Submitted on April 17, 2007
Accepted on October 10, 2007
Trophic action of sphingosine 1-phosphate in denervated rat soleus muscle
Marika Zanin1, Elena Germinario2, Luciano Dalla Libera3, Dorianna Sandona4, Roger A Sabbadini5, Romeo Betto6, and Daniela Danieli-Betto2*
1 Department of Human Anatomy and Physiology, University of Padova, Padova, Padova, Italy
2 Department of Human Anatomy and Physiology, University of Padova, Padova, Italy; Interuniversity Institute of Myology, Padova, Italy
3 Neuroscience Institute, Muscle Biology and Physiopathology Unit, Consiglio Nazionale delle Ricerche, Padova, Italy
4 Department of Biomedical Sciences, University of Padova, Padova, Italy
5 Department of Biology and Heart Institute, San Diego State University, San Diego, California, United States
6 Neuroscience Institute, Muscle Biology and Physiopathology Unit, Consiglio Nazionale delle Ricerche, Padova, Italy; Interuniversity Institute of Myology, Padova, Italy
* To whom correspondence should be addressed. E-mail: daniela.danieli{at}unipd.it.
Sphingosine 1-phosphate (S1P) mediates a number of cellular responses, including growth and proliferation. Skeletal muscle possesses the full enzymatic machinery to generate S1P and expresses the transcripts of S1P receptors. The aim of this work was to localize S1P receptors in rat skeletal muscle and to investigate whether S1P exerts a trophic action on muscle fibers. RT-PCR and Western blot analyses demonstrated the expression of S1P1 and S1P3 receptors by soleus muscle. Immunofluorescence revealed that S1P1 and S1P3 receptors are localized at the cell membrane of muscle fibers and in the T-tubule membranes. The receptors also decorate the nuclear membrane. S1P1 receptors were also present at the neuromuscular junction. The possible trophic action of S1P was investigated by utilizing the denervation atrophy model. Rat soleus muscle was analyzed 7 and 14 days after motor nerve cut. During denervation, S1P was continuously delivered to the muscle through a mini osmotic pump. S1P, and its precursor sphingosine (Sph), significantly attenuated the progress of denervation-induced muscle atrophy. The trophic effect of Sph was prevented by N,N-dimethylsphingosine, an inhibitor of Sph kinase, the enzyme that converts Sph into S1P. Neutralization of circulating S1P by a specific antibody further demonstrated that S1P was responsible for the trophic effects of S1P during denervation atrophy. Denervation produced the down regulation of S1P1 and S1P3 receptors, regardless of the presence of the receptor agonist. In conclusion, the results suggest that S1P acts as a trophic factor of skeletal muscle.
