Different Types Of Skeletal Muscle Research Articles

Revisiting the role of ectonucleotidases in synaptic transmission. Thermal sensitivities of ATP-producing metabolic pathways

The release of ATP as an intermediate at the neuromuscular junction, and acetylcholine, the chief neurotransmitter, may take place by mechanisms responsible for quantal and non-quantal secretion from the motor neurons of the central and peripheral nervous system. The dephosphorylation pathway of ATP that is completed by the hydrolysis of AMP to adenosine in the synaptic cleft is a cascade of reactions catalyzed by ectonucleotidases. These enzymes are of enormous interest, the research in this field is necessary to clarify their role in a complex signaling cascade, since it is known that they have dual functions: ectonucleotidases limit the action of ATP as a neurotransmitter and participate in the formation of other neuromodulators (ADP, AMP and adenosine). In addition, ATP and its metabolites can cause completely different physiological effects. The activity of ectonucleatidases in different types of skeletal muscles was determined, it varies within 5-7 IU. A decrease in temperature to 22°C leads to a multiple decrease in the enzymatic regeneration of ATP in skeletal muscle tissues. It is assumed that enzymatic limitation of ATP and the production of its metabolites ensures stabilization of effective cholinergic neuromuscular transmission in norm and pathology.

The effects of pollutant mixture released from grafted adipose tissues on fatty acid and lipid metabolism in the skeletal muscles, kidney, heart, and lungs of male mice

Persistent organic pollutants (POPs) accumulated in the adipose tissue can affect the fatty acid and lipid metabolism in the body. Gas chromatography-mass spectrometry (GC-MS) metabolomics analysis was carried out to study the metabolic changes induced by internal exposure to the POPs in mouse skeletal muscle (soleus, plantaris, and gastrocnemius), kidney, heart, and lungs. Male donor mice were injected with a mixture of 10 POPs at concentrations of 0 × and 5 × lowest-observed-adverse-effect level (LOAEL). Their adipose tissue (AT) containing the POP was then grafted onto the host mice and the metabolic change of the host mice was monitored for 3 or 21 days. The metabolites related to fatty acid and lipid metabolism were studied. For the host mice engrafted with POP-containing fat pad, there was dysregulation of the fatty acids and glycerides observed in all the organs studied 3 days after the graft. However, there was no longer a significant change in the metabolites 21 days after the graft. The difference in significant values and metabolite regulation in each of the skeletal muscles showed that the POP mixture affects different types of skeletal muscle in a heterogeneous manner. Fold change analysis showed that certain metabolites in the kidney of host mice exposed to POPs for 3 days were greatly affected. Using multivariate analysis, apart from the plantaris, most treated groups exposed to POPs for 3 days are well distinguished from the control groups. However, for host mice exposed to POPs for 21 days, apart from the kidney and heart, groups are not well-distinguished from the control group. This study helps bring new insight into the effects of the pollutants mixture released from AT on fatty acid and lipid metabolism at different periods and how the dysregulation of metabolites might result in diseases associated with the organs.

Treadmill running prevents atrophy differently in fast- versus slow-twitch muscles in a rat model of rheumatoid arthritis.

To investigate the effects of treadmill running on two different types of skeletal muscle, we established a rat model of collagen-induced arthritis (CIA). The skeletal muscles studied were the extensor digitorum longus (EDL), which is rich in fast-twitch muscle fibers, and the soleus, which is rich in slow-twitch muscle fibers. The histological and transcriptional changes in these muscles at 14 and 44days after immunosensitization were compared between rats that were forced to exercise (CIA ex group) and free-reared CIA rats (CIA no group). Change in protein expression was examined on day 14 after a single bout of treadmill running. Treadmill running had different effects on the relative muscle weight and total and fiber cross-sectional areas in each muscle type. In the soleus, it prevented muscle atrophy. Transcriptional analysis revealed increased eukaryotic translation initiation factor 4E (Eif4e) expression on day 14 and increased Atrogin-1 and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) expression on day 44 in the soleus in the CIA ex group, suggesting an interaction between muscle type and exercise. A single bout of treadmill running increased the level of Eif4e and p70S6K and decreased that of Atrogin-1 in the soleus on day 14. Treadmill running prevented muscle atrophy in the soleus in a rat model of rheumatoid arthritis via activation of mitochondrial function, as evidenced by increased PGC-1α expression.

Impairment of Physiological Function in Skeletal Muscle from Sigmar1 Knockout Mice

Rationale Sigmar1 is a widely expressed, multitasking molecular chaperone protein shown to play an important role in several vital cellular processes. Sigmar1 is encoded by SIGMAR1 gene, and mutations in this gene have been linked to several motor neuropathies, including distal hereditary motor neuropathy, amyotrophic lateral sclerosis, silver-like syndrome, and frontotemporal lobar degeneration. All these human mutations associated with motor neuropathies show strong manifestation in skeletal muscle with phenotypes like muscle wasting and atrophy. However, the physiological function of Sigmar1 in skeletal muscle remains unexplored. Objectives We focus on determining the physiological role of Sigmar1 in skeletal muscle structure and function. Methods and Results We first confirmed the mRNA and protein expression of Sigmar1 where different types of skeletal muscle, including gastrocnemius (Gastro), quadriceps (Quad), soleus (Sol), extensor digitorum longus (EDL), and tibialis anterior (TA) isolated from wildtype (Wt) mice showing a differential expression of Sigmar1 in different types of skeletal muscles. Morphometric analysis of different skeletal muscle isolated from Wt and Sigmar1 global knockout (Sigmar1-/-) mice showed a similar weight-to-tibia length ratio across the group in all these muscles. Quantification of myofiber cross-sectional area (CSA) showed Gastro and Quad muscles isolated from Sigmar1-/- mice had larger muscle mass whereas TA, Sol, and EDL from Sigmar1-/- mice had smaller CSA compared to those from Wt mice. We also observed a slow-to-fast fiber-type switch in the skeletal muscle fibers from the Sigmar1-/- mice. Interestingly, ultrastructural analysis by transmission electron microscopy of skeletal muscles from Sigmar1-/- mice showed the presence of tubular aggregates in the Gastro and TA muscles. We also observed derangement in dystrophin localization in skeletal muscles from Sigmar1-/- mice. Additionally, skeletal muscles from Sigmar1-/- mice showed an increased number of central nuclei H&E staining), increased collagen deposition (Picro-Sirius red staining), and fibrosis (Masson's trichrome staining). Functional studies via measurement of grip strength and treadmill exercise showed Sigmar1-/- to have reduced endurance and exercise capacity compared to Wt mice. Conclusions Overall, our studies demonstrate a potential physiological function of Sigmar1 in the skeletal muscle in maintaining healthy muscle structure and function.

Skeletal Muscle Metabolomic Responses to Endurance and Resistance Training in Rats under Chronic Unpredictable Mild Stress.

The objectives of this study were to compare the antidepressant effects between endurance and resistance exercise for optimizing interventions and examine the metabolomic changes in different types of skeletal muscles in response to the exercise, using a rat model of chronic unpredictable mild stress (CUMS)-induced depression. There were 32 male Sprague-Dawley rats randomly divided into a control group (C) and 3 experimental groups: CUMS control (D), endurance exercise (E), and resistance exercise (R). Group E underwent 30 min treadmill running, and group R performed 8 rounds of ladder climbing, 5 sessions per week for 4 weeks. Body weight, sucrose preference, and open field tests were performed pre and post the intervention period for changes in depressant symptoms, and the gastrocnemius and soleus muscles were sampled after the intervention for metabolomic analysis using the 1H-NMR technique. The results showed that both types of exercise effectively improved the depression-like symptoms, and the endurance exercise appeared to have a better effect. The levels of 10 metabolites from the gastrocnemius and 13 metabolites from the soleus of group D were found to be significantly different from that of group C, and both types of exercise had a callback effect on these metabolites, indicating that a number of metabolic pathways were involved in the depression and responded to the exercise interventions.

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.

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.

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.

Evidence of Blood and Muscle Redox Status Imbalance in Experimentally Induced Renal Insufficiency in a Rabbit Model.

Chronic kidney disease (CKD) is accompanied by a disturbed redox homeostasis, especially in end-stage patients, which is associated with pathological complications such as anemia, atherosclerosis, and muscle atrophy. However, limited evidence exists about redox disturbances before the end stage of CKD. Moreover, the available redox literature has not yet provided clear associations between circulating and tissue-specific (muscle) oxidative stress levels. The aim of the study was to evaluate commonly used redox status indices in the blood and in two different types of skeletal muscle (psoas, soleus) in the predialysis stages of CKD, using an animal model of renal insufficiency, and to investigate whether blood redox status indices could be reflecting the skeletal muscle redox status. Indices evaluated included reduced glutathione (GSH), oxidized glutathione (GSSG), glutathione reductase (GR), catalase (CAT), total antioxidant capacity (TAC), protein carbonyls (PC), and thiobarbituric acid reactive substances (TBARS). Results showed that blood GSH was higher in the uremic group compared to the control (17.50 ± 1.73 vs. 12.43 ± 1.01, p = 0.033). In both muscle types, PC levels were higher in the uremic group compared to the control (psoas: 1.086 ± 0.294 vs. 0.596 ± 0.372, soleus: 2.52 ± 0.29 vs. 0.929 ± 0.41, p < 0.05). The soleus had higher levels of TBARS, PC, GSH, CAT, and GR and lower TAC compared to the psoas in both groups. No significant correlations in redox status indices between the blood and skeletal muscles were found. However, in the uremic group, significant correlations between the psoas and soleus muscles in PC, GSSG, and CAT levels emerged, not present in the control. Even in the early stages of CKD, a disturbance in redox homeostasis was observed, which seemed to be muscle type-specific, while blood levels of redox indices did not seem to reflect the intramuscular condition. The above results highlight the need for further research in order to identify the key mechanisms driving the onset and progression of oxidative stress and its detrimental effects on CKD patients.

Discrepant effects of copper (II) stress on different types of skeletal muscles in chicken: Elements and amino acids

Different distributions of 28 elements and 17 amino acids in pectoralis, wing biceps brachii and leg gastrocnemius of chicken upon CuSO4 (300 mg/kg) exposure for 90 days were investigated. Accompanied by copper accumulation, pathological injuries were observed in those three kinds of skeletal muscles using histological and ultrastructural methods. Based on data obtained, we analyzed leg gastrocnemius displayed the most increases (P < 0.000) in all three kinds of elements detected, including macroelements (131%), essential microelements (129%) and toxic microelements (179%) than the other two skeletal muscles. Furthermore, decreased total amino acids (P = 0.006), a susceptibility of lipid peroxidation/oxidative stress and a disequilibrium of nutrition and taste were analyzed in the leg gastrocnemius, indicating an unsuitability for human consumption. Intriguingly, these anomalies were scarce in pectoralis and wing biceps brachii. Combined with multivariate analysis we may conclude that leg gastrocnemius are more vulnerable to copper stress than pectoralis and wing biceps brachii in chicken.

Diversity effect of capsaicin on different types of skeletal muscle.

Capsaicin is a major pungent content in green and red peppers which are widely used as spice, and capsaicin may activate different receptors. To determine whether capsaicin has different effects on different types of skeletal muscle, we applied different concentrations (0, 0.01, and 0.02%) of capsaicin in the normal diet and conducted a four-week experiment on Sprague-Dawley rats. The fiber type composition, glucose metabolism enzyme activity, and different signaling molecules' expressions of receptors were detected. Our results suggested that capsaicin reduced the body fat deposition, while promoting the slow muscle-related gene expression and increasing the enzyme activity in the gastrocnemius and soleus muscles. However, fatty acid metabolism was significantly increased only in the soleus muscle. The study of intracellular signaling suggested that the transient receptor potential vanilloid 1 (TRPV1) and cannabinoid receptors in the soleus muscle were more sensitive to capsaicin. In conclusion, the distribution of TRPV1 and cannabinoid receptors differs in different types of muscle, and the different roles of capsaicin in different types of muscle may be related to the different degrees of activation of receptors.

Colonisation of Meat by Escherichia coli O157:H7: Investigating Bacterial Tropism with Respect to the Different Types of Skeletal Muscles, Subtypes of Myofibres, and Postmortem Time.

Escherichia coli O157:H7 is an enterohaemorrhagic E. coli (EHEC) responsible for serious diseases, especially pediatric, and of great concern for the meat industry. Meat contamination by EHEC occurs at slaughtering, especially at dehiding stage, where bacteria can be transferred from hides to carcasses. The skeletal muscle tissues comprise four major types of myofibres, which differ in their contraction velocity and metabolism. Myofibres are surrounded by the extracellular matrix (ECM). Adhesion of E. coli O157:H7 to meat was investigated considering well-defined types of skeletal muscle and their constituent myofibres as well as postmortem changes in muscle, using fluorescence microscopy and immunohistochemical analyses. By analysing the adhesion of E. coli O157:H7 to model oxidative (soleus) and glycolytic [extensor digitorum longus (EDL)] skeletal muscles, it first appeared that differential adhesion occurred at the surface of these extreme skeletal muscle types. At a cellular level, bacterial adhesion appeared to occur essentially at the ECM. Considering the different constituent myofibres of types I, IIA, IIX and IIB, no significant differences were observed for adhering bacteria. However, bacterial adhesion to the ECM was significantly influenced by postmortem structural modifications of muscle tissues. By providing information on spatial localisation of E. coli O157:H7 on meat, this investigation clearly demonstrated their ability to adhere to skeletal muscle, especially at the ECM, which consequently resulted in their heterogeneous distribution in meat. As discussed, these new findings should help in reassessing and mitigating the risk of contamination of meat, the food chain and ultimately human infection by EHEC.

Mitochondrial respiration is fiber‐type specific in skeletal muscles

IntroductionMitochondria are the power houses of the cells and they also play critical roles in the cellular oxidative stress and apoptosis. It is known that mitochondrial density and morphology are fiber‐type specific. Based on differential contractile properties of different types of skeletal muscles, we hypothesized that the mitochondria respiration is fiber‐type specific. The aim of the study is to compare and contrast mitochondria respiration between type I and type II muscles.MethodSoleus (predominantly composed of type I fibers) and plantaris (predominantly composed of type II fibers) muscles were taken from adult rats. Mitochondrial respiration was determined in duplicate by a high‐resolution respirometry OROBOROS Oxygraph‐2k (O2k). The mitochondrial substrate‐uncoupler‐inhibitor titration (SUIT) protocol was used to determine mitochondrial oxygen consumption rate (O2 flux) of permeabilized myofibers. Paired t test was used to compare parameters between soleus and plantaris muscles.ResultsWe found that basal mitochondrial respiration (i.e. O2 flux_ complex I plus complex II) and leak of permeabilized muscle fibers was similar between soleus and plantaris muscles. Similarly, mitochondrial coupling control ratio defined by leak divided by basal mitochondrial respiration (i.e. leak/O2 flux_ complex I plus complex II) is similar between soleus and plantaris muscles. Maximal electron transport system capacity (maximal mitochondrial respiration) of soleus muscles was greater than that of plantaris muscles. In addition, mitochondrial respiratory reserve capacity defined by subtracting basal mitochondrial respiration from maximal mitochondrial respiration was greater in soleus muscles than in plantaris muscles.ConclusionBasal mitochondrial respiration and leak are similar between type I and type II muscles. However, mitochondria in type I muscles have greater respiratory reserve compared to that in type II muscles. This fiber‐type specific mitochondrial respiration is likely associated with the differential fuel metabolism and contractile properties of muscle fibers.

Transcriptional response of skeletal muscle to a low protein perinatal diet in rat offspring at different ages: The role of key enzymes of glucose-fatty acid oxidation

Skeletal muscle is a plastic tissue during development with distinctive acute and chronic response to maternal protein restriction. This study evaluated gene and protein expression of key-enzymes of glycolytic pathway (HK2, PFK, PDK4 and CS), and fatty acid oxidation (CPT1 and β-HAD) of two different types of skeletal muscle [soleus and extensor digitorium longus (EDL)] from offspring rats at 30 and 90 days of age, exposed to maternal isoenergetic low protein diet throughout gestation and lactation. Pups from dams fed 17% protein diet (n=5, normal protein, Np), and low protein pups from dams fed 8% casein diet (low protein, Lp, n=5) were evaluated. Offspring were sacrificed either 30 or 90 days old. Soleus and EDL were analyzed for mRNA and protein expression by quantitative PCR and western blotting, respectively. Soleus was more affected by Lp maternal diet at 90 days by down-regulation of key enzymes of glycolytic pathway, in particular HK2 and PDK4 with a concomitant reduction of β-HAD mRNA. For EDL, the effects of Lp maternal diet were more pronounced at 30 days, as the transcriptional key enzymes of glycolytic pathway were down-regulated. One important finding was that the observed acute (30 days) transcriptional changes did not remain in adult Lp rats (90 days), except for PDK4. The robust PDK4 mRNA down-regulation, observed in both soleus and EDL, and at both ages, and the consequent down-regulation of the PDK4 protein expression can be responsible for a state of reduced metabolic flexibility of skeletal muscle in response to maternal low protein diet.

Effects of Heat Stress Treatment on Age-dependent Unfolded Protein Response in Different Types of Skeletal Muscle.

Mitochondrial and endoplasmic reticulum (ER) stress, and subsequently activated responses (mitochondrial/ER unfolded protein responses; UPRmt/UPRER), are involved in the pathogenesis of sarcopenia. To extend both basic and translational knowledge, we examined (i) whether age-induced mitochondrial and ER stress depend on skeletal muscle type in mice and (ii) whether heat stress treatment, a suggested strategy for sarcopenia, improves age-induced mitochondrial and ER stress. Aged (21-month-old) mice showed more severe mitochondrial stress and UPRmt than young (12-week-old) mice, based on increased oxidative stress, mitochondrial proteases, and mitochondrial E3 ubiquitin ligase. The aged mice also showed ER stress and UPRER, based on decreased ER enzymes and increased ER stress-related cell death. These changes were much more evident in soleus muscle than in gastrocnemius and plantaris muscles. After daily heat stress treatment (40 °C chamber for 30 minutes per day) for 4 weeks, mice showed remarkable improvements in age-related changes in soleus muscle. Heat stress had only minor effects in gastrocnemius and plantaris muscles. Based on these findings, age-associated mitochondrial stress, ER stress, and UPRmt/ER vary qualitatively with skeletal muscle type. Our results suggest a molecular basis for the beneficial effects of heat stress on muscle atrophy with age in soleus muscle.

Signaling Pathways Related to Protein Synthesis and Amino Acid Concentration in Pig Skeletal Muscles Depend on the Dietary Protein Level, Genotype and Developmental Stages.

Muscle growth is regulated by the homeostatic balance of the biosynthesis and degradation of muscle proteins. To elucidate the molecular interactions among diet, pig genotype, and physiological stage, we examined the effect of dietary protein concentration, pig genotype, and physiological stages on amino acid (AA) pools, protein deposition, and related signaling pathways in different types of skeletal muscles. The study used 48 Landrace pigs and 48 pure-bred Bama mini-pigs assigned to each of 2 dietary treatments: lower/GB (Chinese conventional diet)- or higher/NRC (National Research Council)-protein diet. Diets were fed from 5 weeks of age to respective market weights of each genotype. Samples of biceps femoris muscle (BFM, type I) and longissimus dorsi muscle (LDM, type II) were collected at nursery, growing, and finishing phases according to the physiological stage of each genotype, to determine the AA concentrations, mRNA levels for growth-related genes in muscles, and protein abundances of mechanistic target of rapamycin (mTOR) signaling pathway. Our data showed that the concentrations of most AAs in LDM and BFM of pigs increased (P<0.05) gradually with increasing age. Bama mini-pigs had generally higher (P<0.05) muscle concentrations of flavor-related AA, including Met, Phe, Tyr, Pro, and Ser, compared with Landrace pigs. The mRNA levels for myogenic determining factor, myogenin, myocyte-specific enhancer binding factor 2 A, and myostatin of Bama mini-pigs were higher (P<0.05) than those of Landrace pigs, while total and phosphorylated protein levels for protein kinase B, mTOR, and p70 ribosomal protein S6 kinases (p70S6K), and ratios of p-mTOR/mTOR, p-AKT/AKT, and p-p70S6K/p70S6K were lower (P<0.05). There was a significant pig genotype-dependent effect of dietary protein on the levels for mTOR and p70S6K. When compared with the higher protein-NRC diet, the lower protein-GB diet increased (P<0.05) the levels for mTOR and p70S6K in Bama mini-pigs, but repressed (P<0.05) the level for p70S6K in Landrace pigs. The higher protein-NRC diet increased ratio of p-mTOR/mTOR in Landrace pigs. These findings indicated that the dynamic consequences of AA profile and protein deposition in muscle tissues are the concerted effort of distinctive genotype, nutrient status, age, and muscle type. Our results provide valuable information for animal feeding strategy.

Inhibition of Ceramide De Novo Synthesis Ameliorates Diet Induced Skeletal Muscles Insulin Resistance.

Nowadays wrong nutritional habits and lack of physical activity give a rich soil for the development of insulin resistance and obesity. Many researches indicate lipids, especially the one from the sphingolipids class, as the group of molecules heavily implicated in the progress of insulin resistance in skeletal muscle. Recently, scientists have focused their scrutiny on myriocin, a potent chemical compound that inhibits ceramide (i.e., central hub of sphingolipids signaling pathway) de novo synthesis. In the present research we evaluated the effects of myriocin application on type 2 diabetes mellitus in three different types of skeletal muscles: (1) slow-oxidative (red gastrocnemius), (2) oxidative-glycolytic (soleus), and (3) glycolytic (white gastrocnemius). For these reasons the animals were randomly divided into four groups: “control” (C), “myriocin” (M), “high fat diet” (HFD), “high fat diet” (HFD), and “high fat diet + myriocin” (HFD + M). Our in vivo study demonstrated that ceramide synthesis inhibition reduces intramuscular ceramide, its precursor sphinganine, and its derivatives sphingosine and sphingosine-1-phosphate concentrations. Moreover, FFA and TG contents were also decreased after myriocin treatment. Thus, myriocin presents potential therapeutic perspectives with respect to the treatment of insulin resistance and its serious consequences in obese patients.

Macrophage migration inhibitory factor diminishes muscle glucose transport induced by insulin and AICAR in a muscle type-dependent manner

Skeletal muscle is a primary organ that uses blood glucose. Insulin- and 5′AMP-activated protein kinase (AMPK)-regulated intracellular signaling pathways are known as major mechanisms that regulate muscle glucose transport. It has been reported that macrophage migration inhibitory factor (MIF) is secreted from adipose tissue and heart, and affects these two pathways. In this study, we examined whether MIF is a myokine that is secreted from skeletal muscles and affects muscle glucose transport induced by these two pathways. We found that MIF is expressed in several different types of skeletal muscle. Its secretion was also confirmed in C2C12 myotubes, a skeletal muscle cell line. Next, the extensor digitorum longus (EDL) and soleus muscles were isolated from mice and treated with recombinant MIF in an in vitro muscle incubation system. MIF itself did not have any effect on glucose transport in both types of muscles. However, glucose transport induced by a submaximal dose of insulin was diminished by co-incubation with MIF in the soleus muscle. MIF also diminished glucose transport induced by a maximal dose of 5-aminoimidazole-4-carboxyamide ribonucleoside (AICAR), an AMPK activator, in the EDL muscle. These results suggest that MIF is a negative regulator of insulin- and AICAR-induced glucose transport in skeletal muscle. Since MIF secretion from C2C12 myotubes to the culture medium decreased during contraction evoked by electrical stimulations, MIF may be involved in the mechanisms underlying exercise-induced sensitization of glucose transport in skeletal muscle.

A novel human aquaporin-4 splice variant exhibits a dominant-negative activity: a new mechanism to regulate water permeability

Two major isoforms of aquaporin-4 (AQP4) have been described in human tissue. Here we report the identification and functional analysis of an alternatively spliced transcript of human AQP4, AQP4-Δ4, that lacks exon 4. In transfected cells AQP4-Δ4 is mainly retained in the endoplasmic reticulum and shows no water transport properties. When AQP4-Δ4 is transfected into cells stably expressing functional AQP4, the surface expression of the full-length protein is reduced. Furthermore, the water transport activity of the cotransfectants is diminished in comparison to transfectants expressing only AQP4. The observed down-regulation of both the expression and water channel activity of AQP4 is likely to originate from a dominant-negative effect caused by heterodimerization between AQP4 and AQP4-Δ4, which was detected in coimmunoprecipitation studies. In skeletal muscles, AQP4-Δ4 mRNA expression inversely correlates with the level of AQP4 protein and is physiologically associated with different types of skeletal muscles. The expression of AQP4-Δ4 may represent a new regulatory mechanism through which the cell-surface expression and therefore the activity of AQP4 can be physiologically modulated.