Effects of exercise on AMPK signaling and downstream components to PI3K in rat with type 2 diabetes

Effects of different pre-conditioning exercise on leptin synthesis and its downstream signalling pathway in T2DM rats

Objectives

This study aimed to evaluate the effects of pre-conditioning exercise on body lipid metabolism, leptin secretion, and the downstream pathways at the early stage of type 2 diabetes mellitus (T2DM).

Materials and Methods

The T2DM model was established using an 8-week high-sugar, high-fat diet combined. The T2DM model was established using an 8-week high-sugar, high-fat diet combined with streptozocin (STZ) injection. Two exercise interventions, high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) were performed during the model-building process. One week following the STZ injection, rats were euthanized. Blood, gastrocnemius muscle, and epididymal fat pad were collected. Plasma leptin content was measured by ELISA. The expression of leptin-mRNA in epididymal adipose tissue was measured using RT-qPCR, and its protein expression was detected by a western blot. Leptin, leptin-R, and AMPK (AMP-activated protein kinase) - ACC (Acetyl-CoA carboxylase) expression in gastrocnemius muscle was also detected by western blot. Free fatty acids (FFA) and triglycerides (TG) contents in gastrocnemius muscle were measured using a biochemical assay.

Results

In the HIIT group, glucose tolerance and leptin receptor expression increased, as did the expression and phosphorylation of AMPK protein. At the early stage of T2DM, it increased significantly in the gastrocnemius muscle in the MICT group.

Conclusion

At the early stage of T2DM, pre-conditioning exercise in the form of HIIT was found to inhibit the leptin-mRNA expression in adipose tissue, suppress leptin synthesis, up-regulate AMPK-ACC signaling pathway, and promote lipid decomposition in skeletal muscle tissue. Pre-conditioning of MICT led to the accumulation of FFA and TG in skeletal muscle, likely due to exercise adaptation rather than ectopic deposition of lipids.

Exercise as a therapeutic approach to alleviate diabetic kidney disease: mechanisms, clinical evidence and potential exercise prescriptions

Diabetic kidney disease (DKD) is a global and severe complication that imposes a significant burden on individual health, families, and society. Currently, the main treatment approaches for DKD include medication, blood glucose control, protein-restricted diet, and blood pressure management, all of which have certain limitations. Exercise, as a non-pharmacological intervention, has attracted increasing attention. This review introduces the mechanisms and clinical evidence of exercise on DKD, and proposes potential exercise prescriptions. Exercise can improve blood glucose stability related to DKD and the renin-angiotensin-aldosterone system (RAAS), reduce renal oxidative stress and inflammation, enhance the crosstalk between muscle and kidneys, and improve endothelial cell function. These mechanisms contribute to the comprehensive improvement of DKD. Compared to traditional treatment methods, exercise has several advantages, including safety, effectiveness, and no significant side effects. It can be used as an adjunct therapy to medication, blood glucose control, protein-restricted diet, and blood pressure management. Despite the evident benefits of exercise in DKD management, there is still a lack of large-scale, long-term randomized controlled trials to provide more evidence and develop exercise guidelines for DKD. Healthcare professionals should actively encourage exercise in DKD patients and develop personalized exercise plans based on individual circumstances.

Exercise couples mitochondrial function with skeletal muscle fiber type via ROS-mediated epigenetic modification

Skeletal muscle is a heterogeneous tissue composed of different types of muscle fibers, demonstrating substantial plasticity. Physiological or pathological stimuli can induce transitions in muscle fiber types. However, the precise regulatory mechanisms behind these transitions remains unclear. This paper reviews the classification and characteristics of muscle fibers, along with the classical mechanisms of muscle fiber type transitions. Additionally, the role of exercise-induced muscle fiber type transitions in disease intervention is reviewed. Epigenetic pathways mediate cellular adaptations and thus represent potential targets for regulating muscle fiber type transitions. This paper focuses on the mechanisms by which epigenetic modifications couple mitochondrial function and contraction characteristics. Reactive Oxygen Species (ROS) are critical signaling regulators for the health-promoting effects of exercise. Finally, we discuss the role of exercise-induced ROS in regulating epigenetic modifications and the transition of muscle fiber types.

AMPK and Beyond: The Signaling Network Controlling RabGAPs and Contraction-Mediated Glucose Uptake in Skeletal Muscle

Impaired skeletal muscle glucose uptake is a key feature in the development of insulin resistance and type 2 diabetes. Skeletal muscle glucose uptake can be enhanced by a variety of different stimuli, including insulin and contraction as the most prominent. In contrast to the clearance of glucose from the bloodstream in response to insulin stimulation, exercise-induced glucose uptake into skeletal muscle is unaffected during the progression of insulin resistance, placing physical activity at the center of prevention and treatment of metabolic diseases. The two Rab GTPase-activating proteins (RabGAPs), TBC1D1 and TBC1D4, represent critical nodes at the convergence of insulin- and exercise-stimulated signaling pathways, as phosphorylation of the two closely related signaling factors leads to enhanced translocation of glucose transporter 4 (GLUT4) to the plasma membrane, resulting in increased cellular glucose uptake. However, the full network of intracellular signaling pathways that control exercise-induced glucose uptake and that overlap with the insulin-stimulated pathway upstream of the RabGAPs is not fully understood. In this review, we discuss the current state of knowledge on exercise- and insulin-regulated kinases as well as hypoxia as stimulus that may be involved in the regulation of skeletal muscle glucose uptake.

Effects of aerobic training and vitamin D supplementation on glycemic indices and adipose tissue gene expression in type 2 diabetic rats

Type 2 diabetes mellitus (T2DM) is a progressive metabolic disorder mainly caused by overweight and obesity that accumulates pro-inflammatory factors in adipose tissue. Studies have confirmed the efficacy of exercise and vitamin D supplementation in preventing, controlling, and treating diabetes. While, reduced physical activity and vitamin D deficiency are related to increased adiposity, blood glucose level, insulin concentration, and insulin resistance. This study purposed to investigate the effect of 8-week aerobic training with vitamin D supplementation on the expression of AMPK, PGC-1α, and UCP-1 genes expression in the visceral adipose tissue of obese rats with T2DM. In this experimental study, fifty male Wistar rats were divided into 5 groups (n = 10): aerobic training and vitamin D supplementation (AT + Vit D), aerobic training (5 days/week for 8 weeks; AT), vitamin D supplementation (Vit D), diabetic control (C) and NC (Non-Diabetic Control). AT + Vit D and AT groups practiced an 8-week aerobic training, 5 days a week. Vit D and AT + Vit D groups receive 5000 IU of vitamin D by injection once a week while AT and C received sesame oil. After blood sampling, visceral fat was taken to measure AMPK, PGC-1α, and UCP1 gene expression. Data were statistically analyzed by One-way ANOVA and paired sample t-test at a significance level of p < 0.05. Based on our results BW, BMI, WC, visceral fat, insulin, glucose, and HOMA-IR were significantly lower in the AT + Vit D, AT, and Vit D groups compared with the C group (p < 0.01). Furthermore, AT + Vit D, AT, and Vit D upregulated AMPK, PGC-1α, and UCP1 gene expression compared to the C. Based on the results compared to AT and Vit D, AT + Vit D significantly upregulated AMPK (p = 0.004; p = 0.001), PGC-1α (p = 0.010; p = 0.001), and UCP1 (p = 0.032; p = 0.001) gene expression, respectively. Also, AT induced more significant upregulations in the AMPK (p = 0.001), PGC-1α (p = 0.001), and UCP1 gene expression (p = 0.001) than Vit D. Vitamin D supplementation enhanced the beneficial effects of aerobic training on BW, BMI, WC, visceral fat, insulin, glucose, and HOMA-IR in diabetic rats. We also observed that separate AT or Vit D upregulated the gene expression of AMPK, PGC-1α, and UCP1 however, combined AT + Vit D upregulated AMPK, PGC-1α, and UCP1 more significantly. These results suggested that combining aerobic training and vitamin D supplementation exerted incremental effects on the gene expressions related to adipose tissue in animal models of diabetes.

Therapeutic effects of icariin and icariside II on diabetes mellitus and its complications

Diabetes mellitus (DM) is a global health issue in the twenty-first century, and there are numerous challenges in preventing and alleviating its chronic complications. The herb Epimedium has beneficial therapeutic effects on various human diseases, including DM. Its major flavonoid component, icariin, has significant anti-DM activity and may help improve pancreatic β-cell dysfunction and insulin resistance. Furthermore, preclinical evidence has shown that icariin and its in vivo bioactive form, icariside II, have preventive and therapeutic effects on several diabetic complications, including diabetic cardiomyopathy, diabetic vascular endothelial disorder, diabetic nephropathy, and diabetic erectile dysfunction. In this review, we present the general and toxicological information concerning icariin and icariside II and review the anti-DM effects of icariin from a molecular perspective. Additionally, we discuss the potential benefits of icariin and icariside II on the important pathological mechanisms of various diabetic complications. Despite positive preclinical evidence, additional investigations are needed before relevant clinical studies can be conducted. Therefore, we conclude with suggestions for future research. Hopefully, this review will provide a comprehensive molecular perspective for future research and product development related to icariin and icariside II in treating DM and diabetic complications.

Cardioprotective Signaling Pathways in Obese Mice Submitted to Regular Exercise: Effect on Oxysterols

Exercise induces cardioprotection against myocardial infarction, despite obesity, by restoring pro-survival pathways and increasing resistance of mitochondrial permeability transition pore (mPTP) opening at reperfusion. Among the mechanisms involved in the inactivation of these pathways, oxysterols appear interesting. Thus, we investigated the influence of regular exercise on the reperfusion injury salvage kinase (RISK) pathway, oxysterols, and mitochondria, in the absence of ischemia-reperfusion. We also studied 7β-hydroxycholesterol (7βOH) concentration (mass spectrometry) in human lean and obese subjects. Wild-type (WT) and obese (ob/ob) mice were assigned to sedentary conditions or regular treadmill exercise. Exercise significantly increased Akt phosphorylation, whereas 7βOH concentration was reduced. Moreover, exercise induced the translocation of PKCε from the cytosol to mitochondria. However, exercise did not affect the calcium concentration required to open mPTP in the mitochondria, neither in WT nor in ob/ob animals. Finally, human plasma 7βOH concentration was consistent with observations made in mice. In conclusion, regular exercise enhanced the RISK pathway by increasing kinase phosphorylation and PKCε translocation and decreasing 7βOH concentration. This activation needs the combination with stress conditions, i.e., ischemia-reperfusion, in order to inhibit mPTP opening at the onset of reperfusion. The human findings suggest 7βOH as a candidate marker for evaluating cardiovascular risk factors in obesity.

Effects of Physical Exercise on Mitochondrial Biogenesis of Skeletal Muscle Modulated by Histones Modifications in Type 2 Diabetes

Epigenetic modification in skeletal muscle induced by environmental factors seems to modulate several metabolic pathways that underlie Type 2 Diabetes Mellitus (T2DM) development. Mitochondrial biogenesis is an important process for maintaining lipid metabolism homeostasis, as well as epigenetic modifications in proteins that regulate this pathway have been observed in the skeletal muscle of T2DM subjects. Moreover, physical exercise affects several metabolic pathways attenuating metabolic deregulation observed in T2DM. The pathways that regulate mitochondrial homeostasis are one of the key components for understanding such physical exercise beneficial effects. Thus, in this study, we investigate the epigenetic mechanisms underlying mitochondrial biogenesis in the skeletal muscle in T2DM, focusing on histone modifications and the possible mechanisms by which physical exercise delay or inhibit T2DM onset. The results indicate that exercise promotes improvements in cellular metabolism through increasing enzymes of the antioxidant system, AMPK and ATP-citrate lyase activity, Acetyl-CoA concentration, and enhancing the acetylation of histones. A key mediator of mitochondrial biogenesis such as peroxisome proliferator-activated receptor γ coactivator-1α (PGC1) seems to be upregulated by exercise in T2DM and such factor positively regulates the skeletal muscle mitochondrial biogenesis, which improves energy metabolism and glucose homeostasis inhibiting or delaying insulin resistance and further T2DM. 

The Effect of Various Training on the Expression of the 5’amp-Activated Protein Kinase Α2 and Glucose Transporter - 4 in Type-2 Diabetes Mellitus Rat

BACKGROUND: Exercise is the main pillar in Type 2 Diabetes Mellitus (T2DM) management. The mechanism of glucose uptake mediated by exercise is different from insulin, and this mechanism is not disturbed in T2DM. One of the mechanisms is through the activation of 5’AMP-activated protein kinase (AMPK). AMPK also regulates the glucose transporter 4 (GLUT4) expression. Effect various types of exercise to AMPK α2 and GLUT-4 of the skeletal muscle still limited. AIM: This study aims to determine the effect of various physical training on the expression of Ampk α2 and Glut 4 in skeletal muscle of T2DM rats. METHODS: This study used stored skeletal muscles of 25 T2DM Wistar rats. Previously, the rats were divided into groups of K1 (control, not given exercise), K2 (moderate continuous training), K3 (severe continuous training), K4 (slow interval training), and K5 (fast interval training). Running on a treadmill frequency 3 times a week for 8 weeks. The relative expression of Ampk α2 and Glut 4 were assessed using Real Time-PCR and were compared among the groups using the Livak formula. RESULTS: Moderate intensity continuous training increased Ampk α2 and Glut 4 expression by 1.45 and 2.39 times, respectively. Severe intensity continuous training increased the expression of Ampk α2 and Glut 4 by 1.55 and 2.56 times, respectively. Slow interval training increased the expression of Ampk α2 and Glut 4 by 4.41 and 3.76 times, respectively. The expression of Ampk α2 and Glut4 in fast interval training was 4.56 and 4.79 times more than control. CONCLUSION: Continuous and interval training increase Ampk α2 and Glut 4 expression. The fast interval training showed the highest expression of Ampk α2 and Glut 4.

The Role of Obesity-Induced Perivascular Adipose Tissue (PVAT) Dysfunction in Vascular Homeostasis

Perivascular adipose tissue (PVAT) is an additional special type of adipose tissue surrounding blood vessels. Under physiological conditions, PVAT plays a significant role in regulation of vascular tone, intravascular thermoregulation, and vascular smooth muscle cell (VSMC) proliferation. PVAT is responsible for releasing adipocytes-derived relaxing factors (ADRF) and perivascular-derived relaxing factors (PDRF), which have anticontractile properties. Obesity induces increased oxidative stress, an inflammatory state, and hypoxia, which contribute to PVAT dysfunction. The exact mechanism of vascular dysfunction in obesity is still not well clarified; however, there are some pathways such as renin-angiotensin-aldosterone system (RAAS) disorders and PVAT-derived factor dysregulation, which are involved in hypertension and endothelial dysfunction development. Physical activity has a beneficial effect on PVAT function among obese patients by reducing the oxidative stress and inflammatory state. Diet, which is the second most beneficial non-invasive strategy in obesity treatment, may have a positive impact on PVAT-derived factors and may restore the balance in their concentration.

Icariin treatment reduces blood glucose levels in type 2 diabetic rats and protects pancreatic function

Icariin, a flavonoid isolated from traditional oriental herbal medicines, has been demonstrated to exhibit several health benefits in animal models and in humans. The aim of the present study was to investigate the effect of Icariin on hyperglycemia in type 2 diabetes mellitus (T2DM) in rats. A model of diabetes was established in 50 Sprague Dawley rats using a high-sugar and high-fat diet and peritoneal injection of streptozotocin. Diabetic rats were divided into five groups: Diabetic control; metformin; and rats treated with three different doses of Icariin, 5, 10 and 20 mg/kg. Body weight and blood glucose levels were measured, and serum adiponectin levels, expression of phospho-AMP mediated protein kinase (p-AMPK) and glucose transporter isoform 4 (GLUT-4) were measured using ELISA, Realtime PCR and western blotting, respectively. Diabetic rats without drug treatment exhibited reduced body weight, increased blood glucose levels and decreased the number of islets. In T2DM rats treated with 10 or 20 mg/kg Icariin, the blood glucose levels were reduced, whereas serum adiponectin levels were not affected. Additionally, the mRNA and protein expression levels of p-AMPK and GLUT-4 protein were increased in the T2DM rats treated with Icariin. In conclusion, in the diabetes rat model, Icariin alleviated the severity of diabetes, and the effects may be associated with reduction of hyperglycemia by activating an AMPK/GLUT-4 pathway.

Mechanical stretch activates glycometabolism-related enzymes via estrogen in C2 C12 myoblasts

Moderate exercise improves glycometabolic disorder and type 2 diabetes mellitus in menopausal females. So far, the effect of exercise-induced estrogen on muscular glycometabolism is not well defined. The current study was designed to explore the effect of mechanical stretch-induced estrogen on glycometabolism in mouse C₂ C₁₂ myoblasts. The mouse C₂ C₁₂ myoblasts in vitro were assigned randomly to the control (C), stretch (S), and stretch plus aromatase inhibitor anastrozole (SA) groups. Cells in the S group were stretched by the Flexcell FX-5000™ system (15% magnitude, 1 Hz frequency, and 6-hr duration) whereas those in the SA group were treated with 400 μg/ml anastrozole before the same stretching. Glucose uptake, estradiol levels, PFK-1 levels, and oxygen consumption rate were determined, and the expression of HK, PI3K, p-AKT, AKT, and GLUT4 proteins were semiquantified with western blot analysis. Compared to the control, the estradiol level, oxygen consumption rate, expression of HK, PI3K, and PFK-1 proteins, the ratio of p-AKT to AKT, and the ratio of GLUT4 in the cell membrane to that in the whole cell were higher in the S group. On the other hand, the estradiol level, glucose uptake, expression of PFK-1 and GLUT4 proteins, oxygen consumption rate, expression of HK protein, and the ratio of p-AKT/AKT were lower in the myoblasts in the SA group than those in the S group. The level of estradiol was positively correlated with glucose uptake (p < .01, r = .818). Therefore, mechanical stretch-induced estrogen increased the expression of glycometabolism-related enzymes and proteins in the mouse C₂ C₁₂ myoblasts.

Antihyperglycemic effect of rice husk derived xylooligosaccharides in high-fat diet and low-dose streptozotocin-induced type 2 diabetic rat model

Rice husk (RH) is an agricultural waste obtained from rice milling process. Our previous study demonstrated the optimized process of extracting xylooligosaccharides (XOS), a prebiotic that can support the growth and activity of beneficial gut microbiota, from RH. Accumulated evidences indicate that the composition of gut microbiota is involved in the progression of insulin resistance and diabetes. This study aims to evaluate the antihyperglycemic effect and putative mechanisms of RH-XOS using a diabetic rat model induced by high-fat diet and streptozotocin injection. Diabetic rats were randomly assigned to receive vehicle (DMC), XOS (DM-XOS), metformin (DMM), and a combination of XOS and metformin (DMM-XOS). An additional group of rats were fed with normal diet plus vehicle (NDC) and normal diet plus XOS (ND-XOS). Supplementation with RH-XOS for 12 weeks successfully decreased the fasting plasma glucose, insulin, leptin, and LPS levels in DM-XOS compared with DMC. Likewise, the insulin-stimulated glucose uptake assessed by in vitro study was significantly enhanced in DM-XOS, DMM, and DMM-XOS. The diminished protein expressions of GLUT4 and pAktSer473 as well as pAMPKThr172 were significantly modulated in DM-XOS, DMM, and DMM-XOS groups. Interestingly, RH-XOS supplementation reversed the changed gut permeability, elevated the number of beneficial bacteria, both Lactobacillus and Bifidobacterium spp., and increased SCFAs production. Taken together, the results confirm the efficacy of RH-XOS in achieving good glycemic control in diabetes by maintenance of gut microbiota and attenuation of endotoxemia. The findings reveal the benefits of RH-XOS and open an opportunity to improve its value by its development as a nutraceutical for diabetes.

Impaired enhancement of insulin action in cultured skeletal muscle cells from insulin resistant type 2 diabetic patients in response to contraction using electrical pulse stimulation

AIMS

Skeletal muscle insulin resistance is a characteristic feature of type 2 diabetes. The aim of this study was to examine the effect of contraction on insulin action using electrical pulse stimulation (EPS) in cultured skeletal muscle cells from insulin resistant type 2 diabetic patients.

METHODS

Skeletal muscle cell cultures were established from 6 insulin resistant type 2 diabetic subjects and age and BMI matched non-diabetic control subjects. Day 7 differentiated myotubes were treated with or without EPS for 16 h, after which glucose uptake and AS160 phosphorylation were measured in the presence or absence of insulin.

RESULTS

In control myotubes, EPS resulted in increased phosphorylation of AMPKThr¹⁷² (vs no EPS; p < 0.01), and this was associated with increased glucose uptake (p < 0.05). Insulin in the absence of EPS increased glucose uptake and AS160Thr⁶⁴² phosphorylation, and both effects were significantly enhanced by prior EPS. In the absence of EPS, AMPK activation was significantly increased (p < 0.01) in the diabetic vs control myotubes. Despite a comparable degree of AMPK activation following EPS, the action of insulin on glucose uptake (p < 0.05) and AS160Thr⁶⁴² phosphorylation (p < 0.001) was decreased in the diabetic vs control myotubes.

CONCLUSION

EPS mediated AMPK activation enhances the effect of insulin on glucose uptake and AS160Thr⁶⁴² phosphorylation in control myotubes replicating key metabolic benefits of exercise on insulin action in man. Conversely, insulin mediated glucose uptake and AS160Thr⁶⁴² phosphorylation remain significantly decreased in diabetic vs control myotubes despite a comparable degree of AMPK activation following EPS.

Effects of food restriction and/or aerobic exercise on the GLUT4 in type 2 diabetic male rats

Background

The aim of present study was to compare the effects of negative energy balance with food restriction and/or aerobic exercise on the glucose, insulin, and GLUT4 levels in diabetic male rats.

Methods

Fifty-six 10-week old male Wistar rats were randomly assigned to seven groups: a non-diabetic (ND) group and six diabetic groups. After an infusion of type 2 diabetes, the diabetic groups were given labels as well, namely diabetic control (DC) group, exercise (Ex) group, food restriction with standard diet (FRSD) group, food restriction with low-carbohydrate diet (FRLCD) group, food restriction with standard diet combination in exercise (FRSDE) group, and food restriction with low-carbohydrate diet combination in exercise (FRLCDE) group. Further, to induce caloric restriction (CR), food intake was reduced by 20% and given to food restriction consists of both of (FRSD and FRLCD). Hundred percent food consumption for the Ex group was fixed, but instead, 20% of their energy intake in exercise was calculated, and time of daily exercise was determined. Finally, a combination of reduced food intake (10%) and exercise (10%) was applied in each group FRSDE and FRLCDE for 8 weeks.

Results

The results showed that type 2 diabetes inductions had reduced glucose, insulin, and GLUT4 gene expression compared to the ND group (P = 0.001). However, there were significant differences in GLUT4 gene expression between groups after 8 weeks of intervention (P = 0.001). A post hoc least significant difference test show that compared to DC group, GLUT4 gene expression level of Ex, FRSDE, and FRLCDE groups was significantly increased 47% (P = 0.004), 60% (P = 0.001), and 65% (P = 0.001), respectively after 8 week of intervention, but it was not significant or with any other diabetic groups (P > 0.05). Moreover, glucose levels were significantly higher in the FRLCDE, FRLCD, FRSD, FRSDE, Ex groups compared with the DC group in the same period (P = 0.0.01).

Conclusions

It was concluded that FRSD and FRLCD combination in regular exercise was elevated of GLUT4 gene expression in type 2 diabetes. These results may help to develop new methods for the treatment of obesity and type 2 diabetes mellitus.

Early intervention with Didang decoction delays macrovascular lesions in diabetic rats through regulating AMP-activated protein kinase signaling pathway

The study aimed to investigate the intervening role of Didang decoction (DDD) at different times in macrovascular endothelial defense function, focusing on its effects on the AMP-activated protein kinase (AMPK) signaling pathway. The effects of DDD on mitochondrial energy metabolism were also investigated in rat aortic endothelial cells (RAECs). Type 2 diabetes were induced in rats by streptozotocin (STZ) combined with high fat diet. Rats were randomly divided into non-intervention group, metformin group, simvastatin group, and early-, middle-, late-stage DDD groups. Normal rats were used as control. All the rats received 12 weeks of intervention or control treatment. Western blots were used to detect the expression of AMP-activated protein kinase α1 (AMPKα1) and peroxisome proliferator-activated receptor 1α (PGC-1α). Changes in the intracellular AMP and ATP levels were detected with ELISA. Real-time-PCR was used to detect the mRNA level of caspase-3, endothelial nitric oxide synthase (eNOS), and Bcl-2. Compared to the diabetic non-intervention group, a significant increase in the expression of AMPKα1 and PGC-1α were observed in the early-stage, middle-stage DDD groups and simvastatin group (P < 0.05). The levels of Bcl-2, eNOS, and ATP were significantly increased (P < 0.05), while the level of AMP and caspase-3 were decreased (P < 0.05) in the early-stage DDD group and simvastatin group. Early intervention with DDD enhances mitochondrial energy metabolism by regulating the AMPK signaling pathway and therefore may play a role in strengthening the defense function of large vascular endothelial cells and postpone the development of macrovascular diseases in diabetes.

Effects of detraining and retraining on muscle energy-sensing network and meteorin-like levels in obese mice

Background

Increased intramuscular peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) with exercise directly or indirectly affects other tissues, but the effector pathway of PGC-1α has not been clearly elucidated. The purpose of this study was to investigate the effect of exercise and/or dietary change on the protein levels of the soleus muscle energy-sensing network and meteorin-like (Metrnl), and additionally to analyze the detraining and retraining effects in high-fat diet (HFD)-induced obese mice.

Methods

One hundred male C57BL/6 mice were divided into normal-diet + sedentary (CO, n = 20) and HFD + sedentary (HF, n = 80) groups, and obesity was induced in the HF group through consumption of a 45% HFD for 6 weeks. The HF group was subdivided into HF only (n = 20), HF + training (HFT, n = 20), dietary change + sedentary (HFND, n = 20), and HFND + training (HFNDT, n = 20) groups, and the mice in the training groups underwent a treadmill training for 8 weeks, 5 times per week, 40 min per day. The HFT and HFNDT groups underwent 8-week training, 8-week detraining, and 4-week retraining.

Results

An 8-week training was effective in increasing the protein levels of soleus muscle AMP-activated protein kinase (AMPK), PGC-1α, and plasma Metrnl in the obese mice (P < 0.05). Moreover, exercise in obesity reduced body weight (P < 0.05), and exercise with dietary conversion was effective in reducing body weight (P < 0.05) and fat mass (P < 0.05) after 8-week training. 8-week detraining restored the increased protein level to the pre-exercise state, but, the previous exercise effect in body weight and fat mass (P < 0.05) of the HFNDT group remained until the end of 4-week detraining. 4-week retraining was effective in increasing the protein levels of soleus muscle AMPK, PGC-1α, blood Metrnl (P < 0.05), and reducing in body weight (P < 0.05) and fat mass (P < 0.05), when retraining with dietary change.

Conclusions

The results of this study suggest that regular exercise is indispensable to reduce body weight and fat mass through upregulation of the muscle energy-sensing network and Metrnl protein levels, and retraining with dietary change is necessary to obtain the retraining effects more quickly.

Electronic supplementary material

The online version of this article (10.1186/s12944-018-0751-3) contains supplementary material, which is available to authorized users.

Cardiac, Metabolic and Molecular Profiles of Sedentary Rats in the Initial Moment of Obesity

BACKGROUND

Different types of high-fat and/or high-energy diets have been used to induce obesity in rodents. However, few studies have reported on the effects observed at the initial stage of obesity induced by high-fat feeding on cardiac functional and structural remodelling.

OBJECTIVE

To characterize the initial moment of obesity and investigate both metabolic and cardiac parameters. In addition, the role of Ca2+ handling in short-term exposure to obesity was verified.

METHODS

Thirty-day-old male Wistar rats were randomized into two groups (n = 19 each): control (C; standard diet) and high-fat diet (HF, unsaturated high-fat diet). The initial moment of obesity was defined by weekly measurement of body weight (BW) complemented by adiposity index (AI). Cardiac remodelling was assessed by morphological, histological, echocardiographic and papillary muscle analysis. Ca2+ handling proteins were determined by Western Blot.

RESULTS

The initial moment of obesity occurred at the 3rd week. Compared with C rats, the HF rats had higher final BW (4%), body fat (20%), AI (14.5%), insulin levels (39.7%), leptin (62.4%) and low-density lipoprotein cholesterol (15.5%) but did not exhibit alterations in systolic blood pressure. Echocardiographic evaluation did not show alterations in cardiac parameters. In the HF group, muscles were observed to increase their +dT/dt (C: 52.6 ± 9.0 g/mm2/s and HF: 68.0 ± 17.0 g/mm2/s; p < 0.05). In addition, there was no changes in the cardiac expression of Ca2+ handling proteins.

CONCLUSION

The initial moment of obesity promotes alterations to hormonal and lipid profiles without cardiac damage or changes in Ca2+ handling.

Maternal exercise modifies body composition and energy substrates handling in male offspring fed a high-fat/high-sucrose diet

KEY POINTS

Maternal training during gestation enhances offspring body composition and energy substrates handling in early adulthood. Offspring nutrition also plays a role as some beneficial effects of maternal training during gestation disappear after consumption of a high-fat diet.

ABSTRACT

Maternal exercise during gestation has been reported to modify offspring metabolism and health. Whether these effects are exacerbated when offspring are receiving a high-fat diet remains unclear. Our purpose was to evaluate the effect of maternal exercise before and during gestation on the offspring fed a high-fat/high-sucrose diet (HF) by assessing its body composition, pancreatic function and energy substrates handling by two major glucose-utilizing tissues: liver and muscle. Fifteen-week-old nulliparous female Wistar rats exercised 4 weeks before as well as during gestation at a constant submaximal intensity (TR) or remained sedentary (CT). At weaning, pups from each group were fed either a standard diet (TRCD or CTCD) or a high-fat/high-sucrose diet (TRHF or CTHF) for 10 weeks. Offspring from TR dams gained less weight compared to those from CT dams. Selected fat depots were larger with the HF diet compared to control diet (CD) but significantly smaller in TRHF compared to CTHF. Surprisingly, the insulin secretion index was higher in islets from HF offspring compared to CD. TR offspring showed a higher muscle insulin sensitivity estimated by the ratio of phosphorylated protein kinase B to total protein kinase B compared with CT offspring (+48%, P < 0.05). With CD, permeabilized isolated muscle fibres from TR rats displayed a lower apparent affinity constant (K_m ) for pyruvate and palmitoyl coenzyme A as substrates compared to the CT group (-46% and -58%, respectively, P < 0.05). These results suggest that maternal exercise has positive effects on young adult offspring body composition and on muscle carbohydrate and lipid metabolism depending on the nutritional status.

Exercise effects on perivascular adipose tissue: endocrine and paracrine determinants of vascular function

Obesity is a global epidemic, accompanied by increased risk of type 2 diabetes and cardiovascular disease. Adipose tissue hypertrophy is associated with adipose tissue inflammation, which alters the secretion of adipose tissue-derived bioactive products, known as adipokines. Adipokines determine vessel wall properties such as smooth muscle tone and vessel wall inflammation. Exercise is a mainstay of prevention of chronic, non-communicable diseases, type 2 diabetes and cardiovascular disease in particular. Aside from reducing adipose tissue mass, exercise has been shown to reduce inflammatory activity in this tissue. Mechanistically, contracting muscles release bioactive molecules known as myokines, which alter the metabolic phenotype of adipose tissue. In adipose tissue, myokines induce browning, enhance fatty acid oxidation and improve insulin sensitivity. In the past years, the perivascular adipose tissue (PVAT) which surrounds the vasculature, has been shown to control vascular tone and inflammation through local release of adipokines. In obesity, an increase in mass and inflammation of PVAT culminate in dysregulation of adipokine secretion, which contributes to vascular dysfunction. This review describes our current understanding of the mechanisms by which active muscles interact with adipose tissue and improve vascular function. Aside from the exercise-dependent regulation of canonical adipose tissue function, we will focus on the interactions between skeletal muscle and PVAT and the role of novel myokines, such as IL-15, FGF21 and irisin, in these interactions.

LINKED ARTICLES

This article is part of a themed section on Molecular Mechanisms Regulating Perivascular Adipose Tissue - Potential Pharmacological Targets? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.20/issuetoc.

Exercise-induced ROS in heat shock proteins response

Cells have evolved multiple and sophisticated stress response mechanisms aiming to prevent macromolecular (including proteins, lipids, and nucleic acids) damage and to maintain or re-establish cellular homeostasis. Heat shock proteins (HSPs) are among the most highly conserved, ubiquitous, and abundant proteins in all organisms. Originally discovered more than 50 years ago through heat shock stress, they display multiple, remarkable roles inside and outside cells under a variety of stresses, including also oxidative stress and radiation, recognizing unfolded or misfolded proteins and facilitating their restructuring. Exercise consists in a combination of physiological stresses, such as metabolic disturbances, changes in circulating levels of hormones, increased temperature, induction of mild to severe inflammatory state, increased production of reactive oxygen and nitrogen species (ROS and RNS). As a consequence, exercise is one of the main stimuli associated with a robust increase in different HSPs in several tissues, which appears to be also fundamental in facilitating the cellular remodeling processes related to the training regime. Among all factors involved in the exercise-related modulation of HSPs level, the ROS production in the contracting muscle or in other tissues represents one of the most attracting, but still under discussion, mechanism. Following exhaustive or damaging muscle exercise, major oxidative damage to proteins and lipids is likely involved in HSP expression, together with mechanically induced damage to muscle proteins and the inflammatory response occurring several days into the recovery period. Instead, the transient and reversible oxidation of proteins by physiological concentrations of ROS seems to be involved in the activation of stress response following non-damaging muscle exercise. This review aims to provide a critical update on the role of HSPs response in exercise-induced adaptation or damage in humans, focusing on experimental results where the link between redox homeostasis and HSPs expression by exercise has been addressed. Further, with the support of in vivo and in vitro studies, we discuss the putative molecular mechanisms underlying the ROS-mediated modulation of HSP expression and/or activity during exercise.

Neurolytic celiac plexus block enhances skeletal muscle insulin signaling and attenuates insulin resistance in GK rats

Non-insulin-dependent diabetes mellitus (NIDDM) is associated with chronic inflammatory activity and disrupted insulin signaling, leading to insulin resistance (IR). The present study investigated the benefits of neurolytic celiac plexus block (NCPB) on IR in a rat NIDDM model. Goto-Kakizaki rats fed a high-fat, high-glucose diet to induce signs of NIDDM were randomly divided into NCPB and control groups; these received daily bilateral 0.5% lidocaine or 0.9% saline injections into the celiac plexus, respectively. Following 14 and 28 daily injections, rats were subject to oral glucose tolerance tests (OGTTs) or sacrificed for the analysis of serum free fatty acids (FFAs), serum inflammatory cytokines and skeletal muscle insulin signaling. Compared with controls, rats in the NCPB group demonstrated significantly (P<0.05) lower baseline, 60-min and 120-min OGTT values, lower 120-min serum insulin, lower IR [higher insulin sensitivity index (ISI₁) and lower ISI₂) and lower serum FFAs, tumor necrosis factor-α, interleukin (IL)-1β and IL-6. Conversely, NCPB rats exhibited higher basal and insulin-stimulated skeletal muscle glucose uptake and higher skeletal muscle insulin receptor substrate-1 (IRS-1) and glucose transporter type 4 expression. There were no differences between the groups in insulin receptor β (Rβ) or Akt expression; however Rβ-Y1162/Y1163 and Akt-S473 phosphorylation levels were higher and IRS-1-S307 phosphorylation were lower in NCPB rats than in the controls. These results indicate that NCPB improved insulin signaling and reduced IR, possibly by inhibiting inflammatory cytokine release.

Endurance exercise ameliorates low birthweight developed catch-up growth related metabolic dysfunctions in a mouse model

Low birthweight is known to predict high risk of metabolic diseases in adulthood, while regular endurance exercises are believed sufficient to improve metabolic dysfunction. In this study, we established a mouse model to determine whether long-term exercise training could ameliorate catch-up growth, and we explored the possible underlying mechanisms. By restricting maternal food intake during the last week of gestation, we successfully produced low birthweight pups. Further, normal birthweight mice and low birthweight mice were randomly distributed into one of three groups receiving either a normal fat diet, high fat diet, or high fat diet with exercise training. The growth/metabolism, mitochondrial content and functions were assessed at 6 months of age. Through group comparisons and correlation analyses, the 4th week was demonstrated to be the period of crucial growth and chosen to be the precise point of intervention, as the growth rate at this point is significantly correlated with body weight, intraperitoneal glucose tolerance test (IPGTT), Lee's index and fat mass in adulthood. In addition, regular endurance exercises when started from 4 weeks remarkably ameliorated low birthweight outcomes and induced catch-up growth and glucose intolerance in the 25th week. Furthermore, real-time PCR and western blot results indicated that the effect of long-term exercise on mitochondrial functions alleviated catch-up related metabolic dysfunction. To conclude, long-term exercise training from the 4th week is sufficient to ameliorate catch-up growth and related metabolic disturbances in adulthood by promoting mitochondrial functions in skeletal muscle.

Rab-GAP TBC1D4 (AS160) is dispensable for the renal control of sodium and water homeostasis but regulates GLUT4 in mouse kidney

The Rab GTPase-activating protein TBC1D4 (AS160) controls trafficking of the glucose transporter GLUT4 in adipocytes and skeletal muscle cells. TBC1D4 is also highly abundant in the renal distal tubule, although its role in this tubule is so far unknown. In vitro studies suggest that it is involved in the regulation of renal transporters and channels such as the epithelial sodium channel (ENaC), aquaporin-2 (AQP2), and the Na+-K+-ATPase. To assess the physiological role of TBC1D4 in the kidney, wild-type (TBC1D4+/+) and TBC1D4-deficient (TBC1D4-/-) mice were studied. Unexpectedly, neither under standard nor under challenging conditions (low Na+/high K+, water restriction) did TBC1D4-/- mice show any difference in urinary Na+ and K+ excretion, urine osmolarity, plasma ion and aldosterone levels, and blood pressure compared with TBC1D4+/+ mice. Also, immunoblotting did not reveal any change in the abundance of major renal sodium- and water-transporting proteins [Na-K-2Cl cotransporter (NKCC2) NKCC2, NaCl cotransporter (NCC), ENaC, AQP2, and the Na+-K+-ATPase]. However, the abundance of GLUT4, which colocalizes with TBC1D4 along the distal nephron of TBC1D4+/+ mice, was lower in whole kidney lysates of TBC1D4-/- mice than in TBC1D4+/+ mice. Likewise, primary thick ascending limb (TAL) cells isolated from TBC1D4-/- mice showed an increased basal glucose uptake and an abrogated insulin response compared with TAL cells from TBC1D4+/+ mice. Thus, TBC1D4 is dispensable for the regulation of renal Na+ and water transport, but may play a role for GLUT4-mediated basolateral glucose uptake in distal tubules. The latter may contribute to the known anaerobic glycolytic capacity of distal tubules during renal ischemia.

Vibration exercise decreases insulin resistance and modulates the insulin signaling pathway in a type 2 diabetic rat model

Vibration exercise (VE) is a new type of physical training, but little is known about its effects on insulin resistance at the molecular level. A Sprague-Dawley rat model of type 2 diabetes with insulin resistance was induced with a high-fat diet and low-dose streptozotocin. Animals were then subjected to 8 wk of VE consisting of placing the rats on a vibration stand bracket (8 cm × 8 cm × 20 cm) with a maximum vertical vibration displacement of 52 mm for 15 min twice a day, 6 d each week. Various metabolic markers and the phosphorylation and expression of proteins within the PI3K/AKT insulin signaling pathway were assessed. The high-fat diet and low-dose streptozotocin increased food intake, body weight, and levels of blood glucose, triglycerides, total cholesterol, and free fatty acids, while Kitt rate, 2-deoxyglucose uptake, and glycogen levels were decreased. These effects were ameliorated in animals receiving VE. VE treatment activated the PI3K/AKT insulin-signaling pathway, and also increased the expression of GLUT4. In conclusion, VE improved the metabolic issues associated with the diabetic state by suppressing the reduction of IRS1, AKT2, and GLUT4 in the diabetic condition, indicating that VE could be used as a therapeutic intervention for insulin resistance and type 2 diabetes.

Isomeric effects of anti-diabetic α-lipoic acid with γ-cyclodextrin

AIMS

Previous studies reported the anti-diabetic effects of α-lipoic acid (αLA) isomers: racemic-αLA, R-αLA, or S-αLA. Previously, we examined the anti-diabetic effects of αLA administered as a food additive, but were unable to demonstrate the differences among different isomers. In this study, αLAs were complexed with γ-cyclodextrin (γCD) for the stability.We then investigated the anti-diabetic effects of racemic-, R-, and S-αLA/γCDs in KKAy mice.

MAIN METHODS

Male type 2 diabetic KKAy mice were divided into 5 groups, and fed either a high-fat-diet (HFD),HFD supplemented with γCD, or HFD supplemented with racemic-αLA/γCD, R-αLA/γCD, or S-αLA/γCD for 4 weeks. At the end of the feeding period, HbA1c and adiponectin levels were measured, PPARγ2mRNA expression levels were assessed in adipose tissues using real-time PCR, and AMP-activated protein kinase (AMPK) phosphorylation levels were evaluated in the liver by Western blotting.

KEY FINDINGS

The anti-diabetic effects of αLA; the isomeric compounds racemic-, R-, and S-αLA/γCD were investigated using amale type 2 diabetic KKAy mousemodel. Significant differences were observed in HbA1c and plasma adiponectin levels between R-αLA/γCD-treated mice and control mice. PPARγ2 mRNA expression levels were slightly higher in racemic- and R-αLA/γCD-treated mice. Moreover, AMPK phosphorylation levels were elevated in racemic-αLA/γCD- and R-αLA/γCD-treated mice, but remained unchanged in S-αLA/γCD-treated mice.

SIGNIFICANCE

These results suggested that the stereoisomerism mediates a difference in the anti-diabetic effects of racemic-, R-, and S-αLA/γCDs. Furthermore, the anti-diabetic mechanism of αLA/γCD action may be attributed to the activation of AMPK in the liver.

Roles of TBC1D1 and TBC1D4 in insulin- and exercise-stimulated glucose transport of skeletal muscle

This review focuses on two paralogue Rab GTPase activating proteins known as TBC1D1 Tre-2/BUB2/cdc 1 domain family (TBC1D) 1 and TBC1D4 (also called Akt Substrate of 160 kDa, AS160) and their roles in controlling skeletal muscle glucose transport in response to the independent and combined effects of insulin and exercise. Convincing evidence implicates Akt2-dependent TBC1D4 phosphorylation on T642 as a key part of the mechanism for insulin-stimulated glucose uptake by skeletal muscle. TBC1D1 phosphorylation on several insulin-responsive sites (including T596, a site corresponding to T642 in TBC1D4) does not appear to be essential for in vivo insulin-stimulated glucose uptake by skeletal muscle. In vivo exercise or ex vivo contraction of muscle result in greater TBC1D1 phosphorylation on S237 that is likely to be secondary to increased AMP-activated protein kinase activity and potentially important for contraction-stimulated glucose uptake. Several studies that evaluated both normal and insulin-resistant skeletal muscle stimulated with a physiological insulin concentration after a single exercise session found that greater post-exercise insulin-stimulated glucose uptake was accompanied by greater TBC1D4 phosphorylation on several sites. In contrast, enhanced post-exercise insulin sensitivity was not accompanied by greater insulin-stimulated TBC1D1 phosphorylation. The mechanism for greater TBC1D4 phosphorylation in insulin-stimulated muscles after acute exercise is uncertain, and a causal link between enhanced TBC1D4 phosphorylation and increased post-exercise insulin sensitivity has yet to be established. In summary, TBC1D1 and TBC1D4 have important, but distinct roles in regulating muscle glucose transport in response to insulin and exercise.

Rosuvastatin alleviates diabetic cardiomyopathy by inhibiting NLRP3 inflammasome and MAPK pathways in a type 2 diabetes rat model

PURPOSE

Nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome is important in inflammation of several diabetic complications. However, the potential role of NLRP3 inflammasome in the inflammatory process of diabetic cardiomyopathy (DCM) remains unclear. Although rosuvastatin (RSV) has an anti-inflammatory effect on some cardiovascular diseases, its influence on DCM is incompletely understood. We aimed to explore the effect on and underlying mechanism of RSV in DCM, and whether NLRP3 is a target for RSV.

METHODS

Type 2 diabetes was induced in rat. The characteristics of type 2 DCM were evaluated by metabolic tests, echocardiography and histopathology. The expression of factors was determined by real-time RT-PCR and western blot. Eight-week RSV treatment and NLRP3 gene silencing were used to investigate the effect and underlying target of RSV in DCM.

RESULTS

Compared with controls, diabetic rats showed severe metabolic disorder, cardiac dysfunction, fibrosis, disorganized ultrastructure, and excessive activation of thioredoxin interacting/inhibiting protein (TXNIP, p < 0.05), NLRP3 inflammasome (NLRP3, p < 0.01; apoptosis-associated speck-like protein containing a caspase recruitment domain [ASC], p < 0.05; caspase-1, p < 0.01), interleukin-1β (p < 0.01) and mitogen-activated protein kinases (MAPKs, all p < 0.01). Compared with diabetes alone, RSV ameliorated the overexpression of NLRP3 inflammasome (NLRP3, p < 0.05; ASC, p < 0.05; pro-caspase-1 p < 0.05, caspase-1 p20, p < 0.01) and MAPKs (all p < 0.05), which paralleled the cardiac protection of RSV. Silencing NLRP3 ameliorated cardiac remodeling and dysfunction. The beneficial effects of RSV in vehicle-treated rats were all abrogated in NLRP3-silenced rats.

CONCLUSIONS

The beneficial effect of RSV on DCM depended on inhibited NLRP3 inflammasome, and correlated with suppression of the MAPKs.

You are what you eat, or are you? The challenges of translating high-fat-fed rodents to human obesity and diabetes

Obesity and type 2 diabetes mellitus (T2DM) are rapidly growing worldwide epidemics with major health consequences. Various human-based studies have confirmed that both genetic and environmental factors (particularly high-caloric diets and sedentary lifestyle) greatly contribute to human T2DM. Interactions between obesity, insulin resistance and β-cell dysfunction result in human T2DM, but the mechanisms regulating the interplay among these impairments remain unclear. Rodent models of high-fat diet (HFD)-induced obesity have been used widely to study human obesity and T2DM. With >9000 publications on PubMed over the past decade alone, many aspects of rodent T2DM have been elucidated; however, correlation to human obesity/diabetes remains poor. This review investigates the reasons for this translational discrepancy by critically evaluating rodent HFD models. Dietary modification in rodents appears to have limited translatable benefit for understanding and treating human obesity and diabetes due—at least in part—to divergent dietary compositions, species/strain and gender variability, inconsistent disease penetrance, severity and duration and lack of resemblance to human obesogenic pathophysiology. Therefore future research efforts dedicated to acquiring translationally relevant data—specifically human data, rather than findings based on rodent studies—would accelerate our understanding of disease mechanisms and development of therapeutics for human obesity/T2DM.

Antidiabetic effect of the α-lipoic acid γ-cyclodextrin complex

In recent years, the number of patients suffering from diabetes mellitus has been increasing worldwide. In particular, type 2 diabetes mellitus, a lifestyle-related disease, is recognized as a serious disease with various complications. Many types of pharmaceutics or specific health foods have been used for the management of diabetes mellitus. At the same time, the relationship between diabetes mellitus and α-lipoic acid has been recognized for many years. In this study, we found that the α-lipoic acid γ-cyclodextrin complex exhibited an HbA_1c lowering effect for treating type 2 diabetes mellitus in animal models. Moreover, in this study, we investigated the activation of phosphorylation of AMP-activated protein kinase, which plays a role in cellular energy homeostasis, in the liver of KKA^y mice by using α-lipoic acid and the α-lipoic acid γ-cyclodextrin complex. Our results show that the α-lipoic acid γ-cyclodextrin complex strongly induced the phosphorylation of AMP-activated protein kinase. Thus, we concluded that intake of the α-lipoic acid γ-cyclodextrin complex exerted an antidiabetic effect by suppressing the elevation of postprandial hyperglycemia as well as doing exercise.

Postexercise improvement in insulin-stimulated glucose uptake occurs concomitant with greater AS160 phosphorylation in muscle from normal and insulin-resistant rats

Earlier research on rats with normal insulin sensitivity demonstrated that acute exercise increased insulin-stimulated glucose uptake (GU) concomitant with greater phosphorylation of Akt substrate of 160 kDa (pAS160). Because mechanisms for exercise effects on GU in insulin-resistant muscle are unknown, our primary objective was to assess insulin-stimulated GU, proximal insulin signaling (insulin receptor [IR] tyrosine phosphorylation, IR substrate 1-phosphatidylinositol-3-kinase, and Akt phosphorylation and activity), and pAS160 in muscles from acutely exercised (one session) and sedentary rats fed either chow (low-fat diet [LFD]; normal insulin sensitivity) or a high-fat diet (HFD; for 2 weeks, insulin-resistant). At 3 h postexercise (3hPEX), isolated epitrochlearis muscles were used for insulin-stimulated GU and insulin signaling measurements. Although exercise did not enhance proximal signaling in either group, insulin-stimulated GU at 3hPEX exceeded respective sedentary control subjects (Sedentary) in both diet groups. Furthermore, insulin-stimulated GU for LFD-3hPEX was greater than HFD-3hPEX values. For HFD-3hPEX muscles, pAS160 exceeded HFD-Sedentary, but in muscle from LFD-3hPEX rats, pAS160 was greater still than HFD-3hPEX values. These results implicated pAS160 as a potential determinant of the exercise-induced elevation in insulin-stimulated GU for each diet group and also revealed pAS160 as a possible mediator of greater postexercise GU of insulin-stimulated muscles from the insulin-sensitive versus insulin-resistant group.

Insulin therapy improves islet functions by restoring pancreatic vasculature in high-fat diet-fed streptozotocin-diabetic rats

BACKGROUND

In a previous study, we showed early insulin therapy could improve β-cell function in type 2 diabetic patients. However, the molecular mechanism was not clear. In the present study, we addressed this question by analyzing the pancreatic microvasculature in diabetic rats after insulin treatment.

METHODS

Diabetes was induced in rats by a combination of low dose streptozotocin (STZ; 40 mg/kg) and feeding of a high-fat diet. After the induction of diabetes, rats were treated with neutral protamine Hagedorn insulin (NPH; 6–8 U/day, s.c.) for 3 weeks. Three days after the end of treatment, rats were subjected to an intraperitoneal glucose tolerance test (IPGTT). The pancreatic microvasculature and the amount and size of the islets were evaluated by immunohistochemistry. Western blot analysis was used to determine levels of vascular endothelial growth factor (VEGF) and VEGF receptor 2 (VEGF-R2) protein.

RESULTS

Treatment with NPH improved insulin secretion from β-cells during the IPGTT and increased pancreatic islet size. The density of the microvasculature in the pancreas was determined by quantification of CD31, a marker of endothelial cells. Insulin treatment increased CD31 protein levels, as well as the expression of VEGF and VEGFR2.

CONCLUSIONS

The results suggest that insulin treatment improves islet recovery by increasing angiogenesis in the pancreas. The mechanism is related to the induction of VEGF and VEGFR2 expression in diabetic rats.

Swimming improves high-fat induced insulin resistance by regulating lipid and energy metabolism and the insulin pathway in rats

In this study, we aimed to determine the preventive and therapeutic effects of swimming on insulin resistance in high-fat-fed rats. Sprague-Dawley rats were divided into 4 groups and fed for 8 weeks as follows: i) the control (Con) group fed a control diet; ii) the high-fat (HF) group fed a high-fat diet; iii) the treatment (ST) group fed a high-fat diet and trained with swimming from the 4th week; and iv) the prevention (SP) group fed a high-fat diet and trained with swimming from the 1st week of the experiment. A hyperinsulinemic-euglycemic clamp was used to evaluate the insulin sensitivity of the rats. The ultrastructure of the liver cells was observed by electron microscopy. Hepatic lipid accumulation was observed by Oil Red O staining. Quantitative RT-PCR and western blot analysis were performed to detect the expression of proteins related to lipid metabolism, energy metabolism and insulin signaling transduction. After 8 weeks of feeding, compared with the Con group, the glucose infusion rate (GIR) was significantly decreased; a significant lipid accumulation was observed in the liver, while the ultrastructure of the liver cells was damaged in the HF group. Proteins related to lipid metabolism in the liver and skeletal muscle, including FAT and FABP were upregulated, while CPT1 and PPAR levels were downregulated in the HF group. The levels of the energy-metabolism-related molecules, AMPKα2, PGC1α, PGC1β and MFN2 were downregulated in skeletal muscle in the HF group. The expression levels of insulin signaling transduction molecules, INSR, IRS1, PI3K/p85, AKT2 and GLUT4, as well as the phosphorylation levels of INSR, IRS1, PI3K/p85 and AKT2 were lower in skeletal muscles in the HF rats. Compared with HF group, the GIR levels were significantly increased in the ST and SP groups. Lipid accumulation and damage to the ultrastructure of the liver cells were improved in both groups. The expression of molecules related to lipid metabolism in the liver and skeletal muscle, energy metabolism in skeletal muscle and insulin signaling transduction were all markedly upregulated. In conclusion, swimming can effectively improve insulin sensitivity and even prevent insulin resistance by affecting the expression of proteins related to lipid metabolism, energy metabolism and insulin signaling transduction in rats fed a high-fat diet.

Liraglutide Exerts Antidiabetic Effect via PTP1B and PI3K/Akt2 Signaling Pathway in Skeletal Muscle of KKAy Mice

Background. Liraglutide (a glucagon-like peptide 1 analog) was used for the treatment of type 2 diabetes (T2DM) which could produce glucose-dependent insulin secretion. Aim. The aim was to investigate whether liraglutide could improve myofibril and mitochondria injury in skeletal muscle and the mechanisms in diabetic KKAy mice. Method. We divided the male KKAy mice into 2 groups: liraglutide group (250 μg/kg/day liraglutide subcutaneous injection) and model group; meanwhile, the male C57BL/6J mice were considered as the control. After 6 weeks, the ultrastructure of skeletal muscle was observed by electron microscope. The gene expressions of protein tyrosine phosphatase 1B (PTP1B), phosphatidylinositol 3-kinase (PI3K), and glucose transporter type 4 (GLUT4) were determined by real-time PCR. The protein levels of the above molecules and phospho-Akt2 (p-Akt2) were measured by Western blot. Results. Liraglutide significantly ameliorated the injury of mitochondria by increasing the number (+441%) and the area (+113%) of mitochondria and mitochondrial area/100 µm(2) (+396%) in skeletal muscle of KKAy mice. The results of real-time PCR and Western blot showed that liraglutide downregulated PTP1B while it upregulated PI3K and GLUT4 (P < 0.01). The protein level of p-Akt2/Akt2 was also increased (P < 0.01). Conclusion. These results revealed that liraglutide could improve myofibril and mitochondria injury in skeletal muscle against T2DM via PTP1B and PI3K/Akt2 signaling pathway.

Neuroprotective effects of treadmill exercise on BDNF and PI3-K/Akt signaling pathway in the cortex of transgenic mice model of Alzheimer's disease

(AD). Although physical exercise and AD have received attention in the scientific literature, the mechanism through which treadmill exercise may impact the brain insulin signaling of AD has not been elucidated. This study aimed to evaluate the neuroprotective effects of treadmill exercise on apoptotic factors (Bcl-2/Bax ratio, caspase-3), HSP70, COX-2, BDNF and PI3-K/Akt signaling pathway in the cortex of NSE/hPS2m transgenic mice model of AD. Treadmill exercise ameliorated cognitive function in water maze test and significantly increased the level of Bcl-2/Bax ratio and HSP-70 in Tg-exe group compared to Tg-con group; on the other hand, it significantly decreased the expression of caspase-3 and COX-2 in Tg-exe group compared to Tg-con group. In addition, treadmill exercise significantly increased the expression of BDNF and PI3K/Akt in Tg-exe group compared to Tg-con group. Consequently, treadmill exercise improves cognitive function possibly via activating neurotrophic factor, BDNF and PI3k/Akt signaling pathway, and Aβ-induced neuronal cell death in the cortex of Tg mice was markedly suppressed following treadmill exercise. These results suggest that treadmill exercise may be beneficial in preventing or treating Alzheimer's disease.

Cardiac metabolism in a new rat model of type 2 diabetes using high-fat diet with low dose streptozotocin

BACKGROUND

To study the pathogenesis of diabetic cardiomyopathy, reliable animal models of type 2 diabetes are required. Physiologically relevant rodent models are needed, which not only replicate the human pathology but also mimic the disease process. Here we characterised cardiac metabolic abnormalities, and investigated the optimal experimental approach for inducing disease, in a new model of type 2 diabetes.

METHODS AND RESULTS

Male Wistar rats were fed a high-fat diet for three weeks, with a single intraperitoneal injection of low dose streptozotocin (STZ) after fourteen days at 15, 20, 25 or 30 mg/kg body weight. Compared with chow-fed or high-fat diet fed control rats, a high-fat diet in combination with doses of 15-25 mg/kg STZ did not change insulin concentrations and rats maintained body weight. In contrast, 30 mg/kg STZ induced hypoinsulinaemia, hyperketonaemia and weight loss. There was a dose-dependent increase in blood glucose and plasma lipids with increasing concentrations of STZ. Cardiac and hepatic triglycerides were increased by all doses of STZ, in contrast, cardiac glycogen concentrations increased in a dose-dependent manner with increasing STZ concentrations. Cardiac glucose transporter 4 protein levels were decreased, whereas fatty acid metabolism-regulated proteins, including uncoupling protein 3 and pyruvate dehydrogenase (PDH) kinase 4, were increased with increasing doses of STZ. Cardiac PDH activity displayed a dose-dependent relationship between enzyme activity and STZ concentration. Cardiac insulin-stimulated glycolytic rates were decreased by 17% in 15 mg/kg STZ high-fat fed diabetic rats compared with control rats, with no effect on cardiac contractile function.

CONCLUSIONS

High-fat feeding in combination with a low dose of STZ induced cardiac metabolic changes that mirror the decrease in glucose metabolism and increase in fat metabolism in diabetic patients. While low doses of 15-25 mg/kg STZ induced a type 2 diabetic phenotype, higher doses more closely recapitulated type 1 diabetes, demonstrating that the severity of diabetes can be modified according to the requirements of the study.

Anti-hyperlipidemic effects and potential mechanisms of action of the caffeoylquinic acid-rich Pandanus tectorius fruit extract in hamsters fed a high fat-diet

Hyperlipidemia is considered to be one of the greatest risk factors contributing to the prevalence and severity of cardiovascular diseases. In this work, we investigated the anti-hyperlipidemic effect and potential mechanism of action of the Pandanus tectorius fruit extract in hamsters fed a high fat-diet (HFD). The n-butanol fraction of the P. tectorius fruit ethanol extract (PTF-b) was rich in caffeoylquinic acids (CQAs). Administration of PTF-b for 4 weeks effectively decreased retroperitoneal fat and the serum levels of total cholesterol (TC), triglycerides (TG) and low density lipoprotein-cholesterol (LDL-c) and hepatic TC and TG. The lipid signals (fatty acids, and cholesterol) in the liver as determined by nuclear magnetic resonance (NMR) were correspondingly reduced. Realtime quantitative PCR showed that the mRNA levels of PPARα and PPARα-regulated genes such as ACO, CPT1, LPL and HSL were largely enhanced by PTF-b. The transcription of LDLR, CYP7A1, and PPARγ was also upregulated. Treatment with PTF-b significantly stimulated the activation of AMP-activated protein kinase (AMPK) as well as the activity of serum and hepatic lipoprotein lipase (LPL). Together, these results suggest that administration of the PTF-b enriched in CQAs moderates hyperlipidemia and improves the liver lipid profile. These effects may be caused, at least in part, by increasing the expression of PPARα and its downstream genes and by upregulation of LPL and AMPK activities.

Effects of acute exercise and chronic exercise on the liver leptin-AMPK-ACC signaling pathway in rats with type 2 diabetes

AIM

To investigate the effects of acute and chronic exercise on glucose and lipid metabolism in liver of rats with type 2 diabetes caused by a high fat diet and low dose streptozotocin (STZ).

METHODS

Animals were classified into control (CON), diabetes (DC), diabetic chronic exercise (DCE), and diabetic acute exercise (DAE) groups.

RESULTS

Compared to CON, the leptin levels in serum and liver and ACC phosphorylation were significantly higher in DC, but the levels of liver leptin receptor, AMPK α 1/2, AMPK α 1, and ACC proteins expression and phosphorylation were significantly lower in DC. In addition, the levels of liver glycogen reduced significantly, and the levels of TG and FFA increased significantly in DC compared to CON. Compared to DC, the levels of liver AMPK α 1/2, AMPK α 2, AMPK α 1, and ACC phosphorylation significantly increased in DCE and DAE. However, significant increase of the level of liver leptin receptor and glycogen as well as significant decrease of the level of TG and FFA were observed only in DEC.

CONCLUSION

Our study demonstrated that both acute and chronic exercise indirectly activated the leptin-AMPK-ACC signaling pathway and increased insulin sensitivity in the liver of type 2 diabetic rats. However, only chronic and long-term exercise improved glucose and lipid metabolism of the liver.