Skeletal Muscle Type Research Articles

Muscle hypertrophy and ladder-based resistance training for rodents: A systematic review and meta-analysis.

This study aimed to review the effects of ladder‐based resistance training (LRT) on muscle hypertrophy and strength in rodents through a systematic review with meta‐analysis. We systematically searched PubMed/Medline, SportDiscuss, Scopus, Google Scholar, Science Direct, and Scielo database on May 18, 2020. Thirty‐four studies were included measuring total (mCSA) or mean muscle fibers cross‐sectional area (fCSA) or maximum load‐carrying capacity (MLCC) or muscle mass (MM). About the main results, LRT provides sufficient mechanical stimulation to increase mCSA and fCSA. Meta‐analysis showed a significant overall effect on the fCSA (SMD 1.89, 95% CI [1.18, 2.61], p < .00001, I 2 = 85%); however, subgroup analysis showed that some muscle types might not be hypertrophied through the LRT. Meta‐analysis showed a significant training effect on the MM (SMD 0.92, 95% CI [0.52, 1.32], p < .00001, I 2 = 72%). Sub‐group analysis revealed that soleus (SMD 1.32, 95% CI [0.11, 2.54], p = .03, I 2 = 86%) and FHL (SMD 1.92, 95% CI [1.00, 2.85], p < .0001, I 2 = 71%) presented significant training effects, despite moderate heterogeneity levels (I 2 = 72%). MLCC increases considerably after a period of LRT, regardless of its duration and the characteristics of the protocols (SMD 12.37, 95% CI [9.36, 15.37], p < .00001, I 2 = 90%). Through these results, we reach the following conclusions: (a) LRT is efficient to induce muscle hypertrophy, although this effect varies between different types of skeletal muscles, and; (b) the ability of rodents to carry load increases regardless of the type and duration of the protocol used.

Pathway attenuation of fatty acid beta-oxidation in the skeletal muscle of a type 2 diabetic mouse model.

Whether catabolic abnormalities of fatty acids exist in the skeletal muscle of type 2 diabetes mellitus (T2DM) has not been determined. In this study, we postulated that a systematic evaluation of the protein abundance and metabolic activity related to fatty acids in the skeletal muscle tissues of a T2DM mouse model was feasible to address this question. Mitochondria were extracted from wild-type (WT) and db/db mice followed by quantitative analysis of the proteins involved in mitochondrial fatty acid oxidation (mFAO). The pathway activity of mFAO in skeletal muscle tissues was monitored in vitro using mass spectrometry, and tissue lipidomic analysis was conducted in profiling and target mode to distinguish the levels of long-chain acylcarnitines between WT and db/db mice. Two proteins related to the mFAO pathway were significantly downregulated in the skeletal muscle mitochondria of db/db mice. The measurement of mFAO pathway activity in vitro revealed that the abundance of long-chain acylcarnitines (C14 to C18) in db/db mice was lower than that in WT mice, and the determination of acylcarnitines in skeletal muscle tissues in vivo revealed that most long-chain acylcarnitines were decreased in db/db mice. The findings of lower abundance of ACAD9 and CPT1B, reduced activity of the mFAO pathway in vitro and decreased acylcarnitines in vivo firmly support that the mFAO pathway in the skeletal muscle of diabetic mice is attenuated, possibly resulting in cell/tissue dysfunction in diabetes.

Effect of post-exercise lactate administration on glycogen repletion and signaling activation in different types of mouse skeletal muscle.

Lactate is not merely a metabolic intermediate that serves as an oxidizable and glyconeogenic substrate, but it is also a potential signaling molecule. The objectives of this study were to investigate whether lactate administration enhances post-exercise glycogen repletion in association with cellular signaling activation in different types of skeletal muscle. Eight-week-old male ICR mice performed treadmill running (20 m/min for 60 min) following overnight fasting (16 h). Immediately after the exercise, animals received an intraperitoneal injection of phosphate-buffered saline or sodium lactate (equivalent to 1 g/kg body weight), followed by oral ingestion of water or glucose (2 g/kg body weight). At 60 min of recovery, glucose ingestion enhanced glycogen content in the soleus, plantaris, and gastrocnemius muscles. In addition, lactate injection additively increased glycogen content in the plantaris and gastrocnemius muscles, but not in the soleus muscle. Nevertheless, lactate administration did not significantly alter protein levels related to glucose uptake and oxidation in the plantaris muscle, but enhanced phosphorylation of TBC1D1, a distal protein regulating GLUT4 translocation, was observed in the soleus muscle. Muscle FBP2 protein content was significantly higher in the plantaris and gastrocnemius muscles than in the soleus muscle, whereas MCT1 protein content was significantly higher in the soleus muscle than in the plantaris and gastrocnemius muscles. The current findings suggest that an elevated blood lactate concentration and post-exercise glucose ingestion additively enhance glycogen recovery in glycolytic phenotype muscles. This appears to be associated with glyconeogenic protein content, but not with enhanced glucose uptake, attenuated glucose oxidation, or lactate transport protein.

Research on kick motion before Sanda based on 3D wireless sensor network image

SummaryThe biomechanical analysis of the pushing kick in the conventional free combat was aimed at the crowds with different ages and different types of skeletal muscles. The analysis precision was low. Therefore, this article put forward the biomechanical analysis of push‐kick of free combat based on 3D image. Three‐dimensional image technique and Hill equation were used to construct the biomechanical model of muscles of free‐combat athletes and describe the leg mechanics in the kicking process. Pattern system provides an up‐to‐date and authoritative fuzzy model, which is an intelligent recognition algorithm. Then, the image analysis was used to build the motion model of knee joint, so as to determine the dynamic equation of knee joint of pushing kick. Based on the above model, the characteristics such as the strike force of push kick, the peak characteristic of leg joint angular velocity and the joint torque were analyzed to achieve the biomechanical analysis of the pushing kick in free combat. Experimental data show that combined the proposed biomechanical analysis method with the traditional analysis method, the precision has improved by 47.69%. Meanwhile, it is suitable for the biomechanics analysis of different free combat crowds.

Characterization Of Muscle Inflammation Susceptibility: A Potential Prognostic Factor For Optimal Post-surgical Rehabilitation

BACKGROUND: Many individuals with end-stage osteoarthritis undergo elective total hip/knee arthroplasty (THA/TKA) to relieve pain and improve mobility and quality of life. However, ~35% suffer long-term mobility impairment following surgery. Previously, we have shown this may be in part due to muscle inflammation susceptibility (MuIS(+)), an overt pro-inflammatory state localized to skeletal muscle surrounding the diseased joint, found in some but not all TKA/THA patients. PURPOSE: We are interrogating the hypotheses that a) MuIS(+/-) status will result in a differential perioperative expression profile that may partially explain low functional outcomes, and b) resistance training rehabilitation will more effectively overcome MuIS(+) status than usual care for effective recovery post-surgery. METHODS: Muscle samples were leveraged from our ongoing two-site, randomized, controlled trial (N=84). Participants were dichotomized to MuIS status (+/-) based on surgical (SX) muscle gene expression of Fn14 which drives pro-inflammatory signaling via NFκB. MuIS(+/-) samples were probed for pro-inflammatory gene and protein expression targets, and indices of skeletal muscle function. Preliminary perioperative comparisons were made using two-tailed T-tests; alpha P≤0.05. RESULTS: 84 participants (29M/55F; 62±8yrs; BMI 30.7±5.4kg/m2) undergoing THA/TKA were assessed. Thus far, 37 have been clustered as MuIS(+) (n=14, ~4-fold greater Fn14 mRNA) or MuIS(-) (n=23). SX thigh muscle mass (TMM), quadriceps power and torque were lower (P<0.05) than the contralateral limb (CTR). Additionally, skeletal muscle fibrosis and type II cross-sectional area were greater in the SX leg and MuIS(+) respectively (P<0.05). Tumor necrosis factor-α receptor and IL-6 trended higher in MuIS(+) (P>0.05). Phosphorylated (P)-RPS6 was lower in the SX leg and P-4E-BP1 was significantly lower in MuIS(+) (P>0.05). CONCLUSIONS: Preliminary results suggest patients undergoing TKA/THA exhibit more inflammation on the SX limb, accompanied by lower TMM, torque and power. MuIS(+) leads to greater inflammation and blunted anabolic signaling, highlighting the profound impact of muscle inflammation and emphasizing the potential value in perioperative MuIS assessment to inform optimal post-surgical care. Grant: R01HD084124

Myosin Heavy Chain Isoform Mrna Expression In Low- And High-capacity Running Rats

Differential expression of Myosin Heavy Chain (MHC) isoforms in skeletal muscle determines its metabolic and functional characteristics. Endurance exercise training is associated with fast-to-slow MHC isoform transition, and which is considered to mediate the beneficial effects of exercise on metabolic health. Rats genetically bred for low-capacity running (LCR) and high-capacity running (HCR) are characterized by the health benefits typically described after endurance exercise training. LCR and HCR rats differed in maximal running capacity 14 fold. PURPOSE: To quantify mRNA expression for slow (MHC-I) and fast (MCH-IIa, MCH-IIb) MHC isoforms in soleus, gastrocnemius and vastus skeletal muscle of LCR and HCR male adult rats, and determine if HCR rats have higher mRNA expression for slow, and lower mRNA expression for fast, MHC isoforms. METHODS: Muscle tissue from 5 HCR and 5 LCR rats was homogenized and mRNA was isolated. The mRNA content of MHC isoforms in muscle was quantified using reverse transcriptase polymerase chain reaction (RT-PCR), and standardized to the 18S mRNA content in muscle. Differences between groups were calculated using the comparative CT method (2-ΔΔCT). LCR were the control group. RESULTS: Expression of mRNA of the MHC isoforms differed between groups and the type of skeletal muscle analyzed. MHC-I mRNA expression was lower in the HCR compared to LCR across all muscle groups, but this difference (2-ΔΔCT) was more pronounced for the gastrocnemius muscle [LCR: 1.0 ± 0.6 (mean±SE); HCR: 0.3 ± 0.2; P = 0.08]. Although MHC-IIa mRNA expression appeared lower in soleus and vastus in the HCR, it was higher in the HCR compared to LCR in the gastrocnemius muscle [LCR: 1.0 ± 1.0; HCR: 4.6 ± 3.6; P = 0.07]. MHC-IIb mRNA expression was lower in the HCR compared to LCR across all muscle groups, but this difference was more pronounced for the soleus muscle [LCR: 1.0 ± 1.1; HCR: 0.2 ± 0.4; P = 0.08]. CONCLUSION: Genetic differences linked to the MHC transcriptome (i.e., decrease in MHC-I mRNA) in muscle do not explain the exercise performance observed in HCR rats. Changes in the muscle MHC transcriptome may not directly be responsible for the health benefits associated with exercise training. It remains to be determined on whether the differences we observed at the MHC mRNA level are translated to the MHC proteome level.

Joint impact of muscle mass and waist circumference on type 2 diabetes in Japanese middle-aged adults: The Circulatory Risk in Communities Study (CIRCS).

Although evidence about skeletal muscle mass loss and type 2 diabetes risk has accumulated, little information is available on the combined effect of skeletal muscle mass and abdominal obesity on type 2 diabetes. We examined whether skeletal muscle mass and abdominal obesity were synergistically associated with the prevalence of type 2 diabetes. Skeletal muscle mass and waist circumference (WC) were measured in 1515 Japanese aged 40 to 69 years. Relative muscle mass was calculated as percentage of total skeletal muscle mass in body weight (SMM%). Type 2 diabetes was identified as fasting serum glucose ≥7.0 mmol/L (126 mg/dL), nonfasting serum glucose ≥11.1 mmol/L (200 mg/dL), glycosylated hemoglobin ≥ 6.5%, and/or diabetes medication use. The multivariable-adjusted odds ratio (OR) of prevalent diabetes from the lowest to the third quartile of SMM% compared to the highest quartile gradually increased in both sexes. The association between a high WC and prevalent diabetes was similar. The multivariable-adjusted OR (95% confidence intervals) for the prevalence of type 2 diabetes in the low skeletal muscle mass/high WC group was 3.19 (1.78-5.71) for men and 4.46 (2.09-9.51) for women compared with the high skeletal muscle mass/low WC group. The relative excess risk due to interaction was 2.2 (0.5-3.9) in men and 2.8 (0.2-5.3) in women for an excess burden of type 2 diabetes for low skeletal muscle mass and high WC. Low skeletal muscle mass and abdominal obesity were synergistically associated with presence of type 2 diabetes.

Активность ферментов в тканях скелетных мышц у морских свинок под функциональной нагрузкой

Abstract. The study is aimed at identifying the nature and intensity of age-related changes in the activity of AsAT and AlAT enzymes under a load of “Proserin” in the tissues of the triceps brachii, pectoralis major muscle, rectus abdominis, gluteus and calf muscles in guinea pigs grown under the conditions of the Scientific and Educational Center “Studencheskiy” of FSBEI HE “Chuvash State Agricultural Academy”. Methodology and methods: The activity of the enzymes AsAT and AlAT was determined by the universal method of S. Wrightman and S. Frenkel (1957) in the modification of V. V. Menshikov (1977) by the spectrophotometric method in the scientific laboratory of Chuvash State Agricultural Academy. Statistical reliability was determined by Student's criterion according to R. Kh. Tukshaitov (2001). Results and scope: analysis of changes in the activity of the enzymes aspartate and alanine aminotransferases indicates that during loading by introducing “Proserin” in the tissues of skeletal muscles, regular changes in all studied parameters with certain features depending on the age of the animal and the type of skeletal muscle are detected. The consistency of changes in the studied parameters in guinea pigs of different ages is manifested in the fact that, under experimental conditions, an increase in the activity of alanine and aspartate aminotransferase enzymes in the tissues of skeletal muscles is detected. The scientific novelty of the study lies in the fact that under conditions of functional load it was revealed that changes in the activity of these enzymes are associated with muscle growth and development in the postnatal period, including various alternating phases of improving the structural and functional organization of organs and the body as a whole.

The Physiological Function of Sigmar1 in the Skeletal Muscle in Mice

RationaleSigmar1 is an abundantly expressed molecular chaperone protein encoded by the SIGMAR1 gene. Mutations in SIGMAR1 have been associated with distal hereditary motor neuropathy, amyotrophic lateral sclerosis, silver‐like syndrome, and frontotemporal lobar degeneration. All these human mutation associated pathologies show skeletal muscle phenotypes like muscle wasting and atrophy. However, the physiological function of Sigmar1 in skeletal muscle has not been explored yet.ObjectivesWe aim to determine the expression and physiological function of Sigmar1 in skeletal muscle structure and function in mice.Methods and ResultsWe first confirmed the Sigmar1 mRNA and protein expression in different types of skeletal muscles (gastrocnemius, quadriceps, soleus, extensor digitorum longus (EDL), and tibialis anterior (TA)) isolated from mice. Immunostaining with the Sigmar1 antibody demonstrated Sigmar1’s localization predominantly in type 1 muscle. We used Sigmar1 global knockout (Sigmar1−/−) mice to determine the physiological function of Sigmar1 in skeletal muscle. Morphometric analysis showed normal muscle weight‐to‐tibia length ratio in all these muscles across the group. The cross‐sectional area of the muscles determined by WGA staining showed that quadriceps and gastrocnemius muscles isolated from Sigmar1−/− mice have bigger muscle fibers compared to wildtype (Wt) mice. Interestingly, absence of Sigmar1 in gastrocnemius and quadriceps muscle of Sigmar1−/− mice results in slow‐to‐fast fiber‐type switch. Interestingly, absence of Sigmar1 in different types of skeletal muscle isolated from Sigmar1−/− mice showed an increased number of central nuclei (H&amp;E staining), increased collagen deposition (Picro‐Sirius red staining) and fibrosis (Masson’s trichrome staining) compared to Wt mice.ConclusionsOur findings suggested an abundant expression of Sigmar1 in different types of skeletal muscle and possess an essential physiological function in these muscles. Sigmar1 absence results in alterations in muscle fiber size, increased number of central nuclei, fiber‐type switch, and fibrotic remodeling suggesting Sigmar1’s function in maintaining healthy skeletal muscle.Support or Funding InformationThis work was supported by NIH/NHLBI grants R00 HL122354, R01HL145753, R01HL145753‐01S1 and PGM121307A to Dr. Bhuiyan. American Heart Association postdoctoral fellowship to Dr. Alam; Malcolm Fiest post‐ and pre‐doctoral fellowships to Dr. Abdullah and Aishwarya by CCDS, LSUHSC‐S.

Deletion of SIRT1 in the skeletal muscle decreases type IIa oxidative muscle fiber in mice.

Background and AimSIRT1 is an NAD+‐dependent protein deacetylase, which exerts cytoprotective effects. We previously reported that resveratrol, an activator of SIRT1, improves exercise tolerance with upregulation oxidative type of muscle fibers in a mouse model of Duchenne muscular dystrophy. SIRT1 deacetylates and activates PGC‐1α, a co‐activator to promote expression of oxidative muscle fibers. The purpose of this study was to examine whether SIRT1 maintains oxidative muscle fibers for exercise capacity in the skeletal muscle using muscle‐specific SIRT1 knockout mice (SIRT1MKO).Methods and ResultsWe first compared the expression level of SIRT1 in several types of skeletal muscles in wild‐type mouse (WT). The SIRT1 protein level was the highest in the soleus muscle (+3.5‐fold), which is mainly made up of oxidative fibers, compared to the other glycolytic muscles such as quadriceps, gastrocnemius, tibial anterior, and extensor digitorum longus muscles. The SIRT1 mRNA level was most abundant also in the soleus. Immunohistological analysis using soleus muscle sections showed that the percentage of type IIa, one of oxidative muscle fibers, was significantly lower in the SIRT1MKO than that in WT (42% vs. 56%) at 26–32 months old. In contrast, the percentage of glycolytic type IIx+IIb muscle fibers was higher in the SIRT1MKO (15%) compared to WT (11%). Treadmill running distance at 30 months old was significantly shorter in SIRT1MKO (78±8 m) than that in WT (592±10 m).ConclusionThese results suggest that deletion of SIRT1 in the skeletal muscle reduces exercise capacity by decreases type IIa oxidative muscle fiber.

Strenuous Acute Exercise Induces Slow and Fast Twitch-Dependent NADPH Oxidase Expression in Rat Skeletal Muscle.

The enzymatic complex Nicotinamide Adenine Dinucleotide Phosphate (NADPH) oxidase (NOx) may be the principal source of reactive oxygen species (ROS). The NOX2 and NOX4 isoforms are tissue-dependent and are differentially expressed in slow-twitch fibers (type I fibers) and fast-twitch fibers (type II fibers) of skeletal muscle, making them different markers of ROS metabolism induced by physical exercise. The aim of this study was to investigate NOx signaling, as a non-adaptive and non-cumulative response, in the predominant fiber types of rat skeletal muscles 24 h after one strenuous treadmill exercise session. The levels of mRNA, reduced glycogen, thiol content, NOx, superoxide dismutase, catalase, glutathione peroxidase activity, and PPARGC1α and SLC2A4 gene expression were measured in the white gastrocnemius (WG) portion, the red gastrocnemius (RG) portion, and the soleus muscle (SOL). NOx activity showed higher values in the SOL muscle compared to the RG and WG portions. The same was true of the NOX2 and NOX4 mRNA levels, antioxidant enzymatic activities, glycogen content. Twenty-four hours after the strenuous exercise session, NOx expression increased in slow-twitch oxidative fibers. The acute strenuous exercise condition showed an attenuation of oxidative stress and an upregulation of antioxidant activity through PPARGC1α gene activity, antioxidant defense adaptations, and differential gene expression according to the predominant fiber type. The most prominent location of detoxification (indicated by NOX4 activation) in the slow-twitch oxidative SOL muscle was the mitochondria, while the fast-twitch oxidative RG portion showed a more cytosolic location. Glycolytic metabolism in the WG portion suggested possible NOX2/NOX4 non-regulation, indicating other possible ROS regulation pathways.

Highly bioavailable Berberine formulation improves Glucocorticoid Receptor-mediated Insulin Resistance via reduction in association of the Glucocorticoid Receptor with phosphatidylinositol-3-kinase.

Excess glucocorticoid (GC) production is known to induce obesity and insulin resistance through increased activation of the glucocorticoid receptor (GR). The molecular mechanism for the non-genomic effects of excessive circulating GC on the insulin-signalling pathway in skeletal muscle is unknown. The plant alkaloid berberine has been shown to attenuate insulin resistance and inhibit gluconeogenesis in type 2 diabetic animals. A highly bioavailable berberine formulation termed Huang-Gui solid dispersion (HGSD), is a preparation of berberine coupled to sodium caprate and this markedly improving berberines bioavailability. Here we examined how HGSD treatment attenuated GR-mediated alteration in PI3K signalling and insulin resistance in diabetic rats, dexamethasone-treated mice and in insulin resistant C2C12 skeletal muscle cells. Blood glucose and skeletal muscle GC levels were increased and insulin signalling impaired in skeletal muscle of type 2 diabetic rats compared to controls. Treatment of these animals with HGSD restored blood glucose and skeletal muscle GC levels to that of controls. Insulin resistant C2C12 skeletal muscle cells exhibited impaired insulin signalling compared to controls and treatment of HGSD and RU486, an antagonist of GR, restored insulin signalling to that of control cells. Administration of dexamethasone to mice increased GR/GRα-associated PI3K and reduced IRS1-associated PI3K, phosphorylated-AKT, and membrane GLUT4 translocation resulting in a higher blood glucose concentration compared to controls. HGSD treatment of these mice improved insulin resistance by reducing the association of GR/GRα with PI3K. Excess GC-induced insulin resistance is mediated by increased association of GR with PI3K and treatment with HGSD attenuates these effects. We hypothesize that HGSD may be a promising candidate drug for the treatment of type 2 diabetes by reducing the association of GR with PI3K in skeletal muscle.

저항성 운동과 커큐민 보충 복합 중재가 제2형 당뇨 쥐의 골격근 내 염증 촉진 사이토카인의 mRNA 발현에 미치는 영향: 예비연구

저항성 운동과 커큐민 보충 복합 중재가 제2형 당뇨 쥐의 골격근 내 염증 촉진 사이토카인의 mRNA 발현에 미치는 영향: 예비연구

Effects of metformin treatment on expression and activity of AMP-activated protein kinase α in skeletal muscle in type 2 diabetes

Objective To investigate the effects of metformin treatment on fatty acid metabolism and expression and activity of AMP-activated protein kinase (AMPK)α in skeletal muscle in type 2 diabetes. Methods A total of 30 cases with or without type 2 diabetes mellitus (T2DM) who received selective surgery were enrolled from department of orthopaedics. These patients were divided into three groups: DM group, DM+ MET group and NC group. Blood samples were drawn from an antecubial vein for measurement of plasma glucose, insulin, lipid and free fatty acid (FFA). Insulin sensitivity index (ISI) was calculated. Skeletal muscle was freezed in liquid nitrogen during orthopaedics surgery and was kept at -70 ℃ until assay. Skeletal muscle tissue was analysed en bloc for triglyceride, long chain fatty acyl-CoA (LCACoAs), AMPKα1 and AMPKα2 mRNA expression [quantitative real-time polymerase chain reaction (qRT-PCR)], as well as protein expression of AMPKα1, AMPKα2 and phosphorylated AMPKα (p-AMPKα) (Western blot). Results ⑴ Compared with NC group, HbA1c, fasting blood glucose (FBG), fasting insulin (FINS), FFA and triglyceride(TG) were increased in DM group, while metformin treatment decreased FFA and TG; ISI was reduced in DM group than that in NC group, but ISI was higher in DM+ MET group compared with DM group (P 0.05). Compared with NC group, AMPKα2 mRNA expression and protein levels of AMPKα2 and p-AMPKα in skeletal muscle were decreased in DM group, while metformin treatment increased protein level of p-AMPKα (P<0.05). Conclusions Compared with NC group, muscle lipid accumulation and insulin resistance always exist in T2DM patients. Metformin treatment may increase activity of AMPKα, resulting in a decrease in lipid accumulation in skeletal muscle and increase insulin sensitivity in T2DM patients. Key words: Metformin; Diabetes mellitus, type 2; Muscle, skeletal; AMP-activated protein kinases; Insulin resistance

Effect of acute exercise on mRNA and protein expression of main components of the lipolytic complex in different skeletal muscle types in the rat.

Adipose triglyceride lipase (ATGL) hydrolyses the first bond of triacylglycerols. The activity of the enzyme is elevated by comparative gene identification 58 (CGI-58), and reduced by G0/G1 switch gene 2 (G0S2) protein. There are no data on the effect of acute exercise on the behavior of particular components of the lipolytic complex in different skeletal muscle types, therefore, the aim of the present study was to examine that topic. The experiments were carried out on four groups of male Wistar rats: 1) control 2) rats running on a treadmill at the speed of 18 m/min for 30 min, 3) at the speed of 18 m/min for 120 min, 4) for 30 min at the speed of 28 m/min. We found that each exercise bout induced numerous changes in the expression of mRNA and protein ATGL, hormone-sensitive lipase, CGI-58 and G0S2 in the investigated muscles. These changes, depended to a large extent on a muscle type. In general, the strongest pro-lipolytic response was observed in the soleus, followed by the red section of the gastrocnemius (RG). On the other hand, in the white section of the gastrocnemius protein expression of the components of the lipolytic complex was reduced in response to exercise. These changes were not accompanied by alterations in muscle triacylglycerol content, with the exception of a reduction observed in the RG following 2-hour run. We conclude that a single bout of exercise induces significant effect on the expression of components of the lipolytic complex in skeletal muscle, and that the magnitude of this effect depends on muscle oxidative capacity, as well as the duration and intensity of exercise.

Differential regulation of protein synthesis by skeletal muscle type in chickens

In mammalian skeletal muscles, protein synthesis rates vary according to fiber types. We herein demonstrated differences in the regulatory mechanism underlying the protein synthesis in the pectoralis major (a glycolytic twitch muscle), adductor superficialis (an oxidative twitch muscle), and adductor profound (a tonic muscle) muscles of 14-day-old chickens. Under ad libitum feeding conditions, protein synthesis is significantly higher in the adductor superficialis muscle than in the pectoralis major muscle, suggesting that protein synthesis is upregulated in oxidative muscles in chickens, similar to that in mammals. In the pectoralis major muscle, fasting significantly inhibited the Akt/S6 pathway and protein synthesis with a corresponding decrease in plasma insulin concentration. Conversely, the insulin like growth factor-1 (IGF-1) mRNA levels significantly increased. These findings suggest that the insulin/Akt/S6 pathway plays an important role in the regulation of protein synthesis in the pectoralis major muscle. Interestingly, protein synthesis in the adductor superficialis muscle appears to be regulated in an Akt-independent manner, because fasting significantly decreased S6 phosphorylation and protein synthesis without affecting Akt phosphorylation. In the adductor profound muscle, IGF-1 expression, phosphorylation of Akt and S6, and protein synthesis were decreased by fasting, suggesting that insulin and/or skeletal IGF-1 appear contribute to protein synthesis via the Akt/S6 pathway. These findings revealed the differential regulation of protein synthesis depending on skeletal muscle types in chickens.

Identification of the fructose transporter GLUT5 (SLC2A5) as a novel target of nuclear receptor LXR

Fructose has become a major constituent of our modern diet and is implicated as an underlying cause in the development of metabolic diseases. The fructose transporter GLUT5 (SLC2A5) is required for intestinal fructose absorption. GLUT5 expression is induced in the intestine and skeletal muscle of type 2 diabetes (T2D) patients and in certain cancers that are dependent on fructose metabolism, indicating that modulation of GLUT5 levels could have potential in the treatment of these diseases. Using an unbiased screen for transcriptional control of the human GLUT5 promoter we identified a strong and specific regulation by liver X receptor α (LXRα, NR1H3). Using promoter truncations and site-directed mutagenesis we identified a functional LXR response element (LXRE) in the human GLUT5 promoter, located at −385 bp relative to the transcriptional start site (TSS). Finally, mice treated with LXR agonist T0901317 showed an increase in Glut5 mRNA and protein levels in duodenum and adipose tissue, underscoring the in vivo relevance of its regulation by LXR. Together, our findings show that LXRα regulates GLUT5 in mice and humans. As a ligand-activated transcription factor, LXRα might provide novel pharmacologic strategies for the selective modulation of GLUT5 activity in the treatment of metabolic disease as well as cancer.

2267-PUB: Skeletal Muscle mRNA Transcriptional Signature of Response to Exercise of Patients in Different Stages of Glucose Tolerance

Physical activity is an effective method to prevent and treat type 2 diabetes (T2D); however, the mechanisms of its beneficial effects have not been precisely elucidated. Skeletal muscle is a major contributor to overall glucose homeostasis in the body and is responsible for the efficacy of exercise intervention in the prevention and treatment of T2D. Currently, there is a lack of studies investigating the transcriptional signature of exercise training on skeletal muscles of patients with different stages of glucose tolerance. Thus, the aim of this study was to identify the mRNA signature of skeletal muscle adaptation to three-month exercise intervention in patients with different dysregulations of glucose metabolism. For this project we included 35 sedentary males, aged 24-65 years old, with BMI 26-33 kg/m2, divided into three groups: 15 normoglycemics, 12 prediabetics and 8 subjects with type 2 diabetes, treated with metformin only. RNA samples were obtained from biopsied Vastus lateralis muscles, before and after a 3-month supervised exercise intervention that occurred thrice weekly and consisted of mixed aerobic (60-70% of individual’s VO2max) and strength (60-70% of the repetition maximum for each exercise) activities. Selected groups of patients did not differ in age, BMI, number of performed trainings or diet during the intervention. mRNA sequencing was performed on an Illumina HiSeq 4000. We found highly significant differential mRNA expression in normoglycemics vs. T2D and prediabetic subjects, mostly related to mitochondrial processes, including the oxidative phosphorylation and thermogenesis pathways. Furthermore, we found that exercise intervention mostly affected these pathways, suggesting that a major defect of skeletal muscle in type 2 diabetes development is related to mitochondrial function and can be diminished by exercise. Disclosure L. Szczerbinski: None. M. Niemira: None. K. Szczerbinski: None. U. Puchta: None. A. Citko: None. E. Siewiec: None. J. Zapolska: None. M. Taylor: None. S. Larsen: None. M. Gorska: None. A. Kretowski: None. Funding Polish Diabetes Association; Polish Ministry of Science and Higher Education

Evaluation of Yanagihara facial nerve grading system based on a muscle fiber analysis of human facial muscles

PurposeWe morphometrically analyzed human facial muscles, and evaluated the Yanagihara facial nerve grading system using our data.MethodsWe used 15 types of human facial muscle, 2 types of masticatory muscle and 2 types of skeletal muscle. The materials were obtained from 11 Japanese male cadavers aged 43–86 years. We counted the muscle fibers and measured the transverse area of the muscle fibers (TAMF), and then calculated the number of muscle fibers (NMF) per mm2 and the average TAMF.ResultsWe found a significant correlation between average TAMF and NMF (r = − 0.70; p < 0.01). We classified facial muscles into three types based on the correlational results. Type A had a low average TAMF and high NMF. Type C had a high average TAMF and low NMF. Masticatory and skeletal muscles were characterized as Type C. Type B was intermediate between Types A and C.ConclusionsPathological changes in the facial muscles in facial nerve palsy seem to vary according to the type of facial muscle, because each facial muscle has a unique fiber-type composition. As the nine discrete facial expressive states evaluated in the Yanagihara system involve all three facial muscle types of our classification, the Yanagihara system is an outstanding system for grading facial nerve palsy in terms of the facial muscle morphology.

A Global Loss of Dio2 Leads to Unexpected Changes in Function and Fiber Types of Slow Skeletal Muscle in Male Mice.

The type 2 iodothyronine-deiodinase (D2) enzyme converts T4 to T3, and mice deficient in this enzyme [D2 knockout (D2KO) mice] have decreased T3 derived from T4 in skeletal muscle despite normal circulating T3 levels. Because slow skeletal muscle is particularly susceptible to changes in T3 levels, we expected D2 inactivation to result in more pronounced slow-muscle characteristics in the soleus muscle, mirroring hypothyroidism. However, ex vivo studies of D2KO soleus revealed higher rates of twitch contraction and relaxation and reduced resistance to fatigue. Immunostaining of D2KO soleus showed that these properties were associated with changes in muscle fiber type composition, including a marked increase in the number of fast, glycolytic type IIB fibers. D2KO soleus muscle fibers had a larger cross-sectional area, and this correlated with increased myonuclear accretion in myotubes formed from D2KO skeletal muscle precursor cells differentiated in vitro. Consistent with our functional findings, D2KO soleus gene expression was markedly different from that in hypothyroid wild-type (WT) mice. Comparison of gene expression between euthyroid WT and D2KO mice indicated that PGC-1α, a T3-dependent regulator of slow muscle fiber type, was decreased by ∼50% in D2KO soleus. Disruption of Dio2 in the C2C12 myoblast cell line led to a significant decrease in PGC-1α expression and a faster muscle phenotype upon differentiation. These results indicate that D2 loss leads to significant changes in soleus contractile function and fiber type composition that are inconsistent with local hypothyroidism and suggest that reduced levels of PCG-1α may contribute to the observed phenotypical changes.