Reduced mitochondrial respiration and increased calcium deposits in the EDL muscle, but not in soleus, from 12-week-old dystrophic mdx mice

Abstract

Mitochondria play an important role in providing ATP for muscle contraction. Muscle physiology is compromised in Duchenne muscular dystrophy (DMD) and several studies have shown the involvement of bioenergetics. In this work we investigated the mitochondrial physiology in fibers from fast-twitch muscle (EDL) and slow-twitch muscle (soleus) in the mdx mouse model for DMD and in control C57BL/10J mice. In our study, multiple mitochondrial respiratory parameters were investigated in permeabilized muscle fibers from 12-week-old animals, a critical age where muscle regeneration is observed in the mdx mouse. Using substrates of complex I and complex II from the electron transport chain, ADP and mitochondrial inhibitors, we found in the mdx EDL, but not in the mdx soleus, a reduction in coupled respiration suggesting that ATP synthesis is affected. In addition, the oxygen consumption after addition of complex II substrate is reduced in mdx EDL; the maximal consumption rate (measured in the presence of uncoupler) also seems to be reduced. Mitochondria are involved in calcium regulation and we observed, using alizarin stain, calcium deposits in mdx muscles but not in control muscles. Interestingly, more calcium deposits were found in mdx EDL than in mdx soleus. These data provide evidence that in 12-week-old mdx mice, calcium is accumulated and mitochondrial function is disturbed in the fast-twitch muscle EDL, but not in the slow-twitch muscle soleus.

Mitochondrial Dysfunction Is an Early Consequence of Partial or Complete Dystrophin Loss in mdx Mice

“…To our knowledge, this work represents the first to suggest that mitochondrial ultrastructure is impacted prior to muscle fiber damage. We further observed impaired complex IV enzymatic activity as previously described (Gaglianone et al, 2019). While not extensively tested, published research does suggest a mitochondrial phenotype occurring early in muscular dystrophy disease progression (Nghiem et al, 2017;Vila et al, 2017;Barker et al, 2018).…”

Targeting Nrf2 for the treatment of Duchenne Muscular Dystrophy

“…DMD pathogenesis is multifaceted and only partially understood. We and others have documented mitochondrial dysfunction [ 19 , 62 , 68 , 69 ] and oxidative stress [ 17 , 19 , [70] , [71] , [72] ] as central features of the disease. Specifically, we discovered that a mitochondrial Complex I deficit was implicit in the cascade leading to energy depletion, which could be partially recovered by re-routing metabolic flux through Complex II (and chemically inhibiting Complex I) [ 62 ].…”

“…Others have reported similar mitochondrial aberrations [ 20 , 73 , 74 ] culminating in energy production deficits [ 62 , 73 ], which may influence the capacity of the muscle to mitigate damage and initiate repair since these processes are energetically-expensive. Furthermore, dysfunctional dystrophic mitochondria generate toxic amounts of ROS [ 17 , 19 , 62 , 68 , 69 , 75 ] resulting in protein and lipid damage via elevated 4-hydroxynonenal (4-HNE) [ 76 ], peroxynitrite [ 75 ], and oxidative [ 17 ] and nitrosative stress [ 75 ], all of which drive the dystrophic condition. Despite dystrophic muscle – from human patients and the genetically homologous mdx mouse model – expressing higher levels of antioxidants including SOD and CAT during peak muscle damage periods [ [77] , [78] , [79] ], overall antioxidant capacity appears to be insufficient to mitigate ROS as evidenced by lipid [ 80 ] and protein [ 81 ] peroxidation and hypersecretion of pro-inflammatory cytokines [ 22 , 82 ].…”

Metabolic remodeling of dystrophic skeletal muscle reveals biological roles for dystrophin and utrophin in adaptation and plasticity

“…Muscles of DMD patients and mouse models of dystrophy have impaired oxidative phosphorylation and mitochondrial function [ [9] , [10] , [11] ], which contribute to the disease etiology. Chronic low-frequency electrical stimulation (LFS) has improved understanding of the adaptive and metabolic plasticity of skeletal muscle [ 12 , 13 ], and in preliminary trials, this approach has shown potential for improving muscle strength in DMD patients [ [14] , [15] , [16] , [17] ] and in mouse models of muscular dystrophy [ [18] , [19] , [20] ].…”