Myogenic differentiation factor 1 and myogenin expression not elevated in regenerated masticatory muscles of dystrophic (mdx) mice

Orofacial muscles in mdx mice, a model of Duchenne muscular dystrophy (DMD), undergo muscle necrosis followed by muscle regeneration. The activity of myogenic regulatory factors (MRF) in muscles that regenerate may reveal specific changes. Little is known about the role of MRF, particularly their expression after muscle necrosis in the orofacial muscles of mdx mice and in DMD. Patients suffering from DMD present characteristic malocclusions in association with orofacial dysfunctions. Investigating the role of MRFs in mdx masticatory muscles may help to develop preventive and therapeutic strategies for DMD. Using Western Blot analysis, we examined the protein expression of MRFs (myogenin and MyoD1) in masticatory muscles such as masseter, temporal, and tongue muscle and one hindlimb muscle, the soleus of control and mdx mice (n = 6-7). The mean optical density (MOD) of proteins was measured for quantification. Myogenin and MyoD1 were detected in mdx and control mice. The amount of myogenin in masseter (MOD, mean +/- standard error of the mean (SEM), control vs. mdx: 3.08 +/- 0.67 vs. 1.83 +/- 0.33), tongue (MOD control vs. mdx: 1.53 +/- 0.22 vs. 1.41 +/- 0.14), temporal (MOD control vs. mdx: 1.23 +/- 0.16 vs. 1.43 +/- 0.35), and soleus muscles (MOD, control vs. mdx: 1.95 +/- 0.26 vs. 2.31 +/- 0.42) did not differ between the mouse strains. MyoD1 amounts in mdx, similar to that of myogenin, remained unchanged when compared to control mice (MOD control vs. mdx: masseter 0.75 +/- 0.09 vs. 0.86 +/- 0.13; tongue 1.55 +/- 0.25 vs. 1.41 +/- 0.28; temporal 0.71 +/- 0.10 vs. 0.73 +/- 0.11; soleus 1.09 +/- 0.26 vs. 1.03 +/- 0.24). The results indicate that protein expression of MyoD1 and myogenin in mdx mice does not differ from controls, suggesting a secondary role of MyoD1 and myogenin in the regeneration stage of mdx orofacial muscles.