bims-moremu 2023-10-22 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–10–22
25 papers selected by
Anna Vainshtein, Craft Science Inc.

Resistance training in humans and mechanical overload in rodents do not elevate muscle protein lactylation.
Klotho regulates the myogenic response of muscle to mechanical loading and exercise.
Inherited myogenic abilities in muscle precursor cells defined by the mitochondrial complex I-encoding protein.
Cellular pathogenesis of Duchenne muscular dystrophy: progressive myofibre degeneration, chronic inflammation, reactive myofibrosis and satellite cell dysfunction.
Hypochlorous acid exposure impairs skeletal muscle function and Ca2+ signalling: implications for Duchenne muscular dystrophy pathology.
The Effect of Heat Stress on Heat Shock Protein Expression and Hypertrophy Related Signaling in the Skeletal Muscle of Trained Individuals.
A single bout of prior resistance exercise attenuates muscle atrophy and declines in myofibrillar protein synthesis during bed-rest in older men.
Overcoming muscle stem cell aging.
Reprogramming of cis-regulatory networks during skeletal muscle atrophy in male mice.
High-fat diet increases electron transfer flavoprotein synthesis and lipid respiration in skeletal muscle during exercise training in female mice.
Intravital microscopy of satellite cell dynamics and their interaction with myeloid cells during skeletal muscle regeneration.
SIRT4 is a regulator of human skeletal muscle fatty acid metabolism influencing inner and outer mitochondrial-mediated fusion.
Myopathologic trajectory in Duchenne muscular dystrophy (DMD) reveals lack of regeneration due to senescence in satellite cells.
Divergent Skeletal Muscle Metabolomic Signatures of Different Exercise Training Modes Independently Predict Cardiometabolic Risk Factors.
FSHD muscle shows perturbation in fibroadipogenic progenitor cells, mitochondrial function and alternative splicing independently of inflammation.
The effects of environmental enrichment on voluntary physical activity and muscle mass gain in growing rats.
High-Intensity Interval Training Attenuates Impairment in Regulatory Protein Machinery of Mitochondrial Quality Control in Skeletal Muscle of Diet-Induced Obese Mice.
One bout of endurance exercise does not change gene expression or proliferation in a C26 colon carcinoma in immunocompetent mice.
Mechanism of Skeletal Muscle Atrophy by Muscle Fiber Types in Male Rats under Long-term Fasting Stress.
Staufen1 controls mitochondrial metabolism via HIF2α in embryonal rhabdomyosarcoma and promotes tumorigenesis.
Exerkines: A Crosstalk between Lactate Production, Exercise and Mental Health.
Traumatic muscle injury.
Skeletal muscle injury in COVID infection: Frequency and patterns.
Vitamin D status associates with skeletal muscle loss after anterior cruciate ligament reconstruction.
StarD7 deficiency switches on glycolysis and promotes mitophagy flux in C2C12 myoblasts.

Front Physiol. 2023 ;14 1281702

Resistance training in humans and mechanical overload in rodents do not elevate muscle protein lactylation.

Madison L Mattingly, Bradley A Ruple, Casey L Sexton, Joshua S Godwin, Mason C McIntosh, Morgan A Smith, Daniel L Plotkin, J Max Michel, Derick A Anglin, Nicholas J Kontos, Shengyi Fei, Stuart M Phillips, C Brooks Mobley, Ivan Vechetti, Christopher G Vann, Michael D Roberts.

  Although several reports have hypothesized that exercise may increase skeletal muscle protein lactylation, empirical evidence in humans is lacking. Thus, we adopted a multi-faceted approach to examine if acute and subchronic resistance training (RT) altered skeletal muscle protein lactylation levels. In mice, we also sought to examine if surgical ablation-induced plantaris hypertrophy coincided with increases in muscle protein lactylation. To examine acute responses, participants' blood lactate concentrations were assessed before, during, and after eight sets of an exhaustive lower body RT bout (n = 10 trained college-aged men). Vastus lateralis biopsies were also taken before, 3-h post, and 6-h post-exercise to assess muscle protein lactylation. To identify training responses, another cohort of trained college-aged men (n = 14) partook in 6 weeks of lower-body RT (3x/week) and biopsies were obtained before and following the intervention. Five-month-old C57BL/6 mice were subjected to 10 days of plantaris overload (OV, n = 8) or served as age-matched sham surgery controls (Sham, n = 8). Although acute resistance training significantly increased blood lactate responses ∼7.2-fold (p < 0.001), cytoplasmic and nuclear protein lactylation levels were not significantly altered at the post-exercise time points, and no putative lactylation-dependent mRNA was altered following exercise. Six weeks of RT did not alter cytoplasmic protein lactylation (p = 0.800) despite significantly increasing VL muscle size (+3.5%, p = 0.037), and again, no putative lactylation-dependent mRNA was significantly affected by training. Plantaris muscles were larger in OV versus Sham mice (+43.7%, p < 0.001). However, cytoplasmic protein lactylation was similar between groups (p = 0.369), and nuclear protein lactylation was significantly lower in OV versus Sham mice (p < 0.001). The current null findings, along with other recent null findings in the literature, challenge the thesis that lactate has an appreciable role in promoting skeletal muscle hypertrophy.

Keywords:  hypertrophy; lactate; lactylation; posttranslational modification; skeletal muscle

DOI:  https://doi.org/10.3389/fphys.2023.1281702
Exp Physiol. 2023 Oct 20.

Klotho regulates the myogenic response of muscle to mechanical loading and exercise.

Eisuke Ochi, Alice Barrington, Michelle Wehling-Henricks, Marcus Avila, Makoto Kuro-O, James G Tidball.

   NEW FINDINGS: What is the central question of this study? Does the hormone Klotho affect the myogenic response of muscle cells to mechanical loading or exercise? What is the main finding and its importance? Klotho prevents direct, mechanical activation of genes that regulate muscle differentiation, including genes that encode the myogenic regulatory factor myogenin and proteins in the canonical Wnt signalling pathway. Similarly, elevated levels of klotho expression in vivo prevent the exercise-induced increase in myogenin-expressing cells and reduce exercise-induced activation of the Wnt pathway. These findings demonstrate a new mechanism through which the responses of muscle to the mechanical environment are regulated.
ABSTRACT: Muscle growth is influenced by changes in the mechanical environment that affect the expression of genes that regulate myogenesis. We tested whether the hormone Klotho could influence the response of muscle to mechanical loading. Applying mechanical loads to myoblasts in vitro increased RNA encoding transcription factors that are expressed in activated myoblasts (Myod) and in myogenic cells that have initiated terminal differentiation (Myog). However, application of Klotho to myoblasts prevented the loading-induced activation of Myog without affecting loading-induced activation of Myod. This indicates that elevated Klotho inhibits mechanically-induced differentiation of myogenic cells. Elevated Klotho also reduced the transcription of genes encoding proteins involved in the canonical Wnt pathway or their target genes (Wnt9a, Wnt10a, Ccnd1). Because the canonical Wnt pathway promotes differentiation of myogenic cells, these findings indicate that Klotho inhibits the differentiation of myogenic cells experiencing mechanical loading. We then tested whether these effects of Klotho occurred in muscles of mice experiencing high-intensity interval training (HIIT) by comparing wild-type mice and klotho transgenic mice. The expression of a klotho transgene combined with HIIT synergized to tremendously elevate numbers of Pax7+ satellite cells and activated MyoD+ cells. However, transgene expression prevented the increase in myogenin+ cells caused by HIIT in wild-type mice. Furthermore, transgene expression diminished the HIIT-induced activation of the canonical Wnt pathway in Pax7+ satellite cells. Collectively, these findings show that Klotho inhibits loading- or exercise-induced activation of muscle differentiation and indicate a new mechanism through which the responses of muscle to the mechanical environment are regulated.

Keywords:  Klotho; Wnt; exercise; myogenesis; satellite cell; skeletal muscle

DOI:  https://doi.org/10.1113/EP091263
Cell Death Dis. 2023 Oct 19. 14(10): 689

Inherited myogenic abilities in muscle precursor cells defined by the mitochondrial complex I-encoding protein.

Norio Motohashi, Katsura Minegishi, Yoshitsugu Aoki.

Skeletal muscle comprises different muscle fibers, including slow- and fast-type muscles, and satellite cells (SCs), which exist in individual muscle fibers and possess different myogenic properties. Previously, we reported that myoblasts (MBs) from slow-type enriched soleus (SOL) had a high potential to self-renew compared with cells derived from fast-type enriched tibialis anterior (TA). However, whether the functionality of myogenic cells in adult muscles is attributed to the muscle fiber in which they reside and whether the characteristics of myogenic cells derived from slow- and fast-type fibers can be distinguished at the genetic level remain unknown. Global gene expression analysis revealed that the myogenic potential of MBs was independent of the muscle fiber type they reside in but dependent on the region of muscles they are derived from. Thus, in this study, proteomic analysis was conducted to clarify the molecular differences between MBs derived from TA and SOL. NADH dehydrogenase (ubiquinone) iron-sulfur protein 8 (Ndufs8), a subunit of NADH dehydrogenase in mitochondrial complex I, significantly increased in SOL-derived MBs compared with that in TA-derived cells. Moreover, the expression level of Ndufs8 in MBs significantly decreased with age. Gain- and loss-of-function experiments revealed that Ndufs8 expression in MBs promoted differentiation, self-renewal, and apoptosis resistance. In particular, Ndufs8 suppression in MBs increased p53 acetylation, followed by a decline in NAD/NADH ratio. Nicotinamide mononucleotide treatment, which restores the intracellular NAD+ level, could decrease p53 acetylation and increase myogenic cell self-renewal ability in vivo. These results suggested that the functional differences in MBs derived from SOL and TA governed by the mitochondrial complex I-encoding gene reflect the magnitude of the decline in SC number observed with aging, indicating that the replenishment of NAD+ is a possible approach for improving impaired cellular functions caused by aging or diseases.

DOI: https://doi.org/10.1038/s41419-023-06192-2
Eur J Transl Myol. 2023 10 16.

Cellular pathogenesis of Duchenne muscular dystrophy: progressive myofibre degeneration, chronic inflammation, reactive myofibrosis and satellite cell dysfunction.

Paul Dowling, Dieter Swandulla, Kay Ohlendieck.

Duchenne muscular dystrophy is a highly progressive muscle wasting disease of early childhood and characterized by complex pathophysiological and histopathological changes in the voluntary contractile system, including myonecrosis, chronic inflammation, fat substitution and reactive myofibrosis. The continued loss of functional myofibres and replacement with non-contractile cells, as well as extensive tissue scarring and decline in tissue elasticity, leads to severe skeletal muscle weakness. In addition, dystrophic muscles exhibit a greatly diminished regenerative capacity to counteract the ongoing process of fibre degeneration. In normal muscle tissues, an abundant stem cell pool consisting of satellite cells that are localized between the sarcolemma and basal lamina, provides a rich source for the production of activated myogenic progenitor cells that are involved in efficient myofibre repair and tissue regeneration. Interestingly, the self-renewal of satellite cells for maintaining an essential pool of stem cells in matured skeletal muscles is increased in dystrophin-deficient fibres. However, satellite cell hyperplasia does not result in efficient recovery of dystrophic muscles due to impaired asymmetric cell divisions. The lack of expression of the full-length dystrophin isoform Dp427-M, which is due to primary defects in the DMD gene, appears to affect key regulators of satellite cell polarity causing a reduced differentiation of myogenic progenitors, which are essential for myofibre regeneration. This review outlines the complexity of dystrophinopathy and describes the importance of the pathophysiological role of satellite cell dysfunction. A brief discussion of the bioanalytical usefulness of single cell proteomics for future studies of satellite cell biology is provided.

DOI: https://doi.org/10.4081/ejtm.2023.11856
J Physiol. 2023 Oct 21.

Hypochlorous acid exposure impairs skeletal muscle function and Ca2+ signalling: implications for Duchenne muscular dystrophy pathology.

Thomas A Lea, Peter M Panizza, Peter G Arthur, Anthony J Bakker, Gavin J Pinniger.

  Duchenne muscular dystrophy (DMD) is a fatal X-linked disease characterised by severe muscle wasting. The mechanisms underlying the DMD pathology likely involve the interaction between inflammation, oxidative stress and impaired Ca2+ signalling. Hypochlorous acid (HOCl) is a highly reactive oxidant produced endogenously via myeloperoxidase; an enzyme secreted by neutrophils that is significantly elevated in dystrophic muscle. Oxidation of Ca2+ -handling proteins by HOCl may impair Ca2+ signalling. This study aimed to determine the effects of HOCl on skeletal muscle function and its potential contribution to the dystrophic pathology. Extensor digitorum longus (EDL), soleus and interosseous muscles were surgically isolated from anaesthetised C57 (wild-type) and mdx (dystrophic) mice for measurement of ex vivo force production and intracellular Ca2+ concentration. In whole EDL muscle, HOCl (200 μM) significantly decreased maximal force and increased resting muscle tension which was only partially reversible by dithiothreitol. The effects of HOCl (200 μM) on maximal force in slow-twitch soleus were lower than found in the fast-twitch EDL muscle. In single interosseous myofibres, HOCl (10 μM) significantly increased resting intracellular Ca2+ concentration and decreased Ca2+ transient amplitude. These effects of HOCl were reduced by the application of tetracaine, Gd3+ or streptomycin, implicating involvement of ryanodine receptors and transient receptor potential channels. These results demonstrate the potent effects of HOCl on skeletal muscle function potentially mediated by HOCl-induced oxidation to Ca2+ signalling proteins. Hence, HOCl may provide a link between chronic inflammation, oxidative stress and impaired Ca2+ handling that is characteristic of DMD and presents a potential therapeutic target for DMD. KEY POINTS: Duchenne muscular dystrophy is a fatal genetic disease with pathological mechanisms which involve the complex interaction of chronic inflammation, increased reactive oxygen species production and increased cytosolic Ca2+ concentrations. Hypochlorous acid can be endogenously produced by neutrophils via the enzyme myeloperoxidase. Both neutrophil and myeloperoxidase activity are increased in dystrophic mice. This study found that hypochlorous acid decreased muscle force production and increased cytosolic Ca2+ concentrations in isolated muscles from wild-type and dystrophic mice at relatively low concentrations of hypochlorous acid. These results indicate that hypochlorous acid may be key in the Duchenne muscular dystrophy disease pathology and may provide a unifying link between the chronic inflammation, increased reactive oxygen species production and increased cytosolic Ca2+ concentrations observed in Duchenne muscular dystrophy. Hypochlorous acid production may be a potential target for therapeutic treatments of Duchenne muscular dystrophy.

Keywords:  Ca2+; Duchenne muscular dystrophy; hypochlorous acid; inflammation; myeloperoxidase; neutrophils; reactive oxygen species; skeletal muscle

DOI:  https://doi.org/10.1113/JP285263
Am J Physiol Regul Integr Comp Physiol. 2023 Oct 16.

The Effect of Heat Stress on Heat Shock Protein Expression and Hypertrophy Related Signaling in the Skeletal Muscle of Trained Individuals.

Zachary J Fennel, Jeremy B Ducharme, Quint N Berkemeier, Jonathan W Specht, Zachary J McKenna, Shandy E Simpson, Roberto C Nava, Kurt A Escobar, Paul S Hafen, Michael R Deyhle, Fabiano T Amorim, Christine M Mermier.

  Muscle mass is balanced between hypertrophy and atrophy by cellular processes, including activation of the Akt-mTOR signaling cascade. Stressors apart from exercise and nutrition, such as heat stress, can stimulate the heat shock protein A (HSPA) and C (HSPC) families alongside hypertrophic signaling factors and muscle growth. The effects of heat stress on HSP expression and Akt-mTOR activation in human skeletal muscle, and their magnitude of activation compared to known hypertrophic stimuli is unclear. Here we show a single session of whole-body heat stress followed by resistance exercise increases the expression of HSPA as well as activation of the Akt-mTOR cascade in skeletal muscle compared to resistance exercise in a healthy, resistance trained population. Heat stress alone may also exert similar effects, though the responses are notably variable and require further investigation. Additionally, acute heat stress in C2C12 muscle cells enhanced myotube growth and myogenic fusion, albeit to a lesser degree than growth factor mediated hypertrophy. Though the mechanisms by which heat stress stimulates hypertrophy related signaling and the potential mechanistic role of HSPs remain unclear, these findings provide additional evidence implicating heat stress as a novel growth stimulus when combined with resistance exercise in human skeletal muscle and alone in isolated murine muscle cells. We believe these findings will help drive further applied and mechanistic investigation into how heat stress influences muscular hypertrophy and atrophy.

Keywords:  Heat Shock Proteins; Heat Stress; Hypertrophy; Resistance Exercise

DOI:  https://doi.org/10.1152/ajpregu.00031.2023
J Physiol. 2023 Oct 19.

A single bout of prior resistance exercise attenuates muscle atrophy and declines in myofibrillar protein synthesis during bed-rest in older men.

Benoit Smeuninx, Yasir S Elhassan, Elizabeth Sapey, Alison B Rushton, Paul T Morgan, Marie Korzepa, Archie E Belfield, Andrew Philp, Matthew S Brook, Nima Gharahdaghi, Daniel Wilkinson, Kenneth Smith, Philip J Atherton, Leigh Breen.

  Impairments in myofibrillar protein synthesis (MyoPS) during bed rest accelerate skeletal muscle loss in older adults, increasing the risk of adverse secondary health outcomes. We investigated the effect of prior resistance exercise (RE) on MyoPS and muscle morphology during a disuse event in 10 healthy older men (65-80 years). Participants completed a single bout of unilateral leg RE the evening prior to 5 days of in-patient bed-rest. Quadriceps cross-sectional area (CSA) was determined prior to and following bed-rest. Serial muscle biopsies and dual stable isotope tracers were used to determine rates of integrated MyoPS (iMyoPS) over a 7 day habitual 'free-living' phase and the bed-rest phase, and rates of acute postabsorptive and postprandial MyoPS (aMyoPS) at the end of bed rest. Quadriceps CSA at 40%, 60% and 80% of muscle length significantly decreased in exercised (EX) and non-exercised control (CTL) legs with bed-rest. The decline in quadriceps CSA at 40% and 60% of muscle length was attenuated in EX compared with CTL. During bed-rest, iMyoPS rates decreased from habitual values in CTL, but not EX, and were significantly different between legs. Postprandial aMyoPS rates increased above postabsorptive values in EX only. The change in iMyoPS over bed-rest correlated with the change in quadriceps CSA in CTL, but not EX. A single bout of RE attenuated the decline in iMyoPS rates and quadriceps atrophy with 5 days of bed-rest in older men. Further work is required to understand the functional and clinical implications of prior RE in older patient populations. KEY POINTS: Age-related skeletal muscle deterioration, linked to numerous adverse health outcomes, is driven by impairments in muscle protein synthesis that are accelerated during periods of disuse. Resistance exercise can stimulate muscle protein synthesis over several days of recovery and therefore could counteract impairments in this process that occur in the early phase of disuse. In the present study, we demonstrate that the decline in myofibrillar protein synthesis and muscle atrophy over 5 days of bed-rest in older men was attenuated by a single bout of unilateral resistance exercise performed the evening prior to bed-rest. These findings suggest that concise resistance exercise intervention holds the potential to support muscle mass retention in older individuals during short-term disuse, with implications for delaying sarcopenia progression in ageing populations.

Keywords:  disuse; exercise training; muscle anabolism; sarcopenia

DOI:  https://doi.org/10.1113/JP285130
Curr Opin Genet Dev. 2023 Oct 13. pii: S0959-437X(23)00107-7. [Epub ahead of print]83 102127

Overcoming muscle stem cell aging.

Sebastian Memczak, Juan Ci Belmonte.

Reduced muscle strength and mass is one of the hallmarks of physiological aging in humans and can result in severe impairment of the quality of life. In part this is caused by a functional loss of the highly specialized muscle stem cells (MuSCs), which in healthy conditions provide maintenance, growth, and regeneration. Recent progress in understanding of the stem cell niche and results from single cell technologies reveal exciting insights at unprecedented detail into MuSCs and muscle biology during aging. Here, we review this field and discuss the implications of current findings with a focus on cellular reprogramming approaches as a novel therapeutic avenue for age-related muscle decline.

DOI: https://doi.org/10.1016/j.gde.2023.102127
Nat Commun. 2023 Oct 18. 14(1): 6581

Reprogramming of cis-regulatory networks during skeletal muscle atrophy in male mice.

Hongchun Lin, Hui Peng, Yuxiang Sun, Meijun Si, Jiao Wu, Yanlin Wang, Sandhya S Thomas, Zheng Sun, Zhaoyong Hu.

A comprehensive atlas of cis-regulatory elements and their dynamic activity is necessary to understand the transcriptional basis of cellular structure maintenance, metabolism, and responses to the environment. Here we show, using matched single-nucleus chromatin accessibility and RNA-sequencing from juvenile male C57BL6 mice, an atlas of accessible chromatin regions in both normal and denervated skeletal muscles. We identified cell-type-specific cis-regulatory networks, highlighting the dynamic regulatory circuits mediating transitions between myonuclear types. Through comparison of normal and perturbed muscle, we delineated the reprogramming of cis-regulatory networks in response to denervation, described the interplay of promoters/enhancers and target genes. We further unveil a hierarchical structure of transcription factors that delineate a regulatory network in atrophic muscle, identifying ELK4 as a key atrophy-related transcription factor that instigates muscle atrophy through TGF-β1 regulation. This study furnishes a rich genomic resource, essential for decoding the regulatory dynamics of skeletal muscle in both physiological and pathological states.

DOI: https://doi.org/10.1038/s41467-023-42313-3
Physiol Rep. 2023 Oct;11(20): e15840

High-fat diet increases electron transfer flavoprotein synthesis and lipid respiration in skeletal muscle during exercise training in female mice.

Philip M Batterson, Erin M McGowan, Agnieszka K Borowik, Michael T Kinter, Benjamin F Miller, Sean A Newsom, Matthew M Robinson.

  High-fat diet (HFD) and exercise remodel skeletal muscle mitochondria. The electron transfer flavoproteins (ETF) transfer reducing equivalents from β-oxidation into the electron transfer system. Exercise may stimulate the synthesis of ETF proteins to increase lipid respiration. We determined mitochondrial remodeling for lipid respiration through ETF in the context of higher mitochondrial abundance/capacity seen in female mice. We hypothesized HFD would be a greater stimulus than exercise to remodel ETF and lipid pathways through increased protein synthesis alongside increased lipid respiration. Female C57BL/6J mice (n = 15 per group) consumed HFD or low-fat diet (LFD) for 4 weeks then remained sedentary (SED) or completed 8 weeks of treadmill training (EX). We determined mitochondrial lipid respiration, RNA abundance, individual protein synthesis, and abundance for ETFα, ETFβ, and ETF dehydrogenase (ETFDH). HFD increased absolute and relative lipid respiration (p = 0.018 and p = 0.034) and RNA abundance for ETFα (p = 0.026), ETFβ (p = 0.003), and ETFDH (p = 0.0003). HFD increased synthesis for ETFα and ETFDH (p = 0.0007 and p = 0.002). EX increased synthesis of ETFβ and ETFDH (p = 0.008 and p = 0.006). Higher synthesis rates of ETF were not always reflected in greater protein abundance. Greater synthesis of ETF during HFD indicates mitochondrial remodeling which may contribute higher mitochondrial lipid respiration through enhanced ETF function.

Keywords:  exercise; females; high-fat feeding; mitochondrial respiration; skeletal muscle

DOI:  https://doi.org/10.14814/phy2.15840
Sci Adv. 2023 Oct 20. 9(42): eadi1891

Intravital microscopy of satellite cell dynamics and their interaction with myeloid cells during skeletal muscle regeneration.

Yingzhu He, Youshan Heng, Zhongya Qin, Xiuqing Wei, Zhenguo Wu, Jianan Qu.

Skeletal muscle regeneration requires the highly coordinated cooperation of muscle satellite cells (MuSCs) with other cellular components. Upon injury, myeloid cells populate the wound site, concomitant with MuSC activation. However, detailed analysis of MuSC-myeloid cell interaction is hindered by the lack of suitable live animal imaging technology. Here, we developed a dual-laser multimodal nonlinear optical microscope platform to study the dynamics of MuSCs and their interaction with nonmyogenic cells during muscle regeneration. Using three-dimensional time-lapse imaging on live reporter mice and taking advantages of the autofluorescence of reduced nicotinamide adenine dinucleotide (NADH), we studied the spatiotemporal interaction between nonmyogenic cells and muscle stem/progenitor cells during MuSC activation and proliferation. We discovered that their cell-cell contact was transient in nature. Moreover, MuSCs could activate with notably reduced infiltration of neutrophils and macrophages, and their proliferation, although dependent on macrophages, did not require constant contact with them. These findings provide a fresh perspective on myeloid cells' role during muscle regeneration.

DOI: https://doi.org/10.1126/sciadv.adi1891
Cell Signal. 2023 Oct 17. pii: S0898-6568(23)00346-7. [Epub ahead of print] 110931

SIRT4 is a regulator of human skeletal muscle fatty acid metabolism influencing inner and outer mitochondrial-mediated fusion.

John Noone, Keith D Rochfort, Finbarr O'Sullivan, Donal J O'Gorman.

   OBJECTIVE: The mitochondrial phenotype, governed by the balance of fusion-fission, is a key determinant of energy metabolism. The inner and outer mitochondrial membrane (IMM) fusion proteins optic atrophy 1 (OPA1) and Mitofusin 1 and 2 (Mfn1/2) play an important role in this process. Recent evidence also shows that Sirtuin 4 (SIRT4), located within the mitochondria, is involved in the regulation of fatty acid oxidation. The purpose of this study was to determine if SIRT4 expression regulates inner and outer mitochondrial-mediated fusion and substrate utilization within differentiated human skeletal muscle cells (HSkMC).
MATERIAL AND METHODS: SIRT4 expression was knocked down using small interfering RNA (siRNA) transfection in differentiated HSkMC. Following knockdown, mitochondrial respiration was determined by high-resolution respirometry (HRR) using the Oroboros Oxygraph O2k. Live cell confocal microscopy, quantified using the Mitochondrial Network Analysis (MiNA) toolset, was used to examine mitochondrial morphological change. This was further examined through the measurement of key metabolic and mitochondrial morphological regulators (mRNA and protein) induced by knockdown.
RESULTS: SIRT4 knockdown resulted in a significant decrease in LEAK respiration, potentially explained by a decrease in ANT1 protein expression. Knockdown further increased oxidative phosphorylation and protein expression of key regulators of fatty acid metabolism. Quantitative analysis of live confocal imaging of fluorescently labelled mitochondria following SIRT4 knockdown supported the role SIRT4 plays in the regulation of mitochondrial morphology, as emphasized by an increase in mitochondrial network branches and junctions. Measurement of key regulators of mitochondrial dynamics illustrated a significant increase in mitochondrial fusion proteins Mfn1, OPA1 respectively, indicative of an increase in mitochondrial size.
CONCLUSIONS: This study provides evidence of a direct relationship between the mitochondrial phenotype and substrate oxidation in HSkMC. We identify SIRT4 as a key protagonist of energy metabolism via its regulation of IMM and OMM fusion proteins, OPA1 and Mfn1. SIRT4 knockdown increases mitochondrial capacity to oxidize fatty acids, decreasing LEAK respiration and further increasing mitochondrial elongation via its regulation of mitochondrial fusion.

Keywords:  Metabolism; Mitochondrial dynamics; Mitochondrial function; OPA1; Sirtuin; Skeletal muscle

DOI:  https://doi.org/10.1016/j.cellsig.2023.110931
Acta Neuropathol Commun. 2023 Oct 19. 11(1): 167

Myopathologic trajectory in Duchenne muscular dystrophy (DMD) reveals lack of regeneration due to senescence in satellite cells.

Nastasia Cardone, Valentina Taglietti, Serena Baratto, Kaouthar Kefi, Baptiste Periou, Ciryl Gitiaux, Christine Barnerias, Peggy Lafuste, France Leturcq Pharm, Juliette Nectoux Pharm, Chiara Panicucci, Isabelle Desguerre, Claudio Bruno, François-Jerome Authier, Chiara Fiorillo, Frederic Relaix, Edoardo Malfatti.

  Duchenne muscular dystrophy (DMD) is a devastating X-linked muscular disease, caused by mutations in the DMD gene encoding Dystrophin and affecting 1:5000 boys worldwide. Lack of Dystrophin leads to progressive muscle wasting and degeneration resulting in cardiorespiratory failure. Despite the absence of a definitive cure, innovative therapeutic avenues are emerging. Myopathologic studies are important to further understand the biological mechanisms of the disease and to identify histopathologic benchmarks for clinical evaluations. We conducted a myopathologic analysis on twenty-four muscle biopsies from DMD patients, with particular emphasis on regeneration, fibro-adipogenic progenitors and muscle stem cells behavior. We describe an increase in content of fibro-adipogenic progenitors, central orchestrators of fibrotic progression and lipid deposition, concurrently with a decline in muscle regenerative capacity. This regenerative impairment strongly correlates with compromised activation and expansion of muscle stem cells. Furthermore, our study uncovers an early acquisition of a senescence phenotype by DMD-afflicted muscle stem cells. Here we describe the myopathologic trajectory intrinsic to DMD and establish muscle stem cell senescence as a pivotal readout for future therapeutic interventions.

Keywords:  Cellular senescence; Duchenne muscular dystrophy; FAPs; Fibrosis; Muscle regeneration

DOI:  https://doi.org/10.1186/s40478-023-01657-z
Diabetes. 2023 Oct 20. pii: db230142. [Epub ahead of print]

Divergent Skeletal Muscle Metabolomic Signatures of Different Exercise Training Modes Independently Predict Cardiometabolic Risk Factors.

Mark W Pataky, Arathi Prabha Kumar, David A Gaul, Samuel G Moore, Surendra Dasari, Matthew M Robinson, Katherine A Klaus, A Aneesh Kumar, Facundo M Fernandez, K Sreekumaran Nair.

We investigated the link between enhancement of insulin sensitivity (SI) (by hyperinsulinemiceuglycemic clamp) and muscle metabolites following 12-weeks of aerobic (high-intensity interval training, HIIT), resistance (RT), or combined (CT) exercise training in 52 lean healthy people. Muscle RNA-sequencing revealed a significant association between SI following both HIIT and RT and the branched chain amino acid (BCAA) metabolic pathway. Concurrent to increased expression and activity of branched chain ketoacid dehydrogenase enzyme, many muscle amino metabolites including BCAAs, glutamate, phenylalanine, aspartate, asparagine, methionine, and GABA increased by HIIT, supporting substantial impact of HIIT on amino acid metabolism. Short-chain C3 and C5 acylcarnitines were reduced in muscle by all three training modes, but unlike RT, both HIIT and CT increased TCA metabolites and cardiolipins, supporting greater mitochondrial activity by aerobic training. Conversely, RT and CT increased more plasma membrane phospholipids than HIIT, suggesting a resistance exercise effect on cellular membrane protection against environmental damage. Sex and age contributed modestly to the exerciseinduced changes in metabolites and their association to cardiometabolic parameters. Integrated transcriptomic and metabolomic analyses suggest various clusters of genes and metabolites are involved in distinct effects of HIIT, RT, and CT. These distinct metabolic signatures of different exercise modes independently link each type of exercise training to improved SI and cardiometabolic risk.

DOI: https://doi.org/10.2337/db23-0142
Hum Mol Genet. 2023 Oct 19. pii: ddad175. [Epub ahead of print]

FSHD muscle shows perturbation in fibroadipogenic progenitor cells, mitochondrial function and alternative splicing independently of inflammation.

Elise N Engquist, Anna Greco, Leo A B Joosten, Baziel G M van Engelen, Peter S Zammit, Christopher R S Banerji.

  Facioscapulohumeral muscular dystrophy (FSHD) is a prevalent, incurable myopathy. FSHD is highly heterogeneous, with patients following a variety of clinical trajectories, complicating clinical trials. Skeletal muscle in FSHD undergoes fibrosis and fatty replacement that can be accelerated by inflammation, adding to heterogeneity. Well controlled molecular studies are thus essential to both categorise FSHD patients into distinct subtypes and understand pathomechanisms. Here, we further analysed RNA-sequencing data from 24 FSHD patients, each of whom donated a biopsy from both a non-inflamed (TIRM-) and inflamed (TIRM+) muscle, and 15 FSHD patients who donated peripheral blood mononucleated cells (PBMCs), alongside non-affected control individuals. Differential gene expression analysis identified suppression of mitochondrial biogenesis and up-regulation of fibroadipogenic progenitor (FAP) gene expression in FSHD muscle, which was particularly marked on inflamed samples. PBMCs demonstrated suppression of antigen presentation in FSHD. Gene expression deconvolution revealed FAP expansion as a consistent feature of FSHD muscle, via meta-analysis of 7 independent transcriptomic datasets. Clustering of muscle biopsies separated patients in an unbiased manner into clinically mild and severe subtypes, independently of known disease modifiers (age, sex, D4Z4 repeat length). Lastly, the first genome-wide analysis of alternative splicing in FSHD muscle revealed perturbation of autophagy, BMP2 and HMGB1 signalling. Overall, our findings reveal molecular subtypes of FSHD with clinical relevance and identify novel pathomechanisms for this highly heterogeneous condition.

Keywords:  alterrnative splicing; facioscapulohumeral muscular dystropy (FSHD); fibroadipogenic progenitor cells (FAPs); mitochondrial function; transcriptomics

DOI:  https://doi.org/10.1093/hmg/ddad175
Front Physiol. 2023 ;14 1265871

The effects of environmental enrichment on voluntary physical activity and muscle mass gain in growing rats.

Mizuki Sudo, Yutaka Kano, Soichi Ando.

  Introduction: Environmental enrichment (EE) for rodents involves housing conditions that facilitate enhanced sensory, cognitive, and motor stimulation relative to standard housing conditions. A recent study suggested that EE induces muscle hypertrophy. However, it remains unclear whether muscle hypertrophy in EE is associated with voluntary physical activity, and the characteristics of muscle adaptation to EE remain unclarified. Therefore, this study investigated whether muscle adaptation to EE is associated with voluntary physical activity, and assessed the changes in the muscle fiber-type distribution and fiber-type-specific cross-sectional area in response to EE. Methods: Wistar rats (6 weeks of age) were randomly assigned to either the standard environment group (n = 10) or the EE group (n = 10). The voluntary physical activity of rats housed in EE conditions was measured using a recently developed three-axis accelerometer. After exposure to the standard or enriched environment for 30 days, the tibialis anterior, extensor digitorum longus, soleus, plantaris, and gastrocnemius muscles were removed and weighed. Immunohistochemistry analysis was performed on the surface (anterior) and deep (posterior) areas of the tibialis anterior and soleus muscles. Results and discussion: The EE group showed increased voluntary physical activity during the dark period compared with the standard environment group (p = 0.005). EE induced muscle mass gain in the soleus muscle (p = 0.002) and increased the slow-twitch muscle fiber cross-sectional area of the soleus muscle (p = 0.025). EE also increased the distribution of high-oxidative type IIa fibers of the surface area (p = 0.001) and type I fibers of the deep area (p = 0.037) of the tibialis anterior muscle. These findings suggest that EE is an effective approach to induce slow-twitch muscle fiber hypertrophy through increased daily voluntary physical activity.

Keywords:  environmental enrichment; hypertrophy; physical activity level; skeletal muscle; slow-twitch muscle fiber

DOI:  https://doi.org/10.3389/fphys.2023.1265871
Appl Physiol Nutr Metab. 2023 Oct 18.

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

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

Mitochondrial quality control processes are essential in governing mitochondrial integrity and function. The purpose of the study was to examine the effects of 10 weeks of HIIT on the regulatory protein machinery of skeletal muscle mitochondrial quality control and whole-body glucose homeostasis in diet-induced obese mice. Male C57BL/6 mice were assigned to low-fat diet (LFD) or high-fat diet (HFD) group. After 10 weeks, HFD-fed mice were divided into sedentary and HIIT (HFD+HIIT) groups for another 10 weeks (n=9/group). Graded exercise test, glucose and insulin tolerance tests, mitochondrial respiration and protein markers of mitochondrial quality control processes were determined. HFD-fed mice exhibited lower ADP-stimulated mitochondrial respiration (P<0.05). However, ten weeks of HIIT prevented this impairment (P < 0.05).. Importantly, the ratio of Drp1(Ser616) over Drp1(Ser637) phosphorylation, an indicator of mitochondrial fission, was significantly higher in HFD-fed mice (P<0.05), but such increase was attenuated in HFD-HIIT compared to HFD (-35.7%, P < 0.05). Regarding autophagy, skeletal muscle p62 content was lower in HFD group than LFD group (-35.1%, P < 0.05), however, such reduction was disappeared in HFD+HIIT group. In addition, LC3B II/I ratio was higher in HFD than LFD group (15.5%, P < 0.05) but was ameliorated in HFD+HIIT group (-29.9%, P < 0.05). Overall, our study demonstrated that 10 weeks of HIIT was effective in improving skeletal muscle mitochondrial respiration and the regulatory protein machinery of mitochondrial quality control in diet-induced obese mice through the alterations of mitochondrial fission protein Drp1 phosphorylations and p62/LC3B-mediated regulatory machinery of autophagy.

DOI: https://doi.org/10.1139/apnm-2023-0286
J Cancer Res Clin Oncol. 2023 Oct 16.

One bout of endurance exercise does not change gene expression or proliferation in a C26 colon carcinoma in immunocompetent mice.

Nik Mahnic, Alessia Geremia, Tobias Straub, Sabrina Zorzato, Martin Schönfelder, Irene von Lüttichau, Katja Steiger, Maximilian Michael Saller, Bert Blaauw, Henning Wackerhage.

   PURPOSE: Exercise typically reduces tumour growth, proliferation and improves outcomes. Many of these effects require exercise to change gene expression within a tumour, but whether exercise actually affects gene expression within a tumour has not been investigated yet. The aim of this study was, therefore, to find out whether one bout of endurance exercise alters gene expression and proliferation in a C26 carcinoma in immunocompetent mice.
METHODS: BALB/c were injected with C26 colon carcinoma cells. Once the tumours had formed, the mice either ran for 65 min with increasing intensity or rested before the tumour was dissected. The tumours were then analysed by RNA-Seq and stained for the proliferation marker KI67.
RESULTS: One bout of running for 65 min did not systematically change gene expression in C26 carcinomas of BALB/c mice when compared to BALB/c mice that were rested. However, when analysed for sex, the expression of 17, mostly skeletal muscle-related genes was higher in the samples of the female mice taken post-exercise. Further histological analysis showed that this signal likely comes from the presence of muscle fibres from the panniculus carnosus muscle inside the tumours. Also, we found no differences in the positivity for the proliferation marker KI67 in the control and exercise C26 carcinomas.
CONCLUSION: A bout of exercise did not systematically affect gene expression or proliferation in C26 carcinomas in immunocompetent BALB/c mice.

Keywords:  BALB/c mice; C26 colon carcinoma; Cancer; Exercise

DOI:  https://doi.org/10.1007/s00432-023-05447-x
Steroids. 2023 Oct 18. pii: S0039-128X(23)00156-3. [Epub ahead of print] 109328

Mechanism of Skeletal Muscle Atrophy by Muscle Fiber Types in Male Rats under Long-term Fasting Stress.

Takahiro Ieko, Jumpei Fujiki, Yasuhiro Hasegawa, Tomohito Iwasaki, Hidetomo Iwano, Naoyuki Maeda.

  Fasting induces metabolic changes in muscles, which are differentiated by muscle fiber type. In this study, the mechanism of fasting-induced muscle atrophy in rats was examined to determine the differences between muscle fiber types in energy production. Fasting for 96 h did not alter the weight of the soleus (SOL), a fiber type I muscle, but did significantly reduce the weight of gastrocnemius (GM), a fiber type II muscle. GM, SOL and blood pregnenolone and testosterone levels decreased under fasting, which induced energy deprivation, whereas corticosterone (CORT) levels significantly increased. However, the expression of 3β-HSD and P45011β in GM was unaffected by fasting. The decrease in GM weight may be due to decreased levels of testosterone and reduced synthesis of mammalian target of rapamycin (mTOR). Significant increases in CORT both GM and SOL were associated with increases in the amount of branched-chain amino acids available for energy production. However, decreased levels of mTOR and IGF1 and increased levels of CORT and IL-6 in SOL suggest that GM proteolysis was followed by SOL proteolysis for additional energy production. In conclusion, IGF1 levels decreased significantly in SOL, whereas those of IL-6 significantly increased in SOL and blood but decreased in GM. Blood branched-chain amino acids (BCAA) levels were unaffected due to fasting, whereas an increase was noted in the levels of BCAA in GM and SOL. These results show that fasting for 96 h restricts energy supply, producing fast-twitch muscle atrophy followed by slow-twitch muscle atrophy.

Keywords:  and fasting stress; branched-chain amino acids; corticosterone; interleukin-6; mammalian target of rapamycin

DOI:  https://doi.org/10.1016/j.steroids.2023.109328
Cell Mol Life Sci. 2023 Oct 17. 80(11): 328

Staufen1 controls mitochondrial metabolism via HIF2α in embryonal rhabdomyosarcoma and promotes tumorigenesis.

Shekoufeh Almasi, Sahar SarmastiEmami, Stephen Baird, Zhibin Ning, Daniel Figeys, Jocelyn Côté, Kyle N Cowan, Bernard J Jasmin.

  Elevated mitochondrial metabolism promotes tumorigenesis of Embryonal Rhabdomyosarcomas (ERMS). Accordingly, targeting oxidative phosphorylation (OXPHOS) could represent a therapeutic strategy for ERMS. We previously demonstrated that genetic reduction of Staufen1 (STAU1) levels results in the inhibition of ERMS tumorigenicity. Here, we examined STAU1-mediated mechanisms in ERMS and focused on its potential involvement in regulating OXPHOS. We report the novel and differential role of STAU1 in mitochondrial metabolism in cancerous versus non-malignant skeletal muscle cells (NMSkMCs). Specifically, our data show that STAU1 depletion reduces OXPHOS and inhibits proliferation of ERMS cells. Our findings further reveal the binding of STAU1 to several OXPHOS mRNAs which affects their stability. Indeed, STAU1 depletion reduced the stability of OXPHOS mRNAs, causing inhibition of mitochondrial metabolism. In parallel, STAU1 depletion impacted negatively the HIF2α pathway which further modulates mitochondrial metabolism. Exogenous expression of HIF2α in STAU1-depleted cells reversed the mitochondrial inhibition and induced cell proliferation. However, opposite effects were observed in NMSkMCs. Altogether, these findings revealed the impact of STAU1 in the regulation of mitochondrial OXPHOS in cancer cells as well as its differential role in NMSkMCs. Overall, our results highlight the therapeutic potential of targeting STAU1 as a novel approach for inhibiting mitochondrial metabolism in ERMS.

Keywords:  Embryonal rhabdomyosarcoma; Mitochondrial metabolism; OXPHOS; STAU1

DOI:  https://doi.org/10.1007/s00018-023-04969-4
CNS Neurol Disord Drug Targets. 2023 Oct 12.

Exerkines: A Crosstalk between Lactate Production, Exercise and Mental Health.

Alberto Souza Sá Filho, Silvio Roberto Barsanulfo, Sara Socorro Faria, Pedro Augusto Inacio, Faranahz Ayatizadeh, Sérgio Machado.

  Muscle skeletal striated cells secrete a wide range of proteins called myokines or "exerkines", which in turn perform autocrine, paracrine, or endocrine functions. For being able to act in the communication between skeletal muscle, adipose tissue, and mainly the brain, exerkines play a prominent role and potential influence on health promotion. Furthermore, we detected in the literature that one of these potential therapeutic substances derived from muscle contraction is a molecule derived from glycolytic metabolism that in the past was largely marginalized, the lactate. Currently, studies are dedicated to examining the target structures for exerkines that may contribute to the maintenance and restoration of mental health. Thus, lactate appears to be recognized as a critical mediator of exercise-related changes and their health benefits, particularly in their role in communication and coordination between organs. It is inferred that the BDNF expression mechanism can be induced by lactate, which in turn derives from the activation of SIRT pathways 1 and 2 and activates the PGC1-α cascade. The behavior of lactate concentration is intensity-dependent, directly related to the type of fast-twitch fibers (type IIb) and the recruitment of these fibers would potentiate the responses in the brain. In this sense, high-intensity exercise would establish itself as an important strategy to be considered. Despite this understanding, there is still much to be done. However, lactate appears to be a highly promising exerkine for future research initiatives and a potential biomarker to reduce illness and promote mental health.

Keywords:  Exerkines; Myokines; biomarker; exercise; lactate; mental health

DOI:  https://doi.org/10.2174/0118715273250928231009054658
Nat Rev Dis Primers. 2023 Oct 19. 9(1): 56

Traumatic muscle injury.

Pascal Edouard, Gustaaf Reurink, Abigail L Mackey, Richard L Lieber, Tania Pizzari, Tero A H Järvinen, Thomas Gronwald, Karsten Hollander.

Traumatic muscle injury represents a collection of skeletal muscle pathologies caused by trauma to the muscle tissue and is defined as damage to the muscle tissue that can result in a functional deficit. Traumatic muscle injury can affect people across the lifespan and can result from high stresses and strains to skeletal muscle tissue, often due to muscle activation while the muscle is lengthening, resulting in indirect and non-contact muscle injuries (strains or ruptures), or from external impact, resulting in direct muscle injuries (contusion or laceration). At a microscopic level, muscle fibres can repair focal damage but must be completely regenerated after full myofibre necrosis. The diagnosis of muscle injury is based on patient history and physical examination. Imaging may be indicated to eliminate differential diagnoses. The management of muscle injury has changed within the past 5 years from initial rest, immobilization and (over)protection to early activation and progressive loading using an active approach. One challenge of muscle injury management is that numerous medical treatment options, such as medications and injections, are often used or proposed to try to accelerate muscle recovery despite very limited efficacy evidence. Another challenge is the prevention of muscle injury owing to the multifactorial and complex nature of this injury.

DOI: https://doi.org/10.1038/s41572-023-00469-8
Muscle Nerve. 2023 Oct 20.

Skeletal muscle injury in COVID infection: Frequency and patterns.

Saurabh Singh Rajput, Rajeswari Aghoram, Vaibhav Wadwekar, Nivedita Nanda.

   INTRODUCTION/AIMS: Little is known about skeletal muscle injury with coronavirus disease 2019 (COVID-19). We estimate the frequency and explore the patterns of skeletal muscle injury in acute COVID-19.
METHODS: A cohort of COVID patients with mild to moderate symptoms were evaluatedin a COVID designated hospitalbetween May andDecember 2021 and followed for 2 weeks. Skeletal muscle injury was assessed with creatine kinase (CK) levels, manual muscletesting 8(MMT-8) and the Health Assessment Questionnaire (HAQ); and was defined as CK >200 IU/L with MMT-8 < 76. The association between such injury, and severity and outcomes wereevaluated using cross tabulations.
RESULTS: Two hundred and fifty participants with a mean age of 50.2 years (SD: 17.2) were included. One hundred and nine (43.6%) were women; 84 (34%) developedsevere disease. Median CK levels were 91 IU/L (IQR: 56,181). Weaknesson MMT-8 (247, 98.8%) and disability on HAQ (107; 42.8%) were common. Neck flexor muscles wereprominently affected. Skeletal muscle injury was seen in 22.4% (95% CI: 17.4-28.1). There was nosignificant association between skeletal muscle injury and maximal severity of illness or short term outcomes. Disability increased over 14 days in most survivors (172; 72.3%) and this was not seen in those with mild disease (OR:0.4; 95% CI: 0.22-0.70).
DISCUSSION: Skeletal muscle injury appears to be common in people presenting with mild to moderate COVID infection.

Keywords:  COVID-19 infections; Creatine kinase; health assessment questionnaire; manual muscle testing-8; skeletal muscle injury

DOI:  https://doi.org/10.1002/mus.27990
JCI Insight. 2023 Oct 19. pii: e170518. [Epub ahead of print]

Vitamin D status associates with skeletal muscle loss after anterior cruciate ligament reconstruction.

Yuan Wen, Christine M Latham, Angelique N Moore, Nicholas T Thomas, Brooke D Lancaster, Kelsey A Reeves, Alexander R Keeble, Christopher S Fry, Darren L Johnson, Katherine L Thompson, Brian Noehren, Jean L Fry.

   BACKGROUND: Although 25-hydroxyvitamin D (25(OH)D) concentrations ≥30ng/mL are known to reduce injury risk and boost strength, the influence on anterior cruciate ligament reconstruction (ACLR) outcomes remains unexamined. This study aimed to define the vitamin D signaling response to ACLR, assess the relationship between vitamin D status and muscle fiber cross-sectional area (CSA) and bone density outcomes, and discover vitamin D receptor (VDR) targets post-ACLR.
METHODS: 21 young, healthy, physically active participants with recent ACL tears were enrolled (17.8 ± 3.2 yr, BMI: 26.0 ± 3.5 kg/m2). Data were collected through blood samples, vastus lateralis biopsies, DXA bone density measurements, and isokinetic dynamometer measures at baseline, 1 week, 4 months, and 6 months post-ACLR. The biopsies facilitated CSA, western blot, RNA-seq, and VDR ChIP-seq analyses.
RESULTS: ACLR surgery led to decreased circulating bioactive vitamin D and increased VDR and activating enzyme expression in skeletal muscle one week post-operation. Participants with < 30 ng/mL 25(OH)D levels (n = 13) displayed more significant quadriceps fiber CSA loss one week and 4 months post-ACLR than those with ≥30 ng/mL (n = 8; P < 0.01 for post-hoc comparisons; P = 0.041 for time x vitamin D status interaction). RNA-seq and ChIP-seq data integration revealed genes associated with energy metabolism and skeletal muscle recovery, potentially mediating the impact of vitamin D status on ACLR recovery. No difference in bone mineral density (BMD) losses between groups was observed.
CONCLUSION: Correcting vitamin D status prior to ACLR may aid in preserving skeletal muscle during recovery.

Keywords:  Bioinformatics; Muscle Biology; Orthopedics; Skeletal muscle

DOI:  https://doi.org/10.1172/jci.insight.170518
FEBS J. 2023 Oct 16.

StarD7 deficiency switches on glycolysis and promotes mitophagy flux in C2C12 myoblasts.

María L Rojas, Juan Pablo Muñoz, Jésica Flores-Martín, Paula Sànchez-Fernàndez-de-Landa, Mariano Cruz Del Puerto, Susana Genti-Raimondi, Antonio Zorzano.

  StarD7 is a member of the START protein family required for phosphatidylcholine delivery to the mitochondria, thus key to maintain mitochondrial structure. Its deficiency has been associated with an impairment of cellular processes, such as proliferation and migration, and it has also been reported that it is needed in myogenic differentiation. Here, we show that StarD7 deficiency in C2C12 muscle cells results in the accumulation of abnormal mitochondria, a reduced number of mitochondria per cell area and increased glycolysis. In addition, StarD7-deficient cells undergo an increase in mitochondria-ER contact sites, reduced connexin 43 expression, and disturbances in lipid handling, evidenced by lipid droplet accumulation and decreased levels in phosphatidylserine synthase 1 and 2 expression. Interestingly, StarD7-deficient cells showed alterations in mitophagy markers. We observed accumulation of LC3B-II and BNIP3 proteins in mitochondria-enriched fractions and accumulation of autophagolysosomal and lysosomal vesicles in StarD7-deficient cells. Furthermore, live-cell imaging experiments of StarD7 knockdown cells expressing mitochondria-targeted mKeima indicated an enhanced mitochondria delivery into lysosomes. Importantly, StarD7 reconstitution in StarD7-deficient cells restores LC3B-II expression in mitochondria-enriched fractions at similar levels to those observed in control cells. Collectively, these findings suggest that StarD7-deficient C2C12 myoblasts are associated with altered cristae structure, disturbances in neutral lipid accumulation, glucose metabolism, and increased mitophagy flux. The alterations mentioned above allow for the maintenance of mitochondrial function.

Keywords:  StarD7; cristae morphology; lipid droplet; mitophagy

DOI:  https://doi.org/10.1111/febs.16979