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 1

Expression of TRAF6 in satellite cells.

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Expression of TRAF6 in satellite cells. Primary mononucleated cells were...
Primary mononucleated cells were isolated from hind limb muscle of WT mice and subjected for FACS analysis for the expression of α7-integrin and TRAF6, either immediately after isolation (quiescent) or after purification and culturing (activated). (A) Representative dot plots from 4 independent experiments displaying enrichment of TRAF6+ cells among α7-intigrin+ population in both freshly isolated and cultured myoblasts. (B) Primary myogenic cells were immunostained for TRAF6 and PAX7 proteins. The nuclei were labeled using DAPI. Representative photomicrographs from 3 replicates show colocalization of TRAF6 and PAX7 in mouse primary myoblasts. Original magnification, ×20. (C) Freshly sorted satellite cells were either frozen at isolation (QC, quiescent cells) or seeded and cultured in DM for various time points. Immunoblots demonstrate the levels of TRAF6, PAX7, MyoD, MyHC, and unrelated protein GAPDH in QC and in cultured primary myoblasts at different time points after addition of DM.