Histological analysis of a Becker muscular dystrophy case, diurnal expression of dystrophin in control mice and decreased expression of dystrophin in Bmal1 knockout mice.

Becker muscular dystrophy (BMD) is a hereditary disease characterized by dystrophin deletion that consequently induces muscle weakness, cardiac hypertrophy and cardiac failure; These conditions are similar to those in Duchenne muscular dystrophy. The circadian rhythm is a physiological phenomenon that is predominantly regulated by the transcription and translation of clock genes. Bmal1 (Brain and muscle Arnt-like protein 1) is one of the core clock genes, and its deficiency disturbs the circadian rhythm, results in cardiac hypertrophy and cardiac failure. Dystrophin expression under diurnal conditions and in Bmal1 deficiency is yet to be elucidated. In this study, we analyzed the heart and lungs sampled during a BMD autopsy. Macroscopical examination revealed a large heart and dilated cardiomyopathy. Microscopical examination revealed an undulated structure, as well as the degeneration, and necrosis of myocardial cells. We also analyzed dystrophin expression in tissues obtained from human autopsies and mice. In human autopsy cases, dystrophin expression was lower in the heart with BMD compared that in the heart with non-BMD hypertrophy. In the heart and muscle of control mice, dystrophin expression was higher at ZT0 than at ZT12. The dystrophin expression was found to be lower in heart-specific Bmal1 knockout mice compared to that in the control mice. Hence, our study indicated that BMD was closely associated with cardiac hypertrophy and cardiac failure, while dystrophin had a diurnal expression pattern in control mice that was regulated by Bmal1.