EFFECTS OF PGC1-a OVEREXPRESSION AT THE ONSET OF MUSCLE REGENERATION

Wesley S. Haynie, Richard, A. Perry, Lemuel A. Brown, David E. Lee, Jacob L. Brown, Megan E. Rosa, Nicholas P. Greene, Tyrone A. Washington. University of Arkansas, Fayetteville, Arkansas Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) is a transcriptional activator shown to stimulate mitochondrial biogenesis. Down-regulation of PGC-1α is observed during muscular dystrophy, a model of impaired regeneration. However, in healthy muscle PGC-1α expression is unaltered during muscle regeneration. Therefore, the role of PGC-1α at the onset of skeletal muscle regeneration is unclear and needs further elucidation. PURPOSE: To examine the effects of overexpression of PGC-1α on gene expression of lactate dehydrogenase (LDH), TNF-a, and myogenesis markers MyoD and Myogenin at the onset of muscle regeneration. METHODS: 23 C57BL/6 (WT) and 24 Transgenic (A1) mice were used for this study, with A1 mice genetically modified to overexpress the protein PGC-1a. Mice were injected with either PBS or Bupivacaine (MAR) at 12 weeks of age. Tibialis anterior (TA) muscle and tibias were excised 3-days post injection. Tissue was immediately frozen for gene expression analysis using RT-qPCR. RESULTS: There were no differences in body weight, TA weight, tibia length (TL), or TA to TL ratio in any mice 3-days post injection. PGC-1α gene expression was 13-fold greater in the A1-PBS group compared to the WT-PBS group (p\u3c0.05). The A1-MAR group however, expressed approximately 4-fold less PGC-1a compared to the A1-PBS group 3-days post injection (p\u3c0.05). In WT mice, MyoD gene expression was 1.5 fold greater in the MAR group compared to the PBS group (p\u3c0.05). In A1 mice, there was no difference in MyoD expression between the MAR and PBS groups. There was a main effect of MAR to increase Myogenin gene expression in both WT and A1 mice. There was a main effect of genotype to decrease LDH-A expression in both A1 groups (p\u3c0.05). There was a 4-fold increase in LDH-B expression in the A1-PBS group compared to the WT-PBS group (p\u3c0.05). In WT mice, there was no effect of MAR on LDH-B gene expression. However, in A1 mice there was a 50% decrease in the A1-MAR group compared to the A1-PBS group (p\u3c0.05). The inflammation marker TNF-a increased approximately 2-fold as a main effect of genotype in both A1 mice groups (p\u3c0.05). CONCLUSION: A surplus of mitochondria may result in more ROS production and higher levels of TNF-α. Lowered expression of MyoD 3-days post-injection in A1 mice could be attributed to the increased levels in TNF-α. With TNF-α possibly activating NF-κB, a nuclear factor shown to negatively regulate myogenesis