Tumour necrosis factor-alpha (TNF-α) is a pleiotropic cytokine well characterised as a mediator of skeletal muscle wasting. However, the role of interlukin-6 (IL-6) in skeletal muscle remains controversial.
Objectives: We therefore investigated the potential interactive effects of TNF-α and IL-6 on murine C2 skeletal myoblast survival, differentiation and proliferation.
Methods: Real time-PCR, creatine kinase assay, western blot and flow cytometry techniques were used to investigate the potential effect of TNF/IL-6 on C2 myoblasts cells.
Results: A novel and unexpected positive temporal interaction between TNF-α and IL-6 on cell growth (30±5%; P<0.05) was identified, with maximal beneficial effects obtained when IL-6 was added 24 h after TNF-α. Total cellular protein (35%), extracellular signal-regulated kinase (ERK) phosphorylation (40%), and S phase (2.5- fold) increased significantly (P<0.05), confirming cell growth. The expression of mRNAs of key regulators of muscle mass: insulin-like growth factor binding protein-5 (IGFBP-5), insulin-like growth -II receptor (IGF-IIR), IGF-II and insulin-like growth-I receptor (IGF-IR) were significantly (P<0.05) increased by 1600-fold, 2.0-fold, 4.5-fold, 13-fold respectively giving an indication of the regulatory mechanisms of this interaction. Moreover, the level of expression signal-transducing gp130 was induced up to 3.5-fold in the cells administrated with IL-6 at 24 h after TNF-α but not after either treatments alone. This may not only explain the beneficial effects of this treatment on skeletal myoblast numbers but also define a functional role of gp130 in skeletal muscle cells.
Conclusions: Our data suggest that in the presence of TNF-α/IL-6 functions positively and potentially also cooperatively with the insulin growth factor (IGF) system to achieve the maximal beneficial effect on skeletal myoblast numbers.