Administration of S1P leads to increased levels of S1PR1 and P-rpS6 in vivo . ( A ) Experimental schematic of S1P and PBS (vehicle) injected daily for the first 72 hours into TAs of uninjured mdx4cv mice (n = 4, 2.5-MO, left TAs injected S1P, right TAs injected PBS). ( B ) Western blot analysis of injected TAs (n = 3, 2.5-MO mdx4cv) indicates that administration of S1P significantly increases S1PR1 levels. ( C ) Western blot analysis of injected TAs (n = 4, 2.5-MO mdx4cv) for total, and P-Akt, P-mTOR and P-rpS6, reveals that total and P-rpS6 were significantly higher with S1P treatment. Increased levels of total and P-rpS6 suggest that S1P administration promotes protein synthesis in mdx muscles. *P <0.05 by student’s t-test. Error bars represent SEM. MO, month-old; P-Akt, phosphorylated Akt; P-mTOR, phosphorylated mammalian target of rapamycin; P-rpS6, phosphorylated ribosomal protein S6; rpS6, ribosomal protein S6; S1P, sphingosine-1-phoshate; S1PR1, S1P receptor 1; SEM, standard error of the mean; TA, tibialis anterior.