Background: Duchenne muscular dystrophy (DMD) is caused by mutations in dystrophin gene, impairing skeletal muscle integrity and stability. The mdx mice (X-chromosome-linked muscular
dystrophy), an experimental model of DMD, also have mutation in the dystrophin gene, leading to mechanical instability for skeletal muscle. Due to regeneration-degeneration cycle, muscle tissue begins
to show chronic inflammation and histopathological changes and muscle fibrosis. The physical exercise may have local and systemic effects due to action of cytokines released after training session.
Cytokines concentration increased in blood induces systemic anti-inflammatory action, resulting in an important mechanism for everse or minimize chronic inflammatory processes. The aim of this study
was to analyze the effects of aerobic exercise training on the histopathology and fibrosis in a jaw muscle of the mdx mice.
Methods: C57BL/10 and C57BL/10-Dmdmdx male mice with eight weeks old were distributed into four groups (n=5): Sedentary Control (SC), Trained Control (TC), Sedentary Mdx (S-Mdx) and
Trained Mdx (T-Mdx). Procedures were approved by the Experimental Animal Use Committee of UNIFESP (CEUA 8165240614). Trained groups were submitted to seven weeks of aerobic exercise, five times a week
at a high intensity speed for 60 minutes with treadmill downward of -15°. After euthanasia, masseter muscles were taken and specimens were stained with hematoxylin and eosin and Sirius Red.
Histopathological and connective tissue (ct) analysis was performed through semiquantitative score. Statistical analysis of data was performed using two-way ANOVA.
Results: In SC and TC histopathological analysis showed muscle fibers with homogeneous morphology, polygonal shape and peripheral nuclei. In contrast, S-Mdx and T-Mdx showed
morphological variety of cells (polygonal and round muscle fibers), size variety, centralized nuclei, fiber necrosis and inflammatory infiltrate. Mdx groups had higher histopathological scores than C
groups (p<0.05). Mdx groups was influenced by physical training, and T-Mdx group had the lowest score that S-Mdx (p<0.05). Connective tissue analysis of SC and TC presented ct in endomysium and
perimysium regions. In contrast, S-Mdx and T-Mdx showed thickened ct in endomysium and perimysium, characterized by intense muscle fibrosis process. The semiquantitative results of ct evidenced that
Mdx groups had higher percentages of ct than Control groups (p<0.05). Furthermore, masseter muscle was influenced by physical training and T-Mdx showed lower percentage of ct than S-Mdx (p<0.05).
Conclusions: The exercise training protocol reduced the histopathology and fibrosis in masseter muscle of mdx mice as a systemic effect of aerobic exercise.