Dimethyl fumarate modulates the dystrophic disease program following short-term treatment

Repurposed Nrf2 activator dimethyl fumarate rescues muscle inflammation and fibrosis in an aggravated mdx mouse model of Duchenne muscular dystrophy

In inherited neuromuscular disease, Duchenne muscular dystrophy (DMD), glucocorticoids significantly slow disease progression yet impart side effects severe enough to preclude use in a significant proportion of patients. Extending our findings that acute treatment with FDA approved multiple sclerosis drug, dimethyl fumarate (DMF), rescues muscle pathology in juvenile mdx mice, we aimed to conduct tiered pre-clinical testing toward translation. To aggravate disease phenotype in adult mdx muscles that usually lack human equivalent muscle pathology, we used bi-weekly treadmill running for 4 weeks which increased plasma DMD biomarker, creatine kinase, by 2-fold and quadriceps fibrosis by ∼30 %. Using this model, we screened DMF for 5 weeks in a head-to-head comparison, and in combination, with standard-of-care prednisone (PRED), to model the most likely clinical trial scenario. We show comparable efficacy between DMF and PRED at reducing inflammation via NF-κB suppression and CD68+ macrophage infiltration. Moderate term DMF monotherapy had additional anti-fibrotic and anti-lipogenic effects on skeletal and cardiac muscle beyond those seen with PRED treatment, although combination therapy exacerbated fibrosis in quadriceps. Our study supports DMF as a repurposing candidate for DMD, especially for patients who cannot tolerate chronic glucocorticoid treatment. We also highlight the importance of evaluating combination therapy to identify potential off-target effects between emerging therapeutics and glucocorticoids towards better designed clinical trials.

Redox signaling‑mediated muscle atrophy in ACL injury: Role of physical exercise (Review)

Muscle atrophy frequently occurs in patients with anterior cruciate ligament (ACL) injury, despite active participation in muscle strengthening programs. Without appropriate countermeasures such as exercise and pharmacological interventions, the atrophy may worsen. At the cellular and molecular levels, various protein synthesis‑related pathways and redox‑dependent molecules regulate processes associated with atrophy by activating or deactivating key signaling pathways. Muscle atrophy and the associated dysfunction can be reversed by physical exercise, which increases protein synthesis, thereby improving muscle strength and function around the ACL. However, the influence of different features of exercise protocols, including exercise type, intensity and duration, as well as the individual capacity of the patient, on the activity of the aforementioned pathways requires further investigation. Additionally, the mechanism by which redox‑sensitive molecules attenuate atrophy in ACL injury remains to be fully understood. The present review discusses exercise, signaling pathways and muscle atrophy in ACL injury, and highlights potential therapeutic strategies. These findings may also have implications for other joint diseases associated with ACL‑related injury.

Model organisms for investigating the functional involvement of NRF2 in non-communicable diseases

Non-communicable chronic diseases (NCDs) are most commonly characterized by age-related loss of homeostasis and/or by cumulative exposures to environmental factors, which lead to low-grade sustained generation of reactive oxygen species (ROS), chronic inflammation and metabolic imbalance. Nuclear factor erythroid 2-like 2 (NRF2) is a basic leucine-zipper transcription factor that regulates the cellular redox homeostasis. NRF2 controls the expression of more than 250 human genes that share in their regulatory regions a cis-acting enhancer termed the antioxidant response element (ARE). The products of these genes participate in numerous functions including biotransformation and redox homeostasis, lipid and iron metabolism, inflammation, proteostasis, as well as mitochondrial dynamics and energetics. Thus, it is possible that a single pharmacological NRF2 modulator might mitigate the effect of the main hallmarks of NCDs, including oxidative, proteostatic, inflammatory and/or metabolic stress. Research on model organisms has provided tremendous knowledge of the molecular mechanisms by which NRF2 affects NCDs pathogenesis. This review is a comprehensive summary of the most commonly used model organisms of NCDs in which NRF2 has been genetically or pharmacologically modulated, paving the way for drug development to combat NCDs. We discuss the validity and use of these models and identify future challenges.

Current insights in ultra-rare adenylosuccinate synthetase 1 myopathy - meeting report on the First Clinical and Scientific Conference. 3 June 2024, National Centre for Advancing Translational Science, Rockville, Maryland, the United States of America

The inaugural Clinical and Scientific Conference on Adenylosuccinate Synthetase 1 (ADSS1) myopathy was held on June 3, 2024, at the National Institutes of Health (NIH) National Center for Advancing Translational Sciences (NCATS) in Rockville, Maryland, USA.

ADSS1 myopathy is an ultra-rare, inherited neuromuscular disease.

Features of geographical patient clusters in South Korea, Japan, India and the United States of America were characterised and discussed.

Pre-clinical animal and cell-based models were discussed, providing unique insight into disease pathogenesis.

The biochemical pathogenesis was discussed, and potential therapeutic targets identified.

Potential clinical and pre-clinical biomarkers were discussed.

An ADSS1 myopathy consortium was established and a roadmap for therapeutic development created.

Loss of endogenous estrogen alters mitochondrial metabolism and muscle clock-related protein Rbm20 in female mdx mice

Female carriers of a Duchenne muscular dystrophy (DMD) gene mutation manifest exercise intolerance and metabolic anomalies that may be exacerbated following menopause due to the loss of estrogen, a known regulator of skeletal muscle function and metabolism. Here, we studied the impact of estrogen depletion (via ovariectomy) on exercise tolerance and muscle mitochondrial metabolism in female mdx mice and the potential of estrogen replacement therapy (using estradiol) to protect against functional and metabolic perturbations. We also investigated the effect of estrogen depletion, and replacement, on the skeletal muscle proteome through an untargeted proteomic approach with TMT-labelling. Our study confirms that loss of estrogen in female mdx mice reduces exercise capacity, tricarboxylic acid cycle intermediates, and citrate synthase activity but that these deficits are offset through estrogen replacement therapy. Furthermore, ovariectomy downregulated protein expression of RNA-binding motif factor 20 (Rbm20), a critical regulator of sarcomeric and muscle homeostasis gene splicing, which impacted pathways involving ribosomal and mitochondrial translation. Estrogen replacement modulated Rbm20 protein expression and promoted metabolic processes and the upregulation of proteins involved in mitochondrial dynamics and metabolism. Our data suggest that estrogen mitigates dystrophinopathic features in female mdx mice and that estrogen replacement may be a potential therapy for post-menopausal DMD carriers.

Mitochondria and Reactive Oxygen Species: The Therapeutic Balance of Powers for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a genetic progressive muscle-wasting disorder that leads to rapid loss of mobility and premature death. The absence of functional dystrophin in DMD patients reduces sarcolemma stiffness and increases contraction damage, triggering a cascade of events leading to muscle cell degeneration, chronic inflammation, and deposition of fibrotic and adipose tissue. Efforts in the last decade have led to the clinical approval of novel drugs for DMD that aim to restore dystrophin function. However, combination therapies able to restore dystrophin expression and target the myriad of cellular events found impaired in dystrophic muscle are desirable. Muscles are higher energy consumers susceptible to mitochondrial defects. Mitochondria generate a significant source of reactive oxygen species (ROS), and they are, in turn, sensitive to proper redox balance. In both DMD patients and animal models there is compelling evidence that mitochondrial impairments have a key role in the failure of energy homeostasis. Here, we highlighted the main aspects of mitochondrial dysfunction and oxidative stress in DMD and discussed the recent findings linked to mitochondria/ROS-targeted molecules as a therapeutic approach. In this respect, dual targeting of both mitochondria and redox homeostasis emerges as a potential clinical option in DMD.

MCU-independent Ca2+ uptake mediates mitochondrial Ca2+ overload and necrotic cell death in a mouse model of Duchenne muscular dystrophy

Mitochondrial Ca2+ overload can mediate mitochondria-dependent cell death, a major contributor to several human diseases. Indeed, Duchenne muscular dystrophy (MD) is driven by dysfunctional Ca2+ influx across the sarcolemma that causes mitochondrial Ca2+ overload, organelle rupture, and muscle necrosis. The mitochondrial Ca2+ uniporter (MCU) complex is the primary characterized mechanism for acute mitochondrial Ca2+ uptake. One strategy for preventing mitochondrial Ca2+ overload is deletion of the Mcu gene, the pore forming subunit of the MCU-complex. Conversely, enhanced MCU-complex Ca2+ uptake is achieved by deleting the inhibitory Mcub gene. Here we show that myofiber-specific Mcu deletion was not protective in a mouse model of Duchenne MD. Specifically, Mcu gene deletion did not reduce muscle histopathology, did not improve muscle function, and did not prevent mitochondrial Ca2+ overload. Moreover, myofiber specific Mcub gene deletion did not augment Duchenne MD muscle pathology. Interestingly, we observed MCU-independent Ca2+ uptake in dystrophic mitochondria that was sufficient to drive mitochondrial permeability transition pore (MPTP) activation and skeletal muscle necrosis, and this same type of activity was observed in heart, liver, and brain mitochondria. These results demonstrate that mitochondria possess an uncharacterized MCU-independent Ca2+ uptake mechanism that is sufficient to drive MPTP-dependent necrosis in MD in vivo.