Tumor Necrosis Factor-α Augments Matrix Metalloproteinase-9 Production in Skeletal Muscle Cells through the Activation of Transforming Growth Factor-β-activated Kinase 1 (TAK1)-dependent Signaling Pathway

We have investigated the effect of tumor necrosis factor-α (TNF-α) on the production of extracellular matrix-degrading proteases in skeletal muscles. Using microarray, quantitative PCR, Western blotting, and zymography, we found that TNF-α drastically increases the production of matrix metalloproteinase (MMP)-9 from C2C12 myotubes. In vivo administration of TNF-α in mice increased the transcript level of MMP-9 in skeletal muscle tissues. Although TNF-α activated all the three MAPKs (i.e. ERK1/2, JNK, and p38), inhibition of ERK1/2 or p38 but not JNK blunted the TNF-α-induced production of MMP-9 from myotubes. Inhibition of Akt also inhibited the TNF-α-induced production of MMP-9. TNF-α increased the activation of transcription factors NF-κB and AP-1 but not SP-1 in myotubes. Overexpression of a dominant negative inhibitor of NF-κB or AP-1 blocked the TNF-α-induced expression of MMP-9 in myotubes. Similarly, point mutations in AP-1- or NF-κB-binding sites in MMP-9 promoter inhibited the TNF-α-induced expression of a reporter gene. TNF-α increased the activity of transforming growth factor-β-activating kinase-1 (TAK1). Furthermore, overexpression of a dominant negative mutant of TAK1 blocked the TNF-α-induced expression of MMP-9 and activation of NF-κB and AP-1. Our results also suggest that TNF-α induces MMP-9 expression in muscle cells through the recruitment of TRAF-2, Fas-associated protein with death domain, and TNF receptor-associated protein with death domain but not NIK or TRAF-6 proteins. We conclude that TAK1-mediated pathways are involved in TNF-α-induced MMP-9 production in skeletal muscle cells.