Muscle catabolic mechanisms:from disuse atrophy to cachexia.

2006/2007The phatophysiology of muscle atrophy is a complex multifactor process, which occurs in response to environmental solicitations, injury, various disease states, disuse and normal aging. Persistent low-grade or acute activation of inflammatory/oxidative cascade, acute stress, altered energy intake, or reduced mechanical action, contribute to muscle decline, as well as to the progression of chronic and acute associated disease. Elevated concentrations of pro-inflammatory markers have also devastating effects on the vasculature and are implicated in the pathogenesis of atherosclerosis, which at peripheral level contributes to muscle suffering. A more understanding of the molecular relationships underpinning muscle atrophy, inflammation and cardiovascular risk in different human clinical models should be helpful to design new therapies to the recovery of muscle. Thus, we investigated the effect of some effectors of inflammatory/oxidative responses on muscle atrophy, inflammation and cardiovascular dysfunction, in chronic, acute or healthy conditions. We explored: a) the interaction between energy restriction and muscle unloading in the regulation of lean body mass, protein kinetics or inflammatory response in healthy subjects; b) the links among inflammation, organ failure, cardiovascular risk and cytokine genotypes, in models of chronic muscle atrophy; c) the cross-interaction connecting translational machinery, proteolysis and apoptotic response with skeletal muscle atrophy induced by acute stress. We highlighted a link between inflammatory process, cardiovascular risk and muscle unloading, likely involving leptin hormone and the long pentraxin PTX3; the latter may represent a novel key of reading of some bed-rest effect on vasculature or inflammatory system. Cytokine genotypes (interpheron-gamma), and the extent of renal functions on cytokine clearence, may account of intraindividual variability and vulnerability to the process. Finally, we gained knowledge about a novel catabolic mechanism, involving the eukariotic elongation factor EEF1A1 and the stress response protein p66(ShcA) in acute muscle atrophy. We suggest that, a more controlled energy intake combined with various exercise regimes might protect from the effects of unloading and may be a reasonable approach to maintain muscle mass in health but also in disease conditions.La patofisiologia dell’atrofia muscolare è un complesso processo multifattoriale, che avviene in risposta a sollecitazioni ambientali, ferite, vari stati di malattia, disuso e nel normale invecchiamento. La persistente lieve od acuta attivazione della cascata infiammatoria/ossidativa, lo stress acuto, un alterato apporto energetico o una ridotta azione meccanica, contribuiscono al declino muscolare ed alla progressione di malattie croniche o acute ad esso associate. Le elevate concentrazioni di markers pro-infiammatori hanno effetti devastanti anche sul sistema vascolare e sono implicate nella patogenesi dell’aterosclerosi, la quale a livello periferico contribuisce alla sofferenza muscolare. Una maggior comprensione delle relazioni molecolari che sostengono l’atrofia muscolare, l’infiammazione ed il rischio cardiovasolare in diversi modelli clinici umani, dovrebbe essere utile per disegnare nuove terapie dirette al recupero del muscolo. Perciò, abbiamo investigato gli effetti di alcuni effettori della risposta infiammatoria/ossidativa sull’atrofia muscolare, l’infiammazione e la disfunzione cardiovascolare, in condizioni croniche, acute o di salute. Abbiamo esplorato: a) l’effetto dell’interazione tra la restrizione energetica e l’inattività muscolare sulla regolazione della massa magra corporea, sulla cinetica delle proteine e sulla risposta infiammatoria in soggetti sani; b) i legami tra l’infiammazione, il danno d’organo, il rischio cardiovascolare e i genotipi delle citochine in modelli di atrofia muscolare cronica; c) l’interazione che connette il maccanismo traduzionale, la proteolisi e l’apoptosi, con l’atrofia del muscolo scheletrico indotta da stress acuto. Abbiamo evidenziato un legame tra processo infiammatorio, rischio cardiovascolare ed inattività muscolare, probabilmente legato all’ormone leptina e alla pentraxina lunga PTX3; quest’ultima potrebbe rappresentare una nuova chiave di lettura di alcuni effetti del bed-rest sulla vascolatura o il sistema infiammatorio. I genotipi delle citochine (interferon-gamma), e la portata della funzione renale sulla loro clearence, potrebbero esser causa della variabilità e vulnerabilità intraindividuale al processo. Per ultimo, abbiamo ottenuto conoscenza di un nuovo meccanismo catabolico, riguardante il fattore di elongazione eucariotico EEF1A1 e la proteina di risposta allo stress p66(ShcA) nell’atrofia muscolare acuta. Noi suggeriamo che, un maggior controllo dell’introito energetico combinato con vari regimi di esercizio, potrebbe proteggere dagli effetti dell’inattività muscolare e potrebbe essere un approccio ragionevole per mantenere la massa muscolare in salute, ma anche in condizioni di malattia

Effects of 21 days of bed rest and whey protein supplementation on plantar flexor muscle fatigue resistance during repeated shortening contractions.

PURPOSE:Space flight and bed rest (BR) lead to a rapid decline in exercise capacity. Whey protein plus potassium bicarbonate diet-supplementation (NUTR) could attenuate this effect by improving oxidative metabolism. We evaluated the impact of 21-day BR and NUTR on fatigue resistance of plantar flexor muscles (PF) during repeated shortening contractions, and whether any change was related to altered energy metabolism and muscle oxygenation. METHODS:Ten healthy men received a standardized isocaloric diet with (n = 5) or without (n = 5) NUTR. Eight bouts of 24 concentric plantar flexions (30 s each bout) with 20 s rest between bouts were employed. PF muscle size was assessed by means of peripheral quantitative computed tomography. PF muscle volume was assessed with magnetic resonance imaging. PF muscle force, contraction velocity, power and surface electromyogram signals were recorded during each contraction, as well as energy metabolism (31P nuclear magnetic resonance spectroscopy) and oxygenation (near-infrared spectroscopy). Cardiopulmonary parameters were measured during an incremental cycle exercise test. RESULTS:BR caused 10-15% loss of PF volume that was partly recovered 3 days after re-ambulation, as a consequence of fluid redistribution. Unexpectedly, PF fatigue resistance was not affected by BR or NUTR. BR induced a shift in muscle metabolism toward glycolysis and some signs of impaired muscle oxygen extraction. NUTR did not attenuate the BR-induced-shift in energy metabolism. CONCLUSIONS:Twenty-one days' BR did not impair PF fatigue resistance, but the shift to glycolytic metabolism and indications of impaired oxygen extraction may be early signs of developing reduced muscle fatigue resistance

GT75 aptamer against eukaryotic elongation factor 1A as potential anticancer drug for castrate-resistant prostate cancer (CRPC).

Prostate cancer diagnosis is increasing, being the second most frequently cancer in men worldwide. The treatment of castrate-resistant prostate cancer is often unsuccessfully and new therapeutic interventions are searching for. Nucleic acid aptamers targeting eEF1A proteins are emerging molecular tools for the control of cancer growth. We found that an aptamer named GT75 was able to bind to eEF1A proteins of human prostate cancer cell lines and to significantly and specifically reduce their growth with respect to the control oligomer CT75. The highest anti-proliferation effect was found in the androgen-independent PC-3 cells. Interestingly, GT75 was able to specifically inhibit the migration of PC-3 cells but not that of the nontumorigenic PZHPV-7 cells. The overall results suggest that the GT75 aptamer targeting eEF1A proteins is a promising molecular drug to develop for the control of the castrate-resistant prostate cance

The State of the Art of Piezo1 Channels in Skeletal Muscle Regeneration

Piezo1 channels are highly mechanically-activated cation channels that can sense and transduce the mechanical stimuli into physiological signals in different tissues including skeletal muscle. In this focused review, we summarize the emerging evidence of Piezo1 channel-mediated effects in the physiology of skeletal muscle, with a particular focus on the role of Piezo1 in controlling myogenic precursor activity and skeletal muscle regeneration and vascularization. The disclosed effects reported by pharmacological activation of Piezo1 channels with the selective agonist Yoda1 indicate a potential impact of Piezo1 channel activity in skeletal muscle regeneration, which is disrupted in various muscular pathological states. All findings reported so far agree with the idea that Piezo1 channels represent a novel, powerful molecular target to develop new therapeutic strategies for preventing or ameliorating skeletal muscle disorders characterized by an impairment of tissue regenerative potential

Capillary rarefaction during bed rest is proportionally less than fibre atrophy and loss of oxidative capacity

Background Muscle disuse from bed rest or spaceflight results in losses in muscle mass, strength and oxidative capacity. Capillary rarefaction may contribute to muscle atrophy and the reduction in oxidative capacity during bed rest. Artificial gravity may attenuate the negative effects of long-term space missions or bed rest. The aim of the present study was to assess (1) the effects of bed rest on muscle fibre size, fibre type composition, capillarization and oxidative capacity in the vastus lateralis and soleus muscles after 6 and 55 days of bed rest and (2) the effectiveness of artificial gravity in mitigating bed-rest-induced detriments to these parameters. Methods Nineteen participants were assigned to a control group (control, n = 6) or an intervention group undergoing 30 min of centrifugation (n = 13). All underwent 55 days of head-down tilt bed rest. Vastus lateralis and soleus biopsies were taken at baseline and after 6 and 55 days of bed rest. Fibre type composition, fibre cross-sectional area, capillarization indices and oxidative capacity were determined. Results After just 6 days of bed rest, fibre atrophy ( 23.2 ± 12.4%, P < 0.001) and reductions in capillary-to-fibre ratio (C:F; 1.97 ± 0.57 vs. 1.56 ± 0.41, P < 0.001) were proportional in both muscles as reflected by a maintained capillary density. Fibre atrophy proceeded at a much slower rate between 6 and 55 days of bed rest ( 11.6 ± 12.1% of 6 days, P = 0.032) and was accompanied by a 19.1% reduction in succinate dehydrogenase stain optical density (P < 0.001), without any further significant decrements in C:F (1.56 ± 0.41 vs. 1.49 ± 0.37, P = 0.459). Consequently, after 55 days of bed rest, the capillary supply–oxidative capacity ratio of a fibre had increased by 41.9% (P < 0.001), indicating a capillarization in relative excess of oxidative capacity. Even though the heterogeneity of capillary spacing (LogRSD) was increased after 55 days by 12.7% (P = 0.004), tissue oxygenation at maximal oxygen consumption of the fibres was improved after 55 days bed rest. Daily centrifugation failed to blunt the bed-rest-induced reductions in fibre size and oxidative capacity and capillary rarefaction. Conclusions The relationship between fibre size and oxidative capacity with the capillary supply of a fibre is uncoupled during prolonged bed rest as reflected by a rapid loss of muscle mass and capillaries, followed at later stages by a more than proportional loss of mitochondria without further capillary loss. The resulting excessive capillary supply of the muscle after prolonged bed rest is advantageous for the delivery of substrates needed for subsequent muscle recovery

Whey protein with potassium bicarbonate supplement attenuates the reduction in muscle oxidative capacity during 19 days bed rest.

The effectiveness of whey protein plus potassium bicarbonate enriched-diet (WP+KHCO3) to mitigate disuse-induced changes in muscle fibre oxidative capacity and capillarization was investigated in a 21-day crossover design bed rest study. Ten healthy men (31±6 years) once received WP+KHCO3 and once received a standardized isocaloric diet. Muscle biopsies were taken two days before and during the 19th day of bed rest (BR) from the soleus (SOL) and vastus lateralis (VL) muscle. Whole body aerobic power (VO2max), muscle fatigue and isometric strength of knee extensor and plantar flexor muscles were monitored. Muscle fiber types and capillaries were identified by immunohistochemistry. Fiber oxidative capacity was determined as the optical density (OD) at 660 nm of succinate dehydrogenase (SDH)-stained sections. The product of fiber cross-sectional area and SDH-OD (integrated SDH) indicated the maximal oxygen consumption of that fiber. The maximal oxygen consumption supported by a capillary was calculated as the integrated SDH in its supply area. BR reduced isometric strength of knee extensor muscles (P<0.05), and the fiber oxidative capacity (P<0.001) and VO2max (P=0.042), but had no significant impact on muscle capillarization or fatigue resistance of thigh muscles. The maximal oxygen consumption supported by a capillary was reduced by 24% in SOL and 16% in VL (P<0.001). WP+KHCO3 attenuated the disuse-induced reduction in fiber oxidative capacity in both muscles (P<0.01). In conclusion, following 19 days bed rest, the decrement in fiber oxidative capacity is proportionally larger than the loss of capillaries. WP+KHCO3 appears to attenuate disuse-induced reductions in fiber oxidative capacity

The impact of bed rest on human skeletal muscle metabolism

Insulin sensitivity and metabolic flexibility decrease in response to bed rest, but the temporal and causal adaptations in human skeletal muscle metabolism are not fully defined. Here, we use an integrative approach to assess human skeletal muscle metabolism during bed rest and provide a multi-system analysis of how skeletal muscle and the circulatory system adapt to short- and long-term bed rest (German Clinical Trials: DRKS00015677). We uncover that intracellular glycogen accumulation after short-term bed rest accompanies a rapid reduction in systemic insulin sensitivity and less GLUT4 localization at the muscle cell membrane, preventing further intracellular glycogen deposition after long-term bed rest. We provide evidence of a temporal link between the accumulation of intracellular triglycerides, lipotoxic ceramides, and sphingomyelins and an altered skeletal muscle mitochondrial structure and function after long-term bed rest. An intracellular nutrient overload therefore represents a crucial determinant for rapid skeletal muscle insulin insensitivity and mitochondrial alterations after prolonged bed rest

Head-down tilt bed rest with or without artificial gravity is not associated with motor unit remodeling

© 2020, The Author(s). Purpose: The objective of this study was to assess whether artificial gravity attenuates any long-duration head-down 60 bed rest (HDBR)-induced alterations in motor unit (MU) properties. Methods: Twenty-four healthy participants (16 men; 8 women; 26–54 years) underwent 60-day HDBR with (n = 16) or without (n = 8) 30 min artificial gravity daily induced by whole-body centrifugation. Compound muscle action potential (CMAP), MU number (MUNIX) and MU size (MUSIX) were estimated using the method of Motor Unit Number Index in the Abductor digiti minimi and tibialis anterior muscles 5 days before (BDC-5), and during day 4 (HDT4) and 59 (HDT59) of HDBR. Results: The CMAP, MUNIX, and MUSIX at baseline did not change significantly in either muscle, irrespective of the intervention (p > 0.05). Across groups, there were no significant differences in any variable during HDBR, compared to BDC-5. Conclusion: Sixty days of HDBR with or without artificial gravity does not induce alterations in motor unit number and size in the ADM or TA muscles in healthy individuals

Sixty days of head-down tilt bed rest with or without artificial gravity do not affect the neuromuscular secretome.

Artificial gravity is a potential countermeasure to attenuate effects of weightlessness during long-term spaceflight, including losses of muscle mass and function, possibly to some extent attributable to disturbed neuromuscular interaction. The 60-day AGBRESA bed-rest study was conducted with 24 participants (16 men, 8 women; 33 ± 9 years; 175 ± 9 cm; 74 ± 10 kg; 8 control group, 8 continuous (cAG) and 8 intermittent (iAG) centrifugation) to assess the impact of bed rest with or without daily 30-min continuous/intermittent centrifugation with 1G at the centre of mass. Fasting blood samples were collected before and on day 6, 20, 40 and 57 during 6° head-down tilt bed rest. Concentrations of circulating markers of muscle wasting (GDF-8/myostatin; slow skeletal muscle troponin T; prostaglandin E2), neurotrophic factors (BDNF; GDNF) and C-terminal Agrin Fragment (CAF) were determined by ELISAs. Creatine kinase activity was assessed by colorimetric enzyme assay. Repeated-measures ANOVAs were conducted with TIME as within-subject, and INTERVENTION and SEX as between-subject factors. The analyses revealed no significant effect of bed rest or sex on any of the parameters. Continuous or intermittent artificial gravity is a safe intervention that does not have a negative impact of the neuromuscular secretome

Whey protein supplementation attenuates the reduction in muscle oxidative capacity during 21 days bed rest

Muscle unloading, as encountered during space flight and disuse, induces skeletal muscle atrophy and weakness, switch of fibre types and loss of capillaries. Less attention has been given to disuse-induced changes in oxidative capacity, which may affect endurance. Here we investigated the impact of 21 days, 60 head-down bed rest on muscle fibre size, fibre type composition, capillarisation and muscle oxidative capacity and the efficacy of milk-based proteins (whey protein) to counteract disuse-induced muscle changes. Muscle biopsies were taken from the soleus (SOL) and vastus lateralis (VL)muscles before and after bed rest from10 healthy men (aged 31 ± 6 years). Subjects were assigned to two groups and studied twice in two follow-up campaigns, in once receiving whey protein and once receiving a standardized isocaloric diet. Fibre types and capillaries were identified by immunohistochemical staining of muscle section with anti-myosin type1 and lectin. Analysis was done with the method of capillary domains.Oxidative capacity of individual fibres was determined as the optical density (OD) at 660 nm of succinate dehydrogenase (SDH) stained histological sections. The fibre cross-sectional area times the SDH-OD of that fibre (integrated SDH) was index of maximal oxygen consumption of that fibre(VO2max). Statistical analysis was done by repeated measures ANOVA. Bed rest did not induce significant changes infibre type composition, fibre size or capillarisation, but decreased SDH activity (p\0.001) and fibre VO2max (p\0.01) in both muscles. Whey protein partially counteracted the decrease in oxidative capacity. Our results suggest that decrements in oxidative capacity may be an early hallmark of disuse-induced muscle adaptations and occurs even in the absence of significant fibre atrophy and capillary rarefaction. The Whey diet attenuated these effects and may thus be an effective supplement to sustain oxidative capacity during space flight and long-term bed rest