Slow Fibers Research Articles

Effects of Camellia japonica Roots Extract on Myoblast Differentiation and Muscle Atrophy in Association with Mitochondrial Function

ObjectivesSkeletal muscle atrophy is caused by various diseases and conditions including aging, cancer, and cancer treatments. Chemotherapy-induced muscle atrophy leads to decrease quality of life and increase morbidity and mortality. Recent evidence suggests oxidative stress is a cause and/or consequence of mitochondrial dysfunction, which is strongly associated with muscle atrophy. Given Camellia japonica roots extract (CJT) has antioxidant property, we investigated whether CJT would ameliorate myoblast differentiation and chemotherapy-induced muscle atrophy in vitro and in vivo to provide evidence for candidates to prevent and treat muscle atrophy. MethodsC2C12 myoblasts were differentiated in the presence of CJT (0.1, 1, 10, and 100 ng/mL) and cells were collected to perform myosin heavy chain (MHC) immunostaining and qRT-PCR for the measurement of markers related with myogenesis and mitochondrial function. Wild type AB * zebrafish (Danio rerio) embryos were treated with FOLFIRI (5-FU, LV, and CPT-11) and CJT, and immunostained to detect slow and fast types of muscle. The Tg(Xla.Eef1a1: mlsEGFP) zebrafish line expressing mitochondria-targeted green fluorescent protein (mito-GFP) was used to monitor mitochondrial morphology. ResultsCJT increased the formation of MHC-positive multinucleated myotubes (≥5 nuclei) in a dose-dependent manner, while it decreased the number of mononuclear myotubes. CJT significantly enhanced the expression of myogenic differentiation markers including Myod (early stage), Myog (mid stage), and MHC isoforms (late stage) including Myh 1, Myh 2, Myh 4, and Myh7. Mitochondrial biogenesis markers such as SDHA (Complex Ⅱ) and COX1 (Complex IV) were significantly increased at 100 ng/mL of CJT than control. CJT tended to increase the expression of MFN2 and NRF1 involved in mitochondrial fusion and biogenesis, respectively. In addition, CJT alleviated FOLFIRI-induced muscle atrophy both in slow and fast muscle fibers in zebrafish embryos. Similarly, CJT improved FOLFIRI-induced mitochondrial dysfunction in a dose-dependent manner. ConclusionsOur data indicates that CJT promotes myogenesis and alleviates muscle atrophy in association with mitochondrial function, suggesting CJT has potential as a nutritional supplement for the prevention and treatment of muscle atrophy. Funding SourcesNRF (2020R1C1C1007553 to S-EK)

Effect of dietary L-theanine supplementation on skeletal muscle fiber type transformation in weaning piglets

The aim of this study was to explore the effect of dietary L-theanine (LT) supplementation on skeletal muscle fiber type transformation in weaning piglets. Our data showed that LT significantly increased the slow-twitch fiber-related genes expression and the percentage of slow oxidative fiber, and decreased the MyHC IIb mRNA expression and the percentage of fast glycolytic fiber. In addition, LT significantly increased the succinic dehydrogenase (SDH) and malate dehydrogenase (MDH) activities and increased the LDH activities. In addition, LT significantly affected mitochondrial biogenesis and function and antioxidative related genes expression, and increased the protein expression of p-adenosine monophosphate (AMP)-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), nuclear factor E2-related factor 2 (Nrf2), NADPH quinone oxidoreductase-1 (NQO1) and heme oxygenase-1 (HO-1) and decreased the Keap1 protein levels. Furthermore, our data indicated that LT significantly increased the mRNA and protein expression of prospero-related homeobox 1 (Prox1), calcineurin A (CnA), and NFATc1, suggesting that dietary LT supplementation promoted skeletal muscle fiber transition from types II to I might be via activation of calcineurin signaling pathway. Taken together, these findings suggested that LT promoted the transformation of muscle fiber types from slow oxidative to fast glycolytic by increasing antioxidant capacity and improving mitochondrial biogenesis and function and activation of calcineurin signaling pathway.

Severe Diaphragm Fiber Weakness And Normal Response To Intraoperative Phrenic Stimulation In An ECMO‐Dependent Adult Receiving Lung Transplant

IntroductionProlonged mechanical ventilation (MV) places patients at an increased risk for ventilator‐induced diaphragm dysfunction (VIDD), which can delay weaning from MV. We previously reported that intraoperative phrenic stimulation may preserve diaphragm fiber contractile function in those undergoing cardiac surgeries, but benefits are unclear in those with significant pulmonary disease who require extracorporeal membrane oxygenation (ECMO) support.Case DescriptionA 55‐year‐old male with end‐stage pulmonary fibrosis underwent bilateral lung transplantation (LTX) after a two‐week pre‐operative hospitalization that included ECMO support. Phrenic stimulation commenced upon initial surgical exposure of the diaphragm, and supramaximal twitch stimulations were administered every 30 minutes to one hemidiaphragm over 136 minutes. The contralateral side served as an inactive control. Diaphragm biopsies of the LTX patient were acquired after 5 stimulations. Maximal single‐fiber diaphragm twitch force was then compared to nine male participants (56 (12) years) admitted for cardiac bypass or valvuloplasty surgery, who underwent 6 (1) bouts of unilateral intraoperative stimulation followed by diaphragm biopsy. In each subject, we tested maximal single‐fiber force on an average of 22 (4) slow‐ and 22 (3) fast‐twitch fibers.Compared to cardiac surgical patients, the LTX subject had increased slow fiber cross‐sectional area (CSA) (Control side, cardiac: slow 5166 (1645) mm2; fast 6792 (732) mm2; LTX: slow 6827 (1504) mm2; fast 6159 (1173) mm2). Diaphragm fiber CSA of the stimulated side trended higher in the LTX patient (slow: 8588 (1908) mm2, p=0.080 vs control side; fast: 7232 (1976) mm2, p=0.094 vs control). Specific force (absolute force normalized to fiber CSA) in LTX was reduced by ~32% in slow fibers and ~30% in fast fibers (Table), as compared to cardiac patients. Specific force of stimulated fibers trended higher for slow‐ but not fast‐twitch fibers in LTX; response to stimulation resembled that of cardiac surgical patients. The patient was extubated 26 hours post‐LTX, as compared to 12 (7) hours in the cardiac patients.Impact (Novelty and Importance)This novel model of functional electrical stimulation suggests that phrenic stimulation preserved fiber CSA in an ECMO‐dependent adult with pulmonary fibrosis. Phrenic stimulation increased maximal specific force in slow‐twitch fibers, but responding forces remained well below expected values. These findings suggest that critically ill adult recipients of LTX may require additional duration and volume of diaphragm training, whether through voluntary or evoked contractions, to recover functional inspiratory muscle strength post‐operatively.

RPI‐194 is a Novel Troponin Activator that Increases the Calcium Sensitivity of Striated Muscle Contraction

IntroductionSystolic heart failure is a cardiac disease in which the contractile function of heart muscle becomes weakened and unable to pump blood with adequate force. As of yet, no existing positive inotrope is able to lower the mortality rate in systolic heart failure. Cardiac troponin complex (cTn) is a trimeric complex consisting of troponin C (cTnC), troponin I (cTnI) and troponin T (cTnT). cTnC regulates blood supply to the heart by turning muscle contraction on and off in a calcium‐dependent manner. More precisely, the regulatory N‐domain of cTnC (cNTnC) binds the switch region of cTnI to activate contraction. Drug‐like molecules need to bind to this cNTnC‐cTnI switch region interface and modulate the pumping activity of the heart. Our objective was to identify a small molecule that has the ability to stabilize the activated conformation of cTn by binding to this interface and thereby enhance cardiac muscle contraction.HypothesisA cardiac troponin activator could potentially compensate the impaired contractile function of the heart in the treatment of systolic heart failureMethodsA total of 47 new compounds were designed using existing knowledge of calcium sensitizers. The compounds were screened against a recombinantly purified cNTnC‐cTnI chimeric construct, named gChimera, using nuclear magnetic resonance and fluorescence spectroscopy. We identified a novel small molecule cardiac troponin activator, RPI‐194, and measured its binding affinity to recombinantly purified cNTnC and gChimera. We also investigated the activity of RPI‐194 in rat skinned cardiac muscle trabeculae, isolated mouse cardiomyocytes, and isolated working mouse hearts. RPI‐194 activity was also tested in skinned skeletal muscle fibers from rats as both cardiac and slow skeletal muscle share the same isoform of cTnC.ResultsWe demonstrated that a small molecule troponin activator RPI‐194 binds to gChimera with a KD of 12‐24 µM and is able to stabilize activated cTn. It also slowed down the rate of calcium release from reconstituted cTn. RPI‐194 showed increasing calcium sensitivity of isometric contraction in skinned cardiac muscle trabeculae, as well as in slow and fast skeletal muscle fibers, suggesting it to be a calcium sensitizer, with cross‐reactivity within striated muscle. Contrarily, RPI‐194 was unable to slow down calcium release from isolated cNTnC. It also reduced the velocity of unloaded shortening in skeletal muscle fibers, suggesting that it slows the rate of actin‐myosin cross‐bridging, although no effect on myosin ATPase activity was found. RPI‐194 decreased the velocity and amplitude of contractions in isolated cardiomyocytes but contractility was preserved in isolated working hearts.ConclusionsRPI‐194 is a small molecule troponin activator that acts as a calcium sensitizer in striated muscle. Because of the isoform sharing of cTnC in cardiac and slow skeletal muscle, it is nearly impossible to develop a cardiac‐specific troponin activator. Whole animal model studies are needed to determine the impact of RPI‐194 on the different striated muscle types and whether this would be acceptable for therapeutic intervention.

Impaired signaling for neuromuscular synaptic maintenance is a feature of Motor Neuron Disease

A central event in the pathogenesis of motor neuron disease (MND) is the loss of neuromuscular junctions (NMJs), yet the mechanisms that lead to this event in MND remain to be fully elucidated. Maintenance of the NMJ relies upon neural agrin (n-agrin) which, when released from the nerve terminal, activates the postsynaptic Muscle Specific Kinase (MuSK) signaling complex to stabilize clusters of acetylcholine receptors. Here, we report that muscle from MND patients has an increased proportion of slow fibers and muscle fibers with smaller diameter. Muscle cells cultured from MND biopsies failed to form large clusters of acetylcholine receptors in response to either non-MND human motor axons or n-agrin. Furthermore, levels of expression of MuSK, and MuSK-complex components: LRP4, Caveolin-3, and Dok7 differed between muscle cells cultured from MND patients compared to those from non-MND controls. To our knowledge, this is the first time a fault in the n-agrin-LRP4-MuSK signaling pathway has been identified in muscle from MND patients. Our results highlight the n-agrin-LRP4-MuSK signaling pathway as a potential therapeutic target to prolong muscle function in MND.

Muscle fiber type-dependence effect of exercise on genomic networks in aged mice models.

Skeletal muscles are made up of various muscle fiber type including slow and fast-twitch fibers. Because each muscle fiber has its own physiological characteristics, the effects of aging and exercise vary depending on the type of muscle fiber. We used bioinformatics screening techniques such as differentially expressed gene analysis, gene ontology analysis and gene set enrichment analysis, to try to understand the genetic differences between muscle fiber types. The experiment and gene expression profiling in this study used the soleus (SOL, slow-twitch muscle) and gastrocnemius (GAS, fast-twitch muscle). According to our findings, fatty acid metabolism is significantly up-regulated in SOL compared to GAS, whereas the glucose metabolism pathway is significantly down-regulated in SOL compared to GAS.Furthermore, apoptosis and myogenesis patterns differ between SOL and GAS. SOL did not show differences in apoptosis due to the aging effect, but apoptosis in GAS was significantly up-regulated with age. Apoptosis in GAS of old groups is significantly reduced after 4 weeks of aerobic exercise, but no such finding was found in SOL. In terms of myogenesis, exercise intervention up-regulated this process in GAS of old groups but not in SOL. Taken together, muscle fiber type significantly interacts with aging and exercise. Despite the importance of the interaction between these factors, large-scale gene expression data has rarely been studied. We hope to contribute to a better understanding of the relationship between muscle fiber type, aging and exercise at the molecular level.

The beneficial effect of chronic muscular exercise on muscle fragility is increased by Prox1 gene transfer in dystrophic mdx muscle.

Greater muscle fragility is thought to cause the exhaustion of the muscle stem cells during successive degeneration/repair cycles, leading to muscle wasting and weakness in Duchenne muscular dystrophy. Chronic voluntary exercise can partially reduce the susceptibility to contraction induced-muscle damage, i.e., muscle fragility, as shown by a reduced immediate maximal force drop following lengthening contractions, in the dystrophic mdx mice. Here, we studied the effect of Prospero-related homeobox factor 1 gene (Prox1) transfer (overexpression) using an AAV on fragility in chronically exercised mdx mice, because Prox1 promotes slower type fibres in healthy mice and slower fibres are less fragile in mdx muscle. Both tibialis anterior muscles of the same mdx mouse received the transfer of Prox1 and PBS and the mice performed voluntary running into a wheel during 1 month. We also performed Prox1 transfer in sedentary mdx mice. In situ maximal force production of the muscle in response to nerve stimulation was assessed before, during and after 10 lengthening contractions. Molecular muscle parameters were also evaluated. Interestingly, Prox1 transfer reduced the isometric force drop following lengthening contractions in exercised mdx mice (p < 0.05 to 0.01), but not in sedentary mdx mice. It also increased the muscle expression of Myh7 (p < 0.001), MHC-2x (p < 0.01) and Trpc1 (p < 0.01), whereas it reduced that one of Myh4 (p < 0.001) and MHC-2b (p < 0.01) in exercised mdx mice. Moreover, Prox1 transfer decreased the absolute maximal isometric force (p < 0.01), but not the specific maximal isometric force, before lengthening contraction in exercised (p < 0.01) and sedentary mdx mice. Our results indicate that Prox1 transfer increased the beneficial effect of chronic exercise on muscle fragility in mdx mice, but reduced absolute maximal force. Thus, the potential clinical benefit of the transfer of Prox1 into exercised dystrophic muscle can merit further investigation.

Sirt6 reprograms myofibers to oxidative type through CREB-dependent Sox6 suppression

Expanding the exercise capacity of skeletal muscle is an emerging strategy to combat obesity-related metabolic diseases and this can be achieved by shifting skeletal muscle fibers toward slow-twitch oxidative type. Here, we report that Sirt6, an anti-aging histone deacetylase, is critical in regulating myofiber configuration toward oxidative type and that Sirt6 activator can be an exercise mimetic. Genetic inactivation of Sirt6 in skeletal muscle reduced while its transgenic overexpression increased mitochondrial oxidative capacity and exercise performance in mice. Mechanistically, we show that Sirt6 downregulated Sox6, a key repressor of slow fiber specific gene, by increasing the transcription of CREB. Sirt6 expression is elevated in chronically exercised humans, and mice treated with an activator of Sirt6 showed an increase in exercise endurance as compared to exercise-trained controls. Thus, the current study identifies Sirt6 as a molecular target for reprogramming myofiber composition toward the oxidative type and for improving muscle performance.

Numerical Analysis of Parameter Optimization in Slow Light Phase-Shifted Fiber Bragg Gratings

Numerical Analysis of Parameter Optimization in Slow Light Phase-Shifted Fiber Bragg Gratings

Transcriptomic Analysis for Pork Color—The Ham Halo Effect in Biceps Femoris

Pork color is a major indicator of product quality that guides consumer purchasing decisions. Recently, industryhas received an increase in consumer complaints about the lightness and nonuniformity of ham color, primarily lighter colorin the periphery termed “ham halo” that is not caused by manufacturing procedures. This effect is seen in fresh and processed hams and the outer lighter muscle is associated with lower myoglobin concentration, pH, and type I fibers. The objective of this study was to identify differences in gene expression profiles between light and normal-colored portions of the biceps femoris muscle from pork hams. RNA-sequencing (RNA-seq) was performed for paired light and normal-colored muscle samples from 10 animals showing the ham halo effect. Over 50 million paired-end reads (2×75 bp) per library were obtained. An average of 99.74% of trimmed high-quality reads was mapped to the Sscrofa 11.1 genome assembly. Differentially expressed genes (DEGs) were identified using both the DESeq2 and GFOLD software packages. A total of 14,049 genes were expressed in the biceps femoris; 13,907 were expressed in both light and normal muscle, while 56 and 86 genes were only expressed in light and normal muscle, respectively. Analysis with DESeq2 identified 392 DEGs with 359 genes being more highly expressed in normal-colored muscle. A total of 61 DEGs were identified in the DESeq2 analysis and identified in at least 7 of the 10 individual animal analyses. All 61 of these DEGs were up-regulated in normal-colored muscle. Gene Ontology enrichment analysis of DEGs identified the transition between fast and slow fibers and skeletal muscle adaptation and contraction as the most significant biological process terms. The evaluation of gene expression by RNA-seq identified DEGs between regions of the biceps femoris with the ham halo effect that are associated with variation in pork color.

Exercise-mediated reinnervation of skeletal muscle in elderly people: An update.

Sarcopenia is defined by the loss of muscle mass and function. In aging sarcopenia is due to mild chronic inflammation but also to fiber-intrinsic defects, such as mitochondrial dysfunction. Age-related sarcopenia is associated with physical disability and lowered quality of life. In addition to skeletal muscle, the nervous tissue is also affected in elderly people. With aging, type 2 fast fibers preferentially undergo denervation and are reinnervated by slow-twitch motor neurons. They spread forming new neuro-muscular junctions with the denervated fibers: the result is an increased proportion of slow fibers that group together since they are associated in the same motor unit. Grouping and fiber type shifting are indeed major histological features of aging skeletal muscle. Exercise has been proposed as an intervention for age-related sarcopenia due to its numerous beneficial effects on muscle mechanical and biochemical features. In 2013, a precursor study in humans was published in the European Journal of Translation Myology (formerly known as Basic and Applied Myology), highlighting the occurrence of reinnervation in the musculature of aged, exercise-trained individuals as compared to the matching control. This paper, entitled «Reinnervation of Vastus lateralis is increased significantly in seniors (70-years old) with a lifelong history of high-level exercise», is now being reprinted for the second issue of the «Ejtm Seminal Paper Series». In this short review we discuss those results in the light of the most recent advances confirming the occurrence of exercise-mediated reinnervation, ultimately preserving muscle structure and function in elderly people who exercise.

MiR-208b Regulates the Conversion of Skeletal Muscle Fiber Types by Inhibiting Mettl8 Expression

Skeletal muscle, the main source of animal meat products, contains muscle fiber as a key unit. It is well known that transformation takes place between different types of muscle fibers, however, the conversion mechanism is not clear. In a previous study, our lab has demonstrated that there is a decrease in type I muscle fibers and an increase in type IIB muscle fibers in skeletal muscle of myostatin gene-edited Meishan pigs. Very interestingly, we observed the down regulation of miR-208b expression and an increase in expression the predicted target gene Mettl8 (Methyltransferase like 8) in skeletal muscle of MSTN gene-edited Meishan pigs. These results reveal that there is a potential connection between the conversion of skeletal muscle fiber types and miR-208b and Mettl8 expression. In this study, we first explored the expression patterns of miR-208b and Mettl8 in skeletal muscle in Meishan pigs; and then C2C12 cells were used to simulate the development and maturation of muscle fibers. Our results indicated that Myh4 expression level decreased and Myh7 expression level increased following overexpression of miR-208b in C2C12 cells. We therefore speculate that miR-208b can promote the conversion of fast-twitch fibers to slow-twitch fibers. The targeting relationship between Mettl8 and miR-208b was confirmed by results obtained using dual luciferase assay, RT-qPCR, and WB analysis. Following the transfection of Mettl8 siRNA into C2C12 cells, we observed that Mettl8 expression decreased significantly while Myh7 expression increased and Myh4 expression decreased, indicating that Mettl8 promotes the conversion of slow muscle fibers to fast muscle fibers. Additionally, changes in skeletal muscle fiber types are observed in those mice where miR-208b and Mettl8 genes are knocked out. The miR-208b knockout inhibits the formation of slow muscle fibers, and the Mettl8 knockout inhibits the formation of fast muscle fibers. In conclusion, our research results show that miR-208b regulates the conversion of different muscle fiber types by inhibiting Mettl8 expression.

DHA alleviates diet-induced skeletal muscle fiber remodeling via FTO/m6A/DDIT4/PGC1\u03b1 signaling

BackgroundObesity leads to a decline in the exercise capacity of skeletal muscle, thereby reducing mobility and promoting obesity-associated health risks. Dietary intervention has been shown to be an important measure to regulate skeletal muscle function, and previous studies have demonstrated the beneficial effects of docosahexaenoic acid (DHA; 22:6 ω-3) on skeletal muscle function. At the molecular level, DHA and its metabolites were shown to be extensively involved in regulating epigenetic modifications, including DNA methylation, histone modifications, and small non-coding microRNAs. However, whether and how epigenetic modification of mRNA such as N6-methyladenosine (m6A) mediates DHA regulation of skeletal muscle function remains unknown. Here, we analyze the regulatory effect of DHA on skeletal muscle function and explore the involvement of m6A mRNA modifications in mediating such regulation.ResultsDHA supplement prevented HFD-induced decline in exercise capacity and conversion of muscle fiber types from slow to fast in mice. DHA-treated myoblasts display increased mitochondrial biogenesis, while slow muscle fiber formation was promoted through DHA-induced expression of PGC1α. Further analysis of the associated molecular mechanism revealed that DHA enhanced expression of the fat mass and obesity-associated gene (FTO), leading to reduced m6A levels of DNA damage-induced transcript 4 (Ddit4). Ddit4 mRNA with lower m6A marks could not be recognized and bound by the cytoplasmic m6A reader YTH domain family 2 (YTHDF2), thereby blocking the decay of Ddit4 mRNA. Accumulated Ddit4 mRNA levels accelerated its protein translation, and the consequential increased DDIT4 protein abundance promoted the expression of PGC1α, which finally elevated mitochondria biogenesis and slow muscle fiber formation.ConclusionsDHA promotes mitochondrial biogenesis and skeletal muscle fiber remodeling via FTO/m6A/DDIT4/PGC1α signaling, protecting against obesity-induced decline in skeletal muscle function.

Muscle length has a greater effect on the rate of relaxation in slow-twitch rat soleus muscle than fast-twitch EDL muscle

Mammalian skeletal muscle is composed of mixtures of slow-twitch fibers and fast-twitch fibers. We compared the relaxation kinetics of purely fast fiber rat EDL muscle and highly pure slow fiber rat soleus muscle from both intact and permeabilized preparations at different lengths. In the intact muscle study, the muscles were activated at optimal length (Lo), 95% of Lo, and 90% of Lo. After a tetanus, EDL relaxed with a half-time of 65±2 ms at Lo, 64±1 ms at 95% of Lo, and 63±1 ms at 90% of Lo (p< 0.05).

Effect of Porcine Whole Blood Protein Hydrolysate on Slow-Twitch Muscle Fiber Expression and Mitochondrial Biogenesis via the AMPK/SIRT1 Pathway

Skeletal muscle is a heterogeneous tissue composed of a variety of functionally different fiber types. Slow-twitch type I muscle fibers are rich with mitochondria, and mitochondrial biogenesis promotes a shift towards more slow fibers. Leucine, a branched-chain amino acid (BCAA), regulates slow-twitch muscle fiber expression and mitochondrial function. The BCAA content is increased in porcine whole-blood protein hydrolysates (PWBPH) but the effect of PWBPH on muscle fiber type conversion is unknown. Supplementation with PWBPH (250 and 500 mg/kg for 5 weeks) increased time to exhaustion in the forced swimming test and the mass of the quadriceps femoris muscle but decreased the levels of blood markers of exercise-induced fatigue. PWBPH also promoted fast-twitch to slow-twitch muscle fiber conversion, elevated the levels of mitochondrial biogenesis markers (SIRT1, p-AMPK, PGC-1α, NRF1 and TFAM) and increased succinate dehydrogenase and malate dehydrogenase activities in ICR mice. Similarly, PWBPH induced markers of slow-twitch muscle fibers and mitochondrial biogenesis in C2C12 myotubes. Moreover, AMPK and SIRT1 inhibition blocked the PWBPH-induced muscle fiber type conversion in C2C12 myotubes. These results indicate that PWBPH enhances exercise performance by promoting slow-twitch muscle fiber expression and mitochondrial function via the AMPK/SIRT1 signaling pathway.

Exercise Capacity Is Improved by Levosimendan in Heart Failure and Sarcopenia via Alleviation of Apoptosis of Skeletal Muscle.

BackgroundPatients suffering from chronic heart failure (CHF) show an increased prevalence of sarcopenia. Levosimendan is an effective drug for the treatment of heart failure, but its effect on sarcopenia is still unclear. We aimed to explore whether levosimendan could enhance skeletal muscle contractibility, improve skeletal muscle atrophy, and thus improve exercise tolerance of individuals with heart failure.MethodsC57BL6/J mice were used to establish the heart failure with sarcopenia model and injected of levosimendan. Mice were separated into control group, sham operation group, HF group, HF + solvent group, HF + levosimendan group, HF + sarcopenia group, HF + sarcopenia + solvent group, HF + sarcopenia + levosimendan group (n = 5–12). After the treatment, exercise capacity and cardiac function were evaluated. Muscle morphology, inflammation level and apoptosis levels were detected, in which mitochondrial function and oxidative stress level were also assessed.ResultLevosimendan could increase forelimb grip strength/body weight, hanging impulse, maximum running distance and time in mice with HF and sarcopenia (P < 0.0001 for all), and these improvements were independent of EF (P = 0.0019 for hanging impulse, P < 0.001 for forelimb grip strength/body weight and maximum running distance). Levosimendan directly increased the CSA of gastrocnemius in mice with HF and sarcopenia (P < 0.0001). After levosimendan injection, the proportion of slow muscle fibers increased (P < 0.0001), but this improvement of muscle fiber typing might be attributed to improved cardiac function (P > 0.05). Levosimendan also maintained mitochondrial membrane potential, decreased cleaved caspase-3 (P = 0.034), cleaved caspase-9 (P < 0.0001), Bax expression (P < 0.0001), and increased Bcl2 expression (P = 0.0036). This effect is independent of improved cardiac function (P = 0.028 for bax, P < 0.001 for cleaved caspase-9 and Bcl2). IL-6, TNF-α expression (P < 0.0001 for both) decreased, and SOD activity (P = 0.0038), GSH/GSSG ratio (P = 0.002) significantly increased in skeletal muscle after injection of levosimendan. The improvement in oxidative stress level was attributed to improved cardiac function (P > 0.05).ConclusionLevosimendan reduce the loss of skeletal muscle mitochondrial membrane potential, decrease the apoptosis, alleviate the inflammation and oxidative stress, and ultimately improve the exercise capacity of mice with heart failure and sarcopenia. Therefore, levosimendan may be a potential drug for the treatment of heart failure with sarcopenia.

Luteolin increases slow muscle fibers via FLCN-AMPK-PGC-1α signaling pathway

• Luteolin may improve endurance exercise capacity of mice. • Luteolin may increase slow muscle fibers proportion both in mice and C2C12 myotubes. • Luteolin may activate FLCN-AMPK-PGC-1α axis in mice’s muscle and C2C12 myotubes. • FLCN-AMPK-PGC-1α axis may play key role in luteolin induced slow myofibers increasing. While the regulating mechanisms of slow myofibers have been gradually explored, there are currently a lack of effective means to increase slow myofibers proportion. Here, we have showed that luteolin could markedly improve endurance exercise performance and increase body oxygen consumption of mice, and activate aerobic enzyme activity and slow myofibers related genes and proteins expression in mice’s skeletal muscle. Meanwhile, folliculin (FLCN)-AMP-activated protein kinase (AMPK) -peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) pathway was activated by treatment luteolin in the tissues. Furthermore, by in vitro investigation and FLCN lentivirus infection, we have found that the over-expression of FLCN significantly reduces the effects of luteolin on slow myofibers expression and AMPK-PGC-1α axis activation. Together, our results indicate that luteolin can increase the proportion of slow myofibers probably by FLCN-AMPK-PGC-1α pathway. These findings provide a novel approach to increase slow muscle fibers proportion and improve skeletal muscle fitness.

Modified collision study to isolate and study small fibre neuropathy in patients with Type 2 diabetes.

Introduction:Diabetic distal symmetrical polyneuropathy (DSPN) can be categorized as small fibre, large fibre, and mixed neuropathy. Even though small fibre neuropathy is the most prevalent, unfortunately it is usually not recognized by routine electrophysiologic studies. In this study, we intend to examine the slow velocity small fibres responsible for small fibre DSPN, by isolating them using collision technique principle in patients with diabetes.Methods:This is an observational case-control study designed to compare nerve conduction values with application of collision technique in 60 patients with T2D and in 60 age and sex matched controls.Results:The collision study in patients with Type 2 Diabetes showed mean Latency of 10.5 ± 1.7 ms and mean Amplitude of 3.4 ± 2.3 mV on the right side and mean Latency of 10.5 ± 1.7 ms and the mean Amplitude of 3.5 ± 2.2 mV on the left side. There was a statistically significant difference (P value < 0.001) in the amplitute and latency of CNAPs of small fibres in median nerve innervated APBs of both arms between those with T2D and controls.Discussion and Conclusion:Collision study helps to examine the slower conducting fibres of the larger nerves. Our study suggests that the Collision Technique can be used to identify early peripheral neuropathy regardless of the diabetes status, thus making it more practically feasible and cost-effective.

Analysis of Masticatory Muscle Tendon-aponeurosis Hyperplasia by Using Next-generation Sequencing.

Masticatory muscle tendon-aponeurosis hyperplasia (MMTAH) is a disease associated with a mouth opening limitation. Here, we conducted a bioinformatics analysis to examine gene expression patterns in patients with MMTAH in comparison to those with facial deformity (FD). Seven MMTAH patients and three FD patients were recruited. We conducted RNA sequencing analysis, quantitative reverse transcription polymerase chain reaction and immunoblot analysis. Of the identified 19,767 mapped read tags that showed clear differential expression, 2,471 genes were significantly up-regulated and 2,849 genes were significantly down-regulated in patients with MMTAH compared to those in patients with FD. Among the up-regulated genes, ten genes were significantly increased. The distribution of up-regulated and down-regulated genes at different ages tended to be similar. Moreover, the protein levels of Ankyrin Repeat Domain 2, Troponin T1 and myosin heavy chain 7, which are associated with slow twitch fibers and mechanical loading, were strongly expressed in patients with MMTAH compared to those in patients with FD. The gene expression pattern in MMTAH patients was similar regardless of age. As the transition of fast-to-slow twitch in the skeletal muscle is induced by mechanical loading, and up-regulation of slow twitch molecules was observed in MMTAH patients, mechanical loading is suggested to be implicated in MMTAH.

Transient neonatal exposure to hyperoxia, an experimental model of preterm birth, leads to skeletal muscle atrophy and fiber type switching.

Individuals born preterm show reduced exercise capacity and increased risk for pulmonary and cardiovascular diseases, but the impact of preterm birth on skeletal muscle, an inherently critical part of cardiorespiratory fitness, remains unknown. We evaluated the impacts of preterm birth-related conditions on the development, growth, and function of skeletal muscle using a recognized preclinical rodent model in which newborn rats are exposed to 80% oxygen from days 3 to 10 of life. We analyzed different hindlimb muscles of male and female rats at 10 days (neonatal), 4 weeks (juvenile), and 16 weeks (young adults). Neonatal high oxygen exposure increased the generation of reactive oxygen species (ROS) and the signs of inflammation in skeletal muscles, which was associated with muscle fiber atrophy, fiber type shifting (reduced proportion of type I slow fibers and increased proportion of type IIb fast-fatigable fibers), and impairment in muscle function. These effects were maintained until adulthood. Fast-twitch muscles were more vulnerable to the effects of hyperoxia than slow-twitch muscles. Male rats, which expressed lower antioxidant defenses, were more susceptible than females to oxygen-induced myopathy. Overall, preterm birth-related conditions have long-lasting effects on the composition, morphology, and function of skeletal muscles; and these effects are sex-specific. Oxygen-induced changes in skeletal muscles could contribute to the reduced exercise capacity and to increased risk of diseases of preterm born individuals.