Rejuvenation of the aged neuromuscular junction by exercise

Mature and Juvenile Neuromuscular Plasticity in Response to Unloading

The neuromuscular junction (NMJ) is the synapse that enables the requisite electrical communication between the motor nervous system and the myofibers that respond to such electrical stimulation with movement and force development. Changes in an NMJ's normal activity pattern have been demonstrated to remodel both the synapse and the myofibers that comprise the NMJ. Significant amounts of research have been devoted to the study of aging on the neuromuscular system. Far less, however, has been focused on revealing the effects of reduced activity on the NMJ and myofibers comprising juvenile neuromuscular systems. In the present investigation, the consequences of decreased activity imposed by muscle unloading (UL) via hindlimb suspension for 2 weeks (a period known to induce muscle remodeling) were examined in both young adult, that is, mature (8 mo), and juvenile (3 mo) neuromuscular systems. In total, 4 treatment groups comprised of 10 animals (Juvenile-Control, Juvenile-Unloaded, Mature-Control, and Mature-Unloaded) were studied. Immunofluorescent procedures, coupled with confocal microscopy, were used to quantify remodeling of both the pre- and postsynaptic features of NMJs, as well as assessing the myofiber profiles of the soleus muscles housing the NMJs of interest. Results of ANOVA procedures revealed that there were significant (p < 0.05) main effects for both treatment, whereby UL consistently led to expanded size of the NMJ, and Age where expanded NMJ dimensions were consistently linked with mature compared to juvenile neuromuscular systems. Moreover, only sporadically was interaction between the main effects of Age and Treatment noted. Importantly, one variable that remained impressively resistant to the effects of both Age and Treatment was the critical parameter of pre- to postsynaptic coupling suggesting stability in effective communication at the NMJ throughout the lifespan and despite changes in activity patterns. The data presented here suggest that further inquiry must be performed regarding disuse-related plasticity of the neuromuscular system in adolescent individuals as those individuals regularly suffer injuries resulting in periods of muscle UL.

Microgravity-induced changes in skeletal muscle and possible countermeasures: What we can learn from bed rest and human space studies

Despite exercise countermeasures to sustain health and performance in spaceflight, complete maintenance of muscle mass and functions in microgravity is still not possible for most astronauts. The principal cause of the limited effectiveness of existing exercise countermeasures is the difficulty in achieving full loading forces in space. The implementation of countermeasures which require small devices and simulate Earth-like loading forces to maintain muscle mass, strength and endurance is therefore highly desirable. At present, the cellular mechanisms that induce muscle atrophy in weightlessness are not yet fully known; a better understanding of how skeletal muscle cells adapt to microgravity will help in designing more effective countermeasures to sustain the health and operational capacity of the crew during long- and short-duration missions. The 6° head-down-tilt bed rest is a powerful ground-based analogue platform to simulate and study the physiological effects of spaceflight on the human body, and test the effectiveness of countermeasures before they are potentially applied in space. The aims of this narrative review are therefore to provide an overview of (i) the main mechanisms underlining muscle atrophy learnt from space and bed rest studies, (ii) the currently available countermeasures, and (iii) potential suitable countermeasures - such as neuromuscular electrical stimulation that is delivered with light and small portable units - to attenuate muscle wasting in astronauts during spaceflight.

Emerging Targets and Treatments for Sarcopenia: A Narrative Review

BACKGROUND

Sarcopenia is characterized by the progressive loss of skeletal muscle mass, strength, and function, significantly impacting overall health and quality of life in older adults. This narrative review explores emerging targets and potential treatments for sarcopenia, aiming to provide a comprehensive overview of current and prospective interventions.

METHODS

The review synthesizes current literature on sarcopenia treatment, focusing on recent advancements in muscle regeneration, mitochondrial function, nutritional strategies, and the muscle-microbiome axis. Additionally, pharmacological and lifestyle interventions targeting anabolic resistance and neuromuscular junction integrity are discussed.

RESULTS

Resistance training and adequate protein intake remain the cornerstone of sarcopenia management. Emerging strategies include targeting muscle regeneration through myosatellite cell activation, signaling pathways, and chronic inflammation control. Gene editing, stem cell therapy, and microRNA modulation show promise in enhancing muscle repair. Addressing mitochondrial dysfunction through interventions aimed at improving biogenesis, ATP production, and reducing oxidative stress is also highlighted. Nutritional strategies such as leucine supplementation and anti-inflammatory nutrients, along with dietary modifications and probiotics targeting the muscle-microbiome interplay, are discussed as potential treatment options. Hydration and muscle-water balance are emphasized as critical in maintaining muscle health in older adults.

CONCLUSIONS

A combination of resistance training, nutrition, and emerging therapeutic interventions holds potential to significantly improve muscle function and overall health in the aging population. This review provides a detailed exploration of both established and novel approaches for the prevention and management of sarcopenia, highlighting the need for further research to optimize these strategies.

Sarcopenia and Ageing

Musculoskeletal ageing is a major health challenge as muscles and bones constitute around 55-60% of body weight. Ageing muscles will result in sarcopenia that is characterized by progressive and generalized loss of skeletal muscle mass and strength with a risk of adverse outcomes. In recent years, a few consensus panels provide new definitions for sarcopenia. It was officially recognized as a disease in 2016 with an ICD-10-CM disease code, M62.84, in the International Classification of Diseases (ICD). With the new definitions, there are many studies emerging to investigate the pathogenesis of sarcopenia, exploring new interventions to treat sarcopenia and evaluating the efficacy of combination treatments for sarcopenia. The scope of this chapter is to summarize and appraise the evidence in terms of (1) clinical signs, symptoms, screening, and diagnosis, (2) pathogenesis of sarcopenia with emphasis on mitochondrial dysfunction, intramuscular fat infiltration and neuromuscular junction deterioration, and (3) current treatments with regard to physical exercises and nutritional supplement.

Evaluation of Sarcopenia Using Biomarkers of the Neuromuscular Junction in Parkinson's Disease

Patients with Parkinson's disease (PD) present with an advanced form of age-related muscle loss or sarcopenia. However, the search for a biomarker to accurately predict muscle loss in PD remains elusive. We evaluated the biomarkers of neuromuscular junction (NMJ) stability, including c-terminal agrin fragment-22 (CAF22), brain-derived neurotrophic factor (BDNF), and glial cell line-derived neurotrophic factor (GDNF) as predictors of muscle wasting and physical capacity in PD. Male, 63-78 years patients of PD, were investigated for physical capacity, handgrip strength (HGS), and circulating biomarkers at the diagnosis and follow-up during rehabilitation 6 months apart. Patients with PD presented with elevated CAF22 and reduced BDNF and GDNF levels, which were partially restored to normal levels with rehabilitation. All three biomarkers showed significant dynamic associations with HGS and indexes of sarcopenia. Logistic regression revealed that the combination of biomarkers levels into a cumulative risk score enhanced the diagnostic accuracy of sarcopenia. In brief, measurements of plasma BDNF, GDNF, and CAF22 may be helpful in timely diagnosis and/or evaluation of sarcopenia.

Structural and Functional Changes in the Coupling of Fascial Tissue, Skeletal Muscle, and Nerves During Aging

Aging is a one-way process associated with profound structural and functional changes in the organism. Indeed, the neuromuscular system undergoes a wide remodeling, which involves muscles, fascia, and the central and peripheral nervous systems. As a result, intrinsic features of tissues, as well as their functional and structural coupling, are affected and a decline in overall physical performance occurs. Evidence from the scientific literature demonstrates that senescence is associated with increased stiffness and reduced elasticity of fascia, as well as loss of skeletal muscle mass, strength, and regenerative potential. The interaction between muscular and fascial structures is also weakened. As for the nervous system, aging leads to motor cortex atrophy, reduced motor cortical excitability, and plasticity, thus leading to accumulation of denervated muscle fibers. As a result, the magnitude of force generated by the neuromuscular apparatus, its transmission along the myofascial chain, joint mobility, and movement coordination are impaired. In this review, we summarize the evidence about the deleterious effect of aging on skeletal muscle, fascial tissue, and the nervous system. In particular, we address the structural and functional changes occurring within and between these tissues and discuss the effect of inflammation in aging. From the clinical perspective, this article outlines promising approaches for analyzing the composition and the viscoelastic properties of skeletal muscle, such as ultrasonography and elastography, which could be applied for a better understanding of musculoskeletal modifications occurring with aging. Moreover, we describe the use of tissue manipulation techniques, such as massage, traction, mobilization as well as acupuncture, dry needling, and nerve block, to enhance fascial repair.