| 1. |
- Barnes, Brian R, et al.
(författare)
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5'-AMP-activated protein kinase regulates skeletal muscle glycogen content and ergogenics
- 2005
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Ingår i: The FASEB Journal. - : Wiley. - 0892-6638 .- 1530-6860. ; 19:7, s. 773-779
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Tidskriftsartikel (refereegranskat)abstract
- 5'-AMP-activated protein kinase (AMPK) activity is increased during exercise in an intensity- and glycogen-dependent manner. We previously reported that a mutation in the AMPK3 subunit (Prkag3225Q) increases AMPK activity and skeletal muscle glycogen content. Transfection experiments revealed the R225Q mutation is associated with high basal AMPK activity and diminished AMP dependence. Thus, the R225Q mutation can be considered a loss-of-function mutation that abolished allosteric regulation by AMP/ATP, causing increased basal AMPK activity. We used AMPK3 transgenic (Tg-Prkag3225Q) and knockout (Prkag3-/-) mice to determine the relationship between AMPK activity, glycogen content, and ergogenics (ability to perform work) in isolated extensor digitorum longus skeletal muscle after contractions induced by electrical stimulation. Contraction-induced AMPK activity was inversely coupled to glycogen content in wild-type and Tg-Prkag3225Q mice, but not in Prkag3-/- mice, highlighting a partial feedback control of glycogen on contraction-induced AMPK activity in the presence of a functional AMPK3 isoform. Skeletal muscle glycogen content was positively correlated to work performance, regardless of genotype. Thus, chronic activation of AMPK by the Prkag3225Q mutation directly influences skeletal muscle ergogenics by enhancing glycogen content. In conclusion, functional studies of the AMPK3 isoform further support the close connection between glycogen content and exercise performance in skeletal muscle.
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| 2. |
- Long, Yun Chau
(författare)
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Skeletal muscle metabolic flexibility : the roles of AMP-activated protein kinase and calcineurin
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Skeletal muscle fibers differ considerably in their metabolic and physiological properties. The metabolic properties of skeletal muscle display a high degree of flexibility which adapts to various physiological demands by shifting energy substrate metabolism. Studies were conducted to evaluate the roles of AMP-activated protein kinase (AMPK) and calcineurin in the regulation of skeletal muscle metabolism. Fasting elicited a coordinated expression of genes involved in lipid utilization and glucose metabolism in white gastrocnemius muscle from wild-type mice. The fasting-induced transcriptional responses were impaired in the AMPKgamma3 knockout (Prkag3-/-) mice. Conversely, in mice transgenic for an activating mutant form of AMPKã3(R225Q) (Tg-Prkag3225Q), an enhanced expression of several fasting-responsive metabolic genes, and a reciprocal down-regulation of glycolytic genes was observed. The results support the role of AMPKã3 subunit in the coordinated expression of fasting-responsive metabolic genes in skeletal muscle. Exercise stimulated glucose uptake in EDL muscles from wild-type, Tg-Prkag3225Q and Prkag3-/ mice to the same degree. In Tg-Prkag3225Q mice, elevated acetyl-CoA carboxylase phosphorylation, enhanced intramuscular triglyceride utilization and metabolic gene expression was observed after exercise. Conversely, an impaired gene expression was seen in the Prkag3-/- mice. Thus, the AMPKã3 subunit is dispensable for exercise-stimulated glucose transport and the mutant AMPKã3(R225Q) subunit promotes metabolic and gene expression adaptations in response to exercise. Enhanced insulin-, but suppressed AICAR-induced glucose uptake was observed in EDL muscles from transgenic mice expressing an activated form of the calcium/calmodulin dependent protein phosphatase calcineurin (MCK-CnA*). Impaired AMPK-activated glucose uptake was associated with a decrease in the expression of the AMPKã3 subunit. Contractioninduced glucose uptake however was unaltered in MCK-CnA* mice, despite a decrease in contraction-induced AMPK phosphorylation. Therefore, calcineurin-induced skeletal muscle remodeling altered AMPK-activated glucose uptake. An enhanced glucose incorporation into glycogen and a reciprocal suppression of glucose oxidation was seen in the EDL muscle from MCK-CnA* mice. These changes were accompanied by an increase in lipid oxidation and lactate release. The alterations in glucose partitioning were supported by a coordinated decrease in glycolytic genes and an elevation in Pdk4 expression. Consistent with the increase in lipid oxidation, expression lipid metabolic and mitochondrial genes were activated in EDL muscle from MCK-CnA* mice, concomitant with an induction of several transcription regulators including PPARá, PPARä and PGC1á. Therefore, calcineurin altered skeletal muscle metabolism via coordinated changes in gene expression. In conclusion, AMPK regulates skeletal muscle lipid and glucose metabolism, as well as gene regulatory responses to fasting and exercise. Calcineurin-mediated skeletal muscle remodeling alters the expression of AMPK subunits and AMPK-mediated glucose uptake. Furthermore, calcineurin alters lipid and glucose metabolism in skeletal muscle via coordinated changes in gene expression program. Therefore, the flexibility of lipid and glucose utilization in skeletal muscle is not only regulated at the level of covalent and allosteric modifications, but the reciprocity is also conserved at transcriptional level.
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| 3. |
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| 4. |
- Treebak, Jonas T, et al.
(författare)
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AMPK-mediated AS160 phosphorylation in skeletal muscle is dependent on AMPK catalytic and regulatory subunits.
- 2006
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 55:7, s. 2051-2058
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Tidskriftsartikel (refereegranskat)abstract
- AMP-activated protein kinase (AMPK) is a heterotrimeric protein that regulates glucose transport mediated by cellular stress or pharmacological agonists such as 5-aminoimidazole-4-carboxamide 1 beta-D-ribonucleoside (AICAR). AS160, a Rab GTPase-activating protein, provides a mechanism linking AMPK signaling to glucose uptake. We show that AICAR increases AMPK, acetyl-CoA carboxylase, and AS160 phosphorylation by insulin-independent mechanisms in isolated skeletal muscle. Recombinant AMPK heterotrimeric complexes (alpha 1 beta 1 gamma l and alpha 2 beta 2 gamma 1) phosphorylate AS160 in a cell-free assay. In mice deficient in AMPK signaling (alpha 2 AMPK knockout [KO], alpha 2 AMPK kinase dead [KD], and gamma 3 AMPK KO), AICAR effects on AS160 phosphorylation were severely blunted, highlighting that complexes containing alpha 2 and gamma 3 are necessary for AICAR-stimulated AS160 phosphorylation in intact skeletal muscle. Contraction-mediated AS160 phosphorylation was also impaired in alpha 2 AMPK KO and KD but not gamma 3 AMPK KO mice. Our results implicate AS160 as a downstream target of AMPK.
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| 5. |
- Vieira, Elaine, et al.
(författare)
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Relationship between AMPK and the transcriptional balance of clock-related genes in skeletal muscle
- 2008
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Ingår i: American Journal of Physiology-Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 295:5
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Tidskriftsartikel (refereegranskat)abstract
- Circadian clocks coordinate physiological, behavioral, and biochemical events with predictable daily environmental changes by a self-sustained transcriptional feedback loop. CLOCK and ARNTL are transcriptional activators that regulate Per and Cry gene expression. PER and CRY inhibit their own transcription, and their turnover allows this cycle to restart. The transcription factors BHLHB2 and BHLHB3 repress Per activation, whereas orphan nuclear receptors of the NR1D and ROR families control Arntl expression. Here we show the AMP-activated protein kinase (AMPK)γ3 subunit is involved in the regulation of peripheral circadian clock function. AMPKγ3 knockout ( Prkag3−/−) mice or wild-type littermates were injected with saline or an AMPK activator, 5-amino-4-imidazole-carboxamide riboside (AICAR), and white glycolytic gastrocnemius muscle was removed for gene expression analysis. Genes involved in the regulation of circadian rhythms ( Cry2, Nr1d1, and Bhlhb2) were differentially regulated in response to AICAR in wild-type mice but remained unaltered in Prkag3−/− mice. Basal expression of Per1 was higher in Prkag3−/− mice compared with wild-type mice. Distinct diurnal changes in the respiratory exchange ratio (RER) between the light and dark phase of the day were observed in wild-type mice but not Prkag3−/− mice. In summary, the expression profile of clock-related genes in skeletal muscle in response to AICAR, as well as the diurnal shift in energy utilization, is impaired in AMPKγ3 subunit knockout mice. Our results indicate AMPK heterotrimeric complexes containing the AMPKγ3 subunit may play a specific role in linking circadian oscillators and energy metabolism in skeletal muscle.
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