TRAF6 regulates satellite stem cell self-renewal and function during regenerative myogenesis
Sajedah M. Hindi, Ashok Kumar
Sajedah M. Hindi, Ashok Kumar
Published November 30, 2015
Citation Information: J Clin Invest. 2016;126(1):151-168. https://doi.org/10.1172/JCI81655.
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Research Article Muscle biology

TRAF6 regulates satellite stem cell self-renewal and function during regenerative myogenesis

Abstract

Satellite cells are a stem cell population within adult muscle and are responsible for myofiber regeneration upon injury. Satellite cell dysfunction has been shown to underlie the loss of skeletal muscle mass in many acquired and genetic muscle disorders. The transcription factor paired box-protein-7 (PAX7) is indispensable for supplementing the reservoir of satellite cells and driving regeneration in normal and diseased muscle. TNF receptor–associated factor 6 (TRAF6) is an adaptor protein and an E3 ubiquitin ligase that mediates the activation of multiple cell signaling pathways in a context-dependent manner. Here, we demonstrated that TRAF6-mediated signaling is critical for homeostasis of satellite cells and their function during regenerative myogenesis. Selective deletion of Traf6 in satellite cells of adult mice led to profound muscle regeneration defects and dramatically reduced levels of PAX7 and late myogenesis markers. TRAF6 was required for the activation of MAPKs ERK1/2 and JNK1/2, which in turn activated the transcription factor c-JUN, which binds the Pax7 promoter and augments Pax7 expression. Moreover, TRAF6/c-JUN signaling repressed the levels of the microRNAs miR-1 and miR-206, which promote differentiation, to maintain PAX7 levels in satellite cells. We also determined that satellite cell–specific deletion of Traf6 exaggerates the dystrophic phenotype in the mdx (a mouse model of Duchenne muscular dystrophy) mouse by blunting the regeneration of injured myofibers. Collectively, our study reveals an essential role for TRAF6 in satellite stem cell function.

Authors

Sajedah M. Hindi, Ashok Kumar

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Figure 8

Role of TRAF6 in stabilization of c-JUN protein in satellite cells.

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Role of TRAF6 in stabilization of c-JUN protein in satellite cells. (A) ...
(A) Relative mRNA levels of Jun in Traf6+/+ and Traf6–/– myogenic cultures assayed by performing qPCR. (B) Traf6+/+ and Traf6–/– cells were treated with vehicle alone or 3 μM MG132 (a proteasome inhibitor) for 12h, and the protein levels of c-JUN, PAX7, TRAF6 and unrelated protein GAPDH were measured by Western blot. Representative immunoblots from 2 independent experiments. (C) Traf6+/+ and Traf6–/– cells were transfected with scrambled shRNA or that targeting Murf1, Fbw7, Det1, Itch1, or Mekk1 mRNA for 72h, and the cells were processed to measure protein levels of c-JUN, PAX7, and TRAF6. Immunoblots demonstrate the levels of c-JUN, PAX7, TRAF6, and unrelated protein GAPDH. (D) Relative mRNA levels of Murf1, Fbw7, Det1, Itch1, and Mekk1 after transfection of WT cultures with their respective shRNA constructs. n = 3 in each group. Error bars represent SD. *P < 0.05 (vs. scrambled shRNA-transfected cultures) by unpaired t test.