Erratum: Voluntary wheel running complements microdystrophin gene therapy to improve muscle function in mdx mice.

[This corrects the article DOI: 10.1016/j.omtm.2021.02.024.].

Voluntary wheel running complements microdystrophin gene therapy to improve muscle function in mdx mice.

We tested the hypothesis that voluntary wheel running would complement microdystrophin gene therapy to improve muscle function in young mdx mice, a model of Duchenne muscular dystrophy. mdx mice injected with a single dose of AAV9-CK8-microdystrophin or vehicle at age 7 weeks were assigned to three groups: mdxRGT (run, gene therapy), mdxGT (no run, gene therapy), or mdx (no run, no gene therapy). Wild-type (WT) mice were assigned to WTR (run) and WT (no run) groups. WTR and mdxRGT performed voluntary wheel running for 21 weeks; remaining groups were cage active. Robust expression of microdystrophin occurred in heart and limb muscles of treated mice. mdxRGT versus mdxGT mice showed increased microdystrophin in quadriceps but decreased levels in diaphragm. mdx final treadmill fatigue time was depressed compared to all groups, improved in mdxGT, and highest in mdxRGT. Both weekly running distance (km) and final treadmill fatigue time for mdxRGT and WTR were similar. Remarkably, mdxRGT diaphragm power was only rescued to 60% of WT, suggesting a negative impact of running. However, potential changes in fiber type distribution in mdxRGT diaphragms could indicate an adaptation to trade power for endurance. Post-treatment in vivo maximal plantar flexor torque relative to baseline values was greater for mdxGT and mdxRGT versus all other groups. Mitochondrial respiration rates from red quadriceps fibers were significantly improved in mdxGT animals, but the greatest bioenergetic benefit was observed in the mdxRGT group. Additional assessments revealed partial to full functional restoration in mdxGT and mdxRGT muscles relative to WT. These data demonstrate that voluntary wheel running combined with microdystrophin gene therapy in young mdx mice improved whole-body performance, affected muscle function differentially, mitigated energetic deficits, but also revealed some detrimental effects of exercise. With microdystrophin gene therapy currently in clinical trials, these data may help us understand the potential impact of exercise in treated patients.

The cardiolipin-binding peptide elamipretide mitigates fragmentation of cristae networks following cardiac ischemia reperfusion in rats.

Mitochondrial dysfunction contributes to cardiac pathologies. Barriers to new therapies include an incomplete understanding of underlying molecular culprits and a lack of effective mitochondria-targeted medicines. Here, we test the hypothesis that the cardiolipin-binding peptide elamipretide, a clinical-stage compound under investigation for diseases of mitochondrial dysfunction, mitigates impairments in mitochondrial structure-function observed after rat cardiac ischemia-reperfusion. Respirometry with permeabilized ventricular fibers indicates that ischemia-reperfusion induced decrements in the activity of complexes I, II, and IV are alleviated with elamipretide. Serial block face scanning electron microscopy used to create 3D reconstructions of cristae ultrastructure reveals that disease-induced fragmentation of cristae networks are improved with elamipretide. Mass spectrometry shows elamipretide did not protect against the reduction of cardiolipin concentration after ischemia-reperfusion. Finally, elamipretide improves biophysical properties of biomimetic membranes by aggregating cardiolipin. The data suggest mitochondrial structure-function are interdependent and demonstrate elamipretide targets mitochondrial membranes to sustain cristae networks and improve bioenergetic function.

Bioenergetics underlying single-cell migration on aligned nanofiber scaffolds.

Cell migration is centrally involved in a myriad of physiological processes, including morphogenesis, wound healing, tissue repair, and metastatic growth. The bioenergetics that underlie migratory behavior are not fully understood, in part because of variations in cell culture media and utilization of experimental cell culture systems that do not model physiological connective extracellular fibrous networks. In this study, we evaluated the bioenergetics of C2C12 myoblast migration and force production on fibronectin-coated nanofiber scaffolds of controlled diameter and alignment, fabricated using a nonelectrospinning spinneret-based tunable engineered parameters (STEP) platform. The contribution of various metabolic pathways to cellular migration was determined using inhibitors of cellular respiration, ATP synthesis, glycolysis, or glucose uptake. Despite immediate effects on oxygen consumption, mitochondrial inhibition only modestly reduced cell migration velocity, whereas inhibitors of glycolysis and cellular glucose uptake led to striking decreases in migration. The migratory metabolic sensitivity was modifiable based on the substrates present in cell culture media. Cells cultured in galactose (instead of glucose) showed substantial migratory sensitivity to mitochondrial inhibition. We used nanonet force microscopy to determine the bioenergetic factors responsible for single-cell force production and observed that neither mitochondrial nor glycolytic inhibition altered single-cell force production. These data suggest that myoblast migration is heavily reliant on glycolysis in cells grown in conventional media. These studies have wide-ranging implications for the causes, consequences, and putative therapeutic treatments aimed at cellular migration.

Progression-Mediated Changes in Mitochondrial Morphology Promotes Adaptation to Hypoxic Peritoneal Conditions in Serous Ovarian Cancer.

Ovarian cancer is the deadliest gynecological cancer in women, with a survival rate of less than 30% when the cancer has spread throughout the peritoneal cavity. Aggregation of cancer cells increases their viability and metastatic potential; however, there are limited studies that correlate these functional changes to specific phenotypic alterations. In this study, we investigated changes in mitochondrial morphology and dynamics during malignant transition using our MOSE cell model for progressive serous ovarian cancer. Mitochondrial morphology was changed with increasing malignancy from a filamentous network to single, enlarged organelles due to an imbalance of mitochondrial dynamic proteins (fusion: MFN1/OPA1, fission: DRP1/FIS1). These phenotypic alterations aided the adaptation to hypoxia through the promotion of autophagy and were accompanied by changes in the mitochondrial ultrastructure, mitochondrial membrane potential, and the regulation of reactive oxygen species (ROS) levels. The tumor-initiating cells increased mitochondrial fragmentation after aggregation and exposure to hypoxia that correlated well with our previously observed reduced growth and respiration in spheroids, suggesting that these alterations promote viability in non-permissive conditions. Our identification of such mitochondrial phenotypic changes in malignancy provides a model in which to identify targets for interventions aimed at suppressing metastases.

Pulmonary Exposure to Magnéli Phase Titanium Suboxides Results in Significant Macrophage Abnormalities and Decreased Lung Function.

Coal is one of the most abundant and economic sources for global energy production. However, the burning of coal is widely recognized as a significant contributor to atmospheric particulate matter linked to deleterious respiratory impacts. Recently, we have discovered that burning coal generates large quantities of otherwise rare Magnéli phase titanium suboxides from TiO2 minerals naturally present in coal. These nanoscale Magnéli phases are biologically active without photostimulation and toxic to airway epithelial cells in vitro and to zebrafish in vivo. Here, we sought to determine the clinical and physiological impact of pulmonary exposure to Magnéli phases using mice as mammalian model organisms. Mice were exposed to the most frequently found Magnéli phases, Ti6O11, at 100 parts per million (ppm) via intratracheal administration. Local and systemic titanium concentrations, lung pathology, and changes in airway mechanics were assessed. Additional mechanistic studies were conducted with primary bone marrow derived macrophages. Our results indicate that macrophages are the cell type most impacted by exposure to these nanoscale particles. Following phagocytosis, macrophages fail to properly eliminate Magnéli phases, resulting in increased oxidative stress, mitochondrial dysfunction, and ultimately apoptosis. In the lungs, these nanoparticles become concentrated in macrophages, resulting in a feedback loop of reactive oxygen species production, cell death, and the initiation of gene expression profiles consistent with lung injury within 6 weeks of exposure. Chronic exposure and accumulation of Magnéli phases ultimately results in significantly reduced lung function impacting airway resistance, compliance, and elastance. Together, these studies demonstrate that Magnéli phases are toxic in the mammalian airway and are likely a significant nanoscale environmental pollutant, especially in geographic regions where coal combustion is a major contributor to atmospheric particulate matter.

Cardioprotective effects of idebenone do not involve ROS scavenging: Evidence for mitochondrial complex I bypass in ischemia/reperfusion injury.

Novel therapeutic strategies to treat mitochondrial deficiencies in acute coronary syndromes are needed. Complex I of the mitochondrial electron transport system is damaged following ischemia/reperfusion (I/R) injury. This disruption contributes to aberrant electron transport, diminished bioenergetics, an altered redox environment, and mitochondrial damage involved in tissue injury. In this study, we determined the cardiac and mitochondrial effects of idebenone, a benzoquinone currently in several clinical trials with purported 'antioxidant' effects. We employed complimentary models of ischemia/reperfusion injury in perfused hearts, permeabilized cardiac fibers, isolated mitochondria, and in cells to elucidate idebenone's cardioprotective mechanism(s). In ex vivo whole hearts, infarct size was markedly reduced with post-ischemic idebenone treatment (25 ±â€¯5% area at risk, AAR) compared to controls (56 ±â€¯6% AAR, P < .05). Several parameters of hemodynamic function were also significantly improved after idebenone treatment. Parallel studies of anoxia/reoxygenation were conducted using isolated mitochondria and permeabilized ventricular fibers. In isolated mitochondria, we simultaneously monitored respiration and ROS emission. Idebenone treatment modestly elevated succinate-derived H2O2 production when compared to vehicle control (1.34 ±â€¯0.05 vs 1.21 ±â€¯0.05%, H2O2/O2 respectively, P < .05). Isolated mitochondria subjected to anoxia/reoxygenation demonstrated higher rates of respiration with idebenone treatment (2360 ±â€¯69 pmol/s*mg) versus vehicle control (1995 ±â€¯101 pmol/s*mg). Both mitochondria and permeabilized cardiac fibers produced high rates of H2O2 after anoxia/reoxygenation, with idebenone showing no discernable attenuation on H2O2 production. These insights were further investigated with studies in mitochondria isolated from reperfused ventricle. The profound decrease in complex-I dependent respiration after ischemia/reperfusion (701 ±â€¯59 pmolO2/s*mg compared to 1816 ±â€¯105 pmol O2/s*mg in normoxic mitochondria) was attenuated with idebenone treatment (994 ±â€¯76 vs pmol O2/s*mg, P < .05). Finally, the effects of idebenone were determined using permeabilized cell models with chemical inhibition of complex I. ADP-dependent oxidative phosphorylation capacity was significantly higher in complex-I inhibited cells treated acutely with idebenone (89.0 ±â€¯4.2 pmol/s*million cells versus 70.1 ±â€¯8.2 pmol/s*million cells in untreated cells). Taken together, these data indicate that the cardioprotective effects of idebenone treatment do not involve ROS-scavenging but appear to involve augmentation of the quinone pool, thus providing reducing equivalents downstream of complex I. As this compound is already in clinical trials for other indications, it may provide a safe and useful approach to mitigate ischemia/reperfusion injury in patients.

Influence of Pulsed Electric Fields and Mitochondria-Cytoskeleton Interactions on Cell Respiration.

Pulsed electric fields with microsecond pulse width (µsPEFs) are used clinically; namely, irreversible electroporation/Nanoknife is used for soft tissue tumor ablation. The µsPEF pulse parameters used in irreversible electroporation (0.5-1 kV/cm, 80-100 pulses, ∼100 µs each, 1 Hz frequency) may cause an internal field to develop within the cell because of the disruption of the outer cell membrane and subsequent penetration of the electric field. An internal field may disrupt voltage-sensitive mitochondria, although the research literature has been relatively unclear regarding whether such disruptions occur with µsPEFs. This investigation reports the influence of clinically used µsPEF parameters on mitochondrial respiration in live cells. Using a high-throughput Agilent Seahorse machine, it was observed that µsPEF exposure comprising 80 pulses with amplitudes of 600 or 700 V/cm did not alter mitochondrial respiration in 4T1 cells measured after overnight postexposure recovery. To record alterations in mitochondrial function immediately after µsPEF exposure, high-resolution respirometry was used to measure the electron transport chain state via responses to glutamate-malate and ADP and mitochondrial membrane potential via response to carbonyl cyanide-p-trifluoromethoxyphenylhydrazone. In addition to measuring immediate mitochondrial responses to µsPEF exposure, measurements were also made on cells permeabilized using digitonin and those with compromised cytoskeleton due to actin depolymerization via treatment with the drug latrunculin B. The former treatment was used as a control to tease out the effects of plasma membrane permeabilization, whereas the latter was used to investigate indirect effects on the mitochondria that may occur if µsPEFs impact the cytoskeleton on which the mitochondria are anchored. Based on the results, it was concluded that within the pulse parameters tested, µsPEFs alone do not hinder mitochondrial physiology but can be used to impact the mitochondria upon compromising the actin. Mitochondrial susceptibility to µsPEF after actin depolymerization provides, to our knowledge, a novel avenue for cancer therapeutics.

Expert consensus document: Mitochondrial function as a therapeutic target in heart failure.

Heart failure is a pressing worldwide public-health problem with millions of patients having worsening heart failure. Despite all the available therapies, the condition carries a very poor prognosis. Existing therapies provide symptomatic and clinical benefit, but do not fully address molecular abnormalities that occur in cardiomyocytes. This shortcoming is particularly important given that most patients with heart failure have viable dysfunctional myocardium, in which an improvement or normalization of function might be possible. Although the pathophysiology of heart failure is complex, mitochondrial dysfunction seems to be an important target for therapy to improve cardiac function directly. Mitochondrial abnormalities include impaired mitochondrial electron transport chain activity, increased formation of reactive oxygen species, shifted metabolic substrate utilization, aberrant mitochondrial dynamics, and altered ion homeostasis. In this Consensus Statement, insights into the mechanisms of mitochondrial dysfunction in heart failure are presented, along with an overview of emerging treatments with the potential to improve the function of the failing heart by targeting mitochondria.

Cardioprotective Effects of Mitochondria-Targeted Peptide SBT-20 in two Different Models of Rat Ischemia/Reperfusion.

PURPOSE: Dysfunctional mitochondria are considered to be the major source of intracellular reactive oxygen species and play a central role in the pathophysiology of myocardial ischemia/reperfusion. This study sought to determine effects of mitochondria-targeted cytoprotective peptide SBT-20 on myocardial infarct size in two different models of ischemia/reperfusion. METHODS: For in vivo studies, anesthetized Sprague Dawley rats were subjected to 30 min of coronary artery occlusion followed by 3 h of reperfusion. Rats received saline (control), low dose SBT-20 (0.3 mg/kg/h) or high dose SBT-20 (3 mg/kg/h) treatment (n = 15 rats in each group). Saline or SBT-20 were delivered into the jugular vein starting 5 min after coronary artery occlusion and were continued for one hour post coronary artery reperfusion. Body temperature, heart rate and blood pressure were monitored during the procedure. At the end of 3 h reperfusion, the ischemic risk area, no-reflow area, and infarct size were measured. In separate in vitro studies, isolated rat hearts were exposed to 20 min global ischemia, followed by SBT-20 administration (1 µM) or no SBT-20 (control) throughout the 2 h reperfusion. In vitro studies were conducted in cells and heart mitochondria to ascertain the mitochondrial effects of SBT-20 on mitochondrial respiration and reactive oxygen species production. RESULTS: In the in vivo study, the ischemic risk areas (as a percentage of the left ventricle) were similar among the saline (49.5 ± 2.3 %), low dose SBT-20 (48.6 ± 2.1 %), and high dose SBT-20 groups (48.7 ± 3.0 %). Treatment with SBT-20 significantly reduced infarct size ( as a percentage of risk area) in low dose (62.1 ± 4.4 %) and high dose (64.0 ± 4.9 %) compared with saline treatment (77.6 ± 2.6 %, p = 0.001 for both doses). There was no difference in infarct size between low and high dose SBT-20 treatment. The no-reflow areas (as a percentage of the risk area) were comparable among the saline (23.9 ± 1.7 %), low dose SBT-20 (23.7 ± 2.8 %), and high dose groups (25.0 ± 2.1 %). Body temperature, heart rate and blood pressure were comparable among the 3 groups at baseline, during ischemia, and at the end of 3 h of reperfusion. In the in vitro study, infarct size was reduced from 43.3 ± 2.6 % in control group (n = 11) to 17.2 ± 2.8 % in the SBT-20 treatment group (n = 5, p < 0.05). There were no benefits of SBT-20 on recovery of left ventricular developed pressure, coronary flow, or maximal rates of contraction/relaxation. In cell studies, treatment with SBT-20 significantly improved maximal mitochondrial respiration in response to an H2O2 challenge. In isolated mitochondria, reactive oxygen species production was significantly blunted following treatment with SBT-20. CONCLUSIONS: In summary, SBT-20 significantly reduced infarct size in two different models of myocardial injury, but did not affect hemodynamics or no-reflow area in rat heart. The reduction in injury is postulated to involve stabilization of mitochondrial function and reduced mitochondrial production of ROS.