Contribution of muscle satellite cells to sarcopenia

Probiotics Attenuate Myopathic Changes in Aging Rats via Activation of the Myogenic Stellate Cells

Aging represents a complex biological process associated with decline in skeletal muscle functions. Aging impairs satellite cells that serve as muscle progenitor cells. Probiotic supplementation may have many beneficial effects via various mechanisms. We examined the possible effects of probiotics in stimulating the proliferation of myogenic stellate cells in aging rats. Twenty-four male albino Sprague-Dawley rats were classified equally into four groups: adult control, old control, adult + probiotics, and old + probiotics. Probiotics (Lactobacillus LB) were administered gavage at a dose of 1 ml (1 × 109 CFU/ml/day) for 4 weeks. A significant increase in the relative gastrocnemius weight ratio and improvement of contractile parameters was detected in the old + probiotics group (0.6 ± 0.01) compared to the old control group (0.47 ± 0.01; P < 0.001). Probiotics significantly upregulated the activities of GSH, while NO and MDA were markedly decreased compared to control groups (P ≤ 0.001). Also, probiotics increased the mRNA and protein expressions of myogenin and CD34 (P < 0.05) as determined by real-time PCR and immunohistochemistry. Moreover, the old + probiotics group showed apparent restoration of the connective tissue spaces, reflecting the all-beneficial effects of probiotics. Our findings indicated that probiotics attenuated myopathic changes in aging rats probably through activation of the myogenic stellate cells. Probiotics improved the muscle weight, function, antioxidant activity, and myogenic transcription factors of the skeletal muscle.

Role of brain-derived neurotrophic factor in frailty: From mechanisms to interventions

Frailty is a common medical syndrome which largely increases the risk of disability, depression, falls, hospitalization and mortality. An increasing number of research suggests that frailty is reversible by medical interventions at its early stage. Therefore, efficient detection is utterly important for frail population. Since numerous biological processes have been indicated in frail population, the critical regulators in these biological processes could provide biomarkers for early detection or treatment for frailty. The brain-derived neurotrophic factor (BDNF) has been associated with several biological process ranging from cognitive function to inflammation, therefore it could be an important regulator for frailty. In this review, we would discuss the mechanism association between different indicators of frailty and BDNF. Furthermore, we summarize the approaches to interfere with BDNF in healthy and pathologic condition, which could lead to identification of potential interventional strategies for frailty.

Mesenchymal stem cell-specific Sirt1 overexpression prevents sarcopenia induced by 1,25-dihydroxyvitamin D deficiency

Sarcopenia, characterized by an age-related decline in skeletal muscle mass and function, is closely linked to vitamin D deficiency. This study examines the role of Sirtuin 1 (Sirt1) and its regulation by vitamin D in preventing sarcopenia. Utilizing wild-type, 1α-hydroxylase knockout (1α(OH)ase-/-), and Sirt1 transgenic (Sirt1Tg) 1α(OH)ase-/- mice, we investigated muscle Sirt1 levels, muscle mass, fiber type, and senescence markers. Our results demonstrated that 1,25-Dihydroxyvitamin D (1,25(OH)2D3) upregulated Sirt1 and myogenic factor MyoD1 expression in C2C12 myoblasts via VDR-mediated transcription. Sirt1 overexpression in mesenchymal stem cells (MSCs) significantly mitigated muscle mass reduction, improved fiber cross-sectional area, and increased type II fiber numbers in 1α(OH)ase-/- mice. Mechanistically, 1,25(OH)2D3 promoted muscle cell health by enhancing Sirt1 expression, which in turn reduced muscle cell senescence and the senescence-associated secretory phenotype (SASP) through decreased levels of acetylated nuclear p53 and p65, maintaining their cytoplasmic localization. Additionally, Sirt1 overexpression accelerated muscle regeneration post-injury by increasing embryonic myosin heavy chain expression and cell proliferation. These findings underscore the therapeutic potential of targeting vitamin D and Sirt1 pathways to prevent sarcopenia, suggesting that supplementation with active vitamin D and consequent Sirt1 activation could be effective strategies for managing age-related muscle wasting.

The link between sarcopenic obesity and Alzheimer's disease: a brain-derived neurotrophic factor point of view

Age-related diseases are becoming more prominent as the lifespan of the global population rises. Many of these diseases coincide with each other and can even influence the onset of additional comorbidities. Sarcopenic obesity is described as age-related loss of muscle mass that concurs with excessive weight gain and tends to increase the risk of comorbidity development, including Alzheimer's disease (AD). Though the exact link between sarcopenic obesity and AD is not known, this review explores the possibility that reduced levels of brain-derived neurotrophic factor (BDNF) throughout the body may serve as the underlying commonality. In AD, reductions in BDNF signalling through its receptor promote the activation of glycogen synthase kinase 3 beta (GSK3β), which subsequently increases the production of amyloid beta (Aβ) peptides and neurofibrillary tangles (NFTs). In the skeletal muscle, lower BDNF concentrations are linked to impaired muscle fibre repair and regeneration, increasing the likelihood of sarcopenia. Furthermore, the absence of BDNF impairs mitochondrial function, leading to insulin resistance and increased adiposity. BDNF concentration has a negative relationship with obesogenic markers in adipose tissue, and as such, lower concentrations of BDNF lead to weight gain. Collectively, current literature suggests that BDNF attenuates AD pathology while improving skeletal muscle mitochondrial function, whole-body insulin resistance and facilitating adipocyte browning. Therefore, BDNF may be a viable target for multiple age-related diseases, but more research is required to substantiate this claim, with a particular focus on examining any potential influence of biological sex, as women are at a higher risk for both AD and sarcopenic obesity.

Medical Nutrition Therapy and Physical Exercise for Acute and Chronic Hyperglycemic Patients with Sarcopenia

A wide range of factors contribute to the overlap of hyperglycemia-acute or chronic-and sarcopenia, as well as their associated adverse consequences, which can lead to impaired physical function, reduced quality of life, and increased mortality risk. These factors include malnutrition (both overnutrition and undernutrition) and low levels of physical activity. Hyperglycemia and sarcopenia are interconnected through a vicious cycle of events that mutually reinforce and worsen each other. To explore this association, our review compiles evidence on: (i) the impact of hyperglycemia on motor and muscle function, with a focus on the mechanisms underlying biochemical changes in the muscles of individuals with or at risk of diabetes and sarcopenia; (ii) the importance of the clinical assessment and control of sarcopenia under hyperglycemic conditions; and (iii) the potential benefits of medical nutrition therapy and increased physical activity as muscle-targeted treatments for this population. Based on the reviewed evidence, we conclude that a regular intake of key functional nutrients, together with structured and supervised resistance and/or aerobic physical activity, can help maintain euglycemia and improve muscle status in all patients with hyperglycemia and sarcopenia.

Effects of Aging on Orbicularis Oculi Muscle Strength and Ultrastructure in Dermatochalasis: A Pilot Study

Background: Age-related changes to the orbicularis oculi muscle include impaired eyelid function, such as lagophthalmos, alterations in tear film dynamics, and aesthetic changes like wrinkles, festoons, and the descent of soft tissue. To date, the structural and functional changes that would comprehensively increase our understanding of orbicularis aging have not been analyzed. This study aims to investigate functional outcomes using surface electromyography and correlate them with ultrastructural changes in orbicularis during aging. Methods: This study enrolled 26 patients aged 37 to 78 years with a clinical diagnosis of dermatochalasis. Patients were divided into two age groups (<60 years; ≥60 years). Ultrastructural and electromyographical examinations were performed, and the electromyographical signals were correlated with the ultrastructural damage in the orbicularis. Results: This study revealed significantly lower values of average voluntary contraction and RMS of the surface electromyography signals in the older age group compared to the younger age group (p = 0.029 and p = 0.045, respectively). There was no statistically significant association between age and muscle damage (χ2(2) = 2.86, p > 0.05). There was no correlation between average voluntary contraction and the degree of ultrastructural damage in both groups (Spearman's coefficient equaled 0.06923 and 0.64366, respectively). Conclusions: sEMG measurements are valuable for monitoring age-related functional changes in the orbicularis. Aging diminishes the functional capacity of the orbicularis, as evidenced by reduced contraction strength. This study, the first to compare ultrastructural and electromyographical changes in the orbicularis among dermatochalasis patients of different ages, finds that ultrastructural damage to muscle fibers is not directly responsible for the contraction strength decline.

Serum concentrations of different or multiple vitamins and Sarcopenia risk among US adults: insights from NHANES

BACKGROUND

The relationship between serum concentrations of different or multiple vitamins and sarcopenia remains underexplored. This investigation evaluates potential links between serum concentrations of different or multiple vitamins and sarcopenia prevalence among adults in the United States.

METHODS

Utilizing a cross-sectional design, this research draws from the National Health and Nutrition Examination Survey (NHANES) dataset of 2003-2006, encompassing 5,060 participants with comprehensive serum vitamin A, E, B9, B12, C, and D concentrations, alongside sarcopenia and covariate measurements. Participant stratification into distinct vitamin co-exposure clusters was achieved through K-means clustering. Analytical models, including weighted logistic regression, restricted cubic splines (RCS), weighted quantile sum regression (WQS), quantile g-computation (Q-gcomp), and Bayesian kernel machine regression (BKMR), were employed to evaluate the association between serum concentrations of different or multiple vitamins and sarcopenia risk, with an emphasis on nonlinearity.

RESULTS

In this study, sarcopenia was detected in 681 individuals (13.46%). Logistic regression results did not demonstrate any linear association between individual vitamin levels and sarcopenia risk (PFDR > 0.05). Contrastingly, the RCS model unveiled significant non-linear relationships for vitamins A and D (P_non-linear < 0.05). The K-means clustering results showed that participants in high-level vitamin exposure group had lower sarcopenia risk compared with those in low-level vitamin exposure group (OR (95% CI): 0.582 (0.397, 0.852)). Additionally, higher serum concentrations of different or multiple vitamins correlated inversely with sarcopenia risk (P_trend = 0.002). This inverse association was corroborated by WQS, Q-gcomp, and theBKMR models and remained consistent upon sensitivity analysis.

CONCLUSIONS

This study elucidates an inverse correlation between serum concentrations of different or multiple vitamins and sarcopenia risk, emphasizing a non-linear association, particularly with suboptimal vitamin D concentrations. Given the limitations of the NHANES study, further researches are required to clarify the existence of these relationships.

Mechanisms of muscle cells alterations and regeneration decline during aging

Skeletal muscles are essential for locomotion and body metabolism regulation. As muscles age, they lose strength, elasticity, and metabolic capability, leading to ineffective motion and metabolic derangement. Both cellular and extracellular alterations significantly influence muscle aging. Satellite cells (SCs), the primary muscle stem cells responsible for muscle regeneration, become exhausted, resulting in diminished population and functionality during aging. This decline in SC function impairs intercellular interactions as well as extracellular matrix production, further hindering muscle regeneration. Other muscle-resident cells, such as fibro-adipogenic progenitors (FAPs), pericytes, and immune cells, also deteriorate with age, reducing local growth factor activities and responsiveness to stress or injury. Systemic signaling, including hormonal changes, contributes to muscle cellular catabolism and disrupts muscle homeostasis. Collectively, these cellular and environmental components interact, disrupting muscle homeostasis and regeneration in advancing age. Understanding these complex interactions offers insights into potential regenerative strategies to mitigate age-related muscle degeneration.

Ratio of red blood cell distribution width to albumin level and risk of mortality in sarcopenic obesity

The aim of this study was to investigate the relationship between red blood cell distribution width and albumin ratio (RAR) levels and mortality in adult patients with sarcopenic obesity in the United States. The study included 1,361 adult patients with sarcopenic obesity from the National Health and Nutrition Examination Survey (1999-2006). The X-tile was used to determine the optimal subgroup thresholds for RAR values, and propensity score matching (PSM) was employed to reduce baseline bias. Cox regression analysis, Kaplan-Meier survival curves, and restricted cubic spline analysis were utilized to assess the relationship between RAR levels and all-cause and cardiovascular mortality. Subgroup analysis and the Subpopulation Treatment Effect Pattern Plot were employed to determine survival advantages across different subgroups. Time-dependent ROC analysis to evaluate the accuracy of RAR level in predicting survival outcomes at different time points. Post-PSM multifactorial Cox regression analyses revealed that RAR was a significant independent predictor of all-cause mortality (HR 1.487, 95% CI: 1.259-1.756) and an independent risk factor for cardiovascular mortality (HR 1.487, 95% CI: 1.260-1.758) in patients with sarcopenic obesity. The survival advantage was consistent across subgroups. Restricted cubic spline analysis indicated an approximate S-shaped association between RAR levels and mortality. Time-dependent ROC curves demonstrate that the areas under the all-cause mortality curves at the RAR level for 1-year, 3-year, 5-year, and 10-year are 0.79, 0.66, 0.64, and 0.63, respectively. The areas under the cardiovascular mortality curve are 0.80, 0.70, 0.66, and 0.61, respectively. Moreover, in comparison to the baseline model lacking covariates, the AUC values of the joint model exhibited heightened levels at various time points. Therefore, We demonstrated that the RAR level is an independent prognostic factor for mortality risk in the American population with sarcopenic obesity, and it is reasonable to consider the RAR level as a simple and effective risk prediction tool.

Androgen receptor regulates the differentiation of myoblasts under cyclic mechanical stretch and its upstream and downstream signals

Our previous studies have demonstrated the important roles of androgen receptor (AR) in myoblast proliferation regulated by 15 % (mimic appropriate exercise) and 20 % (mimic excessive exercise) mechanical stretches. Except for myoblast proliferation, differentiation is also an important factor affecting muscle mass and strength. But the role of AR in stretch-regulated myoblast differentiation and AR's upstream and downstream signals remain unknown. In the present study, firstly the differences of myogenic differentiation between C2C12 (with AR expression) and L6 (without AR expression) myoblasts induced by 15 % and 20 % mechanical stretches were compared; secondly, AR antagonist flutamide and AR agonist GTx-007 were used in 15 % and 20 % stretched myoblasts respectively to confirm AR's roles in stretch-regulated myoblast differentiation; thirdly, RNA-seq, molecular dynamic simulation (MD) and co-immunoprecipitation were performed to screen the downstream and upstream molecules of AR during stretches. We found that (1) 15 % stretch increased while 20 % stretch decreased myotube number in differentiating C2C12 and L6 myoblasts, with more significant changes in C2C12 cells than L6 cells; (2) in stretched C2C12 myoblasts, AR antagonist flutamide inhibited 15 % stretch-promoted differentiation while AR agonist GTx-007 reversed 20 % stretch-inhibited differentiation (reflected by changes in myotube number, MHC contents of fast-twitch and slow-twitch fiber, and the levels of myogenic regulatory factors (MRFs) such as MyoD and myogenin); (3) KEGG analysis of RNA-seq showed that the differently expressed genes (DEGs) in C2C12 cells induced by 15 % stretch were enriched in FoxO and JAK-STAT signaling pathways, while DEGs by 20 % stretch were enriched in FoxO and MAPK signaling pathways; (4) MD and co-immunoprecipitation showed that β1 integrin could interact with AR and influence AR's activity in C2C12 cells. In conclusion, AR plays important roles in myoblast differentiation promoted by 15 % stretch while inhibited by 20 % stretch, which was fulfilled through FoxO-MRFs. In addition, α7β1 integrin may be a bridge linking mechanical stretch and AR. This study is beneficial to deeply understand the roles and mechanisms of AR in stretch-regulated muscle mass and strength; and reports firstly that myoblasts sense mechanical stimulus and transmit into intracellular AR via α7β1 integrin.

Sarcopenia-related changes in serum GLP-1 level affect myogenic differentiation

BACKGROUND

Sarcopenia, a group of muscle-related disorders, leads to the gradual decline and weakening of skeletal muscle over time. Recognizing the pivotal role of gastrointestinal conditions in maintaining metabolic homeostasis within skeletal muscle, we hypothesize that the effectiveness of the myogenic programme is influenced by the levels of gastrointestinal hormones in the bloodstream, and this connection is associated with the onset of sarcopenia.

METHODS

We first categorized 145 individuals from the Emergency Room of Taipei Veterans General Hospital into sarcopenia and non-sarcopenia groups, following the criteria established by the Asian Working Group for Sarcopenia. A thorough examination of specific gastrointestinal hormone levels in plasma was conducted to identify the one most closely associated with sarcopenia. Techniques, including immunofluorescence, western blotting, glucose uptake assays, seahorse real-time cell metabolic analysis, flow cytometry analysis, kinesin-1 activity assays and qPCR analysis, were applied to investigate its impacts and mechanisms on myogenic differentiation.

RESULTS

Individuals in the sarcopenia group exhibited elevated plasma levels of glucagon-like peptide 1 (GLP-1) at 1021.5 ± 313.5 pg/mL, in contrast to non-sarcopenic individuals with levels at 351.1 ± 39.0 pg/mL (P < 0.05). Although it is typical for GLP-1 levels to rise post-meal and subsequently drop naturally, detecting higher GLP-1 levels in starving individuals with sarcopenia raised the possibility of GLP-1 influencing myogenic differentiation in skeletal muscle. Further investigation using a cell model revealed that GLP-1 (1, 10 and 100 ng/mL) dose-dependently suppressed the expression of the myogenic marker, impeding myocyte fusion and the formation of polarized myotubes during differentiation. GLP-1 significantly inhibited the activity of the microtubule motor kinesin-1, interfering with the translocation of glucose transporter 4 (GLUT4) to the cell membrane and the dispersion of mitochondria. These impairments subsequently led to a reduction in glucose uptake to 0.81 ± 0.04 fold (P < 0.01) and mitochondrial adenosine triphosphate (ATP) production from 25.24 ± 1.57 pmol/min to 18.83 ± 1.11 pmol/min (P < 0.05). Continuous exposure to GLP-1, even under insulin induction, attenuated the elevated glucose uptake.

CONCLUSIONS

The elevated GLP-1 levels observed in individuals with sarcopenia are associated with a reduction in myogenic differentiation. The impact of GLP-1 on both the membrane translocation of GLUT4 and the dispersion of mitochondria significantly hinders glucose uptake and the production of mitochondrial ATP necessary for the myogenic programme. These findings point us towards strategies to establish the muscle-gut axis, particularly in the context of sarcopenia. Additionally, these results present the potential of identifying relevant diagnostic biomarkers.

Liver-secreted FGF21 induces sarcopenia by inhibiting satellite cell myogenesis via klotho beta in decompensated cirrhosis

BACKGROUND & AIMS

Sarcopenia, a prevalent condition, significantly impacts the prognosis of patients with decompensated cirrhosis (DC). Serum fibroblast growth factor 21 (FGF21) levels are significantly higher in DC patients with sarcopenia. Satellite cells (SCs) play a role in aging- and cancer-induced sarcopenia. Here, we investigated the roles of FGF21 and SCs in DC-related sarcopenia as well as the underlying mechanisms.

METHODS

We developed two DC mouse models and performed in vivo and in vitro experiments. Klotho beta (KLB) knockout mice in SCs were constructed to investigate the role of KLB downstream of FGF21. In addition, biological samples were collected from patients with DC and control patients to validate the results.

RESULTS

Muscle wasting and impaired SC myogenesis were observed in the DC mouse model and patients with DC. Elevated circulating levels of liver-derived FGF21 were observed, which were significantly negatively correlated with skeletal muscle mass/skeletal muscle index. Liver-secreted FGF21 induces SC dysfunction, contributing to sarcopenia. Mechanistically, FGF21 in the DC state exhibits enhanced interactions with KLB on SC surfaces, leading to downstream phosphatase and tensin homolog upregulation. This inhibits the protein kinase B (PI3K/Akt) pathway, hampering SC proliferation and differentiation, and blocking new myotube formation to repair atrophy. Neutralizing circulating FGF21 using neutralizing antibodies, knockdown of hepatic FGF21 by adeno-associated virus, or knockout of KLB in SCs effectively improved or reversed DC-related sarcopenia.

CONCLUSIONS

Hepatocyte-derived FGF21 mediates liver-muscle crosstalk, which impairs muscle regeneration via the inhibition of the PI3K/Akt pathway, thereby demonstrating a novel therapeutic strategy for DC-related sarcopenia.

Effects and Mechanisms of Polyunsaturated Fatty Acids on Age-Related Musculoskeletal Diseases: Sarcopenia, Osteoporosis, and Osteoarthritis-A Narrative Review

Background: The process of the globally aging population has been accelerating, leading to an increasing social burden. As people age, the musculoskeletal system will gradually go through a series of degenerative and loss of function and eventually develop age-related musculoskeletal diseases, like sarcopenia, osteoporosis, and osteoarthritis. On the other hand, several studies have shown that polyunsaturated fatty acids (PUFAs) possess various important physiological functions on the health of muscles, bones, and joints. Objective: This narrative review paper provides a summary of the literature about the effects and mechanisms of PUFAs on age-related musculoskeletal diseases for the prevention and management of these diseases. Methods: Web of Science, PubMed, Science Direct, and Scopus databases have been searched to select the relevant literature on epidemiological, cellular, and animal experiments and clinical evidence in recent decades with keywords "polyunsaturated fatty acids", "PUFAs", "omega-3", "omega-6", "musculoskeletal diseases", "sarcopenia", "osteoporosis", "osteoarthritis", and so on. Results: PUFAs could prevent and treat age-related musculoskeletal diseases (sarcopenia, osteoporosis, and osteoarthritis) by reducing oxidative stress and inflammation and controlling the growth, differentiation, apoptosis, and autophagy of cells. This review paper provides comprehensive evidence of PUFAs on age-related musculoskeletal diseases, which will be helpful for exploitation into functional foods and drugs for their prevention and treatment. Conclusions: PUFAs could play an important role in the prevention and treatment of sarcopenia, osteoporosis, and osteoarthritis.

Age-related differences in the loss and recovery of serial sarcomere number following disuse atrophy in rats

BACKGROUND

Older adults exhibit a slower recovery of muscle mass following disuse atrophy than young adults. At a smaller scale, muscle fibre cross-sectional area (i.e., sarcomeres in parallel) exhibits this same pattern. Less is known, however, about age-related differences in the recovery of muscle fibre length, driven by increases in serial sarcomere number (SSN), following disuse. The purpose of this study was to investigate age-related differences in SSN adaptations and muscle mechanical function during and following muscle immobilization. We hypothesized that older adult rats would experience a similar magnitude of SSN loss during immobilization, however, take longer to recover SSN than young following cast removal, which would limit the recovery of muscle mechanical function.

METHODS

We casted the plantar flexors of young (8 months) and old (32 months) male rats in a shortened position for 2 weeks, and assessed recovery during 4 weeks of voluntary ambulation. Following sacrifice, legs were fixed in formalin for measurement of soleus SSN and physiological cross-sectional area (PCSA) with the un-casted soleus acting as a control. Ultrasonographic measurements of pennation angle (PA) and muscle thickness (MT) were conducted weekly. In-vivo active and passive torque-angle relationships were constructed pre-cast, post-cast, and following 4 weeks of recovery.

RESULTS

From pre- to post-cast, young and older adult rats experienced similar decreases in SSN (-20%, P < 0.001), muscle wet weight (-25%, P < 0.001), MT (-30%), PA (-15%, P < 0.001), and maximum isometric torque (-40%, P < 0.001), but there was a greater increase in passive torque in older (+ 180%, P < 0.001) compared to young adult rats (+ 68%, P = 0.006). Following cast removal, young exhibited quicker recovery of SSN and MT than old, but SSN recovered sooner than PA and MT in both young and old. PCSA nearly recovered and active torque fully recovered in young adult rats, whereas in older adult rats these remained unrecovered at ∼ 75%.

CONCLUSIONS

This study showed that older adult rats retain a better ability to recover longitudinal compared to parallel muscle morphology following cast removal, making SSN a highly adaptable target for improving muscle function in elderly populations early on during rehabilitation.

Sarcopenic obesity in older adults: a clinical overview

Sarcopenic obesity is characterized by a concurrent decline in muscle mass and function, along with increased adipose tissue. Sarcopenic obesity is a growing concern in older adults owing to significant health consequences, including implications for mortality, comorbidities and risk of developing geriatric syndromes. A 2022 consensus statement established a new definition and diagnostic criteria for sarcopenic obesity. The pathophysiology of this condition involves a complex interplay between muscle, adipose tissue, hormonal changes, inflammation, oxidative stress and lifestyle factors, among others. Sarcopenic obesity is treated with a range of management approaches, such as lifestyle interventions, exercise, nutrition and medical therapies. Emerging therapies that were developed for treating other conditions may be relevant to sarcopenic obesity, including novel pharmacological agents and personalized approaches such as precision medicine. In this Review, we synthesize the current knowledge of the clinical importance of sarcopenic obesity, its assessment and diagnosis, along with current and emerging management strategies.

Effect of whole-body vibration stimulation on plasma soluble TNF receptors in elderly with sarcopenia: a randomized controlled trial

Sarcopenia is a pathology resulting from a progressive and severe loss of muscle mass, strength, and function in the course of aging, which has deleterious consequences on quality of life. Among the most widespread studies on the issue are those focused on the effect of different types of physical exercise on patients with sarcopenia. This randomized controlled study aimed to compare the effects of a whole-body vibration exercise (WBV) session on the inflammatory parameters of non-sarcopenic (NSG, n=22) and sarcopenic elderly (SG, n=22). NSG and SG participants were randomly divided into two protocols: intervention (squat with WBV) and control (squat without WBV). After a one-week washout period, participants switched protocols, so that everyone performed both protocols. Body composition was assessed by dual-energy radiological absorptiometry (DXA) and function through the six-minute walk test (6MWD) and Short Physical Performance Battery (SPPB). Plasma soluble tumor necrosis factor receptors (sTNFR) were determined by enzyme-linked immunosorbent assay (ELISA) and measured before and immediately after each protocol. After exercise with WBV, there was an increase in sTNFR2 levels in the NSG (P<0.01; d=-0.69 (-1.30; -0.08) and SG (P<0.01, d=-0.95 (-1.57; -0.32) groups. In conclusion, an acute session of WBV influenced sTNFr2 levels, with sarcopenic individuals showing a greater effect. This suggested that WBV had a more pronounced impact on sTNFr2 in those with loss of muscle strength and/or physical performance. Additionally, WBV is gaining recognition as an efficient strategy for those with persistent health issues.

Deficiency of skeletal muscle Agrin contributes to the pathogenesis of age-related sarcopenia in mice

Sarcopenia, a progressive and prevalent neuromuscular disorder, is characterized by age-related muscle wasting and weakening. Despite its widespread occurrence, the molecular underpinnings of this disease remain poorly understood. Herein, we report that levels of Agrin, an extracellular matrix (ECM) protein critical for neuromuscular formation, were decreased with age in the skeletal muscles of mice. The conditional loss of Agrin in myogenic progenitors and satellite cells (SCs) (Pax7 Cre:: Agrin flox/flox) causes premature muscle aging, manifesting a distinct sarcopenic phenotype in mice. Conversely, the elevation of a miniaturized form of Agrin in skeletal muscle through adenovirus-mediated gene transfer induces enhanced muscle capacity in aged mice. Mechanistic investigations suggest that Agrin-mediated improvement in muscle function occurs through the stimulation of Yap signaling and the concurrent upregulation of dystroglycan expression. Collectively, our findings underscore the pivotal role of Agrin in the aging process of skeletal muscles and propose Agrin as a potential therapeutic target for addressing sarcopenia.

Mitochondrial involvement in sarcopenia

Sarcopenia lowers the quality-of-life for millions of people across the world, as accelerated loss of skeletal muscle mass and function contributes to both age- and disease-related frailty. Physical activity remains the only proven therapy for sarcopenia to date, but alternatives are much sought after to manage this progressive muscle disorder in individuals who are unable to exercise. Mitochondria have been widely implicated in the etiology of sarcopenia and are increasingly suggested as attractive therapeutic targets to help restore the perturbed balance between protein synthesis and breakdown that underpins skeletal muscle atrophy. Reviewing current literature, we note that mitochondrial bioenergetic changes in sarcopenia are generally interpreted as intrinsic dysfunction that renders muscle cells incapable of making sufficient ATP to fuel protein synthesis. Based on the reported mitochondrial effects of therapeutic interventions, however, we argue that the observed bioenergetic changes may instead reflect an adaptation to pathologically decreased energy expenditure in sarcopenic muscle. Discrimination between these mechanistic possibilities will be crucial for improving the management of sarcopenia.

The Current Landscape of Pharmacotherapies for Sarcopenia

Sarcopenia is a skeletal muscle disorder characterized by progressive and generalized decline in muscle mass and function. Although it is mostly known as an age-related disorder, it can also occur secondary to systemic diseases such as malignancy or organ failure. It has demonstrated a significant relationship with adverse outcomes, e.g., falls, disabilities, and even mortality. Several breakthroughs have been made to find a pharmaceutical therapy for sarcopenia over the years, and some have come up with promising findings. Yet still no drug has been approved for its treatment. The key factor that makes finding an effective pharmacotherapy so challenging is the general paradigm of standalone/single diseases, traditionally adopted in medicine. Today, it is well known that sarcopenia is a complex disorder caused by multiple factors, e.g., imbalance in protein turnover, satellite cell and mitochondrial dysfunction, hormonal changes, low-grade inflammation, senescence, anorexia of aging, and behavioral factors such as low physical activity. Therefore, pharmaceuticals, either alone or combined, that exhibit multiple actions on these factors simultaneously will likely be the drug of choice to manage sarcopenia. Among various drug options explored throughout the years, testosterone still has the most cumulated evidence regarding its effects on muscle health and its safety. A mas receptor agonist, BIO101, stands out as a recent promising pharmaceutical. In addition to the conventional strategies (i.e., nutritional support and physical exercise), therapeutics with multiple targets of action or combination of multiple therapeutics with different targets/modes of action appear to promise greater benefit for the prevention and treatment of sarcopenia.

Regulation of Satellite Cells Functions during Skeletal Muscle Regeneration: A Critical Step in Physiological and Pathological Conditions

Skeletal muscle regeneration is a complex process involving the generation of new myofibers after trauma, competitive physical activity, or disease. In this context, adult skeletal muscle stem cells, also known as satellite cells (SCs), play a crucial role in regulating muscle tissue homeostasis and activating regeneration. Alterations in their number or function have been associated with various pathological conditions. The main factors involved in the dysregulation of SCs' activity are inflammation, oxidative stress, and fibrosis. This review critically summarizes the current knowledge on the role of SCs in skeletal muscle regeneration. It examines the changes in the activity of SCs in three of the most common and severe muscle disorders: sarcopenia, muscular dystrophy, and cancer cachexia. Understanding the molecular mechanisms involved in their dysregulations is essential for improving current treatments, such as exercise, and developing personalized approaches to reactivate SCs.

Sarcopenia and Mortality in Critically Ill COVID-19 Patients

COVID-19 can manifest as either asymptomatic or progressing to a severe phase in some patients, which may require hospitalization. These patients may experience dyspnea and hypoxia, leading to the development of acute respiratory distress syndrome. Studies have reported an increased risk of severe sarcopenia in COVID-19 patients during and after recovery. This narrative review aimed to summarize and synthesize available studies on the association between sarcopenia and mortality in critically ill COVID-19 patients. A total of 22 studies conducted on hospitalized COVID-19 patients were included in this review. Of those, 17 studies reported a direct association, while 5 studies showed no association between sarcopenia and mortality in severe COVID-19 patients. It is important to maintain muscle quality and quantity in defense against COVID-19. The measurement of lean muscle mass should be included in the risk assessment of severely ill COVID-19 patients as part of the therapy plan.

Age Is Just a Number: Progress and Obstacles in the Discovery of New Candidate Drugs for Sarcopenia

Sarcopenia is a disease characterized by the progressive loss of skeletal muscle mass and function that occurs with aging. The progression of sarcopenia is correlated with the onset of physical disability, the inability to live independently, and increased mortality. Due to global increases in lifespan and demographic aging in developed countries, sarcopenia has become a major socioeconomic burden. Clinical therapies for sarcopenia are based on physical therapy and nutritional support, although these may suffer from low adherence and variable outcomes. There are currently no clinically approved drugs for sarcopenia. Consequently, there is a large amount of pre-clinical research focusing on discovering new candidate drugs and novel targets. In this review, recent progress in this research will be discussed, along with the challenges that may preclude successful translational research in the clinic. The types of drugs examined include mitochondria-targeting compounds, anti-diabetes agents, small molecules that target non-coding RNAs, protein therapeutics, natural products, and repositioning candidates. In light of the large number of drugs and targets being reported, it can be envisioned that clinically approved pharmaceuticals to prevent the progression or even mitigate sarcopenia may be within reach.

Metallosis after Hip Arthroplasty Damages Skeletal Muscle: A Case Report

Good musculoskeletal quality dramatically influences the outcome of an arthroplasty operation in geriatric patients, as well as is a key element for optimal osseointegration. In this context, metallosis is a complication associated with the type of prosthesis used, as implants with a chromium-cobalt interface are known to alter the bone microarchitecture and reduce the ratio of muscle to fat, resulting in lipid accumulation. Therefore, the aim of our study was to investigate possible muscle changes by histological, morphometric, and immunohistochemical analyses in a patient undergoing hip replacement revision with elevated blood and urinary concentrations of chromium and cobalt. Interestingly, the muscle tissue showed significant structural changes and a massive infiltration of adipose tissue between muscle fibers in association with an altered expression pattern of important biomarkers of musculoskeletal health and oxidative stress, such as myostatin and NADPH Oxidase 4. Overall, our results confirm the very serious impact of metallosis on musculoskeletal health, suggesting the need for further studies to adopt a diagnostic approach to identify the cause of metallosis early and eliminate it as part of the prosthesis revision surgery.

BTG2 acts as an inducer of muscle stem cell senescence

BACKGROUND

Muscle aging is associated with muscle stem cell (MuSC) senescence, a process of whose DNA damage accumulation is considered as one of the leading causes. BTG2 had been identified as a mediator of genotoxic and cellular stress signaling pathways, however, its role in senescence of stem cells, including MuSC, remains unknown.

METHOD

We first compared MuSCs isolated from young and old mice to evaluate our in vitro model of natural senescence. CCK8 and EdU assays were utilized to assess the proliferation capacity of the MuSCs. Cellular senescence was further assessed at biochemical levels by SA-β-Gal and γHA2.X staining, and at molecular levels by quantifying the expression of senescence-associated genes. Next, by performing genetic analysis, we identified Btg2 as a potential regulator of MuSC senescence, which was experimentally validated by Btg2 overexpression and knockdown in primary MuSCs. Lastly, we extended our research to humans by analyzing the potential links between BTG2 and muscle function decline in aging.

RESULTS

BTG2 is highly expressed in MuSCs from elder mice showing senescent phenotypes. Overexpression and knockdown of Btg2 stimulates and prevents MuSCs senescence, respectively. In humans, high level of BTG2 is associated with low muscle mass in aging, and is a risk factor of aging-related diseases, such as diabetic retinopathy and HDL cholesterol.

CONCLUSION

Our work demonstrates BTG2 as a regulator of MuSC senescence and may serve as an intervention target for muscle aging.

Chemokine/ITGA4 Interaction Directs iPSC-Derived Myogenic Progenitor Migration to Injury Sites in Aging Muscle for Regeneration

The failure of muscle to repair after injury during aging may be a major contributor to muscle mass loss. We recently generated muscle progenitor cells (MPCs) from human-induced pluripotent stem-cell (iPSC) cell lines using small molecules, CHIR99021 and Givinostat (Givi-MPCs) sequentially. Here, we test whether the chemokines overexpressed in injured endothelial cells direct MPC migration to the site by binding to their receptor, ITGA4. ITGA4 was heavily expressed in Givi-MPCs. To study the effects on the mobilization of Givi-MPCs, ITGA4 was knocked down by an ITGA4 shRNA lentiviral vector. With and without ITGA4 knocked down, cell migration in vitro and cell mobilization in vivo using aged NOD scid gamma (NSG) mice and mdx/scid mice were analyzed. The migration of shITGA4-Givi-MPCs was significantly impaired, as shown in a wound-healing assay. The knockdown of ITGA4 impaired the migration of Givi-MPCs towards human aortic endothelial cells (HAECs), in which CX3CL1 and VCAM-1 were up-regulated by the treatment of TNF-α compared with scramble ones using a transwell system. MPCs expressing ITGA4 sensed chemokines secreted by endothelial cells at the injury site as a chemoattracting signal to migrate to the injured muscle. The mobilization of Givi-MPCs was mediated by the ligand-receptor interaction, which facilitated their engraftment for repairing the sarcopenic muscle with injury.

Relationship of Serum 25-Hydroxyvitamin D Levels With Sarcopenia and Body Composition in Community-Dwelling Older Adults: A Paired Case-Control Study

OBJECTIVE

Sarcopenia is a leading health problem among older adults. However, few studies have explored the relationship between serum 25-hydroxyvitamin D [25(OH)D] levels, sarcopenia, and body composition in older Chinese individuals. The aim of this study was to investigate the relationship of serum 25(OH)D levels with sarcopenia, sarcopenia indices, and body composition in community-dwelling older Chinese adults.

DESIGN

Paired case-control study.

SETTING AND PARTICIPANTS

This case-control study enrolled 66 older adults newly diagnosed with sarcopenia (sarcopenia group) and 66 older adults without sarcopenia (non-sarcopenia group) after screening in the community.

METHODS

The definition of sarcopenia was based on the Asian Working Group for Sarcopenia 2019 criteria. Serum levels of 25(OH)D were measured using an enzyme-linked immunosorbent assay. Conditional logistic regression analysis was performed to estimate odds ratios (ORs) and 95% CIs. Spearman's correlation was used to examine the correlations among sarcopenia indices, body composition, and serum 25(OH)D.

RESULTS

Serum 25(OH)D levels were significantly lower in the sarcopenia group (29.08 ± 15.11 ng/mL) than in the non-sarcopenia group (36.28 ± 14.68 ng/mL) (P < .05). Vitamin D deficiency was associated with an increased risk of sarcopenia (OR, 7.749; 95% CI, 1.955-30.714). Serum 25(OH)D levels in men were positively correlated with skeletal muscle mass index (SMI) (r = 0.450; P < .001) and negatively correlated with gait speed (r = -0.282; P = .032). Serum 25(OH)D levels in women were positively correlated with SMI (r = 0.286; P < .001), skeletal muscle mass (r = 0.395; P < .001), and fat-free mass (r = 0.412; P < .001).

CONCLUSIONS AND IMPLICATIONS

Serum 25(OH)D levels were lower in older adults with sarcopenia than those in adults without sarcopenia. Vitamin D deficiency was associated with increased risk of sarcopenia, and serum 25(OH)D levels were positively correlated with SMI.

A Comprehensive Review of Pathological Mechanisms and Natural Dietary Ingredients for the Management and Prevention of Sarcopenia

Sarcopenia is characterized by an age-related loss of skeletal muscle mass and function and has been recognized as a clinical disease by the World Health Organization since 2016. Substantial evidence has suggested that dietary modification can be a feasible tool to combat sarcopenia. Among various natural dietary ingredients, the present study focused on botanical and marine extracts, phytochemicals, and probiotics. Aims of this review were (1) to provide basic concepts including the definition, diagnosis, prevalence, and adverse effects of sarcopenia, (2) to describe possible pathological mechanisms including protein homeostasis imbalance, inflammation, mitochondrial dysfunction, and satellite cells dysfunction, and (3) to analyze recent experimental studies reporting potential biological functions against sarcopenia. A recent literature review for dietary ingredients demonstrated that protein homeostasis is maintained via an increase in the PI3K/Akt pathway and/or a decrease in the ubiquitin-proteasome system. Regulation of inflammation has primarily targeted inhibition of NF-κB signaling. Elevated Pgc-1α or Pax7 expression reverses mitochondrial or satellite cell dysfunction. This review provides the current knowledge on dietary components with the potential to assist sarcopenia prevention and/or treatment. Further in-depth studies are required to elucidate the role of and develop various dietary materials for healthier aging, particularly concerning muscle health.

Sarcopenic Obesity: Involvement of Oxidative Stress and Beneficial Role of Antioxidant Flavonoids

Sarcopenic obesity, which refers to concurrent sarcopenia and obesity, is characterized by decreased muscle mass, strength, and performance along with abnormally excessive fat mass. Sarcopenic obesity has received considerable attention as a major health threat in older people. However, it has recently become a health problem in the general population. Sarcopenic obesity is a major risk factor for metabolic syndrome and other complications such as osteoarthritis, osteoporosis, liver disease, lung disease, renal disease, mental disease and functional disability. The pathogenesis of sarcopenic obesity is multifactorial and complicated, and it is caused by insulin resistance, inflammation, hormonal changes, decreased physical activity, poor diet and aging. Oxidative stress is a core mechanism underlying sarcopenic obesity. Some evidence indicates a protective role of antioxidant flavonoids in sarcopenic obesity, although the precise mechanisms remain unclear. This review summarizes the general characteristics and pathophysiology of sarcopenic obesity and focuses on the role of oxidative stress in sarcopenic obesity. The potential benefits of flavonoids in sarcopenic obesity have also been discussed.

Interplay of skeletal muscle and adipose tissue: sarcopenic obesity

Sarcopenic obesity is becoming a global health concern, owing to the rising older population, causing cardiometabolic morbidity and mortality. Loss of muscle exceeding normal age-related changes has been revealed to be associated with obesity, aggravating each other through complex interactions. Physiological regeneration and proliferation of muscle tissue are achieved through harmonious processes of regulated inflammation, autophagy, muscle satellite cell proliferation, and signaling molecule function. Adipokines and myokines are signaling molecules from adipose tissue and muscle, respectively, that exert autocrine, paracrine, and endocrine effects on fat and muscle tissues. These signaling molecules interact with each other to regulate metabolic homeostasis. However, excessive adiposity creates pro-inflammatory conditions, leading to metabolic disorders and the disorganization of systemic homeostasis. Therefore, obesity impedes muscle tissue regeneration and induces the loss of muscle mass and function. Numerous studies have attempted to demonstrate the pathophysiological interaction between sarcopenia and obesity, but the interwoven matrix of the relationship between myokines and adipokines has made it difficult for researchers to understand them. This review briefly describes updated information about the crosstalk between muscle and adipose tissue.

Fiber-Type Shifting in Sarcopenia of Old Age: Proteomic Profiling of the Contractile Apparatus of Skeletal Muscles

The progressive loss of skeletal muscle mass and concomitant reduction in contractile strength plays a central role in frailty syndrome. Age-related neuronal impairments are closely associated with sarcopenia in the elderly, which is characterized by severe muscular atrophy that can considerably lessen the overall quality of life at old age. Mass-spectrometry-based proteomic surveys of senescent human skeletal muscles, as well as animal models of sarcopenia, have decisively improved our understanding of the molecular and cellular consequences of muscular atrophy and associated fiber-type shifting during aging. This review outlines the mass spectrometric identification of proteome-wide changes in atrophying skeletal muscles, with a focus on contractile proteins as potential markers of changes in fiber-type distribution patterns. The observed trend of fast-to-slow transitions in individual human skeletal muscles during the aging process is most likely linked to a preferential susceptibility of fast-twitching muscle fibers to muscular atrophy. Studies with senescent animal models, including mostly aged rodent skeletal muscles, have confirmed fiber-type shifting. The proteomic analysis of fast versus slow isoforms of key contractile proteins, such as myosin heavy chains, myosin light chains, actins, troponins and tropomyosins, suggests them as suitable bioanalytical tools of fiber-type transitions during aging.

Mechanisms of RNA and Protein Quality Control and Their Roles in Cellular Senescence and Age-Related Diseases

Cellular senescence, a hallmark of aging, is defined as irreversible cell cycle arrest in response to various stimuli. It plays both beneficial and detrimental roles in cellular homeostasis and diseases. Quality control (QC) is important for the proper maintenance of cellular homeostasis. The QC machineries regulate the integrity of RNA and protein by repairing or degrading them, and are dysregulated during cellular senescence. QC dysfunction also contributes to multiple age-related diseases, including cancers and neurodegenerative, muscle, and cardiovascular diseases. In this review, we describe the characters of cellular senescence, discuss the major mechanisms of RNA and protein QC in cellular senescence and aging, and comprehensively describe the involvement of these QC machineries in age-related diseases. There are many open questions regarding RNA and protein QC in cellular senescence and aging. We believe that a better understanding of these topics could propel the development of new strategies for addressing age-related diseases.