Role of Sphingosine 1-Phosphate Signalling Axis in Muscle Atrophy Induced by TNFα in C2C12 Myotubes

Skeletal muscle atrophy is characterized by a decrease in muscle mass causing reduced agility, increased fatigability and higher risk of bone fractures. Inflammatory cytokines, such as tumor necrosis factor-alpha (TNF alpha), are strong inducers of skeletal muscle atrophy. The bioactive sphingolipid sphingosine 1-phoshate (S1P) plays an important role in skeletal muscle biology. S1P, generated by the phosphorylation of sphingosine catalyzed by sphingosine kinase (SK1/2), exerts most of its actions through its specific receptors, S1P(1-5). Here, we provide experimental evidence that TNF alpha induces atrophy and autophagy in skeletal muscle C2C12 myotubes, modulating the expression of specific markers and both active and passive membrane electrophysiological properties. NMR-metabolomics provided a clear picture of the deep remodelling of skeletal muscle fibre metabolism induced by TNF alpha challenge. The cytokine is responsible for the modulation of S1P signalling axis, upregulating mRNA levels of S1P(2) and S1P(3) and downregulating those of SK2. TNF alpha increases the phosphorylated form of SK1, readout of its activation. Interestingly, pharmacological inhibition of SK1 and specific antagonism of S1P(3) prevented the increase in autophagy markers and the changes in the electrophysiological properties of C2C12 myotubes without affecting metabolic remodelling induced by the cytokine, highlighting the involvement of S1P signalling axis on TNF alpha-induced atrophy in skeletal muscle.

Automated summary

Skeletal muscle atrophy is characterized by a decrease in muscle mass causing reduced agility, increased fatigability, and higher risk of bone fractures. Inflammatory cytokine TNF alpha is a strong inducer of skeletal muscle atrophy. The bioactive sphingolipid S1P plays an important role in skeletal muscle biology, exerting most of its actions through its specific receptors.