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

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.

Effect of the Non-Immunosuppressive MPT Pore Inhibitor Alisporivir on the Functioning of Heart Mitochondria in Dystrophin-Deficient mdx Mice

“…Earlier, other groups and we found significant changes in the nature of mitochondrial dysregulation in the cardiac muscle of mdx animals, which contrasted with a decrease in the functional activity of organelles in skeletal muscles already at the early stages of the development of pathology. On the contrary, in this case, we noted an increase in the functional activity of heart mitochondria accompanied by a high intensity of oxidative phosphorylation and the ability to transport and retain calcium ions in the matrix of organelles [ 15 , 16 , 17 ]. We hypothesized that such a picture might contribute to the adaptation of the heart to the development of muscular dystrophy and delay cardiac pathology.…”

The Interplay of Mitophagy and Inflammation in Duchenne Muscular Dystrophy

“…Importantly, therapeutic approaches that increase mitophagy with a concomitant reduction in ROS levels have been shown to be effective in ameliorating DMD pathological outcomes. There are different ways to target this mechanism, including treating with antioxidants [ 52 , 53 ], activating the AMP kinase (AMPK) pathway [ 54 , 55 , 56 ], increasing NAD + -dependent Sirtuin 1 (SIRT1)/peroxisome proliferator-activated receptor gamma coactivator (PGC-1α) pathway [ 44 , 46 , 57 , 58 , 59 , 60 ], and upregulating mitophagy-related genes [ 39 ]. Many antioxidants have shown the therapeutic efficacy in DMD mice as seen by improvement of DMD muscle outcomes, either by acting as an ROS scavenger or by preventing the ROS formation [ 51 ].…”

“…Consistent with this, treatment with a different synthetic agonist of AMPK, metformin, in mdx mice also resulted in an amelioration of dystrophic pathology by the upregulation of PGC-1α and utrophin expression [ 74 ]. Furthermore, a recent study demonstrated that metformin treatment was also able to reduce the detrimental SR/ER-mitochondrial interaction seen in dystrophic cardiomyocytes and restore mitochondrial function [ 55 ].…”

Structure and Function of Mitochondria‐Associated Endoplasmic Reticulum Membranes (MAMs) and Their Role in Cardiovascular Diseases

“…Since MAMs modulate the calcium dynamics, it has a vital role in mediating the opening of mPTP and the damage in I/R. The CypD-GRP75-IP3R-VDAC complex inhibition improved hypoxia/reoxygenation injury in cardiomyocytes [147]. The hypoxia/reoxygenation process induced the increased interaction of CypD-GRP75-IP3R-VDAC complex and GSK3β, leading to cell death.…”