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

Caterina Bernacchioni,Paola Bruni,Francesca Cencetti,Eglantina Idrizaj,Rachele Garella,Roberta Squecco,Chiara Donati,Veronica Ghini,Elisa Puliti

doi:10.3390/ijms22031280

Abstract

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 (TNFα), 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, S1P1–5. Here, we provide experimental evidence that TNFα 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 TNFα challenge. The cytokine is responsible for the modulation of S1P signalling axis, upregulating mRNA levels of S1P2 and S1P3 and downregulating those of SK2. TNFα increases the phosphorylated form of SK1, readout of its activation. Interestingly, pharmacological inhibition of SK1 and specific antagonism of S1P3 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 TNFα-induced atrophy in skeletal muscle.

Highlights

Introduction iationsSkeletal muscle atrophy is characterized by a decrease in muscle mass and fiber size as a result of different conditions such as aging, bed rest, cancer, denervation and motor neuron disease [1]
We previously showed that low doses of TNFα promote myogenesis in C2C12 myoblasts and inhibition of sphingosine kinase (SK) and S1P2 abrogated its pro-myogenic effect [31]
Since TNFα is responsible for a deep modulation of S1PR expression in C2C12 myotubes, we examined whether the atrophic action exerted by the cytokine was S1PRmediated

Summary

Introduction

Skeletal muscle atrophy is characterized by a decrease in muscle mass and fiber size as a result of different conditions such as aging, bed rest, cancer, denervation and motor neuron disease [1]. Skeletal muscle atrophy causes reduced agility, increased fatigability and higher risk of bone fractures, representing a major burden for health systems, lowering response to treatments and decreasing life expectancy. The knowledge on muscle wasting has been advanced during the last 10 years, the dissection of the molecular signalling pathways regulating skeletal muscle atrophy will pave the way for innovative interventions for the discovery of drugs to prevent this pathological condition, which are crucially relevant for neuromuscular diseases, muscle disuse and aging. The regulation of muscle mass depends on the balance between protein synthesis and degradation: during muscle atrophy, the main degradation pathways of the cell are activated.

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Conclusion