Figure 1. VD3 protects C2C12 myotubes and isolated myofibers from IL6-induced atrophy. (A) Myotubes were treated in serum-free medium with 100 nM VD3, 20 ng/ml IL6 alone or in combination with decreasing concentrations (100 – 0.01 nM) of VD3 for 24 h. At the end of the indicated treatments, myotube diameters were measured either in phase-contrast images or after immunofluorescence (IF) with anti-MyHC antibody and DAPI counterstaining. Representative images of myotubes in both phase-contrast and IF are shown at the bottom of the panel. Scale bar, 100 μm (B) Single myofibers were isolated from C57BL/6 mice and treated with 20 ng/ml IL6 alone or in combination with 100nM VD3. Myofiber diameters were acquired from phase-contrast images (representative images at the bottom of the panel). (C) Differentiation and (D) fusion indexes after 24 h of VD3 and IL6 treatments compared to the time of treatment administration (0 h; C2C12 differentiated for at least 4 days in DM). Data are presented as the mean ± SEM. *P < 0.05; **P < 0.01; ***P < 0.001.