bims-moremu 2023-07-16 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–07–16
33 papers selected by
Anna Vainshtein, Craft Science Inc.

Age-related gene expression signatures from limb skeletal muscles and the diaphragm in mice and rats reveal common and species-specific changes.
Dynamic regulation of inter-organelle communication by ubiquitylation controls skeletal muscle development and disease onset.
Impaired proteostatic mechanisms other than decreased protein synthesis limit old skeletal muscle recovery after disuse atrophy.
Irisin Is Target of Sphingosine-1-Phosphate/Sphingosine-1-Phosphate Receptor-Mediated Signaling in Skeletal Muscle Cells.
Interplay between Protein Kinase C Epsilon and Reactive Oxygen Species during Myogenic Differentiation.
Microvascular Skeletal-Muscle Crosstalk in Health and Disease.
Numerous Trigger-like Interactions of Kinases/Protein Phosphatases in Human Skeletal Muscles Can Underlie Transient Processes in Activation of Signaling Pathways during Exercise.
Netrin-4 synthesized in satellite cell-derived myoblasts stimulates autonomous fusion.
Mitochondrial Dysfunction and Skeletal Muscle Atrophy: Causes, Mechanisms, and Treatment Strategies.
Myofibrillar myopathy hallmarks associated with ZAK deficiency.
The aminopeptidase LAP3 suppression accelerates myogenic differentiation via the AKT-TFE3 pathway in C2C12 myoblasts.
Cancer-cell-secreted extracellular vesicles target p53 to impair mitochondrial function in muscle.
Tetraspanin CD82 Associates with Trafficking Vesicle in Muscle Cells and Binds to Dysferlin and Myoferlin.
Regulation of mitochondrial morphology and cristae architecture by the TLR4 pathway in human skeletal muscle.
Cathepsin S deficiency improves muscle mass loss and dysfunction via the modulation of protein metabolism in mice under pathological stress conditions.
The super-healing MRL strain promotes muscle growth in muscular dystrophy through a regenerative extracellular matrix.
LKB1 signaling is altered in skeletal muscle of a Duchenne muscular dystrophy mouse model.
Lysine Methyltransferase SMYD1 Regulates Myogenesis via skNAC Methylation.
Duchenne muscular dystrophy: disease mechanism and therapeutic strategies.
Sex differences in skeletal muscle fiber types: A meta-analysis.
Aberrations in energetic metabolism and stress-related pathways contribute to pathophysiology in the Neb cKO mouse model of nemaline myopathy.
Acyl-CoA thioesterase-2 facilitates β-oxidation in glycolytic skeletal muscle in a lipid supply dependent manner.
High-Intensity Interval Training Attenuates Impairment in Regulatory Protein Machinery of Mitochondrial Quality Control in Skeletal Muscle of Diet-Induced Obese Mice.
Intrafusal cross-bridge dynamics shape history-dependent muscle spindle responses to stretch.
Prolonged voluntary wheel running reveals unique adaptations in mdx mice treated with microdystrophin constructs ± the nNOS-binding site.
TOMM40 and TOMM22 of the Translocase Outer Mitochondrial Membrane Complex rescue statin-impaired mitochondrial dynamics, morphology, and mitophagy in skeletal myotubes.
Short-term disuse does not affect postabsorptive or postprandial muscle protein fractional breakdown rates.
The Impact of SRT2104 on Skeletal Muscle Mitochondrial Function, Redox Biology, and Loss of Muscle Mass in Hindlimb Unloaded Rats.
Determining the feasibility of characterising cellular senescence in human skeletal muscle and exploring associations with muscle morphology and physical function at different ages: findings from the MASS_Lifecourse Study.
A dysfunctional miR-1-TRPS1-MYOG axis drives ERMS by suppressing terminal myogenic differentiation.
Multi-omics characterization of partial chemical reprogramming reveals evidence of cell rejuvenation.
Cytochrome c lysine acetylation regulates cellular respiration and cell death in ischemic skeletal muscle.
GDF15 boosts muscle energy burn.

Skelet Muscle. 2023 07 12. 13(1): 11

Age-related gene expression signatures from limb skeletal muscles and the diaphragm in mice and rats reveal common and species-specific changes.

Tea Shavlakadze, Kun Xiong, Shawn Mishra, Corissa McEwen, Abhilash Gadi, Matthew Wakai, Hunter Salmon, Michael J Stec, Nicole Negron, Min Ni, Yi Wei, Gurinder S Atwal, Yu Bai, David J Glass.

   BACKGROUND: As a result of aging, skeletal muscle undergoes atrophy and a decrease in function. This age-related skeletal muscle weakness is known as "sarcopenia". Sarcopenia is part of the frailty observed in humans. In order to discover treatments for sarcopenia, it is necessary to determine appropriate preclinical models and the genes and signaling pathways that change with age in these models.
METHODS AND RESULTS: To understand the changes in gene expression that occur as a result of aging in skeletal muscles, we generated a multi-time-point gene expression signature throughout the lifespan of mice and rats, as these are the most commonly used species in preclinical research and intervention testing. Gastrocnemius, tibialis anterior, soleus, and diaphragm muscles from male and female C57Bl/6J mice and male Sprague Dawley rats were analyzed at ages 6, 12, 18, 21, 24, and 27 months, plus an additional 9-month group was used for rats. More age-related genes were identified in rat skeletal muscles compared with mice; this was consistent with the finding that rat muscles undergo more robust age-related decline in mass. In both species, pathways associated with innate immunity and inflammation linearly increased with age. Pathways linked with extracellular matrix remodeling were also universally downregulated. Interestingly, late downregulated pathways were exclusively found in the rat limb muscles and these were linked to metabolism and mitochondrial respiration; this was not seen in the mouse.
CONCLUSIONS: This extensive, side-by-side transcriptomic profiling shows that the skeletal muscle in rats is impacted more by aging compared with mice, and the pattern of decline in the rat may be more representative of the human. The observed changes point to potential therapeutic interventions to avoid age-related decline in skeletal muscle function.

Keywords:  Aging; Aging gene signature; Frailty; Inflammation; Mitochondria; RNA-seq; Sarcopenia; Skeletal muscle atrophy

DOI:  https://doi.org/10.1186/s13395-023-00321-3
Elife. 2023 Jul 11. pii: e81966. [Epub ahead of print]12

Dynamic regulation of inter-organelle communication by ubiquitylation controls skeletal muscle development and disease onset.

Arian Mansur, Remi Joseph, Euri Kim, Pierre M Jean-Beltran, Namrata D Udeshi, Cadence Pearce, Hanjie Jiang, Reina Iwase, Miroslav P Milev, Hashem A Almousa, Elyshia McNamara, Jeffrey Widrick, Claudio Perez, Gianina Ravenscroft, Michael Sacher, Philip A Cole, Steven A Carr, Vandana A Gupta.

  Ubiquitin-proteasome system (UPS) dysfunction is associated with the pathology of a wide range of human diseases, including myopathies and muscular atrophy. However, the mechanistic understanding of specific components of the regulation of protein turnover during development and disease progression in skeletal muscle is unclear. Mutations in KLHL40, an E3 ubiquitin ligase cullin3 (CUL3) substrate-specific adapter protein, result in severe congenital nemaline myopathy, but the events that initiate the pathology and the mechanism through which it becomes pervasive remain poorly understood. To characterize the KLHL40-regulated ubiquitin-modified proteome during skeletal muscle development and disease onset, we used global, quantitative mass spectrometry-based ubiquitylome and global proteome analyses of klhl40a mutant zebrafish during disease progression. Global proteomics during skeletal muscle development revealed extensive remodeling of functional modules linked with sarcomere formation, energy, biosynthetic metabolic processes, and vesicle trafficking. Combined analysis of klh40 mutant muscle proteome and ubiquitylome identified thin filament proteins, metabolic enzymes, and ER-Golgi vesicle trafficking pathway proteins regulated by ubiquitylation during muscle development. Our studies identified a role for KLHL40 as a regulator of ER-Golgi anterograde trafficking through ubiquitin-mediated protein degradation of secretion-associated Ras-related GTPase1a (Sar1a). In KLHL40 deficient muscle, defects in ER exit site vesicle formation and downstream transport of extracellular cargo proteins result in structural and functional abnormalities. Our work reveals that the muscle proteome is dynamically fine-tuned by ubiquitylation to regulate skeletal muscle development and uncovers new disease mechanisms for therapeutic development in patients.

Keywords:  cell biology; developmental biology; zebrafish

DOI:  https://doi.org/10.7554/eLife.81966
J Cachexia Sarcopenia Muscle. 2023 Jul 14.

Impaired proteostatic mechanisms other than decreased protein synthesis limit old skeletal muscle recovery after disuse atrophy.

Jordan D Fuqua, Marcus M Lawrence, Zachary R Hettinger, Agnieszka K Borowik, Parker L Brecheen, Marcelina M Szczygiel, Claire B Abbott, Frederick F Peelor, Amy L Confides, Michael Kinter, Sue C Bodine, Esther E Dupont-Versteegden, Benjamin F Miller.

   BACKGROUND: Skeletal muscle mass and strength diminish during periods of disuse but recover upon return to weight bearing in healthy adults but are incomplete in old muscle. Efforts to improve muscle recovery in older individuals commonly aim at increasing myofibrillar protein synthesis via mammalian target of rapamycin (mTOR) stimulation despite evidence demonstrating that old muscle has chronically elevated levels of mammalian target of rapamycin complex 1 (mTORC1) activity. We hypothesized that protein synthesis is higher in old muscle than adult muscle, which contributes to a proteostatic stress that impairs recovery.
METHODS: We unloaded hindlimbs of adult (10-month) and old (28-month) F344BN rats for 14 days to induce atrophy, followed by reloading up to 60 days with deuterium oxide (D2 O) labelling to study muscle regrowth and proteostasis.
RESULTS: We found that old muscle has limited recovery of muscle mass during reloading despite having higher translational capacity and myofibrillar protein synthesis (0.029 k/day ± 0.002 vs. 0.039 k/day ± 0.002, P < 0.0001) than adult muscle. We showed that collagen protein synthesis was not different (0.005 k (1/day) ± 0.0005 vs. 0.004 k (1/day) ± 0.0005, P = 0.15) in old compared to adult, but old muscle had higher collagen concentration (4.5 μg/mg ± 1.2 vs. 9.8 μg/mg ± 0.96, P < 0.01), implying that collagen breakdown was slower in old muscle than adult muscle. This finding was supported by old muscle having more insoluble collagen (4.0 ± 1.1 vs. 9.2 ± 0.9, P < 0.01) and an accumulation of advanced glycation end products (1.0 ± 0.06 vs. 1.5 ± 0.08, P < 0.001) than adult muscle during reloading. Limited recovery of muscle mass during reloading is in part due to higher protein degradation (0.017 1/t ± 0.002 vs. 0.028 1/t ± 0.004, P < 0.05) and/or compromised proteostasis as evidenced by accumulation of ubiquitinated insoluble proteins (1.02 ± 0.06 vs. 1.22 ± 0.06, P < 0.05). Last, we showed that synthesis of individual proteins related to protein folding/refolding, protein degradation and neural-related biological processes was higher in old muscle during reloading than adult muscle.
CONCLUSIONS: Our data suggest that the failure of old muscle to recover after disuse is not due to limitations in the ability to synthesize myofibrillar proteins but because of other impaired proteostatic mechanisms (e.g., protein folding and degradation). These data provide novel information on individual proteins that accumulate in protein aggregates after disuse and certain biological processes such as protein folding and degradation that likely play a role in impaired recovery. Therefore, interventions to enhance regrowth of old muscle after disuse should be directed towards the identified impaired proteostatic mechanisms and not aimed at increasing protein synthesis.

Keywords:  collagen; isotope labelling; protein aggregates; protein turnover; proteomics; ribosome biogenesis

DOI:  https://doi.org/10.1002/jcsm.13285
Int J Mol Sci. 2023 Jun 23. pii: 10548. [Epub ahead of print]24(13):

Irisin Is Target of Sphingosine-1-Phosphate/Sphingosine-1-Phosphate Receptor-Mediated Signaling in Skeletal Muscle Cells.

Federica Pierucci, Antony Chirco, Elisabetta Meacci.

  Irisin is a hormone-like myokine produced in abundance by skeletal muscle (SkM) in response to exercise. This myokine, identical in humans and mice, is involved in many signaling pathways related to metabolic processes. Despite much evidence on the regulators of irisin and the relevance of sphingolipids for SkM cell biology, the contribution of these latter bioactive lipids to the modulation of the myokine in SkM is missing. In particular, we have examined the potential involvement in irisin formation/release of sphingosine-1-phosphate (S1P), an interesting bioactive molecule able to act as an intracellular lipid mediator as well as a ligand of specific G-protein-coupled receptors (S1PR). We demonstrate the existence of distinct intracellular pools of S1P able to affect the expression of the irisin precursor FNDC. In addition, we establish the crucial role of the S1P/S1PR axis in irisin formation/release as well as the autocrine/paracrine effects of irisin on myoblast proliferation and myogenic differentiation. Altogether, these findings provide the first evidence for a functional crosstalk between the S1P/S1PR axis and irisin signaling, which may open new windows for potential therapeutic treatment of SkM dysfunctions.

Keywords:  C2C12 skeletal muscle cells; irisin; myokines; skeletal muscle; sphingolipids; sphingosine-1-phosphate; sphingosine-1-phosphate receptors

DOI:  https://doi.org/10.3390/ijms241310548
Cells. 2023 Jul 05. pii: 1792. [Epub ahead of print]12(13):

Interplay between Protein Kinase C Epsilon and Reactive Oxygen Species during Myogenic Differentiation.

Giulia Pozzi, Valentina Presta, Elena Masselli, Giancarlo Condello, Samuele Cortellazzi, Maria Luisa Arcari, Cristina Micheloni, Marco Vitale, Giuliana Gobbi, Prisco Mirandola, Cecilia Carubbi.

  Reactive oxygen species (ROS) are currently recognized as a key driver of several physiological processes. Increasing evidence indicates that ROS levels can affect myogenic differentiation, but the molecular mechanisms still need to be elucidated. Protein kinase C (PKC) epsilon (PKCe) promotes muscle stem cell differentiation and regeneration of skeletal muscle after injury. PKCs play a tissue-specific role in redox biology, with specific isoforms being both a target of ROS and an up-stream regulator of ROS production. Therefore, we hypothesized that PKCe represents a molecular link between redox homeostasis and myogenic differentiation. We used an in vitro model of a mouse myoblast cell line (C2C12) to study the PKC-redox axis. We demonstrated that the transition from a myoblast to myotube is typified by increased PKCe protein content and decreased ROS. Intriguingly, the expression of the antioxidant enzyme superoxide dismutase 2 (SOD2) is significantly higher in the late phases of myogenic differentiation, mimicking PKCe protein content. Furthermore, we demonstrated that PKCe inhibition increases ROS and reduces SOD2 protein content while SOD2 silencing did not affect PKCe protein content, suggesting that the kinase could be an up-stream regulator of SOD2. To support this hypothesis, we found that in C2C12 cells, PKCe interacts with Nrf2, whose activation induces SOD2 transcription. Overall, our results indicate that PKCe is capable of activating the antioxidant signaling preventing ROS accumulation in a myotube, eventually promoting myogenic differentiation.

Keywords:  PKC epsilon; SOD2; antioxidant; myogenesis; reactive oxygen species; skeletal muscle

DOI:  https://doi.org/10.3390/cells12131792
Int J Mol Sci. 2023 Jun 21. pii: 10425. [Epub ahead of print]24(13):

Microvascular Skeletal-Muscle Crosstalk in Health and Disease.

Gerald J Pepe, Eugene D Albrecht.

  As an organ system, skeletal muscle is essential for the generation of energy that underpins muscle contraction, plays a critical role in controlling energy balance and insulin-dependent glucose homeostasis, as well as vascular well-being, and regenerates following injury. To achieve homeostasis, there is requirement for "cross-talk" between the myogenic and vascular components and their regulatory factors that comprise skeletal muscle. Accordingly, this review will describe the following: [a] the embryonic cell-signaling events important in establishing vascular and myogenic cell-lineage, the cross-talk between endothelial cells (EC) and myogenic precursors underpinning the development of muscle, its vasculature and the satellite-stem-cell (SC) pool, and the EC-SC cross-talk that maintains SC quiescence and localizes ECs to SCs and angio-myogenesis postnatally; [b] the vascular-myocyte cross-talk and the actions of insulin on vasodilation and capillary surface area important for the uptake of glucose/insulin by myofibers and vascular homeostasis, the microvascular-myocyte dysfunction that characterizes the development of insulin resistance, diabetes and hypertension, and the actions of estrogen on muscle vasodilation and growth in adults; [c] the role of estrogen in utero on the development of fetal skeletal-muscle microvascularization and myofiber hypertrophy required for metabolic/vascular homeostasis after birth; [d] the EC-SC interactions that underpin myofiber vascular regeneration post-injury; and [e] the role of the skeletal-muscle vasculature in Duchenne muscular dystrophy.

Keywords:  cross-talk; diabetes; fetus; hypertension; insulin resistance; microvasculature; skeletal muscle

DOI:  https://doi.org/10.3390/ijms241310425
Int J Mol Sci. 2023 Jul 07. pii: 11223. [Epub ahead of print]24(13):

Numerous Trigger-like Interactions of Kinases/Protein Phosphatases in Human Skeletal Muscles Can Underlie Transient Processes in Activation of Signaling Pathways during Exercise.

Alexander Yu Vertyshev, Ilya R Akberdin, Fedor A Kolpakov.

  Optimizing physical training regimens to increase muscle aerobic capacity requires an understanding of the internal processes that occur during exercise that initiate subsequent adaptation. During exercise, muscle cells undergo a series of metabolic events that trigger downstream signaling pathways and induce the expression of many genes in working muscle fibers. There are a number of studies that show the dependence of changes in the activity of AMP-activated protein kinase (AMPK), one of the mediators of cellular signaling pathways, on the duration and intensity of single exercises. The activity of various AMPK isoforms can change in different directions, increasing for some isoforms and decreasing for others, depending on the intensity and duration of the load. This review summarizes research data on changes in the activity of AMPK, Ca2+/calmodulin-dependent protein kinase II (CaMKII), and other components of the signaling pathways in skeletal muscles during exercise. Based on these data, we hypothesize that the observed changes in AMPK activity may be largely related to metabolic and signaling transients rather than exercise intensity per se. Probably, the main events associated with these transients occur at the beginning of the exercise in a time window of about 1-10 min. We hypothesize that these transients may be partly due to putative trigger-like kinase/protein phosphatase interactions regulated by feedback loops. In addition, numerous dynamically changing factors, such as [Ca2+], metabolite concentration, and reactive oxygen and nitrogen species (RONS), can shift the switching thresholds and change the states of these triggers, thereby affecting the activity of kinases (in particular, AMPK and CaMKII) and phosphatases. The review considers the putative molecular mechanisms underlying trigger-like interactions. The proposed hypothesis allows for a reinterpretation of the experimental data available in the literature as well as the generation of ideas to optimize future training regimens.

Keywords:  AMPK signalling; Ca2+-dependent signalling; mathematical model; physical exercise; protein phosphatases; skeletal muscle; transient process

DOI:  https://doi.org/10.3390/ijms241311223
Exp Cell Res. 2023 Jul 10. pii: S0014-4827(23)00246-X. [Epub ahead of print]430(1): 113698

Netrin-4 synthesized in satellite cell-derived myoblasts stimulates autonomous fusion.

Takahiro Maeno, Rio Arimatsu, Koichi Ojima, Yuki Yamaya, Hikaru Imakyure, Naruha Watanabe, Yusuke Komiya, Ken Kobayashi, Mako Nakamura, Takanori Nishimura, Ryuichi Tatsumi, Takahiro Suzuki.

  Satellite cells are indispensable for skeletal muscle regeneration and hypertrophy by forming nascent myofibers (myotubes). They synthesize multi-potent modulator netrins (secreted subtypes: netrin-1, -3, and -4), originally found as classical neural axon guidance molecules. While netrin-1 and -3 have key roles in myogenic differentiation, the physiological significance of netrin-4 is still unclear. This study examined whether netrin-4 regulates myofiber type commitment and myotube formation. Initially, the expression profiles indicated that satellite cells isolated from the extensor digitorum longus muscle (EDL muscle: fast-twitch myofiber-abundant) expressed slightly more netrin-4 than the soleus muscle (slow-type abundant) cells. As netrin-4 knockdown inhibited both slow- and fast-type myotube formation, netrin-4 may not directly regulate myofiber type commitment. However, netrin-4 knockdown in satellite cell-derived myoblasts reduced the myotube fusion index, while exogenous netrin-4 promoted myotube formation, even though netrin-4 expression level was maximum during the initiation stage of myogenic differentiation. Furthermore, netrin-4 knockdown also inhibited MyoD (a master transcriptional factor of myogenesis) and Myomixer (a myoblast fusogenic molecule) expression. These data suggest that satellite cells synthesize netrin-4 during myogenic differentiation initiation to promote their own fusion, stimulating the MyoD-Myomixer signaling axis.

Keywords:  Myoblasts; Myoblast–myoblast fusion; Myofiber types; Myotubes; Netrin-4; Satellite cells

DOI:  https://doi.org/10.1016/j.yexcr.2023.113698
Mitochondrion. 2023 Jul 12. pii: S1567-7249(23)00066-1. [Epub ahead of print]

Mitochondrial Dysfunction and Skeletal Muscle Atrophy: Causes, Mechanisms, and Treatment Strategies.

Gokhan Burcin Kubat, Esmaa Bouhamida, Oner Ulger, Ibrahim Turkel, Gaia Pedriali, Daniela Ramaccini, Ozgur Ekinci, Berkay Ozerklig, Ozbeyen Atalay, Simone Patergnani, Beyza Nur Sahin, Giampaolo Morciano, Meltem Tuncer, Elena Tremoli, Paolo Pinton.

  Skeletal muscle, which accounts for approximately 40% of total body weight, is one of the most dynamic and plastic tissues in the human body and plays a vital role in movement, posture and force production. More than just a component of the locomotor system, skeletal muscle functions as an endocrine organ capable of producing and secreting hundreds of bioactive molecules. Therefore, maintaining healthy skeletal muscles is crucial for supporting overall body health. Various pathological conditions, such as prolonged immobilization, cachexia, aging, drug-induced toxicity, and cardiovascular diseases (CVDs), can disrupt the balance between muscle protein synthesis and degradation, leading to skeletal muscle atrophy. Mitochondrial dysfunction is a major contributing mechanism to skeletal muscle atrophy, as it plays crucial roles in various biological processes, including energy production, metabolic flexibility, maintenance of redox homeostasis, and regulation of apoptosis. In this review, we critically examine recent knowledge regarding the causes of muscle atrophy (disuse, cachexia, aging, etc.) and its contribution to CVDs. Additionally, we highlight the mitochondrial signaling pathways involvement to skeletal muscle atrophy, such as the ubiquitin-proteasome system, autophagy and mitophagy, mitochondrial fission-fusion, and mitochondrial biogenesis. Furthermore, we discuss current strategies, including exercise, mitochondria-targeted antioxidants, in vivo transfection of PGC-1α, and the potential use of mitochondrial transplantation as a possible therapeutic approach.

Keywords:  Skeletal muscle atrophy; cardiovascular diseases; exercise; mitochondria; mitochondrial transplantation

DOI:  https://doi.org/10.1016/j.mito.2023.07.003
Hum Mol Genet. 2023 Jul 10. pii: ddad113. [Epub ahead of print]

Myofibrillar myopathy hallmarks associated with ZAK deficiency.

Amy Stonadge, Aitana Victoria Genzor, Alex Russell, Mohamed F Hamed, Norma Romero, Gareth Evans, Betsy Pownall, Simon Bekker-Jensen, Gonzalo Blanco.

The ZAK gene encodes two functionally distinct kinases, ZAKɑ and ZAKβ. Homozygous loss of function mutations affecting both isoforms cause a congenital muscle disease. ZAKβ is the only isoform expressed in skeletal muscle and is activated by muscle contraction and cellular compression. The ZAKβ substrates in skeletal muscle or the mechanism whereby ZAKβ senses mechanical stress remain to be determined. To gain insights into the pathogenic mechanism, we exploited ZAK-deficient cell lines, zebrafish, mice and a human biopsy. ZAK-deficient mice and zebrafish show a mild phenotype. In mice, comparative histopathology data from regeneration, overloading, ageing and sex conditions indicate that while age and activity are drivers of the pathology, ZAKβ appears to have a marginal role in myoblast fusion in vitro or muscle regeneration in vivo. The presence of SYNPO2, BAG3 and FLNC in a phosphoproteomics assay and extended analyses suggested a role for ZAKβ in the turnover of FLNC. Immunofluorescence analysis of muscle sections from mice and a human biopsy showed evidence of FLNC and BAG3 accumulations as well as other myofibrillar myopathy markers. Moreover, endogenous overloading of skeletal muscle exacerbated the presence of fibres with FLNC accumulations in mice, indicating that ZAKβ signalling is necessary for an adaptive turnover of FLNC that allows for the normal physiological response to sustained mechanical stress. We suggest that accumulation of mislocalized FLNC and BAG3 in highly immunoreactive fibres contributes to the pathogenic mechanism of ZAK-deficiency.

DOI: https://doi.org/10.1093/hmg/ddad113
J Cell Physiol. 2023 Jul 12.

The aminopeptidase LAP3 suppression accelerates myogenic differentiation via the AKT-TFE3 pathway in C2C12 myoblasts.

Shion Osana, Yasuo Kitajima, Suzuki Naoki, Kazutaka Murayama, Hiroaki Takada, Ayaka Tabuchi, Yutaka Kano, Ryoichi Nagatomi.

  Skeletal muscle maintenance depends largely on muscle stem cells (satellite cells) that supply myoblasts required for muscle regeneration and growth. The ubiquitin-proteasome system is the major intracellular protein degradation pathway. We previously reported that proteasome dysfunction in skeletal muscle significantly impairs muscle growth and development. Furthermore, the inhibition of aminopeptidase, a proteolytic enzyme that removes amino acids from the termini of peptides derived from proteasomal proteolysis, impairs the proliferation and differentiation ability of C2C12 myoblasts. However, no evidence has been reported on the role of aminopeptidases with different substrate specificities on myogenesis. In this study, therefore, we investigated whether the knockdown of aminopeptidases in differentiating C2C12 myoblasts affects myogenesis. The knockdown of the X-prolyl aminopeptidase 1, aspartyl aminopeptidase, leucyl-cystinyl aminopeptidase, methionyl aminopeptidase 1, methionyl aminopeptidase 2, puromycine-sensitive aminopeptidase, and arginyl aminopeptidase like 1 gene in C2C12 myoblasts resulted in defective myogenic differentiation. Surprisingly, the knockdown of leucine aminopeptidase 3 (LAP3) in C2C12 myoblasts promoted myogenic differentiation. We also found that suppression of LAP3 expression in C2C12 myoblasts resulted in the inhibition of proteasomal proteolysis, decreased intracellular branched-chain amino acid levels, and enhanced mTORC2-mediated AKT phosphorylation (S473). Furthermore, phosphorylated AKT induced the translocation of TFE3 from the nucleus to the cytoplasm, promoting myogenic differentiation through increased expression of myogenin. Overall, our study highlights the association of aminopeptidases with myogenic differentiation.

Keywords:  C2C12 myoblast; LAP3; TFE3; aminopeptidase; myogenic differentiation; myogenin

DOI:  https://doi.org/10.1002/jcp.31070
EMBO Rep. 2023 Jul 13. e56464

Cancer-cell-secreted extracellular vesicles target p53 to impair mitochondrial function in muscle.

Xianhui Ruan, Minghui Cao, Wei Yan, Ying Z Jones, Åsa B Gustafsson, Hemal H Patel, Simon Schenk, Shizhen Emily Wang.

  Skeletal muscle loss and weakness are associated with bad prognosis and poorer quality of life in cancer patients. Tumor-derived factors have been implicated in muscle dysregulation by inducing cachexia and apoptosis. Here, we show that extracellular vesicles secreted by breast cancer cells impair mitochondrial homeostasis and function in skeletal muscle, leading to decreased mitochondrial content and energy production and increased oxidative stress. Mechanistically, miR-122-5p in cancer-cell-secreted EVs is transferred to myocytes, where it targets the tumor suppressor TP53 to decrease the expression of TP53 target genes involved in mitochondrial regulation, including Tfam, Pgc-1α, Sco2, and 16S rRNA. Restoration of Tp53 in muscle abolishes mitochondrial myopathology in mice carrying breast tumors and partially rescues their impaired running capacity without significantly affecting muscle mass. We conclude that extracellular vesicles from breast cancer cells mediate skeletal muscle mitochondrial dysfunction in cancer and may contribute to muscle weakness in some cancer patients.

Keywords:  breast cancer; extracellular vesicles; microRNA; p53; skeletal muscle

DOI:  https://doi.org/10.15252/embr.202256464
Adv Biol (Weinh). 2023 Jul 12. e2300157

Tetraspanin CD82 Associates with Trafficking Vesicle in Muscle Cells and Binds to Dysferlin and Myoferlin.

Tatiana Fontelonga, Arielle J Hall, Jaedon L Brown, Youngsook L Jung, Matthew S Alexander, Janice A Dominov, Vincent Mouly, Natassia Vieira, Mayana Zatz, Mariz Vainzof, Emanuela Gussoni.

  Tetraspanins organize protein complexes at the cell membrane and are responsible for assembling diverse binding partners in changing cellular states. Tetraspanin CD82 is a useful cell surface marker for prospective isolation of human myogenic progenitors and its expression is decreased in Duchenne muscular dystrophy (DMD) cell lines. The function of CD82 in skeletal muscle remains elusive, partly because the binding partners of this tetraspanin in muscle cells have not been identified. CD82-associated proteins are sought to be identified in human myotubes via mass spectrometry proteomics, which identifies dysferlin and myoferlin as CD82-binding partners. In human dysferlinopathy (Limb girdle muscular dystrophy R2, LGMDR2) myogenic cell lines, expression of CD82 protein is near absent in two of four patient samples. In the cell lines where CD82 protein levels are unaffected, increased expression of the ≈72 kDa mini-dysferlin product is identified using an antibody recognizing the dysferlin C-terminus. These data demonstrate that CD82 binds dysferlin/myoferlin in differentiating muscle cells and its expression can be affected by loss of dysferlin in human myogenic cells.

Keywords:  Miyoshi myopathy; dysferlin; dysferlinopathy; limb girdle muscular dystrophy; myoferlin; satellite cells

DOI:  https://doi.org/10.1002/adbi.202300157
Front Cell Dev Biol. 2023 ;11 1212779

Regulation of mitochondrial morphology and cristae architecture by the TLR4 pathway in human skeletal muscle.

Mauricio Castro-Sepulveda, Mauro Tuñón-Suárez, Giovanni Rosales-Soto, Ronald Vargas-Foitzick, Louise Deldicque, Hermann Zbinden-Foncea.

  In skeletal muscle (SkM), a reduced mitochondrial elongate phenotype is associated with several metabolic disorders like type 2 diabetes mellitus (T2DM). However, the mechanisms contributing to this reduction in mitochondrial elongate phenotype in SkM have not been fully elucidated. It has recently been shown in a SkM cell line that toll-like receptor 4 (TLR4) contributes to the regulation of mitochondrial morphology. However, this has not been investigated in human SkM. Here we found that in human SkM biopsies, TLR4 protein correlated negatively with Opa1 (pro-mitochondrial fusion protein). Moreover, the incubation of human myotubes with LPS reduced mitochondrial size and elongation and induced abnormal mitochondrial cristae, which was prevented with the co-incubation of LPS with TAK242. Finally, T2DM myotubes were found to have reduced mitochondrial elongation and mitochondrial cristae density. Mitochondrial morphology, membrane structure, and insulin-stimulated glucose uptake were restored to healthy levels in T2DM myotubes treated with TAK242. In conclusion, mitochondrial morphology and mitochondrial cristae seem to be regulated by the TLR4 pathway in human SkM. Those mitochondrial alterations might potentially contribute to insulin resistance in the SkM of patients with T2DM.

Keywords:  Lipopolysaccharide; TAK242; mitochondrial dynamics; mitochondrial nanotunnels; skeletal muscle function; type 2 diabetes

DOI:  https://doi.org/10.3389/fcell.2023.1212779
FASEB J. 2023 08;37(8): e23086

Cathepsin S deficiency improves muscle mass loss and dysfunction via the modulation of protein metabolism in mice under pathological stress conditions.

Ying Wan, Limei Piao, Shengnan Xu, Aiko Inoue, Xiangkun Meng, Yanna Lei, Zhe Huang, Hailong Wang, Xueling Yue, Guo-Ping Shi, Masafumi Kuzuya, Xian Wu Cheng.

  Cathepsin S (CTSS) is a widely expressed cysteinyl protease that has garnered attention because of its enzymatic and non-enzymatic functions under inflammatory and metabolic pathological conditions. Here, we examined whether CTSS participates in stress-related skeletal muscle mass loss and dysfunction, focusing on protein metabolic imbalance. Eight-week-old male wildtype (CTSS+/+ ) and CTSS-knockout (CTSS-/- ) mice were randomly assigned to non-stress and variable-stress groups for 2 weeks, and then processed for morphological and biochemical studies. Compared with non-stressed mice, stressed CTSS+/+ mice showed significant losses of muscle mass, muscle function, and muscle fiber area. In this setting, the stress-induced harmful changes in the levels of oxidative stress-related (gp91phox and p22phox ,), inflammation-related (SDF-1, CXCR4, IL-1β, TNF-α, MCP-1, ICAM-1, and VCAM-1), mitochondrial biogenesis-related (PPAR-γ and PGC-1α) genes and/or proteins and protein metabolism-related (p-PI3K, p-Akt, p-FoxO3α, MuRF-1, and MAFbx1) proteins; and these alterations were rectified by CTSS deletion. Metabolomic analysis revealed that stressed CTSS-/- mice exhibited a significant improvement in the levels of glutamine metabolism pathway products. Thus, these findings indicated that CTSS can control chronic stress-related skeletal muscle atrophy and dysfunction by modulating protein metabolic imbalance, and thus CTSS was suggested to be a promising new therapeutic target for chronic stress-related muscular diseases.

Keywords:  cathepsin Sinflammationmuscle atrophystress; oxidative stress

DOI:  https://doi.org/10.1096/fj.202300395RRR
bioRxiv. 2023 Jun 30. pii: 2023.06.29.547098. [Epub ahead of print]

The super-healing MRL strain promotes muscle growth in muscular dystrophy through a regenerative extracellular matrix.

Joseph G O'Brien, Alexander B Willis, Ashlee M Long, Jason Kwon, GaHyun Lee, Frank Li, Patrick G T Page, Andy H Vo, Michele Hadhazy, Rachelle H Crosbie, Alexis R Demonbreun, Elizabeth M McNally.

Genetic background shifts the severity of muscular dystrophy. In mice, the DBA/2J strain confers a more severe muscular dystrophy phenotype, whereas the Murphy's Roth Large (MRL) strain has "super-healing" properties that reduce fibrosis. A comparative analysis of the Sgcg null model of Limb Girdle Muscular Dystrophy in the DBA/2J versus MRL strain showed the MRL background was associated with greater myofiber regeneration and reduced structural degradation of muscle. Transcriptomic profiling of dystrophic muscle in the DBA/2J and MRL strains indicated strain-dependent expression of the extracellular matrix (ECM) and TGF-β signaling genes. To investigate the MRL ECM, cellular components were removed from dystrophic muscle sections to generate decellularized "myoscaffolds". Decellularized myoscaffolds from dystrophic mice in the protective MRL strain had significantly less deposition of collagen and matrix-bound TGF-β1 and TGF-β3 throughout the matrix, and dystrophic myoscaffolds from the MRL background were enriched in myokines. C2C12 myoblasts were seeded onto decellularized matrices from Sgcg -/- MRL and Sgcg -/- DBA/2J matrices. Acellular myoscaffolds from the dystrophic MRL background induced myoblast differentiation and growth compared to dystrophic myoscaffolds from the DBA/2J matrices. These studies establish that the MRL background also generates its effect through a highly regenerative ECM, which is active even in muscular dystrophy.
Brief Summary: The extracellular matrix of the super-healing MRL mouse strain harbors regenerative myokines that improve skeletal muscle growth and function in muscular dystrophy.

DOI: https://doi.org/10.1101/2023.06.29.547098
Dis Model Mech. 2023 Jul 01. pii: dmm049930. [Epub ahead of print]16(7):

LKB1 signaling is altered in skeletal muscle of a Duchenne muscular dystrophy mouse model.

Brigida Boccanegra, Paola Mantuano, Elena Conte, Alessandro Giovanni Cerchiara, Lisamaura Tulimiero, Raffaella Quarta, Erika Caputo, Francesca Sanarica, Monica Forino, Valeria Spadotto, Ornella Cappellari, Gianluca Fossati, Christian Steinkühler, Annamaria De Luca.

  The potential role of liver kinase B1 (LKB1) in the altered activation of the master metabolic and epigenetic regulator adenosine monophosphate-activated protein kinase (AMPK) in Duchenne muscular dystrophy has not been investigated so far. Hence, we analyzed both gene and protein levels of LKB1 and its related targets in gastrocnemius muscles of adult C57BL/10 mdx mice and D2 mdx mice, a model with a more severe dystrophic phenotype, as well as the sensitivity of the LKB1-AMPK pathway to AMPK activators, such as chronic exercise. Our data show, for the first time, a reduction in the levels of LKB1 and accessory proteins, MO25 and STRADα, in both mdx strains versus the respective wild type, which was further impaired by exercise, in parallel with a lack of further phosphorylation of AMPK. The AMPK-like kinase salt-inducible kinase (SIK) and class II histone deacetylases, along with expression of the HDAC target gene Mef2c, were also altered, supporting an impairment of LKB1-SIK-class II histone deacetylase signaling. Our results demonstrate that LKB1 may be involved in dystrophic progression, paving the way for future preclinical studies.

Keywords:  AMPK; Duchenne muscular dystrophy; Epigenetic; LKB1; Mouse models; Muscle metabolism

DOI:  https://doi.org/10.1242/dmm.049930
Cells. 2023 Jun 22. pii: 1695. [Epub ahead of print]12(13):

Lysine Methyltransferase SMYD1 Regulates Myogenesis via skNAC Methylation.

Li Zhu, Mark A Brown, Robert J Sims, Gayatri R Tiwari, Hui Nie, R Dayne Mayfield, Haley O Tucker.

  The SMYD family is a unique class of lysine methyltransferases (KMTases) whose catalytic SET domain is split by a MYND domain. Among these, Smyd1 was identified as a heart- and skeletal muscle-specific KMTase and is essential for cardiogenesis and skeletal muscle development. SMYD1 has been characterized as a histone methyltransferase (HMTase). Here we demonstrated that SMYD1 methylates is the Skeletal muscle-specific splice variant of the Nascent polypeptide-Associated Complex (skNAC) transcription factor. SMYD1-mediated methylation of skNAC targets K1975 within the carboxy-terminus region of skNAC. Catalysis requires physical interaction of SMYD1 and skNAC via the conserved MYND domain of SMYD1 and the PXLXP motif of skNAC. Our data indicated that skNAC methylation is required for the direct transcriptional activation of myoglobin (Mb), a heart- and skeletal muscle-specific hemoprotein that facilitates oxygen transport. Our study revealed that the skNAC, as a methylation target of SMYD1, illuminates the molecular mechanism by which SMYD1 cooperates with skNAC to regulate transcriptional activation of genes crucial for muscle functions and implicates the MYND domain of the SMYD-family KMTases as an adaptor to target substrates for methylation.

Keywords:  heart and skeletal muscle; methyltransferase; transcriptional regulation

DOI:  https://doi.org/10.3390/cells12131695
Front Physiol. 2023 ;14 1183101

Duchenne muscular dystrophy: disease mechanism and therapeutic strategies.

Addeli Bez Batti Angulski, Nora Hosny, Houda Cohen, Ashley A Martin, Dongwoo Hahn, Jack Bauer, Joseph M Metzger.

  Duchenne muscular dystrophy (DMD) is a severe, progressive, and ultimately fatal disease of skeletal muscle wasting, respiratory insufficiency, and cardiomyopathy. The identification of the dystrophin gene as central to DMD pathogenesis has led to the understanding of the muscle membrane and the proteins involved in membrane stability as the focal point of the disease. The lessons learned from decades of research in human genetics, biochemistry, and physiology have culminated in establishing the myriad functionalities of dystrophin in striated muscle biology. Here, we review the pathophysiological basis of DMD and discuss recent progress toward the development of therapeutic strategies for DMD that are currently close to or are in human clinical trials. The first section of the review focuses on DMD and the mechanisms contributing to membrane instability, inflammation, and fibrosis. The second section discusses therapeutic strategies currently used to treat DMD. This includes a focus on outlining the strengths and limitations of approaches directed at correcting the genetic defect through dystrophin gene replacement, modification, repair, and/or a range of dystrophin-independent approaches. The final section highlights the different therapeutic strategies for DMD currently in clinical trials.

Keywords:  Duchenne muscular dystrophy; dystrophin; muscle disease; pathophysiology; skeletal muscle; therapeutic strategies

DOI:  https://doi.org/10.3389/fphys.2023.1183101
Clin Anat. 2023 Jul 10.

Sex differences in skeletal muscle fiber types: A meta-analysis.

James L Nuzzo.

  Biopsies have been acquired from living men and women to determine proportions of Type I (slow-twitch) and II (fast-twitch) skeletal muscle fibers since the 1970s. Sex differences have been assumed but the literature has not been submitted to meta-analysis. Here, the aim was to generate effect sizes of sex differences in muscle fiber cross-sectional areas, distribution percentages, and area percentages. Data from 2875 men and 2452 women, who participated in 110 studies, were analyzed. Myofibrillar adenosine triphosphatase histochemistry was used in 71.8% of studies to classify fibers as Type I, II, IIA, and/or IIX; immunohistochemistry, immunofluorescence, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis were used in 35.4% of studies to similarly classify myosin heavy chain (MHC) isoform content. Most studies involved biopsies from vastus lateralis (79.1%) in healthy individuals (92.7%) between 18 and 59 years old (80.9%). Men exhibited greater cross-sectional areas for all fiber types (g = 0.40-1.68); greater distribution percentages for Type II, MHC II, IIA, IIX fibers (g = 0.26-0.34); greater area percentages for Type II, IIA, MHC IIA, IIX fibers (g = 0.39-0.93); greater Type II/I and Type IIA/I fiber area ratios (g = 0.63, 0.94). Women exhibited greater Type I and MHC I distribution percentages (g = -0.13, -0.44); greater Type I and MHC I area percentages (g = -0.53, -0.69); greater Type I/II fiber area ratios (g = -1.24). These data, which represent the largest repository of comparative muscle fiber type data from living men and women, can inform discussions about biological sex and its impact on pathologies and sports performance (e.g., explaining sex differences in muscle strength and muscle endurance).

Keywords:  anatomy; biopsy; men; muscles; physiology; quadriceps muscle; sex; women

DOI:  https://doi.org/10.1002/ca.24091
Am J Pathol. 2023 Jul 06. pii: S0002-9440(23)00240-7. [Epub ahead of print]

Aberrations in energetic metabolism and stress-related pathways contribute to pathophysiology in the Neb cKO mouse model of nemaline myopathy.

Rebecca A Slick, Jennifer A Tinklenberg, Jessica Sutton, Liwen Zhang, Hui Meng, Margaret Beatka, Mark Vanden Avond, Mariah J Prom, Emily Ott, Federica Montanaro, James Heisner, Rafael Toro, Henk Granzier, Aron M Geurts, David Stowe, R Blake Hill, Michael W Lawlor.

Nemaline myopathy (NM) is a genetically and clinically heterogeneous disease that is diagnosed based on the presence of nemaline rods on skeletal muscle biopsy. While NM has typically been classified by causative genes, disease severity or prognosis cannot be predicted well. The common pathological endpoint of nemaline rods (despite diverse genetic causes) and an unexplained range of muscle weakness suggests that shared secondary processes contributed to the pathogenesis of NM. We speculated that these processes could be identified through a proteome wide interrogation utilizing a mouse model of severe NM in combination with pathway validation and structural/functional analyses. A proteomic analysis was performed using skeletal muscle tissue from the Neb cKO mouse model compared with its wild-type counterpart to identify pathophysiologically relevant biological processes that might impact disease severity or provide new treatment targets. A differential expression analysis and Ingenuity Pathway core analysis predicted perturbations in several cellular processes including mitochondrial dysfunction and changes in energetic metabolism and stress-related pathways. Subsequent structural and functional studies have demonstrated abnormal mitochondrial distribution, decreased mitochondrial respiratory function, an increase in mitochondrial membrane potential (ΔΨm), and extremely low ATP content in Neb cKO muscles relative to wild type. Overall, the findings of these studies support a role for severe mitochondrial dysfunction as a novel contributor to muscle weakness in NM.

DOI: https://doi.org/10.1016/j.ajpath.2023.06.009
bioRxiv. 2023 Jun 27. pii: 2023.06.27.546724. [Epub ahead of print]

Acyl-CoA thioesterase-2 facilitates β-oxidation in glycolytic skeletal muscle in a lipid supply dependent manner.

Carmen Bekeova, Ji In Han, Heli Xu, Evan Kerr, Brittney Blackburne, Shannon C Lynch, Clementina Mesaros, Marta Murgia, Rajanikanth Vadigepalli, Joris Beld, Roberta Leonardi, Nathaniel W Snyder, Erin L Seifert.

Acyl-Coenzyme A (acyl-CoA) thioesters are compartmentalized intermediates that participate in in multiple metabolic reactions within the mitochondrial matrix. The limited availability of free CoA (CoASH) in the matrix raises the question of how the local acyl-CoA concentration is regulated to prevent trapping of CoASH from overload of any specific substrate. Acyl-CoA thioesterase-2 (ACOT2) hydrolyzes long-chain acyl-CoAs to their constituent fatty acids and CoASH, and is the only mitochondrial matrix ACOT refractory to inhibition by CoASH. Thus, we reasoned that ACOT2 may constitutively regulate matrix acyl-CoA levels. Acot2 deletion in murine skeletal muscle (SM) resulted in acyl-CoA build-up when lipid supply and energy demands were modest. When energy demand and pyruvate availability were elevated, lack of ACOT2 activity promoted glucose oxidation. This preference for glucose over fatty acid oxidation was recapitulated in C2C12 myotubes with acute depletion of Acot2 , and overt inhibition of β-oxidation was demonstrated in isolated mitochondria from Acot2 -depleted glycolytic SM. In mice fed a high fat diet, ACOT2 enabled the accretion of acyl-CoAs and ceramide derivatives in glycolytic SM, and this was associated with worse glucose homeostasis compared to when ACOT2 was absent. These observations suggest that ACOT2 supports CoASH availability to facilitate β-oxidation in glycolytic SM when lipid supply is modest. However, when lipid supply is high, ACOT2 enables acyl-CoA and lipid accumulation, CoASH sequestration, and poor glucose homeostasis. Thus, ACOT2 regulates matrix acyl-CoA concentration in glycolytic muscle, and its impact depends on lipid supply.

DOI: https://doi.org/10.1101/2023.06.27.546724
bioRxiv. 2023 Jun 29. pii: 2023.06.28.546902. [Epub ahead of print]

High-Intensity Interval Training Attenuates Impairment in Regulatory Protein Machinery of Mitochondrial Quality Control in Skeletal Muscle of Diet-Induced Obese Mice.

James B Tincknell, Benjamin Kugler, Haley Spicuzza, Huimin Yan, Tongjian You, Kai Zou.

Mitochondrial quality control processes are essential in governing mitochondrial integrity and function. The purpose of the study was to examine the effects of 10 weeks of HIIT on the regulatory protein machinery of skeletal muscle mitochondrial quality control and whole-body glucose homeostasis in diet-induced obese mice. Male C57BL/6 mice were randomly assigned to a low-fat diet (LFD) or high-fat diet (HFD) group. After 10 weeks, HFD-fed mice were divided into sedentary and HIIT (HFD+HIIT) groups and remained on HFD for another 10 weeks (n=9/group). Graded exercise test, glucose and insulin tolerance tests, mitochondrial respiration and regulatory protein markers of mitochondrial quality control processes were determined by immunoblots. Ten weeks of HIIT enhanced ADP-stimulated mitochondrial respiration in diet-induced obese mice (P < 0.05) but did not improve whole-body insulin sensitivity. Importantly, the ratio of Drp1(Ser 616 ) over Drp1(Ser 637 ) phosphorylation, an indicator of mitochondrial fission, was attenuated in HFD-HIIT compared to HFD (-35.7%, P < 0.05). Regarding autophagy, skeletal muscle p62 content was lower in HFD group than LFD group (-35.1%, P < 0.05), however, such reduction was disappeared in HFD+HIIT group. In addition, LC3B II/I ratio was higher in HFD than LFD group (15.5%, P < 0.05) but was ameliorated in HFD+HIIT group (-29.9%, P < 0.05). Overall, our study demonstrated that 10 weeks of HIIT was effective in improving skeletal muscle mitochondrial respiration and the regulatory protein machinery of mitochondrial quality control in diet-induced obese mice through the alterations of mitochondrial fission protein Drp1 activity and p62/LC3B-mediated regulatory machinery of autophagy.

DOI: https://doi.org/10.1101/2023.06.28.546902
Exp Physiol. 2023 Jul 10.

Intrafusal cross-bridge dynamics shape history-dependent muscle spindle responses to stretch.

Surabhi N Simha, Lena H Ting.

   NEW FINDINGS: What is the central question of the study? A computational biophysical muscle model was used to ask how muscle cross-bridge dynamics shape the information that can be encoded by intrafusal muscle fibres within the muscle spindle. What is the main finding and its importance? Both actin and myosin dynamics and their interactions can shape muscle spindle sensory signals and are necessary to simulate history-dependent muscle spindle firing properties to be more in line with experimental observations. The tuned muscle spindle model shows that non-linear and history-dependent muscle spindle firing properties to sinusoids reported previously emerge from intrafusal cross-bridge dynamics.
ABSTRACT: Computational models can be critical to linking complex properties of muscle spindle organs to the sensory information that they encode during behaviours such as postural sway and locomotion where few muscle spindle recordings exist. Here, we augment a biophysical muscle spindle model to predict the muscle spindle sensory signal. Muscle spindles comprise several intrafusal muscle fibres with varied myosin expression and are innervated by sensory neurons that fire during muscle stretch. We demonstrate how cross-bridge dynamics from thick and thin filament interactions affect the sensory receptor potential at the spike initiating region. Equivalent to the Ia afferent's instantaneous firing rate, the receptor potential is modelled as a linear sum of the force and rate change of force (yank) of a dynamic bag1 fibre and the force of a static bag2/chain fibre. We show the importance of inter-filament interactions in (i) generating large changes in force at stretch onset that drive initial bursts and (ii) faster recovery of bag fibre force and receptor potential following a shortening. We show how myosin attachment and detachment rates qualitatively alter the receptor potential. Finally, we show the effect of faster recovery of receptor potential on cyclic stretch-shorten cycles. Specifically, the model predicts history-dependence in muscle spindle receptor potentials as a function of inter-stretch interval (ISI), pre-stretch amplitude and the amplitude of sinusoidal stretches. This model provides a computational platform for predicting muscle spindle response in behaviourally relevant stretches and can link myosin expression seen in healthy and diseased intrafusal muscle fibres to muscle spindle function.

Keywords:  muscle spindle firing; sensory encoding; short-range stiffness

DOI:  https://doi.org/10.1113/EP090767
Front Physiol. 2023 ;14 1166206

Prolonged voluntary wheel running reveals unique adaptations in mdx mice treated with microdystrophin constructs ± the nNOS-binding site.

S E Hamm, C Yuan, L F McQueen, M A Wallace, H Zhang, A Arora, A M Garafalo, R P McMillan, M W Lawlor, M J Prom, E M Ott, J Yan, A K Addington, C A Morris, J P Gonzalez, R W Grange.

  We tested the effects of prolonged voluntary wheel running on the muscle function of mdx mice treated with one of two different microdystrophin constructs. At 7 weeks of age mdx mice were injected with a single dose of AAV9-CK8-microdystrophin with (gene therapy 1, GT1) or without (gene therapy 2, GT2) the nNOS-binding domain and were assigned to one of four gene therapy treated groups: mdxRGT1 (run, GT1), mdxGT1 (no run, GT1), or mdxRGT2 (run,GT2), mdxGT2 (no run, GT2). There were two mdx untreated groups injected with excipient: mdxR (run, no gene therapy) and mdx (no run, no gene therapy). A third no treatment group, Wildtype (WT) received no injection and did not run. mdxRGT1, mdxRGT2 and mdxR performed voluntary wheel running for 52 weeks; WT and remaining mdx groups were cage active. Robust expression of microdystrophin occurred in diaphragm, quadriceps, and heart muscles of all treated mice. Dystrophic muscle pathology was high in diaphragms of non-treated mdx and mdxR mice and improved in all treated groups. Endurance capacity was rescued by both voluntary wheel running and gene therapy alone, but their combination was most beneficial. All treated groups increased in vivo plantarflexor torque over both mdx and mdxR mice. mdx and mdxR mice displayed ∼3-fold lower diaphragm force and power compared to WT values. Treated groups demonstrated partial improvements in diaphragm force and power, with mdxRGT2 mice experiencing the greatest improvement at ∼60% of WT values. Evaluation of oxidative red quadriceps fibers revealed the greatest improvements in mitochondrial respiration in mdxRGT1 mice, reaching WT levels. Interestingly, mdxGT2 mice displayed diaphragm mitochondrial respiration values similar to WT but mdxRGT2 animals showed relative decreases compared to the no run group. Collectively, these data demonstrate that either microdystrophin construct combined with voluntary wheel running increased in vivo maximal muscle strength, power, and endurance. However, these data also highlighted important differences between the two microdystrophin constructs. GT1, with the nNOS-binding site, improved more markers of exercise-driven adaptations in metabolic enzyme activity of limb muscles, while GT2, without the nNOS-binding site, demonstrated greater protection of diaphragm strength after chronic voluntary endurance exercise but decreased mitochondrial respiration in the context of running.

Keywords:  AAV (adeno-associated virus); endurance; longevity; microdystrophin; muscle strength

DOI:  https://doi.org/10.3389/fphys.2023.1166206
bioRxiv. 2023 Jun 26. pii: 2023.06.24.546411. [Epub ahead of print]

TOMM40 and TOMM22 of the Translocase Outer Mitochondrial Membrane Complex rescue statin-impaired mitochondrial dynamics, morphology, and mitophagy in skeletal myotubes.

Neil V Yang, Sean Rogers, Rachel Guerra, David J Pagliarini, Elizabeth Theusch, Ronald M Krauss.

Background: Statins are the drugs most commonly used for lowering plasma low-density lipoprotein (LDL) cholesterol levels and reducing cardiovascular disease risk. Although generally well tolerated, statins can induce myopathy, a major cause of non-adherence to treatment. Impaired mitochondrial function has been implicated as a cause of statin-induced myopathy, but the underlying mechanism remains unclear. We have shown that simvastatin downregulates transcription of TOMM40 and TOMM22 , genes that encode major subunits of the translocase of outer mitochondrial membrane (TOM) complex which is responsible for importing nuclear-encoded proteins and maintaining mitochondrial function. We therefore investigated the role of TOMM40 and TOMM22 in mediating statin effects on mitochondrial function, dynamics, and mitophagy.
Methods: Cellular and biochemical assays and transmission electron microscopy were used to investigate effects of simvastatin and TOMM40 and TOMM22 expression on measures of mitochondrial function and dynamics in C2C12 and primary human skeletal cell myotubes.
Results: Knockdown of TOMM40 and TOMM22 in skeletal cell myotubes impaired mitochondrial oxidative function, increased production of mitochondrial superoxide, reduced mitochondrial cholesterol and CoQ levels, disrupted mitochondrial dynamics and morphology, and increased mitophagy, with similar effects resulting from simvastatin treatment. Overexpression of TOMM40 and TOMM22 in simvastatin-treated muscle cells rescued statin effects on mitochondrial dynamics, but not on mitochondrial function or cholesterol and CoQ levels. Moreover, overexpression of these genes resulted in an increase in number and density of cellular mitochondria.
Conclusion: These results confirm that TOMM40 and TOMM22 are central in regulating mitochondrial homeostasis and demonstrate that downregulation of these genes by statin treatment mediates disruption of mitochondrial dynamics, morphology, and mitophagy, effects that may contribute to statin-induced myopathy.
GRAPHICAL ABSTRACT:

DOI: https://doi.org/10.1101/2023.06.24.546411
J Cachexia Sarcopenia Muscle. 2023 Jul 11.

Short-term disuse does not affect postabsorptive or postprandial muscle protein fractional breakdown rates.

George F Pavis, Doaa R Abdelrahman, Andrew J Murton, Benjamin T Wall, Francis B Stephens, Marlou L Dirks.

   BACKGROUND: The decline in postabsorptive and postprandial muscle protein fractional synthesis rates (FSR) does not quantitatively account for muscle atrophy during uncomplicated, short-term disuse, when atrophy rates are the highest. We sought to determine whether 2 days of unilateral knee immobilization affects mixed muscle protein fractional breakdown rates (FBR) during postabsorptive and simulated postprandial conditions.
METHODS: Twenty-three healthy, male participants (age: 22 ± 1 year; height: 179 ± 1 cm; body mass: 73.4 ± 1.5 kg; body mass index 22.8 ± 0.5 kg·m-2 ) took part in this randomized, controlled study. After 48 h of unilateral knee immobilization, primed continuous intravenous l-[15 N]-phenylalanine and l-[ring-2 H5 ]-phenylalanine infusions were used for parallel determinations of FBR and FSR, respectively, in a postabsorptive (saline infusion; FAST) or simulated postprandial state (67.5 mg·kg body mass-1 ·h-1 amino acid infusion; FED). Bilateral m. vastus lateralis biopsies from the control (CON) and immobilized (IMM) legs, and arterialized-venous blood samples, were collected throughout.
RESULTS: Amino acid infusion rapidly increased plasma phenylalanine (59 ± 9%), leucine (76 ± 5%), isoleucine (109 ± 7%) and valine (42 ± 4%) concentrations in FED only (all P < 0.001), which was sustained for the remainder of infusion. Serum insulin concentrations peaked at 21.8 ± 2.2 mU·L-1 at 15 min in FED only (P < 0.001) and were 60% greater in FED than FAST (P < 0.01). Immobilization did not influence FBR in either FAST (CON: 0.150 ± 0.018; IMM: 0.143 ± 0.017%·h-1 ) or FED (CON: 0.134 ± 0.012; IMM: 0.160 ± 0.018%·h-1 ; all effects P > 0.05). However, immobilization decreased FSR (P < 0.05) in both FAST (0.071 ± 0.004 vs. 0.086 ± 0.007%·h-1 ; IMM vs CON, respectively) and FED (0.066 ± 0.016 vs. 0.119 ± 0.016%·h-1 ; IMM vs CON, respectively). Consequently, immobilization decreased net muscle protein balance (P < 0.05) and to a greater extent in FED (CON: -0.012 ± 0.025; IMM: -0.095 ± 0.023%·h-1 ; P < 0.05) than FAST (CON: -0.064 ± 0.020; IMM: -0.072 ± 0.017%·h-1 ).
CONCLUSIONS: We conclude that merely 2 days of leg immobilization does not modulate postabsorptive and simulated postprandial muscle protein breakdown rates. Instead, under these conditions the muscle negative muscle protein balance associated with brief periods of experimental disuse is driven near exclusively by reduced basal muscle protein synthesis rates and anabolic resistance to amino acid administration.

Keywords:  Amino acids; Immobilization; Muscle disuse atrophy; Muscle protein breakdown; Protein synthesis

DOI:  https://doi.org/10.1002/jcsm.13284
Int J Mol Sci. 2023 Jul 06. pii: 11135. [Epub ahead of print]24(13):

The Impact of SRT2104 on Skeletal Muscle Mitochondrial Function, Redox Biology, and Loss of Muscle Mass in Hindlimb Unloaded Rats.

Lauren T Wesolowski, Jessica L Simons, Pier L Semanchik, Mariam A Othman, Joo-Hyun Kim, John M Lawler, Khaled Y Kamal, Sarah H White-Springer.

  Mechanical unloading during microgravity causes skeletal muscle atrophy and impairs mitochondrial energetics. The elevated production of reactive oxygen species (ROS) by mitochondria and Nox2, coupled with impairment of stress protection (e.g., SIRT1, antioxidant enzymes), contribute to atrophy. We tested the hypothesis that the SIRT1 activator, SRT2104 would rescue unloading-induced mitochondrial dysfunction. Mitochondrial function in rat gastrocnemius and soleus muscles were evaluated under three conditions (10 days): ambulatory control (CON), hindlimb unloaded (HU), and hindlimb-unloaded-treated with SRT2104 (SIRT). Oxidative phosphorylation, electron transfer capacities, H2O2 production, and oxidative and antioxidant enzymes were quantified using high-resolution respirometry and colorimetry. In the gastrocnemius, (1) integrative (per mg tissue) proton LEAK was lesser in SIRT than in HU or CON; (2) intrinsic (relative to citrate synthase) maximal noncoupled electron transfer capacity (ECI+II) was lesser, while complex I-supported oxidative phosphorylation to ECI+II was greater in HU than CON; (3) the contribution of LEAK to ECI+II was greatest, but cytochrome c oxidase activity was lowest in HU. In both muscles, H2O2 production and concentration was greatest in SIRT, as was gastrocnemius superoxide dismutase activity. In the soleus, H2O2 concentration was greater in HU compared to CON. These results indicate that SRT2104 preserves mitochondrial function in unloaded skeletal muscle, suggesting its potential to support healthy muscle cells in microgravity by promoting necessary energy production in mitochondria.

Keywords:  SRT2104; antioxidants; electron transfer system; hindlimb unloading; mitochondria; oxidative stress; respiration; skeletal muscle; spaceflight

DOI:  https://doi.org/10.3390/ijms241311135
Geroscience. 2023 Jul 11.

Determining the feasibility of characterising cellular senescence in human skeletal muscle and exploring associations with muscle morphology and physical function at different ages: findings from the MASS_Lifecourse Study.

Leena Habiballa, Adam Hruby, Antoneta Granic, Richard M Dodds, Susan J Hillman, Diana Jurk, João F Passos, Avan A Sayer.

  Cellular senescence may be associated with morphological changes in skeletal muscle and changes in physical function with age although there have been few human studies. We aimed to determine the feasibility of characterising cellular senescence in skeletal muscle and explored sex-specific associations between markers of cellular senescence, muscle morphology, and physical function in participants from the MASS_Lifecourse Study. Senescence markers (p16, TAF (Telomere-Associated DNA Damage Foci), HMGB1 (High Mobility Group Box 1), and Lamin B1) and morphological characteristics (fibre size, number, fibrosis, and centrally nucleated fibres) were assessed in muscle biopsies from 40 men and women (age range 47-84) using spatially-resolved methods (immunohistochemistry, immunofluorescence, and RNA and fluorescence in situ hybridisation). The associations between senescence, morphology, and physical function (muscle strength, mass, and physical performance) at different ages were explored. We found that most senescence markers and morphological characteristics were weakly associated with age in men but more strongly, although non-significantly, associated with age in women. Associations between senescence markers, morphology, and physical function were also stronger in women for HMGB1 and grip strength (r = 0.52); TAF, BMI, and muscle mass (r > 0.4); Lamin B1 and fibrosis (r = - 0.5); fibre size and muscle mass (r ≥ 0.4); and gait speed (r = - 0.5). However, these associations were non-significant. In conclusion, we have demonstrated that it is feasible to characterise cellular senescence in human skeletal muscle and to explore associations with morphology and physical function in women and men of different ages. The findings require replication in larger studies.

Keywords:  Cellular senescence; Human skeletal muscle ageing; Muscle morphology; Physical function; Sarcopenia

DOI:  https://doi.org/10.1007/s11357-023-00869-4
Mol Ther. 2023 Jul 13. pii: S1525-0016(23)00383-0. [Epub ahead of print]

A dysfunctional miR-1-TRPS1-MYOG axis drives ERMS by suppressing terminal myogenic differentiation.

Sören S Hüttner, Henriette Henze, Dana Elster, Philipp Koch, Ursula Anderer, Björn von Eyss, Julia von Maltzahn.

Rhabdomyosarcoma is the most common pediatric soft tissue tumor comprising two major subtypes, the PAX3/7-FOXO1 fusion negative embryonal and the PAX3/7-FOXO1 fusion positive alveolar subtype. Here, we demonstrate that the expression levels of the transcriptional repressor TRPS1 are specifically enhanced in the embryonal subtype resulting in impaired terminal myogenic differentiation and tumor growth. During normal myogenesis, expression levels of TRPS1 have to decrease to allow myogenic progression, as demonstrated by overexpression of TRPS1 in myoblasts impairing myotube formation. Consequentially, myogenic differentiation in embryonal rhabdomyosarcoma in vitro as well as in vivo can be achieved by reducing TRPS1 levels. Furthermore, we show that TRPS1 levels in RD cells, the bona fide model cell line for embryonal rhabdomyosarcoma, are regulated by miR-1 and that TRPS1 and MYOD1 share common genomic binding sites. The MYOG promoter is one of the critical targets of TRPS1 and MYOD1, we demonstrate that TRPS1 restricts MYOG expression and thereby inhibits terminal myogenic differentiation. Therefore, reduction of TRPS1 levels in embryonal rhabdomyosarcoma might be a therapeutic approach to drive embryonal rhabdomyosarcoma cells into myogenic differentiation thereby generating postmitotic myotubes.

DOI: https://doi.org/10.1016/j.ymthe.2023.07.003
bioRxiv. 2023 Jun 30. pii: 2023.06.30.546730. [Epub ahead of print]

Multi-omics characterization of partial chemical reprogramming reveals evidence of cell rejuvenation.

Wayne Mitchell, Ludger J E Goeminne, Alexander Tyshkovskiy, Sirui Zhang, Joao A Paulo, Kerry A Pierce, Angelina H Choy, Clary B Clish, Steven P Gygi, Vadim N Gladyshev.

Partial reprogramming by cyclic short-term expression of Yamanaka factors holds promise for shifting cells to younger states and consequently delaying the onset of many diseases of aging. However, the delivery of transgenes and potential risk of teratoma formation present challenges for in vivo applications. Recent advances include the use of cocktails of compounds to reprogram somatic cells, but the characteristics and mechanisms of partial cellular reprogramming by chemicals remain unclear. Here, we report a multi-omics characterization of partial chemical reprogramming in fibroblasts from young and aged mice. We measured the effects of partial chemical reprogramming on the epigenome, transcriptome, proteome, phosphoproteome, and metabolome. At the transcriptome, proteome, and phosphoproteome levels, we saw widescale changes induced by this treatment, with the most notable signature being an upregulation of mitochondrial oxidative phosphorylation. Furthermore, at the metabolome level, we observed a reduction in the accumulation of aging-related metabolites. Using both transcriptomic and epigenetic clock-based analyses, we show that partial chemical reprogramming reduces the biological age of mouse fibroblasts. We demonstrate that these changes have functional impacts, as evidenced by changes in cellular respiration and mitochondrial membrane potential. Taken together, these results illuminate the potential for chemical reprogramming reagents to rejuvenate aged biological systems, and warrant further investigation into adapting these approaches for in vivo age reversal.

DOI: https://doi.org/10.1101/2023.06.30.546730
Nat Commun. 2023 Jul 13. 14(1): 4166

Cytochrome c lysine acetylation regulates cellular respiration and cell death in ischemic skeletal muscle.

Paul T Morse, Gonzalo Pérez-Mejías, Junmei Wan, Alice A Turner, Inmaculada Márquez, Hasini A Kalpage, Asmita Vaishnav, Matthew P Zurek, Philipp P Huettemann, Katherine Kim, Tasnim Arroum, Miguel A De la Rosa, Dipanwita Dutta Chowdhury, Icksoo Lee, Joseph S Brunzelle, Thomas H Sanderson, Moh H Malek, David Meierhofer, Brian F P Edwards, Irene Díaz-Moreno, Maik Hüttemann.

Skeletal muscle is more resilient to ischemia-reperfusion injury than other organs. Tissue specific post-translational modifications of cytochrome c (Cytc) are involved in ischemia-reperfusion injury by regulating mitochondrial respiration and apoptosis. Here, we describe an acetylation site of Cytc, lysine 39 (K39), which was mapped in ischemic porcine skeletal muscle and removed by sirtuin5 in vitro. Using purified protein and cellular double knockout models, we show that K39 acetylation and acetylmimetic K39Q replacement increases cytochrome c oxidase (COX) activity and ROS scavenging while inhibiting apoptosis via decreased binding to Apaf-1, caspase cleavage and activity, and cardiolipin peroxidase activity. These results are discussed with X-ray crystallography structures of K39 acetylated (1.50 Å) and acetylmimetic K39Q Cytc (1.36 Å) and NMR dynamics. We propose that K39 acetylation is an adaptive response that controls electron transport chain flux, allowing skeletal muscle to meet heightened energy demand while simultaneously providing the tissue with robust resilience to ischemia-reperfusion injury.

DOI: https://doi.org/10.1038/s41467-023-39820-8
Nat Rev Endocrinol. 2023 Jul 14.

GDF15 boosts muscle energy burn.

Shimona Starling.

DOI: https://doi.org/10.1038/s41574-023-00877-6