PGC-1α4 GENE EXPRESSION IS SUPPRESSED BY THE IL-6-ERK1/2 MAPK SIGNALING AXIS

Jacob L. Brown1, Megan E. Rosa1, David E. Lee1, Lemuel A. Brown1, Richard A. Perry1, James A. Carson2, Sami Dridi1, Tyrone A. Washington1,2, Nicholas P. Greene1,2 1University of Arkansas, Fayetteville, AR; 2University of South Carolina, Columbia, SC; e-mail: jb024@uark.edu Maintenance and promotion of skeletal muscle mass and function are critical for both daily living and exercise performance. Lost muscle mass and function are associated with reduced quality of life in many disease conditions. Recently, the peroxisome proliferator-activated receptor γ coactivator-1α4 (PGC-1α4) isoform has been shown to play a key role in the promotion of skeletal muscle mass; however its specific regulation under normal and stress (inflammatory) conditions is still unknown. PURPOSE: To elicit signaling mechanisms regulating the gene expression of Pgc-1α4 during inflammation and particularly by IL-6. METHODS: Female C57BL/6J (WT) and C57BL/6J × IL-6−/− (IL-6 KO) mice were euthanized and tibialis anterior muscles were excised, snap-frozen in liquid nitrogen and processed for gene expression analysis. To further determine the underlying mechanisms by which IL-6 governs PGC-1α4 expression, C2C12 myotubes were treated with recombinant IL-6 (50 ng/ml), recombinant TNF-α (20 ng/ml), Pyrrolidine dithiocarbamate (PDTC, 50 µM) and PD098059 (20 µM; MEK1/2 inhibitor preventing ERK1/2 activity). RNA was isolated from WT and IL-6 KO mice as well as C2C12 myotubes. RNA was analyzed by real time RT PCR for mRNA content analysis of 18S and Pgc-1α4. Protein analysis was performed by immunoblot for P-STAT3, STAT3, P-ERK 1/2 and ERK 1/2 and normalized to Ponceau S. A student t-test or one way ANOVA was employed as appropriate with α set at 0.05. RESULTS: Pgc-1α4 mRNA content was 10-fold greater in IL-6 KO mice compared to WT. In C2C12 myotubes, IL-6 significantly repressed Pgc-1α4 mRNA content by ~70% while TNF-α and PDTC treated cells were not different from control. In the following experiment, similar IL-6 repression of Pgc-1α4 mRNA was abrogated when IL-6 was combined with ERK1/2 inhibition via MEK (PD098059 + IL6). There was a significant 40% increase in the P-STAT3/STAT3 ratio and the P-ERK/ ERK ratio with IL-6 treatment while inhibitors of STAT3 (PDTC) and ERK 1/2 (PD098059) significantly decreased these ratios by 30% and 50 %, respectively. CONCLUSION: PGC-1α4 expression is repressed by IL-6 through the ERK1/2 signaling axis. These findings may have significant impact in treatment to prevent and ameliorate muscle wasting conditions