Metformin Reverses the Enhanced Myocardial SR/ER-Mitochondria Interaction and Impaired Complex I-Driven Respiration in Dystrophin-Deficient Mice.

Claire Angebault,Alain Lacampagne,Mathieu Panel,Jennifer Rieusset,Jérémy Fauconnier,Mathilde Lacôte

doi:10.3389/fcell.2020.609493

Abstract

Besides skeletal muscle dysfunction, Duchenne muscular dystrophy (DMD) exhibits a progressive cardiomyopathy characterized by an impaired calcium (Ca2+) homeostasis and a mitochondrial dysfunction. Here we aimed to determine whether sarco-endoplasmic reticulum (SR/ER)–mitochondria interactions and mitochondrial function were impaired in dystrophic heart at the early stage of the pathology. For this purpose, ventricular cardiomyocytes and mitochondria were isolated from 3-month-old dystrophin-deficient mice (mdx mice). The number of contacts points between the SR/ER Ca2+ release channels (IP3R1) and the porine of the outer membrane of the mitochondria, VDAC1, measured using in situ proximity ligation assay, was greater in mdx cardiomyocytes. Expression levels of IP3R1 as well as the mitochondrial Ca2+ uniporter (MCU) and its regulated subunit, MICU1, were also increased in mdx heart. MICU2 expression was however unchanged. Furthermore, the mitochondrial Ca2+ uptake kinetics and the mitochondrial Ca2+ content were significantly increased. Meanwhile, the Ca2+-dependent pyruvate dehydrogenase phosphorylation was reduced, and its activity significantly increased. In Ca2+-free conditions, pyruvate-driven complex I respiration was decreased whereas in the presence of Ca2+, complex I-mediated respiration was boosted. Further, impaired complex I-mediated respiration was independent of its intrinsic activity or expression, which remains unchanged but is accompanied by an increase in mitochondrial reactive oxygen species production. Finally, mdx mice were treated with the complex I modulator metformin for 1 month. Metformin normalized the SR/ER-mitochondria interaction, decreased MICU1 expression and mitochondrial Ca2+ content, and enhanced complex I-driven respiration. In summary, before any sign of dilated cardiomyopathy, the DMD heart displays an aberrant SR/ER-mitochondria coupling with an increase mitochondrial Ca2+ homeostasis and a complex I dysfunction. Such remodeling could be reversed by metformin providing a novel therapeutic perspective in DMD.

Highlights

Duchenne muscular dystrophy (DMD) is the most common X-linked disorder (1/3,500 newborn male affected) caused by non-sense mutations in dystrophin gene and resulting in the absence of the large protein dystrophin (427 kDa) (Hoffman, 2020)
We first determined whether sarco-endoplasmic reticulum (SR/ER)–mitochondria interactions are altered in mdx mouse cardiomyocytes as previously reported in skeletal muscle, namely, a decrease in sarcoplasmic reticulum (SR)/ER–mitochondria interaction (Pauly et al, 2017)
We first measured the expression level of proteins involved in the SR/ERmitochondria tethering

Summary

Introduction

Duchenne muscular dystrophy (DMD) is the most common X-linked disorder (1/3,500 newborn male affected) caused by non-sense mutations in dystrophin gene and resulting in the absence of the large protein dystrophin (427 kDa) (Hoffman, 2020). Dystrophin deficiency causes progressive muscle weakness and cardiac failure. Cardiac involvement is inevitable and progresses with age toward a dilated cardiomyopathy (DCM) with an increased frequency of ventricular arrhythmia and sudden cardiac death. Among DMD patients, the cardiac phenotype varies with age from no discernible cardiac remodeling or dysfunction to early onset of DCM with heart failure (Sasaki et al, 1998; Amedro et al, 2019; Segawa et al, 2020). Whereas more than 90% of DMD patients display echocardiographic features of left ventricular remodeling and contractile dysfunction by the age of 18 years 11/26/20 5:34:00 PM, in the murine model of DMD, the mdx mice, similar defects are evident at 42 weeks of age (Quinlan et al, 2004)

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