Selenoprotein N (SELENON) is an endoplasmic reticulum (ER) protein whose loss of function leads to human SELENON-related myopathies. SelenoN knockout (KO) mouse limb muscles, however, are protected from the disease, and display no major alterations in muscle histology or contractile properties. Interestingly, we find that the highly active diaphragm muscle shows impaired force production, in line with the human phenotype. In addition, after repeated stimulation with a protocol which induces muscle fatigue, also hind limb muscles show altered relaxation times. Mechanistically, muscle SELENON loss alters activity-dependent calcium handling selectively impinging on the Ca2+ uptake of the sarcoplasmic reticulum and elicits an ER stress response, including the expression of the maladaptive CHOP-induced ERO1. In SELENON-devoid models, ERO1 shifts ER redox to a more oxidised poise, and further affects Ca2+ uptake. Importantly, CHOP ablation in SelenoN KO mice completely prevents diaphragm dysfunction, the prolonged limb muscle relaxation after fatigue, and restores Ca2+ uptake by attenuating the induction of ERO1. These findings suggest that SELENON is part of an ER stress-dependent antioxidant response and that the CHOP/ERO1 branch of the ER stress response is a novel pathogenic mechanism underlying SELENON-related myopathies.

Cardiovascular diseases (CVD) can cause various conditions, including an increase in reactive oxygen species (ROS) levels that can decrease nitric oxide (NO) availability and promote vasoconstriction, leading to arterial hypertension. Physical exercise (PE) has been found to be protective against CVD by helping to maintain redox homeostasis through a decrease in ROS levels, achieved by increased expression of antioxidant enzymes (AOEs) and modulation of heat shock proteins (HSPs). Extracellular vesicles (EVs) circulating in the body are a major source of regulatory signals, including proteins and nucleic acids. Interestingly, the cardioprotective role of EVs released after PE has not been fully described. The aim of this study was to investigate the role of circulating EVs, obtained through Size Exclusion Chromatography (SEC) of plasma samples from healthy young males (age: 26.95 ± 3.07; estimated maximum oxygen consumption rate (VO2max): 51.22 ± 4.85 (mL/kg/min)) at basal level (Pre_EVs) and immediately after a single bout of endurance exercise (30' treadmill, 70% heart rate (HR) -Post_EVs). Gene ontology (GO) analysis of proteomic data from isolated EVs, revealed enrichment in proteins endowed with catalytic activity in Post_EVs, compare to Pre_EVs, with MAP2K1 being the most significantly upregulated protein. Enzymatic assays on EVs derived from Pre and Post samples showed increment in Glutathione Reductase (GR) and Catalase (CAT) activity in Post_EVs. At functional level, Post_EVs, but not Pre_EVs, enhanced the activity of antioxidant enzymes (AOEs) and reduced oxidative damage accumulation in treated human iPS-derived cardiomyocytes (hCM) at basal level and under stress conditions (Hydrogen Peroxide (H2O2) treatment), resulting in a global cardioprotective effect. In conclusion, our data demonstrated, for the first time, that a single 30-min endurance exercise is able to alter the cargo of circulating EVs, resulting in cardioprotective effect through antioxidant activity.