Model Hirano Bodies Protect against Tau-Independent and Tau-Dependent Cell Death Initiated by the Amyloid Precursor Protein Intracellular Domain Matthew Furgerson 1 , Marcus Fechheimer2, Ruth Furukawa 2 * 1 Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia, United States of America, 2 Department of Cellular Biology, University of Georgia, Athens, Georgia, United States of America Abstract The main pathological hallmarks of Alzheimer’s disease are amyloid-beta plaques and neurofibrillary tangles, which are primarily composed of amyloid precursor protein (APP) and tau, respectively. These proteins and their role in the mechanism of neurodegeneration have been extensively studied. Hirano bodies are a frequently occurring pathology in Alzheimer’s disease as well as other neurodegenerative diseases. However, the physiological role of Hirano bodies in neurodegenerative diseases has yet to be determined. We have established cell culture models to study the role of Hirano bodies in amyloid precursor protein and tau-induced cell death mechanisms. Exogenous expression of APP and either of its c-terminal fragments c31 or Amyloid Precursor Protein Intracellular Domain c58 (AICDc58) enhance cell death. The presence of tau is not required for this enhanced cell death. However, the addition of a hyperphosphorylated tau mimic 352PHPtau significantly increases cell death in the presence of both APP and c31 or AICDc58 alone. The mechanism of cell death induced by APP and its c-terminal fragments and tau was investigated. Fe65, Tip60, p53, and caspases play a role in tau- independent and tau-dependent cell death. In addition, apoptosis was determined to contribute to cell death. The presence of model Hirano bodies protected against cell death, indicating Hirano bodies may play a protective role in neurodegeneration. Citation: Furgerson M, Fechheimer M, Furukawa R (2012) Model Hirano Bodies Protect against Tau-Independent and Tau-Dependent Cell Death Initiated by the Amyloid Precursor Protein Intracellular Domain. PLoS ONE 7(9): e44996. doi:10.1371/journal.pone.0044996 Editor: Bernadette Allinquant, INSERM U894, France Received January 31, 2012; Accepted August 14, 2012; Published September 18, 2012 Copyright: 2012 Furgerson 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: Funding for this work was provided by United States National Institutes of Health R01 N5046451 (www.ninds.nih.gov/) to R. Furukawa and M. Fechheimer. The funders had no role in the 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: furukawa@uga.edu Introduction Alzheimer’s disease is a growing, worldwide neurodegenerative disease affecting millions of elderly. Alzheimer’s disease (AD) patients experience progressive dementia as a result of severe neurodegeneration. The autopsied brains of AD patients reveal two hallmark neuropathological protein aggregates, amyloid-beta plaques and neurofibrillary tangles (reviewed in [1,2]) and also have a higher frequency of intracellular F-actin-rich Hirano bodies than age matched normal subjects [2,3,4,5,6]. Investigating how these pathologies relate to molecular events leading to neurode- generation is an extensive and often controversial area of research. The amyloid cascade hypothesis of Alzheimer’s disease [7,8,9,10,11,12] and subsequent refinements positing that oligo- meric amyloid-beta species are neurotoxic [13] (reviews [14,15,16]) have explained a vast amount of the data and pathology in both humans and model systems. Proteolytic processing of the type 1 transmembrane protein amyloid precursor protein (APP) [17,18,19] and sequential cleavage of APP by beta- and gamma-secretase releases an extracellular peptide, amyloid- beta, which aggregates to form plaques (reviewed in [20]). Gamma-secretase cleavage of APP also results in the release of a c-terminal intracellular domain, Amyloid Precursor Protein Intracellular Domain (AICD). Additional caspase cleavage results in another smaller c-terminal intracellular peptide, c31 (reviewed in [20]). Although controversial, it is thought that AICD can participate in signaling pathways (reviewed in [21,22,23]). The second pathological hallmark, neurofibrillary tangles, is derived from the aggregation of the microtubule binding protein tau [24,25]. Tauopathies such as Frontal Temporal Dementias with Parkinsonism (FTDP) are diseases linked to mutations in tau (reviewed in [26,27]). These diseases exhibit tau pathology, but unlike AD, no amyloid-beta pathology exists. Thus, mutant tau contributes to neurodegeneration without amyloid-beta. Numer- ous observations suggest a link between the cleavage products of APP and tau in neurodegeneration. Amyloid-beta plaques appear before neurofibrillary tangles in brains during neurodegeneration. Furthermore, reduction of tau levels in a mouse model of Alzheimer’s disease prevented amyloid-beta induced defects [28,29]. Turning off tau expression in a mouse model of tauopathy rescued memory defects even though cells still contain neurofi- brillary tangles [30]. These observations suggests that tau pathology arises downstream of amyloid-beta pathology. Howev- er, the exact mechanism, interaction, and timing of these two pathologies remain to be elucidated. In contrast to the extensive research on APP and tau, very little attention has been given to Hirano bodies, intracellular protein inclusions. They develop in the brain during normal aging, but are highly prevalent in neurodegenerative diseases such as AD, PLOS ONE | www.plosone.org 1 September 2012 | Volume 7 | Issue 9 | e44996