Glucose Transporter Type 4 Protein Research Articles

Effect of Exercise and Insulin Signaling on Glucose Transporter Type 4 in Skeletal Muscles: A narrative review

Introduction: Glucose transporter type 4 (GLUT4) is a membrane glucose transporter that is influenced by insulin signaling and muscle contraction. The aim of the present study was to review the function of GLUT4 in normal conditions and insulin resistance, as well as the role of exercise training on the kinetics of GLUT4 in skeletal muscles. In the present study, by searching for sports keywords; exercise; sports adaptations; glucose transporter; absorption of glucose; glucose transporter type 4; type 2 diabetes; insulin signaling; and insulin resistance was searched from electronic databases of related articles until November 2022 and entered into the study.
 Conclusion: Due to the pathological factors of type 2 diabetes, skeletal muscles are disturbed in the delivery, absorption, and metabolism of glucose; pathological disorders of muscle tissue affect insulin signaling and the quantity and function of GLUT4. In the present review, it was found that an exercise training session initiated the GLUT4 gene expression and protein production and its transfer from intracellular stores to sarcolemma; this effect of local exercise was related to muscle contraction. GLUT4 gene and protein expression increased in response to regular exercise and led to an increase in the total level of GLUT4 protein in skeletal muscles; furthermore, regular exercise has improve insulin signaling and, as a result, improved muscle efficiency for blood glucose collection. Considering the role of physical activity on muscle function in blood glucose collection, one of the treatment goals in type 2 diabetes is maintaining muscle mass, increasing muscle mass and also increasing muscle function (muscle quality).

Limonin mitigates cardiometabolic complications in rats with metabolic syndrome through regulation of the IRS-1/GLUT4 signalling pathway

Limonin is a natural triterpenoid isolated from citrus fruit. In the present study, we examined the effects of limonin on cardiometabolic alterations in diet-induced metabolic syndrome. Metabolic syndrome was induced in rats by feeding them a high-fat (HF) diet plus 15% fructose in drinking water for 16 weeks. They were treated with limonin (50 or 100 mg/kg) (n = 8/group) for the final 4 weeks. Increases in body weight (BW), fasting blood glucose (FBG), serum insulin, total cholesterol (TC), blood pressure (BP), liver fat accumulation, and adipocyte hypertrophy, as well as oral glucose tolerance in rats with metabolic syndrome were alleviated by limonin treatment (p < 0.05). Limonin improved ejection fraction and left ventricular (LV) hypertrophy, and reduced angiotensin converting enzyme (ACE) activity and angiotensin II (Ang II) concentration in rats with metabolic syndrome (p < 0.05). It also reduced plasma tumour necrosis factor (TNF)-α, interleukin (IL)− 6, leptin, malonaldehyde (MDA), and superoxide generation, and increased catalase activity in rats with metabolic syndrome compared to controls (p < 0.05). Downregulation of insulin receptor substrate 1 (IRS-1) and glucose transporter type 4 (GLUT4) protein expression in epididymal fat pads and cardiac, liver, and gastrocnemius tissues was present in metabolic syndrome, and these were restored by limonin treatment (p < 0.05). In conclusion, limonin shows a potential effect in alleviating symptoms and improving cardiometabolic disorders. These beneficial effects are linked to the reduction of the renin-angiotensin system, inflammation, oxidative stress, and improvement of IRS-1/GLUT4 protein expression in the target tissue.

Renin-Angiotensin System Antagonism Protects the Diabetic Heart from Ischemia/Reperfusion Injury in Variable Hyperglycemia Duration Settings by a Glucose Transporter Type 4-Mediated Pathway.

Diabetes mellitus (DM) is a risk factor for cardiovascular diseases, specifically, the ischemic heart diseases (IHD). The renin-angiotensin system (RAS) affects the heart directly and indirectly. However, its role in the protection of the heart against I/R injury is not completely understood. The aim of the current study was to evaluate the efficacy of the angiotensin-converting enzyme (ACE) inhibitor and Angiotensin II receptor (AT1R) blocker or a combination thereof in protection of the heart from I/R injury. Hearts isolated from adult male Wistar rats (n = 8) were subjected to high glucose levels; acute hyperglycemia or streptozotocin (STZ)-induced diabetes were used in this study. Hearts were subjected to I/R injury, treated with Captopril, an ACE inhibitor; Losartan, an AT1R antagonist; or a combination thereof. Hemodynamics data were measured using a suitable software for that purpose. Additionally, infarct size was evaluated using 2,3,5-Triphenyltetrazolium chloride (TTC) staining. The levels of apoptosis markers (caspase-3 and -8), antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), nitric oxide synthase (eNOS), and glucose transporter type 4 (GLUT-4) protein levels were evaluated by Western blotting. Pro-inflammatory and anti-inflammatory cytokines levels were evaluated by enzyme-linked immunosorbent assay (ELISA). Captopril and Losartan alone or in combination abolished the effect of I/R injury in hearts subjected to acute hyperglycemia or STZ-induced diabetes. There was a significant (p < 0.05) recovery in hemodynamics, infarct size, and apoptosis markers following the treatment with Captopril, Losartan, or their combination. Treatment with Captopril, Losartan, or their combination significantly (p < 0.05) reduced pro-inflammatory cytokines and increased GLUT-4 protein levels. The blockade of the RAS system protected the diabetic heart from I/R injury. This protection followed a pathway that utilizes GLUT-4 to decrease the apoptosis markers, pro-inflammatory cytokines, and to increase the anti-inflammatory cytokines. This protection seems to employ a pathway which is not involving ERK1/2 and eNOS.

P-606 Androgen receptor splice variant lead to PCOS with insulin resistance via IRS1/AKT signaling pathway in mice

Abstract Study question How does the androgen receptor splice variant (ARSV) contribute to insulin resistance in polycystic ovary syndrome (PCOS) patients? Summary answer ARSV inhibited the intracellular signaling pathway of insulin, resulting in decreased glucose transporter type 4 (GLUT4) translocation, impaired cellular glucose uptake, and insulin resistance. What is known already PCOS is the most common endocrine disorder in women of reproductive age and characterized by hyperandrogenism, ovulation dysfunction, and ovarian polycystic changes. In addition, a significant proportion of PCOS patients will experience insulin resistance. Our previous study identified an ARSV in granulosa cells from PCOS patients, which may be associated with higher insulin levels in follicular fluid. Study design, size, duration / Participants/materials, setting, methods Glucose metabolism of a mouse model presenting ARSV by CRISPR-Cas9 was measured by glucose tolerance test and insulin tolerance test. Body composition was measured by a nuclear magnetic resonance system. KGN cell lines stably overexpressing wild type androgen receptor (AR group) or ARSV (ARSV group) were successfully constructed by lentivirus infection. The process of glucose uptake by GLUT4, and the expression of target genes in the glucose uptake pathway were detected in cells. Main results and the role of chance The mice expressing ARSV had higher body weight and body fat content than the wild type mice, while the muscle content was equivalent.ARSV mice displayed diabetes with impaired glucose tolerance and insulin tolerance at 48 week-age. The levels of fasting glucose and insulin levels were significantly higher in ARSV mice. The basal and insulin-stimulated glucose uptake capacity were also found impaired in ARSV group. Immunofluorescence demonstrated that under insulin stimulation, GLUT4 protein was less expressed in the membrane and more expressed in the cytoplasm in ARSV group. Similar results were obtained by detecting the expression of GLUT4 protein after separating the cell membrane and cytoplasmic proteins. Further detection of the upstream signaling molecules of GLUT4 revealed that the phosphorylation levels of insulin receptor substrate 1 (IRS1) at Ser1101 were slightly increased in ARSV group, after stimulation with insulin and DHT. Besides, the phosphorylation levels of protein kinase B (AKT) were also found significantly decreased at Thr308 and slightly decreased at Ser473 in ARSV group. ARSV inhibited the intracellular signaling pathway of insulin by altering the phosphorylation level of IRS1/AKT signaling, resulting in decreased GLUT4 translocation, impaired cellular glucose uptake, and insulin resistance. Limitations, reasons for caution In this study, we failed to obtain clinical samples of PCOS to prospectively verify the association between ARSV and glucose uptake, insulin resistance, and subsequent onset diabetes. Wider implications of the findings This transgenic animal model can simulate the reproductive and metabolic phenotypes of PCOS patients, providing a model for future PCOS research. PCOS patients with ARSV should delay the onset of insulin resistance through lifestyle intervention, exercise, and drug therapy as early as possible. Trial registration number NA

Electroacupuncture at Bilateral ST36 Acupoints: Inducing the Hypoglycemic Effect through Enhancing Insulin Signal Proteins in a Streptozotocin-Induced Rat Model during Isoflurane Anesthesia.

In rats with 2-deoxy-2-(3-(methyl-3-nitrosoureido)-d-glucopyranose streptozotocin- (STZ-) induced insulin-dependent diabetes (IDDM), continuous 15 Hz electrical stimulation at bilateral ST36 acupoints for 30 and 60 minutes has been shown to prevent hyperglycemia. We hypothesized that the mechanism of action in STZ-induced IDDM rats is that electrical stimulation at bilateral ST36 acupoints is effective in improving insulin receptor substrate type 1 (IRS-1) and glucose transporter type 4 (GLUT4) protein expressions associated with counteracting both plasma glucose and free fatty acid (FFA) levels during isoflurane anesthesia. In this study, twenty-six healthy male Wistar rats, weighing 250–350 g and aged 8–10 weeks were tested. Rats in the experimental electroacupuncture (EA) group (n = 13) received 15 Hz electrical stimulation at bilateral ST 36 acupoints for 30 and 60 minutes. Rats in the control group (n = 13) were handled but not subjected to the stimulation treatment. In both IDDM and normal Wistar rats, we observed a negative change in plasma glucose levels when rats were given the EA treatment, but a positive change in plasma glucose without EA treatment relative to baseline. Within the IDDM group, a negative change in FFA levels was observed when rats were given the EA treatment, while a positive change in the FFA level was shown without the EA treatment. In the expressed protein signals, we found a significant elevation in both GLUT4 and IRS-1 proteins in the IDDM group treated by EA. Moreover, we found a significant mean difference between GLUT4 and IRS-1 protein expression levels relative to β-actin. Our findings suggested that EA at bilateral ST36 acupoints could serve as an effective strategy for lowering plasma glucose by decreasing free fatty acid levels and improving the expression of IRS-1 and GLUT4 proteins in a STZ-IDDM rat model during isoflurane anesthesia.

Antioxidant and anti-inflammatory properties of gamma- oryzanol attenuates insulin resistance by increasing GLUT- 4 expression in skeletal muscle of obese animals

BackgroundSkeletal muscle is the most important organ for whole-body glucose homeostasis. However, it has been suggested that obesity-related inflammation could be involved in insulin resistance and diabetes mellitus type 2 (DM2) development due several mechanisms, among them, the reduced expression of the glucose transporter type 4 (GLUT-4). Gamma-oryzanol (γOz) is a compound present in the whole grain of rice that presents anti-inflammatory and antioxidant activities. The aim of this study was to verify if the effect antioxidant and anti-inflammatory of yOz attenuate insulin resistance in skeletal muscle of obese rats by increasing GLUT- 4 expression. MethodsMale Wistar rats (±187 g) were initially randomly distributed into 2 experimental groups (control, n = 6, and high sugar-fat diet (HSF), n = 12) for 20 weeks. At week 20th of this study, once obesity and insulin resistance were detected in the HSF group, animals were divided to begin the treatment with γOz or continue receiving HSF for 10 more weeks. At the end it was analyzed nutritional, metabolic, inflammatory and oxidative stress parameters and GLUT-4 protein expression. ResultsThe treatment improved insulin resistance, reduced inflammation, increased antioxidant response and GLUT-4 expression. ConclusionIt is possible to conclude that the antioxidant and anti-inflammatory activity of yOz attenuates insulin resistance by increasing GLUT-4 expression in skeletal muscle of obese animals.

Potential Anti-Diabetic Activity of Pueraria lobata Flower (Flos Puerariae) Extracts

Pueraria lobata (Wild.) Ohwi. (P. lobata) flowers known as ‘Kudzu flower’ contain isoflavonoids and essential oil components. They have a wide range of biological and pharmacological activities, including protective effects against non-alcoholic fatty liver disease, hyperglycemia, and hypolipidemia, anti-mutagenic effects, and benefits for weight loss. However, the molecular mechanism of these effects remains unclear. Our study aimed to systematically examine the effects of flos puerariae crude extract (FPE) as an anti-diabetic agent using in vitro assays. The cytotoxicity of FPE was evaluated using MTS assay in L6 rat myocyte and 3T3-L1 murine fibroblast cell lines. PPARγ binding activity and adipogenesis were examined using dual-luciferase and differentiation assays, respectively. For investigating the anti-diabetic activity, glucose utilization, including GLUT4 protein expression, glucose uptake assay, and GLUT4 translocation using immunofluorescence microscopy were conducted in L6 cells. Furthermore, we assessed the antioxidant and anti-inflammatory activities of FPE. Our results demonstrated the ability to augment glucose uptake in L6 cells and enhance glucose utilization activity by increasing the expression of glucose transporter type 4 (GLUT4). In summary, our findings suggest that FPE may be a potential anti-diabetic substance for the treatment of diabetic patients and can prevent inflammatory or oxidation-related diseases.

Hydroxytyrosol modifies skeletal muscle GLUT4/AKT/Rac1 axis in trained rats.

Training induces a number of healthy effects including a rise in skeletal muscle (SKM) glucose uptake. These adaptations are at least in part due to the reactive oxygen species produced within SKM, which is in agreement with the notion that antioxidant supplementation blunts some training-induced adaptations. Here, we tested whether hydroxytyrosol (HT), the main polyphenol of olive oil, would modify the molecular regulators of glucose uptake when HT is supplemented during exercise. Rats were included into sedentary and exercised (EXE) groups. EXE group was further divided into a group consuming a low HT dose (0.31 mg·kg·d; EXElow), a moderate HT dose (4.61 mg·kg·d; EXEmid), and a control group (EXE). EXE raised glucose transporter type 4 (GLUT4) protein content, Ras-related C3 botulinum toxin substrate 1 (Rac1) activity, andprotein kinase b (AKT) phosphorylation in SKM. Furthermore, EXElow blunted GLUT4 protein content and AKT phosphorylation while EXEmid showed a downregulation of the GLUT4/AKT/Rac1 axis. Hence, a low-to-moderate dose of HT, when it is supplemented as an isolated compound, might alter the beneficial effect of training on basal AKT phosphorylation and Rac1 activity in rats.

Pectin lyase-modified red ginseng extract improves glucose homeostasis in high fat diet-fed mice

Red ginseng has long been used as a traditional folk medicine for various diseases including diabetes. Recently, a preparation of red ginseng extract by pectin lyase modification has been developed and named as GS-E3D. The aim of this study is to evaluate the preventive effect of GS-E3D on hyperglycemia induced by feeding a high fat diet (HFD) in mice. GS-E3D was orally administered to C57BL/6J mice at different doses (250, 500, or 1000 mg/kg/day) for 6 weeks while on a HFD. Body weight and blood glucose were monitored weekly, and oral glucose tolerance test (OGTT) was performed at 5th week of the experiment. Glycemic indications and metabolic parameters were further measured in serum. Six weeks of GS-E3D treatment to mice significantly inhibited HFD-induced body weight gain, hyperglycemia, hyperinsulinemia and hypertriglyceridemia. Notably, GS-E3D treated mice at doses of 250, 500 and 1000 mg/kg showed 41.8%, 45.0% and 55.1% reduction in insulin resistance index, respectively, compared to HFD control mice. OGTT revealed that GS-E3D markedly prevented steep rise of blood glucose and insulin levels after glucose challenge and ameliorated HFD-induced glucose and insulin intolerance. The histological analysis showed enlarged adipocytes in HFD-fed mice whereas the adipocyte hypertrophy was prevented in GS-E3D treated mice in a dose-dependent manner. Furthermore, when peripheral glucose uptake level was assessed by total and membranous glucose transporter type 4 (GLUT4) protein contents, GS-E3D restored GLUT4 protein expression to the levels of regular diet fed mice, and dose-dependently translocated them to the plasma membrane. The results collectively show that GS-E3D ameliorates obesity-related impaired glucose tolerance by improving insulin sensitivity in the epidydimal adipose tissue.

GLP‑1 improves palmitate‑induced insulin resistance in human skeletal muscle via SIRT1 activity.

The present study investigated whether glucagon like peptide‑1 (GLP‑1) improves glucose uptake through glucose transporter type 4 (GLUT4), mediated by the activation of sirtuin 1 (SIRT1), in skeletal muscle cells with palmitate induced‑insulin resistance. The levels of glucose uptake, GLUT4, protein kinase A (PKA), and cyclic adenosine monophosphate (cAMP) were determined in human skeletal muscle myotubes (HSMMs) exposed to palmitate and GLP‑1. Then, to determine whether PKA/cAMP were downstream signals of GLP‑1, a PKA inhibitor was used. To determine whether SIRT‑1 contributes to GLP‑1 action in HSMMs with palmitate‑induced insulin resistance, the levels of peroxisome proliferator‑activated receptor γ coactivator 1α (PGC1α) deacetylation and SIRT‑1 activity were assessed using a SIRT1 inhibitor and small interfering RNA (siRNA). The phosphorylation levels of protein kinase B (Akt) and insulin receptor substrate 1 (IRS‑1) as insulin signaling pathways, were assessed in GLP‑1‑treated HSMMs exposed to palmitate. The influence of SIRT1 on the GLP‑1‑induced activation of insulin signaling pathway was determined using a SIRT1 inhibitor. GLP‑1 restored the palmitate‑induced reductions in the levels of glucose uptake, GLUT4 mRNA, GLUT4 promoter activity, and GLUT4 protein in HSMMs. PKA and cAMP, as GLP‑1 downstream signals, played a role in this process. GLP‑1 increased the deacetylation levels of PGC1α, and stimulated SIRT1 in HSMMs. Moreover, the SIRT1 inhibitor and siRNA of SIRT1 suppressed the effect of GLP‑1 on GLUT4 expression in HSMMs exposed to palmitate. The SIRT1 inhibitor also prevented the GLP‑1‑induced phosphorylation of IRS‑1 and Akt in palmitate‑treated HSMMs. The present findings suggest that in palmitate‑induced insulin‑resistant HSMM, GLP‑1 activates SIRT1 through the PKA/cAMP pathway, which in turn enhances glucose uptake through GLUT4 and the insulin signaling pathway.

AMPK and PPARβ positive feedback loop regulates endurance exercise training-mediated GLUT4 expression in skeletal muscle.

The objective of this study is to determine whether AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α), or peroxisome proliferator-activated receptor β (PPARβ) can independently mediate the increase of glucose transporter type 4 (GLUT4) expression that occurs in response to exercise training. We found that PPARβ can regulate GLUT4 expression without PGC-1α. We also found AMPK and PPARβ are important for maintaining normal physiological levels of GLUT4 protein in the sedentary condition as well following exercise training. However, AMPK and PPARβ are not essential for the increase in GLUT4 protein expression that occurs in response to exercise training. We discovered that AMPK activation increases PPARβ via myocyte enhancer factor 2A (MEF2A), which acted as a transcription factor for PPARβ. Furthermore, exercise training increases the cooperation of AMPK and PPARβ to regulate glucose uptake. In conclusion, cooperation between AMPK and PPARβ via NRF-1/MEF2A pathway enhances the exercise training mediated adaptive increase in GLUT4 expression and subsequent glucose uptake in skeletal muscle.

Therapeutic effect of catalpol on type 2 diabetic mice induced by STZ and high-fat diet and its possible mechanism

To explore the therapeutic effect and possible mechanism of catalpol on type 2 diabetic mice. Twenty-four C57/BL6 male mice were randomly divided into four groups—normal control group (CON, n = 6), diabetic model group (DM, n = 6), the lower dose catalpol treatment (80 mg/kg body weight) group (DM+L, n = 6), and the higher dose catalpol treatment (160 mg/kg body weight) group (DM+H, n = 6). Intraperitoneal glucose tolerance test was performed after 30 days of treatment. Fasting blood glucose (FBG), triglyceride (TG), and total cholesterol (TC) in serum were detected by full automatic biochemical instrument. Enzyme-linked immunosorbent assay was used to detect insulin levels in serum. Insulin resistance level was calculated by trapezoid rule. The morphological changes of pancreatic tissue were observed through HE staining. The protein levels of insulin receptor substrate 1 (IRS1) and glucose transporter type 4 (GLUT4) in the liver and muscle were measured by Western blot (WB). Compared with the DM group mice, the glucose tolerance and insulin resistance in the DM+H group and the DM+L group were improved, the levels of TG, TC, and FBG decreased (p < 0.01). The blood insulin levels were elevated in the DM+H group and the DM+L group (p < 0.01) and the insulin resistance level decreased (p < 0.01, p < 0.05). IRS1 and GLUT4 protein levels in the liver and muscle increased in the DM+H group and the DM+L group (p < 0.01, p < 0.05). Catalpol could be potential medicine to treat type 2 diabetes. Its therapeutic mechanism might be improving insulin-stimulated glucose uptake in the liver and muscle.

Effect of TNF-α on Molecules Related to the Insulin Action in Endometrial Cells Exposed to Hyperandrogenic and Hyperinsulinic Conditions Characteristics of Polycystic Ovary Syndrome.

Polycystic ovary syndrome (PCOS) affects not only ovarian functions but is also able to affect endometrium metabolism. Around 80% of women with PCOS are obese. High tumor necrosis factor (TNF)-α production and low adiponectin levels are characteristics of obesity. Interestingly, endometrium from obese women with PCOS presents an insulin-resistance condition, high TNF-α levels, and low adiponectin levels. However, TNF-α effect on molecules associated with insulin action in endometrial cells remains unclear. Therefore, the objective of this work was to evaluate TNF-α effect on expression of molecules associated with adiponectin (insulin sensitizing) and TNF-α signaling pathways and on Glucose Transporter type 4 (GLUT-4) levels in human endometrial cells under the characteristic conditions of hyperandrogenic/hyperinsulinic (HA/HI) PCOS. Two human endometrial stromal cell lines (T-HESC/St-T1b) under HA/HI conditions were used to assay the effect of high TNF-α concentration (100 ng/mL) on adiponectin, AdipoR1-AdipoR2 receptors, Adaptor protein phosphotyrosine interacting with PH domain and leucine zipper 1 (APPL1), Phospho-AMP-activated protein kinase T172 (p-AMPKT172), GLUT-4, Tumor necrosis factor receptor 1 (TNFR1)-Tumor necrosis factor receptor 2 (TNFR2) receptors protein levels, and nuclear factor κB (NFκB) nuclear content, by Western blot or immunocytochemistry. The NFκB participation in TNF-α effect on adiponectin expression was assayed using an NFκB inhibitor (pyrrolidine dithiocarbamate). The TNF-α increases the expression of molecules associated with its own signaling pathway ( P < .05) and decreases the protein levels of adiponectin and its associated molecules ( P < .05). Moreover, TNF-α increases NFκB nuclear content ( P < .001), whereas with NFκB inhibition the decrease in adiponectin content induced by TNF-α was not observed. GLUT-4 levels were lower with TNF-α treatment ( P < .01). Thus, in human endometrial stromal cells, high TNF-α levels negatively affect the insulin action through decreased adiponectin signaling and GLUT-4 protein. This could explain the failures observed in endometrial function of obese women with PCOS.

Elevated GLUT4 and glycogenin protein abundance correspond to increased glycogen content in the soleus muscle of mdx mice with no benefit associated with taurine supplementation.

Duchenne muscular dystrophy (DMD) patients and the dystrophic mdx mouse have an elevated demand for ATP requiring processes, including Ca2+ regulation and skeletal muscle regeneration. As a key substrate for cellular ATP production, altered glycogen metabolism may contribute significantly to dystrophic pathology and explain reports of mild glucose intolerance. We compare the soleus and extensor digitorum longus (EDL) muscles of the mdx mouse during active muscle necrosis (at 28 days) and at 70 days where pathology is stable. We further investigate the impact of taurine (tau) on dystrophic glycogen metabolism to identify if the benefit seen with tau in a previous study (Barker et al. 2017) was in part owed to altered glycogen handling. The soleus muscle of 28‐ and 70‐day‐old mdx mice had elevated glucose transporter type 4 (GLUT4), glycogenin protein abundances and glycogen content compared to WT (C57BL10/ScSn) controls. Mdx tau mice exhibited modestly reduced glycogen compared to their respective mdx group. The EDL muscle of 28 days mdx tau mice had a ~70% increase in glycogenin protein abundance compared to the mdx but 50% less glycogen content. A twofold greater phosphorylated glycogen synthase (p‐GS) and glycogen phosphorylase (p‐GP) protein abundance was observed in the 70‐day‐old mdx soleus muscle than in the 28‐day‐old mdx soleus muscle. Glycogen debranching enzyme (GDE) protein abundance was elevated in both 28‐ and 70‐day‐old mdx soleus muscles compared to WT controls. We identified an increase in proteins associated with glucose uptake and utilization specific to the predominantly slow‐twitch soleus muscle of mdx mice regardless of age and that taurine affords no obvious benefit to glycogen metabolism in the mdx mouse.

Feeding influences adipose tissue responses to exercise in overweight men.

Feeding profoundly affects metabolic responses to exercise in various tissues, but the effect of feeding status on human adipose tissue responses to exercise has never been studied. Ten healthy overweight men aged 26 ± 5 yr (mean ± SD) with a waist circumference of 105 ± 10 cm walked at 60% of maximum oxygen uptake under either fasted or fed conditions in a randomized, counterbalanced design. Feeding comprised 648 ± 115 kcal 2 h before exercise. Blood samples were collected at regular intervals to examine changes in metabolic parameters and adipokine concentrations. Adipose tissue samples were obtained at baseline and 1 h after exercise to examine changes in adipose tissue mRNA expression and secretion of selected adipokines ex vivo. Adipose tissue mRNA expression of pyruvate dehydrogenase kinase isozyme 4 (PDK4), adipose triglyceride lipase, hormone-sensitive lipase (HSL), fatty acid translocase/CD36, glucose transporter type 4 (GLUT4), and insulin receptor substrate 2 (IRS2) in response to exercise were lower in fed compared with fasted conditions (all P ≤ 0.05). Postexercise adipose IRS2 protein was affected by feeding (P ≤ 0.05), but Akt2, AMPK, IRS1, GLUT4, PDK4, and HSL protein levels were not different. Feeding status did not impact serum and ex vivo adipose secretion of IL-6, leptin, or adiponectin in response to exercise. This is the first study to show that feeding before acute exercise affects postexercise adipose tissue gene expression, and we propose that feeding is likely to blunt long-term adipose tissue adaptation to regular exercise.

Low-dose testosterone alleviates vascular damage caused by castration in male rats in puberty via modulation of the PI3K/AKT signaling pathway.

The aim of the present study was to investigate the effect of testosterone on glucolipid metabolism and vascular injury in male rats, and examine the underlying molecular mechanisms. A total of 40 male Sprague-Dawley rats were divided into a control group (n=10), high-fat-diet + castration group (n=10), high-fat-diet + castration + low dose testosterone group (n=10), and high-fat-diet + castration + high dose testosterone group (n=10). Hematoxylin and eosin staining was performed to evaluate the morphology of the thoracic aortic tissues. Immunohistochemical staining was used to detect biomarkers of the phosphoinositide 3-kinase (PI3K) signaling pathway. The mRNA and protein expression levels of PI3K, AKT, insulin receptor substrate-1 (IRS-1), glucose transporter type 4 (GLUT-4), nuclear factor (NF)-κB and tumor necrosis factor (TNF)-α in the aortas were determined using quantitative polymerase chain reaction and Western blot analyses, respectively. Apoptosis in the aortic tissues was detected using a TUNEL assay. Castration induced apoptosis in the animals fed a high-fat-diet, whereas low dose testosterone replacement ameliorated the apoptosis in the aorta. However, the levels of apoptosis was more severe following high-dose testosterone treatment. Low-dose testosterone induced upregulation in the levels of IRS-1, AKT, GLUT-4 protein, NF-κB, TNF-α and PI3K, compared with those in the animals fed a high-fat diet following castration. A high dose of testosterone resulted in a significant decrease in the levels of IRS-1, AKT, GLUT-4, NF-κB, TNF-α and PI3K. Compared with the rats in the high-fat diet + castration group, a low dose of testosterone induced upregulation in the mRNA levels of IRS-1, AKT and GLUT-4, and downregulation of the mRNA levels of NF-κB, TNF-α and PI3K. A high dose of testosterone resulted in a significant decrease in the levels of IRS-1, AKT and GLUT-4, and marked increases in the mRNA levels of NF-κB, TNF-α and PI3K, compared with the low dose group. Castration induced marked disorders of glucolipid metabolism and vascular injuries in the pubescent male rats. Low-dose testosterone treatment was found to ameliorate the vascular damage caused by castration via the PI3K/AKT signaling pathway.

Conjugated linoleic acid supplementation enhances insulin sensitivity and peroxisome proliferator-activated receptor gamma and glucose transporter type 4 protein expression in the skeletal muscles of rats during endurance exercise.

This study examined whether conjugated linoleic acid (CLA) supplementation affects insulin sensitivity and peroxisome proliferator-activated receptor gamma (PPAR-γ) and glucose transporter type 4 (GLUT-4) protein expressions in the skeletal muscles of rats during endurance exercise. Sprague-Dawley male rats were randomly divided into HS (high-fat diet (HFD) sedentary group, n = 8), CS (1.0% CLA supplemented HFD sedentary group, n = 8), and CE (1.0% CLA supplemented HFD exercise group, n = 8). The rats in the CE swam for 60 min a day, 5 days a week for 8 weeks. The serum glucose and insulin contents and homeostasis model assessment of insulin resistance (HOMA-IR) value of the CS and CE were significantly decreased compared to those of the HS. The PPAR-γ protein expressions in the soleus muscle (SOM) and extensor digitorum longus muscle (EDL) were significantly higher in the CE than in the HS. In addition, the PPAR-γ protein expression in the SOM of the CS was significantly higher than that in the HS. On the other hand, the GLUT-4 protein expression of the SOM in the CE was significantly higher compared to that in the HS. However, there was no significant difference in GLUT-4 protein expression in the EDL among the groups. CLA supplementation with/without endurance exercise has role in improvement of insulin sensitivity. Moreover, when CLA supplementation was accompanied by endurance exercise, the PPAR-γ protein expression in SOM and EDL and the GLUT-4 protein expression in SOM were enhanced compared with the control group.

Chromium Propionate Enhances Adipogenic Differentiation of Bovine Intramuscular Adipocytes.

In vitro experiments were performed to determine the effects of increasing concentrations of chromium propionate (CrPro) on mRNA and protein abundance of different enzymes and receptors. Intramuscular (IM) and subcutaneous (SC) preadipocytes and bovine satellite cells were isolated from the longissimus muscle to determine the effect of treatment on glucose transporter type 4 (GLUT4) and peroxisome proliferator-activated receptor γ mRNA and GLUT4 protein abundance. Preadipocyte cultures were treated with differentiation media plus either sodium propionate or different concentrations of CrPro for 96, 120, and 144 h before harvest. This study indicated that adipogenesis of the bovine IM adipocytes were more sensitive to the treatment of CrPro as compared to SC adipocytes. Enhancement of adenosine monophosphate-activated protein kinase and GLUT4 mRNA by CrPro treatment may enhance glucose uptake in IM adipocytes. CrPro decreased GLUT4 protein levels in muscle cell cultures suggesting that those cells have increased efficiency of glucose uptake due to exposure to increased levels of CrPro. In contrast, each of the two adipogenic lines had opposing responses to the CrPro. It appeared that CrPro had the most stimulative effect of GLUT4 response in the IM adipocytes as compared to SC adipocytes. These findings indicated opportunities to potentially augment marbling in beef cattle fed CrPro during the finishing phase.

Effects of Various 5,7-Dihydroxyflavone Analogs on Adipogenesis in 3T3-L1 Cells.

We studied the effects of twelve 5,7-dihydroxyflavone analogs on adipogenesis in 3T3-L1 cells. Among the compounds, luteolin, diosmetin, and chrysoeriol partly inhibited adipogenesis by blocking the accumulation of triacylglycerol in the cells. Conversely, tricetin facilitated triacylglycerol accumulation in the cells. The induction of lipogenesis or lipolysis may depend on the number and bonding position of hydroxyl or methoxy groups on the B ring of 5,7-dihydroxyflavone. The mRNA expression levels of adipogenic and lipogenic genes were suppressed by luteolin treatment in the cells, while the mRNA levels of lipolytic genes were not affected. However, the expression levels of the adipogenic, lipogenic, and lipolytic genes, except for adipocyte protein 2 (aP2), were not affected by the addition of tricetin. Moreover, luteolin suppressed glucose transporter type 4 (GLUT4) gene and protein levels. These results indicate that luteolin decreased triacylglycerol levels in 3T3-L1 cells during adipogenesis through the suppression of adipogenic/lipogenic and GLUT4 genes and GLUT4 protein.

Functional and Muscular Adaptations in an Experimental Model for Isometric Strength Training in Mice

Exercise training induces muscular adaptations that are highly specific to the type of exercise. For a systematic study of the differentiated exercise adaptations on a molecular level mouse models have been used successfully. The aim of the current study was to develop a suitable mouse model of isometric strength exercise training characterized by specific adaptations known from strength training. C57BL/6 mice performed an isometric strength training (ST) for 10 weeks 5 days/week. Additionally, either a sedentary control group (CT) or a regular endurance training group (ET) groups were used as controls. Performance capacity was determined by maximum holding time (MHT) and treadmill spirometry, respectively. Furthermore, muscle fiber types and diameter, muscular concentration of phosphofructokinase 1 (PFK), succinate dehydrogenase (SDHa), and glucose transporter type 4 (GLUT4) were determined. In a further approach, the effect of ST on glucose intolerance was tested in diabetic mice. In mice of the ST group we observed an increase of MHT in isometric strength tests, a type II fiber hypertrophy, and an increased GLUT4 protein content in the membrane fraction. In contrast, in mice of the ET group an increase of VO2max, a shift to oxidative muscle fiber type and an increase of oxidative enzyme content was measured. Furthermore strength training was effective in reducing glucose intolerance in mice fed a high fat diet. An effective murine strength training model was developed and evaluated, which revealed marked differences in adaptations known from endurance training. This approach seems also suitable to test for therapeutical effects of strength training.