bims-moremu 2024-01-21 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2024–01–21
thirty-one papers selected by
Anna Vainshtein, Craft Science Inc.

Machine learning inference of continuous single-cell state transitions during myoblast differentiation and fusion.
Antibody blockade of activin type II receptors preserves skeletal muscle mass and enhances fat loss during GLP-1 receptor agonism.
Revisiting the roles of glucose transporters in skeletal muscle physiology: is GLUT10 a novel player?
Native collagen VI delays muscle stem cell early differentiation.
SERCA1 Overexpression in Skeletal Muscle Attenuates Muscle Atrophy and Improves Motor Function in a Mouse Model of ALS.
The mitochondrial ATP-dependent potassium channel (mitoKATP) controls skeletal muscle structure and function.
Muscle fibre mitochondrial [Ca2+ ] dynamics during Ca2+ waves in RYR1 gain-of-function mouse.
Senolytic treatment does not mitigate oxidative stress-induced muscle atrophy but improves muscle force generation in CuZn superoxide dismutase knockout mice.
Unraveling the causes of sarcopenia: Roles of neuromuscular junction impairment and mitochondrial dysfunction.
Ca2+ storage function is altered in the sarcoplasmic reticulum of skeletal muscle lacking mitsugumin 23.
Gpcpd1-GPC metabolic pathway is dysfunctional in aging and its deficiency severely perturbs glucose metabolism.
The impact of bed rest on human skeletal muscle metabolism.
Transcriptional dysregulation of autophagy in the muscle of a mouse model of Duchenne muscular dystrophy.
Mechanism and physical activities in bone-skeletal muscle crosstalk.
Depletion of SAM leading to loss of heterochromatin drives muscle stem cell ageing.
PROKR1-CREB-NR4A2 axis for oxidative muscle fiber specification and improvement of metabolic function.
HDAC9 inhibition reduces skeletal muscle atrophy and enhances regeneration in mice with cigarette smoke-induced COPD.
Exercise-induced Musclin determines the fate of fibro-adipogenic progenitors to control muscle homeostasis.
AMPKα2 regulates fasting-induced hyperketonemia by suppressing SCOT ubiquitination and degradation.
An optogenetic cell therapy to restore control of target muscles in an aggressive mouse model of amyotrophic lateral sclerosis.
Duchenne and Becker muscular dystrophy: Cellular mechanisms, image analysis, and computational models: A review.
Acute Exercise Increases GDF15 and Unfolded Protein Response/Integrated Stress Response in Muscle in Type 2 diabetes.
Editorial: Molecular and physiological aspects of sarcopenia in the older person: mechanisms, diagnostics and therapy.
Exercise-induced redox modulation as a mediator of DNA methylation in health maintenance and disease prevention.
Small-molecule inhibition of glycogen synthase 1 for the treatment of Pompe disease and other glycogen storage disorders.
Acute exercise-induced release of innate immune proteins via small extracellular vesicles changes with aerobic fitness and age.
Multi-level profiling unravels mitochondrial dysfunction in myotonic dystrophy type 2.
The BCKDH kinase inhibitor BT2 promotes BCAA disposal and mitochondrial proton leak in both insulin-sensitive and insulin-resistant C2C12 myotubes.
Exercise influence on monocarboxylate transporter 1 (MCT1) and 4 (MCT4) in the skeletal muscle: A systematic review.
An ETFDH-driven metabolon supports OXPHOS efficiency in skeletal muscle by regulating coenzyme Q homeostasis.
Molecular Insights From Multiomics Studies of Physical Activity.

Mol Syst Biol. 2024 Jan 18.

Machine learning inference of continuous single-cell state transitions during myoblast differentiation and fusion.

Amit Shakarchy, Giulia Zarfati, Adi Hazak, Reut Mealem, Karina Huk, Tamar Ziv, Ori Avinoam, Assaf Zaritsky.

  Cells modify their internal organization during continuous state transitions, supporting functions from cell division to differentiation. However, tools to measure dynamic physiological states of individual transitioning cells are lacking. We combined live-cell imaging and machine learning to monitor ERK1/2-inhibited primary murine skeletal muscle precursor cells, that transition rapidly and robustly from proliferating myoblasts to post-mitotic myocytes and then fuse, forming multinucleated myotubes. Our models, trained using motility or actin intensity features from single-cell tracking data, effectively tracked real-time continuous differentiation, revealing that differentiation occurs 7.5-14.5 h post induction, followed by fusion ~3 h later. Co-inhibition of ERK1/2 and p38 led to differentiation without fusion. Our model inferred co-inhibition leads to terminal differentiation, indicating that p38 is specifically required for transitioning from terminal differentiation to fusion. Our model also predicted that co-inhibition leads to changes in actin dynamics. Mass spectrometry supported these in silico predictions and suggested novel fusion and maturation regulators downstream of differentiation. Collectively, this approach can be adapted to various biological processes to uncover novel links between dynamic single-cell states and their functional outcomes.

Keywords:  Differentiation; Machine Learning; Myoblast Fusion; Myogenesis; State Transition

DOI:  https://doi.org/10.1038/s44320-024-00010-3
Mol Metab. 2024 Jan 11. pii: S2212-8778(24)00011-5. [Epub ahead of print] 101880

Antibody blockade of activin type II receptors preserves skeletal muscle mass and enhances fat loss during GLP-1 receptor agonism.

Elizabeth Nunn, Natasha Jaiswal, Matthew Gavin, Kahealani Uehara, Megan Stefkovich, Karima Drareni, Ryan Calhoun, Michelle Lee, Corey D Holman, Joseph A Baur, Patrick Seale, Paul M Titchenell.

   OBJECTIVE: Glucagon-like peptide 1 (GLP-1) receptor agonists reduce food intake, producing remarkable weight loss in overweight and obese individuals. While much of this weight loss is fat mass, there is also a loss of lean mass, similar to other approaches that induce calorie deficit. Targeting signaling pathways that regulate skeletal muscle hypertrophy is a promising avenue to preserve lean mass and modulate body composition. Myostatin and Activin A are TGFβ-like ligands that signal via the activin type II receptors (ActRII) to antagonize muscle growth. Pre-clinical and clinical studies demonstrate that ActRII blockade induces skeletal muscle hypertrophy and reduces fat mass. In this manuscript, we test the hypothesis that combined ActRII blockade plus GLP-1 receptor agonist will preserve muscle mass leading to improvements in skeletomuscular and metabolic function and enhanced fat loss.
METHODS: In this study, we explore the therapeutic potential of bimagrumab, a monoclonal antibody against ActRII, to modify body composition alone and during weight loss induced by GLP-1 receptor agonist semaglutide in diet-induced obese mice. Mechanistically, we define the specific role of the anabolic kinase Akt in mediating the hypertrophic muscle effects of ActRII inhibition in vivo.
RESULTS: Treatment of obese mice with bimagrumab induced a ∼10 % increase in lean mass while simultaneously decreasing fat mass. Daily treatment of obese mice with semaglutide potently decreased body weight; this included a significant decrease in both muscle and fat mass. Combination treatment with bimagrumab and semaglutide led to superior fat mass loss while simultaneously preserving lean mass despite reduced food intake. Treatment with both drugs was associated with improved metabolic outcomes, and increased lean mass was associated with improved exercise performance. Deletion of both Akt isoforms in skeletal muscle modestly reduced, but did not prevent, muscle hypertrophy driven by ActRII inhbition.
CONCLUSIONS: Collectively, these data demonstrate that blockade of ActRII signaling improves body composition and metabolic parameters during calorie deficit driven by GLP-1 receptor agonism and demonstrate the existence of Akt-independent pathways supporting muscle hypertrophy in the absence of ActRII signaling.

Keywords:  Activin type II receptor (ActRII); Akt; Body composition; Glucagon-like peptide 1 (GLP-1); Obesity; Weight loss

DOI:  https://doi.org/10.1016/j.molmet.2024.101880
Biochem Biophys Res Commun. 2024 Jan 08. pii: S0006-291X(24)00029-9. [Epub ahead of print]696 149494

Revisiting the roles of glucose transporters in skeletal muscle physiology: is GLUT10 a novel player?

Wei-Sheng Lin, Ting-Rong Hsu.

  Skeletal muscle is the largest metabolic tissue responsible for systemic glucose handling. Glucose uptake into skeletal tissue is highly dynamic and delicately regulated, in part through the controlled expression and subcellular trafficking of multiple types of glucose transporters. Although the roles of GLUT4 in skeletal muscle metabolism are well established, the physiological significance of other, seemingly redundant, glucose transporters remain incompletely understood. Nonetheless, recent studies have shed light on the roles of several glucose transporters, such as GLUT1 and GLUT10, in skeletal muscle. Mice experiments suggest that GLUT10 could be a novel player in skeletal muscle metabolism in the context of mechanical overload, which is in line with the meta-analytical results of gene expression changes after resistance exercise in humans. Herein we discuss the knowns, unknowns, and implications of these recent findings.

Keywords:  GLUT10; Glucose transporter; Glucose uptake; Resistance exercise; Skeletal muscle

DOI:  https://doi.org/10.1016/j.bbrc.2024.149494
J Cell Sci. 2024 Jan 15. pii: jcs.261419. [Epub ahead of print]

Native collagen VI delays muscle stem cell early differentiation.

Samuele Metti, Francesco Da Ros, Giorgia Toniato, Matilde Cescon, Paolo Bonaldo.

  Adult muscle stem cells (MuSCs) are critical for muscle homeostasis and regeneration, and their behavior relies on a finely regulated niche made of specific extracellular matrix (ECM) components and soluble factors. Among ECM proteins, collagen VI (Col6) influences the mechanical properties of the niche and, in turn, MuSC self-renewal capabilities. Here we investigated whether Col6 can exert a direct function as a biochemical signal for regulating the stemness and differentiation processes of murine MuSCs and myoblasts. Native Col6, but not its pepsin-resistant fragment, counteracts the early differentiation of myogenic cells by reducing the expression of differentiation marker genes and preserving stemness features, with inhibition of the canonical Wnt pathway. Our data indicate that extracellular Col6 acts as a soluble ligand in delaying myogenic early differentiation by regulating intracellular signals involved in adult myogenesis.

Keywords:  Collagen VI; Extracellular matrix; Muscle stem cells; Skeletal muscle

DOI:  https://doi.org/10.1242/jcs.261419
J Neuromuscul Dis. 2024 Jan 10.

SERCA1 Overexpression in Skeletal Muscle Attenuates Muscle Atrophy and Improves Motor Function in a Mouse Model of ALS.

Davi A G Mázala, Dapeng Chen, Eva R Chin.

   BACKGROUND: Amyotrophic lateral sclerosis (ALS) is characterized by progressive loss of muscle mass and muscle function. Previous work from our lab demonstrated that skeletal muscles from a mouse model of ALS show elevated intracellular calcium (Ca2 +) levels and heightened endoplasmic reticulum (ER) stress.
OBJECTIVE: To investigate whether overexpression of sarcoplasmic reticulum (SR) Ca2 + ATPase 1 (SERCA1) in skeletal muscle would improve intracellular Ca2 + handling, attenuate ER stress, and improve motor function ALS transgenic mice.
METHODS: B6SJL-Tg (SOD1*G93A)1Gur/J (ALS-Tg) mice were bred with skeletal muscle α-actinin SERCA1 overexpressing mice to generate wild type (WT), SERCA1 overexpression (WT/+SERCA1), ALS-Tg, and SERCA1 overexpressing ALS-Tg (ALS-Tg/+SERCA1) mice. Motor function (grip test) was assessed weekly and skeletal muscles were harvested at 16 weeks of age to evaluate muscle mass, SR-Ca2 + ATPase activity, levels of SERCA1 and ER stress proteins - protein disulfide isomerase (PDI), Grp78/BiP, and C/EBP homologous protein (CHOP). Single muscle fibers were also isolated from the flexor digitorum brevis muscle to assess changes in resting and peak Fura-2 ratios.
RESULTS: ALS-Tg/+SERCA1 mice showed improved motor function, delayed onset of disease, and improved muscle mass compared to ALS-Tg. Further, ALS-Tg/+SERCA1 mice returned levels of SERCA1 protein and SR-Ca2 + ATPase activity back to levels in WT mice. Unexpectedly, SERCA-1 overexpression increased levels of the ER stress maker Grp78/BiP in both WT and ALS-Tg mice, while not altering protein levels of PDI or CHOP. Lastly, single muscle fibers from ALS-Tg/+SERCA1 had similar resting but lower peak Fura-2 levels (at 30 Hz and 100 Hz) compared to ALS-Tg mice.
CONCLUSIONS: These data indicate that SERCA1 overexpression attenuates the progressive loss of muscle mass and maintains motor function in ALS-Tg mice while not lowering resting Ca2 + levels or ER stress.

Keywords:  Amyotrophic lateral sclerosis; ER stress; SERCA1; SOD1; calcium

DOI:  https://doi.org/10.3233/JND-230123
Cell Death Dis. 2024 Jan 17. 15(1): 58

The mitochondrial ATP-dependent potassium channel (mitoKATP) controls skeletal muscle structure and function.

Giulia Di Marco, Gaia Gherardi, Agnese De Mario, Ilaria Piazza, Martina Baraldo, Andrea Mattarei, Bert Blaauw, Rosario Rizzuto, Diego De Stefani, Cristina Mammucari.

MitoKATP is a channel of the inner mitochondrial membrane that controls mitochondrial K+ influx according to ATP availability. Recently, the genes encoding the pore-forming (MITOK) and the regulatory ATP-sensitive (MITOSUR) subunits of mitoKATP were identified, allowing the genetic manipulation of the channel. Here, we analyzed the role of mitoKATP in determining skeletal muscle structure and activity. Mitok-/- muscles were characterized by mitochondrial cristae remodeling and defective oxidative metabolism, with consequent impairment of exercise performance and altered response to damaging muscle contractions. On the other hand, constitutive mitochondrial K+ influx by MITOK overexpression in the skeletal muscle triggered overt mitochondrial dysfunction and energy default, increased protein polyubiquitination, aberrant autophagy flux, and induction of a stress response program. MITOK overexpressing muscles were therefore severely atrophic. Thus, the proper modulation of mitoKATP activity is required for the maintenance of skeletal muscle homeostasis and function.

DOI: https://doi.org/10.1038/s41419-024-06426-x
Acta Physiol (Oxf). 2024 Jan 19. e14098

Muscle fibre mitochondrial [Ca2+ ] dynamics during Ca2+ waves in RYR1 gain-of-function mouse.

Rhayanna B Gaglianone, Bradley S Launikonis.

   AIM: A fraction of the Ca2+ released from the sarcoplasmic reticulum (SR) enters mitochondria to transiently increase its [Ca2+ ] ([Ca2+ ]mito ). This transient [Ca2+ ]mito increase may be important in the resynthesis of ATP and other processes. The resynthesis of ATP in the mitochondria generates heat that can lead to hypermetabolic reactions in muscle with ryanodine receptor 1 (RyR1) variants during the cyclic releasing of SR Ca2+ in the presence of a RyR1 agonist. We aimed to analyse whether the mitochondria of RYR1 variant muscle handles Ca2+ differently from healthy muscle.
METHODS: We used confocal microscopy to track mitochondrial and cytoplasmic Ca2+ with fluorescent dyes simultaneously during caffeine-induced Ca2+ waves in extensor digitorum longus muscle fibres from healthy mice and mice heterozygous (HET) for a malignant hyperthermia-causative RYR1 variant.
RESULTS: Mitochondrial Ca2+ -transient peaks trailed the peak of cytoplasmic Ca2+ transients by many seconds with [Ca2+ ]mito not increasing by more than 250 nM. A strong linear relationship between cytoplasmic Ca2+ and [Ca2+ ]mito amplitudes was observed in HET RYR1 KI fibres but not wild type (WT).
CONCLUSION: Our results indicate that [Ca2+ ]mito change within the nM range during SR Ca2+ release. HET fibre mitochondria are more sensitive to SR Ca2+ release flux than WT. This may indicate post-translation modification differences of the mitochondrial Ca2+ uniporter between the genotypes.

Keywords:  Ca2+; confocal; malignant hyperthermia; mitochondria; ryanodine receptor; skeletal muscle

DOI:  https://doi.org/10.1111/apha.14098
Geroscience. 2024 Jan 18.

Senolytic treatment does not mitigate oxidative stress-induced muscle atrophy but improves muscle force generation in CuZn superoxide dismutase knockout mice.

Agnieszka K Borowik, Marcus M Lawrence, Frederick F Peelor, Katarzyna M Piekarz, Abby Crosswhite, Arlan Richardson, Benjamin F Miller, Holly Van Remmen, Jacob L Brown.

  Oxidative stress is associated with tissue dysfunctions that can lead to reduced health. Prior work has shown that oxidative stress contributes to both muscle atrophy and cellular senescence, which is a hallmark of aging that may drive in muscle atrophy and muscle contractile dysfunction. The purpose of the study was to test the hypothesis that cellular senescence contributes to muscle atrophy or weakness. To increase potential senescence in skeletal muscle, we used a model of oxidative stress-induced muscle frailty, the CuZn superoxide dismutase knockout (Sod1KO) mouse. We treated 6-month-old wildtype (WT) and Sod1KO mice with either vehicle or a senolytic treatment of combined dasatinib (5 mg/kg) + quercetin (50 mg/kg) (D + Q) for 3 consecutive days every 15 days. We continued treatment for 7 months and sacrificed the mice at 13 months of age. Treatment with D + Q did not preserve muscle mass, reduce NMJ fragmentation, or alter muscle protein synthesis in Sod1KO mice when compared to the vehicle-treated group. However, we observed an improvement in muscle-specific force generation in Sod1KO mice treated with D + Q when compared to Sod1KO-vehicle mice. Overall, these data suggest that reducing cellular senescence via D + Q is not sufficient to mitigate loss of muscle mass in a mouse model of oxidative stress-induced muscle frailty but may mitigate some aspects of oxidative stress-induced muscle dysfunction.

Keywords:  Cellular senescence; Muscle atrophy; Oxidative stress

DOI:  https://doi.org/10.1007/s11357-024-01070-x
Physiol Rep. 2024 Jan;12(1): e15917

Unraveling the causes of sarcopenia: Roles of neuromuscular junction impairment and mitochondrial dysfunction.

Yanmei Miao, Leiyu Xie, Jiamei Song, Xing Cai, Jinghe Yang, Xinglong Ma, Shaolin Chen, Peng Xie.

  Sarcopenia is a systemic skeletal muscle disease characterized by a decline in skeletal muscle mass and function. Originally defined as an age-associated condition, sarcopenia presently also encompasses muscular atrophy due to various pathological factors, such as intensive care unit-acquired weakness, inactivity, and malnutrition. The exact pathogenesis of sarcopenia is still unknown; herein, we review the pathological roles of the neuromuscular junction and mitochondria in this condition. Sarcopenia is caused by complex and interdependent pathophysiological mechanisms, including aging, neuromuscular junction impairment, mitochondrial dysfunction, insulin resistance, lipotoxicity, endocrine factors, oxidative stress, and inflammation. Among these, neuromuscular junction instability and mitochondrial dysfunction are particularly significant. Dysfunction in neuromuscular junction can lead to muscle weakness or paralysis. Mitochondria, which are plentiful in neurons and muscle fibers, play an important role in neuromuscular junction transmission. Therefore, impairments in both mitochondria and neuromuscular junction may be one of the key pathophysiological mechanisms leading to sarcopenia. Moreover, this article explores the structural and functional alterations in the neuromuscular junction and mitochondria in sarcopenia, suggesting that a deeper understanding of these changes could provide valuable insights for the prevention or treatment of sarcopenia.

Keywords:  Sarcopenia; mitochondrion; neuromuscular junction

DOI:  https://doi.org/10.14814/phy2.15917
Am J Physiol Cell Physiol. 2024 Jan 15.

Ca2+ storage function is altered in the sarcoplasmic reticulum of skeletal muscle lacking mitsugumin 23.

Daiki Watanabe, Miyuki Nishi, Feng Liu, Yuhan Bian, Hiroshi Takeshima.

  Mitsugumin 23 (MG23) has been identified as a ball-shaped cation channel in the sarcoplasmic reticulum (SR) but its physiological role remains unclear. This study aimed to examine the contribution of MG23 to Ca2+ storage function in skeletal muscle by using Mg23-knockout (Mg23-/-) mice. There was no difference in the isometric specific force of the extensor digitorum longus (EDL) and soleus (SOL) muscles between Mg23-/- and wild-type (Wt) mice. In Mg23-/- mice, the calsequestrin 2 content in the EDL muscle and SR Ca2+-ATPase 2 content in the SOL were increased. We have examined SR and myofibril functions using mechanically skinned fibers and determined their fiber types based on the response to Sr2+, which showed that Mg23-/- mice, compared to Wt, had: i) elevated total Ca2+ content in the membranous components including SR, mitochondria and transverse tubular system, referred to as endogenous Ca2+ content, in both type I and II fibers of the EDL and SOL; ii) increased maximal Ca2+ content in both type I and II fibers of the EDL and SOL; iii) decreased SR Ca2+ leakage in type I fibers of the SOL; and iv) enhanced SR Ca2+ uptake in type I fibers of the SOL, although myofibril function was not different in both type I and II fibers of the SOL and EDL muscles. These results suggest that MG23 decreases SR Ca2+ storage in both type I and type II fibers, likely due to increased SR Ca2+ leakage.

Keywords:  calcium; calcium leak channel; mitsugumin 23/TMEM109; skinned fiber

DOI:  https://doi.org/10.1152/ajpcell.00440.2023
Nat Aging. 2024 Jan;4(1): 80-94

Gpcpd1-GPC metabolic pathway is dysfunctional in aging and its deficiency severely perturbs glucose metabolism.

Domagoj Cikes, Michael Leutner, Shane J F Cronin, Maria Novatchkova, Lorenz Pfleger, Radka Klepochová, Benjamin Lair, Marlène Lac, Camille Bergoglio, Nathalie Viguerie, Gerhard Dürnberger, Elisabeth Roitinger, Mihaela Grivej, Eric Rullman, Thomas Gustafsson, Astrid Hagelkruys, Geneviève Tavernier, Virginie Bourlier, Claude Knauf, Michael Krebs, Alexandra Kautzky-Willer, Cedric Moro, Martin Krssak, Michael Orthofer, Josef M Penninger.

Skeletal muscle plays a central role in the regulation of systemic metabolism during lifespan. With aging, this function is perturbed, initiating multiple chronic diseases. Our knowledge of mechanisms responsible for this decline is limited. Glycerophosphocholine phosphodiesterase 1 (Gpcpd1) is a highly abundant muscle enzyme that hydrolyzes glycerophosphocholine (GPC). The physiological functions of Gpcpd1 remain largely unknown. Here we show, in mice, that the Gpcpd1-GPC metabolic pathway is perturbed in aged muscles. Further, muscle-specific, but not liver- or fat-specific, inactivation of Gpcpd1 resulted in severely impaired glucose metabolism. Western-type diets markedly worsened this condition. Mechanistically, Gpcpd1 muscle deficiency resulted in accumulation of GPC, causing an 'aged-like' transcriptomic signature and impaired insulin signaling in young Gpcpd1-deficient muscles. Finally, we report that the muscle GPC levels are markedly altered in both aged humans and patients with type 2 diabetes, displaying a high positive correlation between GPC levels and chronological age. Our findings reveal that the muscle GPCPD1-GPC metabolic pathway has an important role in the regulation of glucose homeostasis and that it is impaired during aging, which may contribute to glucose intolerance in aging.

DOI: https://doi.org/10.1038/s43587-023-00551-6
Cell Rep Med. 2024 Jan 16. pii: S2666-3791(23)00601-8. [Epub ahead of print]5(1): 101372

The impact of bed rest on human skeletal muscle metabolism.

Moritz Eggelbusch, Braeden T Charlton, Alessandra Bosutti, Bergita Ganse, Ifigenia Giakoumaki, Anita E Grootemaat, Paul W Hendrickse, Yorrick Jaspers, Stephan Kemp, Tom J Kerkhoff, Wendy Noort, Michel van Weeghel, Nicole N van der Wel, Julia R Wesseling, Petra Frings-Meuthen, Jörn Rittweger, Edwin R Mulder, Richard T Jaspers, Hans Degens, Rob C I Wüst.

  Insulin sensitivity and metabolic flexibility decrease in response to bed rest, but the temporal and causal adaptations in human skeletal muscle metabolism are not fully defined. Here, we use an integrative approach to assess human skeletal muscle metabolism during bed rest and provide a multi-system analysis of how skeletal muscle and the circulatory system adapt to short- and long-term bed rest (German Clinical Trials: DRKS00015677). We uncover that intracellular glycogen accumulation after short-term bed rest accompanies a rapid reduction in systemic insulin sensitivity and less GLUT4 localization at the muscle cell membrane, preventing further intracellular glycogen deposition after long-term bed rest. We provide evidence of a temporal link between the accumulation of intracellular triglycerides, lipotoxic ceramides, and sphingomyelins and an altered skeletal muscle mitochondrial structure and function after long-term bed rest. An intracellular nutrient overload therefore represents a crucial determinant for rapid skeletal muscle insulin insensitivity and mitochondrial alterations after prolonged bed rest.

Keywords:  GLUT4; bed rest; insulin sensitivity; lipotoxicity; metabolism; mitochondria; nutrient overload; physical inactivity; skeletal muscle

DOI:  https://doi.org/10.1016/j.xcrm.2023.101372
Sci Rep. 2024 01 16. 14(1): 1365

Transcriptional dysregulation of autophagy in the muscle of a mouse model of Duchenne muscular dystrophy.

Ryuta Nakashima, Ryusuke Hosoda, Yuki Tatekoshi, Naotoshi Iwahara, Yukika Saga, Atsushi Kuno.

It has been reported that autophagic activity is disturbed in the skeletal muscles of dystrophin-deficient mdx mice and patients with Duchenne muscular dystrophy (DMD). Transcriptional regulations of autophagy by FoxO transcription factors (FoxOs) and transcription factor EB (TFEB) play critical roles in adaptation to cellular stress conditions. Here, we investigated whether autophagic activity is dysregulated at the transcription level in dystrophin-deficient muscles. Expression levels of autophagy-related genes were globally decreased in tibialis anterior and soleus muscles of mdx mice compared with those of wild-type mice. DNA microarray data from the NCBI database also showed that genes related to autophagy were globally downregulated in muscles from patients with DMD. These downregulated genes are known as targets of FoxOs and TFEB. Immunostaining showed that nuclear localization of FoxO1 and FoxO3a was decreased in mdx mice. Western blot analyses demonstrated increases in phosphorylation levels of FoxO1 and FoxO3a in mdx mice. Nuclear localization of TFEB was also reduced in mdx mice, which was associated with elevated phosphorylation levels of TFEB. Collectively, the results suggest that autophagy is disturbed in dystrophin-deficient muscles via transcriptional downregulation due to phosphorylation-mediated suppression of FoxOs and TFEB.

DOI: https://doi.org/10.1038/s41598-024-51746-9
Front Endocrinol (Lausanne). 2023 ;14 1287972

Mechanism and physical activities in bone-skeletal muscle crosstalk.

Zhonghan Zhao, Kai Yan, Qiao Guan, Qiang Guo, Can Zhao.

  Bone and skeletal muscle work in coordination to maintain the function of the musculoskeletal system, in which skeletal muscle contraction drives the movement of the bone lever system while bone provides insert sites for skeletal muscle through the bone-muscle junction. Existing evidence suggests that factors secreted by skeletal muscle and bone mediate the interaction between the two tissues. Herein, we focused on the relationship between skeletal muscle and bone and the underlying mechanism of the interaction. Exercise can promote bone strength and secrete osteocalcin and insulin-like growth factor I into the blood, thus improving muscle quality. In addition, exercise can also promote myostatin, interleukin-6, Irisin, and apelin in muscles to enter the blood so that they can act on bones to maintain the balance between bone absorption and bone formation. There is a special regulatory axis interleukin-6/osteocalcin between myokines and osteokines, which is mainly influenced by exercise. Therefore, we pay attention to the important factors in the bone-muscle intersection that are affected by exercise, which were found or their functions were expanded, which strengthened the connection between organs of the whole body, highlighting the importance of exercise and contributing to the diagnosis, prevention, and treatment of osteoporosis and sarcopenia in the clinic.

Keywords:  IGF-1; IL-6; OCN; bone-skeletal muscle crosstalk; irisin; myostatin; physical activities; sclerostin

DOI:  https://doi.org/10.3389/fendo.2023.1287972
Nat Metab. 2024 Jan 19.

Depletion of SAM leading to loss of heterochromatin drives muscle stem cell ageing.

Jengmin Kang, Daniel I Benjamin, Soochi Kim, Jayesh S Salvi, Gurkamal Dhaliwal, Richard Lam, Armon Goshayeshi, Jamie O Brett, Ling Liu, Thomas A Rando.

The global loss of heterochromatin during ageing has been observed in eukaryotes from yeast to humans, and this has been proposed as one of the causes of ageing. However, the cause of this age-associated loss of heterochromatin has remained enigmatic. Here we show that heterochromatin markers, including histone H3K9 di/tri-methylation and HP1, decrease with age in muscle stem cells (MuSCs) as a consequence of the depletion of the methyl donor S-adenosylmethionine (SAM). We find that restoration of intracellular SAM in aged MuSCs restores heterochromatin content to youthful levels and rejuvenates age-associated features, including DNA damage accumulation, increased cell death, and defective muscle regeneration. SAM is not only a methyl group donor for transmethylation, but it is also an aminopropyl donor for polyamine synthesis. Excessive consumption of SAM in polyamine synthesis may reduce its availability for transmethylation. Consistent with this premise, we observe that perturbation of increased polyamine synthesis by inhibiting spermidine synthase restores intracellular SAM content and heterochromatin formation, leading to improvements in aged MuSC function and regenerative capacity in male and female mice. Together, our studies demonstrate a direct causal link between polyamine metabolism and epigenetic dysregulation during murine MuSC ageing.

DOI: https://doi.org/10.1038/s42255-023-00955-z
Proc Natl Acad Sci U S A. 2024 Jan 23. 121(4): e2308960121

PROKR1-CREB-NR4A2 axis for oxidative muscle fiber specification and improvement of metabolic function.

Jongsoo Mok, Jeong Hwan Park, Su Chong Yeom, Joonghoon Park.

  Metabolic disorders are characterized by an imbalance in muscle fiber composition, and a potential therapeutic approach involves increasing the proportion of oxidative muscle fibers. Prokineticin receptor 1 (PROKR1) is a G protein-coupled receptor that plays a role in various metabolic functions, but its specific involvement in oxidative fiber specification is not fully understood. Here, we investigated the functions of PROKR1 in muscle development to address metabolic disorders and muscular diseases. A meta-analysis revealed that the activation of PROKR1 upregulated exercise-responsive genes, particularly nuclear receptor subfamily 4 group A member 2 (NR4A2). Further investigations using ChIP-PCR, luciferase assays, and pharmacological interventions demonstrated that PROKR1 signaling enhanced NR4A2 expression by Gs-mediated phosphorylation of cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB) in both mouse and human myotubes. Genetic and pharmacological interventions showed that the PROKR1-NR4A2 axis promotes the specification of oxidative muscle fibers in both myocytes by promoting mitochondrial biogenesis and metabolic function. Prokr1-deficient mice displayed unfavorable metabolic phenotypes, such as lower lean mass, enlarged muscle fibers, impaired glucose, and insulin tolerance. These mice also exhibited reduced energy expenditure and exercise performance. The deletion of Prokr1 resulted in decreased oxidative muscle fiber composition and reduced activity in the Prokr1-CREB-Nr4a2 pathway, which were restored by AAV-mediated Prokr1 rescue. In summary, our findings highlight the activation of the PROKR1-CREB-NR4A2 axis as a mechanism for increasing the oxidative muscle fiber composition, which positively impacts overall metabolic function. This study lays an important scientific foundation for the development of effective muscular-metabolic therapeutics with unique mechanisms of action.

Keywords:  NR4A2; PROKR1; oxidative muscle fiber

DOI:  https://doi.org/10.1073/pnas.2308960121
Biochim Biophys Acta Mol Basis Dis. 2024 Jan 11. pii: S0925-4439(24)00008-5. [Epub ahead of print]1870(3): 167023

HDAC9 inhibition reduces skeletal muscle atrophy and enhances regeneration in mice with cigarette smoke-induced COPD.

Guixian Zheng, Chao Li, Xiaoli Chen, Zhaohui Deng, Ting Xie, Zengyu Huo, Xinyan Wei, Yanbing Huang, Xia Zeng, Yu Luo, Jing Bai.

  Cigarette smoke (CS) is the major risk factor for chronic obstructive pulmonary disease (COPD), and sarcopenia is one of the significant comorbidities of COPD. However, the pathogenesis of CS-related deficient skeletal muscle regeneration has yet to be clarified. The impact of CS on myoblast differentiation was examined, and then we determined which HDAC influenced the myogenic process and muscle atrophy in vitro and in vivo. Finally, we further investigated the potential mechanisms via RNA sequencing. Long-term CS exposure activated skeletal muscle primary satellite cells (SCs) while inhibiting differentiation, and defective myogenesis was also observed in C2C12 cells treated with CS extract (CSE). The level of HDAC9 changed in vitro and in vivo in CS exposure models as well as COPD patients, as detected by bioinformatics analysis. Our data showed that CSE impaired myogenic capacity and myotube formation in C2C12 cells via HDAC9. Moreover, inhibition of HDAC9 in mice exposed to CS prevented skeletal muscle dysfunction and promoted SC differentiation. The results of RNA-Seq analysis and verification indicated that HDAC9 knockout improved muscle differentiation in CS-exposed mice, probably by acting on the AKT/mTOR pathway and inhibiting the P53/P21 pathway. More importantly, the serum of HDAC9 KO mice exposed to CS alleviated the differentiation impairment of C2C12 cells caused by serum intervention in CS-exposed mice, and this effect was inhibited by LY294002 (an AKT/mTOR pathway inhibitor). These results suggest that HDAC9 plays an essential role in the defective regeneration induced by chronic exposure to CS.

Keywords:  COPD; Cigarette smoke; HDAC9; Regeneration; Skeletal muscle atrophy

DOI:  https://doi.org/10.1016/j.bbadis.2024.167023
Cell Stem Cell. 2024 Jan 10. pii: S1934-5909(23)00441-1. [Epub ahead of print]

Exercise-induced Musclin determines the fate of fibro-adipogenic progenitors to control muscle homeostasis.

Xia Kang, Jin Qian, You-Xing Shi, Xu-Ting Bian, Li-Dan Zhang, Gao-Ming Li, Li-Ting Wang, Jing Zhao, Zhen-Yu Dong, Meng-Meng Yang, Yu-Jia-Nan Chen, Kang-Lai Tang, Hong-Ming Miao.

  The effects of exercise on fibro-adipogenic progenitors (FAPs) are unclear, and the direct molecular link is still unknown. In this study, we reveal that exercise reduces the frequency of FAPs and attenuates collagen deposition and adipose formation in injured or disused muscles through Musclin. Mechanistically, Musclin inhibits FAP proliferation and promotes apoptosis in FAPs by upregulating FILIP1L. Chromatin immunoprecipitation (ChIP)-qPCR confirms that FoxO3a is the transcription factor of FILIP1L. In addition, the Musclin/FILIP1L pathway facilitates the phagocytosis of apoptotic FAPs by macrophages through downregulating the expression of CD47. Genetic ablation of FILIP1L in FAPs abolishes the effects of exercise or Musclin on FAPs and the benefits on the reduction of fibrosis and fatty infiltration. Overall, exercise forms a microenvironment of myokines in muscle and prevents the abnormal accumulation of FAPs in a Musclin/FILIP1L-dependent manner. The administration of exogenous Musclin exerts a therapeutic effect, demonstrating a potential therapeutic approach for muscle atrophy or acute muscle injury.

Keywords:  Musclin; apoptosis; exercise; fatty infiltration; fibro-adipogenic progenitors; fibrosis; phagocytosis; proliferation

DOI:  https://doi.org/10.1016/j.stem.2023.12.011
Sci Rep. 2024 Jan 19. 14(1): 1713

AMPKα2 regulates fasting-induced hyperketonemia by suppressing SCOT ubiquitination and degradation.

Lingxue Zhang, Yanqiao Lu, Junqing An, Yin Wu, Zhixue Liu, Ming-Hui Zou.

Ketone bodies serve as an energy source, especially in the absence of carbohydrates or in the extended exercise. Adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a crucial energy sensor that regulates lipid and glucose metabolism. However, whether AMPK regulates ketone metabolism in whole body is unclear even though AMPK regulates ketogenesis in liver. Prolonged resulted in a significant increase in blood and urine levels of ketone bodies in wild-type (WT) mice. Interestingly, fasting AMPKα2-/- and AMPKα1-/- mice exhibited significantly higher levels of ketone bodies in both blood and urine compared to fasting WT mice. BHB tolerance assays revealed that both AMPKα2-/- and AMPKα1-/- mice exhibited slower ketone consumption compared to WT mice, as indicated by higher blood BHB or urine BHB levels in the AMPKα2-/- and AMPKα1-/- mice even after the peak. Interestingly, fasting AMPKα2-/- and AMPKα1-/- mice exhibited significantly higher levels of ketone bodies in both blood and urine compared to fasting WT mice. . Specifically, AMPKα2ΔMusc mice showed approximately a twofold increase in blood BHB levels, and AMPKα2ΔMyo mice exhibited a 1.5-fold increase compared to their WT littermates after a 48-h fasting. However, blood BHB levels in AMPKα1ΔMusc and AMPKα1ΔMyo mice were as same as in WT mice. Notably, AMPKα2ΔMusc mice demonstrated a slower rate of BHB consumption in the BHB tolerance assay, whereas AMPKα1ΔMusc mice did not show such an effect. Declining rates of body weights and blood glucoses were similar among all the mice. Protein levels of SCOT, the rate-limiting enzyme of ketolysis, decreased in skeletal muscle of AMPKα2-/- mice. Moreover, SCOT protein ubiquitination increased in C2C12 cells either transfected with kinase-dead AMPKα2 or subjected to AMPKα2 inhibition. AMPKα2 physiologically binds and stabilizes SCOT, which is dependent on AMPKα2 activity.

DOI: https://doi.org/10.1038/s41598-023-49991-5
Elife. 2024 Jan 18. pii: RP88250. [Epub ahead of print]12

An optogenetic cell therapy to restore control of target muscles in an aggressive mouse model of amyotrophic lateral sclerosis.

J Barney Bryson, Alexandra Kourgiantaki, Dai Jiang, Andreas Demosthenous, Linda Greensmith.

  Breakdown of neuromuscular junctions (NMJs) is an early pathological hallmark of amyotrophic lateral sclerosis (ALS) that blocks neuromuscular transmission, leading to muscle weakness, paralysis and, ultimately, premature death. Currently, no therapies exist that can prevent progressive motor neuron degeneration, muscle denervation, or paralysis in ALS. Here, we report important advances in the development of an optogenetic, neural replacement strategy that can effectively restore innervation of severely affected skeletal muscles in the aggressive SOD1G93A mouse model of ALS, thus providing an interface to selectively control the function of targeted muscles using optical stimulation. We also identify a specific approach to confer complete survival of allogeneic replacement motor neurons. Furthermore, we demonstrate that an optical stimulation training paradigm can prevent atrophy of reinnervated muscle fibers and results in a tenfold increase in optically evoked contractile force. Together, these advances pave the way for an assistive therapy that could benefit all ALS patients.

Keywords:  ALS; Amyotrophic Lateral Sclerosis; cell transplant; motor neurons; mouse; optogenetics; paralysis; regenerative medicine; stem cells

DOI:  https://doi.org/10.7554/eLife.88250
Cytoskeleton (Hoboken). 2024 Jan 15.

Duchenne and Becker muscular dystrophy: Cellular mechanisms, image analysis, and computational models: A review.

J F Escobar-Huertas, Juan Jairo Vaca-González, Johana María Guevara, Angelica M Ramirez-Martinez, Olfa Trabelsi, D A Garzón-Alvarado.

  The muscle is the principal tissue that is capable to transform potential energy into kinetic energy. This process is due to the transformation of chemical energy into mechanical energy to enhance the movements and all the daily activities. However, muscular tissues can be affected by some pathologies associated with genetic alterations that affect the expression of proteins. As the muscle is a highly organized structure in which most of the signaling pathways and proteins are related to one another, pathologies may overlap. Duchenne muscular dystrophy (DMD) is one of the most severe muscle pathologies triggering degeneration and muscle necrosis. Several mathematical models have been developed to predict muscle response to different scenarios and pathologies. The aim of this review is to describe DMD and Becker muscular dystrophy in terms of cellular behavior and molecular disorders and to present an overview of the computational models implemented to understand muscle behavior with the aim of improving regenerative therapy.

Keywords:  Duchenne muscular dystrophy; computational models for muscle; muscle degeneration; muscle dystrophy

DOI:  https://doi.org/10.1002/cm.21826
J Clin Endocrinol Metab. 2024 Jan 18. pii: dgae032. [Epub ahead of print]

Acute Exercise Increases GDF15 and Unfolded Protein Response/Integrated Stress Response in Muscle in Type 2 diabetes.

Rugivan Sabaratnam, Jonas M Kristensen, Andreas J T Pedersen, Rikke Kruse, Aase Handberg, Jørgen F P Wojtaszewski, Kurt Højlund.

   CONTEXT: Regular exercise is a key prevention strategy for obesity and type 2 diabetes (T2D). Exerkines secreted in response to exercise or recovery may contribute to improved systemic metabolism. Conversely, an impaired exerkine response to exercise and recovery may contribute to cardiometabolic diseases.
OBJECTIVE: We investigated if the exercise-induced regulation of the exerkine, growth/differentiation factor 15 (GDF15) and its putative upstream regulators of the unfolded protein response (UPR)/integrated stress response (ISR) is impaired in skeletal muscle in patients with T2D compared with weight-matched glucose-tolerant men.
METHODS: Thirteen male patients with T2D and 14 age- and weight-matched overweight/obese glucose-tolerant men exercised at 70% of VO2max for 1-h. Blood and skeletal muscle biopsies were sampled before, immediately after, and 3-h into recovery. Serum and muscle transcript levels of GDF15 and key markers of UPR/ISR were determined. Additionally, protein/phosphorylation levels of key regulators in UPR/ISR were investigated.
RESULTS: Acute exercise increased muscle gene expression and serum GDF15 levels in both groups. In recovery, muscle expression of GDF15 decreased toward baseline, whereas serum GDF15 remained elevated. In both groups, acute exercise increased the expression of UPR/ISR markers, including ATF4, CHOP, EIF2K3 (encoding PERK) and PPP1R15A (encoding GADD34), of which only CHOP remained elevated 3-h into recovery. Downstream molecules of the UPR/ISR including XBP1-U, XBP1-S, and EDEM1 were increased with exercise and 3-h into recovery in both groups. The phosphorylation levels of eIF2α-Ser51, a common marker of UPR and ISR, increased immediately after exercise in controls, but decreased 3-h into recovery in both groups.
CONCLUSION: In conclusion, exercise-induced regulation of GDF15 and key markers of UPR/ISR are not compromised in patients with type 2 diabetes compared with weight-matched controls.

Keywords:  GDF15; Type 2 diabetes; UPR/ISR; exerkine; obesity; skeletal muscle

DOI:  https://doi.org/10.1210/clinem/dgae032
Front Med (Lausanne). 2023 ;10 1330893

Editorial: Molecular and physiological aspects of sarcopenia in the older person: mechanisms, diagnostics and therapy.

Guilherme Eustáquio Furtado, Marco Vincenzo Narici, Tzvi Dwolatzky.



Keywords:  aging and muscle health; geriatric research; inflammaging; muscle atrophy mechanisms; muscle mass assessment; sarcopenia

DOI:  https://doi.org/10.3389/fmed.2023.1330893
Free Radic Biol Med. 2024 Jan 17. pii: S0891-5849(24)00023-6. [Epub ahead of print]

Exercise-induced redox modulation as a mediator of DNA methylation in health maintenance and disease prevention.

Daniela Caporossi, Ivan Dimauro.

  The evidence for physical activity (PA) as a major public health preventive approach and a potent medical therapy has increased exponentially in the last decades. The biomolecular mechanisms supporting the associations between PA and/or structured exercise training with health maintenance and disease prevention are not completely characterized. However, increasing evidence pointed out the role of epigenetic modifications in exercise adaptation and health-enhancing PA throughout life, DNA methylation being the most intensely studied epigenetic modification induced by acute and chronic exercise. The current data on the modulation of DNA methylation determined by physically active behavior or exercise interventions points out genes related to energy regulation, mitochondrial function, and biosynthesis, as well as muscle regeneration, calcium signaling pathways, and brain plasticity, all consistent with the known exercise-induced redox signaling and/or reactive oxygen species (ROS) unbalance. Thus, the main focus of this review is to discuss the role of ROS and redox-signaling on DNA methylation profile and its impact on exercise-induced health benefits in humans.

Keywords:  Ageing; DNA methylation; Diseases; Exercise; Reactive oxygen species; Redox signaling

DOI:  https://doi.org/10.1016/j.freeradbiomed.2024.01.023
Sci Transl Med. 2024 Jan 17. 16(730): eadf1691

Small-molecule inhibition of glycogen synthase 1 for the treatment of Pompe disease and other glycogen storage disorders.

Julie C Ullman, Kevin T Mellem, Yannan Xi, Vyas Ramanan, Hanne Merritt, Rebeca Choy, Tarunmeet Gujral, Lyndsay E A Young, Kerrigan Blake, Samnang Tep, Julian R Homburger, Adam O'Regan, Sandya Ganesh, Perryn Wong, Terrence F Satterfield, Baiwei Lin, Eva Situ, Cecile Yu, Bryan Espanol, Richa Sarwaikar, Nathan Fastman, Christos Tzitzilonis, Patrick Lee, Daniel Reiton, Vivian Morton, Pam Santiago, Walter Won, Hannah Powers, Beryl B Cummings, Maarten Hoek, Robert R Graham, Sanjay J Chandriani, Russell Bainer, Anna A DePaoli-Roach, Peter J Roach, Thomas D Hurley, Ramon C Sun, Matthew S Gentry, Christopher Sinz, Ryan A Dick, Sarah B Noonberg, David T Beattie, David J Morgans, Eric M Green.

Glycogen synthase 1 (GYS1), the rate-limiting enzyme in muscle glycogen synthesis, plays a central role in energy homeostasis and has been proposed as a therapeutic target in multiple glycogen storage diseases. Despite decades of investigation, there are no known potent, selective small-molecule inhibitors of this enzyme. Here, we report the preclinical characterization of MZ-101, a small molecule that potently inhibits GYS1 in vitro and in vivo without inhibiting GYS2, a related isoform essential for synthesizing liver glycogen. Chronic treatment with MZ-101 depleted muscle glycogen and was well tolerated in mice. Pompe disease, a glycogen storage disease caused by mutations in acid α glucosidase (GAA), results in pathological accumulation of glycogen and consequent autophagolysosomal abnormalities, metabolic dysregulation, and muscle atrophy. Enzyme replacement therapy (ERT) with recombinant GAA is the only approved treatment for Pompe disease, but it requires frequent infusions, and efficacy is limited by suboptimal skeletal muscle distribution. In a mouse model of Pompe disease, chronic oral administration of MZ-101 alone reduced glycogen buildup in skeletal muscle with comparable efficacy to ERT. In addition, treatment with MZ-101 in combination with ERT had an additive effect and could normalize muscle glycogen concentrations. Biochemical, metabolomic, and transcriptomic analyses of muscle tissue demonstrated that lowering of glycogen concentrations with MZ-101, alone or in combination with ERT, corrected the cellular pathology in this mouse model. These data suggest that substrate reduction therapy with GYS1 inhibition may be a promising therapeutic approach for Pompe disease and other glycogen storage diseases.

DOI: https://doi.org/10.1126/scitranslmed.adf1691
Acta Physiol (Oxf). 2024 Jan 20. e14095

Acute exercise-induced release of innate immune proteins via small extracellular vesicles changes with aerobic fitness and age.

Mee Chee Chong, Anup D Shah, Ralf B Schittenhelm, Anabel Silva, Patrick F James, Sam Shi Xuan Wu, Jason Howitt.

   AIM: Physical exercise triggers the secretion of small extracellular vesicles (sEVs) into the circulation in humans, enabling signalling crosstalk between tissues. Exercise-derived EVs and their cargo have been proposed to mediate adaptations to exercise; however, our understanding of how exercise-derived EV protein cargo is modulated by factors such as aerobic fitness and age of an individual is currently unknown. Here, we examined the circulating sEV proteome following aerobic exercise in healthy males of different ages and aerobic fitness to understand exercise-induced EV response during the aging process.
METHODS: Twenty-eight healthy men completed a bout of 20-min cycling exercise at 70% estimated VO2peak . Small EVs were isolated from blood samples collected before and immediately after exercise, and then quantified using particle analysis and Western blotting. Small EV proteome was examined using quantitative proteomic analysis.
RESULTS: We identified a significant increase in 13 proteins in small plasma EVs following moderate-to-vigorous intensity exercise. We observed distinct changes in sEV proteome after exercise in young, mature, unfit, and fit individuals, highlighting the impact of aerobic fitness and age on sEV protein secretion. Functional enrichment and pathway analysis identified that the majority of the significantly altered sEV proteins are associated with the innate immune system, including proteins known to be damage-associated molecular patterns (DAMPs).
CONCLUSION: Together, our findings suggest that exercise-evoked acute stress can positively challenge the innate immune system through the release of signalling molecules such as DAMPs in sEVs, proposing a novel EV-based mechanism for moderate-to-vigorous intensity exercise in immune surveillance pathways.

Keywords:  DAMPs; aging; exosomes; immune surveillance; inflammaging

DOI:  https://doi.org/10.1111/apha.14095
Acta Neuropathol. 2024 Jan 19. 147(1): 19

Multi-level profiling unravels mitochondrial dysfunction in myotonic dystrophy type 2.

Felix Kleefeld, Rita Horvath, Iago Pinal-Fernandez, Andrew L Mammen, Maria Casal-Dominguez, Denisa Hathazi, Sarah Melchert, Katrin Hahn, Albert Sickmann, Claudia Muselmann-Genschow, Andreas Hentschel, Corinna Preuße, Andreas Roos, Benedikt Schoser, Werner Stenzel.

  Myotonic dystrophy type 2 (DM2) is an autosomal-dominant multisystemic disease with a core manifestation of proximal muscle weakness, muscle atrophy, myotonia, and myalgia. The disease-causing CCTG tetranucleotide expansion within the CNBP gene on chromosome 3 leads to an RNA-dominated spliceopathy, which is currently untreatable. Research exploring the pathophysiological mechanisms in myotonic dystrophy type 1 has resulted in new insights into disease mechanisms and identified mitochondrial dysfunction as a promising therapeutic target. It remains unclear whether similar mechanisms underlie DM2 and, if so, whether these might also serve as potential therapeutic targets. In this cross-sectional study, we studied DM2 skeletal muscle biopsy specimens on proteomic, molecular, and morphological, including ultrastructural levels in two separate patient cohorts consisting of 8 (explorative cohort) and 40 (confirmatory cohort) patients. Seven muscle biopsy specimens from four female and three male DM2 patients underwent proteomic analysis and respiratory chain enzymology. We performed bulk RNA sequencing, immunoblotting of respiratory chain complexes, mitochondrial DNA copy number determination, and long-range PCR (LR-PCR) to study mitochondrial DNA deletions on six biopsies. Proteomic and transcriptomic analyses revealed a downregulation of essential mitochondrial proteins and their respective RNA transcripts, namely of subunits of respiratory chain complexes I, III, and IV (e.g., mt-CO1, mt-ND1, mt-CYB, NDUFB6) and associated translation factors (TACO1). Light microscopy showed mitochondrial abnormalities (e.g., an age-inappropriate amount of COX-deficient fibers, subsarcolemmal accumulation) in most biopsy specimens. Electron microscopy revealed widespread ultrastructural mitochondrial abnormalities, including dysmorphic mitochondria with paracrystalline inclusions. Immunofluorescence studies with co-localization of autophagy (p62, LC-3) and mitochondrial marker proteins (TOM20, COX-IV), as well as immunohistochemistry for mitophagy marker BNIP3 indicated impaired mitophagic flux. Immunoblotting and LR-PCR did not reveal significant differences between patients and controls. In contrast, mtDNA copy number measurement showed a reduction of mtDNA copy numbers in the patient group compared to controls. This first multi-level study of DM2 unravels thus far undescribed functional and structural mitochondrial abnormalities. However, the molecular link between the tetranucleotide expansion and mitochondrial dysfunction needs to be further elucidated.

Keywords:  Mitochondrial dysfunction; Myotonic dystrophy type 2; Proximal myotonic myopathy

DOI:  https://doi.org/10.1007/s00401-023-02673-y
J Cell Biochem. 2024 Jan 16.

The BCKDH kinase inhibitor BT2 promotes BCAA disposal and mitochondrial proton leak in both insulin-sensitive and insulin-resistant C2C12 myotubes.

Caroline N Rivera, Carly E Smith, Lillian V Draper, Madison E Kee, Norah E Cook, Macey R McGovern, Rachel M Watne, Andrew J Wommack, Roger A Vaughan.

  Elevated circulating branched-chain amino acids (BCAAs) have been correlated with the severity of insulin resistance, leading to recent investigations that stimulate BCAA metabolism for the potential benefit of metabolic diseases. BT2 (3,6-dichlorobenzo[b]thiophene-2-carboxylic acid), an inhibitor of branched-chain ketoacid dehydrogenase kinase, promotes BCAA metabolism by enhancing BCKDH complex activity. The purpose of this report was to investigate the effects of BT2 on mitochondrial and glycolytic metabolism, insulin sensitivity, and de novo lipogenesis both with and without insulin resistance. C2C12 myotubes were treated with or without low or moderate levels of BT2 with or without insulin resistance. Western blot and quantitative real-time polymerase chain reaction were used to assess protein and gene expression, respectively. Mitochondrial, nuclei, and lipid content were measured using fluorescent staining and microscopy. Cell metabolism was assessed via oxygen consumption and extracellular acidification rate. Liquid chromatography-mass spectrometry was used to quantify BCAA media content. BT2 treatment consistently promoted mitochondrial uncoupling following 24-h treatment, which occurred largely independent of changes in expressional profiles associated with mitochondrial biogenesis, mitochondrial dynamics, BCAA catabolism, insulin sensitivity, or lipogenesis. Acute metabolic studies revealed a significant and dose-dependent effect of BT2 on mitochondrial proton leak, suggesting BT2 functions as a small-molecule uncoupler. Additionally, BT2 treatment consistently and dose-dependently reduced extracellular BCAA levels without altering expression of BCAA catabolic enzymes or pBCKDHa activation. BT2 appears to act as a small-molecule mitochondrial uncoupler that promotes BCAA utilization, though the interplay between these two observations requires further investigation.

Keywords:  diabetes; insulin resistance; isoleucine; leucine; pAkt/Akt; skeletal muscle; valine

DOI:  https://doi.org/10.1002/jcb.30520
Acta Physiol (Oxf). 2024 Jan 19. e14083

Exercise influence on monocarboxylate transporter 1 (MCT1) and 4 (MCT4) in the skeletal muscle: A systematic review.

José Antonio Benítez-Muñoz, Rocío Cupeiro, Jacobo Á Rubio-Arias, Teresa Amigo, Domingo González-Lamuño.

  This review aims to systematically analyze the effect of exercise on muscle MCT protein levels and mRNA expression of their respective genes, considering exercise intensity, and duration (single-exercise session and training program) in humans and rodents, to observe whether both models offer aligned results. The review also aims to report methodological aspects that need to be improved in future studies. A systematic search was conducted in the PubMed and Web of Science databases, and the Preferred Reporting Items for Systematic review and Meta-Analyses (PRISMA) checklist was followed. After applying inclusion and exclusion criteria, 41 studies were included and evaluated using the Cochrane collaboration tool for risk of bias assessment. The main findings indicate that exercise is a powerful stimulus to increase MCT1 protein content in human muscle. MCT4 protein level increases can also be observed after a training program, although its responsiveness is lower compared to MCT1. Both transporters seem to change independently of exercise intensity, but the responses that occur with each intensity and each duration need to be better defined. The effect of exercise on muscle mRNA results is less defined, and more research is needed especially in humans. Moreover, results in rodents only agree with human results on the effect of a training program on MCT1 protein levels, indicating increases in both. Finally, we addressed important and feasible methodological aspects to improve the design of future studies.

Keywords:  ARNm expression; lactate; lactate shuttle; protein levels; sport; training

DOI:  https://doi.org/10.1111/apha.14083
Nat Metab. 2024 Jan 19.

An ETFDH-driven metabolon supports OXPHOS efficiency in skeletal muscle by regulating coenzyme Q homeostasis.

Juan Cruz Herrero Martín, Beñat Salegi Ansa, Gerardo Álvarez-Rivera, Sonia Domínguez-Zorita, Pilar Rodríguez-Pombo, Belén Pérez, Enrique Calvo, Alberto Paradela, David G Miguez, Alejandro Cifuentes, José M Cuezva, Laura Formentini.

Coenzyme Q (Q) is a key lipid electron transporter, but several aspects of its biosynthesis and redox homeostasis remain undefined. Various flavoproteins reduce ubiquinone (oxidized form of Q) to ubiquinol (QH2); however, in eukaryotes, only oxidative phosphorylation (OXPHOS) complex III (CIII) oxidizes QH2 to Q. The mechanism of action of CIII is still debated. Herein, we show that the Q reductase electron-transfer flavoprotein dehydrogenase (ETFDH) is essential for CIII activity in skeletal muscle. We identify a complex (comprising ETFDH, CIII and the Q-biosynthesis regulator COQ2) that directs electrons from lipid substrates to the respiratory chain, thereby reducing electron leaks and reactive oxygen species production. This metabolon maintains total Q levels, minimizes QH2-reductive stress and improves OXPHOS efficiency. Muscle-specific Etfdh-/- mice develop myopathy due to CIII dysfunction, indicating that ETFDH is a required OXPHOS component and a potential therapeutic target for mitochondrial redox medicine.

DOI: https://doi.org/10.1038/s42255-023-00956-y
Diabetes. 2024 Feb 01. 73(2): 162-168

Molecular Insights From Multiomics Studies of Physical Activity.

Wei Wei, Steffen H Raun, Jonathan Z Long.

Physical activity confers systemic health benefits and provides powerful protection against disease. There has been tremendous interest in understanding the molecular effectors of exercise that mediate these physiologic effects. The modern growth of multiomics technologies-including metabolomics, proteomics, phosphoproteomics, lipidomics, single-cell RNA sequencing, and epigenomics-has provided unparalleled opportunities to systematically investigate the molecular changes associated with physical activity on an organism-wide scale. Here, we discuss how multiomics technologies provide new insights into the systemic effects of physical activity, including the integrative responses across organs as well as the molecules and mechanisms mediating tissue communication during exercise. We also highlight critical unanswered questions that can now be addressed using these high-dimensional tools and provide perspectives on fertile future research directions.

DOI: https://doi.org/10.2337/dbi23-0004