title: Apolipoprotein E-deficient mice exhibit increased vulnerability to intermittent hypoxia-induced spatial learning deficits.
abstract: Exposure to intermittent hypoxia, such as occurs in sleep-disordered breathing, is associated with oxidative stress, cognitive impairments, and increased neuronal apoptosis in brain regions involved in learning and memory. Apolipoprotein E (ApoE) has been implicated in neurodegenerative disorders, and in vitro studies suggest that one of the functions of ApoE may be to confer protection from oxidant stress-induced neuronal cell loss. Therefore, we hypothesized that ApoE-deficient (ApoE-/-) mice would display increased cognitive impairments following intermittent hypoxia. Twenty-four young adult male mice (ApoE-/-) and 24 wild-type littermates (ApoE +/+) were exposed to 14 days of normoxia (room air; n=12 per group) or intermittent hypoxia (5.7% O2 alternating with 21% O2 every 90 seconds, 12 daylight hours per day; n=12 per group). Behavioral testing consisting of a standard place-training reference memory task in the water maze revealed that ApoE+/+ and ApoE-/- mice exposed to intermittent hypoxia were found to require significantly longer times (latency) and distances (pathlength) to locate the hidden platform (P < .005), compared to mice exposed to room air. However, only intermittent hypoxia-exposed ApoE-/- mice were impaired on the final two days of training (P < .03), as well as on measures of spatial bias conducted 24 hours after completion of training (P < .02). Furthermore, increased prostaglandin E2 and malondiadehyde concentrations were present in hippocampal brain tissues following intermittent hypoxia but were significantly higher in ApoE-/- mice (P < .01). Thus, decreased ApoE function is associated with increased susceptibility to neurocognitive dysfunction in a rodent model of sleep-disordered breathing and may underlie the increased prevalence of Apolipoprotein E4 in patients with sleep-disordered breathing.
authors.affiliation: Kosair Children's Hospital Research Institute, Department of Pediatrics, University of Louisville, KY 40202, USA.
authors.forename: Leila
authors.initials: L
authors.lastname: Kheirandish
authors.forename: Barry W
authors.initials: BW
authors.lastname: Row
authors.forename: Richard C
authors.initials: RC
authors.lastname: Li
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Brittian
authors.forename: David
authors.initials: D
authors.lastname: Gozal
mesh_terms: D000818:Animals; D001057:Apolipoproteins E / Q000378:metabolism*; D003072:Cognition Disorders / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D051546:Cyclooxygenase 2 / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism / Q000503:physiopathology; D000860:Hypoxia / Q000150:complications / Q000378:metabolism / Q000503:physiopathology; D015227:Lipid Peroxidation / Q000502:physiology; D008297:Male; D018782:Maze Learning / Q000502:physiology*; D051379:Mice; D018384:Oxidative Stress / Q000502:physiology; D010468:Perceptual Disorders / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology; D012720:Severity of Illness Index; D013028:Space Perception; D013997:Time Factors
chemical_list: D001057:Apolipoproteins E; D051546:Cyclooxygenase 2; D015232:Dinoprostone