bims-moremu Biomed News
on Molecular regulators of muscle mass
Issue of 2021‒10‒31
thirty-six papers selected by
Anna Vainshtein
Craft Science Inc.

  1. Sci Rep. 2021 Oct 29. 11(1): 21327
      Skeletal muscle is an adaptive tissue with the ability to regenerate in response to exercise training. Cross-sectional area (CSA) quantification, as a main parameter to assess muscle regeneration capability, is highly tedious and time-consuming, necessitating an accurate and automated approach to analysis. Although several excellent programs are available to automate analysis of muscle histology, they fail to efficiently and accurately measure CSA in regenerating myofibers in response to exercise training. Here, we have developed a novel fully-automated image segmentation method based on neutrosophic set algorithms to analyse whole skeletal muscle cross sections in exercise-induced regenerating myofibers, referred as MyoView, designed to obtain accurate fiber size and distribution measurements. MyoView provides relatively efficient, accurate, and reliable measurements for CSA quantification and detecting different myofibers, myonuclei and satellite cells in response to the post-exercise regenerating process. We showed that MyoView is comparable with manual quantification. We also showed that MyoView is more accurate and efficient to measure CSA in post-exercise regenerating myofibers as compared with Open-CSAM, MuscleJ, SMASH and MyoVision. Furthermore, we demonstrated that to obtain an accurate CSA quantification of exercise-induced regenerating myofibers, whole muscle cross-section analysis is an essential part, especially for the measurement of different fiber-types. We present MyoView as a new tool to quantify CSA, myonuclei and satellite cells in skeletal muscle from any experimental condition including exercise-induced regenerating myofibers.
  2. Cell Commun Signal. 2021 Oct 27. 19(1): 105
      BACKGROUND: The absence of dystrophin has gave a massive impact on myotube development in Muscular Dystrophy pathogenesis. One of the conserved signaling pathways involved in skeletal muscle differentiation is the PI3K/Akt/mTOR pathway that plays a vital role in autophagy regulation. To further understand and establish targeted therapy in dystrophin-deficient myoblasts, protein expression profiling has been determined which provides information on perturbed autophagy modulation and activation.METHODS: In this study, a dystrophin-deficient myoblast cell line established from the skeletal muscle of a dystrophic (mdx) mouse was used as a model. The dfd13 (dystrophin-deficient) and C2C12 (non-dystrophic) myoblasts were cultured in low mitogen conditions for 10 days to induce differentiation. The cells were subjected to total protein extraction prior to Western blotting assay technique. Protein sub-fractionation has been conducted to determine protein localization. The live-cell analysis of autophagy assay was done using a flow cytometer.
    RESULTS: In our culture system, the dfd13 myoblasts did not achieve terminal differentiation. PTEN expression was profoundly increased in dfd13 myoblasts throughout the differentiation day subsequently indicates perturbation of PI3K/Akt/mTOR regulation. In addition, rictor-mTORC2 was also found inactivated in this event. This occurrence has caused FoxO3 misregulation leads to higher activation of autophagy-related genes in dfd13 myoblasts. Autophagosome formation was increased as LC3B-I/II showed accumulation upon differentiation. However, the ratio of LC3B lipidation and autophagic flux were shown decreased which exhibited dystrophic features.
    CONCLUSION: Perturbation of the PTEN-PI3K/Akt pathway triggers excessive autophagosome formation and subsequently reduced autophagic flux within dystrophin-deficient myoblasts where these findings are of importance to understand Duchenne Muscular Dystrophy (DMD) patients. We believe that some manipulation within its regulatory signaling reported in this study could help restore muscle homeostasis and attenuate disease progression. Video Abstract.
    Keywords:  Autophagy; Duchenne muscular dystrophy; Dystrophin; Myoblasts; PI3K/Akt signalling
  3. Korean J Physiol Pharmacol. 2021 Nov 01. 25(6): 585-592
      Cisplatin has been reported to cause side effects such as muscle wasting in humans and rodents. The physiological mechanisms involved in preventing muscle wasting, such as the regulation of AKT, PGC1-α, and autophagy-related factor FOXO3a by MuRF 1 and Atrogin-1, remain unclear following different types of exercise and in various skeletal muscle types. Eight-week-old male Wistar rats (n = 34) were assigned to one of four groups: control (CON, n = 6), cisplatin injection (1 mg/kg) without exercise (CC, n = 8), cisplatin (1 mg/kg) + resistance exercise (CRE, n = 9) group, and cisplatin (1 mg/kg) + aerobic exercise (CAE, n = 11). The CRE group performed progressive ladder exercise (starting with 10% of body weight on a 1-m ladder with 2-cm-interval grids, at 85°) for 8 weeks. The CAE group exercised by treadmill running (20 m/min for 60 min daily, 4 times/week) for 8 weeks. Compared with the CC group, the levels of the autophagy-related factors BNIP3, Beclin 1, LC3-II/I ratio, p62, and FOXO3a in the gastrocnemius and soleus muscles were significantly decreased in the CRE and CAE groups. The CRE and CAE groups further showed significantly decreased MuRF 1 and Atrogin-1 levels and increased phosphorylation of AKT, FOXO3a, and PGC1-α. These results suggest that both ladder and aerobic exercise directly affected muscle wasting by modulating the AKT/PGC1-α/FOXO3a signaling pathways regardless of the skeletal muscle type.
    Keywords:  Autophagy; Cisplatin; Exercise training; Muscle atrophy; Skeletal muscle
  4. Am J Pathol. 2021 Oct 25. pii: S0002-9440(21)00441-7. [Epub ahead of print]
      Sigmar1 is a widely expressed, multitasking molecular chaperone protein playing functional roles in several cellular processes. Mutations in the Sigmar1 gene have been reported to associate with several distal neuropathies with strong manifestation in skeletal muscle dysfunction with phenotypes like muscle wasting and atrophy. However, the physiological function of Sigmar1 in skeletal muscle remained unknown. Here, the physiological role of Sigmar1 in skeletal muscle structure and function in gastrocnemius (Gastro), quadriceps (Quad), soleus (Sol), extensor digitorum longus (EDL), and tibialis anterior (TA) muscles was determined. Quantification of myofiber cross-sectional area (CSA) showed altered myofiber size distribution and changes in myofiber-type in the skeletal muscle of the Sigmar1-/- mice. Interestingly, ultrastructural analysis by transmission electron microscopy showed the presence of abnormal mitochondria, and immunostaining showed derangements in dystrophin localization in skeletal muscles from Sigmar1-/- mice. Additionally, myopathy in Sigmar1-/- mice was associated with an increased number of central nuclei, increased collagen deposition, and fibrosis. Functional studies also showed reduced endurance and exercise capacity in the Sigmar1-/- mice without any changes in voluntary locomotion, markers for muscle denervation, and muscle atrophy. Overall, for the first time, a potential physiological function of Sigmar1 in maintaining healthy skeletal muscle structure and function was demonstrated in this manuscript.
  5. J Cachexia Sarcopenia Muscle. 2021 Oct 26.
      BACKGROUND: Skeletal muscle atrophy is a debilitating complication of many chronic diseases, disuse conditions, and ageing. Genome-wide gene expression analyses have identified that elevated levels of microRNAs encoded by the H19X locus are among the most significant changes in skeletal muscles in a wide scope of human cachectic conditions. We have previously reported that the H19X locus is important for the establishment of striated muscle fate during embryogenesis. However, the role of H19X-encoded microRNAs in regulating skeletal mass in adults is unknown.METHODS: We have created a transgenic mouse strain in which ectopic expression of miR-322/miR-503 is driven by the skeletal muscle-specific muscle creatine kinase promoter. We also used an H19X mutant mouse strain in which transcription from the locus is interrupted by a gene trap. Animal phenotypes were analysed by standard histological methods. Underlying mechanisms were explored by using transcriptome profiling and validated in the two animal models and cultured myotubes.
    RESULTS: Our results demonstrate that the levels of H19X microRNAs are inversely related to postnatal skeletal muscle growth. Targeted overexpression of miR-322/miR-503 impeded skeletal muscle growth. The weight of gastrocnemius muscles of transgenic mice was only 54.5% of the counterparts of wild-type littermates. By contrast, interruption of transcription from the H19X locus stimulates postnatal muscle growth by 14.4-14.9% and attenuates the loss of skeletal muscle mass in response to starvation by 12.8-21.0%. Impeded muscle growth was not caused by impaired IGF1/AKT/mTOR signalling or a hyperactive ubiquitin-proteasome system, instead accompanied by markedly dropped abundance of translation initiation factors in transgenic mice. miR-322/miR-503 directly targets eIF4E, eIF4G1, eIF4B, eIF2B5, and eIF3M.
    CONCLUSIONS: Our study illustrates a novel pathway wherein H19X microRNAs regulate skeletal muscle growth and atrophy through regulating the abundance of translation initiation factors, thereby protein synthesis. The study highlights how translation initiation factors lie at the crux of multiple signalling pathways that control skeletal muscle mass.
    Keywords:  AtromiR; H19X; MicroRNAs; Protein synthesis; Skeletal muscle atrophy; Translation initiation; miR-322; miR-424; miR-503; miR-542
  6. Can J Physiol Pharmacol. 2021 Oct 25.
      Sarco(endo)plasmic reticulum calcium (Ca2+) ATPase (SERCA) transports Ca2+ in muscle. Impaired SERCA activity contributes to diabetic myopathy. Sirtuin (SIRT) 3 regulates muscle metabolism and function. However, it is unknown if SIRT3 regulates muscle SERCA activity. We determined if SIRT3 overexpression enhances SERCA activity in mouse gastrocnemius muscle and if SIRT3 overexpression preserves gastrocnemius SERCA activity in a model of type 2 diabetes, induced by high fat-high sucrose (HFHS)-feeding. We also determined if the acetylation status of SERCA proteins in mouse gastrocnemius is altered by SIRT3 overexpression or HFHS-feeding. Wild-type (WT) mice and SIRT3 transgenic (SIRT3TG) mice, overexpressing SIRT3 in skeletal muscle, were fed a standard- or HFHS-diet for 4-months. SIRT3TG and WT mice developed obesity and glucose intolerance after 4-months of HFHS-feeding. SERCA Vmax was higher in gastrocnemius of SIRT3TG mice, compared to WT mice. HFHS-fed mice had lower SERCA1a protein levels and lower SERCA Vmax in their gastrocnemius than control-fed mice. The decrease in SERCA Vmax in gastrocnemius muscle due to HFHS-feeding was attenuated by SIRT3 overexpression in HFHS-fed SIRT3TG mice. SERCA1a and SERCA2a acetylation in mouse gastrocnemius was not altered by genotype or diet. These findings suggest SIRT3 overexpression improves SERCA function in diabetic mouse skeletal muscle.
  7. Biochem Biophys Res Commun. 2021 Oct 20. pii: S0006-291X(21)01450-9. [Epub ahead of print]582 111-117
      Skeletal muscle is known to regulate bone homeostasis through muscle-bone interaction, although factors that control this activity remain unclear. Here, we newly established Smad3-flox mice, and then generated skeletal muscle-specific Smad2/Smad3 double conditional knockout mice (DcKO) by crossing Smad3-flox with skeletal muscle-specific Ckmm Cre and Smad2-flox mice. We show that immobilization-induced gastrocnemius muscle atrophy occurring due to sciatic nerve denervation was partially but significantly inhibited in DcKO mice, suggesting that skeletal muscle cell-intrinsic Smad2/3 is required for immobilization-induced muscle atrophy. Also, tibial bone atrophy seen after sciatic nerve denervation was partially but significantly inhibited in DcKO mice. Bone formation rate in wild-type mouse tibia was significantly inhibited by immobilization, but inhibition was abrogated in DcKO mice. We propose that skeletal muscle regulates immobilization-induced bone atrophy via Smad2/3, and Smad2/3 represent potential therapeutic targets to prevent both immobilization-induced bone and muscle atrophy.
    Keywords:  Atrophy; Bone; Immobilization; Skeletal muscle; Smad2; Smad3
  8. Nat Commun. 2021 Oct 29. 12(1): 6264
      Lack of dystrophin causes muscle degeneration, which is exacerbated by chronic inflammation and reduced regenerative capacity of muscle stem cells in Duchenne Muscular Dystrophy (DMD). To date, glucocorticoids remain the gold standard for the treatment of DMD. These drugs are able to slow down the progression of the disease and increase lifespan by dampening the chronic and excessive inflammatory process; however, they also have numerous harmful side effects that hamper their therapeutic potential. Here, we investigated Resolvin-D2 as a new therapeutic alternative having the potential to target multiple key features contributing to the disease progression. Our in vitro findings showed that Resolvin-D2 promotes the switch of macrophages toward their anti-inflammatory phenotype and increases their secretion of pro-myogenic factors. Moreover, Resolvin-D2 directly targets myogenic cells and promotes their differentiation and the expansion of the pool of myogenic progenitor cells leading to increased myogenesis. These effects are ablated when the receptor Gpr18 is knocked-out, knocked-down, or blocked by the pharmacological antagonist O-1918. Using different mouse models of DMD, we showed that Resolvin-D2 targets both inflammation and myogenesis leading to enhanced muscle function compared to glucocorticoids. Overall, this preclinical study has identified a new therapeutic approach that is more potent than the gold-standard treatment for DMD.
  9. Am J Physiol Cell Physiol. 2021 Oct 27.
      Our laboratory has discovered that dysregulation in microRNA (miRNA) that target anabolic signaling between younger and older adults is a potential molecular mechanism resulting in age-associated decreases in skeletal muscle mass and function (sarcopenia). Whether differences in miRNA expression profiles account for inter-individual variability in exercise adaptation in older adults is unclear. Understanding paradoxical responses to anabolic stimulation and identifying the mechanisms for this inconsistency in mobility-limited older adults may provide new targets for the treatment of sarcopenia. The objective of the current study was to assess circulating miRNA expression profiles in diametric response of leg lean mass in mobility-limited older individuals after a 6 month progressive resistance exercise training intervention (PRET). Participants were dichotomized by gain (Gainers; n = 33) or loss (Losers; n = 40) of leg lean mass after PRET. Gainers signifcantly increased fat-free mass. Six miRNA (miR-1-3p, miR-19b-3p, miR-92a, miR-126, miR-133a-3p, and miR-133b) were identified to be differentially expressed between Gainers and Losers, with miR-19b-3p being the miRNA most highly associated with increases in fat-free mass. We then used a novel integrative approach to determine if differences in circulating miR-19b-3p potentially translate to augmented anabolic response in human skeletal muscle cells in vitro. Results from this analysis identified that overexpression of miR-19b-3p targeted and downregulated PTEN to facilitate increases in muscle protein synthetic rate. Together these data identify miR-19b-3p as a potent regulator of muscle anabolism that may contribute to an inter-individual response to PRET in mobility-limited older adults.
    Keywords:  Aging; Exercise; Sarcopenia; Skeletal Muscle; microRNA
  10. Int J Sport Nutr Exerc Metab. 2021 Oct 25. pii: ijsnem.2021-0139. [Epub ahead of print] 1-13
      The acute response of muscle protein synthesis (MPS) to resistance exercise and nutrition is often used to inform recommendations for exercise programming and dietary interventions, particularly protein nutrition, to support and enhance muscle growth with training. Those recommendations are worthwhile only if there is a predictive relationship between the acute response of MPS and subsequent muscle hypertrophy during resistance exercise training. The metabolic basis for muscle hypertrophy is the dynamic balance between the synthesis and degradation of myofibrillar proteins in muscle. There is ample evidence that the process of MPS is much more responsive to exercise and nutrition interventions than muscle protein breakdown. Thus, it is intuitively satisfying to translate the acute changes in MPS to muscle hypertrophy with training over a longer time frame. Our aim is to examine and critically evaluate the strength and nature of this relationship. Moreover, we examine the methodological and physiological factors related to measurement of MPS and changes in muscle hypertrophy that contribute to uncertainty regarding this relationship. Finally, we attempt to offer recommendations for practical and contextually relevant application of the information available from studies of the acute response of MPS to optimize muscle hypertrophy with training.
    Keywords:  muscle hypertrophy; muscle remodeling; myofibrillar protein synthesis; ribosomal biogenesis; stable isotopes; translational efficiency
  11. Nat Commun. 2021 Oct 27. 12(1): 6079
      While the importance of RNA localization in highly differentiated cells is well appreciated, basic principles of RNA localization in skeletal muscle remain poorly characterized. Here, we develop a method to detect and quantify single molecule RNA localization patterns in skeletal myofibers, and uncover a critical role for directed transport of RNPs in muscle. We find that RNAs localize and are translated along sarcomere Z-disks, dispersing tens of microns from progenitor nuclei, regardless of encoded protein function. We find that directed transport along the lattice-like microtubule network of myofibers becomes essential to achieve this localization pattern as muscle development progresses; disruption of this network leads to extreme accumulation of RNPs and nascent protein around myonuclei. Our observations suggest that global active RNP transport may be required to distribute RNAs in highly differentiated cells and reveal fundamental mechanisms of gene regulation, with consequences for myopathies caused by perturbations to RNPs or microtubules.
  12. Sci Rep. 2021 Oct 27. 11(1): 21224
      Skeletal muscle mass is critical for good quality of life. Mesenchymal stem cells (MSCs) are multipotent stem cells distributed across various tissues. They are characterized by the capacity to secrete growth factors and differentiate into skeletal muscle cells. These capabilities suggest that MSCs might be beneficial for muscle growth. Nevertheless, little is known regarding the effects on muscle protein anabolic and catabolic systems of intramuscular injection of MSCs into skeletal muscle. Therefore, in the present study, we measured changes in mechanistic target of rapamycin complex 1 (mTORC1) signaling, the ubiquitin-proteasome system, and autophagy-lysosome system-related factors after a single intramuscular injection of MSCs with green fluorescence protein (GFP) into mouse muscles. The intramuscularly-injected MSCs were retained in the gastrocnemius muscle for 7 days after the injection, indicated by detection of GFP and expression of platelet-derived growth factor receptor-alpha. The injection of MSCs increased the expression of satellite cell-related genes, activated mTORC1 signaling and muscle protein synthesis, and increased protein ubiquitination and autophagosome formation (indicated by the expression of microtubule-associated protein 1 light chain 3-II). These results suggest that the intramuscular injection of MSCs activated muscle anabolic and catabolic systems and accelerated muscle protein turnover.
  13. Front Endocrinol (Lausanne). 2021 ;12 733625
      Individuals with hepatic steatosis often display several metabolic abnormalities including insulin resistance and muscle atrophy. Previously, we found that hepatic steatosis results in an altered hepatokine secretion profile, thereby inducing skeletal muscle insulin resistance via inter-organ crosstalk. In this study, we aimed to investigate whether the altered secretion profile in the state of hepatic steatosis also induces skeletal muscle atrophy via effects on muscle protein turnover. To investigate this, eight-week-old male C57BL/6J mice were fed a chow (4.5% fat) or a high-fat diet (HFD; 45% fat) for 12 weeks to induce hepatic steatosis, after which the livers were excised and cut into ~200-µm slices. Slices were cultured to collect secretion products (conditioned medium; CM). Differentiated L6-GLUT4myc myotubes were incubated with chow or HFD CM to measure glucose uptake. Differentiated C2C12 myotubes were incubated with chow or HFD CM to measure protein synthesis and breakdown, and gene expression via RNA sequencing. Furthermore, proteomics analysis was performed in chow and HFD CM. It was found that HFD CM caused insulin resistance in L6-GLUT4myc myotubes compared with chow CM, as indicated by a blunted insulin-stimulated increase in glucose uptake. Furthermore, protein breakdown was increased in C2C12 cells incubated with HFD CM, while there was no effect on protein synthesis. RNA profiling of C2C12 cells indicated that 197 genes were differentially expressed after incubation with HFD CM, compared with chow CM, and pathway analysis showed that pathways related to anatomical structure and function were enriched. Proteomics analysis of the CM showed that 32 proteins were differentially expressed in HFD CM compared with chow CM. Pathway enrichment analysis indicated that these proteins had important functions with respect to insulin-like growth factor transport and uptake, and affect post-translational processes, including protein folding, protein secretion and protein phosphorylation. In conclusion, the results of this study support the hypothesis that secretion products from the liver contribute to the development of muscle atrophy in individuals with hepatic steatosis.
    Keywords:  NAFLD; hepatic steatosis; insulin resistance, metabolism; inter-organ crosstalk; muscle atrophy; sarcopenia
  14. Curr Issues Mol Biol. 2021 Oct 09. 43(3): 1473-1488
      Profound skeletal muscle loss can lead to severe disability and cosmetic deformities. Mesenchymal stem cell (MSC)-derived exosomes have shown potential as an effective therapeutic tool for tissue regeneration. This study aimed to determine the regenerative capacity of MSC-derived exosomes for skeletal muscle regeneration. Exosomes were isolated from human adipose tissue-derived MSCs (AD-MSCs). The effects of MSC-derived exosomes on satellite cells were investigated using cell viability, relevant genes, and protein analyses. Moreover, NOD-SCID mice were used and randomly assigned to the healthy control (n = 4), muscle defect (n = 6), and muscle defect + exosome (n = 6) groups. Muscle defects were created using a biopsy punch on the quadriceps of the hind limb. Four weeks after the surgery, the quadriceps muscles were harvested, weighed, and histologically analyzed. MSC-derived exosome treatment increased the proliferation and expression of myocyte-related genes, and immunofluorescence analysis for myogenin revealed a similar trend. Histologically, MSC-derived exosome-treated mice showed relatively preserved shapes and sizes of the muscle bundles. Immunohistochemical staining revealed greater expression of myogenin and myoblast determination protein 1 in the MSC-derived exosome-treated group. These results indicate that exosomes extracted from AD-MSCs have the therapeutic potential for skeletal muscle regeneration.
    Keywords:  exosome; mesenchymal stem cell; muscle; regeneration; satellite cell
  15. Front Genet. 2021 ;12 762012
      Vps54 is an integral subunit of the Golgi-associated retrograde protein (GARP) complex, which is involved in tethering endosome-derived vesicles to the trans-Golgi network (TGN). A destabilizing missense mutation in Vps54 causes the age-progressive motor neuron (MN) degeneration, muscle weakness, and muscle atrophy observed in the wobbler mouse, an established animal model for human MN disease. It is currently unclear how the disruption of Vps54, and thereby the GARP complex, leads to MN and muscle phenotypes. To develop a new tool to address this question, we have created an analogous model in Drosophila by generating novel loss-of-function alleles of the fly Vps54 ortholog (scattered/scat). We find that null scat mutant adults are viable but have a significantly shortened lifespan. Like phenotypes observed in the wobbler mouse, we show that scat mutant adults are male sterile and have significantly reduced body size and muscle area. Moreover, we demonstrate that scat mutant adults have significant age-progressive defects in locomotor function. Interestingly, we see sexually dimorphic effects, with scat mutant adult females exhibiting significantly stronger phenotypes. Finally, we show that scat interacts genetically with rab11 in MNs to control age-progressive muscle atrophy in adults. Together, these data suggest that scat mutant flies share mutant phenotypes with the wobbler mouse and may serve as a new genetic model system to study the cellular and molecular mechanisms underlying MN disease.
    Keywords:  MN disease; Vps54; drosophila; membrane traffic; wobbler mice
  16. Front Physiol. 2021 ;12 742034
      Treatment strategies and training regimens, which induce longitudinal muscle growth and increase the muscles' length range of active force exertion, are important to improve muscle function and to reduce muscle strain injuries in clinical populations and in athletes with limited muscle extensibility. Animal studies have shown several specific loading strategies resulting in longitudinal muscle fiber growth by addition of sarcomeres in series. Currently, such strategies are also applied to humans in order to induce similar adaptations. However, there is no clear scientific evidence that specific strategies result in longitudinal growth of human muscles. Therefore, the question remains what triggers longitudinal muscle growth in humans. The aim of this review was to identify strategies that induce longitudinal human muscle growth. For this purpose, literature was reviewed and summarized with regard to the following topics: (1) Key determinants of typical muscle length and the length range of active force exertion; (2) Information on typical muscle growth and the effects of mechanical loading on growth and adaptation of muscle and tendinous tissues in healthy animals and humans; (3) The current knowledge and research gaps on the regulation of longitudinal muscle growth; and (4) Potential strategies to induce longitudinal muscle growth. The following potential strategies and important aspects that may positively affect longitudinal muscle growth were deduced: (1) Muscle length at which the loading is performed seems to be decisive, i.e., greater elongations after active or passive mechanical loading at long muscle length are expected; (2) Concentric, isometric and eccentric exercises may induce longitudinal muscle growth by stimulating different muscular adaptations (i.e., increases in fiber cross-sectional area and/or fiber length). Mechanical loading intensity also plays an important role. All three training strategies may increase tendon stiffness, but whether and how these changes may influence muscle growth remains to be elucidated. (3) The approach to combine stretching with activation seems promising (e.g., static stretching and electrical stimulation, loaded inter-set stretching) and warrants further research. Finally, our work shows the need for detailed investigation of the mechanisms of growth of pennate muscles, as those may longitudinally grow by both trophy and addition of sarcomeres in series.
    Keywords:  cerebral palsy; growth; hypertrophy; lengthening; muscle-tendon complex; stretching; training; treatment
  17. Exerc Sport Sci Rev. 2021 Oct 22.
      ABSTRACT: Inducible heme oxygenase (HO)-1 catalyzes the breakdown of heme to biliverdin, iron and carbon monoxide (CO). CO binds to cytochrome c oxidase and alters mitochondrial redox balance and coordinately regulates mitochondrial quality control (MQC) during oxidant stress and inflammation. The hypothesis presented is that skeletal muscle HO-1/CO system helps modulate components in the MQC cycle during metabolic stress.
  18. Physiol Rep. 2021 Nov;9(21): e15077
      Insight into the bidirectional signaling between primary human myogenic cells and neurons is lacking. For this purpose, human myogenic cells were derived from the semitendinosus and gracilis muscles of five healthy individuals and co-cultured with cerebellar granule neurons from two litters of 7-day-old Wistar rat pups, in muscle medium or neural medium, alongside monocultures of myogenic cells or neurons. RT-PCR was performed to determine human mRNA levels of GAPDH, Ki67, myogenin, and MUSK, and the acetylcholine receptor subtypes CHRNA1, CHRNB1, CHRNG, CHRND, and CHRNE, and rat mRNA levels of GAPDH, Fth1, Rack1, vimentin, Cdh13, and Ppp1r1a. Immunocytochemistry was used to evaluate neurite outgrowth (GAP43) in the presence and absence of myogenic cells. Co-culture with primary neurons lead to higher myogenic cell gene expression levels of GAPDH, myogenin, MUSK, CHRNA1, CHRNG, and CHRND, compared to myogenic cells cultured alone. It appeared that neurons preferentially attached to myotubes and that neurite outgrowth was enhanced when neurons were cultured with myogenic cells compared to monoculture. In neural medium, rat mRNA levels of GAPDH, vimentin, Cdh13, and Ppp1r1a were greater in co-culture, versus monoculture, whereas in muscle medium co-culture lead to lower levels of Fth1, Rack1, vimentin, and Cdh13 than monoculture. These findings demonstrate mutually beneficial stimulatory signaling between rat cerebellar granule neurons and human myogenic cells, providing support for an active role for both the neuron and the muscle cell in stimulating neurite growth and myogenesis. Bidirectional muscle nerve signaling.
    Keywords:  acetylcholine receptor; innervation; myogenesis; neuron; skeletal muscle
  19. J Cachexia Sarcopenia Muscle. 2021 Oct 26.
      BACKGROUND: Frailty is a major age-associated syndrome leading to disability. Oxidative damage plays a significant role in the promotion of frailty. The cellular antioxidant system relies on reduced nicotinamide adenine dinucleotide phosphate (NADPH) that is highly dependent on glucose 6-P dehydrogenase (G6PD). The G6PD-overexpressing mouse (G6PD-Tg) is protected against metabolic stresses. Our aim was to examine whether this protection delays frailty.METHODS: Old wild-type (WT) and G6PD-Tg mice were evaluated longitudinally in terms of frailty. Indirect calorimetry, transcriptomic profile, and different skeletal muscle quality markers and muscle regenerative capacity were also investigated.
    RESULTS: The percentage of frail mice was significantly lower in the G6PD-Tg than in the WT genotype, especially in 26-month-old mice where 50% of the WT were frail vs. only 13% of the Tg ones (P < 0.001). Skeletal muscle transcriptomic analysis showed an up-regulation of respiratory chain and oxidative phosphorylation (P = 0.009) as well as glutathione metabolism (P = 0.035) pathways in the G6PD-Tg mice. Accordingly, the Tg animals exhibited an increase in reduced glutathione (34.5%, P < 0.01) and a decrease on its oxidized form (-69%, P < 0.05) and in lipid peroxidation (4-HNE: -20.5%, P < 0.05). The G6PD-Tg mice also showed reduced apoptosis (BAX/Bcl2: -25.5%, P < 0.05; and Bcl-xL: -20.5%, P < 0.05), lower levels of the intramuscular adipocyte marker FABP4 (-54.7%, P < 0.05), and increased markers of mitochondrial content (COX IV: 89.7%, P < 0.05; Grp75: 37.8%, P < 0.05) and mitochondrial OXPHOS complexes (CII: 81.25%, P < 0.01; CIII: 52.5%, P < 0.01; and CV: 37.2%, P < 0.05). Energy expenditure (-4.29%, P < 0.001) and the respiratory exchange ratio were lower (-13.4%, P < 0.0001) while the locomotor activity was higher (43.4%, P < 0.0001) in the 20-month-old Tg, indicating a major energetic advantage in these mice. Short-term exercise training in young C57BL76J mice induced a robust activation of G6PD in skeletal muscle (203.4%, P < 0.05), similar to that achieved in the G6PD-Tg mice (142.3%, P < 0.01).
    CONCLUSIONS: Glucose 6-P dehydrogenase deficiency can be an underestimated risk factor for several human pathologies and even frailty. By overexpressing G6PD, we provide the first molecular model of robustness. Because G6PD is regulated by pharmacological and physiological interventions like exercise, our results provide molecular bases for interventions that by increasing G6PD will delay the onset of frailty.
    Keywords:  Aging; Antioxidant; Disability; Healthspan; Mitochondria; NADPH; Reactive oxygen species
  20. Natl Sci Rev. 2021 Feb;8(2): nwaa127
      Aging-related degeneration of pancreatic islet cells contributes to impaired glucose tolerance and diabetes. Endocrine cells age heterogeneously, complicating the efforts to unravel the molecular drivers underlying endocrine aging. To overcome these obstacles, we undertook single-cell RNA sequencing of pancreatic islet cells obtained from young and aged non-diabetic cynomolgus monkeys. Despite sex differences and increased transcriptional variations, aged β-cells showed increased unfolded protein response (UPR) along with the accumulation of protein aggregates. We observed transcriptomic dysregulation of UPR components linked to canonical ATF6 and IRE1 signaling pathways, comprising adaptive UPR during pancreatic aging. Notably, we found aging-related β-cell-specific upregulation of HSP90B1, an endoplasmic reticulum-located chaperone, impeded high glucose-induced insulin secretion. Our work decodes aging-associated transcriptomic changes that underlie pancreatic islet functional decay at single-cell resolution and indicates that targeting UPR components may prevent loss of proteostasis, suggesting an avenue to delaying β-cell aging and preventing aging-related diabetes.
    Keywords:  aging; islet; primate; single-cell RNA sequencing; β-cell
  21. Front Endocrinol (Lausanne). 2021 ;12 732338
      Women with polycystic ovary syndrome (PCOS), commonly have profound skeletal muscle insulin resistance which can worsen other clinical features. The heterogeneity of the condition has made it challenging to identify the precise mechanisms that cause this insulin resistance. A possible explanation for the underlying insulin resistance may be the dysregulation of Transforming Growth Factor-beta (TGFβ) signalling. TGFβ signalling contributes to the remodelling of reproductive and hepatic tissues in women with PCOS. Given the systemic nature of TGFβ signalling and its role in skeletal muscle homeostasis, it may be possible that these adverse effects extend to other peripheral tissues. We aimed to determine if TGFβ1 could negatively regulate glucose uptake and insulin signalling in skeletal muscle of women with PCOS. We show that both myotubes from women with PCOS and healthy women displayed an increase in glucose uptake, independent of changes in insulin signalling, following short term (16 hr) TGFβ1 treatment. This increase occurred despite pro-fibrotic signalling increasing via SMAD3 and connective tissue growth factor in both groups following treatment with TGFβ1. Collectively, our findings show that short-term treatment with TGFβ1 does not appear to influence insulin signalling or promote insulin resistance in myotubes. These findings suggest that aberrant TGFβ signalling is unlikely to directly contribute to skeletal muscle insulin resistance in women with PCOS in the short term but does not rule out indirect or longer-term effects.
    Keywords:  Extracellular matrix; cytokines; endocrinology; fibrosis; insulin resistance; skeletal muscle
  22. Antioxid Redox Signal. 2021 Oct 29.
      SIGNIFICANCE: Aging is a natural process that affects most living organisms, resulting in increased mortality. As the world population ages, the prevalence of age-associated diseases, and their associated healthcare costs, has increased sharply. A better understanding of the molecular mechanisms that lead to cellular dysfunction may provide important targets for interventions to prevent or treat these diseases. Recent Advances: Although the mitochondrial theory of aging has been proposed over 40 years ago, recent new data has given stronger support for a central role for mitochondrial dysfunction in several pathways that are deregulated during normal aging and age-associated disease.CRITICAL ISSUES: Several of the experimental evidence linking mitochondrial alterations to age-associated loss of function are correlative and mechanistic insight are still elusive. Here, we review how mitochondrial dysfunction may be involved in many of the known hallmarks of aging, and how these pathways interact in an intricate net of molecular relationships.
    FUTURE DIRECTIONS: As it has become clear that mitochondrial dysfunction plays causative roles in normal aging and age-associated diseases, it is necessary to better define the molecular interactions and the temporal and causal relations between these changes and the relevant phenotypes seen during the aging process.
  23. Am J Physiol Cell Physiol. 2021 Oct 27.
      Chemotherapeutic agents (CAs) are first-line antineoplastic treatments in a wide variety of cancers. These agents can induce oxidative stress and promote muscle loss. CAs trigger local and systemic oxidative stress by increasing mitochondrial reactive oxygen species (ROS) and thereby stimulate protein breakdown. However, whether CAs can directly impact muscle protein synthesis independent of ROS production is currently unknown. To address this problem, first, we identified the mechanism by which oxidative stress impairs myotube protein synthesis. Transient elevations in ROS production resulted in protein synthesis deficits, reduced ribosomal (r)RNA levels and increased rRNA oxidation. We then investigated the effects of CAs on protein synthesis in the absence of detectable elevations in ROS levels (sub-ROS). Paclitaxel (PTX), Doxorubicin (DXR) and Marizomib (Mzb) diminished protein synthesis and ribosomal capacity, and also impaired transcription of the rRNA genes (rDNA). These results indicate that while oxidative stress disrupted protein synthesis by compromising ribosome quantity and quality, CAs at sub-ROS doses also impaired protein synthesis and ribosomal capacity by reducing rDNA transcription. Therefore, CAs can negatively modulate myotube protein synthesis in a ROS-independent manner by altering the capacity for protein synthesis.
    Keywords:  chemotherapy; muscle atrophy; oxidative stress; protein synthesis; ribosomal RNA
  24. Mol Metab. 2021 Oct 22. pii: S2212-8778(21)00206-4. [Epub ahead of print] 101359
      OBJECTIVE: Liver mitochondria adapt to high calorie intake. We investigated how exercise alters the early compensatory response of mitochondria and thus prevents fatty liver disease as a long-term consequence of overnutrition.METHODS: We compared the effects of a steatogenic high-energy diet (HED, for 6 weeks) on mitochondrial metabolism of sedentary and treadmill-trained C57BL/6N mice. We applied multi-OMICs analyses to study the alterations in the proteome, transcriptome and lipids in isolated mitochondria of liver and skeletal muscle as well as in whole tissue and examined the functional consequences by high resolution respirometry.
    RESULTS: HED increased the respiratory capacity of isolated liver mitochondria, both in sedentary and in trained mice. However, proteomics analysis of the mitochondria and transcriptomics indicated that training modified the adaptation of the hepatic metabolism to HED on the level of respiratory complex I, glucose oxidation, pyruvate and acetyl-CoA metabolism and lipogenesis. Training also counteracted the HED-induced increase in fasting insulin, glucose tolerance, and liver fat. This was accompanied by lower diacylglycerol species and JNK phosphorylation in the livers of trained HED-fed mice, two mechanisms that can reverse hepatic insulin resistance. In skeletal muscle, the combination of HED and training improved the oxidative capacity to a greater extent than training alone by increasing respiration of isolated mitochondria and total mitochondrial protein content.
    CONCLUSION: We provide a comprehensive insight into the early adaptations of mitochondria in liver and skeletal muscle to HED and endurance training. Our results suggest that exercise disconnects the HED-induced increase in mitochondrial substrate oxidation from pyruvate and acetyl-CoA-driven lipid synthesis. This could contribute to the prevention of deleterious long-term effects of high fat and sugar intake on hepatic mitochondrial function and insulin sensitivity.
    Keywords:  MAFLD; acetyl-CoA; exercise; lipidomics; mitochondrial supercomplexes; proteomics
  25. Dev Cell. 2021 Oct 22. pii: S1534-5807(21)00809-1. [Epub ahead of print]
      In order to combat molecular damage, most cellular proteins undergo rapid turnover. We have previously identified large nuclear protein assemblies that can persist for years in post-mitotic tissues and are subject to age-related decline. Here, we report that mitochondria can be long lived in the mouse brain and reveal that specific mitochondrial proteins have half-lives longer than the average proteome. These mitochondrial long-lived proteins (mitoLLPs) are core components of the electron transport chain (ETC) and display increased longevity in respiratory supercomplexes. We find that COX7C, a mitoLLP that forms a stable contact site between complexes I and IV, is required for complex IV and supercomplex assembly. Remarkably, even upon depletion of COX7C transcripts, ETC function is maintained for days, effectively uncoupling mitochondrial function from ongoing transcription of its mitoLLPs. Our results suggest that modulating protein longevity within the ETC is critical for mitochondrial proteome maintenance and the robustness of mitochondrial function.
    Keywords:  age mosaicism; aging; electron transport chain; heterogeneity; long-lived proteins; mitochondria; muscle; neurons; protein homeostasis; supercomplexes
  26. Med Sci Sports Exerc. 2021 Oct 22.
      Satellite cells (SC) are of importance for muscular adaptation to various forms of exercise. A single bout of high-force eccentric exercise has been shown to induce SC activation and, for electrically stimulated exercise, SC differentiation.PURPOSE: This study aimed to assess if one bout of concentric/eccentric exercise with damaging eccentric overload (CON/ECC+) provides a sufficient stimulus to induce SC activation, proliferation and differentiation.
    METHODS: Biopsies from the vastus lateralis muscle of recreationally active males were obtained in the rested condition and again from the contralateral leg seven days after exhaustive concentric/eccentric (CON/ECC, n = 15) or CON/ECC+ (n = 15) leg extension exercise and in a non-exercising control group (CG, n = 10). Total SC number (Pax7+), activated (Pax7+/MyoD+), and differentiating (myogenin+) SCs, fiber type distribution, and myofibers expressing neonatal myosin heavy chain (MHCneo) were determined immunohistochemically. Creatine kinase (CK) and myoglobin were measured in venous blood. Isokinetic strength tests were repeatedly conducted.
    RESULTS: Significant increases in CK and myoglobin (p = 0.001) indicated myofiber damage while maximal strength was not impaired. Only after CON/ECC+, SC content (p = 0.019) and SC related to type II fibers (p = 0.011) were significantly increased. A significant increase in the proportion of activated SCs occurred after CON/ECC+ only (p = 0.003), the increase being significantly (p < 0.05) different from the changes after CON/ECC and in CG. The number of differentiating SC and MHCneo remained unchanged.
    CONCLUSION: Eccentric overload during leg extension exercise induced significant SC activation, increases in SC content and in SC number related to type II myofibers. However, there were no signs of increased SC differentiation or formation of new myofibers.
  27. J Med Food. 2021 Oct 29.
      Sarcopenia and muscle wasting have many negative impacts on health and well-being. Evidence suggests that high rates of COVID-19 hospitalizations and lockdown conditions will lead to a marked increase in musculoskeletal disorders associated with sarcopenia in older adults. The molecular etiology of sarcopenia is complex, but physical inactivity, poor diet, and age diminished ability to stimulate muscle protein synthesis (MPS) remain important drivers. A body of evidence shows that, acting through the highly conserved nutrient sensor pathway mTORc1, the branch chain amino acid leucine can trigger and enhance MPS in older adults, and thus has a role in the medical management of sarcopenia. Whey protein-enriched enteral supplements are a low cost, easily accessible source of highly bioavailable leucine used clinically in older adults for preservation of lean body mass in long-term care setting. Therefore, given the evidence of leucine's ability to stimulate MPS in older adults, we argue that meal supplementation with whey-enriched enteral products, which can provide the 3-5 g of leucine necessary to trigger MPS in older adults, should be given serious consideration by medical and nutrition professionals to potentially mitigate muscle wasting and sarcopenia risk associated with prolonged COVID-19 lockdown measures.
    Keywords:  COVID-19; leucine; mTOR1c; nutrition; older adults; sarcopenia
  28. Med Sci Sports Exerc. 2021 Oct 27.
      INTRODUCTION: D-Glucosamine (GlcN) is one of the most widely consumed dietary supplements and complementary medicines in the world and has been traditionally used to attenuate osteoarthritis in humans. GlcN extends lifespan in different animal models. In humans, its supplementation has been strongly associated with decreased total mortality and improved vascular endothelial function. GlcN acts as a suppressor of inflammation and by inhibiting glycolysis, it can activate the metabolism of stored fat and mitochondrial respiration.METHODS: The conventional human GlcN dose is 1,500 mg x day-1 but extensive evidence indicates that much higher doses are well tolerated. GlcN is one of the supplements that has experienced a greater use in the last years in elite athletes mainly due to its potential chondroprotective effects that may promote cartilage health. However, the possibility of it being an ergogenic aid has not been explored. We aimed to study the potential beneficial effects of GlcN on mitochondrial content, on physical performance and oxidative stress in mice that were aerobically trained and supplemented with three different doses of glucosamine (250, 500, and 1,000 mg x Kg-1) for six weeks. We measured exercise performance (grip strength, motor coordination and running capacity) before and after the training period. Proteins involved in mitochondrial biogenesis (AMPK, PGC-1, NRF-1, SIRT-1, cytochrome c, citrate synthase), markers of oxidative stress (GSSG/GSH) or damage (MDA, carbonylated proteins), antioxidant enzymes (NRF-2, SOD1, SOD2, Catalase and PRDX6) and MAPKs (p38 and ERK ½) were also determined in skeletal muscle.
    RESULTS AND CONCLUSIONS: Our results show that GlcN supplementation in aerobically trained mice, at doses equivalent to those conventionally used in humans, increases the protein levels of mitochondrial biogenesis markers, improves motor coordination and may have a synergistic effect with exercise training on running distance.
  29. Neuromuscul Disord. 2021 Oct 02. pii: S0960-8966(21)00656-8. [Epub ahead of print]
      Facioscapulohumeral muscular dystrophy (FSHD) is a common genetic disease of the skeletal muscle with a characteristic pattern of weakness. Facioscapulohumeral muscular dystrophy type 2 (FSHD2) accounts for approximately 5% of all cases of FSHD and describes patients without a D4Z4 repeat contraction on chromosome 4. Phenotypically FSHD2 shows virtually no difference from FSHD1 and both forms of FSHD arise via a common downstream mechanism of epigenetic derepression of the transcription factor DUX4 in skeletal muscle cells. This results in expression of DUX4 and target genes leading to skeletal muscle toxicity. Over the past decade, major progress has been made in our understanding of the genetic and epigenetic architecture that underlies FSHD2 pathogenesis, as well as the clinical manifestations and disease progression. These include the finding that FSHD2 is a digenic disease and that mutations in the genes SMCHD1, DNMT3B, and more recently LRIF1, can cause FSHD2. FSHD2 is complex and it is important that clinicians keep abreast of recent developments; this review aims to serve as an update of the clinical, genetic, and molecular research into this condition.
    Keywords:  DNMT3B; DUX4; Epigenetic derepression; Facioscapulohumeral muscular dystrophy type 2; LRIF1; SMCHD1
  30. Mol Cell Biol. 2021 Oct 25. MCB0032721
      The activity of AMPKα is reduced in type-2 diabetes, and type-2 diabetes is associated with muscular atrophy. To date, there is little known about the mechanism by which FFA participates in muscular impairment. The purpose of the present study was to explore whether FFA damages myogenesis through AMPKα-HDAC4-miR-206 pathway. The results showed that 1mM FFA produced lipid accumulation, significantly impaired insulin signaling pathway and decreased myogenic differentiation of C2C12 myoblast cells. FFA reduced LKB1-AMPKα pathway; activation of AMPKα rescued the myogenic impairment caused by FFA (P < 0.05). AMPKα promoted myogenesis by regulating the expression of miR-206 through HDAC4 (P < 0.05); AMPKα affected cell cycle and cell proliferation to promote myogenesis by regulating miR-206 and miR-206's target gene - cyclin D1. In addition, AICAR and HDAC4 siRNA promoted myogenic differentiation compared with FFA group; however, this positive effect was significantly down-regulated after transfection of miR-206 inhibitor. In summary, AMPKα plays positive roles in myogenic differentiation and myogenesis, and FFA decreased myogenic differentiation and myotubes formation through AMPKα-HDAC4-miR-206 pathway.
  31. Scand J Med Sci Sports. 2021 Oct 27.
      The study aimed to identify and quantify the metabolites profile and metabolic pathways in human muscle tissue engaged during exhaustive high-intensity cycling exercise. Seven healthy physically active men performed a graded exercise test and an exhaustive supramaximal effort at 115% of maximal aerobic power with muscles biopsies performed in rest and immediately after exhaustion for quantifying of muscle metabolites changes by 1 H-NMR spectroscopy. The time until exhaustion (tlim) recorded was 224.7 ± 35.5 s whereas the muscle pH at exhaustion was 6.48 ± 0.05. A total of 54 metabolites were identified and quantified. The most enriched and impacted pathways included: beta oxidation of very long chain fatty acids, mitochondrial electron transport chain, alanine aspartate and glutamate metabolism, citric acid cycle, arginine biosynthesis, propanoate metabolism, threonine and 2-oxobutanoate degradation and pyruvate metabolism. In addition, the muscle concentrations in Post exercise, compared to Pre increased significantly (P < 0.0398) for fumarate (42.0%), succinate (101.2%), glucose (249.7%), lactate (122.8%), O-acetylcarnitine (164.7%), glycerol (79.3%), AMP (288.2%), 2-oxobutyrate (121.0%) and methanol (58.5%), whereas decreased significantly (P < 0.010) for creatine phosphate (-70.2%), ADP (-56.5%), carnitine (-33.5%) and glutamate (-42.3%). Only the succinate was significantly correlated with tlim (r = -0.76; P = 0.0497). Besides the classical expected contribution of glycolytic and phosphagen energetic pathways, it was demonstrated that the high-intensity exercise is also associated with pathways indicatives of amino acid and fatty acid oxidation metabolisms, highlighting the inverse relation between changes in the intramuscular succinate levels and tlim.
    Keywords:  Exercise Metabolism; Metabolomic; Skeletal Muscle; Supramaximal effort
  32. Curr Issues Mol Biol. 2021 Sep 25. 43(3): 1267-1281
      Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease caused by out-of-frame or nonsense mutation in the dystrophin gene. It begins with a loss of ambulation between 9 and 14 years of age, followed by various other symptoms including cardiac dysfunction. Exon skipping of patients' DMD pre-mRNA induced by antisense oligonucleotides (AOs) is expected to produce shorter but partly functional dystrophin proteins, such as those possessed by patients with the less severe Becker muscular dystrophy. We are working on developing modified nucleotides, such as 2'-O,4'-C-ethylene-bridged nucleic acids (ENAs), possessing high nuclease resistance and high affinity for complementary RNA strands. Here, we demonstrate the preclinical characteristics (exon-skipping activity in vivo, stability in blood, pharmacokinetics, and tissue distribution) of renadirsen, a novel AO modified with 2'-O-methyl RNA/ENA chimera phosphorothioate designed for dystrophin exon 45 skipping and currently under clinical trials. Notably, systemic delivery of renadirsen sodium promoted dystrophin exon skipping in cardiac muscle, skeletal muscle, and diaphragm, compared with AOs with the same sequence as renadirsen but conventionally modified by PMO and 2'OMePS. These findings suggest the promise of renadirsen sodium as a therapeutic agent that improves not only skeletal muscle symptoms but also other symptoms in DMD patients, such as cardiac dysfunction.
    Keywords:  2′-O,4′-C-ethylene-bridged nucleic acid (ENA); Duchenne muscular dystrophy; antisense oligonucleotide; cardiac muscle; dystrophin; exon skipping; renadirsen sodium
  33. Curr Issues Mol Biol. 2021 Sep 26. 43(3): 1293-1306
      Muscle is the largest tissue in our body and plays an important role in glucose homeostasis and hence diabetes. In the present study, we examined the effects of taxifolin (TXF) on glucose metabolism in cultured L6 muscle cells (myotubes) and in type 2 diabetic (T2D) model KK-Ay/Ta mice. TXF dose-dependently increased glucose uptake (GU) in L6 myotubes under the condition of insulin absence. This increase in GU was partially, but significantly canceled by TXF treatment in combination with either LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3K), which phosphorylates protein kinase B (Akt) or Compound C, an inhibitor of 5'-adenosine monophosphate-activated protein kinase (AMPK). Furthermore, TXF was demonstrated to activate (=phosphorylate) both Akt and AMPK, and promote glucose transporter 4 (GLUT4) translocation to the plasma membrane from cytosol of L6 myotubes via both PI3K/Akt and AMPK signaling pathways. Based on these in vitro findings, we conducted an in vivo experiment in KK-Ay/Ta mice with hyperglycemia and hyperuricemia. Fasting plasma glucose, insulin, uric acid levels and an index of insulin resistance (HOMA-IR) increased significantly in the T2D model mice compared with normal ones. Such rises in the T2D state were significantly suppressed by oral administration of TXF for four weeks. These results suggest that TXF is a potent antihyperglycemic and antihyperuricemic phytochemical in the T2D state.
    Keywords:  AMPK; Akt; GLUT4; KK-Ay/Ta mouse; L6 myotube; PI3K; hyperglycemia; hyperuricemia; taxifolin; type 2 diabetes
  34. Noncoding RNA. 2021 Oct 11. pii: 65. [Epub ahead of print]7(4):
      Despite advances in treatments and therapies, cardiovascular diseases (CVDs) remain one of the leading causes of death worldwide. The discovery that most of the human genome, although transcribed, does not encode proteins was crucial for focusing on the potential of long non-coding RNAs (lncRNAs) as essential regulators of cell function at the epigenetic, transcriptional, and post-transcriptional levels. This class of non-coding RNAs is related to the pathophysiology of the cardiovascular system. The different expression profiles of lncRNAs, in different contexts of CVDs, change a great potential in their use as a biomarker and targets of therapeutic intervention. Furthermore, regular physical exercise plays a protective role against CVDs; on the other hand, little is known about its underlying molecular mechanisms. In this review, we look at the accumulated knowledge on lncRNAs and their functions in the cardiovascular system, focusing on the cardiovascular pathology of arterial hypertension, coronary heart disease, acute myocardial infarction, and heart failure. We discuss the potential of these molecules as biomarkers for clinical use, their limitations, and how the manipulation of the expression profile of these transcripts through physical exercise can begin to be suggested as a strategy for the treatment of CVDs.
    Keywords:  aerobic training; biomarkers; cardiovascular disease; lncRNAs
  35. Autophagy. 2021 Oct 25. 1-18
      Mitochondrial remodeling is dysregulated in metabolic diseases but the underlying mechanism is not fully understood. We report here that BDNF (brain derived neurotrophic factor) provokes mitochondrial fission and clearance in skeletal muscle via the PRKAA/AMPK-PINK1-PRKN/Parkin and PRKAA-DNM1L/DRP1-MFF pathways. Depleting Bdnf expression in myotubes reduced fatty acid-induced mitofission and mitophagy, which was associated with mitochondrial elongation and impaired lipid handling. Muscle-specific bdnf knockout (MBKO) mice displayed defective mitofission and mitophagy, and accumulation of dysfunctional mitochondria in the muscle when they were fed with a high-fat diet (HFD). These animals also have exacerbated body weight gain, increased intramyocellular lipid deposition, reduced energy expenditure, poor metabolic flexibility, and more insulin resistance. In contrast, consuming a BDNF mimetic (7,8-dihydroxyflavone) increased mitochondrial content, and enhanced mitofission and mitophagy in the skeletal muscles. Hence, BDNF is an essential myokine to maintain mitochondrial quality and function, and its repression in obesity might contribute to impaired metabolism.Abbreviation: 7,8-DHF: 7,8-dihydroxyflavone; ACACA/ACC: acetyl Coenzyme A carboxylase alpha; ACAD: acyl-Coenzyme A dehydrogenase family; ACADVL: acyl-Coenzyme A dehydrogenase, very long chain; ACOT: acyl-CoA thioesterase; CAMKK2: calcium/calmodulin-dependent protein kinase kinase 2, beta; BDNF: brain derived neurotrophic factor; BNIP3: BCL2/adenovirus E1B interacting protein 3; BNIP3L/NIX: BCL2/adenovirus E1B interacting protein 3-like; CCL2/MCP-1: chemokine (C-C motif) ligand 2; CCL5: chemokine (C-C motif) ligand 5; CNS: central nervous system; CPT1B: carnitine palmitoyltransferase 1b, muscle; Cpt2: carnitine palmitoyltransferase 2; CREB: cAMP responsive element binding protein; DNM1L/DRP1: dynamin 1-like; E2: estrogen; EHHADH: enoyl-CoenzymeA hydratase/3-hydroxyacyl CoenzymeA dehydrogenase; ESR1/ER-alpha: estrogen receptor 1 (alpha); FA: fatty acid; FAO: fatty acid oxidation; FCCP: carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone; FFA: free fatty acids; FGF21: fibroblast growth factor 21; FUNDC1: FUN14 domain containing 1; HADHA: hydroxyacyl-CoA dehydrogenase trifunctional multienzyme complex subunit alpha; HFD: high-fat diet; iWAT: inguinal white adipose tissues; MAP1LC3A/LC3A: microtubule-associated protein 1 light chain 3 alpha; MBKO; muscle-specific bdnf knockout; IL6/IL-6: interleukin 6; MCEE: methylmalonyl CoA epimerase; MFF: mitochondrial fission factor; NTRK2/TRKB: neurotrophic tyrosine kinase, receptor, type 2; OPTN: optineurin; PA: palmitic acid; PARL: presenilin associated, rhomboid-like; PDH: pyruvate dehydrogenase; PINK1: PTEN induced putative kinase 1; PPARGC1A/PGC-1α: peroxisome proliferative activated receptor, gamma, coactivator 1 alpha; PRKAA/AMPK: protein kinase, AMP-activated, alpha 2 catalytic subunit; ROS: reactive oxygen species; TBK1: TANK-binding kinase 1; TG: triacylglycerides; TNF/TNFα: tumor necrosis factor; TOMM20: translocase of outer mitochondrial membrane 20; ULK1: unc-51 like kinase 1.
    Keywords:  BDNF; mitochondria; mitophagy; muscle; obesity
  36. Pak J Med Sci. 2021 ;37(6): 1569-1573
      Objective: To discuss the effects and function of LIPUS on muscle atrophy (MA), analysis from various aspects through the study of low-intensity pulsed ultrasound (LIPUS) information technology intervention (ITI) in diagnosis and the prediction of muscle atrophy..Method: In this study conducted in our university, 74 healthy female SD rats aged three months, weighing 100-200g were selected. All rats were placed in sterile cages from June 2020 to September 2020. They were divided into three groups. In the OVO group and OVE group, the mice are treated with LIPUS, Finally, the changes of body weight, grasping power, biochemical indexes and glycogen content of gastrocnemius muscle were analyzed and recorded to explore the effect and value of LIPUS ITI combined with intermittent weight-bearing exercise in the treatment of MA.
    Results: After weight-bearing running, the body weight of model (OVO) group, exercise (OVE) group and NC group had significant statistical significance (P<0.01). It was found that the weight of OVE group was much more as compared to OVO group. There was significant difference in body weight between OVO group and NC group (P<0.05). After LIPUS treatment, it was found that the weight of OVO group, OVE group, LIPUS group and OVE +LIPUS group increased. Compared with the NC group, there was significant statistical difference (P<0.01).
    Conclusion: Low intensity pulsed ultrasound ITI has a good effect on improving MA, so as to effectively improve the weight of gastrocnemius muscle. The combined application of the two is better for the improvement of muscular atrophy.
    Keywords:  LIPUS; MA; information technology; weight-bearing exercise