Differential Expression Of Pgc1α4 During Skeletal Muscle Regeneration And Myogenic Differentiation

Abstract

Skeletal muscle regeneration is a vital process to maintain physical function and adapt to exercise, characterized by alterations in multiple processes including inflammation, satellite cell proliferation and cell cycle alterations, and protein synthesis. The PGC-1α isoform, PGC-1α4 promotes muscle growth via IGF-1 and myostatin. However, whether PGC-1α4 plays a role in muscle regeneration following injury and by extension during myogenic differentiation, as occurs in satellite cell proliferation, is unknown. PURPOSE: To determine alterations in Pgc1α4 mRNA content during muscle regeneration and myogenic differentiation. METHODS: C57BL/6J mice were submitted to muscle damage by intramuscular injection of the myotoxin bupivacaine (BUPI) or PBS (control) to the tibialis anterior (TA) muscle. Mice from BUPI and PBS groups were humanely euthanized and TAs collected at 3, 5, and 28d post-injection. To examine Pgc1α4 mRNA content during myogenic differentiation C2C12 myoblasts were differentiated beginning at confluence and collected at 1d prior to confluence, and 0, 1, 2, 3, 4, 5d of differentiation. TAs and C2C12 cells were analyzed for Pgc1α4 mRNA by real time RT-PCR. For animal studies data were analyzed by t-test within each timepoint to compare PBS and BUPI groups. For cell culture, data were analyzed across time by one-way ANOVA, α was set at 0.05 for all experiments. RESULTS: Following muscle injury: 3d post injury Pgc1α4 mRNA content was 70% lower in BUPI compared to PBS control, >2-fold elevated at 5d in BUPI compared to PBS control, while 65% greater Pgc1α4 mRNA content at 28d in BUPI compared to PBS was not significant (P=0.09). During differentiation Pgc1α4 mRNA peaked at 3d at ~11-fold greater than 0d and was significantly elevated over all other timepoints except 4d. Muscle differentiation factor myogenin peaked in content at 2d differentiation (535 fold, elevated at all points after 0d) while Igf1 peaked at 4d (2.15 fold). CONCLUSION: During muscle regeneration Pgc1α4 mRNA is repressed during phases associated with elevated inflammation (3d) and is elevated at timepoints associated with muscle growth (5d). These data are concomitant with expression changes during myogenic differentiation and suggest a potentially significant role of PGC-1α4 in muscle regeneration and differentiation.