bims-moremu 2023-10-29 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023‒10‒29
34 papers selected by
Anna Vainshtein, Craft Science Inc.

Modulation of sarcopenia phenotypes by glutathione peroxidase 4 overexpression in mice.
Sex-Specific Impact of CARM1 in Skeletal Muscle Adaptations to Exercise.
Proteomics analysis of C2C12 myotubes treated with atrophy inducing cancer cell-derived factors.
Inhibition of p53-MDM2 binding reduces senescent cell abundance and improves the adaptive responses of skeletal muscle from aged mice.
The roles of miRNAs in adult skeletal muscle satellite cells.
Muscle Fiber Phenotype: A Culprit of Abnormal Metabolism and Function in Skeletal Muscle of Humans with Obesity.
The role of extracellular vesicles in skeletal muscle wasting.
Morphological and functional alterations of neuromuscular synapses in a mouse model of ACTA1 congenital myopathy.
Klotho, the Greek goddess controlling the fate of skeletal muscle satellite cells.
Gastric inhibitory polypeptide receptor antagonism suppresses intramuscular adipose tissue accumulation and ameliorates sarcopenia.
The Ca2+/Calmodulin-dependent Calcineurin/NFAT Signaling Pathway in the Pathogenesis of Insulin Resistance in Skeletal Muscle.
The C5aR1 complement receptor: A novel immunomodulator of insulin action in skeletal muscle.
Skeletal Muscle Transcriptome Alterations Related to Declining Physical Function in Older Mice.
Myotube growth is associated with cancer-like metabolic reprogramming and is limited by phosphoglycerate dehydrogenase.
PRMT5 mediates FoxO1 methylation and subcellular localization to regulate lipophagy in myogenic progenitors.
Pharmacological Inhibition of Myostatin in a Mouse Model of Typical Nemaline Myopathy Increases Muscle Size and Force.
Naringenin improves muscle endurance via activation of the Sp1-ERRγ transcriptional axis.
Protocol for the isolation of mouse muscle stem cells using fluorescence-activated cell sorting.
Epitranscriptomics as a New Layer of Regulation of Gene Expression in Skeletal Muscle: Known Functions and Future Perspectives.
L-Isoleucine reverses hyperammonemia-induced myotube mitochondrial dysfunction and post-mitotic senescence: L-isoleucine reverses ammonia induced perturbations.
Empagliflozin induces the transcriptional program for nutrient homeostasis in skeletal muscle in normal mice.
One episode of low intensity aerobic exercise prior to systemic AAV9 administration augments transgene delivery to the heart and skeletal muscle.
Ythdf2-mediated STK11 mRNA decay supports myogenesis by inhibiting the AMPK/mTOR pathway.
The role of ZBP1 in eccentric exercise-induced skeletal muscle necroptosis.
Integrative profiling of metabolome and transcriptome of skeletal muscle after acute exercise intervention in mice.
Exercise training induces alteration of clock genes and myokines expression in tumor-bearing mice.
The impact of life-long strength versus endurance training on muscle fiber morphology2 and phenotype composition in older men.
Single-Cell RNA-Sequencing Provides Insight into Skeletal Muscle Evolution during the Selection of Muscle Characteristics.
Differential activation of AKT isoforms by growth factors in human myotubes.
Prior Treatment with AICAR Causes the Selective Phosphorylation of mTOR Substrates in C2C12 Cells.
The Functional and Anatomical Impacts of Healthy Muscle Ageing.
Pathophysiology of sarcopenia: Genetic factors and their interplay with environmental factors.
The roles of P-selectin in cancer cachexia.
Skeletal muscles and gut microbiota-derived metabolites: novel modulators of adipocyte thermogenesis.

J Physiol. 2023 Oct 25.

Modulation of sarcopenia phenotypes by glutathione peroxidase 4 overexpression in mice.

Hongyang Xu, Agnieszka Czyżowska, Holly Van Remmen, Jacob L Brown.

  Our laboratory previously showed lipid hydroperoxides and oxylipin levels are elevated in response to loss of skeletal muscle innervation and are associated with muscle pathologies. To elucidate the pathological impact of lipid hydroperoxides, we overexpressed glutathione peroxidase 4 (GPx4), an enzyme that targets reduction of lipid hydroperoxides in membranes, in adult CuZn superoxide dismutase knockout (Sod1KO) mice that show accelerated muscle atrophy associated with loss of innervation. The gastrocnemius muscle from Sod1KO mice shows reduced mitochondrial respiration and elevated oxidative stress (F2 -isoprostanes and hydroperoxides) compared to wild-type (WT) mice. Overexpression of GPx4 improved mitochondrial respiration and reduced hydroperoxide generation in Sod1KO mice, but did not attenuate the muscle loss that occurs in Sod1KO mice. In contrast, contractile force generation is reduced in EDL muscle in Sod1KO mice relative to WT mice, and overexpression of GPx4 restored force generation to WT levels in Sod1KO mice. GPx4 overexpression also prevented loss of muscle contractility at the single fibre level in fast-twitch fibres from Sod1KO mice. Muscle fibres from Sod1KO mice were less sensitive to both depolarization and calcium at the single fibre level and exhibited a reduced activation by S-glutathionylation. GPx4 overexpression in Sod1KO mice rescued the deficits in both membrane excitability and calcium sensitivity of fast-twitch muscle fibres. Overexpression of GPx4 also restored the sarco/endoplasmic reticulum Ca2+ -ATPase activity in Sod1KO gastrocnemius muscles. These data suggest that GPx4 plays an important role in preserving excitation-contraction coupling function and Ca2+ homeostasis, and in maintaining muscle and mitochondrial function in oxidative stress-induced sarcopenia. KEY POINTS: Knockout of CuZn superoxide dismutase (Sod1KO) induces elevated oxidative stress with accelerated muscle atrophy and weakness. Glutathione peroxidase 4 (GPx4) plays a fundamental role in the reduction of lipid hydroperoxides in membranes, and overexpression of GPx4 improves mitochondrial respiration and reduces hydroperoxide generation in Sod1KO mice. Muscle contractile function deficits in Sod1KO mice are alleviated by the overexpression of GPx4. GPx4 overexpression in Sod1KO mice rescues the impaired muscle membrane excitability of fast-twitch muscle fibres and improves their calcium sensitivity. Sarco/endoplasmic reticulum Ca2+ -ATPase activity in Sod1KO muscles is decreased, and it is restored by the overexpression of GPx4. Our results confirm that GPx4 plays an important role in preserving excitation-contraction coupling function and Ca2+ homeostasis, and maintaining muscle and mitochondrial function in oxidative stress-induced sarcopenia.

Keywords:  Ca2+ sensitivity; E-C coupling; SERCA activity; lipid peroxidation; mitochondria; muscle function; oxidative stress

DOI:  https://doi.org/10.1113/JP285259
Med Sci Sports Exerc. 2023 Oct 26.

Sex-Specific Impact of CARM1 in Skeletal Muscle Adaptations to Exercise.

Tiffany L vanLieshout, Derek W Stouth, Rozhin Raziee, Anne-Sophie J Sraka, Hooriya A Masood, Sean Y Ng, Stephanie R Mattina, Andrew I Mikhail, Alexander Manta, Vladimir Ljubicic.

PURPOSE: The purpose of this study was to determine how the intersection of coactivator-associated arginine methyltransferase 1 (CARM1) and biological sex impacts skeletal muscle adaptations to chronic physical activity.METHODS: 12-week-old female (F) and male (M) wild-type (WT) and CARM1 skeletal muscle-specific knockout mice (mKO) were randomly assigned to sedentary (SED) or voluntary wheel running (VWR) experimental groups. For 8 weeks, the animals in the VWR cohort had volitional access to running wheels. Subsequently, we performed whole-body functional tests, and 48 hours later muscles were harvested for molecular analysis. Western blotting, enzyme activity assays, as well as confocal and transmission electron microscopy (TEM) were used to examine skeletal muscle biology.
RESULTS: Our data reveal a sex-dependent reduction in VWR volume caused by muscle-specific ablation of CARM1, as F CARM1 mKO mice performed less chronic, volitional exercise than their WT counterparts. Regardless of VWR output, exercise-induced adaptations in physiological function were similar between experimental groups. A broad panel of protein arginine methyltransferase (PRMT) biology measurements, including markers of arginine methyltransferase expression and activity, were unaffected by VWR, except for CARM1 and PRMT7 protein levels, which decreased and increased with VWR, respectively. Changes in myofiber morphology and mitochondrial protein content showed similar trends among animals. However, a closer examination of TEM images revealed contrasting responses to VWR in CARM1 mKO mice compared to WT littermates, particularly in mitochondrial size and fractional area.
CONCLUSIONS: The present findings demonstrate that CARM1 mKO reduces daily running volume in F mice, as well as exercise-evoked skeletal muscle mitochondrial plasticity, which indicates that this enzyme plays an essential role in sex-dependent differences in exercise performance and mitochondrial health.

DOI: https://doi.org/10.1249/MSS.0000000000003333
Proteomics. 2023 Oct 26. e2300020

Proteomics analysis of C2C12 myotubes treated with atrophy inducing cancer cell-derived factors.

Akbar L Marzan, Sai V Chitti, Sriram Gummadi, Taeyoung Kang, Ching-Seng Ang, Suresh Mathivanan.

  Cancer-associated cachexia is a wasting syndrome that results in dramatic loss of whole-body weight, predominantly due to loss of skeletal muscle mass. It has been established that cachexia inducing cancer cells secrete proteins and extracellular vesicles (EVs) that can induce muscle atrophy. Though several studies examined these cancer-cell derived factors, targeting some of these components have shown little or no clinical benefit. To develop new therapies, understanding of the dysregulated proteins and signaling pathways that regulate catabolic gene expression during muscle wasting is essential. Here, we sought to examine the effect of conditioned media (CM) that contain secreted factors and EVs from cachexia inducing C26 colon cancer cells on C2C12 myotubes using mass spectrometry-based label-free quantitative proteomics. We identified significant changes in the protein profile of C2C12 cells upon exposure to C26-derived CM. Functional enrichment analysis revealed enrichment of proteins associated with inflammation, mitochondrial dysfunction, muscle catabolism, ROS production, and ER stress in CM treated myotubes. Furthermore, strong downregulation in muscle structural integrity and development and/or regenerative pathways were observed. Together, these enriched proteins in atrophied muscle could be utilized as potential muscle wasting markers and the dysregulated biological processes could be employed for therapeutic benefit in cancer-induced muscle wasting.

Keywords:  C26 colon carcinoma; C2C12 myotubes; cancer-associated cachexia; impaired myogenesis; muscle atrophy

DOI:  https://doi.org/10.1002/pmic.202300020
Geroscience. 2023 Oct 24.

Inhibition of p53-MDM2 binding reduces senescent cell abundance and improves the adaptive responses of skeletal muscle from aged mice.

Georgia L Nolt, Alexander R Keeble, Yuan Wen, Aubrey C Strong, Nicholas T Thomas, Taylor R Valentino, Camille R Brightwell, Kevin A Murach, Sini Patrizia, Harald Weinstabl, Andreas Gollner, John J McCarthy, Christopher S Fry, Michael Franti, Antonio Filareto, Charlotte A Peterson, Cory M Dungan.

  Skeletal muscle adaptation to external stimuli, such as regeneration following injury and hypertrophy in response to resistance exercise, are blunted with advanced age. The accumulation of senescent cells, along with defects in myogenic progenitor cell (MPC) proliferation, have been strongly linked as contributing factors to age-associated impairment in muscle adaptation. p53 plays an integral role in all these processes, as upregulation of p53 causes apoptosis in senescent cells and prevents mitotic catastrophe in MPCs from old mice. The goal of this study was to determine if a novel pharmaceutical agent (BI01), which functions by upregulating p53 through inhibition of binding to MDM2, the primary p53 regulatory protein, improves muscle regeneration and hypertrophy in old mice. BI01 effectively reduced the number of senescent cells in vitro but had no effect on MPC survival or proliferation at a comparable dose. Following repeated oral gavage with 2 mg/kg of BI01 (OS) or vehicle (OV), old mice (24 months) underwent unilateral BaCl2 injury in the tibialis anterior (TA) muscle, with PBS injections serving as controls. After 7 days, satellite cell number was higher in the TA of OS compared to OV mice, as was the expression of genes involved in ATP production. By 35 days, old mice treated with BI01 displayed reduced senescent cell burden, enhanced regeneration (higher muscle mass and fiber cross-sectional area) and restoration of muscle function relative to OV mice. To examine the impact of 2 mg/kg BI01 on muscle hypertrophy, the plantaris muscle was subjected to 28 days of mechanical overload (MOV) in OS and OV mice. In response to MOV, OS mice had larger plantaris muscles and muscle fibers than OV mice, particularly type 2b + x fibers, associated with reduced senescent cells. Together our data show that BI01 is an effective senolytic agent that may also augment muscle metabolism to enhance muscle regeneration and hypertrophy in old mice.

Keywords:  Hypertrophy; Regeneration; Senescence; Senolytics; Skeletal Muscle

DOI:  https://doi.org/10.1007/s11357-023-00976-2
Free Radic Biol Med. 2023 Oct 23. pii: S0891-5849(23)01075-4. [Epub ahead of print]

The roles of miRNAs in adult skeletal muscle satellite cells.

Pieter Jan Koopmans, Ahmed Ismaeel, Katarzyna Goljanek-Whysall, Kevin A Murach.

  Satellite cells are bona fide muscle stem cells that are indispensable for successful post-natal muscle growth and regeneration after severe injury. These cells also participate in adult muscle adaptation in several capacities. microRNA (miRNA) are post-transcriptional regulators of mRNA that are implicated in several aspects of stem cell function. There is evidence to suggest that miRNAs affect satellite cell behavior in vivo and myogenic progenitor behavior in vitro, but the role of miRNAs in adult skeletal muscle satellite cells is less studied. In this review, we provide evidence for how miRNAs control satellite cell behavior with emphasis on satellite cells of adult muscle in vivo. We first outline how miRNAs are indispensable for satellite cell viability and control the phases of myogenesis. Next, we discuss the interplay between miRNAs and myogenic cell redox status, senescence, and communication to other muscle-resident cells during muscle adaptation. Results from recent satellite cell miRNA profiling studies are also summarized. In vitro experiments in primary myogenic cells and cell lines have been invaluable for exploring the influence of miRNAs, but we identify a need for novel genetic tools to further interrogate how miRNAs control satellite cell behavior in adult skeletal muscle in vivo.

Keywords:  Myogenesis; Senescence; Stem cells; Transcriptomics; myomiRs

DOI:  https://doi.org/10.1016/j.freeradbiomed.2023.10.403
Am J Physiol Endocrinol Metab. 2023 Oct 25.

Muscle Fiber Phenotype: A Culprit of Abnormal Metabolism and Function in Skeletal Muscle of Humans with Obesity.

Nathan Serrano, Jon-Philippe K Hyatt, Joseph A Houmard, Marta Murgia, Christos S Katsanos.

  The proportion of the different types of fibers in a given skeletal muscle contributes to its overall metabolic and functional characteristics. Greater proportion of Type I muscle fibers is associated with favorable oxidative metabolism and function of the muscle. Humans with obesity have lower proportion of Type I muscle fibers. We discuss how lower proportion of Type I fibers in skeletal muscle of humans with obesity may explain metabolic and functional abnormalities reported in these individuals. These include lower muscle glucose disposal rate, mitochondrial content, protein synthesis, and quality/contractile function, as well as increased risk for heart disease, lower levels of physical activity, and propensity for weight gain/resistance to weight loss. We delineate future research directions and the need to examine hybrid muscle fiber populations, which are indicative of a transitory state of fiber phenotype within skeletal muscle. We also describe methodologies for precisely characterizing muscle fibers and gene expression at the single muscle fiber level to enhance our understanding of the regulation of muscle fiber phenotype in obesity. By contextualizing research in the field of muscle fiber type in obesity, we lay a foundation for future advancements and pave the way for translation of this knowledge to address impaired metabolism and function in obesity.

Keywords:  metabolism; muscle fibers; myosin heavy chain; obesity; skeletal muscle

DOI:  https://doi.org/10.1152/ajpendo.00190.2023
J Cachexia Sarcopenia Muscle. 2023 Oct 22.

The role of extracellular vesicles in skeletal muscle wasting.

Xiaohui Zhang, Yanxia Zhao, Wei Yan.

  Skeletal muscle wasting is a complicated metabolic syndrome accompanied by multiple diseases ranging from cancer to metabolic disorders and infectious conditions. The loss of muscle mass significantly impairs muscle function, resulting in poor quality of life and high mortality of associated diseases. The fundamental cellular and molecular mechanisms inducing muscle wasting have been well established, and those related pathways can be activated by a variety of extracellular signals, including inflammatory cytokines and catabolic stimuli. As an emerging messenger of cell-to-cell communications, extracellular vesicles (EVs) also get involved in the progression of muscle wasting by transferring bioactive cargoes including various proteins and non-coding RNAs to skeletal muscle. Like a double-edged sword, EVs play either a pro-wasting or anti-wasting role in the progression of muscle wasting, highly dependent on their parental cells as well as the specific type of cargo they encapsulate. This review aims to illustrate the current knowledge about the biological function of EVs cargoes in skeletal muscle wasting. Additionally, the potential therapeutic implications of EVs in the diagnosis and treatment of skeletal muscle wasting are also discussed. Simultaneously, several outstanding questions are included to shed light on future research.

Keywords:  Exosomes; Extracellular vesicles; Muscle wasting; Therapeutic implications

DOI:  https://doi.org/10.1002/jcsm.13364
Hum Mol Genet. 2023 Oct 26. pii: ddad183. [Epub ahead of print]

Morphological and functional alterations of neuromuscular synapses in a mouse model of ACTA1 congenital myopathy.

Yun Liu, Weichun Lin.

  Mutations in skeletal muscle α-actin (Acta1) cause myopathies. In a mouse model of congenital myopathy, heterozygous Acta1 (H40Y) knock-in (Acta1+/Ki) mice exhibit features of human nemaline myopathy, including premature lethality, severe muscle weakness, reduced mobility, and the presence of nemaline rods in muscle fibers. In this study, we investigated the impact of Acta1 (H40Y) mutation on the neuromuscular junction (NMJ). We found that the NMJs were markedly fragmented in Acta1+/Ki mice. Electrophysiological analysis revealed a decrease in amplitude but increase in frequency of miniature end-plate potential (mEPP) at the NMJs in Acta1+/Ki mice, compared with those in wild type (Acta1+/+) mice. Evoked end-plate potential (EPP) remained similar at the NMJs in Acta1+/Ki and Acta1+/+ mice, but quantal content was increased at the NMJs in Acta1+/Ki, compared with Acta1+/+ mice, suggesting a homeostatic compensation at the NMJs in Acta1+/Ki mice to maintain normal levels of neurotransmitter release. Furthermore, short-term synaptic plasticity of the NMJs was compromised in Acta1+/Ki mice. Together, these results demonstrate that skeletal Acta1 H40Y mutation, albeit muscle-origin, leads to both morphological and functional defects at the NMJ.

Keywords:  acetylcholine receptor; nemaline myopathy; neuromuscular junction; skeletal muscle α-actin; synapse

DOI:  https://doi.org/10.1093/hmg/ddad183
Exp Physiol. 2023 Oct 26.

Klotho, the Greek goddess controlling the fate of skeletal muscle satellite cells.

Mark C Turner.



Keywords:  differentiation; exercise; mechanical loading; myogenesis; satellite cells; wnt signalling

DOI:  https://doi.org/10.1113/EP091515
J Cachexia Sarcopenia Muscle. 2023 Oct 27.

Gastric inhibitory polypeptide receptor antagonism suppresses intramuscular adipose tissue accumulation and ameliorates sarcopenia.

Yuya Takahashi, Hiroki Fujita, Yusuke Seino, Satoko Hattori, Shihomi Hidaka, Tsuyoshi Miyakawa, Atsushi Suzuki, Hironori Waki, Daisuke Yabe, Yutaka Seino, Yuichiro Yamada.

  BACKGROUND: Intramuscular adipose tissue (IMAT) formation derived from muscle fibro-adipogenic progenitors (FAPs) has been recognized as a pathological feature of sarcopenia. This study aimed to explore whether genetic and pharmacological gastric inhibitory polypeptide (GIP) receptor antagonism suppresses IMAT accumulation and ameliorates sarcopenia in mice.METHODS: Whole body composition, grip strength, skeletal muscle weight, tibialis anterior (TA) muscle fibre cross-sectional area (CSA) and TA muscle IMAT area were measured in young and aged male C57BL/6 strain GIP receptor (Gipr)-knockout (Gipr-/- ) and wild-type (Gipr+/+ ) mice. FAPs isolated from lower limb muscles of 12-week-old Gipr+/+ mice were cultured with GIP, and their differentiation into mature adipocytes was examined. Furthermore, TA muscle IMAT area and fibre CSA were measured in untreated Gipr-/- mice and GIP receptor antagonist-treated Gipr+/+ mice after glycerol injection into the TA muscles.
RESULTS: Body composition analysis revealed that 104-week-old Gipr-/- mice had a greater proportion of lean tissue mass (73.7 ± 1.2% vs. 66.5 ± 2.7%, P < 0.05 vs. 104-week-old Gipr+/+ mice) and less adipose tissue mass (13.1 ± 1.3% vs. 19.4 ± 2.6%, P < 0.05 vs. 104-week-old Gipr+/+ mice). Eighty-four-week-old Gipr-/- mice exhibited increases in grip strength (P < 0.05), weights of TA (P < 0.05), soleus (P < 0.01), gastrocnemius (P < 0.05) and quadriceps femoris (P < 0.01) muscles, and average TA muscle fibre CSA (P < 0.05) along with a reduction in TA muscle IMAT area assessed by the number of perilipin-positive cells (P < 0.0001) compared with 84-week-old Gipr+/+ mice. Oil Red O staining analysis revealed 1.6- and 1.7-fold increased adipogenesis in muscle FAPs cultured with 10 and 100 nM of GIP (P < 0.01 and P < 0.001 vs. 0 nM of GIP, respectively). Furthermore, both untreated Gipr-/- mice and GIP receptor antagonist-treated Gipr+/+ mice for 14 days after glycerol injection into the TA muscles at 12 weeks of age showed reduced TA muscle IMAT area (1.39 ± 0.38% and 2.65 ± 0.36% vs. 6.54 ± 1.30%, P < 0.001 and P < 0.01 vs. untreated Gipr+/+ mice, respectively) and increased average TA muscle fibre CSA (P < 0.01 and P < 0.05 vs. untreated Gipr+/+ mice, respectively).
CONCLUSIONS: GIP promotes the differentiation of muscle FAPs into adipocytes and its receptor antagonism suppresses IMAT accumulation and promotes muscle regeneration. Pharmacological GIP receptor antagonism may serve as a novel therapeutic approach for sarcopenia.

Keywords:  GIP receptor; aging; fibro-adipogenic progenitors; intramuscular adipose tissue; sarcopenia

DOI:  https://doi.org/10.1002/jcsm.13346
Exp Clin Endocrinol Diabetes. 2023 Oct 24.

The Ca2+/Calmodulin-dependent Calcineurin/NFAT Signaling Pathway in the Pathogenesis of Insulin Resistance in Skeletal Muscle.

Magdalena Danowska, Marek Strączkowski.

Skeletal muscle is the tissue directly involved in insulin-stimulated glucose uptake. Glucose is the primary energy substrate for contracting muscles, and proper metabolism of glucose is essential for health. Contractile activity and the associated Ca2+signaling regulate functional capacity and muscle mass. A high concentration of Ca2+and the presence of calmodulin (CaM) leads to the activation of calcineurin (CaN), a protein with serine-threonine phosphatase activity. The signaling pathway linked with CaN and transcription factors like the nuclear factor of activated T cells (NFAT) is essential for skeletal muscle development and reprogramming of fast-twitch to slow-twitch fibers. CaN activation may promote metabolic adaptations in muscle cells, resulting in better insulin-stimulated glucose transport. The molecular mechanisms underlying the altered insulin response remain unclear. The role of the CaN/NFAT pathway in regulating skeletal muscle hypertrophy is better described than its involvement in the pathogenesis of insulin resistance. Thus, there are opportunities for future research in that field. This review presents the role of CaN/NFAT signaling and suggests the relationship with insulin-resistant muscles.

DOI: https://doi.org/10.1055/a-2174-7958
Cell Signal. 2023 Oct 25. pii: S0898-6568(23)00359-5. [Epub ahead of print] 110944

The C5aR1 complement receptor: A novel immunomodulator of insulin action in skeletal muscle.

Dinesh S Shah, Alison D McNeilly, Rory J McCrimmon, Harinder S Hundal.

  The complement system constitutes an integral component of the innate immune system and plays a critical role in adaptive immunity. Activation of this system engenders the production of complement peptide fragments, including C5a, which engage G-protein coupled receptors predominantly expressed in immune-associated cells, such as neutrophils, initiating pro-inflammatory responses. Intriguingly, our investigation has unveiled the presence of C5a receptor 1 (C5aR1) expression within skeletal muscle, a key metabolic tissue and primary target of insulin. Herein, we demonstrate that C5aR1 activation by C5a in differentiated human skeletal muscle cells elicits acute suppression of insulin signalling. This suppression manifests as impaired insulin-dependent association between IRS1 and the p85 subunit of PI3-kinase, a 50% reduction in Akt phosphorylation, and a 60% decline in insulin-stimulated glucose uptake. This impairment in insulin signalling is associated with a three-fold elevation in intramyocellular diacylglycerol (DAG) levels and a two-fold increase in cytosolic calcium content, which promote PKC-mediated IRS1 inhibition via enhanced phosphorylation at IRS1 Ser1101. Significantly, our findings demonstrate that structurally diverse C5aR1 antagonists, along with genetic deletion or stable silencing of C5aR1 by 80% using short-hairpin RNA, effectively attenuate repression of insulin signalling by C5a in LHCN-M2 human skeletal myotubes. These results underscore the potential of heightened C5aR1 activation, characteristic of obesity and chronic inflammatory conditions, to detrimentally impact insulin function within skeletal muscle cells. Additionally, the study suggests that agents targeting the C5a-C5aR axis, originally devised for mitigating complement-dependent inflammatory conditions, may offer therapeutic avenues to ameliorate immune-driven insulin resistance in key peripheral metabolic tissues, including skeletal muscle.

Keywords:  Akt; C5aR1; DAG; Glucose uptake; IRS1; PKC

DOI:  https://doi.org/10.1016/j.cellsig.2023.110944
J Ageing Longev. 2023 Jun;3(2): 159-178

Skeletal Muscle Transcriptome Alterations Related to Declining Physical Function in Older Mice.

Ted G Graber, Rosario Maroto, Jill K Thompson, Steven G Widen, Zhaohui Man, Megan L Pajski, Blake B Rasmussen.

  One inevitable consequence of aging is the gradual deterioration of physical function and exercise capacity, driven in part by the adverse effect of age on muscle tissue. We hypothesized that relationships exist between age-related differentially expressed genes (DEGs) in skeletal muscle and age-associated declines in physical function and exercise capacity. Previously, male C57BL/6mice (6m, months old, 24m, and 28m) were tested for physical function using a composite scoring system (comprehensive functional assessment battery, CFAB) comprised of five well-validated tests of physical function. In this study, total RNA was isolated from tibialis anterior samples (n = 8) randomly selected from each age group in the parent study. Using Next Generation Sequencing RNAseq to determine DEGs during aging (6m vs. 28m, and 6m vs. 24m), we found a greater than five-fold increase in DEGs in 28m compared to the 24m. Furthermore, regression of the normalized expression of each DEG with the CFAB score of the corresponding mouse revealed many more DEGs strongly associated (R ≥ |0.70|) with functional status in the older mice. Gene ontology results indicate highly enriched axon guidance and acetyl choline receptor gene sets, suggesting that denervation/reinnervation flux might potentially play a critical role in functional decline. We conclude that specific age-related DEG patterns are associated with declines in physical function, and the data suggest accelerated aging occurring between 24 and 28 months.

Keywords:  RNAseq; frailty; gene expression; physical function; sarcopenia

DOI:  https://doi.org/10.3390/jal3020013
Exp Cell Res. 2023 Oct 23. pii: S0014-4827(23)00371-3. [Epub ahead of print] 113820

Myotube growth is associated with cancer-like metabolic reprogramming and is limited by phosphoglycerate dehydrogenase.

Lian E M Stadhouders, Jonathon A B Smith, Brendan M Gabriel, Sander A J Verbrugge, Tim D Hammersen, Detmar Kolijn, Ilse S P Vogel, Abdalla D Mohamed, Gerard M J de Wit, Carla Offringa, Willem M H Hoogaars, Sebastian Gehlert, Henning Wackerhage, Richard T Jaspers.

  The Warburg effect links growth and glycolysis in cancer. A key purpose of the Warburg effect is to generate glycolytic intermediates for anabolic reactions, such as nucleotides → RNA/DNA and amino acids → protein synthesis. The aim of this study was to investigate whether a similar 'glycolysis-for-anabolism' metabolic reprogramming also occurs in hypertrophying muscles. To interrogate this, we first induced C2C12 myotube hypertrophy with IGF-1. We then added 14C glucose to the differentiation medium and measured radioactivity in isolated protein and RNA to establish whether 14C had entered anabolism. We found that especially protein became radioactive, suggesting a glucose → glycolytic intermediates → non-essential amino acid(s) → protein series of reactions, the rate of which was increased by IGF-1. Next, to investigate the importance of glycolytic flux and non-essential amino acid synthesis for myotube hypertrophy, we exposed C2C12 and primary mouse myotubes to the glycolysis inhibitor 2-Deoxy-d-glucose (2DG). We found that inhibiting glycolysis lowered C2C12 and primary myotube size. Similarly, siRNA silencing of PHGDH, the key enzyme of the serine biosynthesis pathway, decreased C2C12 and primary myotube size; whereas retroviral PHGDH overexpression increased C2C12 myotube size. Together these results suggest that glycolysis is important for hypertrophying myotubes, which reprogram their metabolism to facilitate anabolism, similar to cancer cells.

Keywords:  Glycolysis; Hypertrophy; Insulin-like growth factor I; Metabolism; Skeletal muscle; Warburg effect

DOI:  https://doi.org/10.1016/j.yexcr.2023.113820
Cell Rep. 2023 Oct 24. pii: S2211-1247(23)01341-4. [Epub ahead of print]42(11): 113329

PRMT5 mediates FoxO1 methylation and subcellular localization to regulate lipophagy in myogenic progenitors.

Kun Ho Kim, Stephanie N Oprescu, Madigan M Snyder, Aran Kim, Zhihao Jia, Feng Yue, Shihuan Kuang.

  Development is regulated by various factors, including protein methylation status. While PRMT5 is well known for its roles in oncogenesis by mediating symmetric di-methylation of arginine, its role in normal development remains elusive. Using Myod1Cre to drive Prmt5 knockout in embryonic myoblasts (Prmt5MKO), we dissected the role of PRMT5 in myogenesis. The Prmt5MKO mice are born normally but exhibit progressive muscle atrophy and premature death. Prmt5MKO inhibits proliferation and promotes premature differentiation of embryonic myoblasts, reducing the number and regenerative function of satellite cells in postnatal mice. Mechanistically, PRMT5 methylates and destabilizes FoxO1. Prmt5MKO increases the total FoxO1 level and promotes its cytoplasmic accumulation, leading to activation of autophagy and depletion of lipid droplets (LDs). Systemic inhibition of autophagy in Prmt5MKO mice restores LDs in myoblasts and moderately improves muscle regeneration. Together, PRMT5 is essential for muscle development and regeneration at least partially through mediating FoxO1 methylation and LD turnover.

Keywords:  CP: Developmental biology; CP: Molecular biology; PRMT; PTM; SCs; autophagy; myogenesis; posttranslational modification; protein arginine methyltransferase; satellite cells

DOI:  https://doi.org/10.1016/j.celrep.2023.113329
Int J Mol Sci. 2023 Oct 12. pii: 15124. [Epub ahead of print]24(20):

Pharmacological Inhibition of Myostatin in a Mouse Model of Typical Nemaline Myopathy Increases Muscle Size and Force.

Johan Lindqvist, Henk Granzier.

  Nemaline myopathy is one of the most common non-dystrophic congenital myopathies. Individuals affected by this condition experience muscle weakness and muscle smallness, often requiring supportive measures like wheelchairs or respiratory support. A significant proportion of patients, approximately one-third, exhibit compound heterozygous nebulin mutations, which usually give rise to the typical form of the disease. Currently, there are no approved treatments available for nemaline myopathy. Our research explored the modulation of myostatin, a negative regulator of muscle mass, in combating the muscle smallness associated with the disease. To investigate the effect of myostatin inhibition, we employed a mouse model with compound heterozygous nebulin mutations that mimic the typical form of the disease. The mice were treated with mRK35, a myostatin antibody, through weekly intraperitoneal injections of 10 mg/kg mRK35, commencing at two weeks of age and continuing until the mice reached four months of age. The treatment resulted in an increase in body weight and an approximate 20% muscle weight gain across most skeletal muscles, without affecting the heart. The minimum Feret diameter of type IIA and IIB fibers exhibited an increase in compound heterozygous mice, while only type IIB fibers demonstrated an increase in wild-type mice. In vitro mechanical experiments conducted on intact extensor digitorum longus muscle revealed that mRK35 augmented the physiological cross-sectional area of muscle fibers and enhanced absolute tetanic force in both wild-type and compound heterozygous mice. Furthermore, mRK35 administration improved grip strength in treated mice. Collectively, these findings indicate that inhibiting myostatin can mitigate the muscle deficits in nebulin-based typical nemaline myopathy, potentially serving as a much-needed therapeutic option.

Keywords:  myostatin; nebulin; nemaline myopathy

DOI:  https://doi.org/10.3390/ijms242015124
Cell Rep. 2023 Oct 23. pii: S2211-1247(23)01300-1. [Epub ahead of print]42(11): 113288

Naringenin improves muscle endurance via activation of the Sp1-ERRγ transcriptional axis.

Zhenyu Lv, Jiao Meng, Sheng Yao, Fu Xiao, Shilong Li, Haoyang Shi, Chen Cui, Kaixian Chen, Xiaomin Luo, Yang Ye, Chang Chen.

  Skeletal muscle function declines in the aging process or disease; however, until now, skeletal muscle has remained one of the organs most undertreated with medication. In this study, naringenin (NAR) was found to build muscle endurance in wild-type mice of different ages by increasing oxidative myofiber numbers and aerobic metabolism, and it ameliorates muscle dysfunction in mdx mice. The transcription factor Sp1 was identified as a direct target of NAR and was shown to mediate the function of NAR on muscle. Moreover, the binding site of NAR on Sp1 was further validated as GLN-110. NAR enhances the binding of Sp1 to the CCCTGCCCTC sequence of the Esrrg promoter by promoting Sp1 phosphorylation, thus upregulating Esrrg expression. The identification of the Sp1-ERRγ transcriptional axis is of great significance in basic muscle research, and this function of NAR has potential implications for the improvement of muscle function and the prevention of muscle atrophy.

Keywords:  CP: Metabolism; CP: Molecular biology; Duchenne muscular dystrophy; energy metabolism; fiber type; muscle atrophy; naringenin; skeletal muscle

DOI:  https://doi.org/10.1016/j.celrep.2023.113288
STAR Protoc. 2023 Oct 22. pii: S2666-1667(23)00623-8. [Epub ahead of print]4(4): 102656

Protocol for the isolation of mouse muscle stem cells using fluorescence-activated cell sorting.

Gabriel Elizalde, Alma Zuniga Munoz, Albert E Almada.

  Muscle stem cells (MuSCs) are the building blocks for regenerating skeletal muscle after trauma. If we intend to maximize the therapeutic potential of MuSCs, we must further study their molecular and functional properties. Here, we present a protocol for the isolation of mouse MuSCs via a two-step enzymatic and mechanical dissociation of skeletal muscle coupled with fluorescence-activated cell sorting (FACS). FACS-isolated MuSCs can be used for various downstream applications including cell culture, cell transduction, immunofluorescence, and gene expression assays. For complete details on the use and execution of this protocol, please refer to Almada et al. (2021).1.

Keywords:  Antibody; Cell Differentiation; Cell isolation; Flow Cytometry; Gene Expression; Stem Cells

DOI:  https://doi.org/10.1016/j.xpro.2023.102656
Int J Mol Sci. 2023 Oct 13. pii: 15161. [Epub ahead of print]24(20):

Epitranscriptomics as a New Layer of Regulation of Gene Expression in Skeletal Muscle: Known Functions and Future Perspectives.

Carol Imbriano, Viviana Moresi, Silvia Belluti, Alessandra Renzini, Giorgia Cavioli, Eleonora Maretti, Susanna Molinari.

  Epitranscriptomics refers to post-transcriptional regulation of gene expression via RNA modifications and editing that affect RNA functions. Many kinds of modifications of mRNA have been described, among which are N6-methyladenosine (m6A), N1-methyladenosine (m1A), 7-methylguanosine (m7G), pseudouridine (Ψ), and 5-methylcytidine (m5C). They alter mRNA structure and consequently stability, localization and translation efficiency. Perturbation of the epitranscriptome is associated with human diseases, thus opening the opportunity for potential manipulations as a therapeutic approach. In this review, we aim to provide an overview of the functional roles of epitranscriptomic marks in the skeletal muscle system, in particular in embryonic myogenesis, muscle cell differentiation and muscle homeostasis processes. Further, we explored high-throughput epitranscriptome sequencing data to identify RNA chemical modifications in muscle-specific genes and we discuss the possible functional role and the potential therapeutic applications.

Keywords:  RNA modifications; epitranscriptomics; gene expression; m6A; skeletal muscle

DOI:  https://doi.org/10.3390/ijms242015161
J Nutr Biochem. 2023 Oct 21. pii: S0955-2863(23)00231-0. [Epub ahead of print] 109498

L-Isoleucine reverses hyperammonemia-induced myotube mitochondrial dysfunction and post-mitotic senescence: L-isoleucine reverses ammonia induced perturbations.

Avinash Kumar, Annette Bellar, Saurabh Mishra, Jinendiran Sekar, Nicole Welch.

  Perturbations in the metabolism of ammonia, a cytotoxic endogenous metabolite, occur in a number of chronic diseases, with consequent hyperammonemia. Increased skeletal muscle ammonia uptake causes metabolic, molecular and phenotype alterations including cataplerosis of (loss of tricarboxylic acid cycle (TCA) cycle intermediate) α-ketoglutarate (αKG), mitochondrial oxidative dysfunction, and a senescence associated molecular phenotype (SAMP). L-Isoleucine (Ile) is an essential, branched-chain amino acid (BCAA) that simultaneously provides acetyl-CoA as an oxidative substrate and succinyl-CoA for anaplerosis (providing TCA cycle intermediates). Our multiomics analyses in myotubes and skeletal muscle from hyperammonemic mice and human patients with cirrhosis showed perturbations in BCAA transporters and catabolism. We therefore determined if Ile reverses hyperammonemia-induced impaired mitochondrial oxidative function and SAMP. Studies were performed in differentiated murine C2C12 myotubes that were early passage, late passage (senescent), or those depleted of LAT1/SLC7A5 and human induced pluripotent stem cell-derived myotubes (hiPSCM). Ile reverses hyperammonemia-induced reduction in maximum respiratory capacity, complex I,II and III function in early passage murine myotubes and hiPSCM. Consistently, low ATP content and impaired global protein synthesis (high energy requiring cellular process) during hyperammonemia are reversed by Ile in murine myotubes and hiPSCM. Lower abundance of critical regulators of protein synthesis in mTORC1 signaling, and increased phosphorylation of eukaryotic initiation factor 2α are also reversed by Ile. Genetic depletion studies showed that Ile responses are independent of the amino acid transporter LAT1/SLC7A5. Our studies show that Ile reverses the hyperammonemia-induced impaired mitochondrial oxidative function, cataplerosis and SAMP in a LAT1/SLC7A5 transporter-independent manner.

Keywords:  L-isoleucine; anaplerosis; cataplerosis; hyperammonemia; mitochondrial oxidation; myotube

DOI:  https://doi.org/10.1016/j.jnutbio.2023.109498
Sci Rep. 2023 Oct 21. 13(1): 18025

Empagliflozin induces the transcriptional program for nutrient homeostasis in skeletal muscle in normal mice.

Ryo Kawakami, Hiroki Matsui, Miki Matsui, Tatsuya Iso, Tomoyuki Yokoyama, Hideki Ishii, Masahiko Kurabayashi.

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) improve heart failure (HF) outcomes across a range of patient characteristics. A hypothesis that SGLT2i induce metabolic change similar to fasting has recently been proposed to explain their profound clinical benefits. However, it remains unclear whether SGLT2i primarily induce this change in physiological settings. Here, we demonstrate that empagliflozin administration under ad libitum feeding did not cause weight loss but did increase transcripts of the key nutrient sensors, AMP-activated protein kinase and nicotinamide phosphoribosyltransferase, and the master regulator of mitochondrial gene expression, PGC-1α, in quadriceps muscle in healthy mice. Expression of these genes correlated with that of PPARα and PPARδ target genes related to mitochondrial metabolism and oxidative stress response, and also correlated with serum ketone body β-hydroxybutyrate. These results were not observed in the heart. Collectively, this study revealed that empagliflozin activates transcriptional programs critical for sensing and adaptation to nutrient availability intrinsic to skeletal muscle rather than the heart even in normocaloric condition. As activation of PGC-1α is sufficient for metabolic switch from fatigable, glycolytic metabolism toward fatigue-resistant, oxidative mechanism in skeletal muscle myofibers, our findings may partly explain the improvement of exercise tolerance in patients with HF receiving empagliflozin.

DOI: https://doi.org/10.1038/s41598-023-45390-y
J Transl Med. 2023 10 24. 21(1): 748

One episode of low intensity aerobic exercise prior to systemic AAV9 administration augments transgene delivery to the heart and skeletal muscle.

Christina A Pacak, Silveli Suzuki-Hatano, Fatemeh Khadir, Audrey L Daugherty, Mughil Sriramvenugopal, Bennett J Gosiker, Peter B Kang, William Todd Cade.

  INTRODUCTION: The promising potential of adeno-associated virus (AAV) gene delivery strategies to treat genetic disorders continues to grow with an additional three AAV-based therapies recently approved by the Food and Drug Administration and dozens of others currently under evaluation in clinical trials. With these developments, it has become increasingly apparent that the high doses currently needed for efficacy carry risks of toxicity and entail enormous manufacturing costs, especially for clinical grade products. Strategies to increase the therapeutic efficacy of AAV-mediated gene delivery and reduce the minimal effective dose would have a substantial impact on this field. We hypothesized that an exercise-induced redistribution of tissue perfusion in the body to favor specific target organs via acute aerobic exercise prior to systemic intravenous (IV) AAV administration could increase efficacy.BACKGROUND: Aerobic exercise triggers an array of downstream physiological effects including increased perfusion of heart and skeletal muscle, which we expected could enhance AAV transduction. Prior preclinical studies have shown promising results for a gene therapy approach to treat Barth syndrome (BTHS), a rare monogenic cardioskeletal myopathy, and clinical studies have shown the benefit of low intensity exercise in these patients, making this a suitable disease in which to test the ability of aerobic exercise to enhance AAV transduction.
METHODS: Wild-type (WT) and BTHS mice were either systemically administered AAV9 or completed one episode of low intensity treadmill exercise immediately prior to systemic administration of AAV9.
RESULTS: We demonstrate that a single episode of acute low intensity aerobic exercise immediately prior to IV AAV9 administration improves marker transgene delivery in WT mice as compared to mice injected without the exercise pre-treatment. In BTHS mice, prior exercise improved transgene delivery and additionally increased improvement in mitochondrial gene transcription levels and mitochondrial function in the heart and gastrocnemius muscles as compared to mice treated without exercise.
CONCLUSIONS: Our findings suggest that one episode of acute low intensity aerobic exercise improves AAV9 transduction of heart and skeletal muscle. This low-risk, cost effective intervention could be implemented in clinical trials of individuals with inherited cardioskeletal disease as a potential means of improving patient safety for human gene therapy.

Keywords:  AAV; AAV9; Adeno-associated virus; Aerobic exercise; Barth syndrome; Cardioskeletal myopathy; Gene therapy; Systemic gene delivery; TAFAZZIN

DOI:  https://doi.org/10.1186/s12967-023-04626-1
Int J Biol Macromol. 2023 Oct 24. pii: S0141-8130(23)04512-9. [Epub ahead of print] 127614

Ythdf2-mediated STK11 mRNA decay supports myogenesis by inhibiting the AMPK/mTOR pathway.

Kaiping Deng, Zhipeng Liu, Xiaodan Li, Caifang Ren, Yixuan Fan, Jinjing Guo, Peizhen Li, Mingtian Deng, Gang Xue, Xiaorong Yu, Jianfei Shi, Yanli Zhang, Feng Wang.

  An emerging research focus is the role of m6A modifications in mediating the post-transcriptional regulation of mRNA during mammalian development. Recent evidence suggests that m6A methyltransferases and demethylases play critical roles in skeletal muscle development. Ythdf2 is a m6A "reader" protein that mediates mRNA degradation in an m6A-dependent manner. However, the specific function of Ythdf2 in skeletal muscle development and the underlying mechanisms remain unclear. Here, we observed that Ythdf2 expression was significantly upregulated during myogenic differentiation, whereas Ythdf2 knockdown markedly inhibited myoblast proliferation and differentiation. Combined analysis of high-throughput sequencing, Co-IP, and RIP assay revealed that Ythdf2 could bind to m6A sites in STK11 mRNA and form an Ago2 silencing complex to promote its degradation, thereby regulating its expression and consequently, the AMPK/mTOR pathway. Furthermore, STK11 downregulation partially rescued Ythdf2 knockdown-induced impairment of proliferation and myogenic differentiation by inhibiting the AMPK/mTOR pathway. Collectively, our results indicate that Ythdf2 mediates the decay of STK11 mRNA, an AMPK activator, in an Ago2 system-dependent manner, thereby driving skeletal myogenesis by suppressing the AMPK/mTOR pathway. These findings further enhance our understanding of the molecular mechanisms underlying RNA methylation in the regulation of myogenesis and provide valuable insights for conducting in-depth studies on myogenesis.

Keywords:  Myogenesis; RNA degradation; STK11; Ythdf2; m(6)A modification

DOI:  https://doi.org/10.1016/j.ijbiomac.2023.127614
J Muscle Res Cell Motil. 2023 Oct 27.

The role of ZBP1 in eccentric exercise-induced skeletal muscle necroptosis.

Kexin Shi, Xiaoxue Wang, Zhifei Ke, Junping Li.

  This study aimed to explore the occurrence of necroptosis in skeletal muscle after eccentric exercise and investigate the role and possible mechanisms of ZBP1 and its related pathway proteins in the process, providing a theoretical basis for the study of exercise-induced skeletal muscle injury and recovery. Forty-eight male adult Sprague-Dawley rats were randomly divided into a control group (C, n = 8) and an exercise group (E, n = 40). The exercise group was further divided into 0 h (E0), 12 h (E12), 24 h (E24), 48 h (E48), and 72 h (E72) after exercise, with 8 rats in each subgroup. At each time point, gastrocnemius muscle was collected under general anesthesia. The expression levels of ZBP1 and its related pathway proteins were assessed using Western blot analysis. The colocalization of pathway proteins was examined using immunofluorescence staining. After 48 h of eccentric exercise, the expression of necroptosis marker protein MLKL reached its peak (P < 0.01), and the protein levels of ZBP1, RIPK3, and HMGB1 also peaked (P < 0.01). At 48 h post high-load eccentric exercise, there was a significant increase in colocalization of ZBP1/RIPK3 pathway proteins, reaching a peak (P < 0.01). (1) Eccentric exercise induced necroptosis in skeletal muscle, with MLKL, p-MLKLS358, and HMGB1 significantly elevated, especially at 48 h after exercise. (2) After eccentric exercise, the ZBP1/RIPK3-related pathway proteins ZBP1, RIPK3, and p-RIPK3S232 were significantly elevated, particularly at 48 h after exercise. (3) Following high-load eccentric exercise, there was a significant increase in the colocalization of ZBP1/RIPK3 pathway proteins, with a particularly pronounced elevation observed at 48 h post-exercise.

Keywords:  Exercise; MLKL; Necroptosis; Skeletal muscle; ZBP1

DOI:  https://doi.org/10.1007/s10974-023-09660-6
Front Physiol. 2023 ;14 1273342

Integrative profiling of metabolome and transcriptome of skeletal muscle after acute exercise intervention in mice.

Xing Ye, Renyi Liu, Zhixian Qiao, Xiaocui Chai, Yan Wang.

  This study aims to explore the molecular regulatory mechanisms of acute exercise in the skeletal muscle of mice. Male C57BL/6 mice were randomly assigned to the control group, and the exercise group, which were sacrificed immediately after an acute bout of exercise. The study was conducted to investigate the metabolic and transcriptional profiling in the quadriceps muscles of mice. The results demonstrated the identification of 34 differentially expressed metabolites (DEMs), with 28 upregulated and 6 downregulated, between the two groups. Metabolic pathway analysis revealed that these DEMs were primarily enriched in several, including the citrate cycle, propanoate metabolism, and lysine degradation pathways. In addition, the results showed a total of 245 differentially expressed genes (DEGs), with 155 genes upregulated and 90 genes downregulated. KEGG analysis indicated that these DEGs were mainly enriched in various pathways such as ubiquitin mediated proteolysis and FoxO signaling pathway. Furthermore, the analysis revealed significant enrichment of DEMs and DEGs in signaling pathways such as protein digestion and absorption, ferroptosis signaling pathway. In summary, the identified multiple metabolic pathways and signaling pathways were involved in the exercise-induced physiological regulation of skeletal muscle, such as the TCA cycle, oxidative phosphorylation, protein digestion and absorption, the FoxO signaling pathway, ubiquitin mediated proteolysis, ferroptosis signaling pathway, and the upregulation of KLF-15, FoxO1, MAFbx, and MuRF1 expression could play a critical role in enhancing skeletal muscle proteolysis.

Keywords:  acute exercise; metabolome; mice; quadriceps; skeletal muscle; transcriptome

DOI:  https://doi.org/10.3389/fphys.2023.1273342
Cell Biochem Funct. 2023 Oct 25.

Exercise training induces alteration of clock genes and myokines expression in tumor-bearing mice.

Alexandre Abilio de Souza Teixeira, Luana Biondo, Loreana Sanches Silveira, Edson A Lima, Tiego A Diniz, Fabio Santos Lira, Marilia Seelaender, José Cesar Rosa Neto.

  To investigate the impact of different exercise training schedules (following a fixed schedule or at random times of the day) on clock genes and myokine expression patterns in the skeletal muscle of tumor-bearing mice. Mice were divided into three groups: tumor (LLC), tumor + exercise training (LLC + T) always performed at the same time of the day (ZT2) and exercise training at random times of the day (ZTAlt). Mice were inoculated subcutaneously with Lewis lung carcinoma cells. The gastrocnemius muscle was dissected and the clock gene expression (Clock/Per1/Per2/Per3/Rev-Erbα/GAPDH) was investigated by quantitative reverse transcription polymerase chain reaction with SYBR® Green. Myokine content in muscle (tumour necrosis factor alpha/IL-10/IL-4) was assessed by enzyme-linked immunosorbent assay. At the end of the protocol, the trained groups showed a reduction in total weight, when compared to Lewis lung carcinoma. Tumor weight was lower in the LLC + T (ZTAlt), when compared to LLC. Clock gene mRNA expression showed a significant increase for ZT20 in the groups that performed physical exercise at LLC + T (ZTAlt), when compared with LLC. The Per family showed increased mRNA expression in ZT4 in both trained mice groups, when compared with LLC. LLC + T (ZTAlt) presented reduction of the expression of anti-inflammatory myokines (Il-10/IL-4) during the night, compared with LLC + T(ZT2). Exercise training is able to induce marked modification of clock gene expression and of the production of myokines, in a way that is dependent on schedule exercise training strategy. Taken together, the results show that exercise is a potent Zeitgeber and may thus contribute to change clock genes expression and myokines that are able to reduce the tumor weight.

Keywords:  cancer; circadian rhythms; health; muscle; physical exercise

DOI:  https://doi.org/10.1002/cbf.3872
J Appl Physiol (1985). 2023 Oct 26.

The impact of life-long strength versus endurance training on muscle fiber morphology2 and phenotype composition in older men.

Tiril Tøien, Jakob Lindberg Nielsen, Ole Kristian Berg, Mathias Forsberg Brobakken, Stian Kwak Nyberg, Lars Espedal, Thomas Malmo, Ulrik Frandsen, Per Aaagard, Eivind Wang.

  Aging is typically associated with decreased muscle strength and rate of force development (RFD), partly explained by motor unit remodeling due to denervation, and subsequent loss of fast-twitch type II myofibers. Exercise is commonly advocated to counteract this detrimental loss. However, it is unclear how life-long strength- versus endurance-training may differentially affect markers of denervation and reinnervation of skeletal myofibers and, in turn, affect the proportion and morphology of fast-twitch type II musculature. Thus, we compared fiber type distribution, fiber type grouping, and the prevalence of atrophic myofibers (≤1494µm2) in strength-trained (OS) versus endurance-trained (OE) master athletes and compared the results to recreationally active older adults (all >70yr, OC) and young habitually active references (<30yr, YC). Immunofluorescent stainings were performed on biopsy samples from vastus lateralis, along with leg press maximal strength and RFD measurements. OS demonstrated similar type II fiber distribution (OS:52.0±16.4%; YC:51.1±14.4%), fiber type grouping, maximal strength (OS:170.0±18.9kg, YC:151.0±24.4kg), and RFD (OS:3993±894N‧s-1, YC:3470±1394N‧s-1) as young, and absence of atrophic myofibers (OS:0.2±0.7%; YC: 0.1±0.4%). In contrast, OE and OC exhibited more atrophic fibers (OE:1.2±1.0%; OC: 1.1±1.4%), more grouped fibers, and smaller proportion of type II fibers (OE:39.3±11.9%; OC: 35.0±12.4%) than OS and YC (all p<0.05). In conclusion, strength-trained master athletes were characterized by similar muscle morphology as young, which was not the case for recreationally active or endurance-trained old. These results indicate that strength training may preserve type II fibers with advancing age in older men, likely as a result of chronic use of high contractile force generation.

Keywords:  denervation; fast-twitch type II fibres; neural cell adhesion molecule (NCAM); older adults; pyknotic nuclei

DOI:  https://doi.org/10.1152/japplphysiol.00208.2023
Adv Sci (Weinh). 2023 Oct 23. e2305080

Single-Cell RNA-Sequencing Provides Insight into Skeletal Muscle Evolution during the Selection of Muscle Characteristics.

Doudou Xu, Boyang Wan, Kai Qiu, Yubo Wang, Xin Zhang, Ning Jiao, Enfa Yan, Jiangwei Wu, Run Yu, Shuai Gao, Min Du, Chousheng Liu, Mingzhou Li, Guoping Fan, Jingdong Yin.

  Skeletal muscle comprises a large, heterogeneous assortment of cell populations that interact to maintain muscle homeostasis, but little is known about the mechanism that controls myogenic development in response to artificial selection. Different pig (Sus scrofa) breeds exhibit distinct muscle phenotypes resulting from domestication and selective breeding. Using unbiased single-cell transcriptomic sequencing analysis (scRNA-seq), the impact of artificial selection on cell profiles is investigated in neonatal skeletal muscle of pigs. This work provides panoramic muscle-resident cell profiles and identifies novel and breed-specific cells, mapping them on pseudotime trajectories. Artificial selection has elicited significant changes in muscle-resident cell profiles, while conserving signs of generational environmental challenges. These results suggest that fibro-adipogenic progenitors serve as a cellular interaction hub and that specific transcription factors identified here may serve as candidate target regulons for the pursuit of a specific muscle phenotype. Furthermore, a cross-species comparison of humans, mice, and pigs illustrates the conservation and divergence of mammalian muscle ontology. The findings of this study reveal shifts in cellular heterogeneity, novel cell subpopulations, and their interactions that may greatly facilitate the understanding of the mechanism underlying divergent muscle phenotypes arising from artificial selection.

Keywords:  fibro-adipogenic progenitors; muscle characteristics; neonatal myogenesis; pigs, single-cell RNA-sequencing

DOI:  https://doi.org/10.1002/advs.202305080
Physiol Rep. 2023 Oct;11(20): e15805

Differential activation of AKT isoforms by growth factors in human myotubes.

Brandon M Roberts, Alyssa V Geddis, Ronald W Matheny.

  AKT signaling plays a crucial role in muscle physiology, and is activated by stimuli, including insulin, growth factors, and exercise. Three AKT isoforms have been identified in mammals, and they possess both distinct and redundant functions. However, it is currently unknown what the predominant AKT isoform is in primary human skeletal myotubes, and very little is known regarding the effects of insulin and insulin-like growth factor-I (IGF-I) on AKT isoforms activation in human myotubes. Thus, we sought to determine the abundances of each AKT isoform in primary human skeletal myotubes and their responses to insulin or IGF-I. Analysis of protein lysates by liquid chromatography-parallel reaction monitoring/mass spectrometry revealed that AKT1 was the most abundant AKT isoform and AKT3 was the least-abundant isoform. Next, myotubes were treated with either 100 nM insulin or 10 nM IGF-I for 5, 20, 45, or 60 min. In response to insulin, there was a significant treatment effect on phosphorylation of AKT1 and AKT2, but not AKT3 (p < 0.01). In response to IGF-I, there was a significant treatment effect on phosphorylation of pan-AKT at all timepoints compared to control (p < 0.01). Next, we determined how much of the total AKT isoform pool was phosphorylated. For insulin stimulation, AKT1 was significantly higher than AKT2 at 5 min and 60 min posttreatment (p < 0.05 both) and significantly different than AKT3 at all timepoints (p < 0.05). For IGF-I stimulation, AKT1 was significantly higher than AKT2 at 45 and 60 min posttreatment (p < 0.05 both) and significantly higher than AKT3 at all timepoints (p < 0.05). Our findings reveal the differential phosphorylation patterns among the AKT isoforms and suggest a potential explanation for the regulatory role of AKT1 in skeletal muscle.

Keywords:  PKB; anabolic; myosin; protein synthesis; skeletal muscle

DOI:  https://doi.org/10.14814/phy2.15805
Curr Issues Mol Biol. 2023 Sep 30. 45(10): 8040-8052

Prior Treatment with AICAR Causes the Selective Phosphorylation of mTOR Substrates in C2C12 Cells.

Cass J Dedert, Kazimir R Bagdady, Jonathan S Fisher.

  Metabolic stress in skeletal muscle cells causes sustained metabolic changes, but the mechanisms of the prolonged effects are not fully known. In this study, we tested C2C12 cells with the AMP-activated protein kinase (AMPK) stimulator AICAR and measured the changes in the metabolic pathways and signaling kinases. AICAR caused an acute increase in the phosphorylation of the AMPK target ULK1, the mTORC1 substrate S6K, and the mTORC2 target Akt. Intriguingly, prior exposure to AICAR only decreased glucose-6 phosphate dehydrogenase activity when it underwent three-hour recovery after exposure to AICAR in a bicarbonate buffer containing glucose (KHB) instead of Dulbecco's Minimum Essential Medium (DMEM). The phosphorylation of the mTORC1 target S6K was increased after recovery in DMEM but not KHB, although this appeared to be specific to S6K, as the phosphorylation of the mTORC1 target site on ULK1 was not altered when the cells recovered in DMEM. The phosphorylation of mTORC2 target sites was also heterogenous under these conditions, with Akt increasing at serine 473 while other targets (SGK1 and PKCα) were unaffected. The exposure of cells to rapamycin (an mTORC1 inhibitor) and PP242 (an inhibitor of both mTOR complexes) revealed the differential phosphorylation of mTORC2 substrates. Taken together, the data suggest that prior exposure to AICAR causes the selective phosphorylation of mTOR substrates, even after prolonged recovery in a nutrient-replete medium.

Keywords:  5-aminoimidazole-4-carboxamide ribonucleoside; C2C12 cells; mammalian target of rapamycin; mechanistic target of rapamycin; unc-like kinase 1

DOI:  https://doi.org/10.3390/cimb45100508
Biology (Basel). 2023 Oct 23. pii: 1357. [Epub ahead of print]12(10):

The Functional and Anatomical Impacts of Healthy Muscle Ageing.

James P Charles, Karl T Bates.

  Even "healthy" muscle ageing is often associated with substantial changes in muscle form and function and can lead to increased injury risks and significant negative impacts on quality of life. However, the impacts of healthy muscle ageing on the fibre architecture and microstructure of different muscles and muscle groups throughout the lower limb, and how these are related to their functional capabilities, are not fully understood. Here, a previously established framework of magnetic resonance and diffusion tensor imaging was used to measure the muscle volumes, intramuscular fat, fibre lengths and physiological cross-sectional areas of 12 lower limb muscles in a cohort of healthily aged individuals, which were compared to the same data from a young population. Maximum muscle forces were also measured from an isokinetic dynamometer. The more substantial interpopulation differences in architecture and functional performance were located within the knee extensor muscles, while the aged muscles were also more heterogeneous in muscle fibre type and atrophy. The relationships between architecture and muscle strength were also more significant in the knee extensors compared to other functional groups. These data highlight the importance of the knee extensors as a potential focus for interventions to negate the impacts of muscle ageing.

Keywords:  diffusion tensor imaging; magnetic resonance imaging; muscle architecture

DOI:  https://doi.org/10.3390/biology12101357
Metabolism. 2023 Oct 21. pii: S0026-0495(23)00315-3. [Epub ahead of print]149 155711

Pathophysiology of sarcopenia: Genetic factors and their interplay with environmental factors.

Muhammad Arif Aslam, Eun Bi Ma, Joo Young Huh.

  Sarcopenia is a geriatric disorder characterized by a progressive decline in muscle mass and function. This disorder has been associated with a range of adverse health outcomes, including fractures, functional deterioration, and increased mortality. The pathophysiology of sarcopenia is highly complex and multifactorial, involving both genetic and environmental factors as key contributors. This review consolidates current knowledge on the genetic factors influencing the pathogenesis of sarcopenia, particularly focusing on the altered gene expression of structural and metabolic proteins, growth factors, hormones, and inflammatory cytokines. While the influence of environmental factors such as physical inactivity, chronic diseases, smoking, alcohol consumption, and sleep disturbances on sarcopenia is relatively well understood, there is a dearth of studies examining their mechanistic roles. Therefore, this review emphasizes the interplay between genetic and environmental factors, elucidating their cumulative role in exacerbating the progression of sarcopenia beyond their individual effects. The unique contribution of this review lies in synthesizing the latest evidence on the genetic factors and their interaction with environmental factors, aiming to inform the development of novel therapeutic or preventive interventions for sarcopenia.

Keywords:  Aging; Environmental factors; Genetics; Muscle atrophy; Sarcopenia

DOI:  https://doi.org/10.1016/j.metabol.2023.155711
Med Oncol. 2023 Oct 23. 40(11): 338

The roles of P-selectin in cancer cachexia.

Tingting Ling, Jing Liu, Liang Dong, Ju Liu.

  P-selectin, a cell adhesion molecule of the selectin family, is expressed on the surface of activated endothelial cells (ECs) and platelets. Binding of P-selectin to P-selectin glycoprotein ligand-1 (PSGL-1) supports the leukocytes capture and rolling on stimulated ECs and increases the aggregation of leukocytes and activated platelets. Cancer cachexia is a systemic inflammation disorder characterized by metabolic disturbances, reduced body weight, loss of appetite, fat depletion, and progressive muscle atrophy. Cachexia status is associated with increased pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α), which activates ECs to release P-selectin. Single-nucleotide polymorphisms (SNPs) loci of P-selectin encoding gene SELP are associated with higher level of plasma P-selectin and increase the susceptibility to cachexia in cancer patients. Elevated P-selectin expression has been observed in the hypothalamus, liver, and gastrocnemius muscle in animal models with cancer cachexia. Increased P-selectin may cause excessive inflammatory processes, muscle atrophy, and blood hypercoagulation, thus facilitating the development of cancer cachexia. In this review, physiological functions of P-selectin and its potential roles in cancer cachexia have been summarized. We also discuss the therapeutic potential of P-selectin inhibitors for the treatment of cancer cachexia.

Keywords:  Cancer cachexia; Hypercoagulation; Inflammation; Muscle atrophy; P-selectin; Single-nucleotide polymorphisms

DOI:  https://doi.org/10.1007/s12032-023-02207-2
Front Endocrinol (Lausanne). 2023 ;14 1265175

Skeletal muscles and gut microbiota-derived metabolites: novel modulators of adipocyte thermogenesis.

Yi Tang, Ya-Di Wang, Yuan-Yuan Wang, Zhe-Zhen Liao, Xin-Hua Xiao.

  Obesity occurs when overall energy intake surpasses energy expenditure. White adipose tissue is an energy storage site, whereas brown and beige adipose tissues catabolize stored energy to generate heat, which protects against obesity and obesity-associated metabolic disorders. Metabolites are substrates in metabolic reactions that act as signaling molecules, mediating communication between metabolic sites (i.e., adipose tissue, skeletal muscle, and gut microbiota). Although the effects of metabolites from peripheral organs on adipose tissue have been extensively studied, their role in regulating adipocyte thermogenesis requires further investigation. Skeletal muscles and intestinal microorganisms are important metabolic sites in the body, and their metabolites play an important role in obesity. In this review, we consolidated the latest research on skeletal muscles and gut microbiota-derived metabolites that potentially promote adipocyte thermogenesis. Skeletal muscles can release lactate, kynurenic acid, inosine, and β-aminoisobutyric acid, whereas the gut secretes bile acids, butyrate, succinate, cinnabarinic acid, urolithin A, and asparagine. These metabolites function as signaling molecules by interacting with membrane receptors or controlling intracellular enzyme activity. The mechanisms underlying the reciprocal exchange of metabolites between the adipose tissue and other metabolic organs will be a focal point in future studies on obesity. Furthermore, understanding how metabolites regulate adipocyte thermogenesis will provide a basis for establishing new therapeutic targets for obesity.

Keywords:  adipocyte; energy expenditure; gut microbiota; metabolite; obesity; signaling molecules; skeletal muscles

DOI:  https://doi.org/10.3389/fendo.2023.1265175