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      Nuclear translocation of AMPK-α1 potentiates striatal neurodegeneration in Huntington’s disease

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          Abstract

          Nuclear accumulation of AMPK-α1 induces brain atrophy, neuronal loss, and formation of Htt aggregates in a Huntington’s disease model.

          Abstract

          Adenosine monophosphate–activated protein kinase (AMPK) is a major energy sensor that maintains cellular energy homeostasis. Huntington’s disease (HD) is a neurodegenerative disorder caused by the expansion of CAG repeats in the huntingtin ( Htt) gene. In this paper, we report that activation of the α1 isoform of AMPK (AMPK-α1) occurred in striatal neurons of humans and mice with HD. Overactivation of AMPK in the striatum caused brain atrophy, facilitated neuronal loss, and increased formation of Htt aggregates in a transgenic mouse model (R6/2) of HD. Such nuclear accumulation of AMPK-α1 was activity dependent. Prevention of nuclear translocation or inactivation of AMPK-α1 ameliorated cell death and down-regulation of Bcl2 caused by mutant Htt (mHtt). Conversely, enhanced expression of Bcl2 protected striatal cells from the toxicity evoked by mHtt and AMPK overactivation. These data demonstrate that aberrant activation of AMPK-α1 in the nuclei of striatal cells represents a new toxic pathway induced by mHtt.

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          AMP-activated protein kinase (AMPK) action in skeletal muscle via direct phosphorylation of PGC-1alpha.

          Sibylle Jager, Christoph Handschin, Julie St-Pierre … (2007)
          Activation of AMP-activated kinase (AMPK) in skeletal muscle increases glucose uptake, fatty acid oxidation, and mitochondrial biogenesis by increasing gene expression in these pathways. However, the transcriptional components that are directly targeted by AMPK are still elusive. The peroxisome-proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha) has emerged as a master regulator of mitochondrial biogenesis; furthermore, it has been shown that PGC-1alpha gene expression is induced by exercise and by chemical activation of AMPK in skeletal muscle. Using primary muscle cells and mice deficient in PGC-1alpha, we found that the effects of AMPK on gene expression of glucose transporter 4, mitochondrial genes, and PGC-1alpha itself are almost entirely dependent on the function of PGC-1alpha protein. Furthermore, AMPK phosphorylates PGC-1alpha directly both in vitro and in cells. These direct phosphorylations of the PGC-1alpha protein at threonine-177 and serine-538 are required for the PGC-1alpha-dependent induction of the PGC-1alpha promoter. These data indicate that AMPK phosphorylation of PGC-1alpha initiates many of the important gene regulatory functions of AMPK in skeletal muscle.
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            Antidiabetic drug metformin (GlucophageR) increases biogenesis of Alzheimer's amyloid peptides via up-regulating BACE1 transcription.

            Yaomin Chen, Kun Zhou, Ruishan Wang … (2009)
            Epidemiological, clinical and experimental evidence suggests a link between type 2 diabetes and Alzheimer's disease (AD). Insulin modulates metabolism of beta-amyloid precursor protein (APP) in neurons, decreasing the intracellular accumulation of beta-amyloid (Abeta) peptides, which are pivotal in AD pathogenesis. The present study investigates whether the widely prescribed insulin-sensitizing drug, metformin (Glucophage(R)), affects APP metabolism and Abeta generation in various cell models. We demonstrate that metformin, at doses that lead to activation of the AMP-activated protein kinase (AMPK), significantly increases the generation of both intracellular and extracellular Abeta species. Furthermore, the effect of metformin on Abeta generation is mediated by transcriptional up-regulation of beta-secretase (BACE1), which results in an elevated protein level and increased enzymatic activity. Unlike insulin, metformin exerts no effect on Abeta degradation. In addition, we found that glucose deprivation and various tyrphostins, known inhibitors of insulin-like growth factors/insulin receptor tyrosine kinases, do not modulate the effect of metformin on Abeta. Finally, inhibition of AMP-activated protein kinase (AMPK) by the pharmacological inhibitor Compound C largely suppresses metformin's effect on Abeta generation and BACE1 transcription, suggesting an AMPK-dependent mechanism. Although insulin and metformin display opposing effects on Abeta generation, in combined use, metformin enhances insulin's effect in reducing Abeta levels. Our findings suggest a potentially harmful consequence of this widely prescribed antidiabetic drug when used as a monotherapy in elderly diabetic patients.
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              The regulation of AMP-activated protein kinase by phosphorylation.

              Gary Stein, Andrea N. Jones, D Davison … (2000)
              The AMP-activated protein kinase (AMPK) cascade is activated by an increase in the AMP/ATP ratio within the cell. AMPK is regulated allosterically by AMP and by reversible phosphorylation. Threonine-172 within the catalytic subunit (alpha) of AMPK (Thr(172)) was identified as the major site phosphorylated by the AMP-activated protein kinase kinase (AMPKK) in vitro. We have used site-directed mutagenesis to study the role of phosphorylation of Thr(172) on AMPK activity. Mutation of Thr(172) to an aspartic acid residue (T172D) in either alpha1 or alpha2 resulted in a kinase complex with approx. 50% the activity of the corresponding wild-type complex. The activity of wild-type AMPK decreased by greater than 90% following treatment with protein phosphatases, whereas the activity of the T172D mutant complex fell by only 10-15%. Mutation of Thr(172) to an alanine residue (T172A) almost completely abolished kinase activity. These results indicate that phosphorylation of Thr(172) accounts for most of the activation by AMPKK, but that other sites are involved. In support of this we have shown that AMPKK phosphorylates at least two other sites on the alpha subunit and one site on the beta subunit. Furthermore, we provide evidence that phosphorylation of Thr(172) may be involved in the sensitivity of the AMPK complex to AMP.
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                Author and article information

                Journal
                Journal ID (nlm-ta): J Cell Biol
                Journal ID (iso-abbrev): J. Cell Biol
                Journal ID (hwp): jcb
                Title: The Journal of Cell Biology
                Publisher: The Rockefeller University Press
                ISSN (Print): 0021-9525
                ISSN (Electronic): 1540-8140
                Publication date (Print): 25 July 2011
                Volume: 194
                Issue: 2
                Pages: 209-227
                Affiliations
                [1 ]Institute of Neuroscience and [2 ]Institute of Biochemistry and Molecular Biology, School of Life Sciences, National Yang Ming University, Taipei 112, Taiwan
                [3 ]Division of Neuroscience, Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
                [4 ]Department of Neuroscience, Mayo Clinic College of Medicine, Jacksonville, FL 32224
                Author notes
                Correspondence to Yijuang Chern: bmychern@ 123456ibms.sinica.edu.tw
                Article
                Publisher ID: 201105010
                DOI: 10.1083/jcb.201105010
                PMC ID: 3144412
                PubMed ID: 21768291
                SO-VID: 9d0b4f8d-2d59-47c6-8e2a-f17da2ea1cf1
                Copyright statement: © 2011 Ju et al.
                License:

                This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

                History
                Date received : 3 May 2011
                Date accepted : 21 June 2011
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                Subject: Research Articles
                Subject: Article

                ScienceOpen disciplines: Cell biology
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                ScienceOpen disciplines: Cell biology

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