Intermittent Hypoxia-Induced Cognitive Deficits Are Mediated by NADPH Oxidase Activity in a Murine Model of Sleep Apnea Deepti Nair, Ehab A. Dayyat, Shelley X. Zhang, Yang Wang, David Gozal* Department of Pediatrics, Pritzker School of Medicine, University of Chicago, Chicago, Illinois, United States of America Abstract Background: In rodents, exposure to intermittent hypoxia (IH), a hallmark of obstructive sleep apnea (OSA), is associated with neurobehavioral impairments, increased apoptosis in the hippocampus and cortex, as well as increased oxidant stress and inflammation. Excessive NADPH oxidase activity may play a role in IH-induced CNS dysfunction. Methods and Findings: The effect of IH during light period on two forms of spatial learning in the water maze and well as markers of oxidative stress was assessed in mice lacking NADPH oxidase activity (gp91phox_/Y) and wild-type littermates. On a standard place training task, gp91phox_/Y displayed normal learning, and were protected from the spatial learning deficits observed in wild-type littermates exposed to IH. Moreover, anxiety levels were increased in wild-type mice exposed to IH as compared to room air (RA) controls, while no changes emerged in gp91phox_/Y mice. Additionally, wild-type mice, but not gp91phox_/Y mice had significantly elevated levels of NADPH oxidase expression and activity, as well as MDA and 8-OHDG in cortical and hippocampal lysates following IH exposures. Conclusions: The oxidative stress responses and neurobehavioral impairments induced by IH during sleep are mediated, at least in part, by excessive NADPH oxidase activity, and thus pharmacological agents targeting NADPH oxidase may provide a therapeutic strategy in sleep-disordered breathing. Citation: Nair D, Dayyat EA, Zhang SX, Wang Y, Gozal D (2011) Intermittent Hypoxia-Induced Cognitive Deficits Are Mediated by NADPH Oxidase Activity in a Murine Model of Sleep Apnea. PLoS ONE 6(5): e19847. doi:10.1371/journal.pone.0019847 Editor: Ya-Ping Tang, Louisiana State University Health Sciences Center, United States of America Received November 9, 2010; Accepted April 18, 2011; Published May 23, 2011 Copyright: 2011 Nair 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 study was supported by National Institutes of Health grant HL-086662. 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: dgozal@uchicago.edu Introduction Obstructive Sleep Apnea (OSA), a clinical syndrome charac- terized by repeated episodes of upper airway obstruction during sleep, is now recognized as a significant and highly prevalent health problem, due not only to its cardiovascular and metabolic morbidity, but also because of the prominent cognitive and behavioral implications of the disease. The neuropsychological impairments are accompanied by increased levels of systemic markers of oxidative stress and inflammation in addition to gray matter loss in neural sites contributing to cognitive function [1–5]. The inordinate sensitivity of neuronal tissues to alterations in oxygen homeostasis has led to the hypothesis that the behavioral consequences and cellular losses observed in OSA patients are produced, at least in part, by the episodic hypoxia-reoxygenation cycles during sleep that characterize OSA. In support of this hypothesis, rodent models have demonstrated that chronic exposure to intermittent hypoxia during the rest period (IH), in the absence of significant sleep fragmentation, is accompanied by neurodegenerative changes, increased oxidant stress and inflam- mation, and impaired spatial learning in the Morris water maze [6–18], and that genetic or pharmacological manipulations of oxidative stress pathways attenuated IH-induced deficits [18,19]. NADPH oxidase has been primarily studied in the context of its role in phagocyte oxidative burst [20]. This enzyme has however emerged as a major source of ROS generation in mammalian cells, including the CNS [21–24], and a role for NADPH oxidase in astrocyte function has been described [25]. Moreover, it has been demonstrated that NADPH oxidase is expressed in neurons [26,23] and localized at synapses [26]. NADPH oxidase is composed of two membrane-bound subunits (gp91phox and p22phox) and three cytosolic subunits, which include p47phox, p67phox, and Rac [27]. The membrane-bound subunits form a heterodimer that stabilizes them within the membrane, whereas the cytosolic subunits are recruited to the membrane following stimulation. Complete complex assembly is necessary for full NADPH oxidase activity [28]. Mutations in the gp91phox and p47phox genes are the most common mutations that cause chronic granulomatous disease (CGD; [29]). These mutations disable the NADPH oxidase complex, thereby preventing the oxidation of NADPH and the subsequent production of superoxide [30,31], which is required for pathogen destruction as well as most superoxide-dependent signal transduction in nonphagocytic cells [27,32,33]. gp91phox [34] and p47phox [35] mutant mice have been generated and can therefore be used to explore the putative role of NADPH oxidase in murine models of sleep apnea. PLoS ONE | www.plosone.org 1 May 2011 | Volume 6 | Issue 5 | e19847