Energy sensing by the AMP-activated protein kinase and its effects on muscle metabolism

Oyster (Ostrea Plicatula Gmelin) Peptides Improve Exercise Endurance Capacity via Activating AMPK and HO-1

OBJECTIVE

Previous studies have shown that oyster peptides (OPs) have antioxidant and anti-fatigue activities. This study aimed to investigate the effects of OPs on swimming endurance in mice and the underlying mechanisms.

METHODS

The mice were subjected to gavage with OPs and subjected to exercise training. After 14 days, various biochemical indicators in the blood and gastrocnemius muscle of mice were assessed, and real-time PCR was utilized to detect the level of signal pathway regulation by OPs in the gastrocnemius muscle. Molecular docking technology was employed to observe the potential active components in OPs that regulate signal pathways.

RESULTS

In this study, OPs supplementation combined with and without exercise significantly extended swimming time compared to the sedentary group. OPs supplementation with exercise also increased glycogen levels and decreased blood urea nitrogen, lactate dehydrogenase, and lactic acid levels. Additionally, mice in the exercise with OPs group exhibited higher activities of antioxidant enzymes. OPs can upregulate metabolic regulatory factors such as AMP-activated protein kinase, peroxisome proliferator-activated receptor gamma coactivator-1 alpha, peroxisome proliferator-activated receptor delta, and glucose transporter 4, thereby increasing energy supply during exercise. Additionally, OPs enhances the expression of heme oxygenase 1 and superoxide dismutase 2, thereby reducing oxidative stress during physical activity. Molecular docking analyses revealed that peptides found in OPs formed hydrogen bonds with AMPK and HO-1, indicating that they can exert bioactivity by activating target proteins such as AMPK and HO-1.

CONCLUSIONS

OPs supplementation improved energy reserves, modulated energy metabolism pathways, and coordinated antioxidative stress responses, ultimately enhancing swimming endurance. These findings suggest that OPs have the potential to improve exercise levels by promoting metabolism and improving energy utilization efficiency.

Network model of skeletal muscle cell signalling predicts differential responses to endurance and resistance exercise training

Exercise-induced muscle adaptations vary based on exercise modality and intensity. We constructed a signalling network model from 87 published studies of human or rodent skeletal muscle cell responses to endurance or resistance exercise in vivo or simulated exercise in vitro. The network comprises 259 signalling interactions between 120 nodes, representing eight membrane receptors and eight canonical signalling pathways regulating 14 transcriptional regulators, 28 target genes and 12 exercise-induced phenotypes. Using this network, we formulated a logic-based ordinary differential equation model predicting time-dependent molecular and phenotypic alterations following acute endurance and resistance exercises. Compared with nine independent studies, the model accurately predicted 18/21 (85%) acute responses to resistance exercise and 12/16 (75%) acute responses to endurance exercise. Detailed sensitivity analysis of differential phenotypic responses to resistance and endurance training showed that, in the model, exercise regulates cell growth and protein synthesis primarily by signalling via mechanistic target of rapamycin, which is activated by Akt and inhibited in endurance exercise by AMP-activated protein kinase. Endurance exercise preferentially activates inflammation via reactive oxygen species and nuclear factor κB signalling. Furthermore, the expected preferential activation of mitochondrial biogenesis by endurance exercise was counterbalanced in the model by protein kinase C in response to resistance training. This model provides a new tool for investigating cross-talk between skeletal muscle signalling pathways activated by endurance and resistance exercise, and the mechanisms of interactions such as the interference effects of endurance training on resistance exercise outcomes.

SMEK1 ablation promotes glucose uptake and improves obesity-related metabolic dysfunction via AMPK signaling pathway

Obesity has become a major risk of global public health. SMEK1 is also known as a regulatory subunit of protein phosphatase 4 (PP4). Both PP4 and SMEK1 have been clarified in many metabolic functions, including the regulation of hepatic gluconeogenesis and glucose transporter gene expression in yeast. Whether SMEK1 participates in obesity and the broader metabolic role in mammals is unknown. Thus, we investigated the function of SMEK1 in white adipose tissue and glucose uptake. GWAS/GEPIA/GEO database was used to analyze the correlation between SMEK1 and metabolic phenotypes/lipid metabolism-related genes/obesity. Smek1 KO mice were generated to identify the role of SMEK1 in obesity and glucose homeostasis. Cell culture and differentiation of stromal-vascular fractions (SVFs) and 3T3-L1 were used to determine the mechanism. 2-NBDG was used to measure the glucose uptake. Compound C was used to confirm the role of AMPK. We elucidated that SMEK1 was correlated with obesity and adipogenesis. Smek1 deletion enhanced adipogenesis in both SVFs and 3T3-L1. Smek1 KO protected mice from obesity and had protective effects on metabolic disorders, including insulin resistance and inflammation. Smek1 KO mice had lower levels of fasting serum glucose. We found that SMEK1 ablation promoted glucose uptake by increasing p-AMPKα(T172) and the transcription of Glut4 when the effect on AMPK-regulated glucose uptake was due to the PP4 catalytic subunits (PPP4C). Our findings reveal a novel role of SMEK1 in obesity and glucose homeostasis, providing a potential new therapeutic target for obesity and metabolic dysfunction.NEW & NOTEWORTHY Our study clarified the relationship between SMEK1 and obesity for the first time and validated the conclusion in multiple ways by combining available data from public databases, human samples, and animal models. In addition, we clarified the role of SMEK1 in glucose uptake, providing an in-depth interpretation for the study of its function in glucose metabolism.

Resistance-only and concurrent exercise induce similar myofibrillar protein synthesis rates and associated molecular responses in moderately active men before and after training

Aerobic and resistance exercise (RE) induce distinct molecular responses. One hypothesis is that these responses are antagonistic and unfavorable for the anabolic response to RE when concurrent exercise is performed. This thesis may also depend on the participants' training status and concurrent exercise order. We measured free-living myofibrillar protein synthesis (MyoPS) rates and associated molecular responses to resistance-only and concurrent exercise (with different exercise orders), before and after training. Moderately active men completed one of three exercise interventions (matched for age, baseline strength, body composition, and aerobic capacity): resistance-only exercise (RE, n = 8), RE plus high-intensity interval exercise (RE+HIIE, n = 8), or HIIE+RE (n = 9). Participants trained 3 days/week for 10 weeks; concurrent sessions were separated by 3 h. On the first day of Weeks 1 and 10, muscle was sampled immediately before and after, and 3 h after each exercise mode and analyzed for molecular markers of MyoPS and muscle glycogen. Additional muscle, sampled pre- and post-training, was used to determine MyoPS using orally administered deuterium oxide (D2 O). In both weeks, MyoPS rates were comparable between groups. Post-exercise changes in proteins reflective of protein synthesis were also similar between groups, though MuRF1 and MAFbx mRNA exhibited some exercise order-dependent responses. In Week 10, exercise-induced changes in MyoPS and some genes (PGC-1ɑ and MuRF1) were dampened from Week 1. Concurrent exercise (in either order) did not compromise the anabolic response to resistance-only exercise, before or after training. MyoPS rates and some molecular responses to exercise are diminished after training.

Interplay between Cultured Human Osteoblastic and Skeletal Muscle Cells: Effects of Conditioned Media on Glucose and Fatty Acid Metabolism

The interplay between skeletal muscle and bone is primarily mechanical; however, biochemical crosstalk by secreted mediators has recently gained increased attention. The aim of this study was to investigate metabolic effects of conditioned medium from osteoblasts (OB-CM) on myotubes and vice versa. Human skeletal muscle cells incubated with OB-CM showed increased glucose uptake and oxidation, and mRNA expression of the glucose transporter (GLUT) 1, while fatty acid uptake and oxidation, and mRNA expression of the fatty acid transporter CD36 were decreased. This was supported by proteomic analysis, where expression of proteins involved in glucose uptake, glycolytic pathways, and the TCA cycle were enhanced, and expression of several proteins involved in fatty acid metabolism were reduced. Similar effects on energy metabolism were observed in human bone marrow stromal cells differentiated to osteoblastic cells incubated with conditioned medium from myotubes (SKM-CM), with increased glucose uptake and reduced oleic acid uptake. Proteomic analyses of the two conditioned media revealed many common proteins. Thus, our data may indicate a shift in fuel preference from fatty acid to glucose metabolism in both cell types, induced by conditioned media from the opposite cell type, possibly indicating a more general pattern in communication between these tissues.

Potentilla fulgens upregulate GLUT4, AMPK, AKT and insulin in alloxan-induced diabetic mice: an in vivo and in silico study

OBJECTIVE

This study was designed to investigate whether the glucose lowering effects of Potentilla fulgens acts by modulating GLUT4, AKT2 and AMPK expression in the skeletal muscle and liver tissues.

METHODOLOGY

Alloxan-induced diabetic mice treated with Potentilla fulgens was assessed for their blood glucose and insulin level, mRNA and protein expression using distinguished methods. Additionally, GLUT4, AKT2 and AMPK were docked with catechin, epicatechin, kaempferol, metformin, quercetin and ursolic acid reportedly present in Potentilla fulgens.

RESULTS

Potentilla fulgens ameliorates hyperglycaemia and insulin sensitivity via activation of AKT2 and AMPK, increases the expression of GLUT4, AKT2, AMPKα1 and AMPKα2 whose levels are reduced under diabetic condition. Molecular docking revealed interacting residues and their binding affinities (-4.56 to -8.95 Kcal/mol).

CONCLUSIONS

These findings provide more clarity vis-avis the mechanism of action of the phytoceuticals present in Potentilla fulgens extract which function through their action on GLUT4, PKB and AMPK.

Discovery and validation of metabolite markers in bloodstains for bloodstain age estimation

Bloodstain age estimation involves measuring time-dependent changes in the levels of biomolecules in bloodstains. Although several studies have identified bloodstain metabolites as markers for estimating bloodstain age, none have considered sex, age-related metabolomic differences, or long-time bloodstain age. Therefore, we aimed to identify metabolite markers for estimating the age of bloodstains at weekly intervals within 28 days and validate them through multiple reaction monitoring. Adenosine 5'-monophosphate, choline, and pyroglutamic acid were selected as markers. Seven metabolites were validated, including five previously reported metabolites, ergothioneine, hypoxanthine, L-isoleucine, L-tryptophan, and pyroglutamic acid. Choline and hypoxanthine can be used to differentiate bloodstains between days 0 and 14 after deposition at weekly intervals, whereas L-isoleucine and L-tryptophan can help distinguish bloodstains between 7 days before and 14 days after deposition. Evaluation of the changes in metabolite levels according to sex and age revealed that the average levels of all seven metabolites were higher in women on day 0. Moreover, the level of ergothioneine was significantly higher in elderly individuals than in young individuals at all time points. In this study, we confirmed the potential effectiveness of metabolites in bloodstains as forensic markers and provided a new perspective on metabolomic approaches linked to forensic science.

EVALUATION OF HIGH LEVELS OF SPORTS ACTIVITY AND THE BENEFICIAL EFFECT ON POSTPRANDIAL BLOOD GLUCOSE PROFILES

ABSTRACT Introduction: Hyperglycemia is the principal characteristic component of type 2 diabetes. High blood glucose concentrations for long periods can be countered with postprandial exercise by increasing glucose retention involuntary muscles. However, no research is present on the relationship between exercise time and glucose levels. Objective: This study evaluates the relationship between sports activity and postprandial glycemia levels. Methodology: Forty-five individuals were included in the study, 10 males and 35 females with an age of 27.11±2.8 years; a body fat percentage of 25.02% ±5.04%; and a body mass index of 22.74±4.55 kg/m2. Participants were included via WhatsApp for daily information on postprandial activity levels. WhatsApp messages were forwarded to a total of 2,500 people at different colleges and universities. Out of the total 60 active people (2.40%) who responded, 45 individuals participated in the study. They were divided into three categories based on self-reported postprandial activity: not very active (15), quite active (15), highly active (15). All active individuals completed an oral glucose intake test with blood samples obtained for evaluation at 15, 30, 45, 60, 90, and 120 minutes post-rest. On a gender basis, the groups could not be associated (P =.057). Results: All active groups showed a remarkable effect on blood glucose level at one hour (P =.031). A mean increase in blood glucose level in the first hour of 1.50 mmol/L was observed for every extra 1.0 mmol/L of standard glycemic amount, on average, women had a higher blood glucose amount of 1.35 mmol/L than men. Conclusion: It can be concluded that a high amount of postprandial activity generates a good outcome on glycemic parameters. Evidence Level II; Therapeutic Studies – Investigating the results.

Exploring the Muscle Metabolomics in the Mouse Model of Sepsis-Induced Acquired Weakness

Background/Aim

We aimed to identify the differentially expressing metabolites (DEMs) in the muscles of the mouse model of sepsis-induced acquired weakness (sepsis-AW) using liquid chromatography-mass spectrometry (LC-MS).

Materials and Methods

Sepsis by cecal ligation puncture (CLP) with lower limb immobilization was used to produce a sepsis-AW model. After this, the grip strength of the C57BL/6 male mice was investigated. The transmission electron microscopy was utilized to determine the pathological model. LC-MS was used to detect the metabolic profiles within the mouse muscles. Additionally, a statistically diversified analysis was carried out.

Results

Compared to the sepsis group, 30 DEMs, including 17 upregulated and 13 down-regulated metabolites, were found in the sepsis-AW group. The enriched metabolic pathways including purine metabolism, valine/leucine/isoleucine biosynthesis, cGMP-PKG pathway, mTOR pathway, FoxO pathway, and PI3K-Akt pathway were found to differ between the two groups. The targeted metabolomics analysis explored significant differences between four amino acid metabolites (leucine, cysteine, tyrosine, and serine) and two energy metabolites (AMP and cAMP) in the muscles of the sepsis-AW experimental model group, which was comparable to the sepsis group.

Conclusion

The present work identified DEMs and metabolism-related pathways within the muscles of the sepsis-AW mice, which offered valuable experimental data for diagnosis and identification of the pathogenic mechanism underlying sepsis-AW.

Emerging Link between Tsc1 and FNIP Co-Chaperones of Hsp90 and Cancer

Heat shock protein-90 (Hsp90) is an ATP-dependent molecular chaperone that is tightly regulated by a group of proteins termed co-chaperones. This chaperone system is essential for the stabilization and activation of many key signaling proteins. Recent identification of the co-chaperones FNIP1, FNIP2, and Tsc1 has broadened the spectrum of Hsp90 regulators. These new co-chaperones mediate the stability of critical tumor suppressors FLCN and Tsc2 as well as the various classes of Hsp90 kinase and non-kinase clients. Many early observations of the roles of FNIP1, FNIP2, and Tsc1 suggested functions independent of FLCN and Tsc2 but have not been fully delineated. Given the broad cellular impact of Hsp90-dependent signaling, it is possible to explain the cellular activities of these new co-chaperones by their influence on Hsp90 function. Here, we review the literature on FNIP1, FNIP2, and Tsc1 as co-chaperones and discuss the potential downstream impact of this regulation on normal cellular function and in human diseases.

Irisin Attenuates Muscle Impairment during Bed Rest through Muscle-Adipose Tissue Crosstalk

The detrimental effect of physical inactivity on muscle characteristics are well known. Irisin, an exercise-induced myokine cleaved from membrane protein fibronectin type III domain-containing protein-5 (FNDC5), mediates at least partially the metabolic benefits of exercise. This study aimed to assess the interplay between prolonged inactivity, circulating irisin, muscle performance, muscle fibers characteristics, as well as the FNDC5 gene expression (FNDC5ge) in muscle and adipose tissue among healthy subjects. Twenty-three healthy volunteers were tested before and after 14 days of Bed Rest, (BR). Post-BR circulating levels of irisin significantly increased, whereas body composition, muscle performance, and muscle fiber characteristics deteriorated. Among the subjects achieving the highest post-BR increase of irisin, the lowest reduction in maximal voluntary contraction and specific force of Fiber Slow/1, the highest increase of FNDC5ge in adipose tissue, and no variation of FNDC5ge in skeletal muscle were recorded. Subjects who had the highest FNDC5ge in adipose tissue but not in muscle tissue showed the highest circulating irisin levels and could better withstand the harmful effect of BR.

Proteomics and metabolomics combined study on endopathic changes of water-soluble precursors in Tan lamb during postmortem aging

Tan lamb is highly recommended breed in China. It is of great significance to understand the underlying mechanism of how water‐soluble flavor precursors metabolize in Tan lamb muscles during the postmortem aging period. In this study, we investigated the muscle pH, lactate dehydrogenase (LDH) activity, and the variations in water‐soluble flavor‐related metabolites. The proteome changes were profiled to provide insights into the biochemical changes affecting accumulation of water‐soluble flavor precursors in different aging stages (days 0, 4, and 8). The results indicated that pH value considerably decreased from day 0 to day 4, and increased from day 4 to day 8 (p < .05). The activity of LDH significantly increased from day 0 to day 4, and decreased from day 4 to day 8 (p < .05). Postmortem glycolysis was activated in 4 days, which directly affected the variations in metabolic enzymes and triggered the accumulation of flavor‐related carbohydrates. The free amino acids accumulated due to hydrolysis of structural proteins, with 3‐hydroxy‐L‐proline, aspartic acid, and methionine increasing from day 0 to day 4, and aspartic acid, serine, threonine, tyrosine, phenylalanine, and D‐phenylalanine from day 4 to day 8. The inosine and hypoxanthine accumulated due to the degradation of ATP. The results of the present study provide insightful information, revealing the differences in biochemical attributes in Tan lamb muscles caused by postmortem aging.

Drug Discovery of Plausible Lead Natural Compounds That Target the Insulin Signaling Pathway: Bioinformatics Approaches

The growing smooth talk in the field of natural compounds is due to the ancient and current interest in herbal medicine and their potentially positive effects on health. Dozens of antidiabetic natural compounds were reported and tested in vivo, in silico, and in vitro. The role of these natural compounds, their actions on the insulin signaling pathway, and the stimulation of the glucose transporter-4 (GLUT4) insulin-responsive translocation to the plasma membrane (PM) are all crucial in the treatment of diabetes and insulin resistance. In this review, we collected and summarized a group of available in vivo and in vitro studies which targeted isolated phytochemicals with possible antidiabetic activity. Moreover, the in silico docking of natural compounds with some of the insulin signaling cascade key proteins is also summarized based on the current literature. In this review, hundreds of recent studies on pure natural compounds that alleviate type II diabetes mellitus (type II DM) were revised. We focused on natural compounds that could potentially regulate blood glucose and stimulate GLUT4 translocation through the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway. On attempt to point out potential new natural antidiabetic compounds, this review also focuses on natural ingredients that were shown to interact with proteins in the insulin signaling pathway in silico, regardless of their in vitro/in vivo antidiabetic activity. We invite interested researchers to test these compounds as potential novel type II DM drugs and explore their therapeutic mechanisms.

Factors Influencing AMPK Activation During Cycling Exercise: A Pooled Analysis and Meta-Regression

BACKGROUND

The 5' adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a cellular energy sensor that is activated by increases in the cellular AMP/adenosine diphosphate:adenosine triphosphate (ADP:ATP) ratios and plays a key role in metabolic adaptations to endurance training. The degree of AMPK activation during exercise can be influenced by many factors that impact on cellular energetics, including exercise intensity, exercise duration, muscle glycogen, fitness level, and nutrient availability. However, the relative importance of these factors for inducing AMPK activation remains unclear, and robust relationships between exercise-related variables and indices of AMPK activation have not been established.

OBJECTIVES

The purpose of this analysis was to (1) investigate correlations between factors influencing AMPK activation and the magnitude of change in AMPK activity during cycling exercise, (2) investigate correlations between commonly reported measures of AMPK activation (AMPK-α2 activity, phosphorylated (p)-AMPK, and p-acetyl coenzyme A carboxylase (p-ACC), and (3) formulate linear regression models to determine the most important factors for AMPK activation during exercise.

METHODS

Data were pooled from 89 studies, including 982 participants (93.8% male, maximal oxygen consumption [[Formula: see text]] 51.9 ± 7.8 mL kg^-1 min^-1). Pearson's correlation analysis was performed to determine relationships between effect sizes for each of the primary outcome markers (AMPK-α2 activity, p-AMPK, p-ACC) and factors purported to influence AMPK signaling (muscle glycogen, carbohydrate ingestion, exercise duration and intensity, fitness level, and muscle metabolites). General linear mixed-effect models were used to examine which factors influenced AMPK activation.

RESULTS

Significant correlations (r = 0.19-0.55, p < .05) with AMPK activity were found between end-exercise muscle glycogen, exercise intensity, and muscle metabolites phosphocreatine, creatine, and free ADP. All markers of AMPK activation were significantly correlated, with the strongest relationship between AMPK-α2 activity and p-AMPK (r = 0.56, p < 0.001). The most important predictors of AMPK activation were the muscle metabolites and exercise intensity.

CONCLUSION

Muscle glycogen, fitness level, exercise intensity, and exercise duration each influence AMPK activity during exercise when all other factors are held constant. However, disrupting cellular energy charge is the most influential factor for AMPK activation during endurance exercise.

New Insights into Molecular Mechanisms Mediating Adaptation to Exercise; A Review Focusing on Mitochondrial Biogenesis, Mitochondrial Function, Mitophagy and Autophagy

Exercise itself is fundamental for good health, and when practiced regularly confers a myriad of metabolic benefits in a range of tissues. These benefits are mediated by a range of adaptive responses in a coordinated, multi-organ manner. The continued understanding of the molecular mechanisms of action which confer beneficial effects of exercise on the body will identify more specific pathways which can be manipulated by therapeutic intervention in order to prevent or treat various metabolism-associated diseases. This is particularly important as exercise is not an available option to all and so novel methods must be identified to confer the beneficial effects of exercise in a therapeutic manner. This review will focus on key emerging molecular mechanisms of mitochondrial biogenesis, autophagy and mitophagy in selected, highly metabolic tissues, describing their regulation and contribution to beneficial adaptations to exercise.

Discovery of donor age markers from bloodstain by LC-MS/MS using a metabolic approach

Bloodstains are frequently encountered at crime scenes and they provide important evidence about the incident, such as information about the victim or suspect and the time of death or other events. Efforts have been made to identify the age of the bloodstain's donor through genomic approaches, but there are some limitations, such as the availability of databases and the quality dependence of DNA. There is a need for the development of a tool that can obtain information at once from a small blood sample. The aim of this study is to identify bloodstain metabolite candidates that can be used to determine donor age. We prepared bloodstain samples and analyzed metabolites using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Eighteen molecular features (MFs) were selected as candidates using volcano plots and multivariate analysis. Based on the MS/MS spectrum of the MFs, the following nine metabolites were identified from the METaboliteLINk database: Δ2-cis eicosenoic acid, ergothioneine, adenosine 5'-monophosphate, benzaldehyde, phenacylamine, myristic acid ethyl ester, p-coumaric acid, niacinamide, and N-arachidonoyl-L-alanine. These nine age markers at high or low abundances could be used to estimate the age of a bloodstain's donor. This study was the first to develop metabolite age markers that can be used to analyze crime scene bloodstains.

Regulation of Energy Substrate Metabolism in Endurance Exercise

The human body requires energy to function. Adenosine triphosphate (ATP) is the cellular currency for energy-requiring processes including mechanical work (i.e., exercise). ATP used by the cells is ultimately derived from the catabolism of energy substrate molecules—carbohydrates, fat, and protein. In prolonged moderate to high-intensity exercise, there is a delicate interplay between carbohydrate and fat metabolism, and this bioenergetic process is tightly regulated by numerous physiological, nutritional, and environmental factors such as exercise intensity and duration, body mass and feeding state. Carbohydrate metabolism is of critical importance during prolonged endurance-type exercise, reflecting the physiological need to regulate glucose homeostasis, assuring optimal glycogen storage, proper muscle fuelling, and delaying the onset of fatigue. Fat metabolism represents a sustainable source of energy to meet energy demands and preserve the ‘limited’ carbohydrate stores. Coordinated neural, hormonal and circulatory events occur during prolonged endurance-type exercise, facilitating the delivery of fatty acids from adipose tissue to the working muscle for oxidation. However, with increasing exercise intensity, fat oxidation declines and is unable to supply ATP at the rate of the exercise demand. Protein is considered a subsidiary source of energy supporting carbohydrates and fat metabolism, contributing to approximately 10% of total ATP turnover during prolonged endurance-type exercise. In this review we present an overview of substrate metabolism during prolonged endurance-type exercise and the regulatory mechanisms involved in ATP turnover to meet the energetic demands of exercise.

Daidzein alleviates cisplatin-induced muscle atrophy by regulating Glut4/AMPK/FoxO pathway

Cisplatin (DDP) is widely used in cancer treatment, but DDP can cause skeletal muscle atrophy and cachexia. This study explored the effect and mechanism of daidzein (DAI) in reducing DDP-induced skeletal muscle atrophy and cachexia in vivo and in vitro. DAI alleviated the weight, food intake, muscle, adipose tissue, kidney weight and forelimb grip of LLC tumour-bearing mice after DDP treatment, and did not affect the antitumour effect of DDP. DAI can reduce the decrease of the cross-sectional area of skeletal muscle fibre-induced by DDP and prevent the change of fibre type proportion. In skeletal muscle, it can inhibit Glut4/AMPK/FoxO pathway, down-regulate the expression of atrogin1 and MuRF1, and inhibit skeletal muscle protein degradation. In DDP treated C2C12 myotubes, DAI could inhibit Glut4/AMPK/FoxO pathway to reduce myotubes atrophy, while AMPK agonist MK-3903 could reverse the protective effect of DAI. These results suggest that DAI can alleviate DDP-induced skeletal muscle atrophy by downregulating the expression of Atrogin1 and MuRF1 through the regulation of Glut4/AMPK/FoxO pathway.

Quantitative Proteomic Approach Reveals Altered Metabolic Pathways in Response to the Inhibition of Lysine Deacetylases in A549 Cells under Normoxia and Hypoxia

Growing evidence is showing that acetylation plays an essential role in cancer, but studies on the impact of KDAC inhibition (KDACi) on the metabolic profile are still in their infancy. Here, we analyzed, by using an iTRAQ-based quantitative proteomics approach, the changes in the proteome of KRAS-mutated non-small cell lung cancer (NSCLC) A549 cells in response to trichostatin-A (TSA) and nicotinamide (NAM) under normoxia and hypoxia. Part of this response was further validated by molecular and biochemical analyses and correlated with the proliferation rates, apoptotic cell death, and activation of ROS scavenging mechanisms in opposition to the ROS production. Despite the differences among the KDAC inhibitors, up-regulation of glycolysis, TCA cycle, oxidative phosphorylation and fatty acid synthesis emerged as a common metabolic response underlying KDACi. We also observed that some of the KDACi effects at metabolic levels are enhanced under hypoxia. Furthermore, we used a drug repositioning machine learning approach to list candidate metabolic therapeutic agents for KRAS mutated NSCLC. Together, these results allow us to better understand the metabolic regulations underlying KDACi in NSCLC, taking into account the microenvironment of tumors related to hypoxia, and bring new insights for the future rational design of new therapies.

Guanidino-Acetic Acid: A Scarce Substance in Biomass That Can Regulate Postmortem Meat Glycolysis of Broilers Subjected to Pre-slaughter Transportation

The different substances in biomass can regulate the metabolism and reproduction of broilers. Guanidino-acetic acid (GAA) is a natural feed additive that showed a potential application in dietary for broilers, while its amount is scarce in biomass. The objective of the present study was to investigate the effects of dietary supplemented with GAA on muscle glycolysis of broilers subjected to pre-slaughter transportation. A total of 160 Qiandongnan Xiaoxiang chickens were randomly assigned into three treatments, including a basal control diet without GAA supplementation (80 birds) or supplemented with 600 mg/kg (40 birds) or 1,200 mg/kg (40 birds) GAA for 14 days. At the end of the experiment, the control group was equally divided into two groups, thus resulting in four groups. All birds in the four groups aforementioned were separately treated according to the following protocols: (1) no transport of birds of the control group fed with the basal diet; (2) a 3-h transport of birds of the control group fed with the basal diet; (3) a 3-h transport of birds fed with diets supplemented with 600 mg/kg GAA; and (4) a 3-h transport of birds fed with diets supplemented with 1,200 mg/kg GAA. The results demonstrated that 3-h pre-slaughter transport stress increased corticosterone contents and lowered glucose contents in plasma (P < 0.05), decreased pH_{24 h} (P < 0.05), and resulted in inferior meat quality evidenced by elevating the drip loss, cooking loss, and L^∗ value (P < 0.05). Meanwhile, 3-h pre-slaughter transport stress decreased the contents of Cr and ATP in muscle (P < 0.05) and elevated the ratio of AMP:ATP and the glycolytic potential of muscle (P < 0.05). Moreover, 3-h pre-slaughter transport resulted in a significant elevation of mRNA expressions of LKB1 and AMPKα2 (P < 0.05), as well as the increase in protein abundances of LKB1 phosphorylation and AMPKα phosphorylation (P < 0.05). However, 1,200 mg/kg GAA supplementation alleviated negative parameters in plasma, improved meat quality, and ameliorated postmortem glycolysis and energy metabolism through regulating the creatine-phosphocreatine cycle and key factors of AMPK signaling. In conclusion, dietary supplementation with 1,200 mg/kg GAA contributed to improving meat quality via ameliorating muscle energy expenditure and delaying anaerobic glycolysis of broilers subjected to the 3-h pre-slaughter transport.

Responses to oral glucose challenge differ by physical activity volume and intensity: A pilot study

BACKGROUND

One-hour postprandial hyperglycemia is associated with increased risk of type 2 diabetes and cardiovascular disease. Physical activity (PA) has short-term beneficial effects on post-meal glucose response. This study compared the oral glucose tolerance test results of 3 groups of people with habitually different levels of PA.

METHODS

Thirty-one adults without diabetes (age 25.9 ± 6.6 years; body mass index 23.8 ± 3.8 kg/m²; mean ± SD) were recruited and divided into 3 groups based on self-reported PA volume and intensity: low activity < 30 min/day of moderate-intensity activity (n = 11), moderately active ≥ 30 min/day of moderate-intensity PA (n = 10), and very active ≥ 60 min/day of PA at high intensity (n = 10). Participants completed an oral glucose tolerance test (50 g glucose) with capillary blood samples obtained at baseline, 15 min, 30 min, 45 min, 60 min, 90 min, and 120 min post-ingestion.

RESULTS

There were no significant differences between groups for age or body fat percentage or glycated hemoglobin (p > 0.05). The groups were significantly different in terms of baseline glucose level (p = 0.003) and, marginally, for gender (p = 0.053) and BMI (p = 0.050). There was a statistically significant effect of PA on the 1-h postprandial glucose results (p = 0.029), with differences between very active and low activity groups (p = 0.008) but not between the moderately active and low activity groups (p = 0.360), even when baseline glucose level and gender differences were accounted for. For incremental area under the curve there was no significant effect of activity group once gender and body fat percentage had been accounted for (p = 0.401). Those in the low activity group took 15 min longer to reach peak glucose level than those in the very active group (p = 0.012).

CONCLUSION

The results suggest that high levels of PA have a beneficial effect on postprandial blood glucose profiles when compared to low and moderate levels of activity.

ProNGF/p75NTR Axis Drives Fiber Type Specification by Inducing the Fast-Glycolytic Phenotype in Mouse Skeletal Muscle Cells

Despite its undisputable role in the homeostatic regulation of the nervous system, the nerve growth factor (NGF) also governs the relevant cellular processes in other tissues and organs. In this study, we aimed at assessing the expression and the putative involvement of NGF signaling in skeletal muscle physiology. To reach this objective, we employed satellite cell-derived myoblasts as an in vitro culture model. In vivo experiments were performed on Tibialis anterior from wild-type mice and an mdx mouse model of Duchenne muscular dystrophy. Targets of interest were mainly assessed by means of morphological, Western blot and qRT-PCR analysis. The results show that proNGF is involved in myogenic differentiation. Importantly, the proNGF/p75NTR pathway orchestrates a slow-to-fast fiber type transition by counteracting the expression of slow myosin heavy chain and that of oxidative markers. Concurrently, proNGF/p75NTR activation facilitates the induction of fast myosin heavy chain and of fast/glycolytic markers. Furthermore, we also provided evidence that the oxidative metabolism is impaired in mdx mice, and that these alterations are paralleled by a prominent buildup of proNGF and p75NTR. These findings underline that the proNGF/p75NTR pathway may play a crucial role in fiber type determination and suggest its prospective modulation as an innovative therapeutic approach to counteract muscle disorders.

Manipulating Cellular Energetics to Slow Aging of Tissues and Organs

Up to now numerous studies in the field of gerontology have been published. Nevertheless, a well-known food restriction remains the most reliable and efficient way of lifespan extension. Physical activity is also a well-documented anti-aging intervention being especially efficient in slowing down the age-associated decline of skeletal muscle mass. In this review we focus on the molecular mechanisms of the effect of physical exercise on muscle tissues. We also discuss the possibilities of pharmacological extension of this effect to the rest of the tissues. During the exercise, the level of ATP decreases triggering activation of AMP-dependent protein kinase (AMPK). This kinase stimulates antioxidant potential of the cells and their mitochondrial respiratory capacity. The exercise also induces mild oxidative stress, which, in turn, mediates the stimulation via hormetic response. Furthermore, during the exercise cells generate activators of mammalian target of rapamycin (mTOR). The intracellular ATP level increases during the rest periods between exercises thus promoting mTOR activation. Therefore, regular exercise intermittently activates anti-oxidant defenses and mitochondrial biogenesis (via AMPK and the hormetic response) of the muscle tissue, as well as its proliferative potential (via mTOR), which, in turn, impedes the age-dependent muscle atrophy. Thus, the intermittent treatment with activators of (i) AMPK combined with the inducers of hormetic response and of (ii) mTOR might partly mimic the effects of physical exercise. Importantly, pharmacological activation of AMPK takes place in the absence of ATP level decrease. The use of uncouplers of respiration and oxidative phosphorylation at the phase of AMPK activation could also prevent negative consequences of the cellular hyper-energization. It is believed that the decline of both antioxidant and proliferative potentials of the cells causes the age-dependent decline of multiple tissues, rather than only the muscular one. We argue that the approach above is applicable for the majority of tissues in an organism.

AMP-activated protein kinase controls lipid and lactose synthesis in bovine mammary epithelial cells

The synthesis of milk components in bovine mammary epithelial cells (BMEC) requires an adequate supply of energy. The AMP-activated protein kinase (AMPK) is a cellular energy gauge that controls anabolic and catabolic processes to maintain a balance between energy supply and demand. The objectives of this study were to assess the role of AMPK on de novo lipid and lactose synthesis, as well as its regulation by glucose and acetate availability in BMEC. We isolated primary BMEC from the mammary tissue of 3 lactating Holstein cows and differentiated them with lactogenic hormones for 4 d. We measured protein abundance, site-specific phosphorylation, and proteolytic processing by immunoblotting. We quantified the expression of genes involved in lipid and lactose synthesis using real-time quantitative PCR. We measured de novo lipid and lactose synthesis by incorporation of radioactive substrates. We analyzed data by ANOVA using a randomized complete block design with PROC MIXED in SAS. To assess the effect of AMPK activation on milk component synthesis, we treated BMEC with 100 μM A-769662 (A76; an allosteric activator of AMPK) or vehicle control for 16 h. Consistent with activation of AMPK, A76 increased phosphorylation of its downstream targets ACC Ser79 and TSC2 Ser1387 by 144% and 26%, respectively. Activation of AMPK decreased lipid synthesis by 19%. This effect was accompanied by increased expression of FABP3. Activation of AMPK reduced the proportion of mature SREBP-1c. In addition, AMPK activation reduced lactose synthesis by 24% and lowered the expression of SLC2A1, the gene encoding GLUT1. To assess the regulation of AMPK by energy substrate availability, we incubated BMEC in a control medium containing 4 mM D-glucose and 1 mM sodium acetate, or medium lacking glucose or acetate, for 4 h. Compared with the control medium, deprivation of glucose or acetate promoted AMPKα phosphorylation at Thr172 by 84% or 58%, respectively. Activation of AMPK was significantly increased in BMEC only when the medium was devoid of glucose for at least 4 h. We concluded that activation of AMPK inhibits de novo lipid and lactose synthesis in BMEC. Further studies are needed to assess the physiological relevance of AMPK activation for milk composition in vivo and to identify the mechanisms mediating its effects on milk component synthesis.

The Regulation of Lipokines by Environmental Factors

Adipose tissue is a highly metabolically-active tissue that senses and secretes hormonal and lipid mediators that facilitate adaptations to metabolic tissues. In recent years, the role of lipokines, which are lipid species predominantly secreted from adipose tissue that act as hormonal regulators in many metabolic tissues, has been an important area of research for obesity and diabetes. Previous studies have identified that these secreted lipids, including palmitoleate, 12,13-diHOME, and fatty acid-hydroxy-fatty acids (FAHFA) species, are important regulators of metabolism. Moreover, environmental factors that directly affect the secretion of lipokines such as diet, exercise, and exposure to cold temperatures constitute attractive therapeutic strategies, but the mechanisms that regulate lipokine stimulation have not been thoroughly reviewed. In this study, we will discuss the chemical characteristics of lipokines that position them as attractive targets for chronic disease treatment and prevention and the emerging roles of lipokines as regulators of inter-tissue communication. We will define the target tissues of lipokines, and explore the ability of lipokines to prevent or delay the onset and development of chronic diseases. Comprehensive understanding of the lipokine synthesis and lipokine-driven regulation of metabolic outcomes is instrumental for developing novel preventative and therapeutic strategies that harness adipose tissue-derived lipokines.

Control strategies in systemic metabolism

Metabolic control systems coordinate myriad processes across the cellular, tissue and organismal levels to optimize the allocation of limited supplies across multiple, often competing, metabolic demands. As such, the regulation of metabolism can be analysed from the perspective of the economic theory of supply and demand. Here, we discuss how such analyses can provide new insights into the logic of metabolic control. In particular, we suggest that, in addition to being subject to well-appreciated homeostatic control, metabolism is subject to supply-driven and demand-driven controls, each operated by a dedicated set of signals throughout various physiological states, including inflammation. Furthermore, we argue that systemic homeostasis is a derived feature that evolved from the control systems that monitor metabolic supply and demand.

Metformin promotes mitophagy in mononuclear cells: a potential in vitro model for unraveling metformin's mechanism of action

Increased oxidative stress in patients with type 2 diabetes mellitus (T2DM) results in abnormalities in cell repair processes, such as mitophagy, which compromises mitochondrial function and contributes to insulin resistance and β cell failure. Metformin, widely recommended in the management of T2DM, exerts its pleiotropic effects via 5'-AMP-activated protein kinase (AMPK); however, its effect on mitophagy remains elusive. Recent evidence demonstrates that peripheral blood mononuclear cells (PBMCs) express insulin receptors and the human organic cation transporter protein, and they are extensively being used as a surrogate for examining mitochondrial function in T2DM. Metformin treatment increased the formation of acidic vesicles and mitophagosomes, upregulated mitophagy markers, and enhanced mitophagic flux, as indicated by increased LC3-II expression and reduced p62 protein levels. In addition, pretreatment with compound C (an AMPK inhibitor) significantly decreased the expression of mitophagy markers in metformin-treated cells, indicating that metformin induces mitophagy via the AMPK pathway. In conclusion, metformin-induced mitophagy may improve cellular function, including in β cells, by restoring normal mitochondrial phenotype, which may prove beneficial in patients with T2DM and other mitochondrial-related diseases. Moreover, PBMCs may be used as a novel diagnostic biomarker for identifying mitochondrial disorders.

Progress in the discovery of naturally occurring anti-diabetic drugs and in the identification of their molecular targets

Diabetes mellitus (DM), a chronic metabolic disease, severely affects patients' life and intensively increases risks of developing other diseases. It is estimated that 0.4 billion individuals worldwide are subjected to diabetes, especially type 2 diabetes mellitus. At present, although various synthetic drugs for diabetes such as Alogliptin and Rosiglitazone, etc. have been used to manage diabetes, some of them showed severe side effects. Given that the pathogenesis of type 2 diabetes mellitus, natural occurring drugs are beneficial alternatives for diabetes therapy with low adverse effects or toxicity. Recently, more and more plant-derived extracts or compounds were evaluated to have anti-diabetic activities. Their anti-diabetic mechanisms involve certain key targets like α-glucosidase, α-amylase, DPP-4, PPAR γ, PTP1B, and GLUT4, etc. Here, we summarize the newly found anti-diabetic (type 2 diabetes mellitus) natural compounds and extracts from 2011-2017, and give the identification of their molecular targets. This review could provide references for the research of natural agents curing type 2 diabetes mellitus (T2DM).

Identification of baicalin from Bofutsushosan and Daisaikoto as a potent inducer of glucose uptake and modulator of insulin signaling-associated pathways

Type 2 diabetes mellitus (T2DM) is a chronic disease characterized by hyperglycemia that can lead to long-term complications including heart diseases, stroke, retinopathy, and renal failure. Treatment strategies include stimulating glucose uptake and controlling blood glucose level. Bofutsushosan (BOF) and Daisaikoto (DAI) are two herb-based kampo medicines that have been demonstrated to improve metabolism-associated disorders including obesity, hyperlipidemia, and nonalcoholic fatty liver. Given their bioactivities against metabolic syndromes, we explored in this study the effect of BOF and DAI extracts on glucose absorption and used them as source to identify phytochemical stimulator of glucose absorption. Glucose uptake and mechanistic studies were evaluated in differentiated C2C12 skeletal muscle cells, and HPLC analysis was used to determine the molecular bioactive constituents. Our results indicated that the ethanolic extracts of BOF and DAI (BOFEE and DAIEE, respectively) enhanced the glucose uptake ratio in the differentiated C2C12 cells, and further analysis identified the flavone baicalin as a major constituent capable of efficiently stimulating glucose absorption. Mechanistic studies revealed that the effect from baicalin involved the activation of IRS-1 and GLUT-4, and implicated the AMPK, PI3K/Akt, and MAPK/ERK signaling cascades. Due to its potency, we suggest that baicalin merit further evaluation as a potential candidate anti-hyperglycemic agent for the treatment and management of T2DM.

Damage to the myogenic differentiation of C2C12 cells by heat stress is associated with up-regulation of several selenoproteins

This study was conducted to profile the selenoprotein encoding genes or proteins in mouse C2C12 cells and integrate their roles in the skeletal cell damage induced by heat stress (HS). Cells were cultured at 37.0 °C or 41.5 °C for 4, 6 or 8 days. The mRNA expression of 24 selenoprotein encoding genes and abundance of 5 selenoproteins were investigated. HS suppressed myogenic differentiation and impaired the development of muscle myotubes. HS down-regulated (P < 0.01) mRNA abundance of MYOD and MYOGENIN, and decreased (P < 0.01) MYOGENIN protein expression, HS elevated (P < 0.01) HSP70 and (P < 0.01) the ratio of BCL-2 to BAX at both mRNA and protein level. Meanwhile, HS up-regulated (P < 0.01–0.05) expressions of 18, 11 and 8 selenoprotein encoding genes after 4, 6 and 8 days of hyperthermia, and only down-regulated (P < 0.01) DIO2 after 6 and 8 days of hyperthermia, respectively. Furthermore, HS influenced expression of selenoproteins and up-regulated (P < 0.01–0.05) GPX1, GPX4 and SEPN1 after 6 days of HS. The damage to development of mouse skeletal muscle myotubes by HS accompanied with the up-regulation of both selenoprotein encoding genes and proteins, which suggested a potential protective effect of selenoprotein on hyperthermia associated damage in C2C12 cells.

Overnight fasting compromises exercise intensity and volume during sprint interval training but improves high-intensity aerobic endurance

BACKGROUND

The combined effects of sprint interval training (SIT) and exercising in the fasted state are unknown. We compared the effects of SIT with exogenous carbohydrate supplementation (SIT-CHO) and SIT following overnight fast (SIT-Fast) on aerobic capacity (peak oxygen consumption: V̇O2peak) and high-intensity aerobic endurance (time-to-exhaustion at 85% V̇O2peak [T85%]).

METHODS

Twenty male cyclists were randomized to SIT-CHO and SIT-Fast. Both groups performed 30-second all-out cycling followed by 4-minute active recovery 3 times per week for 4 weeks, with the number of sprint bouts progressing from 4 to 7. Peak power output (PPO) and total mechanical work were measured for each sprint interval bout. The SIT-CHO group performed exercise sessions following breakfast and consumed carbohydrate drink during exercise, whereas the SIT-Fast group performed exercise sessions following overnight fast and consumed water during exercise. Before and after training, V̇O2peak and T85% were assessed. Blood glucose, non-esterified fatty acids, insulin and glucagon concentrations were measured during T85%.

RESULTS

Overall PPO and mechanical work were lower in SIT-Fast than SIT-CHO (3664.9 vs. 3871.7 J/kg; P=0.021 and 10.6 vs. 9.9 W/kg; P=0.010, respectively). Post-training V̇O2peak did not differ between groups. Baseline-adjusted post-training T85% was longer in SIT-Fast compared to SIT-CHO (19.7±3.0 vs. 16.6±3.0 minutes, ANCOVA P=0.038) despite no changes in circulating energy substrates or hormones.

CONCLUSIONS

Our results suggest that SIT-Fast compromises exercise intensity and volume but still can have a greater impact on the ability to sustain high-intensity aerobic endurance exercise compared to SIT-CHO.

Mechanisms of thermal adaptation and evolutionary potential of conspecific populations to changing environments

Heterogeneous and ever-changing thermal environments drive the evolution of populations and species, especially when extreme conditions increase selection pressure for traits influencing fitness. However, projections of biological diversity under scenarios of climate change rarely consider evolutionary adaptive potential of natural species. In this study, we tested for mechanistic evidence of evolutionary thermal adaptation among ecologically divergent redband trout populations (Oncorhynchus mykiss gairdneri) in cardiorespiratory function, cellular response and genomic variation. In a common garden environment, fish from an extreme desert climate had significantly higher critical thermal maximum (p < .05) and broader optimum thermal window for aerobic scope (>3°C) than fish from cooler montane climate. In addition, the desert population had the highest maximum heart rate during warming (20% greater than montane populations), indicating improved capacity to deliver oxygen to internal tissues. In response to acute heat stress, distinct sets of cardiac genes were induced among ecotypes, which helps to explain the differences in cardiorespiratory function. Candidate genomic markers and genes underlying these physiological adaptations were also pinpointed, such as genes involved in stress response and metabolic activity (hsp40, ldh-b and camkk2). These markers were developed into a multivariate model that not only accurately predicted critical thermal maxima, but also evolutionary limit of thermal adaptation in these specific redband trout populations relative to the expected limit for the species. This study demonstrates mechanisms and limitations of an aquatic species to evolve under changing environments that can be incorporated into advanced models to predict ecological consequences of climate change for natural organisms.

AMPK in skeletal muscle function and metabolism

Skeletal muscle possesses a remarkable ability to adapt to various physiologic conditions. AMPK is a sensor of intracellular energy status that maintains energy stores by fine-tuning anabolic and catabolic pathways. AMPK’s role as an energy sensor is particularly critical in tissues displaying highly changeable energy turnover. Due to the drastic changes in energy demand that occur between the resting and exercising state, skeletal muscle is one such tissue. Here, we review the complex regulation of AMPK in skeletal muscle and its consequences on metabolism (e.g., substrate uptake, oxidation, and storage as well as mitochondrial function of skeletal muscle fibers). We focus on the role of AMPK in skeletal muscle during exercise and in exercise recovery. We also address adaptations to exercise training, including skeletal muscle plasticity, highlighting novel concepts and future perspectives that need to be investigated. Furthermore, we discuss the possible role of AMPK as a therapeutic target as well as different AMPK activators and their potential for future drug development.—Kjøbsted, R., Hingst, J. R., Fentz, J., Foretz, M., Sanz, M.-N., Pehmøller, C., Shum, M., Marette, A., Mounier, R., Treebak, J. T., Wojtaszewski, J. F. P., Viollet, B., Lantier, L. AMPK in skeletal muscle function and metabolism.

Akebia saponin D alleviates hepatic steatosis through BNip3 induced mitophagy

Akebia Saponin D (ASD) is the most abundant constituent of the rhizome of Dipsacus asper Wall. The prior studies have shown that ASD alleviates hepatic steatosis targeted at the modulation of autophagy and exerts hepatoprotective effects through mitochondria. However, it is still unclear which signal transduction pathway that ASD increase autophagy and protect the mitochondria. The purpose of this paper was to explore the mechanisms through which ASD alleviates hepatic steatosis. ASD significantly reduced lipid accumulation in BRL cells. Furthermore, ASD significantly increased the mitophagy acting as increase the colocalization between mitochondria and punctate EGFP-LC3. ASD treatment increased the expression of BNip3, phospho-AMPK, prevented oleic acid (OA) induced LC3-II and phospho-mTOR expression. These effects were similar to the effects cotreatment with rapamycin. ASD treatment could not attenuate the expression of BNip3 blocked by chloroquine (CQ) or siRNA-mediated knockdown of BNip3. These results suggest that Akebia saponin D alleviates hepatic steatosis targeted at BNip3 mediated mitophagy. Activation of BNip3 via ASD may offer a new strategy for treating NAFLD.

Intake of a Ketone Ester Drink during Recovery from Exercise Promotes mTORC1 Signaling but Not Glycogen Resynthesis in Human Muscle

Purpose: Ketone bodies are energy substrates produced by the liver during prolonged fasting or low-carbohydrate diet. The ingestion of a ketone ester (KE) rapidly increases blood ketone levels independent of nutritional status. KE has recently been shown to improve exercise performance, but whether it can also promote post-exercise muscle protein or glycogen synthesis is unknown. Methods: Eight healthy trained males participated in a randomized double-blind placebo-controlled crossover study. In each session, subjects undertook a bout of intense one-leg glycogen-depleting exercise followed by a 5-h recovery period during which they ingested a protein/carbohydrate mixture. Additionally, subjects ingested a ketone ester (KE) or an isocaloric placebo (PL). Results: KE intake did not affect muscle glycogen resynthesis, but more rapidly lowered post-exercise AMPK phosphorylation and resulted in higher mTORC1 activation, as evidenced by the higher phosphorylation of its main downstream targets S6K1 and 4E-BP1. As enhanced mTORC1 activation following KE suggests higher protein synthesis rates, we used myogenic C₂C₁₂ cells to further confirm that ketone bodies increase both leucine-mediated mTORC1 activation and protein synthesis in muscle cells. Conclusion: Our results indicate that adding KE to a standard post-exercise recovery beverage enhances the post-exercise activation of mTORC1 but does not affect muscle glycogen resynthesis in young healthy volunteers. In vitro, we confirmed that ketone bodies potentiate the increase in mTORC1 activation and protein synthesis in leucine-stimulated myotubes. Whether, chronic oral KE intake during recovery from exercise can facilitate training-induced muscular adaptation and remodeling need to be further investigated.

Spatholobus suberectus Exhibits Antidiabetic Activity In Vitro and In Vivo through Activation of AKT-AMPK Pathway

Glucose deposition in peripheral tissue is an important parameter for the treatment of type 2 diabetes mellitus. The aim of this study was to investigate the effects of Spatholobus suberectus (Ss) on glucose disposal in skeletal muscle cells and additionally explore its in vivo antidiabetic potential. Treatment of ethanolic extract of S. suberectus (EeSs) significantly enhanced the glucose uptake, mediated through the enhanced expression of GLUT4 in skeletal muscle via the stimulation of AKT and AMPK pathways in C2C12 cells. Moreover, EeSs have potential inhibitory action on α-glucosidase activity and significantly lowered the postprandial blood glucose levels in STZ-induced diabetic mice, associated with increased expression of GLUT4 and AKT and/or AMPK-mediated signaling cascade in skeletal muscle. Furthermore, administration of EeSs significantly boosted up the antioxidant enzyme expression and also mitigated the gluconeogenesis enzyme such as PEPCK and G-6-Pase enzyme expression in liver tissue of STZ-induced diabetic mice model. Collectively, these findings suggest that EeSs have a high potentiality to mitigate diabetic symptoms through stimulating glucose uptake in peripheral tissue via the activation of AKT and AMPK signaling cascade and augmenting antioxidant potentiality as well as blocking the gluconeogenesis process in diabetic mice.

AMPK expression patterns are significantly associated with poor prognosis in breast cancer patients

Many investigators have examined the functions of AMP-activated protein kinase (AMPK) in cancer biology and its anti-neoplastic features in cancer models. The goal of this research is to assess the association of the immunohistochemical expression of AMPK in human mammary tumours with the clinical data of breast cancer patients. 449 cases of previously diagnosed breast cancer, and 27 tissue samples of fibroadenomas and normal breast were utilized for detection of AMPK expression using tissue microarrays and immunohistochemistry. Brownish nuclear and cytoplasmic staining were present in epithelial cells and stromal cells in 333 (74.16%) and 348 (77.5%) cancer cases respectively indicating AMPK expression. Twenty two (81.48%) control cases showed AMPK immunoexpression in both epithelial and stromal cells. Significant statistical association has been found between advanced stages of breast cancer and increased intensity of AMPK immunostaining only in epithelial cells (p-value=0.0001). Histotypes have been correlated with AMPK immunostaining in epithelial cells only (p-value=0.029). Low AMPK immunostaining scores were more dominant in DCIS, ductal and mixed type's ductal and mucinous histotypes, while high intense staining was more common in the lobular type. Furthermore, breast tumour cases with lymph node metastases showed significant AMPK expression in both epithelial and stromal cells (p-value=0.0001 and p-value=0.026). Low scores of AMPK immunostaining were common in breast cancer cases with positive vascular invasion (p-value=0.007) and disease recurrence (p-value=0.008). No significant differences in survival behavior distributions were observed for the different categories of AMPK immunostaining in epithelial and stromal cells. In conclusion, our results showed decreased AMPK expression in breast cancer in comparison with the control group. AMPK expression was significantly correlated with some clinicopathological factors like advanced stage, lymph node involvement, vascular invasion and disease recurrence which give indications for poor clinical outcomes. Immunohistochemical staining of AMPK protein is a valuable method which could predict cases of breast cancer with poor prognosis.

Treadmill exercise ameliorates the regulation of energy metabolism in skeletal muscle of NSE/PS2mtransgenic mice with Alzheimer's disease

[Purpose]

Alzheimer’s disease (AD) is classified as a progressive neurological disorder, which not only causes cognitive impairment but also abnormal weight loss, with a reduction of muscle mass related to the accumulation of amyloid-β (Aβ) in skeletal muscle. Thus, we investigated the effect of treadmill exercise on Aβ deposition, and p-AMPK, p-ACC, BDNF, and GLUT4 protein levels the regulation of muscle energy metabolism using an AD mouse.

[Methods]

At 13 months of age, NSE/PS2m mice (Tg) and control mice (non-Tg) were assigned to non-exercise control (Con) and exercise groups (Exe). The four groups were as follows: non-Tg Con, non-Tg Exe, Tg Con, and Tg Exe. The treadmill exercise was carried out for 12 weeks.

[Results]

The highest levels of Aβ expression in the skeletal muscle were in the Tg Con group. Aβ expression was significantly reduced in the Tg Exe group, compared to the Tg Con group. Congo red staining showed remarkable diffuse red amyloid deposition in the Tg Con group, while Aβ-deposition in the skeletal was reduced with muscle exercise in the Tg Exe group. Exercise also increased AMPK and ACC phosphorylation and BDNF and GLUT4 expression in the skeletal muscle of non-Tg and Tg mice.

[Conclusion]

Treadmill exercise reduces Aβ-deposition in the skeletal muscle and improves the regulation of energy metabolism. Thus, collectively, these results suggest that exercise could be a positive therapeutic strategy for skeletal muscle dysfunction in AD patients.

Glucose deprivation attenuates sortilin levels in skeletal muscle cells

In skeletal muscle, sortilin plays a predominant role in the sorting of glucose transporter 4 (Glut4), thereby controlling glucose uptake. Moreover, our previous study suggested that the sortilin expression levels are also implicated in myogenesis. Despite the importance of sortilin in skeletal muscle, however, the regulation of sortilin expression has not been completely understood. In the present study, we analyzed if the sortilin expression is regulated by glucose in C2C12 myocytes and rat skeletal muscles in vivo. Sortilin protein expression was elevated upon C2C12 cell differentiation and was further enhanced in the presence of a high concentration of glucose. The gene expression and protein degradation of sortilin were not affected by glucose. On the other hand, rapamycin partially reduced sortilin induction by a high concentration of glucose, which suggested that sortilin translation could be regulated by glucose, at least in part. We also examined if the sortilin regulation by glucose was also observed in skeletal muscles that were obtained from fed or fasted rats. Sortilin expression in both gastrocnemius and extensor digitorum longus (EDL) muscle was significantly decreased by 17-18h of starvation. On the other hand, pathological levels of high blood glucose did not alter the sortilin expression in rat skeletal muscle. Overall, the present study suggests that sortilin protein levels are reduced under hypoglycemic conditions by post-transcriptional control in skeletal muscles.

Procyanidin Promotes Translocation of Glucose Transporter 4 in Muscle of Mice through Activation of Insulin and AMPK Signaling Pathways

Procyanidins are the oligomeric or polymeric forms of epicatechin and catechin. In this study, we isolated and purified dimer to tetramer procyanidins from black soybean seed coat and investigated the anti-hyperglycemic effects by focusing on glucose transporter 4 (GLUT4) translocation and the underlying molecular mechanism in skeletal muscle of mice. The anti-hyperglycemic effects of procyanidins were also compared with those of monomer (-)-epicatechin (EC) and major anthocyanin, cyanidin-3-O-β-glucoside (C3G). To investigate GLUT4 translocation and its related signaling pathways, ICR mice were orally given procyanidins, EC and C3G in water at 10 μg/kg body weight. The mice were sacrificed 60 min after the dose of polyphenols, and soleus muscle was extracted from the hind legs. The results showed that trimeric and tetrameric procyanidins activated both insulin- and AMPK-signaling pathways to induce GLUT4 translocation in muscle of ICR mice. We confirmed that procyanidins suppressed acute hyperglycemia with an oral glucose tolerance test in a dose-dependent manner. Of these beneficial effects, cinnamtannin A2, one of the tetramers, was the most effective. In conclusion, procyanidins, especially cinnamtannin A2, significantly ameliorate postprandial hyperglycemia at least in part by promoting GLUT4 translocation to the plasma membrane by activating both insulin- and AMPK-signaling pathways.

AMPK activators: mechanisms of action and physiological activities

AMP-activated protein kinase (AMPK) is a central regulator of energy homeostasis, which coordinates metabolic pathways and thus balances nutrient supply with energy demand. Because of the favorable physiological outcomes of AMPK activation on metabolism, AMPK has been considered to be an important therapeutic target for controlling human diseases including metabolic syndrome and cancer. Thus, activators of AMPK may have potential as novel therapeutics for these diseases. In this review, we provide a comprehensive summary of both indirect and direct AMPK activators and their modes of action in relation to the structure of AMPK. We discuss the functional differences among isoform-specific AMPK complexes and their significance regarding the development of novel AMPK activators and the potential for combining different AMPK activators in the treatment of human disease.

The effect of age and unilateral leg immobilization for 2 weeks on substrate utilization during moderate-intensity exercise in human skeletal muscle

KEY POINTS

This study aimed to provide molecular insight into the differential effects of age and physical inactivity on the regulation of substrate metabolism during moderate-intensity exercise. Using the arteriovenous balance technique, we studied the effect of immobilization of one leg for 2 weeks on leg substrate utilization in young and older men during two-legged dynamic knee-extensor moderate-intensity exercise, as well as changes in key proteins in muscle metabolism before and after exercise. Age and immobilization did not affect relative carbohydrate and fat utilization during exercise, but the older men had higher uptake of exogenous fatty acids, whereas the young men relied more on endogenous fatty acids during exercise. Using a combined whole-leg and molecular approach, we provide evidence that both age and physical inactivity result in intramuscular lipid accumulation, but this occurs only in part through the same mechanisms.

ABSTRACT

Age and inactivity have been associated with intramuscular triglyceride (IMTG) accumulation. Here, we attempt to disentangle these factors by studying the effect of 2 weeks of unilateral leg immobilization on substrate utilization across the legs during moderate-intensity exercise in young (n = 17; 23 ± 1 years old) and older men (n = 15; 68 ± 1 years old), while the contralateral leg served as the control. After immobilization, the participants performed two-legged isolated knee-extensor exercise at 20 ± 1 W (∼50% maximal work capacity) for 45 min with catheters inserted in the brachial artery and both femoral veins. Biopsy samples obtained from vastus lateralis muscles of both legs before and after exercise were used for analysis of substrates, protein content and enzyme activities. During exercise, leg substrate utilization (respiratory quotient) did not differ between groups or legs. Leg fatty acid uptake was greater in older than in young men, and although young men demonstrated net leg glycerol release during exercise, older men showed net glycerol uptake. At baseline, IMTG, muscle pyruvate dehydrogenase complex activity and the protein content of adipose triglyceride lipase, acetyl-CoA carboxylase 2 and AMP-activated protein kinase (AMPK)γ3 were higher in young than in older men. Furthermore, adipose triglyceride lipase, plasma membrane-associated fatty acid binding protein and AMPKγ3 subunit protein contents were lower and IMTG was higher in the immobilized than the contralateral leg in young and older men. Thus, immobilization and age did not affect substrate choice (respiratory quotient) during moderate exercise, but the whole-leg and molecular differences in fatty acid mobilization could explain the age- and immobilization-induced IMTG accumulation.

The Hippo signal transduction network for exercise physiologists

The ubiquitous transcriptional coactivators Yap (gene symbol Yap1) and Taz (gene symbol Wwtr1) regulate gene expression mainly by coactivating the Tead transcription factors. Being at the center of the Hippo signaling network, Yap and Taz are regulated by the Hippo kinase cassette and additionally by a plethora of exercise-associated signals and signaling modules. These include mechanotransduction, the AKT-mTORC1 network, the SMAD transcription factors, hypoxia, glucose homeostasis, AMPK, adrenaline/epinephrine and angiotensin II through G protein-coupled receptors, and IL-6. Consequently, exercise should alter Hippo signaling in several organs to mediate at least some aspects of the organ-specific adaptations to exercise. Indeed, Tead1 overexpression in muscle fibers has been shown to promote a fast-to-slow fiber type switch, whereas Yap in muscle fibers and cardiomyocytes promotes skeletal muscle hypertrophy and cardiomyocyte adaptations, respectively. Finally, genome-wide association studies in humans have linked the Hippo pathway members LATS2, TEAD1, YAP1, VGLL2, VGLL3, and VGLL4 to body height, which is a key factor in sports.

The regulation of autophagy during exercise in skeletal muscle

The merits of exercise on muscle health and well-being are numerous and well documented. However, the mechanisms underlying the robust adaptations induced by exercise, particularly on mitochondria, are less clear and much sought after. Recently, an evolutionary conserved cellular recycling mechanism known as autophagy has been implicated in the adaptations to acute and chronic exercise. A basal level of autophagy is constantly ongoing in cells and tissues, ensuring cellular clearance and energy homeostasis. This pathway can be further induced, as a survival mechanism, by cellular perturbations, such as energetic imbalance and oxidative stress. During exercise, a biphasic autophagy response is mobilized, leading to both an acute induction and a long-term potentiation of the process. Posttranslational modifications arising from upstream signaling cascades induce an acute autophagic response during a single bout of exercise by mobilizing core autophagy machinery. A transcriptional program involving the regulators Forkhead box O, transcription factor EB, p53, and peroxisome proliferator coactivator-1α is also induced to fuel sustained increases in autophagic capacity. Autophagy has also been documented to mediate chronic exercise-induced metabolic benefits, and animal models in which autophagy is perturbed do not adapt to exercise to the same extent. In this review, we discuss recent developments in the field of autophagy and exercise. We specifically highlight the molecular mechanisms activated during acute exercise that lead to a prolonged adaptive response.

Contraction stimulates muscle glucose uptake independent of atypical PKC

Exercise increases skeletal muscle glucose uptake, but the underlying mechanisms are only partially understood. The atypical protein kinase C (PKC) isoforms λ and ζ (PKC‐λ/ζ) have been shown to be necessary for insulin‐, AICAR‐, and metformin‐stimulated glucose uptake in skeletal muscle, but not for treadmill exercise‐stimulated muscle glucose uptake. To investigate if PKC‐λ/ζ activity is required for contraction‐stimulated muscle glucose uptake, we used mice with tibialis anterior muscle‐specific overexpression of an empty vector (WT), wild‐type PKC‐ζ (PKC‐ζ^WT), or an enzymatically inactive T410A‐PKC‐ζ mutant (PKC‐ζ^T410A). We also studied skeletal muscle‐specific PKC‐λ knockout (MλKO) mice. Basal glucose uptake was similar between WT, PKC‐ζ^WT, and PKC‐ζ^T410A tibialis anterior muscles. In contrast, in situ contraction‐stimulated glucose uptake was increased in PKC‐ζ^T410A tibialis anterior muscles compared to WT or PKC‐ζ^WT tibialis anterior muscles. Furthermore, in vitro contraction‐stimulated glucose uptake was greater in soleus muscles of MλKO mice than WT controls. Thus, loss of PKC‐λ/ζ activity increases contraction‐stimulated muscle glucose uptake. These data clearly demonstrate that PKC‐λ/ζ activity is not necessary for contraction‐stimulated glucose uptake.

Involvement of AMPK in regulating slow-twitch muscle atrophy during hindlimb unloading in mice

AMPK is considered to have a role in regulating skeletal muscle mass. However, there are no studies investigating the function of AMPK in modulating skeletal muscle mass during atrophic conditions. In the present study, we investigated the difference in unloading-associated muscle atrophy and molecular functions in response to 2-wk hindlimb suspension between transgenic mice overexpressing the dominant-negative mutant of AMPK (AMPK-DN) and their wild-type (WT) littermates. Male WT (n = 24) and AMPK-DN (n = 24) mice were randomly divided into two groups: an untreated preexperimental control group (n = 12 in each group) and an unloading (n = 12 in each group) group. The relative soleus muscle weight and fiber cross-sectional area to body weight were decreased by ∼30% in WT mice by hindlimb unloading and by ∼20% in AMPK-DN mice. There were no changes in puromycin-labeled protein or Akt/70-kDa ribosomal S6 kinase signaling, the indicators of protein synthesis. The expressions of ubiquitinated proteins and muscle RING finger 1 mRNA and protein, markers of the ubiquitin-proteasome system, were increased by hindlimb unloading in WT mice but not in AMPK-DN mice. The expressions of molecules related to the protein degradation system, phosphorylated forkhead box class O3a, inhibitor of κBα, microRNA (miR)-1, and miR-23a, were decreased only in WT mice in response to hindlimb unloading, and 72-kDa heat shock protein expression was higher in AMPK-DN mice than in WT mice. These results imply that AMPK partially regulates unloading-induced atrophy of slow-twitch muscle possibly through modulation of the protein degradation system, especially the ubiquitin-proteasome system.

Exercise and Regulation of Carbohydrate Metabolism

Carbohydrates are the preferred substrate for contracting skeletal muscles during high-intensity exercise and are also readily utilized during moderate intensity exercise. This use of carbohydrates during physical activity likely played an important role during the survival of early Homo sapiens, and genes and traits regulating physical activity, carbohydrate metabolism, and energy storage have undoubtedly been selected throughout evolution. In contrast to the life of early H. sapiens, modern lifestyles are predominantly sedentary. As a result, intake of excessive amounts of carbohydrates due to the easy and continuous accessibility to modern high-energy food and drinks has not only become unnecessary but also led to metabolic diseases in the face of physical inactivity. A resulting metabolic disease is type 2 diabetes, a complex endocrine disorder characterized by abnormally high concentrations of circulating glucose. This disease now affects millions of people worldwide. Exercise has beneficial effects to help control impaired glucose homeostasis with metabolic disease, and is a well-established tool to prevent and combat type 2 diabetes. This chapter focuses on the effects of exercise on carbohydrate metabolism in skeletal muscle and systemic glucose homeostasis. We will also focus on the molecular mechanisms that mediate the effects of exercise to increase glucose uptake in skeletal muscle. It is now well established that there are different proximal signaling pathways that mediate the effects of exercise and insulin on glucose uptake, and these distinct mechanisms are consistent with the ability of exercise to increase glucose uptake in the face of insulin resistance in people with type 2 diabetes. Ongoing research in this area is aimed at defining the precise mechanism by which exercise increases glucose uptake and insulin sensitivity and the types of exercise necessary for these important health benefits.

Cardiac contraction-induced GLUT4 translocation requires dual signaling input

Contraction-induced translocation of glucose transporter type-4 (GLUT4) to the sarcolemma is essential to stimulate cardiac glucose uptake during increased energy demand. As such, this process is a target for therapeutic strategies aiming at increasing glucose uptake in insulin-resistant and/or diabetic hearts. AMP-activated protein kinase (AMPK) and its upstream kinases form part of a signaling axis essential for contraction-induced GLUT4 translocation. Recently, activation of protein kinase-D1 (PKD1) was also shown to be as obligatory for contraction-induced GLUT4 translocation in cardiac muscle. However, contraction-induced PKD1 activation in this context occurs independently from AMPK signaling, suggesting that contraction-induced GLUT4 translocation requires the input of two separate signaling pathways. Necessity for dual input would more tightly couple GLUT4 translocation to stimuli that are inherent to cardiac contraction.