Mechanisms of muscle atrophy and hypertrophy: implications in health and disease

Identifying the potential therapeutic effects of miR‑6516 on muscle disuse atrophy

Muscle atrophy is a debilitating condition with various causes; while aging is one of these causes, reduced engagement in routine muscle‑strengthening activities also markedly contributes to muscle loss. Although extensive research has been conducted on microRNAs (miRNAs/miRs) and their associations with muscle atrophy, the roles played by miRNA precursors remain underexplored. The present study detected the upregulation of the miR‑206 precursor in cell‑free (cf)RNA from the plasma of patients at risk of sarcopenia, and in cfRNAs from the muscles of mice subjected to muscle atrophy. Additionally, a decline in the levels of the miR‑6516 precursor was observed in mice with muscle atrophy. The administration of mimic‑miR‑6516 to mice immobilized due to injury inhibited muscle atrophy by targeting and inhibiting cyclin‑dependent kinase inhibitor 1b (Cdkn1b). Based on these results, the miR‑206 precursor appears to be a potential biomarker of muscle atrophy, whereas miR‑6516 shows promise as a therapeutic target to alleviate muscle deterioration in patients with muscle disuse and atrophy.

Unravelling the complexity of the mitochondrial Ca2+ uniporter: regulation, tissue specificity, and physiological implications

Calcium (Ca2+) signalling acts a pleiotropic message within the cell that is decoded by the mitochondria through a sophisticated ion channel known as the Mitochondrial Ca2+ Uniporter (MCU) complex. Under physiological conditions, mitochondrial Ca2+ signalling is crucial for coordinating cell activation with energy production. Conversely, in pathological scenarios, it can determine the fine balance between cell survival and death. Over the last decade, significant progress has been made in understanding the molecular bases of mitochondrial Ca2+ signalling. This began with the elucidation of the MCU channel components and extended to the elucidation of the mechanisms that regulate its activity. Additionally, increasing evidence suggests molecular mechanisms allowing tissue-specific modulation of the MCU complex, tailoring channel activity to the specific needs of different tissues or cell types. This review aims to explore the latest evidence elucidating the regulation of the MCU complex, the molecular factors controlling the tissue-specific properties of the channel, and the physiological and pathological implications of mitochondrial Ca2+ signalling in different tissues.

The role of TGF-β signaling in muscle atrophy, sarcopenia and cancer cachexia

Skeletal muscle, comprising a significant proportion (40 to 50 percent) of total body weight in humans, plays a critical role in maintaining normal physiological conditions. Muscle atrophy occurs when the rate of protein degradation exceeds protein synthesis. Sarcopenia refers to age-related muscle atrophy, while cachexia represents a more complex form of muscle wasting associated with various diseases such as cancer, heart failure, and AIDS. Recent research has highlighted the involvement of signaling pathways, including IGF1-Akt-mTOR, MuRF1-MAFbx, and FOXO, in regulating the delicate balance between muscle protein synthesis and breakdown. Myostatin, a member of the TGF-β superfamily, negatively regulates muscle growth and promotes muscle atrophy by activating Smad2 and Smad3. It also interacts with other signaling pathways in cachexia and sarcopenia. Inhibition of myostatin has emerged as a promising therapeutic approach for sarcopenia and cachexia. Additionally, other TGF-β family members, such as TGF-β1, activin A, and GDF11, have been implicated in the regulation of skeletal muscle mass. Furthermore, myostatin cooperates with these family members to impair muscle differentiation and contribute to muscle loss. This review provides an overview of the significance of myostatin and other TGF-β signaling pathway members in muscular dystrophy, sarcopenia, and cachexia. It also discusses potential novel therapeutic strategies targeting myostatin and TGF-β signaling for the treatment of muscle atrophy.

Whole-genome SNP allele frequency differences between Tibetan and Large white pigs reveal genes associated with skeletal muscle growth

BACKGROUND

The skeletal muscle growth rate and body size of Tibetan pigs (TIB) are lower than Large white pigs (LW). However, the underlying genetic basis attributing to these differences remains uncertain. To address this knowledge gap, the present study employed whole-genome sequencing of TIB (slow growth) and LW (fast growth) individuals, and integrated with existing NCBI sequencing datasets of TIB and LW individuals, enabling the identification of a comprehensive set of genetic variations for each breed. The specific and predominant SNPs in the TIB and LW populations were detected by using a cutoff value of 0.50 for SNP allele frequency and absolute allele frequency differences (△AF) between the TIB and LW populations.

RESULTS

A total of 21,767,938 SNPs were retrieved from 44 TIB and 29 LW genomes. The analysis detected 2,893,106 (13.29%) and 813,310 (3.74%) specific and predominant SNPs in the TIB and LW populations, and annotated to 24,560 genes. Further GO analysis revealed 291 genes involved in biological processes related to striated and/or skeletal muscle differentiation, proliferation, hypertrophy, regulation of striated muscle cell differentiation and proliferation, and myoblast differentiation and fusion. These 291 genes included crucial regulators of muscle cell determination, proliferation, differentiation, and hypertrophy, such as members of the Myogenic regulatory factors (MRF) (MYOD, MYF5, MYOG, MYF6) and Myocyte enhancer factor 2 (MEF2) (MEF2A, MEF2C, MEF2D) families, as well as muscle growth inhibitors (MSTN, ACVR1, and SMAD1); KEGG pathway analysis revealed 106 and 20 genes were found in muscle growth related positive and negative regulatory signaling pathways. Notably, genes critical for protein synthesis, such as MTOR, IGF1, IGF1R, IRS1, INSR, and RPS6KA6, were implicated in these pathways.

CONCLUSION

This study employed an effective methodology to rigorously identify the potential genes associated with skeletal muscle development. A substantial number of SNPs and genes that potentially play roles in the divergence observed in skeletal muscle growth between the TIB and LW breeds were identified. These findings offer valuable insights into the genetic underpinnings of skeletal muscle development and present opportunities for enhancing meat production through pig breeding.

Bioreactor development for skeletal muscle hypertrophy and atrophy by manipulating uniaxial cyclic strain: proof of concept

Skeletal muscles overcome terrestrial, gravitational loading by producing tensile forces that produce movement through joint rotation. Conversely, the microgravity of spaceflight reduces tensile loads in working skeletal muscles, causing an adaptive muscle atrophy. Unfortunately, the design of stable, physiological bioreactors to model skeletal muscle tensile loading during spaceflight experiments remains challenging. Here, we tested a bioreactor that uses initiation and cessation of cyclic, tensile strain to induce hypertrophy and atrophy, respectively, in murine lineage (C2C12) skeletal muscle myotubes. Uniaxial cyclic stretch of myotubes was conducted using a StrexCell® (STB-1400) stepper motor system (0.75 Hz, 12% strain, 60 min day^-1). Myotube groups were assigned as follows: (a) quiescent over 2- or (b) 5-day (no stretch), (c) experienced 2-days (2dHY) or (d) 5-days (5dHY) of cyclic stretch, or (e) 2-days of cyclic stretch followed by a 3-day cessation of stretch (3dAT). Using ß-sarcoglycan as a sarcolemmal marker, mean myotube diameter increased significantly following 2dAT (51%) and 5dAT (94%) vs. matched controls. The hypertrophic, anabolic markers talin and Akt phosphorylation (Thr308) were elevated with 2dHY but not in 3dAT myotubes. Inflammatory, catabolic markers IL-1ß, IL6, and NF-kappaB p65 subunit were significantly higher in the 3dAT group vs. all other groups. The ratio of phosphorylated FoxO3a/total FoxO3a was significantly lower in 3dAT than in the 2dHY group, consistent with elevated catabolic signaling during unloading. In summary, we demonstrated proof-of-concept for a spaceflight research bioreactor, using uniaxial cyclic stretch to produce myotube hypertrophy with increased tensile loading, and myotube atrophy with subsequent cessation of stretch.

Cancer anorexia-cachexia syndrome is characterized by more than one inflammatory pathway

BACKGROUND

The interdependence of cytokines and appetite-modifying hormones implicated in cancer anorexia-cachexia syndrome (CACS) remains unclear. This study aimed to regroup these cytokines and hormones into distinct inflammatory (or non-inflammatory) pathways and determine whether these pathways can classify patients with CACS phenotypes.

METHODS

Clinical characteristics of 133 patients [61.7% male; mean age = 63.4 (SD: 13.1) years] with advanced cancer prior to oncology treatments were documented, including weight loss history. Patients completed the Functional Assessment of Anorexia-Cachexia Therapy (FAACT) questionnaire and Timed Up and Go test and had their sex-standardized skeletal muscle index (z-SMI) and fat mass index (z-FMI) derived using computed tomography scans. Their plasma levels of cytokines and appetite-modifying hormones were also determined. Date of death was recorded. Exploratory factor analysis (EFA) was used to regroup 15 cytokines and hormone into distinct inflammatory pathways (factors). For each patient, regression factor scores (RFS), which tell how strongly the patient associates with each factor, were derived. Two-step cluster analysis on the RFS was used to classify patients into groups. CACS phenotypes were correlated with RFS and compared between groups. Groups' survival was estimated using Kaplan-Meier analysis.

RESULTS

Patients had low z-SMI (mean = -3.78 cm2/m2; SD: 8.88) and z-FMI (mean = 0.08 kg2/m2; SD: 56.25), and 62 (46.6%) had cachexia. EFA identified three factors: (F-1) IFN-γ, IL-1β, Il-4, IL-6, IL-10, IL-12, TGFβ1 (positive contribution), and IL-18 (negative); (F-2) IL-8, IL-18, MCP-1, TGFβ1, TNF-α (positive), and ghrelin (negative); and (F-3) TRAIL and leptin (positive), and TGFβ1 and adiponectin (negative). RFS-1 was associated with cachexia (P = 0.002); RFS-2, with higher CRP (P < 0.0001) and decreased physical function (P = 0.01); and RFS-3 with better appetite (P = 0.04), lower CRP (P = 0.002), higher z-SMI (P = 0.04) and z-FMI (P < 0.0001), and less cachexia characteristics (all P < 0.001). Four patient groups were identified with specific RFS clusters aligning with the CACS continuum from no cachexia to pre-cachexia, cachexia, and terminal cachexia. Compared to the other two groups, groups 1 and 2 had higher plasma levels of IL-18 and TRAIL. Group 1 also had lower inflammatory cytokines, adiponectin, and CRP compared to the other three groups. Group 3 had inflammatory cytokine levels similar to group 2, except for TNF-α and leptin which were lower. Group 4 had very high inflammatory cytokines, adiponectin, and CRP compared to the other 3 groups (all P < 0.0001). Groups 3 and 4 had worse cachexia characteristics (P < 0.05) and shorter survival (log rank: P = 0.0009) than the other two groups.

CONCLUSIONS

This exploratory study identified three distinct pathways of inflammation, or lack thereof, characterizing different CACS phenotypes.

Clinical outcomes of multidimensional association of type 2 diabetes mellitus, COVID-19 and sarcopenia: an algorithm and scoping systematic evaluation

BACKGROUND

The aim of this study was to provide a scoping and comprehensive review for the clinical outcomes from the cross-link of Type 2 diabetes mellitus (T2DM), COVID-19, and sarcopenia.

METHODS

By using PRISMA guidelines and searching through different databases that could provide findings of evidence on the association of T2DM, COVID-19, and sarcopenia.

RESULTS

Thirty-three studies reported a relationship between sarcopenia with T2DM, twenty-one studies reported the prognosis COVID-19 in patients with T2DM, ten studies reported the prognosis of COVID-19 in patients with sarcopenia, five studies discussed the outcomes of sarcopenia in patients with COVID-19, and one study reported sarcopenia outcomes in the presence of T2DM and COVID-19.

CONCLUSION

There is an obvious multidimensional relationship between T2DM, COVID-19 and sarcopenia which can cause prejudicial effects, poor prognosis, prolonged hospitalisation, lowered quality of life and a higher mortality rate during the current COVID-19 pandemic.

Circulating myostatin as a biomarker of muscle mass and strength in individuals with cancer or obesity

BACKGROUND & AIMS

Our study aims to determine whether myostatin (MSTN) is associated with muscle mass and strength in individuals with cancer or obesity, as well as with cancer cachexia (CC) or sarcopenic obesity (SO).

METHODS

The ACTICA study included individuals with CC (n = 70) or without CC (NC, n = 73). The MYDIASECRET study included individuals with obesity evaluated before (T0) and 3 months (T3) after bariatric surgery (n = 62). Body composition was assessed using bioelectrical impedance analysis (BIA). Skeletal muscle mass (SMM) and appendicular SMM (ASMM) were calculated from Janssen's and Sergi's equations, respectively, and expressed as indexes (SMMI and ASMMI). Handgrip strength (HGS) was assessed using a Jamar hand-held dynamometer. MSTN plasma levels were measured using ELISA. Spearman's coefficient was used to correlate MSTN with muscle mass and strength. Receiver operating characteristic (ROC) curve analysis was performed to identify an optimal MSTN cutoff level for the prediction of CC or SO.

RESULTS

In the ACTICA study, muscle mass and strength were lower in CC individuals than in NC individuals (SMMI: 8.0 kg/m2vs 9.0 kg/m2, p = 0.004; ASMMI: 6.2 kg/m2vs 7.2 kg/m2, p < 0.001; HGS: 28 kg vs 38 kg, p < 0.001). MSTN was also lower in CC individuals than in NC individuals (1434 pg/mL vs 2149 pg/mL, p < 0.001). Muscle mass and strength were positively correlated with MSTN (SMMI: R = 0.500, p < 0.001; ASMMI: R = 0.479, p < 0.001; HGS: R = 0.495, p < 0.001). ROC curve analysis showed a MSTN cutoff level of 1548 pg/mL (AUC 0.684, sensitivity 57%, specificity 75%, p < 0.001) for the prediction of CC. In the MYDIASECRET study, muscle mass and strength were reduced at T3 (SMMI: -8%, p < 0.001; ASMMI: -12%, p < 0.001; HGS: -6%, p = 0.005). MSTN was also reduced at T3 (1773 pg/mL vs 2582 pg/mL, p < 0.001). Muscle mass and strength were positively correlated with MSTN at T0 and T3 (SMMI-T0: R = 0.388, p = 0.002; SMMI-T3: R = 0.435, p < 0.001; HGS-T0: R = 0.337, p = 0.007; HGS-T3: R = 0.313, p = 0.013). ROC curve analysis showed a MSTN cutoff level of 4225 pg/mL (AUC 0.835, sensitivity 98%, specificity 100%, p = 0.014) for the prediction of SO at T3.

CONCLUSIONS

MSTN is positively correlated with muscle mass and strength in individuals with cancer or obesity, suggesting its potential use as a biomarker of muscle mass and strength. The ROC curve analysis suggests the potential use of MSTN as a screening tool for CC and SO.

Fermented Yak-Kong using Bifidobacterium animalis derived from Korean infant intestine effectively relieves muscle atrophy in an aging mouse model

Yak-Kong (YK) is a small black soybean widely cultivated in Korea. It is considered to have excellent health functionality, as it has been reported to have better antioxidant efficacy than conventional black or yellow soybeans. Since YK has been described as good for the muscle health of the elderly in old oriental medicine books, this study sought to investigate the effect of fermented YK with Bifidobacterium animalis subsp. lactis LDTM 8102 (FYK) on muscle atrophy. In C2C12 mouse myoblasts, FYK elevated the expression of MyoD, total MHC, phosphorylated AKT, and PGC1α. In addition, two kinds of in vivo studies were conducted using both an induced and normal aging mouse model. The behavioral test results showed that in the induced aging mouse model, FYK intake alleviated age-related muscle weakness and loss of exercise performance. In addition, FYK alleviated muscle mass decrease and improved the expression of biomarkers including total MHC, myf6, phosphorylated AKT, PGC1α, and Tfam, which are related to myoblast differentiation, muscle protein synthesis, and mitochondrial generation in the muscle. In the normal aging model, FYK consumption did not increase muscle mass, but did upregulate the expression levels of biomarkers related to myoblast differentiation, muscle hypertrophy, and muscle function. Furthermore, it mitigated age-related declines in skeletal muscle force production and functional limitation by enhancing exercise performance and grip strength. Taken together, the results suggest that FYK has the potential to be a new functional food material that can alleviate the loss of muscle mass and strength caused by aging and prevent sarcopenia.

Thbs1 regulates skeletal muscle mass in a TGFβ-Smad2/3-ATF4-dependent manner

Loss of muscle mass is a feature of chronic illness and aging. Here, we report that skeletal muscle-specific thrombospondin-1 transgenic mice (Thbs1 Tg) have profound muscle atrophy with age-dependent decreases in exercise capacity and premature lethality. Mechanistically, Thbs1 activates transforming growth factor β (TGFβ)-Smad2/3 signaling, which also induces activating transcription factor 4 (ATF4) expression that together modulates the autophagy-lysosomal pathway (ALP) and ubiquitin-proteasome system (UPS) to facilitate muscle atrophy. Indeed, myofiber-specific inhibition of TGFβ-receptor signaling represses the induction of ATF4, normalizes ALP and UPS, and partially restores muscle mass in Thbs1 Tg mice. Similarly, myofiber-specific deletion of Smad2 and Smad3 or the Atf4 gene antagonizes Thbs1-induced muscle atrophy. More importantly, Thbs1-/- mice show significantly reduced levels of denervation- and caloric restriction-mediated muscle atrophy, along with blunted TGFβ-Smad3-ATF4 signaling. Thus, Thbs1-mediated TGFβ-Smad3-ATF4 signaling in skeletal muscle regulates tissue rarefaction, suggesting a target for atrophy-based muscle diseases and sarcopenia with aging.

Association between the systemic immune-inflammation index and sarcopenia: a systematic review and meta-analysis

BACKGROUND

Sarcopenia is associated with increased morbidity and mortality. The systemic immune-inflammation index (SII) has been correlated to a variety of disorders. The present study conducted a systematic review and meta-analysis to investigate the relationship between SII and sarcopenia.

METHODS

A literature search was performed in Web of Science, PubMed, Embase, Cochrane Library, CINAHL, China National Knowledge Infrastructure, Chinese Biomedical Literature Database, Wanfang Database, and VIP Chinese Science and Technology Database, from inception to March 2024. Then, the literature quality was assessed. After the heterogeneity test, a random effects or fixed effects model was applied to establish the forest plot, and investigate the relationship between SII and sarcopenia. Then, the sensitivity analysis and publication bias were examined.

RESULTS

Nine articles, which included 18,634 adults, were analyzed. Sarcopenic adults had higher SII levels, when compared to non-sarcopenic adults (standardized mean difference [SMD] = 0.66, 95% confidence interval [CI] = 0.22 - 0.19, p = 0.003). The high SII level was associated to the increased risk of sarcopenia (odds ratio = 1.52, 95% CI = 1.09-2.13, p = 0.01). In addition, the subgroup analysis revealed that the SII levels were higher in the sarcopenic group, when compared to the non-sarcopenic group, in elderly adults, as well as in adults with or without gastrointestinal disorders. The analysis was robust with a low risk of publication bias.

CONCLUSIONS

SII is closely associated to sarcopenia. Sarcopenic adults had elevated SII levels. The high SII level increased the risk of sarcopenia. Large scale multi-center prospective studies are required to validate these study findings.

Lactobacillus-derived protoporphyrin IX and SCFAs regulate the fiber size via glucose metabolism in the skeletal muscle of chickens

The gut microbiota contributes to skeletal muscle energy metabolism and is an indirect factor affecting meat quality. However, the role of specific gut microbes in energy metabolism and fiber size of skeletal muscle in chickens remains largely unknown. In this study, we first performed cecal microbiota transplantation from Chinese indigenous Jingyuan chickens (JY) to Arbor Acres chickens (AA), to determine the effects of microbiota on skeletal muscle fiber and energy metabolism. Then, we used metagenomics, gas chromatography, and metabolomics analysis to identify functional microbes. Finally, we validated the role of these functional microbes in regulating the fiber size via glucose metabolism in the skeletal muscle of chickens through feeding experiments. The results showed that the skeletal muscle characteristics of AA after microbiota transplantation tended to be consistent with that of JY, as the fiber diameter was significantly increased, and glucose metabolism level was significantly enhanced in the pectoralis muscle. L. plantarum, L. ingluviei, L. salivarius, and their mixture could increase the production of the microbial metabolites protoporphyrin IX and short-chain fatty acids, therefore increasing the expression levels of genes related to the oxidative fiber type (MyHC SM and MyHC FRM), mitochondrial function (Tfam and CoxVa), and glucose metabolism (PFK, PK, PDH, IDH, and SDH), thereby increasing the fiber diameter and density. These three Lactobacillus species could be promising probiotics to improve the meat quality of chicken.IMPORTANCEThis study revealed that the L. plantarum, L. ingluviei, and L. salivarius could enhance the production of protoporphyrin IX and short-chain fatty acids in the cecum of chickens, improving glucose metabolism, and finally cause the increase in fiber diameter and density of skeletal muscle. These three microbes could be potential probiotic candidates to regulate glucose metabolism in skeletal muscle to improve the meat quality of chicken in broiler production.

AMPK as a mediator of tissue preservation: time for a shift in dogma?

Ground-breaking discoveries have established 5'-AMP-activated protein kinase (AMPK) as a central sensor of metabolic stress in cells and tissues. AMPK is activated through cellular starvation, exercise and drugs by either directly or indirectly affecting the intracellular AMP (or ADP) to ATP ratio. In turn, AMPK regulates multiple processes of cell metabolism, such as the maintenance of cellular ATP levels, via the regulation of fatty acid oxidation, glucose uptake, glycolysis, autophagy, mitochondrial biogenesis and degradation, and insulin sensitivity. Moreover, AMPK inhibits anabolic processes, such as lipogenesis and protein synthesis. These findings support the notion that AMPK is a crucial regulator of cell catabolism. However, studies have revealed that AMPK's role in cell homeostasis might not be as unidirectional as originally thought. This Review explores emerging evidence for AMPK as a promoter of cell survival and an enhancer of anabolic capacity in skeletal muscle and adipose tissue during catabolic crises. We discuss AMPK-activating interventions for tissue preservation during tissue wasting in cancer-associated cachexia and explore the clinical potential of AMPK activation in wasting conditions. Overall, we provide arguments that call for a shift in the current dogma of AMPK as a mere regulator of cell catabolism, concluding that AMPK has an unexpected role in tissue preservation.

LncRNA 4930581F22Rik promotes myogenic differentiation by regulating the ERK/MAPK signaling pathway

The skeletal muscle is the largest organ in mammals and is the primary motor function organ of the body. Our previous research has shown that long non-coding RNAs (lncRNAs) are significant in the epigenetic control of skeletal muscle development. Here, we observed progressive upregulation of lncRNA 4930581F22Rik expression during skeletal muscle differentiation. Knockdown of lncRNA 4930581F22Rik hindered skeletal muscle differentiation and resulted in the inhibition of the myogenic markers MyHC and MEF2C. Furthermore, we found that lncRNA 4930581F22Rik regulates myogenesis via the ERK/MAPK signaling pathway, and this effect could be attenuated by the ERK-specific inhibitor PD0325901. Additionally, in vivo mice injury model results revealed that lncRNA 4930581F22Rik is involved in skeletal muscle regeneration. These results establish a theoretical basis for understanding the contribution of lncRNAs in skeletal muscle development and regeneration.

Microbiota-derived 3-phenylpropionic acid promotes myotube hypertrophy by Foxo3/NAD+ signaling pathway

BACKGROUND

Gut microbiota and their metabolites play a regulatory role in skeletal muscle growth and development, which be known as gut-muscle axis. 3-phenylpropionic acid (3-PPA), a metabolite produced by colonic microorganisms from phenylalanine in the gut, presents in large quantities in the blood circulation. But few study revealed its function in skeletal muscle development.

RESULTS

Here, we demonstrated the beneficial effects of 3-PPA on muscle mass increase and myotubes hypertrophy both in vivo and vitro. Further, we discovered the 3-PPA effectively inhibited protein degradation and promoted protein acetylation in C2C12 and chick embryo primary skeletal muscle myotubes. Mechanistically, we supported that 3-PPA reduced NAD+ synthesis and subsequently suppressed tricarboxylic acid cycle and the mRNA expression of SIRT1/3, thus promoting the acetylation of total protein and Foxo3. Moreover, 3-PPA may inhibit Foxo3 activity by directly binding.

CONCLUSIONS

This study firstly revealed the effect of 3-PPA on skeletal muscle growth and development, and newly discovered the interaction between 3-PPA and Foxo3/NAD+ which mechanically promote myotubes hypertrophy. These results expand new understanding for the regulation of gut microbiota metabolites on skeletal muscle growth and development.

Considerations for cultivated crustacean meat: potential cell sources, potential differentiation and immortalization strategies, and lessons from crustacean and other animal models

Cultivated crustacean meat (CCM) is a means to create highly valued shrimp, lobster, and crab products directly from stem cells, thus removing the need to farm or fish live animals. Conventional crustacean enterprises face increasing pressures in managing overfishing, pollution, and the warming climate, so CCM may provide a way to ensure sufficient supply as global demand for these products grows. To support the development of CCM, this review briefly details crustacean cell culture work to date, before addressing what is presently known about crustacean muscle development, particularly the molecular mechanisms involved, and how this might relate to recent work on cultivated meat production in vertebrate species. Recognizing the current lack of cell lines available to establish CCM cultures, we also consider primary stem cell sources that can be obtained non-lethally including tissues from limbs which are readily released and regrown, and putative stem cells in circulating hemolymph. Molecular approaches to inducing myogenic differentiation and immortalization of putative stem cells are also reviewed. Finally, we assess the current status of tools available to CCM researchers, particularly antibodies, and propose avenues to address existing shortfalls in order to see the field progress.

Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies

Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.

Systemic LPS Administration Stimulates the Activation of Non-Neuronal Cells in an Experimental Model of Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by deficiency of the survival motor neuron (SMN) protein. Although SMA is a genetic disease, environmental factors contribute to disease progression. Common pathogen components such as lipopolysaccharides (LPS) are considered significant contributors to inflammation and have been associated with muscle atrophy, which is considered a hallmark of SMA. In this study, we used the SMNΔ7 experimental mouse model of SMA to scrutinize the effect of systemic LPS administration, a strong pro-inflammatory stimulus, on disease outcome. Systemic LPS administration promoted a reduction in SMN expression levels in CNS, peripheral lymphoid organs, and skeletal muscles. Moreover, peripheral tissues were more vulnerable to LPS-induced damage compared to CNS tissues. Furthermore, systemic LPS administration resulted in a profound increase in microglia and astrocytes with reactive phenotypes in the CNS of SMNΔ7 mice. In conclusion, we hereby show for the first time that systemic LPS administration, although it may not precipitate alterations in terms of deficits of motor functions in a mouse model of SMA, it may, however, lead to a reduction in the SMN protein expression levels in the skeletal muscles and the CNS, thus promoting synapse damage and glial cells' reactive phenotype.

Brain-muscle communication prevents muscle aging by maintaining daily physiology

A molecular clock network is crucial for daily physiology and maintaining organismal health. We examined the interactions and importance of intratissue clock networks in muscle tissue maintenance. In arrhythmic mice showing premature aging, we created a basic clock module involving a central and a peripheral (muscle) clock. Reconstituting the brain-muscle clock network is sufficient to preserve fundamental daily homeostatic functions and prevent premature muscle aging. However, achieving whole muscle physiology requires contributions from other peripheral clocks. Mechanistically, the muscle peripheral clock acts as a gatekeeper, selectively suppressing detrimental signals from the central clock while integrating important muscle homeostatic functions. Our research reveals the interplay between the central and peripheral clocks in daily muscle function and underscores the impact of eating patterns on these interactions.

Coculture with Colon-26 cancer cells decreases the protein synthesis rate and shifts energy metabolism toward glycolysis dominance in C2C12 myotubes

Cancer cachexia is the result of complex interorgan interactions initiated by cancer cells and changes in patient behavior such as decreased physical activity and energy intake. Therefore, it is crucial to distinguish between the direct and indirect effects of cancer cells on muscle mass regulation and bioenergetics to identify novel therapeutic targets. In this study, we investigated the direct effects of Colon-26 cancer cells on the molecular regulating machinery of muscle mass and its bioenergetics using a coculture system with C2C12 myotubes. Our results demonstrated that coculture with Colon-26 cells induced myotube atrophy and reduced skeletal muscle protein synthesis and its regulating mechanistic target of rapamycin complex 1 signal transduction. However, we did not observe any activating effects on protein degradation pathways including ubiquitin-proteasome and autophagy-lysosome systems. From a bioenergetic perspective, coculture with Colon-26 cells decreased the complex I-driven, but not complex II-driven, mitochondrial ATP production capacity, while increasing glycolytic enzyme activity and glycolytic metabolites, suggesting a shift in energy metabolism toward glycolysis dominance. Gene expression profiling by RNA sequencing showed that the increased activity of glycolytic enzymes was consistent with changes in gene expression. However, the decreased ATP production capacity of mitochondria was not in line with the gene expression. The potential direct interaction between cancer cells and skeletal muscle cells revealed in this study may contribute to a better fundamental understanding of the complex pathophysiology of cancer cachexia.NEW & NOTEWORTHY We explored the potential direct interplay between colon cancer cells (Colon-26) and skeletal muscle cells (C2C12 myotubes) employing a noncontact coculture experimental model. Our findings reveal that coculturing with Colon-26 cells substantially impairs the protein synthesis rate, concurrently instigating a metabolic shift toward glycolytic dominance in C2C12 myotubes. This research unveils critical insights into the intricate cellular cross talk underpinning the complex pathophysiology of cancer cachexia.

Preventive effect of fermented whey protein mediated by Lactobacillus gasseri IM13 via the PI3K/AKT/FOXO pathway in muscle atrophy

This study investigated the preventive effects of whey protein fermented with Lactobacillus gasseri IM13 (F-WP) against dexamethasone (DEX)-induced muscle atrophy. C2C12 muscle cells were treated with F-WP followed by DEX treatment. Dexamethasone treatment inhibited myotube formation and the expression of myogenic regulatory factors; however, pretreatment with F-WP attenuated DEX-induced damage. The F-WP significantly activated the phosphorylation of the IGF-1/PI3K/AKT pathway and improved muscle homeostasis suppressed by DEX. Moreover, F-WP alleviated the phosphorylation of mTOR, S6K1, and 4E-BP1 and enhanced muscle protein synthesis. Muscle-specific ubiquitin ligases and autophagy lysosomes, which were activated by the dephosphorylation of FOXO3a by DEX treatment, were significantly attenuated by F-WP pretreatment of myotubes. For peptidomic analysis, F-WP was fractionated using preparative HPLC (prep-HPLC), and the AA sequences of 11 peptides were identified using MALDI-TOF/MS/MS. In conclusion, fermentation of whey protein by the specific probiotic strain IM13 produced bioactive peptides with high antioxidant and anti-sarcopenic-sarcopenic effects, which markedly enhanced myogenesis and muscle protein synthesis while diminishing muscle protein degradation compared with intact whey protein.

Equisetum arvense standardized dried extract hinders age-related osteosarcopenia

Age-associated osteosarcopenia is an unresolved syndrome characterized by the concomitant loss of bone (osteopenia) and skeletal muscle (sarcopenia) tissues increasing falls, immobility, morbidity, and mortality. Unbalanced resorption of bone in the remodeling process and excessive protein breakdown, especially fast type II myosin heavy chain (MyHC-II) isoform and myofiber metabolic shift, are the leading causes of bone and muscle deterioration in the elderly, respectively. Equisetum arvense (EQ) is a plant traditionally recommended for many pathological conditions due to its anti-inflammatory properties. Thus, considering that a chronic low-grade inflammatory state predisposes to both osteoporosis and sarcopenia, we tested a standardized hydroalcoholic extract of EQ in in vitro models of muscle atrophy [C2C12 myotubes treated with proinflammatory cytokines (TNFα/IFNγ), excess glucocorticoids (dexamethasone), or the osteokine, receptor activator of nuclear factor kappa-B ligand (RANKL)] and osteoclastogenesis (RAW 264.7 cells treated with RANKL). We found that EQ counteracted myotube atrophy, blunting the activity of several pathways depending on the applied stimulus, and reduced osteoclast formation and activity. By in silico target fishing, IKKB-dependent nuclear factor kappa-B (NF-κB) inhibition emerges as a potential common mechanism underlying EQ's anti-atrophic effects. Consumption of EQ (500 mg/kg/day) by pre-geriatric C57BL/6 mice for 3 months translated into: i) maintenance of muscle mass and performance; ii) restrained myofiber oxidative shift; iii) slowed down age-related modifications in osteoporotic bone, significantly preserving trabecular connectivity density; iv) reduced muscle- and spleen-related inflammation. EQ can preserve muscle functionality and bone remodeling during aging, potentially valuable as a natural treatment for osteosarcopenia.

MFN2 overexpression in skeletal muscles of young and old mice causes a mild hypertrophy without altering mitochondrial respiration and H2O2 emission

AIM

Sarcopenia, the aging-related loss of muscle mass and function, is a debilitating process negatively impacting the quality of life of affected individuals. Although the mechanisms underlying sarcopenia are incompletely understood, impairments in mitochondrial dynamics, including mitochondrial fusion, have been proposed as a contributing factor. However, the potential of upregulating mitochondrial fusion proteins to alleviate the effects of aging on skeletal muscles remains unexplored. We therefore hypothesized that overexpressing Mitofusin 2 (MFN2) in skeletal muscle in vivo would mitigate the effects of aging on muscle mass and improve mitochondrial function.

METHODS

MFN2 was overexpressed in young (7 mo) and old (24 mo) male mice for 4 months through intramuscular injections of an adeno-associated viruses. The impacts of MFN2 overexpression on muscle mass and fiber size (histology), mitochondrial respiration, and H2O2 emission (Oroboros fluororespirometry), and various signaling pathways (qPCR and western blotting) were investigated.

RESULTS

MFN2 overexpression increased muscle mass and fiber size in both young and old mice. No sign of fibrosis, necrosis, or inflammation was found upon MFN2 overexpression, indicating that the hypertrophy triggered by MFN2 overexpression was not pathological. MFN2 overexpression even reduced the proportion of fibers with central nuclei in old muscles. Importantly, MFN2 overexpression had no impact on muscle mitochondrial respiration and H2O2 emission in both young and old mice. MFN2 overexpression attenuated the increase in markers of impaired autophagy in old muscles.

CONCLUSION

MFN2 overexpression may be a viable approach to mitigate aging-related muscle atrophy and may have applications for other muscle disorders.

Nutritional Strategies for Muscle Atrophy: Current Evidence and Underlying Mechanisms

Skeletal muscle can undergo detrimental changes in various diseases, leading to muscle dysfunction and atrophy, thus severely affecting people's lives. Along with exercise, there is a growing interest in the potential of nutritional support against muscle atrophy. This review provides a brief overview of the molecular mechanisms driving skeletal muscle atrophy and summarizes recent advances in nutritional interventions for preventing and treating muscle atrophy. The nutritional supplements include amino acids and their derivatives (such as leucine, β-hydroxy, β-methylbutyrate, and creatine), various antioxidant supplements (like Coenzyme Q10 and mitoquinone, resveratrol, curcumin, quercetin, Omega 3 fatty acids), minerals (such as magnesium and selenium), and vitamins (such as vitamin B, vitamin C, vitamin D, and vitamin E), as well as probiotics and prebiotics (like Lactobacillus, Bifidobacterium, and 1-kestose). Furthermore, the study discusses the impact of a combined approach involving nutritional support and physical therapy to prevent muscle atrophy, suggests appropriate multi-nutritional and multi-modal interventions based on individual conditions to optimize treatment outcomes, and enhances the recovery of muscle function for patients. By understanding the molecular mechanisms behind skeletal muscle atrophy and implementing appropriate interventions, it is possible to enhance the recovery of muscle function and improve patients' quality of life.

Fasting mimicking diet in diabetic mice partially preserves glomerular endothelial glycocalyx coverage, without changing the diabetic metabolic environment

Intermittent fasting has become of interest for its possible metabolic benefits and reduction of inflammation and oxidative damage, all of which play a role in the pathophysiology of diabetic nephropathy. We tested in a streptozotocin (60 mg/kg)-induced diabetic apolipoprotein E knockout mouse model whether repeated fasting mimicking diet (FMD) prevents glomerular damage. Diabetic mice received 5 FMD cycles in 10 wk, and during cycles 1 and 5 caloric measurements were performed. After 10 wk, glomerular endothelial morphology was determined together with albuminuria, urinary heparanase-1 activity, and spatial mass spectrometry imaging to identify specific glomerular metabolic dysregulation. During FMD cycles, blood glucose levels dropped while a temporal metabolic switch was observed to increase fatty acid oxidation. Overall body weight at the end of the study was reduced together with albuminuria, although urine production was dramatically increased without affecting urinary heparanase-1 activity. Weight loss was found to be due to lean mass and water, not fat mass. Although capillary loop morphology and endothelial glycocalyx heparan sulfate contents were preserved, hyaluronan surface expression was reduced together with the presence of UDP-glucuronic acid. Mass spectrometry imaging further revealed reduced protein catabolic breakdown products and increased oxidative stress, not different from diabetic mice. In conclusion, although FMD preserves partially glomerular endothelial glycocalyx, loss of lean mass and increased glomerular oxidative stress argue whether such diet regimes are safe in patients with diabetes.NEW & NOTEWORTHY Repeated fasting mimicking diet (FMD) partially prevents glomerular damage in a diabetic mouse model; however, although endothelial glycocalyx heparan sulfate contents were preserved, hyaluronan surface expression was reduced in the presence of UDP-glucuronic acid. The weight loss observed was of lean mass, not fat mass, and increased glomerular oxidative stress argue whether such a diet is safe in patients with diabetes.

Multimodal cell atlas of the ageing human skeletal muscle

Muscle atrophy and functional decline (sarcopenia) are common manifestations of frailty and are critical contributors to morbidity and mortality in older people1. Deciphering the molecular mechanisms underlying sarcopenia has major implications for understanding human ageing2. Yet, progress has been slow, partly due to the difficulties of characterizing skeletal muscle niche heterogeneity (whereby myofibres are the most abundant) and obtaining well-characterized human samples3,4. Here we generate a single-cell/single-nucleus transcriptomic and chromatin accessibility map of human limb skeletal muscles encompassing over 387,000 cells/nuclei from individuals aged 15 to 99 years with distinct fitness and frailty levels. We describe how cell populations change during ageing, including the emergence of new populations in older people, and the cell-specific and multicellular network features (at the transcriptomic and epigenetic levels) associated with these changes. On the basis of cross-comparison with genetic data, we also identify key elements of chromatin architecture that mark susceptibility to sarcopenia. Our study provides a basis for identifying targets in the skeletal muscle that are amenable to medical, pharmacological and lifestyle interventions in late life.

CRISPR Screen Identifies the RNA-Binding Protein Eef1a1 as a Key Regulator of Myogenesis

Skeletal muscle myogenesis hinges on gene regulation, meticulously orchestrated by molecular mechanisms. While the roles of transcription factors and non-coding RNAs in myogenesis are widely known, the contribution of RNA-binding proteins (RBPs) has remained unclear until now. Therefore, to investigate the functions of post-transcriptional regulators in myogenesis and uncover new functional RBPs regulating myogenesis, we employed CRISPR high-throughput RBP-KO (RBP-wide knockout) library screening. Through this approach, we successfully identified Eef1a1 as a novel regulatory factor in myogenesis. Using CRISPR knockout (CRISPRko) and CRISPR interference (CRISPRi) technologies, we successfully established cellular models for both CRISPRko and CRISPRi. Our findings demonstrated that Eef1a1 plays a crucial role in promoting proliferation in C2C12 myoblasts. Through siRNA inhibition and overexpression methods, we further elucidated the involvement of Eef1a1 in promoting proliferation and suppressing differentiation processes. RIP (RNA immunoprecipitation), miRNA pull-down, and Dual-luciferase reporter assays confirmed that miR-133a-3p targets Eef1a1. Co-transfection experiments indicated that miR-133a-3p can rescue the effect of Eef1a1 on C2C12 myoblasts. In summary, our study utilized CRISPR library high-throughput screening to unveil a novel RBP, Eef1a1, involved in regulating myogenesis. Eef1a1 promotes the proliferation of myoblasts while inhibiting the differentiation process. Additionally, it acts as an antagonist to miR-133a-3p, thus modulating the process of myogenesis.

Triptolide, a Cancer Cell Proliferation Inhibitor, Causes Zebrafish Muscle Defects by Regulating Notch and STAT3 Signaling Pathways

Triptolide is a natural compound in herbal remedies with anti-inflammatory and anti-proliferative properties. We studied its effects on critical signaling processes within the cell, including Notch1 and STAT3 signaling. Our research showed that triptolide reduces cancer cell proliferation by decreasing the expression of downstream targets of these signals. The levels of each signal-related protein and mRNA were analyzed using Western blot and qPCR methods. Interestingly, inhibiting one signal with a single inhibitor alone did not significantly reduce cancer cell proliferation. Instead, MTT assays showed that the simultaneous inhibition of Notch1 and STAT3 signaling reduced cell proliferation. The effect of triptolide was similar to a combination treatment with inhibitors for both signals. When we conducted a study on the impact of triptolide on zebrafish larvae, we found that it inhibited muscle development and interfered with muscle cell proliferation, as evidenced by differences in the staining of myosin heavy chain and F-actin proteins in confocal fluorescence microscopy. Additionally, we noticed that inhibiting a single type of signaling did not lead to any significant muscle defects. This implies that triptolide obstructs multiple signals simultaneously, including Notch1 and STAT3, during muscle development. Chemotherapy is commonly used to treat cancer, but it may cause muscle loss due to drug-related adverse reactions or other complex mechanisms. Our study suggests that anticancer agents like triptolide, inhibiting essential signaling pathways including Notch1 and STAT3 signaling, may cause muscle atrophy through anti-proliferative activity.

Targeting Molecular Mechanisms of Obesity- and Type 2 Diabetes Mellitus-Induced Skeletal Muscle Atrophy with Nerve Growth Factor

Skeletal muscle plays a critical role in metabolic diseases, such as obesity and type 2 diabetes mellitus (T2DM). Muscle atrophy, characterized by a decrease in muscle mass and function, occurs due to an imbalance between the rates of muscle protein synthesis and degradation. This study aimed to investigate the molecular mechanisms that lead to muscle atrophy in obese and T2DM mouse models. Additionally, the effect of nerve growth factor (NGF) on the protein synthesis and degradation pathways was examined. Male mice were divided into three groups: a control group that was fed a standard chow diet, and two experimental groups that were fed a Western diet. After 8 weeks, the diabetic group was injected with streptozotocin to induce T2DM. Each group was then further divided into NGF-treated or non-treated control group. In the gastrocnemius muscles of the Western diet group, increased expressions of myostatin, autophagy markers, and ubiquitin ligases were observed. Skeletal muscle tissue morphology indicated signs of muscle atrophy in both obese and diabetic mice. The NGF-treated group showed a prominent decrease in the protein levels of myostatin and autophagy markers. Furthermore, the NGF-treated group showed an increased Cyclin D1 level. Western diet-induced obesity and T2DM may be linked to muscle atrophy through upregulation of myostatin and subsequent increase in the ubiquitin and autophagy systems. Moreover, NGF treatment may improve muscle protein synthesis and cell cycling.

Skeletal muscle of young females under resistance exercise exhibits a unique innate immune cell infiltration profile compared to males and elderly individuals

Muscle damage resulting from physical activities such as exercise triggers an immune response crucial for tissue repair and recovery. This study investigates the immune cell profiles in muscle biopsies of individuals engaged in resistance exercise (RE) and explores the impact of age and sex on the immune response following exercise-induced muscle damage. Microarray datasets from muscle biopsies of young and old subjects were analyzed, focusing on the gene expression patterns associated with immune cell activation. Genes were compared with immune cell signatures to reveal the cellular landscape during exercise. Results show that the most significant modulated gene after RE was Folliculin Interacting Protein 2 (FNIP2) a crucial regulator in cellular homeostasis. Moreover, the transcriptome was stratified based on the expression of FNIP2 and the 203 genes common to the groups obtained based on sex and age. Gene ontology analysis highlighted the FLCN-FNIP1-FNIP2 complex, which exerts as a negative feedback loop to Pi3k-Akt-mTORC1 pathway. Furthermore, we highlighted that the young females exhibit a distinct innate immune cell activation signature compared to males after a RE session. Specifically, young females demonstrate a notable overlap with dendritic cells (DCs), M1 macrophages, M2 macrophages, and neutrophils, while young males overlap with M1 macrophages, M2 macrophages, and motor neurons. Interestingly, in elderly subjects, both sexes display M1 macrophage activation signatures. Comparison of young and elderly signatures reveals an increased M1 macrophage percentage in young subjects. Additionally, common genes were identified in both sexes across different age groups, elucidating biological functions related to cell remodeling and immune activation. This study underscores the intricate interplay between sex, age, and the immune response in muscle tissue following RE, offering potential directions for future research. Nevertheless, there is a need for further studies to delve deeper and confirm the dynamics of immune cells in response to exercise-induced muscle damage.

Potential of Lycii Radicis Cortex as an Ameliorative Agent for Skeletal Muscle Atrophy

Lycii Radicis Cortex (LRC) is a traditional medicine in East Asia with various beneficial effects, including antioxidant, anti-inflammatory, anti-tumor, anti-diabetic, and anti-depressant properties. However, its potential effects on skeletal muscle atrophy have not been studied. In this study, the protective effects of LRC extract (LRCE) on dexamethasone (DEX)-induced muscle atrophy were investigated in C2C12 myotubes and mice. We evaluated the effect of LRCE on improving muscle atrophy using a variety of methods, including immunofluorescence staining, quantitative polymerase chain reaction (qPCR), Western blot, measurements of oxidative stress, apoptosis, ATP levels, and muscle tissue analysis. The results showed that LRCE improved myotube diameter, fusion index, superoxide dismutase (SOD) activity, mitochondrial content, ATP levels, expression of myogenin and myosin heavy chain (MHC), and reduced reactive oxygen species (ROS) production in dexamethasone-induced C2C12 myotubes. LRCE also enhanced protein synthesis and reduced protein degradation in the myotubes. In mice treated with DEX, LRCE restored calf thickness, decreased mRNA levels of muscle-specific RING finger protein 1 (MuRF1) and atrogin-1, and increased insulin-like growth factor 1 (IGF-1) mRNA level. Moreover, LRCE also repaired gastrocnemius muscle atrophy caused by DEX. Although human studies are not available, various preclinical studies have identified potential protective effects of LRCE against muscle atrophy, suggesting that it could be utilized in the prevention and treatment of muscle atrophy.

Streptococcal quorum sensing peptide CSP-7 contributes to muscle inflammation and wasting

Muscle wasting diseases, such as cancer cachexia and age-associated sarcopenia, have a profound and detrimental impact on functional independence, quality of life, and survival. Our understanding of the underlying mechanisms is currently limited, which has significantly hindered the development of targeted therapies. In this study, we explored the possibility that the streptococcal quorum sensing peptide Competence Stimulating Peptide 7 (CSP-7) might be a previously unidentified contributor to clinical muscle wasting. We found that CSP-7 selectively triggers muscle cell inflammation in vitro, specifically the release of IL-6. Furthermore, we demonstrated that CSP-7 can traverse the gastrointestinal barrier in vitro and is present in the systemic circulation in humans in vivo. Importantly, CSP-7 was associated with a muscle wasting phenotype in mice in vivo. Overall, our findings provide new mechanistic insights into the pathophysiology of muscle inflammation and wasting.

Oleanolic acid alleviates obesity-induced skeletal muscle atrophy via the PI3K/Akt signaling pathway

Oleanolic acid (OA) is a pentacyclic triterpene with reported protective effects against various diseases, including diabetes, hepatitis, and different cancers. However, the effects of OA on obesity-induced muscle atrophy remain largely unknown. This study investigated the effects of OA on skeletal muscle production and proliferation of C2C12 cells. We report that OA significantly increased skeletal muscle mass and improved glucose intolerance and insulin resistance. OA inhibited dexamethasone (Dex)-induced muscle atrophy in C2C12 myoblasts by regulating the PI3K/Akt signaling pathway. In addition, it also inhibited expression of MuRF1 and Atrogin1 genes in skeletal muscle of obese mice suffering from muscle atrophy, and increased the activation of PI3K and Akt, thereby promoting protein synthesis, and eventually alleviating muscle atrophy. Taken together, these findings suggest OA may have potential for the prevention and treatment of muscle atrophy.

Age-dependent loss of Crls1 causes myopathy and skeletal muscle regeneration failure

Skeletal muscle aging results in the gradual suppression of myogenesis, leading to muscle mass loss. However, the specific role of cardiolipin in myogenesis has not been determined. This study investigated the crucial role of mitochondrial cardiolipin and cardiolipin synthase 1 (Crls1) in age-related muscle deterioration and myogenesis. Our findings demonstrated that cardiolipin and Crls1 are downregulated in aged skeletal muscle. Moreover, the knockdown of Crls1 in myoblasts reduced mitochondrial mass, activity, and OXPHOS complex IV expression and disrupted the structure of the mitochondrial cristae. AAV9-shCrls1-mediated downregulation of Crls1 impaired muscle regeneration in a mouse model of cardiotoxin (CTX)-induced muscle damage, whereas AAV9-mCrls1-mediated Crls1 overexpression improved regeneration. Overall, our results highlight that the age-dependent decrease in CRLS1 expression contributes to muscle loss by diminishing mitochondrial quality in skeletal muscle myoblasts. Hence, modulating CRLS1 expression is a promising therapeutic strategy for mitigating muscle deterioration associated with aging, suggesting potential avenues for developing interventions to improve overall muscle health and quality of life in elderly individuals.

Celecoxib attenuates hindlimb unloading-induced muscle atrophy via suppressing inflammation, oxidative stress and ER stress by inhibiting STAT3

Improving inflammation may serve as useful therapeutic interventions for the hindlimb unloading-induced disuse muscle atrophy. Celecoxib is a selective non-steroidal anti-inflammatory drug. We aimed to determine the role and mechanism of celecoxib in hindlimb unloading-induced disuse muscle atrophy. Celecoxib significantly attenuated the decrease in soleus muscle mass, hindlimb muscle function and the shift from slow- to fast-twitch muscle fibers caused by hindlimb unloading in rats. Importantly, celecoxib inhibited the increased expression of inflammatory factors, macrophage infiltration in damaged soleus muscle. Mechanistically, Celecoxib could significantly reduce oxidative stress and endoplasmic reticulum stress in soleus muscle of unloaded rats. Furthermore, celecoxib inhibited muscle proteolysis by reducing the levels of MAFbx, MuRF1, and autophagy related proteins maybe by inhibiting the activation of pro-inflammatory STAT3 pathway in vivo and in vitro. This study is the first to demonstrate that celecoxib can attenuate disuse muscle atrophy caused by hindlimb unloading via suppressing inflammation, oxidative stress and endoplasmic reticulum stress probably, improving target muscle function and reversing the shift of muscle fiber types by inhibiting STAT3 pathways-mediated inflammatory cascade. This study not only enriches the potential molecular regulatory mechanisms, but also provides new potential therapeutic targets for disuse muscle atrophy.

Advances in sarcopenia: mechanisms, therapeutic targets, and intervention strategies

Sarcopenia is a multifactorial condition characterized by loss of muscle mass. It poses significant health risks in older adults worldwide. Both pharmacological and non-pharmacological approaches are reported to address this disease. Certain dietary patterns, such as adequate energy intake and essential amino acids, have shown positive outcomes in preserving muscle function. Various medications, including myostatin inhibitors, growth hormones, and activin type II receptor inhibitors, have been evaluated for their effectiveness in managing sarcopenia. However, it is important to consider the variable efficacy and potential side effects associated with these treatments. There are currently no drugs approved by the Food and Drug Administration for sarcopenia. The ongoing research aims to develop more effective strategies in the future. Our review of research on disease mechanisms and drug development will be a valuable contribution to future research endeavors.

Synergistically Acting on Myostatin and Agrin Pathways Increases Neuromuscular Junction Stability and Endurance in Old Mice

Sarcopenia is the primary cause of impaired motor performance in the elderly. The current prevailing approach to counteract such condition is increasing the muscle mass through inhibition of the myostatin system: however, this strategy only moderately improves muscular strength, not being able to sustain the innervation of the hypertrophic muscle per se, leading to a progressive worsening of motor performances. Thus, we proposed the administration of ActR-Fc-nLG3, a protein that combines the soluble activin receptor, a strong myostatin inhibitor, with the C-terminal agrin nLG3 domain. This compound has the potential of reinforcing neuro-muscular stability to the hypertrophic muscle. We previously demonstrated an enhancement of motor endurance and ACh receptor aggregation in young mice after ActR-Fc-nLG3 administration. Now we extended these observations by demonstrating that also in aged (2 years-old) mice, long-term administration of ActR-Fc-nLG3 increases in a sustained way both motor endurance and muscle strength, compared with ActR-Fc, a myostatin inhibitor, alone. Histological data demonstrate that the administration of this biological improves neuromuscular stability and fiber innervation maintenance, preventing muscle fiber atrophy and inducing only moderate hypertrophy. Moreover, at the postsynaptic site we observe an increased folding in the soleplate, a likely anatomical substrate for improved neurotransmission efficiency in the NMJ, that may lead to enhanced motor endurance. We suggest that ActR-Fc-nLG3 may become a valid option for treating sarcopenia and possibly other disorders of striatal muscles.

Resistance exercise preconditioning prevents disuse muscle atrophy by inhibiting apoptosis and protein degradation via SESN2 in C57BL/6J mice

AIM

To compare the effects of different exercise preconditioning in the context of skeletal muscle atrophy and to investigate the potential involvement of Sestrin2 (SESN2), a stress-inducible protein that can be regulated by exercise, in exercise preconditioning on preventing disuse muscle atrophy.

METHODS

Eight-week-old male C57BL/6J mice were randomly assigned to sedentary groups (SD), aerobic exercise groups (AE), resistance exercise groups (RE), and combined exercise groups (CE) with or without 7 days of immobilization. The duration of the exercise intervention was 10 weeks. The effects of different exercise preconditioning to prevent muscle atrophy were analyzed by evaluating skeletal muscle function and mass. Additionally, to investigate the potential underlying mechanism of exercise-induced protection of skeletal muscle, wild-type and SESN2--/-- mice were randomly divided into sedentary group and resistance exercise preconditioning group. C2C12 cells were treated with SESN2 adenoviruses and MK2206 (an AKT inhibitor) for 48 h to elucidate the underlined mechanism.

RESULTS

RE was more effective in preserving skeletal muscle function, muscle mass and maintaining skeletal muscle protein homeostasis than AE and CE under immobilized condition. Importantly, exercise performance, muscle mass to body weight ratio, and the cross-sectional area of muscle fibers were significantly lower in SESN2-/- mice than wild-type mice after resistance exercise preconditioning. Mechanistically, the absence of SESN2 led to activation of the ubiquitin-proteasome system and induction of apoptosis. In vitro experiments showed that MK2206 treatment mitigated the regulatory effects of overexpression-SESN2 on protein hydrolysis and apoptosis.

CONCLUSION

RE was more effective than AE or CE in preventing disuse muscle atrophy. SESN2 mediated the protective effects of resistance exercise preconditioning on skeletal muscle atrophy.

The key role of myostatin b in somatic growth in fishes derived from distant hybridization

The basic mechanism of heterosis has not been systematically and completely characterized. In previous studies, we obtained three economically important fishes that exhibit rapid growth, WR (WCC ♀ × RCC ♂), WR-II (WR ♀ × WCC ♂), and WR-III (WR-II ♀ × 4nAU ♂), through distant hybridization. However, the mechanism underlying this rapid growth remains unclear. In this study, we found that WR, WR-II, and WR-III showed muscle hypertrophy and higher muscle protein and fat contents compared with their parent species (RCC and WCC). Candidate genes responsible for this rapid growth were then obtained through an analysis of 12 muscle transcriptomes. Notably, the mRNA level of mstnb (myostatin b), which is a negative regulator of myogenesis, was significantly reduced in WR, WR-II, and WR-III compared with the parent species. To verify the function of mstnb, a mstnb-deficient mutant RCC line was generated using the CRISPR-Cas9 technique. The average body weight of mstnb-deficient RCC at 12 months of age was significantly increased by 29.57% compared with that in wild-type siblings. Moreover, the area and number of muscle fibers were significantly increased in mstnb-deficient RCC, indicating hypertrophy and hyperplasia. Furthermore, the muscle protein and fat contents were significantly increased in mstnb-deficient RCC. The molecular regulatory mechanism of mstnb was then revealed by transcription profiling, which showed that genes related to myogenesis (myod, myog, and myf5), protein synthesis (PI3K-AKT-mTOR), and lipogenesis (pparγ and fabp3) were highly activated in hybrid fishes and mstnb-deficient RCC. This study revealed that low expression or deficiency of mstnb regulates somatic growth by promoting myogenesis, protein synthesis, and lipogenesis in hybrid fishes and mstnb-deficient RCC, which provides evidence for the molecular mechanism of heterosis via distant hybridization.

Poly(ADP-Ribose) Polymerases-Inhibitor Talazoparib Inhibits Muscle Atrophy and Fatty Infiltration in a Tendon Release Infraspinatus Sheep Model: A Pilot Study

Structural muscle changes, including muscle atrophy and fatty infiltration, follow rotator cuff tendon tear and are associated with a high repair failure rate. Despite extensive research efforts, no pharmacological therapy is available to successfully prevent both muscle atrophy and fatty infiltration after tenotomy of tendomuscular unit without surgical repair. Poly(ADP-ribose) polymerases (PARPs) are identified as a key transcription factors involved in the maintenance of cellular homeostasis. PARP inhibitors have been shown to influence muscle degeneration, including mitochondrial hemostasis, oxidative stress, inflammation and metabolic activity, and reduced degenerative changes in a knockout mouse model. Tenotomized infraspinatus were assessed for muscle degeneration for 16 weeks using a Swiss Alpine sheep model (n = 6). All sheep received daily oral administration of 0.5 mg Talazoparib. Due to animal ethics, the treatment group was compared with three different controls from prior studies of our institution. To mitigate potential batch heterogeneity, PARP-I was evaluated in comparison with three distinct control groups (n = 6 per control group) using the same protocol without treatment. The control sheep were treated with an identical study protocol without Talazoparib treatment. Muscle atrophy and fatty infiltration were evaluated at 0, 6 and 16 weeks post-tenotomy using DIXON-MRI. The controls and PARP-I showed a significant (control p < 0.001, PARP-I p = 0.01) decrease in muscle volume after 6 weeks. However, significantly less (p = 0.01) atrophy was observed in PARP-I after 6 weeks (control 1: 76.6 ± 8.7%; control 2: 80.3 ± 9.3%, control 3: 73.8 ± 6.7% vs. PARP-I: 90.8 ± 5.1% of the original volume) and 16 weeks (control 1: 75.7 ± 9.9; control 2: 74.2 ± 5.6%; control 3: 75.3 ± 7.4% vs. PARP-I 93.3 ± 10.6% of the original volume). All experimental groups exhibited a statistically significant (p < 0.001) augmentation in fatty infiltration following a 16-week period when compared to the initial timepoint. However, the PARP-I showed significantly less fatty infiltration (p < 0.003) compared to all controls (control 1: 55.6 ± 6.7%, control 2: 53.4 ± 9.4%, control 3: 52.0 ± 12.8% vs. PARP-I: 33.5 ± 8.4%). Finally, a significantly (p < 0.04) higher proportion and size of fast myosin heavy chain-II fiber type was observed in the treatment group. This study shows that PARP-inhibition with Talazoparib inhibits the progression of both muscle atrophy and fatty infiltration over 16 weeks in retracted sheep musculotendinous units.

Common mouse models of chronic kidney disease are not associated with cachexia

The 5/6 nephrectomy and adenine-induced nephropathy mouse models have been extensively used to study Chronic Kidney Disease (CKD)-related cachexia. One common caveat of these CKD models is the cross-sectional nature of comparisons made versus controls. We here performed a comprehensive longitudinal assessment of body composition and energy metabolism in both models. The most striking finding is that weight loss is largely driven by reduced food intake which promotes rapid loss of lean and fat mass. However, in both models, mice catch up weight and lean mass a few days after the surgery or when they are switched back to standard chow diet. Muscle force and mass are fully recovered and no sign of cachexia is observed. Our data demonstrate that the time-course of kidney failure and weight loss are unrelated in these common CKD models. These data highlight the need to reconsider the relative contribution of direct and indirect mechanisms to muscle wasting observed in CKD.

Inhibition of CERS1 in skeletal muscle exacerbates age-related muscle dysfunction

Age-related muscle wasting and dysfunction render the elderly population vulnerable and incapacitated, while underlying mechanisms are poorly understood. Here, we implicate the CERS1 enzyme of the de novo sphingolipid synthesis pathway in the pathogenesis of age-related skeletal muscle impairment. In humans, CERS1 abundance declines with aging in skeletal muscle cells and, correlates with biological pathways involved in muscle function and myogenesis. Furthermore, CERS1 is upregulated during myogenic differentiation. Pharmacological or genetic inhibition of CERS1 in aged mice blunts myogenesis and deteriorates aged skeletal muscle mass and function, which is associated with the occurrence of morphological features typical of inflammation and fibrosis. Ablation of the CERS1 orthologue lagr-1 in Caenorhabditis elegans similarly exacerbates the age-associated decline in muscle function and integrity. We discover genetic variants reducing CERS1 expression in human skeletal muscle and Mendelian randomization analysis in the UK biobank cohort shows that these variants reduce muscle grip strength and overall health. In summary, our findings link age-related impairments in muscle function to a reduction in CERS1, thereby underlining the importance of the sphingolipid biosynthesis pathway in age-related muscle homeostasis.

A first characterization of the microbiota-resilience link in swine

BACKGROUND

The gut microbiome plays a crucial role in understanding complex biological mechanisms, including host resilience to stressors. Investigating the microbiota-resilience link in animals and plants holds relevance in addressing challenges like adaptation of agricultural species to a warming environment. This study aims to characterize the microbiota-resilience connection in swine. As resilience is not directly observable, we estimated it using four distinct indicators based on daily feed consumption variability, assuming animals with greater intake variation may face challenges in maintaining stable physiological status. These indicators were analyzed both as linear and categorical variables. In our first set of analyses, we explored the microbiota-resilience link using PERMANOVA, α-diversity analysis, and discriminant analysis. Additionally, we quantified the ratio of estimated microbiota variance to total phenotypic variance (microbiability). Finally, we conducted a Partial Least Squares-Discriminant Analysis (PLS-DA) to assess the classification performance of the microbiota with indicators expressed in classes.

RESULTS

This study offers four key insights. Firstly, among all indicators, two effectively captured resilience. Secondly, our analyses revealed robust relationship between microbial composition and resilience in terms of both composition and richness. We found decreased α-diversity in less-resilient animals, while specific amplicon sequence variants (ASVs) and KEGG pathways associated with inflammatory responses were negatively linked to resilience. Thirdly, considering resilience indicators in classes, we observed significant differences in microbial composition primarily in animals with lower resilience. Lastly, our study indicates that gut microbial composition can serve as a reliable biomarker for distinguishing individuals with lower resilience.

CONCLUSION

Our comprehensive analyses have highlighted the host-microbiota and resilience connection, contributing valuable insights to the existing scientific knowledge. The practical implications of PLS-DA and microbiability results are noteworthy. PLS-DA suggests that host-microbiota interactions could be utilized as biomarkers for monitoring resilience. Furthermore, the microbiability findings show that leveraging host-microbiota insights may improve the identification of resilient animals, supporting their adaptive capacity in response to changing environmental conditions. These practical implications offer promising avenues for enhancing animal well-being and adaptation strategies in the context of environmental challenges faced by livestock populations. Video Abstract.

Licochalcone A and B enhance muscle proliferation and differentiation by regulating Myostatin

BACKGROUND

Myostatin (MSTN) inhibition has demonstrated promise for the treatment of diseases associated with muscle loss. In a previous study, we discovered that Glycyrrhiza uralensis (G. uralensis) crude water extract (CWE) inhibits MSTN expression while promoting myogenesis. Furthermore, three specific compounds of G. uralensis, namely liquiritigenin, tetrahydroxymethoxychalcone, and Licochalcone B (Lic B), were found to promote myoblast proliferation and differentiation, as well as accelerate the regeneration of injured muscle tissue.

PURPOSE

The purpose of this study was to build on our previous findings on G. uralensis and demonstrate the potential of its two components, Licochalcone A (Lic A) and Lic B, in muscle mass regulation (by inhibiting MSTN), aging and muscle formation.

METHODS

G. uralensis, Lic A, and Lic B were evaluated thoroughly using in silico, in vitro and in vivo approaches. In silico analyses included molecular docking, and dynamics simulations of these compounds with MSTN. Protein-protein docking was carried out for MSTN, as well as for the docked complex of MSTN-Lic with its receptor, activin type IIB receptor (ACVRIIB). Subsequent in vitro studies used C2C12 cell lines and primary mouse muscle stem cells to acess the cell proliferation and differentiation of normal and aged cells, levels of MSTN, Atrogin 1, and MuRF1, and plasma MSTN concentrations, employing techniques such as western blotting, immunohistochemistry, immunocytochemistry, cell proliferation and differentiation assays, and real-time RT-PCR. Furthermore, in vivo experiments using mouse models focused on measuring muscle fiber diameters.

RESULTS

CWE of G. uralensis and two of its components, namely Lic A and B, promote myoblast proliferation and differentiation by inhibiting MSTN and reducing Atrogin1 and MuRF1 expressions and MSTN protein concentration in serum. In silico interaction analysis revealed that Lic A (binding energy -6.9 Kcal/mol) and B (binding energy -5.9 Kcal/mol) bind to MSTN and reduce binding between it and ACVRIIB, thereby inhibiting downstream signaling. The experimental analysis, which involved both in vitro and in vivo studies, demonstrated that the levels of MSTN, Atrogin 1, and MuRF1 were decreased when G. uralensis CWE, Lic A, or Lic B were administered into mice or treated in the mouse primary muscle satellite cells (MSCs) and C2C12 myoblasts. The diameters of muscle fibers increased in orally treated mice, and the differentiation and proliferation of C2C12 cells were enhanced. G. uralensis CWE, Lic A, and Lic B also promoted cell proliferation in aged cells, suggesting that they may have anti-muslce aging properties. They also reduced the expression and phosphorylation of SMAD2 and SMAD3 (MSTN downstream effectors), adding to the evidence that MSTN is inhibited.

CONCLUSION

These findings suggest that CWE and its active constituents Lic A and Lic B have anti-mauscle aging potential. They also have the potential to be used as natural inhibitors of MSTN and as therapeutic options for disorders associated with muscle atrophy.

Circulating myomiRNAs as biomarkers in patients with Cushing's syndrome

PURPOSE

Impairment of skeletal muscle mass and strength affects 40-70% of patients with active Cushing's syndrome (CS). Glucocorticoid excess sustains muscle atrophy and weakness, while muscle-specific microRNAs (myomiRs) level changes were associated with muscle organization and function perturbation. The aim of the current study is to explore changes in circulating myomiRs in CS patients compared to healthy controls and their involvement in IGFI/PI3K/Akt/mTOR pathway regulation in skeletal muscle.

METHODS

C2C12, mouse myocytes, were exposed to hydrocortisone (HC), and atrophy-related gene expression was investigated by RT-qPCR, WB and IF to assess HC-mediated atrophic signalling. miRNAs were evaluated in HC-treated C2C12 by PCR Arrays. MyomiRs significantly overexpressed in C2C12 were investigated in 37 CS patients and 24 healthy controls serum by RT-qPCR. The anti-anabolic role of circulating miRNAs significantly upregulated in CS patients was explored in C2C12 by investigating the IGFI/PI3K/Akt/mTOR pathway regulation.

RESULTS

HC induced higher expression of atrophy-related genes, miR-133a-3p, miR-122-5p and miR-200b-3p in C2C12 compared to untreated cells. Conversely, the anabolic IGFI/PI3K/Akt/mTOR signalling was reduced and this effect was mediated by miR-133a-3p. In CS patients miR-133a-3p and miR-200b-3p revealed higher circulating levels (p < 0.0001, respectively) compared to controls. ROC curves for miR-133a-3p (AUC 0.823, p < 0.0001) and miR-200b-3p (AUC 0.850, p < 0.0001) demonstrated that both myomiRs represent potential biomarkers to discriminate between CS and healthy subjects. Pearson's correlation analysis revealed that circulating levels of miR-133a-3p are directly correlated with 24 h urinary-free cortisol level (r = 0.468, p = 0.004) in CS patients.

CONCLUSIONS

HC induces atrophic signals by miR-133a-3p overexpression in mouse myocytes and humans. Circulating miR-133a-3p is promising biomarkers of hypercortisolism.

Chronic melatonin treatment improves obesity by inducing uncoupling of skeletal muscle SERCA-SLN mediated by CaMKII/AMPK/PGC1α pathway and mitochondrial biogenesis in female and male Zücker diabetic fatty rats

Melatonin acute treatment limits obesity of young Zücker diabetic fatty (ZDF) rats by non-shivering thermogenesis (NST). We recently showed melatonin chronically increases the oxidative status of vastus lateralis (VL) in both obese and lean adult male animals. The identification of VL skeletal muscle-based NST by uncoupling of sarcoendoplasmic reticulum Ca2+-ATPase (SERCA)- sarcolipin (SLN) prompted us to investigate whether melatonin is a SERCA-SLN calcium futile cycle uncoupling and mitochondrial biogenesis enhancer. Obese ZDF rats and lean littermates (ZL) of both sexes were subdivided into two subgroups: control (C) and 12 weeks orally melatonin treated (M) (10 mg/kg/day). Compared to the control groups, melatonin decreased the body weight gain and visceral fat in ZDF rats of both sexes. Melatonin treatment in both sex obese rats restored the VL muscle skin temperature and sensitized the thermogenic effect of acute cold exposure. Moreover, melatonin not only raised SLN protein levels in the VL of obese and lean rats of both sexes; also, the SERCA activity. Melatonin treatment increased the SERCA2 expression in obese and lean rats (both sexes), with no effects on SERCA1 expression. Melatonin increased the expression of thermogenic genes and proteins (PGC1-α, PPARγ, and NRF1). Furthermore, melatonin treatment enhanced the expression ratio of P-CaMKII/CaMKII and P-AMPK/AMPK. In addition, it rose mitochondrial biogenesis. These results provided the initial evidence that chronic oral melatonin treatment triggers the CaMKII/AMPK/PGC1α axis by upregulating SERCA2-SLN-mediated NST in ZDF diabetic rats of both sexes. This may further contribute to the body weight control and metabolic benefits of melatonin.

Effects of hindlimb unloading on the mevalonate and mechanistic target of rapamycin complex 1 signaling pathways in a fast-twitch muscle in rats

Fast-twitch muscles are less susceptible to disuse atrophy, activate the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway, and increase protein synthesis under prolonged muscle disuse conditions. However, the mechanism underlying prolonged muscle disuse-induced mTORC1 signaling activation remains unclear. The mevalonate pathway activates the mTORC1 signaling pathway via the prenylation and activation of Ras homolog enriched in brain (Rheb). Therefore, we investigated the effects of hindlimb unloading (HU) for 14 days on the mevalonate and mTORC1 signaling pathways in the plantaris muscle, a fast-twitch muscle, in adult male rats. Rats were divided into HU and control groups. The plantaris muscles of both groups were harvested after the treatment period, and the expression and phosphorylation levels of metabolic and intracellular signaling proteins were analyzed using Western blotting. We found that HU increased the expression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the rate-limiting enzyme of the mevalonate pathway, and activated the mTORC1 signaling pathway without activating AKT, an upstream activator of mTORC1. Furthermore, HU increased prenylated Rheb. Collectively, these findings suggest that the activated mevalonate pathway may be involved in the activation of the Rheb/mTORC1 signaling pathway without AKT activation in fast-twitch muscles under prolonged disuse conditions.

Moderating AKT signaling with baicalein protects against weight loss by preventing muscle atrophy in a cachexia model caused by CT26 colon cancer

Cancer cachexia is a type of energy-wasting syndrome characterized by fatigue, anorexia, muscle weakness, fat loss, and systemic inflammation. Baicalein, a flavonoid with bioactive properties, has demonstrated the ability to mitigate cardiac and skeletal muscle atrophy in different experimental settings. This effect is achieved through the inhibition of muscle proteolysis, suggesting its potential in preserving skeletal muscle homeostasis. In this study, we investigated the anti-cancer cachexia effects of baicalein in the regulation of muscle and fat wasting, both in vivo and in vitro. Baicalein attenuated body weight loss, including skeletal muscle and white adipose tissue (WAT), in CT26-induced cachectic mice. Moreover, baicalein increased muscle fiber thickness and suppressed the muscle-specific ubiquitin-protease system, including F-box only protein 32 and muscle RING-finger protein-1, by activating AKT phosphorylation both in vivo and in vitro. The use of LY294002, a particular inhibitor of AKT, eliminated the observed impact of baicalein on the improvement of muscle atrophy. In conclusion, baicalein inhibits muscle proteolysis and enhances AKT phosphorylation, indicating its potential role in cancer cachexia-associated muscle atrophy.

5'-Cytimidine Monophosphate Ameliorates H2O2-Induced Muscular Atrophy in C2C12 Myotubes by Activating IRS-1/Akt/S6K Pathway

Age-related muscle atrophy (sarcopenia), characterized by reduced skeletal muscle mass and muscle strength, is becoming increasingly prevalent worldwide, which is especially true for older people, and can seriously damage health and quality of life in older adults. This study aims to investigate the beneficial effects of 5'-cytimidine monophosphate (CMP) on H2O2-induced muscular atrophy in C2C12 myotubes. C2C12 myotubes were treated with H2O2 in the presence and absence of CMP and the changes in the anti-oxidation, mitochondrial functions, and expression of sarcopenia-related proteins were observed. Immunofluorescence analysis showed that CMP significantly increased the diameter of myotubes. We found that CMP could increase the activity of antioxidant enzymes and improve mitochondrial dysfunction, as well as reduce inflammatory cytokine levels associated with sarcopenia. RNA-seq analysis showed that CMP could relieve insulin resistance and promote protein digestion and absorption. Western blot analysis further confirmed that CMP could promote the activation of the IRS-1/Akt/S6K signaling pathway and decrease the expression of MuRF1 and Atrogin-1, which are important markers of muscle atrophy. The above results suggest that CMP protects myotubes from H2O2-induced atrophy and that its potential mechanism is associated with activating the IRS-1/Akt/S6K pathway to promote protein synthesis by improving mitochondrial dysfunction and insulin resistance. These results indicate that CMP can improve aging-related sarcopenia.