The role of mTORC1 in the regulation of skeletal muscle mass

Biomarkers of aging: from molecules and surrogates to physiology and function

Many countries face an unprecedented challenge in aging demographics. This has led to an exponential growth in research on aging, which, coupled to a massive financial influx of funding in the private and public sectors, has resulted in seminal insights into the underpinnings of this biological process. However, critical validation in humans has been hampered by the limited translatability of results obtained in model organisms, additionally confined by the need for extremely time-consuming clinical studies in the ostensible absence of robust biomarkers that would allow monitoring in shorter time frames. In the future, molecular parameters might hold great promise in this regard. In contrast, biomarkers centered on function, resilience, and frailty are available at the present time, with proven predictive value for morbidity and mortality. In this review, the current knowledge of molecular and physiological aspects of human aging, potential antiaging strategies, and the basis, evidence, and potential application of physiological biomarkers in human aging are discussed.

Distinct roles of the circMKNK2/miR-15a Axis in regulating chicken skeletal muscle development and glucose metabolism

Circular RNAs (circRNAs) have emerged as critical regulators of biological processes, but their roles in avian muscle development remain less explored. Here we characterize circMKNK2, a novel circRNA derived from the MKNK2 gene, which is highly expressed in slow-growing Silky chickens compared to fast-growing broilers. Functional studies demonstrate that circMKNK2 acts as a sponge for miR-15a, with overexpression inhibiting myoblast proliferation, differentiation, apoptosis, and glucose metabolism, while miR-15a knockdown produces similar effects except for enhanced glucose uptake. RNA-seq analysis identified 2189 differentially expressed genes regulated by circMKNK2 in chicken primary myoblasts, including key targets of the circMKNK2/miR-15a axis such as PIK3R1 (a core node regulating PI3K-Akt signaling), BHLHE41, KANK1, and ARHGAP20. Pathway analysis revealed modulation of myogenesis through Calcium signaling pathway, ECM-receptor interaction, Neuroactive ligand-receptor interaction and immune-related pathways (Toll-like receptor, cytokine-cytokine receptor interactions). Further analysis highlighted the circMKNK2/miR-15a axis's role in suppressing myogenesis through transcriptional regulation of key factors (e.g., SOX7, MAF) and metabolic reprogramming. Unlike pro-myogenic circRNAs, circMKNK2 uniquely inhibited muscle development and glucose metabolism, suggesting its involvement in breed-specific phenotypic differences. This study provides insights into circRNA-mediated regulation of muscle biology and offers potential targets for improving poultry production through genetic and metabolic modulation.

The impact of a selective androgen receptor modulator (RAD140) on frailty and underlying mechanisms in older male and female C57Bl/6 mice

BACKGROUND

Androgen receptors (AR) are promising therapeutic targets for mechanisms of aging, including chronic inflammation, lean mass loss, and worsening bone health. We investigated the impact of RAD140, a selective AR modulator that activates ARs, on frailty and underlying mechanisms in older C57BL/6 mice.

METHODS

Mice (23.7-25.5 months; N = 21 males; 15 females) received RAD140 (5 mg/kg/day) or placebo (DMSO) daily for 6-weeks. Frailty (clinical and lab-based), body composition, circulating inflammatory markers, grip strength, and genes relating to function/hypertrophy in quadriceps femoris muscles were assessed.

RESULTS

Despite no differences in frailty between treatment and control, there were positive effects in male, but not female mice. RAD140 treated male mice had preserved lean mass (p = 0.024) and bone mineral density (p = 0.004) and lower serum interleukin-6 (p = 0.043) versus controls. In contrast, benefits to body composition and inflammatory markers were not seen in females. In either sex, grip strength, fat mass, and skeletal muscle genes were unaffected.

CONCLUSION

Six-weeks of RAD140 treatment did not affect frailty in older male or female mice. The beneficial effects in lean mass, bone mineral density, and systemic inflammation warrant longer treatments to explore any positive impact on frailty in males. RAD140 may not be ideal for achieving these in females.

Endoplasmic reticulum stress and unfolded protein response: Roles in skeletal muscle atrophy

Skeletal muscle atrophy is commonly present in various pathological states, posing a huge burden on society and patients. Increased protein hydrolysis, decreased protein synthesis, inflammatory response, oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress (ERS) and unfolded protein response (UPR) are all important molecular mechanisms involved in the occurrence and development of skeletal muscle atrophy. The potential mechanisms of ERS and UPR in skeletal muscle atrophy are extremely complex and have not yet been fully elucidated. This article elucidates the molecular mechanisms of ERS and UPR, and discusses their effects on different types of muscle atrophy (muscle atrophy caused by disuse, cachexia, chronic kidney disease (CKD), diabetes mellitus (DM), amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), spinal and bulbar muscular atrophy (SBMA), aging, sarcopenia, obesity, and starvation), and explores the preventive and therapeutic strategies targeting ERS and UPR in skeletal muscle atrophy, including inhibitor therapy and drug therapy. This review aims to emphasize the importance of endoplasmic reticulum (ER) in maintaining skeletal muscle homeostasis, which helps us further understand the molecular mechanisms of skeletal muscle atrophy and provides new ideas and insights for the development of effective therapeutic drugs and preventive measures for skeletal muscle atrophy.

Critical Review on Anti-Obesity Effects of Anthocyanins Through PI3K/Akt Signaling Pathways

Obesity is a global health crisis and is one of the major reasons for the rising prevalence of metabolic disorders such as type 2 diabetes, cardiovascular diseases, and certain cancers. There has been growing interest in the search for natural molecules with potential anti-obesity effects; among the phytochemicals of interest are anthocyanins, which are flavonoid pigments present in many fruits and vegetables. Anthocyanins influence obesity via several signaling pathways. The PI3K/Akt signaling pathway plays a major role with a focus on downstream targets such as GLUT4, FOXO, GSK3β, and mTOR, which play a central role in the regulation of glucose metabolism, lipid storage, and adipogenesis. The influence of critical factors such as oxidative stress and inflammation also affect the pathophysiology of obesity. However, the studies reviewed have certain limitations, including variations in experimental models, bioavailability challenges, and a lack of extensive clinical validation. While anthocyanin shows tremendous potential, challenges such as poor bioavailability, stability, and regulatory matters must be overcome for successful functional food inclusion of anthocyanins. The future of anthocyanin-derived functional foods lies in their ability to overcome hurdles. Therefore, this review highlights the molecular mechanisms of obesity through the PI3K/Akt signaling pathways and explores how anthocyanins can modulate these signaling pathways to address obesity and related metabolic disorders. It also addresses some ways to solve the challenges, like bioavailability and stability, while emphasizing future possibilities for anthocyanin-based functional foods in obesity management.

Skeletal muscle growth to combat diabetes and obesity: the potential role of muscle-secreted factors

As the prevalence of obesity and metabolic disease continues to climb, the need for effective therapeutic interventions remains high. The growth of skeletal muscle (SkM) greatly influences systemic metabolism across the whole body, making this tissue an important therapeutic target to combat the rise of metabolic dysfunction. Transgenic rodent models of targeted SkM growth exhibit profound improvements in various remote tissues, including adipose tissue and the liver. It is currently unclear how selective stimulation of SkM growth alters the metabolism of distant tissues; however, evidence suggests that muscle-secreted factors may be involved. Here, we aim to provide basic biomedical researchers with a summary of the current knowledge regarding various muscle-secreted factors regulated by anabolic pathways and proteins in SkM, as well as their systemic metabolic effects, to implicate them in the whole-body metabolic effects of SkM growth. In this review, we also identify several knowledge gaps in this field, future directions of investigation, and implications for therapeutic interventions such as resistance exercise and pharmacology.

Malformations of Core M3 on α-Dystroglycan Are the Leading Cause of Dystroglycanopathies

Dystroglycanopathies (DGPs) are a group of autosomal recessive neuromuscular diseases with significant clinical and genetic heterogeneity. They originate due to defects in the O-mannosyl glycosylation of α-dystroglycan (α-DG), a prominent linker between the intracellular cytoskeleton and the extracellular matrix (ECM). Fundamentally, such interactions are crucial for the integrity of muscle fibers and neuromuscular synapses, where their defects are mainly associated with muscle and brain dysfunction. To date, biallelic variants in 18 genes have been associated with DGPs, where the underlying cause is still undefined in a significant proportion of patients. Glycosylation of α-DG generates three core motifs where the core M3 is responsible for interaction with the basement membrane. Consistently, all gene defects that corrupt core M3 maturation have been identified as causes of DGPs. POMGNT1 which stimulates the generation of core M1 is also associated with DGPs, as it plays a central role in core M3 processing. Other genes involved in the glycosylation of α-DG seem unrelated to DPGs. The current review illustrates the O-mannosylation pathway of α-DG highlighting the functional properties of related genes and their contribution to the progression of DPGs. Different classes of DPGs are also elaborated characterizing the clinical features of each distinct type and phenotypes associated with each single gene. Finally, current therapeutic approaches with favorable outcomes are addressed. Potential achievements of preclinical and clinical studies would introduce effective curative therapies for this group of disorders in the near future.

Unlocking the therapeutic potential of WISP-1: A comprehensive exploration of its role in age-related musculoskeletal disorders

As the global population ages, the incidence of age-related musculoskeletal diseases continues to increase, driven by numerous complex and poorly understood factors. WNT-1 inducible secreted protein 1 (WISP-1), a secreted matrix protein, plays a critical role in the growth and development of the musculoskeletal system, including chondrogenesis, osteogenesis, and myogenesis. Numerous in vivo and in vitro studies have demonstrated that WISP-1 is significantly upregulated in age-related musculoskeletal conditions, such as osteoarthritis, osteoporosis, and sarcopenia, suggesting its involvement in the pathogenesis of these diseases. Regulating WISP-1 expression holds promise as a therapeutic strategy for improving musculoskeletal function, potentially offering new avenues for treating age-related musculoskeletal diseases in clinical practice. This review highlights the signaling pathways associated with WISP-1, its physiological roles within the musculoskeletal system, and its therapeutic potential in treating age-related musculoskeletal disorders.

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.

Double-Edge Effects of Leucine on Cancer Cells

Leucine is an essential amino acid that cannot be produced endogenously in the human body and therefore needs to be obtained from dietary sources. Leucine plays a pivotal role in stimulating muscle protein synthesis, along with isoleucine and valine, as the group of branched-chain amino acids, making them one of the most popular dietary supplements for athletes and gym-goers. The individual effects of leucine, however, have not been fully clarified, as most of the studies so far have focused on the grouped effects of branched-chain amino acids. In recent years, leucine and its metabolites have been shown to stimulate muscle protein synthesis mainly via the mammalian target of the rapamycin complex 1 signaling pathway, thereby improving muscle atrophy in cancer cachexia. Interestingly, cancer research suggests that leucine may have either anti-cancer or pro-tumorigenic effects. In the current manuscript, we aim to review leucine's roles in muscle protein synthesis, tumor suppression, and tumor progression, specifically summarizing the molecular mechanisms of leucine's action. The role of leucine is controversial in hepatocellular carcinoma, whereas its pro-tumorigenic effects have been demonstrated in breast and pancreatic cancers. In summary, leucine being used as nutritional supplement for athletes needs more attention, as its pro-oncogenic effects may have been identified by recent studies. Anti-cancer or pro-tumorigenic effects of leucine in various cancers should be further investigated to achieve clear conclusions.

Advancements in sarcopenia diagnosis: from imaging techniques to non-radiation assessments

Sarcopenia is a prevalent condition with significant clinical implications, and it is expected to escalate globally, demanding for effective diagnostic strategies, possibly at an early stage of the disease. Imaging techniques play a pivotal role in comprehensively evaluating sarcopenia, offering insights into both muscle quantity and quality. Among all the imaging techniques currently used for the diagnosis and follow up of sarcopenia, it is possible to distinguish two classes: Rx based techniques, using ionizing radiations, and non-invasive techniques, which are based on the use of safe and low risk diagnostic procedures. Dual-energy x-ray Absorptiometry and Computed Tomography, while widely utilized, entail radiation exposure concerns. Ultrasound imaging offers portability, real-time imaging, and absence of ionizing radiation, making it a promising tool Magnetic Resonance Imaging, particularly T1-weighted and Dixon sequences, provides cross- sectional and high-resolution images and fat-water separation capabilities, facilitating precise sarcopenia quantification. Bioelectrical Impedance Analysis (BIA), a non-invasive technique, estimates body composition, including muscle mass, albeit influenced by hydration status. Standardized protocols, such as those proposed by the Sarcopenia through Ultrasound (SARCUS) Working Group, are imperative for ensuring consistency across assessments. Future research should focus on refining these techniques and harnessing the potential of radiomics and artificial intelligence to enhance diagnostic accuracy and prognostic capabilities in sarcopenia.

Exercise-specific adaptations in human skeletal muscle: Molecular mechanisms of making muscles fit and mighty

The mechanisms leading to a predominantly hypertrophied phenotype versus a predominantly oxidative phenotype, the hallmarks of resistance training (RT) or aerobic training (AT), respectively, are being unraveled. In humans, exposure of naïve persons to either AT or RT results in their skeletal muscle exhibiting generic 'exercise stress-related' signaling, transcription, and translation responses. However, with increasing engagement in AT or RT, the responses become refined, and the phenotype typically associated with each form of exercise emerges. Here, we review some of the mechanisms underpinning the adaptations of how muscles become, through AT, 'fit' and RT, 'mighty.' Much of our understanding of molecular exercise physiology has arisen from targeted analysis of post-translational modifications and measures of protein synthesis. Phosphorylation of specific residue sites has been a dominant focus, with canonical signaling pathways (AMPK and mTOR) studied extensively in the context of AT and RT, respectively. These alone, along with protein synthesis, have only begun to elucidate key differences in AT and RT signaling. Still, key yet uncharacterized differences exist in signaling and regulation of protein synthesis that drive unique adaptation to AT and RT. Omic studies are required to better understand the divergent relationship between exercise and phenotypic outcomes of training.

The Association of the Essential Amino Acids Lysine, Methionine, and Threonine with Clinical Outcomes in Patients at Nutritional Risk: Secondary Analysis of a Randomized Clinical Trial

Lysine, methionine, and threonine are essential amino acids with vital functions for muscle and connective tissue health, metabolic balance, and the immune system. During illness, the demand for these amino acids typically increases, which puts patients at risk for deficiencies with harmful clinical consequences. In a secondary analysis of the Effect of Early Nutritional Support on Frailty, Functional Outcomes, and Recovery of Malnourished Medical Inpatients Trial (EFFORT), which compared individualized nutritional support to usual care nutrition in patients at nutritional risk, we investigated the prognostic impact of the lysine, methionine, and threonine metabolism. We had complete clinical and amino acid data in 237 patients, 58 of whom reached the primary endpoint of death at 30 days. In a model adjusted for comorbidities, sex, nutritional risk, and trial intervention, low plasma methionine levels were associated with 30-day mortality (adjusted HR 1.98 [95% CI 1.16 to 3.36], p = 0.01) and with a decline in functional status (adjusted OR 2.06 [95% CI 1.06 to 4.01], p = 0.03). The results for lysine and threonine did not show statistically significant differences regarding clinical outcomes. These findings suggest that low levels of methionine may be critical during hospitalization among patients at nutritional risk. Further studies should investigate the effect of supplementation of methionine in this patient group to improve outcomes.

Vertical Strength Transfer Phenomenon Between Upper Body and Lower Body Exercise: Systematic Scoping Review

BACKGROUND

There are a myriad of exercise variations in which upper body (UB) and lower body (LB) exercises have been intermittently used. However, it is still unclear how training of one body region (e.g. LB) affects adaptations in distant body areas (e.g. UB), and how different UB and LB exercise configurations could help facilitate physiological adaptations of either region; both referred to in this review as vertical strength transfer.

OBJECTIVE

We aimed to investigate the existence of the vertical strength transfer phenomenon as a response to various UB and LB exercise configurations and to identify potential mechanisms underpinning its occurrence.

METHODS

A systematic search using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) for Scoping Reviews protocol was conducted in February 2024 using four databases (Web of Science, MEDLINE, Scopus and CINAHL) to identify peer-reviewed articles that investigated the vertical strength transfer phenomenon.

RESULTS

Of the 5242 identified articles, 24 studies met the inclusion criteria. Findings suggest that the addition of UB strength training to LB endurance exercise may help preserve power-generating capacity for the leg muscle fibres. Furthermore, systemic endocrine responses to high-volume resistance exercise may beneficially modulate adaptations in precedingly or subsequently trained muscles from a different body region, augmenting their strength gains. Last, strength training for LB could result in improved strength of untrained UB, likely due to the increased central neural drive.

CONCLUSIONS

Vertical strength transfer existence is enabled by neurophysiological mechanisms. Future research should involve athletic populations, examining the potential of vertical strength transfer to facilitate athletic performance and preserve strength in injured extremities.

Nicotinamide N-methyltransferase inhibition mimics and boosts exercise-mediated improvements in muscle function in aged mice

Human hallmarks of sarcopenia include muscle weakness and a blunted response to exercise. Nicotinamide N-methyltransferase inhibitors (NNMTis) increase strength and promote the regenerative capacity of aged muscle, thus offering a promising treatment for sarcopenia. Since human hallmarks of sarcopenia are recapitulated in aged (24-month-old) mice, we treated mice from 22 to 24 months of age with NNMTi, intensive exercise, or a combination of both, and compared skeletal muscle adaptations, including grip strength, longitudinal running capacity, plantarflexor peak torque, fatigue, and muscle mass, fiber type, cross-sectional area, and intramyocellular lipid (IMCL) content. Exhaustive proteome and metabolome analyses were completed to identify the molecular mechanisms underlying the measured changes in skeletal muscle pathophysiology. Remarkably, NNMTi-treated aged sedentary mice showed ~ 40% greater grip strength than sedentary controls, while aged exercised mice only showed a 20% increase relative to controls. Importantly, the grip strength improvements resulting from NNMTi treatment and exercise were additive, with NNMTi-treated exercised mice developing a 60% increase in grip strength relative to sedentary controls. NNMTi treatment also promoted quantifiable improvements in IMCL content and, in combination with exercise, significantly increased gastrocnemius fiber CSA. Detailed skeletal muscle proteome and metabolome analyses revealed unique molecular mechanisms associated with NNMTi treatment and distinct molecular mechanisms and cellular processes arising from a combination of NNMTi and exercise relative to those given a single intervention. These studies suggest that NNMTi-based drugs, either alone or combined with exercise, will be beneficial in treating sarcopenia and a wide range of age-related myopathies.

mTORC1 and BMP-Smad1/5 regulation of serum-stimulated myotube hypertrophy: a role for autophagy

Protein synthesis regulation is critical for skeletal muscle hypertrophy, yet other established cellular processes are necessary for growth-related cellular remodeling. Autophagy has a well-acknowledged role in muscle quality control, but evidence for its role in myofiber hypertrophy remains equivocal. Both mammalian target of rapamycin complex I (mTORC1) and bone morphogenetic protein (BMP)-Smad1/5 (Sma and Mad proteins from Caenorhabditis elegans and Drosophila, respectively) signaling are reported regulators of myofiber hypertrophy; however, gaps remain in our understanding of how this regulation is integrated with growth processes and autophagy regulation. Therefore, we investigated the mTORC1 and Smad1/5 regulation of protein synthesis and autophagy flux during serum-stimulated myotube growth. Chronic serum stimulation experiments were performed on day 5 differentiated C2C12 myotubes incubated in differentiation medium [2% horse serum (HS)] or growth medium [5% fetal bovine serum (FBS)] for 48 h. Rapamycin or LDN193189 was dosed for 48 h to inhibit mTORC1 and BMP-Smad1/5 signaling, respectively. Acute serum stimulation was examined in day 7 differentiated myotubes. Protein synthesis was measured by puromycin incorporation. Bafilomycin A1 and immunoblotting for LC3B were used to assess autophagy flux. Chronic serum stimulation increased myotube diameter 22%, total protein 21%, total RNA 100%, and Smad1/5 phosphorylation 404% and suppressed autophagy flux. Rapamycin, but not LDN193189, blocked serum-induced myotube hypertrophy and the increase in total RNA. Acute serum stimulation increased protein synthesis 111%, Smad1/5 phosphorylation 559%, and rpS6 phosphorylation 117% and suppressed autophagy flux. Rapamycin increased autophagy flux during acute serum stimulation. These results provide evidence for mTORC1, but not BMP-Smad1/5, signaling being required for serum-induced myotube hypertrophy and autophagy flux by measuring LC3BII/I expression. Further investigation is warranted to examine the role of autophagy flux in myotube hypertrophy.NEW & NOTEWORTHY The present study demonstrates that myotube hypertrophy caused by chronic serum stimulation requires mammalian target of rapamycin complex 1 (mTORC1) signaling but not bone morphogenetic protein (BMP)-Smad1/5 signaling. The suppression of autophagy flux was associated with serum-induced myotube hypertrophy and mTORC1 regulation of autophagy flux by measuring LC3BII/I expression. Rapamycin is widely investigated for beneficial effects in aging skeletal muscle and sarcopenia; our results provide evidence that rapamycin can regulate autophagy-related signaling during myotube growth, which could benefit skeletal muscle functional and metabolic health.

H2A.Z is involved in premature aging and DSB repair initiation in muscle fibers

Histone variants are key epigenetic players, but their functional and physiological roles remain poorly understood. Here, we show that depletion of the histone variant H2A.Z in mouse skeletal muscle causes oxidative stress, oxidation of proteins, accumulation of DNA damages, and both neuromuscular junction and mitochondria lesions that consequently lead to premature muscle aging and reduced life span. Investigation of the molecular mechanisms involved shows that H2A.Z is required to initiate DNA double strand break repair by recruiting Ku80 at DNA lesions. This is achieved via specific interactions of Ku80 vWA domain with H2A.Z. Taken as a whole, our data reveal that H2A.Z containing nucleosomes act as a molecular platform to bring together the proteins required to initiate and process DNA double strand break repair.

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.

The Current Landscape of Pharmacotherapies for Sarcopenia

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

Cancer cachexia: molecular mechanisms and treatment strategies

Muscle wasting is a consequence of physiological changes or a pathology characterized by increased catabolic activity that leads to progressive loss of skeletal muscle mass and strength. Numerous diseases, including cancer, organ failure, infection, and aging-associated diseases, are associated with muscle wasting. Cancer cachexia is a multifactorial syndrome characterized by loss of skeletal muscle mass, with or without the loss of fat mass, resulting in functional impairment and reduced quality of life. It is caused by the upregulation of systemic inflammation and catabolic stimuli, leading to inhibition of protein synthesis and enhancement of muscle catabolism. Here, we summarize the complex molecular networks that regulate muscle mass and function. Moreover, we describe complex multi-organ roles in cancer cachexia. Although cachexia is one of the main causes of cancer-related deaths, there are still no approved drugs for cancer cachexia. Thus, we compiled recent ongoing pre-clinical and clinical trials and further discussed potential therapeutic approaches for cancer cachexia.

Effects of Turmeric Extract on Age-Related Skeletal Muscle Atrophy in Senescence-Accelerated Mice

Muscle atrophy is one of the main causes of sarcopenia—the age-related loss of skeletal muscle. In this study, we investigated the effect of turmeric (Curcuma longa) extract (TE) supplementation on age-related muscle atrophy in a senescence-accelerated mouse model and explored the underlying mechanisms. Twenty-six-week-old male, senescence-accelerated mouse resistant (SAMR) mice received the AIN-93G basal diet, while twenty-six-week-old male, senescence-accelerated mouse prone 8 (SAMP8) mice received the AIN-93G basal diet or a 2% TE powder-supplemented diet for ten weeks. Our findings revealed that TE supplementation showed certain effects on ameliorating the decrease in body weight, tibialis anterior weight, and mesenteric fat tissue weight in SAMP8 mice. TE improved gene expression in the glucocorticoid receptor-FoxO signaling pathway in skeletal muscle, including redd1, klf15, foxo1, murf1, and mafbx. Furthermore, TE might have the certain potential on improving the dynamic balance between anabolic and catabolic processes by inhibiting the binding of glucocorticoid receptor or FoxO1 to the glucocorticoid response element or FoxO-binding element in the MuRF1 promoter in skeletal muscle, thereby promoting muscle mass and strength, and preventing muscle atrophy and sarcopenia prevention. Moreover, TE may have reduced mitochondrial damage and maintained cell growth and division by downregulating the mRNA expression of the genes mfn2 and tsc2. Thus, the results indicated TE’s potential for preventing age-related muscle atrophy and sarcopenia.