BACKGROUND: Cardiomyopathy is a common and lethal complication in patients with limb-girdle muscular dystrophy (LGMD), one of the most prevalent forms of muscular dystrophy. The pathogenesis underlying LGMD-related cardiomyopathy remains unclear. NRIP (gene name DCAF6), a Ca2+-dependent calmodulin binding protein, was reduced in dystrophic muscles from LGMD patients. Mice lacking NRIP exhibit a myopathic phenotype resembling that in LGMD patients, making NRIP deficiency a potential culprit leading to cardiomyopathy. This study aimed to determine if NRIP deficiency leads to cardiomyopathy and to explore the underlying molecular mechanisms. METHODS AND RESULTS: NRIP expression was reduced in both human and mouse failing hearts. Muscle-specific NRIP knockout (MCK-Cre::Dcaf6flox/flox) mouse heart and isolated cardiomyocytes exhibited markedly reduced contractility. Transmission electron microscopy revealed abnormal sarcomere structures and mitochondrial morphology in MCK-Cre::Dcaf6flox/flox hearts. Protein co-immunoprecipitation and confocal imaging revealed that NRIP interacts with α-actinin 2 (ACTN2) at the Z-disc. We found that NRIP facilitated ACTN2-mediated F-actin bundling, and that NRIP deficiency resulted in reduced binding between Z-disc proteins ACTN2 and Cap-Z. In addition, NRIP-deficiency led to increased mitochondrial ROS and impaired mitochondrial respiration/ATP production owing to elevated cellular NADH/NAD+ ratios. Treatment with mitochondria-directed antioxidant mitoTEMPO or NAD+ precursor nicotinic acid restored mitochondrial function and cardiac contractility in MCK-Cre::Dcaf6flox/flox mice. CONCLUSIONS: NRIP is essential to maintain sarcomere structure and mitochondrial/contractile function in cardiomyocytes. Our results revealed a novel role for NRIP deficiency in the pathogenesis of LGMD and heart failure. Targeting NRIP, therefore, could be a powerful new approach to treat myocardial dysfunction in LGMD and heart failure patients.
Cardiomyopathies/metabolism , Mitochondria, Heart/metabolism , Nuclear Receptor Interacting Protein 1/metabolism , Sarcomeres/metabolism , Actinin/metabolism , Actins/metabolism , Adenosine Triphosphate/metabolism , Animals , Calcium/metabolism , Cardiomyopathies/physiopathology , Cell Respiration/drug effects , Down-Regulation/drug effects , Down-Regulation/genetics , Heart Failure/genetics , Homeostasis/drug effects , Humans , Male , Mice , Mitochondria, Heart/drug effects , Mitochondria, Heart/ultrastructure , Models, Biological , Myocardial Contraction/drug effects , Myocardium/metabolism , Myocardium/pathology , Myocytes, Cardiac/drug effects , Myocytes, Cardiac/metabolism , NAD/metabolism , Niacin/pharmacology , Nuclear Receptor Interacting Protein 1/chemistry , Phenotype , Protein Binding/drug effects , Protein Domains , Reactive Oxygen Species/metabolism , Sarcomeres/drug effects , Sarcomeres/ultrastructure
