bims-moremu 2023-11-19 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–11–19
thirty-one papers selected by
Anna Vainshtein, Craft Science Inc.

A Critical Discussion on the relationship between E3 ubiquitin ligases, Protein Degradation and Skeletal Muscle Wasting: It's not that simple.
The emerging role of Piezo1 channels in skeletal muscle physiology.
Physical exercise ameliorates age-related deterioration of skeletal muscle and mortality by activating Pten-related pathways in Drosophila on a high-salt diet.
Stuart has got the PoWeR! Skeletal muscle adaptations to a novel heavy progressive weighted wheel running exercise model in C57BL/6 mice.
The multifaceted role of macrophages in homeostatic and injured skeletal muscle.
Ryanodine receptor type 1 content decrease-induced endoplasmic reticulum stress is a hallmark of myopathies.
Iron deficiency-induced ferritinophagy impairs skeletal muscle regeneration through RNF20-mediated H2Bub1 modification.
Interactions of mitochondrial and skeletal muscle biology in mitochondrial myopathy.
The L27 Domain of MPP7 enhances TAZ-YY1 Cooperation to Renew Muscle Stem Cells.
'Enhancing' skeletal muscle and stem cells in three-dimensional: genome regulation of skeletal muscle in development and disease.
Skeletal muscle TFEB signaling promotes central nervous system function and reduces neuroinflammation during aging and neurodegenerative disease.
Examining the calcium sensitivity of skeletal muscle thick filaments.
Effects of acute exercise and training status on glucocorticoid-induced leucine zipper (GILZ) expression in human skeletal muscle.
High-mobility group box-1 impedes skeletal muscle regeneration via downregulation of Pax-7 synthesis by increasing miR-342-5p expression.
Weakened Contractile Performance and Mitochondrial Respiratory Complex Activity in Skeletal Muscle Improve during Interbout Arousal in Hibernating Daurian Ground Squirrel, Spermophilus dauricus.
Cold-induced muscle atrophy in zebrafish: Insights from swimming activity and gene expression analysis.
Human skeletal muscle organoids model fetal myogenesis and sustain uncommitted PAX7 myogenic progenitors.
Electrical stimulation mitigates muscle degradation shift in gene expressions during 12-h mechanical ventilation.
Higher Expression of Denervation-responsive Genes is Negatively Associated with Muscle Volume and Performance Traits in the Study of Muscle, Mobility and Aging (SOMMA).
The MuSK-BMP pathway regulates synaptic Nav1.4 localization and muscle excitability.
MCUb is an inducible regulator of calcium-dependent mitochondrial metabolism and substrate utilization in muscle.
Autophagy gene expression in skeletal muscle of older individuals is associated with physical performance, muscle volume and mitochondrial function in the Study of Muscle, Mobility and Aging (SOMMA).
Tanshinone IIA promotes the proliferation and differentiation ability of primary muscle stem cells via MAPK and Akt signaling.
Fast myosin binding protein C knockout in skeletal muscle alters length-dependent activation and myofilament structure.
Skeletal muscle cells opto-stimulation by intramembrane molecular transducers.
Effects of sclerostin injection on soleus and extensor digitorum longus muscle tissue in male mice.
3D reconstruction of murine mitochondria reveals changes in structure during aging linked to the MICOS complex.
Epigenetic and "redoxogenetic" adaptation to physical exercise.
Potential role of Akt in the regulation of fibroblast growth factor 21 by berberine.
LMNA-related muscular dystrophy involving myoblast proliferation and apoptosis through the FOXO1/GADD45A pathway.
Towards unravelling the exercise-induced adaptations in circulating extracellular vesicles.

Am J Physiol Cell Physiol. 2023 Nov 13.

A Critical Discussion on the relationship between E3 ubiquitin ligases, Protein Degradation and Skeletal Muscle Wasting: It's not that simple.

David C Hughes, Craig A Goodman, Leslie M Baehr, Paul Gregorevic, Sue C Bodine.

  Ubiquitination is an important post-translational modification for protein substrates, whereby ubiquitin is added to proteins through the coordinated activity of activating (E1), ubiquitin-conjugating (E2), and ubiquitin ligase (E3) enzymes. The E3s provide key functions in the recognition of specific protein substrates to be ubiquitinated and aid in determining their proteolytic or non-proteolytic fates, which has led to their study as indicators of altered cellular processes. MuRF1 and MAFbx/Atrogin-1 were two of the first E3 ubiquitin ligases identified as being upregulated in a range of different skeletal muscle atrophy models. Since their discovery, the expression of these E3 ubiquitin ligases has often been studied as a surrogate measure of changes to bulk protein degradation rates. However, emerging evidence has highlighted the dynamic and complex regulation of the ubiquitin proteasome system in skeletal muscle and demonstrated that protein ubiquitination is not necessarily equivalent to protein degradation. These observations highlight the potential challenges of quantifying E3 ubiquitin ligases as markers of protein degradation rates or ubiquitin proteasome system (UPS) activation. This perspective examines the usefulness of monitoring E3 ubiquitin ligases for determining specific or bulk protein degradation rates in settings of skeletal muscle atrophy. Specific questions that remain unanswered within the skeletal muscle atrophy field are also identified, to encourage the pursuit of new research that will be critical in moving forward our understanding of the molecular mechanisms that govern protein function and degradation in muscle.

Keywords:  Atrophy; disuse; proteasome system; protein degradation; ubiquitination

DOI:  https://doi.org/10.1152/ajpcell.00457.2023
Biophys Rev. 2023 Oct;15(5): 1171-1184

The emerging role of Piezo1 channels in skeletal muscle physiology.

Timur M Mirzoev.

  Piezo1 channels are mechanically activated (MA) cation channels that are involved in sensing of various mechanical perturbations, such as membrane stretch and shear stress, and play a crucial role in cell mechanotransduction. In response to mechanical stimuli, these channels open up and allow cations to travel into the cell and induce biochemical reactions that can change the cell's metabolism and function. Skeletal muscle cells/fibers inherently depend upon mechanical cues in the form of fluid shear stress and contractions (physical exercise). For example, an exposure of skeletal muscles to chronic mechanical loading leads to increased anabolism and fiber hypertrophy, while prolonged mechanical unloading results in muscle atrophy. MA Piezo1 channels have recently emerged as key mechanosensors that are capable of linking mechanical signals and intramuscular signaling in skeletal muscle cells/fibers. This review will summarize the emerging role of Piezo1 channels in the development and regeneration of skeletal muscle tissue as well as in the regulation of skeletal muscle atrophy. In addition, an overview of potential Piezo1-related signaling pathways underlying anabolic and catabolic processes will be provided. A better understanding of Piezo1's role in skeletal muscle mechanotransduction may represent an important basis for the development of therapeutic strategies for maintaining muscle functions under disuse conditions and in some disease states.

Keywords:  Intracellular signaling; Mechanotransduction; Myogenesis; Piezo1; Skeletal muscle

DOI:  https://doi.org/10.1007/s12551-023-01154-6
FASEB J. 2023 Dec;37(12): e23304

Physical exercise ameliorates age-related deterioration of skeletal muscle and mortality by activating Pten-related pathways in Drosophila on a high-salt diet.

Wen-Qi Hou, Deng-Tai Wen, Qi Zhong, Lan Mo, Shuo Wang, Xin-Yuan Yin, Xing-Feng Ma.

  The phosphatase and tensin congeners (Pten) gene affects cell growth, cell proliferation, and rearrangement of connections, and it is closely related to cellular senescence, but it remains unclear the role of muscle-Pten gene in exercise against age-related deterioration in skeletal muscle and mortality induced by a high-salt diet (HSD). In here, overexpression and knockdown of muscle Pten gene were constructed by building MhcGAL4 /PtenUAS-overexpression and MhcGAL4 /PtenUAS-RNAi system in flies, and flies were given exercise training and a HSD for 2 weeks. The results showed that muscle Pten knockdown significantly reduced the climbing speed, climbing endurance, GPX activity, and the expression of Pten, Sirt1, PGC-1α genes, and it significantly increased the expression of Akt and ROS level, and impaired myofibril and mitochondria of aged skeletal muscle. Pten knockdown prevented exercise from countering the HSD-induced age-related deterioration of skeletal muscle. Pten overexpression has the opposite effect on skeletal muscle aging when compared to it knockdown, and it promoted exercise against HSD-induced age-related deterioration of skeletal muscle. Pten overexpression significantly increased lifespan, but its knockdown significantly decreased lifespan of flies. Thus, current results confirmed that differential expression of muscle Pten gene played an important role in regulating skeletal muscle aging and lifespan, and it also affected the adaptability of aging skeletal muscle to physical exercise since it determined the activity of muscle Pten/Akt pathway and Pten/Sirt1/PGC-1α pathway.

Keywords:  Pten/Akt; Sirt1/PGC-1α; exercise; high-salt diet; muscle aging

DOI:  https://doi.org/10.1096/fj.202301099R
Exp Physiol. 2023 Nov 16.

Stuart has got the PoWeR! Skeletal muscle adaptations to a novel heavy progressive weighted wheel running exercise model in C57BL/6 mice.

Pieter J Koopmans, Therin D Williams-Frey, Kevin A Zwetsloot.

  Murine exercise models are developed to study the molecular and cellular mechanisms regulating muscle mass. A progressive weighted wheel running model, named 'PoWeR', was previously developed to serve as a more translatable alternative to involuntary resistance-type exercise models in rodents, such as synergist ablation. However, mice still run great distances despite the added resistance as evidenced by a large glycolytic-to-oxidative shift in muscle fibre type. Thus, PoWeR reflects a blended resistance/endurance model. In an attempt to bias PoWeR further towards resistance-type exercise, we developed a novel heavy PoWeR model (hPoWeR) utilizing higher wheel loads (max of 12.5 g vs 6 g). Adult male C57BL/6 mice voluntarily performed an 8-week progressive loading protocol (PoWeR or hPoWeR). Running distance peaked at ∼5-6 km day-1 in both treatments and was maintained by PoWeR mice, but declined in the hPoWeR mice as load increased beyond 7.5 g. Peak isometric force of the gastrocnemius-soleus-plantaris complex tended to increase in wheel running treatments. Soleus mass increased by 19% and 24% in PoWeR and hPoWeR treatments, respectively, and plantaris fibre cross-sectional area was greater in hPoWeR, compared to PoWeR. There were fewer glycolytic and more oxidative fibres in the soleus and plantaris muscles in the PoWeR treatment, but not hPoWeR. Collectively, these data suggest hPoWeR may modestly alter skeletal muscle supporting the aim of better reflecting typical resistance training adaptations, in line with decreased running volume and exposure to higher resistance. Regardless, PoWeR remains an effective hypertrophic concurrent training model in mice. NEW FINDINGS: What is the central question of this study? Can utilizing a heavier loading protocol, compared to the previously developed progressive weighted wheel running (PoWeR) exercise model, bias skeletal muscle adaptations further towards resistance-type exercise in mice? What is the main finding and its importance? Utilizing a significantly heavier wheel loading protocol, which may better reflect traditional resistance-type exercise training, only modestly alters skeletal muscle adaptations. These results intuitively demonstrate decreased running distance with exposure to higher resistance, compared to PoWeR; however, murine wheel running models may always inherently possess a strong endurance training component.

Keywords:  murine exercise models; muscle hypertrophy; resistance exercise

DOI:  https://doi.org/10.1113/EP091494
Front Immunol. 2023 ;14 1274816

The multifaceted role of macrophages in homeostatic and injured skeletal muscle.

Xingyu Wang, Lan Zhou.

  Skeletal muscle is essential for body physical activity, energy metabolism, and temperature maintenance. It has excellent capabilities to maintain homeostasis and to regenerate after injury, which indispensably relies on muscle stem cells, satellite cells (MuSCs). The quiescence, activation, and differentiation of MuSCs are tightly regulated in homeostatic and regenerating muscles. Among the important regulators are intramuscular macrophages, which are functionally heterogeneous with different subtypes present in a spatiotemporal manner to regulate the balance of different MuSC statuses. During chronic injury and aging, intramuscular macrophages often undergo aberrant activation, which in turn disrupts muscle homeostasis and regenerative repair. Growing evidence suggests that the aberrant activation is mainly triggered by altered muscle microenvironment. The trained immunity that affects myeloid progenitors during hematopoiesis may also contribute. Aged immune system may contribute, in part, to the aging-related sarcopenia and compromised skeletal muscle injury repair. As macrophages are actively involved in the progression of many muscle diseases, manipulating their functional activation has become a promising therapeutic approach, which requires comprehensive knowledge of the cellular and molecular mechanisms underlying the diverse activation. To this end, we discuss here the current knowledge of multifaceted role of macrophages in skeletal muscle homeostasis, injury, and repair.

Keywords:  aging; homeostasis; injury repair; macrophage; skeletal muscle

DOI:  https://doi.org/10.3389/fimmu.2023.1274816
J Cachexia Sarcopenia Muscle. 2023 Nov 15.

Ryanodine receptor type 1 content decrease-induced endoplasmic reticulum stress is a hallmark of myopathies.

Jeremy Vidal, Eric A Fernandez, Martin Wohlwend, Pirkka-Pekka Laurila, Andrea Lopez-Mejia, Julien Ochala, Alexander J Lobrinus, Bengt Kayser, Isabel C Lopez-Mejia, Nicolas Place, Nadège Zanou.

   BACKGROUND: Decreased ryanodine receptor type 1 (RyR1) protein levels are a well-described feature of recessive RYR1-related myopathies. The aim of the present study was twofold: (1) to determine whether RyR1 content is also decreased in other myopathies and (2) to investigate the mechanisms by which decreased RyR1 protein triggers muscular disorders.
METHODS: We used publicly available datasets, muscles from human inflammatory and mitochondrial myopathies, an inducible muscle-specific RYR1 recessive mouse model and RyR1 knockdown in C2C12 muscle cells to measure RyR1 content and endoplasmic reticulum (ER) stress markers. Proteomics, lipidomics, molecular biology and transmission electron microscopy approaches were used to decipher the alterations associated with the reduction of RyR1 protein levels.
RESULTS: RYR1 transcripts were reduced in muscle samples of patients suffering from necrotizing myopathy (P = 0.026), inclusion body myopathy (P = 0.003), polymyositis (P < 0.001) and juvenile dermatomyositis (P < 0.001) and in muscle samples of myotonic dystrophy type 2 (P < 0.001), presymptomatic (P < 0.001) and symptomatic (P < 0.001) Duchenne muscular dystrophy, Becker muscular dystrophy (P = 0.004) and limb-girdle muscular dystrophy type 2A (P = 0.004). RyR1 protein content was also significantly decreased in inflammatory myopathy (-75%, P < 0.001) and mitochondrial myopathy (-71%, P < 0.001) muscles. Proteomics data showed that depletion of RyR1 protein in C2C12 myoblasts leads to myotubes recapitulating the common molecular alterations observed in myopathies. Mechanistically, RyR1 protein depletion reduces ER-mitochondria contact length (-26%, P < 0.001), Ca2+ transfer to mitochondria (-48%, P = 0.002) and the mitophagy gene Parkinson protein 2 transcripts (P = 0.037) and induces mitochondrial accumulation (+99%, P = 0.005) and dysfunction (P < 0.001). This was associated to the accumulation of deleterious sphingolipid species. Our data showed increased levels of the ER stress marker chaperone-binding protein/glucose regulated protein 78, GRP78-Bip, in RyR1 knockdown myotubes (+45%, P = 0.046), in mouse RyR1 recessive muscles (+58%, P = 0.001) and in human inflammatory (+96%, P = 0.006) and mitochondrial (+64%, P = 0.049) myopathy muscles. This was accompanied by increased protein levels of the pro-apoptotic protein CCAAT-enhancer-binding protein homologous protein, CHOP-DDIT3, in RyR1 knockdown myotubes (+27%, P < 0.001), mouse RyR1 recessive muscles (+63%, P = 0.009), human inflammatory (+50%, P = 0.038) and mitochondrial (+51%, P = 0.035) myopathy muscles. In publicly available datasets, the decrease in RYR1 content in myopathies was also associated to increased ER stress markers and RYR1 transcript levels are inversely correlated with ER stress markers in the control population.
CONCLUSIONS: Decreased RyR1 is commonly observed in myopathies and associated to ER stress in vitro, in mouse muscle and in human myopathy muscles, suggesting a potent role of RyR1 depletion-induced ER stress in the pathogenesis of myopathies.

Keywords:  CHOP; GRP78-Bip; calcium; lipid droplet; mitophagy; muscle

DOI:  https://doi.org/10.1002/jcsm.13349
Sci Adv. 2023 Nov 15. 9(46): eadf4345

Iron deficiency-induced ferritinophagy impairs skeletal muscle regeneration through RNF20-mediated H2Bub1 modification.

Yunshu Che, Jinteng Li, Peng Wang, Wenhui Yu, Jiajie Lin, Zepeng Su, Feng Ye, Zhaoqiang Zhang, Peitao Xu, Zhongyu Xie, Yanfeng Wu, Huiyong Shen.

Iron deficiency (ID) is a widespread condition concomitant with disease and results in systemic dysfunction of target tissues including skeletal muscle. Activated by ID, ferritinophagy is a recently found type of selective autophagy, which plays an important role in various physiological and pathological conditions. In this study, we demonstrated that ID-mediated ferritinophagy impeded myogenic differentiation. Mechanistically, ferritinophagy induced RNF20 degradation through the autophagy-lysosomal pathway and then negatively regulated histone H2B monoubiquitination at lysine-120 in the promoters of the myogenic markers MyoD and MyoG, which inhibited myogenic differentiation and regeneration. Conditional knockout of NCOA4 in satellite cells, overexpression of RNF20 or treatment with 3-methyladenine restored skeletal muscle regenerative potential under ID conditions. In patients with ID, RNF20 and H2Bub1 protein expression is downregulated in skeletal muscle. In conclusion, our study indicated that the ferritinophagy-RNF20-H2Bub1 axis is a pathological molecular mechanism underlying ID-induced skeletal muscle impairment, suggesting potential therapeutic prospects.

DOI: https://doi.org/10.1126/sciadv.adf4345
Biochem J. 2023 Nov 15. 480(21): 1767-1789

Interactions of mitochondrial and skeletal muscle biology in mitochondrial myopathy.

Valeria Di Leo, Tiago M Bernardino Gomes, Amy E Vincent.

  Mitochondrial dysfunction in skeletal muscle fibres occurs with both healthy aging and a range of neuromuscular diseases. The impact of mitochondrial dysfunction in skeletal muscle and the way muscle fibres adapt to this dysfunction is important to understand disease mechanisms and to develop therapeutic interventions. Furthermore, interactions between mitochondrial dysfunction and skeletal muscle biology, in mitochondrial myopathy, likely have important implications for normal muscle function and physiology. In this review, we will try to give an overview of what is known to date about these interactions including metabolic remodelling, mitochondrial morphology, mitochondrial turnover, cellular processes and muscle cell structure and function. Each of these topics is at a different stage of understanding, with some being well researched and understood, and others in their infancy. Furthermore, some of what we know comes from disease models. Whilst some findings are confirmed in humans, where this is not yet the case, we must be cautious in interpreting findings in the context of human muscle and disease. Here, our goal is to discuss what is known, highlight what is unknown and give a perspective on the future direction of research in this area.

Keywords:  function; metabolism; mitochondria; mitochondrial dysfunction; structure

DOI:  https://doi.org/10.1042/BCJ20220233
bioRxiv. 2023 Nov 04. pii: 2023.11.01.565166. [Epub ahead of print]

The L27 Domain of MPP7 enhances TAZ-YY1 Cooperation to Renew Muscle Stem Cells.

Anwen Shao, Joseph L Kissil, Chen-Ming Fan.

Stem cells regenerate differentiated cells to maintain and repair tissues and organs. They also replenish themselves, i.e. self-renewal, for the regenerative process to last a lifetime. How stem cells renew is of critical biological and medical significance. Here we use the skeletal muscle stem cell (MuSC) to study this process. Using a combination of genetic, molecular, and biochemical approaches, we show that MPP7, AMOT, and TAZ/YAP form a complex that activates a common set of target genes. Among these targets, Carm1 can direct MuSC renewal. In the absence of MPP7, TAZ can support regenerative progenitors and activate Carm1 expression, but not to a level needed for self-renewal. Facilitated by the actin polymerization-responsive AMOT, TAZ recruits the L27 domain of MPP7 to up-regulate Carm1 to the level necessary to drive MuSC renewal. The promoter of Carm1 , and those of other common downstream genes, also contain binding site(s) for YY1. We further demonstrate that the L27 domain of MPP7 enhances the interaction between TAZ and YY1 to activate Carm1 . Our results define a renewal transcriptional program embedded within the progenitor program, by selectively up-regulating key gene(s) within the latter, through the combination of protein interactions and in a manner dependent on the promoter context.

DOI: https://doi.org/10.1101/2023.11.01.565166
Curr Opin Genet Dev. 2023 Nov 09. pii: S0959-437X(23)00113-2. [Epub ahead of print]83 102133

'Enhancing' skeletal muscle and stem cells in three-dimensional: genome regulation of skeletal muscle in development and disease.

Matthew A Romero, April D Pyle.

The noncoding genome imparts important regulatory control over gene expression. In particular, gene enhancers represent a critical layer of control that integrates developmental and differentiation signals outside the cell into transcriptional outputs inside the cell. Recently, there has been an explosion in genomic techniques to probe enhancer control, function, and regulation. How enhancers are regulated and integrate signals in stem cell development and differentiation is largely an open question. In this review, we focus on the role gene enhancers play in muscle stem cell specification, differentiation, and progression. We pay specific attention toward the identification of muscle-specific enhancers, the binding of transcription factors to these enhancers, and how enhancers communicate to their target genes via three-dimensional looping.

DOI: https://doi.org/10.1016/j.gde.2023.102133
Cell Rep. 2023 Nov 10. pii: S2211-1247(23)01448-1. [Epub ahead of print]42(11): 113436

Skeletal muscle TFEB signaling promotes central nervous system function and reduces neuroinflammation during aging and neurodegenerative disease.

Ian Matthews, Allison Birnbaum, Anastasia Gromova, Amy W Huang, Kailin Liu, Eleanor A Liu, Kristen Coutinho, Megan McGraw, Dalton C Patterson, Macy T Banks, Amber C Nobles, Nhat Nguyen, Gennifer E Merrihew, Lu Wang, Eric Baeuerle, Elizabeth Fernandez, Nicolas Musi, Michael J MacCoss, Helen C Miranda, Albert R La Spada, Constanza J Cortes.

  Skeletal muscle has recently arisen as a regulator of central nervous system (CNS) function and aging, secreting bioactive molecules known as myokines with metabolism-modifying functions in targeted tissues, including the CNS. Here, we report the generation of a transgenic mouse with enhanced skeletal muscle lysosomal and mitochondrial function via targeted overexpression of transcription factor E-B (TFEB). We discovered that the resulting geroprotective effects in skeletal muscle reduce neuroinflammation and the accumulation of tau-associated pathological hallmarks in a mouse model of tauopathy. Muscle-specific TFEB overexpression significantly ameliorates proteotoxicity, reduces neuroinflammation, and promotes transcriptional remodeling of the aged CNS, preserving cognition and memory in aged mice. Our results implicate the maintenance of skeletal muscle function throughout aging in direct regulation of CNS health and disease and suggest that skeletal muscle originating factors may act as therapeutic targets against age-associated neurodegenerative disorders.

Keywords:  CP: Neuroscience; TFEB; aging; brain; exercise; muscle; neurodegeneration; tau

DOI:  https://doi.org/10.1016/j.celrep.2023.113436
J Gen Physiol. 2023 Dec 04. pii: e202313501. [Epub ahead of print]155(12):

Examining the calcium sensitivity of skeletal muscle thick filaments.

Ben Short.

JGP study (this issue, Caremani et al. https://doi.org/10.1085/jgp.202313393) reveals that the calcium sensitivity of thick filament structure in skeletal muscle is greater than that of force, offering new insights into the mechanisms of thick filament activation.

DOI: https://doi.org/10.1085/jgp.202313501
J Sci Med Sport. 2023 Oct 21. pii: S1440-2440(23)00428-0. [Epub ahead of print]

Effects of acute exercise and training status on glucocorticoid-induced leucine zipper (GILZ) expression in human skeletal muscle.

A Hecksteden, J Hoppstädter, D A Bizjak, A Jerg, J Kirsten, K Krüger, A Niess, J Steinacker, A K Kiemer.

  Interactions between statin therapy and physical exercise complicate effective cardiovascular prevention. Emerging evidence suggests that muscle strain related changes in the expression of the glucocorticoid-induced leucine zipper (GILZ) may be involved. Therefore, we measured GILZ mRNA expression levels in M. vastus lateralis samples of 32 healthy individuals before and after a standardized bout of strength or endurance exercise. Overall, we found a highly significant downregulation of GILZ after exercise training (p < 0.001). Within-subgroup changes were statistically significant only after strength training, supporting the role of muscle (as opposed to cardiocirculatory) strain. If confirmed, this may help fitting training recommendations and medication.

Keywords:  Exercise training; Glucocorticoid; Myopathy; Strength training

DOI:  https://doi.org/10.1016/j.jsams.2023.10.007
Aging (Albany NY). 2023 Nov 13. 15

High-mobility group box-1 impedes skeletal muscle regeneration via downregulation of Pax-7 synthesis by increasing miR-342-5p expression.

Trung-Loc Ho, Yu-Liang Lai, Chin-Jung Hsu, Chen-Ming Su, Chih-Hsin Tang.

  High mobility group box-1 (HMGB1) is a driver of inflammation in various muscular diseases. In a previous study, we determined that HMGB1 induced the atrophy of skeletal muscle by impairing myogenesis. Skeletal muscle regeneration after injury is dependent on pair box 7 (Pax-7)-mediated myogenic differentiation. In the current study, we determined that the HMGB1-induced downregulation of Pax-7 expression in myoblasts inhibited the regeneration of skeletal muscle. We also determined that HMGB1 inhibits Pax-7 and muscle differentiation by increasing miR-342-5p synthesis via receptors for advanced glycation end-products (RAGE), toll-like receptor (TLR) 2, TLR4, and c-Src signaling pathways. In a mouse model involving glycerol-induced muscle injury, the therapeutic inhibition of HMGB1 was shown to rescue Pax-7 expression and muscle regeneration. The HMGB1/Pax-7 axis is a promising therapeutic target to promote muscular regeneration.

Keywords:  HMGB1; Pax-7; miR-342-5p; muscle regeneration; myoblasts

DOI:  https://doi.org/10.18632/aging.205202
Int J Mol Sci. 2023 Oct 30. pii: 15785. [Epub ahead of print]24(21):

Weakened Contractile Performance and Mitochondrial Respiratory Complex Activity in Skeletal Muscle Improve during Interbout Arousal in Hibernating Daurian Ground Squirrel, Spermophilus dauricus.

Huiping Wang, Yuxi Guo, Wenjing Yan, Liqi Cao, Xiaozhuo Bai, Jing Zhao, Kai Dang, Yunfang Gao.

  Mammalian hibernation is composed of multiple episodes of torpor bout, separated by phases of interbout arousal. During torpor, the skeletal muscles of mammals are undoubtedly inactive, but it has been proven to mitigate disuse atrophy. While interbout arousal has been implicated in the prevention of muscle atrophy, the underlying mechanisms sustaining muscle contraction remain to be explored. In the present study, Daurian ground squirrels (Spermophilus dauricus) were divided into four groups: pre-hibernation (PRE), torpor (TOR), interbout arousal (IBA), and post-hibernation (POST). The contractile performance of slow-twitch soleus muscle (SOL) and fast-twitch extensor digitorum longus muscle (EDL) was detected both in situ and in vitro. Concurrently, mitochondrial respiratory chain complex activity in these muscles was quantified. Our findings revealed that in situ contractile properties of both muscles, including force, power output, time duration, and force development/relaxation rates of twitch contraction, and force and power output of tetanic contraction declined in the TOR group compared to the PRE group, but improved in the IBA and POST groups. Fatigue resistance of muscles, determined by the power output of repetitive tetanic contractions in situ, decreased in the TOR group but recovered in the IBA and POST groups. In vitro studies demonstrated that tetanic contraction power output in isolated muscles increased with muscle temperature in both TOR and IBA groups. However, at the same temperature, power output was consistently lower in the TOR group compared to the IBA group. Moreover, the activity of the mitochondrial respiratory chain complex, especially Complexes I and II, decreased in the TOR group but showed recovery in the IBA and POST groups. These findings suggest that both the contractile performance and fatigue resistance of mammalian skeletal muscle are compromised during torpor but can be improved during interbout arousal and post-hibernation. The rebound in body temperature and rise in mitochondrial respiratory chain complex activity in skeletal muscle are involved in enhancing contractile performance and fatigue resistance. This study suggests that interbout arousal functions as a vital temporal interval during which skeletal muscles can transition from the inactivity induced by torpor to a state of restored contractile functionality. Thus, interbout arousal serves as a behavioral safeguard against disuse-induced damage to skeletal muscles during hibernation.

Keywords:  Daurian ground squirrels; contractile properties; hibernation; interbout arousal; mitochondrial respiratory chain complex; skeletal muscle

DOI:  https://doi.org/10.3390/ijms242115785
Biochem Biophys Rep. 2023 Dec;36 101570

Cold-induced muscle atrophy in zebrafish: Insights from swimming activity and gene expression analysis.

Daisuke Ikeda, Seina Fujita, Kaito Toda, Yuma Yaginuma, Nobuhiro Kan-No, Shugo Watabe.

  The investigation into the effects of cold acclimation on fish skeletal muscle function and its potential implications for muscle atrophy is of great interest to us. This study examines how rearing zebrafish at low temperatures affects their locomotor activity and the expression of genes associated with muscle atrophy. Zebrafish were exposed to temperatures ranging from 10 °C to 25 °C, and their swimming distance was measured. The expression levels of important muscle atrophy genes, Atrogin-1 and MuRF1, were also evaluated. Our findings show that swimming activity significantly decreases when the water temperature ranges from 10 °C to 15 °C, indicating a decrease in voluntary movement. Additionally, gene expression analysis shows a significant increase in the expression of Atrogin-1 and MuRF1 at 10 °C. This up-regulation could lead to muscle atrophy caused by decreased activity in cold temperatures. To investigate the effects of exercise on reducing muscle atrophy, we subjected zebrafish to forced swimming at a temperature of 8 °C for ten days. This treatment significantly reduced the expression of Atrogin-1 and MuRF1, emphasizing the importance of muscle stimulation in preventing muscle atrophy in zebrafish. These findings suggest that zebrafish can serve as a valuable model organism for studying muscle atrophy and can be utilized in drug screening for muscle atrophy-related disorders. Cold-reared zebrafish provide a practical and ethical approach to inducing disuse muscle atrophy, providing valuable insights into potential therapeutic strategies for addressing skeletal muscle atrophy.

Keywords:  Atrogenes; Cold rearing; Muscle atrophy; Sarcopenia; Swimming activity; Zebrafish

DOI:  https://doi.org/10.1016/j.bbrep.2023.101570
Elife. 2023 Nov 14. pii: RP87081. [Epub ahead of print]12

Human skeletal muscle organoids model fetal myogenesis and sustain uncommitted PAX7 myogenic progenitors.

Lampros Mavrommatis, Hyun-Woo Jeong, Urs Kindler, Gemma Gomez-Giro, Marie-Cecile Kienitz, Martin Stehling, Olympia E Psathaki, Dagmar Zeuschner, M Gabriele Bixel, Dong Han, Gabriela Morosan-Puopolo, Daniela Gerovska, Ji Hun Yang, Jeong Beom Kim, Marcos J Arauzo-Bravo, Jens C Schwamborn, Stephan A Hahn, Ralf H Adams, Hans R Schöler, Matthias Vorgerd, Beate Brand-Saberi, Holm Zaehres.

  In vitro culture systems that structurally model human myogenesis and promote PAX7+ myogenic progenitor maturation have not been established. Here we report that human skeletal muscle organoids can be differentiated from induced pluripotent stem cell lines to contain paraxial mesoderm and neuromesodermal progenitors and develop into organized structures reassembling neural plate border and dermomyotome. Culture conditions instigate neural lineage arrest and promote fetal hypaxial myogenesis toward limb axial anatomical identity, with generation of sustainable uncommitted PAX7 myogenic progenitors and fibroadipogenic (PDGFRa+) progenitor populations equivalent to those from the second trimester of human gestation. Single-cell comparison to human fetal and adult myogenic progenitor /satellite cells reveals distinct molecular signatures for non-dividing myogenic progenitors in activated (CD44High/CD98+/MYOD1+) and dormant (PAX7High/FBN1High/SPRY1High) states. Our approach provides a robust 3D in vitro developmental system for investigating muscle tissue morphogenesis and homeostasis.

Keywords:  Myogenesis; Organoids; Pax7; human; ips cells; regenerative medicine; satellite cells; skeletal muscle; stem cells

DOI:  https://doi.org/10.7554/eLife.87081
Sci Rep. 2023 Nov 17. 13(1): 20136

Electrical stimulation mitigates muscle degradation shift in gene expressions during 12-h mechanical ventilation.

Hideki Nakai, Yutaka Hirata, Hidemasa Furue, Yoshitaka Oku.

Ventilator-induced diaphragm dysfunction (VIDD), a dysfunction of the diaphragm muscle caused by prolonged mechanical ventilation (MV), is an important factor that hinders successful weaning from ventilation. We evaluated the effects of electrical stimulation of the diaphragm muscle (pulsed current with off-time intervals) on genetic changes during 12 h of MV (E-V12). Rats were divided into four groups: control, 12-h MV, sham operation, and E-V12 groups. Transcriptome analysis using an RNA microarray revealed that 12-h MV caused upregulation of genes promoting muscle atrophy and downregulation of genes facilitating muscle synthesis, suggesting that 12-h MV is a reasonable method for establishing a VIDD rat model. Of the genes upregulated by 12-h MV, 18 genes were not affected by the sham operation but were downregulated by E-V12. These included genes related to catabolic processes, inflammatory cytokines, and skeletal muscle homeostasis. Of the genes downregulated by 12-h MV, 6 genes were not affected by the sham operation but were upregulated by E-V12. These included genes related to oxygen transport and mitochondrial respiration. These results suggested that 12-h MV shifted gene expression in the diaphragm muscle toward muscle degradation and that electrical stimulation counteracted this shift by suppressing catabolic processes and increasing mitochondrial respiration.

DOI: https://doi.org/10.1038/s41598-023-47093-w
medRxiv. 2023 Nov 05. pii: 2023.11.04.23298090. [Epub ahead of print]

Higher Expression of Denervation-responsive Genes is Negatively Associated with Muscle Volume and Performance Traits in the Study of Muscle, Mobility and Aging (SOMMA).

Cole J Lukasiewicz, Gregory J Tranah, Daniel S Evans, Paul M Coen, Haley N Barnes, Zhiguang Huo, Karyn A Esser, Nancy E Lane, Steven B Kritchevsky, Anne B Newman, Steven R Cummings, Peggy M Cawthon, Russell T Hepple.

With aging skeletal muscle fibers undergo repeating cycles of denervation and reinnervation. In approximately the 8 th decade of life reinnervation no longer keeps pace, resulting in the accumulation of persistently denervated muscle fibers that in turn cause an acceleration of muscle dysfunction. The significance of denervation in important clinical outcomes with aging is poorly studied. The Study of Muscle, Mobility and Aging (SOMMA) is a large cohort study with the primary objective to assess how aging muscle biology impacts clinically important traits. Using transcriptomics data from vastus lateralis muscle biopsies in 575 participants we have selected 49 denervation-responsive genes to provide insights to the burden of denervation in SOMMA, to test the hypothesis that greater expression of denervation-responsive genes negatively associates with SOMMA participant traits that included time to walk 400 meters, fitness (VO 2peak ), maximal mitochondrial respiration, muscle mass and volume, and leg muscle strength and power. Consistent with our hypothesis, increased transcript levels of: a calcium-dependent intercellular adhesion glycoprotein (CDH15), acetylcholine receptor subunits (Chrna1, Chrnd, Chrne), a glycoprotein promoting reinnervation (NCAM1), a transcription factor regulating aspects of muscle organization (RUNX1), and a sodium channel (SCN5A) were each negatively associated with at least 3 of these traits. VO 2peak and maximal respiration had the strongest negative associations with 15 and 19 denervation-responsive genes, respectively. In conclusion, the abundance of denervation-responsive gene transcripts is a significant determinant of muscle and mobility outcomes in aging humans, supporting the imperative to identify new treatment strategies to restore innervation in advanced age.

DOI: https://doi.org/10.1101/2023.11.04.23298090
bioRxiv. 2023 Oct 29. pii: 2023.10.24.563837. [Epub ahead of print]

The MuSK-BMP pathway regulates synaptic Nav1.4 localization and muscle excitability.

L A Fish, M D Ewing, D Jaime, K A Rich, C Xi, X Wang, R E Feder, K A Wharton, M M Rich, W D Arnold, J R Fallon.

The neuromuscular junction (NMJ) is the linchpin of nerve-evoked muscle contraction. Broadly considered, the function of the NMJ is to transduce a nerve action potential into a muscle fiber action potential (MFAP). Efficient information transfer requires both cholinergic signaling, responsible for the generation of endplate potentials (EPPs), and excitation, the activation of postsynaptic voltage-gated sodium channels (Nav1.4) to trigger MFAPs. In contrast to the cholinergic apparatus, the signaling pathways that organize Nav1.4 and muscle fiber excitability are poorly characterized. Muscle-specific kinase (MuSK), in addition to its Ig1 domain-dependent role as an agrin-LRP4 receptor, is also a BMP co-receptor that binds BMPs via its Ig3 domain and shapes BMP-induced signaling and transcriptional output. Here we probed the function of the MuSK-BMP pathway at the NMJ using mice lacking the MuSK Ig3 domain ('ΔIg3-MuSK'). Synapses formed normally in ΔIg3-MuSK animals, but the postsynaptic apparatus was fragmented from the first weeks of life. Anatomical denervation was not observed at any age examined. Moreover, spontaneous and nerve-evoked acetylcholine release, AChR density, and endplate currents were comparable to WT. However, trains of nerve-evoked MFAPs in ΔIg3-MuSK muscle were abnormal as revealed by increased jitter and blocking in single fiber electromyography. Further, nerve-evoked compound muscle action potentials (CMAPs), as well as twitch and tetanic muscle torque force production, were also diminished. Finally, Nav1.4 levels were reduced at ΔIg3-MuSK synapses but not at the extrajunctional sarcolemma, indicating that the observed excitability defects are the result of impaired localization of this voltage-gated ion channel at the NMJ. We propose that MuSK plays two distinct roles at the NMJ: as an agrin-LRP4 receptor necessary for establishing and maintaining cholinergic signaling, and as a BMP co-receptor required for maintaining proper Nav1.4 density, nerve-evoked muscle excitability and force production. The MuSK-BMP pathway thus emerges as a target for modulating excitability and functional innervation, which are defective in conditions such as congenital myasthenic syndromes and aging.
Significance Statement: The neuromuscular junction (NMJ) is required for nerve-evoked muscle contraction and movement, and its function is compromised during aging and disease. Although the mechanisms underlying neurotransmitter release and cholinergic response at this synapse have been studied extensively, the machinery necessary for nerve-evoked muscle excitation are incompletely characterized. We show that MuSK (Muscle-specific kinase), in its role as a BMP co-receptor, regulates NMJ structure as well as the localization of the voltage-gated sodium channels necessary for full nerve-evoked muscle fiber excitation and force production. This novel function of MuSK is structurally and mechanistically distinct from its role in organizing cholinergic machinery. The MuSK-BMP pathway thus presents a new opportunity to understand mechanisms that may preserve or enhance neuromuscular excitability in the face of aging and disease.

DOI: https://doi.org/10.1101/2023.10.24.563837
Cell Rep. 2023 Nov 16. pii: S2211-1247(23)01477-8. [Epub ahead of print]42(11): 113465

MCUb is an inducible regulator of calcium-dependent mitochondrial metabolism and substrate utilization in muscle.

Jiuzhou Huo, Vikram Prasad, Kelly M Grimes, Davy Vanhoutte, N Scott Blair, Suh-Chin Lin, Michael J Bround, Donald M Bers, Jeffery D Molkentin.

  Mitochondria use the electron transport chain to generate high-energy phosphate from oxidative phosphorylation, a process also regulated by the mitochondrial Ca2+ uniporter (MCU) and Ca2+ levels. Here, we show that MCUb, an inhibitor of MCU-mediated Ca2+ influx, is induced by caloric restriction, where it increases mitochondrial fatty acid utilization. To mimic the fasted state with reduced mitochondrial Ca2+ influx, we generated genetically altered mice with skeletal muscle-specific MCUb expression that showed greater fatty acid usage, less fat accumulation, and lower body weight. In contrast, mice lacking Mcub in skeletal muscle showed increased pyruvate dehydrogenase activity, increased muscle malonyl coenzyme A (CoA), reduced fatty acid utilization, glucose intolerance, and increased adiposity. Mechanistically, pyruvate dehydrogenase kinase 4 (PDK4) overexpression in muscle of Mcub-deleted mice abolished altered substrate preference. Thus, MCUb is an inducible control point in regulating skeletal muscle mitochondrial Ca2+ levels and substrate utilization that impacts total metabolic balance.

Keywords:  CP: Metabolism; metabolism; mitochondria; obesity; skeletal muscle; substrate utilization

DOI:  https://doi.org/10.1016/j.celrep.2023.113465
medRxiv. 2023 Nov 05. pii: 2023.11.04.23297979. [Epub ahead of print]

Autophagy gene expression in skeletal muscle of older individuals is associated with physical performance, muscle volume and mitochondrial function in the Study of Muscle, Mobility and Aging (SOMMA).

Paul M Coen, Zhiguang Huo, Gregory J Tranah, Haley N Barnes, Peggy M Cawthon, Russell T Hepple, Frederico G S Toledo, Daniel S Evans, Olaya Santiago Fernández, Ana Maria Cuervo, Steven B Kritchevsky, Anne B Newman, Steven R Cummings, Karyn A Esser.

Autophagy is an essential component of proteostasis and a key pathway in aging. Identifying associations between autophagy gene expression patterns in skeletal muscle and physical performance outcomes would further our knowledge of mechanisms related with proteostasis and healthy aging. Muscle biopsies were obtained from participants in the Study of Muscle, Mobility and Aging (SOMMA). For 575 participants, RNA was sequenced and expression of 281 genes related to autophagy regulation, mitophagy and mTOR/upstream pathways were determined. Associations between gene expression and outcomes including mitochondrial respiration in muscle fiber bundles (MAX OXPHOS), physical performance (VO 2 peak, 400m walking speed, and leg power), and thigh muscle volume were determined using negative binomial regression models. For autophagy, key transcriptional regulators including TFE3 and NFKB-related genes (RELA, RELB, NFKB1) were negatively associated with outcomes. On the contrary, regulators of oxidative metabolism that also promote overall autophagy, mitophagy and pexophagy (PPARGC1A, PPARA, EPAS1) were positively associated with multiple outcomes. In line with this, several mitophagy, fusion and fission related genes (NIPSNAP2, DNM1L, OPA1) were also positively associated with outcomes. For mTOR pathway and related genes, expression of WDR59 and WDR24, both subunits of GATOR2 complex (an indirect inhibitor of mTORC1) and PRKAG3, which is a regulatory subunit of AMPK, were negatively correlated with multiple outcomes. Our study identifies autophagy and selective autophagy such as mitophagy gene expression patterns in human skeletal muscle related to physical performance, muscle volume and mitochondrial function in older persons which may lead to target identification to preserve mobility and independence.

DOI: https://doi.org/10.1101/2023.11.04.23297979
Biochem Biophys Res Commun. 2023 Nov 10. pii: S0006-291X(23)01329-3. [Epub ahead of print]689 149235

Tanshinone IIA promotes the proliferation and differentiation ability of primary muscle stem cells via MAPK and Akt signaling.

Wenbin Liu, Tihui Wang, Wei Wang, Xingzuan Lin, Kailuo Xie.

  Salvia miltiorrhiza Bunge is a widely-used traditional Chinese medicine to treat a variety of diseases including muscle disorders. The underlying pharmacological mechanisms of which active component and how it functions are still unknown. Tanshinone IIA (Tan IIA) is the main active lipophilic compound in Salvia miltiorrhiza Bunge. Muscle stem cells (MuSCs) play a crucial role in maintaining healthy physiological function of skeletal muscle. For the purpose of this study, we investigated the effects of Tan IIA on primary MuSCs as well as mechanism. The EdU staining, cell counts assay and RT-qPCR results of proliferative genes revealed increased proliferation ability of MuSCs after Tan IIA treatment. Immunofluorescent staining of MyHC and RT-qPCR results of myogenic genes found Tan IIA contributed to promoting differentiation of MuSCs. In addition, enrichment analysis of RNA-seq data and Western blot assay results demonstrated activated MAPK and Akt signaling after treatment of Tan IIA during proliferation and differentiation. The above proliferative and differentiative phonotypes could be suppressed by the combination of MAPK inhibitor U0126 and Akt inhibitor Akti 1/2, respectively. Furthermore, HE staining found significantly improved myofiber regeneration of injured muscle after Tan IIA treatment, which also contributed to muscle force and running performance recovery. Thus, Tan IIA could promote proliferation and differentiation ability of MuSCs through activating MAPK and Akt signaling, respectively. These beneficial effects also significantly contributed to muscle regeneration and muscle function recovery after muscle injury.

Keywords:  Differentiation; Muscle injury; Muscle stem cells; Proliferation; Tanshinone IIA

DOI:  https://doi.org/10.1016/j.bbrc.2023.149235
bioRxiv. 2023 Oct 23. pii: 2023.10.19.563160. [Epub ahead of print]

Fast myosin binding protein C knockout in skeletal muscle alters length-dependent activation and myofilament structure.

Anthony L Hessel, Michel Kuehn, Seong-Won Han, Weikang Ma, Thomas C Irving, Brent A Momb, Taejeong Song, Sakthivel Sadayappan, Wolfgang A Linke, Bradley M Palmer.

In striated muscle, some sarcomere proteins regulate crossbridge cycling by varying the propensity of myosin heads to interact with actin. Myosin-binding protein C (MyBP-C) is bound to the myosin thick filament and is predicted to interact and stabilize myosin heads in a docked position against the thick filament and limit crossbridge formation, the so-called OFF state. Via an unknown mechanism, MyBP-C is thought to release heads into the so-called ON state, where they are more likely to form crossbridges. To study this proposed mechanism, we used the C2 -/- mouse line to knock down fast-isoform MyBP-C completely and total MyBP-C by ∼24%, and conducted mechanical functional studies in parallel with small-angle X-ray diffraction to evaluate the myofilament structure. We report that C2 -/- fibers presented deficits in force production and reduced calcium sensitivity. Structurally, passive C2 -/- fibers presented altered SL-independent and SL-dependent regulation of myosin head ON/OFF states, with a shift of myosin heads towards the ON state. Unexpectedly, at shorter sarcomere lengths, the thin filament was axially extended in C2 -/- vs. non-transgenic controls, which we postulate is due to increased low-level crossbridge formation arising from relatively more ON myosins in the passive muscle that elongates the thin filament. The downstream effect of increasing crossbridge formation in a passive muscle on contraction performance is not known. Such widespread structural changes to sarcomere proteins provide testable mechanisms to explain the etiology of debilitating MyBP-C-associated diseases.

DOI: https://doi.org/10.1101/2023.10.19.563160
Commun Biol. 2023 11 11. 6(1): 1148

Skeletal muscle cells opto-stimulation by intramembrane molecular transducers.

Ilaria Venturino, Vito Vurro, Silvio Bonfadini, Matteo Moschetta, Sara Perotto, Valentina Sesti, Luigino Criante, Chiara Bertarelli, Guglielmo Lanzani.

Optical stimulation and control of muscle cell contraction opens up a number of interesting applications in hybrid robotic and medicine. Here we show that recently designed molecular phototransducer can be used to stimulate C2C12 skeletal muscle cells, properly grown to exhibit collective behaviour. C2C12 is a skeletal muscle cell line that does not require animal sacrifice Furthermore, it is an ideal cell model for evaluating the phototransducer pacing ability due to its negligible spontaneous activity. We study the stimulation process and analyse the distribution of responses in multinuclear cells, in particular looking at the consistency between stimulus and contraction. Contractions are detected by using an imaging software for object recognition. We find a deterministic response to light stimuli, yet with a certain distribution of erratic behaviour that is quantified and correlated to light intensity or stimulation frequency. Finally, we compare our optical stimulation with electrical stimulation showing advantages of the optical approach, like the reduced cell stress.

DOI: https://doi.org/10.1038/s42003-023-05538-y
Can J Physiol Pharmacol. 2023 Nov 17.

Effects of sclerostin injection on soleus and extensor digitorum longus muscle tissue in male mice.

Joshua Stoikos, Nigel Kurgan, Steven Kottaras, Val A Fajardo, William Gittings, Panagiota Klentrou.

Sclerostin, a potent inhibitor of the Wnt signaling pathway, plays a critical role in bone homeostasis. Evidence suggests that sclerostin may also be involved in crosstalk between other tissues, including muscle. This pilot study attempted to examine the effects of sclerostin on soleus and extensor digitorum longus (EDL) muscle tissue from male mice that were given continuous recombinant sclerostin injections for four weeks. A total of 48 10-week-old male C57BL/6J mice were assigned to be sedentary or perform 1-hour treadmill running per day for 4 weeks and administered subcutaneous injections of either saline or recombinant sclerostin 5 days/week. Sclerostin injection led to a reduction in the soleus myosin heavy chain (MHC) I, MHC I/IIA, MHC IIA/X and MHC IIB cross-sectional area (p < 0.05) with no exercise effects on these reductions. In contrast, there were no effects of sclerostin injections or exercise in the fast-twitch EDL muscle in terms of size, MHC protein, or markers of Wnt signaling. These findings provide preliminary evidence of sclerostin's endocrine role in muscle via decreases in myofiber cross-sectional area, which seems to be independent of fiber type but muscle type-specific. More studies, however, are needed to confirm these preliminary results.

DOI: https://doi.org/10.1139/cjpp-2023-0268
Aging Cell. 2023 Nov 13. e14009

3D reconstruction of murine mitochondria reveals changes in structure during aging linked to the MICOS complex.

Zer Vue, Edgar Garza-Lopez, Kit Neikirk, Prasanna Katti, Larry Vang, Heather Beasley, Jianqiang Shao, Andrea G Marshall, Amber Crabtree, Alexandria C Murphy, Brenita C Jenkins, Praveena Prasad, Chantell Evans, Brittany Taylor, Margaret Mungai, Mason Killion, Dominique Stephens, Trace A Christensen, Jacob Lam, Benjamin Rodriguez, Mark A Phillips, Nastaran Daneshgar, Ho-Jin Koh, Alice Koh, Jamaine Davis, Nina Devine, Saleem Muhammod, Estevão Scudese, Kenneth Ryan Arnold, Valeria Vanessa Chavarin, Ryan Daniel Robinson, Moumita Chakraborty, Jennifer A Gaddy, Mariya T Sweetwyne, Genesis Wilson, Elma Zaganjor, James Kezos, Cristiana Dondi, Anilkumar K Reddy, Brian Glancy, Annet Kirabo, Anita M Quintana, Dao-Fu Dai, Karen Ocorr, Sandra A Murray, Steven M Damo, Vernat Exil, Blake Riggs, Bret C Mobley, Jose A Gomez, Melanie R McReynolds, Antentor Hinton.

  During aging, muscle gradually undergoes sarcopenia, the loss of function associated with loss of mass, strength, endurance, and oxidative capacity. However, the 3D structural alterations of mitochondria associated with aging in skeletal muscle and cardiac tissues are not well described. Although mitochondrial aging is associated with decreased mitochondrial capacity, the genes responsible for the morphological changes in mitochondria during aging are poorly characterized. We measured changes in mitochondrial morphology in aged murine gastrocnemius, soleus, and cardiac tissues using serial block-face scanning electron microscopy and 3D reconstructions. We also used reverse transcriptase-quantitative PCR, transmission electron microscopy quantification, Seahorse analysis, and metabolomics and lipidomics to measure changes in mitochondrial morphology and function after loss of mitochondria contact site and cristae organizing system (MICOS) complex genes, Chchd3, Chchd6, and Mitofilin. We identified significant changes in mitochondrial size in aged murine gastrocnemius, soleus, and cardiac tissues. We found that both age-related loss of the MICOS complex and knockouts of MICOS genes in mice altered mitochondrial morphology. Given the critical role of mitochondria in maintaining cellular metabolism, we characterized the metabolomes and lipidomes of young and aged mouse tissues, which showed profound alterations consistent with changes in membrane integrity, supporting our observations of age-related changes in muscle tissues. We found a relationship between changes in the MICOS complex and aging. Thus, it is important to understand the mechanisms that underlie the tissue-dependent 3D mitochondrial phenotypic changes that occur in aging and the evolutionary conservation of these mechanisms between Drosophila and mammals.

Keywords:   Drosophila ; 3D morphometry; MICOS; aging; mitochondria; mitochondrial disease; mitochondrion; reconstruction; reticulum; serial block-face SEM; skeletal muscle

DOI:  https://doi.org/10.1111/acel.14009
Free Radic Biol Med. 2023 Nov 15. pii: S0891-5849(23)01098-5. [Epub ahead of print]

Epigenetic and "redoxogenetic" adaptation to physical exercise.

Zsolt Radak, Lang Pan, Lei Zhou, Soroosh Mozaffaritabar, Yaodong Gu, Ricardo Pinho, Xu Zheng, Xueqing Ba, Istvan Boldogh.

  Exercise-induced adaptation is achieved by altering the epigenetic landscape of the entire genome leading to the expression of genes involved in various processes including regulatory, metabolic, adaptive, immune, and myogenic functions. Clinical and experimental data suggest that the methylation pattern/levels of promoter/enhancer is not linearly correlated with gene expression and proteome levels during physical activity implying a level of complexity and interplay with other regulatory modulators. It has been shown that a higher level of physical fitness is associated with a slower DNA methylation-based aging clock. There is strong evidence supporting exercise-induced ROS being a key regulatory mediator through overlapping events, both as signaling entities and through oxidative modifications to various protein mediators and DNA molecules. ROS generated by physical activity shapes epigenome both directly and indirectly, a complexity we are beginning to unravel within the epigenetic arrangement. Oxidative modification of guanine to 8-oxoguanine is a non-genotoxic alteration, does not distort DNA helix and serves as an epigenetic-like mark. The reader and eraser of oxidized guanine is the 8-oxoguanine DNA glycosylase 1, contributing to changes in gene expression. In fact, it can modulate methylation patterns of promoters/enhancers consequently leading to multiple phenotypic changes. Here, we provide evidence and discuss the potential roles of exercise-induced ROS in altering cytosine methylation patterns during muscle adaptation processes.

Keywords:  8-Oxoguanine DNA glycosylase 1; 8-oxoGua; Adaptation; Exercise; Methylation

DOI:  https://doi.org/10.1016/j.freeradbiomed.2023.11.005
J Nat Med. 2023 Nov 11.

Potential role of Akt in the regulation of fibroblast growth factor 21 by berberine.

Takao Hirai, Wei Wang, Naoko Murono, Kazuo Iwasa, Makoto Inoue.

  Fibroblast growth factor 21 (FGF21) is expressed in several organs, including the liver, adipose tissue, and cardiovascular system, and plays an important role in cross-talk with other organs by binding to specific FGF receptors and their co-receptors. FGF21 represents a potential target for the treatment of obesity, type 2 diabetes mellitus, and non-alcoholic steatohepatitis (NASH). The production of FGF21 in skeletal muscle was recently suggested to be beneficial for metabolic health through its autocrine and paracrine effects. However, the regulatory mechanisms of FGF21 in skeletal muscle remain unclear. In the present study, we showed that berberine regulated FGF21 production in C2C12 myotubes in a dose-dependent manner. We also examined the effects of A-674563, a selective Akt1 inhibitor, on the berberine-mediated regulation of FGF21 expression in C2C12 myotubes. Berberine significantly increased the secretion of FGF21 in C2C12 myotubes, while A-674563 attenuated this effect. Moreover, a pre-treatment with A-674563 effectively suppressed berberine-induced increases in Bmal1 expression in C2C12 myotubes, indicating that the up-regulation of Bmal1 after the berberine treatment was dependent on Akt1. Additionally, berberine-induced increases in FGF21 secretion were significantly attenuated in C2C12 cells transfected with Bmal1 siRNA, indicating the contribution of the core clock transcription factor BMAL1 to Akt-regulated FGF21 in response to berberine. Collectively, these results indicate that berberine regulates the expression of FGF21 through the Akt1 pathway in C2C12 myotubes. Moreover, the core clock gene Bmal1 may participate in the control of the myokine FGF21. Berberine stimulated Akt1-dependent FGF21 expression in C2C12 myotubes. The up-regulation of FGF21 through the modulation of PI3K/AKT1/BMAL1 in response to berberine may be involved in the regulation of cellular function (such as Glut1 expression) by acting in an autocrine and/or paracrine manner in skeletal muscle.

Keywords:  Akt; Berberine; Bmal1; FGF21; Skeletal muscle

DOI:  https://doi.org/10.1007/s11418-023-01755-1
Biochim Biophys Acta Mol Basis Dis. 2023 Nov 09. pii: S0925-4439(23)00309-5. [Epub ahead of print] 166943

LMNA-related muscular dystrophy involving myoblast proliferation and apoptosis through the FOXO1/GADD45A pathway.

Yue Wu, Xintong Zhu, Wen Jiang, Jia Li, Hongyan Li, Kun Zhang, Yixuan Yang, Song Qu, Xingying Guan, Yun Bai, Hong Guo, Limeng Dai.

  LMNA-related muscular dystrophy is a major disease phenotype causing mortality and morbidity in laminopathies, but its pathogenesis is still unclear. To explore the molecular pathogenesis, a knock-in mouse harbouring the Lmna-W520R mutation was modelled. Morphological and motor functional analyses showed that homozygous mutant mice revealed severe muscular atrophy, profound motor dysfunction, and shortened lifespan, while heterozygotes showed a variant arrangement of muscle bundles and mildly reduced motor capacity. Mechanistically, the FOXO1/GADD45A pathway involving muscle atrophy processes was found to be altered in vitro and in vivo assays. The expression levels of FOXO1 and its downstream regulatory molecule GADD45A significantly increased in atrophic muscle tissue. The elevated expression of FOXO1 was associated with decreased H3K27me3 in its gene promotor region. Overexpression of GADD45A induced apoptosis and cell cycle arrest of myoblasts in vitro, and it could be partially restored by the FOXO1 inhibitor AS1842856, which also slowed the muscle atrophy process with improved motor function and prolonged survival time of homozygous mutant mice in vivo. Notably, the inhibitor also partly rescued the apoptosis and cell cycle arrest of hiPSC-derived myoblasts harbouring the LMNA-W520R mutation. Together, these data suggest that the activation of the FOXO1/GADD45A pathway contributes to the pathogenesis of LMNA-related muscle atrophy, and it might serve as a potential therapeutic target for laminopathies.

Keywords:  FOXO1; GADD45A; LMNA-related muscular dystrophy; Laminopathies; iPSC-derived myoblasts

DOI:  https://doi.org/10.1016/j.bbadis.2023.166943
J Physiol. 2023 Nov 14.

Towards unravelling the exercise-induced adaptations in circulating extracellular vesicles.

Gül Turan, Loïs A J J Reijnders, Jelle C B C de Jong.



Keywords:  extracellular vesicles; organ crosstalk; training status

DOI:  https://doi.org/10.1113/JP285726