Elevating S1P levels with THI increases muscle fiber size. ( A ) Staining for laminin (green) and DAPI (blue) depict a dramatic increase in muscle fiber size in both injured and uninjured quadriceps (quads) with THI treatment. Depicted are quadriceps muscles from 11-MO mdx4cv mice. Scale bars = 50 μm. ( B , C , D ) Quantification of minimum muscle fiber diameter reveals a significant increase in myofiber size in THI-treated animals. Increased myofiber diameter was observed in both ( B ) injured and ( C ) uninjured quadriceps from THI-treated 11-MO mdx4cv mice, whereas only ( D ) uninjured quadriceps in THI-treated 16-MO mdx4cv mice showed increased myofiber size compared to vehicle controls. As indicated by the distributions, mean and median values of muscle fiber minimum diameters, there is an overall increase in muscle fiber size with THI treatment. Quantifications were undertaken in random fields in both injured and uninjured muscles in order to obtain an overall representation of fiber size increase for each muscle.*P <0.05, ***P <0.0005 by student’s t-test. Error bars represent SEM. DAPI, 4',6-diamidino-2-phenylindole; MO, month-old; S1P, sphingosine-1-phoshate; SEM, standard error of the mean; THI, 2-acetyl-4(5)-tetrahydroxybutyl imidazole.