UDP‐Glucose pyrophosphorylase is upregulated in carriers of the porcine RN− mutation in the AMP‐activated protein kinase

Hedegaard, Jakob; Horn, Per; Lametsch, René; Møller, Hanne Søndergaard; Roepstorff, Peter; Berthou, Christian; Bendixen, Emøke

doi:10.1002/pmic.200300761

Cited by 41 publications

(33 citation statements)

References 41 publications

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“…Interestingly, the microarray data and qRT-PCR analysis revealed a significant up-and down-regulation of Ugp2 and Gbe1 mRNAs (encoding two key enzymes in glyocogen synthesis) in skeletal muscle from AMPK ␥3 R225Q transgenic and knockout mice, respectively. In agreement with these results, the protein level and enzyme activity of Ugp2 and Gbe1 is increased in RN pigs carrying an R225Q mutant form of the AMPK ␥3-subunit (14,47). Based on these observations, we hypothesize that the differences in the skeletal muscle glycogen re-synthesis rate displayed by ␥3 R225Q transgenic and knock-out mice may be at least partly explained by coordinated differential transcription of Ugp2 and Gbe1.…”

Section: Discussionsupporting

confidence: 73%

Opposite Transcriptional Regulation in Skeletal Muscle of AMP-activated Protein Kinase γ3 R225Q Transgenic Versus Knock-out Mice

Nilsson¹,

Long

Martinsson³

et al. 2006

Journal of Biological Chemistry

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AMP-activated protein kinase (AMPK) is an evolutionarily conserved heterotrimer important for metabolic sensing in all eukaryotes. The muscle-specific isoform of the regulatory ␥-subunit of the kinase, AMPK ␥3, has an important role in glucose uptake, glycogen synthesis, and fat oxidation in white skeletal muscle, as previously demonstrated by physiological characterization of AMPK ␥3 mutant (R225Q) transgenic (TgPrkag3 225Q ) and ␥3 knock-out (Prkag3 ؊/؊ ) mice. We determined AMPK ␥3-dependent regulation of gene expression by analyzing global transcription profiles in glycolytic skeletal muscle from ␥3 mutant transgenic and knock-out mice using oligonucleotide microarray technology. Evidence is provided for coordinated and reciprocal regulation of multiple key components in glucose and fat metabolism, as well as skeletal muscle ergogenics in TgPrkag3 225Q and Prkag3 ؊/؊ mice. The differential gene expression profile was consistent with the physiological differences between the models, providing a molecular mechanism for the observed phenotype. The striking pattern of opposing transcriptional changes between TgPrkag3 225Q and Prkag3 ؊/؊ mice identifies differentially expressed targets being truly regulated by AMPK and is consistent with the view that R225Q is an activating mutation, in terms of its downstream effects. Additionally, we identified a wide array of novel targets and regulatory pathways for AMPK in skeletal muscle.AMP-activated protein kinase (AMPK) 2 is a critical regulator of carbohydrate and fat metabolism in eukaryotic cells (reviewed in Refs. 1 and 2). AMPK is a heterotrimer that consists of ␣-, ␤-, and ␥-subunits, all of which are required for its activity. The catalytic ␣-subunit contains a conventional serine/threonine protein kinase domain, and phosphorylation of Thr-172 residue within the activation loop of the ␣-subunit by upstream kinases is essential for the activity of the heterotrimer (3-6). Once phosphorylated at Thr-172, AMPK can be further activated by allosteric binding of AMP to the evolutionary conserved cystathionine ␤-synthase domains in the regulatory ␥-subunit (7). The AMPK ␤-subunit acts as a scaffold for binding of the ␣-and ␥-subunits (8). The ␤-subunit also contains a glycogen-binding domain, and recent findings provide evidence that this motif is involved in targeting the AMPK complex to cellular glycogen stores (9, 10). The mammalian genome contains seven AMPK genes encoding for two ␣-, two ␤-, and three ␥-isoforms. Thus, there are 12 possible combinations of heterotrimeric AMPK, and the physiological function of the AMPK holoenzyme depends on the particular isoforms present in the complex.We have provided evidence that AMPK ␥3 is the predominant ␥-isoform expressed in glycolytic (white, fast-twitch type II) skeletal muscle (11). In contrast, it is expressed at low levels in oxidative (red, slowtwitch type I) skeletal muscle and is undetectable in brain, liver, heart, or white adipose tissue (11). Thus, the AMPK ␥3-subunit is the only isoform exhibiting tissue-specific ...

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Section: Discussionsupporting

confidence: 73%

Opposite Transcriptional Regulation in Skeletal Muscle of AMP-activated Protein Kinase γ3 R225Q Transgenic Versus Knock-out Mice

Nilsson¹,

Long

Martinsson³

et al. 2006

Journal of Biological Chemistry

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“…We also showed that increased UDPG-PPL expression was independent of increased glucose uptake, because increasing glucose uptake by overexpressing glucose transporter 1 downregulated UDPG-PPL expression. Consistent with this finding, increased Ugp2 mRNA levels have also been shown in the skeletal muscle of mice (R225Q) and pigs (R200Q) bearing mutations at corresponding sites of γ3-AMPK and presenting a glycogen storage phenotype (32,33). These findings collectively suggest that upregulation of UDPG-PPL is a primary response to AMPK mutation rather than an adaptive response to altered glucose metabolism.…”

Section: Figuresupporting

confidence: 75%

Aberrant activation of AMP-activated protein kinase remodels metabolic network in favor of cardiac glycogen storage

Luptak¹,

Shen²,

He³

et al. 2007

J. Clin. Invest.

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AMP-activated protein kinase (AMPK) responds to impaired cellular energy status by stimulating substrate metabolism for ATP generation. Mutation of the γ2 regulatory subunit of AMPK in humans renders the kinase insensitive to energy status and causes glycogen storage cardiomyopathy via unknown mechanisms. Using transgenic mice expressing one of the mutant γ2 subunits (N488I) in the heart, we found that aberrant high activity of AMPK in the absence of energy deficit caused extensive remodeling of the substrate metabolism pathways to accommodate increases in both glucose uptake and fatty acid oxidation in the hearts of γ2 mutant mice via distinct, yet synergistic mechanisms resulting in selective fuel storage as glycogen. Increased glucose entry in the γ2 mutant mouse hearts was directed through the remodeled metabolic network toward glycogen synthesis and, at a substantially higher glycogen level, recycled through the glycogen pool to enter glycolysis. Thus, the metabolic consequences of chronic activation of AMPK in the absence of energy deficiency is distinct from those previously reported during stress conditions. These findings are of particular importance in considering AMPK as a target for the treatment of metabolic diseases.Introduction AMP-activated protein kinase (AMPK) is a serine/threonine kinase that acts as a cellular energy sensor and a master regulator of metabolism in a variety of cell types including cardiac myocytes (1). AMPK responds to increases in the cellular AMP/ATP ratio, an ultrasensitive indicator of impaired energy status, and triggers multiple signaling cascades to restore energy balance by stimulating ATP-generating pathways while inhibiting ATP-consuming pathways (1-3). AMPK is a heterotrimeric protein consisting of a catalytic subunit (α) and 2 regulatory subunits (β and γ). Each subunit has 2-3 isoforms; all except γ3 are expressed in the heart. Mutations in the γ2 subunit (encoded by the PRKAG2 gene) cause human cardiomyopathy characterized by substantial myocardial glycogen accumulation, preexcitation syndrome, and cardiac hypertrophy (4-6). These characteristics closely resemble the cardiac manifestation of glycogen storage disease (7), which prompted us to focus on the mechanisms of glycogen accumulation in the cardiomyopathy caused by mutation of PRKAG2. Interestingly, mutations in the corresponding sites on the γ3 subunits of AMPK in skeletal muscle such as R200Q in pigs and R225Q in mice have also been shown to cause glycogen accumulation (8-10), suggesting an important role of altered glycogen metabolism in the phenotype caused by mutations of γ-AMPK.

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“…Alternatively, the hyperaccumulation of glycogen in RN -carriers could originate from the higher expression of UDP-glucose pyrophosphorylase protein and high activity of the enzyme reported by Hedegaard et al (2004). Furthermore, Hedegaard et al (2004) suggested that the synthesis of glycogen in the muscles of RN -carriers was increased due to increased influx of glucose into the muscle fibres.…”

Section: )mentioning

confidence: 99%

“…Thus, the differences in the activity of GDE between the genotypes do not explain the faster pH decrease early post-mortem in RN -carriers compared with wild type animals. Hedegaard et al (2004) found indications of an up-regulation of phosphofructokinase enzyme in RN -carriers, which is the rate-limiting enzyme in glycolysis, and this would explain the fast glycolysis during early post-mortem in RN -carriers.…”

Section: )mentioning

confidence: 99%

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Post-mortem activity of the glycogen debranching enzyme and change in the glycogen pools in porcine M. longissimus dorsi from carriers and non-carriers of the RN− gene

Ylä-Ajos

Lindahl²,

Young³

et al. 2007

Meat Science

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Glycogen debranching enzyme (GDE) is together with glycogen phosphorylase responsible for the degradation of glycogen. The present study compares the post-mortem activity of GDE and breakdown of the glycogen pools in M. longissimus dorsi of RN -carrier pigs and in wild type animals. The activity of GDE (n=14) and pH (n=20) was measured 0.5, 3, 5, 24 and 48 h post-mortem. The change in pro-glycogen and in macro-glycogen content (n=20) was followed until 216 h post-mortem and the transcription level of GDE, glycogenin and glycogen synthase m-RNA (n=19) were measured 0.5 h post-mortem. Both the activity of GDE and the transcription level of GDE were found to be similar in RN -carriers and wild type animals shortly after slaughter. However, the activity declined faster in wild type animals compared with RN -carriers with increasing time post-mortem. The contents of both proglycogen and macro-glycogen were higher in RN -carriers compared with wild type animals, and further, the proportion of macro-glycogen was higher in RN -carriers compared with wild type animals. During the post-mortem period, only degradation of pro-glycogen was observed in both genotypes. The decrease in pH was faster and the ultimate pH lower in RN -carriers than in wild type animals. It was suggested that the higher GDE activity in the late phase of the post-mortem period in muscles from RN -carriers renders the extended pH decrease in these muscles.

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UDP‐Glucose pyrophosphorylase is upregulated in carriers of the porcine RN⁻ mutation in the AMP‐activated protein kinase

Cited by 41 publications

References 41 publications

Opposite Transcriptional Regulation in Skeletal Muscle of AMP-activated Protein Kinase γ3 R225Q Transgenic Versus Knock-out Mice

Opposite Transcriptional Regulation in Skeletal Muscle of AMP-activated Protein Kinase γ3 R225Q Transgenic Versus Knock-out Mice

Aberrant activation of AMP-activated protein kinase remodels metabolic network in favor of cardiac glycogen storage

Post-mortem activity of the glycogen debranching enzyme and change in the glycogen pools in porcine M. longissimus dorsi from carriers and non-carriers of the RN− gene

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