Dietary Aronia melanocarpa extract enhances mTORC1 signaling, but has no effect on protein synthesis and protein breakdown-related signaling, in response to resistance exercise in rat skeletal muscle.

BACKGROUND: Ursolic acid altered muscle protein metabolism in normal and resting conditions after acute resistance exercise, suggesting that eating fruits rich in ursolic acid could enhance muscle protein synthesis and decrease muscle degradation. Aronia melanocarpa, a member of the family Rosaceae and native to North America and Eastern Canada, is rich in ursolic acid. In this study, we examined the effects of A. melanocarpa extract (AME) supplementation on the mTORC1 signaling pathway and muscle degradation-related factors in rats, both alone and in combination with resistance exercise. METHODS: Male Sprague-Dawley rats were divided into AME and normal chow (NOR) groups. AME group was fed chow providing a dose of 3 g/kg of AME and 115 mg/kg of ursolic acid for 7 days, whereas NOR rats were fed normal powder chow. The right gastrocnemius muscle of each animal was isometrically exercised (5 sets of ten 3-s contractions, with a 7-s interval between contractions and 3-min rest intervals between sets), while the left gastrocnemius muscle served as an internal control. Western blotting and real-time polymerase chain reaction were used to assess expression of factors involved in the mTORC1 signaling pathway and muscle degradation. RESULTS: At 1 h after resistance exercise, phosphorylation of ERK1/2 was significantly increased by AME consumption. At 6 h after resistance exercise, AME consumption significantly increased the phosphorylation of Akt, p70S6K, rpS6, and AMPK. It also increased MAFbx expression. Furthermore, AME significantly increased the phosphorylation of p70S6K and rpS6 in response to resistance exercise. However, AME did not increase muscle protein synthesis (MPS) after resistance exercise. AME did not affect the expression of any of the mediators of protein degradation, with the exception of MAFbx. CONCLUSIONS: Dietary AME enhanced mTORC1 activation in response to resistance exercise without increasing MPS. Moreover, it neither accelerated muscle protein degradation nor otherwise negatively affected protein metabolism. Further study is needed to clarify the effect of the combination of AME and chronic resistance training on muscle hypertrophy.

The effect of different acute muscle contraction regimens on the expression of muscle proteolytic signaling proteins and genes.

Previous studies have reported that different modes of muscle contraction (i.e., eccentric or concentric contraction) with similar contraction times can affect muscle proteolytic responses. However, the effect of different contraction modes on muscle proteolytic response under the same force-time integral (FTI: contraction force × time) has not been investigated. The purpose of this study was to investigate the effect of different contraction modes, with the same FTI, on acute proteolytic signaling responses. Eleven-week-old male Sprague-Dawley rats were randomly assigned to eccentric (EC), concentric (CC), or isometric contraction (IC) groups. Different modes of muscle contraction were performed on the right gastrocnemius muscle using electrical stimulation, with the left muscle acting as a control. In order to apply an equivalent FTI, the number of stimulation sets was modified between the groups. Muscle samples were taken immediately and three hours after exercise. Phosphorylation of FoxO3a at Ser253 was significantly increased immediately after exercise compared to controls irrespective of contraction mode. The mRNA levels of the ubiquitin ligases, MuRF1, and MAFbx mRNA were unchanged by contraction mode or time. Phosphorylation of ULK1 at Ser317 (positive regulatory site) and Ser757 (negative regulatory site) was significantly increased compared to controls, immediately or 3 h after exercise, in all contraction modes. The autophagy markers (LC3B-II/I ratio and p62 expression) were unchanged, regardless of contraction mode. These data suggest that differences in contraction mode during resistance exercise with a constant FTI, are not factors in regulating proteolytic signaling in the early phase of skeletal muscle contraction.

Panaxatriol derived from ginseng augments resistance exercised-induced protein synthesis via mTORC1 signaling in rat skeletal muscle.

Resistance exercise activates muscle protein synthesis via the mammalian target of rapamycin complex 1 (mTORC1) pathway and subsequent muscle hypertrophy. Upstream components of the mTORC1 pathway are widely known to be involved in Akt and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. Previous studies have shown that ginseng stimulated Akt and ERK1/2 signaling. Therefore, we hypothesized that panaxatriol (PT) derived from ginseng triggers mTORC1 signaling and muscle protein synthesis by activating both the Akt and ERK1/2 signaling pathways, and that PT additively stimulates muscle protein synthesis when combined with resistance exercise. The study included male Sprague-Dawley rats. The legs of the rats were divided into control, PT-only, exercise-only, and exercise + PT groups. The right legs were subjected to isometric resistance exercise using percutaneous electrical stimulation, whereas the left legs were used as controls. PT (0.2 g/kg) was administered immediately after exercise. The Akt and ERK1/2 phosphorylation levels were significantly higher in the exercise + PT group than in the exercise-only group 0.5 hour after exercise. The phosphorylation of p70S6K was significantly increased at both 0.5 and 3 hours after exercise, and it was higher in the exercise + PT group than in the exercise-only group at both 0.5 and 3 hours after exercise. Muscle protein synthesis was significantly increased 3 hours after exercise, and it was higher in the exercise + PT group than in the exercise-only group 3 hours after exercise. Our results suggest that PT derived from ginseng enhances resistance exercise-induced protein synthesis via mTORC1 signaling in rat skeletal muscle.

Contraction mode itself does not determine the level of mTORC1 activity in rat skeletal muscle.

Resistance training with eccentric contraction has been shown to augment muscle hypertrophy more than other contraction modes do (i.e., concentric and isometric contraction). However, the molecular mechanisms involved remain unclear. The purpose of this study was to investigate the effect of muscle contraction mode on mammalian target of rapamycin complex 1 (mTORC1) signaling using a standardized force-time integral (load (weight) × contraction time). Male Sprague-Dawley rats were randomly assigned to three groups: eccentric contraction, concentric contraction, and isometric contraction. The right gastrocnemius muscle was exercised via percutaneous electrical stimulation-induced maximal contraction. In experiment 1, different modes of muscle contraction were exerted using the same number of reps in all groups, while in experiment 2, muscle contractions were exerted using a standardized force-time integral. Muscle samples were obtained immediately and 3 h after exercise. Phosphorylation of molecules associated with mTORC1 activity was assessed using western blot analysis. In experiment 1, the force-time integral was significantly different among contraction modes with a higher force-time integral for eccentric contraction compared to that for other contraction modes (P < 0.05). In addition, the force-time integral was higher for concentric contraction compared to that for isometric contraction (P < 0.05). Similarly, p70S6K phosphorylation level was higher for eccentric contraction than for other modes of contraction (P < 0.05), and concentric contraction was higher than isometric contraction (P < 0.05) 3 h after exercise. In experiment 2, under the same force-time integral, p70S6K (Thr389) and 4E-BP1 phosphorylation levels were similar among contraction modes 3 h after exercise. Our results suggest that mTORC1 activity is not determined by differences in muscle contraction mode itself. Instead, mTORC1 activity is determined by differences in the force-time integral during muscle contraction.

Acute resistance exercise-induced IGF1 expression and subsequent GLUT4 translocation.

Acute aerobic exercise (AE) is a major physiological stimulus for skeletal muscle glucose uptake through activation of 5' AMP-activated protein kinase (AMPK). However, the regulation of glucose uptake by acute resistance exercise (RE) remains unclear. To investigate the intracellular regulation of glucose uptake after acute RE versus acute AE, male Sprague-Dawley rats were divided into three groups: RE, AE, or nonexercise control. After fasting for 12 h overnight, the right gastrocnemius muscle in the RE group was exercised at maximum isometric contraction via percutaneous electrical stimulation (3 × 10 sec, 5 sets). The AE group ran on a treadmill (25 m/min, 60 min). Muscle samples were taken 0, 1, and 3 h after completion of the exercises. AMPK, Ca(2+)/calmodulin-dependent protein kinase II, and TBC1D1 phosphorylation were increased immediately after both forms of exercise and returned to baseline levels by 3 h. Muscle IGF1 expression was increased by RE but not AE, and maintained until 3 h after RE Additionally, Akt and AS160 phosphorylation were sustained for 3 h after RE, whereas they returned to baseline levels by 3 h after AE Similarly, GLUT4 translocation remained elevated 3 h after RE, although it returned to the baseline level by 3 h after AE Overall, this study showed that AMPK/TBC1D1 and IGF1/Akt/AS160 signaling were enhanced by acute RE, and that GLUT4 translocation after acute RE was more prolonged than after acute AE These results suggest that acute RE-induced increases in intramuscular IGF1 expression might be a distinct regulator of GLUT4 translocation.

The role of mTOR signalling in the regulation of skeletal muscle mass in a rodent model of resistance exercise.

Resistance exercise (RE) activates signalling by the mammalian target of rapamycin (mTOR), and it has been suggested that rapamycin-sensitive mTOR signalling controls RE-induced changes in protein synthesis, ribosome biogenesis, autophagy, and the expression of peroxisome proliferator gamma coactivator 1 alpha (PGC-1α). However, direct evidence to support the aforementioned relationships is lacking. Therefore, in this study, we investigated the role of rapamycin-sensitive mTOR in the RE-induced activation of muscle protein synthesis, ribosome biogenesis, PGC-1α expression and hypertrophy. The results indicated that the inhibition of rapamycin-sensitive mTOR could prevent the induction of ribosome biogenesis by RE, but it only partially inhibited the activation of muscle protein synthesis. Likewise, the inhibition of rapamycin-sensitive mTOR only partially blocked the hypertrophic effects of chronic RE. Furthermore, both acute and chronic RE promoted an increase in PGC-1α expression and these alterations were not affected by the inhibition of rapamycin-sensitive mTOR. Combined, the results from this study not only establish that rapamycin-sensitive mTOR plays an important role in the RE-induced activation of protein synthesis and the induction of hypertrophy, but they also demonstrate that additional (rapamycin-sensitive mTOR-independent) mechanisms contribute to these fundamentally important events.

Herbal supplement Kamishimotsuto augments resistance exercise-induced mTORC1 signaling in rat skeletal muscle.

OBJECTIVES: Kamishimotsuto (KST) is a supplement containing 13 different herbs including Phellodendron bark, Anemarrhena rhizome and ginseng that have been shown to activate mammalian target of rapamycin complex 1 (mTORC1) and thereby increase muscle protein synthesis in vitro. However, the combined effect of KST and resistance exercise on muscle protein anabolism has not been investigated in vivo. Therefore, the purpose of this study was to investigate the effect of KST supplementation, resistance exercise on (mTORC1) signaling and subsequent muscle protein synthesis. METHODS: Male Sprague-Dawley rats were divided into two groups: one group received KST (500 mg/kg/d in water) and the other group received placebo (PLA) for 7 d. After 12 h of fasting, the right gastrocnemius muscle was isometrically exercised via percutaneous electrical stimulation. Muscle samples were analyzed for muscle protein synthesis (MPS) and by western blotting analysis to assess the phosphorylation of p70S6K (Thr389), rpS6 (Ser240/244), and Akt (Ser473 and Thr308). RESULTS: KST supplementation for 7 d significantly increased basal p-Akt (Ser473) levels compared with PLA, phosphorylation of the signaling proteins and MPS at baseline were otherwise unaffected. p-p70S6K and p-rpS6 levels significantly increased 1 h and 3 h after exercise in the PLA group, and these elevations were augmented in the KST group (P < 0.05). Furthermore, MPS at 6 h after resistance exercise was greater in the KST group than in the PLA group (P < 0.05). CONCLUSIONS: While resistance exercise alone was able to increase p70S6K and rpS6 phosphorylation, Kamishimotsuto supplementation further augmented resistance exercise-induced muscle protein synthesis through mTORC1 signaling.

Role of Exercise and Nutrition in the Prevention of Sarcopenia.

The age-associated loss of skeletal muscle mass and strength (sarcopenia) has been shown to increase the risk of injury due to falls and incidence of metabolic complications including insulin resistance and diabetes, which subsequently becomes a significant factor to disability among the elderly population. Nutrient intake is the most important anabolic stimulus for skeletal muscle. Specifically, the amino acid leucine and meal-induced insulin both independently stimulate muscle protein synthesis. However, age-specific changes in muscle anabolic responses to leucine become apparent when sub-maximal amounts of amino acids are administered in older subjects. Furthermore, insulin resistance of muscle protein metabolism with aging has been demonstrated in healthy non-diabetic older subjects. Resistance exercise is another anabolic stimulus which increases myofibrillar muscle protein synthesis in both young and older individuals. The increased muscle anabolism is apparent within 2-3 h after a single bout of heavy resistance exercise and remains elevated up to 2 d following the exercise. The mTOR signaling pathway in skeletal muscle is associated with an increased rate of muscle protein synthesis during the early recovery phase following a bout of resistance exercise. Finally, recent evidence on the cumulative effect of resistance exercise in combination with nutritional supplement on muscle protein metabolism will be discussed to propose a possible preventative measure against sarcopenia.

Acute bout of resistance exercise increases vitamin D receptor protein expression in rat skeletal muscle.

NEW FINDINGS: What is the central question of this study? Does an acute bout of exercise alter vitamin D receptor expression in rat skeletal muscle? What is the main finding and its importance? Resistance exercise but not endurance exercise increased intramuscular vitamin D receptor expression. Thus, resistance exercise may be an effective way to increase muscle vitamin D receptor expression. Vitamin D and vitamin D receptor (VDR) are involved in the maintenance of skeletal muscle mass and function. Although resistance exercise is well known to enhance muscle growth and improve muscle function, the effect of resistance exercise on VDR has been unclear. We investigated intramuscular VDR expression in response to an acute bout of resistance exercise or endurance exercise. Male adult Sprague-Dawley rats were subjected to either resistance exercise (isometrically exercised via percutaneous electrical stimulation for five sets of ten 3 s contractions, with a 7 s interval between contractions and 3 min rest intervals between sets) or endurance exercise (treadmill at 25 m min(-1) for 60 min). Rats were killed immediately or 1, 3, 6 or 24 h after completion of the resistance or endurance exercise, and gastrocnemius muscles were removed. Non-exercised control animals were killed in a basal state (control group). Intramuscular VDR expression was significantly higher immediately after resistance exercise and elevated for 3 h after exercise compared with the control group (P < 0.05), and the resistance exercise significantly increased phosphorylated ERK1/2 and Mnk1 expression (P < 0.05), which may be associated with VDR expression, immediately after exercise. Additionally, intramuscular expression of cytochrome P450 27B1, an enzyme related to vitamin D metabolism, was significantly higher at 1 and 3 h after exercise (P < 0.05) compared with the control group. In contrast, endurance exercise had no effect on any of the measured proteins. Our results indicate that resistance exercise may be an efficient way to increase intramuscular VDR and related enzyme expression.