Skeletal Muscle Glycogen Content Research Articles

Attenuation of nonenzymatic glycation, hyperglycemia, and hyperlipidemia in streptozotocin-induced diabetic rats by chloroform leaf extract of Azadirachta indica

Background:The hypoglycemic effects of hexane, chloroform and methanol extracts of leaves of Azadirachta indica (AI) were evaluated by oral administration in streptozotocin-induced severe diabetic rats (SD).Materials and Methods:The effect of chronic oral administration of the extract for 28 days was evaluated in streptozotozin diabetic rats. Lipid peroxidation, glycogen content of liver and skeletal muscles, insulin, superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), oxidized glutathione (GSSG) levels were determined. In addition, advanced glycation end product formation (AGEs) was evaluated.Results:The most active extracts were obtained with chloroform. Chloroform extract from AI shows increased levels of SOD, GSH, GSSG and CAT, hepatic glycogen content, glucose-6-phosphatase and insulin plasma levels, which also decreased the glucokinase (GK), lipid peroxidation and insulin resistance. The chloroform extract exhibited significant inhibitory activity against advanced glycation end product formation with an IC50 average range of 79.1 mg/ml.Conclusion:Azadirachta indica can improve hyperlipidemia and hyperinsulinema in streptozocin-induced diabetic rats and, therefore, AI can be potentially considered to be an antidiabetic-safe agent.

Antibody formation and mannose‐6‐phosphate receptor expression impact the efficacy of muscle‐specific transgene expression in murine Pompe disease

Lysosomal storage disorders such as Pompe disease can be more effectively treated, if immune tolerance to enzyme or gene replacement therapy can be achieved. Alternatively, immune responses against acid α-glucosidase (GAA) might be evaded in Pompe disease through muscle-specific expression of GAA with adeno-associated virus (AAV) vectors. An AAV vector containing the MHCK7 regulatory cassette to drive muscle-specific GAA expression was administered to GAA knockout (KO) mice, immune tolerant GAA-KO mice and mannose-6-phosphate deficient GAA-KO mice. GAA activity and glycogen content were analyzed in striated muscle to determine biochemical efficacy. The biochemical efficacy from GAA expression was slightly reduced in GAA-KO mice, as demonstrated by higher residual glycogen content in skeletal muscles. Next, immune tolerance to GAA was induced in GAA-KO mice by co-administration of a second AAV vector encoding liver-specific GAA along with the AAV vector encoding muscle-specific GAA. Antibody formation was prevented by liver-specific GAA, and the biochemical efficacy of GAA expression was improved in the absence of antibodies, as demonstrated by significantly reduced glycogen content in the diaphragm. Efficacy was reduced in old GAA-KO mice despite the absence of antibodies. The greatest impact upon gene therapy was observed in GAA-KO mice lacking the mannose-6-phosphate receptor in muscle. The clearance of stored glycogen was markedly impaired despite high GAA expression in receptor-deficient Pompe disease mice. Overall, antibody formation had a subtle effect upon efficacy, whereas the absence of mannose-6-phosphate receptors markedly impaired muscle-targeted gene therapy in murine Pompe disease.

Subcellular localization-dependent decrements in skeletal muscle glycogen and mitochondria content following short-term disuse in young and old men

Previous studies have shown that skeletal muscle glycogen and mitochondria are distributed in distinct subcellular localizations, but the role and regulation of these subcellular localizations are unclear. In the present study, we used transmission electron microscopy to investigate the effect of disuse and aging on human skeletal muscle glycogen and mitochondria content in subsarcolemmal (SS), intermyofibrillar (IMF), and intramyofibrillar (intra) localizations. Five young (∼23 yr) and five old (∼66 yr) recreationally active men had their quadriceps muscle immobilized for 2 wk by whole leg casting. Biopsies were obtained from m. vastus lateralis before and after the immobilization period. Immobilization induced a decrement of intra glycogen content by 54% (P < 0.001) in both age groups and in two ultrastructurally distinct fiber types, whereas the content of IMF and SS glycogen remained unchanged. A localization-dependent decrease (P = 0.03) in mitochondria content following immobilization was found in both age groups, where SS mitochondria decreased by 33% (P = 0.02), superficial IMF mitochondria decreased by 20% (P = 0.05), and central IMF mitochondria remained unchanged. In conclusion, our findings demonstrate a localization-dependent adaptation to immobilization in glycogen and mitochondria content of skeletal muscles of both young and old individuals. Specifically, this suggests that short-term disuse preferentially affects glycogen particles located inside the myofibrils and that mitochondria volume plasticity can be dependent on the distance to the fiber border.

Long-term feeding of whey protein hydrolysates increases skeletal muscle glycogen levels and improves exercise performance in mice

Background Recently, our studies have shown that co-ingestion of carbohydrate and whey protein hydrolysate (WPH) is more effective for increasing post-exercise skeletal muscle glycogen content than ingestion of other protein sources (whey protein, casein hydrolysate, or branched chain amino acids). We have also shown that chronic feeding of whey protein increases glycogen contents in skeletal muscle of exercise-trained rats to a greater extent than does casein. To confirm our hypothesis that longterm feeding of WPH is more effective for increasing both muscle glycogen content and exercise performance than other protein sources, we compared long-term feeding of WPH to other protein sources for their effects on skeletal muscle glycogen levels and exercise performance. Methods

Antihyperglycemic Effect of a Caffeamide Derivative, KS370G, in Normal and Diabetic Mice

The antihyperglycemic actions of caffeamide derivatives, especially KS370G, in normal ICR, streptozotocin-induced diabetic (T1DM) and diet-induced diabetic (T2DM) mice were investigated in this study. Oral administration of the compound decreased the plasma glucose levels in both normal and diabetic mice, and appeared to be in a dose-dependent manner in normal and diet-induced type 2 diabetic mice. It was found that KS370G could stimulate the release of insulin in both normal and T2DM mice, and a dose of 1 mg per kg KS370G could significantly attenuate the increase of plasma glucose induced by an intraperitoneal glucose challenge test in normal and diabetic mice. Similar treatment with KS370G significantly increased glycogen content in both liver and skeletal muscle. Hence, the hypoglycemic effect of KS370G in normal and diabetic mice could be attributed to the stimulation of insulin release and the increase of glucose utilization.

Antihyperglycemic, Antihyperlipidemic and Antiglycation Effects of Byrsonima crassifolia Fruit and Seed in Normal and Streptozotocin-Induced Diabetic Rats

The hypoglycemic effects of hexane, chloroform and methanol extracts from fruits and seeds of Byrsonima crassifolia were evaluated by oral administration to normoglycemic and streptozotocin-induced severe diabetic rats (SD). The anti-diabetic effect was examined by blood glucose, triglycerides, lipid peroxidation, total cholesterol levels in the serum, glycogen content of liver and skeletal muscles, superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) and oxidized glutathione (GSSG) levels. The most active extracts were obtained with hexane. Hexane and chloroform extracts from fruits and seeds of Byrsonima crassifolia increased the levels of SOD, GSH, GSSG and CAT, hepatic glycogen content, glucose-6-phosphatase (G6Pase) and the plasma insulin levels. They also decreased glucokinase (GK) and TBAR (thiobarbituric acid assay). In conclusion, Byrsonima crassifolia possesses significant antihyperglycemic properties after 4 h of a single oral dose. It can also improve hyperlipidemia and hyperinsulinemia in streptozotocin-induced diabetic rats. Both extracts exhibited significant inhibitory activity against AGEs (advanced glycation end products) formation with IC(50) values ranging from 94.3 to 138.7 μg/ml. Therefore, B. crassifolia can be considered as a potential safe anti-diabetic agent.

Basal and insulin‐stimulated pyruvate dehydrogenase complex activation, glycogen synthesis and metabolic gene expression in human skeletal muscle the day after a single bout of exercise

The role of pyruvate dehydrogenase complex (PDC) in insulin-stimulated glycogen replenishment the day after exercise, and its molecular control, has not been examined. This study investigated the effect of acute exercise on basal and insulin-stimulated PDC activity (the rate-limiting step in glucose oxidation), glycogen synthesis and the expression of metabolic genes and transcription factors associated with changes in PDC activation and glucose metabolism. Eight healthy men (age 24 +/- 2 years, body mass 79 +/- 4 kg) underwent a euglycaemic, hyperinsulinaemic clamp 22 h after 90 min of one-legged cycling at 60% maximal oxygen consumption. Skeletal muscle glycogen content was similar in the exercised (EX) and non-exercised leg (CON) preclamp (471 +/- 30 versus 463 +/- 50 mmol (kg dry matter)(1), respectively) but increased during the clamp in EX to 527 +/- 20 mmol (kg dry matter)(1), such that it was 17% greater than in CON (449 +/- 35 mmol (kg dry matter)(1), P < 0.05). This increase in insulin-mediated glycogen storage was independent of insulin-stimulated Akt serine(473) phosphorylation and activation of PDC. Prior exercise did not modulate the mRNA expression and protein content of pyruvate dehydrogenase kinase 4 (PDK4) in skeletal muscle, but was associated with increased hexokinase II mRNA expression and protein content and upregulation of peroxisome proliferator-activated receptor (PPAR)-gamma coactivator 1alpha (PGC1alpha) and PPARdelta gene expression. Collectively, these findings suggest that prior exercise does not alter basal and insulin-stimulated PDC activation and the protein content of PDK4 the following day, but is associated with increased capacity (through upregulation of hexokinase II content) of muscle to phosphorylate and divert glucose towards glycogen storage.

Effect Of Training Intensity On Skeletal Muscle And Liver Glycogen In Rat

PURPOSE: It has been shown that endurance-trained rats have higher muscle and liver glycogen content than sedentary controls. Whether glycogen content is affected differently by training intensity, however, is undetermined. Therefore, the effects of chronic treadmill exercise at low, moderate, and hard intensity on liver and skeletal muscle glycogen content was investigated. METHODS: Forty male Wistar rats were assigned to control, low (18 m/min), moderate (26 m/min), and high (34 m/min) intensity groups. Training groups underwent treadmill exercise (60 min/day, 5 days/week) for 12 weeks. Liver and gastrocnemius muscle were removed and glycogen content was assessed by colorimetric method. Data was analyzed by ANOVA and significance was P≤0.05. RESULTS: Regardless of exercise intensity, trained groups had significantly higher liver but lower muscle glycogen content compared to controls. However, the high compared to the low and moderate intensity groups possessed significantly lower muscle glycogen levels. CONCLUSIONS: These results indicate that 12 weeks of low, moderate, and hard intensity exercise resulted in elevated liver glycogen but depleted muscle glycogen levels. The greater muscle glycogen depletion after high intensity training may be due to tissue damage. It appears that 12 weeks of treadmill exercise resulted in liver not muscle glycogen compensation in Wistar rats.

Impaired Glucose Tolerance and Predisposition to the Fasted State in Liver Glycogen Synthase Knock-out Mice

Conversion to glycogen is a major fate of ingested glucose in the body. A rate-limiting enzyme in the synthesis of glycogen is glycogen synthase encoded by two genes, GYS1, expressed in muscle and other tissues, and GYS2, primarily expressed in liver (liver glycogen synthase). Defects in GYS2 cause the inherited monogenic disease glycogen storage disease 0. We have generated mice with a liver-specific disruption of the Gys2 gene (liver glycogen synthase knock-out (LGSKO) mice), using Lox-P/Cre technology. Conditional mice carrying floxed Gys2 were crossed with mice expressing Cre recombinase under the albumin promoter. The resulting LGSKO mice are viable, develop liver glycogen synthase deficiency, and have a 95% reduction in fed liver glycogen content. They have mild hypoglycemia but dispose glucose less well in a glucose tolerance test. Fed, LGSKO mice also have a reduced capacity for exhaustive exercise compared with mice carrying floxed alleles, but the difference disappears after an overnight fast. Upon fasting, LGSKO mice reach within 4 h decreased blood glucose levels attained by control floxed mice only after 24 h of food deprivation. The LGSKO mice maintain this low blood glucose for at least 24 h. Basal gluconeogenesis is increased in LGSKO mice, and insulin suppression of endogenous glucose production is impaired as assessed by euglycemic-hyperinsulinemic clamp. This observation correlates with an increase in the liver gluconeogenic enzyme phosphoenolpyruvate carboxykinase expression and activity. This mouse model mimics the pathophysiology of glycogen storage disease 0 patients and highlights the importance of liver glycogen stores in whole body glucose homeostasis.

Antidiabetic effect of Ficus religiosa extract in streptozotocin-induced diabetic rats

In Indian traditional system of medicine, Ficus religiosa (Family Moraceae) is prescribed for the treatment of diabetes mellitus. In the present study, the antidiabetic effect of aqueous extract of Ficus religiosa bark (FRAE) was investigated in normal, glucose-loaded hyperglycemic and streptozotocin (STZ)-induced diabetic rats. Oral administration of FRAE at the doses of 25, 50 and 100mg/kg was studied in normal, glucose-loaded and STZ-diabetic rats. The three doses caused significant reduction in blood glucose levels in all the models. The effect was more pronounced in 50 and 100mg/kg than 25mg/kg. FRAE also showed significant increase in serum insulin, body weight and glycogen content in liver and skeletal muscle of STZ-induced diabetic rats while there was significant reduction in the levels of serum triglyceride and total cholesterol. FRAE also showed significant antilipidperoxidative effect in the pancreas of STZ-induced diabetic rats. The antidiabetic effect of Ficus religiosa was compared with glibenclamide, a well-known hypoglycemic drug. The results indicate that aqueous extract of Ficus religiosa bark possesses significant antidiabetic activity.

Attenuation of Helicteres isora L. bark extracts on streptozotocin-induced alterations in glycogen and carbohydrate metabolism in albino rats

The present study was undertaken to assess the effect of Helicteres isora L. on four important enzymes of carbohydrate metabolism (glucokinase [GK], hexokinase [HK] phosphofructokinase [PFK] and fructose-1, 6-bisphosphatase [FBP]) along with glycogen content of insulin-dependent (skeletal muscle and liver) and insulin-independent tissues (kidneys and brain) in streptozotocin (STZ; 60 mg/kg)-induced model of diabetes for 30 days. Administration of bark extracts (100, 200 mg/kg) for 30 days led to decrease in plasma glucose levels by approximately 9.60% and 22.04% and 19.18% and 33.93% on 15th and 30th day, respectively, of the experiment. Liver and two-kidney weight expressed as percentage of body weight significantly increased in diabetics (P < 0.05) versus normal controls. Renal glycogen content increased by 10 folds while hepatic and skeletal muscle glycogen content decreased by 75% and 68% in diabetic controls versus controls. H. isora did not affect glycogen content in any tissue. The decreased activities of PFK, GK, FBP and HK in diabetic controls were 40%, 50%, 50% and 60% and bark extract of H. isora partially corrected this alteration. The efficacy of the bark extract was comparable with Tolbutamide, a well-known hypoglycemic drug.

Role of thyroid hormones in the developmental control of tissue glycogen in fetal sheep near term

Developmental and glucocorticoid-induced changes in tissue glycogen content occur in the fetus near term coincident with an increase in plasma triiodothyronine (T(3)), although the role of thyroid hormones in mediating these changes is unknown. This study investigated glycogen content in the liver, heart and skeletal muscle of sheep fetuses after experimental manipulation of thyroid hormone concentration in utero by T(3) infusion and fetal thyroidectomy (TX). At 130 days of gestation (term 145 +/- 2 days), hepatic glycogen was greater, and muscle glycogen was lower, in the TX fetuses than in the intact fetuses. However, between 130 and 144 days of gestation the normal increment in hepatic glycogen, and decrement in cardiac glycogen, seen in intact fetuses was abolished when the prepartum rise in T(3), but not cortisol, was prevented by TX. At 144 days of gestation, hepatic glycogen was lower, and cardiac glycogen was higher, in the TX compared with intact fetuses. In intact fetuses at 130 days of gestation, 5 days of intravenous T(3) infusion (8-12 microg kg(-1) day(-1)) caused a small but significant increase in hepatic glycogen, although the concentration achieved was not as great as that observed in intact fetuses infused with cortisol (2-3 mg kg(-1) day(-1)) for 5 days. Infusion of T(3) reduced cardiac glycogen to the level observed in mature fetuses near term and immature fetuses infused with cortisol for 5 days. Glycogen content in fetal skeletal muscle increased between 100 and 115 days of gestation, but was unaffected by cortisol or T(3) infusion. Therefore, thyroid hormones are important in the developmental control of hepatic and cardiac glycogen content in the ovine fetus near term and may mediate, in part, the maturational effects of cortisol.

Changes of glycogen content in liver, skeletal muscle, and heart from fasted rats

Glycogen content of white and red skeletal muscles, cardiac muscle, and liver was investigated in conditions where changes in plasma levels of non-esterified fatty acids (NEFA) occur. The experiments were performed in fed and 12 and 48 h-fasted rats. The animals were also submitted to swimming for 10 and 30 min. Glycogen content was also investigated in both pharmacologically induced low plasma NEFA levels fasted rats and pharmacologically induced high plasma NEFA levels fed rats. The participation of Akt and glycogen synthase kinase-3 (GSK-3) in the changes observed was investigated. Plasma levels of NEFA, glucose, and insulin were determined in all conditions. Fasting increased plasma NEFA levels and reduced glycogen content in the liver and skeletal muscles. However, an increase of glycogen content was observed in the heart under this condition. Akt and GSK-3 phosphorylation was reduced during fasting in the liver and skeletal muscles but it remained unchanged in the heart. Our results suggest that in conditions of increased plasma NEFA levels, changes in insulin-stimulated phosphorylation of Akt and GSK-3 and glycogen content vary differently in liver, skeletal muscles, and heart. Akt and GSK-3 phosphorylation and glycogen content are decreased in liver and skeletal muscles, but in the heart it remain unchanged (Akt and GSK-3 phosphorylation) or increased (glycogen content) due to consistent increase of plasma NEFA levels.

Post-exercise carbohydrate plus whey protein hydrolysates supplementation increases skeletal muscle glycogen level in rats

Recent studies showed that a combination of carbohydrate and protein was more effective than carbohydrate alone for replenishing muscle glycogen after exercise. However, it remains to be unclear whether the source or degree of hydrolysis of dietary protein influences post-exercise glycogen accumulation. The aim of this study was to compare the effect of dietary protein type on glycogen levels in the post-exercise phase, and to investigate the effects of post-exercise carbohydrate and protein supplementation on phosphorylated enzymes of Akt/PKB and atypical PKCs. Male Sprague-Dawley rats, trained for 3 days, swam with a 2% load of body weight for 4 h to deplete skeletal muscle glycogen. Immediately after the glycogen-depleting exercise, one group was killed, whereas the other groups were given either glucose or glucose plus protein (whey protein, whey protein hydrolysates (WPH), casein hydrolysates or branched-chain amino acid (BCAA) solutions. After 2 h, the rats were killed, and the triceps muscles quickly excised. WPH caused significant increases in skeletal muscle glycogen level (5.01 +/- 0.24 mg/g), compared with whey protein (4.23 +/- 0.24 mg/g), BCAA (3.92 +/- 0.18 mg/g) or casein hydrolysates (2.73 +/- 0.22 mg/g). Post-exercise ingestion of glucose plus WPH significantly increased both phosphorylated Akt/PKB (131%) and phosphorylated PKCzeta (154%) levels compared with glucose only. There was a significant positive correlation between skeletal muscle glycogen content and phosphorylated Akt/PKB (r = 0.674, P < 0.001) and PKCzeta (r = 0.481, P = 0.017). Post-exercise supplementation with carbohydrate and WPH increases skeletal muscle glycogen recovery by activating key enzymes such as Akt/PKB and atypical PKCs.

Long-term monitoring of patients with infantile-onset Pompe disease on enzyme replacement therapy using a urinary glucose tetrasaccharide biomarker

PurposeTo investigate the correlation of the urinary glucose tetrasaccharide, Glcα1-6Glcα1-4Glcα1-4Glc, (Glc4) with skeletal muscle glycogen content and the long-term clinical response to enzyme replacement therapy with recombinant human acid alpha glucosidase in infantile Pompe disease. MethodsEighteen patients, ≤6 months old, were enrolled in a clinical trial of enzyme replacement therapy for up to 142 weeks. Urinary Glc4, skeletal muscle glycogen, and other clinical and laboratory assessments were made at baseline and at regular intervals. Urinary Glc4 was determined using an isotope-dilution tandem mass spectrometric assay. The clinical response to treatment was defined according to the motor function response. Trends in urinary Glc4 were correlated with the clinical response and compared with serum enzyme markers of skeletal muscle damage, creatine kinase, aspartate aminotransferase, and alanine aminotransferase. ResultsUrinary Glc4, in contrast to the serum markers, correlated closely with skeletal muscle glycogen content and with the clinical response. Patients with the best response to treatment maintained the lowest levels of Glc4 throughout the trial. ConclusionThe results from this study support the use of urinary Glc4 for monitoring patients with infantile-onset Pompe disease on therapy.

Effects of fibre type and diffusion distance on mouse skeletal muscle glycogen content in vitro

In vitro incubation of isolated rodent skeletal muscle is a widely used procedure in metabolic research. One concern with this method is the development of an anoxic state during the incubation period that can cause muscle glycogen depletion. Our aim was to investigate whether in vitro incubation conditions influence glycogen concentration in glycolytic extensor digitorum longus (EDL) and oxidative soleus mouse muscle. Quantitative immunohistochemistry was applied to assess glycogen content in incubated skeletal muscle. Glycogen concentration was depleted, independent of insulin-stimulation in the incubated skeletal muscle. The extent of glycogen depletion was correlated with the oxidative fibre distribution and with the induction of hypoxia-induced-factor-1-alpha. Insulin exposure partially prevented glycogen depletion in soleus, but not in EDL muscle, providing evidence that glucose diffusion is not a limiting step to maintain glycogen content. Our results provide evidence to suggest that the anoxic milieu and the intrinsic characteristics of the skeletal muscle fibre type play a major role in inducing glycogen depletion in during in vitro incubations.

Hunting for the SNARK in metabolic disease

dysregulation of energy balance is a primary constituent in the etiology of obesity and type 2 diabetes mellitus, which is manifested by altered metabolic homeostasis and insulin resistance in a variety of tissues, including brain, liver, and skeletal muscle. The discovery of the AMP-activated

Glucose ingestion during endurance training does not alter adaptation

Glucose ingestion during exercise attenuates activation of metabolic enzymes and expression of important transport proteins. In light of this, we hypothesized that glucose ingestion during training would result in 1) an attenuation of the increase in fatty acid uptake and oxidation during exercise, 2) lower citrate synthase (CS) and beta-hydroxyacyl-CoA dehydrogenase (beta-HAD) activity and glycogen content in skeletal muscle, and 3) attenuated endurance performance enhancement in the trained state. To investigate this we studied nine male subjects who performed 10 wk of one-legged knee extensor training. They trained one leg while ingesting a 6% glucose solution (Glc) and ingested a sweetened placebo while training the other leg (Plc). The subjects trained their respective legs 2 h at a time on alternate days 5 days a week. Endurance training increased peak power (P(max)) and time to fatigue at 70% of P(max) approximately 14% and approximately 30%, respectively. CS and beta-HAD activity increased and glycogen content was greater after training, but there were no differences between Glc and Plc. After training the rate of oxidation of palmitate (R(ox)) and the % of rate of disappearance that was oxidized (%R(dox)) changed. %R(dox) was on average 16.4% greater during exercise after training whereas, after exercise %R(dox) was 30.4% lower. R(ox) followed the same pattern. However, none of these parameters were different between Glc and Plc. We conclude that glucose ingestion during training does not alter training adaptation related to substrate metabolism, mitochondrial enzyme activity, glycogen content, or performance.

Branched-Chain Amino Acid-Containing Dipeptides, Identified from Whey Protein Hydrolysates, Stimulate Glucose Uptake Rate in L6 Myotubes and Isolated Skeletal Muscles

In earlier studies we showed that dietary whey protein increased skeletal muscle and liver glycogen content in exercise-trained rats. However, little is known about whether ingredients of whey protein stimulate skeletal muscle glycogen accumulation. The aim of this study was to identify bioactive peptides in whey protein hydrolysates (WPH) which stimulated glucose uptake and glycogen synthesis rate in skeletal muscles. Branched-chain amino acid (BCAA)-containing dipeptides in WPH were identified using LC/MS/MS. L6 myotubes and isolated epitrochlearis muscles were used for the glucose uptake assays. The myotubes and muscles were incubated with or without 1 mM dipeptides, LY294002 a phosphoinositide 3-kinase (PI3-kinase) inhibitor, or GF102903X an atypical protein kinase C (aPKC) inhibitor, followed by measurement of 2-deoxyglucose uptake. Isolated muscles were incubated for 3 h with or without 1 mM Ile-Leu to determine glycogen synthesis rate. The BCAA-containing dipeptides, Ile-Val, Leu-Val, Val-Leu, Ile-Ile, Leu-Ile, Ile-Leu, and Leu-Leu were detected in the WPH by LC/MS/MS. These dipeptides caused significant stimulation in glucose uptake rate in the L6 myotubes. Ile-Leu, the main component in WPH, also stimulated glucose uptake in isolated skeletal muscles. Stimulation of glucose uptake by Ile-Leu was completely inhibited by treatment with either LY294002, or GF109203X in both L6 cells and isolated muscles. Ile-Leu increased glycogen contents in isolated muscles. These results suggest that BCAA-containing bioactive dipeptides in WPH stimulate glucose uptake in skeletal muscles via the PI3-kinase and aPKC pathways, resulting in increased skeletal muscle glycogen contents.

Skeletal Muscle-Specific Ablation of raptor, but Not of rictor, Causes Metabolic Changes and Results in Muscle Dystrophy

Mammalian target of rapamycin (mTOR) is a central controller of cell growth. mTOR assembles into two distinct multiprotein complexes called mTOR complex 1 (mTORC1) and mTORC2. Here we show that the mTORC1 component raptor is critical for muscle function and prolonged survival. In contrast, muscles lacking the mTORC2 component rictor are indistinguishable from wild-type controls. Raptor-deficient muscles become progressively dystrophic, are impaired in their oxidative capacity, and contain increased glycogen stores, but they express structural components indicative of oxidative muscle fibers. Biochemical analysis indicates that these changes are probably due to loss of activation of direct downstream targets of mTORC1, downregulation of genes involved in mitochondrial biogenesis, including PGC1alpha, and hyperactivation of PKB/Akt. Finally, we show that activation of PKB/Akt does not require mTORC2. Together, these results demonstrate that muscle mTORC1 has an unexpected role in the regulation of the metabolic properties and that its function is essential for life.