Effects of S1P on skeletal muscle repair/regeneration during eccentric contraction.
Bottom Line: In the present study, we examined the effects of S1P on eccentric contraction (EC)-injured extensor digitorum longus muscle fibres and resident satellite cells.Notably, EC was associated with the activation of sphingosine kinase 1 (SphK1) and with increased endogenous S1P synthesis, further stressing the relevance of S1P in skeletal muscle protection and repair/regeneration.In line with this, the treatment with a selective SphK1 inhibitor during EC, caused an exacerbation of the muscle damage and attenuated MMP-9 expression.
Affiliation: Department of Anatomy, Histology and Forensic Medicine, University of Florence, Florence, Italy.Show MeSH
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Mentions: We first evaluated the effects of EC on EDL skeletal muscle by morphological, biochemical and electrophysiological analyses. At light microscopic examination, skeletal muscle fibres subjected to EC showed extensive and severe morphological alterations (histological score of 2.7 ± .0.1, Table 1; Fig. 1A and B). At the ultrastructural level, the majority of the injured fibres displayed variable degree of myofibrillar disarrangement and Z-disk disruption, dilated cistaerne and tubules of sarcoplasmic reticulum, and swollen mitochondria with shortening and disappearance of cristae (Fig. 1C and D). Biochemical analysis revealed that LDH activity was significantly decreased of approximately 35% in EC-injured muscle compared to control (8.9 ± 0.9 versus 13.7 ± 1.2; mean ± S.E.M.; P < 0.05, n= 3). Moreover, we demonstrated a significant increase in the association of the pro-apoptotic protein, Bax, with mitochondrial fractions, and in the release of respiratory chain protein, Cytc, into the cytosolic fractions obtained from EC-damaged muscle compared to control (Fig. 2A). However, EC damage provoked only a slightly increase in caspase 3/7 activity (Fig. 2B), and a certain positivity to the TUNEL reaction. In particular, positive nuclei were found both in the myofibres and in cells located in the close vicinity, and represented an approximately 2% of the total nuclei (Fig. 2C). The electrophysiological assessment of the effects of EC performed on single muscle fibres showed the occurrence of significant changes in the sarcolemnic functionality (reduced plasma membrane resistance (RmCm) and resting membrane depolarization, Table 2), and in the myofibre excitability (reduced Na+ current amplitude (INa) and altered kinetic, Fig. 3A and C; Table 2). EC also affected the excitation-contraction coupling, reducing L-type-mediated Ca2+ current (ICa) and altering the channel kinetics (Fig. 3B and D; Table 2).
Affiliation: Department of Anatomy, Histology and Forensic Medicine, University of Florence, Florence, Italy.