Spinal muscular atrophy (SMA) is a genetic disorder characterized by the loss of spinal motor neurons leading to muscle weakness and respiratory failure. Mitochondrial dysfunctions are found in the skeletal muscle of patients with SMA. For obvious ethical reasons, the diaphragm muscle is poorly studied, notwithstanding the very important role that respiratory involvement plays in SMA mortality. The main goal of this study was to investigate diaphragm functionality and the underlying molecular adaptations in SMNΔ7 mice, a mouse model that exhibits symptoms similar to that of patients with intermediate type II SMA. Functional, biochemical, and molecular analyses on isolated diaphragm were performed. The obtained results suggest the presence of an intrinsic energetic imbalance associated with mitochondrial dysfunction and a significant accumulation of reactive oxygen species (ROS). In turn, ROS accumulation can affect muscle fatigue, cause diaphragm wasting, and, in the long run, respiratory failure in SMNΔ7 mice. Exposure to the antioxidant molecule ergothioneine leads to the functional recovery of the diaphragm, confirming the presence of mitochondrial impairment and redox imbalance. These findings suggest the possibility of carrying out a dietary supplementation in SMNΔ7 mice to preserve their diaphragm function and increase their lifespan.

BACKGROUND: Heart failure with reduced ejection fraction (HFrEF) affects millions worldwide and is characterized by chronic cardiac dysfunction, impaired perfusion, altered skeletal muscle energetics, and, thus, exercise intolerance. Efficient therapeutic strategies reducing the burden of the impaired muscle metabolism in HFrEF are currently lacking. Hence, in the present study, we sought to determine whether myosin dynamics and its important role in ATP consumption can constitute a potent biochemical target to optimize skeletal muscle energy usage in HFrEF. METHODS: We used skeletal muscle tissue from 11 human patients with HFrEF and 10 controls with comparable age, sex, and body mass index. We isolated individual myofibres and incubated them ex vivo with varying concentrations of a myosin inhibitor, mavacamten. We then performed 2′-(or-3′)-O-(N-Methylanthraniloyl) adenosine 5′-triphosphate chase experiments, together with LC/MS-based proteomics profiling. RESULTS: We observed a distinct regulation of acetyl-lysine sites and higher myosin energy consumption in resting muscle fibers from patients with HFrEF than in controls. When exposed to mavacamten, we found a dose-dependent reduction in myosin ATP consumption in myofibres of patients with HFrEF, reversing the pathological over-consumption. CONCLUSIONS: Skeletal muscle myosin becomes inefficient in HFrEF. Pharmacological inhibition of myosin ATPase activity offers an inventive strategy to lower muscle energy demand and potentially address metabolic disturbances in HFrEF.