Muscle type and fiber type specificity in muscle wasting

Glycine and N-Acetylcysteine (GlyNAC) Combined with Body Weight Support Treadmill Training Improved Spinal Cord and Skeletal Muscle Structure and Function in Rats with Spinal Cord Injury

Skeletal muscle atrophy is a frequent complication after spinal cord injury (SCI) and can influence the recovery of motor function and metabolism in affected patients. Delaying skeletal muscle atrophy can promote functional recovery in SCI rats. In the present study, we investigated whether a combination of body weight support treadmill training (BWSTT) and glycine and N-acetylcysteine (GlyNAC) could exert neuroprotective effects, promote motor function recovery, and delay skeletal muscle atrophy in rats with SCI, and we assessed the therapeutic effects of the double intervention from both a structural and functional viewpoint. We found that, after SCI, rats given GlyNAC alone showed an improvement in Basso-Beattie-Bresnahan (BBB) scores, gait symmetry, and results in the open field test, indicative of improved motor function, while GlyNAC combined with BWSTT was more effective than either treatment alone at ameliorating voluntary motor function in injured rats. Meanwhile, the results of the skeletal muscle myofiber cross-sectional area (CSA), hindlimb grip strength, and acetylcholinesterase (AChE) immunostaining analysis demonstrated that GlyNAC improved the structure and function of the skeletal muscle in rats with SCI and delayed the atrophication of skeletal muscle.

Tongue Strength of Older Adults Requiring Long-Term Care Varies throughout the Day

Physical performance shows approximately 30% diurnal variation; however, diurnal variation in oral function remains unclear. This study aimed to determine the diurnal variation in oral and swallowing function in older adults requiring long-term care. The participants included 13 adults aged >60 years (3 men and 10 women, mean age: 77.2 ± 6.3 years, age range: 62-90 years) requiring long-term care. Tongue strength (TS) and oral mucosal moisture were measured as indices of oral and swallowing function, while hand grip strength was measured as an index of general muscle strength. The patients were asked to participate in a "test" after breakfast, lunch, and dinner on the same day. Multilevel linear regression analysis was used to examine diurnal differences in each item. Multilevel linear regression analysis with adjustment for age and sex revealed that TS was significantly higher at noon (p = 0.001) than in the morning. Therefore, caregivers who provide support during meals to older people requiring long-term care should consider the possibility of swallowing function differing according to the time of the day. In conclusion, it may be beneficial to establish a nutritional therapy that accounts for the diurnal variation in TS.

Sex Differences in the Efficacy of Mediterranean Diet Treatment: A Nutrigenomics Pilot Study

The Mediterranean diet (MedD) has been shown to have beneficial effects on health, well-being, and mental status. It potentially modulates gene expressions linked to oxidative stress, contributing to its beneficial effects on overall health. The aim of this study was to assess the effects of MedD treatment in healthy human volunteers on the expression of ten genes related to oxidative stress and inflammation in women and men. Of 30 enrolled subjects, 17 were eligible, 10 women and 7 men. All of them received the same MedD treatment. Before and after 8 weeks of MedD treatment, an evaluation of body composition, blood tests, and anthropometric and clinical parameters was performed. Furthermore, 10 genes were amplified and analyzed. The study showed significant differences between females and males in body composition and biochemical parameters before and after MedD treatment. Significant differences between females and males in Resistance Force (p < 0.009) and Diastolic Blood Pressure (p < 0.04) before MedD treatment, and in High-Density Lipoprotein (p < 0.02) after MedD treatment, were observed. Moreover, a significant upregulation of Apolipoprotein E and Angiotensin I-Converting Enzyme in females has been shown. Sex differences impact MedD treatment response, and influence the genetic expression of genes related to oxidative stress; our findings may help to personalize diet therapy and contribute to overall health and well-being.

The Functional and Anatomical Impacts of Healthy Muscle Ageing

Even "healthy" muscle ageing is often associated with substantial changes in muscle form and function and can lead to increased injury risks and significant negative impacts on quality of life. However, the impacts of healthy muscle ageing on the fibre architecture and microstructure of different muscles and muscle groups throughout the lower limb, and how these are related to their functional capabilities, are not fully understood. Here, a previously established framework of magnetic resonance and diffusion tensor imaging was used to measure the muscle volumes, intramuscular fat, fibre lengths and physiological cross-sectional areas of 12 lower limb muscles in a cohort of healthily aged individuals, which were compared to the same data from a young population. Maximum muscle forces were also measured from an isokinetic dynamometer. The more substantial interpopulation differences in architecture and functional performance were located within the knee extensor muscles, while the aged muscles were also more heterogeneous in muscle fibre type and atrophy. The relationships between architecture and muscle strength were also more significant in the knee extensors compared to other functional groups. These data highlight the importance of the knee extensors as a potential focus for interventions to negate the impacts of muscle ageing.

Skeletal muscle fibre morphology in childhood-insights into myopenia in pediatric liver disease

TAKE-HOME MESSAGE

Skeletal muscle morphology in healthy children changes with age. Liver disease may preferentially affect type II fibres in adults with end-stage liver disease (ESLD). More research is needed on the effects of ESLD on muscle morphology in children.

Generating fast-twitch myotubes in vitro with an optogenetic-based, quantitative contractility assay

The composition of fiber types within skeletal muscle impacts the tissue's physiological characteristics and susceptibility to disease and ageing. In vitro systems should therefore account for fiber-type composition when modelling muscle conditions. To induce fiber specification in vitro, we designed a quantitative contractility assay based on optogenetics and particle image velocimetry. We submitted cultured myotubes to long-term intermittent light-stimulation patterns and characterized their structural and functional adaptations. After several days of in vitro exercise, myotubes contract faster and are more resistant to fatigue. The enhanced contractile functionality was accompanied by advanced maturation such as increased width and up-regulation of neuron receptor genes. We observed an up-regulation in the expression of fast myosin heavy-chain isoforms, which induced a shift towards a fast-twitch phenotype. This long-term in vitro exercise strategy can be used to study fiber specification and refine muscle disease modelling.

Effects of Moderate Exercise Training on Cancer-Induced Muscle Wasting

BACKGROUND

Muscle wasting is a common phenomenon in oncology and seems to be attenuated by exercise training. The aim of this study is to determine the degree of aggressiveness of cancer-induced muscle wasting in two different phenotypic muscles. It will also determine whether exercise training can attenuate this muscle dysfunction.

METHODS

Fifty Sprague Dawley rats were randomly assigned to four experimental groups: two breast cancer model groups (sedentary and exercise) and two control groups (sedentary and exercise). Breast cancer was induced by 1-methyl-1-nitrosoureia (MNU). After 35 weeks of endurance training, animals were sacrificed, and gastrocnemius and soleus muscles harvested for morphometric analysis.

RESULTS

In sedentary tumor-bearing animals, a significant reduction in cross-sectional area was found in both muscles (p < 0.05). Interstitial fibrosis was significantly higher in the gastrocnemius muscle of the sedentary tumor-bearing animals (p < 0.05), but not in the soleus muscle. In the gastrocnemius of sedentary tumor-bearing animals, a shift from large to small fibers was observed. This cancer-related muscle dysfunction was prevented by long-term exercise training.

CONCLUSIONS

In sedentary animals with tumors, the gastrocnemius muscle showed a very pronounced reduction in cross-sectional area and a marked degree of interstitial fibrosis. There was no difference in collagen deposition between tumor groups, and the soleus muscle showed a less pronounced but significant reduction in cross-sectional area. These contrasting results confirm that cancer-induced muscle wasting can affect specific types of fibers and specific muscles, namely fast glycolytic muscles, and that exercise training can be used to improve it.

Lack of Musashi-2 induces type IIa fiber-dominated muscle atrophy

Skeletal muscle is a highly plastic tissue, adapting its structure and metabolism in response to diverse conditions such as contractile activity, nutrients, and diseases. Finding a novel master regulator of muscle mass and quality will provide new therapeutic targets for the prevention and treatment of muscle weakness. Musashi is an RNA-binding protein that dynamically regulates protein expression; it was originally discovered as a cell fate determination factor in neural cells. Here, we report that Musashi-2 (Msi2) is dominantly expressed in slow-type muscle fibers, fibers characterized by high metabolism and endurance. Msi2 knockout (KO) mice exhibited a decrease in both soleus myofiber size and number compared to control mice. Biochemical and histological analyses revealed that type IIa fibers, which are of the fast type but have high metabolic capacity, were decreased in Msi2 KO mice. The contraction force of isolated soleus muscle was lower in KO mice, and the expression of the metabolic proteins, cytochrome c oxidase and myoglobin, was also decreased in KO muscle. Our data demonstrate the critical role of Msi2 in the maintenance of normal fiber-type composition and metabolism.

MicroRNA-140 is not involved in sepsis-induced muscle atrophy

Sepsis is a life-threatening inflammatory response to infection, often accompanied by skeletal muscle atrophy. A previous study demonstrated that the administration of microRNA-140 (miR-140) attenuated lipopolysaccharide (LPS)-induced muscle atrophy, whereas miR-140 knockdown with siRNA promoted atrophy. Therefore, we investigated whether miR-140 is involved in LPS-induced muscle atrophy using a genetic model, miR-140-/- mice. We found that a single injection of LPS induced atrophy both in slow-twitch and fast-twitch muscles. The muscle weights and fiber cross-sectional areas were significantly reduced in both the wild-type (WT) and miR-140-/- mice, with no difference between genotypes. The expression of several proteolysis markers, muscle-specific RING-finger 1 (MuRF1) and MAFbx/atrogin-1, increased in both groups after LPS injection. The ubiquitinated proteins in the miR-140-/- mice were similar to those in the WT mice. Therefore, the deletion of miR-140 did not affect LPS-induced muscle atrophy.NEW & NOTEWORTHY We used miR-140-/- mice to determine the function of miR-140 in LPS-induced skeletal muscle atrophy. To our knowledge, this study is the first to examine slow-twitch muscles in LPS-induced muscle wasting after miR-140 manipulation.

Slow or fast: Implications of myofibre type and associated differences for manifestation of neuromuscular disorders

Many neuromuscular disorders can have a differential impact on a specific myofibre type, forming the central premise of this review. The many different skeletal muscles in mammals contain a spectrum of slow- to fast-twitch myofibres with varying levels of protein isoforms that determine their distinctive contractile, metabolic, and other properties. The variations in functional properties across the range of classic 'slow' to 'fast' myofibres are outlined, combined with exemplars of the predominantly slow-twitch soleus and fast-twitch extensor digitorum longus muscles, species comparisons, and techniques used to study these properties. Other intrinsic and extrinsic differences are discussed in the context of slow and fast myofibres. These include inherent susceptibility to damage, myonecrosis, and regeneration, plus extrinsic nerves, extracellular matrix, and vasculature, examined in the context of growth, ageing, metabolic syndrome, and sexual dimorphism. These many differences emphasise the importance of carefully considering the influence of myofibre-type composition on manifestation of various neuromuscular disorders across the lifespan for both sexes. Equally, understanding the different responses of slow and fast myofibres due to intrinsic and extrinsic factors can provide deep insight into the precise molecular mechanisms that initiate and exacerbate various neuromuscular disorders. This focus on the influence of different myofibre types is of fundamental importance to enhance translation for clinical management and therapies for many skeletal muscle disorders.

Repurposing Drugs for Diabetes Mellitus as Potential Pharmacological Treatments for Sarcopenia - A Narrative Review

Sarcopenia, the age-related loss of muscle strength and mass or quality, is a common condition with major adverse consequences. Although the pathophysiology is incompletely understood, there are common mechanisms between sarcopenia and the phenomenon of accelerated ageing seen in diabetes mellitus. Drugs currently used to treat type 2 diabetes mellitus may have mechanisms of action that are relevant to the prevention and treatment of sarcopenia, for those with type 2 diabetes and those without diabetes. This review summarises shared pathophysiology between sarcopenia and diabetes mellitus, including the effects of advanced glycation end products, mitochondrial dysfunction, chronic inflammation and changes to the insulin signalling pathway. Cellular and animal models have generated intriguing, albeit mixed, evidence that supports possible beneficial effects on skeletal muscle function for some classes of drugs used to treat diabetes, including metformin and SGLT2 inhibitors. Most human observational and intervention evidence for the effects of these drugs has been derived from populations with type 2 diabetes mellitus, and there is a need for intervention studies for older people with, and at risk of, sarcopenia to further investigate the balance of benefit and risk in these target populations. Not all diabetes treatments will be safe to use in those without diabetes because of variable side effects across classes. However, some agents [including glucagon-like peptide (GLP)-1 receptor agonists and SGLT2 inhibitors] have already demonstrated benefits in populations without diabetes, and it is these agents, along with metformin, that hold out the most promise for further investigation in sarcopenia.

The life and times of cellular senescence in skeletal muscle: friend or foe for homeostasis and adaptation?

A gradual decline in skeletal muscle mass and function is closely tied to increased mortality and disease risk during organismal aging. Exercise training is the most effective way to enhance muscle health, but the adaptive response to exercise as well as muscle repair potential is blunted in older individuals. Numerous mechanisms contribute to the loss of muscle mass and plasticity as aging progresses. An emerging body of recent evidence implicates an accumulation of senescent ("zombie") cells in muscle as a contributing factor to the aging phenotype. Senescent cells cannot divide but can release inflammatory factors and create an unfavorable environment for homeostasis and adaptation. On balance, some evidence indicates that cells with senescent characteristics can be beneficial for the muscle adaptive process, specifically at younger ages. Emerging evidence also suggests that multinuclear muscle fibers could become senescent. In this review, we summarize current literature on the prevalence of senescent cells in skeletal muscle and highlight the consequences of senescent cell removal on muscle mass, function, and adaptability. We examine key limitations in the field of senescence specifically in skeletal muscle and identify areas of research that require future investigation.NEW & NOTEWORTHY There is evidence to suggest that senescent "zombie" cells may or may not accrue in aging skeletal muscle. When muscle is perturbed regardless of age, senescent-like cells do appear, and the benefits of removing them could be age-dependent. More work is needed to determine the magnitude of accumulation and source of senescent cells in muscle. Regardless, pharmacological senolytic treatment of aged muscle is beneficial for adaptation.

Exploring the correlation between serum fibroblast growth factor-21 levels and Sarcopenia: a systematic review and meta-analysis

BACKGROUND

Fibroblast growth factor 21 (FGF-21) plays an important role in the growth and metabolism of skeletal muscle cells. This study aims to systemically review the evidence regarding the relationship between FGF-21 levels and Sarcopenia, as well as the related influential factors.

METHODS

This review was conducted according to the PRISMA guidelines. We comprehensively searched PubMed, EMBASE, the Web of Science, Scopus, and Chinese Databases (CNKI, Wan Fang, VIP, and CBM) up to 1 May 2023. 3 investigators performed independent literature screening and data extraction of the included literature, and two investigators performed an independent quality assessment of case-control studies using the Joanna Briggs Institute (JBI) tool. Data analysis was performed using Review Manager 5.4 software. For continuous various outcomes, mean difference (MD) or standard mean difference (SMD) with 95% confidence intervals (CIs) was applied for assessment by fixed-effect or random-effect model analysis. The heterogeneity test was performed by the Q-statistic and quantified using I², and publication bias was evaluated using a funnel plot.

RESULTS

Five studies with a total of 625 cases were included in the review. Meta-analysis showed lower BMI in the sarcopenia group [MD= -2.88 (95% CI, -3. 49, -2.27); P < 0.00001; I² = 0%], significantly reduced grip strength in the sarcopenia group compared to the non-sarcopenia group [MD = -7.32(95% CI, -10.42,-4.23); P < 0.00001; I² = 93%]. No statistically significant differences in serum FGF21 levels were found when comparing the two groups of subjects [SMD = 0.31(95% CI, -0.42, 1.04); P = 0.41; I² = 94%], and no strong correlation was found between the onset of sarcopenia and serum FGF21 levels.

CONCLUSION

The diagnosis of sarcopenia is followed by a more significant decrease in muscle mass and strength, but there is a lack of strong evidence to support a direct relationship between elevated organismal FGF21 and sarcopenia, and it is not convincing to use FGF21 as a biological or diagnostic marker for sarcopenia. The currently used diagnostic criteria for sarcopenia and setting of cut-off values for each evaluation parameter no longer seem to match clinical practice.

Decreased expression of H19/miR-675 ameliorates muscle atrophy by regulating the IGF1R/Akt/FoxO signaling pathway

BACKGROUND

Long non-coding RNA (lncRNA) H19 is one of the most highly expressed and conserved transcripts in mammalian development, and its functions have been fully discussed in many contexts including tumorigenesis and skeletal muscle development. However, its exact role in muscle atrophy remains largely unknown. This study investigated the effect of lncRNA H19 on muscle atrophy and the potential underlying mechanism.

METHODS

Hindlimb suspension (HS) of C57BL/6 mice and starvation of C2C12 cells with PBS were conducted to induce atrophy. Real-time PCR and Western blotting were used to measure the expression of RNAs and proteins. LncRNA H19 and its encoded miR-675 were overexpressed or inhibited in different models of muscle atrophy. Immunofluorescence was carried out to examine the cross-sectional area (CSA) and minimal Feret's diameter (MFD) of myofibers and myotube diameter.

RESULTS

The expression levels of lncRNA H19 and miR-675 were significantly reduced in both the soleus and gastrocnemius muscles in response to HS. Overexpression of lncRNA H19 led to an increase in Atrogin-1 mRNA expression, and this effect was reversed by inhibiting miR-675. The overexpression of miR-675 aggravated both HS- and starving-induced muscle atrophy by inhibiting the IGF1R/Akt signaling pathway and promoting FoxO/Atrogin-1 expression. Conversely, miR-675 inhibition had the opposite effects.

CONCLUSION

The lncRNA H19/miR-675 axis can induce muscle atrophy, and its downregulation in mice with HS-induced muscle atrophy may act as a protective mechanism against this condition.

Cholic and deoxycholic acids induce mitochondrial dysfunction, impaired biogenesis and autophagic flux in skeletal muscle cells

BACKGROUND

Skeletal muscle is sensitive to bile acids (BA) because it expresses the TGR5 receptor for BA. Cholic (CA) and deoxycholic (DCA) acids induce a sarcopenia-like phenotype through TGR5-dependent mechanisms. Besides, a mouse model of cholestasis-induced sarcopenia was characterised by increased levels of serum BA and muscle weakness, alterations that are dependent on TGR5 expression. Mitochondrial alterations, such as decreased mitochondrial potential and oxygen consumption rate (OCR), increased mitochondrial reactive oxygen species (mtROS) and unbalanced biogenesis and mitophagy, have not been studied in BA-induced sarcopenia.

METHODS

We evaluated the effects of DCA and CA on mitochondrial alterations in C₂C₁₂ myotubes and a mouse model of cholestasis-induced sarcopenia. We measured mitochondrial mass by TOM20 levels and mitochondrial DNA; ultrastructural alterations by transmission electronic microscopy; mitochondrial biogenesis by PGC-1α plasmid reporter activity and protein levels by western blot analysis; mitophagy by the co-localisation of the MitoTracker and LysoTracker fluorescent probes; mitochondrial potential by detecting the TMRE probe signal; protein levels of OXPHOS complexes and LC3B by western blot analysis; OCR by Seahorse measures; and mtROS by MitoSOX probe signals.

RESULTS

DCA and CA caused a reduction in mitochondrial mass and decreased mitochondrial biogenesis. Interestingly, DCA and CA increased LC3II/LC3I ratio and decreased autophagic flux concordant with raised mitophagosome-like structures. In addition, DCA and CA decreased mitochondrial potential and reduced protein levels in OXPHOS complexes I and II. The results also demonstrated that DCA and CA decreased basal, ATP-linked, FCCP-induced maximal respiration and spare OCR. DCA and CA also reduced the number of cristae. In addition, DCA and CA increased the mtROS. In mice with cholestasis-induced sarcopenia, TOM20, OXPHOS complexes I, II and III, and OCR were diminished. Interestingly, the OCR and OXPHOS complexes were correlated with muscle strength and bile acid levels.

CONCLUSION

Our results showed that DCA and CA decreased mitochondrial mass, possibly by reducing mitochondrial biogenesis, which affects mitochondrial function, thereby altering potential OCR and mtROS generation. Some mitochondrial alterations were also observed in a mouse model of cholestasis-induced sarcopenia characterised by increased levels of BA, such as DCA and CA.

Pathogenesis, Intervention, and Current Status of Drug Development for Sarcopenia: A Review

Sarcopenia refers to the loss of muscle strength and mass in older individuals and is a major determinant of fall risk and impaired ability to perform activities of daily living, often leading to disability, loss of independence, and death. Owing to its impact on morbidity, mortality, and healthcare expenditure, sarcopenia in the elderly has become a major focus of research and public policy debates worldwide. Despite its clinical importance, sarcopenia remains under-recognized and poorly managed in routine clinical practice, partly owing to the lack of available diagnostic testing and uniform diagnostic criteria. Since the World Health Organization and the United States assigned a disease code for sarcopenia in 2016, countries worldwide have assigned their own disease codes for sarcopenia. However, there are currently no approved pharmacological agents for the treatment of sarcopenia; therefore, interventions for sarcopenia primarily focus on physical therapy for muscle strengthening and gait training as well as adequate protein intake. In this review, we aimed to examine the latest information on the epidemiology, molecular mechanisms, interventions, and possible treatments with new drugs for sarcopenia.

Saikosaponin A and D attenuate skeletal muscle atrophy in chronic kidney disease by reducing oxidative stress through activation of PI3K/AKT/Nrf2 pathway

BACKGROUND

Skeletal muscle atrophy in chronic kidney disease (CKD) leads to a decline in quality of life and increased risk of morbidity and mortality. We have obtained evidence that oxidative stress is essential in the progression of CKD-related muscle atrophy. Whether Saikosaponin A and D, two emerging antioxidants extracted from Bupleurum chinense DC, alleviate muscle atrophy remains to be further studied. The purpose of this study was to investigate the effects and mechanisms of these two components on CKD complicated with muscle atrophy.

METHODS

In this research, muscle dystrophy model was established using 5/6 nephrectomized mice in vivo and in vitro with Dexamethasone (Dex)-managed C2C12 myotubes.

RESULTS

The results of RNA-sequencing showed that exposure to Dex affected the antioxidant activity, catalytic activity and enzyme regulator activity of C2C12 cells. According to KEGG analysis, the largest numbers of differentially expressed genes detected were enriched in the PI3K/AKT pathway. In vivo, Saikosaponin A and D remain renal function, cross-section size, fiber-type composition and anti-inflammatory ability. These two components suppressed the expression of MuRF-1 and enhanced the expression of MyoD and Dystrophin. In addition, Saikosaponin A and D maintained redox balance by increasing the activities of antioxidant enzymes while inhibiting the excessive accumulation of reactive oxygen species. Furthermore, Saikosaponin A and D stimulated PI3K/AKT and its downstream Nrf2 pathway in CKD mice. The effects of Saikosaponin A and D on increasing the inner diameter of C2C12 myotube, reducing oxidative stress and enhancing expression of p-AKT, p-mTOR, p70S6K, Nrf2 and HO-1 proteins were observed in vitro. Importantly, we verified that these protective effects could be significantly reversed by inhibiting PI3K and knocking out Nrf2.

CONCLUSIONS

In summary, Saikosaponin A and D improve CKD-induced muscle atrophy by reducing oxidative stress through the PI3K/AKT/Nrf2 pathway.

Hindlimb muscle representations in mouse motor cortex defined by viral tracing

Introduction

Descending pathways from the cortex to the spinal cord are involved in the control of natural movement. Although mice are widely used to study the neurobiology of movement and as models of neurodegenerative disease, an understanding of motor cortical organization is lacking, particularly for hindlimb muscles.

Methods

In this study, we used the retrograde transneuronal transport of rabies virus to compare the organization of descending cortical projections to fast- and slow-twitch hindlimb muscles surrounding the ankle joint in mice.

Results

Although the initial stage of virus transport from the soleus muscle (predominantly slow-twitch) appeared to be more rapid than that associated with the tibialis anterior muscle (predominantly fast-twitch), the rate of further transport of virus to cortical projection neurons in layer V was equivalent for the two injected muscles. After appropriate survival times, dense concentrations of layer V projection neurons were identified in three cortical areas: the primary motor cortex (M1), secondary motor cortex (M2), and primary somatosensory cortex (S1).

Discussion

The origin of the cortical projections to each of the two injected muscles overlapped almost entirely within these cortical areas. This organization suggests that cortical projection neurons maintain a high degree of specificity; that is, even when cortical projection neurons are closely located, each neuron could have a distinct functional role (controlling fast- versus slow-twitch and/or extensor versus flexor muscles). Our results represent an important addition to the understanding of the mouse motor system and lay the foundation for future studies investigating the mechanisms underlying motor system dysfunction and degeneration in diseases such as amyotrophic lateral sclerosis and spinal muscular atrophy.

SHRSP5/Dmcr rats fed a high-fat and high-cholesterol diet develop disease-induced sarcopenia as nonalcoholic steatohepatitis progresses

BACKGROUND

Secondary sarcopenia develops as a result of a bedridden state and illnesses, such as cachexia, liver disease, and diabetes. However, there is a lack of animal models to investigate the underlying mechanisms and potential treatments for secondary sarcopenia. Recently, secondary sarcopenia has been associated with the prognosis of nonalcoholic steatohepatitis. This study aimed to investigate whether stroke-prone spontaneously hypertensive rat 5 (SHRSP5/Dmcr) which developed severe nonalcoholic steatohepatitis by a high-fat and high-cholesterol (HFC; containing 2% cholic acid) diet is a useful model of secondary sarcopenia.

METHODS

SHRSP5/Dmcr rats were divided into 6 groups fed with a Stroke-Prone (SP: normal chow) or HFC diets for different periods (4, 12, and 20 weeks), and WKY/Izm rats were divided into 2 groups fed an SP or HFC diet. Body weight, food intake, and muscle force were measured weekly for all rats. After the end of the diet period, skeletal muscle strength evoked by electrical stimulation was recorded, blood was collected, and organ weight was measured. The sera were used for biochemical analysis and the organs were used for histopathological analysis.

RESULTS

SHRSP5/Dmcr rats fed an HFC diet developed nonalcoholic steatohepatitis, and their skeletal muscles, especially fast muscles, showed atrophy, indicating that muscle atrophy is aggravated by the progression of nonalcoholic steatohepatitis. In contrast, WKY/Izm rats fed an HFC diet did not exhibit sarcopenia.

CONCLUSIONS

This study suggests that SHRSP5/Dmcr rats could be a useful novel model for investigate the mechanism of secondary sarcopenia disorder associated with nonalcoholic steatohepatitis.

Do dietary supplements prevent loss of muscle mass and strength during muscle disuse? A systematic review and meta-analysis of randomized controlled trials

Objective

We performed a systematic review and meta-analysis of existing randomized controlled trials (RCTs) to assess whether dietary supplements can prevent loss of muscle mass and strength during muscle disuse.

Methods

We searched the following databases: PubMed, Embase, Cochrane, Scopus, Web of Science, and CINAHL for RCTs assessing the effect of dietary supplements on disuse muscular atrophy without language and time restrictions. Muscle strength and leg lean mass were used as the primary outcome indicators. Muscle cross-sectional area (CSA), muscle fiber type distribution, peak aerobic capacity and muscle volume were used as secondary outcome indicators. The risk of bias was assessed using the Cochrane Collaboration's Risk of Bias tool. Heterogeneity was tested using the I² statistic index. Mean and standard deviation of outcome indicators were extracted from the intervention and control groups to calculate effect sizes and 95% confidence intervals, with the significance level set at P < 0.05.

Results

Twenty RCTs were included with a total of 339 subjects. The results showed that dietary supplements had no effect on muscle strength, CSA, muscle fiber type distribution, peak aerobic capacity or muscle volume. But dietary supplements have a protective effect on the lean mass of the legs.

Conclusion

Dietary supplements can improve lean leg mass, but did not show a tendency to have an effect on muscle strength, CSA, muscle fiber type distribution, peak aerobic capacity or muscle volume during muscle disuse.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/#recordDetails, identifier: CRD42022370230.

3D bioprinted functional skeletal muscle models have potential applications for studies of muscle wasting in cancer cachexia

Acquired muscle diseases such as cancer cachexia are responsible for the poor prognosis of many patients suffering from cancer. In vitro models are needed to study the underlying mechanisms of those pathologies. Extrusion bioprinting is an emerging tool to emulate the aligned architecture of fibers while implementing additive manufacturing techniques in tissue engineering. However, designing bioinks that reconcile the rheological needs of bioprinting and the biological requirements of muscle tissue is a challenging matter. Here we formulate a biomaterial with dual crosslinking to modulate the physical properties of bioprinted models. We design 3D bioprinted muscle models that resemble the mechanical properties of native tissue and show improved proliferation and high maturation of differentiated myotubes suggesting that the GelMA-AlgMA-Fibrin biomaterial possesses myogenic properties. The electrical stimulation of the 3D model confirmed the contractile capability of the tissue and enhanced the formation of sarcomeres. Regarding the functionality of the models, they served as platforms to recapitulate skeletal muscle diseases such as muscle wasting produced by cancer cachexia. The genetic expression of 3D models demonstrated a better resemblance to the muscular biopsies of cachectic mouse models. Altogether, this biomaterial is aimed to fabricate manipulable skeletal muscle in vitro models in a non-costly, fast and feasible manner.

A Lignan from Alnus japonica Activates Myogenesis and Alleviates Dexamethasone-induced Myotube Atrophy

To find inhibitors against skeletal muscle loss, we isolated a lignan compound ((-)-(2R,3R-1,4-O-diferuloylsecoisolarciresinol, DFS) from the stem of Alnus japonica. C2C12 myoblasts were treated with DFS during differentiation. To induce an in vitro atrophic condition, differentiated myotubes were treated with dexamethasone (a synthetic glucocorticoid). DFS (10 nM) increased expression levels of myogenic factors and the number of multi-nucleated myotubes expressing myosin heavy chain (MHC). The myogenic potential of DFS could be attributed to p38 MAPK activation. DFS also protected against dexamethasone-induced damage, showing increased expression of MHC and mammalian target of rapamycin (mTOR), a major anabolic factor. Under atrophic condition, the anti-myopathy effect of DFS was associated with inactivation of NF-κB signaling pathway and the subsequent suppression of muscle degradative E3 ligases and myostatin. DFS treatment also restored fast muscle fiber (type II a, II b, and II x), known to be susceptible to dexamethasone. These results indicate that DFS isolated from A. japonica can stimulate myogenesis via p38 MAPK activation and alleviate muscle atrophy by modulating the expression of genes associated with muscle protein anabolism/catabolism. Thus, we propose that DFS can be used as a pharmacological and nutraceutical agent for increasing muscle strength or protecting muscle loss.

Regulation Mechanism and functional Verification of key functional genes regulating muscle Development in Black Tibetan Sheep

Black Tibetan sheep is a branch of Tibetan sheep on the Qinghai-Tibet Plateau (QTP). It is mainly distributed in Guinan County, Qinghai Province. In order to accurately identify the core regulatory genes in the process of muscle development of black Tibetan sheep, further explore the physiological processes of growth, development and myogenesis of black Tibetan sheep, and carry out molecular breeding of black Tibetan sheep, this experiment took the unique black Tibetan sheep on the Qinghai-Tibet Plateau as the experimental object, and selected three stages of 4-month-old embryo (embryonic stage, MF group), 10-month-old(breeding stage, ML group) and 36-month-old (adult, MA group). The longissimus dorsi tissues of 3 sheep were taken at each stage to quantify the expression of genes during muscle development at different developmental stages. Meanwhile, overexpression and interference techniques were used to detect the role of core genes in the proliferation of primary muscle cells of black Tibetan sheep. In the process from embryonic stage to mature stage and adulthood, more than 1000 genes were up-regulated and more than 4000 down-regulated in black Tibetan sheep, while from breeding to adulthood, there were only 51 up-regulated genes and 83 down-regulated genes. About 998 genes were newly identified in each group. During muscle development from embryonic stage to mature stage to adulthood, two significant differential trend gene sets of Profile1 and Profile 6 were screened and identified, in which there were 121 and 31 core regulatory genes identified, respectively. In the trend of first decreasing and then stable expression in the whole development stage, 121 genes are core regulatory transcripts, which are mainly related to axonal guidance, cell cycle and other functions. 31 genes are core regulatory transcripts in the first rising and then stable expression, which are mainly related to biological metabolic pathway, oxidative phosphorylation and other processes. In the MF-ML stage, 75 genes were selected as the core regulatory gene set, the core genes were PTEN, AKT3, etc., and there were 134 differentially expressed genes in the ML-MA stage, and the core regulatory genes were IL6, ABCA1 and so on. In the MF-ML stage, the core gene set widely plays a role in cell components, cell matrix and other biological processes, while in the ML-MA stage, the core gene set widely plays a role in cell migration, cell differentiation, tissue development and so on. Adenovirus vector overexpressed and interfered with the core gene PTEN in primary muscle satellite cells of black Tibetan sheep shown that, interference and overexpression of PTEN would correspondingly increase and decrease the expression of other core genes, like AKT3, CKD2, CCNB1, ERBB3, HDAC2, but the specific interaction mechanism of each gene still needs to be further explored.

Chemotherapy-Induced Molecular Changes in Skeletal Muscle

Paraneoplastic conditions such as cancer cachexia are often exacerbated by chemotherapy, which affects the patient’s quality of life as well as the response to therapy. The aim of this narrative review was to overview the body-composition-related changes and molecular effects of different chemotherapy agents used in cancer treatment on skeletal-muscle remodeling. A literature search was performed using the Web of Science, Scopus, and Science Direct databases and a total of 77 papers was retrieved. In general, the literature survey showed that the molecular changes induced by chemotherapy in skeletal muscle have been studied mainly in animal models and mostly in non-tumor-bearing rodents, whereas clinical studies have essentially assessed changes in body composition by computerized tomography. Data from preclinical studies showed that chemotherapy modulates several molecular pathways in skeletal muscle, including the ubiquitin–proteasome pathway, autophagy, IGF-1/PI3K/Akt/mTOR, IL-6/JAK/STAT, and NF-κB pathway; however, the newest chemotherapy agents are underexplored. In conclusion, chemotherapy exacerbates skeletal-muscle wasting in cancer patients; however, the incomplete characterization of the chemotherapy-related molecular effects on skeletal muscle makes the development of new preventive anti-wasting strategies difficult. Therefore, further investigation on molecular mechanisms and clinical studies are necessary.

The Relationship between Restrictions on Going Out and Motor Imagery among Medical University Students in Japan—Research with Small Samples

Motor imagery is often used as a training method to improve physical performance. Previous studies have often reported that reduced motor imagery is more likely to occur in older adults and stroke patients. However, it has also been reported that it is difficult to imagine exercises that cannot be performed. Therefore, we hypothesized that this may also have occurred in young people who were physically able to exercise but who were restricted by COVID-19 lockdowns, however, we could find no studies that investigated the impact of restricting outings. In this study, 83 healthy young people were measured for physical performance (maximum walking speed, grasp strength, Timed Up and Go test, imagined Timed Up and Go test, functional reach test, and five chair stand test). It was found that, while restricting outings did not influence physical performance in the subjects, it did influence motor imagery. Therefore, it should be borne in mind that training with motor imagery may not generate adequate actual motor imagery when restrictions are imposed on activities.

Determination of the intermediates in glycolysis and tricarboxylic acid cycle with an improved derivatization strategy using gas chromatography-mass spectrometry in complex samples

Traditional Chinese medicine (TCM) is recognized as a complex matrix, and improved analytical methods are crucial to extract the key indicators and depict the interaction and alteration of the complex matrix. Shenqi Fuzheng Injection (SQ), a water extract of Radix Codonopsis and Radix Astragali, has demonstrated preventative effects on myotube atrophy induced by chemotherapeutic agents. To achieve the improved analytical capability of complex biological samples, we established a highly reproducible, sensitive, specific, and robust gas chromatography-tandem mass spectrometry (GC-MS) method to detect glycolysis and tricarboxylic acid (TCA) cycle intermediates with optimized factors in the extraction and derivatization process. Our method detected fifteen metabolites and covered most intermediate metabolites in glycolysis and TCA cycles, including glucose, glucose-6-phosphate, fructose-6-phosphate, dihydroxyacetone phosphate, 3-diphosphoglycerate, phosphoenolpyruvate, pyruvate, lactate, citrate, cis-aconitate, isocitrate, α-ketoglutarate, succinate, fumarate, and malate. Through methodological verification of the method, it was found that the linear correlation coefficients of each compound in the method were greater than 0.98, all of which had lower limits of quantification, the recovery rate was 84.94-104.45%, and the accuracy was 77.72-104.92%. The intraday precision was 3.72-15.37%, the interday precision was 5.00-18.02%, and the stability was 7.85-15.51%. Therefore, the method has good linearity, accuracy, precision, and stability. The method was further applied to study the attenuating effects of the SQ in a chemotherapeutic agents-induced C2C12 myotube atrophy model to evaluate the changes in the tricarboxylic acid cycle and glycolytic products under the action by the complex systems of TCM and disease model. Our study provided an improved method to explore TCM's pharmacodynamic constituents and action mechanisms.

Effects of Monoamino-Oxidase-A (MAO-A) Inhibition on Skeletal Muscle Inflammation and Wasting through Pancreatic Ductal Adenocarcinoma in Triple Transgenic Mice

Cancer cachexia describes a syndrome of muscle wasting and lipolysis that is still largely untreatable and negatively impacts prognosis, mobility, and healthcare costs. Since upregulation of skeletal muscle monoamine-oxidase-A (MAO-A), a source of reactive oxygen species, may contribute to cachexia, we investigated the effects of the MAO-inhibitor harmine-hydrochloride (HH, intraperitoneal, 8 weeks) on muscle wasting in a triple-transgenic mouse model of pancreatic ductal adenocarcinoma (PDAC) and wild type (WT) mice. Gastrocnemius and soleus muscle cryo-cross-sections were analyzed for fiber type-specific cross-sectional area (CSA), fraction and capillarization using ATPase- and lectin-stainings. Transcripts of pro-apoptotic, -atrophic, and -inflammatory signals were determined by RT-qPCR. Furthermore, we evaluated the integrity of neuromuscular junction (NMJ, pre-/post-synaptic co-staining) and mitochondrial ultrastructure (transmission electron microscopy). MAO-A expression in gastrocnemius muscle was increased with PDAC vs. WT (immunohistochemistry: p < 0.05; Western blot: by trend). PDAC expectedly reduced fiber CSA and upregulated IL-1β in both calf muscles, while MuRF1 expression increased in soleus muscle only. Although IL-1β decreased, HH caused an additional 38.65% (p < 0.001) decrease in gastrocnemius muscle (IIBX) fiber CSA. Moreover, soleus muscle CSA remained unchanged despite the downregulation of E3-ligases FBXO32 (p < 0.05) and MuRF1 (p < 0.01) through HH. Notably, HH significantly decreased the post-synaptic NMJ area (quadriceps muscle) and glutathione levels (gastrocnemius muscle), thereby increasing mitochondrial damage and centronucleation in soleus and gastrocnemius type IIBX fibers. Moreover, although pro-atrophic/-inflammatory signals are reversed, HH unfortunately fails to stop and rather promotes PDAC-related muscle wasting, possibly via denervation or mitochondrial damage. These differential adverse vs. therapeutic effects warrant studies regarding dose-dependent benefits and risks with consideration of other targets of HH, such as the dual-specificity tyrosine phosphorylation regulated kinases 1A and B (DYRK1A/B).

Nicotinamide Phosphoribosyltransferase-elevated NAD+ biosynthesis prevents muscle disuse atrophy by reversing mitochondrial dysfunction

BACKGROUND

It is well known that muscle disuse atrophy is associated with mitochondrial dysfunction, which is implicated in reduced nicotinamide adenine dinucleotide (NAD⁺ ) levels. Nicotinamide phosphoribosyltransferase (NAMPT), a rate-limiting enzyme in NAD⁺ biosynthesis, may serve as a novel strategy to treat muscle disuse atrophy by reversing mitochondrial dysfunction.

METHODS

To investigate the effects of NAMPT on the prevention of disuse atrophy of skeletal muscles predominantly composed of slow-twitch (type I) or fast-twitch (type II) fibres, rabbit models of rotator cuff tear-induced supraspinatus muscle atrophy and anterior cruciate ligament (ACL) transection-induced extensor digitorum longus (EDL) atrophy were established and then administered NAMPT therapy. Muscle mass, fibre cross-sectional area (CSA), fibre type, fatty infiltration, western blot, and mitochondrial function were assayed to analyse the effects and molecular mechanisms of NAMPT in preventing muscle disuse atrophy.

RESULTS

Acute disuse of the supraspinatus muscle exhibited significant loss of mass (8.86 ± 0.25 to 5.10 ± 0.79 g; P < 0.001) and decreased fibre CSA (3939.6 ± 136.1 to 2773.4 ± 217.6 μm² , P < 0.001), which were reversed by NAMPT (muscle mass 6.17 ± 0.54 g, P = 0.0033; fibre CSA, 3219.8 ± 289.4 μm² , P = 0.0018). Disuse-induced impairment of mitochondrial function were significantly improved by NAMPT, including citrate synthase activity (40.8 ± 6.3 to 50.5 ± 5.6 nmol/min/mg, P = 0.0043), and NAD⁺ biosynthesis (279.9 ± 48.7 to 392.2 ± 43.2 pmol/mg, P = 0.0023). Western blot revealed that NAMPT increases NAD⁺ levels by activating NAMPT-dependent NAD⁺ salvage synthesis pathway. In supraspinatus muscle atrophy due to chronic disuse, a combination of NAMPT injection and repair surgery was more effective than repair in reversing muscle atrophy. Although the predominant composition of EDL muscle is fast-twitch (type II) fibre type that differ from supraspinatus muscle, its mitochondrial function and NAD⁺ levels are also susceptible to disuse. Similar to the supraspinatus muscle, NAMPT-elevated NAD⁺ biosynthesis was also efficient in preventing EDL disuse atrophy by reversing mitochondrial dysfunction.

CONCLUSIONS

NAMPT-elevated NAD⁺ biosynthesis can prevent disuse atrophy of skeletal muscles that predominantly composed with either slow-twitch (type I) or fast-twitch (type II) fibres by reversing mitochondrial dysfunction.

The MuSK-BMP pathway maintains myofiber size in slow muscle through regulation of Akt- mTOR signaling

Myofiber size regulation is critical in health, disease, and aging. MuSK (muscle-specific kinase) is a BMP (bone morphogenetic protein) co-receptor that promotes and shapes BMP signaling. MuSK is expressed at all neuromuscular junctions and is also present extrasynaptically in the slow soleus muscle. To investigate the role of the MuSK-BMP pathway in vivo we generated mice lacking the BMP-binding MuSK Ig3 domain. These ΔIg3-MuSKmice are viable and fertile with innervation levels comparable to wild type. In 3-month-old mice myofibers are smaller in the slow soleus, but not in the fast tibialis anterior (TA). Transcriptomic analysis revealed soleus-selective decreases in RNA metabolism and protein synthesis pathways as well as dysregulation of IGF1-Akt-mTOR pathway components. Biochemical analysis showed that Akt-mTOR signaling is reduced in soleus but not TA. We propose that the MuSK-BMP pathway acts extrasynaptically to maintain myofiber size in slow muscle by promoting protein synthetic pathways including IGF1-Akt-mTOR signaling. These results reveal a novel mechanism for regulating myofiber size in slow muscle and introduce the MuSK-BMP pathway as a target for promoting muscle growth and combatting atrophy.

Associations of swallowing-related muscle quantity and quality with sarcopenic parameters

PURPOSE

To examine the associations between swallowing-related muscle characteristics and sarcopenic parameters.

METHODS

We included 147 community-dwelling older adults (age: 71.6 ± 4.7 years, body mass index: 23.0 ± 2.7 kg/m² (mean ± standard deviation), men: 50; women: 97) and categorized them into robust (n = 125), low-function (n = 17), and sarcopenia (n = 5) groups based on the diagnostic criteria of the Asia Working Group for Sarcopenia 2019. We evaluated the geniohyoid muscle (GHM) and tongue characteristics (muscle quantity and quality). The cross-sectional area (CSA) indicated the muscle quantity, and echo intensity (EI) values indicated the muscle quality. A multiple regression analysis was performed to clarify the relationship of swallowing-related muscle characteristics and strength with sarcopenic parameters.

RESULTS

The grip strength (CSA of GHM: β = 1.64, p = 0.03) and skeletal muscle mass index (CSA of tongue: β = 74.81, p = 0.003, EI of tongue: β = 1.92, p = 0.009) were better indicators of swallowing-related muscle characteristics.

CONCLUSION

These findings may facilitate the early detection of aging-related deterioration in swallowing-related musculature through the diagnostic process of sarcopenia and increase our understanding of muscle physiology.

Mechanical loading is required for initiation of extracellular matrix deposition at the developing murine myotendinous junction

The myotendinous junction (MTJ) contributes to the generation of motion by connecting muscle to tendon. At the adult MTJ, a specialized extracellular matrix (ECM) is thought to contribute to the mechanical integrity of the muscle-tendon interface, but the factors that influence MTJ formation during mammalian development are unclear. Here, we combined 3D imaging and proteomics with murine models in which muscle contractility and patterning are disrupted to resolve morphological and compositional changes in the ECM during MTJ development. We found that MTJ-specific ECM deposition can be initiated via static loading due to growth; however, it required cyclic loading to develop a mature morphology. Furthermore, the MTJ can mature without the tendon terminating into cartilage. Based on these results, we describe a model wherein MTJ development depends on mechanical loading but not insertion into an enthesis.

Progressive development of melanoma-induced cachexia differentially impacts organ systems in mice

Cachexia is a systemic wasting syndrome that increases cancer-associated mortality. How cachexia progressively and differentially impacts distinct tissues is largely unknown. Here, we find that the heart and skeletal muscle undergo wasting at early stages and are the tissues transcriptionally most impacted by cachexia. We also identify general and organ-specific transcriptional changes that indicate functional derangement by cachexia even in tissues that do not undergo wasting, such as the brain. Secreted factors constitute a top category of cancer-regulated genes in host tissues, and these changes include upregulation of the angiotensin-converting enzyme (ACE). ACE inhibition with the drug lisinopril improves muscle force and partially impedes cachexia-induced transcriptional changes, although wasting is not prevented, suggesting that cancer-induced host-secreted factors can regulate tissue function during cachexia. Altogether, by defining prevalent and temporal and tissue-specific responses to cachexia, this resource highlights biomarkers and possible targets for general and tissue-tailored anti-cachexia therapies.

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.

LSD1 defines the fiber type-selective responsiveness to environmental stress in skeletal muscle

Skeletal muscle exhibits remarkable plasticity in response to environmental cues, with stress-dependent effects on the fast-twitch and slow-twitch fibers. Although stress-induced gene expression underlies environmental adaptation, it is unclear how transcriptional and epigenetic factors regulate fiber type-specific responses in the muscle. Here, we show that flavin-dependent lysine-specific demethylase-1 (LSD1) differentially controls responses to glucocorticoid and exercise in postnatal skeletal muscle. Using skeletal muscle-specific LSD1-knockout mice and in vitro approaches, we found that LSD1 loss exacerbated glucocorticoid-induced atrophy in the fast fiber-dominant muscles, with reduced nuclear retention of Foxk1, an anti-autophagic transcription factor. Furthermore, LSD1 depletion enhanced endurance exercise-induced hypertrophy in the slow fiber-dominant muscles, by induced expression of ERRγ, a transcription factor that promotes oxidative metabolism genes. Thus, LSD1 serves as an 'epigenetic barrier' that optimizes fiber type-specific responses and muscle mass under the stress conditions. Our results uncover that LSD1 modulators provide emerging therapeutic and preventive strategies against stress-induced myopathies such as sarcopenia, cachexia, and disuse atrophy.

Episodic Binge-like Ethanol Reduces Skeletal Muscle Strength Associated with Atrophy, Fibrosis, and Inflammation in Young Rats

Binge Drinking (BD) corresponds to episodes of ingestion of large amounts of ethanol in a short time, typically ≤2 h. BD occurs across all populations, but young and sports-related people are especially vulnerable. However, the short- and long-term effects of episodic BD on skeletal muscle function have been poorly explored. Young rats were randomized into two groups: control and episodic Binge-Like ethanol protocol (BEP) (ethanol 3 g/kg IP, 4 episodes of 2-days ON-2-days OFF paradigm). Muscle function was evaluated two weeks after the last BEP episode. We found that rats exposed to BEP presented decreased muscle strength and increased fatigability, compared with control animals. Furthermore, we observed that skeletal muscle from rats exposed to BEP presented muscle atrophy, evidenced by reduced fiber size and increased expression of atrophic genes. We also observed that BEP induced fibrotic and inflammation markers, accompanied by mislocalization of nNOSµ and high levels of protein nitration. Our findings suggest that episodic binge-like ethanol exposure alters contractile capacity and increases fatigue by mechanisms involving atrophy, fibrosis, and inflammation, which remain for at least two weeks after ethanol clearance. These pathological features are common to several neuromuscular diseases and might affect muscle performance and health in the long term.

Time Spent Away from Bed to Maintain Swallowing Function in Older Adults

INTRODUCTION

The aim of this study was to determine the associations of time spent away from bed with whole-body muscle mass and swallowing function in older adults with low activities of daily living (ADL).

METHODS

This cross-sectional study was conducted at Tokyo Medical and Dental University and included adults over 65 years of age who underwent a medical intervention at their residence. Data regarding age, sex, body height and weight, activity status, medical history, time spent away from bed, and Functional Oral Intake Scale (FOIS) were collected. We calculated the body mass index, Charlson Comorbidity Index, whole-body muscle mass, the appendicular skeletal muscle mass index (ASMI), and the trunk muscle mass index (TMI). According to the time spent away from bed, the subjects were grouped as follows: <4 but ≥0 h (S), <6 but ≥4 h (M), and ≥6 h (L). These variables were analyzed using the one-way analysis of variance, the Kruskal-Wallis test, and the χ2 test, then differences among the three groups were examined. To adjust for confounding factors, we performed multiple regression analysis with ASMI and TMI as the dependent variables and ordinal logistic regression analysis with FOIS as the objective variable.

RESULTS

Ninety subjects (male: n = 42; female: n = 48; mean age = 82.9 ± 8.8 years, and groups S: n = 23; M: n = 30; L: n = 37) were analyzed. Group L had a significantly higher ASMI, TMI, and FOIS score than groups S and M, while group M had a significantly higher ASMI and FOIS score than group S. After adjusting for confounding factors, the significant explanatory factors for ASMI were sex, activity status, time spent away from bed, and TMI. The factors for TMI were activity status, time spent away from bed, ASMI, and FOIS. The factors for FOIS were time spent away from bed and TMI.

CONCLUSION

Spending 4 or more hours away from the bed is related to appendicular skeletal muscle mass and FOIS, while spending 6 or more hours is related to appendicular skeletal muscle mass, trunk muscle mass, and FOIS in this population. These findings highlight factors that can prevent a decline in swallowing function in the daily life of older adults with low ADL who have difficulty performing exercises to preserve swallowing function.

Simultaneous loss of skeletal muscle myosin heavy chain IIx and IIb causes severe skeletal muscle hypoplasia in postnatal mice

The skeletal muscle myosin heavy chain (MyHC) is a fundamental component of the sarcomere structure and muscle contraction. Two of the three adult fast MyHCs, MyHC-IIx and MyHC-IIb, are encoded by Myh1 and Myh4, respectively. However, skeletal muscle disorders have not yet been linked to these genes in humans. MyHC-IIb is barely detectable in human skeletal muscles. Thus, to characterize the molecular function of skeletal muscle MyHCs in humans, investigation of the effect of simultaneous loss of MyHC-IIb and other MyHCs on skeletal muscle in mice is essential. Here, we generated double knockout (dKO) mice with simultaneous loss of adult fast MyHCs by introducing nonsense frameshift mutations into the Myh1 and Myh4 genes. The dKO mice appeared normal after birth and until 2 weeks of age but showed severe skeletal muscle hypoplasia after 2 weeks. In 3-week-old dKO mice, increased expression of other skeletal muscle MyHCs, such as MyHC-I, MyHC-IIa, MyHC-neo, and MyHC-emb, was observed. However, these expressions were not sufficient to compensate for the loss of MyHC-IIb and MyHC-IIx. Moreover, the aberrant sarcomere structure with altered expression of sarcomere components was observed in dKO mice. Our findings imply that the simultaneous loss of MyHC-IIb and MyHC-IIx is substantially detrimental to postnatal skeletal muscle function and will contribute to elucidating the molecular mechanisms of skeletal muscle wasting disorders caused by the loss of skeletal muscle MyHCs.

Techniques for Injury, Cell Transplantation, and Histological Analysis in Skeletal Muscle

Skeletal muscle can adjust to changes in physiological and pathological environments by regenerating using myogenic progenitor cells or adapting muscle fiber sizes and types, metabolism, and contraction ability. To study these changes, muscle samples should be appropriately prepared. Therefore, reliable techniques to accurately analyze and evaluate skeletal muscle phenotypes are required. However, although technical approaches to genetically investigating skeletal muscle are improving, the fundamental strategies for capturing muscle pathology are the same over the decades. Hematoxylin and eosin (H&E) staining or antibodies are the simplest and standard methodologies for assessing skeletal muscle phenotypes. In this chapter, we describe fundamental techniques and protocols for inducing skeletal muscle regeneration by using chemicals and cell transplantation, in addition to methods of preparing and evaluating skeletal muscle samples.

Histological and Histochemical Microscopy Used to Verify 2D-DIGE Pathoproteomics

Comparative gel electrophoretic analyses of normal versus pathological specimens can swiftly identify proteome-wide changes in the concentration of specific protein isoforms. The application of fluorescence two-dimensional difference gel electrophoresis (2D-DIGE) can be employed for the characterization of complex protein populations in health and disease. In order to verify pathoproteomic findings and correlate them to histopathological alterations, standardized histological and histochemical methodology can be applied for the cell biological analysis of normal versus pathological tissue samples. This chapter outlines the usage of histochemical ATPase staining of fast and slow fiber types in normal versus dystrophic skeletal muscles, as well as the application of hematoxylin and eosin staining of nuclei and the cellular body in kidney cells, and Sudan black staining of lipids in cryo-sections.

Mechanism of skeletal muscle atrophy after spinal cord injury: A narrative review

Spinal cord injury leads to loss of innervation of skeletal muscle, decreased motor function, and significantly reduced load on skeletal muscle, resulting in atrophy. Factors such as braking, hormone level fluctuation, inflammation, and oxidative stress damage accelerate skeletal muscle atrophy. The atrophy process can result in skeletal muscle cell apoptosis, protein degradation, fat deposition, and other pathophysiological changes. Skeletal muscle atrophy not only hinders the recovery of motor function but is also closely related to many systemic dysfunctions, affecting the prognosis of patients with spinal cord injury. Extensive research on the mechanism of skeletal muscle atrophy and intervention at the molecular level has shown that inflammation and oxidative stress injury are the main mechanisms of skeletal muscle atrophy after spinal cord injury and that multiple pathways are involved. These may become targets of future clinical intervention. However, most of the experimental studies are still at the basic research stage and still have some limitations in clinical application, and most of the clinical treatments are focused on rehabilitation training, so how to develop more efficient interventions in clinical treatment still needs to be further explored. Therefore, this review focuses mainly on the mechanisms of skeletal muscle atrophy after spinal cord injury and summarizes the cytokines and signaling pathways associated with skeletal muscle atrophy in recent studies, hoping to provide new therapeutic ideas for future clinical work.

Reduced muscle strength in patients with long-COVID-19 syndrome is mediated by limb muscle mass

Understanding the impact of COVID-19 on muscle strength may help to elucidate the organ systems that contribute to acute and chronic COVID-19 sequelae. We questioned whether patients with postdischarge symptoms after COVID-19 had compromised muscle strength compared with a control group, and if this potential relationship was mediated by the lower appendicular lean mass index (ALMI). A total of 99 patients with long-COVID-19 and 97 control participants were screened. Maximal grip strength was assessed with a TKK 5101 digital dynamometer, and leg extension 1RM was measured using EGYM Smart Strength machines. Body composition (fat mass percentage, lean mass, visceral fat, and appendicular lean mass index) was determined using a whole body dual-energy X-ray densitometer. Results showed that grip strength and leg extension strength were significantly higher in controls than in COVID-19 survivors (mean [SD], 32.82 [10.01] vs. 26.94 [10.33] kg; difference, 5.87 kg; P < 0.001) and (mean [SD], 93.98 [33.73] vs. 71.59 [33.70] kg; difference, 22.38 kg; P < 0.001), respectively). The relationship between long-COVID syndrome and grip/leg strength levels was partly mediated by ALMI, which explained 52% of the association for grip strength and 39% for leg extension. Our findings provide novel insights into the mechanisms underlying the relationship between long-COVID syndrome and grip/leg strength levels, supporting the negative effects of long-COVID syndrome on muscle function.NEW & NOTEWORTHY The causes of post-COVID-19 syndrome are uncertain. Limb muscle wasting common to patients with COVID-19 limits daily activities and exercise. In this cross-sectional study, we found that patients with long-COVID-19 syndrome had significantly lower absolute and relative muscle strength measurements than control participants. Interestingly, we identified that these relationships were mostly mediated by limb muscle mass. Our data thus suggest that the evident reduced upper and lower muscle mass is a putative cause of-or contributor to-the functional limitation of patients with long-COVID-19 syndrome.

Transcriptomic and proteomic time-course analyses based on Metascape reveal mechanisms against muscle atrophy in hibernating Spermophilus dauricus

Hibernating Spermophilus dauricus is resistant to muscle atrophy. Comprehensive transcriptome and proteome time-course analyses based on Metascape can further reveal the underlying processes (pre-hibernation stage, PRE; torpor stage, TOR; interbout arousal stage, IBA; and post-hibernation stage, POST). Transcriptome analysis showed that the cellular responses to growth factor stimulus and discrete oxygen levels continuously changed during hibernation. Proteomic analysis showed that neutrophil degranulation, sulfur compound metabolic process, and generation of precursor metabolites and energy continuously changed during hibernation. Molecular complex detection (MCODE) analysis in both transcriptome and proteome indicated that smooth muscle contraction was involved in the POST versus IBA stage, and peroxisome proliferator-activated receptor delta (Ppard), Myc proto-oncogene (Myc), Sp1 transcription factor (Sp1), and nuclear factor Kappa B subunit 1 (NFκB1) are the common TFs during the hibernation process. Integrated transcriptome and proteome analyses found 18 molecules in the TOR versus PRE stage, 1 molecule in the IBA versus TOR stage, and 16 molecules in the POST versus IBA stage. Among these molecules, carnitine palmitoyltransferase 1A (Cpt1a), SET and MYND domain containing 2 (Smyd2), four and a half LIM domains 1(Fhl1), reactive oxygen species modulator 1 (Romo1), and translocase of the inner mitochondrial membrane 50 (Timm50) were testified by Western blot. In conclusion, novel muscle atrophy resistance mechanisms can be deciphered by time-course transcriptome and proteome analyses based on Metascape.

Zebrafish Models for Skeletal Muscle Senescence: Lessons from Cell Cultures and Rodent Models

Human life expectancy has markedly increased over the past hundred years. Consequently, the percentage of elderly people is increasing. Aging and sarcopenic changes in skeletal muscles not only reduce locomotor activities in elderly people but also increase the chance of trauma, such as bone fractures, and the incidence of other diseases, such as metabolic syndrome, due to reduced physical activity. Exercise therapy is currently the only treatment and prevention approach for skeletal muscle aging. In this review, we aimed to summarize the strategies for modeling skeletal muscle senescence in cell cultures and rodents and provide future perspectives based on zebrafish models. In cell cultures, in addition to myoblast proliferation and myotube differentiation, senescence induction into differentiated myotubes is also promising. In rodents, several models have been reported that reflect the skeletal muscle aging phenotype or parts of it, including the accelerated aging models. Although there are fewer models of skeletal muscle aging in zebrafish than in mice, various models have been reported in recent years with the development of CRISPR/Cas9 technology, and further advancements in the field using zebrafish models are expected in the future.

The inflammatory response, a mixed blessing for muscle homeostasis and plasticity

Skeletal muscle makes up almost half the body weight of heathy individuals and is involved in several vital functions, including breathing, thermogenesis, metabolism, and locomotion. Skeletal muscle exhibits enormous plasticity with its capacity to adapt to stimuli such as changes in mechanical loading, nutritional interventions, or environmental factors (oxidative stress, inflammation, and endocrine changes). Satellite cells and timely recruited inflammatory cells are key actors in muscle homeostasis, injury, and repair processes. Conversely, uncontrolled recruitment of inflammatory cells or chronic inflammatory processes leads to muscle atrophy, fibrosis and, ultimately, impairment of muscle function. Muscle atrophy and loss of function are reported to occur either in physiological situations such as aging, cast immobilization, and prolonged bed rest, as well as in many pathological situations, including cancers, muscular dystrophies, and several other chronic illnesses. In this review, we highlight recent discoveries with respect to the molecular mechanisms leading to muscle atrophy caused by modified mechanical loading, aging, and diseases. We also summarize current perspectives suggesting that the inflammatory process in muscle homeostasis and repair is a double-edged sword. Lastly, we review recent therapeutic approaches for treating muscle wasting disorders, with a focus on the RANK/RANKL/OPG pathway and its involvement in muscle inflammation, protection and regeneration processes.

Eugenol improves high-fat diet/streptomycin-induced type 2 diabetes mellitus (T2DM) mice muscle dysfunction by alleviating inflammation and increasing muscle glucose uptake

Eugenol has been used in dietary interventions for metabolic diseases such as diabetes and obesity. However, the protective effect of eugenol on muscle function in diabetes is unclear. In this study, a high-fat diet (HFD) with a streptozocin (STZ) injection induced type II diabetes mellitus in a mouse model. Oral eugenol lowered blood glucose and insulin resistance of HFD/STZ-treated mice. Eugenol reduced HFD/STZ-induced muscle inflammation and prevented muscle weakness and atrophy. Eugenol administration significantly increased GLUT4 translocation and AMPK phosphorylation in skeletal muscle, thereby enhancing glucose uptake. By silencing the transient receptor potential vanilloid channel 1 (TRPV1) gene in C2C12 myotube cells, eugenol was found to increase intracellular Ca2+ levels through TRPV1, which then activated calmodulin-dependent protein kinase-2 (CaMKK2) and affected AMPK protein phosphorylation. In conclusion, eugenol is a potential nutraceutical for preventing high-glucose-induced muscle impairments, which could be explained by its mediating effects on glucose absorption and inflammatory responses in the muscle.

A handbook for beginners in skeletal muscle diffusion tensor imaging: physical basis and technical adjustments

Magnetic resonance imaging (MRI) of skeletal muscle is routinely performed using morphological sequences to acquire anatomical information. Recently, there is an increasing interest in applying advanced MRI techniques that provide pathophysiologic information for skeletal muscle evaluation to complement standard morphologic information. Among these advanced techniques, diffusion tensor imaging (DTI) has emerged as a potential tool to explore muscle microstructure. DTI can noninvasively assess the movement of water molecules in well-organized tissues with anisotropic diffusion, such as skeletal muscle. The acquisition of DTI studies for skeletal muscle assessment requires specific technical adjustments. Besides, knowledge of DTI physical basis and skeletal muscle physiopathology facilitates the evaluation of this advanced sequence and both image and parameter interpretation. Parameters derived from DTI provide a quantitative assessment of muscle microstructure with potential to become imaging biomarkers of normal and pathological skeletal muscle. KEY POINTS: • Diffusion tensor imaging (DTI) allows to evaluate the three-dimensional movement of water molecules inside biological tissues. • The skeletal muscle structure makes it suitable for being evaluated with DTI. • Several technical adjustments have to be considered for obtaining robust and reproducible DTI studies for skeletal muscle assessment, minimizing potential artifacts.

Age-Related Changes in Skeletal Muscle Oxygen Utilization

The cardiovascular and skeletal muscle systems are intrinsically interconnected, sharing the goal of delivering oxygen to metabolically active tissue. Deficiencies within those systems that affect oxygen delivery to working tissues are a hallmark of advancing age. Oxygen delivery and utilization are reflected as muscle oxygen saturation (SmO2) and are assessed using near-infrared resonance spectroscopy (NIRS). SmO2 has been observed to be reduced by ~38% at rest, ~24% during submaximal exercise, and ~59% during maximal exercise with aging (>65 y). Furthermore, aging prolongs restoration of SmO2 back to baseline by >50% after intense exercise. Regulatory factors that contribute to reduced SmO2 with age include blood flow, capillarization, endothelial cells, nitric oxide, and mitochondrial function. These mechanisms are governed by reactive oxygen species (ROS) at the cellular level. However, mishandling of ROS with age ultimately leads to alterations in structure and function of the regulatory factors tasked with maintaining SmO2. The purpose of this review is to provide an update on the current state of the literature regarding age-related effects in SmO2. Furthermore, we attempt to bridge the gap between SmO2 and associated underlying mechanisms affected by aging.

Impaired regenerative capacity contributes to skeletal muscle dysfunction in chronic obstructive pulmonary disease

Locomotor skeletal muscle dysfunction is a relevant comorbidity of chronic obstructive pulmonary disease (COPD) and is strongly associated with worse clinical outcomes including higher mortality. Over the last decades, a large body of literature helped characterize the process, defining the disruptive muscle phenotype caused by COPD that involves reduction in muscle mass, force-generation capacity, fatigue-tolerance, and regenerative potential following injury. A major limitation in the field has been the scarcity of well-calibrated animal models to conduct mechanistic research based on loss- and gain-of-function studies. This article provides an overall description of the process, the tools available to mechanistically investigate it, and the potential role of mitochondrially driven metabolic signals on the regulation muscle regeneration after injury in COPD. Finally, a description of future avenues to further expand on the area is proposed based on very recent evidence involving mitochondrial metabolic cues affecting myogenesis.

Aging after stroke: how to define post-stroke sarcopenia and what are its risk factors?

BACKGROUND

Sarcopenia, generally described as "aging-related loss of skeletal muscle mass and function", can occur secondary to a systemic disease.

AIM

This project aimed to study the prevalence of sarcopenia in chronic ambulatory stroke survivors and its associated risk factors using the two most recent diagnostic criteria.

DESIGN

A cross-sectional observational study.

SETTING

A scientific laboratory.

POPULATION

Chronic stroke.

METHODS

Twenty-eight ambulatory chronic stroke survivors (12 females; mean age=57.8±11.8 years; time after stroke=76±45 months), hand-grip strength, gait speed, and appendicular skeletal muscle mass (ASM) were measured to define sarcopenia. Risk factors, including motor impairment and spasticity, were identified using regression analysis.

RESULTS

The prevalence of sarcopenia varied between 18% and 25% depending on the diagnostic criteria used. A significant difference was seen in the prevalence of low hand grip strength on the affected side (96%) when compared to the contralateral side (25%). The prevalence of slow gait speed was 86% while low ASM was present in 89% of the subjects. Low ASM was marginally negatively correlated with time since stroke and gait speed, but no correlation was observed with age, motor impairment, or spasticity. ASM loss, bone loss and fat deposition were significantly greater in the affected upper limb than in the affected lower limb. Regression analyses showed that time since stroke was a factor associated with bone and muscle loss in the affected upper limb, spasticity had a protective role for muscle loss in the affected lower limb, and walking had a protective role for bone loss in the lower limb.

CONCLUSIONS

The prevalence of sarcopenia in stroke survivors is high and is a multifactorial process that is not age-related. Different risk factors contribute to muscle loss in the upper and lower limbs after stroke.

CLINICAL REHABILITATION IMPACT

Clinicians need to be aware of high prevalence of sarcopenia in chronic stroke survivors. Sarcopenia is more evident in the upper than lower limbs. Clinicians also need to understand potential protective roles of some factors, such as spasticity and walking for the muscles in the lower limb.