Sphingomyelinase stimulates oxidant signaling to weaken skeletal muscle and promote fatigue.
Sphingomyelinase (SMase) hydrolyzes membrane sphingomyelin into ceramide, which increases oxidants in nonmuscle cells. Serum SMase activity is elevated in sepsis and heart failure, conditions where muscle oxidants are increased, maximal muscle force is diminished, and fatigue is accelerated. We tested the hypotheses that exogenous SMase and accumulation of ceramide in muscle increases oxidants in muscle cells, depresses specific force of unfatigued muscle, and accelerates the fatigue process. We also anticipated that the antioxidant N-acetylcysteine (NAC) would prevent SMase effects on muscle function. We studied the responses of C2C12 myotubes and mouse diaphragm to SMase treatment in vitro. We observed that SMase caused a 2.8-fold increase in total ceramide levels in myotubes. Exogenous ceramide and SMase elevated oxidant activity in C2C12 myotubes by 15-35% (P < 0.05) and in diaphragm muscle fiber bundles by 58-120% (P < 0.05). The SMase-induced increase in diaphragm oxidant activity was prevented by NAC. Exogenous ceramide depressed diaphragm force by 55% (P < 0.05), while SMase depressed maximal force by 30% (P < 0.05) and accelerated fatigue--effects opposed by treatment with NAC. In conclusion, our findings suggest that SMase stimulates a ceramide-oxidant signaling pathway that results in muscle weakness and fatigue.
Ferreira
Leonardo F
LF
Department of Physiology and Center for Muscle Biology, University of Kentucky, Lexington, Kentucky, USA.
Moylan
Jennifer S
JS
Gilliam
Laura A A
LA
Smith
Jeffrey D
JD
Nikolova-Karakashian
Mariana
M
Reid
Michael B
MB
D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001426:Bacterial Proteins / Q000494:pharmacology; D002460:Cell Line; D002518:Ceramides / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D003964:Diaphragm / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction; D018763:Muscle Fatigue / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000502:physiology*; D016877:Oxidants / Q000502:physiology*; D026361:Reactive Nitrogen Species / Q000378:metabolism; D015398:Signal Transduction; D013108:Sphingomyelin Phosphodiesterase / Q000494:pharmacology / Q000502:physiology*
D000975:Antioxidants; D001426:Bacterial Proteins; D002518:Ceramides; D016877:Oxidants; D026361:Reactive Nitrogen Species; D013108:Sphingomyelin Phosphodiesterase; D000111:Acetylcysteine