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Increased sphingosine-1-phosphate improves muscle regeneration in acutely injured mdx mice.

Ieronimakis N, Pantoja M, Hays AL, Dosey TL, Qi J, Fischer KA, Hoofnagle AN, Sadilek M, Chamberlain JS, Ruohola-Baker H, Reyes M - Skelet Muscle (2013)

Bottom Line: Intramuscular injection of biotinylated-S1P localized to muscle fibers, including newly regenerated fibers, which also stained positive for S1P receptor 1 (S1PR1).Intramuscular increases of S1P levels, S1PR1 and phosphorylated ribosomal protein S6 (P-rpS6), and elevated EDL muscle specific force, suggest S1P promoted the upregulation of anabolic pathways that mediate skeletal muscle mass and function.These data show that S1P is beneficial for muscle regeneration and functional gain in dystrophic mice, and that THI, or other pharmacological agents that raise S1P levels systemically, may be developed into an effective treatment for improving muscle function and reducing the pathology of DMD.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pathology, School of Medicine, University of Washington, Seattle, WA 98195, USA. hannele@u.washington.edu.

ABSTRACT

Background: Presently, there is no effective treatment for the lethal muscle wasting disease Duchenne muscular dystrophy (DMD). Here we show that increased sphingosine-1-phoshate (S1P) through direct injection or via the administration of the small molecule 2-acetyl-4(5)-tetrahydroxybutyl imidazole (THI), an S1P lyase inhibitor, has beneficial effects in acutely injured dystrophic muscles of mdx mice.

Methods: We treated mdx mice with and without acute injury and characterized the histopathological and functional effects of increasing S1P levels. We also tested exogenous and direct administration of S1P on mdx muscles to examine the molecular pathways under which S1P promotes regeneration in dystrophic muscles.

Results: Short-term treatment with THI significantly increased muscle fiber size and extensor digitorum longus (EDL) muscle specific force in acutely injured mdx limb muscles. In addition, the accumulation of fibrosis and fat deposition, hallmarks of DMD pathology and impaired muscle regeneration, were lower in the injured muscles of THI-treated mdx mice. Furthermore, increased muscle force was observed in uninjured EDL muscles with a longer-term treatment of THI. Such regenerative effects were linked to the response of myogenic cells, since intramuscular injection of S1P increased the number of Myf5nlacz/+ positive myogenic cells and newly regenerated myofibers in injured mdx muscles. Intramuscular injection of biotinylated-S1P localized to muscle fibers, including newly regenerated fibers, which also stained positive for S1P receptor 1 (S1PR1). Importantly, plasma membrane and perinuclear localization of phosphorylated S1PR1 was observed in regenerating muscle fibers of mdx muscles. Intramuscular increases of S1P levels, S1PR1 and phosphorylated ribosomal protein S6 (P-rpS6), and elevated EDL muscle specific force, suggest S1P promoted the upregulation of anabolic pathways that mediate skeletal muscle mass and function.

Conclusions: These data show that S1P is beneficial for muscle regeneration and functional gain in dystrophic mice, and that THI, or other pharmacological agents that raise S1P levels systemically, may be developed into an effective treatment for improving muscle function and reducing the pathology of DMD.

No MeSH data available.


Related in: MedlinePlus

Longer-term treatment with THI elevated muscle force in uninjured mdx EDL muscles. (A) Experimental schematic outlining the treatment regimen. Beginning at 4 weeks of age, mdx4cv mice (1-MO males) were treated for 4 weeks ad libitum with 50 mg/l THI (n = 4) or vehicle (n = 3) in drinking water. (B) Myography analysis of EDL muscles reveals a significant increase in maximal specific force with THI treatment. *P <0.05 by student’s t-test. Error bars represent SEM. (C) Summary of findings: S1P can act to not only promote myogenic cell activation and muscle repair, but also enhance muscle fiber size and force, possibly through S1PR1 mediated signaling. EDL, extensor digitorum longus; MO, month-old; S1P, sphingosine-1-phoshate; S1PR1, S1P receptor 1; SEM, standard error of the mean; THI, 2-acetyl-4(5)-tetrahydroxybutyl imidazole.
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Figure 8: Longer-term treatment with THI elevated muscle force in uninjured mdx EDL muscles. (A) Experimental schematic outlining the treatment regimen. Beginning at 4 weeks of age, mdx4cv mice (1-MO males) were treated for 4 weeks ad libitum with 50 mg/l THI (n = 4) or vehicle (n = 3) in drinking water. (B) Myography analysis of EDL muscles reveals a significant increase in maximal specific force with THI treatment. *P <0.05 by student’s t-test. Error bars represent SEM. (C) Summary of findings: S1P can act to not only promote myogenic cell activation and muscle repair, but also enhance muscle fiber size and force, possibly through S1PR1 mediated signaling. EDL, extensor digitorum longus; MO, month-old; S1P, sphingosine-1-phoshate; S1PR1, S1P receptor 1; SEM, standard error of the mean; THI, 2-acetyl-4(5)-tetrahydroxybutyl imidazole.

Mentions: To this point we have largely examined the role of S1P in promoting muscle regeneration in acutely injured dystrophic muscles. Since long-term intramuscular injections of S1P are neither feasible nor practical (the injections also cause damage), we decided to revisit the use of THI for elevating S1P muscle content. Although our initial experiments with THI showed little benefit in uninjured mdx muscles, they were short-term and in older animals with severe pathology (Figures 2, 3), or adult animals (Figure 4) at a point when hypertrophy and robust regeneration compensate for degeneration in limb muscles [24,68,69]. Therefore, we examined longer-term treatment of THI in younger mdx mice at 4 weeks of age, a time point characterized by significant muscle degeneration prior to the compensatory period [70]. For this experiment, uninjured mdx4cv animals were treated for 1 month, beginning at 4 weeks of age, with THI or vehicle in the drinking water (Figure 8A) [11]. At 8 weeks of age, we assessed the functional benefit of THI treatment by analyzing EDL specific force via myography. In turn, EDLs from THI-treated animals showed significantly greater specific force compared to vehicle-treated controls (Figure 8B). This data demonstrates that elevating S1P levels is beneficial for the chronic muscle injury that occurs early in muscular dystrophy.


Increased sphingosine-1-phosphate improves muscle regeneration in acutely injured mdx mice.

Ieronimakis N, Pantoja M, Hays AL, Dosey TL, Qi J, Fischer KA, Hoofnagle AN, Sadilek M, Chamberlain JS, Ruohola-Baker H, Reyes M - Skelet Muscle (2013)

Longer-term treatment with THI elevated muscle force in uninjured mdx EDL muscles. (A) Experimental schematic outlining the treatment regimen. Beginning at 4 weeks of age, mdx4cv mice (1-MO males) were treated for 4 weeks ad libitum with 50 mg/l THI (n = 4) or vehicle (n = 3) in drinking water. (B) Myography analysis of EDL muscles reveals a significant increase in maximal specific force with THI treatment. *P <0.05 by student’s t-test. Error bars represent SEM. (C) Summary of findings: S1P can act to not only promote myogenic cell activation and muscle repair, but also enhance muscle fiber size and force, possibly through S1PR1 mediated signaling. EDL, extensor digitorum longus; MO, month-old; S1P, sphingosine-1-phoshate; S1PR1, S1P receptor 1; SEM, standard error of the mean; THI, 2-acetyl-4(5)-tetrahydroxybutyl imidazole.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Figure 8: Longer-term treatment with THI elevated muscle force in uninjured mdx EDL muscles. (A) Experimental schematic outlining the treatment regimen. Beginning at 4 weeks of age, mdx4cv mice (1-MO males) were treated for 4 weeks ad libitum with 50 mg/l THI (n = 4) or vehicle (n = 3) in drinking water. (B) Myography analysis of EDL muscles reveals a significant increase in maximal specific force with THI treatment. *P <0.05 by student’s t-test. Error bars represent SEM. (C) Summary of findings: S1P can act to not only promote myogenic cell activation and muscle repair, but also enhance muscle fiber size and force, possibly through S1PR1 mediated signaling. EDL, extensor digitorum longus; MO, month-old; S1P, sphingosine-1-phoshate; S1PR1, S1P receptor 1; SEM, standard error of the mean; THI, 2-acetyl-4(5)-tetrahydroxybutyl imidazole.
Mentions: To this point we have largely examined the role of S1P in promoting muscle regeneration in acutely injured dystrophic muscles. Since long-term intramuscular injections of S1P are neither feasible nor practical (the injections also cause damage), we decided to revisit the use of THI for elevating S1P muscle content. Although our initial experiments with THI showed little benefit in uninjured mdx muscles, they were short-term and in older animals with severe pathology (Figures 2, 3), or adult animals (Figure 4) at a point when hypertrophy and robust regeneration compensate for degeneration in limb muscles [24,68,69]. Therefore, we examined longer-term treatment of THI in younger mdx mice at 4 weeks of age, a time point characterized by significant muscle degeneration prior to the compensatory period [70]. For this experiment, uninjured mdx4cv animals were treated for 1 month, beginning at 4 weeks of age, with THI or vehicle in the drinking water (Figure 8A) [11]. At 8 weeks of age, we assessed the functional benefit of THI treatment by analyzing EDL specific force via myography. In turn, EDLs from THI-treated animals showed significantly greater specific force compared to vehicle-treated controls (Figure 8B). This data demonstrates that elevating S1P levels is beneficial for the chronic muscle injury that occurs early in muscular dystrophy.

Bottom Line: Intramuscular injection of biotinylated-S1P localized to muscle fibers, including newly regenerated fibers, which also stained positive for S1P receptor 1 (S1PR1).Intramuscular increases of S1P levels, S1PR1 and phosphorylated ribosomal protein S6 (P-rpS6), and elevated EDL muscle specific force, suggest S1P promoted the upregulation of anabolic pathways that mediate skeletal muscle mass and function.These data show that S1P is beneficial for muscle regeneration and functional gain in dystrophic mice, and that THI, or other pharmacological agents that raise S1P levels systemically, may be developed into an effective treatment for improving muscle function and reducing the pathology of DMD.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pathology, School of Medicine, University of Washington, Seattle, WA 98195, USA. hannele@u.washington.edu.

ABSTRACT

Background: Presently, there is no effective treatment for the lethal muscle wasting disease Duchenne muscular dystrophy (DMD). Here we show that increased sphingosine-1-phoshate (S1P) through direct injection or via the administration of the small molecule 2-acetyl-4(5)-tetrahydroxybutyl imidazole (THI), an S1P lyase inhibitor, has beneficial effects in acutely injured dystrophic muscles of mdx mice.

Methods: We treated mdx mice with and without acute injury and characterized the histopathological and functional effects of increasing S1P levels. We also tested exogenous and direct administration of S1P on mdx muscles to examine the molecular pathways under which S1P promotes regeneration in dystrophic muscles.

Results: Short-term treatment with THI significantly increased muscle fiber size and extensor digitorum longus (EDL) muscle specific force in acutely injured mdx limb muscles. In addition, the accumulation of fibrosis and fat deposition, hallmarks of DMD pathology and impaired muscle regeneration, were lower in the injured muscles of THI-treated mdx mice. Furthermore, increased muscle force was observed in uninjured EDL muscles with a longer-term treatment of THI. Such regenerative effects were linked to the response of myogenic cells, since intramuscular injection of S1P increased the number of Myf5nlacz/+ positive myogenic cells and newly regenerated myofibers in injured mdx muscles. Intramuscular injection of biotinylated-S1P localized to muscle fibers, including newly regenerated fibers, which also stained positive for S1P receptor 1 (S1PR1). Importantly, plasma membrane and perinuclear localization of phosphorylated S1PR1 was observed in regenerating muscle fibers of mdx muscles. Intramuscular increases of S1P levels, S1PR1 and phosphorylated ribosomal protein S6 (P-rpS6), and elevated EDL muscle specific force, suggest S1P promoted the upregulation of anabolic pathways that mediate skeletal muscle mass and function.

Conclusions: These data show that S1P is beneficial for muscle regeneration and functional gain in dystrophic mice, and that THI, or other pharmacological agents that raise S1P levels systemically, may be developed into an effective treatment for improving muscle function and reducing the pathology of DMD.

No MeSH data available.


Related in: MedlinePlus