Receptor interacting protein kinase-3 promotes both myopathy and cardiomyopathy in dystrophin-deficient mice

Background Duchenne muscular dystrophy (DMD) is a muscle degenerative disorder that is caused by the absence of dystrophin. From early childhood, multiple rounds of myofibre necrosis and regeneration lead to fibrosis and fat deposition, irreversibly disturbing skeletal muscle function and impairing locomotion. Cell necrosis also affects respiratory muscles and cardiomyocytes, ultimately responsible for the death of DMD boys by respiratory or heart failure. Necroptosis is a genetically programmed form of necrosis requiring the receptor-interacting serine/threonine-protein kinase (RIPK)3 and is a promising new therapeutic target for multiple degenerative disorders. We previously demonstrated that necroptosis mediates hindlimb myofibre degeneration in distinct muscular dystrophies, including in DMD. However, this pathway was recently found to be required for myogenesis. Its prevention might therefore lead to detrimental side effects on muscle repair. Whether necroptosis also participates in the pathogenesis of respiratory and cardiac muscle dysfunction, and whether its long-term inhibition would ultimately be beneficial or detrimental to mdx mice are addressed here. Methods Herein, we examined the effects of RIPK3 depletion on an advanced stage of pathogenesis in mdx mice. Dystrophic mice aged 12 to 18 months were submitted to forced treadmill running to assess their locomotor function. mdx cardiomyopathy was also examined by echocardiography in 40-week-old mice. Limb skeletal muscles, diaphragm and heart were analyzed by histology and molecular biology to compare the phenotype of mdxRipk3+/+ mdxRipk3-/- mice. Results In 18-month-old mdxRipk3-/- mice, we found no sign of muscle regeneration defect compared to mdxRipk3+/+ littermates. mdxRipk3-/- mice had decreased fibrosis in limb muscles, without evidence of muscle atrophy. The size of diaphragm myofibres was slightly reduced and affected by less variability than mdx littermates. Fibrosis was also reduced in the diaphragm of RIPK3-deficient mdx mice. Notably, heart hypertrophy and left ventricle fibrosis were reduced in mdxRipk3-/- mice, and using echocardiography, we found a significant decrease of markers of cardiomyopathy by such as a reduction of the relative wall thickness and left ventricle mass. Conclusions Our data suggest that necroptosis is involved together in the pathogenic phenotype of locomotor, respiratory, and cardiac muscles in dystrophin-deficient mice. The long-term genetic ablation of RIPK3 does not generate evidence of sarcopenia or muscle impairment in mdx mice. Our data suggest that necroptosis may represent a new therapeutic target susceptible to improving the phenotype of myopathy and cardiomyopathy.