HDAC6 Inhibitor Blocks Amyloid Beta-Induced Impairment of Mitochondrial Transport in Hippocampal Neurons Chaeyoung Kim1., Heesun Choi1., Eun Sun Jung 1 , Wonik Lee1, Soojung Oh2,3, Noo Li Jeon2,3, 1 Inhee Mook-Jung * 1 Department of Biochemistry and Biomedical Sciences, Seoul National University College of Medicine, Seoul, Korea, 2 School of Mechanical and Aerospace Engineering, Seoul National University, Seoul, Korea, 3 World Class University (WCU) Program of Multiscale Design, School of Mechanical and Aerospace Engineering, Seoul National University, Seoul, Korea Abstract Even though the disruption of axonal transport is an important pathophysiological factor in neurodegenerative diseases including Alzheimer’s disease (AD), the relationship between disruption of axonal transport and pathogenesis of AD is poorly understood. Considering that a-tubulin acetylation is an important factor in axonal transport and that Ab impairs mitochondrial axonal transport, we manipulated the level of a-tubulin acetylation in hippocampal neurons with Ab cultured in a microfluidic system and examined its effect on mitochondrial axonal transport. We found that inhibiting histone deacetylase 6 (HDAC6), which deacetylates a-tubulin, significantly restored the velocity and motility of the mitochondria in both anterograde and retrograde axonal transports, which would be otherwise compromised by Ab. The inhibition of HDAC6 also recovered the length of the mitochondria that had been shortened by Ab to a normal level. These results suggest that the inhibition of HDAC6 significantly rescues hippocampal neurons from Ab-induced impairment of mitochondrial axonal transport as well as mitochondrial length. The results presented in this paper identify HDAC6 as an important regulator of mitochondrial transport as well as elongation and, thus, a potential target whose pharmacological inhibition contributes to improving mitochondrial dynamics in Ab treated neurons. Citation: Kim C, Choi H, Jung ES, Lee W, Oh S, et al. (2012) HDAC6 Inhibitor Blocks Amyloid Beta-Induced Impairment of Mitochondrial Transport in Hippocampal Neurons. PLoS ONE 7(8): e42983. doi:10.1371/journal.pone.0042983 Editor: Sergio T. Ferreira, Federal University of Rio de Janeiro, Brazil Received February 13, 2012; Accepted July 16, 2012; Published August 22, 2012 Copyright: 2012 Kim 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: This work was supported by grants from the 21C Frontier Functional Proteomics Project (FPR08K1301-02210), National Research Foundation 2009- 0081673, World Class University-Neurocytomics, and the Korean National Institute of Health R&D Program Project (2009-0443) and supported in part by the Basic Research Program (2008-05943) and MRC at SNU (2011-0030738). 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: inhee@snu.ac.kr . These authors contributed equally to this work. Introduction Neurons have extensive processes and asymmetrical organiza- tion. The communication between the cell body and the nerve terminal is critical for neuronal functions, which involves microtubule (MT) based axonal transport. MTs are dynamically assembled polymers of a- and b-tubulin [1]. Tubulin undergoes various post-translational modifications (PTMs), including acety- lation, tyrosination, and phosphorylation [2,3]. PTMs of tubulin regulate not only the interaction between MTs and MT-associated proteins (MAP), but also the stability of the microtubule, contributing to controlling axon guidance, synapse formation, and neuronal transport [2,3,4]. Acetylation of a-tubulin plays a positive role in axonal transport in mammals by increasing microtubule stability [3,5,6]. Histone deacetylase 6 (HDAC6) is a unique cytosolic enzyme that mediates the deacetylation of a- tubulin, which involves two functional deacetylase domains and a zinc finger motif [7]. The level of acetylated a-tubulin is decreased [9,10] as the level of HDAC6 is increased in the AD patients’ brains [11]. Since impaired axonal transport is an important pathophysiological factor in AD [8], HDAC6 may play a role in the disruption of axonal transport in AD pathogenesis. Amyloid beta (Ab), the cleavage product from amyloid precursor protein (APP), is one of the causative factors of AD pathogenesis. Ab interrupts vesicular and axonal transport by inducing alteration in microtubule stability and intracellular signaling pathways [12,13,14]. Ab also causes synaptic degeneration and loss through the disruption of axonal transport [12,15], which leads to impaired trafficking of the mitochondria and neurotransmitters necessary for synaptic function and neuronal viability [8,10,16]. Mitochondria can be delivered along the axon in association with microtubules, which is important for supplying energy required to maintain neuronal functions. During axonal transport, mitochondria are associated with several motor proteins, such as kinesin for anterograde transport and dynein for retrograde transport [1,2]. Adaptor proteins, such as Miro (Miro1 and Miro2 in mammals) and Milton (OIP106 and GRIF1 in mammals), are connected to mitochondria through kinesin [17,18]. Although impaired axonal transport of mitochondria has been reported in the presence of Ab [12], the precise mechanism for this Ab- induced impairment remains unclear. In the present study, we PLOS ONE | www.plosone.org 1 August 2012 | Volume 7 | Issue 8 | e42983