bims-moremu Biomed News
on Molecular regulators of muscle mass
Issue of 2021‒09‒26
forty-two papers selected by
Anna Vainshtein
Craft Science Inc.

  1. J Cachexia Sarcopenia Muscle. 2021 Sep 24.
      BACKGROUND: Oxidative stress and damage are associated with a number of ageing phenotypes, including age-related loss of muscle mass and reduced contractile function (sarcopenia). Our group and others have reported loss of neuromuscular junction (NMJ) integrity and increased denervation as initiating factors in sarcopenia, leading to mitochondrial dysfunction, generation of reactive oxygen species and peroxides, and loss of muscle mass and weakness. Previous studies from our laboratory show that denervation-induced skeletal muscle mitochondrial peroxide generation is highly correlated to muscle atrophy. Here, we directly test the impact of scavenging muscle mitochondrial hydrogen peroxide on the structure and function of the NMJ and muscle mass and function in a mouse model of denervation-induced muscle atrophy CuZnSOD (Sod1-/- mice, Sod1KO).METHODS: Whole-body Sod1KO mice were crossed to mice with increased expression of human catalase (MCAT) targeted specifically to mitochondria in skeletal muscle (mMCAT mice) to determine the impact of reduced hydrogen peroxide levels on key targets of sarcopenia, including mitochondrial function, NMJ structure and function, and indices of muscle mass and function.
    RESULTS: Female adult (~12-month-old) Sod1KO mice show a number of sarcopenia-related phenotypes in skeletal muscle including reduced mitochondrial oxygen consumption and elevated reactive oxygen species generation, fragmentation, and loss of innervated NMJs (P < 0.05), a 30% reduction in muscle mass (P < 0.05), a 36% loss of force generation (P < 0.05), and a loss of exercise capacity (305 vs. 709 m in wild-type mice, P < 0.05). Muscle from Sod1KO mice also shows a 35% reduction in sarco(endo)plasmic reticulum ATPase activity (P < 0.05), changes in the amount of calcium-regulating proteins, and altered fibre-type composition. In contrast, increased catalase expression in the mMCAT × Sod1KO mice completely prevents the mitochondrial and NMJ-related phenotypes and maintains muscle mass and force generation. The reduction in exercise capacity is also partially inhibited (~35%, P < 0.05), and the loss of fibre cross-sectional area is inhibited by ~50% (P < 0.05).
    CONCLUSIONS: Together, these striking findings suggest that scavenging of mitochondrial peroxide generation by mMCAT expression efficiently prevents mitochondrial dysfunction and NMJ disruption associated with denervation-induced atrophy and weakness, supporting mitochondrial H2 O2 as an important effector of NMJ alterations that lead to phenotypes associated with sarcopenia.
    Keywords:  Catalase; Mitochondria; Neuromuscular junction; Oxidative stress; ROS; Skeletal muscle; Sod
  2. Front Pharmacol. 2021 ;12 739510
      Skeletal muscle undergoes vigorous tissue remodeling after injury. However, aging, chronic inflammatory diseases, sarcopenia, and neuromuscular disorders cause muscle loss and degeneration, resulting in muscular dysfunction. Cellular senescence, a state of irreversible cell cycle arrest, acts during normal embryonic development and remodeling after tissue damage; when these processes are complete, the senescent cells are eliminated. However, the accumulation of senescent cells is a hallmark of aging tissues or pathological contexts and may lead to progressive tissue degeneration. The mechanisms responsible for the effects of senescent cells have not been fully elucidated. Here, we review current knowledge about the beneficial and detrimental effects of senescent cells in tissue repair, regeneration, aging, and age-related disease, especially in skeletal muscle. We also discuss how senescence of muscle stem cells and muscle-resident fibro-adipogenic progenitors affects muscle pathologies or regeneration, and consider the possibility that immunosenescence leads to muscle pathogenesis. Finally, we explore senotherapy, the therapeutic targeting of senescence to treat age-related disease, from the standpoint of improving muscle regeneration.
    Keywords:  FAPs; aging; chronic inflammation; fibrosis; muscle regeneration; muscle stem cells; senescence; skeletal muscle
  3. J Neuromuscul Dis. 2021 Sep 17.
      While skeletal muscle remodeling happens throughout life, diseases that result in its dysfunction are accountable for many deaths. Indeed, skeletal muscle is exceptionally capable to respond to stimuli modifying its homeostasis, such as in atrophy, hypertrophy, regeneration and repair. In particular conditions such as genetic diseases (muscular dystrophies), skeletal muscle's capacity to remodel is strongly affected and undergoes continuous cycles of chronic damage. This induces scarring, fatty infiltration, as well as loss of contractibility and of the ability to generate force. In this context, inflammation, primarily mediated by macrophages, plays a central pathogenic role. Macrophages contribute as the primary regulators of inflammation during skeletal muscle regeneration, affecting tissue-resident cells such as myogenic cells and endothelial cells, but also fibro-adipogenic progenitors, which are the main source of the fibro fatty scar. During skeletal muscle regeneration their function is tightly orchestrated, while in dystrophies their fate is strongly disturbed, resulting in chronic inflammation. In this review, we will discuss the latest findings on the role of macrophages in skeletal muscle diseases, and how they are regulated.
    Keywords:  Macrophage; inflammation; muscle dystrophy; repair; skeletal muscle
  4. BMC Musculoskelet Disord. 2021 Sep 21. 22(1): 809
      BACKGROUND: The angiotensin-converting enzyme 2 (ACE2)/angiotensin 1-7 (Ang-(1-7)) axis has been shown to protect against the age-associated decline in skeletal muscle function. Here, we investigated the protective effects of ACE2 in mitigating the age-associated decline of skeletal muscle function and to identify the potential underlying molecular mechanisms.METHODS: We measured the expression levels of Ang-(1-7) in C57BL/6J mice of different ages and correlated these levels with measures of skeletal muscle function. We also investigated the expression of myocyte enhancer factor 2 A (MEF2A) in ACE2 knockout (ACE2KO) mice and its relationship with muscle function. We then treated aged ACE2KO mice for four weeks with Ang-(1-7) and characterized the levels of MEF2A and skeletal muscle function before and after treatment. We assessed the impact of Ang-(1-7) on the growth and differentiation of C2C12 cells in vitro and assessed changes in expression of the glucose transporter type 4 (Glut4).
    RESULTS: Aged mice showed reduced skeletal muscle function and levels of Ang-(1-7) expression in comparison to young and middle-aged mice. In ACE2KO mice, skeletal muscle function and MEF2A protein expression were significantly lower than in age-matched wild-type (WT) mice. After one month of Ang-(1-7) treatment, skeletal muscle function in the aged ACE2KO mice improved, while MEF2A protein expression was similar to that in the untreated group. In C2C12 cells, Ang-(1-7) was shown to promote along with the upregulated expression of Glut4.
    CONCLUSIONS: The ACE2/ Ang-(1-7) axis has a protective function in skeletal muscle and administration of exogenous Ang-(1-7) can delay the age-related decline in the function of skeletal muscle.
    Keywords:  aging; angiotensin 1–7; angiotensin-converting enzyme 2; skeletal muscle
  5. FASEB J. 2021 Oct;35(10): e21933
      In obesity, skeletal muscle mitochondrial activity changes to cope with increased nutrient availability. Autophagy has been proposed as an essential mechanism involved in the regulation of mitochondrial metabolism. Still, the contribution of autophagy to mitochondrial adaptations in skeletal muscle during obesity is unknown. Here, we show that in response to high-fat diet (HFD) feeding, distinct skeletal muscles in mice exhibit differentially regulated autophagy that may modulate mitochondrial activity. We observed that after 4 and 40 weeks of high-fat diet feeding, OXPHOS subunits and mitochondrial DNA content increased in the oxidative soleus muscle. However, in gastrocnemius muscle, which has a mixed fiber-type composition, the mitochondrial mass increased only after 40 weeks of HFD feeding. Interestingly, fatty acid-supported mitochondrial respiration was enhanced in gastrocnemius, but not in soleus muscle after a 4-week HFD feeding. This increased metabolic profile in gastrocnemius was paralleled by preserving autophagy flux, while autophagy flux in soleus was reduced. To determine the role of autophagy in this differential response, we used an autophagy-deficient mouse model with partial deletion of Atg7 specifically in skeletal muscle (SkM-Atg7+/- mice). We observed that Atg7 reduction resulted in diminished autophagic flux in skeletal muscle, alongside blunting the HFD-induced increase in fatty acid-supported mitochondrial respiration observed in gastrocnemius. Remarkably, SkM-Atg7+/- mice did not present increased mitochondria accumulation. Altogether, our results show that HFD triggers specific mitochondrial adaptations in skeletal muscles with different fiber type compositions, and that Atg7-mediated autophagy modulates mitochondrial respiratory capacity but not its content in response to an obesogenic diet.
    Keywords:  Atg7; fatty acids; obesity; skeletal muscle fiber
  6. Aging Cell. 2021 Sep 24. e13475
      Satellite cell-dependent skeletal muscle regeneration declines during aging. Disruptions within the satellite cells and their niche, together with alterations in the myofibrillar environment, contribute to age-related dysfunction and defective muscle regeneration. In this study, we demonstrated an age-related decline in satellite cell viability and myogenic potential and an increase in ROS and cellular senescence. We detected a transient upregulation of miR-24 in regenerating muscle from adult mice and downregulation of miR-24 during muscle regeneration in old mice. FACS-sorted satellite cells were characterized by decreased levels of miR-24 and a concomitant increase in expression of its target: Prdx6. Using GFP reporter constructs, we demonstrated that miR-24 directly binds to its predicted site within Prdx6 mRNA. Subtle changes in Prdx6 levels following changes in miR-24 expression indicate miR-24 plays a role in fine-tuning Prdx6 expression. Changes in miR-24 and Prdx6 levels were associated with altered mitochondrial ROS generation, increase in the DNA damage marker: phosphorylated-H2Ax and changes in viability, senescence, and myogenic potential of myogenic progenitors from mice and humans. The effects of miR-24 were more pronounced in myogenic progenitors from old mice, suggesting a context-dependent role of miR-24 in these cells, with miR-24 downregulation likely a part of a compensatory response to declining satellite cell function during aging. We propose that downregulation of miR-24 and subsequent upregulation of Prdx6 in muscle of old mice following injury are an adaptive response to aging, to maintain satellite cell viability and myogenic potential through regulation of mitochondrial ROS and DNA damage pathways.
    Keywords:  Prdx6; aging; miR-24; muscle regeneration; oxidative stress; satellite cells; senescence
  7. Front Physiol. 2021 ;12 735557
      Hypoxia, defined as a reduced oxygen availability, can be observed in many tissues in response to various physiological and pathological conditions. As a hallmark of the altitude environment, ambient hypoxia results from a drop in the oxygen pressure in the atmosphere with elevation. A hypoxic stress can also occur at the cellular level when the oxygen supply through the local microcirculation cannot match the cells' metabolic needs. This has been suggested in contracting skeletal myofibers during physical exercise. Regardless of its origin, ambient or exercise-induced, muscle hypoxia triggers complex angio-adaptive responses in the skeletal muscle tissue. These can result in the expression of a plethora of angio-adaptive molecules, ultimately leading to the growth, stabilization, or regression of muscle capillaries. This remarkable plasticity of the capillary network is referred to as angio-adaptation. It can alter the capillary-to-myofiber interface, which represent an important determinant of skeletal muscle function. These angio-adaptive molecules can also be released in the circulation as myokines to act on distant tissues. This review addresses the respective and combined potency of ambient hypoxia and exercise to generate a cellular hypoxic stress in skeletal muscle. The major skeletal muscle angio-adaptive responses to hypoxia so far described in this context will be discussed, including existing controversies in the field. Finally, this review will highlight the molecular complexity of the skeletal muscle angio-adaptive response to hypoxia and identify current gaps of knowledges in this field of exercise and environmental physiology.
    Keywords:  VEGF-A; altitude; angiogenesis; capillary; exercise; hypoxia; skeletal muscle; thrombospondin
  8. Exerc Sport Sci Rev. 2021 Oct 01. 49(4): 284-290
      Satellite cells are essential for skeletal muscle regeneration, repair, and adaptation. The activity of satellite cells is influenced by their interactions with muscle-resident endothelial cells. We postulate that the microvascular network between muscle fibers plays a critical role in satellite cell function. Exercise-induced angiogenesis can mitigate the decline in satellite cell function with age.
  9. Aging Cancer. 2021 Jun;2(1-2): 13-35
      Skeletal muscle (muscle) is essential for physical health and for metabolic integrity, with sarcopenia (progressive muscle mass loss and weakness), a pre-curser of aging and chronic disease. Loss of lean mass and muscle quality (force generation per unit of muscle) in the general population are associated with fatigue, weakness, and slowed walking speed, eventually interfering with the ability to maintain physical independence, and impacting participation in social roles and quality of life. Muscle mass and strength impairments are also documented during childhood cancer treatment, which often persist into adult survivorship, and contribute to an aging phenotype in this vulnerable population. Although several treatment exposures appear to confer increased risk for loss of mass and strength that persists after therapy, the pathophysiology responsible for poor muscle quantity and quality is not well understood in the childhood cancer survivor population. This is partly due to limited access to both pediatric and adult survivor muscle tissue samples, and to difficulties surrounding non-invasive investigative approaches for muscle assessment. Because muscle accounts for just under half of the body's mass, and is essential for movement, metabolism and metabolic health, understanding mechanisms of injury responsible for both initial and persistent dysfunction is important, and will provide a foundation for intervention. The purpose of this review is to provide an overview of the available evidence describing associations between childhood cancer, its treatment, and muscle outcomes, identifying gaps in current knowledge.
    Keywords:  childhood cancer; muscle fitness; muscle health; muscle mass; muscle outcomes; muscle quality; skeletal muscle
  10. FASEB J. 2021 Oct;35(10): e21928
      Limb contractures are a debilitating and progressive consequence of a wide range of upper motor neuron injuries that affect skeletal muscle function. One type of perinatal brain injury causes cerebral palsy (CP), which affects a child's ability to move and is often painful. While several rehabilitation therapies are used to treat contractures, their long-term effectiveness is marginal since such therapies do not change muscle biological properties. Therefore, new therapies based on a biological understanding of contracture development are needed. Here, we show that myoblast progenitors from contractured muscle in children with CP are hyperproliferative. This phenotype is associated with DNA hypermethylation and specific gene expression patterns that favor cell proliferation over quiescence. Treatment of CP myoblasts with 5-azacytidine, a DNA hypomethylating agent, reduced this epigenetic imprint to TD levels, promoting exit from mitosis and molecular mechanisms of cellular quiescence. Together with previous studies demonstrating reduction in myoblast differentiation, this suggests a mechanism of contracture formation that is due to epigenetic modifications that alter the myogenic program of muscle-generating stem cells. We suggest that normalization of DNA methylation levels could rescue myogenesis and promote regulated muscle growth in muscle contracture and thus may represent a new nonsurgical approach to treating this devastating neuromuscular condition.
    Keywords:  5-azacytidine; DNA methylation; cerebral palsy; myoblast; satellite cell
  11. J Cachexia Sarcopenia Muscle. 2021 Sep 21.
      BACKGROUND: The discovery of adrenoceptors, which mediate the effects of the sympathetic nervous system neurotransmitter norepinephrine on specific tissues, sparked the development of sympathomimetics that have profound influence on skeletal muscle mass. However, chronic administration has serious side effects that preclude their use for muscle-wasting conditions such as sarcopenia, the age-dependent decline in muscle mass, force, and power. Devising interventions that can adjust neurotransmitter release to changing physiological demands will require understanding how the sympathetic nervous system affects muscle motor innervation and muscle mass, which will prevent sarcopenia-associated impaired mobility, falls, institutionalization, co-morbidity, and premature death. Here, we tested the hypothesis that prolonged heart and neural crest derivative 2 (Hand2) expression in peripheral sympathetic neurons (SNs) ameliorates sympathetic muscle denervation, motor denervation, and sarcopenia in geriatric mice.METHODS: We delivered either a viral vector encoding the transcription factor Hand2 or an empty vector (EV) driven to SNs by the PRSx8 promoter by injecting the saphenous vein in 16-month-old C57BL/6 mice that were sacrificed 10-11 months later. Studies relied on sympathetic and muscle immunohistochemistry analysed by confocal microscopy, nerve and muscle protein expression assessed by immunoblots, nerve-evoked and muscle-evoked maximal muscle contraction force, extensor digitorum longus (EDL) muscle RNA sequencing, SN real-time PCR, and tests of physical performance using an inverted-cling grip test and in an open-arena setting.
    RESULTS: Examining the mice 10-11 months later, we found that inducing Hand2 expression in peripheral SNs preserved (i) the number of neurons (EV: 0.32 ± 0.03/μm2 , n = 6; Hand2: 0.92 ± 0.08/μm2 , n = 7; P < 0.0001) and size (EV: 279 ± 18 μm2 , n = 6; Hand2: 396 ± 18 μm2 , n = 7; P < 0.0001); (ii) lumbricalis muscle sympathetic innervation (EV: 1.4 ± 1.5 μm/μm2 , n = 5; Hand2: 12 ± 1.8 μm/μm2 , n = 5; P < 0.001); (iii) tibialis anterior, gastrocnemius, EDL, and soleus muscles weight and whole-body strength (EV: 48 ± 6.4 s, n = 6; Hand2: 102 ± 6.8 s, n = 6; P < 0.001); (iv) EDL type IIb, IIx, and II/IIx and soleus type I, IIa, IIx, IIa/IIx, and IIb/IIx myofibre cross-sectional area; (v) nerve-evoked (EV: 16 ± 2.7 mN; Hand2: 30 ± 4.4 mN; P < 0.001) and muscle-evoked (EV: 24 ± 3.8 mN, n = 5; Hand2: 38 ± 3.0 mN, n = 8; P < 0.001) muscle force by 150 Hz-3 s pulses; and (vi) motor innervation assessed by measuring presynaptic/postsynaptic neuromuscular junction area overlay.
    CONCLUSIONS: Preserving Hand2 expression in SNs from middle-aged to very old mice attenuates decreases in muscle mass and force by (i) maintaining skeletal muscle sympathetic and motor innervation, (ii) improving membrane and total acetylcholine receptor stability and nerve-evoked and muscle-evoked muscle contraction, (iii) preventing the elevation of inflammation and myofibrillar protein degradation markers, and (iv) increasing muscle autophagy.
    Keywords:  Ageing; Atrophy; Denervation; Hand2; Neuromuscular junction; Skeletal muscle; Sympathetic nervous system
  12. Physiol Rep. 2021 Sep;9(18): e15031
      Skeletal muscle anatomy and physiology are sexually dimorphic but molecular underpinnings and muscle-specificity are not well-established. Variances in metabolic health, fitness level, sedentary behavior, genetics, and age make it difficult to discern inherent sex effects in humans. Therefore, mice under well-controlled conditions were used to determine female and male (n = 19/sex) skeletal muscle fiber type/size and capillarity in superficial and deep gastrocnemius (GA-s, GA-d), soleus (SOL), extensor digitorum longus (EDL), and plantaris (PLT), and transcriptome patterns were also determined (GA, SOL). Summed muscle weight strongly correlated with lean body mass (r2  = 0.67, p < 0.0001, both sexes). Other phenotypes were muscle-specific: e.g., capillarity (higher density, male GA-s), myofiber size (higher, male EDL), and fiber type (higher, lower type I and type II prevalences, respectively, in female SOL). There were broad differences in transcriptomics, with >6000 (GA) and >4000 (SOL) mRNAs differentially-expressed by sex; only a minority of these were shared across GA and SOL. Pathway analyses revealed differences in ribosome biology, transcription, and RNA processing. Curation of sexually dimorphic muscle transcripts shared in GA and SOL, and literature datasets from mice and humans, identified 11 genes that we propose are canonical to innate sex differences in muscle: Xist, Kdm6a, Grb10, Oas2, Rps4x (higher, females) and Ddx3y, Kdm5d, Irx3, Wwp1, Aldh1a1, Cd24a (higher, males). These genes and those with the highest "sex-biased" expression in our study do not contain estrogen-response elements (exception, Greb1), but a subset are proposed to be regulated through androgen response elements. We hypothesize that innate muscle sexual dimorphism in mice and humans is triggered and then maintained by classic X inactivation (Xist, females) and Y activation (Ddx3y, males), with coincident engagement of X encoded (Kdm6a) and Y encoded (Kdm5d) demethylase epigenetic regulators that are complemented by modulation at some regions of the genome that respond to androgen.
    Keywords:  muscle performance; myocyte; neovascularization; sexual dimorphism
  13. Shock. 2021 Sep 23.
      BACKGROUND: Several studies have shown that excessive protein degradation is a major cause of skeletal muscle atrophy induced by sepsis, and autophagy is the main pathway participating in protein degradation. However, the role of autophagy in sepsis is still controversial. Previously, we found that neuregulin-1β (NRG-1β) alleviated sepsis-induced diaphragm atrophy through the PI3K/Akt signaling pathway. Akt/mTOR is a classic signaling pathway to regulate autophagy, which maintains intracellular homeostasis. This study aimed to investigate whether NRG-1β could alleviate sepsis-induced skeletal muscle atrophy by regulating autophagy.METHODS: L6 rat myoblast cells were differentiated using 2% FBS into myotubes, which were divided into four groups: Con group treated with normal serum; Sep group treated with septic serum to form a sepsis cell model; SN group treated with septic serum for 24 h followed by injection with NRG-1β and incubation for another 48 h; and SNLY group, in which the PI3K inhibitor LY294002 was added 30 min before NRG-1β, and other treatments were similar to those in SN group. Effects of NRG-1β was also evaluated in vivo using Sprague-Dawley (SD) rats, in which sepsis was induced by cecal ligation and puncture (CLP).
    RESULTS: In L6 myotubes treated with septic serum, the expression of autophagy-related proteins ULK-1, p-Beclin-1, and Beclin-1, and the ratio of LC3B II/I were highly increased, while protein p62 expression was decreased, indicating that autophagy was excessively activated. Moreover, NRG-1 expression was decreased, as detected by confocal immunofluorescence and western blotting. Upon exogenous addition of NRG-1β, autophagy was inhibited by the activation of Akt/mTOR signaling pathway, and cell viability was also increased. These effects disappeared in the presence of LY294002. In SD rats, sepsis was induced by CLP. NRG-1β was shown to inhibit autophagy in these rats via the Akt/mTOR pathway, leading to increased body weight of the septic SD rats and alleviation of atrophy of the tibialis anterior muscle.
    CONCLUSION: NRG-1β could alleviate sepsis-induced skeletal muscle atrophy by inhibiting autophagy via the AKT/mTOR signaling pathway.
  14. Diabetes. 2021 Sep 24. pii: db210587. [Epub ahead of print]
      The two closely related RabGTPase-activating proteins (RabGAPs) TBC1D1 and TBC1D4, both substrates for the AMP-activated protein kinase AMPK, play important roles in exercise metabolism and contraction-dependent translocation of the glucose transporter GLUT4 in skeletal muscle. However, the specific contribution of each RabGAP in contraction signaling is mostly unknown. In this study, we investigated the cooperative AMPK/RabGAP signaling axis in the metabolic response to exercise/contraction using a novel mouse model deficient in active skeletal muscle AMPK, combined with knockout of either Tbc1d1, Tbc1d4 or both RabGAPs. AMPK-deficiency in muscle reduced treadmill exercise performance. Additional deletion of Tbc1d1 but not Tbc1d4 resulted in further decrease in exercise capacity. In oxidative Soleus muscle, AMPK deficiency reduced contraction-mediated glucose uptake and deletion of each or both RabGAPs had no further effect. In contrast, in glycolytic EDL muscle, AMPK deficiency reduced contraction-stimulated glucose uptake and deletion of Tbc1d1 but not Tbc1d4 led to a further decrease. Importantly, skeletal muscle deficient in AMPK and both RabGAPs still exhibited residual contraction-mediated glucose uptake, which was completely abolished by inhibition of the GTPase Rac1 Our results demonstrate a novel mechanistic link between glucose transport and the GTPase signaling framework in skeletal muscle in response to contraction.
  15. Aging Med (Milton). 2021 Sep;4(3): 221-233
      Sarcopenia is a comprehensive degenerative disease with the progressive loss of skeletal muscle mass with age, accompanied by the loss of muscle strength and muscle dysfunction. As a new type of senile syndrome, sarcopenia seriously threatens the health of the elderly. The first-line treatment for sarcopenia is exercise and nutritional supplements. However, pharmacotherapy will provide more reliable and sustainable interventions in geriatric medicine. Clinical trials of new drugs targeting multiple molecules are ongoing. This article focuses on the latest progress in pharmacotherapeutic approaches of sarcopenia in recent years by comprehensively reviewing the clinical outcomes of the existing and emerging pharmacotherapies as well as the molecular mechanisms underlying their therapeutic benefits and side effects.
    Keywords:  aging; muscle wasting; pathogenesis; pharmacotherapy; sarcopenia; signaling
  16. Front Immunol. 2021 ;12 730070
      Background: Inflammation may trigger skeletal muscle atrophy induced by cancer cachexia. As a pro-inflammatory factor, interleukin-6 may cause skeletal muscle atrophy, but the underlying molecular mechanisms have not been explored.Methods: In this experimental study, we used adult male ICR mice, weighing 25 ± 2 g, and the continuous infusion of interleukin-6 into the tibialis anterior muscle to construct a skeletal muscle atrophy model (experimental group). A control group received a saline infusion. RNA-sequencing was used to analyze the differentially expressed genes in tissue samples after one and three days. Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes analysis were applied to define the function of these genes, and protein-protein interaction analysis was performed to identify potential transcription factors. Fluorescence microscopy was used to determine the muscle fiber cross-sectional area after 14 days.
    Results: Continuous infusion of interleukin-6 for 14 days caused significant muscle atrophy. RNA-sequencing found 359 differentially expressed genes in the 1- and 3-day tissue samples and 1748 differentially expressed genes only in the 3-day samples. Functional analysis showed that the differentially expressed genes found in both the 1- and 3-day samples were associated with immune receptor activation, whereas the differentially expressed genes found only in the 3-day sample were associated with reduced energy metabolism. The expression of multiple genes in the oxidative phosphorylation and tricarboxylic acid cycle pathways was down-regulated. Furthermore, differentially expressed transcription factors were identified, and their interaction with interleukin-6 and the differentially expressed genes was predicted, which indicated that STAT3, NF-κB, TP53 and MyoG may play an important role in the process of interleukin-6-induced muscle atrophy.
    Conclusions: This study found that interleukin-6 caused skeletal muscle atrophy through immune receptor activation and a reduction of the energy metabolism. Several transcription factors downstream of IL-6 have the potential to become new regulators of skeletal muscle atrophy. This study not only enriches the molecular regulation mechanism of muscle atrophy, but also provides a potential target for targeted therapy of muscle atrophy.
    Keywords:  energy metabolism; inflammation; interleukin-6; muscle atrophy; transcription factor
  17. Aging (Albany NY). 2021 Sep 19. 13(undefined):
      Dulaglutide, a glucagon-like peptide-1 receptor (GLP-1R) agonist, is widely used to treat diabetes. However, its effects on muscle wasting due to aging are poorly understood. In the current study, we investigated the therapeutic potential and underlying mechanism of dulaglutide in muscle wasting in aged mice. Dulaglutide improved muscle mass and strength in aged mice. Histological analysis revealed that the cross-sectional area of the tibialis anterior (TA) in the dulaglutide-treated group was thicker than that in the vehicle group. Moreover, dulaglutide increased the shift toward middle and large-sized fibers in both young and aged mice compared to the vehicle. Dulaglutide increased myofiber type I and type IIa in young (18.5% and 8.2%) and aged (1.8% and 19.7%) mice, respectively, compared to the vehicle group. Peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α), a master regulator of mitochondrial biogenesis, decreased but increased by dulaglutide in aged mice. The expression of atrophic factors such as myostatin, atrogin-1, and muscle RING-finger protein-1 was decreased in aged mice, whereas that of the myogenic factor, MyoD, was increased in both young and aged mice following dulaglutide treatment. In aged mice, optic atrophy-1 (OPA-1) protein was decreased, whereas Toll-like receptor-9 (TLR-9) and its targeting inflammatory cytokines (interleukin-6 [IL-6] and tumor necrosis factor-α [TNF-α]) were elevated in the TA and quadriceps (QD) muscles. In contrast, dulaglutide administration reversed this expression pattern, thereby significantly attenuating the expression of inflammatory cytokines in aged mice. These data suggest that dulaglutide may exert beneficial effects in the treatment of muscle wasting due to aging.
    Keywords:  dulaglutide; glucagon-like peptide-1; inflammation; optic atrophy-1; sarcopenia
  18. Cell Death Discov. 2021 Sep 18. 7(1): 251
      Skeletal muscle atrophy is one of the major side effects of high dose or sustained usage of glucocorticoids. Pyroptosis is a novel form of pro-inflammatory programmed cell death that may contribute to skeletal muscle injury. Trimetazidine, a well-known anti-anginal agent, can improve skeletal muscle performance both in humans and mice. We here showed that dexamethasone-induced atrophy, as evidenced by the increase of muscle atrophy F-box (Atrogin-1) and muscle ring finger 1 (MuRF1) expression, and the decrease of myotube diameter in C2C12 myotubes. Dexamethasone also induced pyroptosis, indicated by upregulated pyroptosis-related protein NLR family pyrin domain containing 3 (NLRP3), Caspase-1, and gasdermin-D (GSDMD). Knockdown of NLRP3 or GSDMD attenuated dexamethasone-induced myotube pyroptosis and atrophy. Trimetazidine treatment ameliorated dexamethasone-induced muscle pyroptosis and atrophy both in vivo and in vitro. Activation of NLRP3 using LPS and ATP not only increased the cleavage and activation of Caspase-1 and GSDMD, but also increased the expression levels of atrophy markers MuRF1 and Atrogin-1 in trimetazidine-treated C2C12 myotubes. Mechanically, dexamethasone inhibited the phosphorylation of PI3K/AKT/FoxO3a, which could be attenuated by trimetazidine. Conversely, co-treatment with a PI3K/AKT inhibitor, picropodophyllin, remarkably increased the expression of NLRP3 and reversed the protective effects of trimetazidine against dexamethasone-induced C2C12 myotube pyroptosis and atrophy. Taken together, our study suggests that NLRP3/GSDMD-mediated pyroptosis might be a novel mechanism for dexamethasone-induced skeletal muscle atrophy. Trimetazidine might be developed as a potential therapeutic agent for the treatment of dexamethasone-induced muscle atrophy.
  19. Am J Physiol Endocrinol Metab. 2021 Sep 20.
      Circadian rhythms are central to optimal physiological function as disruption contributes to the development of several chronic diseases. Alcohol (EtOH) intoxication disrupts circadian rhythms within liver, brain, and intestines, but it is unknown whether alcohol also disrupts components of the core clock in skeletal muscle. Female C57BL/6Hsd mice were randomized to receive either saline (control) or alcohol (EtOH) (5g/kg) via intraperitoneal injection at the start of the dark cycle (ZT12), and gastrocnemius was collected every 4hr from Control and EtOH treated mice for the next 48hr following isoflurane anesthetization. In addition, metyrapone was administered prior to alcohol intoxication in separate mice to determine whether the alcohol-induced increase in serum corticosterone contributed to circadian gene regulation. Finally, synchronized C2C12 myotubes were treated with alcohol (100mM) to assess the influence of centrally or peripherally mediated effects of alcohol on the muscle clock. Alcohol significantly disrupted mRNA expression of Bmal1, Per1/2, and Cry1/2 in addition to perturbing the circadian pattern of clock-controlled genes, Myod1, Dbp, Tef, and Bhlhe40 (p<0.05) in muscle. Alcohol increased serum corticosterone levels and glucocorticoid target gene, Redd1, in muscle. Metyrapone prevented the EtOH-mediated increase in serum corticosterone but did not normalize the EtOH-induced change in Per1, Cry1 and Cry2 and Myod1 mRNA expression. Core clock gene expression (Bmal, Per1/2, Cry1/2) was not changed following 4, 8, or 12hrs of alcohol treatment on synchronized C2C12 myotubes. Therefore, binge alcohol disrupted genes of the core molecular clock independently of elevated serum corticosterone or direct effects of EtOH on the muscle.
    Keywords:  Skeletal muscle; alcohol; circadian clock; ethanol
  20. Life Sci. 2021 Sep 21. pii: S0024-3205(21)00960-7. [Epub ahead of print] 119973
      AIMS: Hyperglycemia occurring in the diabetic condition can cause apoptosis via the mitochondrial pathway with higher pro-apoptotic protein expression. Probiotics are viable microorganisms that have anti-diabetic and antioxidant effects. Also, exercise may affect the signaling pathways of skeletal muscle apoptosis. This study examined the aerobic exercise training and probiotic supplementation effects on some apoptotic indices of the soleus muscle in diabetic rats-induced by streptozotocin.MAIN METHODS: We examined 32 male Wistar rats (weight: 250-270 g; age: eight weeks old) and divided them into four groups: control, control + probiotics, aerobic training (AT), and AT + probiotics (ATS). The rats in the training groups aerobically exercised using a treadmill five days per week for five weeks. We evaluated the gene expression of Bax, Bcl2, and p53 using the RT-PCR. We also used a one-way ANOVA for statistical analysis and set the significance level at P ≤ 0.05.
    KEY FINDINGS: The results showed that the fasting blood sugar was significantly higher in the control and control + probiotics groups (P = 0.008). Moreover, the AT + probiotics group showed lower expression of p53 (P = 0.005), Bax (P = 0.001) and the Bax/Bcl2 ratio (P = 0.001). Conversely, Bcl2 expression was higher after aerobic training and receiving probiotics (P = 0.002). However, the groups revealed no significant difference regarding muscle weight (P = 0.053) and the muscle weight/final body weight ratio of the rats (P = 0.26).
    SIGNIFICANCE: It appears that aerobic exercise training with the use of probiotics prevents apoptosis in the muscle with the down-regulation of blood glucose.
    Keywords:  Aerobic exercise; Diabetes mellitus; Mitochondria; Programmed cell death; Soleus muscle
  21. Br J Pharmacol. 2021 Sep 22.
      BACKGROUND AND PURPOSE: Duchenne muscular dystrophy (DMD) is a degenerative muscle disease with no effective drug treatment. This study investigated the positive effects of fenofibrate on dystrophic muscles.EXPERIMENTAL APPROACH: Myostatin expression in serum and muscle tissue of DMD patients and mdx mice were tested. Primary myoblasts isolated from mdx mice were challenged with an inflammatory stimulus and treated with fenofibrate. In animal experiments, 6-week-old male mdx mice were treated with fenofibrate (100 mg/kg) administered orally once per day for 6 weeks. Tests of muscle function plus histology and biochemical analyses of serum were conducted to evaluate the effects of fenofibrate. The expressions of myostatin, MuRF1, and atrogin-1 in skeletal muscle were evaluated by Western blotting and real-time PCR. Total and oxidative myosin heavy chain (MHC) were assessed via immunofluorescence.
    KEY RESULTS: Increased expression of myostatin protein was found in dystrophic muscle of DMD patients and mdx mice. Fenofibrate enhanced myofibre differentiation by downregulating the expression of myostatin protein but not mRNA in primary myoblasts of mdx mice. Fenofibrate significantly improved muscle function while ameliorating muscle damage in mdx mice. These benefits are accompanied by an anti-inflammatory effect. Fenofibrate treatment returned myofibre function by inhibiting the expressions of myostatin, MuRF1, and atrogin-1 protein in the gastrocnemius muscle and diaphragm, while leaving the mRNA level of myostatin unaffected.
    CONCLUSIONS AND IMPLICATIONS: Fenofibrate substantially slows muscle dystrophy by promoting the degradation of myostatin protein, which may indicate a new therapeutic focus for DMD patients.
    Keywords:  Duchenne muscular dystrophy; Fenofibrate; myostatin
  22. Singapore Med J. 2021 Sep 21.
      Muscle fibres are multinuclear cells, and the cytoplasmic territory where a single myonucleus controls transcriptional activity is called the myonuclear domain (MND). MND size shows flexibility during muscle hypertrophy. The MND ceiling hypothesis states that hypertrophy results in the expansion of MND size to an upper limit or MND ceiling, beyond which additional myonuclei via activation of satellite cells are required to support further growth. However, the debate about the MND ceiling hypothesis is far from settled, and various studies show conflicting results about the existence or otherwise of MND ceiling in hypertrophy. The aim of this review is to summarise the literature about the MND ceiling in various settings of hypertrophy and discuss the possible factors contributing to a discrepancy in the literature. We conclude by describing the physiological and clinical significance of the MND ceiling limit in the muscle adaptation process in various physiological and pathological conditions.
    Keywords:  muscle hypertrophy; myonuclear domain; satellite cells; skeletal muscle
  23. Cardiol Rev. 2021 Sep 15.
      Physical activity and its sustained and purposeful performance - exercise - promote a broad and diverse set of metabolic and cardiovascular health benefits. Regular exercise is the most effective way to improve cardiorespiratory fitness, a measure of one's global cardiovascular, pulmonary and metabolic health and one of the strongest predictors of future health risk. Here, we describe how exercise affects individual organ systems related to cardiometabolic health, including the promotion of insulin and glucose homeostasis through improved efficiency in skeletal muscle glucose utilization and enhanced insulin sensitivity; beneficial changes in body composition and adiposity; and improved cardiac mechanics and vascular health. We subsequently identify knowledge gaps that remain in exercise science, including heterogeneity in exercise responsiveness. While the application of molecular profiling technologies in exercise science has begun to illuminate the biochemical pathways that govern exercise-induced health promotion, much of this work has focused on individual organ systems and applied single platforms. New insights into exercise-induced secreted small molecules and proteins that impart their effects in distant organs ("exerkines") highlight the need for an integrated approach towards the study of exercise and its global effects; efforts that are ongoing.
  24. Int J Mol Med. 2021 Nov;pii: 203. [Epub ahead of print]48(5):
      Calpains are a family of Ca2+‑dependent cysteine proteases that participate in various cellular processes. Calpain 3 (CAPN3) is a classical calpain with unique N‑terminus and insertion sequence 1 and 2 domains that confer characteristics such as rapid autolysis, Ca2+‑independent activation and Na+ activation of the protease. CAPN3 is the only muscle‑specific calpain that has important roles in the promotion of calcium release from skeletal muscle fibers, calcium uptake of sarcoplasmic reticulum, muscle formation and muscle remodeling. Studies have indicated that recessive mutations in CAPN3 cause limb‑girdle muscular dystrophy (MD) type 2A and other types of MD; eosinophilic myositis, melanoma and epilepsy are also closely related to CAPN3. In the present review, the characteristics of CAPN3, its biological functions and roles in the pathogenesis of a number of disorders are discussed.
    Keywords:  CAPN3; limb‑girdle muscular dystrophy type 2A; muscle formation; muscle remodeling
  25. Circ Res. 2021 Sep 21.
      Rationale: Fetal growth and survival depend critically on proper development and integrity of the vascular system. Fli1 (Friend leukemia integration 1), a member of the Ets family of transcription factors, plays critical roles in vascular morphogenesis and homeostasis at mid-gestation, the developmental stage at which expression of its upstream regulator, Etv2, ceases. However, molecular mechanisms of Fli1 action in vascular morphogenesis remain incompletely understood. Objective: To dissect molecular mechanisms of vascular morphogenesis governed by Fli1. Methods and Results: Utilizing Fli1 promoter-driven lineage-specific LacZ expression, Fli1 loss-of-function strategies, and a series of molecular techniques, we demonstrate that Fli1 expression in multipotent myogenic progenitor cells (MPCs) occurs independent of Etv2, and loss of Fli1 expression results in a significant increase in LacZ+ cells in mesoderm within somites and limb buds, leading to reciprocal regulation of the expression of several key endothelial and myogenic genes and vascular abnormalities. Conversely, embryos with conditional Fli1 gain-of-function in MPCs manifested aberrant vasculogenesis with lack of myogenesis. Mechanistically, elevated Fli1 activity in myoblasts and in adult MPCs (also called satellite cells) of X-linked muscular dystrophic mdx mice markedly induced endothelial, but attenuated myogenic, gene expression and differentiation. Importantly, ectopic expression of Myf5 or MyoD, two key myogenic regulators, in Fli1-expressing myoblasts restored their differentiation potential, indicating that levels of Fli1 and myogenic regulators in MPCs inversely regulate their endothelial versus myogenic potential. Conclusions:Fli1 governs vascular morphogenesis by regulating endothelial potential by inversely regulating endothelial versus myogenic programs in MPCs. Our data uncover an important and previously unrecognized mechanism of vascular morphogenesis governed by Fli1 and highlight the physiological significance of the fine tuning of Fli1 activity in multipotent progenitors for proper vascular and muscle morphogenesis during development and disease.
  26. Muscle Nerve. 2021 Sep 22.
      INTRODUCTION/AIMS: Mutations in the Anoctamin 5 (ANO5) gene are a common cause of muscular dystrophy. We aimed to investigate whether inflammatory changes in muscle are present in patients with ANO5 myopathy assessed by muscle biopsy and muscle magnetic resonance imaging (MRI).METHODS: Adults with pathogenic variations in ANO5 known to cause muscular dystrophy were included. Muscle biopsies of pelvic and lower extremity muscles were reviewed retrospectively. Muscle MR short tau inversion recovery (STIR) images of a subset of these patients were performed prospectively.
    RESULTS: Muscle biopsies from 24 patients were reviewed. MR STIR images were performed in 17 of these patients. We found inflammatory changes in muscle biopsies of three patients and MRI revealed hyperintense signals on STIR images in 14 of 17 patients.
    DISCUSSION: In this study, we show that muscle edema is very common in patients with ANO5 myopathy and that some patients have inflammatory changes in muscle biopsies. Further studies are needed to determine whether the STIR+ lesions reflect inflammation. This article is protected by copyright. All rights reserved.
    Keywords:  ANO5; Anoctaminopathy; Inflammatory myopathy; LGMD2L; LGMDR12
  27. J Electromyogr Kinesiol. 2021 Sep 16. pii: S1050-6411(21)00085-7. [Epub ahead of print]61 102598
      Neurodegenerative diseases and sarcopenia become more prevalent as individuals age and, therefore, represent a serious issue for the healthcare system. Several studies have reported the relationship between physical activity and reduced incidence of dementia or cognitive deterioration. Thus, exercise and strength training are most recommended treatments, but it is proving difficult to engage individuals to initiate exercise and strength training. Electrical muscle stimulation (EMS) may provide an alternative and more efficient solution. Although EMS has undergone a decline in use, mainly because of stimulation discomfort, new technologies allow painless application of strong contractions. Such activation can be applied in higher exercise dosages and more efficiently than people are likely to achieve with exercise. Unlike orderly recruitment of motor units (MUs) during low intensity voluntary exercise, EMS activates large fast-twitch MUs with glycolytic fibers preferentially and this could have benefit for prevention and treatment of diabetes and chronic diseases associated with muscle atrophy that ultimately lead to bed-ridden conditions. Recent evidence highlights the potential for EMS to make a major impact on these and other lifestyle related diseases and its role as a useful modality for orthopedic and cardiac rehabilitation. This paper will discuss the potential for EMS to break new ground in effective interventions in these frontiers of medical science.
    Keywords:  Aging; Electrical Muscle Stimulation; Muscle Hypertrophy; Muscle Training; Sarcopenia
  28. Pflugers Arch. 2021 Sep 22.
      Duchenne muscular dystrophy is a highly progressive muscle wasting disorder due to primary abnormalities in one of the largest genes in the human genome, the DMD gene, which encodes various tissue-specific isoforms of the protein dystrophin. Although dystrophinopathies are classified as primary neuromuscular disorders, the body-wide abnormalities that are associated with this disorder and the occurrence of organ crosstalk suggest that a multi-systems pathophysiological view should be taken for a better overall understanding of the complex aetiology of X-linked muscular dystrophy. This article reviews the molecular and cellular effects of deficiency in dystrophin isoforms in relation to voluntary striated muscles, the cardio-respiratory system, the kidney, the liver, the gastrointestinal tract, the nervous system and the immune system. Based on the establishment of comprehensive biomarker signatures of X-linked muscular dystrophy using large-scale screening of both patient specimens and genetic animal models, this article also discusses the potential usefulness of novel disease markers for more inclusive approaches to differential diagnosis, prognosis and therapy monitoring that also take into account multi-systems aspects of dystrophinopathy. Current therapeutic approaches to combat muscular dystrophy are summarised.
    Keywords:  Duchenne muscular dystrophy; Dystrophin; Fibrosis; Inflammation; Muscle degeneration; Organ crosstalk
  29. Skelet Muscle. 2021 Sep 22. 11(1): 23
      BACKGROUND: CRISPR/Cas9 is an invaluable tool for studying cell biology and the development of molecular therapies. However, delivery of CRISPR/Cas9 components into some cell types remains a major hurdle. Primary human myoblasts are a valuable cell model for muscle studies, but are notoriously difficult to transfect. There are currently no commercial lipofection protocols tailored for primary myoblasts, and most generic guidelines simply recommend transfecting healthy cells at high confluency. This study aimed to maximize CRISPR/Cas9 transfection and editing in primary human myoblasts.METHODS: Since increased cell proliferation is associated with increased transfection efficiency, we investigated two factors known to influence myoblast proliferation: cell confluency, and a basement membrane matrix, Matrigel. CRISPR/Cas9 editing was performed by delivering Cas9 ribonucleoprotein complexes via lipofection into primary human myoblasts, cultured in wells with or without a Matrigel coating, at low (~ 40%) or high (~ 80%) confluency.
    RESULTS: Cells transfected at low confluency on Matrigel-coated wells had the highest levels of transfection, and were most effectively edited across three different target loci, achieving a maximum editing efficiency of 93.8%. On average, editing under these conditions was >4-fold higher compared to commercial recommendations (high confluency, uncoated wells).
    CONCLUSION: This study presents a simple, effective and economical method of maximizing CRISPR/Cas9-mediated gene editing in primary human myoblasts. This protocol could be a valuable tool for improving the genetic manipulation of cultured human skeletal muscle cells, and potentially be adapted for use in other cell types.
    Keywords:  CRISPR; Confluency; Gene editing efficiency; Matrigel; Primary human myoblasts
  30. Aging Cell. 2021 Sep 23. e13467
      Protein quality control mechanisms decline during the process of cardiac aging. This enables the accumulation of protein aggregates and damaged organelles that contribute to age-associated cardiac dysfunction. Macroautophagy is the process by which post-mitotic cells such as cardiomyocytes clear defective proteins and organelles. We hypothesized that late-in-life exercise training improves autophagy, protein aggregate clearance, and function that is otherwise dysregulated in hearts from old vs. adult mice. As expected, 24-month-old male C57BL/6J mice (old) exhibited repressed autophagosome formation and protein aggregate accumulation in the heart, systolic and diastolic dysfunction, and reduced exercise capacity vs. 8-month-old (adult) mice (all p < 0.05). To investigate the influence of late-in-life exercise training, additional cohorts of 21-month-old mice did (old-ETR) or did not (old-SED) complete a 3-month progressive resistance treadmill running program. Body composition, exercise capacity, and soleus muscle citrate synthase activity improved in old-ETR vs. old-SED mice at 24 months (all p < 0.05). Importantly, protein expression of autophagy markers indicate trafficking of the autophagosome to the lysosome increased, protein aggregate clearance improved, and overall function was enhanced (all p < 0.05) in hearts from old-ETR vs. old-SED mice. These data provide the first evidence that a physiological intervention initiated late-in-life improves autophagic flux, protein aggregate clearance, and contractile performance in mouse hearts.
    Keywords:  aging; cardiac function; exercise; protein aggregates
  31. Physiol Rep. 2021 Sep;9(18): e15055
      Surgery and anesthesia induce a catabolic response that leads to skeletal muscle protein loss. Previous investigations have observed positive effects of perioperative nutrition. Furthermore, the benefits of exogenous amino acids on muscle protein kinetics are well established. However, no investigation has focused on muscle protein kinetics with and without perioperative amino acid infusion. Thus, we aimed to assess the effect of perioperative amino acid (AA) infusion on muscle protein balance in individuals undergoing elective total hip arthroplasty (THA). Elective THA patients were randomized to undergo a metabolic study prior to surgery (n = 5; control [CON]), intraoperative AA infusion (n = 9), or no AA (n = 13; standard of care [SC]). The CON group was studied prior to surgery to provide nonoperative/non-anesthesia muscle protein kinetic reference values. The bolus infusion method with 13 C6 -phenylalanine injected at time 0, and [15 N]-phenylalanine 30 min later was used to calculate muscle protein synthesis (MPS), protein breakdown (MPB), and net balance (MPS-MPB). Perioperative AA significantly improved muscle net balance as compared to SC (-0.005 ± 0.018%/h vs. -0.052 ± 0.011%/h) but not CON (0.003 ± 0.013%/h). The AA infusion significantly increased muscle net balance via a significant increase in MPS (AA = 0.062 ± 0.007%/h; SC = 0.037 ± 0.004%/h; CON = 0.072% ± 0.005%/h), and a nonsignificant attenuation of MPB (AA = 0.067 ± 0.012%/h; SC = 0.089 ± 0.014%/h; CON = 0.075 ± 0.011%/h). Our data support the use of perioperative AA infusion during elective THA as pragmatic strategy to offset the loss of surgically induced skeletal muscle protein.
    Keywords:  amino acids; anabolism; skeletal muscle; stable isotope tracer
  32. J Frailty Aging. 2021 ;10(4): 357-360
      This Brief Report describes a pilot study of the effect of 12 weeks of stationary bicycle high-intensity interval training, stationary bicycle moderate-intensity continuous training, and resistance training on cardiorespiratory, muscular, and physical function measures in insufficiently-active older adults (N=14; 66.4±3.9 years; 3 male, 11 female). After baseline testing, participants were randomly assigned to one of the exercise groups. High-intensity interval training and moderate-intensity continuous training had small-to-large effect sizes on cardiorespiratory/endurance and physical function measures, but very small effect sizes on muscular measures. Resistance training had small-to-large effect sizes on cardiorespiratory, muscular, and physical function measures. This pilot study should be interpreted cautiously, but findings suggest that resistance exercise may be the most effective of the three studied exercise strategies for older adults as it can induce beneficial adaptations across multiple domains. These effect sizes can be used to determine optimal sample sizes for future investigations.
    Keywords:   High-intensity interval training; aging; exercise; muscle; physical function
  33. FASEB J. 2021 Oct;35(10): e21914
      Limb-girdle muscular dystrophy D2 (LGMDD2) is an ultrarare autosomal dominant myopathy caused by mutation of the normal stop codon of the TNPO3 nuclear importin. The mutant protein carries a 15 amino acid C-terminal extension associated with pathogenicity. Here we report the first animal model of the disease by expressing the human mutant TNPO3 gene in Drosophila musculature or motor neurons and concomitantly silencing the endogenous expression of the fly protein ortholog. A similar genotype expressing wildtype TNPO3 served as a control. Phenotypes characterization revealed that mutant TNPO3 expression targeted at muscles or motor neurons caused LGMDD2-like phenotypes such as muscle degeneration and atrophy, and reduced locomotor ability. Notably, LGMDD2 mutation increase TNPO3 at the transcript and protein level in the Drosophila model Upregulated muscle autophagy observed in LGMDD2 patients was also confirmed in the fly model, in which the anti-autophagic drug chloroquine was able to rescue histologic and functional phenotypes. Overall, we provide a proof of concept of autophagy as a target to treat disease phenotypes and propose a neurogenic component to explain mutant TNPO3 pathogenicity in diseased muscles.
    Keywords:   Drosophila melanogaster ; autophagy; chloroquine; limb-girdle muscular dystrophy D2; muscle atrophy; transportin 3
  34. J Tissue Eng Regen Med. 2021 Sep 22.
      Volumetric muscle loss (VML) is traumatic or surgical loss of skeletal muscle with resultant functional impairment. Skeletal muscle's innate capacity for regeneration is lost with VML due to a critical loss of stem cells, extracellular matrix, and neuromuscular junctions. Consequences of VML include permanent disability or delayed amputations of the affected limb. Currently, a successful clinical therapy has not been identified. Mesenchymal stem cells (MSCs) possess regenerative and immunomodulatory properties and their three-dimensional aggregation can further enhance therapeutic efficacy. In this study, MSC aggregation into spheroids was optimized in vitro based on cellular viability, spheroid size, and trophic factor secretion. The regenerative potential of the optimized MSC spheroid therapy was then investigated in a murine model of VML injury. Experimental groups included an untreated VML injury control, intramuscular injection of MSC spheroids, and MSC spheroids encapsulated in a fibrin-laminin hydrogel. Compared to the untreated VML group, the spheroid encapsulating hydrogel group enhanced myogenic marker (i.e., MyoD and myogenin) protein expression, improved muscle mass, increased presence of centrally nucleated myofibers as well as small fibers (<500 µm2), modulated pro- and anti-inflammatory macrophage marker expression (i.e., iNOS and Arginase), and increased the presence of CD146+ pericytes and CD31+ endothelial cells in the VML injured muscles. Future studies will evaluate the extent of functional recovery with the spheroid encapsulating hydrogel therapy. This article is protected by copyright. All rights reserved.
    Keywords:  Volumetric muscle loss; extracellular matrix; hydrogels
  35. Free Radic Biol Med. 2021 Sep 21. pii: S0891-5849(21)00726-7. [Epub ahead of print]
      Accumulating evidence now shows that supplemental antioxidants including vitamin C, vitamin E and N-Acetylcysteine consumption can suppress adaptations to endurance-type exercise by attenuating reactive oxygen and nitrogen species (RONS) formation within skeletal muscle. This emerging evidence points to the importance of pro-oxidation as an important stimulus for endurance-training adaptations, including mitochondrial biogenesis, endogenous antioxidant production, insulin signalling, angiogenesis and growth factor signaling. Although sustained oxidative distress is associated with many chronic diseases, athletes have, on average, elevated levels of certain endogenous antioxidants to maintain redox homeostasis. As a result, trained athletes may have a better capacity to buffer oxidants during and after exercise, resulting in a reduced oxidative eustress stimulus for adaptations. Thus, higher levels of RONS input and exercise-induced oxidative stress may benefit athletes in the pursuit of continuous endurance training redox adaptations. This review addresses why athletes should be looking to enhance exercise-induced oxidative stress and how it can be accomplished. Methods covered include high-intensity interval training, hyperthermia and heat stress, dietary antioxidant restriction and modified antioxidant timing, dietary antioxidants and polyphenols as adjuncts to exercise, and vitamin C as a pro-oxidant.
    Keywords:  Antioxidants; Endurance training; Exercise adaptations; High-intensity interval training; Hormesis; Oxidative distress; Oxidative eustress; Oxidative stress; Prooxidants; Skeletal muscle; Sprint interval training
  36. Dis Model Mech. 2021 Sep 23. pii: dmm.049166. [Epub ahead of print]
      Costello syndrome (CS) is a congenital disorder caused by heterozygous activating germline HRAS mutations in the canonical Ras/mitogen-activated protein kinase (Ras/MAPK) pathway. CS is one of the RASopathies, a large group of syndromes due to mutations within various components of the Ras/MAPK pathway. An important part of the phenotype that greatly impacts quality of life is hypotonia. To gain a better understanding of the mechanisms underlying hypotonia in CS, a mouse model with an activating HrasG12V allele was utilized. We identified a skeletal myopathy that was due in part to an inhibition of embryonic myogenesis and myofiber formation, resulting in a reduction of myofiber size and number that led to reduced muscle mass and strength. In addition to hyperactivation of the Ras/MAPK and PI3K/AKT pathways, there was a significant reduction of p38 signaling, as well as global transcriptional alterations consistent with the myopathic phenotype. Inhibition of Ras/MAPK pathway signaling using a MEK inhibitor rescued the HrasG12V myopathy phenotype both in vitro and in vivo, demonstrating that increased MAPK signaling is the main cause of the muscle phenotype in CS.
    Keywords:  Costello Syndrome; Hypotonia; MEK inhibitor; Myogenesis; RASopathies; Ras/MAPK
  37. Elife. 2021 Sep 20. pii: e68054. [Epub ahead of print]10
      Background: Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by the degeneration of the second motor-neuron. The phenotype ranges from very severe to very mild forms. All patients have the homozygous loss of the SMN1 gene and a variable number of SMN2 (generally two-to-four copies), inversely related with the severity. The amazing results of the available treatments have made compelling the need of prognostic biomarkers to predict the progression trajectories of patients. Beside the SMN2 products, few other biomarkers have been evaluated so far, including some miRs.Methods: We performed whole miRNome analysis of muscle samples of patients and controls (14 biopsies and 9 cultures). The levels of miRs differentially expressed in muscle were evaluated in serum samples (51 patients and 37 controls) and integrated with SMN2 copies, SMN2-full length transcript levels in blood and age (SMA-score).
    Results: Over 100 miRs were differentially expressed in SMA muscle; three of them (HSA-miR-181a-5p, -324-5p, -451a; SMA-miRs) were significantly up-regulated in serum of patients. The severity predicted by the SMA-score was related with that of the clinical classification at a correlation coefficient of 0.87 (p<10-5).
    Conclusions: miRNome analyses suggest the primary involvement of skeletal muscle in SMA pathogenesis. The SMA-miRs are likely actively released in the blood flow; their function and target cells require to be elucidated. The accuracy of the SMA-score needs to be verified in replicative studies: if confirmed, it could be crucial for the routine prognostic assessment, also in pre-symptomatic patients.
    Funding: Telethon Italia (grant # GGP12116).
    Keywords:  genetics; genomics; human; medicine; mouse
  38. Mol Cell Biochem. 2021 Sep 23.
      Several benefits can be acquired through physical exercise. Different classes of biomolecules are responsible for the cross-talk between distant organs. The secretome of skeletal muscles, and more widely the field of organokines, is ever-expanding. "Exerkine" has emerged as the umbrella term covering any humoral factors secreted into circulation by tissues in response to exercise. This review aims at describing the most interesting exerkines discovered in the last 3 years, which are paving the way for both physiological novel insights and potential medical strategies. The five exerkines identified all play a significant role in the healthy effect of exercise. Specifically: miR-1192, released by muscles and myocardium into circulation, by modulating cardioprotective effect in trained mice; miR-342-5p, located into exosomes from vascular endothelial cells, also a cardioprotective miRNA in trained young humans; apelin, released by muscles into circulation, involved in anti-inflammatory pathways and muscle regenerative capacity in rats; GDF-15, released into circulation from yet unknown source, whose effects can be observed on multiple organs in young men after a single bout of exercise; oxytocin, released by myoblasts and myotubes, with autocrine and paracrine functions in myotubes. The systemic transport by vesicles and the crosstalk between distant organs deserve a deep investigation. Sources, targets, transport mechanisms, biological roles, population samples, frequency, intensity, time and type of exercise should be considered for the characterization of existing and novel exerkines. The "exercise is medicine" framework should include exerkines in favor of novel insights for public health.
    Keywords:  Cross-talk; Exosomes; Myokines; Organokines; Physical exercise; miRNA
  39. Nature. 2021 Sep 21.
    Keywords:  Cancer; Medical research; Neuroscience
  40. Clin Obstet Gynecol. 2021 Sep 21.
      Spinal muscular atrophy (SMA) is a life-threatening autosomal recessive disease that leads to progressive muscle weakness and atrophy, respiratory insufficiency and scoliosis. SMA is currently the most common monogenic cause of infant mortality. Amazing advancements have been made in the therapeutic options available for these children since 2016. What has also become clear is that the earlier the treatment is administered, the better the clinical outcome. For several reasons, which we will review in this chapter, SMA may be an excellent disease candidate for in utero therapy.
  41. Scand J Med Sci Sports. 2021 Sep 22.
      The study aimed to determine the levels of skeletal muscle Angiotensin-Converting Enzyme 2 (ACE2, the SARS-CoV-2 receptor) protein expression in men and women and assess whether ACE2 expression in skeletal muscle is associated with cardiorespiratory fitness and adiposity. The level of ACE2 in vastus lateralis muscle biopsies collected in previous studies from 170 men (age:19-65 yrs, weight:56-137 kg, BMI:23-44) and 69 women (age:18-55 yrs, weight:41-126 kg, BMI:22-39) was analysed in duplicate by western blot. VO2 max was determined by ergospirometry and body composition by DXA. ACE2 protein expression was 1.8-fold higher in women than men (p=0.001, n=239). This sex difference disappeared after accounting for the percentage of body fat (fat %), VO2 max per kg of legs lean mass (VO2 max-LLM) and age (p=0.47). Multiple regression analysis showed that the fat % (β=0.47) is the main predictor of the variability in ACE2 protein expression in skeletal muscle, explaining 5.2 % of the variance. VO2 max-LLM had also predictive value (β=0.09). There was a significant fat % by VO2 max-LLM interaction, such that for subjects with low fat %, VO2 max-LLM was positively associated with ACE2 expression while as fat % increased the slope of the positive association between VO2 max-LLM and ACE2 was reduced. In conclusion, women express higher amounts of ACE2 in their skeletal muscles than men. This sexual dimorphism is mainly explained by sex differences in fat % and cardiorespiratory fitness. The percentage of body fat is the main predictor of the variability in ACE2 protein expression in human skeletal muscle.
  42. BMC Musculoskelet Disord. 2021 Sep 20. 22(1): 807
      BACKGROUND: Previous research has described a neuroprotective effect of IGF-I, supporting neuronal survival, axon growth and proliferation of muscle cells. Therefore, the association between IGF-I concentration, muscle histology and electrophysiological markers in a cohort of patients with sarcopenia dares investigation.METHODS: Measurement of serum concentrations of IGF-I and binding partners, electromyographic measurements with the MUNIX (Motor Unit Number Index) method and muscle biopsies were performed in 31 patients with acute hip fracture older age 60 years. Molecular markers for denervation (neural cell adhesion molecule NCAM) and proliferation markers (Ki67) were assessed by immunofluorescence staining of muscle biopsy tissue. Skeletal muscle mass by bioelectrical impedance analysis and hand-grip strength were measured to assess sarcopenia status according to EWGSOP2 criteria.
    RESULTS: Thirty-one patients (20 women) with a mean age of 80.6 ± 7.4 years were included. Concentrations of IGF-I and its binding partners were significantly associated with sarcopenia (ß = - 0.360; p = 0.047) and MUNIX (ß = 0.512; p = 0.005). Further, expression of NCAM (ß = 0.380; p = 0.039) and Ki67 (ß = 0.424; p = 0.022) showed significant associations to IGF-I concentrations.
    CONCLUSIONS: The findings suggest a pathogenetic role of IGF-I in sarcopenia based on muscle denervation.
    Keywords:  Denervation; Insulin-like growth factor 1; MUNIX; Muscle atrophy