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Effect of denervation in WT and Tg (AMPK-inactive or AMPK-DN) mice. AMPK-DN mice (n 11) and WT littermates (n 9) were unilaterally denervated (Den) by severing the sciatic nerve in the right hindlimb, and the contralateral limb (Con) was sham operated to serve as control. All values are reported as means SE. *Statistically significant difference (P 0.001) between Den and Con mice.
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An acute bout of exercise increases muscle GLUT4 mRNA in mice, and denervation decreases GLUT4 mRNA. AMP-activated protein kinase (AMPK) activity in skeletal muscle is also increased by exercise, and GLUT4 mRNA is increased in mouse skeletal muscle after treatment with AMPK activator 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside(AICAR). Th...
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The purpose of this study was to determine the effect of 5'-AMP-activated protein kinase (AMPK) on energy metabolism and myosin heavy chain (MyHC) isoform expression in growing pigs using chronic treatment with 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) as a model. Four-week-old pigs were given daily injections of AICAR or 0.9%...
Citations
... AMPK activation has been shown to increase gene expression of the 2 key glucose-handling intermediates, GLUT4 and HKII, by regulating histone deacetylase 5 (HDAC5) and cAMP response binding-element protein, respectively (327,328). As such, a single injection of AICAR that elevates AMPK activity in skeletal muscle has been shown to increase gene expression of PGC-1a, HKII, and GLUT4 in WT mice but not in skeletal muscle of AMPKa2-deficient mice (329,330). ...
... Acute exercise induces a similar gene response at the level of GLUT4, PGC-1a, and HKII in WT and AMPKa2deficient mice, suggesting that exercise-induced gene expression is orchestrated independently of AMPK (329,330). These findings indicate that repetitive AMPK activation by pharmacological means is sufficient to increase gene expression, whereas signaling parameters other than AMPK may be essential for exercise-induced gene expression. ...
... Nevertheless, acute exercise and exercise training have evoked similar adaptations in skeletal muscle GLUT4 gene expression and protein content, respectively, in WT and AMPKa2-deficient mice, in addition to other metabolic and mitochondrial markers (284,329,330). This prompted McGee et al. (388) to investigate whether HDAC5 was involved in a compensatory mechanism to maintain the adaptive response to exercise in skeletal muscle from AMPKa-deficient mice (29). ...
Skeletal muscle possesses a remarkable ability to adapt to various physiologic conditions. AMPK is a sensor of intracellular energy status that maintains energy stores by fine-tuning anabolic and catabolic pathways. AMPK's role as an energy sensor is particularly critical in tissues displaying highly changeable energy turnover. Due to the drastic changes in energy demand that occur between the resting and exercising state, skeletal muscle is one such tissue. Here, we review the complex regulation of AMPK in skeletal muscle and its consequences on metabolism (e.g., substrate uptake, oxidation, and storage as well as mitochondrial function of skeletal muscle fibers). We focus on the role of AMPK in skeletal muscle during exercise and in exercise recovery. We also address adaptations to exercise training, including skeletal muscle plasticity, highlighting novel concepts and future perspectives that need to be investigated. Furthermore, we discuss the possible role of AMPK as a therapeutic target as well as different AMPK activators and their potential for future drug development.-Kjøbsted, R., Hingst, J. R., Fentz, J., Foretz, M, Sanz, M.-N., Pehmøller, C., Shum, M., Marette, A., Mounier, R., Treebak, J. T., Wojtaszewski, J. F. P., Viollet, B., Lantier, L. AMPK in skeletal muscle function and metabolism.
... This finding indicated that the reg- ulation of HDAC4/5 activation via aerobic exercise is dependent on AMPKα2 in skeletal muscle. However, previous study showed that loss of AMPK did not affect HDAC5 phosphorylation in skeletal muscle of AMPKα2 DN (K45R) transgenic mice after two 3 h bouts of treadmill running (0% incline, 20-28 m/min) separated by 1 h of rest [23,41]. One possible explanation of the discrepant observation is that the dif- ferent animal model and exercise schedule were used in these studies. ...
... This effect was associated with an enhancement in mitochondrial ETC activity and was dependent on muscle AMPK expression, suggesting that impaired complex-1 function is sensed by AMPK which then mediates responses (via the nucleus) to enhance the function of other ETC subunits to compensate, as previously shown in C. elegans [120]. However, whether this pathway is involved in potential mitohormesis signaling during exercise training is unclear given that the ablation of AMPKα2 or PGC1α has little effects on exercise-induced increases in mitochondrial biogenesis and glucose metabolism markers [121][122][123]. Unfortunately, interpretations of results from AMPKα2 knockout mice are complicated by compensatory increases in AMPKα1 activity [121]. ...
Hormesis is a process whereby exposure to a low dose of a potentially harmful stressor promotes adaptive changes to the cell that enables it to better tolerate subsequent stress. In recent years this concept has been applied specifically to the mitochondria (mitohormesis), suggesting that in response to a perturbation the mitochondria can initiate and transduce a signal to the nucleus that coordinates a transcriptional response resulting in both mitochondrial and non-mitochondrial adaptations that return and maintain cellular homeostasis. In this review we summarize the evidence that mitohormesis is a significant adaptive-response signaling pathway, and suggest that it plays a role in mediating exercise-induced adaptations. We discuss potential mitochondrial emitters of retrograde signals that may activate known exercise-sensitive transcription factors to modulate transcription responses to exercise, and draw on evidence from mitochondrial dysfunction animal models to support a role for mitohormesis in mitochondrial biogenesis. Studies directly linking mitohormesis to the exercise training response are lacking, however mounting evidence suggests numerous signals are emitted from the mitochondria during exercise and have the potential to induce a nuclear transcription response, with reactive oxygen species (ROS) being the primary candidate.
... The present observations that the PGC-1␣ mRNA level in skeletal muscle was lower in AMPK␣ mdKO mice than in WT after acute exercise and that GLUT4 mRNA increased only in WT mice support the view of a coordinated AMPK␣-PGC-1␣ pathway regulating GLUT4 gene expression in response to acute exercise. Interestingly, two previous studies in AMPK␣2 KO and AMPK␣2 kinase-dead (KD) mice did not report impaired induction of GLUT4 mRNA with exercise in the AMPK␣2-deficient mice (21,27). Common to all three models (AMPK␣2 KO, AMPK␣2 KD, and AMPK␣ mdKO) is the almost total absence of AMPK␣2 catalytic activity in skeletal muscle. ...
Exercise training increases skeletal muscle expression of metabolic proteins improving the oxidative capacity. Adaptations in skeletal muscle by pharmacologically induced activation of 5'AMP-activated protein kinase (AMPK) are dependent on the AMPKα2 subunit. We hypothesized that exercise training-induced increases in exercise capacity and expression of metabolic proteins as well as acute exercise-induced gene regulation would be compromised in AMPKα1 and -α2 muscle-specific double knockout (mdKO) mice. An acute bout of exercise increased skeletal muscle mRNA content of cytochrome C oxidase subunit I, glucose transporter 4 and VEGF in an AMPK-dependent manner, while cluster of differentiation 36 and fatty acid transport protein 1 mRNA content increased similarly in AMPKα wild type (WT) and mdKO mice. During four weeks of voluntary running wheel exercise training, the AMPKα mdKO mice ran less than WT. Maximal running speed was lower in AMPKα mdKO than WT mice, but increased similarly in both genotypes with exercise training. Exercise training increased quadriceps protein content of ubiquinol-cytochrome-C reductase core protein 1 (UQCRC1), cytochrome C, hexokinase II, plasma membrane fatty acid binding protein and citrate synthase activity more in AMPKα WT than mdKO muscle. However, analysis of a subgroup of mice matched for running distance revealed that only UQCRC1 protein content increased more in WT than mdKO mice with exercise training. Thus, AMPKα1 and -α2 subunits are important for acute exercise-induced mRNA responses of some genes and may be involved in regulating basal metabolic protein expression, but seem to be less important in exercise training-induced adaptations in metabolic proteins.
... This suggests that increased glucose disposal in skeletal muscle via R419 may be mediated in part through increases in GLUT4 expression via AMPK-independent pathways. These findings are consistent with reports that GLUT4 expression is also increased following exercise via AMPK-independent pathways [48,49]. Future studies investigating the AMPK-independent mechanisms controlling GLUT4 transcription are warranted. ...
Objective:
Skeletal muscle AMP-activated protein kinase (AMPK) is important for regulating glucose homeostasis, mitochondrial content and exercise capacity. R419 is a mitochondrial complex-I inhibitor that has recently been shown to acutely activate AMPK in myotubes. Our main objective was to examine whether R419 treatment improves insulin sensitivity and exercise capacity in obese insulin resistant mice and whether skeletal muscle AMPK was important for mediating potential effects.
Methods:
Glucose homeostasis, insulin sensitivity, exercise capacity, and electron transport chain content/activity were examined in wildtype (WT) and AMPK β1β2 muscle-specific null (AMPK-MKO) mice fed a high-fat diet (HFD) with or without R419 supplementation.
Results:
There was no change in weight gain, adiposity, glucose tolerance or insulin sensitivity between HFD-fed WT and AMPK-MKO mice. In both HFD-fed WT and AMPK-MKO mice, R419 enhanced insulin tolerance, insulin-stimulated glucose disposal, skeletal muscle 2-deoxyglucose uptake, Akt phosphorylation and glucose transporter 4 (GLUT4) content independently of alterations in body mass. In WT, but not AMPK-MKO mice, R419 improved treadmill running capacity. Treatment with R419 increased muscle electron transport chain content and activity in WT mice; effects which were blunted in AMPK-MKO mice.
Conclusions:
Treatment of obese mice with R419 improved skeletal muscle insulin sensitivity through a mechanism that is independent of skeletal muscle AMPK. R419 also increases exercise capacity and improves mitochondrial function in obese WT mice; effects that are diminished in the absence of skeletal muscle AMPK. These findings suggest that R419 may be a promising therapy for improving whole-body glucose homeostasis and exercise capacity.
... Using double transgenic (DTG) mice with both SM UCP1 expression and AMPKa2 ablation, we show here that AMPKa2 is in fact dispensable for SM mitochondrial uncoupling induced beneficial metabolic effects on whole body energy balance, glucose homeostasis and basal fatty acid metabolism. This is in line with numerous studies reporting controversial data concerning the importance of AMPKa2 for regulation of glucose uptake and fatty acid oxidation, particularly when studied in SM [51,[62][63][64]. ...
Transgenic (UCP1-TG) mice with ectopic expression of UCP1 in skeletal muscle (SM) show a phenotype of increased energy expenditure, improved glucose tolerance and increase substrate metabolism in SM. To investigate the potential role of skeletal muscle AMPKα2 activation in the metabolic phenotype of UCP1-TG mice we generated double transgenic (DTG) mice, by crossing of UCP1-TG mice with DN-AMPKα2 mice overexpressing a dominant negative α2 subunit of AMPK in SM which resulted in an impaired AMPKα2 activity by 90±9% in SM of DTG mice. Biometric analysis of young male mice showed decreased body weight, lean and fat mass for both UCP1-TG and DTG compared to WT and DN-AMPKα2 mice. Energy intake and weight-specific total energy expenditure were increased, both in UCP1-TG and DTG mice. Moreover, glucose tolerance, insulin sensitivity and fatty acid oxidation were not altered in DTG compared to UCP1-TG. Also uncoupling induced induction and secretion of fibroblast growth factor 21 (FGF21) from SM was preserved in DTG mice. However, voluntary physical cage activity as well as ad libitum running wheel access during night uncovered a severe activity intolerance of DTG mice. Histological analysis showed a progressive degenerative morphology in SM of DTG mice which was not observed in SM of UCP1-TG mice. Moreover, ATP-depletion related cellular stress response via heat shock protein 70 was highly induced, whereas capillarization regulator VEGF was suppressed in DTG muscle. In addition, AMPKα2-mediated induction of mitophagy regulator ULK1 was suppressed in DTG mice, as well as mitochondrial respiratory capacity and content. In conclusion, we demonstrate that AMPKα2 is dispensable for SM mitochondrial uncoupling induced metabolic effects on whole body energy balance, glucose homeostasis and insulin sensitivity. But strikingly, activation of AMPKα2 seems crucial for maintaining SM function, integrity and the ability to compensate chronic metabolic stress induced by SM mitochondrial uncoupling.
... Despite this, however, AMPK does not appear to be an essential component of this network, since transcriptional responses are maintained in response to exercise when examined in AMPK loss-offunction models. For example, the expression of the glucose transporter isoform 4 (GLUT4) is increased in response to exercise in both wild type and muscle-specific AMPK ␣ 2 dominant-negative (DN) mice (18). Furthermore, we have shown that knockout of AMPK ␣ 2 has no effect on exercise-induced increases in peroxisome proliferator-activated receptor ␥ (PPAR␥) coactivator 1␣ (PGC-1␣), FoxO1, hexokinase II (HKII), and pyruvate dehydrogenase kinase 4 (PDK4) gene expression (9). ...
Some gene deletions or mutations have little effect on metabolism and metabolic adaptation because of redundancy and/or compensation in metabolic pathways. The mechanisms for redundancy and/or compensation in metabolic adaptation in mammalian cells are unidentified. Here, we show that in mouse muscle and myogenic cells, compensatory regulation of the histone deacetylase (HDAC5) transcriptional repressor maintains metabolic integrity. HDAC5 phosphorylation regulated the expression of diverse metabolic genes and glucose metabolism in mouse C2C12 myogenic cells. However, loss of AMP-activated protein kinase (AMPK), a HDAC5 kinase, in muscle did not affect HDAC5 phosphorylation in mouse skeletal muscle during exercise, but resulted in a compensatory increase (32.6%) in the activation of protein kinase D (PKD), an alternate HDAC5 kinase. Constitutive PKD activation in mouse C2C12 myogenic cells regulated metabolic genes and glucose metabolism. Although aspects of this response were HDAC5 phosphorylation dependent, blocking HDAC5 phosphorylation when PKD was active engaged an alternative compensatory adaptive mechanism, which involved post-transcriptional reductions in HDAC5 mRNA (-93.1%) and protein. This enhanced the expression of a specific subset of metabolic genes and mitochondrial metabolism. These data show that compensatory regulation of HDAC5 maintains metabolic integrity in mammalian cells and reinforces the importance of preserving the cellular metabolic adaptive response.-McGee, S. L., Swinton, C., Morrison, S., Gaur, V., Campbell, D. E., Jorgensen, S. B., Kemp, B. E., Baar, K., Steinberg, G. R., Hargreaves, M. Compensatory regulation of HDAC5 in muscle maintains metabolic adaptive responses and metabolism in response to energetic stress.
... In addition, oxidative stress alters the transcription of the glucose transporters responsible for basal and insulin-stimulated glucose uptake (GLUT1 and GLUT4, respectively), resulting in increased basal glucose uptake, decreased insulin-stimulated glucose uptake, and the exacerbation of oxidative stress in the cell [44]. In accordance with this, experimental muscle denervation decreases GLUT4 mRNA and impairs GLUT4 translocation, thereby reducing insulin signaling and altering glucose uptake [45,46]. ALS is characterized by oxidative stress, and the accumulation of ROS is believed to play a central role in disease pathogenesis [29]. ...
Background:
Skeletal muscles play an important role in systemic glucose homeostasis and are purported to be the origin of the altered metabolic state observed in amyotrophic lateral sclerosis (ALS).
Objective:
The purpose of this study was to evaluate whole-body and muscle-specific glucose metabolism in the SOD1-G93A mouse model of ALS.
Methods:
We assessed glucose tolerance in early-, middle-, and late-stage SOD1-G93A and control mice using an intraperitoneal glucose tolerance test. We then measured the respiratory exchange ratio (CO2 production/O2 consumption) as a function of fasting and feeding using indirect calorimetry in a subset of male mice at these time points. Finally, muscles from all mice were harvested to evaluate basal and insulin-stimulated glucose transport in fast- and slow-twitch muscles.
Results:
No changes in systemic glucose clearance were observed in SOD1-G93A mice at any stage, nor were there changes in fasting insulin levels. Indirect calorimetry revealed an increase in the respiratory exchange ratio during the fed state at middle, but not at early or late stages of disease. Middle-stage SOD1-G93A mice exhibited decreased insulin-stimulated glucose uptake in fast-twitch, but not slow-twitch, skeletal muscle. Late-stage SOD1-G93A mice exhibited decreased insulin-stimulated glucose uptake in both fast- and slow-twitch muscle, as well as increased basal (non-insulin-stimulated) glucose uptake.
Conclusions:
These results suggest that alterations in muscle metabolism occur in a fiber-type-specific manner in ALS, but do not necessarily lead to whole-body metabolic changes in SOD1-G93A mice.
... Just as has been shown in resting muscle (218), there is likely to be some degree of redundancy in the signaling pathways that mediate the exercise-induced increase in skeletal muscle GLUT4 expression. The exercise-induced increase in GLUT4 mRNA is preserved in transgenic mice expressing a dominant negative AMPK (123), and inhibition of calcineurin does not attenuate the exercise-induced increase in GLUT4 (87). The increase in skeletal muscle GLUT4 following exercise in humans was unaffected by adrenergic receptor blockade (101). ...
Glucose is an important fuel for contracting muscle, and normal glucose metabolism is vital for health. Glucose enters the muscle cell via facilitated diffusion through the GLUT4 glucose transporter which translocates from intracellular storage depots to the plasma membrane and T-tubules upon muscle contraction. Here we discuss the current understanding of how exercise-induced muscle glucose uptake is regulated. We briefly discuss the role of glucose supply and metabolism and concentrate on GLUT4 translocation and the molecular signaling that sets this in motion during muscle contractions. Contraction-induced molecular signaling is complex and involves a variety of signaling molecules including AMPK, Ca(2+), and NOS in the proximal part of the signaling cascade as well as GTPases, Rab, and SNARE proteins and cytoskeletal components in the distal part. While acute regulation of muscle glucose uptake relies on GLUT4 translocation, glucose uptake also depends on muscle GLUT4 expression which is increased following exercise. AMPK and CaMKII are key signaling kinases that appear to regulate GLUT4 expression via the HDAC4/5-MEF2 axis and MEF2-GEF interactions resulting in nuclear export of HDAC4/5 in turn leading to histone hyperacetylation on the GLUT4 promoter and increased GLUT4 transcription. Exercise training is the most potent stimulus to increase skeletal muscle GLUT4 expression, an effect that may partly contribute to improved insulin action and glucose disposal and enhanced muscle glycogen storage following exercise training in health and disease.
... Activation of the AMP-activated protein kinase (AMPK) is known to occur during muscle contraction in response to increased AMP and decreased ATP and phosphocreatine. For this reason, activation of AMPK was thought to mediate the exercise-induced changes in GLUT4 expression; however, expression of dominant-negative AMPK does not inhibit exercise-induced increase in GLUT4 transcriptional activity [123]. Thus, the signaling cascades responsible for exerciseinduced gene expression remain unknown. ...
... Thus, the MEF2 domain functions cooperatively with Domain 1 to support regulated transcription of the human GLUT4 promoter. We, as well as others, have shown that these elements play both a positive role in tissue-specific expression and a negative role under certain physiologic states such as insulin deficiency [123,137,139]. To illustrate this point, transgenic animals described in Figure 1 were subjected to an STZ protocol to induce experimental diabetes and treated with insulin or left untreated, to determine how this affected transgene expression. ...
... CAT mRNA, driven by the truncated promoter fragments was compared to a fully functional human GLUT4 promoter and the endogenous mouse GLUT4 (Figure 1). CAT mRNA, which was driven by both 730 bp or 412 bp fragments of GLUT4 promoter DNA did not respond to either STZ treatment (Figure 1, constructs 5 and 6), or exercise treatment [123]. This shows that sequences somewhere upstream of −730 are required to create changes in gene expression in response to various physiologic state, just as these same sequences are responsible for restricting tissue-specific expression. ...
GLUT4 has long been known to be an insulin responsive glucose transporter. Regulation of GLUT4 has been a major focus of research on the cause and prevention of type 2 diabetes. Understanding how insulin signaling alters the intracellular trafficking of GLUT4 as well as understanding the fate of glucose transported into the cell by GLUT4 will be critically important for seeking solutions to the current rise in diabetes and metabolic disease.
