Introduction: There is great interest about sex differences in neuromuscular function and overall performance but sex-specific responses to bedrest are very limited. Young males showed larger reductions in muscle force after short (10 days) bedrest compared to females, despite a similar loss of muscle mass. Conversely, young females lost greater muscle volume than males after longer (more than 30 days) bedrest. The aim of the present study was to compare sex-specific responses in muscle function after 21 days of head-down bedrest. Methods: Nine young (18–36 years) males (9 YM) and eight young females (8 YF) underwent 21 days of head-down (-6°) bedrest. Before (BDC) and after (BR21), the torque-velocity-power relationship was determined from isokinetic (50-150-250-350°/sec) and unloaded knee extension maximal contractions. Maximum power (Pmax) and maximum unloaded velocity (V0) were calculated. Moreover, optimal torque (Topt) and velocity (Vopt) were identified at the apex of the power-velocity relationship. Maximal voluntary isometric toque (MVIT) and resting single twitch (St) evoked by femoral nerve stimulation were also performed. Vastus lateralis (VL) cross-sectional area (CSA) at 50% of femur length was evaluated by panoramic ultrasound. Statistical differences (p < 0.05) were tested by two-way ANOVA with post hoc analysis (main effects: time or sex; interaction: time x sex). Results: At BDC, Pmax was higher in YM (559±173 W) then YF (319±58 W; p< 0.001). At BR21, Pmax and V0 decreased in both YM (-18±9 % for Pmax) and YF (-17±16 % for Pmax; p=0.0018). At BDC, Topt was higher in YM (92±24 Nm) than in YF (54±9 Nm; p< 0.001) but it decreased only in YM at BR21 (-20±12 %; p=0.047). No time or sex effects were observed for Vopt. At BDC, MVIT was higher in YM (251±63Nm) compared to YF (172±36Nm; p=0.001), showing similar decrement at BR21 (-23±10 % and -27±10 %, in YM and YF respectively; p< 0.001). St showed time effect and time x sex interaction, decreasing only in YM at BR21 (-9 %; p=0.007). Interestingly, St/MCIT ratio showed a time x sex interaction (p=0.01). At BR21, VL CSA was lower in both YM (-12 %; p< 0.001) and YF (-13 %; p< 0.001). Conclusion: Overall, knee extension muscle force, power and unloaded velocity decreased similarly in young males and young females after 21 days of head-down bedrest. This reduction was partially due to loss of muscle size. The sex-specific changes in torque at the apex of the power-velocity relationship, resting twitch torque, and resting twitch – MVIT ratio seem to suggest a slightly greater impairment at skeletal muscle level in young males compared to young females.To establish whether disparities in fibre type proportions or intrinsic mechanical proprieties of single muscle fibres could explain such sex-specific differences, immunohistochemical analysis alongside force and unloaded velocity skinned muscle fibres experiments are in progress. Funding: The study belongs to the “STOP MUSCLE ATROPHY” project which was supported by ASI (Contract n. 2025-6-HB.0). This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

A 91-yr-old female set the W90+ world record in the 200 m sprint in 2024. We characterized her neuromuscular function, fatigability, denervation markers, and single-fiber contractile properties, and, where possible, compared these outcomes with published reference data. Knee extensor muscle architecture, force, power, fatigability, and motor unit (MU) behavior were assessed in vivo, and a vastus lateralis biopsy was analyzed for single-fiber contractile properties and markers of denervation. Quadriceps cross-sectional area was 36.5 cm2, with fascicle length, pennation angle, and muscle thickness of 6.7 cm, 11.6°, and 1.4 cm, respectively. Knee extensor maximal voluntary isometric contraction (MVIC) torque was 79 Nm, power was 28 W, and power declined by 43% during a 4-min fatiguing task. MU recruitment threshold was 12 ± 11% of MVIC. Single-fiber absolute and specific force were 0.88 ± 0.19 mN and 114 ± 10 kN/m2 for myosin heavy chain (MyHC) I and 0.74 ± 0.23 mN and 171 ± 23 kN/m2 for MyHC IIa fibers. Less than 1% of fibers were positive for the denervation marker neural cell adhesion molecule (NCAM), no fibers expressed embryonic MyHC, and ∼1% of MyHC II fibers expressed neonatal MyHC. In vivo muscle size, force, power, and fatigability were largely within the range for individuals one decade younger. MU behavior was comparable with individuals 20 yr younger. MyHC I fibers produced greater absolute force than reported in untrained young females and females in their eighth decade, whereas MyHC II fiber force was lower because of smaller fiber size. Denervation markers were less prevalent than typically reported at this age. Collectively, these findings illustrate the heterogeneous effects of aging on different features of neuromuscular function, even in an elite older female sprint athlete.NEW & NOTEWORTHY We report in vivo neuromuscular function, single-fiber mechanics, and denervation markers in a 91-yr-old female who holds the W90+ 200 m world record. Despite reduced muscle size, force, and power, as well as pronounced fast-fiber atrophy, markers of denervation were similar to those in young females and single-fiber force in slow fibers was preserved. Together, these data highlight the differential effects of lifelong sprint training and aging on neural versus muscular components of the neuromuscular system.

Spinal muscular atrophy (SMA) is a genetic disorder characterized by the loss of spinal motor neurons. The conventional therapy does not always lead to a full restoration of the clinical symptoms, partially due to the need for early treatment. Accumulating evidence describes the crucial role of mitochondrial dysfunction and oxidative stress in skeletal muscle of SMA patients. We aimed to investigate the effects of prenatal supplementation with the antioxidant molecule ergothioneine (ERGO) on an SMNΔ7 mouse model of SMA containing a knockout of survival motor neuron protein (SMN1) and two transgenes, one with a single normal copy of human SMN2 and the second with a human SMN2 promoter and a human SMN2 cDNA lacking exon 7. ERGO had a significant positive effect on the survival and locomotor abilities of SMA pups. In isolated diaphragm muscle, ERGO was found to stimulate mitophagy. The results of the current study highlight the need for further research into ERGO as an adjuvant therapy for SMA. Impact statement Our finding that ergothioneine supplementation improves survival in a murine model of spinal muscular atrophy may aid research into a novel potential adjuvant to alleviate the symptoms of this serious neuromuscular disease in humans.

BACKGROUND: Breast cancer is the most frequently diagnosed malignancy amongst females. Physical activity acts as an excellent preventative therapy and plays a role in maintaining a good quality of life by reducing the incidences of comorbidity and tumor reoccurrences, as well as alleviating the side effects of pharmacological and radiation therapies. This study aims to evaluate the safety and efficacy of physical activity in improving quality of life and aerobic capacity in patients treated for breast cancer. METHODS: From May 2012 to May 2017, 140 patients treated for breast cancer were recruited on a voluntary basis. After the first consultation, 74 patients were evaluated at three months and 41 at nine months. A non-monitored individualized exercise protocol was prescribed according to the American College of Sport Medicine's guidelines (ACSM). Anthropometric analysis, VO2 peak test with ECG monitoring and the presence of medically unexplained symptoms (MUS) were assessed. RESULTS: In the 41 subjects followed for 9 months, no statistical differences were found in BMI and body composition. The VO2 peak value was noted to increase significantly in 24 subjects between the ages of 36 and 58, while in 17 patients over 58 years old the increase was not significant. MUS showed a downward trend over 9 months. CONCLUSIONS: Our study suggests that even a non-monitored physical exercise has positive effects on cardiopulmonary system and psychophysical well-being. A regular physical exercise maintained for at least 3 months is able to improve cardiovascular function. ( Cite this article as: Bidoglio F, Canepari M, De Simone A, Longa E, Poerio CS, Ceccaroli M, et al . Exercise therapy in breast cancer patients: effects on cardiorespiratory fitness and quality of life. Med Sport 2024;77:390-402. DOI: 10.23736/S0025-7826.24.04464-8)

The most prevalent rare genetic disease affecting young individuals is spinal muscular atrophy (SMA), which is caused by a loss-of-function mutation in the telomeric gene survival motor neuron (SMN) 1. The high heterogeneity of the SMA pathophysiology is determined by the number of copies of SMN2, a separate centromeric gene that can transcribe for the same protein, although it is expressed at a slower rate. SMA affects motor neurons. However, a variety of different tissues and organs may also be affected depending on the severity of the condition. Novel pharmacological treatments, such as Spinraza, Onasemnogene abeparvovec-xioi, and Evrysdi, are considered to be disease modifiers because their use can change the phenotypes of the patients. Since oxidative stress has been reported in SMA-affected cells, we studied the impact of antioxidant therapy on neural stem cells (NSCs) that have the potential to differentiate into motor neurons. Antioxidants can act through various pathways; for example, some of them exert their function through nuclear factor (erythroid-derived 2)-like 2 (NRF2). We found that curcumin is able to induce positive effects in healthy and SMA-affected NSCs by activating the nuclear translocation of NRF2, which may use a different mechanism than canonical redox regulation through the antioxidant-response elements and the production of antioxidant molecules.

The field of spinal cord injury (SCI) research has experienced an immense evolution over the past decades whereby results from preclinical studies have significantly facilitated our understanding of pathophysiologic mechanisms underlying SCI, including causes of heterogeneity in outcomes among patients. Notably, in detail knowledge of the pathobiology in SCI will guide us in identifying therapeutic targets and personalizing SCI management. A multitude of exciting preclinical studies are at the edge of translation into clinical trials. However, designing future clinical trials and translational research strategies requires consideration of several key factors. In this chapter, we will discuss the key concepts that need future consideration when translating from preclinical models to clinical trials and provide an overview of promising future directions in translational SCI research.

Several months after mild acute SARS-CoV-2 infection, a substantial proportion of patients present persisting, and often debilitating, symptoms and sequelae. These patients show reduced quality of life due to exercise intolerance, muscle weakness, and fatigue. The present study supports the hypothesis that “peripheral” impairments at skeletal muscle level, namely, reduced mitochondrial function and markers of mitochondrial biogenesis, are major determinants of exercise intolerance and fatigue, “central” phenomena at respiratory, and cardiac level being less relevant.

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.

HISTORY: A 39 years old caucasian healthy female became positive for SARS-CoV-2 infection on November 7, 2020. She was a schoolteacher, moderately trained and without relevant co-morbidities. During the infection she complained loss of taste, headache and cough for 10 days. She also referred dyspnea during usual activities and muscle weakness. Physiological parameters at rest (body temperature, blood pressure, heart rate and oxygen saturation) were monitored remotely and no drugs were prescribed. On January 21, 2021 a nasopharyngeal swab resulted negative for SARS-CoV-2 PHYSICAL EXAMINATION: 90 days post-onset she showed diffuse muscle weakness and dyspnea after mild effort. Vitals: Blood Pressure: 116/88 mmHg, Pulse: 105 bpm, Resp: 17/min, Temp: 36.7 °C, SpO2: 98%. DIFFERENTIAL DIAGNOSIS: Pneumopathy; Anemia; Neurologic disease; COVID Myopathy TEST AND RESULTS: Post COVID functional status questionnaire: general sense of fatigue, myalgia and headache. Blood analyses: hemoglobin: 14.9 g/dl; hematocrit: 43.3%; MCHC: 34.4 g/dl; VES: 6 mm; leucocyte: 7.01 *1000/μl; CRP: 0.07 mg/dl which were within normal range. Neurologic evaluation: normal muscle size and trophism; presence of symmetric reflexes; Lung function test: FEV1: 3.07 L; TLC: 0.58 L; DLCO: 52.09 ml/min/mmHg, which were all within normal range. CPX: exercise terminated for leg muscles pain; Wpeak: 150 W; VO2peak: 30 ml/min/kg (50th percentiles of age-matched sedentary woman); HRpeak: 189 bpm (104% of predicted); [La]peak: 7.79 mmol; RPE: 20/20; RER: 1.19. VE/VCO2@AT is 27.2, Oxygen pulse at peak exercise was 9.5 mL/beat. Exercise ECG response was normal. Fractional O2 extraction by NIRS: 25% of physiological calibration. Slow VO2 kinetics (tau: 31.6 s). Muscle biopsy: normal morphology. High resolution respirometry of permealized muscle fibers showed an impaired muscle oxidative function (complex I + II: ETS: 70.45 pmol/s/mg; OXPHOS: 49.89 pmol/s/mg). FINAL WORKING DIAGNOSIS: exercise intolerance associated to impaired in-vivo and ex-vivo muscle oxidative capacity. Suspected post-COVID19 myopathy. OUTCOMES: Since rehabilitation programs can be effective to reverse muscle oxidative metabolism, individualized training program and follow up after 3 months are suggested.

A large set of FoxOs-dependent genes play a primary role in controlling muscle mass during hindlimb unloading. Mitochondrial dysfunction can modulate such a process. We hypothesized that endurance exercise before disuse can protect against disuse-induced muscle atrophy by enhancing peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α) expression and preventing mitochondrial dysfunction and energy-sensing AMP-activated protein kinase (AMPK) activation. We studied cross sectional area (CSA) of muscle fibers of gastrocnemius muscle by histochemistry following 1, 3, 7, and 14 days of hindlimb unloading (HU). We used Western blotting and qRT-PCR to study mitochondrial dynamics and FoxOs-dependent atrogenes’ expression at 1 and 3 days after HU. Preconditioned animals were submitted to moderate treadmill exercise for 7 days before disuse. Exercise preconditioning protected the gastrocnemius from disuse atrophy until 7 days of HU. It blunted alterations in mitochondrial dynamics up to 3 days after HU and the expression of most atrogenes at 1 day after disuse. In preconditioned mice, the activation of atrogenes resumed 3 days after HU when mitochondrial dynamics, assessed by profusion and pro-fission markers (mitofusin 1, MFN1, mitofusin 2, MFN2, optic atrophy 1, OPA1, dynamin related protein 1, DRP1 and fission 1, FIS1), PGC1α levels, and AMPK activation were at a basal level. Therefore, the normalization of mitochondrial dynamics and function was not sufficient to prevent atrogenes activation just a few days after HU. The time course of sirtuin 1 (SIRT1) expression and content paralleled the time course of atrogenes’ expression. In conclusion, seven days of endurance exercise counteracted alterations of mitochondrial dynamics and the activation of atrogenes early into disuse. Despite the normalization of mitochondrial dynamics, the effect on atrogenes’ suppression died away within 3 days of HU. Interestingly, muscle protection lasted until 7 days of HU. A longer or more intense exercise preconditioning may prolong atrogenes suppression and muscle protection.

AbstractBackgroundAging is associated with a progressive reduction in cellular function leading to poor health and loss of physical performance. Mitochondrial dysfunction is one of the hallmarks of aging; hence, interventions targeting mitochondrial dysfunction have the potential to provide preventive and therapeutic benefits to elderly individuals. Meta‐analyses of age‐related gene expression profiles showed that the expression of Ahnak1, a protein regulating several signal‐transduction pathways including metabolic homeostasis, is increased with age, which is associated with low VO2MAX and poor muscle fitness. However, the role of Ahnak1 in the aging process remained unknown. Here, we investigated the age‐related role of Ahnak1 in murine exercise capacity, mitochondrial function, and contractile function of cardiac and skeletal muscles.MethodsWe employed 15‐ to 16‐month‐old female and male Ahnak1‐knockout (Ahnak1‐KO) and wild‐type (WT) mice and performed morphometric, biochemical, and bioenergetics assays to evaluate the effects of Ahnak1 on exercise capacity and mitochondrial morphology and function in cardiomyocytes and tibialis anterior (TA) muscle. A human left ventricular (LV) cardiomyocyte cell line (AC16) was used to investigate the direct role of Ahnak1 in cardiomyocytes.ResultsWe found that the level of Ahnak1 protein is significantly up‐regulated with age in the murine LV (1.9‐fold) and TA (1.8‐fold) tissues. The suppression of Ahnak1 was associated with improved exercise tolerance, as all aged adult Ahnak1‐KO mice (100%) successfully completed the running programme, whereas approximately 31% male and 8% female WT mice could maintain the required running speed and distance. Transmission electron microscopic studies showed that LV and TA tissue specimens of aged adult Ahnak1‐KO of both sexes have significantly more enlarged/elongated mitochondria and less small mitochondria compared with WT littermates (P < 0.01 and P < 0.001, respectively) at basal level. Further, we observed a shift in mitochondrial fission/fusion balance towards fusion in cardiomyocytes and TA muscle from aged adult Ahnak1‐KO mice. The maximal and reserve respiratory capacities were significantly higher in cardiomyocytes from aged adult Ahnak1‐KO mice compared with the WT counterparts (P < 0.05 and P < 0.01, respectively). Cardiomyocyte contractility and fatigue resistance of TA muscles were significantly increased in Ahnak1‐KO mice of both sexes, compared with the WT groups. In vitro studies using AC16 cells have confirmed that the alteration of mitochondrial function is indeed a direct effect of Ahnak1. Finally, we presented Ahnak1 as a novel cardiac mitochondrial membrane‐associated protein.ConclusionsOur data suggest that Ahnak1 is involved in age‐related cardiac and skeletal muscle dysfunction and could therefore serve as a promising therapeutical target.

Muscular dystrophies (MDs) are a group of genetic diseases characterized by progressive muscle wasting associated to oxidative stress and persistent inflammation. It is essential to deepen our knowledge on the mechanism connecting these two processes because current treatments for MDs have limited efficacy and/or are associated with side effects. Here, we identified the alarmin high-mobility group box 1 (HMGB1) as a functional link between oxidative stress and inflammation in MDs. The oxidation of HMGB1 cysteines switches its extracellular activities from the orchestration of tissue regeneration to the exacerbation of inflammation. Extracellular HMGB1 is present at high amount and undergoes oxidation in patients with MDs and in mouse models of Duchenne muscular dystrophy (DMD) and limb-girdle muscular dystrophy 3 (LGMDR3) compared to controls. Genetic ablation of HMGB1 in muscles of DMD mice leads to an amelioration of the dystrophic phenotype as evidenced by the reduced inflammation and muscle degeneration, indicating that HMGB1 oxidation is a detrimental process in MDs. Pharmacological treatment with an engineered nonoxidizable variant of HMGB1, called 3S, improves functional performance, muscle regeneration, and satellite cell engraftment in dystrophic mice while reducing inflammation and fibrosis. Overall, our data demonstrate that the balance between HMGB1 redox isoforms dictates whether skeletal muscle is in an inflamed or regenerating state, and that the nonoxidizable form of HMGB1 is a possible therapeutic approach to counteract the progression of the dystrophic phenotype. Rebalancing the HMGB1 redox isoforms may also be a therapeutic strategy for other disorders characterized by chronic oxidative stress and inflammation.

Ultrafast force-clamp spectroscopy is a single molecule technique based on laser tweezers with sub-millisecond and sub-nanometer resolution. The technique has been successfully applied to investigate the rapid conformational changes that occur when a myosin II motor from skeletal muscle interacts with an actin filament. Here, we share data on the kinetics of such interaction and experimental records collected under different forces [1]. The data can be valuable for researchers interested in the mechanosensitive properties of myosin II, both from an experimental and modeling point of view. The data is related to the research article "ultrafast force-clamp spectroscopy of single molecules reveals load dependence of myosin working stroke" [2].

The Sarcolab pilot study of 2 crewmembers, investigated before and after a 6-mo International Space Station mission, has demonstrated the substantial muscle wasting and weakness, along with disruption of muscle's oxidative metabolism. The present work aimed at evaluating the pro/anti-inflammatory status in the same 2 crewmembers (A, B). Blood circulating (c-)microRNAs (miRs), c-proteasome, c-mitochondrial DNA, and cytokines were assessed by real-time quantitative PCR or ELISA tests. Time series analysis was performed ( i.e., before flight and after landing) at 1 and 15 d of recovery (R+1 and R+15, respectively). C-biomarkers were compared with an age-matched control population and with 2-dimensional proteomic analysis of the 2 crewmembers' muscle biopsies. Striking differences were observed between the 2 crewmembers at R+1, in terms of inflamma-miRs (c-miRs-21-5p, -126-3p, and -146a-5p), muscle specific (myo)-miR-206, c-proteasome, and IL-6/leptin, thus making the 2 astronauts dissimilar to each other. Final recovery levels of c-proteasome, c-inflamma-miRs, and c-myo-miR-206 were not reverted to the baseline values in crewmember A. In both crewmembers, myo-miR-206 changed significantly after recovery. Muscle biopsy of astronaut A showed an impressive 80% increase of α-1-antitrypsin, a target of miR-126-3p. These results point to a strong stress response induced by spaceflight involving muscle tissue and the proinflammatory setting, where inflamma-miRs and myo-miR-206 mediate the systemic recovery phase after landing

Dopamine is one of the principal neuromodulators in the brain acting on two large families of receptors, namely D1-like and D2-like. It is involved in several important cognitive and motor functions within different brain areas and it is strongly implicated in rewarding and addiction behaviours. In the medial entorhinal cortex (MEC), dopamine is believed to play a crucial role in the spatial cognition functions performed by this area of the brain (Hafting et al., 2005). In particular, type-2 dopamine receptors (D2Rs) appear to be involved in spatial cognition (Mehta et al., 2001) and stellate cells in the MEC contain high levels of D2Rs. Stellate cells in layer II of the MEC are classified as "grid cells" as they provide spatial information to the animal by spanning the environment. The axons of these neurons innervate the hippocampus forming excitatory synapses. Hence, the physiological pathway triggered by D2R activation in MEC stellate cells is likely fundamental for spatial cognition.

Both astronauts and patients affected by chronic movement-limiting pathologies face impairment in muscle and/or brain performance. Increased patient survival expectations and the expected longer stays in space by astronauts may result in prolonged motor deprivation and consequent pathological effects. Severe movement limitation can influence not only the motor and metabolic systems but also the nervous system, altering neurogenesis and the interaction between motoneurons and muscle cells. Little information is yet available about the effect of prolonged muscle disuse on neural stem cells characteristics. Our in vitro study aims to fill this gap by focusing on the biological and molecular properties of neural stem cells (NSCs). Our analysis shows that NSCs derived from the SVZ of HU mice had shown a reduced proliferation capability and an altered cell cycle. Furthermore, NSCs obtained from HU animals present an incomplete differentiation/maturation. The overall results support the existence of a link between reduction of exercise and muscle disuse and metabolism in the brain and thus represent valuable new information that could clarify how circumstances such as the absence of load and the lack of movement that occurs in people with some neurological diseases, may affect the properties of NSCs and contribute to the negative manifestations of these conditions.

Event Abstract Back to Event Disuse skeletal muscle atrophy in humans. Proteomic and molecular adaptations Lorenza Brocca1*, Monica Canepari1, Jörn Rittweger2, Marco V. Narici3, Maria Antonietta Pellegrino1 and Roberto Bottinelli1 1 Department of Molecular Medicine, University of Pavia, Italy 2 Deutsches Zentrum für Luft- und Raumfahrt, Helmholtz-Gemeinschaft Deutscher Forschungszentren (HZ), Germany 3 Dipartimento di Scienze Biomediche, Università degli Studi di Padova, Italy Skeletal muscle atrophy is a multifactorial process common in different catabolic conditions. It can be a consequence of many diseases, e.g., cancers, AIDS, metabolic diseases, sepsis, burn injury, organ failures, and respiratory diseases. However, unloading of skeletal muscles is one of the most frequent and relevant causes of muscle atrophy, being observed in conditions such as limb casting following trauma, limb suspension and bed rest, . Finally, atrophy is a major consequence of muscle unloading in microgravity. Muscle atrophy is characterized by reduced fiber size, loss of force and power and decreased myosin concentration. Muscle atrophy is due to an imbalance between protein synthesis and protein degradation. Most studies carried out on animal models of disuse showed that an initial decrease in protein synthesis is followed by a likely predominant increase in protein breakdown (Pellegrino et al. 2011; Powers et al. 2005; Thomason & Booth, 1990). On the contrary, several human studies seem to indicate that increased protein breakdown, as evidenced by increased expression of the atrogenes, is a transient phenomenon mostly explaining the first few days (˜4 days) of immobilisation and thereafter (Suetta et al. 2012) a decline in muscle protein synthesis (MPS) is the predominant mechanism (Phillips et al. 2014). However, the mechanisms underlying skeletal muscle atrophy likely vary through species and in the same species through different models and muscles (Pellegrino et al. 2011). Disuse muscle atrophy in mice. The hindlimb-unloading is one of the most studied mouse models of disuse atrophy. In this model, mitochondrial dysfunction indicated by several phenomena such as downregulation of mitochondrial enzymes, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) and mitochondrial profusion proteins (Mitofusin 1, Mitofusin 2 and OPA1) have been observed. In particular, downregulation of PGC1α, a master controller of mitochondrial biogenesis, in a slow muscle as Soleus (Cannavino et al. 2014) and a downregulation of mitofusins in a fast muscle as Gastrocnemius (Cannavino et al. 2015) have been indicated as a major cause of disuse atrophy. On the contrary, the data did not support a major role of redox imbalance in triggering the phenomenon (Pellegrino et al. 2011) in contrast to what was previously reported (Powers et al. 2005). The role of a metabolic program causing disuse muscle atrophy is supported by the observations that high PGC-1α levels prevent the detrimental effects of FoxO3, a transcription factor activating the ubiquitin proteasome system, on muscle mass. Consistent with this, skeletal muscles from unloaded transgenic mice overexpressing PGC1α did not show upregulation of catabolic systems (Ubiquitin proteasome system and autophagy system) and downregulation of pro-fusion proteins protecting from disuse muscle atrophy (Cannavino et al. 2014; Cannavino et al. 2015). The same mechanism was observed in other disuse models like denervation and fasting (Sandri et al. 2006). Disuse Human models. In humans, the mechanisms and effectors underlying skeletal disuse atrophy are not fully understood. We studied three different human models, Bed Rest (BR), unilateral lower limb suspension (ULLS) and Space Flight (SP). Healthy young man (age = 18–25 years) were enrolled in BR campaigns and in ULLS program and muscle investigations were carried out on biopsies from vastus lateralis muscle. Moreover, the adaptations of skeletal muscle were studied in soleus muscle from 2 astronauts that have been in the International Space Station for 6 months. All disuse models were associated with single muscle fiber size decrease with BR and ULLS showing similar loss of mass (approximately 25%) while in SP, one astronaut showed atrophy degree comparable to BR and ULLS and the other one 45% of fiber size reduction (Brocca et al. 2012; Brocca et al. 2015; Rittweger et al. 2018) (Fig. 1A). Moreover, all disuse models were characterized by loss of specific force of single muscle fibres (Trappe et al. 2004; Brocca et al. 2015; Rittweger et al. 2018) (Fig. 1B). In BR and ULLS the latter phenomenon could be ascribed to a significant decrease of myosin concentration in single muscle fibres (Borina et al. 2010; Brocca et al. 2015) (Fig. 1C). Notwithstanding the similar adaptations observed in muscle mass and function in all disuse models, the underlying molecular mechanisms were somewhat different. Bed rest. Following 24 days of BR, the increase of polyubiquitinated protein level, Beclin1, P62 and LC3B after 24 days suggested an activation of Ubiquitin proteasome system (UPS) and autophagy (Fig. 2A). On the contrary, the unchanged levels of markers involved in protein synthesis pathways (AKT and P70S6K) did not support a role of lower protein synthesis in muscle mass loss (Brocca et al. 2012) (Fig 2B). Regarding the triggers of the adaptations in intracellular signaling pathways, both mitochondrial dysfunction and the reactive oxygen species (ROS) production can activate degradation pathways and inhibit protein synthesis pathways. In BR, the lower mRNA levels of PGC-1α suggest the presence of mitochondrial impairment (Brocca et al. 2012) (Fig. 2C). Moreover, a significant reduction of Superoxide dismutase 1 (SOD1) and Catalase was found after 8 and 24 days of BR (Brocca et al. 2012) (Fig. 2D). The alterations of antioxidant defense systems occurring in the early phase of disuse lead to protein carbonylation in the last phase of disuse (35 days) (Dalla Libera et al. 2009) (Fig. 2E) indicating the presence of redox imbalance and oxidative stress. Therefore, in BR both mitochondrial impairment and oxidative stress could be potential triggers of the activation of degradation pathways. ULLS. In ULLS (21 days) no changes in UPS and autophagy (Fig. 3A), but a significant reduction of phosphorylated form of AKT, S6 and 4EBP1 (proteins involved in IGF1/AKT/mTOR pathway) were found (Brocca et al. 2015) (Fig. 3B). Indeed, FoxO pathways did not appear activated and even their potential triggers were not induced. In fact, the mRNA levels of PGC-1α were unchanged (Fig. 3C), SOD1 and Catalase were upregulated and no alterations were observed in carbonylated protein level (Brocca et al. 2015) (Fig. 3D). The results suggest that a decreased activation of the protein synthesis pathway could play a major role in muscle mass loss and that oxidatve stress is unlikely to be a major trigger of muscle atrophy. Accordingly, several findings have underlined the role of impaired protein synthesis on human disuse atrophy (Rudrappa et al. 2016). Space flight. 6 months of SF induced an increase of Atrogin1 and Beclin1 in two astronauts and an increase of MurF1and P62 in one astronaut (Fig. 4A). Moreover, a decrease of FAK and FRNK level (−60 and −44% respectively) in two crew members and a reduction of FAK-pY397 (-92%) in one crew member was observed (Rittweger et al. 2018) (Fig. 4B). Importantly, the adaptations in the FAK pathway indicated a reduction in protein synthesis since FAK can modulate the anabolic IGF1/Akt/mTOR pathway linking muscle atrophy to the imbalance between protein synthesis and degradation (de Boer et al. 2007; Graham et al. 2015, Klossner et al. 2009). The present data support a significant contribution of the protein degradation and protein synthesis pathways in muscle atrophy progression in SF, although the number of subjects did not enable to definitely settle the issue. Conclusions The commune features in all human disuse appear to be: 1) atrophy of single muscle fibres, 2) loss of specific force and 3) decrease of myosin concentration (at least for BR and ULLS). Notwithstanding the similar adaptations found in all three models, the mechanisms underlying muscle atrophy seem different. Collectively the data suggest that the atrophy may be related to protein degradation in BR and linked to a down-regulation of protein synthesis in ULLS. In SF both processes could play an important role in muscle mass loss although more subjects are needed to settle such issue. However, although In BR protein synthesis does not seem to play a major role, it should be noted that the phosphorylation of proteins belonging to IGF1/Akt/mTOR pathway might not reflect the actual rate of synthesis in vivo (Glover et al. 2008). Indeed, in humans, dissociation between phosphorylation of signaling proteins and protein turnover has been shown (Crossland et al. 2018). Moreover, in BR, both mitochondrial dysfunction and redox imbalance appear as potential triggers of degradation pathways. However, in hindlimb unloaded mice, although the adaptations were found to be similar as those observed in human BR, a careful analysis of the relative role of mitochondrial dysfunction and redox imbalance indicated a major role for mitochondrial dysfunction and a minor role for redox imbalance. More work is, therefore, needed to understand which of the two conditions actually triggers atrophy, such as in human BR where disuse atrophy progresses slowly. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Acknowledgements This study was supported by the Italian Space Agency (project OSMA ‘Osteoporosis and Muscle Atrophy’) and the European Commission for the MYOAGE grant (no. 22 3576) funded under FP7. References Borina E, Pellegrino MA, D’Antona G & Bottinelli R (2010). Myosin and actin content of human skeletal muscle fibers following 35 days bed rest. Scand J Med Sci Sports 20, 65–73. Doi: 10.1111/j.1600-0838.2009.01029.x Brocca L, Cannavino J, Coletto L, Biolo G, Sandri M, Bottinelli R, and Pellegrino MA (2012). The time course of the adaptations of human muscle proteome to bed rest and the underlying mechanisms. J Physiol 590.20 (2012) pp 5211–5230 5211. doi: 10.1113/jphysiol.2012.240267. Brocca L, Longa E, Cannavino J, Seynnes O, de Vito G, McPhee J, Narici M, Pellegrino MA and Bottinelli R (2015). Human skeletal muscle fibre contractile properties and proteomic profile: adaptations to 3 weeks of unilateral lower limb suspension and active recovery. J Physiol 593.24 (2015) pp 5361–5385 5361. doi: 10.1113/JP271188. Cannavino J, Brocca L, Sandri M, Bottinelli R, Pellegrino MA (2014). PGC1-α over-expression prevents metabolic alterations and soleus muscle atrophy in hindlimb unloaded mice. J Physiol. 15;592(20):4575-89. doi:10.1113/jphysiol.2014.275545. Cannavino J, Brocca L, Sandri M, Grassi B, Bottinelli R, Pellegrino MA (2015). The role of alterations in mitochondrial dynamics and PGC-1α over-expression in fast muscle atrophy following hindlimb unloading. J Physiol. 593(8):1981-95. doi: 10.1113/jphysiol.2014.286740. Crossland H, Skirrow s, Puthucheary ZA, Constantin-Teodosiu D, Greenhaff PL (2018). 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Am J Physiol Regul Integr Comp Physiol 288, R337–344. doi: 10.1152/ajpregu.00469.2004. Rittweger J, Albracht K, Flück M, Ruoss S, Brocca L, Longa E, Moriggi M, Seynnes O, Di Giulio I, Tenori L, Vignoli A, Capri M, Gelfi C, Luchinat C, Francheschi C, Bottinelli R, Cerretelli P and Narici M (2018). Sarcolab pilot study into skeletal muscle’s adaptation to longterm spaceflight npj Microgravity 4:18 ; doi:10.1038/s41526-018-0052-1. Rudrappa SS, Wilkinson DJ, Greenhaff PL, Smith K, Idris I, Atherton PJ (2016). Human Skeletal Muscle Disuse Atrophy: Effects on Muscle Protein Synthesis, Breakdown, and Insulin Resistance-A Qualitative Review. Front Physiol. 25;7:361. doi: 10.3389/fphys.2016.00361. Sandri M, Lin J, Handschin C, Yang W, Arany ZP, Lecker SH, Goldberg AL, Spiegelman BM (2006). PGC-1alpha protects skeletal muscle from atrophy by suppressing FoxO3 action and atrophy-specific gene transcription. Proc Natl Acad Sci U S A. 103(44):16260-5. doi: 10.1073/pnas.0607795103 Suetta C, Frandsen U, Jensen L, Jensen MM, Jespersen JG, Hvid LG, Bayer M, Petersson SJ, Schrøder HD, Andersen JL, Heinemeier KM, Aagaard P, Schjerling P, Kjaer M (2012). Aging affects the transcriptional regulation of human skeletal muscle disuse atrophy. PLoS One. 7(12):e51238. doi: 10.1371/journal.pone.0051238. Thomason DB & Booth FW (1990). Atrophy of the soleus muscle by hindlimb unweighting. J Appl Physiol 68,1–12. doi:10.1152/jappl.1990.68.1.1. Trappe S, Trappe T, Gallagher P, Harber M, Alkner B, Tesch P (2004). Human single muscle fibre function with 84 day bed-rest and resistance exercise. J Physiol. 1; 557(Pt 2): 501–513. doi: 10.1113/jphysiol.2004.062166 Keywords: Human disuse, muscle atrophy, myosin loss, Catabolic Pathways, Synthetic pathway Conference: 39th ISGP Meeting & ESA Life Sciences Meeting, Noordwijk, Netherlands, 18 Jun - 22 Jun, 2018. Presentation Type: Extended abstract Topic: Bones and Muscles Citation: Brocca L, Canepari M, Rittweger J, Narici MV, Pellegrino M and Bottinelli R (2019). Disuse skeletal muscle atrophy in humans. Proteomic and molecular adaptations. Front. Physiol. Conference Abstract: 39th ISGP Meeting & ESA Life Sciences Meeting. doi: 10.3389/conf.fphys.2018.26.00027 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 02 Dec 2018; Published Online: 16 Jan 2019. * Correspondence: Dr. Lorenza Brocca, Department of Molecular Medicine, University of Pavia, Pavia, Italy, lorenza.brocca@unipv.it Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Lorenza Brocca Monica Canepari Jörn Rittweger Marco V Narici Maria Antonietta Pellegrino Roberto Bottinelli Google Lorenza Brocca Monica Canepari Jörn Rittweger Marco V Narici Maria Antonietta Pellegrino Roberto Bottinelli Google Scholar Lorenza Brocca Monica Canepari Jörn Rittweger Marco V Narici Maria Antonietta Pellegrino Roberto Bottinelli PubMed Lorenza Brocca Monica Canepari Jörn Rittweger Marco V Narici Maria Antonietta Pellegrino Roberto Bottinelli Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The central goal of this study was to identify the primary mechanisms triggering steroid atrophy. Adaptations of soleus (Sol) and vastus lateralis (VL) muscles of C57BL/6 female mice were studied following 3, 7 and 15 days of daily intraperitoneal injection (5 mg kg-1 day-1) of dexamethasone (dEx) (chronic treatment) and 1, 3 and 10 hours after a single dEx injection (acute treatment). In the chronic treatment, analyses were performed 24 hours after the last injection. Gene expression of major components of the intracellular signalling pathways controlling mass and metabolism were assessed. Analyses were repeated following dEx and unacylated ghrelin (uAG) (100 μg kg-1day-1), co-administration. We found a significant VL fibres atrophy after 7 (13%) and 15 (28%) days and a Sol fibres atrophy (23%) after 15 days of dEx treatment. The acute treatment showed, in both muscles, several responses in most signalling pathways, among which the enhanced gene expression of Murf-1 (6-fold change in VL and 3-fold in Sol) and myostatin (6-fold change in VL and 20-fold in Sol). In Sol, uAG administration was able to fully counteract muscle atrophy and Murf-1 upregulation, but not the upregulation of myostatin, suggesting a causal relationship between muscle atrophy and Murf-1. Results indicate that: a) the primary mechanism triggering steroid atrophy is an early transient activation of Murf-1; b) uAG inhibits Murf-1 induction counteracting steroid atrophy. The present work contributes to the understanding of the complexity of the muscle response to glucocorticoids.