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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.

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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). The impact of immobilisation and inflammation on the regulation of muscle mass and insulin resistance: different routes to similar end-points. J Physiol 2. doi: 10.1113/JP275444. Dalla Libera L, Ravara B, Gobbo V, Tarricone E, Vitadello M, Biolo G, Vescovo G, Gorza L. (2009). A transient antioxidant stress response accompanies the onset of disuse atrophy in human skeletal muscle. J. Appl. Physiol. (1985) 107, 549–557. doi: 10.1152/japplphysiol.00280.2009 de Boer MD, Selby A, Atherton P, Smith K, Seynnes OR, Maganaris CN, Maffulli N, Movin T, Narici MV, Rennie MJ (2007). The temporal responses of protein synthesis, gene expression and cell signalling in human quadriceps muscle and patellar tendon to disuse. J. Physiol. 585, 241–251. doi: 10.1113/jphysiol.2007.142828 Glover EI, Phillips SM, Oates BR, Tang JE, Tarnopolsky MA, Selbi A, Smith K, Rennie MJ (2008). Immobilization induces anabolic resistance in human myofibrillar protein synthesis with low and high dose amino acid infusion. J Physiol 2008 6049-6061. doi: 10.1113/jphysiol.2008.160333. Graham ZA, Gallagher PM, Cardozo CP (2015). Focal adhesion kinase and its role in skeletal muscle. J Muscle Res Cell Motil. 36(4-5):305-15. doi: 10.1007/s10974-015-9415-3. Klossner S, Durieux AC, Freyssenet D & Fluck M (2009). Mechano-transduction to muscle protein synthesis is modulated by FAK. Eur. J. Appl. Physiol. 106, 389–398. doi: 10.1007/s00421-009-1032-7 Pellegrino MA, Desaphy JF, Brocca L, Pierno S, Camerino DC, Bottinelli R (2011). Redox homeostasis, oxidative stress and disuse muscle atrophy. J Physiol. 1;589(Pt 9):2147-60. doi: 10.1113/jphysiol.2010.203232. Phillips SM and McGlory C (2014). The Journal of Physiology CrossTalk proposal: The dominant mechanism causing disuse muscle atrophy is decreased protein synthesis. J Physiol 592.24: 5341–5343. doi: 10.1113/jphysiol.2014.273615. Powers SK, Kavazis AN & DeRuisseau KC (2005). Mechanisms of disuse muscle atrophy: role of oxidative stress. 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

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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