Inhibition of GSK-3 Ameliorates Ab Pathology in an Adult-Onset Drosophila Model of Alzheimer’s Disease Oyinkan Sofola1., Fiona Kerr1,2., Iain Rogers1., Richard Killick3, Hrvoje Augustin1, Carina Gandy1,2, Marcus J. Allen4, John Hardy5, Simon Lovestone3, Linda Partridge1,2* 1 Institute of Healthy Ageing and Research Department of Genetics, Evolution, and Environment, University College London, London, United Kingdom, 2 Max Planck Institute for Biology of Ageing, K o¨ln, Germany, 3 Institute of Psychiatry, King’s College London, London, United Kingdom, 4 School of Biosciences, University of Kent, Canterbury, United Kingdom, 5 Institute of Neurology, University College London, London, United Kingdom Abstract Ab peptide accumulation is thought to be the primary event in the pathogenesis of Alzheimer’s disease (AD), with downstream neurotoxic effects including the hyperphosphorylation of tau protein. Glycogen synthase kinase-3 (GSK-3) is increasingly implicated as playing a pivotal role in this amyloid cascade. We have developed an adult-onset Drosophila model of AD, using an inducible gene expression system to express Arctic mutant Ab42 specifically in adult neurons, to avoid developmental effects. Ab42 accumulated with age in these flies and they displayed increased mortality together with progressive neuronal dysfunction, but in the apparent absence of neuronal loss. This fly model can thus be used to examine the role of events during adulthood and early AD aetiology. Expression of Ab42 in adult neurons increased GSK-3 activity, and inhibition of GSK-3 (either genetically or pharmacologically by lithium treatment) rescued Ab42 toxicity. Ab42 pathogenesis was also reduced by removal of endogenous fly tau; but, within the limits of detection of available methods, tau phosphorylation did not appear to be altered in flies expressing Ab42. The GSK-3–mediated effects on Ab42 toxicity appear to be at least in part mediated by tau-independent mechanisms, because the protective effect of lithium alone was greater than that of the removal of tau alone. Finally, Ab42 levels were reduced upon GSK-3 inhibition, pointing to a direct role of GSK-3 in the regulation of Ab42 peptide level, in the absence of APP processing. Our study points to the need both to identify the mechanisms by which GSK-3 modulates Ab42 levels in the fly and to determine if similar mechanisms are present in mammals, and it supports the potential therapeutic use of GSK-3 inhibitors in AD. Citation: Sofola O, Kerr F, Rogers I, Killick R, Augustin H, et al. (2010) Inhibition of GSK-3 Ameliorates Ab Pathology in an Adult-Onset Drosophila Model of Alzheimer’s Disease. PLoS Genet 6(9): e1001087. doi:10.1371/journal.pgen.1001087 Editor: Bingwei Lu, Stanford University School of Medicine, United States of America Received August 5, 2009; Accepted July 23, 2010; Published September 2, 2010 Copyright: 2010 Sofola et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: Alzheimer’s Society, the European Commission, Wellcome Trust, Eisai London Research Laboratories (UK), and the Max Planck Institute for the Biology of Ageing. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: l.partridge@ucl.ac.uk . These authors contributed equally to this work. Introduction Alzheimer’s disease (AD) is the leading cause of dementia in the ageing population. Symptoms include, but are not limited to, memory loss, cognitive decline, and deterioration of language skills. The pathological hallmarks of AD are the presence of plaques and neurofibrillary tangles [1]. The tangles are composed of hyperphosphorylated tau protein while the plaques are comprised of amyloid beta (Ab) peptides, various species of which are derived from the amyloid precursor protein (APP), the most abundant being Ab40 and Ab42 [2]. AD-causing mutations either increase the level of Ab42 or the ratio of Ab42/Ab40, indicating that this is the more toxic form of the peptide [2]. The leading candidate explanation for the molecular basis of AD pathology is the amyloid cascade hypothesis. This states that the Ab protein initiates the disease process, activating downstream neurotoxic mechanisms including the dysregulation of tau. Perhaps the strongest support for the amyloid cascade hypothesis is that all of the mutations implicated in early-onset, familial AD, such as the Ab Arctic mutation, increase the aggregation or production of Ab [1]. Although tau mutations exist, none have been linked to familial AD, but rather to fronto-temporal dementia, in which Ab plaques are absent [3,4]. The amyloid cascade has also been tested experimentally in various ways. For example, a double transgenic mouse model expressing APP- V7171 and Tau-P301L, develops amyloid pathology similarly to mice transgenic for APP-V7171 alone, whereas tauopathy is dramatically enhanced in the double transgenic compared to mice transgenic for Tau-P301L alone. This implies that Ab pathology affects tauopathy but not vice versa [5]. Also, clearance of Ab using Ab-specific antibodies reduced early tau burden, while elevating tau burden in transgenic mice had no effect on Ab accumulation [6,7]. Furthermore, a reduction in tau levels rescued learning and memory impairment induced by Ab in a mouse model expressing human APP [8]. Ab increases the phosphorylation of tau protein and concom- itantly activates glycogen synthase kinase, GSK-3 [9,10]. GSK-3 is a multi-functional kinase involved in regulating various cellular processes, including growth and differentiation [9,11]. There are two isoforms of the protein, GSK-3a and GSK-3b. They share 98% identity within their kinase domain, but are not functionally identical, although both have been suggested to be involved in AD PLoS Genetics | www.plosgenetics.org 1 September 2010 | Volume 6 | Issue 9 | e1001087