bims-moremu 2023-06-25 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–06–25
29 papers selected by
Anna Vainshtein, Craft Science Inc.

The life and times of cellular senescence in skeletal muscle: friend or foe for homeostasis and adaptation?
FKBP25 regulates myoblast viability and migration and is differentially expressed in in vivo models of muscle adaptation.
Stimulated myotube contractions regulate membrane-bound and soluble TLR4 to prevent LPS-induced signaling and myotube atrophy in skeletal muscle cells.
Exercise-derived skeletal myogenic exosomes as mediators of intercellular crosstalk: a major player in health, disease, and exercise.
Skeletal Muscle Consequences of Phosphatidylethanolamine Synthesis Deficiency.
Oxidative stress: Roles in skeletal muscle atrophy.
Unfractionated Bulk Culture of Mouse Skeletal Muscle to Recapitulate Niche and Stem Cell Quiescence.
A novel deep proteomic approach in human skeletal muscle unveils distinct molecular signatures affected by aging and resistance training.
Invasive and noninvasive markers of human skeletal muscle mitochondrial function.
RUNX1T1 modulates myogenic differentiation by regulating the calcium signaling pathway and the alternative splicing of ROCK2.
SIRT3 overexpression in rat muscle does not ameliorate peripheral insulin resistance.
GLUT4 dynamic subcellular localization is controlled by AMP kinase activation as revealed by proximal proteome mapping in human muscle cells.
PRMT5 links lipid metabolism to contractile function of skeletal muscles.
Effects of high-intensity interval training (HIIT) on skeletal muscle atrophy, function, and myokine profile in diabetic myopathy.
Protein Arginine Methyltransferase 1 Ablation in Motor Neurons Causes Mitochondrial Dysfunction Leading to Age-related Motor Neuron Degeneration with Muscle Loss.
Scaling of nuclear numbers and their spatial arrangement in skeletal muscle cell size regulation.
Genomic and Epigenetic Changes Drive Aberrant Skeletal Muscle Differentiation in Rhabdomyosarcoma.
ATAC-seq protocol for the profiling of chromatin accessibility of in situ fixed quiescent and activated muscle stem cells.
Exploring skeletal muscle tolerance and whole-body metabolic effects of FDA-approved drugs in a volumetric muscle loss model.
"Diet for the prevention and management of sarcopenia".
Plasma Proteomic Kinetics in Response to Acute Exercise.
Facioscapulohumeral muscular dystrophy is associated with altered myoblast proteome dynamics.
Cross-sectional analysis of healthy individuals across decades: Aging signatures across multiple physiological compartments.
Functional Site-Directed Fluorometry in Native Cells to Study Skeletal Muscle Excitability.
DNAJB6 isoform specific knockdown: Therapeutic potential for limb girdle muscular dystrophy D1.
Muscle-on-a-chip devices: a new era for in vitro modelling of muscular dystrophies.
Decreased expression of H19/miR-675 ameliorates muscle atrophy by regulating the IGF1R/Akt/FoxO signaling pathway.
Exercise-primed extracellular vesicles improve cell-matrix adhesion and chondrocyte health.
Gene expressions associated with longer lifespan and aging exhibit similarity in mammals.

Am J Physiol Cell Physiol. 2023 Jun 19.

The life and times of cellular senescence in skeletal muscle: friend or foe for homeostasis and adaptation?

Cory M Dungan, Jaden M Wells, Kevin A Murach.

  A gradual decline in skeletal muscle mass and function is closely tied to increased mortality and disease risk during organismal aging. Exercise training is the most effective way to enhance muscle health, but the adaptive response to exercise as well as muscle repair potential is blunted in older individuals. Numerous mechanisms contribute to the loss of muscle mass and plasticity as aging progresses. An emerging body of recent evidence implicates an accumulation of senescent ("zombie") cells in muscle as a contributing factor to the aging phenotype. Senescent cells cannot divide but can release inflammatory factors and create an unfavorable environment for homeostasis and adaptation. On balance, some evidence suggests that cells with senescent characteristics can be beneficial for the muscle adaptive process, specifically at younger ages. Emerging evidence also suggests multinuclear post-mitotic muscle fibers could become senescent. In this review, we summarize current literature on the prevalence of senescent cells in skeletal muscle and highlight the consequences of senescent cell removal on muscle mass, function, and adaptability. We examine key limitations in the field of senescence specifically in skeletal muscle and identify areas of research that require future investigation.

Keywords:  Exercise; Myonuclei; SA Beta Gal; p16; p21

DOI:  https://doi.org/10.1152/ajpcell.00553.2022
FEBS J. 2023 Jun 21.

FKBP25 regulates myoblast viability and migration and is differentially expressed in in vivo models of muscle adaptation.

Tabitha Cree, Tania Ruz Gomez, Cara A Timpani, Emma Rybalka, John T Price, Craig A Goodman.

  FKBP25 (FKBP3 gene), is a dual domain PPIase protein that consists of a C-terminal PPIase domain, and an N-terminal basic tilted helix bundle (BTHB). The PPIase domain of FKBP25 has been shown to bind to microtubules, which has impacts upon microtubule polymerisation and cell cycle progression. Using quantitative proteomics, it was recently found that FKBP25 was expressed in the top 10% of the mouse skeletal muscle proteome. However, to date there have been few studies investigating the role of FKBP25 in non-transformed systems. As such, this study aimed to investigate potential roles for FKBP25 in myoblast viability, migration and differentiation and in adaptation of mature skeletal muscle. Doxycycline-inducible FKBP25 knockdown in C2C12 myoblasts revealed an increase in cell accumulation/viability and migration in vitro that was independent of alterations in tubulin dynamics; however, FKBP25 knockdown had no discernible impact on myoblast differentiation into myotubes. Finally, a series of in vivo models of muscle adaptation were assessed, where it was observed that FKBP25 protein expression was increased in hypertrophy and regeneration conditions (chronic mechanical overload and the mdx model of Duchenne muscular dystrophy) but decreased in an atrophy model (denervation). Overall, the findings of this study establish FKBP25 as a regulator of myoblast viability and migration, with possible implications for satellite cell proliferation and migration and muscle regeneration, and as a potential regulator of in vivo skeletal muscle adaptation.

Keywords:  FKBP25; muscle adaptations; myoblast; proliferation; tubulin dynamics

DOI:  https://doi.org/10.1111/febs.16894
Am J Physiol Cell Physiol. 2023 Jun 19.

Stimulated myotube contractions regulate membrane-bound and soluble TLR4 to prevent LPS-induced signaling and myotube atrophy in skeletal muscle cells.

Jeremy B Ducharme, Zachary James Fennel, Zachary J McKenna, Roberto Nava, Michael R Deyhle.

  Toll-like receptor 4 (TLR4) activation by lipopolysaccharides (LPS) increases pro-inflammatory cytokine production and upregulation of muscle atrophy signaling pathways. Muscle contractions can suppress LPS/TLR4 axis activation by reducing the protein expression of TLR4 on immune cells. However, the mechanism by which muscle contractions decreases TLR4 remains undefined. Moreover, it is not clear whether muscle contractions affect TLR4 expressed on skeletal muscle cells. The purpose of this study was to uncover the nature and mechanisms by which stimulated myotube contractions using electrical pulse stimulation (EPS) as an in vitro model of skeletal muscle contractions affect TLR4 expression and intracellular signaling to combat LPS-induced muscle atrophy. C2C12 myotubes were stimulated to contract via EPS with and without subsequent LPS exposure. We then examined the isolated effects of conditioned media (CM) collected following EPS and soluble TLR4 (sTLR4) alone on LPS-induced myotube atrophy. Exposure to LPS decreased membrane-bound and sTLR4, increased TLR4 signaling (decreased inhibitor of κBα), and induced myotube atrophy. However, EPS decreased membrane-bound TLR4, increased sTLR4, and prevented LPS-induced signaling and myotube atrophy. CM, that contained elevated levels of sTLR4, prevented LPS-induced upregulation of atrophy-related gene transcripts muscle ring finger 1 (MuRF1) and atrogin-1 and reduced myotube atrophy. Recombinant sTLR4 added to media prevented LPS-induced myotube atrophy. In summary, our study provides the first evidence that sTLR4 has anti-catabolic effects by reducing TLR4-mediated signaling and atrophy. Additionally, the study reveals a novel finding, by demonstrating that stimulated myotube contractions decrease membrane-bound TLR4 and increase the secretion of sTLR4 by myotubes.

Keywords:  C2C12; conditioned media; electrical pulse stimulation; muscle atrophy; soluble receptor

DOI:  https://doi.org/10.1152/ajpcell.00007.2023
J Physiol Biochem. 2023 Jun 20.

Exercise-derived skeletal myogenic exosomes as mediators of intercellular crosstalk: a major player in health, disease, and exercise.

Pinshi Ni, Luodan Yang, Fanghui Li.

  Exosomes are extracellular membrane vesicles that contain biological macromolecules such as RNAs and proteins. It plays an essential role in physiological and pathological processes as carrier of biologically active substances and new mediator of intercellular communication. It has been reported that myokines secreted by the skeletal muscle are wrapped in small vesicles (e.g., exosomes), secreted into the circulation, and then regulate the receptor cells. This review discussed the regulation of microRNAs (miRNAs), proteins, lipids, and other cargoes carried by skeletal muscle-derived exosomes (SkMCs-Exs) on the body and their effects on pathological states, including injury atrophy, aging, and vascular porosis. We also discussed the role of exercise in regulating skeletal muscle-derived exosomes and its physiological significance.

Keywords:  Exercise; Exosome; Skeletal muscle; microRNAs

DOI:  https://doi.org/10.1007/s13105-023-00969-x
Function (Oxf). 2023 ;4(4): zqad020

Skeletal Muscle Consequences of Phosphatidylethanolamine Synthesis Deficiency.

Sophie Grapentine, Rathnesh K Singh, Marica Bakovic.

  The maintenance of phospholipid homeostasis is increasingly being implicated in metabolic health. Phosphatidylethanolamine (PE) is the most abundant phospholipid on the inner leaflet of cellular membranes, and we have previously shown that mice with a heterozygous ablation of the PE synthesizing enzyme, Pcyt2 (Pcyt2+/-), develop obesity, insulin resistance, and NASH. Skeletal muscle is a major determinant of systemic energy metabolism, making it a key player in metabolic disease development. Both the total PE levels and the ratio of PE to other membrane lipids in skeletal muscle are implicated in insulin resistance; however, the underlying mechanisms and the role of Pcyt2 regulation in this association remain unclear. Here, we show how reduced phospholipid synthesis due to Pcyt2 deficiency causes Pcyt2+/- skeletal muscle dysfunction and metabolic abnormalities. Pcyt2+/- skeletal muscle exhibits damage and degeneration, with skeletal muscle cell vacuolization, disordered sarcomeres, mitochondria ultrastructure irregularities and paucity, inflammation, and fibrosis. There is intramuscular adipose tissue accumulation, and major disturbances in lipid metabolism with impaired FA mobilization and oxidation, elevated lipogenesis, and long-chain fatty acyl-CoA, diacylglycerol, and triacylglycerol accumulation. Pcyt2+/- skeletal muscle exhibits perturbed glucose metabolism with elevated glycogen content, impaired insulin signaling, and reduced glucose uptake. Together, this study lends insight into the critical role of PE homeostasis in skeletal muscle metabolism and health with broad implications on metabolic disease development.

Keywords:  Pcyt2; metabolism; non-alcoholic steatohepatitis; phosphatidylethanolamine; phospholipids; skeletal muscle

DOI:  https://doi.org/10.1093/function/zqad020
Biochem Pharmacol. 2023 Jun 16. pii: S0006-2952(23)00255-1. [Epub ahead of print]214 115664

Oxidative stress: Roles in skeletal muscle atrophy.

Han Zhang, Guangdong Qi, Kexin Wang, Jiawen Yang, Yuntian Shen, Xiaoming Yang, Xin Chen, Xinlei Yao, Xiaosong Gu, Lei Qi, Chun Zhou, Hualin Sun.

  Oxidative stress, inflammation, mitochondrial dysfunction, reduced protein synthesis, and increased proteolysis are all critical factors in the process of muscle atrophy. In particular, oxidative stress is the key factor that triggers skeletal muscle atrophy. It is activated in the early stages of muscle atrophy and can be regulated by various factors. The mechanisms of oxidative stress in the development of muscle atrophy have not been completely elucidated. This review provides an overview of the sources of oxidative stress in skeletal muscle and the correlation of oxidative stress with inflammation, mitochondrial dysfunction, autophagy, protein synthesis, proteolysis, and muscle regeneration in muscle atrophy. Additionally, the role of oxidative stress in skeletal muscle atrophy caused by several pathological conditions, including denervation, unloading, chronic inflammatory diseases (diabetes mellitus, chronic kidney disease, chronic heart failure, and chronic obstructive pulmonary disease), sarcopenia, hereditary neuromuscular diseases (spinal muscular atrophy, amyotrophic lateral sclerosis, and Duchenne muscular dystrophy), and cancer cachexia, have been discussed. Finally, this review proposes the alleviation oxidative stress using antioxidants, Chinese herbal extracts, stem cell and extracellular vesicles as a promising therapeutic strategy for muscle atrophy. This review will aid in the development of novel therapeutic strategies and drugs for muscle atrophy.

Keywords:  Antioxidant treatment; Muscle atrophy; Oxidative stress

DOI:  https://doi.org/10.1016/j.bcp.2023.115664
J Vis Exp. 2023 Jun 02.

Unfractionated Bulk Culture of Mouse Skeletal Muscle to Recapitulate Niche and Stem Cell Quiescence.

Louai Zaidan, Perla Geara, Matthew J Borok, Léo Machado, Despoina Mademtzoglou, Philippos Mourikis, Frederic Relaix.

Skeletal muscle is the largest tissue of the body and performs multiple functions, from locomotion to body temperature control. Its functionality and recovery from injuries depend on a multitude of cell types and on molecular signals between the core muscle cells (myofibers, muscle stem cells) and their niche. Most experimental settings do not preserve this complex physiological microenvironment, and neither do they allow the ex vivo study of muscle stem cells in quiescence, a cell state that is crucial for them. Here, a protocol is outlined for the ex vivo culture of muscle stem cells with cellular components of their niche. Through the mechanical and enzymatic breakdown of muscles, a mixture of cell types is obtained, which is put in 2D culture. Immunostaining shows that within 1 week, multiple niche cells are present in culture alongside myofibers and, importantly, Pax7-positive cells that display the characteristics of quiescent muscle stem cells. These unique properties make this protocol a powerful tool for cell amplification and the generation of quiescent-like stem cells that can be used to address fundamental and translational questions.

DOI: https://doi.org/10.3791/65433
bioRxiv. 2023 Jun 06. pii: 2023.06.02.543459. [Epub ahead of print]

A novel deep proteomic approach in human skeletal muscle unveils distinct molecular signatures affected by aging and resistance training.

Michael D Roberts, Bradley A Ruple, Joshua S Godwin, Mason C McIntosh, Shao-Yung Chen, Nicholas J Kontos, Anthony Agyin-Birikorang, Max J Michel, Daniel L Plotkin, Madison L Mattingly, Brooks C Mobley, Tim N Ziegenfuss, Andrew D Fruge, Andreas N Kavazis.

We examined the myofibrillar (MyoF) and non-myofibrillar (non-MyoF) proteomic profiles of the vastus lateralis (VL) muscle of younger (Y, 22±2 years old; n=5) and middle-aged participants (MA, 56±8 years old; n=6), and MA following eight weeks of knee extensor resistance training (RT, 2d/week). Shotgun/bottom-up proteomics in skeletal muscle typically yields wide protein abundance ranges that mask lowly expressed proteins. Thus, we adopted a novel approach whereby the MyoF and non-MyoF fractions were separately subjected to protein corona nanoparticle complex formation prior to digestion and Liquid Chromatography Mass Spectrometry (LC-MS) analysis. A total of 10,866 proteins (4,421 MyoF and 6,445 non-MyoF) were identified. Across all participants, the number of non-MyoF proteins detected averaged to be 5,645 ± 266 (range: 4,888-5,987) and the number of MyoF proteins detected averaged to be 2,611 ± 326 (range: 1,944-3,101). Differences in the non-MyoF (8.4%) and MyoF (2.5%) proteome were evident between age cohorts. Further, most of these age-related non-MyoF proteins (447/543) were more enriched in MA versus Y. Several biological processes in the non- MyoF fraction were predicted to be operative in MA versus Y including (but not limited to) increased cellular stress, mRNA splicing, translation elongation, and ubiquitin-mediated proteolysis. Non-MyoF proteins associated with splicing and proteostasis were further interrogated, and in agreement with bioinformatics, alternative protein variants, spliceosome- associated proteins (snRNPs), and proteolysis-related targets were more abundant in MA versus Y. RT in MA non-significantly increased VL muscle cross-sectional area (+6.5%, p=0.066) and significantly increased knee extensor strength (+8.7%, p=0.048). However, RT modestly altered the MyoF (∼0.3%, 11 upregulated and two downregulated proteins) and non-MyoF proteomes (∼1.0%, 56 upregulated and eight downregulated proteins, p<0.01). Further, RT did not affect predicted biological processes in either fraction. Although participant numbers were limited, these preliminary results using a novel deep proteomic approach in skeletal muscle suggest that aging and RT predominantly affects protein abundances in the non-contractile protein pool. However, the marginal proteome adaptations occurring with RT suggest either: a) this may be an aging-associated phenomenon, b) more rigorous RT may stimulate more robust effects, or c) RT, regardless of age, subtly affects skeletal muscle protein abundances in the basal state.

DOI: https://doi.org/10.1101/2023.06.02.543459
Physiol Rep. 2023 06;11(12): e15734

Invasive and noninvasive markers of human skeletal muscle mitochondrial function.

Rodrigo Mancilla, Diego Pava-Mejia, Nynke van Polanen, Vera de Wit, Maaike Bergman, Lotte Grevendonk, Johanna Jorgensen, Esther Kornips, Joris Hoeks, Matthijs K C Hesselink, Vera B Schrauwen-Hinderling.

  Mitochondria are organelles that fuel cellular energy requirements by ATP formation via aerobic metabolism. Given the wide variety of methods to assess skeletal muscle mitochondrial capacity, we tested how well different invasive and noninvasive markers of skeletal muscle mitochondrial capacity reflect mitochondrial respiration in permeabilized muscle fibers. Nineteen young men (mean age: 24 ± 4 years) were recruited, and a muscle biopsy was collected to determine mitochondrial respiration from permeabilized muscle fibers and to quantify markers of mitochondrial capacity, content such as citrate synthase (CS) activity, mitochondrial DNA copy number, TOMM20, VDAC, and protein content for complex I-V of the oxidative phosphorylation (OXPHOS) system. Additionally, all participants underwent noninvasive assessments of mitochondrial capacity: PCr recovery postexercise (by 31 P-MRS), maximal aerobic capacity, and gross exercise efficiency by cycling exercise. From the invasive markers, Complex V protein content and CS activity showed the strongest concordance (Rc = 0.50 to 0.72) with ADP-stimulated coupled mitochondrial respiration, fueled by various substrates. Complex V protein content showed the strongest concordance (Rc = 0.72) with maximally uncoupled mitochondrial respiration. From the noninvasive markers, gross exercise efficiency, VO2max , and PCr recovery exhibited concordance values between 0.50 and 0.77 with ADP-stimulated coupled mitochondrial respiration. Gross exercise efficiency showed the strongest concordance with maximally uncoupled mitochondrial respiration (Rc = 0.67). From the invasive markers, Complex V protein content and CS activity are surrogates that best reflect skeletal muscle mitochondrial respiratory capacity. From the noninvasive markers, exercise efficiency and PCr recovery postexercise most closely reflect skeletal muscle mitochondrial respiratory capacity.

Keywords:  human skeletal muscle; mitochondrial function; skeletal muscle mitochondrial respiration

DOI:  https://doi.org/10.14814/phy2.15734
FASEB J. 2023 Jul;37(7): e23044

RUNX1T1 modulates myogenic differentiation by regulating the calcium signaling pathway and the alternative splicing of ROCK2.

Kaiping Deng, Zhipeng Liu, Yalong Su, Zhen Zhang, Yixuan Fan, Yanli Zhang, Feng Wang.

  RUNX1T1 (Runt-related transcription factor 1, translocated to 1) plays a wide-ranging and diverse role in cellular development, including hematopoiesis and adipogenesis. However, little is known about the function of RUNX1T1 in the skeletal muscle development. Here, we assessed the impact of RUNX1T1 on the proliferation and myogenic differentiation of goat primary myoblasts (GPMs). It was observed that RUNX1T1 is highly expressed during the early stages of myogenic differentiation and the fetal stage. Moreover, the knockdown of RUNX1T1 promotes the proliferation and inhibits myogenic differentiation and mitochondrial biogenesis of GPMs. RNA sequencing analysis revealed that significantly differentially expressed genes in RUNX1T1 knockdown cells were enriched in the calcium signaling pathway. Additionally, we discovered that RUNX1T1 regulates alternative splicing (AS) events involved in myogenesis. We also show that silencing RUNX1T1 blocked the Ca2+ -CAMK signaling pathway and reduced the expression levels of muscle-specific isoforms of recombinant rho associated coiled coil containing crotein kinase 2 (ROCK2) during myogenic differentiation, partially explaining why RUNX1T1 deficiency leads to the impairment of myotube formation. These findings suggest that RUNX1T1 is a novel regulator of myogenic differentiation that regulates the calcium signaling pathway and AS of ROCK2. Overall, our results highlight the critical role of RUNX1T1 in myogenesis and broaden our understanding of myogenic differentiation.

Keywords:  ROCK2; RUNX1T1; alternative splicing; calcium signaling pathway; myogenic differentiation

DOI:  https://doi.org/10.1096/fj.202300677R
J Endocrinol. 2023 Jun 01. pii: JOE-22-0101. [Epub ahead of print]

SIRT3 overexpression in rat muscle does not ameliorate peripheral insulin resistance.

Brenna Osborne, Lauren E Wright, Amanda E Brandon, Ella Stuart, Lewin Small, Joris Hoeks, Patrick Schrauwen, David A Sinclair, Magdalene K Montgomery, Gregory J Cooney, Nigel Turner.

Reduced expression of the NAD+-dependent deacetylase, SIRT3, has been associated with insulin resistance and metabolic dysfunction in humans and rodents. In this study we investigated whether specific overexpression of SIRT3 in vivo in skeletal muscle could prevent HFD-induced muscle insulin resistance. To address this we used a muscle-specific adeno-associated virus (AAV) to overexpress SIRT3 in rat tibialis and EDL muscles. Mitochondrial substrate oxidation, substrate switching and oxidative enzyme activity were assessed in skeletal muscle with and without SIRT3 overexpression. Muscle-specific insulin action was also assessed by hyperinsulinaemic-euglycaemic clamps in rats that underwent a 4-week HFD-feeding protocol. Ex vivo functional assays revealed elevated activity of selected SIRT3-target enzymes including hexokinase, isocitrate dehydrogenase and pyruvate dehydrogenase that was associated with an increase in the ability to switch between fatty acid and glucose-derived substrates in muscle with SIRT3 overexpression. However, during the clamp, muscle from rats fed a HFD with increased SIRT3 expression displayed equally impaired glucose uptake and insulin-stimulated glycogen synthesis as the contralateral control muscle. Intramuscular triglyceride content was similarly increased in muscle of high fat fed rats, regardless of SIRT3 status. Thus, despite SIRT3 KO mouse models indicating many beneficial metabolic roles for SIRT3, our findings show that muscle-specific overexpression of SIRT3 has only minor effects on the acute development of skeletal muscle insulin resistance in high fat fed rats.

DOI: https://doi.org/10.1530/JOE-22-0101
bioRxiv. 2023 Jun 07. pii: 2023.06.06.543897. [Epub ahead of print]

GLUT4 dynamic subcellular localization is controlled by AMP kinase activation as revealed by proximal proteome mapping in human muscle cells.

Anuttoma Ray, Jennifer Wen, Lucie Yammine, Jeff Culver, Jeonifer Garren, Liang Xue, Katherine Hales, Qing Xiang, Morris J Birnbaum, Bei B Zhang, Mara Monetti, T E McGraw.

Regulation of glucose transport into muscle and adipocytes, central for control of whole-body metabolism, is determined by the amount of GLUT4 glucose transporter in the plasma membrane ( PM ). Physiologic signals (activated insulin receptor or AMP kinase [ AMPK ]), acutely increase PM GLUT4 to enhance glucose uptake. Here we show in kinetic studies that intracellular GLUT4 is in equilibrium with the PM in unstimulated cultured human skeletal muscle cells, and that AMPK promotes GLUT4 redistribution to the PM by regulating both exocytosis and endocytosis. AMPK-stimulation of exocytosis requires Rab10 and Rab GTPase activating protein TBC1D4, requirements shared with insulin control of GLUT4 in adipocytes. Using APEX2 proximity mapping, we identify, at high-density and high-resolution, the GLUT4 proximal proteome, revealing GLUT4 traverses both PM proximal and distal compartments in unstimulated muscle cells. These data support intracellular retention of GLUT4 in unstimulated muscle cells by a dynamic mechanism dependent on the rates of internalization and recycling. AMPK promoted GLUT4 translocation to the PM involves redistribution of GLUT4 among the same compartments traversed in unstimulated cells, with a significant redistribution of GLUT4 from the PM distal Trans Golgi Network Golgi compartments. The comprehensive proximal protein mapping provides an integrated, whole cell accounting of GLUT4's localization at a resolution of ∼20 nm, a structural framework for understanding the molecular mechanisms regulating GLUT4 trafficking downstream of different signaling inputs in physiologically relevant cell type and as such, sheds new light on novel key pathways and molecular components as potential therapeutic approaches to modulate muscle glucose uptake.

DOI: https://doi.org/10.1101/2023.06.06.543897
EMBO Rep. 2023 Jun 19. e57306

PRMT5 links lipid metabolism to contractile function of skeletal muscles.

Kun Ho Kim, Zhihao Jia, Madigan Snyder, Jingjuan Chen, Jiamin Qiu, Stephanie N Oprescu, Xiyue Chen, Sabriya A Syed, Feng Yue, Bruno T Roseguini, Anthony N Imbalzano, Changdeng Hu, Shihuan Kuang.

  Skeletal muscle plays a key role in systemic energy homeostasis besides its contractile function, but what links these functions is poorly defined. Protein Arginine Methyl Transferase 5 (PRMT5) is a well-known oncoprotein but also expressed in healthy tissues with unclear physiological functions. As adult muscles express high levels of Prmt5, we generated skeletal muscle-specific Prmt5 knockout (Prmt5MKO ) mice. We observe reduced muscle mass, oxidative capacity, force production, and exercise performance in Prmt5MKO mice. The motor deficiency is associated with scarce lipid droplets in myofibers due to defects in lipid biosynthesis and accelerated degradation. Specifically, PRMT5 deletion reduces dimethylation and stability of Sterol Regulatory Element-Binding Transcription Factor 1a (SREBP1a), a master regulator of de novo lipogenesis. Moreover, Prmt5MKO impairs the repressive H4R3 symmetric dimethylation at the Pnpla2 promoter, elevating the level of its encoded protein ATGL, the rate-limiting enzyme catalyzing lipolysis. Accordingly, skeletal muscle-specific double knockout of Pnpla2 and Prmt5 normalizes muscle mass and function. Together, our findings delineate a physiological function of PRMT5 in linking lipid metabolism to contractile function of myofibers.

Keywords:  lipid droplet; lipolysis; myofiber; posttranslational modification; protein arginine methyltransferase

DOI:  https://doi.org/10.15252/embr.202357306
Cytokine. 2023 Jun 15. pii: S1043-4666(23)00157-6. [Epub ahead of print]169 156279

Effects of high-intensity interval training (HIIT) on skeletal muscle atrophy, function, and myokine profile in diabetic myopathy.

Yeşim Özçatal, Fırat Akat, Yakup Tatar, Hakan Fıçıcılar, Bilge Serdaroğlu, Ferda Topal Çelikkan, Metin Baştuğ.

   PURPOSE: Diabetes is a metabolic disorder characterized by chronic hyperglycemia due to insulin deficiency and/or loss of its action. Diabetic myopathy causes functional limitations in diabetic patients. The beneficial effects of high-intensity interval training (HIIT) are widely reported. We have hypothesized that HIIT application would prevent the development of diabetic myopathy.
METHODS: Male, Wistar albino rats (10 W) were randomly divided into four groups (1)Control(C), (2)Diabetes(DM), (3)Training(HIIT), and (4)Diabetes + Training(DM + HIIT). Streptozotocin(60 mg/kg) was injected for the induction of diabetes. The maximum exercise capacity(MEC) of animals was determined by an incremental load test. HIIT protocol (4 min 85-95 % MEC, 2 min 40-50 % MEC, 6 cycles, 5 days/week) was applied for 8 weeks. In the end, functional parameters, atrophy, and resistance to fatigue in soleus and EDL muscles were evaluated. IL-6, FNDC5, and myonectin levels were measured in EDL, soleus, and serum.
RESULTS: We observed atrophy, fatigue sensitivity, and proinflammatory alterations (IL-6 increase) in the EDL samples due to diabetic myopathy which were not observed in the soleus samples. HIIT application prevented the aforementioned detrimental alterations. Both force-frequency response and parallelly the twitch amplitude increased significantly in the DM + HIIT group. Half relaxation time (DT50) increased in both exercising and sedentary diabetics. FNDC5 was significantly higher in the exercising animals in soleus samples. Myonectin was significantly higher in the soleus muscle only in the DM + HIIT group.
CONCLUSION: Current findings show that diabetic myopathy develops earlier in glycolytic-fast-twitch fibers(EDL) than in oxidative-slow-twitch fibers(soleus). Furthermore, HIIT application prevents atrophy in skeletal muscle, increases resistance to fatigue, and has an anti-inflammatory effect.
NEW FINDINGS: The current study analyzes the myokine profile and skeletal muscle function under the effect of diabetes HIIT-type exercise. We also measured maximal exercise capacity and tailored the exercise program individually according to the result. Diabetic myopathy is an important complication of diabetes yet still, it is not understood completely. Our results show that HIIT-type training would be beneficial in diabetic myopathy but further investigation is needed to understand the whole molecular mechanism.

Keywords:  Diabetic myopathy; HIIT; Isolated skeletal muscle; Myokine

DOI:  https://doi.org/10.1016/j.cyto.2023.156279
Research (Wash D C). 2023 ;6 0158

Protein Arginine Methyltransferase 1 Ablation in Motor Neurons Causes Mitochondrial Dysfunction Leading to Age-related Motor Neuron Degeneration with Muscle Loss.

Hyun-Kyung So, Hyebeen Kim, Jinwoo Lee, Chang-Lim You, Chae-Eun Yun, Hyeon-Ju Jeong, Eun-Ju Jin, Yunju Jo, Dongryeol Ryu, Gyu-Un Bae, Jong-Sun Kang.

Neuromuscular dysfunction is tightly associated with muscle wasting that occurs with age or due to degenerative diseases. However, the molecular mechanisms underlying neuromuscular dysfunction are currently unclear. Recent studies have proposed important roles of Protein arginine methyltransferase 1 (Prmt1) in muscle stem cell function and muscle maintenance. In the current study, we set out to determine the role of Prmt1 in neuromuscular function by generating mice with motor neuron-specific ablation of Prmt1 (mnKO) using Hb9-Cre. mnKO exhibited age-related motor neuron degeneration and neuromuscular dysfunction leading to premature muscle loss and lethality. Prmt1 deficiency also impaired motor function recovery and muscle reinnervation after sciatic nerve injury. The transcriptome analysis of aged mnKO lumbar spinal cords revealed alterations in genes related to inflammation, cell death, oxidative stress, and mitochondria. Consistently, mnKO lumbar spinal cords of sciatic nerve injury model or aged mice exhibited elevated cellular stress response in motor neurons. Furthermore, Prmt1 inhibition in motor neurons elicited mitochondrial dysfunction. Our findings demonstrate that Prmt1 ablation in motor neurons causes age-related motor neuron degeneration attributing to muscle loss. Thus, Prmt1 is a potential target for the prevention or intervention of sarcopenia and neuromuscular dysfunction related to aging.

DOI: https://doi.org/10.34133/research.0158
Mol Biol Cell. 2023 Jul 01. 34(8): pe3

Scaling of nuclear numbers and their spatial arrangement in skeletal muscle cell size regulation.

Kenth-Arne Hansson, Einar Eftestøl.

Many cells display considerable functional plasticity and depend on the regulation of numerous organelles and macromolecules for their maintenance. In large cells, organelles also need to be carefully distributed to supply the cell with essential resources and regulate intracellular activities. Having multiple copies of the largest eukaryotic organelle, the nucleus, epitomizes the importance of scaling gene products to large cytoplasmic volumes in skeletal muscle fibers. Scaling of intracellular constituents within mammalian muscle fibers is, however, poorly understood, but according to the myonuclear domain hypothesis, a single nucleus supports a finite amount of cytoplasm and is thus postulated to act autonomously, causing the nuclear number to be commensurate with fiber volume. In addition, the orderly peripheral distribution of myonuclei is a hallmark of normal cell physiology, as nuclear mispositioning is associated with impaired muscle function. Because underlying structures of complex cell behaviors are commonly formalized by scaling laws and thus emphasize emerging principles of size regulation, the work presented herein offers more of a unified conceptual platform based on principles from physics, chemistry, geometry, and biology to explore cell size-dependent correlations of the largest mammalian cell by means of scaling.

DOI: https://doi.org/10.1091/mbc.E22-09-0424
Cancers (Basel). 2023 May 18. pii: 2823. [Epub ahead of print]15(10):

Genomic and Epigenetic Changes Drive Aberrant Skeletal Muscle Differentiation in Rhabdomyosarcoma.

Silvia Pomella, Sara G Danielli, Rita Alaggio, Willemijn B Breunis, Ebrahem Hamed, Joanna Selfe, Marco Wachtel, Zoe S Walters, Beat W Schäfer, Rossella Rota, Janet M Shipley, Simone Hettmer.

  Rhabdomyosarcoma (RMS), the most common soft-tissue sarcoma in children and adolescents, represents an aberrant form of skeletal muscle differentiation. Both skeletal muscle development, as well as regeneration of adult skeletal muscle are governed by members of the myogenic family of regulatory transcription factors (MRFs), which are deployed in a highly controlled, multi-step, bidirectional process. Many aspects of this complex process are deregulated in RMS and contribute to tumorigenesis. Interconnected loops of super-enhancers, called core regulatory circuitries (CRCs), define aberrant muscle differentiation in RMS cells. The transcriptional regulation of MRF expression/activity takes a central role in the CRCs active in skeletal muscle and RMS. In PAX3::FOXO1 fusion-positive (PF+) RMS, CRCs maintain expression of the disease-driving fusion oncogene. Recent single-cell studies have revealed hierarchically organized subsets of cells within the RMS cell pool, which recapitulate developmental myogenesis and appear to drive malignancy. There is a large interest in exploiting the causes of aberrant muscle development in RMS to allow for terminal differentiation as a therapeutic strategy, for example, by interrupting MEK/ERK signaling or by interfering with the epigenetic machinery controlling CRCs. In this review, we provide an overview of the genetic and epigenetic framework of abnormal muscle differentiation in RMS, as it provides insights into fundamental mechanisms of RMS malignancy, its remarkable phenotypic diversity and, ultimately, opportunities for therapeutic intervention.

Keywords:  differentiation; epigenetics; genomics; rhabdomyosarcoma; skeletal muscle

DOI:  https://doi.org/10.3390/cancers15102823
STAR Protoc. 2023 Jun 22. pii: S2666-1667(23)00343-X. [Epub ahead of print]4(3): 102376

ATAC-seq protocol for the profiling of chromatin accessibility of in situ fixed quiescent and activated muscle stem cells.

Anqi Dong, Indigo T C Chan, Tom H Cheung.

  Chromatin accessibility is critical for cell identity. Conventional ATAC-seq can examine chromatin accessibility on freshly prepared muscle stem cells or satellite cells (SCs); however, isolating SCs in mice remains challenging. Here, we present a protocol to preserve the in vivo chromatin profile of SCs by applying paraformaldehyde (PFA) perfusion throughout the mouse before SC isolation. We describe steps for PFA perfusion and FACS sorting of SCs. We then detail library preparation for ATAC-seq. For complete details on the use and execution of this protocol, please refer to Dong et al.1.

Keywords:  Cell Biology; Cell isolation; Molecular Biology; Stem Cells

DOI:  https://doi.org/10.1016/j.xpro.2023.102376
Physiol Rep. 2023 06;11(12): e15756

Exploring skeletal muscle tolerance and whole-body metabolic effects of FDA-approved drugs in a volumetric muscle loss model.

Shefali R Bijwadia, Christiana J Raymond-Pope, Alec M Basten, Mason T Lentz, Thomas J Lillquist, Jarrod A Call, Sarah M Greising.

  Volumetric muscle loss (VML) is associated with persistent functional impairment due to a lack of de novo muscle regeneration. As mechanisms driving the lack of regeneration continue to be established, adjunctive pharmaceuticals to address the pathophysiology of the remaining muscle may offer partial remediation. Studies were designed to evaluate the tolerance and efficacy of two FDA-approved pharmaceutical modalities to address the pathophysiology of the remaining muscle tissue after VML injury: (1) nintedanib (an anti-fibrotic) and (2) combined formoterol and leucine (myogenic promoters). Tolerance was first established by testing low- and high-dosage effects on uninjured skeletal muscle mass and myofiber cross-sectional area in adult male C57BL/6J mice. Next, tolerated doses of the two pharmaceutical modalities were tested in VML-injured adult male C57BL/6J mice after an 8-week treatment period for their ability to modulate muscle strength and whole-body metabolism. The most salient findings indicate that formoterol plus leucine mitigated the loss in muscle mass, myofiber number, whole-body lipid oxidation, and muscle strength, and resulted in a higher whole-body metabolic rate (p ≤ 0.016); nintedanib did not exacerbate or correct aspects of the muscle pathophysiology after VML. This supports ongoing optimization efforts, including scale-up evaluations of formoterol treatment in large animal models of VML.

Keywords:  formoterol; muscle function; neuromusculoskeletal injury; nintedanib; skeletal muscle injury

DOI:  https://doi.org/10.14814/phy2.15756
Metabolism. 2023 Jun 21. pii: S0026-0495(23)00241-X. [Epub ahead of print] 155637

"Diet for the prevention and management of sarcopenia".

Riccardo Calvani, Anna Picca, Hélio José Coelho-Júnior, Matteo Tosato, Emanuele Marzetti, Francesco Landi.

  Sarcopenia is a geriatric condition characterized by a progressive loss of skeletal muscle mass and strength, with an increased risk of adverse health outcomes (e.g., falls, disability, institutionalization, reduced quality of life, mortality). Pharmacological remedies are currently unavailable for preventing the development of sarcopenia, halting its progression, or impeding its negative health outcomes. The most effective strategies to contrast sarcopenia rely on the adoption of healthier lifestyle behaviors, including adherence to high-quality diets and regular physical activity. In this review, the role of nutrition in the prevention and management of sarcopenia is summarized. Special attention is given to current "blockbuster" dietary regimes and agents used to counteract age-related muscle wasting, together with their putative mechanisms of action. Issues related to the design and implementation of effective nutritional strategies are discussed, with a focus on unanswered questions on the most appropriate timing of nutritional interventions to preserve muscle health and function into old age. A brief description is also provided on new technologies that can facilitate the development and implementation of personalized nutrition plans to contrast sarcopenia.

Keywords:  Handgrip strength; Mediterranean diet; Muscle mass; Nutrition; Physical function; Protein

DOI:  https://doi.org/10.1016/j.metabol.2023.155637
Mol Cell Proteomics. 2023 Jun 19. pii: S1535-9476(23)00112-3. [Epub ahead of print] 100601

Plasma Proteomic Kinetics in Response to Acute Exercise.

Michael Y Mi, Jacob L Barber, Prashant Rao, Laurie A Farrell, Mark A Sarzynski, Claude Bouchard, Jeremy M Robbins, Robert E Gerszten.

BACKGROUND: Regular exercise has many favorable effects on human health, which may be mediated in part by the release of circulating bioactive factors during each bout of exercise. Limited data exist regarding the kinetic responses of plasma proteins during and after acute exercise.
METHODS: Proteomic profiling of 4,163 proteins was performed using a large-scale, affinity-based platform in 75 middle-aged adults who were referred for treadmill exercise stress testing. Plasma proteins were quantified at baseline, peak exercise, and 1-hour post-exercise, and those with significant changes at both exercise timepoints were further examined for their associations with cardiometabolic traits and change with aerobic exercise training in the HERITAGE Family Study, a 20-week exercise intervention study.
RESULTS: A total of 765 proteins changed (FDR <0.05) at peak exercise compared to baseline, and 128 proteins changed (FDR <0.05) at 1-hour post-exercise. The 56 proteins that changed at both timepoints included midkine, brain-derived neurotrophic factor, metalloproteinase inhibitor 4, and coiled-coil domain-containing protein 126, and were enriched for secreted proteins. The majority had concordant direction of change at both timepoints. Across all proteins assayed, gene set enrichment analysis showed increased abundance of coagulation related proteins at 1-hour post-exercise. Forty-five proteins were associated with at least one measure of adiposity, lipids, glucose homeostasis, or cardiorespiratory fitness in HERITAGE, and 20 proteins changed with aerobic exercise training.
CONCLUSIONS: We identified hundreds of novel proteins that change during acute exercise, most of which resolved by 1-hour into recovery. Proteins with sustained changes during exercise and recovery may be of particular interest as circulating biomarkers and pathways for further investigation in cardiometabolic diseases. These data will contribute to a biochemical roadmap of acute exercise that will be publicly available for the entire scientific community.

DOI: https://doi.org/10.1016/j.mcpro.2023.100601
Mol Cell Proteomics. 2023 Jun 21. pii: S1535-9476(23)00116-0. [Epub ahead of print] 100605

Facioscapulohumeral muscular dystrophy is associated with altered myoblast proteome dynamics.

Yusuke Nishimura, Adam J Bittel, Connor A Stead, Yi-Wen Chen, Jatin G Burniston.

  Proteomic studies in facioscapulohumeral muscular dystrophy (FSHD) could offer new insight to disease mechanisms underpinned by post-transcriptional processes. We used stable isotope (deuterium oxide; D2O) labelling and peptide mass spectrometry to investigate the abundance and turnover rates of proteins in cultured muscle cells from 2 individuals affected by FSHD and their unaffected siblings (UASb). We measured the abundance of 4420 proteins and the turnover rate of 2324 proteins in each (n = 4) myoblast sample. FSHD myoblasts exhibited a greater abundance but slower turnover rate of subunits of mitochondrial respiratory complexes and mitochondrial ribosomal proteins, which may indicate an accumulation of 'older' less viable mitochondrial proteins in myoblasts from individuals affected by FSHD. Treatment with a 2'-O-methoxyethyl modified antisense oligonucleotide targeting exon 3 of the double homeobox 4 (DUX4) transcript tended to reverse mitochondrial protein dysregulation in FSHD myoblasts, indicating the effect on mitochondrial proteins may be a DUX4-dependent mechanism. Our results highlight the importance of post-transcriptional processes and protein turnover in FSHD pathology and provide a resource for the FSHD research community to explore this burgeoning aspect of FSHD.

Keywords:  FSHD; biosynthetic labelling; deuterium oxide; fractional synthesis rate; heavy water; mitochondria; mitochondrial ribosome; protein turnover; proteome dynamics; skeletal muscle

DOI:  https://doi.org/10.1016/j.mcpro.2023.100605
Aging Cell. 2023 Jun 23. e13902

Cross-sectional analysis of healthy individuals across decades: Aging signatures across multiple physiological compartments.

Ruin Moaddel, Ceereena Ubaida-Mohien, Toshiko Tanaka, Qu Tian, Julián Candia, Ann Zenobia Moore, Jacqueline Lovett, Giovanna Fantoni, Nader Shehadeh, Lisa Turek, Victoria Collingham, Mary Kaileh, Chee W Chia, Ranjan Sen, Josephine M Egan, Luigi Ferrucci.

  The study of age-related biomarkers from different biofluids and tissues within the same individual might provide a more comprehensive understanding of age-related changes within and between compartments as these changes are likely highly interconnected. Understanding age-related differences by compartments may shed light on the mechanism of their reciprocal interactions, which may contribute to the phenotypic manifestations of aging. To study such possible interactions, we carried out a targeted metabolomic analysis of plasma, skeletal muscle, and urine collected from healthy participants, age 22-92 years, and identified 92, 34, and 35 age-associated metabolites, respectively. The metabolic pathways that were identified across compartments included inflammation and cellular senescence, microbial metabolism, mitochondrial health, sphingolipid metabolism, lysosomal membrane permeabilization, vascular aging, and kidney function.

Keywords:  aging; inflammation; kidney function; mitochondrial health; muscle metabolomics; plasma metabolomics; senescence; urine metabolomics

DOI:  https://doi.org/10.1111/acel.13902
J Vis Exp. 2023 Jun 02.

Functional Site-Directed Fluorometry in Native Cells to Study Skeletal Muscle Excitability.

Hugo Bibollet, Daniel F Bennett, Martin F Schneider, Erick O Hernández-Ochoa.

Functional site-directed fluorometry has been the technique of choice to investigate the structure-function relationship of numerous membrane proteins, including voltage-gated ion channels. This approach has been used primarily in heterologous expression systems to simultaneously measure membrane currents, the electrical manifestation of the channels' activity, and fluorescence measurements, reporting local domain rearrangements. Functional site-directed fluorometry combines electrophysiology, molecular biology, chemistry, and fluorescence into a single wide-ranging technique that permits the study of real-time structural rearrangements and function through fluorescence and electrophysiology, respectively. Typically, this approach requires an engineered voltage-gated membrane channel that contains a cysteine that can be tested by a thiol-reactive fluorescent dye. Until recently, the thiol-reactive chemistry used for the site-directed fluorescent labeling of proteins was carried out exclusively in Xenopus oocytes and cell lines, restricting the scope of the approach to primary non-excitable cells. This report describes the applicability of functional site-directed fluorometry in adult skeletal muscle cells to study the early steps of excitation-contraction coupling, the process by which muscle fiber electrical depolarization is linked to the activation of muscle contraction. The present protocol describes the methodologies to design and transfect cysteine-engineered voltage-gated Ca2+ channels (CaV1.1) into muscle fibers of the flexor digitorum brevis of adult mice using in vivo electroporation and the subsequent steps required for functional site-directed fluorometry measurements. This approach can be adapted to study other ion channels and proteins. The use of functional site-directed fluorometry of mammalian muscle is particularly relevant to studying basic mechanisms of excitability.

DOI: https://doi.org/10.3791/65311
Mol Ther Nucleic Acids. 2023 Jun 13. 32 937-948

DNAJB6 isoform specific knockdown: Therapeutic potential for limb girdle muscular dystrophy D1.

Andrew R Findlay, May M Paing, Jil A Daw, Meade Haller, Rocio Bengoechea, Sara K Pittman, Shan Li, Feng Wang, Timothy M Miller, Heather L True, Tsui-Fen Chou, Conrad C Weihl.

  Dominant missense mutations in DNAJB6, a co-chaperone of HSP70, cause limb girdle muscular dystrophy (LGMD) D1. No treatments are currently available. Two isoforms exist, DNAJB6a and DNAJB6b, each with distinct localizations in muscle. Mutations reside in both isoforms, yet evidence suggests that DNAJB6b is primarily responsible for disease pathogenesis. Knockdown treatment strategies involving both isoforms carry risk, as DNAJB6 knockout is embryonic lethal. We therefore developed an isoform-specific knockdown approach using morpholinos. Selective reduction of each isoform was achieved in vitro in primary mouse myotubes and human LGMDD1 myoblasts, as well as in vivo in mouse skeletal muscle. To assess isoform specific knockdown in LGMDD1, we created primary myotube cultures from a knockin LGMDD1 mouse model. Using mass spectrometry, we identified an LGMDD1 protein signature related to protein homeostasis and myofibril structure. Selective reduction of DNAJB6b levels in LGMDD1 myotubes corrected much of the proteomic disease signature toward wild type levels. Additional in vivo functional data is required to determine if selective reduction of DNAJB6b is a viable therapeutic target for LGMDD1.

Keywords:  DNAJB6; MT: Oligonucleotides: Therapies and Applications; isoform specific knockdown; limb girdle muscular dystrophy D1 (LGMDD1); morpholino; proteomics

DOI:  https://doi.org/10.1016/j.omtn.2023.05.017
Dis Model Mech. 2023 Jun 01. pii: dmm050107. [Epub ahead of print]16(6):

Muscle-on-a-chip devices: a new era for in vitro modelling of muscular dystrophies.

Juan M Fernández-Costa, Ainoa Tejedera-Vilafranca, Xiomara Fernández-Garibay, Javier Ramón-Azcón.

Muscular dystrophies are a heterogeneous group of highly debilitating diseases that result in muscle atrophy and weakness. The lack of suitable cellular and animal models that reproduce specific aspects of their pathophysiology is one of the reasons why there are no curative treatments for these disorders. This highlights a considerable gap between current laboratory models and clinical practice. We strongly believe that organs-on-chip could help to fill this gap. Organs-on-chip, and in particular muscles-on-chip, are microfluidic devices that integrate functional skeletal muscle tissues. Biosensors in these systems allow monitoring of muscle homeostasis or drug responses in situ. This Perspective outlines the potential of organs-on-chip as advanced models for muscular dystrophies, as well as the current challenges and future opportunities for this technology.

DOI: https://doi.org/10.1242/dmm.050107
Mol Med. 2023 Jun 21. 29(1): 78

Decreased expression of H19/miR-675 ameliorates muscle atrophy by regulating the IGF1R/Akt/FoxO signaling pathway.

He Zhang, Fei Wang, Xiangsheng Pang, Yue Zhou, Shiming Li, Wenjiong Li, Peng Zhang, Xiaoping Chen.

   BACKGROUND: Long non-coding RNA (lncRNA) H19 is one of the most highly expressed and conserved transcripts in mammalian development, and its functions have been fully discussed in many contexts including tumorigenesis and skeletal muscle development. However, its exact role in muscle atrophy remains largely unknown. This study investigated the effect of lncRNA H19 on muscle atrophy and the potential underlying mechanism.
METHODS: Hindlimb suspension (HS) of C57BL/6 mice and starvation of C2C12 cells with PBS were conducted to induce atrophy. Real-time PCR and Western blotting were used to measure the expression of RNAs and proteins. LncRNA H19 and its encoded miR-675 were overexpressed or inhibited in different models of muscle atrophy. Immunofluorescence was carried out to examine the cross-sectional area (CSA) and minimal Feret's diameter (MFD) of myofibers and myotube diameter.
RESULTS: The expression levels of lncRNA H19 and miR-675 were significantly reduced in both the soleus and gastrocnemius muscles in response to HS. Overexpression of lncRNA H19 led to an increase in Atrogin-1 mRNA expression, and this effect was reversed by inhibiting miR-675. The overexpression of miR-675 aggravated both HS- and starving-induced muscle atrophy by inhibiting the IGF1R/Akt signaling pathway and promoting FoxO/Atrogin-1 expression. Conversely, miR-675 inhibition had the opposite effects.
CONCLUSION: The lncRNA H19/miR-675 axis can induce muscle atrophy, and its downregulation in mice with HS-induced muscle atrophy may act as a protective mechanism against this condition.

Keywords:  Hindlimb suspension; IGF1R; LncRNA H19; Muscle atrophy; Starvation; miR-675

DOI:  https://doi.org/10.1186/s10020-023-00683-w
Res Sq. 2023 Jun 06. pii: rs.3.rs-2958821. [Epub ahead of print]

Exercise-primed extracellular vesicles improve cell-matrix adhesion and chondrocyte health.

Hirotaka Iijima, Kai Wang, Ella D'Amico, Wan-Yee Tang, Renee J Rogers, John M Jakicic, Fabrisia Ambrosio.

Extracellular vesicles (EVs) have been suggested to transmit the health-promoting effects of exercise throughout the body. Yet, the mechanisms by which beneficial information is transmitted from extracellular vesicles to recipient cells are poorly understood, precluding a holistic understanding of how exercise promotes cellular and tissue health. In this study, using articular cartilage as a model, we introduced a network medicine paradigm to simulate how exercise facilitates communication between circulating EVs and chondrocytes, the cells resident in articular cartilage. Using the archived small RNA-seq data of EV before and after aerobic exercise, microRNA regulatory network analysis based on network propagation inferred that circulating EVs activated by aerobic exercise perturb chondrocyte-matrix interactions and downstream cellular aging processes. Building on the mechanistic framework identified through computational analyses, follow up experimental studies interrogated the direct influence of exercise on EV-mediated chondrocyte-matrix interactions. We found that pathogenic matrix signaling in chondrocytes was abrogated in the presence of exercise-primed EVs, restoring a more youthful phenotype, as determined by chondrocyte morphological profiling and evaluation of chondrogenicity. Epigenetic reprograming of the gene encoding the longevity protein, α-Klotho, mediated these effects. These studies provide mechanistic evidence that exercise transduces rejuvenation signals to circulating EVs, endowing EVs with the capacity to ameliorate cellular health even in the presence of an unfavorable microenvironmental signals.

DOI: https://doi.org/10.21203/rs.3.rs-2958821/v1
Nucleic Acids Res. 2023 Jun 23. pii: gkad544. [Epub ahead of print]

Gene expressions associated with longer lifespan and aging exhibit similarity in mammals.

Masaki Takasugi, Yuya Yoshida, Yoshiki Nonaka, Naoko Ohtani.

Although molecular features underlying aging and species maximum lifespan (MLS) have been comprehensively studied by transcriptome analyses, the actual impact of transcriptome on aging and MLS remains elusive. Here, we found that transcriptional signatures that are associated with mammalian MLS exhibited significant similarity to those of aging. Moreover, transcriptional signatures of longer MLS and aging both exhibited significant similarity to that of longer-lived mouse strains, suggesting that gene expression patterns associated with species MLS contribute to extended lifespan even within a species and that aging-related gene expression changes overall represent adaptations that extend lifespan rather than deterioration. Finally, we found evidence of co-evolution of MLS and promoter sequences of MLS-associated genes, highlighting the evolutionary contribution of specific transcription factor binding motifs such as that of E2F1 in shaping MLS-associated gene expression signature. Our results highlight the importance of focusing on adaptive aspects of aging transcriptome and demonstrate that cross-species genomics can be a powerful approach for understanding adaptive aging transcriptome.

DOI: https://doi.org/10.1093/nar/gkad544