a combination of IGF-I and 10 ng/mL FGF2 and 25 ng/mL HGF hastens (P < 0.05) the time to S-phase entry in fresh isolates of SCs. Media supplementation with optimal concentrations of FGF2, HGF, or a combination of HGF and FGF2 suppresses (P < 0.05) the percentage of myogenin immunopositive SCs to levels below that found in control- or IGF-I-treated SCs. These results provide new insight into the combinatorial roles growth factors play during equine SC myogenesis.
Lay Summary
Satellite cells are the resident stem cells found within skeletal muscle. Following strenuous exercise, the cells become mitotically active to supply progenitors for muscle repair. The signals responsible for their exit from the dormant state are largely unknown. Hepatocyte growth factor (HGF), fibroblast growth factor 2 (FGF2), and insulin-like growth factor I (IGF-I) are located within the local environment postexercise suggesting their involvement in mitotic activation. Treatment of satellite cells in vitro with optimal concentrations of HGF, FGF2, or IGF-I did not affect transition into the cell cycle. By contrast, inclusion of all three growth factors in the media caused an increase in the numbers of activated satellite cells. The combination of factors suppressed expression of myogenin, the requisite transcriptional mediator of differentiation. Although IGF-I stimulates myogenin expression in other muscle cell types, a similar response was not observed in equine satellite cells. These results support a role for HGF, FGF2, and IGF-I during the initial postexercise repair period in horses.
