MOTS-c reduces myostatin and muscle atrophy signaling

Non-canonical ORFs-derived protein products in mitochondria: A multifaceted exploration of their functions in health and disease

Traditionally, eukaryotic mRNAs were perceived as inherently monocistronic. However, recent insights from ribosome profiling (Ribo-seq) and proteomics studies challenge this paradigm. These investigations reveal that, beyond the currently annotated reference proteins (RefProts), there exist additional proteins known as alternative proteins (AltProts) and small open reading frames derived microproteins encoded in regions of mRNAs previously considered untranslated or in non-coding transcripts. This experimental evidence broadens the spectrum of functional proteins within cells, tissues, and organs, potentially offering crucial insights into biological processes. Notably, a significant proportion of these newly identified AltProts and microproteins demonstrates localization in mitochondria, contributing to the functions of mitochondrial complexes. This review delves into the overlooked realm of the alternative proteome within mitochondria, exploring the role of nuclear or mitochondrial-genome-encoded AltProts and microproteins in physiological and pathological cellular processes.

MOTS-c Levels and Sarcopenia Risk in Chronic Peritoneal Dialysis Patients: A Pilot Study

Background and Objectives: Sarcopenia is exceedingly frequent in end-stage kidney disease (ESKD) patients on dialysis, including those undergoing peritoneal dialysis (PD), and is of multifactorial origin. MOTS-c is a mitochondrial-derived peptide that promotes muscle growth whose levels are unbalanced in ESKD. In this study, we evaluated MOTS-c balance and its relationship with sarcopenia risk in an ESKD-PD cohort. Materials and Methods: MOTS-c was measured in serum, urine, and dialysate samples of 32 chronic PD patients. Patients were thus screened for sarcopenia risk by the SARC-F tool, anthropometric measurements, and physical performance tests. Results: PD patients with a very high sarcopenia risk (SARC-F ≥ 2) had significantly lower serum (sMOTS-c) and higher dialysate (dMOTS-c) levels, suggesting an increased peritoneal clearance of this substance (d/s MOTS-c). sMOTS-c levels were directly correlated with muscle performance in physical tests, while an opposite relationship was found with dMOTS-c and d/sMOTS-c. ROC analyses demonstrated the diagnostic potential of MOTS-c, particularly in combination with physical and anthropometric assessments, to identify PD patients at very high risk of sarcopenia. Conclusions: Chronic PD may negatively affect MOTS-c balance, which, in turn, may contribute to enhanced sarcopenia risk. Larger studies are needed to confirm these observations and to validate the potential utility of this substance as a biomarker for improving sarcopenia risk stratification in PD patients.

Mitochondrial-derived microproteins: from discovery to function

Given the uniqueness of the mitochondria, and the fact that they have their own genome, mitochondrial-derived microproteins (MDPs) are similar to, but different from, nuclear-encoded microproteins. The discovery of an increasing number of microproteins from this organelle and the importance of mitochondria to cellular and organismal health make it a priority to study this novel class of proteins in search of possible therapeutic targets and cures. In this review, we discuss the history of MDP discovery, describe the function of each MDP, and conclude with future goals and techniques to help discover more MDPs.

Molecular mechanisms and potential interventions during aging-associated sarcopenia

Sarcopenia, a common condition observed in the elderly, presenting a significant public health challenge due to its high prevalence, insidious onset and diverse systemic effects. Despite ongoing research, the precise etiology of sarcopenia remains elusive. Aging-related processes, which included inflammation, oxidative stress, compromised mitochondrial function and apoptosis, have been implicated in its development. Notably, effective pharmacological treatments for sarcopenia are currently lacking, highlighting the necessity for a deeper understanding of its pathogenesis and causative factors to enable proactive interventions. This article is aimed to provide an extensive overview of the pathogenesis of sarcopenia, along with a summary of current treatment and prevention strategies.

Utilizing zebrafish models to elucidate mechanisms and develop therapies for skeletal muscle atrophy

Skeletal muscle atrophy, resulting from an imbalance in muscle protein synthesis and degradation, compromises muscle quality and function, imposing significant burdens on movement and metabolic stability. Animal models are crucial for understanding the mechanisms of skeletal muscle atrophy and developing clinical prevention and treatment strategies. Zebrafish, as small aquatic vertebrates, exhibit high genetic homology with humans and offer advantages such as rapid reproduction, development, and transparent embryos. Their physiological and anatomical similarities to mammals, including a substantial proportion of skeletal muscle and observable swimming behavior reflecting body dysfunction, make zebrafish an ideal model for studying skeletal muscle-related diseases. This review outlines the development of zebrafish skeletal muscle and highlights key pathways regulating muscle proteins, emphasizing their anatomical and genetic consistency with humans. Various zebrafish models of skeletal muscle atrophy created through physical, chemical, and gene-editing methods are systematically summarized. Current challenges and proposed improvement strategies are also discussed to enhance the reliability and applicability of zebrafish models, providing a comprehensive reference for advancing research on skeletal muscle atrophy.

Using β-Elemene to reduce stemness and drug resistance in osteosarcoma: A focus on the AKT/FOXO1 signaling pathway and immune modulation

Objective

Osteosarcoma, a highly malignant bone tumor, poses significant treatment challenges due to its propensity for stemness and drug resistance, particularly against doxorubicin (DOX). This study aims to investigate the mechanism by which β-elemene reduces the stemness of osteosarcoma stem cells and ultimately decreases DOX resistance by inhibiting the Akt/FoxO1 signaling pathway and activating a macrophage-mediated inflammatory microenvironment.

Methods

Osteosarcoma stem cells were isolated and induced for DOX resistance. In vitro and in vivo models were employed to assess β-elemene's impact on cell viability, stemness, and drug resistance. Bioinformatics analysis, flow cytometry, and immunofluorescence staining were used to evaluate signaling pathway activity and macrophage polarization. Additionally, an osteosarcoma xenograft mouse model was established to confirm the therapeutic effects of β-elemene.

Results

In vivo animal experiments demonstrated that β-elemene reduces osteosarcoma resistance. Bioinformatics analysis revealed that AKT1 is a key core gene in osteosarcoma progression, acting through the FOXO signaling pathway. Additionally, AKT inhibits immune cell infiltration in osteosarcoma and suppresses immune responses during osteosarcoma progression. β-elemene may influence osteosarcoma progression by mediating TP53 to regulate PTEN and subsequently AKT1. In vitro experiments showed that β-elemene promotes M1 macrophage activation by inhibiting the Akt/FoxO1 signaling axis, thereby reducing the stemness of osteosarcoma stem cells. Finally, in vivo animal experiments confirmed that β-elemene reduces osteosarcoma resistance by promoting M1 macrophage activation through inhibition of the Akt/FoxO1 signaling axis.

Conclusion

β-Elemene demonstrates promising potential in reducing osteosarcoma stemness and drug resistance via dual mechanisms: targeting the AKT/FOXO1 pathway and modulating the tumor immune microenvironment. These findings suggest β-elemene as a potential adjunct therapy for osteosarcoma, providing novel therapeutic strategies to overcome chemotherapy resistance and improve patient outcomes.

Endurance training enhances skeletal muscle mitochondrial respiration by promoting MOTS-c secretion

The mitochondrial open reading frame of 12S rRNA-c (MOTS-c) is a biologically active mitochondria-derived peptide. However, the relationship between MOTS-c, skeletal muscle mitochondrial function, and endurance exercise adaptations is unknown. Here, we tested indices such as maximal oxygen uptake and serum MOTS-c levels in marathon runners and sedentary subjects. In addition, we tested aerobic exercise capacity, skeletal muscle mitochondrial respiration rate, and serum MOTS-c levels in mice subjected to long-term endurance training groups and sedentary groups. Our results indicated a close association between serum MOTS-c levels and aerobic exercise capacity. Circulating MOTS-c levels are expected to be an important indicator for predicting aerobic exercise capacity and assessing body fat status, endurance training load, and physical function. More importantly, we found that endurance training may enhance the mitochondrial respiratory function of skeletal muscle by promoting the secretion of MOTS-c and activating the AMPK/PGC-1α pathway.

Prospects for the diagnosis and treatment of sarcopenia in the Philippines

Over the past decade, the elderly Filipino population has significantly increased, rising from 4.6 million seniors, which was approximately 6% of the total population in 2000, to 6.5 million, or around 6.9% of the population in 2010. Projections suggest that by 2030, the percentage of the population aged 60 and above will increase to between 10 and 19%, indicating a significant demographic shift toward an aging population. This shift from a predominantly young population to a rapidly growing elderly demographic underscores the urgent need for effective health promotion and management programs targeting older adults. Sarcopenia, a muscle-wasting disorder, represents a significant global health challenge, particularly affecting the elderly. In the Philippines, the impact of sarcopenia is expected to become more pronounced, potentially straining both individuals and the national healthcare system over the next 15 years, despite the country's relatively younger overall population. Despite the expanding research on sarcopenia in the Philippines, there remains an urgent need to raise awareness and implement proactive measures to address this escalating health issue.

MOTS-c modulates skeletal muscle function by directly binding and activating CK2

MOTS-c is a mitochondrial microprotein that improves metabolism. Here, we demonstrate CK2 is a direct and functional target of MOTS-c. MOTS-c directly binds to CK2 and activates it in cell-free systems. MOTS-c administration to mice prevented skeletal muscle atrophy and enhanced muscle glucose uptake, which were blunted by suppressing CK2 activity. Interestingly, the effects of MOTS-c are tissue-specific. Systemically administered MOTS-c binds to CK2 in fat and muscle, yet stimulates CK2 activity in muscle while suppressing it in fat by differentially modifying CK2-interacting proteins. Notably, a naturally occurring MOTS-c variant, K14Q MOTS-c, has reduced binding to CK2 and does not activate it or elicit its effects. Male K14Q MOTS-c carriers exhibited a higher risk of sarcopenia and type 2 diabetes (T2D) in an age- and physical-activity-dependent manner, whereas females had an age-specific reduced risk of T2D. Altogether, these findings provide evidence that CK2 is required for MOTS-c effects.

Muscle-enriched microRNA-486-mediated regulation of muscular atrophy and exercise

The objectives of this review were to understand the impact of microRNA-486 on myogenesis and muscle atrophy, and the change of microRNA-486 following exercise, and provide valuable information for improving muscle atrophy based on exercise intervention targeting microRNA-486. Muscle-enriched microRNAs (miRNAs), also referred to as myomiRs, control various processes in skeletal muscles, from myogenesis and muscle homeostasis to different responses to environmental stimuli such as exercise. MicroRNA-486 is a miRNA in which a stem-loop sequence is embedded within the ANKYRIN1 (ANK1) locus and is strictly conserved across mammals. MicroRNA-486 is involved in the development of muscle atrophy caused by aging, immobility, prolonged exposure to microgravity, or muscular and neuromuscular disorders. PI3K/AKT signaling is a positive pathway, as it increases muscle mass by increasing protein synthesis and decreasing protein degradation. MicroRNA-486 can activate this pathway by inhibiting phosphatase and tensin homolog (PTEN), it may also indirectly inhibit the HIPPO signaling pathway to promote cell growth. Exercises regulate microRNA-486 expression both in blood and muscle. This review focused on the recent elucidation of sarcopenia regulation by microRNA-486 and its effects on pathological states, including primary muscular disease, secondary muscular disorders, and age-related sarcopenia. Additionally, the role of exercise in regulating skeletal muscle-enriched microRNA-486 was highlighted, along with its physiological significance. Growing evidence indicates that microRNA-486 significantly impacts the development of muscle atrophy. MicroRNA-486 has great potential to become a therapeutic target for improving muscle atrophy through exercise intervention.

The Relationship Between MOTS-c K14Q Polymorphism and Sarcopenia, Blood Lipids, and Mental Health in Older Korean Adults

Background/objectives: An East Asian-specific 1382A>C polymorphism in the mitochondrial open reading frame of the 12S rRNA type-c results in an amino acid substitution from Lys (K) to Gln (Q) at the 14th amino acid residue. This study investigated the association between m.1382A>C polymorphism and sarcopenia, blood lipids, and mental health in older Korean adults. Methods: The study included 683 community-dwelling Korean adults (345 men and 338 women) aged 65 years and older. The m.1382A>C polymorphism was genotyped with a 7500 real-time PCR system. Handgrip strength (HGS) was measured, and appendicular skeletal muscle (ASM) mass was calculated. Demographics, blood lipids, falling risk, nutritional intake, cognition function, and depression were additionally measured. Results: Men carrying the C allele had significantly higher ASM (21.6 ± 3.0 vs. 19.5 ± 2.2 kg, p = 0.018), ASM/height2 (7.76 ± 0.76 vs. 7.14 ± 0.62 kg/m2, p = 0.012), lean mass (53.3 ± 6.2 vs. 46.5 ± 4.0 kg, p < 0.001), left HGS (33.3 ± 5.0 vs. 28.9 ± 4.0 kg, p = 0.010), and right HGS (35.6 ± 5.3 vs. 30.9 ± 4.3 kg, p = 0.009) than men carrying the A allele. The genotype differences in ASM (p = 0.017), ASM/height2 (p = 0.011), lean mass (p < 0.001), left HGS (p = 0.010), and right HGS (p = 0.009) remained significant even after adjusting for all measured covariates. By contrast, no significant differences in other measured parameters were found between women carrying the A and C alleles. Conclusions: Our study findings indicate that the m.1382A>C polymorphism may be used as a genetic biomarker of age-related sarcopenia in older Korean men.

Mitochondrial Function and Dysfunction in White Adipocytes and Therapeutic Implications

For a long time, white adipocytes were thought to function as lipid storages due to the sizeable unilocular lipid droplet that occupies most of their space. However, recent discoveries have highlighted the critical role of white adipocytes in maintaining energy homeostasis and contributing to obesity and related metabolic diseases. These physiological and pathological functions depend heavily on the mitochondria that reside in white adipocytes. This article aims to provide an up-to-date overview of the recent research on the function and dysfunction of white adipocyte mitochondria. After briefly summarizing the fundamental aspects of mitochondrial biology, the article describes the protective role of functional mitochondria in white adipocyte and white adipose tissue health and various roles of dysfunctional mitochondria in unhealthy white adipocytes and obesity. Finally, the article emphasizes the importance of enhancing mitochondrial quantity and quality as a therapeutic avenue to correct mitochondrial dysfunction, promote white adipocyte browning, and ultimately improve obesity and its associated metabolic diseases. © 2024 American Physiological Society. Compr Physiol 14:5581-5640, 2024.

Mitochondria-encoded peptide MOTS-c participates in plasma membrane repair by facilitating the translocation of TRIM72 to membrane

Rationale: An impairment of plasma membrane repair has been implicated in various diseases such as muscular dystrophy and ischemia/reperfusion injury. MOTS-c, a short peptide encoded by mitochondria, has been shown to pass through the plasma membrane into the bloodstream. This study determined whether this biological behavior was involved in membrane repair and its underlying mechanism. Methods and Results: In human participants, the level of MOTS-c was positively correlated with the abundance of mitochondria, and the membrane repair molecule TRIM72. In contrast to high-intensity eccentric exercise, moderate-intensity exercise improved sarcolemma integrity and physical performance, accompanied by an increase of mitochondria beneath the damaged sarcolemma and secretion of MOTS-c. Furthermore, moderate-intensity exercise increased the interaction between MOTS-c and TRIM72, and MOTS-c facilitated the trafficking of TRIM72 to the sarcolemma. In vitro studies demonstrated that MOTS-c attenuated membrane damage induced by hypotonic solution, which could be blocked by siRNA-TRIM72, but not AMPK inhibitor. Co-immunoprecipitation study showed that MOTS-c interacted with TRIM72 C-terminus, but not N-terminus. The dynamic membrane repair assay revealed that MOTS-c boosted the trafficking of TRIM72 to the injured membrane. However, MOTS-c itself had negligible effects on membrane repair, which was recapitulated in TRIM72-/- mice. Unexpectedly, MOTS-c still increased the fusion of vesicles with the membrane in TRIM72-/- mice, and dot blot analysis revealed an interaction between MOTS-c and phosphatidylinositol (4,5) bisphosphate [PtdIns (4,5) P2]. Finally, MOTS-c blunted ischemia/reperfusion-induced membrane disruption, and preserved heart function. Conclusions: MOTS-c/TRIM72-mediated membrane integrity improvement participates in mitochondria-triggered membrane repair. An interaction between MOTS-c and plasma lipid contributes to the fusion of vesicles with membrane. Our data provide a novel therapeutic strategy for rescuing organ function by facilitating membrane repair with MOTS-c.

MOTS-c regulates pancreatic alpha and beta cell functions in vitro

The aim of this study is to determine the influence of the mitochondrial open-reading-frame of the twelve S rRNA-c (MOTS-c) peptide on pancreatic cell physiology. Moreover, in this study, we examined the changes in MOTS-c secretion and expression under different conditions. Our experiments were conducted using laboratory cell line cultures, specifically the INS-1E and αTC-1 cell lines, which represent β and α pancreatic cells, respectively. As the pancreas is an endocrine organ, we also tested its hormone regulation capabilities. Furthermore, we assessed the secretion of MOTS-c after incubating the cells with glucose and free fatty acids. Additionally, we examined key cell culture parameters such as cell viability, proliferation, and apoptosis. The results obtained from this study show that MOTS-c has a significant impact on the physiology of pancreatic cells. Specifically, it lowers insulin secretion and expression in INS-1E cells and enhances glucagon secretion and expression in αTC-1 cells. Furthermore, MOTS-c affects cell viability and apoptosis. Interestingly, insulin and glucagon affect the MOTS-c secretion as well as glucose and free fatty acids. These experiments clearly show that MOTS-c is an important regulator of pancreatic metabolism, and there are numerous properties of MOTS-c yet to be discovered.

Satellite Cell-Derived Exosomes: A Novel Approach to Alleviate Skeletal Muscle Atrophy and Fibrosis

Skeletal muscle atrophy coincides with extensive fibrous tissue hyperplasia in muscle-atrophied patients, and fibrous tissue plays a vital role in skeletal muscle function and hinders muscle fiber regeneration. However, effective drugs to manage skeletal muscle atrophy and fibrosis remain elusive. This study isolated and characterized exosomes derived from skeletal muscle satellite cells (MuSC-Exo). The study investigated their effects on denervated skeletal muscle atrophy and fibrosis in Sprague Dawley (SD) rats via intramuscular injection. MuSC-Exo demonstrated the potential to alleviate skeletal muscle atrophy and fibrosis. The underlying mechanism using single-cell RNA sequencing data and functional analysis are analyzed. Mechanistic studies reveal close associations between fibroblasts and myoblasts, with the transforming growth factor β1 (TGF-β1)-Smad3-Pax7 axis governing fibroblast activation in atrophic skeletal muscle. MuSC-Exo intervention inhibited the TGF-β1/Smad3 pathway and improved muscle atrophy and fibrosis. In conclusion, MuSC-Exo-based therapy may represent a novel strategy to alleviate skeletal muscle atrophy and reduce excessive fibrotic tissue by targeting Pax7 through the TGF-β1/Smad3 pathway.

Bioelectrical impedance vector analysis is different according to the comorbidity burden in post-acute myocardial infarction

BACKGROUND

The prevalence of a high comorbidity burden in patients who suffered an acute myocardial infarction (AMI) is increasing with the aging population, and the nutrition status also may be a predictor of clinical outcomes for these patients. This study aimed to investigate the relationship between the comorbidity burden and the characteristics of the bioelectrical impedance vector analysis (BIVA) in patients post-AMI.

METHODS

This prospective observational cohort study was conducted with adult patients who were hospitalized with AMI. Pre-existing comorbidities were assessed by the Charlson comorbidity index (CCI) adjusted by age, and anthropometric and BIVA characteristics were evaluated after the hemodynamic stabilization. All patients were followed-up until hospital discharge, and their length of stay was observed.

RESULTS

A total of 184 patients (75% were males; mean age, 60.2 ± 12.3 years) were included. The most common comorbidities were dyslipidemia (73.9%), hypertension (62%), and type 2 diabetes (34.2%). A higher CCI (≥3) was associated with sex (P = 0.008) and age (P < 0.001). Regarding BIVA, statistically significant differences were detected between sex (P < 0.001), age (P < 0.001), and CCI (P = 0.003), with longer vectors in female, older adults, and those with CCI ≥ 3.

CONCLUSION

Finding a relationship between BIVA and CCI suggests the first identified coherent differences, potentially correlated with diseases, representing a first contribution to support this type of assessment. Therefore, with BIVA, healthcare professionals may monitor abnormalities and adopt preventive nutrition care measures on patients post-AMI to improve their clinical status.

Unraveling proteome changes of Sunit lamb meat in different feeding regimes and its relationship to flavor analyzed by TMT-labeled quantitative proteomic

In order to explore the molecular mechanism of the effect of feeding regimes on lamb flavor, biceps femoris muscle samples from pasture-fed groups (PF) and concentrate-fed groups (CF) were chosen, and tandem mass tag (TMT) labeling combined with mass spectrometry (MS) was performed to find associations between flavor indicators and proteome profiles. The content and composition of amino acids and volatile flavor substances were better in the PF compared to the CF, with higher levels of some beneficial flavor components such as Arg, Pro Pentanal, Heptanal, Octanal, 1-octen-3-ol and 2,3-Octanedione. About 82 differentially abundant proteins (DAPs) were identified. The Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis indicated that the pathways that may be associated with lamb flavor are focused on amino acid anabolism. These results provide a basis for further understanding of the molecular mechanisms of proteins in meat flavor regulation.

Mitochondrial-derived microprotein MOTS-c attenuates immobilization-induced skeletal muscle atrophy by suppressing lipid infiltration

Mitochondrial open reading frame of the 12S ribosomal RNA type-c (MOTS-c), a mitochondrial microprotein, has been described as a novel regulator of glucose and lipid metabolism. In addition to its role as a metabolic regulator, MOTS-c prevents skeletal muscle atrophy in high fat-fed mice. Here, we examined the preventive effect of MOTS-c on skeletal muscle mass, using an immobilization-induced muscle atrophy model, and explored its underlying mechanisms. Male C57BL/6J mice (10 wk old) were randomly assigned to one of the three experimental groups: nonimmobilization control group (sterilized water injection), immobilization control group (sterilized water injection), and immobilization and MOTS-c-treated group (15 mg/kg/day MOTS-c injection). We used casting tape for the immobilization experiment. After 8 days of the experimental period, skeletal muscle samples were collected and used for Western blotting, RNA sequencing, and lipid and collagen assays. Immobilization reduced ∼15% of muscle mass, whereas MOTS-c treatment attenuated muscle loss, with only a 5% reduction. MOTS-c treatment also normalized phospho-AKT, phospho-FOXO1, and phospho-FOXO3a expression levels and reduced circulating inflammatory cytokines, such as interleukin-1b (IL-1β), interleukin-6 (IL-6), chemokine C-X-C motif ligand 1 (CXCL1), and monocyte chemoattractant protein 1 (MCP-1), in immobilized mice. Unbiased RNA sequencing and its downstream analyses demonstrated that MOTS-c modified adipogenesis-modulating gene expression within the peroxisome proliferator-activated receptor (PPAR) pathway. Supporting this observation, muscle fatty acid levels were lower in the MOTS-c-treated group than in the casted control mice. These results suggest that MOTS-c treatment inhibits skeletal muscle lipid infiltration by regulating adipogenesis-related genes and prevents immobilization-induced muscle atrophy.NEW & NOTEWORTHY MOTS-c, a mitochondrial microprotein, attenuates immobilization-induced skeletal muscle atrophy. MOTS-c treatment improves systemic inflammation and skeletal muscle AKT/FOXOs signaling pathways. Furthermore, unbiased RNA sequencing and subsequent assays revealed that MOTS-c prevents lipid infiltration in skeletal muscle. Since lipid accumulation is one of the common pathologies among other skeletal muscle atrophies induced by aging, obesity, cancer cachexia, and denervation, MOTS-c treatment could be effective in other muscle atrophy models as well.

Sarcopenia, sarcopenic obesity and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), sarcopenia and sarcopenic obesity (SO) are highly prevalent conditions that may coexist, especially in the aging population, without any approved pharmacologic treatment for all of them. There are multiple pathophysiologic mechanisms suggested to explain an association between NAFLD and sarcopenia or SO, including alterations in the adipokines, cytokines, hepatokines and myokines, which may interplay with other factors, such as aging, diet and physical inactivity. In clinical terms, most observational studies support an association between NAFLD and sarcopenia or SO; importantly, there are few cohort studies indicating higher mortality in patients with NAFLD and sarcopenia. Their association also bears some treatment considerations: for example, pioglitazone or vitamin E, suggested as off label treatment for selected patients with nonalcoholic steatohepatitis, may be recommended in the coexistence of sarcopenia or SO, since limited evidence did not show adverse effects of them on sarcopenia and abdominal obesity. In this review, evidence linking sarcopenia and SO with NAFLD is summarized, with a special focus on clinical data. A synopsis of the major pathophysiological links between NAFLD and sarcopenia/SO is initially presented, followed by selected clinical studies and, finally, treatment considerations in patients with NAFLD and sarcopenia or SO are discussed.

Irisin Ameliorated Skeletal Muscle Atrophy by Inhibiting Fatty Acid Oxidation and Pyroptosis Induced by Palmitic Acid in Chronic Kidney Disease

INTRODUCTION

Protein-energy waste (PEW) is a common complication in patients with chronic kidney disease (CKD), among which skeletal muscle atrophy is one of the most important clinical features of PEW. Pyroptosis is a type of proinflammatory, programmed cell death associated with skeletal muscle disease. Irisin, as a novel myokine, has attracted extensive attention for its protective role in the complications associated with CKD, but its role in muscle atrophy in CKD is unclear.

METHODS

Palmitic acid (PA)-induced muscular atrophy was evaluated by a reduction in C2C12 myotube diameter. Muscle atrophy model was established in male C57BL/6J mice treated with 0.2% adenine for 4 weeks and then fed a 45% high-fat diet. Blood urea nitrogen and creatinine levels, body and muscle weight, and muscle histology were assessed. The expression of carnitine palmitoyltransferase 1A (CPT1A) and pyroptosis-related protein was analysed by Western blots or immunohistochemistry. The release of IL-1β was detected by enzyme-linked immunosorbent assay.

RESULTS

In this study, we showed that PA-induced muscular atrophy manifested as a reduction in C2C12 myotube diameter. During this process, PA can also induce pyroptosis, as shown by the upregulation of NLRP3, cleaved caspase-1 and GSDMD-N expression and the increased IL-1β release and PI-positive cell rate. Inhibition of caspase-1 or NLRP3 attenuated PA-induced pyroptosis and myotube atrophy in C2C12 cells. Importantly, irisin treatment significantly ameliorated PA-induced skeletal muscle pyroptosis and atrophy. In terms of mechanism, PA upregulated CPT1A, a key enzyme of fatty acid oxidation (FAO), and irisin attenuated this effect, which was consistent with etomoxir (CPT1A inhibitor) treatment. Moreover, irisin improved skeletal muscle atrophy and pyroptosis in adenine-induced mice by regulating FAO.

CONCLUSION

Our study firstly verifies that pyroptosis is a novel mechanism of skeletal muscle atrophy in CKD. Irisin ameliorates skeletal muscle atrophy by inhibiting FAO and pyroptosis in CKD, and irisin may be developed as a potential therapeutic agent for the treatment of muscle wasting in CKD patients.

Mitochondrial-derived vesicles in skeletal muscle remodeling and adaptation

Mitochondrial remodeling is crucial to meet the bioenergetic demand to support muscle contractile activity during daily tasks and muscle regeneration following injury. A set of mitochondrial quality control (MQC) processes, including mitochondrial biogenesis, dynamics, and mitophagy, are in place to maintain a well-functioning mitochondrial network and support muscle regeneration. Alterations in any of these pathways compromises mitochondrial quality and may potentially lead to impaired myogenesis, defective muscle regeneration, and ultimately loss of muscle function. Among MQC processes, mitophagy has gained special attention for its implication in the clearance of dysfunctional mitochondria via crosstalk with the endo-lysosomal system, a major cell degradative route. Along this pathway, additional opportunities for mitochondrial disposal have been identified that may also signal at the systemic level. This communication occurs via inclusion of mitochondrial components within membranous shuttles named mitochondrial-derived vesicles (MDVs). Here, we discuss MDV generation and release as a mitophagy-complementing route for the maintenance of mitochondrial homeostasis in skeletal myocytes. We also illustrate the possible role of muscle-derived MDVs in immune signaling during muscle remodeling and adaptation.

Myostatin: a potential therapeutic target for metabolic syndrome

Metabolic syndrome is a complex metabolic disorder, its main clinical manifestations are obesity, hyperglycemia, hypertension and hyperlipidemia. Although metabolic syndrome has been the focus of research in recent decades, it has been proposed that the occurrence and development of metabolic syndrome is related to pathophysiological processes such as insulin resistance, adipose tissue dysfunction and chronic inflammation, but there is still a lack of favorable clinical prevention and treatment measures for metabolic syndrome. Multiple studies have shown that myostatin (MSTN), a member of the TGF-β family, is involved in the development and development of obesity, hyperlipidemia, diabetes, and hypertension (clinical manifestations of metabolic syndrome), and thus may be a potential therapeutic target for metabolic syndrome. In this review, we describe the transcriptional regulation and receptor binding pathway of MSTN, then introduce the role of MSTN in regulating mitochondrial function and autophagy, review the research progress of MSTN in metabolic syndrome. Finally summarize some MSTN inhibitors under clinical trial and proposed the use of MSTN inhibitor as a potential target for the treatment of metabolic syndrome.

Tensile Loaded Tissue-Engineered Human Tendon Constructs Stimulate Myotube Formation

Skeletal muscle possesses adaptability to mechanical loading and regenerative potential following muscle injury due to muscle stem cell activity. So far, it is known that muscle stem cell activity is supported by the roles of several interstitial cells within skeletal muscle in response to muscle damage. The adjacent tendon is also exposed to repetitive mechanical loading and possesses plasticity like skeletal muscle. However, the interplay between the skeletal muscle and adjacent tendon tissue has not been fully investigated. In this study, we tested whether factors released by three-dimensional engineered human tendon constructs in response to uniaxial tensile loading can stimulate the proliferation and differentiation of human-derived myogenic cells (myoblasts). Tendon constructs were subjected to repetitive mechanical loading (4% strain at 0.5 Hz for 4 h) and nonrepetitive loading (0% strain at 0 Hz for 4 h), and the conditioned media from mechanically loaded and nonmechanically loaded control constructs were applied to myoblasts. Immunofluorescence analysis revealed both an increase of myotube fusion index (≥5 nuclei within one desmin+ myotube) and the myotube diameter when conditioned medium from mechanically loaded tendon constructs was applied. Myostatin, myosin heavy chain 7, and AXIN2 gene expressions were downregulated in myotubes treated with conditioned medium from mechanically loaded tendon constructs. However, proliferative potential (number of Ki67+ and bromodeoxyuridine+ myoblasts) did not differ between the two groups. These results indicate that tendon fibroblasts enhance myotube formation by mechanical loading-induced factors. Our finding suggests that mechanical loading affects the signaling interplay between skeletal muscle and tendon tissue and is thus important for musculoskeletal tissue development and regeneration in humans. Impact statement The interplay between satellite cells and various types of resident cells within the skeletal muscle for muscle regeneration has been extensively studied. However, even though tendon tissue is located adjacent to skeletal muscle tissue and cells in these tissues are exposed to repetitive mechanical loading together, the interaction between muscle and tendon tissues for muscle regeneration remains to be elucidated. In this study, we report that the conditioned media from engineered human tendon tissues undergoing repetitive tensile mechanical loading enhanced myotube formation. Our in vitro findings extend the fundamental understanding of the crosstalk between adjacent tissues of the muscle-tendon unit.

Novel Insights into Mitochondrial DNA: Mitochondrial Microproteins and mtDNA Variants Modulate Athletic Performance and Age-Related Diseases

Sports genetics research began in the late 1990s and over 200 variants have been reported as athletic performance- and sports injuries-related genetic polymorphisms. Genetic polymorphisms in the α-actinin-3 (ACTN3) and angiotensin-converting enzyme (ACE) genes are well-established for athletic performance, while collagen-, inflammation-, and estrogen-related genetic polymorphisms are reported as genetic markers for sports injuries. Although the Human Genome Project was completed in the early 2000s, recent studies have discovered previously unannotated microproteins encoded in small open reading frames. Mitochondrial microproteins (also called mitochondrial-derived peptides) are encoded in the mtDNA, and ten mitochondrial microproteins, such as humanin, MOTS-c (mitochondrial ORF of the 12S rRNA type-c), SHLPs 1-6 (small humanin-like peptides 1 to 6), SHMOOSE (Small Human Mitochondrial ORF Over SErine tRNA), and Gau (gene antisense ubiquitous in mtDNAs) have been identified to date. Some of those microproteins have crucial roles in human biology by regulating mitochondrial function, and those, including those to be discovered in the future, could contribute to a better understanding of human biology. This review describes a basic concept of mitochondrial microproteins and discusses recent findings about the potential roles of mitochondrial microproteins in athletic performance as well as age-related diseases.

MOTS-c Functionally Prevents Metabolic Disorders

Mitochondrial-derived peptides are a family of peptides encoded by short open reading frames in the mitochondrial genome, which have regulatory effects on mitochondrial functions, gene expression, and metabolic homeostasis of the body. As a new member of the mitochondrial-derived peptide family, mitochondrial open reading frame of the 12S rRNA-c (MOTS-c) is regarding a peptide hormone that could reduce insulin resistance, prevent obesity, improve muscle function, promote bone metabolism, enhance immune regulation, and postpone aging. MOTS-c plays these physiological functions mainly through activating the AICAR-AMPK signaling pathways by disrupting the folate-methionine cycle in cells. Recent studies have shown that the above hormonal effect can be achieved through MOTS-c regulating the expression of genes such as GLUT4, STAT3, and IL-10. However, there is a lack of articles summarizing the genes and pathways involved in the physiological activity of MOTS-c. This article aims to summarize and interpret the interesting and updated findings of MOTS-c-associated genes and pathways involved in pathological metabolic processes. Finally, it is expected to develop novel diagnostic markers and treatment approaches with MOTS-c to prevent and treat metabolic disorders in the future.

Forkhead Box O Signaling Pathway in Skeletal Muscle Atrophy

Skeletal muscle atrophy is the consequence of protein degradation exceeding protein synthesis because of disease, aging, and physical inactivity. Patients with skeletal muscle atrophy have decreased muscle mass and fiber cross-sectional area, and experience reduced survival quality and motor function. The forkhead box O (FOXO) signaling pathway plays an important role in the pathogenesis of skeletal muscle atrophy by regulating E3 ubiquitin ligases and some autophagy factors. However, the mechanism of FOXO signaling pathway leading to skeletal muscle atrophy is still unclear. The development of treatment strategies for skeletal muscle atrophy has been a thorny clinical problem. FOXO-targeted therapy to treat skeletal muscle atrophy is a promising approach, and an increasing number of relevant studies have been reported. This article reviews the mechanism and therapeutic targets of the FOXO signaling pathway mediating skeletal muscle atrophy, and provides ideas for the clinical treatment of this condition.

Transcriptome Sequencing Analysis of circRNA in Skeletal Muscle between Fast- and Slow-Growing Chickens at Embryonic Stages

Skeletal muscle growth has always been the focus of the broiler industry, and circRNAs play a significant role in this process. We collected leg muscles of slow- and fast-growing Bian chicken embryos in the study at 14 (S14 and F14) and 20 (S20 and F20) days for RNA-seq. Finally, 123 and 121 differentially expressed circRNAs (DECs) were identified in S14 vs. F14 and S20 vs. F20, respectively. GO enrichment analysis for DECs obtained important biological process (BP) terms including nicotinate nucleotide biosynthetic process, nicotinate nucleotide salvage, and NAD salvage in S20 vs. F20 and protein mannosylation in S14 vs. F14. KEGG pathway analysis showed Wnt signaling pathway, Tight junction, Ubiquitin mediated proteolysis, and Notch signaling pathway were enriched in the top 20. Based on the GO and KEGG analysis results, we found some significant host genes and circRNAs such as NAPRT and novel_circ_0004547, DVL1 and novel_circ_0003578, JAK2 and novel_circ_0010289, DERA and novel_circ_0003082, etc. Further analysis found 19 co-differentially expressed circRNAs between the two comparison groups. We next constructed a circRNA-miRNA network for them, and some candidate circRNA-miRNA pairs related to skeletal muscle were obtained, such as novel_circ_0002153-miR-12219-5p, novel_circ_0003578-miR-3064-3p, and novel_circ_0010661-miR-12260-3p. These results would help to reveal the mechanism for circRNAs in skeletal muscle and also provide some guidance for the breeding of broilers.

MOTS-c promotes muscle differentiation in vitro

MOTS-c (mitochondrial open reading frame of the 12 S rRNA-c) is a newly discovered peptide that has been shown to have a protective role in whole-body metabolic homeostasis. This could be a consequence of the effect of MOTS-c on muscle tissue. Here, we investigated the role of MOTS-c in the differentiation of human (LHCN-M2) and murine (C2C12) muscle progenitor cells. Cells were treated with peptides at the onset of differentiation or after myotubes had been formed. We identified in silico a putative Src Homology 2 (SH2) binding motif in the YIFY region of the MOTS-c sequence, and created a Y8F mutant MOTS-c peptide to explore the role of this region. In both cellular models, treatment with wild-type MOTS-c peptide increased myotube formation whereas treatment with the Y8F peptide did not. MOTS-c wild-type, but not Y8F peptide, also protected against interleukin-6 (IL-6)-induced reduction of nuclear myogenin staining in myocytes. Thus, we investigated whether MOTS-c interacts with the IL-6/Janus kinase/ Signal transducer and activator of transcription 3 (STAT3) pathway, and found that MOTS-c, but not the Y8F peptide, blocked the transcriptional activity of STAT3 induced by IL-6. Altogether, our findings suggest that, in muscle cells, MOTS-c interacts with STAT3 via the putative SH2 binding motif in the YIFY region to reduce STAT3 transcriptional activity, which enhances myotube formation. This newly discovered mechanism of action highlights MOTS-c as a potential therapeutic target against muscle-wasting in several diseases.

Mitochondrial-derived peptides as a novel intervention for obesity and cardiac diseases: bench evidence for potential bedside application

Currently, obesity is the most common major health problem for people worldwide. Obesity is known to be a significant risk factor for several diseases, including metabolic syndrome, insulin resistance and type 2 diabetes, eventually leading to the development of chronic systemic disorders. Previous studies showed that mitochondrial dysfunction could be one of the potential mechanisms for obesity progression. Most interventions used for combating obesity have also been reported to modulate mitochondrial function, suggesting the potential role of mitochondria in the pathology of the obese condition. Recent studies have shown that peptides produced by mitochondria, mitochondrial-derived peptides (MDPs), potentially improve metabolic function and exert benefits in obesity-associated diabetes and various heart pathologies. In this review, the roles of MDPs in the metabolic pathways and their use in the treatment of various adverse effects of obesity are comprehensively summarised based on collective evidence from in vitro, in vivo and clinical studies. The roles of MDPs as novel therapeutic interventions for cardiac dysfunction caused by various stresses or toxicities are also presented and discussed. This review aims to summarise the knowledge regarding the effects of MDPs on obesity, with a particular emphasis on their potential protective effects on the impaired cardiac function associated with obesity. The information from this review will also encourage further clinical investigations to warrant the potential application of MDP interventions in the clinical setting in the future.

Mitochondria-derived peptides in aging and healthspan

The mechanisms that explain mitochondrial dysfunction in aging and healthspan continue to be studied, but one element has been unexplored: microproteins. Small open reading frames in circular mitochondria DNA can encode multiple microproteins, called mitochondria-derived peptides (MDPs). Currently, eight MDPs have been published: humanin, MOTS-c, and SHLPs 1–6. This Review describes recent advances in microprotein discovery with a focus on MDPs. It discusses what is currently known about MDPs in aging and how this new understanding could add to the way we understand age-related diseases including type 2 diabetes, cancer, and neurodegenerative diseases at the genomic, proteomic, and drug-development levels.

Exercise, Mitohormesis, and Mitochondrial ORF of the 12S rRNA Type-C (MOTS-c)

Low levels of mitochondrial stress are beneficial for organismal health and survival through a process known as mitohormesis. Mitohormetic responses occur during or after exercise and may mediate some salutary effects of exercise on metabolism. Exercise-related mitohormesis involves reactive oxygen species production, mitochondrial unfolded protein response (UPRmt), and release of mitochondria-derived peptides (MDPs). MDPs are a group of small peptides encoded by mitochondrial DNA with beneficial metabolic effects. Among MDPs, mitochondrial ORF of the 12S rRNA type-c (MOTS-c) is the most associated with exercise. MOTS-c expression levels increase in skeletal muscles, systemic circulation, and the hypothalamus upon exercise. Systemic MOTS-c administration increases exercise performance by boosting skeletal muscle stress responses and by enhancing metabolic adaptation to exercise. Exogenous MOTS-c also stimulates thermogenesis in subcutaneous white adipose tissues, thereby enhancing energy expenditure and contributing to the anti-obesity effects of exercise training. This review briefly summarizes the mitohormetic mechanisms of exercise with an emphasis on MOTS-c.

The MOTS-c K14Q polymorphism in the mtDNA is associated with muscle fiber composition and muscular performance

Human skeletal muscle fiber is heterogenous due to its diversity of slow- and fast-twitch fibers. In human, slow-twitched fiber gene expression is correlated to MOTS-c, a mitochondria-derived peptide that has been characterized as an exercise mimetic. Within the MOTS-c open reading frame, there is an East Asian-specific m.1382A>C polymorphism (rs111033358) that changes the 14th amino acid of MOTS-c (i.e., K14Q), a variant of MOTS-c that has less biological activity. Here, we examined the influence of the m.1382A>C polymorphism causing MOTS-c K14Q on skeletal muscle fiber composition and physical performance. The myosin heavy chain (MHC) isoforms (MHC-I, MHC-IIa, and MHC-IIx) as an indicator of muscle fiber composition were assessed in 211 Japanese healthy individuals (102 men and 109 women). Muscular strength was measured in 86 physically active young Japanese men by using an isokinetic dynamometer. The allele frequency of the m.1382A>C polymorphism was assessed in 721 Japanese athletes and 873 ethnicity-matched controls. The m.1382A>C polymorphism genotype was analyzed by TaqMan SNP Genotyping Assay. Individuals with the C allele of the m.1382A>C exhibited a higher proportion of MHC-IIx, an index of fast-twitched fiber, than the A allele carriers. Men with the C allele of m.1382A>C exhibited significantly higher peak torques of leg flexion and extension. Furthermore, the C allele frequency was higher in the order of sprint/power athletes (6.5%), controls (5.1%), and endurance athletes (2.9%). Additionally, young male mice were injected with the MOTS-c neutralizing antibody once a week for four weeks to mimic the C allele of the m.1382A>C and assessed for protein expression levels of MHC-fast and MHC-slow. Mice injected with MOTS-c neutralizing antibody showed a higher expression of MHC-fast than the control mice. These results suggest that the C allele of the East Asian-specific m.1382A>C polymorphism leads to the MOTS-c K14Q contributes to the sprint/power performance through regulating skeletal muscle fiber composition.

Extending human healthspan and longevity: a symposium report

For many years, it was believed that the aging process was inevitable and that age-related diseases could not be prevented or reversed. The geroscience hypothesis, however, posits that aging is, in fact, malleable and, by targeting the hallmarks of biological aging, it is indeed possible to alleviate age-related diseases and dysfunction and extend longevity. This field of geroscience thus aims to prevent the development of multiple disorders with age, thereby extending healthspan, with the reduction of morbidity toward the end of life. Experts in the field have made remarkable advancements in understanding the mechanisms underlying biological aging and identified ways to target aging pathways using both novel agents and repurposed therapies. While geroscience researchers currently face significant barriers in bringing therapies through clinical development, proof-of-concept studies, as well as early-stage clinical trials, are underway to assess the feasibility of drug evaluation and lay a regulatory foundation for future FDA approvals in the future.

Plasma mitochondrial derived peptides MOTS-c and SHLP2 positively associate with android and liver fat in people without diabetes

Mitochondrial-derived peptides (MDPs) are encoded by the mitochondrial genome and hypothesised to form part of a retrograde signalling network that modulates adaptive responses to metabolic stress. To understand how metabolic stress regulates MDPs in humans we assessed the association between circulating MOTS-c and SHLP2 and components of metabolic syndrome (MS), as well as depot-specific fat mass in participants without overt type 2 diabetes or cardiovascular disease. One-hundred and twenty-five Chinese participants (91 male, 34 female) had anthropometry, whole body dual-energy X-ray absorptiometry scans and fasted blood samples analysed. Chinese female participants and an additional 34 European Caucasian female participants also underwent magnetic resonance imaging and spectroscopy (MRI/S) for visceral, pancreatic and liver fat quantification. In Chinese participants (age = 41 ± 1 years, BMI = 27.8 ± 3.9 kg/m²), plasma MOTS-c (315 ± 27 pg/ml) and SHLP2 (1393 ± 82 pg/ml) were elevated in those with MS (n = 26). While multiple components of the MS sequelae positively associated with both MOTS-c and SHLP2, including blood pressure, fasting plasma glucose and triglycerides, the most significant of these was waist circumference (p < 0.0001). Android fat had a greater effect on increasing plasma MOTS-c (p < 0.004) and SHLP2 (p < 0.009) relative to whole body fat. Associations with MRI/S parameters corrected for total body fat mass revealed that liver fat positively associated with plasma MOTS-c and SHLP2 and visceral fat with SHLP2. Consistent with hepatic stress being a driver of circulating MDP concentrations, plasma MOTS-c and SHLP2 were higher in participants with elevated liver damage markers and in male C57Bl/6j mice fed a diet that induces hepatic lipid accumulation and damage. Our findings provide evidence that in the absence of overt type 2 diabetes, components of the MS positively associated with levels of MOTS-c and SHLP2 and that android fat, in particular liver fat, is a primary driver of these associations. MOTS-c and SHLP2 have previously been shown to have cyto- and metabolo-protective properties, therefore we suggest that liver stress may be a mitochondrial peptide signal, and that mitochondrial peptides are part of a hepatic centric-hormetic response intended to restore metabolic balance.

The Role of the Skeletal Muscle Secretome in Mediating Endurance and Resistance Training Adaptations

Exercise, in the form of endurance or resistance training, leads to specific molecular and cellular adaptions not only in skeletal muscles, but also in many other organs such as the brain, liver, fat or bone. In addition to direct effects of exercise on these organs, the production and release of a plethora of different signaling molecules from skeletal muscle are a centerpiece of systemic plasticity. Most studies have so far focused on the regulation and function of such myokines in acute exercise bouts. In contrast, the secretome of long-term training adaptation remains less well understood, and the contribution of non-myokine factors, including metabolites, enzymes, microRNAs or mitochondrial DNA transported in extracellular vesicles or by other means, is underappreciated. In this review, we therefore provide an overview on the current knowledge of endurance and resistance exercise-induced factors of the skeletal muscle secretome that mediate muscular and systemic adaptations to long-term training. Targeting these factors and leveraging their functions could not only have broad implications for athletic performance, but also for the prevention and therapy in diseased and elderly populations.