bims-moremu 2024-12-22 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2024–12–22
29 papers selected by
Anna Vainshtein, Craft Science Inc.

The expanding roles of myonuclei in adult skeletal muscle health and function.
Wnt7a is required for regeneration of dystrophic skeletal muscle.
Myoblast-derived ADAMTS-like 2 promotes skeletal muscle regeneration after injury.
Cytokine expression and cytokine-mediated cell-cell communication during skeletal muscle regeneration revealed by integrative analysis of single-cell RNA sequencing data.
Transcriptomic and lipidomic profiling reveals distinct bioactive lipid signatures in slow and fast muscles and highlights the role of resolvin-D2 in fiber type determination during myogenesis.
Effects of contraction frequency during high-intensity training on fatigue resistance and aerobic adaptations in mouse skeletal muscle.
Acute treadmill exercise induces mitochondrial unfolded protein response in skeletal muscle of male rats.
Regulation of injury-induced skeletal myofiber regeneration by glucose transporter 4 (GLUT4).
The muscle stem cell case of Benjamin Button: rejuvenating muscle regenerative capacity through nutraceuticals.
FAPs orchestrate homeostasis of muscle physiology and pathophysiology.
MiR-495 reverses in the mechanical unloading, random rotating and aging induced muscle atrophy via targeting MyoD and inactivating the Myostatin/TGF-β/Smad3 axis.
Muscle PGC-1α Overexpression Drives Metabolite Secretion Boosting Subcutaneous Adipocyte Browning.
Visualizing sarcomere and cellular dynamics in skeletal muscle to improve cell therapies.
Mavacamten facilitates myosin head ON-to-OFF transitions and shortens thin filament length in relaxed skeletal muscle.
Impact of exercise and fasting on mitochondrial regulators in human muscle.
Sarcopenic obesity is attenuated by E-syt1 inhibition via improving skeletal muscle mitochondrial function.
Lonafarnib Protects Against Muscle Atrophy Induced by Dexamethasone.
The distinctive mechanical and structural signatures of residual force enhancement in myofibers.
Human iPSC-derived motor neuron innervation enhances the differentiation of muscle bundles engineered with benchtop fabrication techniques.
PPARβ/δ upregulates the insulin receptor β subunit in skeletal muscle by reducing lysosomal activity and EphB4 levels.
Adipose-derived exosomes ameliorate skeletal muscle atrophy via miR-146a-5p/IGF-1R signaling.
Identification of ZNF850 as a novel CTG repeat expansion-related gene in myotonic dystrophy type 1 patient-derived iPSCs.
Rethinking the physiological cross-sectional area of skeletal muscle reveals the mechanical advantage of pennation.
Functional dissection of metabolic trait-associated gene regulation in steady state and stimulated human skeletal muscle cells.
Fibre type differences in the organisation of mononuclear cells and myonuclei at the tips of human myofibres.
Mitochondrial respiration atlas reveals differential changes in mitochondrial function across sex and age.
MicroRNA biogenesis pathway alterations in aging.
The Cajal body marker protein coilin is SUMOylated and possesses SUMO E3 ligase-like activity.
Exercise as Mitochondrial Medicine: How Does the Exercise Prescription Affect Mitochondrial Adaptations to Training?

Biochem Soc Trans. 2024 Dec 19. 52(6): 1-14

The expanding roles of myonuclei in adult skeletal muscle health and function.

Agnieszka K Borowik, Kevin A Murach, Benjamin F Miller.

  Skeletal muscle cells (myofibers) require multiple nuclei to support a cytoplasmic volume that is larger than other mononuclear cell types. It is dogmatic that mammalian resident myonuclei rely on stem cells (specifically satellite cells) for adding new DNA to muscle fibers to facilitate cytoplasmic expansion that occurs during muscle growth. In this review, we discuss the relationship between cell size and supporting genetic material. We present evidence that myonuclei may undergo DNA synthesis as a strategy to increase genetic material in myofibers independent from satellite cells. We then describe the details of our experiments that demonstrated that mammalian myonuclei can replicate DNA in vivo. Finally, we present our findings in the context of expanding knowledge about myonuclear heterogeneity, myonuclear mobility and shape. We also address why myonuclear replication is potentially important and provide future directions for remaining unknowns. Myonuclear DNA replication, coupled with new discoveries about myonuclear transcription, morphology, and behavior in response to stress, may provide opportunities to leverage previously unappreciated skeletal muscle biological processes for therapeutic targets that support muscle mass, function, and plasticity.

Keywords:  adaptation; endoreplication; mobility; myonuclear domain; skeletal muscle; stable isotope

DOI:  https://doi.org/10.1042/BST20241637
Skelet Muscle. 2024 Dec 19. 14(1): 34

Wnt7a is required for regeneration of dystrophic skeletal muscle.

Uxia Gurriaran-Rodriguez, Kasun Kodippili, David Datzkiw, Ehsan Javandoost, Fan Xiao, Maria Teresa Rejas, Michael A Rudnicki.

  Intramuscular injection of Wnt7a has been shown to accelerate and augment skeletal muscle regeneration and to ameliorate dystrophic progression in mdx muscle, a model for Duchenne muscular dystrophy (DMD). Here, we assessed muscle regeneration and function in wild type (WT) and mdx mice where Wnt7a was deleted in muscle using a conditional Wnt7a floxed allele and a Myf5-Cre driver. We found that both WT and mdx mice lacking Wnt7a in muscle, exhibited marked deficiencies in muscle regeneration at 21 d following cardiotoxin (CTX) induced injury. Unlike WT, deletion of Wnt7a in mdx resulted in decreased force generation prior to CTX injury. However, both WT and mdx muscle lacking Wnt7a displayed decreased force generation following CTX injection. Notably the regeneration deficit in mdx mice was rescued by a single tail vein injection of extracellular vesicles containing Wnt7a (Wnt7a-EVs). Therefore, we conclude that the regenerative capacity of muscle in mdx mice is highly dependant on the upregulation of endogenous Wnt7a following injury, and that systemic delivery of Wnt7a-EVs represents a therapeutic strategy for treating DMD.

Keywords:  Duchenne muscular dystrophy; Regeneration, Wnt7a, Extracellular vesicles; Skeletal muscle

DOI:  https://doi.org/10.1186/s13395-024-00367-x
NPJ Regen Med. 2024 Dec 19. 9(1): 39

Myoblast-derived ADAMTS-like 2 promotes skeletal muscle regeneration after injury.

Nandaraj Taye, Levon Rodriguez, James C Iatridis, Woojin M Han, Dirk Hubmacher.

Skeletal muscle regeneration and functional recovery after minor injuries requires the activation of muscle-resident myogenic muscle stem cells (i.e. satellite cells) and their subsequent differentiation into myoblasts, myocytes, and ultimately myofibers. We recently identified secreted ADAMTS-like 2 (ADAMTSL2) as a pro-myogenic regulator of muscle development, where it promoted myoblast differentiation. Since myoblast differentiation is a key process in skeletal muscle regeneration, we here examined the role of ADAMTSL2 during muscle regeneration after BaCl2 injury. Specifically, we found that muscle regeneration was delayed after ablation of ADAMTSL2 in myogenic precursor cells and accelerated following injection of pro-myogenic ADAMTSL2 protein domains. Mechanistically, ADAMTSL2 regulated the number of committed myoblasts, which are the precursors for myocytes and regenerating myofibers. Collectively, our data support a role for myoblast-derived ADAMTSL2 as a positive regulator of muscle regeneration and provide a proof-of-concept for potential therapeutic applications.

DOI: https://doi.org/10.1038/s41536-024-00383-x
J Cell Commun Signal. 2024 Dec;18(4): e12055

Cytokine expression and cytokine-mediated cell-cell communication during skeletal muscle regeneration revealed by integrative analysis of single-cell RNA sequencing data.

Pallob Barai, Jie Chen.

  Skeletal muscles undergo self-repair upon injury, owing to the resident muscle stem cells and their extensive communication with the microenvironment of injured muscles. Cytokines play a critical role in orchestrating intercell communication to ensure successful regeneration. Immune cells as well as other types of cells in the injury site, including muscle stem cells, are known to secret cytokines. However, the extent to which various cell types express distinct cytokines and how the secreted cytokines are involved in intercell communication during regeneration are largely unknown. Here we integrated 15 publicly available single-cell RNA-sequencing (scRNA-seq) datasets of mouse skeletal muscles at early regeneration timepoints (0, 2, 5, and 7 days after injury). The resulting dataset was analyzed for the expression of 393 annotated mouse cytokines. We found widespread and dynamic cytokine expression by all cell types in the regenerating muscle. Interrogating the integrated dataset using CellChat revealed extensive, bidirectional cell-cell communications during regeneration. Our findings provide a comprehensive view of cytokine signaling in the regenerating muscle, which can guide future studies of ligand-receptor signaling and cell-cell interaction to achieve new mechanistic insights into the regulation of muscle regeneration.

Keywords:  cell–cell communication; cytokines; muscle stem cells; scRNA‐seq; skeletal muscle regeneration

DOI:  https://doi.org/10.1002/ccs3.12055
FASEB J. 2024 Dec 13. 38(24): e70250

Transcriptomic and lipidomic profiling reveals distinct bioactive lipid signatures in slow and fast muscles and highlights the role of resolvin-D2 in fiber type determination during myogenesis.

Lupann Rieger, Thomas Molina, Paul Fabre, Karine Greffard, Ornella Pellerito, Junio Dort, Jean-François Bilodeau, Nicolas A Dumont.

  Skeletal muscles are predominantly composed of long, multinucleated muscle fibers, classified according to their metabolic and contractile phenotype. The determination of fiber types is influenced by various factors (e.g., innervation, hormones, physical demand). Our laboratory and others showed that resolvins, lipid mediators derived from omega-3 fatty acids, promote muscle regeneration and function after an injury or in models of muscular dystrophies; however, the effect of resolvins on the determination of muscle phenotype remains unknown. Here, we investigated the impact of lipid mediators on muscle phenotype during myogenesis. Transcriptomics analysis of single-nuclei RNAseq data sets revealed that the enzymes responsible for bioactive lipids biosynthesis are differentially expressed in slow fibers versus fast fibers. Lipidomics analysis of slow-twitch muscle (soleus) versus fast-twitch muscle (tibialis anterior) showed that the levels of lipids derived from arachidonic acid are similar between muscle groups, but lipids derived from alpha-linolenic acid, linoleic acid, eicosapentaenoic acid, and docosahexaenoic acid are enriched in slow-twitch muscle. Screening for different lipids in vitro showed that resolvin-D2 enhances the formation of myotubes expressing the slow myosin heavy chain isoform. In vivo, the administration of resolvin-D2 enhances muscle strength, increases myofiber size, and affects fiber typing in injured muscles but not in uninjured muscles. Resolvin-D2 promoted the transition toward the dominant fiber types in regenerating muscle (i.e., type I in the slow-twitch soleus and type IIB in the fast-twitch tibialis anterior muscle), suggesting its participation in fiber typing in conjunction with other factors. Overall, these findings identified new roles of bioactive lipids in the regulation of fiber typing, which could have therapeutic applicability in muscle injuries or dystrophies.

Keywords:  bioactive lipids; fiber types; myogenesis; resolvin; satellite cells; skeletal muscle

DOI:  https://doi.org/10.1096/fj.202401747R
J Appl Physiol (1985). 2024 Dec 16.

Effects of contraction frequency during high-intensity training on fatigue resistance and aerobic adaptations in mouse skeletal muscle.

Azuma Naito, Tatsuya Sato, Iori Kimura, Nao Tokuda, Nao Yamauchi, Hiroyori Fusagawa, Takashi Yamada.

  In high-intensity and sprint interval training, the frequency of contractions is typically higher compared to moderate-intensity continuous training, but it remains unclear whether this contributes to the effective increase in fatigue resistance mechanisms. Here, we investigated the role of contraction frequency in high-intensity training on endurance adaptations of mouse skeletal muscle. Male C57BL/6 mice were divided into groups based on high (0.25 s contraction every 0.5 s) and low (0.25 s contraction every 4.5 s) contraction frequencies, with either 360 contractions per session (Hi360 and Lo360) or 30 contractions per session (Hi30 and Lo30). The plantar flexor muscles were stimulated using in vivo supramaximal electrical stimulation, where all muscle fibers were maximally activated, every other day for 5 weeks. In both the Hi360 and Lo360 groups, where force production declined to less than 40% of the initial value during the training session, muscle endurance, as well as mitochondrial content and respiratory capacity, were increased to a similar extent. In contrast, the rate of torque decline during the training session was more pronounced in the Hi30 group compared to the Lo30 group. In response, the Hi30 group, but not the Lo30 group, exhibited increased fatigue resistance and mitochondrial respiration, which was accompanied by increased PGC-1α expression and an activation of AMPK/Ulk1 pathway. These data suggest that the frequency of contractions is a critical factor in determining the efficient enhancement of mitochondrial respiratory capacity and muscle endurance through high-intensity training, presumably due to promotion of mitochondrial quality control.

Keywords:  contraction frequency; fatigue resistance; high-intensity interval training; mitochondria

DOI:  https://doi.org/10.1152/japplphysiol.00530.2024
Biochim Biophys Acta Bioenerg. 2024 Dec 13. pii: S0005-2728(24)00502-4. [Epub ahead of print]1866(2): 149532

Acute treadmill exercise induces mitochondrial unfolded protein response in skeletal muscle of male rats.

Ibrahim Turkel, Gokhan Burcin Kubat, Tugba Fatsa, Ozgu Acet, Berkay Ozerklig, Burak Yazgan, Gulcin Simsek, Keshav K Singh, Sukran Nazan Kosar.

  Mitochondria are often referred to as the energy centers of the cell and are recognized as key players in signal transduction, sensing, and responding to internal and external stimuli. Under stress conditions, the mitochondrial unfolded protein response (UPRmt), a conserved mitochondrial quality control mechanism, is activated to maintain mitochondrial and cellular homeostasis. As a physiological stimulus, exercise-induced mitochondrial perturbations trigger UPRmt, coordinating mitochondria-to-nucleus communication and initiating a transcriptional program to restore mitochondrial function. The aim of this study was to evaluate the UPRmt signaling response to acute exercise in skeletal muscle. Male rats were subjected to acute treadmill exercise at 25 m/min for 60 min on a 0 % grade. Plantaris muscles were collected from both sedentary and exercise groups at various times: immediately (0), and at 1, 3, 6, 12, and 24 h post-exercise. Reactive oxygen species (ROS) production was assessed using hydrogen peroxide assay and dihydroethidium staining. Additionally, the mRNA and protein expression of UPRmt markers were measured using ELISA and real-time PCR. Mitochondrial activity was assessed using succinate dehydrogenase (SDH) and cytochrome c oxidase (COX) staining. Our results demonstrated that acute exercise increased ROS production and upregulated UPRmt markers at both gene and protein levels. Moreover, skeletal muscle exhibited an increase in mitochondrial activity in response to exercise, as indicated by SDH and COX staining. These findings suggest that acute treadmill exercise is sufficient to induce ROS production, activate UPRmt signaling, and enhance mitochondrial activity in skeletal muscle, expanding our understanding of mitochondrial adaptations to exercise.

Keywords:  Exercise; Mitochondria; Mitochondrial proteostasis; Mitochondrial unfolded protein response; Skeletal muscle; UPR(mt)

DOI:  https://doi.org/10.1016/j.bbabio.2024.149532
Skelet Muscle. 2024 Dec 19. 14(1): 33

Regulation of injury-induced skeletal myofiber regeneration by glucose transporter 4 (GLUT4).

Tyler J Sermersheim, LeAnna J Phillips, Parker L Evans, Barbara B Kahn, Steven S Welc, Carol A Witczak.

   BACKGROUND: Insulin resistance and type 2 diabetes impair cellular regeneration in multiple tissues including skeletal muscle. The molecular basis for this impairment is largely unknown. Glucose uptake via glucose transporter GLUT4 is impaired in insulin resistance. In healthy muscle, acute injury stimulates glucose uptake. Whether decreased glucose uptake via GLUT4 impairs muscle regeneration is presently unknown. The goal of this study was to determine whether GLUT4 regulates muscle glucose uptake and/or regeneration following acute injury.
METHODS: Tibialis anterior and extensor digitorum longus muscles from wild-type, control, or muscle-specific GLUT4 knockout (mG4KO) mice were injected with the myotoxin barium chloride to induce muscle injury. After 3, 5, 7, 10, 14, or 21 days (in wild-type mice), or after 7 or 14 days (in control & mG4KO) mice, muscles were isolated to examine [3H]-2-deoxyglucose uptake, GLUT4 levels, extracellular fluid space, fibrosis, myofiber cross-sectional area, and myofiber centralized nuclei.
RESULTS: In wild-type mice, muscle glucose uptake was increased 3, 5, 7, and 10 days post-injury. There was a rapid decrease in GLUT4 protein levels that were restored to baseline at 5-7 days post-injury, followed by a super-compensation at 10-21 days. In mG4KO mice, there were no differences in muscle glucose uptake, extracellular fluid space, muscle fibrosis, myofiber cross-sectional areas, or percentage of centrally nucleated myofibers at 7 days post-injury. In contrast, at 14 days injured muscles from mG4KO mice exhibited decreased glucose uptake, muscle weight, myofiber cross sectional areas, and centrally nucleated myofibers, with no change in extracellular fluid space or fibrosis.
CONCLUSIONS: Collectively, these findings demonstrate that glucose uptake via GLUT4 regulates skeletal myofiber regeneration following acute injury.

Keywords:  Barium chloride; Diabetes mellitus type 2; Extracellular fluid; Fibrosis; Glucose; Glucose transporter type 4; Insulin resistance; Knockout; Mice; Muscle; Regeneration

DOI:  https://doi.org/10.1186/s13395-024-00366-y
J Clin Invest. 2024 Dec 16. pii: e185054. [Epub ahead of print]134(24):

The muscle stem cell case of Benjamin Button: rejuvenating muscle regenerative capacity through nutraceuticals.

Taylor Peach, Mattia Quattrocelli.

Aging negatively affects the capacity of muscle stem cells (MuSCs) to regenerate muscle. In this issue of the JCI, Ancel, Michaud, and colleagues used a high-content imaging screen to identify nicotinamide and pyridoxine as promoters of MuSC function. The combination of the two compounds promoted MuSC function in vivo in aged mice and in primary cells isolated from older individuals. Furthermore, the two compounds were lower in the circulation of older men, paralleling decreases in lean mass and gait speed. These results advance the translational perspective of rejuvenating MuSC function through nutraceuticals.

DOI: https://doi.org/10.1172/JCI185054
FASEB J. 2024 Dec 13. 38(24): e70234

FAPs orchestrate homeostasis of muscle physiology and pathophysiology.

Kai Yin, Chengmin Zhang, Zihan Deng, Xiaoyu Wei, Tingwen Xiang, Chuan Yang, Can Chen, Yueqi Chen, Fei Luo.

  As a common clinical manifestation, muscle weakness is prevalent in people with mobility disorders. Further studies of muscle weakness have found that patients with muscle weakness present with persistent muscle inflammation, loss of muscle fibers, fat infiltration, and interstitial fibrosis. Therefore, we propose the concept of muscle microenvironment homeostasis, which explains the abnormal pathological changes in muscles through the imbalance of muscle microenvironment homeostasis. And we identified an interstitial progenitor cell FAP during the transition from normal muscle microenvironment homeostasis to muscle microenvironment imbalance caused by muscle damage diseases. As a kind of pluripotent stem cell, FAPs do not participate in myogenic differentiation, but can differentiate into fibroblasts, adipocytes, osteoblasts, and chondrocytes. As a kind of mesenchymal progenitor cell, it is involved in the generation of extracellular matrix, regulate muscle regeneration, and maintain neuromuscular junction. However, the muscle microenvironment is disrupted by the causative factors, and the abnormal activities of FAPs eventually contribute to the complex pathological changes in muscles. Targeting the mechanisms of these muscle pathological changes, we have identified appropriate signaling targets for FAPs to improve and even treat muscle damage diseases. In this review, we propose the construction of muscle microenvironmental homeostasis and find the key cells that cause pathological changes in muscle after homeostasis is broken. By studying the mechanism of abnormal differentiation and apoptosis of FAPs, we found a strategy to inhibit the abnormal pathological changes in muscle damage diseases and improve muscle regeneration.

Keywords:  fibro/adipogenic progenitors; muscle weakness and fatigue; muscular dystrophy; myopathy muscle disorder

DOI:  https://doi.org/10.1096/fj.202400381R
Arch Biochem Biophys. 2024 Dec 17. pii: S0003-9861(24)00395-3. [Epub ahead of print] 110273

MiR-495 reverses in the mechanical unloading, random rotating and aging induced muscle atrophy via targeting MyoD and inactivating the Myostatin/TGF-β/Smad3 axis.

Chenyan Zhang, Yile Tian, Xinli Liu, Xuezhou Yang, Shanfeng Jiang, Ge Zhang, Changqing Yang, Wenjing Liu, Weihong Guo, Wenzhe Zhao, Dachuan Yin.

  Mechanical unloading can lead to homeostasis imbalance and severe muscle disease, in which muscle atrophy was one of the disused diseases. However, there were limited therapeutic targets for such diseases. In this study, miR-495 was found dramatically reduced in atrophic skeletal muscle induced by mechanical unloading models both in vitro and in vivo, including the random positioning model (RPM), tail-suspension (TS) model, and aged mice model. Enforced miR-495 expression by its mimic could enormously facilitate the differentiation and regeneration of both mouse myoblast C2C12 cells and muscle satellite cells. Furthermore, MyoD was proved as the directly interacted gene of miR-495, and their interaction was crucial for myotube formation. Enforced miR-495 expression could intensively strengthen the muscle mass, in situ muscular electrophysiological indexes, including peak tetanic tension (Po) and peak twitch tension (Pt), and the cross-sectional areas (CSA) of muscle fibers via targeting MyoD and inactivating the Myostatin/TGF-β/Smad3 signaling pathway, indicating that miR-495 can be proposed as an effective target for muscle atrophy treatment induced by in the mechanical unloading, random rotating and aging.

Keywords:  Aging-associated muscle atrophy; Mechanical unloading; MiR-495; MyoD; Myostatin/TGF-β/Smad3 axis

DOI:  https://doi.org/10.1016/j.abb.2024.110273
J Cell Physiol. 2024 Dec 15.

Muscle PGC-1α Overexpression Drives Metabolite Secretion Boosting Subcutaneous Adipocyte Browning.

Caterina Miro, Ciro Menale, Lucia Acampora, Annarita Nappi, Serena Sagliocchi, Federica Restolfer, Sepehr Torabinejad, Mariano Stornaiuolo, Monica Dentice, Annunziata Gaetana Cicatiello.

  Muscle and adipose tissue (AT) are in mutual interaction through the integration of endocrine and biochemical signals, thus regulating whole-body function and physiology. Besides a traditional view of endocrine relationships that imply the release of cytokines and growth factors, it is becoming increasingly clear that a metabolic network involving metabolites as signal molecules also exists between the two tissues. By elevating the number and functionality of mitochondria, a key role in muscle metabolism is played by the master regulator of mitochondrial biogenesis peroxisome-proliferator-activated receptor-γ coactivator-1α (PGC-1α), that induces a fiber type shift from glycolytic to oxidative myofibers. As a consequence, the upregulation of muscle respiratory rate might affect metabolite production and consumption. However, the underlying mechanisms have not yet been fully elucidated. Here, we used a muscle-specific PGC-1α overexpressing mouse model (MCK-PGC-1α) to analyze the metabolite secretion profile of serum and culture medium recovered from MCK-PGC-1α muscle fibers by NMR. We revealed modified levels of different metabolites that might be ascribed to the metabolic activation of the skeletal muscle fibers. Notably, the dysregulated levels of these metabolites affected adipocyte differentiation, as well as the browning process in vitro and in vivo. Interestingly such effect was exacerbated in the subcutaneous WAT, while only barely present in the visceral WAT. Our data confirm a prominent role of PGC-1α as a trigger of mitochondrial function in skeletal muscle and propose a novel function of this master regulator gene in modulating the metabolite production in turn affecting the activation of WAT and its conversion toward the browning.

Keywords:  PGC‐1α; adipocytes; browning; metabolites; skeletal muscle

DOI:  https://doi.org/10.1002/jcp.31480
Elife. 2024 Dec 17. pii: e95597. [Epub ahead of print]13

Visualizing sarcomere and cellular dynamics in skeletal muscle to improve cell therapies.

Judith Hüttemeister, Franziska Rudolph, Michael H Radke, Claudia Fink, Dhana Friedrich, Stephan Preibisch, Martin Falcke, Eva Wagner, Stephan E Lehnart, Michael Gotthardt.

  The giant striated muscle protein titin integrates into the developing sarcomere to form a stable myofilament system that is extended as myocytes fuse. The logistics underlying myofilament assembly and disassembly have started to emerge with the possibility to follow labeled sarcomere components. Here, we generated the mCherry knock-in at titin's Z-disk to study skeletal muscle development and remodeling. We find titin's integration into the sarcomere tightly regulated and its unexpected mobility facilitating a homogeneous distribution of titin after cell fusion - an integral part of syncytium formation and maturation of skeletal muscle. In adult mCherry-titin mice, treatment of muscle injury by implantation of titin-eGFP myoblasts reveals how myocytes integrate, fuse, and contribute to the continuous myofilament system across cell boundaries. Unlike in immature primary cells, titin proteins are retained at the proximal nucleus and do not diffuse across the whole syncytium with implications for future cell-based therapies of skeletal muscle disease.

Keywords:  cell biology; live imaging; medicine; mouse; muscle; proteostasis; regeneration; sarcomere; titin

DOI:  https://doi.org/10.7554/eLife.95597
bioRxiv. 2024 Dec 03. pii: 2024.11.29.626031. [Epub ahead of print]

Mavacamten facilitates myosin head ON-to-OFF transitions and shortens thin filament length in relaxed skeletal muscle.

Michel N Kuehn, Nichlas M Engels, Devin L Nissen, Johanna K Freundt, Weikang Ma, Thomas C Irving, Wolfgang A Linke, Anthony L Hessel.

  The first-in-its-class cardiac drug mavacamten reduces the proportion of so-called ON-state myosin heads in relaxed sarcomeres, altering contraction performance. However, mavacamten is not completely specific to cardiac myosin and can also affect skeletal muscle myosin, an important consideration since mavacamten is administered orally and so will also be present in skeletal tissue. Here, we studied the effect of mavacamten on skeletal muscle structure using small-angle X-ray diffraction. Mavacamten treatment reduced the proportion of ON myosin heads but did not eliminate the molecular underpinnings of length-dependent activation, demonstrating similar effects to those observed in cardiac muscle. These findings provide valuable insights for the potential use of mavacamten as a tool to study muscle contraction across striated muscle.

Keywords:  Major classification – Biological Sciences; Minor classification – Physiology; X-ray diffraction; mouse; myosin inhibitors; ultrastructure

DOI:  https://doi.org/10.1101/2024.11.29.626031
Transl Exerc Biomed. 2024 Sep;1(3-4): 183-194

Impact of exercise and fasting on mitochondrial regulators in human muscle.

Eveline S Menezes, Hashim Islam, Benjamin B Arhen, Craig A Simpson, Chris McGlory, Brendon J Gurd.

   Objectives: To investigate the impact of acute energetic stress (acute HIIE and fasting) on ERRγ, PPARβ, NR1D1, NR4A1, and TFEB in human skeletal muscle.
Methods: The current study performed secondary analyses using muscle biopsy samples from two previously published studies: study 1) leg muscle biopsies from nine men and eight women were obtained pre and 3 h following acute high-intensity interval cycling exercise (HIIE); study 2) leg muscle biopsies were obtained from nine men pre-, during, and post-an 8 h fast with or without 2 h of arm ergometer exercise. RT-PCR was performed on samples from each study to determine the mRNA expression of ERRγ, PPARβ, NR1D1, NR4A1, and TFEB. Additionally, we retrieved data from meta-analyzed human muscle gene expression using the publicly available database MetaMex.
Results: PGC-1α (p<0.01, d=1.98) and NR4A1 (p<0.01, d=1.36) mRNA expression significantly increased while TFEB (p≤0.05, d=0.70) decreased following HIIE. Significant decreases in NR4A1 and NR1D1 mRNA expression were observed following an 8 h fast. Our MetaMex analyses revealed significant increases (p<0.05) in PGC-1α and NR4A1 expression following aerobic and resistance exercise, and in PPARβ expression following resistance exercise.
Conclusions: Our data indicate that acute HIIE stimulates increases in NR4A1 and PGC-1α and decreases in TFEB mRNA expression in human skeletal muscle. Additionally, a short term (8 h) fast reduced the mRNA expression of the transcriptional regulators NR4A1 and NR1D1 - potentially as a mechanism of decreasing mitochondrial biogenesis to reduce energy expenditure during a period of restricted energy availability.

Keywords:  aerobic exercise; caloric restriction; food deprivation; muscle remodeling; transcriptional regulators

DOI:  https://doi.org/10.1515/teb-2024-0014
Redox Biol. 2024 Dec 12. pii: S2213-2317(24)00445-2. [Epub ahead of print]79 103467

Sarcopenic obesity is attenuated by E-syt1 inhibition via improving skeletal muscle mitochondrial function.

Chao Song, Wu Zheng, Guoming Liu, Yiyang Xu, Zhibo Deng, Yu Xiu, Rongsheng Zhang, Linhai Yang, Yifei Zhang, Guoyu Yu, Yibin Su, Jun Luo, Bingwei He, Jie Xu, Hanhao Dai.

  In aging and metabolic disease, sarcopenic obesity (SO) correlates with intramuscular adipose tissue (IMAT). Using bioinformatics analysis, we found a potential target protein Extended Synaptotagmin 1 (E-syt1) in SO. To investigate the regulatory role of E-syt1 in muscle metabolism, we performed in vivo and in vitro experiments through E-syt1 loss- and gain-of-function on muscle physiology. When E-syt1 is overexpressed in vitro, myoblast proliferation, differentiation, mitochondrial respiration, biogenesis, and mitochondrial dynamics are impaired, which were alleviated by the silence of E-syt1. Furthermore, overexpression of E-syt1 inhibited mitophagic flux. Mechanistically, E-syt1 overexpression leads to mitochondrial calcium overload and mitochondrial ROS burst, inhibits the fusion of mitophagosomes with lysosomes, and impedes the acidification of lysosomes. Animal experiments demonstrated the inhibition of E-syt1 increased the capacity of endurance exercise, muscle mass, mitochondrial function, and oxidative capacity of the muscle fibers in OVX mice. These findings establish E-syt1 as a novel contributor to the pathogenesis of skeletal muscle metabolic disorders in SO. Consequently, targeting E-syt1-induced dysfunction may serve as a viable strategy for attenuating SO.

Keywords:  E-syt1; Mitochondria; Mitophagy; Myogenesis; Sarcopenic obesity

DOI:  https://doi.org/10.1016/j.redox.2024.103467
J Cachexia Sarcopenia Muscle. 2024 Dec 17.

Lonafarnib Protects Against Muscle Atrophy Induced by Dexamethasone.

Sanghoon Bae, Van-Hieu Mai, Seyoung Mun, Dalong Dong, Kyudong Han, Sunghyouk Park, Jung Keun Hyun.

   BACKGROUND: Muscle atrophy, including glucocorticoid-induced muscle wasting from treatments such as dexamethasone (DEX), results in significant reductions in muscle mass, strength and function. This study investigates the potential of lonafarnib, a farnesyltransferase inhibitor, to counteract DEX-induced muscle atrophy by targeting key signalling pathways.
METHODS: We utilized in vitro models with C2C12 myotubes treated with DEX and in vivo models with Caenorhabditis elegans and DEX-treated Sprague-Dawley rats. Myotube morphology was assessed by measuring area, fusion index and diameter. Muscle function was evaluated by grip strength and compound muscle action potential (CMAP) in the gastrocnemius (GC) and tibialis anterior (TA) muscles. Molecular mechanisms were explored through RNA sequencing and Western blotting to assess changes in mitochondrial function and muscle signalling pathways.
RESULTS: Lonafarnib (2 μM) significantly improved myotube area (1.49 ± 0.14 × 105 μm2 vs. 1.03 ± 0.49 × 105 μm2 in DEX, p < 0.05), fusion index (18.73 ± 1.23% vs. 13.3 ± 1.56% in DEX, p < 0.05) and myotube diameter (31.89 ± 0.89 μm vs. 21.56 ± 1.01 μm in DEX, p < 0.05) in C2C12 myotubes. In C. elegans, lonafarnib (100 μM) increased the pharyngeal pumping rate from 212 ± 7.21 contractions/min in controls to 308 ± 17.09 contractions/min at day 4 (p < 0.05), indicating enhanced neuromuscular function. In DEX-induced atrophic rats, lonafarnib improved maximal grip strength (DEX: 13.91 ± 0.78 N vs. 1 μM lonafarnib: 16.18 ± 0.84 N and 5 μM lonafarnib: 16.71 ± 0.83 N, p < 0.05), increased muscle weight in GC, and enhanced CMAP amplitudes in both GC and TA muscles. Western blot analysis showed that lonafarnib treatment upregulated UCP3 and ANGPTL4 and increased phosphorylation of mTOR and S6 ribosomal protein (p < 0.05), indicating enhanced mitochondrial function and protein synthesis. Knockdown models further demonstrated that lonafarnib could partially rescue muscle atrophy phenotypes, indicating its action through multiple molecular pathways.
CONCLUSIONS: Lonafarnib mitigates dexamethasone-induced muscle atrophy by enhancing mitochondrial function and activating anabolic pathways. These findings support further investigation of lonafarnib as a therapeutic agent for muscle atrophy in clinical settings.

Keywords:  ANGPLT4; UCP3; dexamethasone; drug repositioning; lonafarnib; muscle atrophy

DOI:  https://doi.org/10.1002/jcsm.13665
Proc Natl Acad Sci U S A. 2024 Dec 24. 121(52): e2413883121

The distinctive mechanical and structural signatures of residual force enhancement in myofibers.

Anthony L Hessel, Michel N Kuehn, Bradley M Palmer, Devin Nissen, Dhruv Mishra, Venus Joumaa, Johanna K Freundt, Weikang Ma, Kiisa C Nishikawa, Thomas C Irving, Wolfgang A Linke.

  In muscle, titin proteins connect myofilaments together and are thought to be critical for contraction, especially during residual force enhancement (RFE) when steady-state force is elevated after an active stretch. We investigated titin's function during contraction using small-angle X-ray diffraction to track structural changes before and after 50% titin cleavage and in the RFE-deficient, mdm titin mutant. We report that the RFE state is structurally distinct from pure isometric contractions, with increased thick filament strain and decreased lattice spacing, most likely caused by elevated titin-based forces. Furthermore, no RFE structural state was detected in mdm muscle. We posit that decreased lattice spacing, increased thick filament stiffness, and increased non-cross-bridge forces are the major contributors to RFE. We conclude that titin directly contributes to RFE.

Keywords:  X-ray diffraction; elasticity; force transmission; mouse; ultrastructure

DOI:  https://doi.org/10.1073/pnas.2413883121
bioRxiv. 2024 Dec 05. pii: 2024.12.02.626391. [Epub ahead of print]

Human iPSC-derived motor neuron innervation enhances the differentiation of muscle bundles engineered with benchtop fabrication techniques.

Jeffrey W Santoso, Stephanie K Do, Riya Verma, Alexander V Do, Eric Hendricks, Justin K Ichida, Megan L McCain.

  Engineered skeletal muscle tissues are critical tools for disease modeling, drug screening, and regenerative medicine, but are limited by insufficient maturation. Because innervation is a critical regulator of skeletal muscle development and regeneration in vivo, motor neurons are hypothesized to improve the maturity of engineered skeletal muscle tissues. Although motor neurons have been added to pre-engineered muscle constructs, the impact of motor neurons added prior to the onset of muscle differentiation has not been evaluated. In this study, benchtop fabrication equipment was used to facilely fabricate chambers for engineering 3-dimensional (3-D) skeletal muscles bundles and measuring their contractile performance. Primary chick myoblasts were embedded in an extracellular matrix hydrogel solution and differentiated into engineered muscle bundles, with or without the addition of human induced pluripotent stem cell (hiPSC)-derived motor neurons. Muscle bundles differentiated with motor neurons had neurites distributed throughout their volume and a higher myogenic index compared to muscle bundles without motor neurons. Innervated muscle bundles also generated significantly higher twitch and tetanus forces in response to electrical field stimulation after one and two weeks of differentiation compared to non-innervated muscle bundles cultured with or without neurotrophic factors. Non-innervated muscle bundles also experienced a decline in rise and fall times as the culture progressed, whereas innervated muscle bundles and non-innervated muscle bundles with neurotrophic factors maintained more consistent rise and fall times. Innervated muscle bundles also expressed the highest levels of the genes for slow myosin light chain 3 (MYL3) and myoglobin (MB), which are associated with slow twitch fibers. These data suggest that motor neuron innervation enhances the structural and functional development of engineered skeletal muscle constructs and maintains them in a more oxidative phenotype.

Keywords:  3-D printing; PDMS; fast twitch; laser cutter; organ on chip; sarcomere; slow twitch

DOI:  https://doi.org/10.1101/2024.12.02.626391
Cell Commun Signal. 2024 Dec 18. 22(1): 595

PPARβ/δ upregulates the insulin receptor β subunit in skeletal muscle by reducing lysosomal activity and EphB4 levels.

Jue-Rui Wang, Javier Jurado-Aguilar, Emma Barroso, Ricardo Rodríguez-Calvo, Antoni Camins, Walter Wahli, Xavier Palomer, Manuel Vázquez-Carrera.

   BACKGROUND: The increased degradation of the insulin receptor β subunit (InsRβ) in lysosomes contributes to the development of insulin resistance and type 2 diabetes mellitus. Endoplasmic reticulum (ER) stress contributes to insulin resistance through several mechanisms, including the reduction of InsRβ levels. Here, we examined how peroxisome proliferator-activated receptor (PPAR)β/δ regulates InsRβ levels in mouse skeletal muscle and C2C12 myotubes exposed to the ER stressor tunicamycin.
METHODS: Wild-type (WT) and Ppard-/- mice, WT mice treated with vehicle or the PPARβ/δ agonist GW501516, and C2C12 myotubes treated with the ER stressor tunicamycin or different activators or inhibitors were used.
RESULTS: Ppard-/- mice displayed reduced InsRβ protein levels in their skeletal muscle compared to wild-type (WT) mice, while the PPARβ/δ agonist GW501516 increased its levels in WT mice. Co-incubation of tunicamycin-exposed C2C12 myotubes with GW501516 partially reversed the decrease in InsRβ protein levels, attenuating both ER stress and the increase in lysosomal activity. In addition, the protein levels of the tyrosine kinase ephrin receptor B4 (EphB4), which binds to the InsRβ and facilitates its endocytosis and degradation in lysosomes, were increased in the skeletal muscle of Ppard-/- mice, with GW501516 reducing its levels in the skeletal muscle of WT mice.
CONCLUSIONS: Overall, these findings reveal that PPARβ/δ activation increases InsRβ levels by alleviating ER stress and lysosomal degradation.

Keywords:  ER stress; EphB4; GW5101516; InsRβ; PPARβ/δ

DOI:  https://doi.org/10.1186/s12964-024-01972-5
J Nanobiotechnology. 2024 Dec 18. 22(1): 754

Adipose-derived exosomes ameliorate skeletal muscle atrophy via miR-146a-5p/IGF-1R signaling.

Mengran Qin, Jiahao Zhu, Lipeng Xing, Yaotian Fan, Junyi Luo, Jiajie Sun, Ting Chen, Yongliang Zhang, Qianyun Xi.

  The study of muscle disorders has gained popularity, with a particular emphasis on the relationship between adipose tissue and skeletal muscle. In our investigation, we discovered that the deletion of miR-146a-5p specifically in adipose tissue (aKO) led to a notable rise in mice's mass and adiposity. In contrast, it led to a decline in lean mass, ability to exercise, diameter of muscle fibers, and the levels of genes associated with differentiation. The co-culture experiment showed that the transfection of miR-146a-5p mimics to 3T3-L1 significantly suppressive cell growth and promotes myotube differentiation in C2C12 cells. Exosomes from white adipose tissue (WAT) of aKO mice (aKO-WAT-Exos) significantly promoted muscle atrophy and inhibited differentiation of C2C12 cells but were reversed by co-incubation with miR-146a-5p-mimics. The miR-146a-5p can specifically target IGF-1R to improve skeletal muscle wasting. In this process, the PI3K/AKT/mTOR pathway is activated or the FoxO3 pathway is inhibited to enhance the synthesis of skeletal muscle proteins. Significantly, miR-146a-5p serves a crucial function as a microRNA in the communication of the fat-muscle connection. It can be transported through the pathway of exosomes derived from adipose tissue, ultimately ameliorating skeletal muscle atrophy and modulating body mass index (BMI).

Keywords:  Adipose; Exosomes; IGF-1R; Muscle atrophy; Skeletal muscle; miR-146a-5p

DOI:  https://doi.org/10.1186/s12951-024-02983-7
Hum Mol Genet. 2024 Dec 16. pii: ddae186. [Epub ahead of print]

Identification of ZNF850 as a novel CTG repeat expansion-related gene in myotonic dystrophy type 1 patient-derived iPSCs.

Masayoshi Kamon, Shuji Wakatsuki, Masayuki Nakamori, Masanori P Takahashi, Madoka Mori-Yoshimura, Hirofumi Komaki, Toshiyuki Araki.

  Myotonic dystrophy type 1 (DM1) is a dominantly inherited multi-system disease caused by expanded CTG repeats in the 3' untranslated region of the dystrophia myotonica protein kinase (DMPK) gene. Similar to other repeat disorders, the expanded trinucleotide repeat is unstable and demonstrates a tendency to increase repeat size with age in affected tissues. DNA mismatch repair system is implicated in somatic instability. It has been demonstrated that DM1 patient-derived induced pluripotent stem cells (DM1-iPSCs) show repeat instability, in which involvement of mismatch repair proteins has been suggested. Here we identified ZNF850 as a novel CTG repeat expansion-related molecule in DM1-iPSCs. ZNF850 was downregulated in a DM1-iPSC clone whose CTG repeat is exceptionally stable. We found that RNAi-mediated ZNF850 downregulation in DM1-iPSCs significantly reduced the repeat expansion and resulting instability. In adult skeletal muscle tissue of DM1 patients, ZNF850 expression levels were positively correlated with the repeat size. Furthermore, we found that ZNF850 protein can bind to the expanded CTG repeat sequence, and is located in proximity to MutSβ components. These results suggest that ZNF850 might play a role in repeat instability in DM1 by recruiting MutSβ to the repeat sequence.

Keywords:  induced pluripotent stem cells; mismatch repair; myotonic dystrophy type 1; triplet repeat

DOI:  https://doi.org/10.1093/hmg/ddae186
R Soc Open Sci. 2024 Sep;11(9): 240037

Rethinking the physiological cross-sectional area of skeletal muscle reveals the mechanical advantage of pennation.

Robert Rockenfeller, Michael Günther, Christofer J Clemente, Taylor J M Dick.

  The shape of skeletal muscle varies remarkably-with important implications for locomotor performance. In many muscles, the fibres are arranged at an angle relative to the tendons' line of action, termed the pennation angle. These pennate muscles allow more sarcomeres to be packed side by side, enabling the muscle to generate higher maximum forces for a given muscle size. Historically, the physiological cross-sectional area (PCSA) has been used to capture both the size and arrangement of muscle fibres, and is one of the best predictors of a muscles capacity to produce force. However, the anatomical and mechanical implications of PCSA remain ambiguous as misinterpretations have limited our ability to understand the mechanical advantage of pennate muscle designs. We developed geometric models to resolve the mechanistic and functional impacts of pennation angle across a range of muscle shapes and sizes. Comparisons among model predictions and empirical data on human lower limb muscles demonstrated how a pennate arrangement of fibres allows muscles to produce up to six times more isometric force when compared with non-pennate muscles of the same volume. We show that in muscles much longer than thick, an optimal pennation angle exists at which isometric force is maximized. Using empirically informed geometric models we demonstrate the functional significance of a pennate muscle design and provide a new parameter, pennation mechanical advantage, which quantifies this performance improvement.

Keywords:  biomechanics; mathematical modelling; muscle architecture; physiology

DOI:  https://doi.org/10.1098/rsos.240037
bioRxiv. 2024 Dec 03. pii: 2024.11.28.625886. [Epub ahead of print]

Functional dissection of metabolic trait-associated gene regulation in steady state and stimulated human skeletal muscle cells.

Kirsten Nishino, Jacob O Kitzman, Stephen C J Parker, Adelaide Tovar.

Type 2 diabetes (T2D) is a common metabolic disorder characterized by dysregulation of glucose metabolism. Genome-wide association studies have defined hundreds of signals associated with T2D and related metabolic traits, predominantly in noncoding regions. While pancreatic islets have been a focal point given their central role in insulin production and glucose homeostasis, other metabolic tissues, including liver, adipose, and skeletal muscle, also contribute to T2D pathogenesis and risk. Here, we examined context-specific genetic regulation under basal and stimulated states. Using LHCN-M2 human skeletal muscle cells, we generated transcriptomic profiles and characterized regulatory activity of 327 metabolic trait-associated variants via a massively parallel reporter assay (MPRA). To identify condition-specific effects, we compared four different conditions: (1) undifferentiated, or (2) differentiated with basal media, (3) media supplemented with the AMP analog AICAR (to simulate exercise) or (4) media containing sodium palmitate (to induce insulin resistance). RNA-seq revealed these treatments extensively perturbed transcriptional regulation, with 498-3,686 genes showing significant differential expression between pairs of conditions. Among differentially expressed genes, we observed enrichment of relevant biological pathways including muscle differentiation (undifferentiated vs. differentiated), oxidoreductase activity (differentiated vs. AICAR), and glycogen binding (differentiated vs. palmitate). The results of our MPRA found broadly different levels of activity between all conditions. Our MPRA screen revealed a shared set of 7 variants with significant allelic activity across all conditions, along with a proportional number of variants showing condition-specific allelic bias and the total number of active oligos per condition. We found that a lead variant for serum triglyceride levels, rs490972, overlaps SP transcription factor motifs and has differential regulatory activity between conditions. Comparison of MPRA activity with paired gene expression data allowed us to predict that regulatory activity at this locus is mediated by SP1 transcription factor binding. While several of the MPRA variants have been previously characterized in other metabolic tissues, none have been studied in these stimulated states. Together, this work uncovers context-dependent transcriptomic and regulatory dynamics of T2D- and metabolic trait-associated variants in skeletal muscle cells, offering new insights into their functional roles in metabolic processes.

DOI: https://doi.org/10.1101/2024.11.28.625886
J Cell Sci. 2024 Dec 20. pii: jcs.263660. [Epub ahead of print]

Fibre type differences in the organisation of mononuclear cells and myonuclei at the tips of human myofibres.

Christian Hoegsbjerg, Ask Møbjerg, Ching-Yan Chloé Yeung, Peter Schjerling, Michael R Krogsgaard, Manuel Koch, Michael Kjaer, Arvind G von Keudell, Abigail L Mackey.

  The myotendinous junction (MTJ) is a weak link in the musculoskeletal system. Here, we isolated the tips of single myofibres from healthy human hamstring muscles for confocal microscopy (n=6) and RNAscope in situ hybridisation (n=6) to gain insight into the profiles of cells and myonuclei in this region, in a fibre type manner. A marked presence of mononuclear cells was observed coating the myofibre tips (confirmed by serial block face scanning electron microscopy and cryosection immunofluorescence), with higher numbers for type I (median 29; range 16-63) than type II (16; 9-23) myofibres (p<0.05). The number of these cells expressing COL22A1 was comparable between fibre types. Myonuclear number and density gradually increased from the myofibre proper towards the tip for both fibre types (p<0.05). COL22A1 was expressed by similar proportions of myonuclei in type I (median 26%; range 13-56) and type II (19%; 3-67) myofibre tips. 70% of the COL22A1+ nuclei in the MTJ region were myonuclei, and the remaining 30% were MTJ cells. This insight refines our fundamental understanding of the human MTJ at the cell and structural levels.

Keywords:   COL22A1 ; Fibre types; Myonuclear domain; Myotendinous junction; Spinning disc confocal microscopy

DOI:  https://doi.org/10.1242/jcs.263660
Elife. 2024 Dec 20. pii: RP96926. [Epub ahead of print]13

Mitochondrial respiration atlas reveals differential changes in mitochondrial function across sex and age.

Dylan C Sarver, Muzna Saqib, Fangluo Chen, G William Wong.

  Organ function declines with age, and large-scale transcriptomic analyses have highlighted differential aging trajectories across tissues. The mechanism underlying shared and organ-selective functional changes across the lifespan, however, still remains poorly understood. Given the central role of mitochondria in powering cellular processes needed to maintain tissue health, we therefore undertook a systematic assessment of respiratory activity across 33 different tissues in young (2.5 months) and old (20 months) mice of both sexes. Our high-resolution mitochondrial respiration atlas reveals: (1) within any group of mice, mitochondrial activity varies widely across tissues, with the highest values consistently seen in heart, brown fat, and kidney; (2) biological sex is a significant but minor contributor to mitochondrial respiration, and its contributions are tissue-specific, with major differences seen in the pancreas, stomach, and white adipose tissue; (3) age is a dominant factor affecting mitochondrial activity, especially across most brain regions, different fat depots, skeletal muscle groups, eyes, and different regions of the gastrointestinal tract; (4) age effects can be sex- and tissue-specific, with some of the largest effects seen in pancreas, heart, adipose tissue, and skeletal muscle; and (5) while aging alters the functional trajectories of mitochondria in a majority of tissues, some are remarkably resilient to age-induced changes. Altogether, our data provide the most comprehensive compendium of mitochondrial respiration and illuminate functional signatures of aging across diverse tissues and organ systems.

Keywords:  aging; computational biology; mitochondria; mouse; respiration atlas; sex; systems biology

DOI:  https://doi.org/10.7554/eLife.96926
Extracell Vesicles Circ Nucl Acids. 2023 ;4(3): 486-501

MicroRNA biogenesis pathway alterations in aging.

Jorge Sanz-Ros, Cristina Mas-Bargues, Nekane Romero-García, Javier Huete-Acevedo, Mar Dromant, Consuelo Borrás.

  Aging is characterized by genomic instability and dysregulation of gene expression. MicroRNAs (miRNAs) are small non-coding RNAs that play a crucial role in post-transcriptional gene regulation. This work explores the impact of dysregulated miRNA biogenesis on the aging process. During aging, alterations in the transcription of primary miRNAs (pri-miRNAs) occur due to genomic changes, DNA damage, and epigenetic modifications. The microprocessor complex, comprising DGCR8 and Drosha proteins, is vital for pri-miRNA processing. Age-related changes in this complex affect miRNA biogenesis and miRNA expression profiles, linking these alterations with age-related conditions. Conversely, interventions like caloric restriction and mTOR inhibition enhance microprocessor activity, suggesting a connection between microprocessor function, aging-related pathways, and lifespan extension. Exportin-5 mediates the transport of pre-miRNAs from the nucleus to the cytoplasm. Although the role of miRNA export in aging is not well understood, accelerated export of pre-miRNAs is observed in response to DNA damage, and nucleocytoplasmic transport has been linked to cellular senescence. Dicer is responsible for processing pre-miRNAs into mature miRNAs. Reduced Dicer expression during aging is reported in various organisms and tissues and is associated with premature aging phenotypes. Conversely, the upregulation of Dicer improves stress resistance and metabolic adaptations induced by caloric restriction and exercise training. Understanding the role of miRNA biogenesis disruption in aging provides insights into the molecular mechanisms of aging and age-related diseases. Targeting this pathway may hold promise for therapeutic strategies and contribute to healthy aging.

Keywords:  MicroRNA biogenesis; aging process; intercellular communication; lifespan

DOI:  https://doi.org/10.20517/evcna.2023.29
Front RNA Res. 2023 ;pii: 1197990. [Epub ahead of print]1

The Cajal body marker protein coilin is SUMOylated and possesses SUMO E3 ligase-like activity.

Katheryn E Lett, Douglas M McLaurin, Sara K Tucker, Michael D Hebert.

Cajal bodies (CBs) are subnuclear domains that contribute to the biogenesis of several different classes of ribonucleoproteins (RNPs) including small nuclear RNPs. Only some cell types contain abundant CBs, such as neuronal cells and skeletal muscle, but CBs are invariant features of transformed cells. In contrast, coilin, the CB marker protein, is a ubiquitously expressed nuclear protein but the function of coilin in cell types that lack CBs is not well understood. We have previously shown that coilin promotes microRNA biogenesis by promoting phosphorylation of DGCR8, a component of the Microprocessor. Here we identify 7 additional residues of DGCR8 with decreased phosphorylation upon coilin knockdown. In addition to phosphorylation, the addition of a small ubiquitin-like modifier (SUMO) to DGCR8 also increases its stability. Because of coilin's role in the promotion of DGCR8 phosphorylation, we investigated whether coilin is involved in DGCR8 SUMOylation. We show that coilin knockdown results in global decrease of protein SUMOylation, including decreased DGCR8 and Sp100 (a PML body client protein) SUMOylation and decreased SMN expression. Alternatively, we found that coilin expression rescued Sp100 SUMOylation and increased DGCR8 and SMN levels in a coilin knockout cell line. Furthermore, we found that coilin facilitates RanGAP1 SUMOylation, interacts directly with components of the SUMOylation machinery (Ubc9 and SUMO2), and itself is SUMOylated in vitro and in vivo. In summary, we have identified coilin as a regulator of DGCR8 phosphorylation and a promotor of protein SUMOylation with SUMO E3 ligase-like activity.

DOI: https://doi.org/10.3389/frnar.2023.1197990
Annu Rev Physiol. 2024 Dec 10.

Exercise as Mitochondrial Medicine: How Does the Exercise Prescription Affect Mitochondrial Adaptations to Training?

David J Bishop, Matthew J-C Lee, Martin Picard.

Mitochondria are multifaceted organelles with several life-sustaining functions beyond energy transformation, including cell signaling, calcium homeostasis, hormone synthesis, programmed cell death (apoptosis), and others. A defining aspect of these dynamic organelles is their remarkable plasticity, which allows them to sense, respond, and adapt to various stressors. In particular, it is well-established that the stress of exercise provides a powerful stimulus that can trigger transient or enduring changes to mitochondrial molecular features, activities, integrated functions, behaviors, and cell-dependent mitochondrial phenotypes. Evidence documenting the many beneficial mitochondrial adaptations to exercise has led to the notion of exercise as a mitochondrial medicine. However, as with other medicines, it is important to understand the optimal prescription (i.e., type, dose, frequency, duration). In this review, we build on a systematic biological framework that distinguishes between domains of mitochondrial biology to critically evaluate how different exercise prescription variables influence mitochondrial adaptations to training.

DOI: https://doi.org/10.1146/annurev-physiol-022724-104836