Mode of death in Duchenne muscular dystrophy

Chloroquine decreases cardiac fibrosis and improves cardiac function in a mouse model of Duchenne muscular dystrophy

BACKGROUND

Duchenne muscular dystrophy (DMD), a severe degenerative skeletal and cardiac muscle disease, has a poor prognosis, and no curative treatments are available. Because decreased autophagy has been reported to contribute to skeletal muscle degeneration, therapies targeting autophagy are expected to improve skeletal muscle hypofunction. However, the role of this regulatory mechanism has not been evaluated clearly in DMD cardiomyocytes.

METHODS

In this present study, we evaluated myocardial fibrosis and its mechanism in mdx mice, a model of DMD, and also evaluated changes in cardiac function.

RESULTS

As assessed by LC3 immunohistochemistry, a small number of autophagosomes were detected in cardiomyocytes of both mdx mice and control wild-type (WT) mice. The number of autophagosomes was significantly enhanced by 4 weeks of isoproterenol-induced cardiac stress in cardiomyocytes of mdx but not WT mice. Simultaneously, isoproterenol increased cardiomyocyte fibrosis in mdx but not WT mice. Administration of chloroquine significantly decreased cardiomyocyte fibrosis in mdx mice, even after isoproterenol treatment. Left ventricle size and function were evaluated by echocardiography. Left ventricular contraction was decreased in mdx mice after isoproterenol treatment compared with control mice, which was alleviated by chloroquine administration.

CONCLUSIONS

Heart failure in DMD patients is possibly treated with chloroquine, and the mechanism probably involves chloroquine's anti-inflammatory effects.

The intracellular Ca2+ concentration is elevated in cardiomyocytes differentiated from hiPSCs derived from a Duchenne muscular dystrophy patient

Duchenne muscular dystrophy (DMD) is the most common and severe form of muscular dystrophy. The major symptoms of this condition are walking difficulties, dyspnea caused by progressive skeletal muscle weakness, and cardiomyopathy. Recent advances in ventilator support devices have dramatically decreased mortality caused by respiratory distress. Consequently, cardiomyopathy resulting in heart failure is currently the major cause of death among DMD patients. One mechanism by which skeletal muscle is damaged in DMD patients involves elevation of the intracellular Ca2+ concentration. By contrast, the mechanisms underlying the development of cardiomyopathy are unclear. To investigate this, we examined the intracellular Ca2+ concentration and calcium transients in cardiomyocytes differentiated from human induced pluripotent stem cells (hiPSCs). hiPSCs were derived from a DMD patient (DMD-hiPSCs), in whom exon 44 of the gene encoding dystrophin was deleted, and from his parents (control-hiPSCs), who did not carry this mutation. The intracellular Ca2+ concentration was measured using the fluorescent indicator indo-1. The fluorescence ratio (410/490 nm) of indo-1 at rest (R0), the peak of this ratio (Rmax), and the amplitude (Rmax-R0) were significantly higher in cardiomyocytes differentiated from DMD-hiPSCs than in those differentiated from control-hiPSCs. Moreover, mechanical stretching significantly increased the intracellular Ca2+ concentration in cardiomyocytes differentiated from DMD-hiPSCs, but not in those differentiated from control-hiPSCs. These findings indicate that elevation of the intracellular Ca2+ concentration can cause cardiac damage leading to cardiomyopathy in DMD patients.

Ethical challenges in the care of children and families affected by life-limiting neuromuscular diseases

OBJECTIVE

We sought to understand how neuromuscular clinicians respond to the ethical challenges that arise in caring for children with life-limiting neuromuscular diseases.

METHODS

We conducted a national survey of interdisciplinary professionals who care for children with Duchenne Muscular Dystrophy and Spinal Muscular Atrophy Type-1 to document their knowledge, attitudes, beliefs and reported practices with regard to prominent ethical challenges, and their suggestions for ethics interventions that would assist them in improving clinical practice.

RESULTS

157 participants completed paper or electronic surveys for an overall participation rate of 24%. A significant minority of respondents were either unaware of or chose not to adopt relevant ethical guidelines, and reported experiencing crises of conscience in the care of their patients. In response to 8 ethical dilemmas, there was variability in how often respondents encountered them, their comfort in addressing them, and their reported practices, including only 24% who have requested ethics consultation.

CONCLUSION

Training of interdisciplinary clinicians is needed to improve their adoption of relevant ethical guidelines, cultivate greater awareness of diverse attitudes regarding the ethical permissibility of different treatment options and the utility of ethics consultation, and foster greater confidence and competence in responding to ethical challenges that arise in pediatric neuromuscular practice.