Redox proteomics identification of oxidatively modified hippocampal proteins in mild cognitive impairment: Insights into the development of Alzheimer’s disease D. Allan Butterfield, a,b,c, * H. Fai Poon, a Daret St. Clair, d Jeffery N. Keller, b,e William M. Pierce, f Jon B. Klein, g and William R. Markesbery b,h a Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055, USA b Sanders-Brown Center on Aging, University of Kentucky, Lexington, KY 40506, USA c Center of Membrane Sciences, University of Kentucky, Lexington, KY 40506, USA d Graduate Center for Toxicology, University of Kentucky, Lexington, KY 40506, USA e Department of Anatomy and Neurobiology, University of Kentucky, Lexington, KY 40506, USA f Department of Pharmacology and Core Proteomics Laboratory, University of Louisville, Louisville, KY 40208, USA g Kidney Disease Program and Core Proteomics Laboratory, University of Louisville, Louisville, KY 40208, USA h Departments of Pathology and Neurology, University of Kentucky, Lexington, KY 40506, USA Received 8 September 2005; revised 24 October 2005; accepted 1 November 2005 Available online 8 February 2006 Mild cognitive impairment (MCI) is generally referred to the transitional zone between normal cognitive function and early dementia or clinically probable Alzheimer’s disease (AD). Oxidative stress plays a significant role in AD and is increased in the superior/ middle temporal gyri of MCI subjects. Because AD involves hippo- campal-resident memory dysfunction, we determined protein oxidation and identified the oxidized proteins in the hippocampi of MCI subjects. We found that protein oxidation is significantly increased in the hippocampi of MCI subjects when compared to age- and sex-matched controls. By using redox proteomics, we determined the oxidatively modified proteins in MCI hippocampus to be A-enolase (ENO1), glutamine synthetase (GLUL), pyruvate kinase M2 (PKM2) and peptidyl-prolyl cis /trans isomerase 1 (PIN1). The interacteome of these proteins revealed that these proteins functionally interact with SRC, hypoxia-inducible factor 1, plasminogen (PLG), MYC, tissue plasmin- ogen activator (PLAT) and BCL2L1. Moreover, the interacteome indicates the functional involvement of energy metabolism, synaptic plasticity and mitogenesis/proliferation. Therefore, oxidative inactiva- tion of ENO1, GLUL and PIN1 may alter these cellular processes and lead to the development of AD from MCI. We conclude that protein oxidation plays a significant role in the development of AD from MCI and that the oxidative inactivation of ENO1, GLUL, PKM2 and PIN1 is involved in the progression of AD from MCI. The current study provides a framework for future studies on the development of AD from MCI relevant to oxidative stress. D 2005 Elsevier Inc. All rights reserved. Introduction Mild cognitive impairment (MCI) is generally referred to the transitional zone between normal cognitive aging and early dementia or clinically probable Alzheimer’s disease (AD) (Win- blad et al., 2004). Most individuals with MCI eventually develop AD, which suggests that MCI may be the earliest phase of the AD (Almkvist et al., 1998; Flicker et al., 1991; Luis et al., 2003; Morris et al., 2001). Although a variety of criteria are used to define MCI, they have in common that (a) MCI is referred to as the measurable cognitive deficits of non-demented persons and (b) MCI represents a clinical syndrome that does not fulfil a diagnosis of dementia but leads to a high risk of progressing to a dementia disorder (Winblad et al., 2004). When persons are diagnosed with MCI, most progress to AD and other dementia types, but some are stable or even recover (Winblad et al., 2004). Moreover, neuroimaging studies by magnetic resonance imaging (MRI) demonstrate the atrophy of the hippocampus or entorhinal cortex in MCI patients, indicating the relationships with transition of normal aging to MCI then later to clinical AD (de Leon et al., 2004). Oxidative stress plays a significant role in AD (Butterfield et al., 2001; Butterfield and Lauderback, 2002; Giasson et al., 2002; Markesbery, 1997; Zhu et al., 2004). Manifested by elevated levels of nucleic acid oxidation, protein oxidation and lipid peroxidation, oxidative damage is most severe in AD hippocampus, a brain 0969-9961/$ - see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.nbd.2005.11.002 * Corresponding author. Department of Chemistry, Center of Membrane Sciences, and Sanders-Brown Center on Aging, University of Kentucky, Lexington, KY 40506, USA. Fax: +1 859 257 5876. E-mail address: dabcns@uky.edu (D.A. Butterfield). Available online on ScienceDirect (www.sciencedirect.com). www.elsevier.com/locate/ynbdi Neurobiology of Disease 22 (2006) 223 – 232