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Sirago G, Pellegrino MA, Bottinelli R, Franchi MV, Narici MV. Loss of neuromuscular junction integrity and muscle atrophy in skeletal muscle disuse. Ageing Res Rev 2023; 83:101810. [PMID: 36471545 DOI: 10.1016/j.arr.2022.101810] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2022] [Revised: 11/25/2022] [Accepted: 11/25/2022] [Indexed: 11/27/2022]
Abstract
Physical inactivity (PI) is a major risk factor of chronic diseases. A major aspect of PI is loss of muscle mass and strength. The latter phenomenon significantly impacts daily life and represent a major issue for global health. Understandably, skeletal muscle itself has been the major focus of studies aimed at understanding the mechanisms underlying loss of mass and strength. Relatively lesser attention has been given to the contribution of alterations in somatomotor control, despite the fact that these changes can start very early and can occur at multiple levels, from the cortex down to the neuromuscular junction (NMJ). It is well known that exposure to chronic inactivity or immobilization causes a disproportionate loss of force compared to muscle mass, i.e. a loss of specific or intrinsic whole muscle force. The latter phenomenon may be partially explained by the loss of specific force of individual muscle fibres, but several other players are very likely to contribute to such detrimental phenomenon. Irrespective of the length of the disuse period, the loss of force is, in fact, more than two-fold greater than that of muscle size. It is very likely that somatomotor alterations may contribute to this loss in intrinsic muscle force. Here we review evidence that alterations of one component of somatomotor control, namely the neuromuscular junction, occur in disuse. We also discuss some of the novel players in NMJ stability (e.g., homer, bassoon, pannexin) and the importance of new established and emerging molecular markers of neurodegenerative processes in humans such as agrin, neural-cell adhesion molecule and light-chain neurofilaments.
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Affiliation(s)
- Giuseppe Sirago
- Department of Biomedical Sciences, University of Padova, Padova 35131, Italy.
| | - Maria A Pellegrino
- Department of Molecular Medicine, University of Pavia, Pavia 27100, Italy
| | - Roberto Bottinelli
- Department of Molecular Medicine, University of Pavia, Pavia 27100, Italy; IRCCS Mondino Foundation, Pavia 27100, Italy
| | - Martino V Franchi
- Department of Biomedical Sciences, University of Padova, Padova 35131, Italy
| | - Marco V Narici
- Department of Biomedical Sciences, University of Padova, Padova 35131, Italy; CIR-MYO Myology Center, University of Padova, Padova 35131, Italy.
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Davis LA, Fogarty MJ, Brown A, Sieck GC. Structure and Function of the Mammalian Neuromuscular Junction. Compr Physiol 2022; 12:3731-3766. [PMID: 35950651 PMCID: PMC10461538 DOI: 10.1002/cphy.c210022] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The mammalian neuromuscular junction (NMJ) comprises a presynaptic terminal, a postsynaptic receptor region on the muscle fiber (endplate), and the perisynaptic (terminal) Schwann cell. As with any synapse, the purpose of the NMJ is to transmit signals from the nervous system to muscle fibers. This neural control of muscle fibers is organized as motor units, which display distinct structural and functional phenotypes including differences in pre- and postsynaptic elements of NMJs. Motor units vary considerably in the frequency of their activation (both motor neuron discharge rate and duration/duty cycle), force generation, and susceptibility to fatigue. For earlier and more frequently recruited motor units, the structure and function of the activated NMJs must have high fidelity to ensure consistent activation and continued contractile response to sustain vital motor behaviors (e.g., breathing and postural balance). Similarly, for higher force less frequent behaviors (e.g., coughing and jumping), the structure and function of recruited NMJs must ensure short-term reliable activation but not activation sustained for a prolonged period in which fatigue may occur. The NMJ is highly plastic, changing structurally and functionally throughout the life span from embryonic development to old age. The NMJ also changes under pathological conditions including acute and chronic disease. Such neuroplasticity often varies across motor unit types. © 2022 American Physiological Society. Compr Physiol 12:1-36, 2022.
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Affiliation(s)
- Leah A. Davis
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Matthew J. Fogarty
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Alyssa Brown
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Gary C. Sieck
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
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Monti E, Reggiani C, Franchi MV, Toniolo L, Sandri M, Armani A, Zampieri S, Giacomello E, Sarto F, Sirago G, Murgia M, Nogara L, Marcucci L, Ciciliot S, Šimunic B, Pišot R, Narici MV. Neuromuscular junction instability and altered intracellular calcium handling as early determinants of force loss during unloading in humans. J Physiol 2021; 599:3037-3061. [PMID: 33881176 PMCID: PMC8359852 DOI: 10.1113/jp281365] [Citation(s) in RCA: 49] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2021] [Accepted: 03/30/2021] [Indexed: 01/18/2023] Open
Abstract
Key points Few days of unloading are sufficient to induce a decline of skeletal muscle mass and function; notably, contractile force is lost at a faster rate than muscle mass. The reasons behind this disproportionate loss of muscle force are still poorly understood. We provide strong evidence of two mechanisms only hypothesized until now for the rapid muscle force loss in only 10 days of bed rest. Our results show that an initial neuromuscular junction instability, accompanied by alterations in the innervation status and impairment of single fibre sarcoplasmic reticulum function contribute to the loss of contractile force in front of a preserved myofibrillar function and central activation capacity. Early onset of neuromuscular junction instability and impairment in calcium dynamics involved in excitation–contraction coupling are proposed as eligible determinants to the greater decline in muscle force than in muscle size during unloading.
Abstract Unloading induces rapid skeletal muscle atrophy and functional decline. Importantly, force is lost at a much higher rate than muscle mass. We aimed to investigate the early determinants of the disproportionate loss of force compared to that of muscle mass in response to unloading. Ten young participants underwent 10 days of bed rest (BR). At baseline (BR0) and at 10 days (BR10), quadriceps femoris (QF) volume (VOL) and isometric maximum voluntary contraction (MVC) were assessed. At BR0 and BR10 blood samples and biopsies of vastus lateralis (VL) muscle were collected. Neuromuscular junction (NMJ) stability and myofibre innervation status were assessed, together with single fibre mechanical properties and sarcoplasmic reticulum (SR) calcium handling. From BR0 to BR10, QFVOL and MVC decreased by 5.2% (P = 0.003) and 14.3% (P < 0.001), respectively. Initial and partial denervation was detected from increased neural cell adhesion molecule (NCAM)‐positive myofibres at BR10 compared with BR0 (+3.4%, P = 0.016). NMJ instability was further inferred from increased C‐terminal agrin fragment concentration in serum (+19.2% at BR10, P = 0.031). Fast fibre cross‐sectional area (CSA) showed a trend to decrease by 15% (P = 0.055) at BR10, while single fibre maximal tension (force/CSA) was unchanged. However, at BR10 SR Ca2+ release in response to caffeine decreased by 35.1% (P < 0.002) and 30.2% (P < 0.001) in fast and slow fibres, respectively, pointing to an impaired excitation–contraction coupling. These findings support the view that the early onset of NMJ instability and impairment in SR function are eligible mechanisms contributing to the greater decline in muscle force than in muscle size during unloading. Few days of unloading are sufficient to induce a decline of skeletal muscle mass and function; notably, contractile force is lost at a faster rate than muscle mass. The reasons behind this disproportionate loss of muscle force are still poorly understood. We provide strong evidence of two mechanisms only hypothesized until now for the rapid muscle force loss in only 10 days of bed rest. Our results show that an initial neuromuscular junction instability, accompanied by alterations in the innervation status and impairment of single fibre sarcoplasmic reticulum function contribute to the loss of contractile force in front of a preserved myofibrillar function and central activation capacity. Early onset of neuromuscular junction instability and impairment in calcium dynamics involved in excitation–contraction coupling are proposed as eligible determinants to the greater decline in muscle force than in muscle size during unloading.
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Affiliation(s)
- Elena Monti
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy
| | - Carlo Reggiani
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy.,Science and Research Center Koper, Institute for Kinesiology Research, Koper, 6000, Slovenia
| | - Martino V Franchi
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy
| | - Luana Toniolo
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy
| | - Marco Sandri
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy.,Department of Biomedical Sciences, Venetian Institute of Molecular Medicine, University of Padova, Via Orus 2, Padova, 35129, Italy
| | - Andrea Armani
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy.,Department of Biomedical Sciences, Venetian Institute of Molecular Medicine, University of Padova, Via Orus 2, Padova, 35129, Italy
| | - Sandra Zampieri
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy.,Department of Surgery, Oncology, and Gastroenterology, University of Padova, Padova, 35124, Italy
| | - Emiliana Giacomello
- Clinical Department of Medical, Surgical and Health Sciences, Strada di Fiume, 447, Trieste, 34149, Italy
| | - Fabio Sarto
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy
| | - Giuseppe Sirago
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy
| | - Marta Murgia
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy.,Department of Proteomics and Signal Transduction, Max-Planck-Institute of Biochemistry Am Klopferspitz 18, Martinsried, 82152, Germany
| | - Leonardo Nogara
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy
| | - Lorenzo Marcucci
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy
| | - Stefano Ciciliot
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy.,Department of Biomedical Sciences, Venetian Institute of Molecular Medicine, University of Padova, Via Orus 2, Padova, 35129, Italy
| | - Boštjan Šimunic
- Science and Research Center Koper, Institute for Kinesiology Research, Koper, 6000, Slovenia
| | - Rado Pišot
- Science and Research Center Koper, Institute for Kinesiology Research, Koper, 6000, Slovenia
| | - Marco V Narici
- Department of Biomedical Sciences, University of Padova, Padova, 35131, Italy.,Science and Research Center Koper, Institute for Kinesiology Research, Koper, 6000, Slovenia.,CIR-MYO Myology Center, University of Padova, Padova, 35131, Italy
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Busetto G, Cangiano A. Pre- and post-synaptic roles of action potential activity in synapse elimination revealed by using ectopic neuromuscular junction formation by a foreign nerve. Neurosci Lett 2020; 722:134835. [PMID: 32057925 DOI: 10.1016/j.neulet.2020.134835] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Revised: 02/07/2020] [Accepted: 02/09/2020] [Indexed: 10/25/2022]
Abstract
The formation of the neuromuscular junction (nmj) is based on molecular cascades initiated by neural agrin as well as electrical activity in the neuromuscular structures. This review focuses on the latter factor, emphasizing the multiplicity of its mechanisms in the process of synapse elimination following initial polyneuronal innervation. Pre- and post-synaptic components of activity have in fact been identified through experiments on an adult model of nmj formation: ectopic reinnervation of the rat soleus muscle by the fibular nerve. Two activity-dependent elimination processes are thus compared: competition between distributed nmjs, which depends on evoked muscle impulse activity, and competition between axons converging on single nmjs, which instead depends on differences in the timing of impulses in the converging axons.
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Affiliation(s)
- Giuseppe Busetto
- Department of Neurosciences Biomedicine and Movement Sciences, University of Verona, Strada Le Grazie 8, 37134, Verona, Italy; National Institute of Neuroscience, Verona, Italy
| | - Alberto Cangiano
- Department of Neurosciences Biomedicine and Movement Sciences, University of Verona, Strada Le Grazie 8, 37134, Verona, Italy; National Institute of Neuroscience, Verona, Italy.
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