bims-moremu 2023-02-12 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023‒02‒12
thirty-two papers selected by
Anna Vainshtein
Craft Science Inc.

Insights into Cell-Specific Functions of Microtubules in Skeletal Muscle Development and Homeostasis.
Efficient Muscle Regeneration by Human PSC-Derived CD82+ ERBB3+ NGFR+ Skeletal Myogenic Progenitors.
Fiber-Type Shifting in Sarcopenia of Old Age: Proteomic Profiling of the Contractile Apparatus of Skeletal Muscles.
Stimulation of soluble guanylate cyclase by vericiguat reduces skeletal muscle atrophy of mice following chemotherapy.
mt-Ty 5´tiRNA regulates skeletal muscle cell proliferation and differentiation.
Introduction to the Special Issue "Skeletal Muscle Atrophy: Mechanisms at a Cellular Level".
Molecular mechanisms of post-burn muscle wasting and the therapeutic potential of physical exercise.
Signatures of muscle disuse in spaceflight and bed rest revealed by single muscle fiber proteomics.
Ion Channels of the Sarcolemma and Intracellular Organelles in Duchenne Muscular Dystrophy: A Role in the Dysregulation of Ion Homeostasis and a Possible Target for Therapy.
Cold exposure alters lipid metabolism of skeletal muscle through HIF-1α-induced mitophagy.
Cardiolipin metabolism regulates expression of muscle transcription factor MyoD1 and muscle development.
Muscle-specific deletion of Arid5b causes metabolic changes in skeletal muscle that affect adipose tissue and liver.
Myosin post-translational modifications and function in the presence of myopathy-linked truncating MYH2 mutations.
Cellular and Subcellular Characteristics of Neuromuscular Junctions in Muscles with Disparate Duty Cycles and Myofiber Profiles.
C-terminal agrin fragment as a biomarker of muscle wasting and weakness: a narrative review.
Defective excitation-contraction coupling and mitochondrial respiration precede mitochondrial Ca2+ accumulation in spinobulbar muscular atrophy skeletal muscle.
Disintegration of the NuRD Complex in Primary Human Muscle Stem Cells in Critical Illness Myopathy.
Neuromuscular junction disorders: Experimental models and pathophysiological mechanisms.
Prevalence and Mechanisms of Skeletal Muscle Atrophy in Metabolic Conditions.
The transcript interactome of skeletal muscle RNA binding protein motif 3 (RBM3).
Molecular characterization of the intact mouse muscle spindle using a multi-omics approach.
Intrafusal-fiber LRP4 for muscle spindle formation and maintenance in adult and aged animals.
Phosphoproteomics Profiling Defines a Target Landscape of the Basophilic Protein Kinases AKT, S6K, and RSK in Skeletal Myotubes.
A transcriptome atlas of leg muscles from healthy human volunteers reveals molecular and cellular signatures associated with muscle location.
Evaluation of Associations of Growth Differentiation Factor-11, Growth Differentiation Factor-8 and their Binding Proteins Follistatin and Follistatin-like protein-3 with Measures of Skeletal Muscle Mass, Muscle Strength and Physical Function in Older Adults.
Muscle disuse as hindlimb unloading in early postnatal mice negatively impacts grip strength in adult mice: A pilot study.
Metformin regulates myoblast differentiation through an AMPK-dependent mechanism.
Sex differences in muscle SIRT1 and SIRT3 and exercise + weight loss effects on muscle sirtuins.
Modulation of the Circulating Extracellular Vesicles in Response to Different Exercise Regimens and Study of Their Inflammatory Effects.
Myonuclear dynamics with age and exercise: shaping up for a good time.
Hippo pathway inhibition promotes metabolic adaptability and antioxidant response in myoblasts.
Autophagy Meets Aging: An Overview.

Int J Mol Sci. 2023 Feb 02. pii: 2903. [Epub ahead of print]24(3):

Insights into Cell-Specific Functions of Microtubules in Skeletal Muscle Development and Homeostasis.

Lathan Lucas, Thomas A Cooper.

  The contractile cells of skeletal muscles, called myofibers, are elongated multinucleated syncytia formed and maintained by the fusion of proliferative myoblasts. Human myofibers can be hundreds of microns in diameter and millimeters in length. Myofibers are non-mitotic, obviating the need for microtubules in cell division. However, microtubules have been adapted to the unique needs of these cells and are critical for myofiber development and function. Microtubules in mature myofibers are highly dynamic, and studies in several experimental systems have demonstrated the requirements for microtubules in the unique features of muscle biology including myoblast fusion, peripheral localization of nuclei, assembly of the sarcomere, transport and signaling. Microtubule-binding proteins have also been adapted to the needs of the skeletal muscle including the expression of skeletal muscle-specific protein isoforms generated by alternative splicing. Here, we will outline the different roles microtubules play in skeletal muscle cells, describe how microtubule abnormalities can lead to muscle disease and discuss the broader implications for microtubule function.

Keywords:  cell-specific; microtubules; muscle development; muscle homeostasis; myofiber; skeletal muscle

DOI:  https://doi.org/10.3390/ijms24032903
Cells. 2023 Jan 18. pii: 362. [Epub ahead of print]12(3):

Efficient Muscle Regeneration by Human PSC-Derived CD82+ ERBB3+ NGFR+ Skeletal Myogenic Progenitors.

Ning Xie, Sabrina N Chu, Cassandra B Schultz, Sunny S K Chan.

  Differentiation of pluripotent stem cells (PSCs) is a promising approach to obtaining large quantities of skeletal myogenic progenitors for disease modeling and cell-based therapy. However, generating skeletal myogenic cells with high regenerative potential is still challenging. We recently reported that skeletal myogenic progenitors generated from mouse PSC-derived teratomas possess robust regenerative potency. We have also found that teratomas derived from human PSCs contain a skeletal myogenic population. Here, we showed that these human PSC-derived skeletal myogenic progenitors had exceptional engraftability. A combination of cell surface markers, CD82, ERBB3, and NGFR enabled efficient purification of skeletal myogenic progenitors. These cells expressed PAX7 and were able to differentiate into MHC+ multinucleated myotubes. We further discovered that these cells are expandable in vitro. Upon transplantation, the expanded cells formed new dystrophin+ fibers that reconstituted almost ¾ of the total muscle volume, and repopulated the muscle stem cell pool. Our study, therefore, demonstrates the possibility of producing large quantities of engraftable skeletal myogenic cells from human PSCs.

Keywords:  cell therapy; muscle stem cells; muscular dystrophy; myogenic differentiation; pluripotent stem cells; transplantation

DOI:  https://doi.org/10.3390/cells12030362
Int J Mol Sci. 2023 Jan 26. pii: 2415. [Epub ahead of print]24(3):

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

Paul Dowling, Stephen Gargan, Dieter Swandulla, Kay Ohlendieck.

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

Keywords:  actin; aging; atrophy; frailty; myosin; sarcomere; sarcopenia; tropomyosin; troponin

DOI:  https://doi.org/10.3390/ijms24032415
Front Pharmacol. 2023 ;14 1112123

Stimulation of soluble guanylate cyclase by vericiguat reduces skeletal muscle atrophy of mice following chemotherapy.

Bo-Ang Hu, Yu-Lin Li, Hai-Tao Han, Bin Lu, Xu Jia, Lu Han, Wei-Xuan Ma, Ping Zhu, Zhi-Hao Wang, Wei Zhang, Ming Zhong, Lei Zhang.

  Background: The chemotherapeutic doxorubicin (DOX) promotes severe skeletal muscle atrophy, which induces skeletal muscle weakness and fatigue. Soluble guanylate cyclase (sGC) contributes to a variety of pathophysiological processes, but whether it is involved in DOX-induced skeletal muscle atrophy is unclear. The present study aimed to stimulate sGC by vericiguat, a new oral sGC stimulator, to test its role in this process. Methods: Mice were randomly divided into four groups: control group, vericiguat group, DOX group, and DOX + vericiguat group. Exercise capacity was evaluated before the mice were sacrificed. Skeletal muscle atrophy was assessed by histopathological and molecular biological methods. Protein synthesis and degradation were monitored in mice and C2C12 cells. Results: In this study, a significant decrease in exercise capacity and cross-sectional area (CSA) of skeletal muscle fibers was found in mice following DOX treatment. Furthermore, DOX decreased sGC activity in mice and C2C12 cells, and a positive correlation was found between sGC activity and CSA of skeletal muscle fibers in skeletal muscle. DOX treatment also impaired protein synthesis, shown by puromycin detection, and activated ubiquitin-proteasome pathway. Following sGC stimulation, the CSA of muscle fibers was elevated, and exercise capacity was enhanced. Stimulation of sGC also increased protein synthesis and decreased ubiquitin-proteasome pathway. In terms of the underlying mechanisms, AKT/mTOR and FoxO1 pathways were impaired following DOX treatment, and stimulation of sGC restored the blunted pathways. Conclusion: These results unravel sGC stimulation can improve skeletal muscle atrophy and increase the exercise capacity of mice in response to DOX treatment by enhancing protein synthesis and inhibiting protein degradation. Stimulation of sGC may be a potential treatment of DOX-induced skeletal muscle dysfunction.

Keywords:  doxorubicin; protein degradation; protein synthesis; skeletal muscle atrophy; soluble guanylate cyclase; vericiguat

DOI:  https://doi.org/10.3389/fphar.2023.1112123
Cell Prolif. 2023 Feb 08. e13416

mt-Ty 5´tiRNA regulates skeletal muscle cell proliferation and differentiation.

Jun Cao, Xin Wang, Vivek Advani, Yao Wei Lu, Andrea P Malizia, Gurinder Bir Singh, Zhan-Peng Huang, Jianming Liu, Chunbo Wang, Edilamar M Oliveira, John D Mably, Kaifu Chen, Da-Zhi Wang.

In this study, we sought to determine the role of tRNA-derived fragments in the regulation of gene expression during skeletal muscle cell proliferation and differentiation. We employed cell culture to examine the function of mt-Ty 5' tiRNAs. Northern blotting, RT-PCR as well as RNA-Seq, were performed to determine the effects of mt-Ty 5' tiRNA loss and gain on gene expression. Standard and transmission electron microscopy (TEM) were used to characterize cell and sub-cellular structures. mt-Ty 5'tiRNAs were found to be enriched in mouse skeletal muscle, showing increased levels in later developmental stages. Gapmer-mediated inhibition of tiRNAs in skeletal muscle C2C12 myoblasts resulted in decreased cell proliferation and myogenic differentiation; consistent with this observation, RNA-Seq, transcriptome analyses, and RT-PCR revealed that skeletal muscle cell differentiation and cell proliferation pathways were also downregulated. Conversely, overexpression of mt-Ty 5'tiRNAs in C2C12 cells led to a reversal of these transcriptional trends. These data reveal that mt-Ty 5'tiRNAs are enriched in skeletal muscle and play an important role in myoblast proliferation and differentiation. Our study also highlights the potential for the development of tiRNAs as novel therapeutic targets for muscle-related diseases.

DOI: https://doi.org/10.1111/cpr.13416
Cells. 2023 Feb 03. pii: 502. [Epub ahead of print]12(3):

Introduction to the Special Issue "Skeletal Muscle Atrophy: Mechanisms at a Cellular Level".

Emanuela Zuccaro, Caterina Marchioretti, Marco Pirazzini, Maria Pennuto.

  Skeletal muscle is the most abundant tissue in the body and requires high levels of energy to function properly. Skeletal muscle allows voluntary movement and body posture, which require different types of fiber, innervation, energy, and metabolism. Here, we summarize the contribution received at the time of publication of this Introductory Issue for the Special Issue dedicated to "Skeletal Muscle Atrophy: Mechanisms at a Cellular Level". The Special Issue is divided into three sections. The first is dedicated to skeletal muscle pathophysiology, the second to disease mechanisms, and the third to therapeutic development.

Keywords:  atrogenes; cancer cachexia; muscle atrophy; muscle degeneration; muscle proteostasis and disuse; myopathies; neuromuscular disorder; neuromuscular paralysis; sarcopenia

DOI:  https://doi.org/10.3390/cells12030502
J Cachexia Sarcopenia Muscle. 2023 Feb 09.

Molecular mechanisms of post-burn muscle wasting and the therapeutic potential of physical exercise.

Dorien Dombrecht, Ulrike Van Daele, Birgit Van Asbroeck, David Schieffelers, Pieter-Jan Guns, Nick Gebruers, Jill Meirte, Eric van Breda.

  After a severe burn injury, a systemic stress response activates metabolic and inflammatory derangements that, among other, leads to muscle mass loss (muscle wasting). These negative effects on skeletal muscle continue for several months or years and are aggravated by short-term and long-term disuse. The dynamic balance between muscle protein synthesis and muscle protein breakdown (proteolysis) is regulated by complex signalling pathways that leads to an overall negative protein balance in skeletal muscle after a burn injury. Research concerning these molecular mechanisms is still scarce and inconclusive, understanding of which, if any, molecular mechanisms contribute to muscle wasting is of fundamental importance in designing of therapeutic interventions for burn patients as well. This review not only summarizes our present knowledge of the molecular mechanisms that underpin muscle protein balance but also summarizes the effects of exercise on muscle wasting post-burn as promising strategy to counteract the detrimental effects on skeletal muscle. Future research focusing on the pathways causing post-burn muscle wasting and the different effects of exercise on them is needed to confirm this hypothesis and to lay the foundation of therapeutic strategies.

Keywords:  Burns; Cachexia; Exercise; Muscle wasting; Signalling pathways

DOI:  https://doi.org/10.1002/jcsm.13188
PNAS Nexus. 2022 Jul;1(3): pgac086

Signatures of muscle disuse in spaceflight and bed rest revealed by single muscle fiber proteomics.

Marta Murgia, Stefano Ciciliot, Nagarjuna Nagaraj, Carlo Reggiani, Stefano Schiaffino, Martino V Franchi, Rado Pišot, Boštjan Šimunič, Luana Toniolo, Bert Blaauw, Marco Sandri, Gianni Biolo, Martin Flück, Marco V Narici, Matthias Mann.

  Astronauts experience dramatic loss of muscle mass, decreased strength, and insulin resistance, despite performing daily intense physical exercise that would lead to muscle growth on Earth. Partially mimicking spaceflight, prolonged bed rest causes muscle atrophy, loss of force, and glucose intolerance. To unravel the underlying mechanisms, we employed highly sensitive single fiber proteomics to detail the molecular remodeling caused by unloading and inactivity during bed rest and changes of the muscle proteome of astronauts before and after a mission on the International Space Station. Muscle focal adhesions, involved in fiber-matrix interaction and insulin receptor stabilization, are prominently downregulated in both bed rest and spaceflight and restored upon reloading. Pathways of antioxidant response increased strongly in slow but not in fast muscle fibers. Unloading alone upregulated markers of neuromuscular damage and the pathway controlling EIF5A hypusination. These proteomic signatures of mechanical unloading in muscle fiber subtypes contribute to disentangle the effect of microgravity from the pleiotropic challenges of spaceflight.

Keywords:  astronauts; bed rest; proteomics; single fibers; skeletal muscle

DOI:  https://doi.org/10.1093/pnasnexus/pgac086
Int J Mol Sci. 2023 Jan 23. pii: 2229. [Epub ahead of print]24(3):

Ion Channels of the Sarcolemma and Intracellular Organelles in Duchenne Muscular Dystrophy: A Role in the Dysregulation of Ion Homeostasis and a Possible Target for Therapy.

Mikhail V Dubinin, Konstantin N Belosludtsev.

  Duchenne muscular dystrophy (DMD) is caused by the absence of the dystrophin protein and a properly functioning dystrophin-associated protein complex (DAPC) in muscle cells. DAPC components act as molecular scaffolds coordinating the assembly of various signaling molecules including ion channels. DMD shows a significant change in the functioning of the ion channels of the sarcolemma and intracellular organelles and, above all, the sarcoplasmic reticulum and mitochondria regulating ion homeostasis, which is necessary for the correct excitation and relaxation of muscles. This review is devoted to the analysis of current data on changes in the structure, functioning, and regulation of the activity of ion channels in striated muscles in DMD and their contribution to the disruption of muscle function and the development of pathology. We note the prospects of therapy based on targeting the channels of the sarcolemma and organelles for the correction and alleviation of pathology, and the problems that arise in the interpretation of data obtained on model dystrophin-deficient objects.

Keywords:  Duchenne muscular dystrophy; cardiomyocytes; dystrophin; ion channels; mdx; mitochondria; sarcolemma; sarcoplasmic reticulum; skeletal muscles

DOI:  https://doi.org/10.3390/ijms24032229
BMC Biol. 2023 Feb 08. 21(1): 27

Cold exposure alters lipid metabolism of skeletal muscle through HIF-1α-induced mitophagy.

Wentao Chen, Ziye Xu, Wenjing You, Yanbing Zhou, Liyi Wang, Yuqin Huang, Tizhong Shan.

  BACKGROUND: In addition to its contractile properties and role in movement, skeletal muscle plays an important function in regulating whole-body glucose and lipid metabolism. A central component of such regulation is mitochondria, whose quality and function are essential in maintaining proper metabolic homeostasis, with defects in processes such as autophagy and mitophagy involved in mitochondria quality control impairing skeletal muscle mass and function, and potentially leading to a number of associated diseases. Cold exposure has been reported to markedly induce metabolic remodeling and enhance insulin sensitivity in the whole body by regulating mitochondrial biogenesis. However, changes in lipid metabolism and lipidomic profiles in skeletal muscle in response to cold exposure are unclear. Here, we generated lipidomic or transcriptome profiles of mouse skeletal muscle following cold induction, to dissect the molecular mechanisms regulating lipid metabolism upon acute cold treatment.RESULTS: Our results indicated that short-term cold exposure (3 days) can lead to a significant increase in intramuscular fat deposition. Lipidomic analyses revealed that a cold challenge altered the overall lipid composition by increasing the content of triglyceride (TG), lysophosphatidylcholine (LPC), and lysophosphatidylethanolamine (LPE), while decreasing sphingomyelin (SM), validating lipid remodeling during the cold environment. In addition, RNA-seq and qPCR analysis showed that cold exposure promoted the expression of genes related to lipolysis and fatty acid biosynthesis. These marked changes in metabolic effects were associated with mitophagy and muscle signaling pathways, which were accompanied by increased TG deposition and impaired fatty acid oxidation. Mechanistically, HIF-1α signaling was highly activated in response to the cold challenge, which may contribute to intramuscular fat deposition and enhanced mitophagy in a cold environment.
CONCLUSIONS: Overall, our data revealed the adaptive changes of skeletal muscle associated with lipidomic and transcriptomic profiles upon cold exposure. We described the significant alterations in the composition of specific lipid species and expression of genes involved in glucose and fatty acid metabolism. Cold-mediated mitophagy may play a critical role in modulating lipid metabolism in skeletal muscle, which is precisely regulated by HIF-1α signaling.

Keywords:  Cold exposure; Lipid remodeling; Lipidomic; Mitophagy; Skeletal muscle; Transcriptome

DOI:  https://doi.org/10.1186/s12915-023-01514-4
J Biol Chem. 2023 Feb 03. pii: S0021-9258(23)00110-2. [Epub ahead of print] 102978

Cardiolipin metabolism regulates expression of muscle transcription factor MyoD1 and muscle development.

Linh Vo, Michael W Schmidtke, Nevton T Da Rosa-Junior, Mindong Ren, Michael Schlame, Miriam L Greenberg.

The mitochondrial phospholipid cardiolipin (CL) is critical for numerous essential biological processes, including mitochondrial dynamics and energy metabolism. Mutations in the CL remodeling enzyme TAFAZZIN cause Barth syndrome (BTHS), a life-threatening genetic disorder that results in severe physiological defects, including cardiomyopathy, skeletal myopathy, and neutropenia. To study the molecular mechanisms whereby CL deficiency leads to skeletal myopathy, we carried out transcriptomic analysis of the TAFAZZIN-knockout (TAZ-KO) mouse myoblast C2C12 cell line. Our data indicated that cardiac and muscle development pathways are highly decreased in TAZ-KO cells, consistent with a previous report of defective myogenesis in this cell line. Interestingly, the muscle transcription factor myoblast determination protein 1 (MyoD1) is significantly repressed in TAZ-KO cells and TAZ-KO mouse hearts. Exogenous expression of MyoD1 rescued the myogenesis defects previously observed in TAZ-KO cells. Our data suggest that MyoD1 repression is caused by up-regulation of the MyoD1 negative regulator, homeobox protein Mohawk (MKX), and decreased Wnt signaling. Our findings reveal, for the first time, that CL metabolism regulates muscle differentiation through MyoD1 and identify the mechanism whereby MyoD1 is repressed in CL-deficient cells.

DOI: https://doi.org/10.1016/j.jbc.2023.102978
Front Endocrinol (Lausanne). 2022 ;13 1083311

Muscle-specific deletion of Arid5b causes metabolic changes in skeletal muscle that affect adipose tissue and liver.

Jennifer Murray, Ali Ehsani, Liza Najjar, Guoxiang Zhang, Keiichi Itakura.

  Emerging evidence suggests that AT-Rich Interaction Domain 5b (Arid5b) may play a role in energy metabolism in various tissues. To study the metabolic function of Arid5b in skeletal muscle, we generated skeletal muscle-specific Arid5b knockout (Arid5b MKO) mice. We found that Arid5b MKO skeletal muscles preferentially utilized fatty acids for energy generation with a corresponding increase in FABP4 expression. Interestingly, in Arid5b MKO mice, the adipose tissue weight decreased significantly. One possible mechanism for the decrease in adipose tissue weight could be the increase in phospho-HSL and HSL expression in white adipose tissue. While glucose uptake increased in an insulin-independent manner in Arid5b MKO skeletal muscle, glucose oxidation was reduced in conjunction with downregulation of the mitochondrial pyruvate carrier (MPC). We found that glucose was diverted into the pentose phosphate pathway as well as converted into lactate through glycolysis for export to the bloodstream, fueling the Cori cycle. Our data show that muscle-specific deletion of Arid5b leads to changes in fuel utilization in skeletal muscle that influences metabolism in other tissues. These results suggest that Arid5b regulates systemic metabolism by modulating fuel selection.

Keywords:  Arid5b; fatty acids; glucose; metabolism; skeletal muscle

DOI:  https://doi.org/10.3389/fendo.2022.1083311
Am J Physiol Cell Physiol. 2023 Feb 06.

Myosin post-translational modifications and function in the presence of myopathy-linked truncating MYH2 mutations.

Alexander Sonne, Lorenzo Peverelli, Aurelio Hernandez-Lain, Cristina Dominguez, Jesper L Andersen, Margherita Milone, Alan H Beggs, Julien Ochala.

  Congenital myopathies are a vast group of genetic muscle diseases. Among the causes are mutations in the MYH2 gene resulting in truncated type IIa myosin heavy chains (MyHCs). The precise cellular and molecular mechanisms by which these mutations induce skeletal muscle symptoms remain obscure. Hence, in the present study, we aimed to explore whether such genetic defects would alter the presence as well as the post-translational modifications of MyHCs and the functionality of myosin molecules. For this, we dissected muscle fibres from four myopathic patients with MYH2 truncating mutations and from five human healthy controls. We then assessed MyHCs presence/post-translational modifications using LC/MS; relaxed myosin conformation and concomitant ATP consumption with a loaded Mant-ATP chase set-up; and myosin activation with an unloaded in vitro motility assay. Interestingly, the type IIa MyHC with one additional acetylated lysine (Lys35-Ac) was present in the patients. This was accompanied by a higher ATP demand of myosin heads in the disordered-relaxed conformation as well as by faster actomyosin kinetics. Overall, our findings indicate that MYH2 truncating mutations impact myosin presence/functionality in human adult mature myofibres by disrupting the ATPase activity and actomyosin complex. These are likely important molecular pathological disturbances leading to the myopathic phenotype in patients.

Keywords:  congenital myopathy; myosin; skeletal muscle

DOI:  https://doi.org/10.1152/ajpcell.00002.2023
Cells. 2023 Jan 18. pii: 361. [Epub ahead of print]12(3):

Cellular and Subcellular Characteristics of Neuromuscular Junctions in Muscles with Disparate Duty Cycles and Myofiber Profiles.

Michael R Deschenes, Mia K Mifsud, Leah G Patek, Rachel E Flannery.

  The neuromuscular system accounts for a large portion (~40%) of whole body mass while enabling body movement, including physical work and exercise. At the core of this system is the neuromuscular junction (NMJ) which is the vital synapse transducing electrical impulses from the motor neurons to their post-synaptic myofibers. Recent findings suggest that subcellular features (active zones) of the NMJ are distinctly sensitive to changes in activity relative to cellular features (nerve terminal branches, vesicles, receptors) of the NMJ. In the present investigation, muscles with different recruitment patterns, functions, and myofiber type profiles (soleus, plantaris, extensor digitorum longus [EDL]) were studied to quantify both cellular and subcellular NMJ characteristics along with myofiber type profiles. Results indicated that, in general, dimensions of subcellular components of NMJs mirrored cellular NMJ features when examining inter-muscle NMJ architecture. Typically, it was noted that the NMJs of the soleus, with its most pronounced recruitment pattern, were larger (p < 0.05) than NMJs of less recruited muscles. Moreover, it was revealed that myofiber size did not dictate NMJ size as soleus muscles displayed the smallest fibers (p < 0.05) while the plantaris muscles exhibited the largest fibers. In total, these data show that activity determines the size of NMJs and that generally, size dimensions of cellular and subcellular components of the NMJ are matched, and that the size of NMJs and their underlying myofibers are uncoupled.

Keywords:  NMJ; acetylcholine; endplate; myofiber; synapse

DOI:  https://doi.org/10.3390/cells12030361
J Cachexia Sarcopenia Muscle. 2023 Feb 11.

C-terminal agrin fragment as a biomarker of muscle wasting and weakness: a narrative review.

Elena Monti, Fabio Sarto, Roberta Sartori, Gianpietro Zanchettin, Stefan Löfler, Helmut Kern, Marco Vincenzo Narici, Sandra Zampieri.

  Ageing is accompanied by an inexorable loss of muscle mass and functionality and represents a major risk factor for numerous diseases such as cancer, diabetes and cardiovascular and pulmonary diseases. This progressive loss of muscle mass and function may also result in the insurgence of a clinical syndrome termed sarcopenia, exacerbated by inactivity and disease. Sarcopenia and muscle weakness yield the risk of falls and injuries, heavily impacting on health and social costs. Thus, screening, monitoring and prevention of conditions inducing muscle wasting and weakness are essential to improve life quality in the ageing modern society. To this aim, the reliability of easily accessible and non-invasive blood-derived biomarkers is being evaluated. C-terminal agrin fragment (CAF) has been widely investigated as a neuromuscular junction (NMJ)-related biomarker of muscle dysfunction. This narrative review summarizes and critically discusses, for the first time, the studies measuring CAF concentration in young and older, healthy and diseased individuals, cross-sectionally and in response to inactivity and physical exercise, providing possible explanations behind the discrepancies observed in the literature. To identify the studies investigating CAF in the above-mentioned conditions, all the publications found in PubMed, written in English and measuring this biomarker in blood from 2013 (when CAF was firstly measured in human serum) to 2022 were included in this review. CAF increases with age and in sarcopenic individuals when compared with age-matched, non-sarcopenic peers. In addition, CAF was found to be higher than controls in other muscle wasting conditions, such as diabetes, COPD, chronic heart failure and stroke, and in pancreatic and colorectal cancer cachectic patients. As agrin is also expressed in kidney glomeruli, chronic kidney disease and transplantation were shown to have a profound impact on CAF independently from muscle wasting. CAF concentration raises following inactivity and seems to be lowered or maintained by exercise training. Finally, CAF was reported to be cross-sectionally correlated to appendicular lean mass, handgrip and gait speed; whether longitudinal changes in CAF are associated with those in muscle mass or performance following physical exercise is still controversial. CAF seems a reliable marker to assess muscle wasting in ageing and disease, also correlating with measurements of appendicular lean mass and muscle function. Future research should aim at enlarging sample size and accurately reporting the medical history of each patient, to normalize for any condition, including chronic kidney disease, that may influence the circulating concentration of this biomarker.

Keywords:  Ageing; C-terminal agrin fragment; Cancer cachexia; Muscle wasting; Muscle weakness; Sarcopenia

DOI:  https://doi.org/10.1002/jcsm.13189
Nat Commun. 2023 Feb 06. 14(1): 602

Defective excitation-contraction coupling and mitochondrial respiration precede mitochondrial Ca2+ accumulation in spinobulbar muscular atrophy skeletal muscle.

Caterina Marchioretti, Giulia Zanetti, Marco Pirazzini, Gaia Gherardi, Leonardo Nogara, Roberta Andreotti, Paolo Martini, Lorenzo Marcucci, Marta Canato, Samir R Nath, Emanuela Zuccaro, Mathilde Chivet, Cristina Mammucari, Marco Pacifici, Anna Raffaello, Rosario Rizzuto, Andrea Mattarei, Maria A Desbats, Leonardo Salviati, Aram Megighian, Gianni Sorarù, Elena Pegoraro, Elisa Belluzzi, Assunta Pozzuoli, Carlo Biz, Pietro Ruggieri, Chiara Romualdi, Andrew P Lieberman, Gopal J Babu, Marco Sandri, Bert Blaauw, Manuela Basso, Maria Pennuto.

Polyglutamine expansion in the androgen receptor (AR) causes spinobulbar muscular atrophy (SBMA). Skeletal muscle is a primary site of toxicity; however, the current understanding of the early pathological processes that occur and how they unfold during disease progression remains limited. Using transgenic and knock-in mice and patient-derived muscle biopsies, we show that SBMA mice in the presymptomatic stage develop a respiratory defect matching defective expression of genes involved in excitation-contraction coupling (ECC), altered contraction dynamics, and increased fatigue. These processes are followed by stimulus-dependent accumulation of calcium into mitochondria and structural disorganization of the muscle triads. Deregulation of expression of ECC genes is concomitant with sexual maturity and androgen raise in the serum. Consistent with the androgen-dependent nature of these alterations, surgical castration and AR silencing alleviate the early and late pathological processes. These observations show that ECC deregulation and defective mitochondrial respiration are early but reversible events followed by altered muscle force, calcium dyshomeostasis, and dismantling of triad structure.

DOI: https://doi.org/10.1038/s41467-023-36185-w
Int J Mol Sci. 2023 Feb 01. pii: 2772. [Epub ahead of print]24(3):

Disintegration of the NuRD Complex in Primary Human Muscle Stem Cells in Critical Illness Myopathy.

Joanna Schneider, Devakumar Sundaravinayagam, Alexander Blume, Andreas Marg, Stefanie Grunwald, Eric Metzler, Helena Escobar, Stefanie Müthel, Haicui Wang, Tobias Wollersheim, Steffen Weber-Carstens, Altuna Akalin, Michela Di Virgilio, Baris Tursun, Simone Spuler.

  Critical illness myopathy (CIM) is an acquired, devastating, multifactorial muscle-wasting disease with incomplete recovery. The impact on hospital costs and permanent loss of quality of life is enormous. Incomplete recovery might imply that the function of muscle stem cells (MuSC) is impaired. We tested whether epigenetic alterations could be in part responsible. We characterized human muscle stem cells (MuSC) isolated from early CIM and analyzed epigenetic alterations (CIM n = 15, controls n = 21) by RNA-Seq, immunofluorescence, analysis of DNA repair, and ATAC-Seq. CIM-MuSC were transplanted into immunodeficient NOG mice to assess their regenerative potential. CIM-MuSC exhibited significant growth deficits, reduced ability to differentiate into myotubes, and impaired DNA repair. The chromatin structure was damaged, as characterized by alterations in mRNA of histone 1, depletion or dislocation of core proteins of nucleosome remodeling and deacetylase complex, and loosening of multiple nucleosome-spanning sites. Functionally, CIM-MuSC had a defect in building new muscle fibers. Further, MuSC obtained from the electrically stimulated muscle of CIM patients was very similar to control MuSC, indicating the impact of muscle contraction in the onset of CIM. CIM not only affects working skeletal muscle but has a lasting and severe epigenetic impact on MuSC.

Keywords:  critical illness; epigenetic; histone 1; muscle stem cell

DOI:  https://doi.org/10.3390/ijms24032772
Acta Neurobiol Exp (Wars). 2022 ;82(4): 501-510

Neuromuscular junction disorders: Experimental models and pathophysiological mechanisms.

Li Yan, Zhao-Xu Yin, Xue-Li Chang, Rui Wang, Xiu-Min Zhang, Jun-Hong Guo.

Located between skeletal muscle fibers and motoneurons, the neuromuscular junction is a chemical synapse essential for the transmission of information from nervous system to skeletal muscle. There are many diseases related to neuromuscular junction dysfunction, including myasthenia gravis, Lambert‑Eaton myasthenic syndrome, congenital myasthenic syndromes, amyotrophic lateral sclerosis, and spinal muscular atrophy. The pathophysiological mechanisms of these diseases have been investigated using many animal models. Among them, mouse models are the most commonly used and have provided the majority of current data. Moreover, advances in human induced pluripotent stem cell technology has resulted in new opportunities to study neuromuscular junction disorders from both patients and healthy individuals. Currently, patient‑specific induced pluripotent stem cells derived from motor neurons have begun to be studied. These studies will help us achieve a more comprehensive understanding of diseases related to neuromuscular junction disorders. We will describe the research models of neuromuscular junction disorders and provide an overview of recent key findings.

DOI: https://doi.org/10.55782/ane-2022-048
Int J Mol Sci. 2023 Feb 03. pii: 2973. [Epub ahead of print]24(3):

Prevalence and Mechanisms of Skeletal Muscle Atrophy in Metabolic Conditions.

Lauren Jun, Megan Robinson, Thangiah Geetha, Tom L Broderick, Jeganathan Ramesh Babu.

  Skeletal muscle atrophy is prevalent in a myriad of pathological conditions, such as diabetes, denervation, long-term immobility, malnutrition, sarcopenia, obesity, Alzheimer's disease, and cachexia. This is a critically important topic that has significance in the health of the current society, particularly older adults. The most damaging effect of muscle atrophy is the decreased quality of life from functional disability, increased risk of fractures, decreased basal metabolic rate, and reduced bone mineral density. Most skeletal muscle in humans contains slow oxidative, fast oxidative, and fast glycolytic muscle fiber types. Depending on the pathological condition, either oxidative or glycolytic muscle type may be affected to a greater extent. This review article discusses the prevalence of skeletal muscle atrophy and several mechanisms, with an emphasis on high-fat, high-sugar diet patterns, obesity, and diabetes, but including other conditions such as sarcopenia, Alzheimer's disease, cancer cachexia, and heart failure.

Keywords:  Alzheimer’s disease; diabetes; muscle atrophy; obesity; sarcopenia; skeletal muscle

DOI:  https://doi.org/10.3390/ijms24032973
Physiol Rep. 2023 Feb;11(3): e15596

The transcript interactome of skeletal muscle RNA binding protein motif 3 (RBM3).

Zachary R Hettinger, Amy L Confides, Peter W Vanderklish, Esther E Dupont-Versteegden.

  Post-transcriptional regulation of gene expression represents a critical regulatory step in the production of a functional proteome. Elevated expression of post-transcriptional regulator RNA binding motif protein 3 (RBM3), an RNA binding protein in the cold-shock family, is positively correlated with skeletal muscle growth in adult mice. However, mechanisms through which RBM3 exerts its effects are largely unknown. The purpose of this study was to perform RNA immunoprecipitation followed by RNA sequencing (RIP-seq) and apply a network science approach to understand biological processes (BPs) most associated with RBM3-bound mRNAs. In addition, through nucleotide-sequence-scanning of enriched transcripts, we predicted the motif for skeletal muscle RBM3 binding. Gene set enrichment analysis followed by enrichment mapping of RBM3-bound transcripts (fold change >3; p.adj <0.01) revealed significant enrichment of BPs associated with "Contractile apparatus," "Translation initiation," and "Proteosome complex." Clusters were driven largely by enrichment of Myh1 (FC: 4.43), Eif4b (FC: 5.03), and Trim63 (FC: 5.84), respectively. Motif scanning of enriched sequences revealed a discrete 14 nucleotide-wide motif found most prominently at the junction between the protein coding region's termination sequence and the start of the 3' untranslated region (UTR; E-Value: 1.1 e-015 ). Proof of concept investigation of motif location along enriched transcripts Myh1 and Myl4 revealed 3' UTR binding, suggesting RBM3 involvement in transcript half-life regulation. Together, these results demonstrate the potential influence of RBM3 in reshaping the skeletal muscle proteome through post-transcriptional regulation of mRNAs crucial to muscle adaptations.

Keywords:  RIP-seq; RNA binding proteins; cold shock protein; mRNA half-life

DOI:  https://doi.org/10.14814/phy2.15596
Elife. 2023 Feb 06. pii: e81843. [Epub ahead of print]12

Molecular characterization of the intact mouse muscle spindle using a multi-omics approach.

Bavat Bornstein, Lia Heinemann-Yerushalmi, Sharon Krief, Ruth Adler, Bareket Dassa, Dena Leshkowitz, Minchul Kim, Guy Bewick, Robert W Banks, Elazar Zelzer.

  The proprioceptive system is essential for the control of coordinated movement, posture and skeletal integrity. The sense of proprioception is produced in the brain using peripheral sensory input from receptors such as the muscle spindle, which detects changes in the length of skeletal muscles. Despite its importance, the molecular composition of the muscle spindle is largely unknown. In this study, we generated comprehensive transcriptomic and proteomic datasets of the entire muscle spindle isolated from the murine deep masseter muscle. We then associated differentially expressed genes with the various tissues composing the spindle using bioinformatic analysis. Immunostaining verified these predictions, thus establishing new markers for the different spindle tissues. Utilizing these markers, we identified the differentiation stages the spindle capsule cells undergo during development. Together, these findings provide comprehensive molecular characterization of the intact spindle as well as new tools to study its development and function in health and disease.

Keywords:  developmental biology; mouse

DOI:  https://doi.org/10.7554/eLife.81843
Nat Commun. 2023 Feb 10. 14(1): 744

Intrafusal-fiber LRP4 for muscle spindle formation and maintenance in adult and aged animals.

Rangjuan Cao, Peng Chen, Hongsheng Wang, Hongyang Jing, Hongsheng Zhang, Guanglin Xing, Bin Luo, Jinxiu Pan, Zheng Yu, Wen-Cheng Xiong, Lin Mei.

Proprioception is sensed by muscle spindles for precise locomotion and body posture. Unlike the neuromuscular junction (NMJ) for muscle contraction which has been well studied, mechanisms of spindle formation are not well understood. Here we show that sensory nerve terminals are disrupted by the mutation of Lrp4, a gene required for NMJ formation; inducible knockout of Lrp4 in adult mice impairs sensory synapses and movement coordination, suggesting that LRP4 is required for spindle formation and maintenance. LRP4 is critical to the expression of Egr3 during development; in adult mice, it interacts in trans with APP and APLP2 on sensory terminals. Finally, spindle sensory endings and function are impaired in aged mice, deficits that could be diminished by LRP4 expression. These observations uncovered LRP4 as an unexpected regulator of muscle spindle formation and maintenance in adult and aged animals and shed light on potential pathological mechanisms of abnormal muscle proprioception.

DOI: https://doi.org/10.1038/s41467-023-36454-8
J Proteome Res. 2023 Feb 10.

Phosphoproteomics Profiling Defines a Target Landscape of the Basophilic Protein Kinases AKT, S6K, and RSK in Skeletal Myotubes.

Anna L Fricke, Wignand W D Mühlhäuser, Lena Reimann, Johannes P Zimmermann, Christa Reichenbach, Bettina Knapp, Christian D Peikert, Alexander M Heberle, Erik Faessler, Sascha Schäuble, Udo Hahn, Kathrin Thedieck, Gerald Radziwill, Bettina Warscheid.

  Phosphorylation-dependent signal transduction plays an important role in regulating the functions and fate of skeletal muscle cells. Central players in the phospho-signaling network are the protein kinases AKT, S6K, and RSK as part of the PI3K-AKT-mTOR-S6K and RAF-MEK-ERK-RSK pathways. However, despite their functional importance, knowledge about their specific targets is incomplete because these kinases share the same basophilic substrate motif RxRxxp[ST]. To address this, we performed a multifaceted quantitative phosphoproteomics study of skeletal myotubes following kinase inhibition. Our data corroborate a cross talk between AKT and RAF, a negative feedback loop of RSK on ERK, and a putative connection between RSK and PI3K signaling. Altogether, we report a kinase target landscape containing 49 so far unknown target sites. AKT, S6K, and RSK phosphorylate numerous proteins involved in muscle development, integrity, and functions, and signaling converges on factors that are central for the skeletal muscle cytoskeleton. Whereas AKT controls insulin signaling and impinges on GTPase signaling, nuclear signaling is characteristic for RSK. Our data further support a role of RSK in glucose metabolism. Shared targets have functions in RNA maturation, stability, and translation, which suggests that these basophilic kinases establish an intricate signaling network to orchestrate and regulate processes involved in translation.

Keywords:  RXRXXS/T motif; cross talk; kinase inhibitors; kinase−substrate enrichment analysis (KSEA); kinase−substrate relationship; label-free; mass spectrometry; parallel reaction monitoring (PRM); protein phosphorylation; quantification; signal transduction; skeletal muscle cells; stable isotope labeling by amino acids in cell culture; text mining

DOI:  https://doi.org/10.1021/acs.jproteome.2c00505
Elife. 2023 Feb 06. pii: e80500. [Epub ahead of print]12

A transcriptome atlas of leg muscles from healthy human volunteers reveals molecular and cellular signatures associated with muscle location.

Tooba Abbassi-Daloii, Salma El Abdellaoui, Lenard M Voortman, Thom T J Veeger, Davy Cats, Hailiang Mei, Duncan E Meuffels, Ewoud van Arkel, Peter A C 't Hoen, Hermien E Kan, Vered Raz.

  Skeletal muscles support the stability and mobility of the skeleton but differ in biomechanical properties and physiological functions. The intrinsic factors that regulate muscle-specific characteristics are poorly understood. To study these, we constructed a large atlas of RNA-seq profiles from six leg muscles and two locations from one muscle, using biopsies from 20 healthy young males. We identified differential expression patterns and cellular composition across the seven tissues using three bioinformatics approaches confirmed by large-scale newly developed quantitative immune-histology procedures. With all three procedures, the muscle samples clustered into three groups congruent with their anatomical location. Concomitant with genes marking oxidative metabolism, genes marking fast- or slow-twitch myofibers differed between the three groups. The groups of muscles with higher expression of slow-twitch genes were enriched in endothelial cells and showed higher capillary content. In addition, expression profiles of Homeobox (HOX) transcription factors differed between the three groups and were confirmed by spatial RNA hybridization. We created an open-source graphical interface to explore and visualize the leg muscle atlas (https://tabbassidaloii.shinyapps.io/muscleAtlasShinyApp/). Our study reveals the molecular specialization of human leg muscles, and provides a novel resource to study muscle-specific molecular features, which could be linked with (patho)physiological processes.

Keywords:  chromosomes; gene expression; human; neuroscience

DOI:  https://doi.org/10.7554/eLife.80500
J Gerontol A Biol Sci Med Sci. 2023 Feb 08. pii: glad045. [Epub ahead of print]

Evaluation of Associations of Growth Differentiation Factor-11, Growth Differentiation Factor-8 and their Binding Proteins Follistatin and Follistatin-like protein-3 with Measures of Skeletal Muscle Mass, Muscle Strength and Physical Function in Older Adults.

Peggy M Cawthon, Sheena Patel, Anne B Newman, Shalender Bhasin, Liming Peng, Russell Tracy, Jorge R Kizer, Se-Jin Lee, Luigi Ferrucci, Peter Ganz, Nathan K LeBrasseur, Steve Cummings.

  BACKGROUND: Based on studies from animal models, growth differentiation factor-11 (GDF-11) may have rejuvenating effects in humans. GDF-11 has high sequence homology with GDF-8 (also known as myostatin); follistatin, and follistatin like 3 protein (FSTL3) are inhibitory proteins of both GDF-8 and GDF-11.METHODS: Using highly specific LC-MS/MS assays for GDF-11 and GDF-8 and immunoassays for follistatin and FSTL3, we quantified the association of these factors with muscle size, strength and physical performance in two prospective cohort studies of community-dwelling older adults (Health ABC and CHS).
RESULTS: GDF-8 levels were positively associated with thigh muscle cross sectional area and density in Health ABC (data not available in CHS). GDF-8 levels were positively associated with lean mass (a surrogate of muscle mass) in Health ABC but not CHS, and grip strength in CHS but not Health ABC. FSTL3 (and perhaps follistatin) were negatively associated with lean mass and had variable associations with other variables. In contrast, GDF-11 was not significantly associated with strength or performance.
CONCLUSIONS: GDF-8 and its binding proteins, follistatin and FSTL3, may constitute a counter-regulatory system (chalones) to restrain age-related loss of muscle mass and strength.

Keywords:  geriatric assessment; physical function; sarcopenia

DOI:  https://doi.org/10.1093/gerona/glad045
J Appl Physiol (1985). 2023 Feb 09.

Muscle disuse as hindlimb unloading in early postnatal mice negatively impacts grip strength in adult mice: A pilot study.

Paul T Reidy, Austin D Smith, Benjamin E Jevnikar, Abbas K Doctor, Ryan W Williams, Anthony A Kachulkin, Jackie M Monning, Dennis K Fix, Jonathan J Petrocelli, Ziad S Mahmassani, Alec I McKenzie, Naomi M M P de Hart, Micah J Drummond.

  Physical inactivity has many detrimental effects on health, yet the impact of physical inactivity in early life on muscle health in adulthood remains unknown. Early postnatal malnutrition has prolonged effects into adulthood and we propose that early postnatal physical inactivity would have similar negative effects. To test this hypothesis, we exposed postnatal mice (~P28, C57BL/6J) to 14 days of physical inactivity (shortly after weaning, from ~28 to 42 days of age) in the form of muscle disuse with hindlimb unloading (HU). After this early-life physical inactivity, they were allowed to normally ambulate until 5 months of age (adulthood) when they underwent 2 weeks of HU with and without 7-day recovery. They were then tested for physical function (grip strength) and muscles were extracted and weighed. Immunofluorescence was carried out on these muscle cross-sections for analysis of myofiber cross-sectional area (fCSA), macrophage density (CD68+ cells) and extracellular matrix (ECM) area. Muscle weights and fCSA and myofiber diameter were used to quantify changes in muscle and fiber size. Compared to age-matched controls, no notable effects of early life physical inactivity (HU) on skeletal muscle and myofiber size were observed. However, a significant reduction in adult grip strength was observed in those exposed to HU early in life. This was associated with reduced muscle macrophages and increased ECM area. Exposure to a short period of early life disuse has negative enduring effects into adulthood impacting grip strength, muscle macrophages and muscle composition as low muscle quality.

Keywords:  Fibrosis; inflammation; macrophages; strength

DOI:  https://doi.org/10.1152/japplphysiol.00681.2022
PLoS One. 2023 ;18(2): e0281718

Metformin regulates myoblast differentiation through an AMPK-dependent mechanism.

Eleonora Maniscalco, Giuliana Abbadessa, Magalì Giordano, Loredana Grasso, Paolo Borrione, Silvia Racca.

This study aims to investigate how metformin (Met) affects muscle tissue by evaluating the drug effects on proliferating, differentiating, and differentiated C2C12 cells. Moreover, we also investigated the role of 5'-adenosine monophosphate-activated protein kinase (AMPK) in the mechanism of action of Met. C2C12 myoblasts were cultured in growth medium with or without Met (250μM, 1mM and 10mM) for different times. Cell proliferation was evaluated by MTT assay, while cell toxicity was assessed by Trypan Blue exclusion test and Lactate Dehydrogenase release. Fluorescence Activated Cell Sorting analysis was performed to study cell cycle. Differentiating myoblasts were incubated in differentiation medium (DM) with or without 10mM Met. For experiments on myotubes, C2C12 were induced to differentiate in DM, and then treated with Met at scalar concentrations and for different times. Western blotting was performed to evaluate the expression of proteins involved in myoblast differentiation, muscle function and metabolism. In differentiating C2C12, Met inhibited cell differentiation, arrested cell cycle progression in G2/M phase and reduced the expression of cyclin-dependent kinase inhibitor 1. These effects were accompanied by activation of AMPK and modulation of the myogenic regulatory factors. Comparable results were obtained in myotubes. The use of Compound C, a specific inhibitor of AMPK, counteracted the above-mentioned Met effects. We reported that Met inhibits C2C12 differentiation probably by blocking cell-cycle progression and preventing cells permanent exit from cell-cycle. Moreover, our study provides solid evidence that most of the effects of Met on myoblasts and myotubes are mediated by AMPK.

DOI: https://doi.org/10.1371/journal.pone.0281718
Exp Biol Med (Maywood). 2023 Feb 05. 15353702221142619

Sex differences in muscle SIRT1 and SIRT3 and exercise + weight loss effects on muscle sirtuins.

Alice S Ryan, Guoyan Li.

  The sirtuins, SIRT1 and SIRT3, are involved in the control of cellular processes to maintain metabolic homeostasis. The purpose of this study was to determine the effects of a 6-month aerobic training + weight loss program and hyperinsulinemia on SIRT1 and SIRT3 expression in skeletal muscle and to compare their expression between men and women. Thirty-five adult men (n = 18) and postmenopausal women (n = 17), (X ± SEM, age: 61 ± 1 years, BMI: 31.3 ± 0.7 kg/m2) completed 6 months 3×/week of aerobic exercise and 1×/week dietary instruction to induce weight loss (EX + WL). Participants had a VO2max test, vastus lateralis muscle biopsies at baseline and 2 h into a hyperinsulinemic-euglycemic clamp, a total body dual-energy X-ray absorptiometry scan, and abdominal computed tomography scan. Skeletal muscle SIRT1, SIRT3, and PGC1-α mRNA expression were quantified by qRT-PCR. Skeletal muscle SIRT1 and SIRT3 mRNA expression are higher in women than men (P < 0.005). Body weight, body fat, and abdominal obesity decreased and VO2max and glucose utilization (M) increased after EX + WL (P < 0.001). Basal SIRT1 decreased following EX + WL (P < 0.05). This change in basal SIRT1 was not related to changes in VO2max, M or fat mass, nor was it different by gender. Insulin stimulation increased SIRT1 expression (P < 0.001) and PGC1-α expression (P < 0.01) following EX + WL (insulin-basal post). Sex differences in the levels of these sirtuins did not affect changes with EX + WL. Skeletal muscle SIRT1 decreases after a long-term combined exercise and weight loss program in middle-aged and older adults.

Keywords:  Exercise; glucose; metabolism; nutrition; obesity; skeletal muscle

DOI:  https://doi.org/10.1177/15353702221142619
Int J Mol Sci. 2023 Feb 03. pii: 3039. [Epub ahead of print]24(3):

Modulation of the Circulating Extracellular Vesicles in Response to Different Exercise Regimens and Study of Their Inflammatory Effects.

Serena Maggio, Barbara Canonico, Paola Ceccaroli, Emanuela Polidori, Andrea Cioccoloni, Luca Giacomelli, Carlo Ferri Marini, Giosuè Annibalini, Marco Gervasi, Piero Benelli, Francesco Fabbri, Laura Del Coco, Francesco Paolo Fanizzi, Anna Maria Giudetti, Francesco Lucertini, Michele Guescini.

  Exercise-released extracellular vesicles (EVs) are emerging as a novel class of exerkines that promotes systemic beneficial effects. However, slight differences in the applied exercise protocols in terms of mode, intensity and duration, as well as the need for standardized protocols for EV isolation, make the comparison of the studies in the literature extremely difficult. This work aims to investigate the EV amount and EV-associated miRNAs released in circulation in response to different physical exercise regimens. Healthy individuals were subjected to different exercise protocols: acute aerobic exercise (AAE) and training (AT), acute maximal aerobic exercise (AMAE) and altitude aerobic training (AAT). We found a tendency for total EVs to increase in the sedentary condition compared to trained participants following AAE. Moreover, the cytofluorimetric analysis showed an increase in CD81+/SGCA+/CD45- EVs in response to AAE. Although a single bout of moderate/maximal exercise did not impact the total EV number, EV-miRNA levels were affected as a result. In detail, EV-associated miR-206, miR-133b and miR-146a were upregulated following AAE, and this trend appeared intensity-dependent. Finally, THP-1 macrophage treatment with exercise-derived EVs induced an increase of the mRNAs encoding for IL-1β, IL-6 and CD163 using baseline and immediately post-exercise EVs. Still, 1 h post-exercise EVs failed to stimulate a pro-inflammatory program. In conclusion, the reported data provide a better understanding of the release of circulating EVs and their role as mediators of the inflammatory processes associated with exercise.

Keywords:  aerobic exercise; aerobic training; exerkines; extracellular vesicles; miRNA expression; myokines

DOI:  https://doi.org/10.3390/ijms24033039
J Physiol. 2023 Feb 06.

Myonuclear dynamics with age and exercise: shaping up for a good time.

Cory M Dungan.



Keywords:  ageing; exercise; myonuclei; nuclear shape

DOI:  https://doi.org/10.1113/JP284303
Sci Rep. 2023 Feb 08. 13(1): 2232

Hippo pathway inhibition promotes metabolic adaptability and antioxidant response in myoblasts.

Qi Liu, Su Pan, Pengyang Li, Richard A F Dixon.

Metabolic plasticity in a hostile environment ensures cell survival. We investigated whether Hippo pathway inhibition contributed to cell adaptations under challenging conditions. We examined metabolic profiles and fuel substrate choices and preferences in C2C12 myoblasts after Hippo pathway inhibition via Salvador knockdown (SAV1 KD). SAV1 KD induced higher ATP production and a more energetic phenotype. Bioenergetic profiling showed enhanced key mitochondrial parameters including spare respiratory capacity. SAV1 KD cells showed markedly elevated glycolysis and glycolytic reserves; blocking other fuel-oxidation pathways enhanced mitochondrial flexibility of glucose oxidation. Under limited glucose, endogenous fatty acid oxidation increased to cope with bioenergetic stress. Gene expression patterns after SAV1 KD suggested transcriptional upregulation of key metabolic network regulators to promote energy production and free radical scavenging that may prevent impaired lipid and glucose metabolism. In SAV1 KD cells, sirtuin signaling was the top enriched canonical pathway linked with enhanced mitochondrial ATP production. Collectively, we demonstrated that Hippo pathway inhibition in SAV1 KD cells induces multiple metabolic properties, including enhancing mitochondrial spare respiratory capacity or glycolytic reserve to cope with stress and upregulating metabolic pathways supporting elevated ATP demand, bioenergetics, and glycolysis and counteracting oxidative stress. In response to metabolic challenges, SAV1 KD cells can increase fatty acid oxidation or glucose-coupled oxidative phosphorylation capacity to compensate for substrate limitations or alternative fuel oxidation pathway inhibition.

DOI: https://doi.org/10.1038/s41598-023-29372-8
Cells. 2023 Feb 02. pii: 489. [Epub ahead of print]12(3):

Autophagy Meets Aging: An Overview.

Anna Picca, Emanuele Marzetti, Christiaan Leeuwenburgh.

Aging is characterized by biological disarrangements that increase vulnerability to stressors, the development of chronic diseases (e [...].

DOI: https://doi.org/10.3390/cells12030489