bims-moremu 2023-10-08 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–10–08
28 papers selected by
Anna Vainshtein, Craft Science Inc.

Early morning run-training results in enhanced endurance performance adaptations in mice.
Human Skeletal myopathy myosin mutations disrupt myosin head sequestration.
Fast, multiplexable and efficient somatic gene deletions in adult mouse skeletal muscle fibers using AAV-CRISPR/Cas9.
Resistance towards endurance training-mediated skeletal muscle mitochondrial adaptations: implications for individuals with type 1 diabetes mellitus.
Plasticity changes in neuromuscular junction morphology and related regulatory proteins in the hibernating ground squirrel.
Activation of Lactate Receptor Positively Regulates Skeletal Muscle Mass in Mice.
Msi2 enhances muscle dysfunction in a myotonic dystrophy type 1 mouse model.
Influence of sexual dimorphism on satellite cell regulation and inflammatory response during skeletal muscle regeneration.
Automated Image Analysis Pipeline Development to Monitor Disease Progression in Muscular Dystrophy Using Cell Profiler.
Moderate intensity continuous versus high intensity interval training: Metabolic responses of slow and fast skeletal muscles in rat.
Nanotopographical Cues Tune the Therapeutic Potential of Extracellular Vesicles for the Treatment of Aged Skeletal Muscle Injuries.
High resolution spatial investigation of intracellular oxygen in muscle cells.
Peripheral limitations for performance: Muscle capillarization.
Acute effect of electrical stimulation on muscle protein synthesis and break-down in the soleus muscle of hindlimb unloaded rats.
Impact of Bmal1 rescue and time-restricted feeding on liver and muscle proteomes during the active phase in mice.
The roles of DGAT1 and DGAT2 in human myotubes are dependent on donor patho-physiological background.
Skeletal muscle myostatin mRNA expression is upregulated in aged human adults with excess adiposity but is not associated with insulin resistance and ageing.
ASIC3 plays a protective role in delayed-onset muscle soreness (DOMS) through muscle acid sensation during exercise.
The influence of biological sex in human skeletal muscle transcriptome during ageing.
Hepatic sialic acid synthesis modulates glucose homeostasis in both liver and skeletal muscle.
Microgravity-induced skeletal muscle atrophy in women and men:Implications for long-duration spaceflights to the Moon and Mars.
International society of sports nutrition position stand: essential amino acid supplementation on skeletal muscle and Performance.
Sarcopenia in a type 2 diabetic state: Reviewing literature on the pathological consequences of oxidative stress and inflammation beyond the neutralizing effect of intracellular antioxidants.
Purification of functional mouse skeletal muscle mitochondria using percoll density gradient centrifugation.
The effect of physical exercise on anticancer immunity.
Protein dose requirements to maximize skeletal muscle protein synthesis after repeated bouts of resistance exercise in young trained women.
Case report: a novel deep intronic splice-altering variant in DMD as a cause of Becker muscular dystrophy.
Role of growth differentiation factor 15 in cancer cachexia (Review).

bioRxiv. 2023 Sep 19. pii: 2023.09.18.557933. [Epub ahead of print]

Early morning run-training results in enhanced endurance performance adaptations in mice.

Stuart J Hesketh, Casey L Sexton, Christopher A Wolff, Mark R Viggars, Karyn A Esser.

Time-of-day differences in acute exercise performance in mice are well established with late active phase (afternoon) runners exhibiting significantly greater endurance performance compared to early active phase (morning) runners. In this study, we asked if performance adaptations would be different when training for 6 weeks at two different times of day, and if this corresponds to steady state changes in the phase of peripheral tissue clocks. To address these questions, we endurance trained female PER2::Luciferase mice, at the same relative workload, either in the morning, at ZT13, or in the afternoon, at ZT22. Then, after training, we recorded luminescence from tissues of PER2::Luciferase mice to report timing of tissue clocks in several peripheral tissues. After 6 weeks, we found that both groups exhibited significant improvements in maximal endurance capacity (total treadmill work)( p < 0.0001), but the morning runners exhibited an enhanced rate of adaptation as there was no detectable difference in maximal endurance capacity (p = 0.2182) between the morning and afternoon runners. In addition, morning and afternoon runners exhibited divergent clock phase shifts with a significant 5-hour phase advance in the EDL ( p < 0.0001) and soleus ( p < 0.0001) of morning runners, but a phase delay in the EDL ( p < 0.0001) and Soleus ( p < 0.0001) of afternoon runners. Therefore, our data demonstrate that morning training enhances endurance adaptations compared to afternoon training in mice, and we suggest this is due to phase advancement of muscle clocks to better align metabolism with exercise performance.
Key points summary: Time-of-day differences in exercise performance are well established in the literature. We observe that after 6 weeks of endurance exercise training there is no longer a time-of-day specific difference in endurance performance.Consistent endurance training performed in morning (ZT13) results in a greater performance increase compared to exercise training during the afternoon (ZT22).Removal of time-of-day differences in performance through exercise training is strongly associated with significant phase shifts (~5 hour advance) of the muscle clock.

DOI: https://doi.org/10.1101/2023.09.18.557933
JCI Insight. 2023 Oct 03. pii: e172322. [Epub ahead of print]

Human Skeletal myopathy myosin mutations disrupt myosin head sequestration.

Glenn Carrington, Hoi Ting Abbi Hau, Sarah Kosta, Hannah F Dugdale, Francesco Muntoni, Adele D'Amico, Peter Y K Van den Bergh, Norma B Romero, Edoardo Malfatti, Juan J Vilchez, Anders Oldfors, Sander Pajusalu, Katrin Õunap, Marta Giralt-Pujol, Edmar Zanoteli, Kenneth S Campbell, Hiroyuki Iwamoto, Michelle Peckham, Julien Ochala.

  Myosin heavy chains encoded by MYH7 and MYH2 are abundant in human skeletal muscle, and important for muscle contraction. However, it is unclear how mutations in these genes disrupt myosin structure and function leading to skeletal muscle myopathies termed myosinopathies. Here, we used multiple approaches to analyse the effects of common MYH7 and MYH2 mutations in the light meromyosin region of myosin (LMM). Analyses of expressed and purified MYH7 and MYH2 LMM mutant proteins combined with in-silico modelling showed that myosin coiled-coil structure and packing of filaments in vitro are commonly disrupted. Using muscle biopsies from patients, and Mant-ATP chase protocols to estimate the proportion of myosin heads that were super-relaxed, together with X-ray diffraction measurements to estimate myosin head order we found that basal myosin ATP consumption was increased and the myosin super-relaxed state was decreased in vivo. In addition, myofibre mechanics experiments to investigate contractile function showed myofibre contractility was not affected. These findings indicate that the structural remodelling associated with LMM mutations induces a pathogenic state in which formation of shutdown heads is impaired, thus increasing myosin head ATP demand in the filaments, rather than affecting contractility. These key findings will help design future therapies for myosinopathies.

Keywords:  Genetic diseases; Muscle Biology; Neuromuscular disease

DOI:  https://doi.org/10.1172/jci.insight.172322
Nat Commun. 2023 09 30. 14(1): 6116

Fast, multiplexable and efficient somatic gene deletions in adult mouse skeletal muscle fibers using AAV-CRISPR/Cas9.

Marco Thürkauf, Shuo Lin, Filippo Oliveri, Dirk Grimm, Randall J Platt, Markus A Rüegg.

Molecular screens comparing different disease states to identify candidate genes rely on the availability of fast, reliable and multiplexable systems to interrogate genes of interest. CRISPR/Cas9-based reverse genetics is a promising method to eventually achieve this. However, such methods are sorely lacking for multi-nucleated muscle fibers, since highly efficient nuclei editing is a requisite to robustly inactive candidate genes. Here, we couple Cre-mediated skeletal muscle fiber-specific Cas9 expression with myotropic adeno-associated virus-mediated sgRNA delivery to establish a system for highly effective somatic gene deletions in mice. Using well-characterized genes, we show that local or systemic inactivation of these genes copy the phenotype of traditional gene-knockout mouse models. Thus, this proof-of-principle study establishes a method to unravel the function of individual genes or entire signaling pathways in adult skeletal muscle fibers without the cumbersome requirement of generating knockout mice.

DOI: https://doi.org/10.1038/s41467-023-41769-7
J Physiol. 2023 Oct 07.

Resistance towards endurance training-mediated skeletal muscle mitochondrial adaptations: implications for individuals with type 1 diabetes mellitus.

Mitchell J Sammut, Andrew W D'Souza.



Keywords:  combined exercise; mitochondria; skeletal muscle; type 1 diabetes mellitus

DOI:  https://doi.org/10.1113/JP285685
J Appl Physiol (1985). 2023 Oct 05.

Plasticity changes in neuromuscular junction morphology and related regulatory proteins in the hibernating ground squirrel.

Yue He, Hui-Ping Wang, Fang-Yang Pan, Shen-Hui Xu, Yun-Fang Gao.

  Skeletal muscle disuse atrophy can cause degenerative changes in neuromuscular junction morphology. Although Daurian ground squirrels (Spermophilus dauricus) are a natural anti-disuse animal model for studying muscle atrophy during hibernation, little is known about the morphological and regulatory mechanisms of their neuromuscular junctions. Here, we found that morphological indices of the soleus muscle were significantly lower during hibernation (torpor and interbout arousal) compared to pre-hibernation but recovered during post-hibernation. In the extensor digitorum longus muscle, neuromuscular junction morphology did not change significantly during hibernation. Agrin-Lrp4-MuSK is a key pathway for the formation and maintenance of the neuromuscular junction. Our results showed that low-density lipoprotein receptor-associated protein 4 (Lrp4) expression in the soleus (slow muscle) decreased by 46.2% in the interbout arousal group compared with the pre-hibernation group (p = 0.019), with recovery in the post-hibernation group. Compared to the pre-hibernation group, agrin expression in the extensor digitorum longus (fast muscle) increased by 67.0% in the interbout arousal group (p = 0.016). In conclusion, periodic up-regulation in agrin expression during interbout arousal may be involved in the maintenance of neuromuscular junction morphology in the extensor digitorum longus muscle during hibernation. The degenerative changes in neuromuscular junction morphology and the periodic decrease in Lrp4 protein expression in the soleus during hibernation, these changes recovered to the pre-hibernation levels in the post-hibernation group, also exhibiting significant plasticity. This plasticity may be an important mechanism for resisting disuse atrophy in hibernating animals.

Keywords:  Daurian ground squirrels; Hibernation; Neuromuscular junction; Skeletal muscle

DOI:  https://doi.org/10.1152/japplphysiol.00334.2023
Physiol Res. 2023 Aug 31. 72(4): 465-473

Activation of Lactate Receptor Positively Regulates Skeletal Muscle Mass in Mice.

Y Ohno, M Nakatani, T Ito, Y Matsui, K Ando, Y Suda, K Ohashi, S Yokoyama, K Goto.

G protein-coupled receptor 81 (GPR81), a selective receptor for lactate, expresses in skeletal muscle cells, but the physiological role of GPR81 in skeletal muscle has not been fully elucidated. As it has been reported that the lactate administration induces muscle hypertrophy, the stimulation of GPR81 has been suggested to mediate muscle hypertrophy. To clarify the contribution of GPR81 activation in skeletal muscle hypertrophy, in the present study, we investigated the effect of GPR81 agonist administration on skeletal muscle mass in mice. Male C57BL/6J mice were randomly divided into control group and GPR81 agonist-administered group that received oral administration of the specific GPR81 agonist 3-Chloro-5-hydroxybenzoic acid (CHBA). In both fast-twitch plantaris and slow-twitch soleus muscles of mice, the protein expression of GPR81 was observed. Oral administration of CHBA to mice significantly increased absolute muscle weight and muscle weight relative to body weight in the two muscles. Moreover, both absolute and relative muscle protein content in the two muscles were significantly increased by CHBA administration. CHBA administration also significantly upregulated the phosphorylation level of p42/44 extracellular signal-regulated kinase-1/2 (ERK1/2) and p90 ribosomal S6 kinase (p90RSK). These observations suggest that activation of GRP81 stimulates increased the mass of two types of skeletal muscle in mice in vivo. Lactate receptor GPR81 may positively affect skeletal muscle mass through activation of ERK pathway.
Biomed J. 2023 Oct 03. pii: S2319-4170(23)00104-X. [Epub ahead of print] 100667

Msi2 enhances muscle dysfunction in a myotonic dystrophy type 1 mouse model.

Maria Sabater-Arcis, Nerea Moreno, Teresa Sevilla, Manuel Perez Alonso, Ariadna Bargiela, Ruben Artero.

   BACKGROUND: Myotonic dystrophy type 1 (DM1) is a rare neuromuscular disease caused by a CTG repeat expansion in the 3' untranslated region of the DM1 protein kinase gene. Characteristic degenerative muscle symptoms include myotonia, atrophy, and weakness. We previously proposed an MSI2>miR-7>autophagy axis whereby MSI2 overexpression repressed miR-7 biogenesis that subsequently de-repressed muscle catabolism through excessive autophagy. Because the DM1 HSALR mouse model expressing expanded CUG repeats shows weak muscle-wasting phenotypes, we hypothesized that MSI2 overexpression was sufficient to promote muscle dysfunction in vivo.
METHODS: By means of recombinant AAV murine Msi2 was overexpressed in neonates HSALR mice skeletal muscle to induce DM1-like phenotypes RESULTS: Sustained overexpression of the murine Msi2 protein in HSALR neonates induced autophagic flux and expression of critical autophagy proteins, increased central nuclei and reduced myofibers area, and weakened muscle strength. Importantly, these changes were independent of Mbnl1, Mbnl2, and Celf1 protein levels, which remained unchanged upon Msi2 overexpression.
CONCLUSIONS: Globally, molecular, histological, and functional data from these experiments in the HSALR mouse model confirms the pathological role of Msi2 expression levels as an atrophy-associated component that impacts the characteristic muscle dysfunction symptoms in DM1 patients.

Keywords:  HSA(LR); Msi2; adeno-associated virus; muscle atrophy; myotonic dystrophy

DOI:  https://doi.org/10.1016/j.bj.2023.100667
Physiol Rep. 2023 Oct;11(19): e15798

Influence of sexual dimorphism on satellite cell regulation and inflammatory response during skeletal muscle regeneration.

Charline Jomard, Julien Gondin.

  After injury, skeletal muscle regenerates thanks to the key role of satellite cells (SC). The regeneration process is supported and coordinated by other cell types among which immune cells. Among the mechanisms involved in skeletal muscle regeneration, a sexual dimorphism, involving sex hormones and more particularly estrogens, has been suggested. However, the role of sexual dimorphism on skeletal muscle regeneration is not fully understood, likely to the use of various experimental settings in both animals and human. This review aims at addressing how sex and estrogens regulate both the SC and the inflammatory response during skeletal muscle regeneration by considering the different experimental designs used in both animal models (i.e., ovarian hormone deficiency, estrogen replacement or supplementation, treatments with estrogen receptors agonists/antagonists and models knockout for estrogen receptors) and human (hormone therapy replacement, pre vs. postmenopausal, menstrual cycle variation…).

Keywords:  estrogens; inflammation; satellite cells; skeletal muscle

DOI:  https://doi.org/10.14814/phy2.15798
Arch Microbiol Immunol. 2023 ;7(3): 178-187

Automated Image Analysis Pipeline Development to Monitor Disease Progression in Muscular Dystrophy Using Cell Profiler.

Alexandra Brown, Brooklyn Morris, John Karanja Kamau, Abdullah A Alshudukhi, Abdulrahman Jama, Hongmei Ren.

  Muscular dystrophies are inherited disorders that are characterized by progressive muscle degeneration. These disorders are caused by mutations in the genes encoding structural elements within the muscle, which leads to increased vulnerability to mechanical stress and sarcolemma damage. Although myofibers have the capacity to regenerate, the newly formed myofibers still harbor genetic mutation, which induces continuous cycles of muscle fiber death and regeneration. This repeated cycling is accompanied by an inflammatory response which eventually provokes excessive fibrotic deposition. The histopathological changes in skeletal muscle tissue are central to the disease pathogenesis. Analysis of muscle histopathology is the gold standard for monitoring muscle health and disease progression. However, manual, or semi-manual quantification methods, are not only immensely tedious but can be subjective. Here, we present four image analysis pipelines built in CellProfiler which enable users without a background in computer vision or programming to quantitatively analyze biological images. These image analysis pipelines are designed to quantify skeletal muscle histopathological staining for membrane damage, the abundance and size distribution of regenerating muscle fibers, inflammation via quantification of CD68+ M1 macrophages, and collagen deposition. Additionally, we discuss methods to address common errors associated with the quantification of microscopy images. These automated tools can not only improve workflow efficiency but can provide a better understanding of the histopathological progression of muscular dystrophy.

Keywords:  Automated Histopathology Analysis; CellProfiler; Evan’s Blue Dye; Fibrosis; Muscle Regeneration; Muscular Dystrophy

DOI:  https://doi.org/10.26502/ami.936500115
PLoS One. 2023 ;18(10): e0292225

Moderate intensity continuous versus high intensity interval training: Metabolic responses of slow and fast skeletal muscles in rat.

Morgane Pengam, Christelle Goanvec, Christine Moisan, Bernard Simon, Gaëlle Albacète, Annie Féray, Anthony Guernec, Aline Amérand.

The healthy benefits of regular physical exercise are mainly mediated by the stimulation of oxidative and antioxidant capacities in skeletal muscle. Our understanding of the cellular and molecular responses involved in these processes remain often uncomplete particularly regarding muscle typology. The main aim of the present study was to compare the effects of two types of exercise training protocol: a moderate-intensity continuous training (MICT) and a high-intensity interval training (HIIT) on metabolic processes in two muscles with different typologies: soleus and extensor digitorum longus (EDL). Training effects in male Wistar rats were studied from whole organism level (maximal aerobic speed, morphometric and systemic parameters) to muscle level (transcripts, protein contents and enzymatic activities involved in antioxidant defences, aerobic and anaerobic metabolisms). Wistar rats were randomly divided into three groups: untrained (UNTR), n = 7; MICT, n = 8; and HIIT, n = 8. Rats of the MICT and HIIT groups ran five times a week for six weeks at moderate and high intensity, respectively. HIIT improved more than MICT the endurance performance (a trend to increased maximal aerobic speed, p = 0.07) and oxidative capacities in both muscles, as determined through protein and transcript assays (AMPK-PGC-1α signalling pathway, antioxidant defences, mitochondrial functioning and dynamics). Whatever the training protocol, the genes involved in these processes were largely more significantly upregulated in soleus (slow-twitch fibres) than in EDL (fast-twitch fibres). Solely on the basis of the transcript changes, we conclude that the training protocols tested here lead to specific muscular responses.

DOI: https://doi.org/10.1371/journal.pone.0292225
ACS Nano. 2023 Oct 05.

Nanotopographical Cues Tune the Therapeutic Potential of Extracellular Vesicles for the Treatment of Aged Skeletal Muscle Injuries.

Kai Wang, Nolan Frey, Andres Garcia, Kun Man, Yong Yang, Alice Gualerzi, Zachary J Clemens, Marzia Bedoni, Philip R LeDuc, Fabrisia Ambrosio.

  Skeletal muscle regeneration relies on the tightly temporally regulated lineage progression of muscle stem/progenitor cells (MPCs) from activation to proliferation and, finally, differentiation. However, with aging, MPC lineage progression is disrupted and delayed, ultimately causing impaired muscle regeneration. Extracellular vesicles (EVs) have attracted broad attention as next-generation therapeutics for promoting tissue regeneration. As a next step toward clinical translation, strategies to manipulate EV effects on downstream cellular targets are needed. Here, we developed an engineering strategy to tune the therapeutic potential of EVs using nanotopographical cues. We found that EVs released by young MPCs cultured on flat substrates (fEVs) promoted the proliferation of aged MPCs while EVs released by MPCs cultured on nanogratings (nEVs) promoted myogenic differentiation. We then employed a bioengineered 3D muscle aging model to optimize the administration protocol and test the therapeutic potential of fEVs and nEVs in a high-throughput manner. We found that the sequential administration first of fEVs during the phase of MPC proliferative expansion (i.e., 1 day after injury) followed by nEV administration at the stage of MPC differentiation (i.e., 3 days after injury) enhanced aged muscle regeneration to a significantly greater extent than fEVs and nEVs delivered either in isolation or mixed. The beneficial effects of the sequential EV treatment strategy were further validated in vivo, as evidenced by increased myofiber size and improved functional recovery. Collectively, our study demonstrates the ability of topographical cues to tune EV therapeutic potential and highlights the importance of optimizing the EV administration strategy to accelerate aged skeletal muscle regeneration.

Keywords:  aging; cell-free therapy; exosomes; nanotopography; skeletal muscle repair

DOI:  https://doi.org/10.1021/acsnano.3c02269
bioRxiv. 2023 Jul 19. pii: 2023.07.18.548845. [Epub ahead of print]

High resolution spatial investigation of intracellular oxygen in muscle cells.

Rozhin Penjweini, Alessandra Pasut, Branden Roarke, Greg Alspaugh, Dan L Sackett, Jay R Knutson.

Molecular oxygen (O 2 ) is one of the most functionally relevant metabolites. O 2 is essential for mito-chondrial aerobic respiration. Changes in O 2 affect muscle metabolism and play a critical role in the maintenance of skeletal muscle mass, with lack of sufficient O 2 resulting in detrimental loss of muscle mass and function. How exactly O 2 is used by muscle cells is less known, mainly due to the lack of tools to address O 2 dynamics at the cellular level. Here we discuss a new imaging method for the real time quantification of intracellular O 2 in muscle cells based on a genetically encoded O 2 -responsive sensor, Myoglobin-mCherry. We show that we can spatially resolve and quantify intracellular O 2 concentration in single muscle cells and that the spatiotemporal O 2 gradient measured by the sensor is linked to, and reflects, functional metabolic changes occurring during the process of muscle differentiation.
Highlights: Real time quantitation of intracellular oxygen with spatial resolutionIdentification of metabolically active sites in single cellsOxygen metabolism is linked to muscle differentiation.

DOI: https://doi.org/10.1101/2023.07.18.548845
Scand J Med Sci Sports. 2023 Sep 28.

Peripheral limitations for performance: Muscle capillarization.

Ylva Hellsten, Lasse Gliemann.

  Sufficient delivery of oxygen and metabolic substrates, together with removal of waste products, are key elements of muscle performance. Capillaries are the primary site for this exchange in skeletal muscle and the degree of muscle capillarization affects diffusion conditions by influencing mean transit time, capillary surface area and diffusion distance. Muscle capillarization may thus represent a limiting factor for performance. Exercise training increases the number of capillaries per muscle fiber by about 10%-20% within a few weeks in untrained subjects, whereas capillary growth progresses more slowly in well-trained endurance athletes. Studies show that capillaries are tortuous, situated along and across the length of the fibers with an arrangement related to muscle fascicles. Although direct data is lacking, it is possible that years of training not only enhances capillary density but also optimizes the positioning of capillaries, to further improve the diffusion conditions. Muscle capillarization has been shown to increase oxygen extraction during exercise in humans, but direct evidence for a causal link between increased muscle capillarization and performance is scarce. This review covers current knowledge on the implications of muscle capillarization for oxygen and glucose uptake as well as performance. A brief overview of the process of capillary growth and of physical factors, inherent to exercise, which promote angiogenesis, provides the foundation for a discussion on how different training modalities may influence muscle capillary growth. Finally, we identify three areas for future research on the role of capillarization for exercise performance.

Keywords:  capillary; exercise training; mean transit time; oxygen extraction

DOI:  https://doi.org/10.1111/sms.14442
Biomed Res. 2023 ;44(5): 209-218

Acute effect of electrical stimulation on muscle protein synthesis and break-down in the soleus muscle of hindlimb unloaded rats.

Miho Kanazashi, Masayuki Tanaka.

Electrical stimulation (ES) is effective for disuse-induced muscle atrophy. However, the acute effect of ES on muscle protein synthesis (MPS) and muscle protein breakdown (MPB) remains unclear. We investigated the effect of a single-session ES treatment on mTORC1 signaling, MPS, and MPB in the soleus muscle of 2-week hindlimb unloaded rats. Sprague Dawley rats (n = 12 male) were randomly divided into control (CON) and hindlimb unloaded (HU) groups. After 2 weeks, the right soleus muscle was percutaneously stimulated and underwent supramaximal isometric contractions. The left soleus muscle served as an internal control. We collected soleus muscle samples 6 h after ES. Two weeks of HU decreased p70S6K and S6rp activation, downstream factors for mTORC1 signaling, and SUnSET method-assessed MPS, but increased the LC3-II/I ratio, an indicator of autophagy. ES on disused muscle successfully activated mTORC1 signaling but did not affect MPS. Contrary, ES decreased ubiquitinated proteins expression and LC3B-II/I ratio. HU might affect mTORC1 activation and MPS differently in response to acute ES possibly due to excessive ROS production caused by ES. Our findings suggest that ES applied to disused skeletal muscles may suppress MPB, but its effect on MPS appears to be attenuated.

DOI: https://doi.org/10.2220/biomedres.44.209
Mol Cell Proteomics. 2023 Oct 02. pii: S1535-9476(23)00166-4. [Epub ahead of print] 100655

Impact of Bmal1 rescue and time-restricted feeding on liver and muscle proteomes during the active phase in mice.

Jacob G Smith, Jeffrey Molendijk, Ronnie Blazev, Wan Hsi Chen, Qing Zhang, Christopher Litwin, Valentina M Zinna, Patrick-Simon Welz, Salvador Aznar Benitah, Carolina M Greco, Paolo Sassone-Corsi, Pura Muñoz-Cánoves, Benjamin L Parker, Kevin B Koronowski.

   OBJECTIVE: Molecular clocks and daily feeding cycles support metabolism in peripheral tissues. Although the roles of local clocks and feeding are well defined at the transcriptional level, their impact on governing protein abundance in peripheral tissues is unclear. Here, we determine the relative contributions of local molecular clocks and daily feeding cycles on liver and muscle proteomes during the active phase in mice.
METHODS: LC-MS/MS was performed on liver and gastrocnemius muscle harvested four hours into the dark phase from wild-type (WT), Bmal1 knockout (KO), and dual liver- and muscle- Bmal1-rescued (LMRE) mice housed under 12-h light/12-h dark cycles with either ad libitum feeding or time-restricted feeding (TRF) in the dark phase. Additional molecular and metabolic analyses were performed on liver and cultured hepatocytes.
RESULTS: Feeding-fasting cycles had only minimal effects on liver and few, if any, on muscle. In contrast, Bmal1 KO altered the abundance of 674 proteins in liver, and 80 in muscle. Rescue of liver and muscle Bmal1 restored ∼50% of proteins in liver and ∼25% in muscle. These included proteins involved in fatty acid oxidation in liver and carbohydrate metabolism in muscle. For liver, proteins involved in de novo lipogenesis were largely dependent on Bmal1 function in other tissues (i.e., the wider clock system). Proteins regulated by BMAL1 in liver and muscle were enriched for secreted proteins. We found that the abundance of FGF1, a liver secreted protein, requires BMAL1, and that autocrine FGF1 signaling modulates mitochondrial respiration in hepatocytes.
CONCLUSIONS: In liver and muscle, BMAL1 is a more potent regulator of dark phase proteomes than daily feeding cycles, highlighting the need to assess protein levels in addition to mRNA when investigating clock mechanisms. The proteome is more extensively regulated by BMAL1 in liver than in muscle and many metabolic pathways in peripheral tissues are reliant on the function of the clock system as a whole.

Keywords:  Bmal1; Circadian clock; FGF1; circadian rhythm; fibroblast growth factor; liver; muscle; time-restricted feeding

DOI:  https://doi.org/10.1016/j.mcpro.2023.100655
FASEB J. 2023 Nov;37(11): e23209

The roles of DGAT1 and DGAT2 in human myotubes are dependent on donor patho-physiological background.

Zehra Irshad, Jenny Lund, Anne Sillars, Nils Gunnar Løvsletten, Seley Gharanei, Ian P Salt, Dilys J Freeman, Jason M R Gill, G Hege Thoresen, Arild C Rustan, Victor A Zammit.

  The roles of DGAT1 and DGAT2 in lipid metabolism and insulin responsiveness of human skeletal muscle were studied using cryosections and myotubes prepared from muscle biopsies from control, athlete, and impaired glucose regulation (IGR) cohorts of men. The previously observed increases in intramuscular triacylglycerol (IMTG) in athletes and IGR were shown to be related to an increase in lipid droplet (LD) area in type I fibers in athletes but, conversely, in type II fibers in IGR subjects. Specific inhibition of both diacylglycerol acyltransferase (DGAT) 1 and 2 decreased fatty acid (FA) uptake by myotubes, whereas only DGAT2 inhibition also decreased fatty acid oxidation. Fatty acid uptake in myotubes was negatively correlated with the lactate thresholds of the respective donors. DGAT2 inhibition lowered acetate uptake and oxidation in myotubes from all cohorts whereas DGAT1 inhibition had no effect. A positive correlation between acetate oxidation in myotubes and resting metabolic rate (RMR) from fatty acid oxidation in vivo was observed. Myotubes from athletes and IGR had higher rates of de novo lipogenesis from acetate that were normalized by DGAT2 inhibition. Moreover, DGAT2 inhibition in myotubes also resulted in increased insulin-induced Akt phosphorylation. The differential effects of DGAT1 and DGAT2 inhibition suggest that the specialized role of DGAT2 in esterifying nascent diacylglycerols and de novo synthesized FA is associated with synthesis of a pool of triacylglycerol, which upon hydrolysis results in effectors that promote mitochondrial fatty acid oxidation but decrease insulin signaling in skeletal muscle cells.

Keywords:  diacylglycerol acyltransferases; fatty acid oxidation; insulin resistance; lipogenesis; muscle lipid; triacylglycerols

DOI:  https://doi.org/10.1096/fj.202300960RR
Geroscience. 2023 Oct 06.

Skeletal muscle myostatin mRNA expression is upregulated in aged human adults with excess adiposity but is not associated with insulin resistance and ageing.

Andrew Wilhelmsen, Francis B Stephens, Andrew J Bennett, Leonidas G Karagounis, Simon W Jones, Kostas Tsintzas.

  Myostatin negatively regulates skeletal muscle growth and appears upregulated in human obesity and associated with insulin resistance. However, observations are confounded by ageing, and the mechanisms responsible are unknown. The aim of this study was to delineate between the effects of excess adiposity, insulin resistance and ageing on myostatin mRNA expression in human skeletal muscle and to investigate causative factors using in vitro models. An in vivo cross-sectional analysis of human skeletal muscle was undertaken to isolate effects of excess adiposity and ageing per se on myostatin expression. In vitro studies employed human primary myotubes to investigate the potential involvement of cross-talk between subcutaneous adipose tissue (SAT) and skeletal muscle, and lipid-induced insulin resistance. Skeletal muscle myostatin mRNA expression was greater in aged adults with excess adiposity than age-matched adults with normal adiposity (2.0-fold higher; P < 0.05) and occurred concurrently with altered expression of genes involved in the maintenance of muscle mass but did not differ between younger and aged adults with normal adiposity. Neither chronic exposure to obese SAT secretome nor acute elevation of fatty acid availability (which induced insulin resistance) replicated the obesity-mediated upregulation of myostatin mRNA expression in vitro. In conclusion, skeletal muscle myostatin mRNA expression is uniquely upregulated in aged adults with excess adiposity and insulin resistance but not by ageing alone. This does not appear to be mediated by the SAT secretome or by lipid-induced insulin resistance. Thus, factors intrinsic to skeletal muscle may be responsible for the obesity-mediated upregulation of myostatin, and future work to establish causality is required.

Keywords:  Ageing; Insulin resistance; Myostatin; Obesity; Primary human myotubes; Skeletal muscle

DOI:  https://doi.org/10.1007/s11357-023-00956-6
Front Pain Res (Lausanne). 2023 ;4 1215197

ASIC3 plays a protective role in delayed-onset muscle soreness (DOMS) through muscle acid sensation during exercise.

Tahsin Khataei, Christopher J Benson.

  Immediate exercise-induced pain (IEIP) and DOMS are two types of exercise-induced muscle pain and can act as barriers to exercise. The burning sensation of IEIP occurs during and immediately after intensive exercise, whereas the soreness of DOMS occurs later. Acid-sensing ion channels (ASICs) within muscle afferents are activated by H+ and other chemicals and have been shown to play a role in various chronic muscle pain conditions. Here, we further defined the role of ASICs in IEIP, and also tested if ASIC3 is required for DOMS. After undergoing exhaustive treadmill exercise, exercise-induced muscle pain was assessed in wild-type (WT) and ASIC3-/- mice at baseline via muscle withdrawal threshold (MWT), immediately, and 24 h after exercise. Locomotor movement, grip strength, and repeat exercise performance were tested at baseline and 24 h after exercise to evaluate DOMS. We found that ASIC3-/- had similar baseline muscle pain, locomotor activity, grip strength, and exercise performance as WT mice. WT showed diminished MWT immediately after exercise indicating they developed IEIP, but ASIC3-/- mice did not. At 24 h after baseline exercise, both ASIC3-/- and WT had similarly lower MWT and grip strength, however, ASIC3-/- displayed significantly lower locomotor activity and repeat exercise performance at 24 h time points compared to WT. In addition, ASIC3-/- mice had higher muscle injury as measured by serum lactate dehydrogenase and creatine kinase levels at 24 h after exercise. These results show that ASIC3 is required for IEIP, but not DOMS, and in fact might play a protective role to prevent muscle injury associated with strenuous exercise.

Keywords:  ASICs; acidosis; delayed-onset muscle soreness; exercise; lactate; muscle afferent; pain; sensory neuron

DOI:  https://doi.org/10.3389/fpain.2023.1215197
Biogerontology. 2023 Oct 04.

The influence of biological sex in human skeletal muscle transcriptome during ageing.

Xiaoyu Huang, Mao Chen, Ya Xiao, Fangyi Zhu, Liying Chen, Xiaoyu Tian, Li Hong.

  Sex is a crucial biological variable, and influence of biological sex on the change of gene expression in ageing skeletal muscle has not yet been fully revealed. In this study, the mRNA expression profiles were obtained from the Gene Expression Omnibus database. Key genes were identified by differential expression analysis and weighted gene co-expression network analysis. The gene set enrichment analysis software and Molecular Signatures Database were used for functional and enrichment analysis. A protein-protein interaction network was constructed using STRING and visualized in Cytoscape. The results were compared between female and male subgroups. Differentially expressed genes and enriched pathways in different sex subgroups shared only limited similarities. The pathways enriched in the female subgroup were more similar to the pathways enriched in the older groups without taking sex difference into consideration. The pathways enriched in the female subgroup were more similar to the pathways enriched in the older groups without taking sex difference into consideration. The muscle myosin filament pathways were downregulated in the both aged female and male samples whereas transforming growth factor beta pathway and extracellular matrix-related pathways were upregulated. With muscle ageing, the metabolism-related pathways, protein synthesis and degradation pathways, results of predicted immune cell infiltration, and gene cluster associated with slow-type myofibers drastically different between the female and male subgroups. This finding may indicate that changes in muscle type with ageing may differ between the sexes in vastus lateralis muscle.

Keywords:  Ageing; Bioinformatics; GEO; Muscle; Sex differences

DOI:  https://doi.org/10.1007/s10522-023-10070-x
Mol Metab. 2023 Sep 28. pii: S2212-8778(23)00146-1. [Epub ahead of print] 101812

Hepatic sialic acid synthesis modulates glucose homeostasis in both liver and skeletal muscle.

Jun Peng, Liming Yu, Linzhang Huang, Vivian A Paschoal, Haiyan Chu, Camila O de Souza, Joseph V Varre, Da Young Oh, Jennifer J Kohler, Xue Xiao, Lin Xu, William L Holland, Philip W Shaul, Chieko Mineo.

   OBJECTIVE: Sialic acid is a terminal monosaccharide of glycans in glycoproteins and glycolipids, and its derivation from glucose is regulated by the rate-limiting enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE). Although the glycans on key endogenous hepatic proteins governing glucose metabolism are sialylated, how sialic acid synthesis and sialylation in the liver influence glucose homeostasis is unknown. Studies were designed to fill this knowledge gap.
METHODS: To decrease the production of sialic acid and sialylation in hepatocytes, a hepatocyte-specific GNE knockdown mouse model was generated, and systemic glucose metabolism, hepatic insulin signaling and glucagon signaling were evaluated in vivo or in primary hepatocytes. Peripheral insulin sensitivity was also assessed. Furthermore, the mechanisms by which sialylation in the liver influences hepatic insulin signaling and glucagon signaling and peripheral insulin sensitivity were identified.
RESULTS: Liver GNE deletion in mice caused an impairment of insulin suppression of hepatic glucose production. This was due to a decrease in the sialylation of hepatic insulin receptors (IR) and a decline in IR abundance due to exaggerated degradation through the Eph receptor B4. Hepatic GNE deficiency also caused a blunting of hepatic glucagon receptor (GCGR) function which was related to a decline in its sialylation and affinity for glucagon. An accompanying upregulation of hepatic FGF21 production caused an enhancement of skeletal muscle glucose disposal that led to an overall increase in glucose tolerance and insulin sensitivity.
CONCLUSION: These collective observations reveal that hepatic sialic acid synthesis and sialylation modulate glucose homeostasis in both the liver and skeletal muscle. By interrogating how hepatic sialic acid synthesis influences glucose control mechanisms in the liver, a new metabolic cycle has been identified in which a key constituent of glycans generated from glucose modulates the systemic control of its precursor.

Keywords:  FGF21; GNE; Glucagon receptor; Glucose; Insulin receptor; Sialic acid

DOI:  https://doi.org/10.1016/j.molmet.2023.101812
J Appl Physiol (1985). 2023 Oct 05.

Microgravity-induced skeletal muscle atrophy in women and men:Implications for long-duration spaceflights to the Moon and Mars.

Todd Trappe, Per Tesch, Björn Alkner, Scott Trappe.

  Inclusion of women on spaceflights has historically been limited. Recently, the first woman that will travel to the Moon was selected and more women are participating in long-duration spaceflights. However, physiological data from real and simulated microgravity exposure are limited in women. This investigation studied women (n=8, 34±1y) and men (n=9, 32±1y) that underwent two (women) or three (men) months of simulated microgravity (6° head-down-tilt bedrest). Quadriceps and triceps surae muscle volumes were assessed via MRI before bedrest, bedrest day 29 (BR29, women and men), bedrest day 57 (BR57, women), and bedrest day 89 (BR89, men). Volume of both muscle groups decreased (p<0.05) in women and men at all bedrest timepoints. Quadriceps muscle volume loss in women was greater than men at one month (BR29: -17% vs. -10%, p<0.05) and this one-month loss for women was similar to men at three months (BR89: -18%, p>0.05). In addition, theloss in women at two months (BR57: -21%) exceeded men at three months (p<0.05). For the triceps surae, there was a trend for greater muscle volume loss in women compared to men at one month (BR29: -18% vs. -16%, p=0.08), and loss in women at two months was similar to men at three months (BR57: -29%, BR89: -29%, p>0.05). The collective evidence suggests that women experience greater lower limb muscle atrophy than men at least through the first four months of microgravity exposure. More sex-specific microgravity studies are needed to help protect the health of women traveling on long-duration orbital and interplanetary spaceflights.

Keywords:  exercise; microgravity; skeletal muscle; weightlessness

DOI:  https://doi.org/10.1152/japplphysiol.00412.2023
J Int Soc Sports Nutr. 2023 Dec;20(1): 2263409

International society of sports nutrition position stand: essential amino acid supplementation on skeletal muscle and Performance.

Arny A Ferrando, Robert R Wolfe, Katie R Hirsch, David D Church, Shiloah A Kviatkovsky, Michael D Roberts, Jeffrey R Stout, Drew E Gonzalez, Ryan J Sowinski, Richard B Kreider, Chad M Kerksick, Nicholas A Burd, Stefan M Pasiakos, Michael J Ormsbee, Shawn M Arent, Paul J Arciero, Bill I Campbell, Trisha A VanDusseldorp, Ralf Jager, Darryn S Willoughby, Douglas S Kalman, Jose Antonio.

  Position Statement: The International Society of Sports Nutrition (ISSN) presents this position based on a critical examination of literature surrounding the effects of essential amino acid (EAA) supplementation on skeletal muscle maintenance and performance. This position stand is intended to provide a scientific foundation to athletes, dietitians, trainers, and other practitioners as to the benefits of supplemental EAA in both healthy and resistant (aging/clinical) populations. EAAs are crucial components of protein intake in humans, as the body cannot synthesize them. The daily recommended intake (DRI) for protein was established to prevent deficiencies due to inadequate EAA consumption. The following conclusions represent the official position of the Society: 1. Initial studies on EAAs' effects on skeletal muscle highlight their primary role in stimulating muscle protein synthesis (MPS) and turnover. Protein turnover is critical for replacing degraded or damaged muscle proteins, laying the metabolic foundation for enhanced functional performance. Consequently, research has shifted to examine the effects of EAA supplementation - with and without the benefits of exercise - on skeletal muscle maintenance and performance. 2. Supplementation with free-form EAAs leads to a quick rise in peripheral EAA concentrations, which in turn stimulates MPS. 3. The safe upper limit of EAA intake (amount), without inborn metabolic disease, can easily accommodate additional supplementation. 4. At rest, stimulation of MPS occurs at relatively small dosages (1.5-3.0 g) and seems to plateau at around 15-18 g. 5. The MPS stimulation by EAAs does not require non-essential amino acids. 6. Free-form EAA ingestion stimulates MPS more than an equivalent amount of intact protein. 7. Repeated EAA-induced MPS stimulation throughout the day does not diminish the anabolic effect of meal intake. 8. Although direct comparisons of various formulas have yet to be investigated, aging requires a greater proportion of leucine to overcome the reduced muscle sensitivity known as "anabolic resistance." 9. Without exercise, EAA supplementation can enhance functional outcomes in anabolic-resistant populations. 10. EAA requirements rise in the face of caloric deficits. During caloric deficit, it's essential to meet whole-body EAA requirements to preserve anabolic sensitivity in skeletal muscle.

Keywords:  Protein; exercise

DOI:  https://doi.org/10.1080/15502783.2023.2263409
Life Sci. 2023 Sep 26. pii: S0024-3205(23)00760-9. [Epub ahead of print]332 122125

Sarcopenia in a type 2 diabetic state: Reviewing literature on the pathological consequences of oxidative stress and inflammation beyond the neutralizing effect of intracellular antioxidants.

Ndivhuwo Muvhulawa, Sithandiwe E Mazibuko-Mbeje, Duduzile Ndwandwe, Sonia Silvestri, Khanyisani Ziqubu, Marakiya T Moetlediwa, Sinenhlanhla X H Mthembu, Jeanine L Marnewick, Francois H Van der Westhuizen, Bongani B Nkambule, Albertus K Basson, Luca Tiano, Phiwayinkosi V Dludla.

  Sarcopenia remains one of the major pathological features of type 2 diabetes (T2D), especially in older individuals. This condition describes gradual loss of muscle mass, strength, and function that reduces the overall vitality and fitness, leading to increased hospitalizations and even fatalities to those affected. Preclinical evidence indicates that dysregulated mitochondrial dynamics, together with impaired activity of the NADPH oxidase system, are the major sources of oxidative stress that drive skeletal muscle damage in T2D. While patients with T2D also display relatively higher levels of circulating inflammatory markers in the serum, including high sensitivity-C-reactive protein, interleukin-6, and tumor necrosis factor-α that are independently linked with the deterioration of muscle function and sarcopenia in T2D. In fact, beyond reporting on the pathological consequences of both oxidative stress and inflammation, the current review highlights the importance of strengthening intracellular antioxidant systems to preserve muscle mass, strength, and function in individuals with T2D.

Keywords:  Inflammation; Muscle wasting; Oxidative stress; Sarcopenia; Therapeutics; Type 2 diabetes

DOI:  https://doi.org/10.1016/j.lfs.2023.122125
BMC Res Notes. 2023 Sep 30. 16(1): 243

Purification of functional mouse skeletal muscle mitochondria using percoll density gradient centrifugation.

Rea Victoria P Anunciado-Koza, Anyonya R Guntur, Calvin P Vary, Carlos A Gartner, Madeleine Nowak, Robert A Koza.

   OBJECTIVE: Our goal was to isolate purified mitochondria from mouse skeletal muscle using a Percoll density gradient and to assess bioenergetic function and purity via Seahorse Extracellular Flux (XF) Analyses and mass spectrometry.
RESULTS: Mitochondria isolated from murine quadriceps femoris skeletal muscle using a Percoll density gradient method allowed for minimally contaminated preparations with time from tissue harvest to mitochondrial isolation and quantification in about 3-4 h. Percoll purification from 100 to 200 mg fresh tissue yielded ~ 200-400 ug protein. Mitochondrial bioenergetics evaluated using the Seahorse XFe96 analyzer, a high-throughput respirometry platform, showed optimum mitochondrial input at 500 ng with respiratory control ratio ranging from 3.9 to 7.1 using various substrates demonstrating a high degree of functionality. Furthermore, proteomic analysis of Percoll-enriched mitochondria isolated from skeletal muscle using this method showed significant enrichment of mitochondrial proteins indicating high sample purity. This study established a methodology that ensures sufficient high quality mitochondria for downstream analyses such as mitochondrial bioenergetics and proteomics.

Keywords:  Bioenergetics; Density gradient; Mitochondria; Percoll purification; Skeletal muscle

DOI:  https://doi.org/10.1186/s13104-023-06519-4
Nat Rev Immunol. 2023 Oct 04.

The effect of physical exercise on anticancer immunity.

Carmen Fiuza-Luces, Pedro L Valenzuela, Beatriz G Gálvez, Manuel Ramírez, Alejandro López-Soto, Richard J Simpson, Alejandro Lucia.

Regular physical activity is associated with lower cancer incidence and mortality, as well as with a lower rate of tumour recurrence. The epidemiological evidence is supported by preclinical studies in animal models showing that regular exercise delays the progression of cancer, including highly aggressive malignancies. Although the mechanisms underlying the antitumorigenic effects of exercise remain to be defined, an improvement in cancer immunosurveillance is likely important, with different immune cell subtypes stimulated by exercise to infiltrate tumours. There is also evidence that immune cells from blood collected after an exercise bout could be used as adoptive cell therapy for cancer. In this Perspective, we address the importance of muscular activity for maintaining a healthy immune system and discuss the effects of a single bout of exercise (that is, 'acute' exercise) and those of 'regular' exercise (that is, repeated bouts) on anticancer immunity, including tumour infiltrates. We also address the postulated mechanisms and the clinical implications of this emerging area of research.

DOI: https://doi.org/10.1038/s41577-023-00943-0
Scand J Med Sci Sports. 2023 Oct 03.

Protein dose requirements to maximize skeletal muscle protein synthesis after repeated bouts of resistance exercise in young trained women.

J E Mallinson, S L Wardle, T J O'Leary, J P Greeves, J Cegielski, J Bass, M S Brook, D J Wilkinson, K Smith, P J Atherton, P L Greenhaff.

  Studies examining the effect of protein (PRO) feeding on post resistance exercise (RE) muscle protein synthesis (MPS) have primarily been performed in men, and little evidence is available regarding the quantity of PRO required to maximally stimulate MPS in trained women following repeated bouts of RE. We therefore quantified acute (4 h and 8 h) and extended (24 h) effects of two bouts of resistance exercise, alongside protein-feeding, in women, and the PRO requirement to maximize MPS. Twenty-four RE trained women (26.6 ± 0.7 years, mean ± SEM) performed two bouts of whole-body RE (3 × 8 repetitions/maneuver at 75% 1-repetition maximum) 4 h apart, with post-exercise ingestion of 15 g, 30 g, or 60 g whey PRO (n = 8/group). Saliva, venous blood, and a vastus lateralis muscle biopsy were taken at 0 h, 4 h, 8 h, and 24 h post-exercise. Plasma leucine and branched chain amino acids were quantified using gas chromatography mass spectrometry (GC-MS) after ingestion of D2 O. Fifteen grams PRO did not alter plasma leucine concentration or myofibrillar synthetic rate (MyoFSR). Thirty and sixty grams PRO increased plasma leucine concentration above baseline (105.5 ± 5.3 μM; 120.2 ± 7.4 μM, respectively) at 4 h (151.5 ± 8.2 μM, p < 0.01; 224.8 ± 16.0 μM, p < 0.001, respectively) and 8 h (176.0 ± 7.3 μM, p < 0.001; 281.7 ± 21.6 μM, p < 0.001, respectively). Ingestion of 30 g PRO increased MyoFSR above baseline (0.068 ± 0.005%/h) from 0 to 4 h (0.140 ± 0.021%/h, p < 0.05), 0 to 8 h (0.121 ± 0.012%/h, p < 0.001), and 0 to 24 h (0.099 ± 0.011%/h, p < 0.01). Ingestion of 60 g PRO increased MyoFSR above baseline (0.063 ± 0.003%/h) from 0 to 4 h (0.109 ± 0.011%/h, p < 0.01), 0 to 8 h (0.093 ± 0.008%/h, p < 0.01), and 0 to 24 h (0.086 ± 0.006%/h, p < 0.01). Post-exercise ingestion of 30 g or 60 g PRO, but not 15 g, acutely increased MyoFSR following two consecutive bouts of RE and extended the anabolic window over 24 h. There was no difference between the 30 g and 60 g responses.

Keywords:  muscle protein synthesis; protein dosing; resistance exercise

DOI:  https://doi.org/10.1111/sms.14506
Front Genet. 2023 ;14 1226766

Case report: a novel deep intronic splice-altering variant in DMD as a cause of Becker muscular dystrophy.

Shala Ghaderi Berntsson, Hans Matsson, Anna Kristoffersson, Valter Niemelä, Hermine A van Duyvenvoorde, Cindy Richel-van Assenbergh, Heleen M van der Klift, Olivera Casar-Borota, Carina Frykholm, Anne-Marie Landtblom.

  We present the case of a male patient who was ultimately diagnosed with Becker muscular dystrophy (BMD; MIM# 300376) after the onset of muscle weakness in his teens progressively led to significant walking difficulties in his twenties. A genetic diagnosis was pursued but initial investigation revealed no aberrations in the dystrophin gene (DMD), although immunohistochemistry and Western blot analysis suggested the diagnosis of dystrophinopathy. Eventually, after more than 10 years, an RNA analysis captured abnormal splicing where 154 nucleotides from intron 43 were inserted between exon 43 and 44 resulting in a frameshift and a premature stop codon. Normal splicing of the DMD gene was also observed. Additionally, a novel variant c.6291-13537A>G in DMD was confirmed in the genomic DNA of the patient. The predicted function of the variant aligns with the mRNA results. To conclude, we here demonstrate that mRNA analysis can guide the diagnosis of non-coding genetic variants in DMD.

Keywords:  Becker muscular dystrophy; MLPA; RNA sequencing; genetics; intronic variant; mRNA

DOI:  https://doi.org/10.3389/fgene.2023.1226766
Oncol Lett. 2023 Nov;26(5): 462

Role of growth differentiation factor 15 in cancer cachexia (Review).

Tingting Ling, Jing Zhang, Fuwan Ding, Lanlan Ma.

  Growth differentiation factor 15 (GDF15), a member of the transforming growth factor-β family, is a stress-induced cytokine. Under normal circumstances, the expression of GDF15 is low in most tissues. It is highly expressed during tissue injury, inflammation, oxidative stress and cancer. GDF15 has been established as a biomarker in patients with cancer, and is associated with cancer cachexia (CC) and poor survival. CC is a multifactorial metabolic disorder characterized by severe muscle and adipose tissue atrophy, loss of appetite, anemia and bone loss. Cachexia leads to reductions in quality of life and tolerance to anticancer therapy, and results in a poor prognosis in cancer patients. Dysregulated GDF15 levels have been discovered in patients with CC and animal models, where they have been found to be involved in anorexia and weight loss. Although studies have suggested that GDF15 mediates anorexia and weight loss in CC through its neuroreceptor, glial cell-lineage neurotrophic factor family receptor α-like, the effects of GDF15 on CC and the potential regulatory mechanisms require further elucidation. In the present review, the characteristics of GDF15 and its roles and molecular mechanisms in CC are elaborated. The targeting of GDF15 as a potential therapeutic strategy for CC is also discussed.

Keywords:  anemia; anorexia; bone loss; cancer cachexia; fat loss; growth differentiation factor 15; muscle atrophy

DOI:  https://doi.org/10.3892/ol.2023.14049