AMPK activation protects from neuronal dysfunction and vulnerability across nematode, cellular and mouse models of Huntington's disease

Human Molecular Genetics, 2016, Vol. 25, No. 6 1043–1058 doi: 10.1093/hmg/ddv513 Advance Access Publication Date: 17 December 2015 Original Article ORIGINAL ARTICLE AMPK activation protects from neuronal dysfunction and vulnerability across nematode, cellular and mouse models of Huntington’s disease 1 CNRS, UMR 8256, Laboratory of Neuronal Cell Biology and Pathology, Paris, France, 2Sorbonnes Universités, University Pierre and Marie Curie (UPMC) Univ Paris 06, Paris, France, 3Molecular, Cellular and Genomic Biomedicine Research Group, Health Research Institute-La Fe and CIBER de Enfermedades Raras (CIBERER), Valencia, Spain, 4Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA), Département des Sciences du Vivant (DSV), Institut d’Imagerie Biomédicale (I2BM), MIRCen, 5Centre National de la Recherche Scientifique (CNRS), Université Paris-Sud, Université Paris-Saclay, UMR 9199, Neurodegenerative Diseases Laboratory, F-92260 Fontenay-aux-Roses, France, 6CRCHUM, Montréal, Canada, 7Department de Neurosciences, Faculté de médecine, Université de Montréal, Montréal, Canada, 8Evotec AG, Manfred Eigen Campus, Hamburg, Germany and 9Department of Clinical Neurosciences (DNC), Lausanne University Hospital (CHUV), Lausanne, Switzerland *To whom correspondence should be addressed at: Centre National de la Recherche Scientifique, UMR 8256, Laboratory of Neuronal Cell Biology and Pathology, Paris, France; Sorbonnes Universités, University Pierre and Marie Curie (UPMC) Univ Paris 06, Paris, France. Tel: +33 144276045; Fax: +33 144275140; Email: (C.N.); (R.P.V.-M.) Abstract The adenosine monophosphate activated kinase protein (AMPK) is an evolutionary-conserved protein important for cell survival and organismal longevity through the modulation of energy homeostasis. Several studies suggested that AMPK activation may improve energy metabolism and protein clearance in the brains of patients with vascular injury or neurodegenerative disease. However, in Huntington’s disease (HD), AMPK may be activated in the striatum of HD mice at a late, post-symptomatic phase of the disease, and high-dose regiments of the AMPK activator 5-aminoimidazole-4-carboxamide ribonucleotide may worsen neuropathological and behavioural phenotypes. Here, we revisited the role of AMPK in HD using models that recapitulate the early features of the disease, including Caenorhabditis elegans neuron dysfunction before cell death and mouse striatal cell vulnerability. Genetic and pharmacological manipulation of aak-2/AMPKα shows that AMPK activation protects C. elegans neurons from the dysfunction induced by human exon-1 huntingtin (Htt) expression, in a daf-16/forkhead box O-dependent manner. Similarly, AMPK activation using genetic manipulation and low-dose metformin treatment protects mouse striatal cells expressing full-length mutant Htt (mHtt), counteracting their vulnerability to stress, with reduction of soluble mHtt levels by metformin and compensation of cytotoxicity by AMPKα1. Furthermore, AMPK protection is active in the Received: September 19, 2015. Revised and Accepted: December 10, 2015 © The Author 2015. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact 1043 Rafael P. Vázquez-Manrique1,2,3, *, Francesca Farina1,2, Karine Cambon4,5, María Dolores Sequedo3, Alex J. Parker6,7, José María Millán3, Andreas Weiss8, Nicole Déglon4,9 and Christian Neri1,2, * 1044 | Human Molecular Genetics, 2016, Vol. 25, No. 6 mouse brain as delivery of gain-of-function AMPK-γ1 to mouse striata slows down the neurodegenerative effects of mHtt. Collectively, these data highlight the importance of considering the dynamic of HD for assessing the therapeutic potential of stress-response targets in the disease. We postulate that AMPK activation is a compensatory response and valid approach for protecting dysfunctional and vulnerable neurons in HD. Introduction Results aak-2/AMPK is protective in a C. elegans model of neuronal dysfunction in HD The function of AMPK has been linked to lifespan and health span increase in nematodes and mice (13,31–33). Hence, we sought to test whether this enzyme may allow neurons to compensate for the stress and dysfunction that may be produced by mHtt expression during the early phases of HD pathology. To this end, we introduced a loss-of-function (LOF) allele of aak-2, namely aak-2(ok524), one of the two worm homologues of AMPKα1 (13) into a nematode model of neuronal dysfunction in HD. While we initially attempt to do the cross in nematodes with stable co-expression of human exon-1 Htt and YFP (29), double mutants could not be isolated likely because the Htt transgene is inserted near to the aak-2 locus. We, then, turned to single-transgenic animals. These animals bear a transgene that expresses the first exon of human Htt, with expanded (128Q) or normal (19Q) polyglutamines ( polyQ) fused to green fluorescent protein (GFP) in touch receptor neurons (34). In 128Q nematodes, response to Adenosine monophosphate activated kinase protein (AMPK) is an obligate heterotrimeric enzyme that is composed of AMPKα (catalytic core), AMPKβ and AMPKγ (regulatory units). AMPK is central to the regulation of energy homeostasis and phosphorylates a wide range of proteins, in response to metabolic changes, mostly ATP fluctuations, through allosteric binding of AMP or ADP to AMPKγ and/or phosphorylation of the α-subunit. After activation, AMPK phosphorylates a range of targets to inhibit catabolic pathways and to activate anabolic pathways to restore ATP homeostasis (1,2). However, AMPK is also able to respond by phosphorylation of different targets to a range of stress conditions to restore homeostatic balance of energy levels. For instance, AMPK can promote initiation of autophagy (2,3) through inhibition of mammalian target of rapamycin (mTOR) (4) or via phosphorylation of the forkhead box O 3a (FOXO3a) (5) under conditions of low levels of ATP or stress of different kinds. The transcription factor FOXO, a member of the FOX (forkhead box) family of proteins, has different isoforms in mammals, although only one gene represents this family in Caenorhabditis elegans, daf-16. This protein is a downstream player of the insulin signalling pathway in C. elegans and mammals and a well-known master regulator of lifespan that interplays upstream and downstream to the AMPK function across living organisms. AMPK also operates in cross-talk with other members of the AMPK-like family. For instance, the liver kinase B1 (LKB1) is a primary upstream kinase of AMPK and it regulates polarity and also is a tumour suppressor (reviewed in 6). Moreover, LKB1 is the kinase responsible for (...truncated)