Exercise-induced AMPK activity in skeletal muscle: role in glucose uptake and insulin sensitivity

Harnessing the melanocortin system in the control of food intake and glucose homeostasis

The central and peripheral melanocortin system, comprising of five receptors and their endogenous ligands, is responsible for a wide array of physiological functions such as skin pigmentation, sexual function and development, and inflammation. A growing body of both clinical and pre-clinical research is demonstrating the relevance of this system in metabolic health. Disruption of hypothalamic melanocortin signalling is the most common cause of monogenic obesity in humans. Setmelanotide, an FDA-approved analogue of alpha-melanocyte stimulating hormone (α-MSH) that functions by restoring central melanocortin signalling, has proven to be a potent pharmacological tool in the treatment of syndromic obesity. As the first effective therapy targeting the melanocortin system to treat metabolic disorders, its approval has sparked research to further harness the links between these melanocortin receptors and metabolic processes. Here, we outline the structure of the central and peripheral melanocortin system, discuss its critical role in the regulation of food intake, and review promising targets that may hold potential to treat metabolic disorders in humans.

Irisin attenuates ventilator-induced diaphragmatic dysfunction by inhibiting endoplasmic reticulum stress through activation of AMPK

Mechanical ventilation (MV) is an essential life-saving technique, but prolonged MV can cause significant diaphragmatic dysfunction due to atrophy and decreased contractility of the diaphragm fibres, called ventilator-induced diaphragmatic dysfunction (VIDD). It is not clear about the mechanism of occurrence and prevention measures of VIDD. Irisin is a newly discovered muscle factor that regulates energy metabolism. Studies have shown that irisin can exhibit protective effects by downregulating endoplasmic reticulum (ER) stress in a variety of diseases; whether irisin plays a protective role in VIDD has not been reported. Sprague-Dawley rats were mechanically ventilated to construct a VIDD model, and intervention was performed by intravenous administration of irisin. Diaphragm contractility, degree of atrophy, cross-sectional areas (CSAs), ER stress markers, AMPK protein expression, oxidative stress indicators and apoptotic cell levels were measured at the end of the experiment.Our findings showed that as the duration of ventilation increased, the more severe the VIDD was, the degree of ER stress increased, and the expression of irisin decreased.ER stress may be one of the causes of VIDD. Intervention with irisin ameliorated VIDD by reducing the degree of ER stress, attenuating oxidative stress, and decreasing the apoptotic index. MV decreases the expression of phosphorylated AMPK in the diaphragm, whereas the use of irisin increases the expression of phosphorylated AMPK. Irisin may exert its protective effect by activating the phosphorylated AMPK pathway.

Effects of exercise on muscle fiber conversion, muscle development and meat quality of Sunit sheep

This study aimed to investigate the effects of exercise on muscle fiber conversion, muscle development and meat quality in the biceps femoris (BF) muscle of Sunit sheep. Twelve Sunit sheep with similar body weight were divided into two groups: control group (C group) and exercise group (E group), E group lambs underwent 6 km of exercise training per day for 90 d. The findings revealed that compared with the C group, exercise training enhanced the expression of MyHC IIa mRNA, decreased the number ratio of type IIB muscle fibers and the expression of MyHC IIb mRNA (P < 0.05). Furthermore, the E group lamb displayed higher creatine kinase (CK) activity, and lactic acid levels (P < 0.05), while glycogen content and lactic dehydrogenase (LDH) activity showed opposite trends (P < 0.05). Exercise significantly up-regulated the mRNA expression of AMP-activated protein kinase α1 (AMPKα1), sirtuin1 (SIRT1), peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α), cytochrome c oxidase IV (COX IV), protein kinase B (Akt), mammalian target of rapamycin (mTOR) and p70 Ribosomal S6 Kinase 1 (p70s6k1) (P < 0.05), suggesting exercise promoted muscle fiber conversion by mediating AMPK/PGC-1α pathway, and improved skeletal muscle development via Akt/mTOR pathway. Besides, backfat thickness and pH45min value in the E group decreased significantly, while the pH24, a*, and shear force value increased significantly (P < 0.05). To conclude, this study suggested that exercise training can be used to alter muscle fiber characteristics and muscle development in lamb production.

Exploring exercise-driven exerkines: unraveling the regulation of metabolism and inflammation

Exercise has many beneficial effects that provide health and metabolic benefits. Signaling molecules are released from organs and tissues in response to exercise stimuli and are widely termed exerkines, which exert influence on a multitude of intricate multi-tissue processes, such as muscle, adipose tissue, pancreas, liver, cardiovascular tissue, kidney, and bone. For the metabolic effect, exerkines regulate the metabolic homeostasis of organisms by increasing glucose uptake and improving fat synthesis. For the anti-inflammatory effect, exerkines positively influence various chronic inflammation-related diseases, such as type 2 diabetes and atherosclerosis. This review highlights the prospective contribution of exerkines in regulating metabolism, augmenting the anti-inflammatory effects, and providing additional advantages associated with exercise. Moreover, a comprehensive overview and analysis of recent advancements are provided in this review, in addition to predicting future applications used as a potential biomarker or therapeutic target to benefit patients with chronic diseases.

A systematic review of the exercise effects on burn wound healing

The emerging evidence has indicated the role of microRNAs (miRNA) in various physiological or pathological processes. Also, documents have suggested that exercise, by affecting miRNA regulation, may enhance burn wound healing. The current study aims to systematically review the role of exercise in regulating miRNAs related to burn wound healing to provide potential therapeutic targets. A comprehensive, systematic search was performed in different international electronic databases, such as Embase, PubMed and Google Scholar search engine, Science Direct, ProQuest and Ovid using keywords extracted from Medical Subject Headings from 2010 to September 2023. The keywords, including 'exercise' AND 'burn wound' AND 'microRNA' and finally, six cases were achieved. Evidence has indicated that exercise may promote the healing of burn wounds by regulating certain miRNAs. Studies have found that exercise regulates the expression of miRNAs such as mir-155, miR-21, let-7a, miR-146a, miR-122 and mir-210 in burn wound tissue, which regulate inflammation and angiogenesis. These findings suggest that miRNAs may play a role in the positive effect of exercise on burn wound healing. However, further research is needed to understand the mechanisms involved fully.

Resveratrol as a potential protective compound against skeletal muscle insulin resistance

The increasing prevalence of type 2 diabetes has become a major global problem. Insulin resistance has a central role in pathophysiology of type 2 diabetes. Skeletal muscle is responsible for the disposal of most of the glucose under conditions of insulin stimulation, and insulin resistance in skeletal muscle causes dysregulation of glucose homeostasis in the whole body. Despite the current pharmaceutical and non-pharmacological treatment strategies to combat diabetes, there is still a need for new therapeutic agents due to the limitations of the therapeutic agents. Meanwhile, plant polyphenols have attracted the attention of researchers for their use in the treatment of diabetes and have gained popularity. Resveratrol, a stilbenoid polyphenol, exists in various plant sources, and a growing body of evidence suggests its beneficial properties, including antidiabetic activities. The present review aimed to provide a summary of the role of resveratrol in insulin resistance in skeletal muscle and its related mechanisms. To achieve the objectives, by searching the PubMed, Scopus and Web of Science databases, we have summarized the results of all cell culture, animal, and human studies that have investigated the effects of resveratrol in different models on insulin resistance in skeletal muscle.

The association between muscle-to-fat ratio and cardiometabolic risks: The China National Health Survey

BACKGROUND

The relationship between muscle mass and fat mass might be an indicator to assess the cardiometabolic risk independently from overweight/obesity, but evidence from a representative general Chinese population is lacking.

OBJECTIVE

To understand the age- and sex-specific associations between muscle-to-fat ratio (MFR) and cardiometabolic risks in Chinese population.

METHODS

31,178 (12,526 men and 18,652 women) subjects from the China National Health Survey were included. Muscle mass and fat mass were assessed by a bioelectrical impedance device. MFR was calculated as muscle mass divided by fat mass. Systolic blood pressure (SBP) and diastolic blood pressure (DBP), serum lipids, fasting plasma glucose and serum uric acid were measured. General linear regressions, quantile regressions and restricted cubic-spline (RCS) regressions were applied to assess the effect of MFR on cardiometabolic profiles.

RESULTS

Per unit increase of MFR was associated with a 0.631 (0.759-0.502) mmHg SBP decrease in men, 2.648 (3.073-2.223) in women; 0.480 (0.568-0.392) mmHg DBP decrease in men, 2.049 (2.325-1.774) in women; a 0.054 (0.062-0.046) mmol/L total cholesterol decrease in men, 0.147 (0.172-0.122) in women; 0.084 (0.098-0.070) mmol/L triglycerides decrease in men, 0.225 (0.256-0.194) in women; a 0.045 (0.054-0.037) mmol/L low-density lipoprotein decrease in men, 0.183 (0.209-0.157) in women; a 2.870 (2.235-3.506) μmol/L serum uric acid decrease in men, 13.352 (14.967-11.737) in women; and a 0.027 (0.020-0.033) mmol/L high-density lipoprotein increase in men, 0.112 (0.098-0.126) mmol/L in women. The effect in overweight/obese people was much significant than in under/normal weight counterparts. The RCS curves revealed both linear and non-linear relationships between increased MFR and lower cardiometabolic risk.

CONCLUSIONS

Muscle-to-fat ratio is independently associated with multiple cardiometabolic parameters among Chinese adults. Higher MFR is related with better cardiometabolic health, and the effect is much significant in overweight/obese people and women.

Successful lifestyle modifications may underlie umbilical cord-mesenchymal stromal cell effects in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a lifelong condition and a grave threat to human health. Innovative efforts to relieve its detrimental effects are acutely needed. The sine qua non in T2DM management is consistent adherence to a prudent lifestyle and nutrition, combined with aerobic and resistance exercise regimens, together repeatedly shown to lead to complete reversal and even long-term remission. Non-adherence to the above lifestyle adjustments condemns any treatment effort and ultimately the patient to a grim fate. It is thus imperative that every study evaluating the effects of innovative interventions in T2DM objectively compares the novel treatment modality to lifestyle modifications, preferably through double-blind controlled randomization, before claiming efficacy.

Therapeutic or lifelong training effects on pancreatic morphological and functional parameters in an animal model of aging and obesity

AIMS

Obesity, aging, and physical training are factors influencing pancreatic functional and morphological parameters. Aiming to clarify the impact of the interaction of these factors, we analyzed the effect of therapeutic or lifelong physical training on body adiposity and pancreatic functional and morphological parameters of aged and obese rats.

METHODS

24 male Wistar rats were (initial age = 4 months and final age = 14 months) randomly divided into three aged and obese experimental groups (n = 8/group): untrained, therapeutic trained, and lifelong trained. Body adiposity, plasmatic concentration and pancreatic immunostaining of insulin, markers of tissue inflammation, lipid peroxidation, activity and immunostaining of antioxidant enzymes, and parameters of pancreatic morphology were evaluated.

RESULTS

Lifelong physical training improved the body adiposity, plasmatic insulin concentration, and macrophage immunostaining in the pancreas. The animals submitted to therapeutic and lifelong training showed an increase in the density of the pancreatic islets; lower insulin, Nuclear Factor Kappa B (NF-κB), and Transforming Growth Factor beta (TGF-β) immunostaining in the pancreatic parenchyma, as well as lower pancreatic tissue lipid peroxidation, lower fibrosis area, increased catalase and glutathione peroxidase (GPx) activity and increased heme oxygenase-1 (HO-1) immunostaining, with the greatest effect in the lifelong training group.

CONCLUSION

Lifelong training promoted greater beneficial effects on the pancreatic functional and morphological parameters of aged and obese animals compared to therapeutic exercise.

CREG1 stimulates AMPK phosphorylation and glucose uptake in skeletal muscle cells

The cellular repressor of adenovirus early region 1A-stimulated gene 1 (CREG1) is a secreted glycoprotein involved in cell differentiation and energy metabolism. It also binds to insulin-like growth factor 2 receptor (IGF2R), a protein implicated in muscle regeneration. However, whether CREG1 regulates the regeneration and metabolism of skeletal muscles via IGF2R remains unclear. This study investigates the role of CREG1 in skeletal muscle regeneration and glucose uptake in C2C12 myotubes and a cardiotoxin (CTX)-induced mouse skeletal muscle regeneration model. CTX-treated skeletal muscle showed significantly higher levels of IGF2R, CREG1, phospho-AMPKα Thr¹⁷², and GLUT4 proteins. Similarly, treatment of myotubes with CREG1 also stimulated AMPKα phosphorylation and GLUT4 expression. CREG1-induced AMPKα phosphorylation and 2DG uptake in myotubes were suppressed by IGF2R knockdown and Compound C, an AMPK inhibitor. These results suggest that CREG1 stimulates glucose uptake in skeletal muscles partially through AMPK activation. Hence, CREG1 plays an essential role in muscle regeneration by affecting glucose metabolism in skeletal muscles.

Responses of complement C1q/tumor necrosis factor-related proteins to acute aerobic exercise

Aerobic exercise is an effective therapeutic strategy to manage metabolic disorders. However, the mechanisms of aerobic exercise-induced improvements in metabolic diseases are not completely understood. Complement C1q/tumor necrosis factor-related protein (CTRP) 1, CTRP3, CTRP5, and CTRP9 have important roles in improving metabolic disorders via the adenosine monophosphate-activated protein kinase signaling pathway. In this study, we investigated the effects of acute aerobic exercise on circulating CTRP1, CTRP3, CTRP5, and CTRP9 levels in human participants. Eight healthy males with an age of 20.4 ± 0.2 years, height 173.1 ± 1.7 cm, body mass 68.0 ± 1.8 kg, body mass index 22.7 ± 0.7 kg/m², and maximal oxygen uptake (VO₂max) 51.3 ± 2.5 mL/kg/min performed acute aerobic cycling exercise at 75 % of their VO₂max for 30 min (data are mean ± standard error). Blood samples were obtained before; immediately after; and 30, 60, and 120 min after exercising. Serum concentrations of CTRP1, CTRP3, CTRP5, CTRP9, tumor necrosis factor-α (TNF-α), and insulin were measured. The CTRP1 concentration significantly increased immediately after exercising and remained elevated for up to 120 min (p < 0.01). The CTRP3 concentration significantly increased at 60 min after exercise (p < 0.05), and the increasing trend continued until at least 120 min after exercise (p < 0.01). The CTRP5, CTRP9, TNF-α, and insulin concentrations significantly increased immediately after exercise (p < 0.05, p < 0.01, p < 0.05, and p < 0.05, respectively) and decreased thereafter. A significant correlation was observed between the peak post-exercise concentrations of CTRP1 and TNF-α (p < 0.05); however, no correlation was observed between the peak post-exercise concentrations of CTRP3 and insulin. The results of this study indicate that acute aerobic exercise may enhance the secretion of CTRP1, CTRP3, CTRP5, and CTRP9 in healthy adults.

Garlic (Allium sativum L.) in diabetes and its complications: Recent advances in mechanisms of action

Diabetes mellitus (DM) is a metabolic disease characterized by chronic hyperglycemia and impaired islet secretion that places a heavy burden on the global health care system due to its high incidence rate, long disease course and many complications. Fortunately, garlic (Allium sativum L.), a well-known medicinal plant and functional food without the toxicity and side effects of conventional drugs, has shown positive effects in the treatment of diabetes and its complications. With interdisciplinary development and in-depth exploration, we offer a clear and comprehensive summary of the research from the past ten years, focusing on the mechanisms and development processes of garlic in the treatment of diabetes and its complications, aiming to provide a new perspective for the treatment of diabetes and promote the efficient development of this field.

The aldolase inhibitor aldometanib mimics glucose starvation to activate lysosomal AMPK

The activity of 5'-adenosine monophosphate-activated protein kinase (AMPK) is inversely correlated with the cellular availability of glucose. When glucose levels are low, the glycolytic enzyme aldolase is not bound to fructose-1,6-bisphosphate (FBP) and, instead, signals to activate lysosomal AMPK. Here, we show that blocking FBP binding to aldolase with the small molecule aldometanib selectively activates the lysosomal pool of AMPK and has beneficial metabolic effects in rodents. We identify aldometanib in a screen for aldolase inhibitors and show that it prevents FBP from binding to v-ATPase-associated aldolase and activates lysosomal AMPK, thereby mimicking a cellular state of glucose starvation. In male mice, aldometanib elicits an insulin-independent glucose-lowering effect, without causing hypoglycaemia. Aldometanib also alleviates fatty liver and nonalcoholic steatohepatitis in obese male rodents. Moreover, aldometanib extends lifespan and healthspan in both Caenorhabditis elegans and mice. Taken together, aldometanib mimics and adopts the lysosomal AMPK activation pathway associated with glucose starvation to exert physiological roles, and might have potential as a therapeutic for metabolic disorders in humans.

Harnessing conserved signaling and metabolic pathways to enhance the maturation of functional engineered tissues

The development of induced-pluripotent stem cell (iPSC)-derived cell types offers promise for basic science, drug testing, disease modeling, personalized medicine, and translatable cell therapies across many tissue types. However, in practice many iPSC-derived cells have presented as immature in physiological function, and despite efforts to recapitulate adult maturity, most have yet to meet the necessary benchmarks for the intended tissues. Here, we summarize the available state of knowledge surrounding the physiological mechanisms underlying cell maturation in several key tissues. Common signaling consolidators, as well as potential synergies between critical signaling pathways are explored. Finally, current practices in physiologically relevant tissue engineering and experimental design are critically examined, with the goal of integrating greater decision paradigms and frameworks towards achieving efficient maturation strategies, which in turn may produce higher-valued iPSC-derived tissues.

N-Octyl Caffeamide, a Caffeic Acid Amide Derivative, Prevents Progression of Diabetes and Hepatic Steatosis in High-Fat Diet Induced Obese Mice

The underlying pathological mechanisms of diabetes are complicated and varied in diabetic patients, which may lead to the current medications often failing to maintain glycemic control in the long term. Thus, the discovery of diverse new compounds for developing medicines to treat diabetes and its complications are urgently needed. Polyphenols are metabolites of plants and have been employed in the prevention and treatment of a variety of diseases. Caffeic acid phenethyl ester (CAPE) is a category of compounds structurally similar to polyphenols. In this study, we aimed to investigate the antidiabetic activity and potential molecular mechanisms of a novel synthetic CAPE derivative N-octyl caffeamide (36M) using high-fat (HF) diet induced obese mouse models. Our results demonstrate that 36M prevented the progression of diabetes in the HF diet fed obese mice via increasing phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and inhibiting expression of protein tyrosine phosphatase 1B (PTP1B). We also found that 36M could prevent hepatic lipid storage in the HF diet fed mice via inhibition of fatty acid synthase and lipid droplet proteins, including perilipins and Fsp27. In conclusion, 36M is a potential candidate compound that can be developed as AMPK inhibitor and PTP1B inhibitor for treating diabetes and hepatic steatosis.

G6PD Deficiency Is Crucial for Insulin Signaling Activation in Skeletal Muscle

Glucose 6-P dehydrogenase (G6PD) is the first rate-limiting enzyme in pentose phosphate pathway (PPP), and it is proverbial that G6PD is absent in skeletal muscle. However, how and why G6PD is down-regulated during skeletal muscle development is unclear. In this study, we confirmed the expression of G6PD was down-regulated during myogenesis in vitro and in vivo. G6PD was absolutely silent in adult skeletal muscle. Histone H3 acetylation and DNA methylation act together on the expression of G6PD. Neither knock-down of G6PD nor over-expression of G6PD affects myogenic differentiation. Knock-down of G6PD significantly promotes the sensitivity and response of skeletal muscle cells to insulin; over-expression of G6PD significantly injures the sensitivity and response of skeletal muscle cells to insulin. High-fat diet treatment impairs insulin signaling by up-regulating G6PD, and knock-down of G6PD rescues the impaired insulin signaling and glucose uptake caused by high-fat diet treatment. Taken together, this study explored the importance of G6PD deficiency during myogenic differentiation, which provides new sight to treat insulin resistance and type-2 diabetes.

Structure-Activity Relationship of Synthetic Ginkgolic Acid Analogs for Treating Type 2 Diabetes by PTPN9 Inhibition

Ginkgolic acid (C13:0) (GA), isolated from Ginkgo biloba, is a potential therapeutic agent for type 2 diabetes. A series of GA analogs were designed and synthesized for the evaluation of their structure–activity relationship with respect to their antidiabetic effects. Unlike GA, the synthetic analog 1e exhibited improved inhibitory activity against PTPN9 and significantly stimulated glucose uptake via AMPK phosphorylation in differentiated 3T3-L1 adipocytes and C2C12 myotubes; it also induced insulin-dependent AKT activation in C2C12 myotubes in a concentration-dependent manner. Docking simulation results showed that 1e had a better binding affinity through a unique hydrophobic interaction with a PTPN9 hydrophobic groove. Moreover, 1e ameliorated palmitate-induced insulin resistance in C2C12 cells. This study showed that 1e increases glucose uptake and suppresses palmitate-induced insulin resistance in C2C12 myotubes via PTPN9 inhibition; thus, it is a promising therapeutic candidate for treating type 2 diabetes.

Antidiabetic profiling of veramycins, polyketides accessible by biosynthesis, chemical synthesis and precursor-directed modification

New polyketides, termed veramycins, were isolated along with their known congeners NFAT-133 and TM-123. Total synthesis from a central building block was accomplished, the BGC identified and a biosynthetic pathway for this molecule class proposed.

Maternal Moderate-to-Vigorous Physical Activity before and during Pregnancy and Maternal Glucose Tolerance: Does Timing Matter?

PURPOSE

To assess prospective associations between moderate-to-vigorous physical activity (MVPA) from preconception through pregnancy and glucose metabolism.

METHODS

The sample consisted of 2,388 women from the NICHD Fetal Growth Studies-Singletons, which enrolled U.S. pregnant women between 8-13 weeks of gestation. Women recalled their MVPA in periconception (past 12 months, inclusive of 1st trimester), early-to-mid (13-20 weeks of gestation), and mid-to-late 2nd trimester (20-29 weeks). These data were obtained at study visits that occurred at enrollment (8-13 weeks) and at follow-up visits at 16-22 and 24-29 weeks. MVPA was recalled using the Pregnancy Physical Activity Questionnaire. Glucose challenge test and oral glucose tolerance test results and gestational diabetes diagnosis (defined by the Carpenter-Coustan criteria) were extracted from medical records. ANCOVA and Poisson regression with robust error variance were performed to estimate associations between MVPA and glucose concentrations and gestational diabetes risk, respectively, controlling for age, race/ethnicity, and pre-pregnancy body mass index.

RESULTS

Women achieving higher levels of MVPA (≥75th percentile; 760.5 MET·min·wk-1) in early-to-mid 2nd trimester had lower glucose concentrations (β = -3.9 mg/dL, 95%CI: -7.4,-0.5) compared to their least-active counterparts (≤25th percentile; ≤117.0 MET·min·wk-1). Women maintaining recommended levels of MVPA from preconception & 1st trimester through 2nd trimester (early-to-mid: β = -3.0 mg/dL, -5.9,-0.1; mid-to-late: β = -4.2 mg/dL,-8.4,-0.1) or maintaining sufficient activity throughout 2nd trimester exhibited lower glucose levels (β = -5.6 mg/dL, -9.8,-1.4) compared to their inactive counterparts. No statistically significant associations with gestational diabetes were observed.

CONCLUSIONS

These findings demonstrate that achieving MVPA of at least 760.0 MET·min·week-1 in early-to-mid 2nd trimester or maintaining at least 500 MET ·min·week-1 from preconception through 2nd trimester may be related to improved maternal glucose metabolism in the 2nd trimester.

Photobiomodulation therapy ameliorates hyperglycemia and insulin resistance by activating cytochrome c oxidase-mediated protein kinase B in muscle

Ameliorating hyperglycemia and insulin resistance are major therapeutic strategies for type 2 diabetes. Previous studies have indicated that photobiomodulation therapy (PBMT) attenuates metabolic abnormalities in insulin-resistant adipose cells and tissues. However, it remains unclear whether PBMT ameliorates glucose metabolism in skeletal muscle in type 2 diabetes models. Here we showed that PBMT reduced blood glucose and insulin resistance, and reversed metabolic abnormalities in skeletal muscle in two diabetic mouse models. PBMT accelerated adenosine triphosphate (ATP) and reactive oxygen species (ROS) generation by elevating cytochrome c oxidase (CcO) activity. ROS-induced activation of phosphatase and tensin homolog (PTEN)/ protein kinase B (AKT) signaling after PBMT promoted glucose transporter GLUT4 translocation and glycogen synthase (GS) activation, accelerating glucose uptake and glycogen synthesis in skeletal muscle. CcO subunit III deficiency, ROS elimination, and AKT inhibition suppressed the PBMT effects of glucose metabolism in skeletal muscle. This study indicated amelioration of glucose metabolism after PBMT in diabetic mouse models and revealed the metabolic regulatory effects and mechanisms of PBMT on skeletal muscle.

Influences of exercise interventions on overweight and obesity in children and adolescents

PURPOSE

Conflicting findings of the effects of exercise on body fat, free fat mass, insulin, insulin resistance, and physical fitness for overweight and obesity in children and adolescents. The purpose of this meta-analysis was to investigate the effects of exercise interventions in children and adolescents with overweight and obesity depending on exercise type and to build effective exercise interventions to reduce risks of metabolic disorders.

METHODS

Databases were used to find eligible studies regarding the effects of exercise interventions on overweight and obesity in children and adolescents in randomized controlled trails. Effect size was calculated using the standardized mean difference statistic and heterogeneity across studies was estimated using the Q statistic.

RESULTS

A total of 27 studies met the inclusion criteria. Children and adolescents with overweight and obesity who participated in aerobic exercise had reduced body mass index, % body fat, fasting insulin, free fat mass, TNF-α, and IL-6, and increased physical fitness compared with control groups. Reduced free fat mass in resistance exercise was not found. Glucose, insulin resistance, blood pressure, C-reactive protein (CRP), and blood markers including total cholesterol (TC), triglyceride, LDL, and HDL did not have significant change. Average exercise interventions were aerobic exercise, 3 times/week, 60 min, and 36 weeks of exercise period.

CONCLUSIONS

Aerobic exercise may be beneficial to reduce body fat, fasting insulin, and inflammatory markers, and increased physical fitness for overweight and obesity in childhood and adolescence, but resistance exercise may be added, which can help avoid muscle loss in children and adolescents with overweight and obesity.

Skeletal muscle mass is associated with glycemic variability in patients with ST-segment elevation myocardial infarction

Skeletal muscle function has been studied to determine its effect on glucose metabolism; however, its effect on glycemic variability (GV), which is a significant glycemic marker in patients with coronary artery disease, is unknown. The aim of the present study was to elucidate the association between skeletal muscle mass and GV. Two hundred and eight consecutive ST-segment elevation myocardial infarction (STEMI) patients who underwent continuous glucose monitoring to evaluate mean amplitude of glycemic excursion (MAGE) as GV and a dual-energy X-ray absorptiometry (DEXA) to evaluate skeletal muscle mass were enrolled. Skeletal muscle index (SMI) level was calculated as skeletal muscle mass divided by height squared (kg/m²). SMI level in men had a weak inverse correlation with Log MAGE level by the linear regression model in diabetes mellitus (DM) patients (R² = 0.139, P = 0.004) and even in non-DM patients (R² = 0.068, P = 0.004). Multivariate linear regression analysis with a stepwise algorithm (age, male sex, body mass index [BMI], hemoglobin A1c [HbA1c], fasting glucose, HOMA-IR, and SMI; R² = 0.203, P < 0.001) demonstrated that HbA1c level (B = 0.077, P < 0.001) and SMI level (B = - 0.062, P < 0.001) were both independently associated with Log MAGE level. This association was also confirmed in limited non-DM patients with a subgroup analysis. SMI level was associated with Log MAGE level (B = - 0.055, P = 0.001) independent of BMI or HbA1c level. SMI level was inversely associated with MAGE level independent of glucose metabolism in STEMI patients, suggesting the significance of skeletal muscle mass as blood glucose storage for glucose homeostasis to reduce GV.

Fat-to-muscle Ratio: A New Indicator for Coronary Artery Disease in Healthy Adults

Background: Coronary artery disease (CAD) is an important issue in public health. Previous studies have shown that the ratio of fat to muscle mass is a significant predictor of metabolic disease, and it is known to be associated with atherosclerosis. In this study, we evaluated the association between the fat-to-muscle ratio (FMR) and CAD in healthy adults. Methods: A total of 617 participants without diabetes mellitus, hypertension, known CAD, or stroke who visited the Health Promotion Center from 2009 to 2018 were included in this study. Computed tomography imaging and bioelectrical impedance analysis were used to ascertain the coronary artery calcium (CAC) score, degree of CAD, and FMR. Results: Univariate logistic regression analysis showed that old age, male sex, smoking history, creatinine, aspartate aminotransferase, gamma-glutamyl transferase, uric acid, total cholesterol, and low-density lipoprotein cholesterol were significantly associated with CAC. After adjusting for potential confounding covariates, the presence of CAC was independently associated with FMR (OR, 1.014; 95% CI, 1.002-1.026; p = 0.019. The association was maintained even after adjusting for body mass index and waist circumference (odds ratio, 1.019; 95% confidence interval, 1.004 -1.034; P = 0.012). Conclusion: In this study, a high FMR was significantly associated with CAC. A large-scale prospective study on the association with FMR and cardiovascular diseases is necessary to confirm this relationship.

Mechanisms underlying the metabolic actions of testosterone in humans: A narrative review

The role of testosterone in improving sexual symptoms in men with hypogonadism is well known. However, recent studies indicate that testosterone plays an important role in several metabolic functions in males. Multiple PubMed searches were conducted with the use of the terms testosterone, insulin sensitivity, obesity, type 2 diabetes, anaemia, bone density, osteoporosis, fat mass, lean mass and body composition. This narrative review is focused on detailing the mechanisms that underlie the metabolic aspects of testosterone therapy in humans. Testosterone enhances insulin sensitivity in obese men with hypogonadism by decreasing fat mass, increasing lean mass, decreasing free fatty acids and suppressing inflammation. At a cellular level, testosterone increases the expression of insulin receptor β subunit, insulin receptor substrate-1, protein kinase B and glucose transporter type 4 in adipose tissue and adenosine 5'-monophosphate-activated protein kinase expression and activity in skeletal muscle. Observational studies show that long-term therapy with testosterone prevents progression from prediabetes to diabetes and improves HbA1c. Testosterone increases skeletal muscle satellite cell activator, fibroblast growth factor-2 and decreases expression of the muscle growth suppressors, myostatin and myogenic regulatory factor 4. Testosterone increases haematocrit by suppressing hepcidin and increasing expression of ferroportin along with that of transferrin receptor and plasma transferrin concentrations. Testosterone also increases serum osteocalcin concentrations, which may account for its anabolic actions on bone. In conclusion, testosterone exerts a series of potent metabolic effects, which include insulin sensitization, maintenance and growth of the skeletal muscle, suppression of adipose tissue growth and maintenance of erythropoiesis and haematocrit.

Aerobic training improves NAFLD markers and insulin resistance through AMPK-PPAR-α signaling in obese mice

Liver steatosis is one of the main drivers for the development of whole-body insulin resistance. Conversely, aerobic training (AT) has been suggested as non-pharmacological tool to improve liver steatosis, however, the underlying molecular mechanism remains unclear. Therefore, the aim of this study was to analyze the effect of 8-weeks AT in non-alcoholic liver disease (NAFLD) outcomes in obese mice. Male C57BL/6 J wild type (WT) were fed with standard (SD) or high-fat diet (HFD) for 12-weeks. Another group fed with HFD underwent 8-weeks of AT (60% of maximum velocity), initiated at the 5th week of experimental protocol. We measured metabolic, body composition parameters, protein and gene expression inflammatory and metabolic mediators. We found that AT attenuates the weight gain, but not body fat accumulation. AT improved triacylglycerol and non-esterified fatty acid plasma concentrations, and also whole-body insulin resistance. Regarding NAFLD, AT decreased the progression of macrovesicular steatosis and inflammation through the upregulation of AMPK Thr172 phosphorylation and PPAR-α protein expression. Moreover, although no effects of intervention in PPAR-γ protein concentration were observed, we found increased levels of its target genes Cd36 and Scd1 in exercised group, demonstrating augmented transcriptional activity. AT reduced liver cytokines concentrations, such as TNF-α, IL-10, MCP-1 and IL-6, regardless of increased Ser536 NF-κB phosphorylation. In fact, none of the interventions regulated NF-κB target genes Il1b and Cccl2, demonstrating its low transcriptional activity. Therefore, we conclude that AT attenuates the progression of liver macrovesicular steatosis and inflammation through AMPK-PPAR-α signaling and PPAR-γ activation, respectively, improving insulin resistance in obese mice.

The effects of aerobic exercise on markers of maternal metabolism during pregnancy

BACKGROUND

Optimal maternal metabolism during pregnancy is essential for healthy fetal growth and development. Chronic exercise is shown to positively affect metabolism, predominantly demonstrated in nonpregnant populations.

OBJECTIVE

To determine the effects of aerobic exercise on maternal metabolic biomarkers during pregnancy, with expected lower levels of glucose, insulin, and lipids among exercise-trained pregnant women.

METHODS

Secondary data analyses were performed using data from two, longitudinal prenatal exercise intervention studies (ENHANCED by MOM and GESTAFIT). Exercisers completed 150 min of weekly moderate-intensity exercise during pregnancy (24+ weeks) while nonexercisers attended stretching sessions. Pregnant women were 31-33 years of age, predominantly non-Hispanic white, and "normal weight" body mass index. At 16 and 36 weeks of gestation, fasting blood samples were collected via fingerstick and venipuncture. Maternal glucose, insulin, insulin resistance (HOMA-IR), total cholesterol (TC), low-density lipoproteins (LDL), high-density lipoproteins (HDL), and triglycerides (TG) were analyzed. ANCOVA analyses were performed to evaluate the effects of aerobic exercise on markers of maternal metabolism in late pregnancy, controlling for baseline levels.

RESULTS

Our sample included 12 aerobic exercisers and 54 nonexercising control groups. Significant between-groups differences at 16 weeks of gestation were found for TG (92.3 vs. 121.2 mg/dl, p = .04), TC (186.8 vs. 219.6 mg/dl, p = .002), and LDL (104.1 vs. 128.8 mg/dl, p = .002). Aerobic-trained pregnant women exhibited lower insulin levels in late pregnancy (β = -2.6 μIU/ml, 95% CI:-4.2, -0.95, p = .002) and a reduced increase in insulin levels from 16 to 36 week of gestation (β = -2.3 μIU/ml, 95% CI: -4.4, -0.2, p = .034) compared with nonexercising pregnant women. No statistically significant effects were observed for maternal HOMA-IR, TC, LDL, HDL, TC:HDL, and TG in late pregnancy.

CONCLUSIONS

The observations of this study demonstrate that prenatal exercise may positively affect maternal insulin, with aerobic-trained pregnant women exhibiting lower insulin levels in late pregnancy. Additionally, we found no appreciable effects of prenatal exercise on maternal lipids in late pregnancy.

Exercise Ameliorates Insulin Resistance of Type 2 Diabetes through Motivating Short-Chain Fatty Acid-Mediated Skeletal Muscle Cell Autophagy

Background: Exercise can ameliorate type II diabetes mellitus (T2DM) by regulating intestinal flora metabolites. However, the detailed mechanism needs to be further explored. Methods: A T2DM model using mice was established by feeding them a high-fat diet and giving them subsequent streptozocin injections. Fasting blood glucose and serum insulin were determined by blood glucose meter and radioimmunoassay, respectively. Intestinal flora was measured by 16sRNA sequencing. SCFA content was measured by gas chromatography (GC) or enzyme-linked immunosorbent assay (ELISA). A fluorescently labeled 2-deoxyglucose (2-NBDG) kit was employed to detect glucose uptake capacity, and western blot was utilized to explore the signaling pathway of insulin resistance and cell autophagy. Results: In the T2DM model, along with a reduction in insulin resistance (IR), exercise reversed the decline of intestinal Bacteroidetes and the increase of Firmicutes. For metabolites of Bacteroides, exercise restored the decline in total intestinal and plasma short-chain fatty acids (SCFAs) in T2DM mice. However, the administration of GLPG0974—the inhibitor of G protein-coupled receptor 43 (GPR43), which is the receptor of SCFAs—abolished exercise-mediated alleviation in IR in vivo and acetate-mediated reduction of skeletal muscle IR (SMIR) in vitro. Mechanistically, exercise induced skeletal muscle cell autophagy, thereby ameliorating SMIR, which was neutralized by GLPG0974 exposure. Conclusions: Exercise-mediated SCFAs-upregulation may ameliorate insulin resistance (IR) through increasing autophagy of skeletal muscle cells by binding to GPR43. This study provides a theoretical basis for targeting gut bacterial metabolites to prevent T2DM.

A single session of physical activity restores the mitochondrial organization disrupted by obesity in skeletal muscle fibers

BACKGROUND

Several studies have proved that physical activity (PA) regulates energetic metabolism associated with mitochondrial dynamics through AMPK activation in healthy subjects. Obesity, a condition that induces oxidative stress, mitochondrial dysfunction, and low AMPK activity leads to mitochondrial fragmentation. However, few studies describe the effect of PA on mitochondrial dynamics regulation in obesity.

AIM

The present study aimed to evaluate the effect of a single session of PA on mitochondrial dynamics regulation as well as its effect on mitochondrial function and organization in skeletal muscles of obese rats (Zucker fa/fa).

MAIN METHODS

Male Zucker lean and Zucker fa/fa rats aged 12 to 13 weeks were divided into sedentary and subjected-to-PA (single session swimming) groups. Gastrocnemius muscle was dissected into isolated fibers, mitochondria, mRNA, and total proteins for their evaluation.

KEY FINDINGS

The results showed that PA increased the Mfn-2 protein level in the lean and obese groups, whereas Drp1 levels decreased in the obese group. OMA1 protease levels increased in the lean group and decreased in the obese group. Additionally, AMPK analysis parameters (expression, protein level, and activity) did not increase in the obese group. These findings correlated with the partial restoration of mitochondrial function in the obese group, increasing the capacity to maintain the membrane potential after adding calcium as a stressor, and increasing the transversal organization level of the mitochondria analyzed in isolated fibers.

SIGNIFICANCE

These results support the notion that obese rats subjected to PA maintain mitochondrial function through mitochondrial fusion activation by an AMPK-independent mechanism.

Effects of phosphorylation on the activity of glycogen phosphorylase in mutton during incubation at 4 °C in vitro

The aim of this study was to assess the effects of the phosphorylation levels of glycogen phosphorylase on its activity in mutton sarcoplasmic protein samples during incubation at 4 °C. Samples of sarcoplasmic proteins from mutton longissimus thoracis muscles were prepared and separated into three treatment groups to obtain glycogen phosphorylase with different phosphorylation levels, which were (1) treated with protein kinase A, (2) treated with alkaline phosphatase, and (3) left untreated (control). Glycogen phosphorylase phosphorylation levels and activity as well as the levels of related endogenous substances were assessed. The results showed that phosphorylation of glycogen phosphorylase in mutton promoted its activity during incubation at 4 °C. The activity of glycogen phosphorylase was also influenced by other factors (glycogen, glucose, glucose 6-phosphate, ATP, etc.) in vitro. The combined effects of phosphorylation and endogenous substances on glycogen phosphorylase activity varied at different incubation times.

Effect of feeding regimen on meat quality, MyHC isoforms, AMPK, and PGC-1α genes expression in the biceps femoris muscle of Mongolia sheep

The effects of two feeding regimens on meat quality, myosin heavy chain (MyHC) types, and key factors regulating muscle fiber type (AMP-activated protein kinase [AMPK] and peroxisome proliferator-activated receptor-coactivator-1α [PGC-1α]) in the biceps femoris muscle of Mongolia sheep were investigated. A total of 20 Mongolia sheep were weaning for 90 days and divided into two groups (pasture group (P) and confinement group (C)) at 10.36 ± 0.35 kg of weaning weight. After weaning, sheep were pasture fed or confinement fed for 9 months. The results showed that live weights, carcass weight, intramuscular fat (IMF), and Warner-Bratzler shear force (WBSF) in P group were significantly lower (p < .05) than that in C group. Compared with P group, color evaluations with respect to L* and b* values were significantly higher (p < .05) in C group. Expression of the MyHC I gene in the P group was significantly higher, while MyHC IIa and MyHC IIb genes expression was significantly lower (p < .05) than that in C group. Also, AMPK activity and expression of AMPKα2 and PGC-1α genes were significantly higher (p < .05) in P group compared with C group. The present study indicated that muscle fiber composition was one of the key differences leading to the differences of meat quality in different feeding regimens. AMPK, particularly AMPKα2, and PGC-1α were considered to be two key factors regulating muscle fiber types in Mongolia sheep. The results support that AMPK activity and the expression of AMPKα2 and PGC-1α genes may affect the composition of muscle fibers; thus, AMPK activity and the expression of AMPKα2 and PGC-1α genes had an effect on meat quality by changed composition of muscle fibers.

Astragalus Polysaccharide Promotes Adriamycin-Induced Apoptosis in Gastric Cancer Cells

Purpose

Astragalus polysaccharide (APS), a common Chinese herbal compound extracted from Astragalus membranaceus, has been proposed to increase the tumour response of and stabilize chemotherapy drugs while reducing their toxicity. Here, we examined the effects of APS on apoptosis in gastric cancer (GC) cells in the presence or absence of adriamycin (0.1 µg/mL).

Methods

GC cells cultured in the presence or absence of adriamycin (0.1 µg/mL) were administered APS (50–200 µg/mL) for 24–72 h and subjected to an MTT assay to examine cell viability. Active caspase-3 expression and DNA fragmentation were assessed to evaluate apoptosis, and real-time PCR was used to analyse the expression levels of multidrug resistance (MDR1) genes and tumour suppressor genes. Western blot analysis was applied to detect cleaved caspase-3 and phosphorylated AMPK (p-AMPK).

Results

Cellular viability was profoundly reduced by APS, and GC cell apoptosis was strongly increased by APS in a time- and dose-dependent manner; these changes may be linked to an increase in p-AMPK levels because the AMPK inhibitor compound C blocked the effects of APS. Similarly, adriamycin-induced decreases in cellular viability and apoptosis of GC cells were enhanced by APS administration. The expression of tumour suppressor genes (SEMA3F, P21^WAF1/CIP1, FBXW7), but not of MDR1, was increased by APS compared to the control, and p-AMPK levels were lower in adriamycin-resistant GC cells than in either adriamycin-sensitive GC cells or an immortalized human gastric epithelial cell line.

Conclusion

APS induces apoptosis independently and strengthens the proapoptotic effect of adriamycin on GC cells, suggesting that APS may act as a chemotherapeutic sensitizer.

Lipid Metabolism Links Nutrient-Exercise Timing to Insulin Sensitivity in Men Classified as Overweight or Obese

CONTEXT

Pre-exercise nutrient availability alters acute metabolic responses to exercise, which could modulate training responsiveness.

OBJECTIVE

To assess acute and chronic effects of exercise performed before versus after nutrient ingestion on whole-body and intramuscular lipid utilization and postprandial glucose metabolism.

DESIGN

(1) Acute, randomized, crossover design (Acute Study); (2) 6-week, randomized, controlled design (Training Study).

SETTING

General community.

PARTICIPANTS

Men with overweight/obesity (mean ± standard deviation, body mass index: 30.2 ± 3.5 kg⋅m-2 for Acute Study, 30.9 ± 4.5 kg⋅m-2 for Training Study).

INTERVENTIONS

Moderate-intensity cycling performed before versus after mixed-macronutrient breakfast (Acute Study) or carbohydrate (Training Study) ingestion.

RESULTS

Acute Study-exercise before versus after breakfast consumption increased net intramuscular lipid utilization in type I (net change: -3.44 ± 2.63% versus 1.44 ± 4.18% area lipid staining, P < 0.01) and type II fibers (-1.89 ± 2.48% versus 1.83 ± 1.92% area lipid staining, P < 0.05). Training Study-postprandial glycemia was not differentially affected by 6 weeks of exercise training performed before versus after carbohydrate intake (P > 0.05). However, postprandial insulinemia was reduced with exercise training performed before but not after carbohydrate ingestion (P = 0.03). This resulted in increased oral glucose insulin sensitivity (25 ± 38 vs -21 ± 32 mL⋅min-1⋅m-2; P = 0.01), associated with increased lipid utilization during exercise (r = 0.50, P = 0.02). Regular exercise before nutrient provision also augmented remodeling of skeletal muscle phospholipids and protein content of the glucose transport protein GLUT4 (P < 0.05).

CONCLUSIONS

Experiments investigating exercise training and metabolic health should consider nutrient-exercise timing, and exercise performed before versus after nutrient intake (ie, in the fasted state) may exert beneficial effects on lipid utilization and reduce postprandial insulinemia.

How autophagy can restore proteostasis defects in multiple diseases?

Cellular evolution develops several conserved mechanisms by which cells can tolerate various difficult conditions and overall maintain homeostasis. Autophagy is a well-developed and evolutionarily conserved mechanism of catabolism, which endorses the degradation of foreign and endogenous materials via autolysosome. To decrease the burden of the ubiquitin-proteasome system (UPS), autophagy also promotes the selective degradation of proteins in a tightly regulated way to improve the physiological balance of cellular proteostasis that may get perturbed due to the accumulation of misfolded proteins. However, the diverse as well as selective clearance of unwanted materials and regulations of several cellular mechanisms via autophagy is still a critical mystery. Also, the failure of autophagy causes an increase in the accumulation of harmful protein aggregates that may lead to neurodegeneration. Therefore, it is necessary to address this multifactorial threat for in-depth research and develop more effective therapeutic strategies against lethal autophagy alterations. In this paper, we discuss the most relevant and recent reports on autophagy modulations and their impact on neurodegeneration and other complex disorders. We have summarized various pharmacological findings linked with the induction and suppression of autophagy mechanism and their promising preclinical and clinical applications to provide therapeutic solutions against neurodegeneration. The conclusion, key questions, and future prospectives sections summarize fundamental challenges and their possible feasible solutions linked with autophagy mechanism to potentially design an impactful therapeutic niche to treat neurodegenerative diseases and imperfect aging.

Oxytocin may have a therapeutical potential against cardiovascular disease. Possible pharmaceutical and behavioral approaches

Based on the ancient role of oxytocin and its homologues as amplifiers of reproduction we argue for an evolutionary coupling of oxytocin to signaling pathway which support restorative mechanisms of cells and tissue. In particular, the survival and function of different categories of stem cells and primordial cells are enhanced by mitogen-activated protein kinase (MAPK) pathways. Furthermore, oxytocin stimulates the AMP-activated protein kinase pathway (AMPK) in numerous of cell types which promotes the maintenance of different cell structures. This involves autophagic processes and, in particular, may support the renewal of mitochondria. Mitochondrial fitness may protect against oxidative and inflammatory stress - a well-documented effect of oxytocin. The combined specific trophic and protective effects oxytocin may delay several degenerative phenomena including sarcopenia, type-2 diabetes and atherosclerosis. These effects may be exerted both on a central level supporting the function and integrity of the hypothalamus and peripherally acting directly on blood vessels, pancreas, heart, skeletal muscles and adipose tissue etc. Furthermore, in the capacity of being both a hormone and neuromodulator, oxytocin interacts with numerous of regulatory mechanisms particularly the autonomic nervous system and HPA-axis which may reduce blood pressure and affect the immune function. The potential of the oxytocin system as a behavioral and molecular target for the prevention and treatment of cardiovascular disease is discussed. Focus is put on the affiliative and sexual significance and the different options and limitations associated with a pharmaceutical approach. MeSH: Aging, Atherosclerosis, Heart, Hypothalamus, Inflammation, Love, Orgasm, Oxytocin.

Immune-mediated anti-tumor effects of metformin; targeting metabolic reprogramming of T cells as a new possible mechanism for anti-cancer effects of metformin

Immunotherapy-based cancer treatment has revolutionized the era of cancer patients recuperation and it has brought a strong hope to treatment of some types of cancers. Metformin, a widely used antidiabetic drug, which has intensely been studied for its anticancer effects, is believed to have positive influences on immune responses against tumor cells. Metformin can affect metabolic pathways within cells mainly through activation of AMPK. Metabolic restriction of tumor microenvironment on effector immune cells is one of the important strategies favoring tumor cells to escape from immunogenic cell death. The metabolism of T cells has an axial role in shaping and supporting immune responses and may have an important role in anticancer immunity, suggesting that the functionality and durability of tumor-specific T cells need sufficient energy and nutrients. Energy biogenesis of tumor-specific cytotoxic T cells has become an interesting field of study and it is suggested that activation and maintenance of effector T cell responses in tumor microenvironment may occur by metabolic reprogramming of T cells. AMPK has been noticed as the main intracellular energy sensor and mitochondrial biogenesis key regulator which can control and regulate metabolic reprogramming in immune cells and increase antitumor immunity. Metabolic reprogramming of T cells to overcome metabolic restriction in tumor microenvironment, maiming effector T cell responses against tumor cells, has been noticed by several studies. Here we represent metformin, an AMPK activator, as a new candidate drug for metabolic reprogramming of tumor-specific T cells to increase the efficacy and accountability of cancer immunotherapy.

Endurance running exercise is an effective alternative to estradiol replacement for restoring hyperglycemia through TBC1D1/GLUT4 pathway in skeletal muscle of ovariectomized rats

Menopause is a risk factor for impaired glucose metabolism. Alternative treatment of estrogen for postmenopausal women is required. The present study was designed to investigate the effects of 5-week endurance running exercise (Ex) by treadmill on hyperglycemia and signal pathway components mediating glucose transport in ovariectomized (OVX) placebo-treated rats, compared with 4-week 17β-estradiol (E2) replacement or pair-feeding (PF) to the E2 group. Ex improved the hyperglycemia and insulin resistance index in OVX rats as much as E2 or PF did. However, Ex had no effect on body weight gain in the OVX rats. Moreover, Ex enhanced the levels of GLUT4 and phospho-TBC1D1 proteins in the gastrocnemius of the OVX rats, but E2 or PF did not. Instead, the E2 increased the Akt2/AS160 expression and activation in the OVX rats. This study suggests that endurance Ex training restored hyperglycemia through the TBC1D1/GLUT4 pathway in muscle by an alternative mechanism to E2 replacement.

Blood flow-restricted training enhances thigh glucose uptake during exercise and muscle antioxidant function in humans

This study examined the effects of blood-flow-restricted (BFR)-training on thigh glucose uptake at rest and during exercise in humans and the muscular mechanisms involved. Ten active men (~25 y; VO_2max ~50 mL/kg/min) completed six weeks of training, where one leg trained with BFR (cuff pressure: ~180 mmHg) and the other leg without BFR. Before and after training, thigh glucose uptake was determined at rest and during exercise at 25% and 90% of leg incremental peak power output by sampling of femoral arterial and venous blood and measurement of femoral arterial blood flow. Furthermore, resting muscle samples were collected. After training, thigh glucose uptake during exercise was higher than before training only in the BFR-trained leg (p < 0.05) due to increased glucose extraction (p < 0.05). Further, BFR-training substantially improved time to exhaustion during exhaustive exercise (11 ± 5% vs. CON-leg; p = 0.001). After but not before training, NAC infusion attenuated (~50-100%) leg net glucose uptake and extraction during exercise only in the BFR-trained leg, which coincided with an increased muscle abundance of Cu/Zn-SOD (39%), GPX-1 (29%), GLUT4 (28%), and nNOS (18%) (p < 0.05). Training did not affect Mn-SOD, catalase, and VEGF abundance in either leg (p > 0.05), although Mn-SOD was higher in BFR-leg vs. CON-leg after training (p < 0.05). The ratios of p-AMPK-Thr¹⁷²/AMPK and p-ACC-Ser⁷⁹/ACC, and p-ACC-Ser⁷⁹, remained unchanged in both legs (p > 0.05), despite a higher p-AMPK-Thr¹⁷² in BFR-leg after training (38%; p < 0.05). In conclusion, BFR-training enhances glucose uptake by exercising muscles in humans probably due to an increase in antioxidant function, GLUT4 abundance, and/or NO availability.

A muscle-specific UBE2O/AMPKα2 axis promotes insulin resistance and metabolic syndrome in obesity

Ubiquitin-conjugating enzyme E2O (UBE2O) is expressed preferentially in metabolic tissues, but its role in regulating energy homeostasis has yet to be defined. Here we find that UBE2O is markedly upregulated in obese subjects with type 2 diabetes and show that whole-body disruption of Ube2o in mouse models in vivo results in improved metabolic profiles and resistance to high-fat diet-induced (HFD-induced) obesity and metabolic syndrome. With no difference in nutrient intake, Ube2o-/- mice were leaner and expended more energy than WT mice. In addition, hyperinsulinemic-euglycemic clamp studies revealed that Ube2o-/- mice were profoundly insulin sensitive. Through phenotype analysis of HFD mice with muscle-, fat-, or liver-specific knockout of Ube2o, we further identified UBE2O as an essential regulator of glucose and lipid metabolism programs in skeletal muscle, but not in adipose or liver tissue. Mechanistically, UBE2O acted as a ubiquitin ligase and targeted AMPKα2 for ubiquitin-dependent degradation in skeletal muscle; further, muscle-specific heterozygous knockout of Prkaa2 ablated UBE2O-controlled metabolic processes. These results identify the UBE2O/AMPKα2 axis as both a potent regulator of metabolic homeostasis in skeletal muscle and a therapeutic target in the treatment of diabetes and metabolic disorders.

AMPK directly activates mTORC2 to promote cell survival during acute energetic stress

AMP-activated protein kinase (AMPK) senses energetic stress and, in turn, promotes catabolic and suppresses anabolic metabolism coordinately to restore energy balance. We found that a diverse array of AMPK activators increased mTOR complex 2 (mTORC2) signaling in an AMPK-dependent manner in cultured cells. Activation of AMPK with the type 2 diabetes drug metformin (GlucoPhage) also increased mTORC2 signaling in liver in vivo and in primary hepatocytes in an AMPK-dependent manner. AMPK-mediated activation of mTORC2 did not result from AMPK-mediated suppression of mTORC1 and thus reduced negative feedback on PI3K flux. Rather, AMPK associated with and directly phosphorylated mTORC2 (mTOR in complex with rictor). As determined by two-stage in vitro kinase assay, phosphorylation of mTORC2 by recombinant AMPK was sufficient to increase mTORC2 catalytic activity toward Akt. Hence, AMPK phosphorylated mTORC2 components directly to increase mTORC2 activity and downstream signaling. Functionally, inactivation of AMPK, mTORC2, and Akt increased apoptosis during acute energetic stress. By showing that AMPK activates mTORC2 to increase cell survival, these data provide a potential mechanism for how AMPK paradoxically promotes tumorigenesis in certain contexts despite its tumor-suppressive function through inhibition of growth-promoting mTORC1. Collectively, these data unveil mTORC2 as a target of AMPK and the AMPK-mTORC2 axis as a promoter of cell survival during energetic stress.

Mitochondrial (Dys)function and Insulin Resistance: From Pathophysiological Molecular Mechanisms to the Impact of Diet

Mitochondrial dysfunction has been implicated in the pathogenesis of insulin resistance, the hallmark of type 2 diabetes mellitus (T2DM). However, the cause-effect relationship remains to be fully elucidated. Compelling evidence suggests that boosting mitochondrial function may represent a valuable therapeutic tool to improve insulin sensitivity. Mitochondria are highly dynamic organelles, which adapt to short- and long-term metabolic perturbations by undergoing fusion and fission cycles, spatial rearrangement of the electron transport chain complexes into supercomplexes and biogenesis governed by peroxisome proliferator-activated receptor γ co-activator 1α (PGC 1α). However, these processes appear to be dysregulated in type 2 diabetic individuals. Herein, we describe the mechanistic link between mitochondrial dysfunction and insulin resistance in skeletal muscle alongside the intracellular pathways orchestrating mitochondrial bioenergetics. We then review current evidence on nutritional tools, including fatty acids, amino acids, caloric restriction and food bioactive derivatives, which may enhance insulin sensitivity by therapeutically targeting mitochondrial function and biogenesis.

Metformin; an old antidiabetic drug with new potentials in bone disorders

The prevalence of diabetes mellitus especially type 2 diabetes mellitus is increasing all over the world. In addition to cardiomyopathy and nephropathy, diabetics are at higher risk of mortality and morbidity due to greater risk of bone fractures and skeletal abnormalities. Patients with diabetes mellitus have lower bone quality in comparison to their non-diabetic counterparts mainly because of hyperglycemia, toxic effects of advanced glycosylation end-products (AGEs) on bone tissue, and impaired bone microvascular system. AGEs may also contribute to the development of osteoarthritis further to osteoporosis. Therefore, glycemic control in diabetic patients is vital for bone health. Metformin, a widely used antidiabetic drug, has been shown to improve bone quality and decrease the risk of fractures in patients with diabetes in addition to glycemic control and improving insulin sensitivity. AMP activated protein kinase (AMPK), the key molecule in metformin antidiabetic mechanism of action, is also effective in signaling pathways involved in bone physiology. This review, discusses the molecules linking diabetes and bone turnover, role of AMPK in bone metabolism, and the effect of metformin as an activator of AMPK on bone disorders and malignancies.

Postexercise improvement in glucose uptake occurs concomitant with greater γ3-AMPK activation and AS160 phosphorylation in rat skeletal muscle

A single exercise session can increase insulin-stimulated glucose uptake (GU) by skeletal muscle, concomitant with greater Akt substrate of 160 kDa (AS160) phosphorylation on Akt-phosphosites (Thr⁶⁴² and Ser⁵⁸⁸) that regulate insulin-stimulated GU. Recent research using mouse skeletal muscle suggested that ex vivo 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) or electrically stimulated contractile activity-inducing increased γ3-AMPK activity and AS160 phosphorylation on a consensus AMPK-motif (Ser⁷⁰⁴) resulted in greater AS160 Thr⁶⁴² phosphorylation and GU by insulin-stimulated muscle. Our primary goal was to determine whether in vivo exercise that increases insulin-stimulated GU in rat skeletal muscle would also increase γ3-AMPK activity and AS160 site-selective phosphorylation (Ser⁵⁸⁸, Thr⁶⁴², and Ser⁷⁰⁴) immediately postexercise (IPEX) and/or 3 h postexercise (3hPEX). Epitrochlearis muscles isolated from sedentary and exercised (2-h swim exercise; studied IPEX and 3hPEX) rats were incubated with 2-deoxyglucose to determine GU (without insulin at IPEX; without or with insulin at 3hPEX). Muscles were also assessed for γ1-AMPK activity, γ3-AMPK activity, phosphorylated AMPK (pAMPK), and phosphorylated AS160 (pAS160). IPEX versus sedentary had greater γ3-AMPK activity, pAS160 (Ser⁵⁸⁸, Thr⁶⁴², Ser⁷⁰⁴), and GU with unaltered γ1-AMPK activity. 3hPEX versus sedentary had greater γ3-AMPK activity, pAS160 Ser⁷⁰⁴, and GU with or without insulin; greater pAS160 Thr⁶⁴² only with insulin; and unaltered γ1-AMPK activity. These results using an in vivo exercise protocol that increased insulin-stimulated GU in rat skeletal muscle are consistent with the hypothesis that in vivo exercise-induced enhancement of γ3-AMPK activation and AS160 Ser⁷⁰⁴ IPEX and 3hPEX are important for greater pAS160 Thr⁶⁴² and enhanced insulin-stimulated GU by skeletal muscle.

2-Bromo-4'-methoxychalcone and 2-Iodo-4'-methoxychalcone Prevent Progression of Hyperglycemia and Obesity via 5'-Adenosine-Monophosphate-Activated Protein Kinase in Diet-Induced Obese Mice

Obesity and diabetes are global health-threatening issues. Interestingly, the mechanism of these pathologies is quite different among individuals. The discovery and development of new categories of medicines from diverse sources are urgently needed for preventing and treating diabetes and other metabolic disorders. Previously, we reported that chalcones are important for preventing biological disorders, such as diabetes. In this study, we demonstrate that the synthetic halogen-containing chalcone derivatives 2-bromo-4′-methoxychalcone (compound 5) and 2-iodo-4′-methoxychalcone (compound 6) can promote glucose consumption and inhibit cellular lipid accumulation via 5′-adenosine-monophosphate-activated protein kinase (AMPK) activation and acetyl-CoA carboxylase 1 (ACC) phosphorylation in 3T3-L1 adipocytes and C2C12 skeletal myotubes. In addition, the two compounds significantly prevented body weight gain and impaired glucose tolerance, hyperinsulinemia, and insulin resistance, which collectively help to delay the progression of hyperglycemia in high-fat-diet-induced obese C57BL/6 mice. These findings indicate that 2-bromo-4′-methoxychalcone and 2-iodo-4′-methoxychalcone could act as AMPK activators, and may serve as lead compounds for a new class of medicines that target obesity and diabetes.

Effect of pre-slaughter shackling and wing flapping on plasma parameters, postmortem metabolism, AMPK, and meat quality of broilers

The objective of this study was to determine the effects of shackling and wing flapping on stress, postmortem metabolism, AMP-activated protein kinase (AMPK), and quality of broiler pectoralis major. Before slaughter, a total of 80 Arbor Acres broilers was randomly categorized into 2 replicate pens (40 broilers per pen) and each pen randomly divided into 2 groups (shackling, T; control, C). Corticosterone, creatine kinase, and lactate dehydrogenase were determined on blood plasma parameters. Pectoralis major were removed after evisceration and used for determination of energy metabolism, meat quality, and AMPK phosphorylation. In this study, shackling and wing flapping increased (P < 0.05) plasma corticosterone level, creatine kinase activity, and lactate dehydrogenase activity. Shackling and wing flapping increased (P < 0.05) AMPKα(Thr172) and acetyl-CoA carboxylase (ACC) phosphorylation, followed by rapid glycolysis and accumulation of lactic acid, and leading to a fast pH decline in the initial postmortem meat. Shackling and wing flapping have an adverse effect on final meat quality, which increased (P < 0.05) muscle lightness, drip loss, and cooking loss. The results indicate that antemortem shackling and wing flapping increased stress and AMPKα(Thr172) phosphorylation, which may accelerate glycolysis and lead to a low water-holding capacity of broiler meat.

Cell-Specific "Competition for Calories" Drives Asymmetric Nutrient-Energy Partitioning, Obesity, and Metabolic Diseases in Human and Non-human Animals

The mammalian body is a complex physiologic “ecosystem” in which cells compete for calories (i.e., nutrient-energy). Axiomatically, cell-types with competitive advantages acquire a greater number of consumed calories, and when possible, increase in size and/or number. Thus, it is logical and parsimonious to posit that obesity is the competitive advantages of fat-cells (adipocytes) driving a disproportionate acquisition and storage of nutrient-energy. Accordingly, we introduce two conceptual frameworks. Asymmetric Nutrient-Energy Partitioning describes the context-dependent, cell-specific competition for calories that determines the partitioning of nutrient-energy to oxidation, anabolism, and/or storage; and Effective Caloric Intake which describes the number of calories available to constrain energy-intake via the inhibition of the sensorimotor appetitive cells in the liver and brain that govern ingestive behaviors. Inherent in these frameworks is the independence and dissociation of the energetic demands of metabolism and the neuro-muscular pathways that initiate ingestive behaviors and energy intake. As we demonstrate, if the sensorimotor cells suffer relative caloric deprivation via asymmetric competition from other cell-types (e.g., skeletal muscle- or fat-cells), energy-intake is increased to compensate for both real and merely apparent deficits in energy-homeostasis (i.e., true and false signals, respectively). Thus, we posit that the chronic positive energy balance (i.e., over-nutrition) that leads to obesity and metabolic diseases is engendered by apparent deficits (i.e., false signals) driven by the asymmetric inter-cellular competition for calories and concomitant differential partitioning of nutrient-energy to storage. These frameworks, in concert with our previous theoretic work, the Maternal Resources Hypothesis, provide a parsimonious and rigorous explanation for the rapid rise in the global prevalence of increased body and fat mass, and associated metabolic dysfunctions in humans and other mammals inclusive of companion, domesticated, laboratory, and feral animals.

Exercise Metabolism: Fuels for the Fire

During exercise, the supply of adenosine triphosphate (ATP) is essential for the energy-dependent processes that underpin ongoing contractile activity. These pathways involve both substrate-level phosphorylation, without any need for oxygen, and oxidative phosphorylation that is critically dependent on oxygen delivery to contracting skeletal muscle by the respiratory and cardiovascular systems and on the supply of reducing equivalents from the degradation of carbohydrate, fat, and, to a limited extent, protein fuel stores. The relative contribution of these pathways is primarily determined by exercise intensity, but also modulated by training status, preceding diet, age, gender, and environmental conditions. Optimal substrate availability and utilization before, during, and after exercise is critical for maintaining exercise performance. This review provides a brief overview of exercise metabolism, with expanded discussion of the regulation of muscle glucose uptake and fatty acid uptake and oxidation.

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.

Neuronal nitric oxide synthase mediates insulin- and oxidative stress-induced glucose uptake in skeletal muscle myotubes

Previously published studies strongly suggested that insulin- and exercise-induced skeletal muscle glucose uptake require nitric oxide (NO) production. However, the signal transduction mechanisms by which insulin and contraction regulated NO production and subsequent glucose transport are not known. In the present study, we utilized the myotube cell lines treated with insulin or hydrogen peroxide, the latter to mimic contraction-induced oxidative stress, to characterize these mechanisms. We found that insulin stimulation of neuronal nitric oxide synthase (nNOS) phosphorylation, NO production, and GLUT4 translocation were all significantly reduced by inhibition of either nNOS or Akt2. Hydrogen peroxide (H₂O₂) induced phosphorylation of nNOS at the same residue as did insulin, and also stimulated NO production and GLUT4 translocation. nNOS inhibition prevented H₂O₂-induced GLUT4 translocation. AMP activated protein kinase (AMPK) inhibition prevented H₂O₂ activation and phosphorylation of nNOS, leading to reduced NO production and significantly attenuated GLUT4 translocation. We conclude that nNOS phosphorylation and subsequently increased NO production are required for both insulin- and H₂O₂-stimulated glucose transport. Although the two stimuli result in phosphorylation of the same residue on nNOS, they do so through distinct protein kinases. Thus, insulin and H₂O₂-activated signaling pathways converge on nNOS, which is a common mediator of glucose uptake in both pathways. However, the fact that different kinases are utilized provides a basis for the use of exercise to activate glucose transport in the face of insulin resistance.