bims-moremu 2023-12-24 papers

bims-moremu

Biomed News

on Molecular regulators of muscle mass

Issue of 2023–12–24
38 papers selected by
Anna Vainshtein, Craft Science Inc.

Marked irregular myofiber shape is a hallmark of human skeletal muscle ageing and is reversed by heavy resistance training.
Inhibition of the skeletal muscle Lands cycle ameliorates weakness induced by physical inactivity.
Intact Short, Intermediate, and Long Skeletal Muscle Fibers Obtained by Enzymatic Dissociation of Six Hindlimb Muscles of Mice: Beyond Flexor Digitorum Brevis.
Muscle immune cells protect mitochondrial organelles during exercise.
Hypoxia enhances human myoblast differentiation: involvement of HIF1α and impact of DUX4, the FSHD causal gene.
Identification and Analysis of Myogenic Progenitors In Vivo During Acute Skeletal Muscle Injury by High-Dimensional Single-Cell Mass Cytometry.
Generation of highly pure pluripotent stem cell-derived myogenic progenitor cells and myotubes.
Low Response to Aerobic Training in Metabolic Disease: Role of Skeletal Muscle.
Translating In Vitro Models of Exercise in Human Muscle Cells: A Mitocentric View.
lncRNA GPRC5D-AS1 as a ceRNA inhibits skeletal muscle aging by regulating miR-520d-5p.
Skeletal Muscle Spheroids as Building Blocks for Engineered Muscle Tissue.
Effect of insulin insufficiency on ultrastructure and function in skeletal muscle.
Senescent skeletal muscle fibroadipogenic progenitors recruit and promote M2 polarization of macrophages.
The Structural Adaptations That Mediate Disuse-Induced Atrophy of Skeletal Muscle.
HIF-1α/MMP-9 Axis Is Required in the Early Phases of Skeletal Myoblast Differentiation under Normoxia Condition In Vitro.
Neuromuscular Dysfunction Precedes Cognitive Impairment in a Mouse Model of Alzheimer's Disease.
Therapeutic Consequences of Targeting the IGF-1/PI3K/AKT/FOXO3 Axis in Sarcopenia: A Narrative Review.
Editorial: Spotlight on aging: physiology, prevention, and management of skeletal muscle atrophy.
Angiotensin-(1-7) improves skeletal muscle regeneration.
From Chronodisruption to Sarcopenia: The Therapeutic Potential of Melatonin.
Proteomic Identification of Seasonally Expressed Proteins Contributing to Heart Function and the Avoidance of Skeletal Muscle Disuse Atrophy in a Hibernating Mammal.
The Role of Exercise in Cancer-Related Sarcopenia and Sarcopenic Obesity.
Regulated dynamic subcellular GLUT4 localization revealed by proximal proteome mapping in human muscle cells.
Alterations in RNA editing in skeletal muscle following exercise training in individuals with Parkinson's disease.
Subcutaneous Infusion of DNA-Aptamer Raised against Advanced Glycation End Products Prevents Loss of Skeletal Muscle Mass and Strength in Accelerated-Aging Mice.
Analysis of the Mitochondrial Density and Longitudinal Distribution in Rat Live-Skeletal Muscle Fibers by Confocal Microscopy.
The mediation roles of intermuscular fat and inflammation in muscle mitochondrial associations with cognition and mobility.
Pax7 reporter mouse models: a pocket guide for satellite cell research.
Lesion level-dependent systemic muscle wasting after spinal cord injury is mediated by glucocorticoid signaling in mice.
Azilsartan Prevents Muscle Loss and Fast to Slow-twitch Muscle Fibre Shift in Natural Ageing Sarcopenic Rats.
The antidiabetic SGLT2 inhibitor canagliflozin reduces mitochondrial metabolism in a model of skeletal muscle insulin resistance.
Efficient generation of a self-organizing neuromuscular junction model from human pluripotent stem cells.
Effects of exercise, metformin, and combination treatments on type 2 diabetic mellitus-induced muscle atrophy in db/db mice: Crosstalk between autophagy and the proteasome.
Myeloma extracellular vesicle-derived RAGE increases inflammatory responses and myotube atrophy in multiple myeloma through activation of the TLR4/NF-κB p65 pathway.
Need for speed: Human fast-twitch mitochondria favor power over efficiency.
Dystrophin deficiency impairs cell junction formation during embryonic myogenesis.
The Information Theory of Aging.
Five Padua days on muscle and mobility medicine (2024Pdm3), Padua, Italy.

J Cachexia Sarcopenia Muscle. 2023 Dec 20.

Marked irregular myofiber shape is a hallmark of human skeletal muscle ageing and is reversed by heavy resistance training.

Casper Soendenbroe, Anders Karlsen, Rene B Svensson, Michael Kjaer, Jesper L Andersen, Abigail L Mackey.

   BACKGROUND: Age-related loss of strength is disproportionally greater than the loss of mass, suggesting maladaptations in the neuro-myo-tendinous system. Myofibers are often misshaped in aged and diseased muscle, but systematic analyses of large sample sets are lacking. Our aim was to investigate myofiber shape in relation to age, exercise, myofiber type, species and sex.
METHODS: Vastus lateralis muscle biopsies (n = 265) from 197 males and females, covering an age span of 20-97 years, were examined. The gastrocnemius and soleus muscles of 11 + 22-month-old male C57BL/6 mice were also examined. Immunofluorescence and ATPase stainings of muscle cross-sections were used to measure myofiber cross-sectional area (CSA) and perimeter. From these, a shape factor index (SFI) was calculated in a fibre-type-specific manner (type I/II in humans; type I/IIa/IIx/IIb in mice), with higher values indicating increased deformity. Heavy resistance training (RT) was performed three times per week for 3-4 months by a subgroup (n = 59). Correlation analyses were performed comparing SFI and CSA with age, muscle mass, maximal voluntary contraction (MVC), rate of force development and specific force (MVC/muscle mass).
RESULTS: In human muscle, SFI was positively correlated with age for both type I (R2 = 0.20) and II (R2 = 0.38) myofibers. When subjects were separated into age cohorts, SFI was lower for type I (4%, P < 0.001) and II (6%, P < 0.001) myofibers in young (20-36) compared with old (60-80) and higher for type I (5%, P < 0.05) and II (14%, P < 0.001) myofibers in the oldest old (>80) compared with old. The increased SFI in old muscle was observed in myofibers of all sizes. Within all three age cohorts, type II myofiber SFI was higher than that for type I myofiber (4-13%, P < 0.001), which was also the case in mice muscles (8-9%, P < 0.001). Across age cohorts, there was no difference between males and females in SFI for either type I (P = 0.496/0.734) or II (P = 0.176/0.585) myofibers. Multiple linear regression revealed that SFI, after adjusting for age and myofiber CSA, has independent explanatory power for 8/10 indices of muscle mass and function. RT reduced SFI of type II myofibers in both young and old (3-4%, P < 0.001).
CONCLUSIONS: Here, we identify type I and II myofiber shape in humans as a hallmark of muscle ageing that independently predicts volumetric and functional assessments of muscle health. RT reverts the shape of type II myofibers, suggesting that a lack of myofiber recruitment might lead to myofiber deformity.

Keywords:  myofiber morphology; physiological function; sarcopenia; shape factor; skeletal muscle

DOI:  https://doi.org/10.1002/jcsm.13405
J Cachexia Sarcopenia Muscle. 2023 Dec 20.

Inhibition of the skeletal muscle Lands cycle ameliorates weakness induced by physical inactivity.

Justin L Shahtout, Hiroaki Eshima, Patrick J Ferrara, J Alan Maschek, James E Cox, Micah J Drummond, Katsuhiko Funai.

   BACKGROUND: Lipid hydroperoxides (LOOH) have been implicated in skeletal muscle atrophy with age and disuse. Lysophosphatidylcholine acyltransferase 3 (LPCAT3), an enzyme of the Lands cycle, conjugates a polyunsaturated fatty acyl chain to a lysophospholipid to form a polyunsaturated fatty acid containing phospholipid (PUFA-PL) molecule, providing substrates for LOOH propagation. Previous studies suggest that inhibition of the Lands cycle is an effective strategy to suppress LOOH. Mice with skeletal muscle-specific tamoxifen-inducible knockout of LPCAT3 (LPCAT3-MKO) were utilized to determine if muscle-specific attenuation of LOOH may alleviate muscle atrophy and weakness with disuse.
METHODS: LPCAT3-MKO and control mice underwent 7 days of sham or hindlimb unloading (HU model) to study muscle mass and force-generating capacity. LOOH was assessed by quantifying 4-hydroxynonenal (4-HNE)-conjugated peptides. Quantitative PCR and lipid mass spectrometry were used to validate LPCAT3 deletion.
RESULTS: Seven days of HU was sufficient to induce muscle atrophy and weakness concomitant to a ~2-fold increase in 4-HNE (P = 0.0069). Deletion of LPCAT3 reversed HU-induced increase in muscle 4-HNE (P = 0.0256). No difference was found in body mass, body composition, or caloric intake between genotypes. The soleus (SOL) and plantaris (PLANT) muscles of the LPCAT3-MKO mice experienced ~15% and ~40% less atrophy than controls, respectively. (P = 0.0011 and P = 0.0265). Type I and IIa SOL myofibers experienced a ~40% decrease in cross sectional area (CSA), which was attenuated to only 15% in the LPCAT3-MKO mice (P = 0.0170 and P = 0.0411, respectively). Strikingly, SOL muscles were fully protected and extensor digitorum longus (EDL) muscles experienced a ~35% protection from HU-induced reduction in force-generating capacity in the LPCAT3-MKO mice compared with controls (P < 0.0001 for both muscles).
CONCLUSIONS: Our findings demonstrate that attenuation of skeletal muscle lipid hydroperoxides is sufficient to restore its function, in particular a protection from reduction in muscle specific force. Our findings suggest muscle lipid peroxidation contributes to atrophy and weakness induced by disuse in mice.

Keywords:  Atrophy; Disuse; Lipid hydroperoxides; Phospholipids; Skeletal muscle

DOI:  https://doi.org/10.1002/jcsm.13406
J Vis Exp. 2023 Dec 01.

Intact Short, Intermediate, and Long Skeletal Muscle Fibers Obtained by Enzymatic Dissociation of Six Hindlimb Muscles of Mice: Beyond Flexor Digitorum Brevis.

Jorge L Petro, Andrés F Milán, Erika Arenas, Laura Valle, Valeria Hernández, Juan C Calderón.

Skeletal muscle fibers obtained by enzymatic dissociation of mouse muscles are a useful model for physiological experiments. However, most papers deal with the short fibers of the flexor digitorum brevis (FDB), which restrains the scope of results dealing with fiber types, limits the amount of biological material available, and impedes a clear connection between cellular physiological phenomena and previous biochemical and dynamical knowledge obtained in other muscles. This paper describes how to obtain intact fibers from six muscles with different fiber type profiles and lengths. Using C57BL/6 adult mice, we show the muscle dissection and fiber isolation protocol and demonstrate the suitability of the fibers for Ca2+ transient studies and their morphometric characterization. The fiber type composition of the muscles is also presented. When dissociated, all muscles rendered intact, living fibers that contract briskly for more than 24 h. FDB gave short (<1 mm), peroneus digiti quarti (PDQA) and peroneus longus (PL) gave intermediate (1-3 mm), while extensor digitorum longus (EDL), extensor hallucis longus (EHL), and soleus muscles released long (3-6 mm) fibers. When recorded with the fast dye Mag-Fluo-4, Ca2+ transients of PDQA, PL, and EHL fibers showed the fast, narrow kinetics reminiscent of the morphology type II (MT-II), known to correspond to type IIX and IIB fibers. This is consistent with the fact that these muscles have over 90% of type II fibers compared with FDB (~80%) and soleus (~65%). Moving beyond FDB, we demonstrate for the first time the dissociation of several muscles, which render fibers spanning a range of lengths between 1 and 6 mm. These fibers are viable and give fast Ca2+ transients, indicating that the MT-II can be generalized to IIX and IIB fast fibers, regardless of their muscle source. These results increase the availability of models for mature skeletal muscle studies.

DOI: https://doi.org/10.3791/65851
Nature. 2024 Jan;625(7993): 35-36

Muscle immune cells protect mitochondrial organelles during exercise.

Gerald Coulis, S Armando Villalta.



Keywords:  Cell biology; Immunology; Physiology

DOI:  https://doi.org/10.1038/d41586-023-03972-w
Skelet Muscle. 2023 Dec 16. 13(1): 21

Hypoxia enhances human myoblast differentiation: involvement of HIF1α and impact of DUX4, the FSHD causal gene.

Thuy-Hang Nguyen, Lise Paprzycki, Alexandre Legrand, Anne-Emilie Declèves, Philipp Heher, Maelle Limpens, Alexandra Belayew, Christopher R S Banerji, Peter S Zammit, Alexandra Tassin.

BACKGROUND: Hypoxia is known to modify skeletal muscle biological functions and muscle regeneration. However, the mechanisms underlying the effects of hypoxia on human myoblast differentiation remain unclear. The hypoxic response pathway is of particular interest in patients with hereditary muscular dystrophies since many present respiratory impairment and muscle regeneration defects. For example, an altered hypoxia response characterizes the muscles of patients with facioscapulohumeral dystrophy (FSHD).
METHODS: We examined the impact of hypoxia on the differentiation of human immortalized myoblasts (LHCN-M2) cultured in normoxia (PO2: 21%) or hypoxia (PO2: 1%). Cells were grown in proliferation (myoblasts) or differentiation medium for 2 (myocytes) or 4 days (myotubes). We evaluated proliferation rate by EdU incorporation, used myogenin-positive nuclei as a differentiation marker for myocytes, and determined the fusion index and myosin heavy chain-positive area in myotubes. The contribution of HIF1α was studied by gain (CoCl2) and loss (siRNAs) of function experiments. We further examined hypoxia in LHCN-M2-iDUX4 myoblasts with inducible expression of DUX4, the transcription factor underlying FSHD pathology.
RESULTS: We found that the hypoxic response did not impact myoblast proliferation but activated precocious myogenic differentiation and that HIF1α was critical for this process. Hypoxia also enhanced the late differentiation of human myocytes, but in an HIF1α-independent manner. Interestingly, the impact of hypoxia on muscle cell proliferation was influenced by dexamethasone. In the FSHD pathological context, DUX4 suppressed HIF1α-mediated precocious muscle differentiation.
CONCLUSION: Hypoxia stimulates myogenic differentiation in healthy myoblasts, with HIF1α-dependent early steps. In FSHD, DUX4-HIF1α interplay indicates a novel mechanism by which DUX4 could interfere with HIF1α function in the myogenic program and therefore with FSHD muscle performance and regeneration.

DOI: https://doi.org/10.1186/s13395-023-00330-2
J Vis Exp. 2023 Dec 01.

Identification and Analysis of Myogenic Progenitors In Vivo During Acute Skeletal Muscle Injury by High-Dimensional Single-Cell Mass Cytometry.

Stig Henrik Andersen, Troels Rønn Kjær, Kedar Ghimire, Ermelinda Porpiglia.

Skeletal muscle regeneration is a dynamic process driven by adult muscle stem cells and their progeny. Mostly quiescent at a steady state, adult muscle stem cells become activated upon muscle injury. Following activation, they proliferate, and most of their progeny differentiate to generate fusion-competent muscle cells while the remaining self-renews to replenish the stem cell pool. While the identity of muscle stem cells was defined more than a decade ago, based on the co-expression of cell surface markers, myogenic progenitors were identified only recently using high-dimensional single-cell approaches. Here, we present a single-cell mass cytometry (cytometry by time of flight [CyTOF]) method to analyze stem cells and progenitor cells in acute muscle injury to resolve the cellular and molecular dynamics that unfold during muscle regeneration. This approach is based on the simultaneous detection of novel cell surface markers and key myogenic transcription factors whose dynamic expression enables the identification of activated stem cells and progenitor cell populations that represent landmarks of myogenesis. Importantly, a sorting strategy based on detecting cell surface markers CD9 and CD104 is described, enabling prospective isolation of muscle stem and progenitor cells using fluorescence-activated cell sorting (FACS) for in-depth studies of their function. Muscle progenitor cells provide a critical missing link to study the control of muscle stem cell fate, identify novel therapeutic targets for muscle diseases, and develop cell therapy applications for regenerative medicine. The approach presented here can be applied to study muscle stem and progenitor cells in vivo in response to perturbations, such as pharmacological interventions targeting specific signaling pathways. It can also be used to investigate the dynamics of muscle stem and progenitor cells in animal models of muscle diseases, advancing our understanding of stem cell diseases and accelerating the development of therapies.

DOI: https://doi.org/10.3791/65944
Stem Cell Reports. 2023 Dec 12. pii: S2213-6711(23)00451-4. [Epub ahead of print]

Generation of highly pure pluripotent stem cell-derived myogenic progenitor cells and myotubes.

Reem Bou Akar, Chéryane Lama, Déborah Aubin, Julien Maruotti, Brigitte Onteniente, Joana Esteves de Lima, Frédéric Relaix.

  Driving efficient and pure skeletal muscle cell differentiation from pluripotent stem cells (PSCs) has been challenging. Here, we report an optimized protocol that generates skeletal muscle progenitor cells with high efficiency and purity in a short period of time. Human induced PSCs (hiPSCs) and murine embryonic stem cells (mESCs) were specified into the mesodermal myogenic fate using distinct and species-specific protocols. We used a specific maturation medium to promote the terminal differentiation of both human and mouse myoblast populations, and generated myotubes associated with a large pool of cell-cycle arrested PAX7+ cells. We also show that myotube maturation is modulated by dish-coating properties, cell density, and percentage of myogenic progenitor cells. Given the high efficiency in the generation of myogenic progenitors and differentiated myofibers, this protocol provides an attractive strategy for tissue engineering, modeling of muscle dystrophies, and evaluation of new therapeutic approaches in vitro.

Keywords:  hiPSC; mESC; muscle progenitors; myogenic differentiation; myotubes

DOI:  https://doi.org/10.1016/j.stemcr.2023.11.002
Exerc Sport Sci Rev. 2023 Dec 18.

Low Response to Aerobic Training in Metabolic Disease: Role of Skeletal Muscle.

Rogerio Nogueira Soares, Sarah J Lessard.

ABSTRACT: Aerobic exercise is established to increase cardiorespiratory fitness (CRF), which is linked to reduced morbidity and mortality. However, people with metabolic diseases such as type 1 and type 2 diabetes may be more likely to display blunted improvements in CRF with training. Here, we present evidence supporting the hypothesis that altered skeletal muscle signaling and remodeling may contribute to low CRF with metabolic disease.

DOI: https://doi.org/10.1249/JES.0000000000000331
Exerc Sport Sci Rev. 2024 Jan 01. 52(1): 3-12

Translating In Vitro Models of Exercise in Human Muscle Cells: A Mitocentric View.

Reichelle X Yeo, John Noone, Lauren M Sparks.

Human skeletal muscle cell (HSkMC) models provide the opportunity to examine in vivo training-induced muscle-specific mitochondrial adaptations, additionally allowing for deeper interrogation into the effect of in vitro exercise models on myocellular mitochondrial quality and quantity. As such, this review will compare and contrast the effects of in vivo and in vitro models of exercise on mitochondrial adaptations in HSkMCs.

DOI: https://doi.org/10.1249/JES.0000000000000330
Aging (Albany NY). 2023 Dec 09. 15(23): 13980-13997

lncRNA GPRC5D-AS1 as a ceRNA inhibits skeletal muscle aging by regulating miR-520d-5p.

Miao Yu, Xiuting He, Ting Liu, Jie Li.

  Sarcopenia induced by muscle aging is associated with negative outcomes in a variety of diseases. Long non-coding RNAs are a class of RNAs longer than 200 nucleotides with lower protein coding potential. An increasing number of studies have shown that lncRNAs play a vital role in skeletal muscle development. According to our previous research, lncRNA GPRC5D-AS1 is selected in the present study as the target gene to further study its effect on skeletal muscle aging in a dexamethasone-induced human muscle atrophy cell model. As a result, GPRC5D-AS1 functions as a ceRNA of miR-520d-5p to repress cell apoptosis and regulate the expression of muscle regulatory factors, including MyoD, MyoG, Mef2c and Myf5, thus accelerating myoblast proliferation and differentiation, facilitating development of skeletal muscle. In conclusion, lncRNA GPRC5D-AS1 could be a novel therapeutic target for treating sarcopenia.

Keywords:  GPRC5D-AS1; competing endogenous RNA; long non-coding RNA; miR-520d-5p; skeletal muscle aging

DOI:  https://doi.org/10.18632/aging.205279
ACS Biomater Sci Eng. 2023 Dec 19.

Skeletal Muscle Spheroids as Building Blocks for Engineered Muscle Tissue.

Nicholas Johnson, Andrea C Filler, Akash Sethi, Lucas R Smith, J Kent Leach.

  Spheroids exhibit enhanced cell-cell interactions that facilitate improved survival and mimic the physiological cellular environment in vivo. Cell spheroids have been successfully used as building blocks for engineered tissues, yet the viability of this approach with skeletal muscle spheroids is poorly understood, particularly when incorporated into three-dimensional (3D) constructs. Bioprinting is a promising strategy to recapitulate the hierarchical organization of native tissue that is fundamental to its function. However, the influence of bioprinting on skeletal muscle cell spheroids and their function are yet to be interrogated. Using C2C12 mouse myoblasts and primary bovine muscle stem cells (MuSCs), we characterized spheroid formation as a function of duration and cell seeding density. We then investigated the potential of skeletal muscle spheroids entrapped in alginate bioink as tissue building blocks for bioprinting myogenic tissue. Both C2C12 and primary bovine MuSCs formed spheroids of similar sizes and remained viable after bioprinting. Spheroids of both cell types fused into larger tissue clusters over time within alginate and exhibited tissue formation comparable to monodisperse cells. Compared to monodisperse cells in alginate gels, C2C12 spheroids exhibited greater MyHC expression after 2 weeks, while cells within bovine MuSC spheroids displayed increased cell spreading. Both monodisperse and MuSC spheroids exhibited increased expression of genes denoting mid- and late-stage myogenic differentiation. Together, these data suggest that skeletal muscle spheroids have the potential for generating myogenic tissue via 3D bioprinting and reveal areas of research that could enhance myogenesis and myogenic differentiation in future studies.

Keywords:  bioprinting; hydrogel; muscle engineering; skeletal muscle; spheroids

DOI:  https://doi.org/10.1021/acsbiomaterials.3c01078
J Cachexia Sarcopenia Muscle. 2023 Dec 20.

Effect of insulin insufficiency on ultrastructure and function in skeletal muscle.

Chantal Kopecky, Michael Haug, Barbara Reischl, Nandan Deshpande, Bikash Manandhar, Thomas W King, Victoria Lee, Marc R Wilkins, Margaret Morris, Patsie Polly, Oliver Friedrich, Kerry-Anne Rye, Blake J Cochran.

   BACKGROUND: Decreased insulin availability and high blood glucose levels, the hallmark features of poorly controlled diabetes, drive disease progression and are associated with decreased skeletal muscle mass. We have shown that mice with β-cell dysfunction and normal insulin sensitivity have decreased skeletal muscle mass. This project asks how insulin deficiency impacts on the structure and function of the remaining skeletal muscle in these animals.
METHODS: Skeletal muscle function was determined by measuring exercise capacity and specific muscle strength prior to and after insulin supplementation for 28 days in 12-week-old mice with conditional β-cell deletion of the ATP binding cassette transporters ABCA1 and ABCG1 (β-DKO mice). Abca1 and Abcg1 floxed (fl/fl) mice were used as controls. RNAseq was used to quantify changes in transcripts in soleus and extensor digitorum longus muscles. Skeletal muscle and mitochondrial morphology were assessed by transmission electron microscopy. Myofibrillar Ca2+ sensitivity and maximum isometric single muscle fibre force were assessed using MyoRobot biomechatronics technology.
RESULTS: RNA transcripts were significantly altered in β-DKO mice compared with fl/fl controls (32 in extensor digitorum longus and 412 in soleus). Exercise capacity and muscle strength were significantly decreased in β-DKO mice compared with fl/fl controls (P = 0.012), and a loss of structural integrity was also observed in skeletal muscle from the β-DKO mice. Supplementation of β-DKO mice with insulin restored muscle integrity, strength and expression of 13 and 16 of the dysregulated transcripts in and extensor digitorum longus and soleus muscles, respectively.
CONCLUSIONS: Insulin insufficiency due to β-cell dysfunction perturbs the structure and function of skeletal muscle. These adverse effects are rectified by insulin supplementation.

Keywords:  Insulin; Muscle function; Muscle structure; Skeletal muscle

DOI:  https://doi.org/10.1002/jcsm.13380
Aging Cell. 2023 Dec 19. e14069

Senescent skeletal muscle fibroadipogenic progenitors recruit and promote M2 polarization of macrophages.

Xu Zhang, Yan Er Ng, Lucas C S Chini, Amanda A Heeren, Thomas A White, Hao Li, Haojie Huang, Madison L Doolittle, Sundeep Khosla, Nathan K LeBrasseur.

  Senescent cells compromise tissue structure and function in older organisms. We recently identified senescent fibroadipogenic progenitors (FAPs) with activated chemokine signaling pathways in the skeletal muscle of old mice, and hypothesized these cells may contribute to the age-associated accumulation of immune cells in skeletal muscle. In this study, through cell-cell communication analysis of skeletal muscle single-cell RNA-sequencing data, we identified unique interactions between senescent FAPs and macrophages, including those mediated by Ccl2 and Spp1. Using mouse primary FAPs in vitro, we verified increased expression of Ccl2 and Spp1 and secretion of their respective proteins in the context of both irradiation- and etoposide-induced senescence. Compared to non-senescent FAPs, the medium of senescent FAPs markedly increased the recruitment of macrophages in an in vitro migration assay, an effect that was mitigated by preincubation with antibodies to either CCL2 or osteopontin (encoded by Spp1). Further studies demonstrated that the secretome of senescent FAPs promotes polarization of macrophages toward an M2 subtype. These data suggest the unique secretome of senescent FAPs may compromise skeletal muscle homeostasis by recruiting and directing the behavior of macrophages.

Keywords:  cellular senescence; fibroadipogenic progenitors (FAPs); macrophages; migration; polarization

DOI:  https://doi.org/10.1111/acel.14069
Cells. 2023 Dec 10. pii: 2811. [Epub ahead of print]12(24):

The Structural Adaptations That Mediate Disuse-Induced Atrophy of Skeletal Muscle.

Ramy K A Sayed, Jamie E Hibbert, Kent W Jorgenson, Troy A Hornberger.

  The maintenance of skeletal muscle mass plays a fundamental role in health and issues associated with quality of life. Mechanical signals are one of the most potent regulators of muscle mass, with a decrease in mechanical loading leading to a decrease in muscle mass. This concept has been supported by a plethora of human- and animal-based studies over the past 100 years and has resulted in the commonly used term of 'disuse atrophy'. These same studies have also provided a great deal of insight into the structural adaptations that mediate disuse-induced atrophy. For instance, disuse results in radial atrophy of fascicles, and this is driven, at least in part, by radial atrophy of the muscle fibers. However, the ultrastructural adaptations that mediate these changes remain far from defined. Indeed, even the most basic questions, such as whether the radial atrophy of muscle fibers is driven by the radial atrophy of myofibrils and/or myofibril hypoplasia, have yet to be answered. In this review, we thoroughly summarize what is known about the macroscopic, microscopic, and ultrastructural adaptations that mediated disuse-induced atrophy and highlight some of the major gaps in knowledge that need to be filled.

Keywords:  disuse; fascicle; hypoplasia; longitudinal atrophy; muscle fibers; myofibril; myofilaments; radial atrophy; sarcomere

DOI:  https://doi.org/10.3390/cells12242811
Cells. 2023 Dec 16. pii: 2851. [Epub ahead of print]12(24):

HIF-1α/MMP-9 Axis Is Required in the Early Phases of Skeletal Myoblast Differentiation under Normoxia Condition In Vitro.

Flaminia Chellini, Alessia Tani, Martina Parigi, Francesco Palmieri, Rachele Garella, Sandra Zecchi-Orlandini, Roberta Squecco, Chiara Sassoli.

  Hypoxia-inducible factor (HIF)-1α represents an oxygen-sensitive subunit of HIF transcriptional factor, which is usually degraded in normoxia and stabilized in hypoxia to regulate several target gene expressions. Nevertheless, in the skeletal muscle satellite stem cells (SCs), an oxygen level-independent regulation of HIF-1α has been observed. Although HIF-1α has been highlighted as a SC function regulator, its spatio-temporal expression and role during myogenic progression remain controversial. Herein, using biomolecular, biochemical, morphological and electrophysiological analyses, we analyzed HIF-1α expression, localization and role in differentiating murine C2C12 myoblasts and SCs under normoxia. In addition, we evaluated the role of matrix metalloproteinase (MMP)-9 as an HIF-1α effector, considering that MMP-9 is involved in myogenesis and is an HIF-1α target in different cell types. HIF-1α expression increased after 24/48 h of differentiating culture and tended to decline after 72 h/5 days. Committed and proliferating mononuclear myoblasts exhibited nuclear HIF-1α expression. Differently, the more differentiated elongated and parallel-aligned cells, which are likely ready to fuse with each other, show a mainly cytoplasmic localization of the factor. Multinucleated myotubes displayed both nuclear and cytoplasmic HIF-1α expression. The MMP-9 and MyoD (myogenic activation marker) expression synchronized with that of HIF-1α, increasing after 24 h of differentiation. By means of silencing HIF-1α and MMP-9 by short-interfering RNA and MMP-9 pharmacological inhibition, this study unraveled MMP-9's role as an HIF-1α downstream effector and the fact that the HIF-1α/MMP-9 axis is essential in morpho-functional cell myogenic commitment.

Keywords:  HIF; MMP-9; electrophysiology; immunofluorescence; myoblasts; myogenesis; normoxia; regeneration; satellite cells; skeletal muscle

DOI:  https://doi.org/10.3390/cells12242851
Function (Oxf). 2024 ;5(1): zqad066

Neuromuscular Dysfunction Precedes Cognitive Impairment in a Mouse Model of Alzheimer's Disease.

Matthew H Brisendine, Anna S Nichenko, Aloka B Bandara, Orion S Willoughby, Niloufar Amiri, Zach Weingrad, Kalyn S Specht, Jacob M Bond, Adele Addington, Ronald G Jones, Kevin A Murach, Steven Poelzing, Siobhan M Craige, Robert W Grange, Joshua C Drake.

  Alzheimer's disease (AD) develops along a continuum that spans years prior to diagnosis. Decreased muscle function and mitochondrial respiration occur years earlier in those that develop AD; however, it is unknown what causes these peripheral phenotypes in a disease of the brain. Exercise promotes muscle, mitochondria, and cognitive health and is proposed to be a potential therapeutic for AD, but no study has investigated how skeletal muscle adapts to exercise training in an AD-like context. Utilizing 5xFAD mice, an AD model that develops ad-like pathology and cognitive impairments around 6 mo of age, we examined in vivo neuromuscular function and exercise adapations (mitochondrial respiration and RNA sequencing) before the manifestation of overt cognitive impairment. We found 5xFAD mice develop neuromuscular dysfunction beginning as early as 4 mo of age, characterized by impaired nerve-stimulated muscle torque production and compound nerve action potential of the sciatic nerve. Furthermore, skeletal muscle in 5xFAD mice had altered, sex-dependent, adaptive responses (mitochondrial respiration and gene expression) to exercise training in the absence of overt cognitive impairment. Changes in peripheral systems, specifically neural communication to skeletal muscle, may be harbingers for AD and have implications for lifestyle interventions, like exercise, in AD.

Keywords:  5xFAD; alzheimer’s disease; exercise; mitochondria; neuromuscular; sciatic nerve

DOI:  https://doi.org/10.1093/function/zqad066
Cells. 2023 Dec 07. pii: 2787. [Epub ahead of print]12(24):

Therapeutic Consequences of Targeting the IGF-1/PI3K/AKT/FOXO3 Axis in Sarcopenia: A Narrative Review.

Benjamin Gellhaus, Kai O Böker, Arndt F Schilling, Dominik Saul.

  The high prevalence of sarcopenia in an aging population has an underestimated impact on quality of life by increasing the risk of falls and subsequent hospitalization. Unfortunately, the application of the major established key therapeutic-physical activity-is challenging in the immobile and injured sarcopenic patient. Consequently, novel therapeutic directions are needed. The transcription factor Forkhead-Box-Protein O3 (FOXO3) may be an option, as it and its targets have been observed to be more highly expressed in sarcopenic muscle. In such catabolic situations, Foxo3 induces the expression of two muscle specific ubiquitin ligases (Atrogin-1 and Murf-1) via the PI3K/AKT pathway. In this review, we particularly evaluate the potential of Foxo3-targeted gene therapy. Foxo3 knockdown has been shown to lead to increased muscle cross sectional area, through both the AKT-dependent and -independent pathways and the reduced impact on the two major downstream targets Atrogin-1 and Murf-1. Moreover, a Foxo3 reduction suppresses apoptosis, activates satellite cells, and initiates their differentiation into muscle cells. While this indicates a critical role in muscle regeneration, this mechanism might exhaust the stem cell pool, limiting its clinical applicability. As systemic Foxo3 knockdown has also been associated with risks of inflammation and cancer progression, a muscle-specific approach would be necessary. In this review, we summarize the current knowledge on Foxo3 and conceptualize a specific and targeted therapy that may circumvent the drawbacks of systemic Foxo3 knockdown. This approach presumably would limit the side effects and enable an activity-independent positive impact on skeletal muscle.

Keywords:  Atrogin-1; FOXO3; Murf-1; aging; sarcopenia; satellite cells; skeletal muscle atrophy

DOI:  https://doi.org/10.3390/cells12242787
Front Physiol. 2023 ;14 1333577

Editorial: Spotlight on aging: physiology, prevention, and management of skeletal muscle atrophy.

Gabriel Nasri Marzuca-Nassr, Luis Peñailillo, Denisse Valladares-Ide, Sergio Martinez-Huenchullan, Rui Curi, Sandro Massao Hirabara, Kaio Fernando Vitzel.



Keywords:  ageing; aging; muscle architecture; sarcopenia; skeletal muscle atrophy

DOI:  https://doi.org/10.3389/fphys.2023.1333577
Eur J Transl Myol. 2023 Dec 15.

Angiotensin-(1-7) improves skeletal muscle regeneration.

Mayalen Valero-Breton, Franco Tacchi, Johanna Abrigo, Felipe Simon, Daniel Cabrera, Claudio Cabello-Verrugio.

Skeletal muscle possesses regenerative potential via satellite cells, compromised in muscular dystrophies leading to fibrosis and fat infiltration. Angiotensin II (Ang-II) is commonly associated with pathological states. In contrast, Angiotensin (1-7) [Ang-(1-7)] counters Ang-II, acting via the Mas receptor. While Ang-II affects skeletal muscle regeneration, the influence of Ang-(1-7) remains to be elucidated. Therefore, this study aims to investigate the role of Ang-(1-7) in skeletal muscle regeneration. C2C12 cells were differentiated in the absence or presence of 10 nM of Ang-(1-7). The diameter of myotubes and protein levels of myogenin and myosin heavy chain (MHC) were determined. C57BL/6 WT male mice 16-18 weeks old) were randomly assigned to injury-vehicle, injury-Ang-(1-7), and control groups. Ang-(1-7) was administered via osmotic pumps, and muscle injury was induced by injecting barium chloride to assess muscle regeneration through histological analyses. Moreover, embryonic myosin (eMHC) and myogenin protein levels were evaluated. C2C12 myotubes incubated with Ang-(1-7) showed larger diameters than the untreated group and increased myogenin and MHC protein levels during differentiation. Ang-(1-7) administration enhances regeneration by promoting a larger diameter of new muscle fibers. Furthermore, higher numbers of eMHC (+) fibers were observed in the injured-Ang-(1-7), which also had a larger diameter. Moreover, eMHC and myogenin protein levels were elevated, supporting enhanced regeneration due to Ang-(1-7) administration. Ang-(1-7) effectively promotes differentiation in vitroand improves muscle regeneration in the context of injuries, with potential implications for treating muscle-related disorders.

DOI: https://doi.org/10.4081/ejtm.2023.12037
Biomolecules. 2023 Dec 12. pii: 1779. [Epub ahead of print]13(12):

From Chronodisruption to Sarcopenia: The Therapeutic Potential of Melatonin.

José Fernández-Martínez, Yolanda Ramírez-Casas, Yang Yang, Paula Aranda-Martínez, Laura Martínez-Ruiz, Germaine Escames, Darío Acuña-Castroviejo.

  Sarcopenia is an age-related condition that involves a progressive decline in muscle mass and function, leading to increased risk of falls, frailty, and mortality. Although the exact mechanisms are not fully understood, aging-related processes like inflammation, oxidative stress, reduced mitochondrial capacity, and cell apoptosis contribute to this decline. Disruption of the circadian system with age may initiate these pathways in skeletal muscle, preceding the onset of sarcopenia. At present, there is no pharmacological treatment for sarcopenia, only resistance exercise and proper nutrition may delay its onset. Melatonin, derived from tryptophan, emerges as an exceptional candidate for treating sarcopenia due to its chronobiotic, antioxidant, and anti-inflammatory properties. Its impact on mitochondria and organelle, where it is synthesized and crucial in aging skeletal muscle, further highlights its potential. In this review, we discuss the influence of clock genes in muscular aging, with special reference to peripheral clock genes in the skeletal muscle, as well as their relationship with melatonin, which is proposed as a potential therapy against sarcopenia.

Keywords:  Bmal1; aging; chronodisruption; clock genes; inflammaging; melatonin; mitochondria; oxidative stress; sarcopenia; skeletal muscle

DOI:  https://doi.org/10.3390/biom13121779
J Proteome Res. 2023 Dec 20.

Proteomic Identification of Seasonally Expressed Proteins Contributing to Heart Function and the Avoidance of Skeletal Muscle Disuse Atrophy in a Hibernating Mammal.

Md Shadman Ridwan Abid, Eric C Bredahl, Ashley D Clifton, Haowen Qiu, Matthew T Andrews, James W Checco.

  Hibernation in the thirteen-lined ground squirrel (Ictidomys tridecemlineatus) takes place over 4-6 months and is characterized by multiday bouts of hypothermic torpor (5-7 °C core body temperature) that are regularly interrupted every 1-2 weeks by brief (12-24 h) normothermic active periods called interbout arousals. Our goal was to gain insight into the molecular mechanisms that underlie the hibernator's ability to preserve heart function and avoid the deleterious effects of skeletal muscle disuse atrophy over prolonged periods of inactivity, starvation, and near-freezing body temperatures. To achieve this goal, we performed organelle enrichment of heart and skeletal muscle at five seasonal time points followed by LC-MS-based label-free quantitative proteomics. In both organs, we saw an increase in the levels of many proteins as ground squirrels transition from an active state to a prehibernation state in the fall. Interestingly, seasonal abundance patterns identified DHRS7C, SRL, TRIM72, RTN2, and MPZ as potential protein candidates for mitigating disuse atrophy in skeletal muscle, and ex vivo contractile mechanics analysis revealed no deleterious effects in the ground squirrel's muscles despite prolonged sedentary activity. Overall, an increased understanding of protein abundance in hibernators may enable novel therapeutic strategies to treat muscle disuse atrophy and heart disease in humans.

Keywords:  disuse atrophy; heart; hibernation; mass spectrometry; organelle enrichment; proteomics; skeletal muscle

DOI:  https://doi.org/10.1021/acs.jproteome.3c00540
Cancers (Basel). 2023 Dec 15. pii: 5856. [Epub ahead of print]15(24):

The Role of Exercise in Cancer-Related Sarcopenia and Sarcopenic Obesity.

Argyro Papadopetraki, Antonios Giannopoulos, Maria Maridaki, Flora Zagouri, Stavroula Droufakou, Michael Koutsilieris, Anastassios Philippou.

  One of the most common adverse effects of cancer and its therapeutic strategies is sarcopenia, a condition which is characterised by excess muscle wasting and muscle strength loss due to the disrupted muscle homeostasis. Moreover, cancer-related sarcopenia may be combined with the increased deposition of fat mass, a syndrome called cancer-associated sarcopenic obesity. Both clinical conditions have significant clinical importance and can predict disease progression and survival. A growing body of evidence supports the claim that physical exercise is a safe and effective complementary therapy for oncology patients which can limit the cancer- and its treatment-related muscle catabolism and promote the maintenance of muscle mass. Moreover, even after the onset of sarcopenia, exercise interventions can counterbalance the muscle mass loss and improve the clinical appearance and quality of life of cancer patients. The aim of this narrative review was to describe the various pathophysiological mechanisms, such as protein synthesis, mitochondrial function, inflammatory response, and the hypothalamic-pituitary-adrenal axis, which are regulated by exercise and contribute to the management of sarcopenia and sarcopenic obesity. Moreover, myokines, factors produced by and released from exercising muscles, are being discussed as they appear to play an important role in mediating the beneficial effects of exercise against sarcopenia.

Keywords:  body composition; cancer; exercise; muscle atrophy; muscle wasting; physical activity; sarcopenia; sarcopenic obesity; weakness

DOI:  https://doi.org/10.3390/cancers15245856
J Cell Sci. 2023 Dec 01. pii: jcs261454. [Epub ahead of print]136(23):

Regulated dynamic subcellular GLUT4 localization revealed by proximal proteome mapping in human muscle cells.

Anuttoma Ray, Jennifer Wen, Lucie Yammine, Jeff Culver, Isabella Supardi Parida, Jeonifer Garren, Liang Xue, Katherine Hales, Qing Xiang, Morris J Birnbaum, Bei B Zhang, Mara Monetti, Timothy E McGraw.

  Regulation of glucose transport, which is central for control of whole-body metabolism, is determined by the amount of GLUT4 glucose transporter (also known as SLC2A4) in the plasma membrane (PM) of fat and muscle cells. Physiologic signals [such as activated insulin receptor or AMP-activated protein kinase (AMPK)] increase PM GLUT4. Here, we show that the distribution of GLUT4 between the PM and interior of human muscle cells is dynamically maintained, and that AMPK promotes PM redistribution of GLUT4 by regulating exocytosis and endocytosis. Stimulation of exocytosis by AMPK is mediated by Rab10 and the Rab GTPase-activating protein TBC1D4. APEX2 proximity mapping reveals that GLUT4 traverses both PM-proximal and PM-distal compartments in unstimulated muscle cells, further supporting retention of GLUT4 by a constitutive retrieval mechanism. AMPK-stimulated translocation involves GLUT4 redistribution among the same compartments traversed in unstimulated cells, with a significant recruitment of GLUT4 from the Golgi and trans-Golgi network compartments. Our comprehensive proximal protein mapping provides an integrated, high-density, whole-cell accounting of the localization of GLUT4 at a resolution of ∼20 nm that serves as a structural framework for understanding the molecular mechanisms regulating GLUT4 trafficking downstream of different signaling inputs in a physiologically relevant cell type.

Keywords:  AMPK regulation of GLUT4; GLUT4 trafficking; GLUT4-proximal proteome; Human muscle cells

DOI:  https://doi.org/10.1242/jcs.261454
PLoS One. 2023 ;18(12): e0287078

Alterations in RNA editing in skeletal muscle following exercise training in individuals with Parkinson's disease.

Heather Milliken Mercer, Aiswarya Mukundan Nair, Angela Ridgel, Helen Piontkivska.

Parkinson's Disease (PD) is the second most common neurodegenerative disease behind Alzheimer's Disease, currently affecting more than 10 million people worldwide and 1.5 times more males than females. The progression of PD results in the loss of function due to neurodegeneration and neuroinflammation. The etiology of PD is multifactorial, including both genetic and environmental origins. Here we explored changes in RNA editing, specifically editing through the actions of the Adenosine Deaminases Acting on RNA (ADARs), in the progression of PD. Analysis of ADAR editing of skeletal muscle transcriptomes from PD patients and controls, including those that engaged in a rehabilitative exercise training program revealed significant differences in ADAR editing patterns based on age, disease status, and following rehabilitative exercise. Further, deleterious editing events in protein coding regions were identified in multiple genes with known associations to PD pathogenesis. Our findings of differential ADAR editing complement findings of changes in transcriptional networks identified by a recent study and offer insights into dynamic ADAR editing changes associated with PD pathogenesis.

DOI: https://doi.org/10.1371/journal.pone.0287078
Biomedicines. 2023 Nov 22. pii: 3112. [Epub ahead of print]11(12):

Subcutaneous Infusion of DNA-Aptamer Raised against Advanced Glycation End Products Prevents Loss of Skeletal Muscle Mass and Strength in Accelerated-Aging Mice.

Yusaku Mori, Makoto Ohara, Michishige Terasaki, Naoya Osaka, Hironori Yashima, Tomomi Saito, Yurie Otoyama-Kataoka, Takemasa Omachi, Yuichiro Higashimoto, Takanori Matsui, Tomoyasu Fukui, Sho-Ichi Yamagishi.

  We have developed DNA aptamers that can inhibit the toxic effects of advanced glycation end products (AGE-Apts). We herein evaluated the effects of AGE-Apts on muscle mass and strength in senescence-accelerated mouse prone 8 (SAMP8) mice. Eight-month-old male SAMP8 mice received subcutaneous infusion of control DNA aptamers (CTR-Apts) or AGE-Apts. Mice in an age-matched senescence-accelerated mouse resistant strain 1 (SAMR1) group were treated with CTR-Apts as controls. The soleus muscles were collected after the 8-week intervention for weight measurement and histological, RT-PCR, and immunofluorescence analyses. Grip strength was measured before and after the 8-week intervention. AGE-Apt treatment inhibited the progressive decrease in the grip strength of SAMP8 mice. SAMP8 mice had lower soleus muscle weight and fiber size than SAMR1 mice, which was partly restored by AGE-Apt treatment. Furthermore, AGE-Apt-treated SAMP8 mice had a lower interstitial fibrosis area of the soleus muscle than CTR-Apt-treated SAMP8 mice. The soleus muscle levels of AGEs, oxidative stress, receptor for AGEs, and muscle ring-finger protein-1 were increased in the CTR-Apt-treated mice, all of which, except for AGEs, were inhibited by AGE-Apt treatment. Our present findings suggest that the subcutaneous delivery of AGE-Apts may be a novel therapeutic strategy for aging-related decrease in skeletal muscle mass and strength.

Keywords:  AGEs; DNA aptamer; MuRF1; muscle atrophy; oxidative stress; sarcopenia

DOI:  https://doi.org/10.3390/biomedicines11123112
J Vis Exp. 2023 Dec 01.

Analysis of the Mitochondrial Density and Longitudinal Distribution in Rat Live-Skeletal Muscle Fibers by Confocal Microscopy.

Perla Pérez-Treviño, Bianca Nieblas, Selma Romina López-Vaquera, Noemí García.

The mitochondrion is an organelle that can be elongated, fragmented, and renovated according to the metabolic requirements of the cells. The remodeling of the mitochondrial network allows healthy mitochondria to meet cellular demands; however, the loss of this capacity has been related to the development or progression of different pathologies. In skeletal muscle, mitochondrial density and distribution changes are observed in physiological and pathological conditions such as exercise, aging, and obesity, among others. Therefore, the study of the mitochondrial network may provide a better understanding of mechanisms related to those conditions. Here, a protocol for mitochondria imaging of live-skeletal muscle fibers from rats is described. Fibers are manually dissected in a relaxing solution and incubated with a fluorescent live-cell imaging indicator of mitochondria (tetramethylrhodamine ethyl ester, TMRE). The mitochondria signal is recorded by confocal microscopy using the XYZ scan mode to obtain confocal images of the intermyofibrillar mitochondrial (IMF) network. After that, the confocal images are processed by thresholding and binarization. The binarized confocal image accounts for the positive pixels for mitochondria, which are then counted to obtain the mitochondrial density. The mitochondrial network in skeletal muscle is characterized by a high density of IMF population, which has a periodic longitudinal distribution similar to that of T-tubules (TT). The Fast Fourier Transform (FFT) is a standard analysis technique performed to evaluate the distribution of TT that allows finding the distribution frequency and the level of their organization. In this protocol, the implementation of the FFT algorithm is described for the analysis of the longitudinal mitochondrial distribution in skeletal muscle.

DOI: https://doi.org/10.3791/65306
J Cachexia Sarcopenia Muscle. 2023 Dec 20.

The mediation roles of intermuscular fat and inflammation in muscle mitochondrial associations with cognition and mobility.

Qu Tian, Philip R Lee, Qi Yang, Anne Z Moore, Bennett A Landman, Susan M Resnick, Luigi Ferrucci.

   BACKGROUND: Mitochondrial dysfunction may contribute to brain and muscle health through inflammation or fat infiltration in the muscle, both of which are associated with cognitive function and mobility. We aimed to examine the association between skeletal muscle mitochondrial function and cognitive and mobility outcomes and tested the mediation effect of inflammation or fat infiltration.
METHODS: We analysed data from 596 Baltimore Longitudinal Study of Aging participants who had concurrent data on skeletal muscle oxidative capacity and cognitive and mobility measures of interest (mean age: 66.1, 55% women, 24% Black). Skeletal muscle oxidative capacity was assessed as post-exercise recovery rate (kPCr) via P31 MR spectroscopy. Fat infiltration was measured as intermuscular fat (IMF) via CT scan and was available for 541 participants. Inflammation markers [IL-6, C-reactive protein (CRP), total white blood cell (WBC), neutrophil count, erythrocyte sedimentation rate (ESR), or albumin] were available in 594 participants. We examined the association of kPCr and cognitive and mobility measures using linear regression and tested the mediation effect of IMF or inflammation using the mediation package in R. Models were adjusted for demographics and PCr depletion.
RESULTS: kPCr and IMF were both significantly associated with specific cognitive domains (DSST, TMA-A, and pegboard dominant hand performance) and mobility (usual gait speed, HABCPPB, 400 m walk time) (all P < 0.05). IMF significantly mediated the relationship between kPCr and these cognitive and mobility measures (all P < 0.05, proportion mediated 13.1% to 27%). Total WBC, neutrophil count, and ESR, but not IL-6 or CRP, also mediated at least one of the cognitive and mobility outcomes (all P < 0.05, proportion mediated 9.4% to 15.3%).
CONCLUSIONS: Skeletal muscle mitochondrial function is associated with cognitive performance involving psychomotor speed. Muscle fat infiltration and specific inflammation markers mediate the relationship between muscle mitochondrial function and cognitive and mobility outcomes. Future studies are needed to confirm these associations longitudinally and to understand their mechanistic underpinnings.

Keywords:  Aging; Cognition; Inflammation; Intermuscular fat; Mitochondrial oxidative capacity; Mobility

DOI:  https://doi.org/10.1002/jcsm.13413
Eur J Transl Myol. 2023 Dec 18.

Pax7 reporter mouse models: a pocket guide for satellite cell research.

Huascar Pedro Ortuste Quiroga, Shin Fujimaki, Yusuke Ono.

Since their discovery, satellite cells have showcased their need as primary contributors to skeletal muscle maintenance and repair. Satellite cells lay dormant, but when needed, activate, differentiate, fuse to fibres and self-renew, that has bestowed satellite cells with the title of muscle stem cells. The satellite cell specific transcription factor Pax7 has enabled researchers to develop animal models against the Pax7 locus in order to isolate and characterise satellite cell-mediated events. This review focuses specifically on describing Pax7 reporter mouse models. Here we describe how each model was generated and the key findings obtained. The strengths and limitations of each model are also discussed. The aim is to provide new and current satellite cell enthusiasts with a basic understanding of the available Pax7 reporter mice and hopefully guide selection of the most appropriate Pax7 model to answer a specific research question.

DOI: https://doi.org/10.4081/ejtm.2023.12174
Sci Transl Med. 2023 Dec 20. 15(727): eadh2156

Lesion level-dependent systemic muscle wasting after spinal cord injury is mediated by glucocorticoid signaling in mice.

Markus E Harrigan, Angela R Filous, Christopher P Vadala, Amy Webb, Maciej Pietrzak, Zarife Sahenk, Harald Prüss, Peter J Reiser, Phillip G Popovich, W David Arnold, Jan M Schwab.

An incomplete mechanistic understanding of skeletal muscle wasting early after spinal cord injury (SCI) precludes targeted molecular interventions. Here, we demonstrated systemic wasting that also affected innervated nonparalyzed (supralesional) muscles and emerged within 1 week after experimental SCI in mice. Systemic muscle wasting caused muscle weakness, affected fast type 2 myofibers preferentially, and became exacerbated after high (T3) compared with low (T9) thoracic paraplegia, indicating lesion level-dependent ("neurogenic") mechanisms. The wasting of nonparalyzed muscle and its rapid onset and severity beyond what can be explained by disuse implied unknown systemic drivers. Muscle transcriptome and biochemical analysis revealed a glucocorticoid-mediated catabolic signature early after T3 SCI. SCI-induced systemic muscle wasting was mitigated by (i) endogenous glucocorticoid ablation (adrenalectomy) and (ii) pharmacological glucocorticoid receptor (GR) blockade and was (iii) completely prevented after T3 relative to T9 SCI by genetic muscle-specific GR deletion. These results suggest that neurogenic hypercortisolism contributes to a rapid systemic and functionally relevant muscle wasting syndrome early after paraplegic SCI in mice.

DOI: https://doi.org/10.1126/scitranslmed.adh2156
Can J Physiol Pharmacol. 2023 Dec 20.

Azilsartan Prevents Muscle Loss and Fast to Slow-twitch Muscle Fibre Shift in Natural Ageing Sarcopenic Rats.

Priyanka Prajapati, Anand Kumar, Shubhada Mangulkar, D R Chaple, Shubhini A Saraf, Sapana Kushwaha.

Sarcopenia is a musculoskeletal disease that reduces muscle mass and strength in older individuals. The study investigates the effects of azilsartan (AZL) on skeletal muscle loss in natural sarcopenic rats. Male Sprague-Dawley rats aged 4-6 months and 18-21 months were selected as young-matched control and natural-aged (sarcopenic) rats, respectively. Rats were allocated into young and old control (YC & OC) and young and old AZL treatment (YT & OT) groups, which received vehicles and azilsartan (8 mg/kg, orally) for six weeks. Rats were then sacrificed after muscle function analysis. Serum and gastrocnemius (GN) muscles were isolated for further endpoints. AZL significantly improved muscle grip strength and antioxidant levels in sarcopenic rats. AZL also restored levels of insulin, testosterone, and muscle biomarkers such as myostatin and creatinine kinase in sarcopenic rats. Furthermore, AZL treatment improved the cellular and ultrastructure of GN muscle and prevented the shift of type II (glycolytic) myofibers to type I (oxidative) myofibers. Results showed that AZL intervention restored protein synthesis in natural sarcopenic rats by increasing p-Akt-1 and decreasing MuRF-1 and TNF-α immunoexpressions. In conclusion, the present findings showed that AZL could be an effective intervention in treating age-related muscle impairments.

DOI: https://doi.org/10.1139/cjpp-2023-0265
Diabet Med. 2023 Dec 23. e15271

The antidiabetic SGLT2 inhibitor canagliflozin reduces mitochondrial metabolism in a model of skeletal muscle insulin resistance.

Lindsey R VanDerStad, Emily C Wyatt, Roger A Vaughan.

   AIMS: Sodium-glucose cotransporter 2 (SGLT2) inhibitors such as canagliflozin (CANA) have emerged as an effective adjuvant therapy in the management of diabetes, however, past observations suggest CANA may alter skeletal muscle mass and function. The purpose of this work was to investigate the effects of CANA on skeletal muscle metabolism both with and without insulin resistance.
METHODS: C2C12 myotubes were treated with CANA with or without insulin resistance. Western blot and qRT-PCR were used to assess protein and gene expression, respectively. Cell metabolism was assessed via oxygen consumption and extracellular acidification rate. Mitochondrial, nuclei and lipid content were measured using fluorescent staining and microscopy.
RESULTS: CANA decreased mitochondrial function and glycolytic metabolism as did insulin resistance, however, these changes occurred without significant alterations in gene expression associated with each pathway. Additionally, while insulin resistance reduced insulin-stimulated pAkt expression, CANA had no significant effect on insulin sensitivity.
CONCLUSIONS: CANA appears to reduce mitochondrial and glycolytic metabolism without altering gene expression governing these pathways, suggesting a reduction in substrate may be responsible for lower metabolism.

Keywords:  diabetes; gliflozin; insulin resistance; pAkt/Akt; skeletal muscle; sodium-glucose cotransporter 2

DOI:  https://doi.org/10.1111/dme.15271
Nat Commun. 2023 Dec 19. 14(1): 8043

Efficient generation of a self-organizing neuromuscular junction model from human pluripotent stem cells.

Alessia Urzi, Ines Lahmann, Lan Vi N Nguyen, Benjamin R Rost, Angélica García-Pérez, Noemie Lelievre, Megan E Merritt-Garza, Han C Phan, Gary J Bassell, Wilfried Rossoll, Sebastian Diecke, Severine Kunz, Dietmar Schmitz, Mina Gouti.

The complex neuromuscular network that controls body movements is the target of severe diseases that result in paralysis and death. Here, we report the development of a robust and efficient self-organizing neuromuscular junction (soNMJ) model from human pluripotent stem cells that can be maintained long-term in simple adherent conditions. The timely application of specific patterning signals instructs the simultaneous development and differentiation of position-specific brachial spinal neurons, skeletal muscles, and terminal Schwann cells. High-content imaging reveals self-organized bundles of aligned muscle fibers surrounded by innervating motor neurons that form functional neuromuscular junctions. Optogenetic activation and pharmacological interventions show that the spinal neurons actively instruct the synchronous skeletal muscle contraction. The generation of a soNMJ model from spinal muscular atrophy patient-specific iPSCs reveals that the number of NMJs and muscle contraction is severely affected, resembling the patient's pathology. In the future, the soNMJ model could be used for high-throughput studies in disease modeling and drug development. Thus, this model will allow us to address unmet needs in the neuromuscular disease field.

DOI: https://doi.org/10.1038/s41467-023-43781-3
J Physiol Biochem. 2023 Dec 19.

Effects of exercise, metformin, and combination treatments on type 2 diabetic mellitus-induced muscle atrophy in db/db mice: Crosstalk between autophagy and the proteasome.

Mengqi Xiang, Xinmeng Yuan, Nianyun Zhang, Liumei Zhang, Yuting Liu, Jingjing Liu, Yaran Gao, Ye Xu, Wen Sun, Qiang Tang, Yuan Zhang, Jiao Lu.

  Both exercise and metformin are common effective clinical treatments of type 2 diabetic mellitus. This study investigated the functional role of exercise, metformin, and combination treatment on type 2 diabetic mellitus-induced muscle atrophy. In this experiment, a total of 10 BKS mice were set as the control group. A total of 40 BKS-db/db mice were randomly divided into the control group (db/db); the exercise intervention group (db/db + Ex), which ran on a treadmill at 7-12 m/min, 30-40 min/day, 5 days/week; the metformin administration group (db/db + Met), which was administered 300 mg/kg of metformin solution by gavage daily; and the exercise combined with metformin administration group (db/db + Ex + Met). After 8 weeks of intervention, their tibialis anterior muscles were removed. The levels of insulin signaling pathway proteins, ubiquitin proteasome, and autophagic lysosome-associated proteins were detected using western blot, the expression of MuRF1 and Atrogin-1 was detected using immunohistochemical staining, and the degradation of autophagosomes was detected using double-labeled immunofluorescence. The db/db mice exhibited reduced insulin sensitivity and inhibition of the autophagic-lysosome system, the ubiquitin-proteasome system was activated, and protein degradation was exacerbated, leading to skeletal muscle atrophy. Exercise and metformin and their combined interventions can increase insulin sensitivity, whereas exercise alone showed more effective in inhibiting the ubiquitin-proteasome system, improving autophagy levels, and alleviating skeletal muscle atrophy. Compared with metformin, exercise demonstrated superior improvement of muscle atrophy by promoting the synthesis and degradation of autophagy through the AMPK/ULK1 pathway. However, the combination treatment exhibits no synergistic effect on muscle atrophy.

Keywords:  Autophagy; Exercise; Metformin; Muscle atrophy; Ubiquitin–proteasome system

DOI:  https://doi.org/10.1007/s13105-023-01001-y
Apoptosis. 2023 Dec 20.

Myeloma extracellular vesicle-derived RAGE increases inflammatory responses and myotube atrophy in multiple myeloma through activation of the TLR4/NF-κB p65 pathway.

Yue Wu, Xingchen Yao, Xiangjun Shi, Ziyu Xu, Jie Ren, Ming Shi, Meng Li, Junpeng Liu, Xinru Du.

  Sarcopenia manifests as muscle atrophy and loss that is complicated with malignancy. This study explored the mechanism of extracellular vesicles (EVs) in multiple myeloma (MM) with sarcopenia. SP2/0 conditioned medium (CM) was collected to isolate SP2/0-EVs. C2C12 cells were incubated with SP2/0 CM or SP2/0-EVs. ROS, TNF-α, IL-6, MuRF1 and MyHC levels were detected by DCF-DA fluorescent probe, ELISA, and Western blot. GW4869 was used to inhibit EV secretion in SP2/0 to confirm its effect on muscle atrophy. Serum was collected from MM patients with or without sarcopenia to detect RAGE mRNA expression. SP2/0 cells were transfected with RAGE siRNA and C2C12 cells were treated with the isolated si-RAGE-EVs or/and TLR4 agonist. SP2/0 tumor-bearing mouse model was established. Healthy mice and SP2/0-tumor bearing mice were treated with SP2/0-EVs or si-RAGE-EVs. SP2/0 CM or SP2/0-EVs stimulated ROS, inflammatory responses, and myotube atrophy in C2C12 cells. GW4869 blocked EV secretion and the effects of SP2/0 CM. RAGE mRNA expression in serum EVs was increased in MM&Sarcopenia patients and RAGE knockdown in SP2/0-EVs partially nullified SP2/0-EVs' effects. SP2/0-EVs activated the TLR4/NF-κB p65 pathway by translocating RAGE. SP2/0-EVs-derived RAGE elevated ROS production, inflammation, and myotube atrophy in C2C12 cells and caused muscle loss in SP2/0 tumor-bearing mice by activating the TLR4/NF-κB p65 pathway. SP2/0-EVs partially recapitulated muscle loss in healthy mice. SP2/0-EVs-derived RAGE increased ROS production, inflammation, and myotube atrophy in MM through TLR4/NF-κB p65 pathway activation.

Keywords:  Extracellular vesicles; Multiple myeloma; NF-κB p65; RAGE; Sarcopenia; TLR4

DOI:  https://doi.org/10.1007/s10495-023-01920-7
Mol Metab. 2023 Dec 15. pii: S2212-8778(23)00188-6. [Epub ahead of print] 101854

Need for speed: Human fast-twitch mitochondria favor power over efficiency.

Sebastian Edman, Mikael Flockhart, Filip J Larsen, William Apró.

OBJECTIVE: Human skeletal muscle consists of a mixture of slow- and fast-twitch fibers with distinct capacities for contraction mechanics, fermentation, and oxidative phosphorylation (OXPHOS). While the divergence in mitochondrial volume favoring slow-twitch fibers is well established, data on the fiber type-specific intrinsic mitochondrial function and morphology are highly limited with existing data mainly being generated in animal models. This highlights the need for more human data on the topic.
METHODS: Here, we utilized THRIFTY, a rapid fiber type identification protocol to detect, sort, and pool fast- and slow-twitch fibers within 6 h of muscle biopsy sampling. Respiration of permeabilized fast- and slow-twitch fiber pools was then analyzed with high-resolution respirometry. Using standardized western blot procedures, muscle fiber pools were subsequently analyzed for control proteins and key proteins related to respiratory capacity.
RESULTS: Maximal complex I CI+II respiration was 25% higher in human slow-twitch fibers compared to fast-twitch fibers. However, per volume, the respiratory rate of mitochondria in fast-twitch fibers was approximately 50% higher for CI+II, which was primarily mediated through elevated CII respiration, but not CI or. Furthermore, the abundance of CII protein and proteins regulating cristae structure were disproportionally elevated in mitochondria of the fast-twitch fibers. The difference in intrinsic respiratory rate was not reflected in fatty acid-or complex I respiration.
CONCLUSION: Mitochondria of human fast-twitch muscle fibers compensate for their lack of volume by substantially elevating intrinsic respiratory rate through increased reliance on complex II.

DOI: https://doi.org/10.1016/j.molmet.2023.101854
bioRxiv. 2023 Dec 07. pii: 2023.12.05.569919. [Epub ahead of print]

Dystrophin deficiency impairs cell junction formation during embryonic myogenesis.

Elise Mozin, Emmanuelle Massouridès, Virginie Mournetas, Clémence Lièvre, Audrey Bourdon, Dana L Jackson, Jonathan S Packer, Cole Trapnell, Caroline Le Guiner, Oumeya Adjali, Christian Pinset, David L Mack, Jean-Baptiste Dupont.

Mutations in the DMD gene lead to Duchenne muscular dystrophy, a severe X-linked neuromuscular disorder which manifests itself as young boys acquire motor functions. DMD is diagnosed after 2 to 4 years, but the absence of dystrophin has an impact before symptoms appear in patients, which poses a serious challenge in the optimization of standards of care. In this report, we investigated the early consequences of dystrophin deficiency during skeletal muscle development. We used single-cell transcriptome profiling to characterize the myogenic trajectory of human pluripotent stem cells and showed that DMD cells bifurcate to an alternative branch when they reach the somite stage. Here, dystrophin deficiency was linked to marked dysregulations of cell junction families involved in the cell state transitions characteristic of somitogenesis. Altogether, this work demonstrates that in vitro , dystrophin deficiency has early consequences during myogenic development, which should be considered in future therapeutic strategies for DMD.

DOI: https://doi.org/10.1101/2023.12.05.569919
Nat Aging. 2023 Dec;3(12): 1486-1499

The Information Theory of Aging.

Yuancheng Ryan Lu, Xiao Tian, David A Sinclair.

Information storage and retrieval is essential for all life. In biology, information is primarily stored in two distinct ways: the genome, comprising nucleic acids, acts as a foundational blueprint and the epigenome, consisting of chemical modifications to DNA and histone proteins, regulates gene expression patterns and endows cells with specific identities and functions. Unlike the stable, digital nature of genetic information, epigenetic information is stored in a digital-analog format, susceptible to alterations induced by diverse environmental signals and cellular damage. The Information Theory of Aging (ITOA) states that the aging process is driven by the progressive loss of youthful epigenetic information, the retrieval of which via epigenetic reprogramming can improve the function of damaged and aged tissues by catalyzing age reversal.

DOI: https://doi.org/10.1038/s43587-023-00527-6
Eur J Transl Myol. 2023 Dec 18.

Five Padua days on muscle and mobility medicine (2024Pdm3), Padua, Italy.

Sandra Zampieri, Ines Bersch, Piera Smeriglio, Elena Barbieri, Massimo Ganassi, Christiaan Leeuwenburg, Riccardo Rosati, Paolo Gargiulo, Amber Pond, H Lee Sweeney, Ugo Carraro.

At the end of the 2023 Padua Days of Muscle and Mobility Medicine the next year's meeting was scheduled from 27 February to 2 March 2024 (2024Pdm3). During the summer and autumn the program was confirmed with Scientific Sessions that will take place over five days, starting in the afternoon of February 27, 2024 at the Conference Room of the Hotel Petrarca, Thermae of Euganean Hills (Padua), Italy. As usual, the next day will be spent in Padua, in this occasion at the San Luca Hall of the Santa Giustina monastery in Prato della Valle, Padua, Italy. Collected during Autumn 2023, many more titles and abstracts than expected were submitted, forcing the organization of parallel sessions both on March 1 and March 2 2024 confirming attractiveness of the 2024 Pdm3. The five days will include oral presentations of scientists and clinicians from Argentina, Austria, Belgium, Brazil, Canada, Denmark, Egypt, France, Germany, Iceland, Ireland, Italy, Romania, Russia, Slovenia, Switzerland, UK and USA. Together with the preliminary Program at December 1, 2023, the early submitted Abstracts is e-published in this Issue 33 (4) 2023 of the European Journal of Translational Myology (EJTM). You are invited to join, submitting your Last Minute Abstracts to ugo.carraro@unipd.it by February 1, 2024. Furthermore, with the more generous deadline of May 20, 2024, submit please "Communications" to the European Journal of Translational Myology (Clarivate's ESCI Impact factor 2.2; SCOPUS Cite Score: 3.2). See you soon at the Hotel Petrarca in Montegrotto Terme, Padua, on February 27, 2024, but the complete program can be followed from home via zoom connection.

DOI: https://doi.org/10.4081/ejtm.2023.12161