bims-moremu 2023-08-20 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023‒08‒20
thirty-two papers selected by
Anna Vainshtein
Craft Science Inc.

Fusion of myofibre branches is a physiological feature of healthy human skeletal muscle regeneration.
Muscle mitochondrial transplantation can rescue and maintain cellular homeostasis.
Autophagy and exercise: current insights and future research directions.
FAM210A mediates an inter-organelle crosstalk essential for protein synthesis and muscle growth in mouse.
Resistance exercise: a mighty tool that adapts, destroys, rebuilds and modulates the molecular and structural environment of skeletal muscle.
Spatial transcriptomics reveal markers of histopathological changes in Duchenne muscular dystrophy mouse models.
ATF3 induction prevents precocious activation of skeletal muscle stem cell by regulating H2B expression.
Urinary titin is not an early biomarker of skeletal muscle atrophy induced by muscle denervation in mice.
AAV-Mediated nuclear localized PGC1α4 delivery in muscle ameliorates sarcopenia and aging-associated metabolic dysfunctions.
NG2-positive pericytes regulate homeostatic maintenance of slow-type skeletal muscle with rapid myonuclear turnover.
SDF-1 and NOTCH signaling in myogenic cell differentiation: the role of miRNA10a, 425, and 5100.
Transcriptomic analysis of paired healthy human skeletal muscles to identify modulators of disease severity in DMD.
Proteolytic markers associated with a gain and loss of leg muscle mass with resistance training followed by high-intensity interval training.
Chemotherapy periodization to maximize resistance training adaptations in oncology.
Natural aging and ovariectomy induces parallel phosphoproteomic alterations in skeletal muscle of female mice.
Mass spectrometry-based multi-omics identifies metabolic signatures of sarcopenia in rhesus monkey skeletal muscle.
Cathepsin S activity controls chronic stress-induced muscle atrophy and dysfunction in mice.
Restoring adiponectin via rosiglitazone ameliorates tissue wasting in mice with lung cancer.
Muscle wasting: emerging pathways and potential drug targets.
Osteopontin May Improve Postinjury Muscle Repair Via Matrix Metalloproteinases And tgf-β Activation in Regular Exercise.
Exercise and fatigue: integrating the role of K+, Na+ and Cl- in the regulation of sarcolemmal excitability of skeletal muscle.
Comprehensive interrogation of human skeletal muscle reveals a dissociation between insulin resistance and mitochondrial capacity.
A TGF-β/KLF10 signaling axis regulates atrophy-associated genes to induce muscle wasting in pancreatic cancer.
miR-378 influences muscle satellite cells and enhances adipogenic potential of fibro-adipogenic progenitors but does not affect muscle regeneration in the glycerol-induced injury model.
Humanization of the mdx Mouse Phenotype for Duchenne Muscular Dystrophy Modeling: A Metabolic Perspective.
Impaired skeletal muscle health in Parkinsonian syndromes: clinical implications, mechanisms and potential treatments.
Endothelial ERα promotes glucose tolerance by enhancing endothelial insulin transport to skeletal muscle.
One Tissue, Many Models: Comprehensive Toolkit For Skeletal Muscle Studies.
Autophagy ablation in skeletal muscles worsens sepsis-induced muscle wasting, impairs whole-body metabolism, and decreases survival.
In vivo imaging of skeletal muscle form and function: 50 years of insight.
A novel splice variant of the human MSTN gene encodes a myostatin-specific myostatin inhibitor.
FIM: A fatigued-injured muscle model based on the sliding filament theory.

Skelet Muscle. 2023 Aug 12. 13(1): 13

Fusion of myofibre branches is a physiological feature of healthy human skeletal muscle regeneration.

Grith Højfeldt, Trent Sorenson, Alana Gonzales, Michael Kjaer, Jesper L Andersen, Abigail L Mackey.

  BACKGROUND: The occurrence of hyperplasia, through myofibre splitting, remains a widely debated phenomenon. Structural alterations and fibre typing of skeletal muscle fibres, as seen during regeneration and in certain muscle diseases, can be challenging to interpret. Neuromuscular electrical stimulation can induce myofibre necrosis followed by changes in spatial and temporal cellular processes. Thirty days following electrical stimulation, remnants of regeneration can be seen in the myofibre and its basement membrane as the presence of small myofibres and encroachment of sarcolemma and basement membrane (suggestive of myofibre branching/splitting). The purpose of this study was to investigate myofibre branching and fibre type in a systematic manner in human skeletal muscle undergoing adult regenerative myogenesis.METHODS: Electrical stimulation was used to induce myofibre necrosis to the vastus lateralis muscle of one leg in 5 young healthy males. Muscle tissue samples were collected from the stimulated leg 30 days later and from the control leg for comparison. Biopsies were sectioned and stained for dystrophin and laminin to label the sarcolemma and basement membrane, respectively, as well as ATPase, and antibodies against types I and II myosin, and embryonic and neonatal myosin. Myofibre branches were followed through 22 serial Sects. (264 μm). Single fibres and tissue blocks were examined by confocal and electron microscopy, respectively.
RESULTS: Regular branching of small myofibre segments was observed (median length 144 μm), most of which were observed to fuse further along the parent fibre. Central nuclei were frequently observed at the point of branching/fusion. The branch commonly presented with a more immature profile (nestin + , neonatal myosin + , disorganised myofilaments) than the parent myofibre, together suggesting fusion of the branch, rather than splitting. Of the 210 regenerating muscle fibres evaluated, 99.5% were type II fibres, indicating preferential damage to type II fibres with our protocol. Furthermore, these fibres demonstrated 7 different stages of "fibre-type" profiles.
CONCLUSIONS: By studying the regenerating tissue 30 days later with a range of microscopy techniques, we find that so-called myofibre branching or splitting is more likely to be fusion of myotubes and is therefore explained by incomplete regeneration after a necrosis-inducing event.

Keywords:  Electrical stimulation; Muscle fibre branching; Muscle fibre splitting; Muscle fibre typing; Muscle injury; Muscle regeneration

DOI:  https://doi.org/10.1186/s13395-023-00322-2
Am J Physiol Cell Physiol. 2023 Aug 14.

Muscle mitochondrial transplantation can rescue and maintain cellular homeostasis.

Debasmita Bhattacharya, Mikhaela B Slavin, David A Hood.

  Mitochondria control cellular functions through their metabolic role. Recent research that has gained considerable attention is their ability to transfer between cells. This has the potential of improving cellular functions in pathological or energy deficit conditions, but little is known about the role of mitochondrial transfer in sustaining cellular homeostasis. Few studies have investigated the potential of skeletal muscle as a source of healthy mitochondria that can be transferred to other cell types. Thus, we isolated intermyofibrillar mitochondria from murine skeletal muscle and incubated them with host cells. We observed dose- and time-dependent increases in mitochondrial incorporation into myoblasts. This resulted in elongated mitochondrial networks and an enhancement of bioenergetic profile of the host cells. Mitochondrial donation also rejuvenated the functional capacities of the myoblasts when respiration efficiency and lysosomal function were inhibited by complex I inhibitor rotenone and bafilomycin A, respectively. Mitochondrial transfer was accomplished via tunneling nanotubes, extracellular vesicles, gap junctions and by macropinocytosis internalization. Murine muscle mitochondria were also effectively transferred to human fibroblast cells having mitochondrial DNA mutations, resulting in augmented mitochondrial dynamics and metabolic functions. This improved cell function by diminishing ROS emission in the diseased cells. Our findings suggest that mitochondria from donor skeletal muscle can be integrated in both healthy and functionally compromised host cells leading to mitochondrial structural refinement and respiratory boost. This mitochondrial trafficking and bioenergetic reprogramming to maintain and revitalise tissue homeostasis could be a useful therapeutic strategy in treating diseases.

Keywords:  Lysosome; Mitochondrial DNA Defects; Mitochondrial Dynamics; Mitochondrial Transplantation; Oxygen Consumption

DOI:  https://doi.org/10.1152/ajpcell.00212.2023
Int J Sports Med. 2023 Aug 15.

Autophagy and exercise: current insights and future research directions.

Javier Botella, Chris Shaw, David Bishop.

Autophagy is a cellular process by which proteins and organelles are degraded inside the lysosome. Exercise is known to influence the regulation of autophagy in skeletal muscle. However, as gold standard techniques to assess autophagy flux in vivo are restricted to animal research, important gaps remain in our understanding of how exercise influences autophagy activity in humans. Using available datasets, we show how the gene expression profile of autophagy receptors and ATG8 family members differ between human and mouse skeletal muscle, providing a potential explanation for their differing exercise-induced autophagy responses. Furthermore, we provide a comprehensive view of autophagy regulation following exercise in humans by summarising human transcriptomic and phosphoproteomic datasets that provide novel targets of potential relevance. These newly identified phosphorylation sites may provide an explanation as to why both endurance and resistance exercise lead to an exercise-induced reduction in LC3B-II, while possibly divergently regulating autophagy receptors, and, potentially, autophagy flux. We also provide recommendations to use ex vivo autophagy flux assays to better understand the influence of exercise, and other stimuli, on autophagy regulation in humans. This review provides a critical overview of the field and points towards novel research areas of autophagy regulation following exercise in humans.

DOI: https://doi.org/10.1055/a-2153-9258
bioRxiv. 2023 Aug 05. pii: 2023.08.03.551853. [Epub ahead of print]

FAM210A mediates an inter-organelle crosstalk essential for protein synthesis and muscle growth in mouse.

Jingjuan Chen, Feng Yue, Kun Ho Kim, Peipei Zhu, Jiamin Qiu, W Andy Tao, Shihuan Kuang.

Mitochondria are not only essential for energy production in eukaryocytes but also a key regulator of intracellular signaling. Here, we report an unappreciated role of mitochondria in regulating cytosolic protein translation in skeletal muscle cells (myofibers). We show that the expression of mitochondrial protein FAM210A (Family With Sequence Similarity 210 Member A) is positively associated with muscle mass in mice and humans. Muscle-specific Myl1 Cre -driven Fam210a knockout ( Fam210a MKO ) in mice reduces mitochondrial density and function, leading to progressive muscle atrophy and premature death. Metabolomic and biochemical analyses reveal that Fam210a MKO reverses the oxidative TCA cycle towards the reductive direction, resulting in acetyl-CoA accumulation and hyperacetylation of cytosolic proteins. Specifically, hyperacetylation of several ribosomal proteins leads to disassembly of ribosomes and translational defects. Transplantation of Fam210a MKO mitochondria into wildtype myoblasts is sufficient to elevate protein acetylation in recipient cells. These findings reveal a novel crosstalk between the mitochondrion and ribosome mediated by FAM210A.

DOI: https://doi.org/10.1101/2023.08.03.551853
Phys Act Nutr. 2023 Jun;27(2): 78-95

Resistance exercise: a mighty tool that adapts, destroys, rebuilds and modulates the molecular and structural environment of skeletal muscle.

Käthe Bersiner, So-Young Park, Kirill Schaaf, Woo-Hwi Yang, Christian Theis, Daniel Jacko, Sebastian Gehlert.

  PURPOSE: Skeletal muscle regulates health and performance by maintaining or increasing strength and muscle mass. Although the molecular mechanisms in response to resistance exercise (RE) significantly target the activation of protein synthesis, a plethora of other mechanisms and structures must be involved in orchestrating the communication, repair, and restoration of homeostasis after RE stimulation. In practice, RE can be modulated by variations in intensity, continuity and volume, which affect molecular responses and skeletal muscle adaptation. Knowledge of these aspects is important with respect to planning of training programs and assessing the impact of RE training on skeletal muscle.METHODS: In this narrative review, we introduce general aspects of skeletal muscle substructures that adapt in response to RE. We further highlighted the molecular mechanisms that control human skeletal muscle anabolism, degradation, repair and memory in response to acute and repeated RE and linked these aspects to major training variables.
RESULTS: Although RE is a key stimulus for the activation of skeletal muscle anabolism, it also induces myofibrillar damage. Nevertheless, to increase muscle mass accompanied by a corresponding adaptation of the essential substructures of the sarcomeric environment, RE must be continuously repeated. This requires the permanent engagement of molecular mechanisms that re-establish skeletal muscle integrity after each RE-induced muscle damage.
CONCLUSION: Various molecular regulators coordinately control the adaptation of skeletal muscle after acute and repeated RE and expand their actions far beyond muscle growth. Variations of key resistance training variables likely affect these mechanisms without affecting muscle growth.

Keywords:  adaptation; hypertrophy; mTOR signaling; muscle damage; proteostasis; resistance exercise; skeletal muscle

DOI:  https://doi.org/10.20463/pan.2023.0021
Nat Commun. 2023 Aug 15. 14(1): 4909

Spatial transcriptomics reveal markers of histopathological changes in Duchenne muscular dystrophy mouse models.

L G M Heezen, T Abdelaal, M van Putten, A Aartsma-Rus, A Mahfouz, P Spitali.

Duchenne muscular dystrophy is caused by mutations in the DMD gene, leading to lack of dystrophin. Chronic muscle damage eventually leads to histological alterations in skeletal muscles. The identification of genes and cell types driving tissue remodeling is a key step to developing effective therapies. Here we use spatial transcriptomics in two Duchenne muscular dystrophy mouse models differing in disease severity to identify gene expression signatures underlying skeletal muscle pathology and to directly link gene expression to muscle histology. We perform deconvolution analysis to identify cell types contributing to histological alterations. We show increased expression of specific genes in areas of muscle regeneration (Myl4, Sparc, Hspg2), fibrosis (Vim, Fn1, Thbs4) and calcification (Bgn, Ctsk, Spp1). These findings are confirmed by smFISH. Finally, we use differentiation dynamic analysis in the D2-mdx muscle to identify muscle fibers in the present state that are predicted to become affected in the future state.

DOI: https://doi.org/10.1038/s41467-023-40555-9
Nat Commun. 2023 Aug 17. 14(1): 4978

ATF3 induction prevents precocious activation of skeletal muscle stem cell by regulating H2B expression.

Suyang Zhang, Feng Yang, Yile Huang, Liangqiang He, Yuying Li, Yi Ching Esther Wan, Yingzhe Ding, Kui Ming Chan, Ting Xie, Hao Sun, Huating Wang.

Skeletal muscle stem cells (also called satellite cells, SCs) are important for maintaining muscle tissue homeostasis and damage-induced regeneration. However, it remains poorly understood how SCs enter cell cycle to become activated upon injury. Here we report that AP-1 family member ATF3 (Activating Transcription Factor 3) prevents SC premature activation. Atf3 is rapidly and transiently induced in SCs upon activation. Short-term deletion of Atf3 in SCs accelerates acute injury-induced regeneration, however, its long-term deletion exhausts the SC pool and thus impairs muscle regeneration. The Atf3 loss also provokes SC activation during voluntary exercise and enhances the activation during endurance exercise. Mechanistically, ATF3 directly activates the transcription of Histone 2B genes, whose reduction accelerates nucleosome displacement and gene transcription required for SC activation. Finally, the ATF3-dependent H2B expression also prevents genome instability and replicative senescence in SCs. Therefore, this study has revealed a previously unknown mechanism for preserving the SC population by actively suppressing precocious activation, in which ATF3 is a key regulator.

DOI: https://doi.org/10.1038/s41467-023-40465-w
PLoS One. 2023 ;18(8): e0289185

Urinary titin is not an early biomarker of skeletal muscle atrophy induced by muscle denervation in mice.

Jun Tanihata, Susumu Minamisawa.

Early detection of skeletal muscle atrophy is important to prevent further muscle weakness. However, there are few non-invasive biomarkers for skeletal muscle atrophy. Recent studies have reported that the N-terminal fragment (N-titin) of titin, a giant sarcomeric protein, is detected in the urine of patients with muscle damage. In this study, we hypothesized that urinary N-titin would be a potential early biomarker of skeletal muscle atrophy in mice caused by sciatic nerve denervation. Male mice were randomly divided into control and denervation groups, and urinary N-titin levels were assessed daily for 9 days using an enzyme-linked immunosorbent assay system. Despite reduced titin protein levels in atrophic muscles 10 days after denervation, cleaved N-titin fragments were not increased in the urine of mice with denervation-induced muscle atrophy. Furthermore, we found no uptake of Evans blue dye from the extracellular space into the cytoplasm in atrophic muscles, suggesting that the sarcomeric membrane is intact in those muscles. The present results suggest that cleaved N-titin in the urine is not suitable as an early biomarker of skeletal muscle atrophy.

DOI: https://doi.org/10.1371/journal.pone.0289185
Aging Cell. 2023 Aug 16. e13961

AAV-Mediated nuclear localized PGC1α4 delivery in muscle ameliorates sarcopenia and aging-associated metabolic dysfunctions.

Mingwei Guo, Jun Zhang, Ying Ma, Zhenzhong Zhu, Hui Zuo, Jing Yao, Xia Wu, Dongmei Wang, Jian Yu, Meiyao Meng, Caizhi Liu, Yi Zhang, Jiangrong Chen, Jian Lu, Shuzhe Ding, Cheng Hu, Xinran Ma, Lingyan Xu.

  Sarcopenia is characterized of muscle mass loss and functional decline in elder individuals which severely affects human physical activity, metabolic homeostasis, and life quality. Physical exercise is considered effective in combating muscle atrophy and sarcopenia, yet it is not feasible to elders with limited mobility. PGC-1α4, a short isoform of PGC-1α, is strongly induced in muscle under resistance training, and promotes muscle hypertrophy. In the present study, we showed that the transcriptional levels and nuclear localization of PGC1α4 was reduced during aging, accompanied with muscle dystrophic morphology, and gene programs. We thus designed NLS-PGC1α4 and ectopically express it in myotubes to enhance PGC1α4 levels and maintain its location in nucleus. Indeed, NLS-PGC1α4 overexpression increased muscle sizes in myotubes. In addition, by utilizing AAV-NLS-PGC1α4 delivery into gastrocnemius muscle, we found that it could improve sarcopenia with grip strength, muscle weights, fiber size and molecular phenotypes, and alleviate age-associated adiposity, insulin resistance and hepatic steatosis, accompanied with altered gene signatures. Mechanistically, we demonstrated that NLS-PGC-1α4 improved insulin signaling and enhanced glucose uptake in skeletal muscle. Besides, via RNA-seq analysis, we identified myokines IGF1 and METRNL as potential targets of NLS-PGC-1α4 that possibly mediate the improvement of muscle and adipose tissue functionality and systemic energy metabolism in aged mice. Moreover, we found a negative correlation between PGC1α4 and age in human skeletal muscle. Together, our results revealed that NLS-PGC1α4 overexpression improves muscle physiology and systematic energy homeostasis during aging and suggested it as a potent therapeutic strategy against sarcopenia and aging-associated metabolic diseases.

Keywords:  PGC1α4; aging; metabolic dysfunctions; nuclear localization; sarcopenia

DOI:  https://doi.org/10.1111/acel.13961
Stem Cell Res Ther. 2023 Aug 17. 14(1): 205

NG2-positive pericytes regulate homeostatic maintenance of slow-type skeletal muscle with rapid myonuclear turnover.

Takamitsu Tatsukawa, Kohei Kano, Kei-Ichi Nakajima, Takashi Yazawa, Ryoji Eguchi, Maki Kabara, Kiwamu Horiuchi, Taiki Hayasaka, Risa Matsuo, Naoyuki Hasebe, Nobuyoshi Azuma, Jun-Ichi Kawabe.

  BACKGROUND: Skeletal muscle comprises almost 40% of the human body and is essential for movement, structural support and metabolic homeostasis. Size of multinuclear skeletal muscle is stably maintained under steady conditions with the sporadic fusion of newly produced myocytes to compensate for the muscular turnover caused by daily wear and tear. It is becoming clear that microvascular pericytes (PCs) exhibit myogenic activity. However, whether PCs act as myogenic stem cells for the homeostatic maintenance of skeletal muscles during adulthood remains uncertain.METHODS: We utilized PC-fused myofibers using PC-specific lineage tracing mouse (NG2-CreERT/Rosa-tdTomato) to observe whether muscle resident PCs have myogenic potential during daily life. Genetic PC deletion mouse model (NG2-CreERT/DTA) was used to test whether PC differentiates to myofibers for maintenance of muscle structure and function under homeostatic condition.
RESULTS: Under steady breeding conditions, tdTomato-expressing PCs were infused into myofibers, and subsequently, PC-derived nuclei were incorporated into myofibers. Especially in type-I slow-type myofibers such as the soleus, tdTomato+ myofibers were already observed 3 days after PC labeling; their ratio reached a peak (approximately 80%) within 1 month and was maintained for more than 1 year. Consistently, the NG2+ PC-specific deletion induced muscular atrophy in a slow-type myofiber-specific manner under steady breeding conditions. The number of myonucleus per volume of each myofiber was constant during observation period.
CONCLUSIONS: These findings demonstrate that the turnover of myonuclei in slow-type myofibers is relatively fast, with PCs acting as myogenic stem cells-the suppliers of new myonuclei under steady conditions-and play a vital role in the homeostatic maintenance of slow-type muscles.

Keywords:  Myogenesis; Pericytes; Skeletal muscle; Slow-type muscle; Stem cells

DOI:  https://doi.org/10.1186/s13287-023-03433-1
Stem Cell Res Ther. 2023 08 15. 14(1): 204

SDF-1 and NOTCH signaling in myogenic cell differentiation: the role of miRNA10a, 425, and 5100.

Bartosz Mierzejewski, Iwona Grabowska, Zuzanna Michalska, Kamila Zdunczyk, Franciszek Zareba, Aliksandra Irhashava, Marta Chrzaszcz, Magdalena Patrycy, Wladyslawa Streminska, Katarzyna Janczyk-Ilach, Marta Koblowska, Roksana Iwanicka-Nowicka, Agnieszka Gromadka, Kamil Kowalski, Maria Anna Ciemerych, Edyta Brzoska.

  BACKGROUND: Skeletal muscle regeneration is a complex process regulated by many cytokines and growth factors. Among the important signaling pathways regulating the myogenic cell identity are these involving SDF-1 and NOTCH. SDF-1 participates in cell mobilization and acts as an important chemoattractant. NOTCH, on the other hand, controls cell activation and myogenic determination of satellite cells. Knowledge about the interaction between SDF-1 and NOTCH signaling is limited.METHODS: We analyzed two populations of myogenic cells isolated from mouse skeletal muscle, that is, myoblasts derived from satellite cells (SCs) and muscle interstitial progenitor cells (MIPCs). First, microRNA level changes in response to SDF-1 treatment were analyzed with next-generation sequencing (NGS). Second, myogenic cells, i.e., SC-derived myoblasts and MIPCs were transfected with miRNA mimics, selected on the basis of NGS results, or their inhibitors. Transcriptional changes, as well as proliferation, migration, and differentiation abilities of SC-derived myoblasts and MIPCs, were analyzed in vitro. Naive myogenic potential was assessed in vivo, using subcutaneous engrafts and analysis of cell contribution to regeneration of the skeletal muscles.
RESULTS: SDF-1 treatment led to down-regulation of miR10a, miR151, miR425, and miR5100 in myoblasts. Interestingly, miR10a, miR425, and miR5100 regulated the expression of factors involved in the NOTCH signaling pathway, including Dll1, Jag2, and NICD. Furthermore, miR10a, miR425, and miR5100 down-regulated the expression of factors involved in cell migration: Acta1, MMP12, and FAK, myogenic differentiation: Pax7, Myf5, Myod, Mef2c, Myog, Musk, and Myh3. However, these changes did not significantly affect myogenic cell migration or fusion either in vitro or in vivo, except when miR425 was overexpressed, or miR5100 inhibitor was used. These two molecules increased the fusion of MIPCs and myoblasts, respectively. Furthermore, miR425-transfected MIPC transplantation into injured skeletal muscle resulted in more efficient regeneration, compared to control cell transplantation. However, skeletal muscles that were injected with miR10a transfected myoblasts regenerated less efficiently.
CONCLUSIONS: SDF-1 down-regulates miR10a, miR425, and miR5100, what could affect NOTCH signaling, differentiation of myogenic cells, and their participation in skeletal muscle regeneration.

Keywords:  Differentiation; Interstitial cells; Mouse; Satellite cells; Skeletal muscle regeneration; miR151; miRNA10a; miRNA425; miRNA5010

DOI:  https://doi.org/10.1186/s13287-023-03429-x
Front Genet. 2023 ;14 1216066

Transcriptomic analysis of paired healthy human skeletal muscles to identify modulators of disease severity in DMD.

Shirley Nieves-Rodriguez, Florian Barthélémy, Jeremy D Woods, Emilie D Douine, Richard T Wang, Deirdre D Scripture-Adams, Kevin N Chesmore, Francesca Galasso, M Carrie Miceli, Stanley F Nelson.

  Muscle damage and fibro-fatty replacement of skeletal muscles is a main pathologic feature of Duchenne muscular dystrophy (DMD) with more proximal muscles affected earlier and more distal affected later in the disease course, suggesting that different skeletal muscle groups possess distinctive characteristics that influence their susceptibility to disease. To explore transcriptomic factors driving differential gene expression and modulating DMD skeletal muscle severity, we characterized the transcriptome of vastus lateralis (VL), a more proximal and susceptible muscle, relative to tibialis anterior (TA), a more distal and protected muscle, in 15 healthy individuals using bulk RNA sequencing to identify gene expression differences that may mediate their relative susceptibility to damage with loss of dystrophin. Matching single nuclei RNA sequencing data was generated for 3 of the healthy individuals, to infer cell composition in the bulk RNA sequencing dataset and to improve mapping of differentially expressed genes to their cell source of expression. A total of 3,410 differentially expressed genes were identified and mapped to cell type using single nuclei RNA sequencing of muscle, including long non-coding RNAs and protein coding genes. There was an enrichment of genes involved in calcium release from the sarcoplasmic reticulum, particularly in the myofibers and these myofiber genes were higher in the VL. There was an enrichment of genes in "Collagen-Containing Extracellular Matrix" expressed by fibroblasts, endothelial, smooth muscle and pericytes, with most genes higher in the TA, as well as genes in "Regulation Of Apoptotic Process" expressed across all cell types. Previously reported genetic modifiers were also enriched within the differentially expressed genes. We also identify 6 genes with differential isoform usage between the VL and TA. Lastly, we integrate our findings with DMD RNA sequencing data from the TA, and identify "Collagen-Containing Extracellular Matrix" and "Negative Regulation Of Apoptotic Process" as differentially expressed between DMD compared to healthy. Collectively, these findings propose novel candidate mechanisms that may mediate differential muscle susceptibility in muscular dystrophies and provide new insight into potential therapeutic targets.

Keywords:  DMD; gene expression; muscle; muscle susceptibility; single nuclei RNAseq; transcriptomics

DOI:  https://doi.org/10.3389/fgene.2023.1216066
Exp Physiol. 2023 Aug 17.

Proteolytic markers associated with a gain and loss of leg muscle mass with resistance training followed by high-intensity interval training.

J Max Michel, Joshua S Godwin, Daniel L Plotkin, Paulo H C Mesquita, Mason C McIntosh, Bradley A Ruple, Cleiton A Libardi, C Brooks Mobley, Andreas N Kavazis, Michael D Roberts.

  We recently reported that vastus lateralis (VL) cross-sectional area (CSA) increases after 7 weeks of resistance training (RT, 2 days/week), with declines occurring following 7 weeks of subsequent treadmill high-intensity interval training (HIIT) (3 days/week). Herein, we examined the effects of this training paradigm on skeletal muscle proteolytic markers. VL biopsies were obtained from 11 untrained college-aged males at baseline (PRE), after 7 weeks of RT (MID), and after 7 weeks of HIIT (POST). Tissues were analysed for proteolysis markers, and in vitro experiments were performed to provide additional insights. Atrogene mRNAs (TRIM63, FBXO32, FOXO3A) were upregulated at POST versus both PRE and MID (P < 0.05). 20S proteasome core protein abundance increased at POST versus PRE (P = 0.031) and MID (P = 0.049). 20S proteasome activity, and protein levels for calpain-2 and Beclin-1 increased at MID and POST versus PRE (P < 0.05). Ubiquitinated proteins showed model significance (P = 0.019) with non-significant increases at MID and POST (P > 0.05). in vitro experiments recapitulated the training phenotype when stimulated with a hypertrophic stimulus (insulin-like growth factor 1; IGF1) followed by a subsequent AMP-activated protein kinase activator (5-aminoimidazole-4-carboxamide ribonucleotide; AICAR), as demonstrated by larger myotube diameter in IGF1-treated cells versus IGF1 followed by AICAR treatments (I+A; P = 0.017). Muscle protein synthesis (MPS) levels were also greater in IGF1-treated versus I+A myotubes (P < 0.001). In summary, the loss in RT-induced VL CSA with HIIT coincided with increases in several proteolytic markers, and sustained proteolysis may have driven this response. Moreover, while not measured in humans, we interpret our in vitro data to suggest that (unlike RT) HIIT does not stimulate MPS. NEW FINDINGS: What is the central question of this study? Determining if HIIT-induced reductions in muscle hypertrophy following a period of resistance training coincided with increases in proteolytic markers. What is the main finding and its importance? Several proteolytic markers were elevated during the HIIT training period implying that increases in muscle proteolysis may have played a role in HIIT-induced reductions in muscle hypertrophy.

Keywords:  autophagy; calpains; proteolysis; skeletal muscle; ubiquitin

DOI:  https://doi.org/10.1113/EP091286
Cancer Chemother Pharmacol. 2023 Aug 15.

Chemotherapy periodization to maximize resistance training adaptations in oncology.

Jonathan H C Nunes, Paola S Cella, Tatiana A S Guimarães, Icaro P Buçu, Rafael Deminice.

  INTRODUCTION: Engaging in exercise programs during cancer treatment is challenging due to the several chemotherapy-induced side effects. Using a pre-clinical model that mimics chemotherapy treatment, we investigated if a periodized-within-chemotherapy training strategy can maximize resistance training (RT) adaptations such as increasing muscle mass and strength.METHODS: Swiss mice were randomly allocated into one of the following five groups (n = 14): control (C), resistance training (RT), chemotherapy-treated non-exercised group (Ch), resistance training chemotherapy treated (RTCh), and resistance training periodized-within-chemotherapy (RTPCh). Doxorubicin (i.p.) was weekly injected for a total of 3 weeks (total dose of 12 mg/kg). Resistance training consisted of ladder climbing with progressive intensity, three times a week for 3 weeks, during chemotherapy treatment. RTPCh prescriptions considered "bad day" adjustments while RTCh did not. "Bad day" adjustments considered the presence or absence of clinical signs (e.g., severe weight loss, diarrhea, mice refusing to train) to replace RT sessions. At the end of the third week, animals were euthanized.
RESULTS: Weekly doxorubicin injection promoted progressive body weight loss, muscle atrophy, strength loss, local oxidative stress, and elevated inflammatory mediators, such as TNF-α and IL-6. Non-periodized-within-chemotherapy RT promoted mild protection against doxorubicin-induced skeletal muscle disturbances; moreover, when periodized-within-chemotherapy was applied, RT prevented elevated skeletal muscle inflammatory mediators and oxidative damage markers and promoted muscle mass and strength gains.
CONCLUSION: Considering chemotherapy-induced side effects is a crucial aspect when prescribing resistance exercise during cancer, it will maximize the effectiveness of exercise in enhancing muscle mass and strength.

Keywords:  Bad-day adjustment; Muscle mass; Oxidative stress; Strength training

DOI:  https://doi.org/10.1007/s00280-023-04576-x
Aging (Albany NY). 2023 Aug 14. undefined

Natural aging and ovariectomy induces parallel phosphoproteomic alterations in skeletal muscle of female mice.

Mina P Peyton, Tzu-Yi Yang, LeeAnn Higgins, Todd W Markowski, Kevin Murray, Cha Vue, Laurie L Parker, Dawn A Lowe.

  The loss of skeletal muscle strength mid-life in females is associated with the decline of estrogen. Here, we questioned how estrogen deficiency might impact the overall skeletal muscle phosphoproteome after contraction, as force production induces phosphorylation of several muscle proteins. Phosphoproteomic analyses of the tibialis anterior muscle after contraction in two mouse models of estrogen deficiency, ovariectomy (Ovariectomized (Ovx) vs. Sham) and natural aging-induced ovarian senescence (Older Adult (OA) vs. Young Adult (YA)), identified a total of 2,593 and 3,507 phosphopeptides in Ovx/Sham and OA/YA datasets, respectively. Further analysis of estrogen deficiency-associated proteins and phosphosites identified 66 proteins and 21 phosphosites from both datasets. Of these, 4 estrogen deficiency-associated proteins and 4 estrogen deficiency-associated phosphosites were significant and differentially phosphorylated or regulated, respectively. Comparative analyses between Ovx/Sham and OA/YA using Ingenuity Pathway Analysis (IPA) found parallel patterns of inhibition and activation across IPA-defined canonical signaling pathways and physiological functional analysis, which were similarly observed in downstream GO, KEGG, and Reactome pathway overrepresentation analysis pertaining to muscle structural integrity and contraction, including AMPK and calcium signaling. IPA Upstream regulator analysis identified MAPK1 and PRKACA as candidate kinases and calcineurin as a candidate phosphatase sensitive to estrogen. Our findings highlight key molecular signatures and pathways in contracted muscle suggesting that the similarities identified across both datasets could elucidate molecular mechanisms that may contribute to skeletal muscle strength loss due to estrogen deficiency.

Keywords:  CAST; MAPK; PKA; calcineurin; estrogen deficiency

DOI:  https://doi.org/10.18632/aging.204959
bioRxiv. 2023 Jul 31. pii: 2023.07.31.551315. [Epub ahead of print]

Mass spectrometry-based multi-omics identifies metabolic signatures of sarcopenia in rhesus monkey skeletal muscle.

Melissa R Pergande, Katie J Osterbauer, Kevin M Buck, David S Roberts, Nina N Wood, Priya Balasubramanian, Morgan W Mann, Kalina Rossler, Gary M Diffee, Ricki J Colman, Rozalyn M Anderson, Ying Ge.

Sarcopenia is a progressive disorder characterized by age-related loss of skeletal muscle mass and function. Although significant progress has been made over the years to identify the molecular determinants of sarcopenia, the precise mechanisms underlying the age-related loss of contractile function remains unclear. Advances in omics technologies, including mass spectrometry-based proteomic and metabolomic analyses, offer great opportunities to better understand sarcopenia. Herein, we performed mass spectrometry-based analyses of the vastus lateralis from young, middle-aged, and older rhesus monkeys to identify molecular signatures of sarcopenia. In our proteomic analysis, we identified numerous proteins that change with age, including those involved in adenosine triphosphate and adenosine monophosphate metabolism as well as fatty acid beta oxidation. In our untargeted metabolomic analysis, we identified multiple metabolites that changed with age largely related to energy metabolism including fatty acid beta oxidation. Pathway analysis of age-responsive proteins and metabolites revealed changes in muscle structure and contraction as well as lipid, carbohydrate, and purine metabolism. Together, this study discovers new metabolic signatures and offer new insights into the molecular mechanism underlying sarcopenia for the evaluation and monitoring of therapeutic treatment of sarcopenia.

DOI: https://doi.org/10.1101/2023.07.31.551315
Cell Mol Life Sci. 2023 Aug 17. 80(9): 254

Cathepsin S activity controls chronic stress-induced muscle atrophy and dysfunction in mice.

Ying Wan, Limei Piao, Shengnan Xu, Xiangkun Meng, Zhe Huang, Aiko Inoue, Hailong Wang, Xueling Yue, Xueying Jin, Yongshan Nan, Guo-Ping Shi, Toyoaki Murohara, Hiroyuki Umegaki, Masafumi Kuzuya, Xian Wu Cheng.

  Exposure to chronic psychological stress (CPS) is an intractable risk factor for inflammatory and metabolic diseases. Lysosomal cysteinyl cathepsins play an important role in human pathobiology. Given that cathepsin S (CTSS) is upregulated in the stressed vascular and adipose tissues, we investigated whether CTSS participates in chronic stress-induced skeletal muscle mass loss and dysfunction, with a special focus on muscle protein metabolic imbalance and apoptosis. Eight-week-old male wildtype (CTSS+/+) and CTSS-knockout (CTSS-/-) mice were randomly assigned to non-stress and variable-stress groups. CTSS+/+ stressed mice showed significant losses of muscle mass, dysfunction, and fiber area, plus significant mitochondrial damage. In this setting, stressed muscle in CTSS+/+ mice presented harmful alterations in the levels of insulin receptor substrate 2 protein content (IRS-2), phospho-phosphatidylinositol 3-kinase, phospho-protein kinase B, and phospho-mammalian target of rapamycin, forkhead box-1, muscle RING-finger protein-1 protein, mitochondrial biogenesis-related peroxisome proliferator-activated receptor-γ coactivator-α, and apoptosis-related B-cell lymphoma 2 and cleaved caspase-3; these alterations were prevented by CTSS deletion. Pharmacological CTSS inhibition mimics its genetic deficiency-mediated muscle benefits. In C2C12 cells, CTSS silencing prevented stressed serum- and oxidative stress-induced IRS-2 protein reduction, loss of the myotube myosin heavy chain content, and apoptosis accompanied by a rectification of investigated molecular harmful changes; these changes were accelerated by CTSS overexpression. These findings demonstrated that CTSS plays a role in IRS-2-related protein anabolism and catabolism and cell apoptosis in stress-induced muscle wasting, suggesting a novel therapeutic strategy for the control of chronic stress-related muscle disease in mice under our experimental conditions by regulating CTSS activity.

Keywords:  Apoptosis; Catabolism; Cathepsin S; Chronic stress; Skeletal muscle injury

DOI:  https://doi.org/10.1007/s00018-023-04888-4
bioRxiv. 2023 Aug 02. pii: 2023.07.31.551241. [Epub ahead of print]

Restoring adiponectin via rosiglitazone ameliorates tissue wasting in mice with lung cancer.

Henning Tim Langer, Shakti Ramsamooj, Ezequiel Dantas, Anirudh Murthy, Mujmmail Ahmed, Seo-Kyoung Hwang, Rahul Grover, Rita Pozovskiy, Roger J Liang, Andre Lima Queiroz, Justin C Brown, Eileen P White, Tobias Janowitz, Marcus D Goncalves.

The cancer associated cachexia syndrome (CACS) is a systemic metabolic disorder resulting in loss of body weight due to skeletal muscle and adipose tissues atrophy. CACS is particularly prominent in lung cancer patients, where it contributes to poor quality of life and excess mortality. Using the Kras/Lkb1 (KL) mouse model, we found that CACS is associated with white adipose tissue (WAT) dysfunction that directly affects skeletal muscle homeostasis. WAT transcriptomes showed evidence of reduced adipogenesis, and, in agreement, we found low levels of circulating adiponectin. To preserve adipogenesis and restore adiponectin levels, we treated mice with the PPAR-γ agonist, rosiglitazone. Rosiglitazone treatment increased serum adiponectin levels, delayed weight loss, and preserved skeletal muscle and adipose tissue mass, as compared to vehicle-treated mice. The preservation of muscle mass with rosiglitazone was associated with increases in AMPK and AKT activity. Similarly, activation of the adiponectin receptors in muscle cells increased AMPK activity, anabolic signaling, and protein synthesis. Our data suggest that PPAR-γ agonists may be a useful adjuvant therapy to preserve tissue mass in lung cancer.Key points: - The PPAR-γ agonist, rosiglitazone, restores circulating adiponectin levels in mice with lung cancer.- Rosiglitazone preserves skeletal muscle and adipose tissue mass in mice with lung cancer.- The preservation of muscle mass with rosiglitazone is associated with increases in AMPK and AKT activity.- Stimulation of adiponectin signaling increases AMPK activity, anabolic signaling, and protein synthesis in muscle cell culture.

DOI: https://doi.org/10.1101/2023.07.31.551241
Trends Pharmacol Sci. 2023 Aug 16. pii: S0165-6147(23)00168-2. [Epub ahead of print]

Muscle wasting: emerging pathways and potential drug targets.

Aylin Domaniku, Sevval Nur Bilgic, Serkan Kir.

  Muscle wasting is a serious comorbidity associated with many disorders, including cancer, kidney disease, heart failure, and aging. Progressive loss of skeletal muscle mass negatively influences prognosis and survival, and is often accompanied by frailty and poor quality of life. Clinical trials testing therapeutics against muscle wasting have yielded limited success. Some therapies improved muscle mass in patients without appreciable differences in physical performance. This review article discusses emerging pathways that regulate muscle atrophy, including oncostatin M (OSM) and ectodysplasin A2 (EDA2) receptor (EDA2R) signaling, outcomes of recent clinical trials, and potential drug targets for future therapies.

Keywords:  cachexia; skeletal muscle atrophy; wasting

DOI:  https://doi.org/10.1016/j.tips.2023.07.006
Int J Med Sci. 2023 ;20(9): 1202-1211

Osteopontin May Improve Postinjury Muscle Repair Via Matrix Metalloproteinases And tgf-β Activation in Regular Exercise.

Yuchong Wang, Liang Hong, Jingjing Jiang, Xujun Zhang, Jianing Chen, Hongyan Diao.

  Skeletal muscle injuries are commonly observed during sports and trauma. Regular exercise promotes muscle repair; however, the underlying mechanisms require further investigation. In addition to exercise, osteopontin (OPN) contributes to skeletal muscle regeneration and fibrosis following injury. However, whether and how OPN affects matrix proteins to promote post-injury muscle repair remains uncertain. We recruited regular exercise (RE) and sedentary control (SC) groups to determine plasma OPN levels. Additionally, we developed a murine model of muscle contusion injury and compared the extent of damage, inflammatory state, and regeneration-related proteins in OPN knockout (OPN KO) and wild-type (WT) mice. Our results show that regular exercise induced the increase of OPN, matrix metalloproteinases (MMPs), and transforming growth factor-β (TGF-β) expression in plasma. Injured muscle fibers were repaired more slowly in OPN-KO mice than in WT mice. The expression levels of genes and proteins related to muscle regeneration were lower in OPN-KO mice after injury. OPN also promotes fibroblast proliferation, differentiation, and migration. Additionally, OPN upregulates MMP expression by activating TGF-β, which promotes muscle repair. OPN can improve post-injury muscle repair by activating MMPs and TGF-β pathways. It is upregulated by regular exercise. Our study provides a potential target for the treatment of muscle injuries and explains why regular physical exercise is beneficial for muscle repair.

Keywords:  Matrix metalloproteinases; Muscle repair; Osteopontin; Regular exercise; TGF-β

DOI:  https://doi.org/10.7150/ijms.82925
Eur J Appl Physiol. 2023 Aug 16.

Exercise and fatigue: integrating the role of K+, Na+ and Cl- in the regulation of sarcolemmal excitability of skeletal muscle.

Jean-Marc Renaud, Niels Ørtenblad, Michael J McKenna, Kristian Overgaard.

  Perturbations in K+ have long been considered a key factor in skeletal muscle fatigue. However, the exercise-induced changes in K+ intra-to-extracellular gradient is by itself insufficiently large to be a major cause for the force decrease during fatigue unless combined to other ion gradient changes such as for Na+. Whilst several studies described K+-induced force depression at high extracellular [K+] ([K+]e), others reported that small increases in [K+]e induced potentiation during submaximal activation frequencies, a finding that has mostly been ignored. There is evidence for decreased Cl- ClC-1 channel activity at muscle activity onset, which may limit K+-induced force depression, and large increases in ClC-1 channel activity during metabolic stress that may enhance K+ induced force depression. The ATP-sensitive K+ channel (KATP channel) is also activated during metabolic stress to lower sarcolemmal excitability. Taking into account all these findings, we propose a revised concept in which K+ has two physiological roles: (1) K+-induced potentiation and (2) K+-induced force depression. During low-moderate intensity muscle contractions, the K+-induced force depression associated with increased [K+]e is prevented by concomitant decreased ClC-1 channel activity, allowing K+-induced potentiation of sub-maximal tetanic contractions to dominate, thereby optimizing muscle performance. When ATP demand exceeds supply, creating metabolic stress, both KATP and ClC-1 channels are activated. KATP channels contribute to force reductions by lowering sarcolemmal generation of action potentials, whilst ClC-1 channel enhances the force-depressing effects of K+, thereby triggering fatigue. The ultimate function of these changes is to preserve the remaining ATP to prevent damaging ATP depletion.

Keywords:  ClC-1 channel; Force depression; Force potentiation; KATP channel; Membrane excitability; Metabolic stress

DOI:  https://doi.org/10.1007/s00421-023-05270-9
Am J Physiol Endocrinol Metab. 2023 Aug 16.

Comprehensive interrogation of human skeletal muscle reveals a dissociation between insulin resistance and mitochondrial capacity.

Katie L Whytock, Maria F Pino, Yifei Sun, Gongxin Yu, Flavia G De Carvalho, Reichelle X Yeo, Rick B Vega, Parmar Gaganvir, Adeline Divoux, Nidhi Kapoor, Fanchao Yi, Heather H Cornnell, David A Patten, Mary-Ellen Harper, Stephen J Gardell, Steven R Smith, Martin J Walsh, Lauren M Sparks.

  Insulin resistance and blunted mitochondrial capacity in skeletal muscle are often synonymous; however, this association remains controversial. The aim of this study was to perform an in-depth multi-factorial comparison of skeletal muscle mitochondrial capacity between individuals who were lean and active (Active- n = 9), individuals with obesity (Obese- n = 9) and individuals with Obesity, insulin resistance and type 2 diabetes (T2D- n = 22). Mitochondrial capacity was assessed by ex vivo mitochondrial respiration with fatty-acid and glycolytic supported protocols adjusted for mitochondrial content (mtDNA and citrate synthase activity). Supercomplex assembly was measured by BN-PAGE and immunoblot. TCA cycle intermediates were assessed with targeted metabolomics. Exploratory transcriptomics and DNA methylation analyses were performed to uncover molecular differences affecting mitochondrial function among the three groups. We reveal no discernable differences in skeletal muscle mitochondrial content, mitochondrial capacity, supercomplex assembly, TCA cycle intermediates and mitochondrial molecular profiles between obese individuals with and without T2D that had comparable levels of confounding factors (BMI, age, aerobic capacity). We highlight that lean, active individuals have greater; mitochondrial content, mitochondrial capacity, supercomplex assembly and TCA cycle intermediates. These phenotypical changes are reflected at the level of DNA methylation and gene transcription. The collective observation of comparable muscle mitochondrial capacity in individuals with obesity and T2D (vs. individuals without T2D) underscores a dissociation from skeletal muscle insulin resistance.

Keywords:  Insulin Resistance; Mitochondrial Capacity; Skeletal Muscle; Transcriptomics; Type 2 Diabetes

DOI:  https://doi.org/10.1152/ajpendo.00143.2023
Proc Natl Acad Sci U S A. 2023 Aug 22. 120(34): e2215095120

A TGF-β/KLF10 signaling axis regulates atrophy-associated genes to induce muscle wasting in pancreatic cancer.

Aneesha Dasgupta, Daniel F Gibbard, Rebecca E Schmitt, Paige C Arneson-Wissink, Alexandra M Ducharme, Elizabeth S Bruinsma, John R Hawse, Aminah Jatoi, Jason D Doles.

  Cancer cachexia, and its associated complications, represent a large and currently untreatable roadblock to effective cancer management. Many potential therapies have been proposed and tested-including appetite stimulants, targeted cytokine blockers, and nutritional supplementation-yet highly effective therapies are lacking. Innovative approaches to treating cancer cachexia are needed. Members of the Kruppel-like factor (KLF) family play wide-ranging and important roles in the development, maintenance, and metabolism of skeletal muscle. Within the KLF family, we identified KLF10 upregulation in a multitude of wasting contexts-including in pancreatic, lung, and colon cancer mouse models as well as in human patients. We subsequently interrogated loss-of-function of KLF10 as a potential strategy to mitigate cancer associated muscle wasting. In vivo studies leveraging orthotopic implantation of pancreas cancer cells into wild-type and KLF10 KO mice revealed significant preservation of lean mass and robust suppression of pro-atrophy muscle-specific ubiquitin ligases Trim63 and Fbxo32, as well as other factors implicated in atrophy, calcium signaling, and autophagy. Bioinformatics analyses identified Transforming growth factor beta (TGF-β), a known inducer of KLF10 and cachexia promoting factor, as a key upstream regulator of KLF10. We provide direct in vivo evidence that KLF10 KO mice are resistant to the atrophic effects of TGF-β. ChIP-based binding studies demonstrated direct binding to Trim63, a known wasting-associated atrogene. Taken together, we report a critical role for the TGF-β/KLF10 axis in the etiology of pancreatic cancer-associated muscle wasting and highlight the utility of targeting KLF10 as a strategy to prevent muscle wasting and limit cancer-associated cachexia.

Keywords:  KLF10; TGF-β; cachexia; muscle wasting; pancreatic cancer

DOI:  https://doi.org/10.1073/pnas.2215095120
Sci Rep. 2023 Aug 18. 13(1): 13434

miR-378 influences muscle satellite cells and enhances adipogenic potential of fibro-adipogenic progenitors but does not affect muscle regeneration in the glycerol-induced injury model.

Olga Mucha, Paulina Podkalicka, Monika Żukowska, Ewelina Pośpiech, Józef Dulak, Agnieszka Łoboda.

Skeletal muscle regeneration relies on the reciprocal interaction between many types of cells. Regenerative capacity may be altered in different disorders. In our study, we investigated whether the deletion of miR-378a (miR-378) affects muscle regeneration. We subjected 6-week-old wild-type (WT) and miR-378 knockout (miR-378-/-) animals to the glycerol-induced muscle injury and performed analyses in various time-points. In miR-378-/- animals, an elevated abundance of muscle satellite cells (mSCs) on day 3 was found. Furthermore, fibro-adipogenic progenitors (FAPs) isolated from the muscle of miR-378-/- mice exhibited enhanced adipogenic potential. At the same time, lack of miR-378 did not affect inflammation, fibrosis, adipose tissue deposition, centrally nucleated fiber count, muscle fiber size, FAP abundance, and muscle contractility at any time point analyzed. To conclude, our study revealed that miR-378 deletion influences the abundance of mSCs and the adipogenic potential of FAPs, but does not affect overall regeneration upon acute, glycerol-induced muscle injury.

DOI: https://doi.org/10.1038/s41598-023-40729-x
J Neuromuscul Dis. 2023 Aug 10.

Humanization of the mdx Mouse Phenotype for Duchenne Muscular Dystrophy Modeling: A Metabolic Perspective.

Graham Donen, Nadia Milad, Pascal Bernatchez.

  Duchenne muscular dystrophy (DMD) is a severe form of muscular dystrophy (MD) that is characterized by early muscle wasting and lethal cardiorespiratory failure. While the mdx mouse is the most common model of DMD, it fails to replicate the severe loss of muscle mass and other complications observed in patients, in part due to the multiple rescue pathways found in mice. This led to several attempts at improving DMD animal models by interfering with these rescue pathways through double transgenic approaches, resulting in more severe phenotypes with mixed relevance to the human pathology. As a growing body of literature depicts DMD as a multi-system metabolic disease, improvements in mdx-based modeling of DMD may be achieved by modulating whole-body metabolism instead of muscle homeostasis. This review provides an overview of the established dual-transgenic approaches that exacerbate the mild mdx phenotype by primarily interfering with muscle homeostasis and highlights how advances in DMD modeling coincide with inducing whole-body metabolic changes. We focus on the DBA2/J strain-based D2.mdx mouse with heightened transforming growth factor (TGF)-β signaling and the dyslipidemic mdx/apolipoprotein E (mdx/ApoE) knock-out (KO) mouse, and summarize how these novel models emulate the metabolic changes observed in DMD.

Keywords:  Duchenne; cholesterol; metabolism; transforming growth factor

DOI:  https://doi.org/10.3233/JND-230126
J Cachexia Sarcopenia Muscle. 2023 Aug 13.

Impaired skeletal muscle health in Parkinsonian syndromes: clinical implications, mechanisms and potential treatments.

Kate T Murphy, Gordon S Lynch.

  There is increasing evidence that neurodegenerative disorders including the Parkinsonian syndromes are associated with impaired skeletal muscle health, manifesting as wasting and weakness. Many of the movement problems, lack of muscle strength and reduction in quality of life that are characteristic of these syndromes can be attributed to impairments in skeletal muscle health, but this concept has been grossly understudied and represents an important area of unmet clinical need. This review describes the changes in skeletal muscle health in idiopathic Parkinson's disease and in two atypical Parkinsonian syndromes, the most aggressive synucleinopathy multiple system atrophy, and the tauopathy progressive supranuclear palsy. The pathogenesis of the skeletal muscle changes is described, including the contribution of impairments to the central and peripheral nervous system and intrinsic alterations. Pharmacological interventions targeting the underlying molecular mechanisms with therapeutic potential to improve skeletal muscle health in affected patients are also discussed. Although little is known about the mechanisms underlying these conditions, current evidence implicates multiple pathways and processes, highlighting the likely need for combination therapies to protect muscle health and emphasizing the merit of personalized interventions for patients with different physical capacities at different stages of their disease. As muscle fatigue is often experienced by patients prior to diagnosis, the identification and measurement of this symptom and related biomarkers to identify early signs of disease require careful interrogation, especially for multiple system atrophy and progressive supranuclear palsy where diagnosis is often made several years after onset of symptoms and only confirmed post-mortem. We propose a multidisciplinary approach for early diagnosis and implementation of personalized interventions to preserve muscle health and improve quality of life for patients with typical and atypical Parkinsonian syndromes.

Keywords:  Multiple system atrophy; Parkinson's disease; Progressive supranuclear palsy; Skeletal muscle; Wasting; Weakness

DOI:  https://doi.org/10.1002/jcsm.13312
Nat Commun. 2023 Aug 17. 14(1): 4989

Endothelial ERα promotes glucose tolerance by enhancing endothelial insulin transport to skeletal muscle.

Anastasia Sacharidou, Ken Chambliss, Jun Peng, Jose Barrera, Keiji Tanigaki, Katherine Luby-Phelps, İpek Özdemir, Sohaib Khan, Shashank R Sirsi, Sung Hoon Kim, Benita S Katzenellenbogen, John A Katzenellenbogen, Mohammed Kanchwala, Adwait A Sathe, Andrew Lemoff, Chao Xing, Kenneth Hoyt, Chieko Mineo, Philip W Shaul.

The estrogen receptor (ER) designated ERα has actions in many cell and tissue types that impact glucose homeostasis. It is unknown if these include mechanisms in endothelial cells, which have the potential to influence relative obesity, and processes in adipose tissue and skeletal muscle that impact glucose control. Here we show that independent of impact on events in adipose tissue, endothelial ERα promotes glucose tolerance by enhancing endothelial insulin transport to skeletal muscle. Endothelial ERα-deficient male mice are glucose intolerant and insulin resistant, and in females the antidiabetogenic actions of estradiol (E2) are absent. The glucose dysregulation is due to impaired skeletal muscle glucose disposal that results from attenuated muscle insulin delivery. Endothelial ERα activation stimulates insulin transcytosis by skeletal muscle microvascular endothelial cells. Mechanistically this involves nuclear ERα-dependent upregulation of vesicular trafficking regulator sorting nexin 5 (SNX5) expression, and PI3 kinase activation that drives plasma membrane recruitment of SNX5. Thus, coupled nuclear and non-nuclear actions of ERα promote endothelial insulin transport to skeletal muscle to foster normal glucose homeostasis.

DOI: https://doi.org/10.1038/s41467-023-40562-w
J Vis Exp. 2023 Jul 14.

One Tissue, Many Models: Comprehensive Toolkit For Skeletal Muscle Studies.

Matthew J Borok, Despoina Mademtzoglou.

DOI: https://doi.org/10.3791/64965
iScience. 2023 Aug 18. 26(8): 107475

Autophagy ablation in skeletal muscles worsens sepsis-induced muscle wasting, impairs whole-body metabolism, and decreases survival.

Jean-Philippe Leduc-Gaudet, Kayla Miguez, Marina Cefis, Julie Faitg, Alaa Moamer, Tomer Jordi Chaffer, Olivier Reynaud, Felipe E Broering, Anwar Shams, Dominique Mayaki, Laurent Huck, Marco Sandri, Gilles Gouspillou, Sabah N A Hussain.

  Septic patients frequently develop skeletal muscle wasting and weakness, resulting in severe clinical consequences and adverse outcomes. Sepsis triggers sustained induction of autophagy, a key cellular degradative pathway, in skeletal muscles. However, the impact of enhanced autophagy on sepsis-induced muscle dysfunction remains unclear. Using an inducible and muscle-specific Atg7 knockout mouse model (Atg7iSkM-KO), we investigated the functional importance of skeletal muscle autophagy in sepsis using the cecal ligation and puncture model. Atg7iSkM-KO mice exhibited a more severe phenotype in response to sepsis, marked by severe muscle wasting, hypoglycemia, higher ketone levels, and a decreased in survival as compared to mice with intact Atg7. Sepsis and Atg7 deletion resulted in the accumulation of mitochondrial dysfunction, although sepsis did not further worsen mitochondrial dysfunction in Atg7iSkM-KO mice. Overall, our study demonstrates that autophagy inactivation in skeletal muscles triggers significant worsening of sepsis-induced muscle and metabolic dysfunctions and negatively impacts survival.

Keywords:  Genetics; Human metabolism; Musculoskeletal medicine

DOI:  https://doi.org/10.1016/j.isci.2023.107475
J Biomech. 2023 Jul 29. pii: S0021-9290(23)00315-9. [Epub ahead of print]158 111745

In vivo imaging of skeletal muscle form and function: 50 years of insight.

Silvia S Blemker.

  Skeletal muscle form and function has fascinated scientists for centuries. Our understanding of muscle function has long been driven by advancements in imaging techniques. For example, the sliding filament theory of muscle, which is now widely leveraged in biomechanics research, stemmed from observations made possible by scanning electron microscopy. Over the last 50 years, advancing in medical imaging, combined with ingenuity and creativity of biomechanists, have provide a wealth of new and important insights into in vivo human muscle function. Incorporation of in vivo imaging has also advanced computational modeling and allowed our research to have an impact in many clinical populations. While this review does not provide a comprehensive or meta-analysis of the all the in vivo muscle imaging work over the last five decades, it provides a narrative about the past, present, and future of in vivo muscle imaging.

Keywords:  Imaging; In vivo; Skeletal muscle

DOI:  https://doi.org/10.1016/j.jbiomech.2023.111745
J Cachexia Sarcopenia Muscle. 2023 Aug 15.

A novel splice variant of the human MSTN gene encodes a myostatin-specific myostatin inhibitor.

Kazuhiro Maeta, Manal Farea, Hisahide Nishio, Masafumi Matsuo.

  BACKGROUND: Myostatin, encoded by the MSTN gene comprising 3 exons, is a potent negative regulator of skeletal muscle growth. Although a variety of myostatin inhibitors have been invented for increasing muscle mass in muscle wasting diseases, no effective inhibitor is currently available for clinical use. Myostatin isoforms in several animals have been reported to inhibit myostatin, but an isoform has never been identified for the human MSTN gene, a conserved gene among animals. Here, a splice variant of the human MSTN gene was explored.METHODS: Transcripts and proteins were analysed by reverse transcription-PCR amplification and western blotting, respectively. Proteins were expressed from expression plasmid. Myostatin signalling was assayed by the SMAD-responsive luciferase activity. Cell proliferation was assayed by the Cell Counting Kit-8 (CCK-8) assay and cell counting. Cell cycle was analysed by the FastFUCCI system.
RESULTS: Reverse transcription-PCR amplification of the full-length MSTN transcript in CRL-2061 rhabdomyosarcoma cells revealed two bands consisting of a thick expected-size product and a thin additional small-size product. Sequencing of the small-size product showed a 963-bp deletion in the 5' end of exon 3, creating exon 3s, which contained unusual splice acceptor TG dinucleotides. The novel variant was identified in other human cell lines, although it was not identified in skeletal muscle. The 251-amino acid isoform encoded by the novel variant (myostatin-b) was identified in CRL-2061 rhabdomyosarcoma cells. Transfection of a myostatin-b expression plasmid into CRL-2061 and myoblast cells inhibited endogenous myostatin signalling (44%, P < 0.001 and 63%, P < 0.001, respectively). Furthermore, myostatin-b inhibited myostatin signalling induced by recombinant myostatin (68.8%, P < 0.001). In remarkable contrast, myostatin-b did not inhibit the myostatin signalling induced by recombinant growth differentiation factor 11 (9.2%, P = 0.70), transforming growth factor β (+3.1%, P = 0.83) or activin A (+1.1%, P = 0.96). These results indicate the myostatin-specific inhibitory effect of myostatin-b. Notably, the expression of myostatin-b in myoblasts significantly enhanced cell proliferation higher than the mock-transfected cells by the CCK-8 and direct cell counting assays (60%, P < 0.05 and 39%, P < 0.05, respectively). Myostatin-b increased the percentage of S-phase cells significantly higher than that of the mock-transfected cells (53% vs. 80%, P < 0.05).
CONCLUSIONS: We cloned a novel human MSTN variant produced by unorthodox splicing. The variant encoded a novel myostatin isoform, myostatin-b, that inhibited myostatin signalling by myostatin-specific manner and enhanced myoblast proliferation by shifting cell cycle. Myostatin-b, which has myostatin-specific inhibitory activity, could be developed as a natural myostatin inhibitor.

Keywords:  MSTN gene; isoform; myostatin; myostatin inhibitor; myostatin-b; splice variant

DOI:  https://doi.org/10.1002/jcsm.13314
Comput Biol Med. 2023 Aug 14. pii: S0010-4825(23)00832-6. [Epub ahead of print]164 107367

FIM: A fatigued-injured muscle model based on the sliding filament theory.

Fatemeh Jalali, Mohammad Ali Nazari, Arash Bahrami, Pascal Perrier, Yohan Payan.

  Skeletal muscle modeling has a vital role in movement studies and the development of therapeutic approaches. In the current study, a Huxley-based model for skeletal muscle is proposed, which demonstrates the impact of impairments in muscle characteristics. This model focuses on three identified ions: H+, inorganic phosphate Pi, and Ca2+. Modifications are made to actin-myosin attachment and detachment rates to study the effects of H+ and Pi. Additionally, an activation coefficient is included to represent the role of calcium ions interacting with troponin, highlighting the importance of Ca2+. It is found that maximum isometric muscle force decreases by 9.5% due to a reduction in pH from 7.4 to 6.5 and by 47.5% in case of the combination of a reduction in pH and an increase of Pi concentration up to 30 mM, respectively. Then the force decline caused by a fall in the active calcium ions is studied. When only 15% of the total calcium in the myofibrillar space is able to interact with troponin, up to 80% force drop is anticipated by the model. The proposed fatigued-injured muscle model is useful to study the effect of various shortening velocities and initial muscle-tendon lengths on muscle force; in addition, the benefits of the model go beyond predicting the force in different conditions as it can also predict muscle stiffness and power. The power and stiffness decrease by 40% and 6.5%, respectively, due to the pH reduction, and the simultaneous accumulation of H+ and Pi leads to a 50% and 18% drop in power and stiffness.

Keywords:  Distribution moments; Huxley sliding filament model; Inorganic phosphate; Muscle fatigue; Musclectomy; pH reduction

DOI:  https://doi.org/10.1016/j.compbiomed.2023.107367