bims-moremu 2023-09-10 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–09–10
34 papers selected by
Anna Vainshtein, Craft Science Inc.

Metallothionein Gene Deficiency Facilitates the Differentiation of C2C12 Myoblasts into Slow-Twitch Myotubes.
Sex differences in muscle protein expression and DNA methylation in response to exercise training.
Lineage tracing of newly accrued nuclei in skeletal myofibers uncovers distinct transcripts and interplay between nuclear populations.
Nonsense-mediated mRNA decay suppresses injury-induced muscle regeneration via inhibiting MyoD transcriptional activity.
Radiation induces long-term muscle fibrosis and promotes a fibrotic phenotype in fibro-adipogenic progenitors.
Caveolin-3 loss linked with the P104L LGMD-1C mutation modulates skeletal muscle mTORC1 signalling and cholesterol homeostasis.
Prolonged mechanical muscle loading increases mechanosensor gene and protein levels and causes a moderate fast-to-slow fiber type switch in mice.
Effects of Aging on Collagen in the Skeletal Muscle of Mice.
Mitochondrial Properties in Skeletal Muscle Fiber.
Foxo3 Knockdown Mediates Decline of Myod1 and Myog Reducing Myoblast Conversion to Myotubes.
Alignment, cross-linking, and beyond: A collagen architect's guide to the skeletal muscle extracellular matrix.
A systematic review and meta-analysis of the SIRT1 response to exercise.
The Effect of Gradual Ovarian Failure on Dynamic Muscle Function and the Role of High Intensity Interval Training on Mitigating Impairments.
Reduced Expression of Septin7 Hinders Skeletal Muscle Regeneration.
In vitro-generated human muscle reserve cells are heterogeneous for Pax7 with distinct molecular states and metabolic profiles.
Downregulation of PGC-1α during cisplatin-induced muscle atrophy in murine skeletal muscle.
Biochemical and proteomic insights into sarcoplasmic reticulum Ca2+-ATPase complexes in skeletal muscles.
The transcriptional regulator KLF15 is necessary for myoblast differentiation and muscle regeneration by activating FKBP5.
Loss of Ptpmt1 limits mitochondrial utilization of carbohydrates and leads to muscle atrophy and heart failure in tissue-specific knockout mice.
Androgen Action on Myogenesis Throughout the Lifespan; Comparison with Neurogenesis.
Function of a mutant ryanodine receptor (T4709M) linked to congenital myopathy.
AMPK Mediates Early Activation of the Unfolded Protein Response through a Positive Feedback Loop in Palmitate-Treated Muscle Cells.
Soluble RAGE and Skeletal Muscle Tissue RAGE Expression Profiles in Lean and Obese Young Adults Across Differential Aerobic Exercise Intensities.
Structural and functional impairments of skeletal muscle in patients with post-acute sequelae of SARS-CoV-2 infection.
Detecting the vitamin D receptor (VDR) protein in mouse and human skeletal muscle: Strain-specific, species-specific and inter-individual variation.
Decoding the transcriptome of Duchenne muscular dystrophy to the single nuclei level reveals clinical-genetic correlations.
PAX7, a Key for Myogenesis Modulation in Muscular Dystrophies through Multiple Signaling Pathways: A Systematic Review.
Increasing enzyme mannose-6-phosphate levels but not miglustat co-administration enhances the efficacy of enzyme replacement therapy in Pompe mice.
Sarcopenia and malignancies: epidemiology, clinical classification and implications.
Disruption of Hepatic Mitochondrial Pyruvate and Amino Acid Metabolism Impairs Gluconeogenesis and Endurance Exercise Capacity in Mice.
Mitochondrial Dysfunction and Sarcopenic Obesity: The Role of Exercise.
The novel role of IFITM1-3 in myogenic differentiation of C2C12 cells.
Elucidation of bioinformatic-guided high-prospect drug repositioning candidates for DMD via Swanson linking of target-focused latent knowledge from text-mined categorical metadata.
Lysosomes mediate the mitochondrial UPR via mTORC1-dependent ATF4 phosphorylation.

Biol Pharm Bull. 2023 ;46(9): 1240-1248

Metallothionein Gene Deficiency Facilitates the Differentiation of C2C12 Myoblasts into Slow-Twitch Myotubes.

Yoshito Kadota, Ryo Yamanokuchi, Nodoka Ohnishi, Mami Matsuoka, Takashige Kawakami, Masao Sato, Shinya Suzuki.

  Metallothionein (MT) 1 and 2 are ubiquitously expressed cysteine-rich, low molecular weight proteins. MT expression is upregulated in skeletal muscle during aging. MTs also play role in multiple types of skeletal muscle atrophy. Meanwhile, it has been reported that MT1 and MT2 gene deficiency increases myogenesis in MT knockout (MTKO) mice. However, little is known about the effect of MTs on muscle formation and atrophy. In this study, we investigated the effect of MT1 and MT2 gene knock-out using the clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (CRISPR-Cas9) system in an in vitro skeletal muscle differentiation model (C2C12 cell line). MT deficiency promoted myogenic differentiation and myotube formation in C2C12 cells. Muscle-specific transcription factors MyoD and myogenin were found to be upregulated at the late stage of myotube differentiation in MTKO cells. Furthermore, the fast-twitch myosin heavy chain (MyHC) protein expression was similar in MTKO and mock-transfected myotubes, but slow-MyHC expression was higher in MTKO cells than in mock cells. The MT gene deletion did not affect the number of fast MyHC-positive myotubes but increased the number of slow MyHC-positive myotubes. Treatment with the antioxidant N-acetylcysteine (NAC) inhibited the increase in the number of slow MyHC-positive myotubes as well as slow-MyHC expression in MTKO cells. In contrast, NAC treatment did not alter the number of fast MyHC-positive myotubes or the expression of fast-MyHC in MTKO cells. These results suggest that the antioxidant effects of MTs may be involved in slow-twitch myofiber formation in skeletal muscle.

Keywords:  C2C12 cell; fast-to-slow myofiber type transition; metallothionein; myotube; skeletal muscle

DOI:  https://doi.org/10.1248/bpb.b23-00165
Biol Sex Differ. 2023 Sep 05. 14(1): 56

Sex differences in muscle protein expression and DNA methylation in response to exercise training.

Shanie Landen, Macsue Jacques, Danielle Hiam, Javier Alvarez-Romero, Ralf B Schittenhelm, Anup D Shah, Cheng Huang, Joel R Steele, Nicholas R Harvey, Larisa M Haupt, Lyn R Griffiths, Kevin J Ashton, Séverine Lamon, Sarah Voisin, Nir Eynon.

   BACKGROUND: Exercise training elicits changes in muscle physiology, epigenomics, transcriptomics, and proteomics, with males and females exhibiting differing physiological responses to exercise training. However, the molecular mechanisms contributing to the differing adaptations between the sexes are poorly understood.
METHODS: We performed a meta-analysis for sex differences in skeletal muscle DNA methylation following an endurance training intervention (Gene SMART cohort and E-MTAB-11282 cohort). We investigated for sex differences in the skeletal muscle proteome following an endurance training intervention (Gene SMART cohort). Lastly, we investigated whether the methylome and proteome are associated with baseline cardiorespiratory fitness (maximal oxygen consumption; VO2max) in a sex-specific manner.
RESULTS: Here, we investigated for the first time, DNA methylome and proteome sex differences in response to exercise training in human skeletal muscle (n = 78; 50 males, 28 females). We identified 92 DNA methylation sites (CpGs) associated with exercise training; however, no CpGs changed in a sex-dependent manner. In contrast, we identified 189 proteins that are differentially expressed between the sexes following training, with 82 proteins differentially expressed between the sexes at baseline. Proteins showing the most robust sex-specific response to exercise include SIRT3, MRPL41, and MBP. Irrespective of sex, cardiorespiratory fitness was associated with robust methylome changes (19,257 CpGs) and no proteomic changes. We did not observe sex differences in the association between cardiorespiratory fitness and the DNA methylome. Integrative multi-omic analysis identified sex-specific mitochondrial metabolism pathways associated with exercise responses. Lastly, exercise training and cardiorespiratory fitness shifted the DNA methylomes to be more similar between the sexes.
CONCLUSIONS: We identified sex differences in protein expression changes, but not DNA methylation changes, following an endurance exercise training intervention; whereas we identified no sex differences in the DNA methylome or proteome response to lifelong training. Given the delicate interaction between sex and training as well as the limitations of the current study, more studies are required to elucidate whether there is a sex-specific training effect on the DNA methylome. We found that genes involved in mitochondrial metabolism pathways are differentially modulated between the sexes following endurance exercise training. These results shed light on sex differences in molecular adaptations to exercise training in skeletal muscle.

Keywords:  DNA methylation; Epigenetics; Exercise; Proteome; Sex differences; Skeletal muscle

DOI:  https://doi.org/10.1186/s13293-023-00539-2
bioRxiv. 2023 Aug 25. pii: 2023.08.24.554609. [Epub ahead of print]

Lineage tracing of newly accrued nuclei in skeletal myofibers uncovers distinct transcripts and interplay between nuclear populations.

Chengyi Sun, Casey O Swoboda, Michael J Petrany, Sreeja Parameswaran, Andrew VonHandorf, Matthew T Weirauch, Christoph Lepper, Douglas P Millay.

Multinucleated skeletal muscle cells have an obligatory need to acquire additional nuclei through fusion with activated skeletal muscle stem cells when responding to both developmental and adaptive growth stimuli. A fundamental question in skeletal muscle biology has been the reason underlying this need for new nuclei in syncytial cells that already harbor hundreds of nuclei. To begin to answer this long-standing question, we utilized nuclear RNA-sequencing approaches and developed a lineage tracing strategy capable of defining the transcriptional state of recently fused nuclei and distinguishing this state from that of pre-existing nuclei. Our findings reveal the presence of conserved markers of newly fused nuclei both during development and after a hypertrophic stimulus in the adult. However, newly fused nuclei also exhibit divergent gene expression that is determined by the myogenic environment to which they fuse. Moreover, accrual of new nuclei through fusion is required for nuclei already resident in adult myofibers to mount a normal transcriptional response to a load-inducing stimulus. We propose a model of mutual regulation in the control of skeletal muscle development and adaptations, where newly fused and pre-existing myonuclear populations influence each other to maintain optimal functional growth.

DOI: https://doi.org/10.1101/2023.08.24.554609
J Cell Physiol. 2023 Sep 08.

Nonsense-mediated mRNA decay suppresses injury-induced muscle regeneration via inhibiting MyoD transcriptional activity.

Yanjie Tan, Jing Zhang, Yi Jin.

  Skeletal muscle regeneration is a crucial physiological process that occurs in response to injury or disease. As an important transcriptome surveillance system that regulates tissue development, the role of nonsense-mediated mRNA decay (NMD) in muscle regeneration remains unclear. Here, we found that NMD inhibits myoblast differentiation by targeting the phosphoinositide-3-kinase regulatory subunit 5 gene, which leads to the suppression of the transcriptional activity of myogenic differentiation (MyoD), a key regulator of myoblast differentiation. This disruption of MyoD transcriptional activity subsequently affects the expression levels of myogenin and myosin heavy chain, crucial markers of myoblast differentiation. Additionally, through up-frameshift protein 1 knockdown experiments, we observed that inhibiting NMD can accelerate muscle regeneration in vivo. These findings highlight the potential of NMD as a novel therapeutic target for the treatment of muscle-related injuries and diseases.

Keywords:  MyoD transcriptional activity; muscle regeneration; myoblast differentiation; nonsense-mediated mRNA decay

DOI:  https://doi.org/10.1002/jcp.31118
J Cachexia Sarcopenia Muscle. 2023 Sep 06.

Radiation induces long-term muscle fibrosis and promotes a fibrotic phenotype in fibro-adipogenic progenitors.

Nicolas Collao, Donna D'Souza, Laura Messeiller, Evan Pilon, Jessica Lloyd, Jillian Larkin, Matthew Ngu, Alexanne Cuillerier, Alexander E Green, Keir J Menzies, Yan Burelle, Michael De Lisio.

   BACKGROUND: Radiation-induced muscle pathology, characterized by muscle atrophy and fibrotic tissue accumulation, is the most common debilitating late effect of therapeutic radiation exposure particularly in juvenile cancer survivors. In healthy muscle, fibro/adipogenic progenitors (FAPs) are required for muscle maintenance and regeneration, while in muscle pathology FAPs are precursors for exacerbated extracellular matrix deposition. However, the role of FAPs in radiation-induced muscle pathology has not previously been explored.
METHODS: Four-week-old Male CBA or C57Bl/6J mice received a single dose (16 Gy) of irradiation (IR) to a single hindlimb with the shielded contralateral limb (CLTR) serving as a non-IR control. Mice were sacrificed 3, 7, 14 (acute IR response), and 56 days post-IR (long-term IR response). Changes in skeletal muscle morphology, myofibre composition, muscle niche cellular dynamics, DNA damage, proliferation, mitochondrial respiration, and metabolism and changes in progenitor cell fate where assessed.
RESULTS: Juvenile radiation exposure resulted in smaller myofibre cross-sectional area, particularly in type I and IIA myofibres (P < 0.05) and reduced the proportion of type I myofibres (P < 0.05). Skeletal muscle fibrosis (P < 0.05) was evident at 56 days post-IR. The IR-limb had fewer endothelial cells (P < 0.05) and fibro-adipogenic progenitors (FAPs) (P < 0.05) at 56 days post-IR. Fewer muscle satellite (stem) cells were detected at 3 and 56 days in the IR-limb (P < 0.05). IR induced FAP senescence (P < 0.05), increased their fibrogenic differentiation (P < 0.01), and promoted their glycolytic metabolism. Further, IR altered the FAP secretome in a manner that impaired muscle satellite (stem) cell differentiation (P < 0.05) and fusion (P < 0.05).
CONCLUSIONS: Our study suggests that following juvenile radiation exposure, FAPs contribute to long-term skeletal muscle atrophy and fibrosis. These findings provide rationale for investigating FAP-targeted therapies to ameliorate the negative late effects of radiation exposure in skeletal muscle.

Keywords:  Atrophy; Differentiation; Extracellular matrix; Mesenchymal progenitors; Metabolism; Myofibroblast; Skeletal muscle

DOI:  https://doi.org/10.1002/jcsm.13320
J Cachexia Sarcopenia Muscle. 2023 Sep 06.

Caveolin-3 loss linked with the P104L LGMD-1C mutation modulates skeletal muscle mTORC1 signalling and cholesterol homeostasis.

Dinesh S Shah, Raid B Nisr, Gabriela Krasteva-Christ, Harinder S Hundal.

   BACKGROUND: Caveolins are the principal structural components of plasma membrane caveolae. Dominant pathogenic mutations in the muscle-specific caveolin-3 (Cav3) gene isoform, such as the limb girdle muscular dystrophy type 1C (LGMD-1C) P104L mutation, result in dramatic loss of the Cav3 protein and pathophysiological muscle weakness/wasting. We hypothesize that such muscle degeneration may be linked to disturbances in signalling events that impact protein turnover. Herein, we report studies assessing the effects of Cav3 deficiency on mammalian or mechanistic target of rapamycin complex 1 (mTORC1) signalling in skeletal muscle cells.
METHODS: L6 myoblasts were stably transfected with Cav3P104L or expression of native Cav3 was abolished by CRISPR/Cas9 genome editing (Cav3 knockout [Cav3KO]) prior to performing subcellular fractionation and immunoblotting, analysis of real-time mitochondrial respiration or fixed cell immunocytochemistry. Skeletal muscle from wild-type and Cav3-/- mice was processed for immunoblot analysis of downstream mTORC1 substrate phosphorylation.
RESULTS: Cav3 was detected in lysosomal-enriched membranes isolated from L6 myoblasts and observed by confocal microscopy to co-localize with lysosomal-specific markers. Cav3P104L expression, which results in significant (~95%) loss of native Cav3, or CRISPR/Cas9-mediated Cav3KO, reduced amino acid-dependent mTORC1 activation. The decline in mTORC1-directed signalling was detected by immunoblot analysis of L6 muscle cells and gastrocnemius Cav3-/- mouse muscle as judged by reduced phosphorylation of mTORC1 substrates that play key roles in the initiation of protein synthesis (4EBP1S65 and S6K1T389 ). S6K1T389 and 4EBP1S65 phosphorylation reduced by over 75% and 80% in Cav3KO muscle cells and by over 90% and 30% in Cav3-/- mouse skeletal muscle, respectively. The reduction in protein synthetic capacity in L6 muscle cells was confirmed by analysis of puromycylated peptides using the SUnSET assay. Cav3 loss was also associated with a 26% increase in lysosomal cholesterol, and pharmacological manipulation of lysosomal cholesterol was effective in replicating the reduction in mTORC1 activity observed in Cav3KO cells. Notably, re-expression of Cav3 in Cav3KO myoblasts normalized lysosomal cholesterol content, which coincided with a recovery in protein translation and an associated increase in mTORC1-directed phosphorylation of downstream targets.
CONCLUSIONS: Our findings indicate that Cav3 can localize on lysosomal membranes and is a novel regulator of mTORC1 signalling in muscle. Cav3 deficiency associated with the Cav3P104L mutation impairs mTORC1 activation and protein synthetic capacity in skeletal muscle cells, which may be linked to disturbances in lysosomal cholesterol trafficking and contribute to the pathology of LGMD-1C.

Keywords:  LGMD-1C; amino acid; caveolin-3; caveolinopathy; lysosome; mTORC1; skeletal muscle

DOI:  https://doi.org/10.1002/jcsm.13317
J Appl Physiol (1985). 2023 Sep 07.

Prolonged mechanical muscle loading increases mechanosensor gene and protein levels and causes a moderate fast-to-slow fiber type switch in mice.

Mathias Vanmunster, Ana Victoria Rojo-Garcia, Alexander Pacolet, Ilse Jonkers, Katrien Koppo, Rik Lories, Frank Suhr.

  Mechanosensing and subsequent mechanotransduction are indispensable for muscle plasticity. Nevertheless, a scarcity of literature exists regarding an all-encompassing understanding of the muscle mechanosensing machinery's response to prolonged loading, especially in conditions that resemble a natural physiological state of skeletal muscle. This study aimed to comprehensively explore the effects of prolonged mechanical loading on mechanosensitive components, skeletal muscle characteristics, and metabolism-related gene clusters. Twenty male C57BL/6J mice were randomly divided into two groups: control and prolonged mechanical loading. To induce prolonged mechanical loading on the triceps brachii (TRI) and biceps brachii (BIC) muscles, a 14-day period of tail suspension was implemented. In TRI only, prolonged mechanical loading caused a mild fast-to-slow fiber type shift together with increased mechanosensor gene and protein levels. It also increased transcription factors associated with slow muscle fibers while decreasing those related to fast-type muscle gene expression. Succinate dehydrogenase activity, a marker of muscle oxidative capacity, and genes involved in oxidative and mitochondrial turnover increased, while glycolytic-related genes decreased. Moreover, prolonged mechanical loading stimulated markers of muscle protein synthesis. Taken together, our data show a collective muscle-specific increase in mechanosensor gene and protein levels upon a period of prolonged mechanical loading in conditions that reflect a more natural physiological state of skeletal muscle in mice. We provide additional proof-of-concept that prolonged tail suspension-induced loading of the forelimbs triggers a muscle-specific fast-to-slow fiber type switch, and this coincides with increased protein synthesis-related signaling.

Keywords:  fiber types; mechanical loading; mechanosensors; muscle metabolism; skeletal muscle

DOI:  https://doi.org/10.1152/japplphysiol.00204.2023
Int J Mol Sci. 2023 Aug 23. pii: 13121. [Epub ahead of print]24(17):

Effects of Aging on Collagen in the Skeletal Muscle of Mice.

Yuji Kanazawa, Ryo Miyachi, Takashi Higuchi, Hiaki Sato.

  Aging affects several tissues in the body, including skeletal muscle. Multiple types of collagens are localized in the skeletal muscle and contribute to the maintenance of normal muscle structure and function. Since the effects of aging on muscle fibers vary by muscle fiber type, it is expected that the effects of aging on intramuscular collagen might be influenced by muscle fiber type. In this study, we examined the effect of aging on collagen levels in the soleus (slow-twitch muscle) and gastrocnemius (fast-twitch muscle) muscles of 3-, 10-, 24-, and 28-month-old male C57BL/6J mice using molecular and morphological analysis. It was found that aging increased collagen I, III, and VI gene expression and immunoreactivity in both slow- and fast-twitch muscles and collagen IV expression in slow-twitch muscles. However, collagen IV gene expression and immunoreactivity in fast-twitch muscle were unaffected by aging. In contrast, the expression of the collagen synthesis marker heat shock protein 47 in both slow- and fast-twitch muscles decreased with aging, while the expression of collagen degradation markers increased with aging. Overall, these results suggest that collagen gene expression and immunoreactivity are influenced by muscle fiber type and collagen type and that the balance between collagen synthesis and degradation tends to tilt toward degradation with aging.

Keywords:  aging; collagen; fast-twitch muscle; skeletal muscle; slow-twitch muscle

DOI:  https://doi.org/10.3390/ijms241713121
Cells. 2023 Aug 30. pii: 2183. [Epub ahead of print]12(17):

Mitochondrial Properties in Skeletal Muscle Fiber.

Han Dong, Shih-Yin Tsai.

  Mitochondria are the primary source of energy production and are implicated in a wide range of biological processes in most eukaryotic cells. Skeletal muscle heavily relies on mitochondria for energy supplements. In addition to being a powerhouse, mitochondria evoke many functions in skeletal muscle, including regulating calcium and reactive oxygen species levels. A healthy mitochondria population is necessary for the preservation of skeletal muscle homeostasis, while mitochondria dysregulation is linked to numerous myopathies. In this review, we summarize the recent studies on mitochondria function and quality control in skeletal muscle, focusing mainly on in vivo studies of rodents and human subjects. With an emphasis on the interplay between mitochondrial functions concerning the muscle fiber type-specific phenotypes, we also discuss the effect of aging and exercise on the remodeling of skeletal muscle and mitochondria properties.

Keywords:  mitochondria; skeletal muscle physiology

DOI:  https://doi.org/10.3390/cells12172183
Cells. 2023 Aug 29. pii: 2167. [Epub ahead of print]12(17):

Foxo3 Knockdown Mediates Decline of Myod1 and Myog Reducing Myoblast Conversion to Myotubes.

Benjamin Gellhaus, Kai O Böker, Marlene Gsaenger, Eyck Rodenwaldt, Marc A Hüser, Arndt F Schilling, Dominik Saul.

  Sarcopenia has a high prevalence among the aging population. Sarcopenia is of tremendous socioeconomic importance because it can lead to falls and hospitalization, subsequently increasing healthcare costs while limiting quality of life. In sarcopenic muscle fibers, the E3 ubiquitin ligase F-Box Protein 32 (Fbxo32) is expressed at substantially higher levels, driving ubiquitin-proteasomal muscle protein degradation. As one of the key regulators of muscular equilibrium, the transcription factor Forkhead Box O3 (FOXO3) can increase the expression of Fbxo32, making it a possible target for the regulation of this detrimental pathway. To test this hypothesis, murine C2C12 myoblasts were transduced with AAVs carrying a plasmid for four specific siRNAs against Foxo3. Successfully transduced myoblasts were selected via FACS cell sorting to establish single clone cell lines. Sorted myoblasts were further differentiated into myotubes and stained for myosin heavy chain (MHC) by immunofluorescence. The resulting area was calculated. Myotube contractions were induced by electrical stimulation and quantified. We found an increased Foxo3 expression in satellite cells in human skeletal muscle and an age-related increase in Foxo3 expression in older mice in silico. We established an in vitro AAV-mediated FOXO3 knockdown on protein level. Surprisingly, the myotubes with FOXO3 knockdown displayed a smaller myotube size and a lower number of nuclei per myotube compared to the control myotubes (AAV-transduced with a functionless control plasmid). During differentiation, a lower level of FOXO3 reduced the expression Fbxo32 within the first three days. Moreover, the expression of Myod1 and Myog via ATM and Tp53 was reduced. Functionally, the Foxo3 knockdown myotubes showed a higher contraction duration and time to peak. Early Foxo3 knockdown seems to terminate the initiation of differentiation due to lack of Myod1 expression, and mediates the inhibition of Myog. Subsequently, the myotube size is reduced and the excitability to electrical stimulation is altered.

Keywords:  Foxo3; Myod1; Myog; Tp53; sarcopenia; skeletal muscle

DOI:  https://doi.org/10.3390/cells12172167
Am J Physiol Cell Physiol. 2023 Sep 04.

Alignment, cross-linking, and beyond: A collagen architect's guide to the skeletal muscle extracellular matrix.

Ross P Wohlgemuth, Sarah E Brashear, Lucas R Smith.

  The muscle extracellular matrix (ECM) forms a complex network of collagens, proteoglycans, and other proteins that produce a favorable environment for muscle regeneration, protect the sarcolemma from contraction-induced damage, and provide a pathway for the lateral transmission of contractile force. In each of these functions, the structure and organization of the muscle ECM plays an important role. Many aspects of collagen architecture, including collagen alignment, cross-linking, and packing density affect the regenerative capacity, passive mechanical properties, and contractile force transmission pathways of skeletal muscle. The balance between fortifying the muscle ECM and maintaining ECM turnover and compliance is highly dependent on the integrated organization, or architecture, of the muscle matrix-especially related to collagen. While muscle ECM remodeling patterns in response to exercise and disease are similar, in that collagen synthesis can increase in both cases, one outcome leads to a stronger muscle and the other leads to fibrosis. In this review we provide a comprehensive analysis of the architectural features of each layer of muscle ECM-epimysium, perimysium, and endomysium. Further, we detail the importance of muscle ECM architecture to biomechanical function in the context of exercise or fibrosis, including disease, injury, and aging. We describe how collagen architecture is linked to active and passive muscle biomechanics, and which architectural features are acutely dynamic and adapt over time. Future studies should investigate the significance of collagen architecture in muscle stiffness, ECM turnover, and lateral force transmission in the context of health and fibrosis.

Keywords:  Collagen; Crosslinking; Extracellular Matrix; Fibrosis; Skeletal muscle

DOI:  https://doi.org/10.1152/ajpcell.00287.2023
Sci Rep. 2023 Sep 07. 13(1): 14752

A systematic review and meta-analysis of the SIRT1 response to exercise.

Ciara Gallardo Juan, Kyle B Matchett, Gareth W Davison.

Sirtuin 1 (SIRT1) is a key physiological regulator of metabolism and a target of therapeutic interventions for cardiometabolic and ageing-related disorders. Determining the factors and possible mechanisms of acute and adaptive SIRT1 response to exercise is essential for optimising exercise interventions aligned to the prevention and onset of disease. Exercise-induced SIRT1 upregulation has been reported in animals, but, to date, data in humans have been inconsistent. This exploratory systematic review and meta-analysis aims to assess various exercise interventions measuring SIRT1 in healthy participants. A total of 34 studies were included in the meta-analysis (13 single bout exercise, 21 training interventions). Studies were grouped according to tissue sample type (blood, muscle), biomarkers (gene expression, protein content, enzyme level, enzyme activity), and exercise protocols. A single bout of high-intensity or fasted exercise per se increases skeletal muscle SIRT1 gene expression as measured by qPCR or RT-PCR, while repeated resistance training alone increases blood SIRT1 levels measured by ELISA. A limited number of studies also show a propensity for an increase in muscle SIRT1 activity as measured by fluorometric or sirtuin activity assay. In conclusion, exercise acutely upregulates muscle SIRT1 gene expression and chronically increases SIRT1 blood enzyme levels.

DOI: https://doi.org/10.1038/s41598-023-38843-x
Am J Physiol Cell Physiol. 2023 Sep 04.

The Effect of Gradual Ovarian Failure on Dynamic Muscle Function and the Role of High Intensity Interval Training on Mitigating Impairments.

Emma F Hubbard, Parastoo Mashouri, W Glen Pyle, Geoffrey A Power.

  Skeletal muscle contractile function is impaired in menopause and exercise may mitigate this decline. We used the VCD model of menopause to investigate the effects of gradual ovarian failure on skeletal muscle contractile function and whether high intensity interval training (HIIT) can mitigate impairments. Sexually mature female CD-1 mice were assigned to one of three groups: control sedentary (n=5), VCD-sedentary (n=5), or VCD-training (n=5). Following ovarian failure (a 4-month process), the VCD-training group underwent 8-weeks of uphill HIIT. Mice were sacrificed 8-weeks after ovarian failure, representing late menopause. Single fibres from the soleus (SOL) and extensor digitorum longus (EDL) muscles were dissected, chemically permeabilized, and mechanically tested. Single muscle fibres were maximally activated (pCa4.5) then isotonic load clamps were performed to evaluate force-velocity-power relationships. Absolute force and peak power were 31% and 32% lower in VCD-sedentary fibres compared to control fibres, respectively, in both SOL and EDL muscles. Despite reductions in absolute force, there were no concomitant increases in contractile velocity to preserve power production. HIIT attenuated force loss in the VCD-training group such that peak force was not different from the control group across muscles and was partially effective at mitigating power loss (22% higher peak power in VCD-training compared to VCD-sedentary), but only in fast-type SOL fibres. These findings indicate that ovarian failure impairs dynamic contractile function - likely through a combination of lower force-generating capacity and slower shortening velocity, and that HIIT may be insufficient to completely counteract the deleterious effects of menopause at the cellular level.

Keywords:  Menopause; Ovarian failure; Power; high intensity interval training; single muscle fibre

DOI:  https://doi.org/10.1152/ajpcell.00318.2023
Int J Mol Sci. 2023 Aug 31. pii: 13536. [Epub ahead of print]24(17):

Reduced Expression of Septin7 Hinders Skeletal Muscle Regeneration.

László Szabó, Andrea Telek, János Fodor, Nóra Dobrosi, Klaudia Dócs, Zoltán Hegyi, Mónika Gönczi, László Csernoch, Beatrix Dienes.

  Septins are considered the fourth component of the cytoskeleton with the septin7 isoform playing a critical role in the formation of diffusion barriers in phospholipid bilayers and intra- and extracellular scaffolds. While its importance has already been confirmed in different intracellular processes, very little is known about its role in skeletal muscle. Muscle regeneration was studied in a Sept7 conditional knock-down mouse model to prove the possible role of septin7 in this process. Sterile inflammation in skeletal muscle was induced which was followed by regeneration resulting in the upregulation of septin7 expression. Partial knock-down of Sept7 resulted in an increased number of inflammatory cells and myofibers containing central nuclei. Taken together, our data suggest that partial knock-down of Sept7 hinders the kinetics of muscle regeneration, indicating its crucial role in skeletal muscle functions.

Keywords:  central nuclei; muscle injury; regeneration; septin7; skeletal muscle

DOI:  https://doi.org/10.3390/ijms241713536
Stem Cell Res Ther. 2023 Sep 08. 14(1): 243

In vitro-generated human muscle reserve cells are heterogeneous for Pax7 with distinct molecular states and metabolic profiles.

Axelle Bouche, Benoit Borner, Chloé Richard, Ysaline Grand, Didier Hannouche, Thomas Laumonier.

   BACKGROUND: The capacity of skeletal muscles to regenerate relies on Pax7+ muscle stem cells (MuSC). While in vitro-amplified MuSC are activated and lose part of their regenerative capacity, in vitro-generated human muscle reserve cells (MuRC) are very similar to quiescent MuSC with properties required for their use in cell-based therapies.
METHODS: In the present study, we investigated the heterogeneity of human MuRC and characterized their molecular signature and metabolic profile.
RESULTS: We observed that Notch signaling is active and essential for the generation of quiescent human Pax7+ MuRC in vitro. We also revealed, by immunofluorescence and flow cytometry, two distinct subpopulations of MuRC distinguished by their relative Pax7 expression. After 48 h in differentiation medium (DM), the Pax7High subpopulation represented 35% of the total MuRC pool and this percentage increased to 61% after 96 h in DM. Transcriptomic analysis revealed that Pax7High MuRC were less primed for myogenic differentiation as compared to Pax7Low MuRC and displayed a metabolic shift from glycolysis toward fatty acid oxidation. The bioenergetic profile of human MuRC displayed a 1.5-fold decrease in glycolysis, basal respiration and ATP-linked respiration as compared to myoblasts. We also observed that AMPKα1 expression was significantly upregulated in human MuRC that correlated with an increased phosphorylation of acetyl-CoA carboxylase (ACC). Finally, we showed that fatty acid uptake was increased in MuRC as compared to myoblasts, whereas no changes were observed for glucose uptake.
CONCLUSIONS: Overall, these data reveal that the quiescent MuRC pool is heterogeneous for Pax7 with a Pax7High subpopulation being in a deeper quiescent state, less committed to differentiation and displaying a reduced metabolic activity. Altogether, our data suggest that human Pax7High MuRC may constitute an appropriate stem cell source for potential therapeutic applications in skeletal muscle diseases.

Keywords:  AMPK; Fatty acid oxidation; Human muscle reserve cell; Metabolism; Pax7 heterogeneity; Quiescence

DOI:  https://doi.org/10.1186/s13287-023-03483-5
Biochim Biophys Acta Mol Basis Dis. 2023 Sep 04. pii: S0925-4439(23)00243-0. [Epub ahead of print]1870(1): 166877

Downregulation of PGC-1α during cisplatin-induced muscle atrophy in murine skeletal muscle.

Ken Sato, Yoshida Satoshi, Yu Miyauchi, Fumiaki Sato, Risako Kon, Nobutomo Ikarashi, Yoshihiko Chiba, Tomoo Hosoe, Hiroyasu Sakai.

  This study aimed to investigate the effects of cisplatin on adenosine triphosphate (ATP) levels, expressions of genes related to mitochondrial oxidative phosphorylation (OXPHOS), and the factors related to mitochondrial biosynthesis in skeletal muscle. Systemic cisplatin administration decreased skeletal muscle mass, skeletal muscle strength, and endurance. The mitochondrial DNA /nuclear DNA ratio was also reduced after treatment with cisplatin. Moreover, among the factors related to mitochondrial biogenesis and function, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) was significantly downregulated in the cisplatin-treated group. Downregulation of PGC-1α in the skeletal muscle may contribute to muscle weakness during cisplatin-induced muscle atrophy.

Keywords:  ATP; Cisplatin; Mitochondria; Muscle atrophy; PGC-1α

DOI:  https://doi.org/10.1016/j.bbadis.2023.166877
Expert Rev Proteomics. 2023 Sep 07. 1-18

Biochemical and proteomic insights into sarcoplasmic reticulum Ca2+-ATPase complexes in skeletal muscles.

Paul Dowling, Dieter Swandulla, Kay Ohlendieck.

   INTRODUCTION: Skeletal muscles contain large numbers of high-molecular-mass protein complexes in elaborate membrane systems. Integral membrane proteins are involved in diverse cellular functions including the regulation of ion handling, membrane homeostasis, energy metabolism and force transmission.
AREAS COVERED: The proteomic profiling of membrane proteins and large protein assemblies in skeletal muscles are outlined in this article. This includes a critical overview of the main biochemical separation techniques and the mass spectrometric approaches taken to study membrane proteins. As an illustrative example of an analytically challenging large protein complex, the proteomic detection and characterization of the Ca2+-ATPase of the sarcoplasmic reticulum is discussed. The biological role of this large protein complex during normal muscle functioning, in the context of fiber type diversity and in relation to mechanisms of physiological adaptations and pathophysiological abnormalities is evaluated from a proteomics perspective.
EXPERT OPINION: Mass spectrometry-based muscle proteomics has decisively advanced the field of basic and applied myology. Although it is technically challenging to study membrane proteins, innovations in protein separation methodology in combination with sensitive mass spectrometry and improved systems bioinformatics has allowed the detailed proteomic detection and characterization of skeletal muscle membrane protein complexes, such as Ca2+-pump proteins of the sarcoplasmic reticulum.

Keywords:  Calcium ATPase; SERCA; calcium homeostasis; calcium pump; membrane protein; muscle relaxation; sarcoplasmic reticulum

DOI:  https://doi.org/10.1080/14789450.2023.2255743
J Biol Chem. 2023 Sep 04. pii: S0021-9258(23)02254-8. [Epub ahead of print] 105226

The transcriptional regulator KLF15 is necessary for myoblast differentiation and muscle regeneration by activating FKBP5.

Shijuan Gao, Shan Huang, Yanhong Zhang, Guangming Fang, Yan Liu, Congcong Zhang, Yulin Li, Jie Du.

  Successful muscle regeneration following injury is essential for functional homeostasis of skeletal muscles. Krüppel-like factor 15 (KLF15) is a metabolic transcriptional regulator in the muscles. However, little is known regarding its function in muscle regeneration. Here, we examined microarray datasets from the Gene Expression Omnibus (GEO) database, which indicated downregulated KLF15 in muscles from patients with various muscle diseases. Additionally, we found that Klf15 knockout (Klf15KO) impaired muscle regeneration following injury in mice. Furthermore, KLF15 expression was robustly induced during myoblast differentiation. Myoblasts with KLF15 deficiency showed a marked reduction in their fusion capacity. Unbiased transcriptome analysis of muscles on day 7 post-injury revealed downregulated genes involved in cell differentiation and metabolic processes in Klf15KO muscles. The FK506-binding protein 51 (FKBP5), a positive regulator of myoblast differentiation, was ranked as one of the most strongly downregulated genes in the Klf15KO group. A mechanistic search revealed that KLF15 binds directly to the promoter region of FKBP5 and activates FKBP5 expression. Local delivery of FKBP5 rescued the impaired muscle regeneration in Klf15KO mice. Our findings reveal a positive regulatory role of KLF15 in myoblast differentiation and muscle regeneration by activating FKBP5 expression. KLF15 signaling may be a novel therapeutic target for muscle disorders associated with injuries or diseases.

Keywords:  FKBP5; KLF15; muscle regeneration; myoblast differentiation

DOI:  https://doi.org/10.1016/j.jbc.2023.105226
Elife. 2023 Sep 06. pii: RP86944. [Epub ahead of print]12

Loss of Ptpmt1 limits mitochondrial utilization of carbohydrates and leads to muscle atrophy and heart failure in tissue-specific knockout mice.

Hong Zheng, Qianjin Li, Shanhu Li, Zhiguo Li, Marco Brotto, Daiana Weiss, Domenick Prosdocimo, Chunhui Xu, Ashruth Reddy, Michelle Puchowicz, Xinyang Zhao, M Neale Weitzmann, Mukesh K Jain, Cheng-Kui Qu.

  While mitochondria in different tissues have distinct preferences for energy sources, they are flexible in utilizing competing substrates for metabolism according to physiological and nutritional circumstances. However, the regulatory mechanisms and significance of metabolic flexibility are not completely understood. Here, we report that the deletion of Ptpmt1, a mitochondria-based phosphatase, critically alters mitochondrial fuel selection - the utilization of pyruvate, a key mitochondrial substrate derived from glucose (the major simple carbohydrate), is inhibited, whereas the fatty acid utilization is enhanced. Ptpmt1 knockout does not impact the development of the skeletal muscle or heart. However, the metabolic inflexibility ultimately leads to muscular atrophy, heart failure, and sudden death. Mechanistic analyses reveal that the prolonged substrate shift from carbohydrates to lipids causes oxidative stress and mitochondrial destruction, which in turn results in marked accumulation of lipids and profound damage in the knockout muscle cells and cardiomyocytes. Interestingly, Ptpmt1 deletion from the liver or adipose tissue does not generate any local or systemic defects. These findings suggest that Ptpmt1 plays an important role in maintaining mitochondrial flexibility and that their balanced utilization of carbohydrates and lipids is essential for both the skeletal muscle and the heart despite the two tissues having different preferred energy sources.

Keywords:  Ptpmt1; bioenergetics; heart; medicine; mitochondria; mouse; skeletal muscle

DOI:  https://doi.org/10.7554/eLife.86944
Front Neuroendocrinol. 2023 Sep 03. pii: S0091-3022(23)00049-3. [Epub ahead of print] 101101

Androgen Action on Myogenesis Throughout the Lifespan; Comparison with Neurogenesis.

Sabrina Tzivia Barsky, Douglas Ashley Monks.

  Androgens' pleiotropic actions in promoting sex differences present not only a challenge to providing a comprehensive account of their function, but also an opportunity to gain insights by comparing androgenic actions across organ systems. Although often overlooked by neuroscientists, skeletal muscle is another androgen-responsive organ system which shares with the nervous system properties of electrochemical excitability, behavioral relevance, and remarkable capacity for adaptive plasticity. Here we review androgenic regulation of mitogenic plasticity in skeletal muscle with the goal of identifying areas of interest to those researching androgenic mechanisms mediating sexual differentiation of neurogenesis. We use an organizational-activational framework to relate broad areas of similarity and difference between androgen effects on mitogenesis in muscle and brain throughout the lifespan, from early organogenesis, through pubertal organization, adult activation, and aging. The focus of the review is androgenic regulation of muscle-specific stem cells (satellite cells), which share with neural stem cells essential functions in development, plasticity, and repair, albeit with distinct, muscle-specific features. Also considered are areas of paracrine and endocrine interaction between androgen action on muscle and nervous system, including mediation of neural plasticity of innervating and distal neural populations by muscle-produced trophic factors.

Keywords:  Satellite cell; androgen receptor; myogenesis; neurogenesis; neuromuscular system

DOI:  https://doi.org/10.1016/j.yfrne.2023.101101
Sci Rep. 2023 Sep 05. 13(1): 14659

Function of a mutant ryanodine receptor (T4709M) linked to congenital myopathy.

Zsuzsanna É Magyar, Judit Hevesi, Linda Groom, Robert T Dirksen, János Almássy.

Physiological muscle contraction requires an intact ligand gating mechanism of the ryanodine receptor 1 (RyR1), the Ca2+-release channel of the sarcoplasmic reticulum. Some mutations impair the gating and thus cause muscle disease. The RyR1 mutation T4706M is linked to a myopathy characterized by muscle weakness. Although, low expression of the T4706M RyR1 protein can explain in part the symptoms, little is known about the function RyR1 channels with this mutation. In order to learn whether this mutation alters channel function in a manner that can account for the observed symptoms, we examined RyR1 channels isolated from mice homozygous for the T4709M (TM) mutation at the single channel level. Ligands, including Ca2+, ATP, Mg2+ and the RyR inhibitor dantrolene were tested. The full conductance of the TM channel was the same as that of wild type (wt) channels and a population of partial open (subconductive) states were not observed. However, two unique sub-populations of TM RyRs were identified. One half of the TM channels exhibited high open probability at low (100 nM) and high (50 μM) cytoplasmic [Ca2+], resulting in Ca2+-insensitive, constitutively high Po channels. The rest of the TM channels exhibited significantly lower activity within the physiologically relevant range of cytoplasmic [Ca2+], compared to wt. TM channels retained normal Mg2+ block, modulation by ATP, and inhibition by dantrolene. Together, these results suggest that the TM mutation results in a combination of primary and secondary RyR1 dysfunctions that contribute to disease pathogenesis.

DOI: https://doi.org/10.1038/s41598-023-41801-2
Front Biosci (Landmark Ed). 2023 08 07. 28(8): 159

AMPK Mediates Early Activation of the Unfolded Protein Response through a Positive Feedback Loop in Palmitate-Treated Muscle Cells.

Jing Gong, Lu Wang, Wuchen Tao, Xiangsheng Pang, Zonghan Liu, Shiming Li, Wenjiong Li, Xiaoping Chen, Peng Zhang.

   BACKGROUND: Activation of the unfolded protein response (UPR) is closely related to the pathogenesis of many metabolic disorders. Accumulating evidence also shows that UPR and metabolic signaling pathways are interdependent. The AMP-activated protein kinase (AMPK) signal pathway controls the energy balance of eukaryotes. The aim of this study was therefore to investigate the possible interaction between AMPK signaling and UPR in muscle cells exposed to saturated fatty acids, as well as the potential mechanism.
METHODS: The saturated fatty acid palmitate was used to induce UPR in C2C12 myotubes. Compound C or knockdown of AMPKα with short hairpin RNA (shRNA) were used to inhibit the AMPK signaling pathway in palmitate-treated muscle cells. AMPK signaling in myotubes was activated using 5-amino-1-β-D-ribofuranosylimidazole-4-carboxamide (AICAR) or ex229. C2C12 myotubes were pre-treated with taurourdodeoxycholic acid (TUDCA) to inhibit UPR before adding palmitate. Real-time PCR and Western blotting were performed to evaluate the expression of UPR markers and activation of AMPK.
RESULTS: Palmitate treatment induced UPR in C2C12 myotubes while activating AMPK signaling. Inhibition of the AMPK pathway with compound C or AMPK shRNA reduced palmitate-induced activation of UPR, while inhibition of UPR with TUDCA reduced palmitate-induced AMPK activation. This indicates a positive feedback loop between UPR and AMPK. Furthermore, activation of the AMPK pathway with AICAR or ex229 caused a dose-dependent upregulation of UPR markers, including activating transcription factor 4 (ATF4), binding immunoglobulin protein (BIP), and growth arrest and DNA damage-inducible 34 (GADD34) protein.
CONCLUSIONS: These results provide the first evidence that AMPK signaling is involved in the early activation of UPR caused by saturated fatty acids in skeletal muscle. Furthermore, they indicate that physiological or pharmacological activation of the AMPK pathway (e.g., by exercise or phenformin, respectively) can promote muscle health and function, thereby improving the quality of life in individuals with metabolic disorders due to a high-fat diet or obesity.

Keywords:  AMPK; C2C12 myotube; ER stress; palmitate; unfolded protein response

DOI:  https://doi.org/10.31083/j.fbl2808159
J Appl Physiol (1985). 2023 Sep 07.

Soluble RAGE and Skeletal Muscle Tissue RAGE Expression Profiles in Lean and Obese Young Adults Across Differential Aerobic Exercise Intensities.

Edwin R Miranda, Jacob T Mey, Brian K Blackburn, Alec B Chaves, Kelly N Z Fuller, Ryan K Perkins, Andrew T Ludlow, Jacob M Haus.

  Nearly 40% of Americans have obesity and are at increased risk for developing type 2 diabetes. Skeletal muscle is responsible for >80% of insulin-stimulated glucose uptake which is attenuated by the inflammatory milieu of obesity and augmented by exercise. The Receptor for Advanced Glycation Endproducts (RAGE) is an inflammatory receptor directly linking metabolic dysfunction with inflammation. Circulating soluble isoforms of RAGE (sRAGE) formed either by proteolytic cleavage (cRAGE) or alternative splicing (esRAGE) act as decoys for RAGE ligands thereby counteracting RAGE-mediated inflammation. PURPOSE We aimed to determine if RAGE expression or alternative splicing of RAGE is altered by obesity in muscle, and whether acute aerobic exercise (AE) modifies RAGE and sRAGE. METHODS Young (20-34y) participants without (n=17; BMI: 22.6±2.6 kg/m2) and with obesity (n=7; BMI: 32.8±2.9 kg/m2) performed acute aerobic exercise (AE) at 40, 65 or 80% of VO2Max (mL/kg/min) on separate visits. Blood was taken before and 30 minutes after each exercise bout. Muscle biopsy samples were taken before, 30 minutes, and 3 hours after the 85% VO2Max exercise bout. RESULTS Individuals with obesity had higher total RAGE and esRAGE mRNA and RAGE protein (p<0.0001). In addition, RAGE and esRAGE transcripts correlated to transcripts of the NF-κB subunit P65 (p<0.05). There was no effect of exercise on total RAGE or esRAGE transcripts, or RAGE protein (p>0.05) and AE tended to decrease circulating sRAGE. CONCLUSIONS RAGE expression is exacerbated in skeletal muscle with obesity, which may contribute to the development of skeletal muscle metabolic dysfunction such as insulin resistance.

Keywords:  Advanced Glycation Endproducts; Exerkines; Inflammaton

DOI:  https://doi.org/10.1152/japplphysiol.00748.2022
J Appl Physiol (1985). 2023 Sep 07.

Structural and functional impairments of skeletal muscle in patients with post-acute sequelae of SARS-CoV-2 infection.

Marta Colosio, Lorenza Brocca, Marco Gatti, Marianna Neri, Emanuela Crea, Francesca Cadile, Monica Canepari, Maria Antonietta Pellegrino, Biagio Polla, Simone Porcelli, Roberto Bottinelli.

   BACKGROUND: Following acute COVID-19, a substantial proportion of patients showed symptoms and sequelae for several months, namely the post-acute sequelae of COVID-19 (PASC) syndrome. Major phenomena are exercise intolerance, muscle weakness and fatigue. We aimed to investigate the physiopathology of exercise intolerance in patients with PASC syndrome by structural and functional analyses of skeletal muscle.
METHODS: At least 3 months after infection, non-hospitalized patients with PASC (n=11,ys:54±11; PASC) and patients without long-term symptoms (n=12,ys:49±9; CTRL) visited the laboratory on four non-consecutive days. Spirometry, lung diffusion capacity and quality of life were assessed at rest. Cardiopulmonary incremental exercise test was performed. Oxygen consumption (VO2) kinetics were determined by moderate-intensity exercises. Muscle oxidative capacity (k) was assessed by near-infrared spectroscopy. Histochemical analysis, O2 flux (JO2) by high-resolution respirometry, and quantification of key molecular markers of mitochondrial biogenesis and dynamics were performed in vastus lateralis biopsies.
RESULTS: Pulmonary and cardiac functions were within normal range in all patients. VO2peak was lower in PASC than CTRL (24.7±5.0vs32.9±7.4mL*min-1*kg-1, respectively, P<.05). VO2 kinetics was slower in PASC than CTRL (41±12vs30±9s-1, P<.05). k was lower in PASC than CTRL (1.54±0.49vs2.07±0.51min-1, P<.05). Citrate synthase, PGC1alfa and JO2 for mitochondrial complex IIwere significantly lower in PASC vs CTRL (all P<.05).
CONCLUSION: In our cohort of patients with PASC, we showed limited exercise tolerance mainly due to "peripheral" determinants. Substantial reductions were observed for biomarkers of mitochondrial function, content, and biogenesis. PASC syndrome appears to negatively impact skeletal muscle function, although the disease is an heterogenous condition.

Keywords:  LongCOVID; Mitochondria; Muscle oxidative metabolism; Muscle weakness; Myopathy

DOI:  https://doi.org/10.1152/japplphysiol.00158.2023
Mol Cell Endocrinol. 2023 Sep 06. pii: S0303-7207(23)00201-0. [Epub ahead of print] 112050

Detecting the vitamin D receptor (VDR) protein in mouse and human skeletal muscle: Strain-specific, species-specific and inter-individual variation.

Hannah Lalunio, Lewan Parker, Erik D Hanson, Paul Gregorevic, Itamar Levinger, Alan Hayes, Craig A Goodman.

  Vitamin D, and its receptor (VDR), play roles in muscle development/function, however, VDR detection in muscle has been controversial. Using different sample preparation methods and antibodies, we examined differences in muscle VDR protein abundance between two mouse strains and between mice and humans. The mouse D-6 VDR antibody was not reliable for detecting VDR in mouse muscle, but was suitable for human muscle, while the rabbit D2K6 W antibody was valid for mouse and human muscle. VDR protein was generally lower in muscles from C57 B l/6 than FVB/N mice and was higher in human than mouse muscle. Two putative VDR bands were detected in human muscle, possibly representing VDR isoforms/splice variants, with marked inter-individual differences. This study provides new information on detecting VDR in muscle and on inter-mouse strain and inter-human individual differences in VDR expression. These findings may have implications for future pre-clinical and clinical studies and prompt further investigation to confirm possible VDR isoforms in human muscle.

Keywords:  Antibodies; Isoforms; Mouse strain; Splice variants; Vitamin D receptor

DOI:  https://doi.org/10.1016/j.mce.2023.112050
Cell Death Dis. 2023 09 07. 14(9): 596

Decoding the transcriptome of Duchenne muscular dystrophy to the single nuclei level reveals clinical-genetic correlations.

Xavier Suárez-Calvet, Esther Fernández-Simón, Daniel Natera, Cristina Jou, Patricia Pinol-Jurado, Elisa Villalobos, Carlos Ortez, Alexandra Monceau, Marianela Schiava, Anna Codina, José Verdu-Díaz, James Clark, Zoe Laidler, Priyanka Mehra, Rasya Gokul-Nath, Jorge Alonso-Perez, Chiara Marini-Bettolo, Giorgio Tasca, Volker Straub, Michela Guglieri, Andrés Nascimento, Jordi Diaz-Manera.

Duchenne muscular dystrophy is a genetic disease produced by mutations in the dystrophin gene characterized by early onset muscle weakness leading to severe and irreversible disability. The cellular and molecular consequences of the lack of dystrophin in humans are only partially known, which is crucial for the development of new therapies aiming to slow or stop the progression of the disease. Here we have analyzed quadriceps muscle biopsies of seven DMD patients aged 2 to 4 years old and five age and gender matched controls using single nuclei RNA sequencing (snRNAseq) and correlated the results obtained with clinical data. SnRNAseq identified significant differences in the proportion of cell population present in the muscle samples, including an increase in the number of regenerative fibers, satellite cells, and fibro-adipogenic progenitor cells (FAPs) and a decrease in the number of slow fibers and smooth muscle cells. Muscle samples from the younger patients with stable mild weakness were characterized by an increase in regenerative fibers, while older patients with moderate and progressive weakness were characterized by loss of muscle fibers and an increase in FAPs. An analysis of the gene expression profile in muscle fibers identified a strong regenerative signature in DMD samples characterized by the upregulation of genes involved in myogenesis and muscle hypertrophy. In the case of FAPs, we observed upregulation of genes involved in the extracellular matrix regeneration but also several signaling pathways. Indeed, further analysis of the potential intercellular communication profile showed a dysregulation of the communication profile in DMD samples identifying FAPs as a key regulator of cell signaling in DMD muscle samples. In conclusion, our study has identified significant differences at the cellular and molecular levels in the different cell populations present in skeletal muscle samples of patients with DMD compared to controls.

DOI: https://doi.org/10.1038/s41419-023-06103-5
Int J Mol Sci. 2023 Aug 22. pii: 13051. [Epub ahead of print]24(17):

PAX7, a Key for Myogenesis Modulation in Muscular Dystrophies through Multiple Signaling Pathways: A Systematic Review.

Nor Idayu A Rahman, Chung Liang Lam, Nadiah Sulaiman, Nur Atiqah Haizum Abdullah, Fazlina Nordin, Shahrul Hisham Zainal Ariffin, Muhammad Dain Yazid.

  Muscular dystrophy is a heterogenous group of hereditary muscle disorders caused by mutations in the genes responsible for muscle development, and is generally defined by a disastrous progression of muscle wasting and massive loss in muscle regeneration. Pax7 is closely associated with myogenesis, which is governed by various signaling pathways throughout a lifetime and is frequently used as an indicator in muscle research. In this review, an extensive literature search adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was performed to identify research that examined signaling pathways in living models, while quantifying Pax7 expression in myogenesis. A total of 247 articles were retrieved from the Web of Science (WoS), PubMed and Scopus databases and were thoroughly examined and evaluated, resulting in 19 articles which met the inclusion criteria. Admittedly, we were only able to discuss the quantification of Pax7 carried out in research affecting various type of genes and signaling pathways, rather than the expression of Pax7 itself, due to the massive differences in approach, factor molecules and signaling pathways analyzed across the research. However, we highlighted the thorough evidence for the alteration of the muscle stem cell precursor Pax7 in multiple signaling pathways described in different living models, with an emphasis on the novel approach that could be taken in manipulating Pax7 expression itself in dystrophic muscle, towards the discovery of an effective treatment for muscular dystrophy. Therefore, we believe that this could be applied to the potential gap in muscle research that could be filled by tuning the well-established marker expression to improve dystrophic muscle.

Keywords:  Pax7; muscular dystrophy; myogenesis; signaling pathways

DOI:  https://doi.org/10.3390/ijms241713051
J Pharmacol Exp Ther. 2023 Sep 07. pii: JPET-AR-2023-001593. [Epub ahead of print]

Increasing enzyme mannose-6-phosphate levels but not miglustat co-administration enhances the efficacy of enzyme replacement therapy in Pompe mice.

Allyson Anding, Sofia Kinton, Kaitlyn Baranowski, Alexander Brezzani, Hilde De Busser, Michael R Dufault, Patrick Finn, Kelly Keefe, Tanya Tetrault, Yi Li, Weiliang Qiu, Katrien Raes, Olivier Vitse, Mindy Zhang, Robin Ziegler, S Pablo Sardi, Bridge Hunter, Kelly George.

  Pompe disease is a rare glycogen storage disorder caused by a deficiency in the lysosomal enzyme acid α-glucosidase, which leads to muscle weakness, cardiac and respiratory failure, and early mortality. Alglucosidase alfa, a recombinant human acid α-glucosidase, was the first approved treatment for Pompe disease, but its uptake into skeletal muscle via the cation-independent mannose-6-phosphate (M6P) receptor (CIMPR) is limited. Avalglucosidase alfa has received marketing authorization in several countries for infantile-onset and/or late-onset Pompe disease. This recently approved enzyme replacement therapy (ERT) was glycoengineered to maximize CIMPR binding through high-affinity interactions with ~7 bis-M6P moieties. Recently, small molecules like the glucosylceramide synthase inhibitor miglustat were reported to increase the stability of recombinant human acid α-glucosidase and it was suggested that an increased serum half-life would result in better glycogen clearance. Here, the effects of miglustat on alglucosidase alfa and avalglucosidase alfa stability, activity, and efficacy in Pompe mice were evaluated. While miglustat increased the stability of both enzymes in fluorescent protein thermal shift assays and when incubated in neutral pH buffer over time, it reduced their enzymatic activity by ~50%. Improvement in tissue glycogen clearance and transcriptional dysregulation in Pompe mice correlated with M6P levels, but not with miglustat co-administration. These results further substantiate the crucial role of CIMPR binding in lysosomal targeting of ERTs. Significance Statement This work describes important new insights into the treatment of Pompe disease using currently approved ERTs co-administered with miglustat. Though miglustat increased the stability of ERTs in vitro, there was no positive impact to glycogen clearance and transcriptional correction in Pompe mice. However, increasing M6P levels resulted in increased cell uptake in vitro, and increased glycogen clearance and transcriptional correction in Pompe mice, further underscoring the crucial role of CIMPR-mediated lysosomal targeting for ERTs.

Keywords:  Autophagy; Transcriptional regulation; animal/nonclinical/preclinical; chaperones; molecular drug targeting; recombinant proteins

DOI:  https://doi.org/10.1124/jpet.123.001593
Ageing Res Rev. 2023 Sep 02. pii: S1568-1637(23)00216-7. [Epub ahead of print] 102057

Sarcopenia and malignancies: epidemiology, clinical classification and implications.

Feng-Min Zhang, Hao-Fan Wu, Han-Ping Shi, Zhen Yu, Cheng-Le Zhuang.

  Sarcopenia is a progressive systemic skeletal muscle disorder characterized by a pathological decline in muscle strength, quantity, and quality, which frequently affects the elderly population. The majority of cancer patients are of advanced age. Patients may already have sarcopenia prior to cancer development, and those with cancer are prone to developing sarcopenia due to hypercatabolism, inflammation, reduced physical fitness, anorexia, adverse effects, and stress associated with anticancer therapy. Based on the timing, sarcopenia in patients with cancer can be categorized into three: pre-existing sarcopenia before the onset of cancer, sarcopenia related to cancer, and sarcopenia related to cancer treatment. Sarcopenia not only changes the body composition of patients with cancer but also increases the incidence of postoperative complications, reduces therapeutic efficacy, impairs quality of life, and results in shortened survival. Different therapeutic strategies are required to match the cancer status and physical condition of patients with different etiologies and stages of sarcopenia. Here, we present a comprehensive review of the epidemiology and diagnosis of sarcopenia in patients with cancer, elucidate the complex interactions between cancer and sarcopenia, and provide evidence-based strategies for sarcopenia management in these patients.

Keywords:  cancer; geriatrics; muscle atrophy; muscle mass; sarcopenia; skeletal muscle

DOI:  https://doi.org/10.1016/j.arr.2023.102057
bioRxiv. 2023 Aug 23. pii: 2023.08.22.554345. [Epub ahead of print]

Disruption of Hepatic Mitochondrial Pyruvate and Amino Acid Metabolism Impairs Gluconeogenesis and Endurance Exercise Capacity in Mice.

Michael R Martino, Mohammad Habibi, Daniel Ferguson, Rita T Brookheart, John P Thyfault, Gretchen A Meyer, Louise Lantier, Curtis C Hughey, Brian N Finck.

Exercise robustly increases the glucose demands of skeletal muscle. This demand is met not only by muscle glycogenolysis, but also by accelerated liver glucose production from hepatic glycogenolysis and gluconeogenesis to fuel mechanical work and prevent hypoglycemia during exercise. Hepatic gluconeogenesis during exercise is dependent on highly coordinated responses within and between muscle and liver. Specifically, exercise increases the rate at which gluconeogenic precursors such as pyruvate/lactate or amino acids are delivered from muscle to the liver, extracted by the liver, and channeled into glucose. Herein, we examined the effects of interrupting gluconeogenic efficiency and capacity on exercise performance by deleting hepatic mitochondrial pyruvate carrier 2 (MPC2) and/or alanine transaminase 2 (ALT2) in mice. We found that deletion of MPC2 or ALT2 alone did not significantly affect time to exhaustion or post-exercise glucose concentrations in treadmill exercise tests, but mice lacking both MPC2 and ALT2 in liver (DKO) reached exhaustion faster and exhibited lower circulating glucose during and after exercise. Use of ²H/¹³C metabolic flux analyses demonstrated that DKO mice exhibited lower endogenous glucose production owing to decreased glycogenolysis and gluconeogenesis at rest and during exercise. The decreased gluconeogenesis was accompanied by lower anaplerotic, cataplerotic, and TCA cycle fluxes. Collectively, these findings demonstrate that the transition of the liver to the gluconeogenic mode is critical for preventing hypoglycemia and sustaining performance during exercise. The results also illustrate the need for interorgan crosstalk during exercise as described by the Cahill and Cori cycles.

DOI: https://doi.org/10.1101/2023.08.22.554345
J Clin Med. 2023 Aug 29. pii: 5628. [Epub ahead of print]12(17):

Mitochondrial Dysfunction and Sarcopenic Obesity: The Role of Exercise.

Spyridon Hadjispyrou, Antonios Giannopoulos, Anastassios Philippou, Apostolos Theos.

  Sarcopenic obesity (SO) constitutes the coexistence of skeletal muscle mass loss (sarcopenia) and excess adiposity (obesity). It is mainly considered as a condition in the elderly with health-threatening impacts ranging from frailty to mortality. Mitochondrial dysfunction consists one of the basic pathophysiological mechanisms leading to the development of SO and its consequences. Indirect indicators of mitochondrial function, such as VO2max and exercise capacity, have been demonstrated to be negatively affected in individuals with SO, while the positive effect of exercise on mitochondrial function has been widely proved; thus, in this review, we aimed at investigating the effects of endurance, resistance, and concurrent exercise training on indexes of mitochondrial dysfunction in SO patients. The results of the clinical trials evaluated reveal positive effects of chronic exercise on VO2max and physical capacity, as well as mitochondrial biogenesis and activity. It has been concluded that utilizing a systematic exercise training program that includes both aerobic and strength exercises can be an effective strategy for managing SO and promoting overall health in these patients.

Keywords:  VO2max; mitochondria; physical capacity; sarcopenia; training

DOI:  https://doi.org/10.3390/jcm12175628
Intractable Rare Dis Res. 2023 Aug;12(3): 180-190

The novel role of IFITM1-3 in myogenic differentiation of C2C12 cells.

Yongtao Zhang, Yanqin Lu, Xianxian Li, Shanshan Zhang, Pengchao Liu, Xiaoyang Hao, Jinxiang Han.

  Interferon-induced transmembrane proteins (IFITMs 1, 2, and 3) play a critical role in preventing pathogen infection in vertebrates. They are also involved in the occurrence and prognosis of cancer. Myogenesis is a complex process regulated by several factors. This study disclosed that Ifitm1-3 were upregulated in the process of myogenic differentiation of C2C12 myoblasts on days 3, 5, and 7. This positively correlated with the expression of differentiation factors MyoD, myogenin, Mrf5, and desmin. Furthermore, knockdown of Ifitm1-3 by their individual siRNAs inhibited myogenesis of C2C12 myoblasts, with relative downregulation of MyoD, myogenin, Mrf5, and desmin. Subsequently, myotube formation and fusion percentage decreased. Co-immunoprecipitation combined with LC-MS/MS analysis uncovered the interaction proteins of IFITM1 and IFITM3 in C2C12 myoblasts. A total of 84 overlapped interaction proteins of IFITM1 and IFITM3 were identified, and one of the clusters was engaged in cytoskeletal and sarcomere proteins, including desmin, myosin, actin, vimentin, nestin, ankycorbin, and nucleolin. Hence, we hypothesize that these interacting proteins may function as scaffolds for IFITM1-3, possibly through the interaction protein desmin to initiate further interaction with other proteins to participate in myogenesis; however, the molecular mechanisms remain unclear. Our study may contribute to the development of novel therapeutics for myopathic diseases.

Keywords:  IFITM1; IFITM3; desmin; myogenesis; sarcomere

DOI:  https://doi.org/10.5582/irdr.2023.01050
Front Cell Dev Biol. 2023 ;11 1226707

Elucidation of bioinformatic-guided high-prospect drug repositioning candidates for DMD via Swanson linking of target-focused latent knowledge from text-mined categorical metadata.

J Wes Ulm, Florian Barthélémy, Stanley F Nelson.

  Duchenne Muscular Dystrophy (DMD)'s complex multi-system pathophysiology, coupled with the cost-prohibitive logistics of multi-year drug screening and follow-up, has hampered the pursuit of new therapeutic approaches. Here we conducted a systematic historical and text mining-based pilot feasibility study to explore the potential of established or previously tested drugs as prospective DMD therapeutic agents. Our approach utilized a Swanson linking-inspired method to uncover meaningful yet largely hidden deep semantic connections between pharmacologically significant DMD targets and drugs developed for unrelated diseases. Specifically, we focused on molecular target-based MeSH terms and categories as high-yield bioinformatic proxies, effectively tagging relevant literature with categorical metadata. To identify promising leads, we comprehensively assembled published reports from 2011 and sampling from subsequent years. We then determined the earliest year when distinct MeSH terms or category labels of the relevant cellular target were referenced in conjunction with the drug, as well as when the pertinent target itself was first conclusively identified as holding therapeutic value for DMD. By comparing the earliest year when the drug was identifiable as a DMD treatment candidate with that of the first actual report confirming this, we computed an Index of Delayed Discovery (IDD), which serves as a metric of Swanson-linked latent knowledge. Using these findings, we identified data from previously unlinked articles subsetted via MeSH-derived Swanson linking or from target classes within the DrugBank repository. This enabled us to identify new but untested high-prospect small-molecule candidates that are of particular interest in repurposing for DMD and warrant further investigations.

Keywords:  DMD; MeSH; Swanson linking; data mining; drug repositioning; drug repurposing; latent knowledge; therapy

DOI:  https://doi.org/10.3389/fcell.2023.1226707
Cell Discov. 2023 Sep 07. 9(1): 92

Lysosomes mediate the mitochondrial UPR via mTORC1-dependent ATF4 phosphorylation.

Terytty Yang Li, Qi Wang, Arwen W Gao, Xiaoxu Li, Yu Sun, Adrienne Mottis, Minho Shong, Johan Auwerx.

Lysosomes are central platforms for not only the degradation of macromolecules but also the integration of multiple signaling pathways. However, whether and how lysosomes mediate the mitochondrial stress response (MSR) remain largely unknown. Here, we demonstrate that lysosomal acidification via the vacuolar H+-ATPase (v-ATPase) is essential for the transcriptional activation of the mitochondrial unfolded protein response (UPRmt). Mitochondrial stress stimulates v-ATPase-mediated lysosomal activation of the mechanistic target of rapamycin complex 1 (mTORC1), which then directly phosphorylates the MSR transcription factor, activating transcription factor 4 (ATF4). Disruption of mTORC1-dependent ATF4 phosphorylation blocks the UPRmt, but not other similar stress responses, such as the UPRER. Finally, ATF4 phosphorylation downstream of the v-ATPase/mTORC1 signaling is indispensable for sustaining mitochondrial redox homeostasis and protecting cells from ROS-associated cell death upon mitochondrial stress. Thus, v-ATPase/mTORC1-mediated ATF4 phosphorylation via lysosomes links mitochondrial stress to UPRmt activation and mitochondrial function resilience.

DOI: https://doi.org/10.1038/s41421-023-00589-1