Neuronal MicroRNA Deregulation in Response to Alzheimer's Disease Amyloid-β

et al. (2010) Neuronal MicroRNA Deregulation in Response to Alzheimer's Disease Amyloid-b. PLoS ONE 5(6): e11070. doi:10.1371/journal.pone.0011070 Neuronal MicroRNA Deregulation in Response to Alzheimer's Disease Amyloid-b Nicole Schonrock 0 Yazi D. Ke 0 David Humphreys 0 Matthias Staufenbiel 0 Lars M. Ittner 0 Thomas 0 Preiss 0 Ju rgen Go tz 0 Mel B. Feany, Brigham and Women's Hospital, Harvard Medical School, United States of America 0 1 Alzheimer's and Parkinson's Disease Laboratory, Brain and Mind Research Institute, University of Sydney , Sydney, New South Wales , Australia , 2 Molecular Genetics Division , Victor Chang Cardiac Research Institute (VCCRI) , Darlinghurst, Sydney, New South Wales , Australia , 3 Novartis Institute for BioMedical Research, Basel, Switzerland, 4 School of Biotechnology and Biomolecular Sciences and St. Vincent's Clinical School, University of New South Wales , Sydney, New South Wales , Australia Normal brain development and function depends on microRNA (miRNA) networks to fine tune the balance between the transcriptome and proteome of the cell. These small non-coding RNA regulators are highly enriched in brain where they play key roles in neuronal development, plasticity and disease. In neurodegenerative disorders such as Alzheimer's disease (AD), brain miRNA profiles are altered; thus miRNA dysfunction could be both a cause and a consequence of disease. Our study dissects the complexity of human AD pathology, and addresses the hypothesis that amyloid-b (Ab) itself, a known causative factor of AD, causes neuronal miRNA deregulation, which could contribute to the pathomechanisms of AD. We used sensitive TaqMan low density miRNA arrays (TLDA) on murine primary hippocampal cultures to show that about half of all miRNAs tested were down-regulated in response to Ab peptides. Time-course assays of neuronal Ab treatments show that Ab is in fact a powerful regulator of miRNA levels as the response of certain mature miRNAs is extremely rapid. Bioinformatic analysis predicts that the deregulated miRNAs are likely to affect target genes present in prominent neuronal pathways known to be disrupted in AD. Remarkably, we also found that the miRNA deregulation in hippocampal cultures was paralleled in vivo by a deregulation in the hippocampus of Ab42-depositing APP23 mice, at the onset of Ab plaque formation. In addition, the miRNA deregulation in hippocampal cultures and APP23 hippocampus overlaps with those obtained in human AD studies. Taken together, our findings suggest that neuronal miRNA deregulation in response to an insult by Ab may be an important factor contributing to the cascade of events leading to AD. - Funding: N.S. is supported by the Human Frontier Science Program. L.I. is supported by the National Health and Medical Research Council (NHMRC) and the Australian Research Council (ARC), and J.G. is supported by grants from the University of Sydney, the National Health and Medical Research Council (NHMRC), the Australian Research Council (ARC), and the J.O. & J.R. Wicking Trust. Postgraduate scholarship support has been provided by the Wenkart Foundation, GlaxoSmithKline and Alzheimers Australia. Novartis (via Matthias Staufenbiel) provided the APP23 mouse strain. All experiments were performed in Sydney, and Novartis did not fund any aspect of this work. 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 a purely academic collaboration with Matthias Staufenbiel of Novartis. There is no commercial interest attached to this work with him. All PLoS ONE policies regarding the sharing of data and materials will be adhered to. Alzheimers disease (AD) is a prominent neurodegenerative disorder characterized by progressive loss of memory and other cognitive functions. Histopathologically, AD is characterized by neurofibrillary tangles (NFTs) consisting of the microtubuleassociated protein tau and neuritic plaques composed of amyloid-b (Ab). Ab is a naturally occurring, predominantly 40 amino acid long polypeptide (Ab40) derived from the larger amyloid precursor protein (APP) [1]. Increases in the proportion of the longer, more neurotoxic form, Ab42, result in the formation of higher order aggregates and subsequently, plaque deposition. In familial AD (FAD), the increases in Ab42 are caused by aberrant processing of APP due to mutations in either the APP gene itself or in genes that encode subunits of the APP processing machinery. In addition, APP promoter polymorphisms [2], gene duplications [3] or trisomy 21 [4] can cause increased APP expression levels, resulting in elevated Ab42. While increased Ab levels characterize AD pathology, the precise mechanism(s) and signaling cascades it uses to cause cellular toxicity and cell death are not fully understood [5,6]. To better understand disease initiation and progression, transgenic animal models have been developed that model aspects of AD [7]. APP23 mice over-express the FAD mutant human APP in brain, and develop amyloid plaques similar to the human pathology [8]. These mice mimic several of the histopathological, biochemical, cognitive and behavioral alterations characteristic for AD. More recently, the research focus has shifted away from plaque formation to earlier events in disease progression such as the deregulation of genes whose impact on disease is still largely unknown [9]. A substantial portion of post-transcriptional gene regulation is controlled by microRNA (miRNA) networks, hence an alteration in the expression of miRNAs is emerging as a significant contributing factor to human neurodegenerative disease [10,11]. miRNAs are evolutionarily conserved non-coding RNAs of ,22 nucleotides that negatively regulate gene expression in a sequence-specific manner. Indeed, profiling of postmortem human AD brain has verified that significant changes in miRNA expression occur in several brain regions [10]. This includes miRNAs that regulate genes such as APP itself, and BACE1, that encodes an enzyme involved in APP processing [12,13,14]. However, whether the deregulated miRNAs are a cause or a consequence of disease, and what triggers miRNA dysfunction in AD is unknown. We therefore explored the hypothesis that Ab itself causes neuronal miRNA deregulation which could contribute to the pathology associated with AD. To remove the complexity inherently associated with human studies, we used mature murine primary hippocampal cultures to determine the effects of Ab specifically on neuronal miRNAs. Sensitive TaqMan low density miRNA arrays (TLDA) revealed that 47% of all miRNAs tested were down-regulated in response to Ab42. This response may be extremely rapid and bioinformatic analysis predicts that the deregulated miRNAs are likely to affect target genes present in prominent neuronal pathways disrupted in AD. Remarkably, when we analyzed hippocampi of APP23 mice at the onset of (...truncated)