bims-moremu 2022-10-30 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2022–10–30
37 papers selected by
Anna Vainshtein, Craft Science Inc.

Palmitate impairs circadian transcriptomics in muscle cells through histone modification of enhancers.
Dual roles of mTORC1-dependent activation of the ubiquitin-proteasome system in muscle proteostasis.
Beyond Mechanical Tension: A Review of Resistance Exercise-Induced Lactate Responses & Muscle Hypertrophy.
NOX4 inhibition promotes the remodeling of dystrophic muscle.
Single-cell sequencing deconvolutes cellular responses to exercise in human skeletal muscle.
Angiotensin 1-7 increases fiber cross sectional area and force in juvenile mouse skeletal muscle.
Sarcomere dynamics revealed by a myofilament integrated FRET-based biosensor in live skeletal muscle fibers.
Aerobic conditioning augments the satellite cell and ribosome response to acute eccentric contractions in young men and women.
Chicken or Egg? Mitochondrial Phospholipids and Oxidative Stress in Disuse-induced Skeletal Muscle Atrophy.
NRF2 Regulates Viability, Proliferation, Resistance to Oxidative Stress, and Differentiation of Murine Myoblasts and Muscle Satellite Cells.
Lipid hydroperoxides and oxylipins are mediators of denervation induced muscle atrophy.
IgLON4 Regulates Myogenesis via Promoting Cell Adhesion and Maintaining Myotube Orientation.
Exogenous Antioxidants in Remyelination and Skeletal Muscle Recovery.
AMPK activation is sufficient to increase skeletal muscle glucose uptake and glycogen synthesis but is not required for contraction-mediated increases in glucose metabolism.
PGC-1α and MEF2 Regulate the Transcription of the Carnitine Transporter OCTN2 Gene in C2C12 Cells and in Mouse Skeletal Muscle.
Mild heat stimulation facilitates muscle hypertrophy in C2C12 and mouse satellite cells through myokine release to the culture medium.
Time-specific effects of acute eccentric exercise on myostatin, follistatin and decorin in the circulation and skeletal muscle in rats.
Multi-scale mechanobiological model for skeletal muscle hypertrophy.
Impact of aging and oxidative stress on specific components of excitation contraction coupling in regulating force generation.
The Effects of Exercise Training on Glucose Homeostasis and Muscle Metabolism in Type 1 Diabetic Female Mice.
A deep redox proteome profiling workflow and its application to skeletal muscle of a Duchenne Muscular Dystrophy model.
Molecular regulation of stretch activation.
The Effect of Heat Shock on Myogenic Differentiation of Human Skeletal-Muscle-Derived Mesenchymal Stem/Stromal Cells.
Early tension regulation coupled to surface myomerger is necessary for the primary fusion of C2C12 myoblasts.
Role of mitochondria-associated endoplasmic reticulum membranes in insulin sensitivity, energy metabolism, and contraction of skeletal muscle.
Sleep, circadian biology and skeletal muscle interactions: Implications for metabolic health.
Brush-Induced Orientation of Collagen Fibers in Layer-by-Layer Nanofilms: A Simple Method for the Development of Human Muscle Fibers.
Collagen cross-links scale with passive stiffness in dystrophic mouse muscles, but are not altered with administration of a lysyl oxidase inhibitor.
Effects of SGLT2 inhibitor dapagliflozin in patients with type 2 diabetes on skeletal muscle cellular metabolism.
TNFα and IFNγ cooperate for efficient pro- to anti-inflammatory transition of macrophages during muscle regeneration.
Skeletal Muscle and Kidney Crosstalk in Chronic Kidney Disease.
Myocytic androgen receptor overexpression does not affect sex differences in adaptation to chronic endurance exercise.
Sarcopenia definition, diagnosis and treatment: consensus is growing.
Back to basics: Optimization of DNA and RNA transfer in muscle cells using recent transfection reagents.
The emerging regulatory mechanisms and biological function of circular RNAs in skeletal muscle development.
The AAA-ATPase ATAD1 and its partners promote degradation of desmin intermediate filaments in muscle.
Nuclear movement in multinucleated cells.

Life Sci Alliance. 2023 Jan;pii: e202201598. [Epub ahead of print]6(1):

Palmitate impairs circadian transcriptomics in muscle cells through histone modification of enhancers.

Nicolas J Pillon, Laura Sardón Puig, Ali Altıntaş, Prasad G Kamble, Salvador Casaní-Galdón, Brendan M Gabriel, Romain Barrès, Ana Conesa, Alexander V Chibalin, Erik Näslund, Anna Krook, Juleen R Zierath.

Obesity and elevated circulating lipids may impair metabolism by disrupting the molecular circadian clock. We tested the hypothesis that lipid overload may interact with the circadian clock and alter the rhythmicity of gene expression through epigenomic mechanisms in skeletal muscle. Palmitate reprogrammed the circadian transcriptome in myotubes without altering the rhythmic mRNA expression of core clock genes. Genes with enhanced cycling in response to palmitate were associated with post-translational modification of histones. The cycling of histone 3 lysine 27 acetylation (H3K27ac), a marker of active gene enhancers, was modified by palmitate treatment. Chromatin immunoprecipitation and sequencing confirmed that palmitate exposure altered the cycling of DNA regions associated with H3K27ac. The overlap between mRNA and DNA regions associated with H3K27ac and the pharmacological inhibition of histone acetyltransferases revealed novel cycling genes associated with lipid exposure of primary human myotubes. Palmitate exposure disrupts transcriptomic rhythmicity and modifies enhancers through changes in histone H3K27 acetylation in a circadian manner. Thus, histone acetylation is responsive to lipid overload and may redirect the circadian chromatin landscape, leading to the reprogramming of circadian genes and pathways involved in lipid biosynthesis in skeletal muscle.

DOI: https://doi.org/10.26508/lsa.202201598
Commun Biol. 2022 Oct 27. 5(1): 1141

Dual roles of mTORC1-dependent activation of the ubiquitin-proteasome system in muscle proteostasis.

Marco S Kaiser, Giulia Milan, Daniel J Ham, Shuo Lin, Filippo Oliveri, Kathrin Chojnowska, Lionel A Tintignac, Nitish Mittal, Christian E Zimmerli, David J Glass, Mihaela Zavolan, Markus A Rüegg.

Muscle size is controlled by the PI3K-PKB/Akt-mTORC1-FoxO pathway, which integrates signals from growth factors, energy and amino acids to activate protein synthesis and inhibit protein breakdown. While mTORC1 activity is necessary for PKB/Akt-induced muscle hypertrophy, its constant activation alone induces muscle atrophy. Here we show that this paradox is based on mTORC1 activity promoting protein breakdown through the ubiquitin-proteasome system (UPS) by simultaneously inducing ubiquitin E3 ligase expression via feedback inhibition of PKB/Akt and proteasome biogenesis via Nuclear Factor Erythroid 2-Like 1 (Nrf1). Muscle growth was restored by reactivation of PKB/Akt, but not by Nrf1 knockdown, implicating ubiquitination as the limiting step. However, both PKB/Akt activation and proteasome depletion by Nrf1 knockdown led to an immediate disruption of proteome integrity with rapid accumulation of damaged material. These data highlight the physiological importance of mTORC1-mediated PKB/Akt inhibition and point to juxtaposed roles of the UPS in atrophy and proteome integrity.

DOI: https://doi.org/10.1038/s42003-022-04097-y
J Funct Morphol Kinesiol. 2022 Oct 04. pii: 81. [Epub ahead of print]7(4):

Beyond Mechanical Tension: A Review of Resistance Exercise-Induced Lactate Responses & Muscle Hypertrophy.

Daniel Lawson, Christopher Vann, Brad J Schoenfeld, Cody Haun.

  The present review aims to explore and discuss recent research relating to the lactate response to resistance training and the potential mechanisms by which lactate may contribute to skeletal muscle hypertrophy or help to prevent muscle atrophy. First, we will discuss foundational information pertaining to lactate including metabolism, measurement, shuttling, and potential (although seemingly elusive) mechanisms for hypertrophy. We will then provide a brief analysis of resistance training protocols and the associated lactate response. Lastly, we will discuss potential shortcomings, resistance training considerations, and future research directions regarding lactate's role as a potential anabolic agent for skeletal muscle hypertrophy.

Keywords:  lactate; muscle hypertrophy; resistance exercise; resistance training

DOI:  https://doi.org/10.3390/jfmk7040081
JCI Insight. 2022 Oct 24. pii: e158316. [Epub ahead of print]7(20):

NOX4 inhibition promotes the remodeling of dystrophic muscle.

David W Hammers.

  The muscular dystrophies (MDs) are genetic muscle diseases that result in progressive muscle degeneration followed by the fibrotic replacement of affected muscles as regenerative processes fail. Therapeutics that specifically address the fibrosis and failed regeneration associated with MDs represent a major unmet clinical need for MD patients, particularly those with advanced-stage disease progression. The current study investigated targeting NAD(P)H oxidase 4 (NOX4) as a potential strategy to reduce fibrosis and promote regeneration in disease-burdened muscle that models Duchenne muscular dystrophy (DMD). NOX4 was elevated in the muscles of dystrophic mice and DMD patients, localizing primarily to interstitial cells located between muscle fibers. Genetic and pharmacological targeting of NOX4 significantly reduced fibrosis in dystrophic respiratory and limb muscles. Mechanistically, NOX4 targeting decreased the number of fibrosis-depositing cells (myofibroblasts) and restored the number of muscle-specific stem cells (satellite cells) localized to their physiological niche, thereby rejuvenating muscle regeneration. Furthermore, acute inhibition of NOX4 was sufficient to induce apoptotic clearing of myofibroblasts within dystrophic muscle. These data indicate that targeting NOX4 is an effective strategy to promote the beneficial remodeling of disease-burdened muscle representative of DMD and, potentially, other MDs and muscle pathologies.

Keywords:  Fibrosis; Muscle Biology; Neuromuscular disease; Skeletal muscle; Therapeutics

DOI:  https://doi.org/10.1172/jci.insight.158316
Commun Biol. 2022 Oct 22. 5(1): 1121

Single-cell sequencing deconvolutes cellular responses to exercise in human skeletal muscle.

Alen Lovrić, Ali Rassolie, Seher Alam, Mirko Mandić, Amarjit Saini, Mikael Altun, Rodrigo Fernandez-Gonzalo, Thomas Gustafsson, Eric Rullman.

Skeletal muscle adaptations to exercise have been associated with a range of health-related benefits, but cell type-specific adaptations within the muscle are incompletely understood. Here we use single-cell sequencing to determine the effects of exercise on cellular composition and cell type-specific processes in human skeletal muscle before and after intense exercise. Fifteen clusters originating from six different cell populations were identified. Most cell populations remained quantitatively stable after exercise, but a large transcriptional response was observed in mesenchymal, endothelial, and myogenic cells, suggesting that these cells are specifically involved in skeletal muscle remodeling. We found three subpopulations of myogenic cells characterized by different maturation stages based on the expression of markers such as PAX7, MYOD1, TNNI1, and TNNI2. Exercise accelerated the trajectory of myogenic progenitor cells towards maturation by increasing the transcriptional features of fast- and slow-twitch muscle fibers. The transcriptional regulation of these contractile elements upon differentiation was validated in vitro on primary myoblast cells. The cell type-specific adaptive mechanisms induced by exercise presented here contribute to the understanding of the skeletal muscle adaptations triggered by physical activity and may ultimately have implications for physiological and pathological processes affecting skeletal muscle, such as sarcopenia, cachexia, and glucose homeostasis.

DOI: https://doi.org/10.1038/s42003-022-04088-z
Am J Physiol Cell Physiol. 2022 Oct 24.

Angiotensin 1-7 increases fiber cross sectional area and force in juvenile mouse skeletal muscle.

Hind Albadrani, T Ammar, Rashida Rajgara, Michael Bader, Nadine Wiper-Bergeron, Jean-Marc Renaud.

  Recent studies reported that in skeletal muscle angiotensin 1-7 (Ang 1-7), via its receptor Mas (MasR), prevents the atrophy induced by angiotensin II and by cast immobilization; it also improves muscle integrity and function in the mdx mouse, a muscular dystrophy model. The objectives of this study were to document i) the extent of the Ang 1-7's hypertrophic effect in terms of muscle mass and muscle fiber cross sectional area (CSA), ii) how Ang 1-7 affects muscle contractile function in terms of twitch and tetanic force, force-frequency relationship, and iii) whether the effect involves MasR. Wild type and MasR deficient (MasR-/-) mice were treated with Ang 1-7 (100 ng/kg body weight·min using an osmotic pump) for 4 or 16 weeks. Ang 1-7 significantly increased skeletal muscle/body weight ratio of soleus, tibialis and gastrocnemius, but not of EDL. It significantly increased fiber cross sectional area in the order of type I>IIA>IIB. In EDL and soleus muscles, it significantly increased twitch and tetanic force while causing a shift in the force-frequency relationship toward lower stimulation frequencies. It had no effect on fiber type composition. None of the Ang 1-7 effects observed in wild type mice were observed in MasR‑/‑ muscles. It caused a transient increase in phosphorylated Akt and 4EBP proteins while having no effect on the phosphorylation of S6, MuRF-1 and atrogin-1 and a decrease in PAX7 expression in satellite cells. This is the first study demonstrating the hypertrophic effects of Ang 1-7 in normal muscle acting via its MasR.

Keywords:  Cross sectional area; Fiber type; Hypertrophy; Skeletal muscle; Tetanic force

DOI:  https://doi.org/10.1152/ajpcell.00271.2021
Sci Rep. 2022 Oct 27. 12(1): 18116

Sarcomere dynamics revealed by a myofilament integrated FRET-based biosensor in live skeletal muscle fibers.

Ashley A Martin, Brian R Thompson, Jonathan P Davis, Hluechy Vang, Dongwoo Hahn, Joseph M Metzger.

The sarcomere is the functional unit of skeletal muscle, essential for proper contraction. Numerous acquired and inherited myopathies impact sarcomere function causing clinically significant disease. Mechanistic investigations of sarcomere activation have been challenging to undertake in the context of intact, live skeletal muscle fibers during real time physiological twitch contractions. Here, a skeletal muscle specific, intramolecular FRET-based biosensor was designed and engineered into fast skeletal muscle troponin C (TnC) to investigate the dynamics of sarcomere activation. In transgenic animals, the TnC biosensor incorporated into the skeletal muscle fiber sarcomeres by stoichiometric replacement of endogenous TnC and did not alter normal skeletal muscle contractile form or function. In intact single adult skeletal muscle fibers, real time twitch contractile data showed the TnC biosensor transient preceding the peak amplitude of contraction. Importantly, under physiological temperatures, inactivation of the TnC biosensor transient decayed significantly more slowly than the Ca2+ transient and contraction. The uncoupling of the TnC biosensor transient from the Ca2+ transient indicates the biosensor is not functioning as a Ca2+ transient reporter, but rather reports dynamic sarcomere activation/ inactivation that, in turn, is due to the ensemble effects of multiple activating ligands within the myofilaments. Together, these findings provide the foundation for implementing this new biosensor in future physiological studies investigating the mechanism of activation of the skeletal muscle sarcomere in health and disease.

DOI: https://doi.org/10.1038/s41598-022-21425-8
Am J Physiol Cell Physiol. 2022 10 24.

Aerobic conditioning augments the satellite cell and ribosome response to acute eccentric contractions in young men and women.

Alex Brown, Aaron C Q Thomas, Aidan A Hatt, Chris McGlory, Stuart M Phillips, Dinesh Kumbhare, Gianni Parise, Sophie Joanisse.

  Satellite cells (SC) and ribosomes are key determinants of the skeletal muscle adaptive response. Both are thought to increase acutely after resistance exercise and chronically with resistance training. However, the acute SC and ribosome exercise response with prior aerobic conditioning is unknown. Fourteen young men and women underwent 6 weeks of single-legged aerobic conditioning followed by an acute bout of 300 eccentric contractions. Muscle biopsies were taken from the vastus lateralis of the aerobically conditioned (AC) and the control (CTL) legs before (Pre), 24 (24h) and 48 (48h) hours post-contractions. SC pool expansion (PAX7+ cells/100 fibres) was greater in type-I (1.3-fold) and mixed-fibres (1.2-fold) in the AC leg compared to the CTL. Pax7 (1.2-fold) and MyoD1 (1.4-fold) mRNA expression was also greater in the AC leg compared to the CTL. AC had greater RNA concentration (1.2-fold) and mRNA expression of Ubf (1.2-fold) and Tif-1a (1.3-fold) compared to CTL. Only the AC leg increased (Pre-48h) c-Myc (3.0-fold), (Pre-24h) 45S pre-rRNA (2.6-fold), 5.8S ITS (2.1-fold) and 28S ITS (2.0-fold) following eccentric contractions. We discovered that aerobic conditioning augmented type-I SC pool expansion and ribosome content following an acute bout of eccentric contractions.

Keywords:  Acute Exercise; Adaptation; Ribosomes; Satellite Cells; Skeletal Muscle

DOI:  https://doi.org/10.1152/ajpcell.00418.2022
Antioxid Redox Signal. 2022 Oct 27.

Chicken or Egg? Mitochondrial Phospholipids and Oxidative Stress in Disuse-induced Skeletal Muscle Atrophy.

Edwin R Miranda, Justin L Shahtout, Katsuhiko Funai.

SIGNIFICANCE: Accumulation of reactive oxygen species (ROS) is known to promote cellular damage in multiple cell-types. In skeletal muscle, ROS has been implicated in disuse-induced muscle atrophy. However, the molecular origin and mechanism of how disuse promotes ROS and muscle dysfunction remains unclear.
RECENT ADVANCES: Recently, we implicated membrane lipids of mitochondria to be a potential source of ROS to promote muscle atrophy.
CRITICAL ISSUES: In this review, we discuss evidence that changes in mitochondrial lipids represent a physiologically-relevant process by which disuse promotes mitochondrial electron leak and oxidative stress.
FUTURE DIRECTIONS: We further discuss lipid hydroperoxides (LOOH) as a potential downstream mediator of ROS to induce muscle atrophy.

DOI: https://doi.org/10.1089/ars.2022.0151
Cells. 2022 Oct 21. pii: 3321. [Epub ahead of print]11(20):

NRF2 Regulates Viability, Proliferation, Resistance to Oxidative Stress, and Differentiation of Murine Myoblasts and Muscle Satellite Cells.

Iwona Bronisz-Budzyńska, Magdalena Kozakowska, Katarzyna Pietraszek-Gremplewicz, Magdalena Madej, Alicja Józkowicz, Agnieszka Łoboda, Józef Dulak.

  Increased oxidative stress can slow down the regeneration of skeletal muscle and affect the activity of muscle satellite cells (mSCs). Therefore, we evaluated the role of the NRF2 transcription factor (encoded by the Nfe2l2 gene), the main regulator of the antioxidant response, in muscle cell biology. We used (i) an immortalized murine myoblast cell line (C2C12) with stable overexpression of NRF2 and (ii) primary mSCs isolated from wild-type and Nfe2l2 (transcriptionally)-deficient mice (Nfe2l2tKO). NRF2 promoted myoblast proliferation and viability under oxidative stress conditions and decreased the production of reactive oxygen species. Furthermore, NRF2 overexpression inhibited C2C12 cell differentiation by down-regulating the expression of myogenic regulatory factors (MRFs) and muscle-specific microRNAs. We also showed that NRF2 is indispensable for the viability of mSCs since the lack of its transcriptional activity caused high mortality of cells cultured in vitro under normoxic conditions. Concomitantly, Nfe2l2tKO mSCs grown and differentiated under hypoxic conditions were viable and much more differentiated compared to cells isolated from wild-type mice. Taken together, NRF2 significantly influences the properties of myoblasts and muscle satellite cells. This effect might be modulated by the muscle microenvironment.

Keywords:  NRF2; muscle regeneration; myoblasts; oxidative stress; satellite cells

DOI:  https://doi.org/10.3390/cells11203321
Redox Biol. 2022 Oct 20. pii: S2213-2317(22)00290-7. [Epub ahead of print]57 102518

Lipid hydroperoxides and oxylipins are mediators of denervation induced muscle atrophy.

Jacob L Brown, Fredrick F Peelor, Constantin Georgescu, Jonathan D Wren, Michael Kinter, Victoria J Tyrrell, Valerie B O'Donnell, Benjamin F Miller, Holly Van Remmen.

  Loss of innervation is a key driver of age associated muscle atrophy and weakness (sarcopenia). Our laboratory has previously shown that denervation induced atrophy is associated with the generation of mitochondrial hydroperoxides and lipid mediators produced downstream of cPLA2 and 12/15 lipoxygenase (12/15-LOX). To define the pathological impact of lipid hydroperoxides generated in denervation-induced atrophy in vivo, we treated mice with liproxstatin-1, a lipid hydroperoxide scavenger. We treated adult male mice with 5 mg/kg liproxstain-1 or vehicle one day prior to sciatic nerve transection and daily for 7 days post-denervation before tissue analysis. Liproxstatin-1 treatment protected gastrocnemius mass and fiber cross sectional area (∼40% less atrophy post-denervation in treated versus untreated mice). Mitochondrial hydroperoxide generation was reduced 80% in vitro and by over 65% in vivo by liproxstatin-1 treatment in denervated permeabilized muscle fibers and decreased the content of 4-HNE by ∼25% post-denervation. Lipidomic analysis revealed detectable levels of 25 oxylipins in denervated gastrocnemius muscle and significantly increased levels for eight oxylipins that are generated by metabolism of fatty acids through 12/15-LOX. Liproxstatin-1 treatment reduced the level of three of the eight denervation-induced oxylipins, specifically 15-HEPE, 13-HOTrE and 17-HDOHE. Denervation elevated protein degradation rates in muscle and treatment with liproxstatin-1 reduced rates of protein breakdown in denervated muscle. In contrast, protein synthesis rates were unchanged by denervation. Targeted proteomics revealed a number of proteins with altered expression after denervation but no effect of liproxstain-1. Transcriptomic analysis revealed 203 differentially expressed genes in denervated muscle from vehicle or liproxstatin-1 treated mice, including ER stress, nitric oxide signaling, Gαi signaling, glucocorticoid receptor signaling, and other pathways. Overall, these data suggest lipid hydroperoxides and oxylipins are key drivers of increased protein breakdown and muscle loss associated with denervation induced atrophy and a potential target for sarcopenia intervention.

Keywords:  Lipoxygenase; Mitochondria; Neuromuscular junction; ROS; Skeletal

DOI:  https://doi.org/10.1016/j.redox.2022.102518
Cells. 2022 Oct 17. pii: 3265. [Epub ahead of print]11(20):

IgLON4 Regulates Myogenesis via Promoting Cell Adhesion and Maintaining Myotube Orientation.

Jeong Ho Lim, Khurshid Ahmad, Hee Jin Chun, Ye Chan Hwang, Afsha Fatima Qadri, Shahid Ali, Syed Sayeed Ahmad, Sibhghatulla Shaikh, Jungseok Choi, Jihoe Kim, Jun-O Jin, Myunghee Kim, Sung Soo Han, Inho Choi, Eun Ju Lee.

  Immunoglobulin-like cell adhesion molecule (IgLON4) is a glycosylphosphatidylinositol-anchored membrane protein that has been associated with neuronal growth and connectivity, and its deficiency has been linked to increased fat mass and low muscle mass. Adequate information on IgLON4 is lacking, especially in the context of skeletal muscle. In this study, we report that IgLON4 is profusely expressed in mouse muscles and is intensely localized on the cell membrane. IgLON4 expression was elevated in CTX-injected mouse muscles, which confirmed its role during muscle regeneration, and was abundantly expressed at high concentrations at cell-to-cell adhesion and interaction sites during muscle differentiation. IgLON4 inhibition profoundly affected myotube alignment, and directional analysis confirmed this effect. Additionally, results demonstrating a link between IgLON4 and lipid rafts during myogenic differentiation suggest that IgLON4 promotes differentiation by increasing lipid raft accumulation. These findings support the notion that a well-aligned environment promotes myoblast differentiation. Collectively, IgLON4 plays a novel role in myogenesis and regeneration, facilitates myotube orientation, and is involved in lipid raft accumulation.

Keywords:  IgLON4; differentiation; lipid raft; myotube alignment; myotube orientation; skeletal muscle

DOI:  https://doi.org/10.3390/cells11203265
Biomedicines. 2022 Oct 13. pii: 2557. [Epub ahead of print]10(10):

Exogenous Antioxidants in Remyelination and Skeletal Muscle Recovery.

Ricardo Julián Cabezas Perez, Marco Fidel Ávila Rodríguez, Doris Haydee Rosero Salazar.

  Inflammatory, oxidative, and autoimmune responses cause severe damage to the nervous system inducing loss of myelin layers or demyelination. Even though demyelination is not considered a direct cause of skeletal muscle disease there is extensive damage in skeletal muscles following demyelination and impaired innervation. In vitro and in vivo evidence using exogenous antioxidants in models of demyelination is showing improvements in myelin formation alongside skeletal muscle recovery. For instance, exogenous antioxidants such as EGCG stimulate nerve structure maintenance, activation of glial cells, and reduction of oxidative stress. Consequently, this evidence is also showing structural and functional recovery of impaired skeletal muscles due to demyelination. Exogenous antioxidants mostly target inflammatory pathways and stimulate remyelinating mechanisms that seem to induce skeletal muscle regeneration. Therefore, the aim of this review is to describe recent evidence related to the molecular mechanisms in nerve and skeletal muscle regeneration induced by exogenous antioxidants. This will be relevant to identifying further targets to improve treatments of neuromuscular demyelinating diseases.

Keywords:  antioxidants; demyelination; inflammation; myelin; nerve; oxidative stress; regeneration; remyelination; skeletal muscle

DOI:  https://doi.org/10.3390/biomedicines10102557
Heliyon. 2022 Oct;8(10): e11091

AMPK activation is sufficient to increase skeletal muscle glucose uptake and glycogen synthesis but is not required for contraction-mediated increases in glucose metabolism.

Ryan M Esquejo, Bina Albuquerque, Anna Sher, Matthew Blatnik, Kyle Wald, Matthew Peloquin, Jake Delmore, Erick Kindt, Wenlin Li, Jamey D Young, Kim Cameron, Russell A Miller.

  The AMP-activated protein kinase (AMPK) is a cellular sensor of energetics and when activated in skeletal muscle during contraction can impart changes in skeletal muscle metabolism. Therapeutics that selectively activate AMPK have been developed to lower glucose levels through increased glucose disposal rates as an approach to abrogate the hyperglycemic state of diabetes; however, the metabolic fate of glucose following AMPK activation remains unclear. We have used a combination of in vivo evaluation of glucose homeostasis and ex vivo skeletal muscle incubation to systematically evaluate metabolism following pharmacological activation of AMPK with PF-739, comparing this with AMPK activation through sustained intermittent electrical stimulation of contraction. These methods to activate AMPK result in increased glucose uptake but divergent metabolism of glucose: pharmacological activation results in increased glycogen accumulation while contraction-induced glucose uptake results in increased lactate formation and glucose oxidation. These results provide additional evidence to support a role for AMPK in control of skeletal muscle metabolism and additional insight into the potential for AMPK stimulation with small molecule direct activators.

Keywords:  AMPK; Metabolism; Pharmacology; Skeletal muscle

DOI:  https://doi.org/10.1016/j.heliyon.2022.e11091
Int J Mol Sci. 2022 Oct 14. pii: 12304. [Epub ahead of print]23(20):

PGC-1α and MEF2 Regulate the Transcription of the Carnitine Transporter OCTN2 Gene in C2C12 Cells and in Mouse Skeletal Muscle.

Katerina Novakova, Michael Török, Miljenko Panajatovic, Jamal Bouitbir, François H T Duong, Christoph Handschin, Stephan Krähenbühl.

  OCTN2 (SLC22A5) is a carnitine transporter whose main function is the active transport of carnitine into cells. In skeletal muscle and other organs, the regulation of the SLC22A5 gene transcription has been shown to depend on the nuclear transcription factor PPAR-α. Due to the observation that the muscle OCTN2 mRNA level is maintained in PPAR-α knock-out mice and that PGC-1α overexpression in C2C12 myoblasts increases OCTN2 mRNA expression, we suspected additional regulatory pathways for SLC22A5 gene transcription. Indeed, we detected several binding sites of the myocyte-enhancing factor MEF2 in the upstream region of the SLC22A5 gene, and MEF2C/MEF2D stimulated the activity of the OCTN2 promoter in gene reporter assays. This stimulation was increased by PGC-1α and was blunted for a SLC22A5 promoter fragment with a mutated MEF2 binding site. Further, we demonstrated the specific binding of MEF2 to the SLC22A5 gene promoter, and a supershift of the MEF2/DNA complex in electrophoretic mobility shift assays. In immunoprecipitation experiments, we could demonstrate the interaction between PGC-1α and MEF2. In addition, SB203580, a specific inhibitor of p38 MAPK, blocked and interferon-γ stimulated the transcriptional activity of the SLC22A5 gene promoter. Finally, mice with muscle-specific overexpression of OCTN2 showed an increase in OCTN2 mRNA and protein expression in skeletal muscle. In conclusion, we detected and characterized a second stimulatory pathway of SLC22A5 gene transcription in skeletal muscle, which involves the nuclear transcription factor MEF2 and co-stimulation by PGC-1α and which is controlled by the p38 MAPK signaling cascade.

Keywords:  MEF2; OCTN2; PGC-1α; SLC22A5 gene transcription; carnitine; p38 MAPK

DOI:  https://doi.org/10.3390/ijms232012304
Biochem Biophys Res Commun. 2022 Oct 14. pii: S0006-291X(22)01403-6. [Epub ahead of print]635 161-168

Mild heat stimulation facilitates muscle hypertrophy in C2C12 and mouse satellite cells through myokine release to the culture medium.

Satoko Hayashi, Shinichi Yonekura.

  Mild heat stimulation is defined as a stimulation that occurs several degrees above optimal cell culture or body temperatures. Muscle hypertrophy in C2C12 cells is reportedly facilitated by 39 °C mild heat stimulation. However, the underlying molecular mechanisms by which 39 °C mild heat stimulation promotes muscle hypertrophy remains elusive. In this study, we aimed at understanding the details of these mechanisms. First, we found that 39 °C mild heat stimulation has little or no effect on Myogenesis-Related Factor (MRF) expression both in C2C12 and mouse primary satellite cells. Therefore, we hypothesized that 39 °C mild heat stimulation promotes muscle hypertrophy through myokines, essential components in myogenesis. Interestingly, we observed muscle hypertrophy in the group cultured at 37 °C in conditioned medium from 39 °C compared to the group cultured at 37 °C in conditioned medium from 37 °C in the case of both C2C12 and mouse primary satellite cells. These results suggest that 39 °C mild heat stimulation promotes muscle hypertrophy through myokines, once released in the culture medium. Finally, we identified Decorin as a hypertrophy-inducing myokine candidate. Therefore, in this study, we demonstrated that 39 °C mild heat stimulation contributes to muscle hypertrophy through enhancing Decorin gene expression in C2C12 and mouse primary satellite cells.

Keywords:  C2C12 cell; Conditioned medium; Decorin; Mild heat stimulation; Muscle hypertrophy; Satellite cell

DOI:  https://doi.org/10.1016/j.bbrc.2022.10.018
Physiol Res. 2022 Oct 13.

Time-specific effects of acute eccentric exercise on myostatin, follistatin and decorin in the circulation and skeletal muscle in rats.

X Liu, N Zhang, B Sun, B Wang.

Myostatin (MSTN), an important negative regulator of skeletal muscle, plays an important role in skeletal muscle health. In previous study, we found that the expression of MSTN was different during skeletal muscle injury repair. Therefore, we explored the expression changes of MSTN at different time points during skeletal muscle injury repair after eccentric exercise. In addition, MSTN is regulated by follistatin (FST) and decorin (DCN) in vivo, so our study examined the time-specific changes of FST, DCN and MSTN in the circulation and skeletal muscle during skeletal muscle injury repair after eccentric exercise, and to explore the reasons for the changes of MSTN in the process of exercise-induced muscle injury repair, to provide a basis for promoting muscle injury repair. The rats performed one-time eccentric exercise. Blood and skeletal muscle were collected at the corresponding time points, respectively immediate after exercise (D0), one day (D1), two days (D2), three days (D3), seven days (W1) and fourteen days (W2) after exercise (n=8). The levels of MSTN, FST, DCN in serum and mRNA and protein expression in muscle were detected. MSTN changes in the blood and changes in DCN and FST showed the opposite trend, except immediately after exercise. The change trends of mRNA and protein of gastrocnemius DCN and MSTN are inconsistent, there is post-transcriptional regulation of MSTN and DCN in gastrocnemius. Acute eccentric exercise might stimulate the secretion of DCN and FST into the circulation and inhibit MSTN. MSTN may be regulated by FST and DCN after acute eccentric exercise.
Front Physiol. 2022 ;13 899784

Multi-scale mechanobiological model for skeletal muscle hypertrophy.

Yesid Villota-Narvaez, Diego A Garzón-Alvarado, Oliver Röhrle, Angelica M Ramírez-Martínez.

  Skeletal muscle adaptation is correlated to training exercise by triggering different signaling pathways that target many functions; in particular, the IGF1-AKT pathway controls protein synthesis and degradation. These two functions regulate the adaptation in size and strength of muscles. Computational models for muscle adaptation have focused on: the biochemical description of signaling pathways or the mechanical description of muscle function at organ scale; however, an interrelation between these two models should be considered to understand how an adaptation in muscle size affects the protein synthesis rate. In this research, a dynamical model for the IGF1-AKT signaling pathway is linked to a continuum-mechanical model describing the active and passive mechanical response of a muscle; this model is used to study the impact of the adaptive muscle geometry on the protein synthesis at the fiber scale. This new computational model links the signaling pathway to the mechanical response by introducing a growth tensor, and links the mechanical response to the signaling pathway through the evolution of the protein synthesis rate. The predicted increase in cross sectional area (CSA) due to an 8 weeks training protocol excellently agreed with experimental data. Further, our results show that muscle growth rate decreases, if the correlation between protein synthesis and CSA is negative. The outcome of this study suggests that multi-scale models coupling continuum mechanical properties and molecular functions may improve muscular therapies and training protocols.

Keywords:  biochemical modeling; biomechanics; cellular signaling pathways; dynamical systems; mechanobiology; muscle adaptation; population dynamics

DOI:  https://doi.org/10.3389/fphys.2022.899784
Sci Adv. 2022 Oct 28. 8(43): eadd7377

Impact of aging and oxidative stress on specific components of excitation contraction coupling in regulating force generation.

Hongyang Xu, Bumsoo Ahn, Holly Van Remmen.

Muscle weakness associated with sarcopenia is a major contributor to reduced health span and quality of life in the elderly. However, the underlying mechanisms of muscle weakness in aging are not fully defined. We investigated the effect of oxidative stress and aging on specific molecular mechanisms involved in muscle force production in mice and skinned permeabilized single fibers in mice lacking the antioxidant enzyme CuZnSod (Sod1KO) and in aging (24-month-old) wild-type mice. Loss of muscle strength occurs in both models, potentially because of reduced membrane excitability with altered NKA signaling and RyR stability, decreased fiber Ca2+ sensitivity and suppressed SERCA activity via modification of the Cys674 residue, dysregulated SR and cytosolic Ca2+ homeostasis, and impaired mitochondrial Ca2+ buffering and respiration. Our results provide a better understanding of the specific impacts of aging and oxidative stress on mechanisms related to muscle weakness that may point to future interventions for countering muscle weakness.

DOI: https://doi.org/10.1126/sciadv.add7377
Metabolites. 2022 Oct 05. pii: 948. [Epub ahead of print]12(10):

The Effects of Exercise Training on Glucose Homeostasis and Muscle Metabolism in Type 1 Diabetic Female Mice.

Caitlin C O'Neill, Erica J Locke, Darren A Sipf, Jack H Thompson, Erin K Drebushenko, Nathan S Berger, Brooke S Segich, Stephen C Kolwicz.

  Although exercise training is an important recommendation for the management of type 1 diabetes (T1D), most of the available research studies predominantly focus on male subjects. Given the importance of sex as a biological variable, additional studies are required to improve the knowledge gap regarding sex differences in T1D research. Therefore, the purpose of this study was to examine the role of exercise training in mediating changes in glucose homeostasis and skeletal muscle metabolism in T1D female mice. Female mice were injected with streptozotocin (STZ) to induce T1D. Two weeks after STZ injection, control (CON) and STZ mice were exercise trained on a treadmill for 4 weeks. Aerobic exercise training failed to improve glucose tolerance, prevent the decrease in body weight and adipose tissue mass, or attenuate muscle atrophy in T1D female mice. However, insulin sensitivity was improved in T1D female mice after exercise training. Aerobic exercise training maintained skeletal muscle triglyceride content but did not prevent depletion of skeletal muscle or liver glycogen in T1D mice. Gene expression analysis suggested that T1D resulted in decreased glucose transport, decreased ketone body oxidation, and increased fatty acid metabolism in the skeletal muscle, which was not altered by exercise training. These data demonstrate that 4 weeks of aerobic exercise training of a moderate intensity is insufficient to counteract the negative effects of T1D in female mice, but does lead to an improvement in insulin sensitivity.

Keywords:  chronic exercise; glucose metabolism; hyperlipidemia; insulin; ketosis; streptozotocin

DOI:  https://doi.org/10.3390/metabo12100948
Free Radic Biol Med. 2022 Oct 25. pii: S0891-5849(22)00931-5. [Epub ahead of print]

A deep redox proteome profiling workflow and its application to skeletal muscle of a Duchenne Muscular Dystrophy model.

Nicholas J Day, Tong Zhang, Matthew J Gaffrey, Rui Zhao, Thomas L Fillmore, Ronald J Moore, George G Rodney, Wei-Jun Qian.

  Perturbation to the redox state accompanies many diseases and its effects are viewed through oxidation of biomolecules, including proteins, lipids, and nucleic acids. The thiol groups of protein cysteine residues undergo an array of redox post-translational modifications (PTMs) that are important for regulation of protein and pathway function. To better understand what proteins are redox regulated following a perturbation, it is important to be able to comprehensively profile protein thiol oxidation at the proteome level. Herein, we report a deep redox proteome profiling workflow and demonstrate its application in measuring the changes in thiol oxidation along with global protein expression in skeletal muscle from mdx mice, a model of Duchenne Muscular Dystrophy (DMD). In depth coverage of the thiol proteome was achieved with >18,000 Cys sites from 5608 proteins in muscle being quantified. Compared to the control group, mdx mice exhibit markedly increased thiol oxidation, where ∼2% shift in the median oxidation occupancy was observed. Pathway analysis for the redox data revealed that coagulation system and immune-related pathways were among the most susceptible to increased thiol oxidation in mdx mice, whereas protein abundance changes were more enriched in pathways associated with bioenergetics. This study illustrates the importance of deep redox profiling in gaining greater insight into oxidative stress regulation and pathways/processes that are perturbed in an oxidizing environment.

Keywords:  Post-translational modifications; Protein thiols; Redox proteomics; Site occupancy; Stoichiometry; Thiol oxidation

DOI:  https://doi.org/10.1016/j.freeradbiomed.2022.10.300
Am J Physiol Cell Physiol. 2022 Oct 24.

Molecular regulation of stretch activation.

Joel C Robinett, Laurin M Hanft, Brandon Biesiadecki, Kerry S McDonald.

  Stretch activation is a delayed increase in force after rapid stretches. While there is evidence for stretch activation in cardiac muscle, few studies have measured mechanisms of stretch activation in mammalian skeletal muscle fibers. We measured stretch activation following rapid step stretches during submaximal Ca2+ activations of rat permeabilized slow-twitch skeletal muscle fibers before and after protein kinase A (PKA), which phosphorylates slow myosin binding protein-C. PKA increased stretch activation and accelerated rates of delayed force development (kdf). Following the step stretches and subsequent force development, fibers were rapidly shortened to original sarcomere length (SL), which elicited a shortening-induced transient force overshoot. After PKA, step shortening-induced transient force overshoot increased ~10-fold following SL shortening during low Ca2+ activation. kdf following step shortening also increased after PKA. We next investigated thin filament regulation of stretch activation. We tested the interplay between cardiac troponin I (cTnI) phosphorylation at canonical PKA and novel tyrosine kinase sites. Slow-skeletal Tn complexes were exchanged with recombinant human cTn complex with different human cTnI N-terminal pseudo-phosphorylation molecules. Pseudo-phosphorylated cTnIs elicited greater stretch activation than WT. Following stretch activation, a higher steady-state force was reached with pseudo-phosphorylated cTnI. Only combinatorial S23/24D + Y26E pseudo-phosphorylated cTnI increased kdf. These results suggest that sMyBP-C PKA phosphorylation modulates stretch activation by a combination of cross-bridge recruitment and faster cycling kinetics, while cTnI phosphorylation regulates stretch activation via redundant and synergistic mechanisms; and, taken together, these sarcomere phospho-proteins offer precision targets for enhanced contractility.

Keywords:  Myosin Binding Protein-C; slow-twitch skeletal muscle fiber,; stretch activation; transient force overshoot; troponin I

DOI:  https://doi.org/10.1152/ajpcell.00101.2022
Cells. 2022 Oct 13. pii: 3209. [Epub ahead of print]11(20):

The Effect of Heat Shock on Myogenic Differentiation of Human Skeletal-Muscle-Derived Mesenchymal Stem/Stromal Cells.

Rokas Mikšiūnas, Siegfried Labeit, Daiva Bironaitė.

  Muscle injuries, degenerative diseases and other lesions negatively affect functioning of human skeletomuscular system and thus quality of life. Therefore, the investigation of molecular mechanisms, stimulating myogenic differentiation of primary skeletal-muscle-derived mesenchymal stem/stromal cells (SM-MSCs), is actual and needed. The aim of the present study was to investigate the myogenic differentiation of CD56 (neural cell adhesion molecule, NCAM)-positive and -negative SM-MSCs and their response to the non-cytotoxic heat stimulus. The SM-MSCs were isolated from the post operation muscle tissue, sorted by flow cytometer according to the CD56 biomarker and morphology, surface profile, proliferation and myogenic differentiation has been investigated. Data show that CD56(+) cells were smaller in size, better proliferated and had significantly higher levels of CD146 (MCAM) and CD318 (CDCP1) compared with the CD56(-) cells. At control level, CD56(+) cells significantly more expressed myogenic differentiation markers MYOD1 and myogenin (MYOG) and better differentiated to the myogenic direction. The non-cytotoxic heat stimulus significantly stronger stimulated expression of myogenic markers in CD56(+) than in CD56(-) cells that correlated with the multinucleated cell formation. Data show that regenerative properties of CD56(+) SM-MSCs can be stimulated by an extracellular stimulus and be used as a promising skeletal muscle regenerating tool in vivo.

Keywords:  CD56; heat shock response; mesenchymal stem/stromal cells; myogenic differentiation; skeletal muscle

DOI:  https://doi.org/10.3390/cells11203209
Front Physiol. 2022 Oct 14. pii: fphys.2022.976715. [Epub ahead of print]13

Early tension regulation coupled to surface myomerger is necessary for the primary fusion of C2C12 myoblasts.

Madhura Chakraborty, Athul Sivan, Arikta Biswas, Bidisha Sinha.

  Here, we study the time-dependent regulation of fluctuation-tension during myogenesis and the role of the fusogen, myomerger. We measure nanometric height fluctuations of the basal membrane of C2C12 cells after triggering differentiation. Fusion of cells increases fluctuation-tension but prefers a transient lowering of tension (at ~2-24 h). Cells fail to fuse if early tension is continuously enhanced by methyl-β-cyclodextrin (MβCD). Perturbing tension regulation also reduces fusion. During this pre-fusion window, cells that finally differentiate usually display lower tension than other non-fusing cells, validating early tension states to be linked to fate decision. Early tension reduction is accompanied by low but gradually increasing level of the surface myomerger. Locally too, regions with higher myomerger intensity display lower tension. However, this negative correlation is lost in the early phase by MβCD-based cholesterol depletion or later as differentiation progresses. We find that with tension and surface-myomerger's enrichment under these conditions, myomerger clusters become pronouncedly diffused. We, therefore, propose that low tension aided by clustered surface-myomerger at the early phase is crucial for fusion and can be disrupted by cholesterol-reducing molecules, implying the potential to affect muscle health.

Keywords:  cholesterol; membrane fluctuations; membrane tension; myoblast fusion; myomerger

DOI:  https://doi.org/10.3389/fphys.2022.976715
Front Mol Biosci. 2022 ;9 959844

Role of mitochondria-associated endoplasmic reticulum membranes in insulin sensitivity, energy metabolism, and contraction of skeletal muscle.

Bianca Nieblas, Perla Pérez-Treviño, Noemí García.

  Skeletal muscle has a critical role in the regulation of the energy balance of the organism, particularly as the principal tissue responsible for insulin-stimulated glucose disposal and as the major site of peripheral insulin resistance (IR), which has been related to accumulation of lipid intermediates, reduced oxidative capacity of mitochondria and endoplasmic reticulum (ER) stress. These organelles form contact sites, known as mitochondria-associated ER membranes (MAMs). This interconnection seems to be involved in various cellular processes, including Ca2+ transport and energy metabolism; therefore, MAMs could play an important role in maintaining cellular homeostasis. Evidence suggests that alterations in MAMs may contribute to IR. However, the evidence does not refer to a specific subcellular location, which is of interest due to the fact that skeletal muscle is constituted by oxidative and glycolytic fibers as well as different mitochondrial populations that appear to respond differently to stimuli and pathological conditions. In this review, we show the available evidence of possible differential responses in the formation of MAMs in skeletal muscle as well as its role in insulin signaling and the beneficial effect it could have in the regulation of energetic metabolism and muscular contraction.

Keywords:  insulin resistance; mitochondria-associated ER membranes (MAMs); mitochondrial dysfunction; mitochondrial skeletal muscle; mitochondrial subpopulations; obesity

DOI:  https://doi.org/10.3389/fmolb.2022.959844
Sleep Med Rev. 2022 Oct 09. pii: S1087-0792(22)00113-7. [Epub ahead of print]66 101700

Sleep, circadian biology and skeletal muscle interactions: Implications for metabolic health.

Matthew Morrison, Shona L Halson, Jonathon Weakley, John A Hawley.

  There currently exists a modern epidemic of sleep loss, triggered by the changing demands of our 21st century lifestyle that embrace 'round-the-clock' remote working hours, access to energy-dense food, prolonged periods of inactivity, and on-line social activities. Disturbances to sleep patterns impart widespread and adverse effects on numerous cells, tissues, and organs. Insufficient sleep causes circadian misalignment in humans, including perturbed peripheral clocks, leading to disrupted skeletal muscle and liver metabolism, and whole-body energy homeostasis. Fragmented or insufficient sleep also perturbs the hormonal milieu, shifting it towards a catabolic state, resulting in reduced rates of skeletal muscle protein synthesis. The interaction between disrupted sleep and skeletal muscle metabolic health is complex, with the mechanisms underpinning sleep-related disturbances on this tissue often multifaceted. Strategies to promote sufficient sleep duration combined with the appropriate timing of meals and physical activity to maintain circadian rhythmicity are important to mitigate the adverse effects of inadequate sleep on whole-body and skeletal muscle metabolic health. This review summarises the complex relationship between sleep, circadian biology, and skeletal muscle, and discusses the effectiveness of several strategies to mitigate the negative effects of disturbed sleep or circadian rhythms on skeletal muscle health.

Keywords:  Chronobiology; Health; Metabolism; Physiology; Protein synthesis; Sleep behaviour

DOI:  https://doi.org/10.1016/j.smrv.2022.101700
ACS Nano. 2022 Oct 27.

Brush-Induced Orientation of Collagen Fibers in Layer-by-Layer Nanofilms: A Simple Method for the Development of Human Muscle Fibers.

Muhammad Haseeb Iqbal, Faratiana Jeanne Rosine Revana, Emeline Pradel, Varvara Gribova, Kamel Mamchaoui, Catherine Coirault, Florent Meyer, Fouzia Boulmedais.

  The engineering of skeletal muscle tissue, a highly organized structure of myotubes, is promising for the treatment of muscle injuries and muscle diseases, for replacement, or for pharmacology research. Muscle tissue development involves differentiation of myoblasts into myotubes with parallel orientation, to ultimately form aligned myofibers, which is challenging to achieve on flat surfaces. In this work, we designed hydrogen-bonded tannic acid/collagen layer-by-layer (TA/COL LbL) nanofilms using a simple brushing method to address this issue. In comparison to films obtained by dipping, brushed TA/COL films showed oriented COL fibers of 60 nm diameter along the brushing direction. Built at acidic pH due to COL solubility, TA/COL films released TA in physiological conditions with a minor loss of thickness. After characterization of COL fibers' orientation, human myoblasts (C25CL48) were seeded on the oriented TA/COL film, ended by COL. After 12 days in a differentiation medium without any other supplement, human myoblasts were able to align on brushed TA/COL films and to differentiate into long aligned myotubes (from hundreds of μm up to 1.7 mm length) thanks to two distinct properties: (i) the orientation of COL fibers guiding myoblasts' alignment and (ii) the TA release favoring the differentiation. This simple and potent brushing process allows the development of anisotropic tissues in vitro which can be used for studies of drug discovery and screening or the replacement of damaged tissue.

Keywords:  multilayers; myogenesis; nanopatterning; orientation; polyelectrolyte

DOI:  https://doi.org/10.1021/acsnano.2c06329
PLoS One. 2022 ;17(10): e0271776

Collagen cross-links scale with passive stiffness in dystrophic mouse muscles, but are not altered with administration of a lysyl oxidase inhibitor.

Sarah E Brashear, Ross P Wohlgemuth, Lin-Ya Hu, Elias H Jbeily, Blaine A Christiansen, Lucas R Smith.

In Duchenne muscular dystrophy (DMD), a lack of functional dystrophin leads to myofiber instability and progressive muscle damage that results in fibrosis. While fibrosis is primarily characterized by an accumulation of extracellular matrix (ECM) components, there are changes in ECM architecture during fibrosis that relate more closely to functional muscle stiffness. One of these architectural changes in dystrophic muscle is collagen cross-linking, which has been shown to increase the passive muscle stiffness in models of fibrosis including the mdx mouse, a model of DMD. We tested whether the intraperitoneal injections of beta-aminopropionitrile (BAPN), an inhibitor of the cross-linking enzyme lysyl oxidase, would reduce collagen cross-linking and passive stiffness in young and adult mdx mice compared to saline-injected controls. We found no significant differences between BAPN treated and saline treated mice in collagen cross-linking and stiffness parameters. However, we observed that while collagen cross-linking and passive stiffness scaled positively in dystrophic muscles, collagen fiber alignment scaled with passive stiffness distinctly between muscles. We also observed that the dystrophic diaphragm showed the most dramatic fibrosis in terms of collagen content, cross-linking, and stiffness. Overall, we show that while BAPN was not effective at reducing collagen cross-linking, the positive association between collagen cross-linking and stiffness in dystrophic muscles still show cross-linking as a viable target for reducing passive muscle stiffness in DMD or other fibrotic muscle conditions.

DOI: https://doi.org/10.1371/journal.pone.0271776
Mol Metab. 2022 Oct 21. pii: S2212-8778(22)00189-2. [Epub ahead of print] 101620

Effects of SGLT2 inhibitor dapagliflozin in patients with type 2 diabetes on skeletal muscle cellular metabolism.

Yvo J M Op den Kamp, Anne Gemmink, Marlies de Ligt, Bas Dautzenberg, Esther Kornips, Johanna A Jorgensen, Gert Schaart, Russell Esterline, Diego A Pava, Joris Hoeks, Vera B Schrauwen-Hinderling, Sander Kersten, Bas Havekes, Timothy R Koves, Deborah M Muoio, Matthijs K C Hesselink, Jan Oscarsson, Esther Phielix, Patrick Schrauwen.

   OBJECTIVE: SGLT2 inhibitors increase urinary glucose excretion and have beneficial effects on cardiovascular and renal outcomes; the underlying mechanism may be metabolic adaptations due to urinary glucose loss. Here, we investigated the cellular and molecular effects of 5 weeks of dapagliflozin treatment on skeletal muscle metabolism in type 2 diabetes patients.
METHODS: Twenty-six type 2 diabetes mellitus patients were randomized to a 5-week double-blind, cross-over study with 6-8-week wash-out. Skeletal muscle acetylcarnitine levels, intramyocellular lipid (IMCL) content and phosphocreatine (PCr) recovery rate were measured by magnetic resonance spectroscopy (MRS). Ex vivo mitochondrial respiration was measured in skeletal muscle fibers using high resolution respirometry. Intramyocellular lipid droplet and mitochondrial network dynamics were investigated using confocal microscopy. Skeletal muscle levels of acylcarnitines, amino acids and TCA cycle intermediates were measured. Expression of genes involved in fatty acid metabolism were investigated.
RESULTS: Mitochondrial function, mitochondrial network integrity and citrate synthase and carnitine acetyltransferase activities in skeletal muscle were unaltered after dapagliflozin treatment. Dapagliflozin treatment increased intramyocellular lipid content (0.060 (0.011, 0.110) %, p=0.019). Myocellular lipid droplets increased in size (0.03 μm2 (0.01-0.06), p<0.05) and number (0.003 μm-2 (-0.001-0.007), p=0.09) upon dapagliflozin treatment. CPT1A, CPT1B and malonyl CoA-decarboxylase mRNA expression was increased by dapagliflozin. Fasting acylcarnitine species and C4-OH carnitine levels (0.4704 (0.1246, 0.8162) pmoles*mg tissue-1, p<0.001) in skeletal muscle were higher after dapagliflozin treatment, while acetylcarnitine levels were lower (-40.0774 (-64.4766, -15.6782) pmoles*mg tissue-1, p<0.001). Fasting levels of several amino acids, succinate, alpha-ketoglutarate and lactate in skeletal muscle were significantly lower after dapagliflozin treatment.
CONCLUSION: Dapagliflozin treatment for 5 weeks leads to adaptive changes in skeletal muscle substrate metabolism favoring metabolism of fatty acid and ketone bodies and reduced glycolytic flux. The trial is registered with ClinicalTrials.gov, number NCT03338855.

Keywords:  Acylcarnitines; Dapagliflozin; Mitochondrial function; Myocellular lipid metabolism; SGLT2i; TCA cycle intermediates

DOI:  https://doi.org/10.1016/j.molmet.2022.101620
Proc Natl Acad Sci U S A. 2022 Nov;119(44): e2209976119

TNFα and IFNγ cooperate for efficient pro- to anti-inflammatory transition of macrophages during muscle regeneration.

Farshad Babaeijandaghi, Adrianna Paiero, Reece Long, Lin Wei Tung, Shannon Percival Smith, Ryan Cheng, Joshua Smandych, Nasim Kajabadi, Chih-Kai Chang, Amirhossein Ghassemi, William D M Kennedy, Hesham Soliman, Peter W Schutz, Fabio M V Rossi.

  IFNγ is traditionally known as a proinflammatory cytokine with diverse roles in antimicrobial and antitumor immunity. Yet, findings regarding its sources and functions during the regeneration process following a sterile injury are conflicting. Here, we show that natural killer (NK) cells are the main source of IFNγ in regenerating muscle. Beyond this cell population, IFNγ production is limited to a small population of T cells. We further show that NK cells do not play a major role in muscle regeneration following an acute injury or in dystrophic mice. Surprisingly, the absence of IFNγ per se also has no effect on muscle regeneration following an acute injury. However, the role of IFNγ is partially unmasked when TNFα is also neutralized, suggesting a compensatory mechanism. Using transgenic mice, we showed that conditional inhibition of IFNGR1 signaling in muscle stem cells or fibro-adipogenic progenitors does not play a major role in muscle regeneration. In contrast to common belief, we found that IFNγ is not present in the early inflammatory phase of the regeneration process but rather peaks when macrophages are acquiring an anti-inflammatory phenotype. Further transcriptomic analysis suggests that IFNγ cooperates with TNFα to regulate the transition of macrophages from pro- to anti-inflammatory states. The absence of the cooperative effect of these cytokines on macrophages, however, does not result in significant regeneration impairment likely due to the presence of other compensatory mechanisms. Our findings support the arising view of IFNγ as a pleiotropic inflammatory regulator rather than an inducer of the inflammatory response.

Keywords:  IFNγ; TNFα; macrophages; muscle regeneration; natural killer cells

DOI:  https://doi.org/10.1073/pnas.2209976119
Cell Physiol Biochem. 2022 Oct 26. 56(5): 587-601

Skeletal Muscle and Kidney Crosstalk in Chronic Kidney Disease.

Kayte A Jenkin, Ben D Perry.

  The functioning of complex organisms requires a constant and delicate balance of processes both between and within cells, tissues, and organ systems. There is growing appreciation for the role of signalling crosstalk connecting different organ systems of the body, even from tissues traditionally classified as "inert" in terms of their capacity to produce chemical signals that can act on other organ systems. Many of these secreted molecules have been shown to contribute to, or exacerbate, a variety of functions and diseases in other organ systems, even if the two organs are not functionally linked. For example, there is a strong association with skeletal muscle atrophy and dysfunction in patients with chronic kidney disease (CKD). Identification of molecules produced and secreted by skeletal muscle has existed for some time, and there is emerging evidence that skeletal muscle may directly affect kidney function. Conversely, factors produced and secreted by the kidneys in various models of CKD have been shown to contribute to reduced muscle functionality. This review will focus on crosstalk in both directions between skeletal muscle and the kidneys. The emphasis will be on direct interaction between these organs using examples of secreted factors that are produced by the muscle or kidneys (including activin A, myostatin, microRNA's, irisin and mitsugumin 53), often under pathophysiological conditions. Our understanding of how the kidneys and skeletal muscle interact with each other is key to elucidating the pathophysiology processes that drive health and disease.

Keywords:  Muscle atrophy; Crosstalk; Kidney; CKD

DOI:  https://doi.org/10.33594/000000578
Biol Sex Differ. 2022 Oct 23. 13(1): 59

Myocytic androgen receptor overexpression does not affect sex differences in adaptation to chronic endurance exercise.

Sabrina Tzivia Barsky, Douglas Ashley Monks.

  Muscle-specific androgen receptor (AR) overexpression (HSAAR transgene) in sedentary male rats results in reduced adiposity, increased mitochondrial enzyme activity, and selective increase in Type 2b myofiber size. Here, we tested chronic endurance exercise interactions with this phenotype in both sexes. Across 9 weeks, rats ran 5×/week on motorized running wheels at increasing speeds and durations. Exercise reduced fat mass in all groups, but sex affected endurance exercise outcomes such that absolute lean mass increased only in females and total body mass decreased only in males. Expected sex differences were observed with males exhibiting greater total body and lean mass; absolute and relative fat mass; bone mineral density; extensor digitorum longus (EDL) myofiber size and glycolytic proportion; but lesser Type 2a and Type 1 myosin expression in tibialis anterior. Observed HSAAR outcomes were not altered by sex, with transgenic rats having greater lean mass, Type 2a myosin expression in soleus, and glycolytic myofiber size in EDL. Tibialis AR content was independently affected by sex, HSAAR, and exercise. No sex differences were observed in tibialis AR expression in wild-type rats, although HSAAR males had greater AR content than HSAAR females. We identified a moderate correlation between AR expression and glycolytic myofiber size, but not whole-body composition. Overall, results suggest myocytic AR overexpression and chronic exercise, despite sharing a similar phenotype to adaptation, are mediated by distinct mechanisms. Further, this study illustrates sex differences in adaptation to chronic endurance exercise, and suggests sex-similarity in the relationship between muscle AR and exercise response.

Keywords:  Body composition; Endurance exercise; Muscle androgen receptor; Sex differences

DOI:  https://doi.org/10.1186/s13293-022-00471-x
Age Ageing. 2022 Oct 06. pii: afac220. [Epub ahead of print]51(10):

Sarcopenia definition, diagnosis and treatment: consensus is growing.

Avan Aihie Sayer, Alfonso Cruz-Jentoft.

  Sarcopenia is a skeletal muscle disorder that commonly occurs with advancing age as well as with a number of long-term conditions. Recognition in clinical practice is relatively recent but important because of the association between sarcopenia and a range of adverse effects on health including impaired mobility, increased morbidity and mortality. Originally characterised as loss of muscle mass, the definition has evolved to focus on loss of skeletal muscle function, particularly strength, through a number of international definitions such as that of the European Working Group on Sarcopenia in Older People most recently revised in 2019. Progress in the decades ahead is likely to be seen with regard to use of routine health data, prescription of resistance exercise, translation of biology and epidemiology into first in man studies for new treatments, and focus on sarcopenia in low and middle-income countries. Immediate next steps include the newly formed Global Leadership Initiative on Sarcopenia to develop international consensus on definition and diagnosis.

Keywords:  muscle function; muscle strength; older people; sarcopenia; skeletal muscle mass

DOI:  https://doi.org/10.1093/ageing/afac220
Exp Cell Res. 2022 Oct 20. pii: S0014-4827(22)00385-8. [Epub ahead of print] 113392

Back to basics: Optimization of DNA and RNA transfer in muscle cells using recent transfection reagents.

Ilaria Cocchiararo, Mélanie Cornut, Hadrien Soldati, Alessandro Bonavoglia, Perrine Castets.

  C2C12 cells are widely used in the muscle field, as they differentiate easily into myotubes and show limited constraints to culture as compared to primary myoblasts. Both C2C12 and primary myoblasts are hard to transfect, which affects downstream experiments. More than 95% of the reports published since 2015 with C2C12 cells have used one gold standard transfectant (i.e., Lipofectamine®), although several studies have suggested less than 30% efficiency of this reagent. In parallel, the capacity of other commercial reagents to transfect muscle cells remains largely unknown. Here, we compared transfection efficiency of five commercial reagents (Lipofectamine® 3000, Viafect™, Fugene® HD, C2C12 Cell Avalanche®, and JetOPTIMUS®) in C2C12 cells. By optimizing DNA:transfectant ratios and cell density, all reagents reached more than 60% transfection efficiency with limited effects on cell growth and viability. GFP-positive myotubes were efficiently generated in cultures transfected with Lipofectamine® 3000, Fugene® HD, C2C12 Cell Avalanche®, and JetOPTIMUS®. Notably, in conditions optimized for DNA transfer in C2C12 cells, these reagents showed low efficiency to transfer siRNA and higher toxicity for primary muscle cells. In conclusion, we reported yet uncharacterized transfection reagents that can serve as a suitable low-cost alternative to the current gold standard in C2C12 cells.

Keywords:  C2C12; Differentiation; Myoblast; Transfection; Viability; siRNA

DOI:  https://doi.org/10.1016/j.yexcr.2022.113392
Biochim Biophys Acta Gene Regul Mech. 2022 Oct 21. pii: S1874-9399(22)00103-1. [Epub ahead of print] 194888

The emerging regulatory mechanisms and biological function of circular RNAs in skeletal muscle development.

Xiaomei Sun, Yan Kang, Mingxun Li, Yongjun Li, Jiuzhou Song.

  Circular RNAs (circRNAs) are novel noncoding RNAs that assume a covalently closed-loop structure. Because of technical limitations in research, circRNAs were long considered to be byproducts of the RNA splicing process. Recently, emerging evidence has indicated that circRNAs can regulate gene expression by sponging microRNAs (miRNAs) or proteins, functioning as protein scaffolds, regulating transcription and splicing, and acting as templates for translation, thereby extending the functional complexity and diversity of eukaryotic transcriptomes. Remarkably, an increasing number of studies have revealed that circRNAs are stable, evolutionarily conserved, and are often expressed in a tissue- or developmental stage-specific patterns, especially abundant in muscle tissue. circRNAs are emerging as powerful regulators in diverse cellular processes and diseases, particularly in skeletal muscle myogenesis. Here, we describe circRNAs discovery, classification, and regulatory mechanisms, highlight the current understanding of circRNAs in regulating skeletal muscle development, and tell the story of how circRNAs, once thought to be "splicing noise", have become "genetic treasures".

Keywords:  Classification; Myogenesis; Regulatory mechanisms; Skeletal muscle; circRNAs

DOI:  https://doi.org/10.1016/j.bbagrm.2022.194888
EMBO Rep. 2022 Oct 24. e55175

The AAA-ATPase ATAD1 and its partners promote degradation of desmin intermediate filaments in muscle.

Dina Aweida, Shenhav Cohen.

  Maintenance of desmin intermediate filaments (IF) is vital for muscle plasticity and function, and their perturbed integrity due to accelerated loss or aggregation causes atrophy and myopathies. Calpain-1-mediated disassembly of ubiquitinated desmin IF is a prerequisite for desmin loss, myofibril breakdown, and atrophy. Because calpain-1 does not harbor a bona fide ubiquitin-binding domain, the precise mechanism for desmin IF disassembly remains unknown. Here, we demonstrate that the AAA-ATPase, ATAD1, is required to facilitate disassembly and turnover of ubiquitinated desmin IF. We identified PLAA and UBXN4 as ATAD1's interacting partners, and their downregulation attenuated desmin loss upon denervation. The ATAD1-PLAA-UBXN4 complex binds desmin filaments and promotes a release of phosphorylated and ubiquitinated species into the cytosol, presenting ATAD1 as the only known AAA-ATPase that preferentially acts on phosphorylated substrates. Desmin filaments disassembly was accelerated by the coordinated functions of Atad1 and calpain-1, which interact in muscle. Thus, by extracting ubiquitinated desmin from the insoluble filament, ATAD1 may expose calpain-1 cleavage sites on desmin, consequently enhancing desmin solubilization and degradation in the cytosol.

Keywords:  ATAD1; desmin; intermediate filaments; muscle atrophy; protein degradation

DOI:  https://doi.org/10.15252/embr.202255175
Development. 2022 Nov 01. pii: dev200749. [Epub ahead of print]149(21):

Nuclear movement in multinucleated cells.

Jorel R Padilla, Lillie M Ferreira, Eric S Folker.

  Nuclear movement is crucial for the development of many cell types and organisms. Nuclear movement is highly conserved, indicating its necessity for cellular function and development. In addition to mononucleated cells, there are several examples of cells in which multiple nuclei exist within a shared cytoplasm. These multinucleated cells and syncytia have important functions for development and homeostasis. Here, we review a subset of the developmental contexts in which the regulation of the movement and positioning of multiple nuclei are well understood, including pronuclear migration, the Drosophila syncytial blastoderm, the Caenorhabditis elegans hypodermis, skeletal muscle and filamentous fungi. We apply the principles learned from these models to other systems.

Keywords:  Cytoskeleton; LINC complex; Nuclear movement; Syncytia

DOI:  https://doi.org/10.1242/dev.200749